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Sample records for 10-ps pulse duration

  1. Generation of intense 10-ps, 193-nm pulses using simple distributed feedback dye lasers and an ArF(*) amplifier.

    PubMed

    Hatten, D L; Cui, Y; Iii, W T; Mikes, T; Goldhar, J

    1992-11-20

    A pair of holographic distributed feedback dye lasers is used to generate 10-ps pulses at two selected wavelengths that are mixed in a BBO crystal to produce a pulse ~ 10 ps in duration at 193 nm. This seed pulse is subsequently amplified in an ArF(*) excimer laser to an energy of 10-15 mJ with <40 microJ in amplified spontaneous emission. The pulses are nearly transform limited and diffraction limited.

  2. PULSE DURATION LENGTHENER

    DOEpatents

    Aiken, W.R.

    1958-02-01

    This patent pertains to pulse modifying apparatus and, more particularly, describes a device to provide a rise time and time base expander for signal pulses having a very short duration. The basic element of the device is a vacuum tube comprising a charged particie beam, grid control means, an accelerating electrode, a drift tube, and a collector electrode. As the short duration input pulse modulates the particle beam through the grid control means, the voltage between the drift tube and accelerating electrode is caused to vary, whereby the output signal from the collector is a pulse having longer rise time, expanded duration and proportionate characteristics of the original pulse. The invention is particuiarly useful where subsequent pulse circultry does not have the frequency bandwidth to handle the short duration pulse without distorting it.

  3. Influence of the Pulse Duration onto the Material Removal Rate and Machining Quality for Different Types of Steel

    NASA Astrophysics Data System (ADS)

    Lauer, Benjamin; Jäggi, Beat; Neuenschwander, Beat

    When high requirements concerning machining quality are demanded, ultra short pulsed lasers with pulse durations from a few 100fs to 10ps may be the tool of choice. For these pulses it is known that the removal rate and machining quality slightly increases with shorter pulse duration. But as cost-effectiveness is also a key factor for a successful transfer of a technology to industrial applications, these systems compete against more cost effective systems with pulse durations from several 10ps to a few ns. It was found in previous work that the removal rate for metals strongly depends on the pulse duration. For steel also the composition and microstructure will influence the ablation processes. A systematic study of the removal rate and the machining quality for different types of steel and for pulse durations of several 100 fs to few ns will be presented.

  4. Control of near-infrared supercontinuum bandwidth by adjusting pump pulse duration.

    PubMed

    Andreana, M; Labruyère, A; Tonello, A; Wabnitz, S; Leproux, P; Couderc, V; Duterte, C; Cserteg, A; Bertrand, A; Hernandez, Y; Giannone, D; Hilaire, S; Huss, G

    2012-05-01

    We experimentally and numerically investigated the impact of input pump pulse duration on the near-infrared bandwidth of supercontinuum generation in a photonic crystal fiber. We continuously stretched the temporal duration of the input pump laser (centered at 1030 nm) pulses from 500 fs up to 10 ps, while keeping fixed the pump peak power. We observed that the long-wavelength edge of the supercontinuum spectrum is increased by 200 nm as the pump pulse duration grows from 500 fs to 10 ps. We provide a quantitative fit of the experimental results by means of numerical simulations. Moreover, we have explained the observed spectral broadening enhancement induced by pump pulse energy by developing an approximate yet fully analytical model for soliton energy exchange through a series of collisions in the presence of stimulated Raman scattering. PMID:22565699

  5. Kilovolt Blumlein pulse generator with variable pulse duration and polarity

    NASA Astrophysics Data System (ADS)

    de Angelis, Andrea; Kolb, Juergen F.; Zeni, Luigi; Schoenbach, Karl H.

    2008-04-01

    A Blumlein pulse generator which utilizes the superposition of electrical pulses launched from two individually switched pulse forming lines has been designed and tested. By using a power metal-oxide-semiconductor field-effect transistor as a switch on each end of the Blumlein line, we were able to generate pulses with amplitudes of 1kV across a 100Ω load. Pulse duration and polarity can be controlled by the temporal delay in the triggering of the two switches. Using this technique, we have demonstrated the generation of pulses with durations between 8 and 60ns. The lower limit in pulse duration was determined by the switch closing time and the upper limit by the length of the pulse forming line. A further advantage of the concept is that pulse distortions caused by the non-negligible on-resistance of a line with a single switch can be eliminated by using switches with identical characteristics.

  6. Kilovolt Blumlein pulse generator with variable pulse duration and polarity.

    PubMed

    de Angelis, Andrea; Kolb, Juergen F; Zeni, Luigi; Schoenbach, Karl H

    2008-04-01

    A Blumlein pulse generator which utilizes the superposition of electrical pulses launched from two individually switched pulse forming lines has been designed and tested. By using a power metal-oxide-semiconductor field-effect transistor as a switch on each end of the Blumlein line, we were able to generate pulses with amplitudes of 1 kV across a 100 Omega load. Pulse duration and polarity can be controlled by the temporal delay in the triggering of the two switches. Using this technique, we have demonstrated the generation of pulses with durations between 8 and 60 ns. The lower limit in pulse duration was determined by the switch closing time and the upper limit by the length of the pulse forming line. A further advantage of the concept is that pulse distortions caused by the non-negligible on-resistance of a line with a single switch can be eliminated by using switches with identical characteristics.

  7. Effects of pulse duration on magnetostimulation thresholds

    SciTech Connect

    Saritas, Emine U.; Goodwill, Patrick W.; Conolly, Steven M.

    2015-06-15

    Purpose: Medical imaging techniques such as magnetic resonance imaging and magnetic particle imaging (MPI) utilize time-varying magnetic fields that are subject to magnetostimulation limits, which often limit the speed of the imaging process. Various human-subject experiments have studied the amplitude and frequency dependence of these thresholds for gradient or homogeneous magnetic fields. Another contributing factor was shown to be number of cycles in a magnetic pulse, where the thresholds decreased with longer pulses. The latter result was demonstrated on two subjects only, at a single frequency of 1.27 kHz. Hence, whether the observed effect was due to the number of cycles or due to the pulse duration was not specified. In addition, a gradient-type field was utilized; hence, whether the same phenomenon applies to homogeneous magnetic fields remained unknown. Here, the authors investigate the pulse duration dependence of magnetostimulation limits for a 20-fold range of frequencies using homogeneous magnetic fields, such as the ones used for the drive field in MPI. Methods: Magnetostimulation thresholds were measured in the arms of six healthy subjects (age: 27 ± 5 yr). Each experiment comprised testing the thresholds at eight different pulse durations between 2 and 125 ms at a single frequency, which took approximately 30–40 min/subject. A total of 34 experiments were performed at three different frequencies: 1.2, 5.7, and 25.5 kHz. A solenoid coil providing homogeneous magnetic field was used to induce stimulation, and the field amplitude was measured in real time. A pre-emphasis based pulse shaping method was employed to accurately control the pulse durations. Subjects reported stimulation via a mouse click whenever they felt a twitching/tingling sensation. A sigmoid function was fitted to the subject responses to find the threshold at a specific frequency and duration, and the whole procedure was repeated at all relevant frequencies and pulse durations

  8. Effects of pulse duration on magnetostimulation thresholds

    PubMed Central

    Saritas, Emine U.; Goodwill, Patrick W.; Conolly, Steven M.

    2015-01-01

    Purpose: Medical imaging techniques such as magnetic resonance imaging and magnetic particle imaging (MPI) utilize time-varying magnetic fields that are subject to magnetostimulation limits, which often limit the speed of the imaging process. Various human-subject experiments have studied the amplitude and frequency dependence of these thresholds for gradient or homogeneous magnetic fields. Another contributing factor was shown to be number of cycles in a magnetic pulse, where the thresholds decreased with longer pulses. The latter result was demonstrated on two subjects only, at a single frequency of 1.27 kHz. Hence, whether the observed effect was due to the number of cycles or due to the pulse duration was not specified. In addition, a gradient-type field was utilized; hence, whether the same phenomenon applies to homogeneous magnetic fields remained unknown. Here, the authors investigate the pulse duration dependence of magnetostimulation limits for a 20-fold range of frequencies using homogeneous magnetic fields, such as the ones used for the drive field in MPI. Methods: Magnetostimulation thresholds were measured in the arms of six healthy subjects (age: 27 ± 5 yr). Each experiment comprised testing the thresholds at eight different pulse durations between 2 and 125 ms at a single frequency, which took approximately 30–40 min/subject. A total of 34 experiments were performed at three different frequencies: 1.2, 5.7, and 25.5 kHz. A solenoid coil providing homogeneous magnetic field was used to induce stimulation, and the field amplitude was measured in real time. A pre-emphasis based pulse shaping method was employed to accurately control the pulse durations. Subjects reported stimulation via a mouse click whenever they felt a twitching/tingling sensation. A sigmoid function was fitted to the subject responses to find the threshold at a specific frequency and duration, and the whole procedure was repeated at all relevant frequencies and pulse durations

  9. Period and pulse duration with "strobe" lights

    NASA Astrophysics Data System (ADS)

    Birriel, Jennifer

    2016-01-01

    Strobe lights have traditionally been discussed in The Physics Teacher in the context of stop action strobe photography. During the Halloween season most department and hardware stores sell inexpensive, compact "strobe" lights (although these can be found online year round). These lights generally sell for under 10 and usually employ LED lights. Most such devices have a rotary switch to adjust the rate at which the LED bulbs flash. This rotary switch is not calibrated—i.e., it has no markings to indicate the rate, but in general the greater the rotation of the switch from the off position, the faster the rate of flashing. We show how these simple devices can be used with a light sensor to study both the frequency of flashing and the duration of the light pulse. We briefly discuss if these devices are truly strobe lights.

  10. Kicking atoms with finite duration pulses

    NASA Astrophysics Data System (ADS)

    Fekete, Julia; Chai, Shijie; Daszuta, Boris; Andersen, Mikkel F.

    2016-05-01

    The atom optics delta-kicked particle is a paradigmatic system for experimental studies of quantum chaos and classical-quantum correspondence. It consists of a cloud of laser cooled atoms exposed to a periodically pulsed standing wave of far off-resonant laser light. A purely quantum phenomena in such systems are quantum resonances which transfers the atoms into a coherent superposition of largely separated momentum states. Using such large momentum transfer ``beamsplitters'' in atom interferometers may have applications in high precision metrology. The growth in momentum separation cannot be maintained indefinitely due to finite laser power. The largest momentum transfer is achieved by violating the usual delta-kick assumption. Therefore we explore the behavior of the atom optics kicked particle with finite pulse duration. We have developed a semi-classical model which shows good agreement with the full quantum description as well as our experiments. Furthermore we have found a simple scaling law that helps to identify optimal parameters for an atom interferometer. We verify this by measurements of the ``Talbot time'' (a measurement of h/m) which together with other well-known constants constitute a measurement of the fine structure constant.

  11. CW seeded optical parametric amplifier providing wavelength and pulse duration tunable nearly transform limited pulses.

    PubMed

    Hädrich, S; Gottschall, T; Rothhardt, J; Limpert, J; Tünnermann, A

    2010-02-01

    An optical parametric amplifier that delivers nearly transform limited pulses is presented. The center wavelength of these pulses can be tuned between 993 nm and 1070 nm and, at the same time, the pulse duration is varied between 206 fs and 650 fs. At the shortest pulse duration the pulse energy was increased up to 7.2 microJ at 50 kHz repetition rate. Variation of the wavelength is achieved by applying a tunable cw seed while the pulse duration can be varied via altering the pump pulse duration. This scheme offers superior flexibility and scaling possibilities.

  12. Inductively stabilized, long pulse duration transverse discharge apparatus

    DOEpatents

    Sze, Robert C.

    1986-01-01

    An inductively stabilized, long pulse duration transverse discharge apparatus. The use of a segmented electrode where each segment is attached to an inductive element permits high energy, high efficiency, long-pulsed laser outputs to be obtained. The present apparatus has been demonstrated with rare-gas halide lasing media. Orders of magnitude increase in pulse repetition frequency are obtained in lasing devices that do not utilize gas flow.

  13. TDR Using Autocorrelation and Varying-Duration Pulses

    NASA Technical Reports Server (NTRS)

    Lucena, Angel; Mullinex, Pam; Huang, PoTien; Santiago, Josephine; Mata, Carlos; Zavala, Carlos; Lane, John

    2008-01-01

    In an alternative to a prior technique of time-domain-reflectometry (TDR) in which very short excitation pulses are used, the pulses have very short rise and fall times and the pulse duration is varied continuously between a minimum and a maximum value. In both the present and prior techniques, the basic idea is to (1) measure the times between the generation of excitation pulses and the reception of reflections of the pulses as indications of the locations of one or more defects along a cable and (2) measure the amplitudes of the reflections as indication of the magnitudes of the defects. In general, an excitation pulse has a duration T. Each leading and trailing edge of an excitation pulse generates a reflection from a defect, so that a unique pair of reflections is associated with each defect. In the present alternative technique, the processing of the measured reflection signal includes computation of the autocorrelation function R(tau) identical with fx(t)x(t-tau)dt where t is time, x(t) is the measured reflection signal at time t, and taus is the correlation interval. The integration is performed over a measurement time interval short enough to enable identification and location of a defect within the corresponding spatial interval along the cable. Typically, where there is a defect, R(tau) exhibits a negative peak having maximum magnitude for tau in the vicinity of T. This peak can be used as a means of identifying a leading-edge/trailing-edge reflection pair. For a given spatial interval, measurements are made and R(tau) computed, as described above, for pulse durations T ranging from the minimum to the maximum value. The advantage of doing this is that the effective signal-to-noise ratio may be significantly increased over that attainable by use of a fixed pulse duration T.

  14. Pump pulse duration dependence of coherent phonon amplitudes in antimony

    NASA Astrophysics Data System (ADS)

    Misochko, O. V.

    2016-08-01

    Coherent optical phonons of A 1 k and E k symmetry in antimony have been studied using the femtosecond pump-probe technique. By varying the pump-pulse duration and keeping the probe duration constant, it was shown that the amplitude of coherent phonons of both symmetries exponentially decreases with increasing pulse width. It was found that the amplitude decay rate for the fully symmetric phonons with larger frequency is greater than that of the doubly degenerate phonons, whereas the frequency and lifetime for coherent phonons of both symmetries do not depend on the pump-pulse duration. Based on this data, the possibility of separation between dynamic and kinematic contributions to the generation mechanism of coherent phonons is discussed.

  15. Local field effect as a function of pulse duration

    SciTech Connect

    Novitsky, Denis V.

    2010-07-15

    In this brief report we give semiclassical consideration to the role of pulse duration in the observation of local field effects in the regime of optical switching. We show that the main parameter governing local field influence is the ratio of peak Rabi frequency corresponding to medium inversion and Lorentz frequency of the medium. To obtain significant local field effect, this parameter should be near unity that is valid only for long enough pulses. We also discuss the role of relaxation and pulse shape in this process.

  16. Widely tunable repetition-rate and pulse-duration nanosecond pulses from two spectral beam combined fiber amplifiers

    NASA Astrophysics Data System (ADS)

    Hu, Man; Zheng, Ye; Yang, Yifeng; Chen, Xiaolong; Zhao, Chun; Liu, Kai; Wang, Jianhua; Qi, Yunfeng; He, Bing; Zhou, Jun

    2016-10-01

    Nanosecond pulses with a widely tunable repetition-rate and pulse-duration at 1 μm wavelength are obtained by spectrally combining two pulse fiber amplifiers using a home-made polarization-independent multilayer dielectric reflective diffraction grating. The width of the combined pulses can be tuned from 4 ns to 800 ns, and the pulse repetition-rate can be ranged from 1 MHz to 200 MHz. Thanks to the spectral beam combining system, the maximum repetition-rate and pulse-duration of the combined pulses are doubled, compared to the single pulse fiber amplifier, by setting a proper temporal delay between the two pulse channels.

  17. Polarimetry diagnostic on OMEGA EP using a 10-ps, 263-nm probe beam.

    PubMed

    Davies, A; Haberberger, D; Boni, R; Ivancic, S; Brown, R; Froula, D H

    2014-11-01

    A polarimetry diagnostic was built and characterized for magnetic-field measurements in laser-plasma experiments on the OMEGA EP laser. This diagnostic was built into the existing 4ω (263-nm) probe system that employs a 10-ps laser pulse collected with an f/4 imaging system. The diagnostic measures the rotation of the probe beam's polarization. The polarimeter uses a Wollaston prism to split the probe beam into orthogonal polarization components. Spatially localized intensity variations between images indicate polarization rotation. Magnetic fields can be calculated by combining the polarimetry data with the measured plasma density profile obtained from angular filter refractometry. PMID:25430357

  18. Polarimetry diagnostic on OMEGA EP using a 10-ps, 263-nm probe beam

    SciTech Connect

    Davies, A. Haberberger, D.; Boni, R.; Ivancic, S.; Brown, R.; Froula, D. H.

    2014-11-15

    A polarimetry diagnostic was built and characterized for magnetic-field measurements in laser-plasma experiments on the OMEGA EP laser. This diagnostic was built into the existing 4ω (263-nm) probe system that employs a 10-ps laser pulse collected with an f/4 imaging system. The diagnostic measures the rotation of the probe beam's polarization. The polarimeter uses a Wollaston prism to split the probe beam into orthogonal polarization components. Spatially localized intensity variations between images indicate polarization rotation. Magnetic fields can be calculated by combining the polarimetry data with the measured plasma density profile obtained from angular filter refractometry.

  19. Influence of pulse duration on the plasma characteristics in high-power pulsed magnetron discharges

    SciTech Connect

    Konstantinidis, S.; Dauchot, J.P.; Ganciu, M.; Ricard, A.; Hecq, M.

    2006-01-01

    High-power pulsed magnetron discharges have drawn an increasing interest as an approach to produce highly ionized metallic vapor. In this paper we propose to study how the plasma composition and the deposition rate are influenced by the pulse duration. The plasma is studied by time-resolved optical emission and absorption spectroscopies and the deposition rate is controlled thanks to a quartz microbalance. The pulse length is varied between 2.5 and 20 {mu}s at 2 and 10 mTorr in pure argon. The sputtered material is titanium. For a constant discharge power, the deposition rate increases as the pulse length decreases. With 5 {mu}s pulse, for an average power of 300 W, the deposition rate is {approx}70% of the deposition rate obtained in direct current magnetron sputtering at the same power. The increase of deposition rate can be related to the sputtering regime. For long pulses, self-sputtering seems to occur as demonstrated by time-resolved optical emission diagnostic of the discharge. In contrary, the metallic vapor ionization rate, as determined by absorption measurements, diminishes as the pulses are shortened. Nevertheless, the ionization rate is in the range of 50% for 5 {mu}s pulses while it lies below 10% in the case of a classical continuous magnetron discharge.

  20. Simple circuit produces high-speed, fixed duration pulses

    NASA Technical Reports Server (NTRS)

    Garrahan, N. M.

    1965-01-01

    Circuit generates an output pulse of fixed width from a variable width input pulse. The circuit consists of a tunnel diode in parallel with an inductance driven by a constant current generator. It is used for pulsed communication equipment design.

  1. Sub-10ps monolithic and low-power photodetector readout

    SciTech Connect

    Varner, Gary S.; Ruckman, Larry L.

    2009-02-20

    Recent advances in photon detectors have resulted in high-density imaging arrays that offer many performance and cost advantages. In particular, the excellent transit time spread of certain devices show promise to provide tangible benefits in applications such as Positron Emission Tomography (PET). Meanwhile, high-density, high-performance readout techniques have not kept on pace for exploiting these developments. Photodetector readout for next generation high event rate particle identification and time-resolved PET requires a highly-integrated, low-power, and cost-effective readout technique. We propose fast waveform sampling as a method that meets these criteria and demonstrate that sub-10ps resolution can be obtained for an existing device.

  2. Performance of Variable Duration STUD Pulses with Fixed Peal Intensity and their Compliments

    NASA Astrophysics Data System (ADS)

    Hüller, Stefan; Afeyan, Bedros

    2015-11-01

    The simplest approach to STUD pulse implementation, given the requisite bandwidth of the laser is to keep the peak spike intensities fixed while modulating the lasers on and off on a 1-10 ps time scale. To what extent spatial scrambling is required in this case is compared to cases where the peak spike intensity varies with the duty cycle at fixed pulse width, to preserve the energy of the overall laser pulse. We compare RPP/CPP, SSD and STUD pulses at fixed energy with both variable pulse width and fixed peak intensity configurations and vice versa. This allows us to highlight the effects of speckle statistics, memory accumulation and pump depletion in setting gain saturation levels from the ideal democratized, incoherent sums of small growth spurts equally from all regions of the plasma, vs localized and highly nonlinear growth and re-amplification due to the unchanging or much too slowly changing nature of the illumination strategy, such as RPP/CPP or SSD. Work supported by the DOE NNSA-OFES Joint Program on HEDLP.

  3. Reaching time resolution of less than 10 ps with plastic scintillation detectors

    NASA Astrophysics Data System (ADS)

    Zhao, J. W.; Sun, B. H.; Tanihata, I.; Terashima, S.; Zhu, L. H.; Enomoto, A.; Nagae, D.; Nishimura, T.; Omika, S.; Ozawa, A.; Takeuchi, Y.; Yamaguchi, T.

    2016-07-01

    Timing-pick up detectors with excellent timing resolutions are essential in many modern nuclear physics experiments. Aiming to develop a Time-Of-Flight system with precision down to about 10 ps, we have made a systematic study of the timing characteristic of TOF detectors, which consist of several combinations of plastic scintillators and photomultiplier tubes. With the conventional electronics, the best timing resolution of about 5.1 ps (σ) has been achieved for detectors with an area size of 3 × 1cm2 . It is found that for data digitalization a combination of TAC and ADC can achieve a better time resolution than the currently available TDC. Simultaneous measurements of both time and pulse height are very valuable for the correction of time-walk effect.

  4. Influence of laser pulse duration on extreme ultraviolet and ion emission features from tin plasmas

    SciTech Connect

    Roy, A. E-mail: aroy@barc.gov.in; Harilal, S. S.; Polek, M. P.; Hassan, S. M.; Hassanein, A.; Endo, A.

    2014-03-15

    We investigated the role of laser pulse duration and intensity on extreme ultraviolet (EUV) generation and ion emission from a laser produced Sn plasma. For producing plasmas, planar slabs of pure Sn were irradiated with 1064 nm Nd:YAG laser pulses with varying pulse duration (5–20 ns) and intensity. Experimental results performed at CMUXE indicate that the conversion efficiency (CE) of the EUV radiation strongly depend on laser pulse width and intensity, with a maximum CE of ∼2.0% measured for the shortest laser pulse width used (5 ns). Faraday Cup ion analysis of Sn plasma showed that the ion flux kinetic profiles are shifted to higher energy side with the reduction in laser pulse duration and narrower ion kinetic profiles are obtained for the longest pulse width used. However, our initial results showed that at a constant laser energy, the ion flux is more or less constant regardless of the excitation laser pulse width. The enhanced EUV emission obtained at shortest laser pulse duration studied is related to efficient laser-plasma reheating supported by presence of higher energy ions at these pulse durations.

  5. Effect of wavelength and pulse duration on laser micro-welding of monocrystalline silicon and glass

    NASA Astrophysics Data System (ADS)

    Nordin, I. H. W.; Okamoto, Y.; Okada, A.; Jiang, H.; Sakagawa, T.

    2016-04-01

    Micro-welding characteristics of silicon and glass by pulsed lasers are described. In this study, four types of laser beam, which are nanosecond pulsed laser and picosecond pulsed laser of 532 and 1064 nm in wavelength, were used for joining monocrystalline silicon and glass. Influence of wavelength and pulse duration on micro-welding of monocrystalline silicon and glass was experimentally investigated under the same spot diameter, and the molten area of monocrystalline silicon and glass was characterized. Finally, the breaking strength was evaluated for the overlap weld joint with different pulse duration and wavelength. A splash area of molten silicon around the weld bead line was obvious in the nanosecond pulsed laser. On the other hand, there was no remarkable molten splash around the weld bead line in the picosecond pulsed laser. Breaking strength of specimens with 1064 nm wavelength was higher than with 532 nm wavelength in nanosecond laser, whereas breaking strength of laser-irradiated specimen by picosecond pulse duration was higher than that by nanosecond pulse duration. It is concluded that the combination of picosecond pulse duration and infrared wavelength leads to the stable molten area appearance of the weld bead and higher breaking strength in micro-welding of glass and monocrystalline silicon.

  6. Investigation on the impact of pulse duration for laser induced lithotripsy

    NASA Astrophysics Data System (ADS)

    Sroka, Ronald; Kiris, Tugba; Fiedler, Sebastian; Scheib, Gabriel; Kuznetsova, Julia; Pongratz, Thomas

    2014-03-01

    Objective: In-vitro investigation of Ho:YAG-laser induced stone fragmentation was performed to identify potential impacts of different pulse durations on stone fragmentation characteristics. Materials and Methods: An innovative Ho:YAG laser system (Swiss LaserClast, EMS S.A., Nyon, Switzerland) with selectable long- or short pulse mode was tested with regard to its fragmentation properties. The pulse duration depends on the specific laser parameter used. Fragmentation tests (hand held, hands free, single pulse induced crater) on artificial BEGO-Stones and fiber burn back tests were performed under reproducible experimental conditions. Additionally, the repulsion of long versus short laser pulses was compared using the pendulum set-up. Results: Differences in fragmentation rates between the two pulse duration regimes were seen. The difference was, however, not statistically significant. Using long pulse mode, the fiber burn back is nearly negligible while in short pulse mode an increased burn back was seen. The results of the pendulum test showed that the deviation induced by the momentum of shorter pulses is increased compared to longer pulses. Conclusion: Long pulse-mode showed reduced side effects like repulsion and fiber burn back in comparison to short pulse-mode while fragmentation rates remained at a comparable level. Lower push back and reduced burn back of longer laser pulses may results in better clinical outcome of laser lithotripsy and more convenient handling during clinical use.

  7. Method and apparatus for producing durationally short ultraviolet or X-ray laser pulses

    DOEpatents

    MacGowan, Brian J.; Matthews, Dennis L.; Trebes, James E.

    1988-01-01

    A method and apparatus is disclosed for producing ultraviolet or X-ray laser pulses of short duration (32). An ultraviolet or X-ray laser pulse of long duration (12) is progressively refracted, across the surface of an opaque barrier (28), by a streaming plasma (22) that is produced by illuminating a solid target (16, 18) with a pulse of conventional line focused high power laser radiation (20). The short pulse of ultraviolet or X-ray laser radiation (32), which may be amplified to high power (40, 42), is separated out by passage through a slit aperture (30) in the opaque barrier (28).

  8. Method and apparatus for producing durationally short ultraviolet or x-ray laser pulses

    DOEpatents

    MacGowan, B.J.; Matthews, D.L.; Trebes, J.E.

    1987-05-05

    A method and apparatus is disclosed for producing ultraviolet or x- ray laser pulses of short duration. An ultraviolet or x-ray laser pulse of long duration is progressively refracted, across the surface of an opaque barrier, by a streaming plasma that is produced by illuminating a solid target with a pulse of conventional line focused high power laser radiation. The short pulse of ultraviolet or x-ray laser radiation, which may be amplified to high power, is separated out by passage through a slit aperture in the opaque barrier.

  9. The effects of pulse duration on ablation pressure driven by laser radiation

    SciTech Connect

    Zhou, Lei; Li, Xiao-Ya Zhu, Wen-Jun; Wang, Jia-Xiang; Tang, Chang-Jian

    2015-03-28

    The effects of laser pulse duration on the ablation pressure induced by laser radiation are investigated using Al target. Numerical simulation results using one dimensional radiation hydro code for laser intensities from 5×10{sup 12}W/cm{sup 2} to 5×10{sup 13}W/cm{sup 2} and pulse durations from 0.5 ns to 20 ns are presented. These results suggest that the laser intensity scaling law of ablation pressure differs for different pulse durations. And the theoretical analysis shows that the effects of laser pulse duration on ablation pressure are mainly caused by two regimes: the unsteady-state flow and the radiative energy loss to vacuum.

  10. Factors influencing the microwave pulse duration in a klystron-like relativistic backward wave oscillator

    SciTech Connect

    Xiao Renzhen; Zhang Xiaowei; Zhang Ligang; Li Xiaoze; Zhang Lijun

    2012-07-15

    In this paper, we analyze the factors that affect the microwave pulse duration in a klystron-like relativistic backward wave oscillator (RBWO), including the diode voltage, the guiding magnetic field, the electron beam collector, the extraction cavity, and the gap between the electron beam and the slow wave structure (SWS). The results show that the microwave pulse duration increases with the diode voltage until breakdown occurs on the surface of the extraction cavity. The pulse duration at low guiding magnetic field is generally 5-10 ns smaller than that at high magnetic field due to the asymmetric electron emission and the larger energy spread of the electron beam. The electron beam collector can affect the microwave pulse duration significantly because of the anode plasma generated by bombardment of the electron beam on the collector surface. The introduction of the extraction cavity only slightly changes the pulse duration. The decrease of the gap between the electron beam and the SWS can increase the microwave pulse duration greatly.

  11. Diffraction response of photorefractive polymers over nine orders of magnitude of pulse duration.

    PubMed

    Blanche, Pierre-Alexandre; Lynn, Brittany; Churin, Dmitriy; Kieu, Khanh; Norwood, Robert A; Peyghambarian, Nasser

    2016-01-01

    The development of a single mode fiber-based pulsed laser with variable pulse duration, energy, and repetition rate has enabled the characterization of photorefractive polymer (PRP) in a previously inaccessible regime located between millisecond and microsecond single pulse illumination. With the addition of CW and nanosecond pulse lasers, four wave mixing measurements covering 9 orders of magnitudes in pulse duration are reported. Reciprocity failure of the diffraction efficiency according to the pulse duration for a constant energy density is observed and attributed to multiple excitation, transport and trapping events of the charge carriers. However, for pulses shorter than 30 μs, the efficiency reaches a plateau where an increase in energy density no longer affects the efficiency. This plateau is due to the saturation of the charge generation at high peak power given the limited number of sensitizer sites. The same behavior is observed in two different types of devices composed of the same material but with or without a buffer layer covering one electrode, which confirm the origin of these mechanisms. This new type of measurement is especially important to optimize PRP for applications using short pulse duration. PMID:27364998

  12. Diffraction response of photorefractive polymers over nine orders of magnitude of pulse duration

    PubMed Central

    Blanche, Pierre-Alexandre; Lynn, Brittany; Churin, Dmitriy; Kieu, Khanh; Norwood, Robert A.; Peyghambarian, Nasser

    2016-01-01

    The development of a single mode fiber-based pulsed laser with variable pulse duration, energy, and repetition rate has enabled the characterization of photorefractive polymer (PRP) in a previously inaccessible regime located between millisecond and microsecond single pulse illumination. With the addition of CW and nanosecond pulse lasers, four wave mixing measurements covering 9 orders of magnitudes in pulse duration are reported. Reciprocity failure of the diffraction efficiency according to the pulse duration for a constant energy density is observed and attributed to multiple excitation, transport and trapping events of the charge carriers. However, for pulses shorter than 30 μs, the efficiency reaches a plateau where an increase in energy density no longer affects the efficiency. This plateau is due to the saturation of the charge generation at high peak power given the limited number of sensitizer sites. The same behavior is observed in two different types of devices composed of the same material but with or without a buffer layer covering one electrode, which confirm the origin of these mechanisms. This new type of measurement is especially important to optimize PRP for applications using short pulse duration. PMID:27364998

  13. Diffraction response of photorefractive polymers over nine orders of magnitude of pulse duration

    NASA Astrophysics Data System (ADS)

    Blanche, Pierre-Alexandre; Lynn, Brittany; Churin, Dmitriy; Kieu, Khanh; Norwood, Robert A.; Peyghambarian, Nasser

    2016-07-01

    The development of a single mode fiber-based pulsed laser with variable pulse duration, energy, and repetition rate has enabled the characterization of photorefractive polymer (PRP) in a previously inaccessible regime located between millisecond and microsecond single pulse illumination. With the addition of CW and nanosecond pulse lasers, four wave mixing measurements covering 9 orders of magnitudes in pulse duration are reported. Reciprocity failure of the diffraction efficiency according to the pulse duration for a constant energy density is observed and attributed to multiple excitation, transport and trapping events of the charge carriers. However, for pulses shorter than 30 μs, the efficiency reaches a plateau where an increase in energy density no longer affects the efficiency. This plateau is due to the saturation of the charge generation at high peak power given the limited number of sensitizer sites. The same behavior is observed in two different types of devices composed of the same material but with or without a buffer layer covering one electrode, which confirm the origin of these mechanisms. This new type of measurement is especially important to optimize PRP for applications using short pulse duration.

  14. Evolution of electron beam pulses of short duration in the solar corona

    NASA Astrophysics Data System (ADS)

    Casillas-Pérez, G. A.; Jeyakumar, S.; Pérez-Enríquez, H. R.; Trinidad, M. A.

    2016-11-01

    Narrowband radio bursts with durations of the order of milliseconds, called spikes, are known to be associated with solar flares. In order to understand the particle beams responsible for the radio spike phenomena, evolution of electron beam pulses injected from a solar flare region into the corona is studied. Numerical integration of the Fokker-Planck (FP) equation is used to follow the evolution of the electron beam pulse. The simulations show that the short duration pulses lose most of their energy within a second of propagation into the corona. Electron beam with a small low energy cut off is thermalized faster than that with a high low energy cut off.

  15. Compression of X-ray Free Electron Laser Pulses to Attosecond Duration

    PubMed Central

    Sadler, James D.; Nathvani, Ricky; Oleśkiewicz, Piotr; Ceurvorst, Luke A.; Ratan, Naren; Kasim, Muhammad F.; Trines, Raoul M. G. M.; Bingham, Robert; Norreys, Peter A.

    2015-01-01

    State of the art X-ray Free Electron Laser facilities currently provide the brightest X-ray pulses available, typically with mJ energy and several hundred femtosecond duration. Here we present one- and two-dimensional Particle-in-Cell simulations, utilising the process of stimulated Raman amplification, showing that these pulses are compressed to a temporally coherent, sub-femtosecond pulse at 8% efficiency. Pulses of this type may pave the way for routine time resolution of electrons in nm size potentials. Furthermore, evidence is presented that significant Landau damping and wave-breaking may be beneficial in distorting the rear of the interaction and further reducing the final pulse duration. PMID:26568520

  16. Compression of X-ray Free Electron Laser Pulses to Attosecond Duration.

    PubMed

    Sadler, James D; Nathvani, Ricky; Oleśkiewicz, Piotr; Ceurvorst, Luke A; Ratan, Naren; Kasim, Muhammad F; Trines, Raoul M G M; Bingham, Robert; Norreys, Peter A

    2015-01-01

    State of the art X-ray Free Electron Laser facilities currently provide the brightest X-ray pulses available, typically with mJ energy and several hundred femtosecond duration. Here we present one- and two-dimensional Particle-in-Cell simulations, utilising the process of stimulated Raman amplification, showing that these pulses are compressed to a temporally coherent, sub-femtosecond pulse at 8% efficiency. Pulses of this type may pave the way for routine time resolution of electrons in nm size potentials. Furthermore, evidence is presented that significant Landau damping and wave-breaking may be beneficial in distorting the rear of the interaction and further reducing the final pulse duration. PMID:26568520

  17. Effect of micropulse duration on tissue ablation using a stretched free electron laser pulse train

    NASA Astrophysics Data System (ADS)

    Kozub, John A.; Mackanos, Mark A.; Mendenhall, Marcus H.; Jansen, E. Duco

    2004-06-01

    The pulse train from a Mark III FEL tuned to a wavelength of 6.45 microns has been shown to be efficient at ablating soft tissue with minimal collateral damage. This laser has a unique pulse structure consisting of a train of 1ps micropulses spaced 350ps apart, which is maintained for 4-5 microseconds (the macropulse) and is repeated at 1-30Hz. We are investigating the role of the pulse structure in the ablation mechanism. In order to determine the importance of non-linear effects potentially induced by the high peak power of the micropulses, we are using a grating pulse stretcher optimized for 6.45 microns to vary the micropulse duration while maintaining the macropulse duration and micropulse frequency. The technique allows use of the same pulse energy and average power with widely variable peak power. Ablation thresholds were measured using PROB-IT analysis and crater depths were measured using OCT imaging. In water, gelatin, and mouse dermis, we have found no statistically significant difference in the ablation threshold of pulses having widths of 1, 30, 60, and 100ps. The measured ablation efficiency of mouse dermis also showed no significant difference over the same range of pulse widths. This data suggests that the ablation characteristics obtained with the FEL at 6.45 microns are independent of the micropulse duration and do not rely on the high peak power of the FEL pulse train.

  18. Reducing the duration of broadband excitation pulses using optimal control with limited RF amplitude.

    PubMed

    Skinner, Thomas E; Reiss, Timo O; Luy, Burkhard; Khaneja, Navin; Glaser, Steffen J

    2004-03-01

    Combining optimal control theory with a new RF limiting step produces pulses with significantly reduced duration and improved performance for a given maximum RF amplitude compared to previous broadband excitation by optimized pulses (BEBOP). The resulting pulses tolerate variations in RF homogeneity relevant for standard high-resolution NMR probes. Design criteria were transformation of Iz-->Ix over resonance offsets of +/-20kHz and RF variability of +/-5%, with a pulse length of 500 micros and peak RF amplitude equal to 17.5 kHz. Simulations transform Iz to greater than 0.995 Ix, with phase deviations of the final magnetization less than 2 degrees, over ranges of resonance offset and RF variability that exceed the design targets. Experimental performance of the pulse is in excellent agreement with the simulations. Performance tradeoffs for yet shorter pulses or pulses with decreased digitization are also investigated. PMID:14987600

  19. Role of PTHrP(1-34) Pulse Frequency Versus Pulse Duration to Enhance Mesenchymal Stromal Cell Chondrogenesis.

    PubMed

    Fischer, Jennifer; Ortel, Marlen; Hagmann, Sebastien; Hoeflich, Andreas; Richter, Wiltrud

    2016-12-01

    Generation of phenotypically stable, articular chondrocytes from mesenchymal stromal cells (MSCs) is still an unaccomplished task, with formation of abundant, hyaline extracellular matrix, and avoidance of hypertrophy being prime challenges. We recently demonstrated that parathyroid hormone-related protein (PTHrP) is a promising factor to direct chondrogenesis of MSCs towards an articular phenotype, since intermittent PTHrP application stimulated cartilage matrix production and reduced undesired hypertrophy. We here investigated the role of frequency, pulse duration, total exposure time, and underlying mechanisms in order to unlock the full potential of PTHrP actions. Human MSC subjected to in vitro chondrogenesis for six weeks were exposed to 2.5 nM PTHrP(1-34) pulses from days 7 to 42. Application frequency was increased from three times weekly (3 × 6 h/week) to daily maintaining either the duration of individual pulses (6 h/day) or total exposure time (18 h/week; 2.6 h/day). Daily PTHrP treatment significantly increased extracellular matrix deposition regardless of pulse duration and suppressed alkaline-phosphatase activity by 87%. High total exposure time significantly reduced cell proliferation at day 14. Pulse duration was critically important to significantly reduce IHH expression, but irrelevant for PTHrP-induced suppression of the hypertrophic markers MEF2C and IBSP. COL10A1, RUNX2, and MMP13 expression remained unaltered. Decreased IGFBP-2, -3, and -6 expression suggested modulated IGF-I availability in PTHrP groups, while drop of SOX9 protein levels during the PTHrP-pulse may delay chondroblast formation and hypertrophy. Overall, the significantly optimized timing of PTHrP-pulses demonstrated a vast potential to enhance chondrogenesis of MSC and suppress hypertrophy possibly via superior balancing of IGF- and SOX9-related mechanisms. J. Cell. Physiol. 231: 2673-2681, 2016. © 2016 Wiley Periodicals, Inc. PMID:27548511

  20. Ventricular myocyte injury by high-intensity electric field: Effect of pulse duration.

    PubMed

    Prado, Luiza Ns; Goulart, Jair T; Zoccoler, Marcelo; Oliveira, Pedro X

    2016-04-01

    Although high-intensity electric fields (HEF) application is currently the only effective therapy available to terminate ventricular fibrillation, it may cause injury to cardiac cells. In this study we determined the relation between HEF pulse length and cardiomyocyte lethal injury. We obtained lethality curves by survival analysis, which were used to determine the value of HEF necessary to kill 50% of cells (E50) and plotted a strength-duration (SxD) curve for lethality with 10 different durations: 0.1, 0.2, 0.5, 1, 3, 5, 10, 20, 35 and 70 ms. For the same durations we also obtained an SxD curve for excitation and established an indicator for stimulatory safeness (stimulation safety factor - SSF) as the ratio between the SxD curve for lethality and one for excitation. We found that the lower the pulse duration, the higher the HEF intensity required to cell death. Contrary to expectations, the highest SSF value does not correspond to the lowest pulse duration but to the one of 0.5 ms. As defibrillation threshold has been described as duration-dependent, our results imply that the use of shorter stimulus duration - instead of the one typically used in the clinic (10 ms) - might increase defibrillation safeness. PMID:26830130

  1. Short-wavelength ablation of solids: pulse duration and wavelength effects

    NASA Astrophysics Data System (ADS)

    Juha, Libor; Bittner, Michal; Chvostova, Dagmar; Letal, Vit; Krasa, Josef; Otcenasek, Zdenek; Kozlova, Michaela; Polan, Jiri; Prag, Ansgar R.; Rus, Bedrich; Stupka, Michal; Krzywinski, Jacek; Andrejczuk, Andrzej; Pelka, Jerzy B.; Sobierajski, Ryszard H.; Ryc, Leszek; Feldhaus, Josef; Boody, Frederick P.; Fiedorowicz, Henryk; Bartnik, Andrzej; Mikolajczyk, Janusz; Rakowski, Rafal; Kubat, P.; Pina, Ladislav; Grisham, Michael E.; Vaschenko, Georgiy O.; Menoni, Carmen S.; Rocca, Jorge J. G.

    2004-11-01

    For conventional wavelength (UV-Vis-IR) lasers delivering radiation energy to the surface of materials, ablation thresholds, ablation (etch) rates, and the quality of ablated structures often differ dramatically between short (typically nanosecond) and ultrashort (typically femtosecond) pulses. Various short-wavelength (l < 100 nm) lasers emitting pulses with durations ranging from ~ 10 fs to ~ 1 ns have recently been put into a routine operation. This makes it possible to investigate how the ablation characteristics depend on the pulse duration in the XUV spectral region. 1.2-ns pulses of 46.9-nm radiation delivered from a capillary-discharge Ne-like Ar laser (Colorado State University, Fort Collins), focused by a spherical Sc/Si multilayer-coated mirror were used for an ablation of organic polymers and silicon. Various materials were irradiated with ellipsoidal-mirror-focused XUV radiation (λ = 86 nm, τ = 30-100 fs) generated by the free-electron laser (FEL) operated at the TESLA Test Facility (TTF1 FEL) in Hamburg. The beam of the Ne-like Zn XUV laser (λ = 21.2 nm, τ < 100 ps) driven by the Prague Asterix Laser System (PALS) was also successfully focused by a spherical Si/Mo multilayer-coated mirror to ablate various materials. Based on the results of the experiments, the etch rates for three different pulse durations are compared using the XUV-ABLATOR code to compensate for the wavelength difference. Comparing the values of etch rates calculated for short pulses with those measured for ultrashort pulses, we can study the influence of pulse duration on XUV ablation efficiency. Ablation efficiencies measured with short pulses at various wavelengths (i.e. 86/46.9/21.2 nm from the above-mentioned lasers and ~ 1 nm from the double stream gas-puff Xe plasma source driven by PALS) show that the wavelength influences the etch rate mainly through the different attenuation lengths.

  2. Dependence of Nd:YAG laser derusting and passivation of iron artifacts on pulse duration

    NASA Astrophysics Data System (ADS)

    Osticioli, Iacopo; Siano, Salvatore

    2013-11-01

    In this work laser derusting and passivation process of iron objects of conservation interest were investigated. In particular, the effects induced by laser irradiation of three lasers with different temporal emission regimes were studied, exhibiting very different behavior. Nd:YAG(1064 nm) laser systems were employed in the experiments: a Q-Switching laser with pulse duration of 8 ns, a Long Q-Switching laser with pulse duration of 120 ns and a Short Free Running pulse duration in a range of 40-120 μs. These lasers are commonly used in conservation. Lasers treatments were applied on iron samples subjected to natural weathering in outdoor conditions for about five years. Moreover some experiments were also performed on metallic parts of an original chandelier from the seventies as well as on a deeply corroded Roman sword. Results obtained reveals that longer pulse duration leads to phase changes on the rust layer and a homogeneous black-grayish coating is formed on the surface (identified as magnetite) after treatment. Whereas, QS laser pulses are capable to induce ablation of the corrosion layer exposing the pure metal underneath. Finally, LQS interaction includes deep ablation with localized micro-melting of the metal surface and partial transformation of the residual mineral areas was observed. The irradiation results were characterized through optical and BS- ESEM along with Raman spectroscopy, which allowed a clear phenomenological differentiation among the three operating regimes and provided information on their optimal exploitation in restoration of iron artifacts.

  3. Wavelength and pulse duration effects on laser induced changes on raw pigments used in paintings.

    PubMed

    Oujja, M; Sanz, M; Rebollar, E; Marco, J F; Domingo, C; Pouli, P; Kogou, S; Fotakis, C; Castillejo, M

    2013-02-01

    In this study, the reaction of widely used artist's pigments in raw form to pulsed laser radiation of different wavelengths and pulse duration was investigated. Vermilion, lead chromate and malachite (in the form of pellets) were irradiated using laser pulses of 500 fs at 248 nm, and pulses of 150 ps and 15 ns at 1064 and 213 nm. Optical microscopy, colorimetry, spectrofluorimetry, micro-Raman spectroscopy and X-ray photoelectron spectroscopy were employed to characterize the physicochemical changes induced to the pigments. Change of crystalline phase was identified for vermilion while reduction processes take place for lead chromate and malachite. It was found that these effects were minimized by application of ultraviolet ultrashort pulses (of femtosecond and picosecond duration) as compared with changes occurring by pulsed infrared irradiation (of both picosecond and nanosecond duration). The results presented are discussed in relation to previous research on painted mock-ups in order to elucidate the role and significance of the binding media in the laser induced discoloration of painted surfaces and thus to propose optimum laser cleaning practices.

  4. Influence of the Nd:YAG Laser Pulse Duration on the Temperature of Primary Enamel

    PubMed Central

    Valério, R. A.; da Cunha, V. S.; Galo, R.; de Lima, F. A.; Bachmann, L.; Corona, S. A. M.; Borsatto, M. C.

    2015-01-01

    The aim of this study is to evaluate the temperature change on specimens of primary enamel irradiated with different pulse duration of Nd:YAG laser. Fifteen sound primary molars were sectioned mesiodistally, resulting in 30 specimens (3.5 × 3.5 × 2.0 mm). Two small holes were made on the dentin surface in which K-type thermocouples were installed to evaluate thermal changes. Specimens were randomly assigned in 3 groups (n = 10): A = EL (extra long pulse, 10.000 μs), B = LP (long pulse, 700 μs), and C = SP (short pulse, 350 μs). Nd:YAG laser (λ = 1.064 μm) was applied at contact mode (10 Hz, 0.8 W, 80 mJ) and energy density of 0.637 mJ/mm2. Analysis of variance (ANOVA) was performed for the statistical analysis (P = 0.46). Nd:YAG laser pulse duration provided no difference on the temperature changes on primary enamel, in which the following means were observed: A = EL (23.15°C ± 7.75), B = LP (27.33°C ± 11.32), and C = SP (26.91°C ± 12.85). It can be concluded that the duration of the laser pulse Nd:YAG increased the temperature of the primary enamel but was not influenced by different pulse durations used in the irradiation. PMID:25874244

  5. Quasi-real-time photon pulse duration measurement by analysis of FEL radiation spectra.

    PubMed

    Engel, Robin; Düsterer, Stefan; Brenner, Günter; Teubner, Ulrich

    2016-01-01

    For photon diagnostics at free-electron lasers (FELs), the determination of the photon pulse duration is an important challenge and a complex task. This is especially true for SASE FELs with strongly fluctuating pulse parameters. However, most techniques require an extensive experimental setup, data acquisition and evaluation time, limiting the usability in all-day operation. In contrast, the presented work uses an existing approach based on the analysis of statistical properties of measured SASE FEL spectra and implements it as a software tool, integrated in FLASH's data acquisition system. This allows the calculation of the average pulse durations from a set of measured spectral distributions with only seconds of delay, whenever high-resolution spectra are recorded. PMID:26698053

  6. Simultaneous optimization of power and duration of radio-frequency pulse in PARACEST MRI.

    PubMed

    Rezaeian, Mohammad-Reza; Hossein-Zadeh, Gholam-Ali; Soltanian-Zadeh, Hamid

    2016-07-01

    Chemical exchange saturation transfer (CEST) MRI is increasingly used to probe mobile proteins and microenvironment properties, and shows great promise for tumor and stroke diagnosis. The CEST effect is complex and depends not only on the CEST agent concentration, exchange rates, the characteristic of the magnetization transfer (MT), and the relaxation properties of the tissue, but also varies with the experimental conditions such as radio-frequency (RF) pulse power and duration. The RF pulse is one of the most important factors that promote the CEST effect for biological properties such as pH, temperature and protein content, especially for contrast agents with intermediate to fast exchange rates. The CEST effect is susceptible to the RF duration and power. The present study aims at determining the optimal power and the corresponding optimal duration (that maximize the CEST effect) using an off-resonance scheme through a new definition of the CEST effect. This definition is formulated by solving the Bloch-McConnell equation through the R1ρ method (based on the eigenspace solution) for both of the MT and CEST effects as well as their interactions. The proposed formulations of the optimal RF pulse power and duration are the first formulations in which the MT effect is considered. The extracted optimal RF pulse duration and power are compared with those of the MTR asymmetry model in two- and three-pool systems, using synthetic data that are similar to the muscle tissue. To validate them further, the formulations are compared with the empirical formulation of the CEST effect and other findings of the previous researches. By extending our formulations, the optimal power and the corresponding optimal duration (in the biological systems with many chemical exchange sites) can be determined. PMID:26956610

  7. Comparison of membrane electroporation and protein denature in response to pulsed electric field with different durations.

    PubMed

    Huang, Feiran; Fang, Zhihui; Mast, Jason; Chen, Wei

    2013-05-01

    In this paper, we compared the minimum potential differences in the electroporation of membrane lipid bilayers and the denaturation of membrane proteins in response to an intensive pulsed electric field with various pulse durations. Single skeletal muscle fibers were exposed to a pulsed external electric field. The field-induced changes in the membrane integrity (leakage current) and the Na channel currents were monitored to identify the minimum electric field needed to damage the membrane lipid bilayer and the membrane proteins, respectively. We found that in response to a relatively long pulsed electric shock (longer than the membrane intrinsic time constant), a lower membrane potential was needed to electroporate the cell membrane than for denaturing the membrane proteins, while for a short pulse a higher membrane potential was needed. In other words, phospholipid bilayers are more sensitive to the electric field than the membrane proteins for a long pulsed shock, while for a short pulse the proteins become more vulnerable. We can predict that for a short or ultrashort pulsed electric shock, the minimum membrane potential required to start to denature the protein functions in the cell plasma membrane is lower than that which starts to reduce the membrane integrity.

  8. The Nature of Emission from Optical Breakdown Induced by Pulses of fs and ns Duration

    SciTech Connect

    Carr, C W; Feit, M D; Rubenchik, A M; Demange, P; Kucheyev, S; Shirk, M D; Radousky, H B; Demos, S G

    2004-11-09

    Spectral emission from optical breakdown in the bulk of a transparent dielectric contains information about the nature of the breakdown medium. We have made time resolved measurements of the breakdown induced emission caused by nanosecond and femtosecond infrared laser pulses. We previously demonstrated that the emission due to ns pulses is blackbody in nature allowing determination of the fireball temperature and pressure during and after the damage event. The emission due to femtosecond pulse breakdown is not blackbody in nature; two different spectral distributions being noted. In one case, the peak spectral distribution occurs at the second harmonic of the incident radiation, in the other the distribution is broader and flatter and presumably due to continuum generation. The differences between ns and fs breakdown emission can be explained by the differing breakdown region geometries for the two pulse durations. The possibility to use spectral emission as a diagnostic of the emission region morphology will be discussed.

  9. Effects of Pulse Duration on Bulk Laser Damage in 350-nm Raster-Scanned DKDP

    SciTech Connect

    Runkel, M; Bruere, J; Sell, W; Weiland, T; Milam, D; Hahn, D E; Nostrand, M C

    2002-10-30

    In this paper we present the results of bulk damage experiments done on Type-I1 DKDP triple harmonic generator crystals that were raster conditioned with 351-355 nm wavelengths and pulse durations of 4 and 23.2 ns. In the first phase of experiments 20 different scan protocols were rastered into a sample of rapid growth DKDP. The sample was then rastered at damage-causing fluences to determine the three most effective protocols. These three protocols were scanned into a 15-cm sample of conventional-growth DKDP and then exposed to single shots of a I-cm beam from LLNL's Optical Sciences Laser at fluences ranging from 0.5 - 1.5X of the 10% damage probability fluence and nominal pulse durations of 0.1,0.3,0.8,3.2,7.0 and 20 ns. The experiment showed that pulse durations in the 1-3 ns range were much more effective at conditioning than pulses in the 16.3 ns range and that the multiple pass 'peak fluence' scan was more effective than the single pass 'leading edge' scan for 23.2 ns XeF scans.

  10. Effects of pulse duration and areal density on ultrathin foil acceleration

    SciTech Connect

    Zhang Xiaomei; Shen Baifei; Ji Liangliang; Wang Fengchao; Wen Meng; Wang Wenpeng; Xu Jiancai; Yu Yahong

    2010-06-15

    The influence of laser pulse duration and areal density of target in the interaction of a circularly polarized pulse with an ultrathin overdense foil is investigated. One-dimensional particle-in-cell simulation shows that with an appropriate laser-pulse rising front, the light pressure acceleration regime is effective even though the thin foil is transparent. As the laser intensity evolves, three stages in the acceleration process can be identified: at first the total reflection of the laser pulse, followed by partial reflection, and then near total reflection again due to the Doppler effect. The influences of the rising front of laser pulse and areal density of the ultrathin foil are investigated. It is found that an optimal laser pulse rising front exists for obtaining high (saturation) ion energy with the same laser energy within a short time. An optimal areal density also exists for obtaining the highest energy. For the same laser pulse, a higher areal density or a higher density with same areal density is more appropriate for obtaining a stationary state for making light pressure acceleration mechanism more effective.

  11. Combining microwave beams with high peak power and long pulse duration

    SciTech Connect

    Li Guolin; Shu Ting; Yuan Chengwei; Zhang Jun; Jin Zhenxing; Yang Jianhua

    2010-03-15

    The beam combining results with a metal dichroic plate illuminated by the S/X band gigawatt level high power microwaves are presented. According to the previous experiments, the microwave breakdown problem becomes obvious when the peak power and the pulse duration increase, thus, several methods for enhancing the power handling capacity have been considered, and the metal dichroic plates are redesigned to handle the S/X band high power microwaves. Then the design, fabrication, and testing procedure are discussed in detail. The further experimental results reveal that, operated on the self-built accelerator Spark-04, the radiated powers from the S and X band sources have reached 1.8 GW with pulse durations of about 80 ns, and both beams have been successfully operated on the selected dichroic plate without microwave breakdown.

  12. Study on the influence of laser pulse duration in the long nanosecond regime on the laser induced plasma spectroscopy

    NASA Astrophysics Data System (ADS)

    Elnasharty, I. Y.

    2016-10-01

    By using a high power pulsed fiber laser, this study reports the experimental investigation of the laser-induced plasma characteristics for the laser pulse duration range extended from 40 ns to 200 ns. The experiments were performed with keeping the laser fluence constant at 64 J/cm2. The measurements show that, for the early phase of plasma formation, the spectral line intensities and the continuum emissions as well as the plasma characteristics decay to a certain extent with the increase of the pulse duration. On the other hand, as the plasma evolves in post laser pulse regime, the electron density and the degree of ionization increase slightly for the longer pulses, while the plume temperature is more or less independent from the pulse duration. Furthermore, the ablation characteristics, such as the ablation rate, coincide with the results of plasma characteristics for the different pulse durations. Eventually, with keeping the laser fluence constant at 64 J/cm2, the analytical performance of Laser-Induced Plasma Spectroscopy (LIPS) for the corresponding pulse duration range is examined by using a temporal gating and non-gating analyses. The measurements show that, in the case of gating analysis, all pulse durations yield almost the same range of limits of detections LODs. On the other hand, for non-gating analysis, the longer pulse durations provide lower LODs (better) than the shorter ones by orders of magnitude. Moreover, the calculated absolute limit of detection (LODAbs) for the longest pulse duration (i.e. 200 ns) is lower by approximately factor 2 than that of the shortest one (i.e. 40 ns).

  13. Methods of Optimal Control of Laser-Plasma Instabilities Using Spike Trains of Uneven Duration and Delay (STUD Pulses)

    NASA Astrophysics Data System (ADS)

    Afeyan, Bedros

    2013-10-01

    We have recently introduced and extensively studied a new adaptive method of LPI control. It promises to extend the effectiveness of laser as inertial fusion drivers by allowing active control of stimulated Raman and Brillouin scattering and crossed beam energy transfer. It breaks multi-nanosecond pulses into a series of picosecond (ps) time scale spikes with comparable gaps in between. The height and width of each spike as well as their separations are optimization parameters. In addition, the spatial speckle patterns are changed after a number of successive spikes as needed (from every spike to never). The combination of these parameters allows the taming of parametric instabilities to conform to any desired reduced reflectivity profile, within the bounds of the performance limitations of the lasers. Instead of pulse shaping on hydrodynamical time scales, far faster (from 1 ps to 10 ps) modulations of the laser profile will be needed to implement the STUD pulse program for full LPI control. We will show theoretical and computational evidence for the effectiveness of the STUD pulse program to control LPI. The physics of why STUD pulses work and how optimization can be implemented efficiently using statistical nonlinear optical models and techniques will be explained. We will also discuss a novel diagnostic system employing STUD pulses that will allow the boosted measurement of velocity distribution function slopes on a ps time scale in the small crossing volume of a pump and a probe beam. Various regimes from weak to strong coupling and weak to strong damping will be treated. Novel pulse modulation schemes and diagnostic tools based on time-lenses used in both microscope and telescope modes will be suggested for the execution of the STUD pule program. Work Supported by the DOE NNSA-OFES Joint Program on HEDLP and DOE OFES SBIR Phase I Grants.

  14. Optimum pulse duration and radiant exposure for vascular laser therapy of dark port-wine skin: a theoretical study.

    PubMed

    Tunnell, James W; Wang, Lihong V; Anvari, Bahman

    2003-03-01

    Laser therapy for cutaneous hypervascular malformations such as port-wine stain birthmarks is currently not feasible for dark-skinned individuals. We study the effects of pulse duration, radiant exposure, and cryogen spray cooling (CSC) on the thermal response of skin, using a Monte Carlo based optical-thermal model. Thermal injury to the epidermis decreases with increasing pulse duration during irradiation at a constant radiant exposure; however, maintaining vascular injury requires that the radiant exposure also increase. At short pulse durations, only a minimal increase in radiant exposure is necessary for a therapeutic effect to be achieved because thermal diffusion from the vessels is minimal. However, at longer pulse durations the radiant exposure must be greatly increased. There exists an optimum pulse duration at which minimal damage to the epidermis and significant injury within the targeted vasculature occur. For example, the model predicts optimum pulse durations of approximately 1.5, 6, and 20 ms for vessel diameters of 40, 80, and 120 microm, respectively. Optimization of laser pulse duration and radiant exposure in combination with CSC may offer a means to treat cutaneous lesions in dark-skinned individuals. PMID:12638894

  15. Optimum Pulse Duration and Radiant Exposure for Vascular Laser Therapy of Dark port-wine Skin: A Theoretical Study

    NASA Astrophysics Data System (ADS)

    Tunnell, James W.; Wang, Lihong V.; Anvari, Bahman

    2003-03-01

    Laser therapy for cutaneous hypervascular malformations such as port-wine stain birthmarks is currently not feasible for dark-skinned individuals. We study the effects of pulse duration, radiant exposure, and cryogen spray cooling (CSC) on the thermal response of skin, using a Monte Carlo based optical-thermal model. Thermal injury to the epidermis decreases with increasing pulse duration during irradiation at a constant radiant exposure; however, maintaining vascular injury requires that the radiant exposure also increase. At short pulse durations, only a minimal increase in radiant exposure is necessary for a therapeutic effect to be achieved because thermal diffusion from the vessels is minimal. However, at longer pulse durations the radiant exposure must be greatly increased. There exists an optimum pulse duration at which minimal damage to the epidermis and significant injury within the targeted vasculature occur. For example, the model predicts optimum pulse durations of approximately 1.5, 6, and 20 ms for vessel diameters of 40, 80, and 120 μm, respectively. Optimization of laser pulse duration and radiant exposure in combination with CSC may offer a means to treat cutaneous lesions in dark-skinned individuals.

  16. Influence of pulse duration on the doping quality in laser chemical processing (LCP)—a simulative approach

    NASA Astrophysics Data System (ADS)

    Fell, Andreas; Granek, Filip

    2013-03-01

    The laser chemical processing (LCP) technique for the local doping of crystalline silicon solar cells is investigated. Here, a liquid jet containing a dopant source acts as a waveguide for pulsed laser light, which results in the melting and subsequent doping of the silicon surface. Typical LCP pulse durations are in the 15 ns range, giving satisfactory results for specific parameter settings. While great potential is assumed to exist, optimization of the pulse duration has until now not been deeply investigated, because it is hard to change this parameter in laser systems. Therefore, this paper accesses the influence of the pulse duration by a simulative approach. The model includes optics, thermodynamics, and melt dynamics induced by the liquid jet and dopant diffusion into the silicon melt. It is solved by coupling our existing finite differences Matlab-code LCPSim with the commercial fluid flow solver Ansys Fluent. Simulations of axial symmetric single pulses were performed for pulse durations ranging from 15 ns to 500 ns. Detailed results are given, which show that for longer pulse durations lateral heat conduction significantly homogenizes the inhomogeneous dopant distribution caused by the speckled intensity profile within the liquid jet cross section. The melt expulsion by the liquid jet is low enough that a sufficiently doped layer remains after full resolidification for all pulse durations. Last, temperature gradients are evaluated to give an indication on the amount of laser damage induced by thermal stress.

  17. Electrical discharge machining (EDM) of Inconel 718 by using copper electrode at higher peak current and pulse duration

    NASA Astrophysics Data System (ADS)

    Ahmad, S.; Lajis, M. A.

    2013-12-01

    This experimental work is an attempt to investigate the performance of Copper electrode when EDM of Nickel Based Super Alloy, Inconel 718 is at higher peak current and pulse duration. Peak current, Ip and pulse duration (pulse on-time), ton are selected as the most important electrical pulse parameters. In addition, their influence on material removal rate (MRR), electrode wear rate (EWR), and surface roughness (Ra) are experimentally investigated. The ranges of 10 mm diameter of Copper electrode are used to EDM of Inconel 718. After the experiments, MRR, EWR, and Ra of the machined surfaces need to be measured in order to evaluate the performance of the EDM process. In order to obtain high MRR, higher peak current in range of 20A to 40A and pulse duration in range of 200μs to 400μs were used. Experimental results have shown that machining at a highest peak current used of 40A and the lowest pulse duration of 200μs used for the experiment yields the highest material removal rate (MRR) with value 34.94 mm3/min, whereas machining at a peak current of 20A and pulse duration of 400μs yields the lowest electrode wear rate (EWR) with value -0.0101 mm3/min. The lowest surface roughness (Ra) is 8.53 μm achieved at a lowest peak current used of 20A and pulse duration of 200μs.

  18. Construction of a two-photon microscope and optimisation of illumination pulse duration.

    PubMed

    Soeller, C; Cannell, M B

    1996-07-01

    The construction of a two-photon/confocal microscope system is described in detail. For two-photon illumination, a Ti:sapphire modelocked laser generating 62-fs pulses at 715 nm was used. The effect of the optical train on illumination pulse width was examined and the observed increase in pulse duration was almost completely removed by the addition/adjustment of a prism compressor system. The imaging capabilities of the two-photon microscope are demonstrated and it is shown that the imaging performance of the two-photon microscope is similar to that of a conventional confocal microscope. With two-photon illumination, the resolution (full width at half-maximum intensity) was 0.42 microM (x-y) and 0.81 microM axially, while with single-photon illumination (at 488 nm in the same instrument with a confocal pinhole detector) the resolution was 0.3 microM (x-y) and 0.75 microM axially. The results are discussed with regard to the general problem of femtosecond pulse distortion in an optical system and a simple procedure for optimal pulse restoration is described. PMID:8766017

  19. Efficient generation of mode-locked pulses in Nd:YVO4 with a pulse duration adjustable between 34 ps and 1 ns.

    PubMed

    Lührmann, Markus; Theobald, Christian; Wallenstein, Richard; L'huillier, Johannes A

    2009-04-13

    We report on the generation of highly stable active continuous mode-locked pulses in diode pumped Nd:YVO(4) with an adjustable pulse duration between 34 ps and 1 ns. With this laser an average output power of up to 7.3 W with an excellent stability and beam quality with a M(2)-value of < 1.1 is obtained. For all pulse durations the pulses were within a factor of 1.15 above the Fourier limit. Due to these characteristics the presented system is an attractive oscillator for OPCPA concepts.

  20. Effects of temporal laser profile on the emission spectra for underwater laser-induced breakdown spectroscopy: Study by short-interval double pulses with different pulse durations

    SciTech Connect

    Tamura, Ayaka Matsumoto, Ayumu; Nishi, Naoya; Sakka, Tetsuo; Nakajima, Takashi; Ogata, Yukio H.; Fukami, Kazuhiro

    2015-01-14

    We investigate the effects of temporal laser profile on the emission spectra of laser ablation plasma in water. We use short-interval (76 ns) double pulses with different pulse durations of the composing two pulses for the irradiation of underwater target. Narrow atomic spectral lines in emission spectra are obtained by the irradiation, where the two pulses are wide enough to be merged into a single-pulse-like temporal profile, while deformed spectra are obtained when the two pulses are fully separated. The behavior of the atomic spectral lines for the different pulse durations is consistent with that of the temporal profiles of the optical emission intensities of the plasma. All these results suggest that continuous excitation of the plasma during the laser irradiation for ∼100 ns is a key to obtain narrow emission spectral lines.

  1. Simulations of drastically reduced SBS with laser pulses composed of a Spike Train of Uneven Duration and Delay (STUD pulses)

    NASA Astrophysics Data System (ADS)

    Hüller, Stefan; Afeyan, Bedros

    2013-11-01

    By comparing the impact of established laser smoothing techniques like Random Phase Plates (RPP) and Smoothing by Spectral Dispersion (SSD) to the concept of "Spike Trains of Uneven Duration and Delay" (STUD pulses) on the amplification of parametric instabilities in laser-produced plasmas, we show with the help of numerical simulations, that STUD pulses can drastically reduce instability growth by orders of magnitude. The simulation results, obtained with the code Harmony in a nonuniformly flowing mm-size plasma for the Stimulated Brillouin Scattering (SBS) instability, show that the efficiency of the STUD pulse technique is due to the fact that successive re-amplification in space and time of parametrically excited plasma waves inside laser hot spots is minimized. An overall mean fluctuation level of ion acoustic waves at low amplitude is established because of the frequent change of the speckle pattern in successive spikes. This level stays orders of magnitude below the levels of ion acoustic waves excited in hot spots of RPP and SSD laser beams.

  2. Atomic ionization by intense laser pulses of short duration: Photoelectron energy and angular distributions

    SciTech Connect

    Dondera, M.

    2010-11-15

    We introduce an adequate integral representation of the wave function in the asymptotic region, valid for the stage postinteraction between a one-electron atom and a laser pulse of short duration, as a superposition of divergent radial spherical waves. Starting with this representation, we derive analytic expressions for the energy and angular distributions of the photoelectrons and we show their connection with expressions used before in the literature. Using our results, we propose a method to extract the photoelectron distributions from the time dependence of the wave function at large distances. Numerical results illustrating the method are presented for the photoionization of hydrogenlike atoms from the ground state and several excited states by extreme ultraviolet pulses with a central wavelength of 13.3 nm and several intensities around the value I{sub 0}{approx_equal}3.51x10{sup 16} W/cm{sup 2}.

  3. Laser initiation and beam quality evolution in a confocal unstable resonator, short-pulse-duration laser.

    PubMed

    Ewanizky, T F

    1997-11-20

    The subjects of laser initiation and beam quality evolution in short-pulse-duration systems that employ confocal unstable resonators motivated this work. Experimentation and analysis of the performance of a laser-pumped, organic dye laser are presented. Combined results indicate that a saturation flux arises through a coalescence of stabilized, diverging-mode components of the initially emitted fluorescence. The ABCD law method was used to devise calculational techniques that clearly demonstrate the particular mechanisms responsible for rapid mode stabilization, subsequent beam quality development, and laser initiation. PMID:18264413

  4. Optical Parameter Variability in Laser Nerve Stimulation: A Study of Pulse Duration, Repetition Rate, and Wavelength

    PubMed Central

    Walsh, Joseph T.; Jansen, E. Duco; Bendett, Mark; Webb, Jim; Ralph, Heather; Richter, Claus-Peter

    2012-01-01

    Pulsed lasers can evoke neural activity from motor as well as sensory neurons in vivo. Lasers allow more selective spatial resolution of stimulation than the conventional electrical stimulation. To date, few studies have examined pulsed, mid-infrared laser stimulation of nerves and very little of the available optical parameter space has been studied. In this study, a pulsed diode laser, with wavelength between 1.844–1.873 μm, was used to elicit compound action potentials (CAPs) from the auditory system of the gerbil. We found that pulse durations as short as 35 μs elicit a CAP from the cochlea. In addition, repetition rates up to 13 Hz can continually stimulate cochlear spiral ganglion cells for extended periods of time. Varying the wavelength and, therefore, the optical penetration depth, allowed different populations of neurons to be stimulated. The technology of optical stimulation could significantly improve cochlear implants, which are hampered by a lack of spatial selectivity. PMID:17554829

  5. Demonstration of negative signal delay with short-duration transient pulse

    NASA Astrophysics Data System (ADS)

    Ravelo, B.

    2011-07-01

    This paper introduces theoretic and experimental analyses of short-duration pulse propagation through a negative group delay (NGD) circuit. The basic analysis method of this electronic circuit operating in baseband and microwave frequencies is investigated. Then, its electrical fundamental characteristics vis-à-vis transient signals are developed. To validate the theoretic concept, planar hybrid devices with one- and two-stage NGD cells were designed, simulated, fabricated and tested. Transient analyses with ultra-wide band (UWB) pulse signals with different widths are realized. Then, experimental results in good agreement with the theoretical predictions were observed. Consequently, group delay going down under -2.5 ns is evidenced in baseband frequency up to 63 MHz with one-stage NGD cell. In time-domain, a Gaussian pulse in advance of about t0 = -1.5 ns or 20% of its half-height time-width was measured. This corresponds to a negative group velocity of about vg = L/t0 = -0.13c (L is the physical length of the tested device and c is light speed in the vacuum). More significant NGD value over 100-MHz bandwidth is stated with two-stage NGD cells. This results in a Gaussian pulse peak advance of about -5 ns (raising a group velocity of about vg = -0.12c) or 31% of its half-height time-width. Finally, some potential applications based on the NGD function are discussed.

  6. Laser-fired contact formation on metallized and passivated silicon wafers under short pulse durations

    NASA Astrophysics Data System (ADS)

    Raghavan, Ashwin S.

    The objective of this work is to develop a comprehensive understanding of the physical processes governing laser-fired contact (LFC) formation under microsecond pulse durations. Primary emphasis is placed on understanding how processing parameters influence contact morphology, passivation layer quality, alloying of Al and Si, and contact resistance. In addition, the research seeks to develop a quantitative method to accurately predict the contact geometry, thermal cycles, heat and mass transfer phenomena, and the influence of contact pitch distance on substrate temperatures in order to improve the physical understanding of the underlying processes. Finally, the work seeks to predict how geometry for LFCs produced with microsecond pulses will influence fabrication and performance factors, such as the rear side contacting scheme, rear surface series resistance and effective rear surface recombination rates. The characterization of LFC cross-sections reveals that the use of microsecond pulse durations results in the formation of three-dimensional hemispherical or half-ellipsoidal contact geometries. The LFC is heavily alloyed with Al and Si and is composed of a two-phase Al-Si microstructure that grows from the Si wafer during resolidification. As a result of forming a large three-dimensional contact geometry, the total contact resistance is governed by the interfacial contact area between the LFC and the wafer rather than the planar contact area at the original Al-Si interface within an opening in the passivation layer. By forming three-dimensional LFCs, the total contact resistance is significantly reduced in comparison to that predicted for planar contacts. In addition, despite the high energy densities associated with microsecond pulse durations, the passivation layer is well preserved outside of the immediate contact region. Therefore, the use of microsecond pulse durations can be used to improve device performance by leading to lower total contact resistances

  7. Alignment and pulse-duration effects in two-photon double ionization of H2 by femtosecond XUV laser pulses

    NASA Astrophysics Data System (ADS)

    Guan, Xiaoxu; Bartschat, Klaus; Schneider, Barry I.; Koesterke, Lars

    2014-10-01

    We present calculations for the dependence of the two-photon double ionization (DI) of H2 on the relative orientation of the linear laser polarization to the internuclear axis and the length of the pulse. We use the fixed-nuclei approximation at the equilibrium distance of 1.4 a0, where a0=0.529 ×10-10m is the Bohr radius. Central photon energies cover the entire direct DI domain from 26.5 to 34.0 eV. In contrast to the parallel geometry studied earlier [X. Guan, K. Bartschat, B. I. Schneider, and L. Koesterke, Phys. Rev. A 83, 043403 (2011), 10.1103/PhysRevA.83.043403], the effect of the pulse duration is almost negligible for the case when the two axes are perpendicular to each other. This is a consequence of the symmetry rules for dipole excitation in the two cases. In the parallel geometry, doubly excited states of 1Σu+ symmetry affect the cross section, while in the perpendicular geometry only much longer-lived 1Πu states are present. This accounts for the different convergence patterns observed in the calculated cross sections as a function of the pulse length. When the photon energy approaches the threshold of sequential DI, a sharp increase of the generalized total cross section (GTCS) with increasing pulse duration is also observed in the perpendicular geometry, very similar to the case of the molecular axis being oriented along the laser polarization direction. Our results differ from those of Colgan et al. [J. Colgan, M. S. Pindzola, and F. Robicheaux, J. Phys. B 41, 121002 (2008), 10.1088/0953-4075/41/12/121002] and Morales et al. [F. Morales, F. Martín, D. A. Horner, T. N. Rescigno, and C. W. McCurdy, J. Phys. B 42, 134013 (2009), 10.1088/0953-4075/42/13/134013], but are in excellent agreement with the GTCSs of Simonsen et al. [A. S. Simonsen, S. A. Sørngård, R. Nepstad, and M. Førre, Phys. Rev. A 85, 063404 (2012), 10.1103/PhysRevA.85.063404] over the entire domain of direct DI.

  8. Demonstration of periodic nanostructure formation with less ablation by double-pulse laser irradiation on titanium

    NASA Astrophysics Data System (ADS)

    Furukawa, Yuki; Sakata, Ryoichi; Konishi, Kazuki; Ono, Koki; Matsuoka, Shusaku; Watanabe, Kota; Inoue, Shunsuke; Hashida, Masaki; Sakabe, Shuji

    2016-06-01

    By pairing femtosecond laser pulses (duration ˜40 fs and central wavelength ˜810 nm) at an appropriate time interval, a laser-induced periodic surface structure (LIPSS) is formed with much less ablation than one formed with a single pulse. On a titanium plate, a pair of laser pulses with fluences of 70 and 140 mJ/cm2 and a rather large time interval (>10 ps) creates a LIPSS with an interspace of 600 nm, the same as that formed by a single pulse of 210 mJ/cm2, while the double pulse ablates only 4 nm, a quarter of the ablation depth of a single pulse.

  9. [An integral chip for the multiphase pulse-duration modulation used for voltage changer in biomedical microprocessor systems].

    PubMed

    Balashov, A M; Selishchev, S V

    2004-01-01

    An integral chip (IC) was designed for controlling the step-down pulse voltage converter, which is based on the multiphase pulse-duration modulation, for use in biomedical microprocessor systems. The CMOS technology was an optimal basis for the IC designing. An additional feedback circuit diminishes the output voltage dispersion at dynamically changing loads.

  10. Effect of pulse duration and strain rate on incipient spall fracture in copper

    SciTech Connect

    Johnson, J.N.; Gray, G.T. III; Bourne, N.K.

    1999-11-01

    Data are presented on real time (VISAR) measurements of the spall fracture of copper for various pulse durations and tensile strain rates at the spall plane. The impactors consist of Teflon, {ital Y}-cut quartz, and a tungsten heavy alloy. VISAR data are compared with finite-difference calculations employing a rate-dependent void-growth model. The data and comparisons show little dependence of the onset of void growth on either pulse duration or tensile strain rate. Also, it is shown that hydrodynamics (wave propagation properties) involving the transmission of the spall signal from the spall plane to the free surface (plane of the VISAR measurement) can mask slight differences in the void-growth or fracture response. In addition, new results are presented for the elastic description of planar wave propagation in {ital Y}-cut quartz; expressions are given for the six independent stress components to second order in infinitesimal Lagrangian strains. A discussion with regard to additional use of {ital Y}-cut quartz in impact experiments is presented. {copyright} {ital 1999 American Institute of Physics.}

  11. Pulse duration determines levels of Hsp70 induction in tissues following laser irradiation

    NASA Astrophysics Data System (ADS)

    Mackanos, Mark A.; Contag, Christopher H.

    2011-07-01

    Induction of heat shock protein (Hsp) expression correlates with cytoprotection, reduced tissue damage, and accelerated healing in animal models. Since Hsps are transcriptionally activated in response to stress, they can act as stress indicators in burn injury or surgical procedures that produce heat and thermal change. A fast in vivo readout for induction of Hsp transcription in tissues would allow for the study of these proteins as therapeutic effect mediators and reporters of thermal stress/damage. We used a transgenic reporter mouse in which a luciferase expression is controlled by the regulatory region of the inducible 70 kilodalton (kDa) Hsp as a rapid readout of cellular responses to laser-mediated thermal stress/injury in mouse skin. We assessed the pulse duration dependence of the Hsp70 expression after irradiation with a CO2 laser at 10.6 μm in wavelength over a range of 1000 to 1 ms. Hsp70 induction varied with changes in laser pulse durations and radiant exposures, which defined the ranges at which thermal activation of Hsp70 can be used to protect cells from subsequent stress, and reveals the window of thermal stress that tissues can endure.

  12. Dependence of core heating properties on heating pulse duration and intensity

    NASA Astrophysics Data System (ADS)

    Johzaki, Tomoyuki; Nagatomo, Hideo; Sunahara, Atsushi; Cai, Hongbo; Sakagami, Hitoshi; Mima, Kunioki

    2009-11-01

    In the cone-guiding fast ignition, an imploded core is heated by the energy transport of fast electrons generated by the ultra-intense short-pulse laser at the cone inner surface. The fast core heating (˜800eV) has been demonstrated at integrated experiments with GEKKO-XII+ PW laser systems. As the next step, experiments using more powerful heating laser, FIREX, have been started at ILE, Osaka university. In FIREX-I (phase-I of FIREX), our goal is the demonstration of efficient core heating (Ti ˜ 5keV) using a newly developed 10kJ LFEX laser. In the first integrated experiments, the LFEX laser is operated with low energy mode (˜0.5kJ/4ps) to validate the previous GEKKO+PW experiments. Between the two experiments, though the laser energy is similar (˜0.5kJ), the duration is different; ˜0.5ps in the PW laser and ˜ 4ps in the LFEX laser. In this paper, we evaluate the dependence of core heating properties on the heating pulse duration on the basis of integrated simulations with FI^3 (Fast Ignition Integrated Interconnecting) code system.

  13. Temperature and pulse duration effects on the growth of MgZnO via pulsed metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Alema, Fikadu; Hertog, Brian; Ledyaev, Oleg; Miller, Ross; Osinsky, Andrei; Schoenfeld, Winston V.

    2016-03-01

    The effect of substrate temperature (TS) and pulse duration (PD) on Mg incorporation, surface quality, and photoresponse properties of MgZnO films grown via PMOCVD were studied. Films grown at TS ranging from 500 to 700 °C but at identical PDs had band gaps varying from 3.38 to 3.87 eV, corresponding to Mg content between x = 0.06 and 0.27. The film with Mg content of 0.27 was the smoothest and achieved at 630 °C-optimal TS. Additionally, pulse time effect was studied by growing films at the same TS but different PDs. A film grown at PD of 12 s has incorporated ∼40% higher Mg than one grown in a continuous mode (PD → ∞), indicting the cruciallity of PMOCVD to realize high Mg film. The peak response spectra of photodetectors were also varied with TS and PD, in accordance with Mg content in the films.

  14. Combined thermocapillary and buoyancy-driven convection within short-duration pulse-heated liquid droplets

    SciTech Connect

    Shen, F.; Khodadadi, J.M.

    1999-12-01

    Containerless processing of advanced materials and thermophysical property determination techniques for high-temperature materials almost exclusively manipulate spherical droplets. Spherical droplets are also observed in other industrial applications and naturally occurring phenomena, such as spray forming, fuel droplet vaporization, thermal storage technology, powder metallurgy, and environmental transport. In addition to the heat diffusion mode of thermal transport, the possible mechanisms of convection that may be encountered within droplets are surface-tension-driven and buoyancy-driven convection. Here, buoyancy-driven convection and its interaction with thermocapillary flow within short-duration-heated liquid droplets was studied computationally. A parametric study was conducted to investigate the effect of the Grashof number Gr and the surface-tension Reynolds number Re for fluids with different Prandtl numbers Pr having both negative and positive surface-tension temperature coefficients ({partial{underscore}derivative}{sigma}/{partial{underscore}derivative}T). Both the additive and impeding effects of buoyancy-driven convection on the thermocapillary flow was observed. The numerical analysis indicated that the buoyancy-driven convection has a weak effect on low-Pr fluids during the short-pulse-heating condition. For mid-Pr fluids the buoyancy effect is more prominent. In monitoring the history of the surface temperature rise, it was found that the buoyancy-driven convection has a weak effect for low-Pr fluids at the side and bottom observation points, whereas buoyancy-driven convection has substantial influence at the bottom observation point for mid-Pr fluids with a positive surface-tension temperature coefficient. It was concluded that the presence of additive or impeding modes depends not only on the sign of the surface-tension temperature coefficient of fluids as proposed by other researchers, but also on Pr, geometry, and boundary conditions. The

  15. Successful management of a refractory case of postoperative herniorrhaphy pain with extended duration pulsed radiofrequency

    PubMed Central

    Thapa, D; Ahuja, V; Verma, P; Das, C

    2016-01-01

    Chronic postsurgical pain (CPSP) is a distressful condition following hernia surgery. A 25-year-old, 55 kg male patient presented with severe pain on the right side of the lower abdomen that radiated to the testicle and the inner side of the thigh. Patient was symptomatic since 5 months following inguinal herniorrhaphy surgery. The pain was not relieved with pharmacological and interventional nerve blocks. An ultrasound-guided ilioinguinal-iliohypogastric (II-IH) block with extended duration (42°C, four cycles of 120 s each) pulsed radiofrequency (PRF) and a diagnostic genital branch of genitofemoral nerve (GGFN) block provided pain relief. After 1-month, an extended duration PRF in GGFN resulted in complete resolution of symptoms. During a regular follow-up of 9 months, patient reported an improved quality-of-life. We believe the successful management of CPSP following hernia repair with single extended duration PRF of II-IH and GGFN has not been described in the literature. PMID:26955321

  16. Ultrashort Two-Photon-Absorption Laser-Induced Fluorescence in Nanosecond-Duration, Repetitively Pulsed Discharges

    NASA Astrophysics Data System (ADS)

    Schmidt, Jacob Brian

    Absolute number densities of atomic species produced by nanosecond duration, repetitively pulsed electric discharges are measured by two-photon absorption laser-induced fluorescence (TALIF). Relatively high plasma discharge pulse energies (=1 mJ/pulse) are used to generate atomic hydrogen, oxygen, and nitrogen in a variety of discharge conditions and geometries. Unique to this work is the development of femtosecond-laser-based TALIF (fs-TALIF). Fs-TALIF offers a number of advantages compared to more conventional ns-pulse-duration laser systems, including better accuracy of direct quenching measurements in challenging environments, significantly reduced photolytic interference including photo-dissociation and photo-ionization, higher signal and increased laser-pulse bandwidth, the ability to collect two-dimensional images of atomic species number densities with far greater spatial resolution compared with more conventional diagnostics, and much higher laser repetition rates allowing for more efficient and accurate measurements of atomic species number densities. In order to fully characterize the fs-TALIF diagnostic and compare it with conventional ns-TALIF, low pressure (100 Torr) ns-duration pulsed discharges are operated in mixtures of H2, O2, and N2 with different buffer gases including argon, helium, and nitrogen. These discharge conditions are used to demonstrate the capability for two-dimensional imaging measurements. The images produced are the first of their kind and offer quantitative insight into spatially and temporally resolved kinetics and transport in ns-pulsed discharge plasmas. The two-dimensional images make possible comparison with high-fidelity plasma kinetics models of the presented data. The comparison with the quasi-one-dimensional kinetic model show good spatial and temporal agreement. The same diagnostics are used at atmospheric pressure, when atomic oxygen fs-TALIF is performed in an atmospheric-pressure plasma jet (APPJ). Here, the

  17. Improving the spatial resolution of epiretinal implants by increasing stimulus pulse duration.

    PubMed

    Weitz, Andrew C; Nanduri, Devyani; Behrend, Matthew R; Gonzalez-Calle, Alejandra; Greenberg, Robert J; Humayun, Mark S; Chow, Robert H; Weiland, James D

    2015-12-16

    Retinal prosthetic implants are the only approved treatment for retinitis pigmentosa, a disease of the eye that causes blindness through gradual degeneration of photoreceptors. An array of microelectrodes triggered by input from a camera stimulates surviving retinal neurons, with each electrode acting as a pixel. Unintended stimulation of retinal ganglion cell axons causes patients to see large oblong shapes of light, rather than focal spots, making it difficult to perceive forms. To address this problem, we performed calcium imaging in isolated retinas and mapped the patterns of cells activated by different electrical stimulation protocols. We found that pulse durations two orders of magnitude longer than those typically used in existing implants stimulated inner retinal neurons while avoiding activation of ganglion cell axons, thus confining retinal responses to the site of the electrode. Multielectrode stimulation with 25-ms pulses can pattern letters on the retina corresponding to a Snellen acuity of 20/312. We validated our findings in a patient with an implanted epiretinal prosthesis by demonstrating that 25-ms pulses evoke focal spots of light. PMID:26676610

  18. Duration of an intense laser pulse can determine the breakage of multiple chemical bonds.

    PubMed

    Xie, Xinhua; Lötstedt, Erik; Roither, Stefan; Schöffler, Markus; Kartashov, Daniil; Midorikawa, Katsumi; Baltuška, Andrius; Yamanouchi, Kaoru; Kitzler, Markus

    2015-08-14

    Control over the breakage of a certain chemical bond in a molecule by an ultrashort laser pulse has been considered for decades. With the availability of intense non-resonant laser fields it became possible to pre-determine femtosecond to picosecond molecular bond breakage dynamics by controlled distortions of the electronic molecular system on sub-femtosecond time scales using field-sensitive processes such as strong-field ionization or excitation. So far, all successful demonstrations in this area considered only fragmentation reactions, where only one bond is broken and the molecule is split into merely two moieties. Here, using ethylene (C2H4) as an example, we experimentally investigate whether complex fragmentation reactions that involve the breakage of more than one chemical bond can be influenced by parameters of an ultrashort intense laser pulse. We show that the dynamics of removing three electrons by strong-field ionization determines the ratio of fragmentation of the molecular trication into two respectively three moieties. We observe a relative increase of two-body fragmentations with the laser pulse duration by almost an order of magnitude. Supported by quantum chemical simulations we explain our experimental results by the interplay between the dynamics of electron removal and nuclear motion.

  19. Shielding properties of laser-induced breakdown in water for pulse durations from 5 ns to 125 fs.

    PubMed

    Hammer, D X; Jansen, E D; Frenz, M; Noojin, G D; Thomas, R J; Noack, J; Vogel, A; Rockwell, B A; Welch, A J

    1997-08-01

    The shielding effectiveness of laser-induced breakdown from focused, visible laser pulses from 5 ns to 125 fs is determined from measurements of transmission of energy through the focal volume. The shielding efficiency decreases as a function of pulse duration from 5 ns to 300 fs and increases from 300 fs to 125 fs. The results are compared with past studies at similar pulse durations. The results of the measurements support laser-induced breakdown models and may lead to an optimization of laser-induced breakdown in ophthalmic surgery by reduction of collateral effects. PMID:18259389

  20. The effect of pulse duration on laser-induced damage by 1053-nm light in potassium dihydrogen phosphate crystals

    SciTech Connect

    Cross, D A; Braunstein, M R; Carr, C W

    2006-11-27

    Laser induced damage in potassium dihydrogen phosphate (KDP) has previously been shown to depend significantly on pulse duration for 351-nm Gaussian pulses. In this work we studied the properties of damage initiated by 1053-nm temporally Gaussian pulses with 10ns and 3ns FWHM durations. Our results indicate that the number of damage sites induced by 1053-nm light scales with pulse duration ({tau}) as ({tau}{sub 1}/{tau}{sub 2}){sup 0.17} in contrast to the previously reported results for 351-nm light as ({tau}{sub 1}/{tau}{sub 2}){sup 0.35}. This indicates that damage site formation is significantly less probable at longer wavelengths for a given fluence.

  1. Pulse duration measurements of a picosecond laser-pumped 14.7 nm x-ray laser

    SciTech Connect

    Dunn, J; Smith, R F; Shepherd, R; Booth, R; Nilsen, J; Hunter, J R; Shlyaptsev, V N

    2004-08-03

    The temporal dependence of the 14.7 nm Ni-like Pd ion x-ray laser is measured as a function of the laser drive conditions with a fast sub-picosecond x-ray streak camera. The chirped pulse amplification laser beam that pumps the inversion process is varied from 0.5 - 27 ps (FWHM) to determine the effect on the x-ray laser pulse duration. The average x-ray laser pulse duration varies by a relatively small factor of 2.5 times from 3.6 ps to 8.1 ps with traveling wave (TW) irradiation conditions. Slightly shorter pulse durations approaching 2 ps are observed with the x-ray laser operating below saturation. The x-ray laser is found to be 4 - 5 times transform-limited for 6 - 13 ps laser pumping conditions.

  2. Ignition and Growth Modeling of Short Pulse Duration Shock Initiation Experiments on HNS IV

    NASA Astrophysics Data System (ADS)

    Tarver, Craig; Chidester, Steven

    2013-06-01

    Short pulse duration shock initiation experiments on 1.60 g/cm3 density (92% TMD) HNS IV have been reported by Schwarz, Bowden et al., Dudley et al., Goveas et al., Greenaway et al., and others. This flyer threshold velocity for detonation/failure data plus measured unreacted HNS Hugoniot data and detonation cylinder test product expansion data were used as the experimental basis for the development of an Ignition and Growth reactive flow model for the shock initiation of HNS IV. The resulting Ignition and Growth HNS IV model parameters yielded good overall agreement with all of this experimental data. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.: Explosive, HNS IV, shock to detonation transition, Ignition and Growth: 82.33.Vx, 82.40.Fp.

  3. Comparison of implosion core metrics: A 10 ps dilation X-ray imager vs a 100 ps gated microchannel plate

    NASA Astrophysics Data System (ADS)

    Nagel, S. R.; Benedetti, L. R.; Bradley, D. K.; Hilsabeck, T. J.; Izumi, N.; Khan, S.; Kyrala, G. A.; Ma, T.; Pak, A.

    2016-11-01

    The dilation x-ray imager (DIXI) [T. J. Hilsabeck et al., Rev. Sci. Instrum. 81, 10E317 (2010); S. R. Nagel et al., ibid. 83, 10E116 (2012); S. R. Nagel et al., ibid. 85, 11E504 (2014)] is a high-speed x-ray framing camera that uses the pulse-dilation technique to achieve a temporal resolution of less than 10 ps. This is a 10 × improvement over conventional framing cameras currently employed on the National Ignition Facility (NIF) (100 ps resolution), and otherwise only achievable with 1D streaked imaging. A side effect of the dramatically reduced gate width is the comparatively lower detected signal level. Therefore we implement a Poisson noise reduction with non-local principal component analysis method [J. Salmon et al., J. Math. Imaging Vision 48, 279294 (2014)] to improve the robustness of the DIXI data analysis. Here we present results on ignition-relevant experiments at the NIF using DIXI. In particular we focus on establishing that/when DIXI gives reliable shape metrics (P0, P2, and P4 Legendre modes, and their temporal evolution/swings).

  4. Ultrashort laser pulse ablation of copper, silicon and gelatin: effect of the pulse duration on the ablation thresholds and the incubation coefficients

    NASA Astrophysics Data System (ADS)

    Nathala, Chandra S. R.; Ajami, Ali; Husinsky, Wolfgang; Farooq, Bilal; Kudryashov, Sergey I.; Daskalova, Albena; Bliznakova, Irina; Assion, Andreas

    2016-02-01

    In this paper, the influence of the pulse duration on the ablation threshold and the incubation coefficient was investigated for three different types of materials: metal (copper), semiconductor (silicon) and biopolymer (gelatin). Ablation threshold values and the incubation coefficients have been measured for multiple Ti:sapphire laser pulses (3 to 1000 pulses) and for four different pulse durations (10, 30, 250 and 550 fs). The ablation threshold fluence was determined by extrapolation of curves from squared crater diameter versus fluence plots. For copper and silicon, the experiments were conducted in vacuum and for gelatin in air. For all materials, the ablation threshold fluence increases with the pulse duration. For copper, the threshold increases as τ 0.05, for silicon as τ 0.12 and for gelatin as τ 0.22. By extrapolating the curves of the threshold fluence versus number of pulses, the single-shot threshold fluence was determined for each sample. For 30 fs pulses, the single-shot threshold fluences were found to be 0.79, 0.35, and 0.99 J/cm2 and the incubation coefficients were found to be 0.75, 0.83 and 0.68 for copper, silicon and gelatin, respectively.

  5. Materials processing by use of a Ti:Sapphire laser with automatically-adjustable pulse duration

    NASA Astrophysics Data System (ADS)

    Kamata, M.; Imahoko, T.; Ozono, K.; Obara, M.

    We have developed an automatic pulsewidth-adjustable femtosecond Ti:Sapphire laser system that can generate an output of 50 fs-1 ps in duration, and sub-mJ/pulse at a repetition rate of 1 kpps. The automatic pulse compressor enables one to control the pulsewidth in the range of 50 fs-1 ps by use of a personal computer (PC). The compressor can change the distance in-between and the tilt angle of the grating pairs by use of two stepping motors and two piezo-electric transducer(PZT) driven actuators, respectively. Both are controlled by a PC. Therefore, not only control of the pulsewidth, but also of the optical chirp becomes easy. By use of this femtosecond laser system, we fabricated a waveguide in fused quartz. The numerical aperture is chosen to 0.007 to loosely focus the femtosecond laser. The fabricated waveguides are well controllable by the incident laser pulsewidth. We also demonstrated the ablation processing of hydroxyapatite (Ca10(PO4)6(OH)2), which is a key component of human tooth and human bone for orthopedics and dentistry. With pulsewidth tunable output from 50 fs through 2 ps at 1 kpps, the chemical content of calcium and phosphorus is kept unchanged before and after 50-fs-2-ps laser ablation. We also demonstrated the precise ablation processing of human tooth enamel with 2 ps Ti:Sapphire laser.

  6. Optimal proton acceleration from lateral limited foil sections and different laser pulse durations at relativistic intensity

    SciTech Connect

    Toncian, T.; Swantusch, M.; Toncian, M.; Willi, O.; Andreev, A. A.; Platonov, K. Y.

    2011-04-15

    The proton acceleration from a thin foil irradiated by a laser pulse at relativistic intensities is a process highly dependent on the electron dynamic at the rear side of the foil. By reducing the lateral size of the laser irradiated foil the hot electrons are confined in a small volume leading to an enhancement of both the maximum proton energy and the conversion efficiency in the target normal sheath acceleration regime. In this paper we demonstrate that an optimal lateral size of the target can be found. While a smaller target surface leads to a better hot electron confinement and enhances the Debye sheath accelerating the protons, it also leads to an increase of preplasma formation due to limited laser contrast available experimentally and hence to a decrease of the proton acceleration. The experimentally found optimum is in good agreement with analytic theory and 2D particle in cell simulations. In addition, the maximum proton energy as a function of pulse duration has been investigated. The experimental results fit to an analytical model.

  7. Effect of gradient pulse duration on MRI estimation of the diffusional kurtosis for a two-compartment exchange model

    NASA Astrophysics Data System (ADS)

    Jensen, Jens H.; Helpern, Joseph A.

    2011-06-01

    Hardware constraints typically require the use of extended gradient pulse durations for clinical applications of diffusion-weighted magnetic resonance imaging (DW-MRI), which can potentially influence the estimation of diffusion metrics. Prior studies have examined this effect for the apparent diffusion coefficient. This study employs a two-compartment exchange model in order to assess the gradient pulse duration sensitivity of the apparent diffusional kurtosis (ADK), a quantitative index of diffusional non-Gaussianity. An analytic expression is derived and numerically evaluated for parameter ranges relevant to DW-MRI of brain. It is found that the ADK differs from the true diffusional kurtosis by at most a few percent. This suggests that ADK estimates for brain may be robust with respect to changes in pulse gradient duration.

  8. Compact femtosecond electron diffractometer with 100 keV electron bunches approaching the single-electron pulse duration limit

    SciTech Connect

    Waldecker, Lutz Bertoni, Roman; Ernstorfer, Ralph

    2015-01-28

    We present the design and implementation of a highly compact femtosecond electron diffractometer working at electron energies up to 100 keV. We use a multi-body particle tracing code to simulate electron bunch propagation through the setup and to calculate pulse durations at the sample position. Our simulations show that electron bunches containing few thousands of electrons per bunch are only weakly broadened by space-charge effects and their pulse duration is thus close to the one of a single-electron wavepacket. With our compact setup, we can create electron bunches containing up to 5000 electrons with a pulse duration below 100 fs on the sample. We use the diffractometer to track the energy transfer from photoexcited electrons to the lattice in a thin film of titanium. This process takes place on the timescale of few-hundred femtoseconds and a fully equilibrated state is reached within 1 ps.

  9. Determination of the pulse duration of an x-ray free electron laser using highly resolved single-shot spectra.

    PubMed

    Inubushi, Yuichi; Tono, Kensuke; Togashi, Tadashi; Sato, Takahiro; Hatsui, Takaki; Kameshima, Takashi; Togawa, Kazuaki; Hara, Toru; Tanaka, Takashi; Tanaka, Hitoshi; Ishikawa, Tetsuya; Yabashi, Makina

    2012-10-01

    We determined the pulse duration of x-ray free electron laser light at 10 keV using highly resolved single-shot spectra, combined with an x-ray free electron laser simulation. Spectral profiles, which were measured with a spectrometer composed of an ultraprecisely figured elliptical mirror and an analyzer flat crystal of silicon (555), changed markedly when we varied the compression strength of the electron bunch. The analysis showed that the pulse durations were reduced from 31 to 4.5 fs for the strongest compression condition. The method, which is readily applicable to evaluate shorter pulse durations, provides a firm basis for the development of femtosecond to attosecond sciences in the x-ray region.

  10. Exact analysis of particle dynamics in combined field of finite duration laser pulse and static axial magnetic field

    SciTech Connect

    Sagar, Vikram; Sengupta, Sudip; Kaw, Predhiman

    2012-11-15

    Dynamics of a charged particle is studied in the field of a relativistically intense linearly polarized finite duration laser pulse in the presence of a static axial magnetic field. For a finite duration laser pulse whose temporal shape is defined by Gaussian profile, exact analytical expressions are derived for the particle trajectory, momentum, and energy as function of laser phase. From the solutions, it is shown that, unlike for the monochromatic plane wave case, resonant phase locking time between the particle and laser pulse is finite. The net energy transferred to the particle does not increase monotonically but tends to saturate. It is further shown that appropriate tuning of cyclotron frequency of the particle with the characteristic frequency in the pulse spectrum can lead to the generation of accelerated particles with variable energies in MeV-TeV range.

  11. Note: Measurement of extreme-short current pulse duration of runaway electron beam in atmospheric pressure air

    SciTech Connect

    Tarasenko, V. F.; Rybka, D. V.; Burachenko, A. G.; Lomaev, M. I.; Balzovsky, E. V.

    2012-08-15

    This note reports the time-amplitude characteristic of the supershort avalanche electron beam with up to 20 ps time resolution. For the first time it is shown that the electron beam downstream of small-diameter diaphragms in atmospheric pressure air has a complex structure which depends on the interelectrode gap width and cathode design. With a spherical cathode and collimator the minimum duration at half maximum of the supershort avalanche electron beam current pulse was shown to be {approx}25 ps. The minimum duration at half maximum of one peak in the pulses with two peaks can reach {approx}25 ps too.

  12. Low dose short duration pulsed electromagnetic field effects on cultured human chondrocytes: An experimental study

    PubMed Central

    Anbarasan, Selvam; Baraneedharan, Ulaganathan; Paul, Solomon FD; Kaur, Harpreet; Rangaswami, Subramoniam; Bhaskar, Emmanuel

    2016-01-01

    Background: Pulsed electromagnetic field (PEMF) is used to treat bone and joint disorders for over 30 years. Recent studies demonstrate a significant effect of PEMF on bone and cartilage proliferation, differentiation, synthesis of extracellular matrix (ECM) and production of growth factors. The aim of this study is to assess if PEMF of low frequency, ultralow field strength and short time exposure have beneficial effects on in-vitro cultured human chondrocytes. Materials and Methods: Primary human chondrocytes cultures were established using articular cartilage obtained from knee joint during joint replacement surgery. Post characterization, the cells were exposed to PEMF at frequencies ranging from 0.1 to 10 Hz and field intensities ranging from 0.65 to 1.95 μT for 60 min/day for 3 consecutive days to analyze the viability, ECM component synthesis, proliferation and morphology related changes post exposure. Association between exposure doses and cellular effects were analyzed with paired't’ test. Results: In-vitro PEMF exposure of 0.1 Hz frequency, 1.95 μT and duration of 60 min/day for 3 consecutive days produced the most favorable response on chondrocytes viability (P < 0.001), ECM component production (P < 0.001) and multiplication. Exposure of identical chondrocyte cultures to PEMFs of 0.65 μT field intensity at 1 Hz frequency resulted in less significant response. Exposure to 1.3 μT PEMFs at 10 Hz frequency does not show any significant effects in different analytical parameters. Conclusions: Short duration PEMF exposure may represent a new therapy for patients with Osteoarthritis (OA). PMID:26955182

  13. Simultaneous observation of nascent plasma and bubble induced by laser ablation in water with various pulse durations

    SciTech Connect

    Tamura, Ayaka Matsumoto, Ayumu; Nishi, Naoya; Sakka, Tetsuo; Fukami, Kazuhiro

    2015-05-07

    We investigate the effects of pulse duration on the dynamics of the nascent plasma and bubble induced by laser ablation in water. To examine the relationship between the nascent plasma and the bubble without disturbed by shot-to-shot fluctuation, we observe the images of the plasma and the bubble simultaneously by using two intensified charge coupled device detectors. We successfully observe the images of the plasma and bubble during the pulsed-irradiation, when the bubble size is as small as 20 μm. The light-emitting region of the plasma during the laser irradiation seems to exceed the bubble boundary in the case of the short-pulse (30-ns pulse) irradiation, while the size of the plasma is significantly smaller than that of the bubble in the case of the long-pulse (100-ns pulse) irradiation. The results suggest that the extent of the plasma quenching in the initial stage significantly depends on the pulse duration. Also, we investigate how the plasma-bubble relationship in the very early stage affects the shape of the atomic spectral lines observed at the later delay time of 600 ns. The present work gives important information to obtain high quality spectra in the application of underwater laser-induced breakdown spectroscopy, as well as to clarify the mechanism of liquid-phase laser ablation.

  14. Optimal control of laser plasma instabilities using Spike Trains of Uneven Duration and Delay (STUD pulses) for ICF and IFE

    NASA Astrophysics Data System (ADS)

    Afeyan, Bedros; Hüller, Stefan

    2013-11-01

    An adaptive method of controlling parametric instabilities in laser produced plasmas is proposed. It involves fast temporal modulation of a laser pulse on the fastest instability's amplification time scale, adapting to changing and unknown plasma conditions. These pulses are comprised of on and off sequences having at least one or two orders of magnitude contrast between them. Such laser illumination profiles are called STUD pulses for Spike Trains of Uneven Duration and Delay. The STUD pulse program includes scrambling the speckle patterns spatially in between the laser spikes. The off times allow damping of driven waves. The scrambling of the hot spots allows tens of damping times to elapse before hot spot locations experience recurring high intensity spikes. Damping in the meantime will have healed the scars of past growth. Another unique feature of STUD pulses on crossing beams is that their temporal profiles can be interlaced or staggered, and their interactions thus controlled with an on-off switch and a dimmer.

  15. Transient Response of a Separated Flow over a Two-Dimensional Wing to a Short Duration Pulse

    NASA Astrophysics Data System (ADS)

    Williams, David; Albrecht, Thomas; Weier, Tom; Gerbeth, G.

    2012-11-01

    A Lorentz force actuator located at the leading edge of a two-dimensional wing at 16 degrees angle of attack was used to introduce short-duration disturbances into a separated flow. The transient response of the separated region at Re = 10,000 was documented using time-resolved PIV measurements. The direction of the Lorentz force was changed between downstream and upstream directed disturbances, and details of the resulting flow field structures and lift measurements were studied. Saturation of the peak lift amplitude occurs as the actuation amplitude is increased from 0.0054 < C μ < 0.21 percent with the pulse duration fixed at 0.1 convective time. The effect of the pulse duration time on the lift response was examined using a fixed pulse amplitude, which showed that saturation occurred when pulse durations exceed 0.5 convective times. Differences in the coherent structures resulting from the upstream/downstream directed actuation were identified using the FTLE method. The initial development of the disturbed shear layer was strongly dependent on the direction of actuation, but the larger-scale separation did not show much difference. The relaxation of the separated region to the original flow state was essentially independent of the direction of actuation. Support by the Deutsche Forschungsgemeinschaft SFB 609 and AFOSR Grant FA9550-09-1-0189 is gratefully acknowledged.

  16. Ignition of pressed granular explosives due to short-duration pulse loading

    NASA Astrophysics Data System (ADS)

    Miller, Christopher; Kim, Seokpum; Zhou, Min

    2015-06-01

    We report the results of micromechanical simulations of a series of experiments on the ignition of pressed granular HMX under loading due to impact by thin flyers. The conditions analyzed concern loading pulses on the order of 50 nanoseconds to 1 microsecond and impact velocities on the order of 200-1600 m/s. The materials studied have average grain sizes of 50-200 microns. The model provides phenomenological account of defects in the forms of microcracks, voids, interfacial debonding, and constituent property variations and material attributes including constituent shock and non-shock responses, fracture, internal contact, frictional heating, and heat conduction. The analysis focuses on the development of hotspots under different material settings and loading conditions. In particular, a hotspot-based ignition criterion developed recently is employed to determine the probability of ignition of each material design under combinations of impact velocity and load duration. The results of parametric studies are compared with experimental observations reported in the literature. AFRL

  17. Plasma processes in water under effect of short duration pulse discharges

    NASA Astrophysics Data System (ADS)

    Gurbanov, Elchin

    2013-09-01

    It is very important to get a clear water without any impurities and bacteria by methods, that don't change the physical and chemical indicators of water now. In this article the plasma processes during the water treatment by strong electric fields and short duration pulse discharges are considered. The crown discharge around an electrode with a small radius of curvature consists of plasma leader channels with a high conductivity, where the thermo ionization processes and UV-radiation are taken place. Simultaneously the partial discharges around potential electrode lead to formation of atomic oxygen and ozone. The spark discharge arises, when plasma leader channels cross the all interelectrode gap, where the temperature and pressure are strongly grown. As a result the shock waves and dispersing liquid streams in all discharge gap are formed. The plasma channels extend, pressure inside it becomes less than hydrostatic one and the collapse and UV-radiation processes are started. The considered physical processes can be successfully used as a basis for development of pilot-industrial installations for conditioning of drinking water and to disinfecting of sewage.

  18. Optimization of interaction conditions for efficient short laser pulse amplification by stimulated Brillouin scattering in the strongly coupled regime

    NASA Astrophysics Data System (ADS)

    Chiaramello, M.; Riconda, C.; Amiranoff, F.; Fuchs, J.; Grech, M.; Lancia, L.; Marquès, J.-R.; Vinci, T.; Weber, S.

    2016-07-01

    Plasma amplification of low energy, a short (˜100-500 fs) laser pulse by an energetic long (˜10 ps) pulse via strong coupling Stimulated Brillouin Backscattering is investigated with an extensive analysis of one-dimensional particle-in-cell simulations. Parameters relevant to nowadays experimental conditions are investigated. The obtained seed pulse spectra are analyzed as a function of the interaction conditions such as plasma profile, pulses delay, and seed or pulse duration. The factors affecting the amount of energy transferred are determined, and the competition between Brillouin-based amplification and parasitic Raman backscattering is analyzed, leading to the optimization of the interaction conditions.

  19. Toxicity of magnesium pulses to tropical freshwater species and the development of a duration-based water quality guideline.

    PubMed

    Hogan, Alicia C; Trenfield, Melanie A; Harford, Andrew J; van Dam, Rick A

    2013-09-01

    Six freshwater species (Chlorella sp., Lemna aequinoctialis, Amerianna cumingi, Hydra viridissima, Moinodaphnia macleayi, and Mogurnda mogurnda) were exposed to 4-h, 8-h, and 24-h Mg pulses in natural creek water. Magnesium toxicity to all species increased with exposure duration; however, the extent of increase and the nature of the relationship differed greatly between species. Based on median inhibitory concentrations (IC50s), and compared with continuous exposure data from a previous study, the increase in toxicity with increasing exposure duration from 4 h to continuous (72-144 h) ranged from approximately 2-fold for Chlorella sp. and H. viridissima to greater than 40-fold for A. cumingi. Moreover, the form of the relationship between Mg toxicity and duration ranged from linear or near-linear to exponential for different species. The life-stage at which M. macleayi was exposed was important, with cladocerans pulsed at the onset of reproductive maturity being approximately 4 times more sensitive (based on IC50s) than younger than 6-h-old neonates. Species sensitivity distributions were constructed for the 4-h, 8-h, and 24-h pulse durations, from which 99% species protection guideline values (95% confidence limits [CLs]) of 94 (6.4-1360) mg/L, 14 (0.5-384) mg/L, and 8.0 (0.5-144) mg/L Mg, respectively, were derived. These values were plotted against exposure duration (h) and polynomial interpolation used to derive a guideline value for any pulse duration within the range assessed. PMID:23613126

  20. Role of wavelength and pulse duration in laser ablation: implications to beam delivery, surface modifications, and diagnostic techniques

    NASA Astrophysics Data System (ADS)

    Serafetinides, Alexander A.

    1999-05-01

    The basic interaction mechanism of pulsed laser ablation of tissue reveals a complexity of parameters, such as the optical properties of the tissue and the technical characteristics of the laser beam. The role of the laser wavelength, the pulse duration, the energy fluence, etc. as well as the implications on the beam delivery means, the ablated surface modifications and the diagnostic techniques employed are under investigation. For example, it was experimentally verified that when using mid-infrared lasers with pulse durations in the ns range, the photothermal mechanism involved exhibits strong absorption restricting the residual thermal damage to a relatively small zone. On the other hand the ablation of tissue with ultrashort, picosecond and femtosecond, visible and near-infrared laser pulses has been investigated as an alternative, as the energy threshold for ablation biological tissue, depends approximately on the square root of the pulse duration. However the pulse length shortening creates problems to the fibers or the waveguides ends, due to the very high laser power densities involved. Conventional and advanced microscopy, scanning electron microscopy--SEM and atomic force microscopy--AFM, were used to study the surface and ends alterations of the delivery system involved and the surface alterations of the soft or the hard tissue target in pulsed laser ablation. Finally differentiation between the normal and the pathological tissue was achieved by employing the laser induced fluorescence--LIF diagnostic technique in a long term effort to develop a computer aided system, which will facilitate the automated, real-time characterization of healthy or atherosclerotic plaques in a less invasive laser ablation clinical procedure.

  1. Optimization of Pulsed-DEER Measurements for Gd-Based Labels: Choice of Operational Frequencies, Pulse Durations and Positions, and Temperature

    SciTech Connect

    Raitsimring, A.; Astashkin, A. V.; Enemark, J. H.; Kaminker, I.; Goldfarb, D.; Walter, E. D.; Song, Y.; Meade, T. J.

    2012-12-29

    In this work, the experimental conditions and parameters necessary to optimize the long-distance (≥ 60 Å) Double Electron-Electron Resonance (DEER) measurements of biomacromolecules labeled with Gd(III) tags are analyzed. The specific parameters discussed are the temperature, microwave band, the separation between the pumping and observation frequencies, pulse train repetition rate, pulse durations and pulse positioning in the electron paramagnetic resonance spectrum. It was found that: (i) in optimized DEER measurements, the observation pulses have to be applied at the maximum of the EPR spectrum; (ii) the optimal temperature range for Ka-band measurements is 14-17 K, while in W-band the optimal temperatures are between 6-9 K; (iii) W-band is preferable to Ka-band for DEER measurements. Recent achievements and the conditions necessary for short-distance measurements (<15 Å) are also briefly discussed.

  2. Nitriding molybdenum: Effects of duration and fill gas pressure when using 100-Hz pulse DC discharge technique

    NASA Astrophysics Data System (ADS)

    Ikhlaq, U.; R., Ahmad; Shafiq, M.; Saleem, S.; S. Shah, M.; Hussain, T.; A. Khan, I.; K., Abbas; S. Abbas, M.

    2014-10-01

    Molybdenum is nitrided by a 100-Hz pulsed DC glow discharge technique for various time durations and fill gas pressures to study the effects on the surface properties of molybdenum. X-ray diffractometry (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM) are used for the structural and morphological analysis of the nitrided layers. Vickers' microhardness tester is utilized to investigate surface microhardness. Phase analysis shows the formation of more molybdenum nitride molecules for longer nitriding durations at fill gas pressures of 2 mbar and 3 mbar (1 bar = 105 Pa). A considerable increase in surface microhardness (approximately by a factor of 2) is observed for longer duration (10 h) and 2-mbar pressure. Longer duration (10 h) and 2-mbar fill gas pressure favors the formation of homogeneous, smooth, hard layers by the incorporation of more nitrogen.

  3. Influence of laser pulse duration on the electrochemical performance of laser structured LiFePO4 composite electrodes

    NASA Astrophysics Data System (ADS)

    Mangang, M.; Seifert, H. J.; Pfleging, W.

    2016-02-01

    Lithium iron phosphate is a promising cathode material for lithium-ion batteries, despite its low electrical conductivity and lithium-ion diffusion kinetic. To overcome the reduced rate performance, three dimensional (3D) architectures were generated in composite cathode layers. By using ultrashort laser radiation with pulse durations in the femtosecond regime the ablation depth per pulse is three times higher compared to nanosecond laser pulses. Due to the 3D structuring, the surface area of the active material which is in direct contact with liquid electrolyte, i.e. the active surface, is increased. As a result the capacity retention and the cycle stability were significantly improved, especially for high charging/discharging currents. Furthermore, a 3D structure leads to higher currents during cyclic voltammetry. Thus, the lithium-ion diffusion kinetic in the cell was improved. In addition, using ultrashort laser pulses results in a high aspect ratio and further improvement of the cell kinetic was achieved.

  4. Laser pulse duration dependence of blister formation on back-radiated Ti thin films for BB-LIFT

    NASA Astrophysics Data System (ADS)

    Goodfriend, N. T.; Starinskiy, S. V.; Nerushev, O. A.; Bulgakova, N. M.; Bulgakov, A. V.; Campbell, E. E. B.

    2016-03-01

    The influence of the laser pulse duration on the mechanism of blister formation in the particle transfer technique, blister-based laser-induced forward transfer, was investigated. Pulses from a fs Ti:Sapphire laser (120 fs, 800 nm) and from a ns Nd:YAG laser (7 ns, 532 nm) were used to directly compare blister formation on thin titanium films of ca. 300 nm thickness, deposited on glass. The different blister morphologies were compared and contrasted by using optical microscopy and atomic force microscopy. The results provide evidence for different blister formation mechanisms: for fs pulses the mechanism is predominantly ablation at the metal-glass interface accompanied by confined plasma expansion and deformation of the remaining metal film; for ns pulses it is heating accompanied by thermal expansion of the metal film.

  5. Duration of Diabetes Predicts Aortic Pulse Wave Velocity and Vascular Events in Alström Syndrome

    PubMed Central

    Smith, Jamie; Carey, Catherine; Barrett, Timothy; Campbell, Fiona; Maffei, Pietro; Marshall, Jan D.; Paisey, Christopher; Steeds, Richard P.; Edwards, Nicola C.; Bunce, Susan; Geberhiwot, Tarekegn

    2015-01-01

    Context: Alström syndrome is characterized by increased risk of cardiovascular disease from childhood. Objective: To explore the association between risk factors for cardiovascular disease, aortic pulse wave velocity, and vascular events in Alström syndrome. Design: Cross-sectional analyses with 5-year follow-up. Setting: The UK NHS nationally commissioned specialist clinics for Alström syndrome. Patients: Thirty-one Alström patients undertook vascular risk assessment, cardiac studies, and aortic pulse wave velocity measurement. Subsequent clinical outcomes were recorded. Interventions: Insulin resistance was treated with lifestyle intervention and metformin, and diabetes with the addition of glitazones, glucagon-like peptide 1 agonists, and/or insulin. Thyroid and T deficiencies were corrected. Dyslipidemia was treated with statins and nicotinic acid derivatives. Cardiomyopathy was treated with standard therapy as required. Main Outcome Measures: The associations of age, gender, and risk factors for cardiovascular disease with aortic pulse wave velocity were assessed and correlated with the effects of reduction in left ventricular function. Vascular events were monitored for 5 years. Results: Aortic pulse wave velocity was positively associated with the duration of diabetes (P = .001) and inversely with left ventricular ejection fraction (P = .036). Five of the cohort with cardiovascular events had higher aortic pulse wave velocity (P = .0247), and all had long duration of diabetes. Conclusions: Duration of diabetes predicted aortic pulse wave velocity in Alström syndrome, which in turn predicted cardiovascular events. This offers hope of secondary prevention because type 2 diabetes can be delayed or reversed by lifestyle interventions. PMID:26066530

  6. Copper vapour laser with an efficient semiconductor pump generator having comparable pump pulse and output pulse durations

    NASA Astrophysics Data System (ADS)

    Yurkin, A. A.

    2016-03-01

    We report the results of experimental studies of a copper vapour laser with a semiconductor pump generator capable of forming virtually optimal pump pulses with a current rise steepness of about 40 A ns-1 in a KULON LT-1.5CU active element. To maintain the operating temperature of the active element's channel, an additional heating pulsed oscillator is used. High efficiency of the pump generator is demonstrated.

  7. Effect of adjusting pulse durations of functional electrical stimulation cycling on energy expenditure and fatigue after spinal cord injury.

    PubMed

    Gorgey, Ashraf S; Poarch, Hunter J; Dolbow, David D; Castillo, Teodoro; Gater, David R

    2014-01-01

    The purpose of the current study was to determine the effects of three different pulse durations (200, 350, and 500 microseconds [P200, P350, and P500, respectively]) on oxygen uptake (VO2), cycling performance, and energy expenditure (EE) percentage of fatigue of the knee extensor muscle group immediately and 48 to 72 h after cycling in persons with spinal cord injury (SCI). A convenience sample of 10 individuals with motor complete SCI participated in a repeated-measures design using a functional electrical stimulation (FES) cycle ergometer over a 3 wk period. There was no difference among the three FES protocols on relative VO2 or cycling EE. Delta EE between exercise and rest was 42% greater in both P500 and P350 compared with P200 (p = 0.07), whereas recovery VO2 was 23% greater in P350 compared with P200 (p = 0.03). There was no difference in the outcomes of the three pulse durations on muscle fatigue. Knee extensor torque significantly decreased immediately after (p < 0.001) and 48 to 72 h after (p < 0.001) FES leg cycling. Lengthening pulse duration did not affect submaximal or relative VO2 or EE, total EE, and time to fatigue. Greater recovery VO2 and delta EE were noted in P350 and P500 compared with P200. An acute bout of FES leg cycling resulted in torque reduction that did not fully recover 48 to 72 h after cycling.

  8. Precision control of lesions by high-intensity focused ultrasound cavitation-based histotripsy through varying pulse duration.

    PubMed

    Xu, Jin; Bigelow, Timothy A; Nagaraju, Ravindra

    2013-07-01

    The goal of this experimental study was to explore the feasibility of acquiring controllable precision through varying pulse duration for lesions generated by cavitation-based histotripsy. Histotripsy uses high-intensity focused ultrasound (HIFU) at low duty factor to create energetic bubble clouds inside tissue to liquefy a region. It uses cavitation-mediated mechanical effects while minimizing heating, and has the advantages of real-time monitoring and lesion fidelity to treatment planning. In our study, histotripsy was applied to three groups of tissue-mimicking agar samples of different stiffnesses (29.4 ± 5.3, 44.8 ± 5.9, and 66.4 ± 7.1 kPa). B-mode imaging was used first to quantify bubble cluster dimensions in both water and agar. Then, a 4.5-mm-wide square (lateral to the focal plane) was scanned in a raster pattern with a step size of 0.75 mm in agar histotripsy experiments to estimate equivalent bubble cluster dimensions based on the histotripsyinduced damage. The 15-s exposure at each treatment location comprised 5000 sine-wave tone bursts at a spatial-peak pulseaverage intensity of 41.1 kW/cm2, with peak compressional and rarefactional pressures of 102 and 17 MPa, respectively. The results showed that bubble cluster width and length increased with pulse duration and decreased with agar stiffness. Therefore, a significant improvement in histotripsy precision could be achieved by reducing the pulse duration.

  9. Effect of adjusting pulse durations of functional electrical stimulation cycling on energy expenditure and fatigue after spinal cord injury.

    PubMed

    Gorgey, Ashraf S; Poarch, Hunter J; Dolbow, David D; Castillo, Teodoro; Gater, David R

    2014-01-01

    The purpose of the current study was to determine the effects of three different pulse durations (200, 350, and 500 microseconds [P200, P350, and P500, respectively]) on oxygen uptake (VO2), cycling performance, and energy expenditure (EE) percentage of fatigue of the knee extensor muscle group immediately and 48 to 72 h after cycling in persons with spinal cord injury (SCI). A convenience sample of 10 individuals with motor complete SCI participated in a repeated-measures design using a functional electrical stimulation (FES) cycle ergometer over a 3 wk period. There was no difference among the three FES protocols on relative VO2 or cycling EE. Delta EE between exercise and rest was 42% greater in both P500 and P350 compared with P200 (p = 0.07), whereas recovery VO2 was 23% greater in P350 compared with P200 (p = 0.03). There was no difference in the outcomes of the three pulse durations on muscle fatigue. Knee extensor torque significantly decreased immediately after (p < 0.001) and 48 to 72 h after (p < 0.001) FES leg cycling. Lengthening pulse duration did not affect submaximal or relative VO2 or EE, total EE, and time to fatigue. Greater recovery VO2 and delta EE were noted in P350 and P500 compared with P200. An acute bout of FES leg cycling resulted in torque reduction that did not fully recover 48 to 72 h after cycling. PMID:25803753

  10. Evolution of few-cycle pulses in nonlinear dispersive media: Velocity of the center of mass and root-mean-square duration

    NASA Astrophysics Data System (ADS)

    Kapoyko, Yury A.; Drozdov, Arkadiy A.; Kozlov, Sergei A.; Zhang, Xi-Cheng

    2016-09-01

    Simple arithmetic dependencies of the velocity of the mass center motion and the root-mean-square duration of initially single-cycle, two-cycle, and Gaussian pulses with a random number of oscillations under the pulse envelope are derived depending on their center frequency, initial duration, and peak field amplitude, as well as on dispersive and nonlinear characteristics of homogeneous isotropic dielectric media. In media with normal group dispersion, it is shown that due to nonresonant dispersion the square of the few-cycle pulse duration increases with distance inversely proportional to the fourth power of the number of input pulse cycles. In media with normal group dispersion, the square of the pulse duration is inversely proportional to the number of input pulse cycles due to cubic nonlinearity. In media with anomalous group dispersion, it is shown that due to cubic nonlinearity, few-cycle pulse self-compression decreases with the reduction of the number of cycles in the initial pulse. This pulse self-compression effect has a threshold nature and terminates at a fixed number of cycles of the input pulse. Such a number of cycles is determined by the input intensity and the central frequency of the pulse, as well as by the dispersive and nonlinear characteristics of the medium.

  11. An investigation of fatigue phenomenon in the upper limb muscle due to short duration pulses in an FES system

    NASA Astrophysics Data System (ADS)

    Naeem, Jannatul; Wong Azman, Amelia; Khan, Sheroz; Mohd Mustafah, Yasir

    2013-12-01

    Functional Electrical Stimulation (FES) is a method of artificially stimulating muscles or nerves in order to result in contraction or relaxation of muscles. Many studies have shown that FES system has helped patients to live a better lives especially those who are suffering from physical mobility. Unfortunately, one of the main limitations of an FES system besides of its high cost is largely due to muscle fatigue. Muscle fatigue will affect the training duration which could delay patients' recovery rate. In this paper, we analyzed the occurrence of this fatigue phenomenon in terms of stimulator parameters such as amplitude, frequency, pulse width and pulse shape. The objective of this investigation is to identify other key features of the FES system parameters in order to prolong the training duration among patients. The experiment has been done on a healthy person for the duration of one minute and later the muscles response will be observed. Resultant muscle response is recorded as force using force resistive sensor. The experimental results show muscles will get fatigue at a different rate as the frequency increases. The experiment also shows that the duty cycle is reciprocal to the resultant force.

  12. Propagation of the pulsed electron beam of nanosecond duration in gas composition of high pressure

    NASA Astrophysics Data System (ADS)

    Kholodnaya, G.; Sazonov, R.; Ponomarev, D.; Remnev, G.

    2015-11-01

    This paper presents the results of the investigation of the propagation of an electron beam in the high-pressure gas compositions (50, 300, and 760 Torr): sulfur hexafluoride and hydrogen, sulfur hexafluoride and nitrogen, sulfur hexafluoride and argon. The experiments have been performed using the TEA-500 laboratory accelerator. The main parameters of the accelerator are as follows: an accelerating voltage of 500 kV; an electron beam current of 10 kA; a pulse width at half maximum of 60 ns; a pulse energy of 200 J; a pulse repetition rate of up to 5 pulses per second, a beam diameter of 5 cm. The pulsed electron beam was injected into a 55 cm metal drift tube. The drift tube is equipped with three reverse-current shunts with simultaneous detecting of signals. The obtained results of the investigation make it possible to conclude that the picture of the processes occurring in the interaction of an electron beam in the high-pressure gas compositions is different from that observed in the propagation of the electron beam in the low-pressure gas compositions (1 Torr).

  13. High power fiber MOPA based QCW laser delivering pulses with arbitrary duration on demand at high modulation bandwidth.

    PubMed

    Petkovšek, Rok; Novak, Vid; Agrež, Vid

    2015-12-28

    We report on a concept of a fiber MOPA based quasi-CW laser working at high modulation bandwidths up to 40 MHz capable of producing arbitrary pulse durations at arbitrary repetition rates. An output power of over 100 W was achieved and an on-off contrast of 25 dB. The laser features a dual-channel (dual-wavelength) seed source, a double stage YDF amplifier and a volume-Bragg-grating-based signal de-multiplexer. Minimization of transients was conducted through experiment and model analysis. PMID:26831982

  14. Analysis of Mg spectral features produced by irradiations of laser pulses with different contrast and pulse durations

    NASA Astrophysics Data System (ADS)

    Stafford, A.; Safronova, A. S.; Safronova, U. I.; Kantsyrev, V. L.; Faenov, A. Y.; Wiewior, P.; Weller, M. E.; Shrestha, I.; Shlyaptseva, V. V.; Paudel, Y.

    2014-03-01

    Experiments performed at the Leopard Laser Facility at the Nevada Terawatt Facility of the University of Nevada, Reno have produced K-shell Mg spectra with complex satellite features. K-shell Mg spectra were collected from experiments comprised of three different conditions related to laser pulse and contrast. Two spectrometers were fielded: a survey convex spectrometer with a potassium hydrogen phthalate (KAP) crystal (R ˜ 300) and a high resolution focusing spectrometer with spatial resolution using a spherically bent mica crystal (R ˜ 3000). These spectra included dielectronic satellite (DS) lines that were investigated using the quasi-relativistic many-body perturbation theory (MZ) code for previously identified transitions from autoionizing 2lnl‧ states in He-like Mg and new transitions involving autoionizing 1s3lnl‧ states in Li-like Mg and 1s3l3l‧3l″ in Be-like Mg calculated using the Hartree-Fock-relativistic method (COWAN code). Radiative and non-radiative data are combined to obtain branching ratios, intensities and effective emission rate coefficients of DS lines. Synthetic spectra were matched to experimental data to identify strong satellite structures to the Heβ (7.8507 Å) and Lyα (8.4192 Å) resonance transitions.

  15. Altered Gene Expression in Cultured Microglia in Response to Simulated Blast Overpressure: Possible Role of Pulse Duration

    PubMed Central

    Kane, Michael J.; Angoa-Pérez, Mariana; Francescutti, Dina M.; Sykes, Catherine E.; Briggs, Denise I.; Leung, Lai Yee; VandeVord, Pamela J.; Kuhn, Donald M.

    2012-01-01

    Blast overpressure has long been known to cause barotrauma to air-filled organs such as lung and middle ear. However, experience in Iraq and Afghanistan is revealing that individuals exposed to explosive munitions can also suffer traumatic brain injury (TBI) even in the absence of obvious external injury. The interaction of a blast shock wave with the brain in the intact cranial vault is extremely complex making it difficult to conclude that a blast wave interacts in a direct manner with the brain to cause injury. In an attempt to “isolate” the shock wave and test its primary effects on cells, we exposed cultured microglia to simulated blast overpressure in a barochamber. Overpressures ranging from 15–45 psi did not change microglial Cox-2 levels or TNF-α secretion nor did they cause cell damage. Microarray analysis revealed increases in expression of a number of microglial genes relating to immune function and inflammatory responses to include Saa3, Irg1, Fas and CxCl10. All changes in gene expression were dependent on pulse duration and were independent of pressure. These results indicate that microglia are mildly activated by blast overpressure and uncover a heretofore undocumented role for pulse duration in this process. PMID:22698585

  16. Flexible control of femtosecond pulse duration and separation using an emittance-spoiling foil in x-ray free-electron lasers

    SciTech Connect

    Ding, Y.; Behrens, C.; Coffee, R.; Decker, F. -J.; Emma, P.; Field, C.; Helml, W.; Huang, Z.; Krejcik, P.; Krzywinski, J.; Loos, H.; Lutman, A.; Marinelli, A.; Maxwell, T. J.; Turner, J.

    2015-06-22

    We report experimental studies of generating and controlling femtosecond x-ray pulses in free-electron lasers (FELs) using an emittance spoiling foil. By selectivity spoiling the transverse emittance of the electron beam, the output pulse duration or double-pulse separation is adjusted with a variable size single or double slotted foil. Measurements were performed with an X-band transverse deflector located downstream of the FEL undulator, from which both the FEL lasing and emittance spoiling effects are observed directly.

  17. Echo frequency selectivity of duration-tuned inferior collicular neurons of the big brown bat, Eptesicus fuscus, determined with pulse-echo pairs.

    PubMed

    Wu, C H; Jen, P H-S

    2008-10-28

    During hunting, insectivorous bats such as Eptesicus fuscus progressively vary the repetition rate, duration, frequency and amplitude of emitted pulses such that analysis of an echo parameter by bats would be inevitably affected by other co-varying echo parameters. The present study is to determine the variation of echo frequency selectivity of duration-tuned inferior collicular neurons during different phases of hunting using pulse-echo (P-E) pairs as stimuli. All collicular neurons discharge maximally to a tone at a particular frequency which is defined as the best frequency (BF). Most collicular neurons also discharge maximally to a BF pulse at a particular duration which is defined as the best duration (BD). A family of echo iso-level frequency tuning curves (iso-level FTC) of these duration-tuned collicular neurons is measured with the number of impulses in response to the echo pulse at selected frequencies when the P-E pairs are presented at varied P-E duration and gap. Our data show that these duration-tuned collicular neurons have narrower echo iso-level FTC when measured with BD than with non-BD echo pulses. Also, IC neurons with low BF and short BD have narrower echo iso-level FTC than IC neurons with high BF and long BD have. The bandwidth of echo iso-level FTC significantly decreases with shortening of P-E duration and P-E gap. These data suggest that duration-tuned collicular neurons not only can facilitate bat's echo recognition but also can enhance echo frequency selectivity for prey feature analysis throughout a target approaching sequence during hunting. These data also support previous behavior studies showing that bats prepare their auditory system to analyze expected returning echoes within a time window to extract target features after pulse emission.

  18. Generation of high-quality parabolic pulses with optimized duration and energy by use of dispersive frequency-to-time mapping.

    PubMed

    Huh, Jeonghyun; Azaña, José

    2015-10-19

    We propose and demonstrate a novel linear-optics method for high-fidelity parabolic pulse generation with durations ranging from the picosecond to the sub-nanosecond range. This method is based on dispersion-induced frequency-to-time mapping combined with spectral shaping in order to overcome constraints of previous linear shaping approaches. Temporal waveform distortions associated with the need to satisfy a far-field condition are eliminated by use of a virtual time-lens process, which is directly implemented in the linear spectral shaping stage. Using this approach, the generated parabolic pulses are able to maintain most energy spectrum available from the input pulse frequency bandwidth, regardless of the target pulse duration, which is not anymore limited by the finest spectral resolution of the optical pulse spectrum shaper. High-quality parabolic pulses, with durations from 25ps to 400ps and output powers exceeding 4dBm before amplification, have been experimentally synthesized from a picosecond mode-locked optical source using a commercial optical pulse shaper with a frequency resolution >10GHz. In particular, we report the synthesis of full-duty cycle parabolic pulses that match up almost exactly with an ideal fitting over the entire pulse period.

  19. Pulse duration effects on laser-assisted electron transfer cross section for He2+ ions colliding with atomic hydrogen

    NASA Astrophysics Data System (ADS)

    Domínguez-Gutiérrez, Francisco Javier; Cabrera-Trujillo, Remigio

    2014-08-01

    We study the effect of the pulse duration for an ultra-fast and intense laser on the fundamental process of electron capture by analyzing the excitation probability into the n = 2 and n = 3 states when He2+ collides with atomic hydrogen in the 0.05-10 keV/amu energy range, a region of interest for diagnostic processes on plasma and fusion power reactors. We solve the time-dependent Schrödinger equation to calculate the electron capture probability by means of a finite-differences, as well as by an electron-nuclear dynamics approach. In particular, we study the effects of 1, 3, 6, and 10 fs laser pulses at FWHM, wavelength of 780 nm and intensity of 3.5 × 1012 W/cm2. We report good agreement for the laser-free state and total electron transfer cross-sections when compared to available theoretical and experimental data. The effect of the laser pulse on the electron capture probability as a function of the impact parameter is such that the charge exchange probability increases considerably in the impact parameter radial region with an increase in the amplitude oscillations and a phase shift on the Stückelberg oscillations. We find an increase on the total electron exchange cross-section for low projectile collision energy when compared to the laser-free case with a minimal effect at high collision energies. We find that the 1 fs laser pulse has a minimal effect, except for very low collision energies. Although in general, the longer the laser pulse, the larger the electron capture probability, at very low collision energies all pulse widths have an effect. For processes in the atto-second region, our findings suggest that to enhance the laser-assisted charge exchange, the best region for short pulses is at very low collision energies. We also find that the s and p state charge exchange cross section are equally affected. We provide a qualitative discussion of these findings.

  20. Two-photon double-ionization of the H2 molecule: effects of pulse duration

    NASA Astrophysics Data System (ADS)

    Guan, Xiaoxu; Bartschat, Klaus; Koesterke, Lars; Schneider, Barry

    2013-05-01

    In previous work, we solved the time-dependent Schrödinger equation to calculate the two-photon double ionization of the hydrogen molecule induced by non-sequential absorption of photons with a central energy of 30 eV in a short laser pulse lasting for about 1.6 femtoseconds. At the equilibrium internuclear separation, however, several doubly excited 1Σg , u states lie about 30 eV above the ground X1Σg state. There is significant disagreement among various results published to date on this problem already for the angle-integrated cross section, and hence for the angular distribution as well. In the present work we address and clarify the fundamental role of those doubly excited states, which are accessible through photon absorption, on the two-photon breakup process. This can only be achieved by allowing for much longer laser pulses. Work supported by the NSF under PHY-1068140 and the XSEDE allocation PHY-090031.

  1. The effect of pulse duration on the growth rate of laser-induced damage sites at 351 nm on fused silica surfaces

    SciTech Connect

    Negres, R A; Norton, M A; Liao, Z M; Cross, D A; Bude, J D; Carr, C W

    2009-10-29

    Past work in the area of laser-induced damage growth has shown growth rates to be primarily dependent on the laser fluence and wavelength. More recent studies suggest that growth rate, similar to the damage initiation process, is affected by a number of additional parameters including pulse duration, pulse shape, site size, and internal structure. In this study, we focus on the effect of pulse duration on the growth rate of laser damage sites located on the exit surface of fused silica optics. Our results demonstrate, for the first time, a significant dependence of growth rate at 351 nm on pulse duration from 1 ns to 15 ns as {tau}{sup 0.3} for sites in the 50-100 {micro}m size range.

  2. A new sealed RF-excited CO2 laser for enamel ablation operating at 9.4μm with pulse duration of 26 μs

    NASA Astrophysics Data System (ADS)

    Chan, Kenneth H.; Jew, Jamison M.; Fried, Daniel

    2016-02-01

    Several studies over the past 20 years have identified that carbon dioxide lasers operating at wavelengths between 9.3 and 9.6-μm with pulse durations near 20-µs are ideal for hard tissue ablation. Those wavelengths are coincident with the peak absorption of the mineral phase and the pulse duration is close to the thermal relaxation time of the deposited energy of a few microseconds to minimize peripheral thermal damage and long enough to minimize plasma shielding effects to allow efficient ablation at practical rates. The desired pulse duration near 20-μs has been difficult to achieve since it is too long for TEA lasers and too short for RF-excited lasers for efficient operation. Recently, Coherent Inc. (Santa Clara, CA) developed the J5-V laser for microvia drilling which can produce laser pulses greater than 100 mJ in energy at 9.4-μm with a pulse duration of 26-µs and it can achieve pulse repetition rates of 3 KHz. We report the first results using this laser to ablate enamel and dentin. The onset of plasma shielding does not occur until the fluence exceeds 100 J/cm2 allowing efficient ablation at rates exceeding 50-μm per pulse. This laser is ideally suited for the selective ablation of carious lesions.

  3. Convoluted effect of laser fluence and pulse duration on the property of a nanosecond laser-induced plasma into an argon ambient gas at the atmospheric pressure

    SciTech Connect

    Bai Xueshi; Ma Qianli; Motto-Ros, Vincent; Yu Jin; Sabourdy, David; Nguyen, Luc; Jalocha, Alain

    2013-01-07

    We studied the behavior of the plasma induced by a nanosecond infrared (1064 nm) laser pulse on a metallic target (Al) during its propagation into argon ambient gas at the atmospheric pressure and especially over the delay interval ranging from several hundred nanoseconds to several microseconds. In such interval, the plasma is particularly interesting as a spectroscopic emission source for laser-induced plasma spectroscopy (LIBS). We show a convoluted effect between laser fluence and pulse duration on the structure and the emission property of the plasma. With a relatively high fluence of about 160 J/cm{sup 2} where a strong plasma shielding effect is observed, a short pulse of about 4 ns duration is shown to be significantly more efficient to excite the optical emission from the ablation vapor than a long pulse of about 25 ns duration. While with a lower fluence of about 65 J/cm{sup 2}, a significantly more efficient excitation is observed with the long pulse. We interpret our observations by considering the post-ablation interaction between the generated plume and the tailing part of the laser pulse. We demonstrate that the ionization of the layer of ambient gas surrounding the ablation vapor plays an important role in plasma shielding. Such ionization is the consequence of laser-supported absorption wave and directly dependent on the laser fluence and the pulse duration. Further observations of the structure of the generated plume in its early stage of expansion support our explanations.

  4. Effects of Biphasic Current Pulse Frequency, Amplitude, Duration and Interphase Gap on Eye Movement Responses to Prosthetic Electrical Stimulation of the Vestibular Nerve

    PubMed Central

    Davidovics, Natan S.; Fridman, Gene Y.; Chiang, Bryce; Della Santina, Charles C.

    2011-01-01

    An implantable prosthesis that stimulates vestibular nerve branches to restore sensation of head rotation and vision-stabilizing reflexes could benefit individuals disabled by bilateral loss of vestibular (inner ear balance) function. We developed a prosthesis that partly restores normal function in animals by delivering pulse frequency modulated (PFM) biphasic current pulses via electrodes implanted in semicircular canals. Because the optimal stimulus encoding strategy is not yet known, we investigated effects of varying biphasic current pulse frequency, amplitude, duration and interphase gap on vestibulo-ocular reflex (VOR) eye movements in chinchillas. Increasing pulse frequency increased response amplitude while maintaining a relatively constant axis of rotation. Increasing pulse amplitude (range 0–325 μA) also increased response amplitude but spuriously shifted eye movement axis, probably due to current spread beyond the target nerve. Shorter pulse durations (range 28–340 μs) required less charge to elicit a given response amplitude and caused less axis shift than longer durations. Varying interphase gap (range 25–175 μs) had no significant effect. While specific values reported herein depend on microanatomy and electrode location in each case, we conclude that PFM with short duration biphasic pulses should form the foundation for further optimization of stimulus encoding strategies for vestibular prostheses intended to restore sensation of head rotation. PMID:20813652

  5. Evolution dynamics of charge state distribution in neon interaction with x-ray pulses of variant intensities and durations

    NASA Astrophysics Data System (ADS)

    Gao, Cheng; Zeng, Jiaolong; Yuan, Jianmin

    2015-03-01

    The level population and charge state distribution (CSD) of the neon atomic system interacting with x-ray pulses of variant intensities and durations at a central photon energy of 1110 eV are investigated by solving the time-dependent rate equations. The laser beam has a circular spot size with a Gaussian intensity pattern and the time history of the intensity is represented by Gaussian distribution in time. As an example, the CSD as a function of time is given at different distances from the spot center for an x-ray beam of intensity 1.5 × 1017 W/cm2 and duration 75 fs (fs) for a spot size of 1 μm (full width at half maximum). The final CSD after averaging over the space and time is compared with a recent experiment and good agreement is found between the theory and experiment. Then systematic investigations are carried out to study the evolution of CSD with a wide range of intensity from 1.0 × 1015 W/cm2 to 1.0 × 1019 W/cm2 and duration from 30 fs to 100 fs. The results show that at intensities lower than 1.0 × 1015 W/cm2, the CSD shows a typical physical picture of weak x-ray photoionization of the neutral atomic neon. At higher intensity, i.e., larger than 5.0 × 1016 W/cm2, the dominant ionization stages are Ne7+ and Ne8+, while the fractions of ions in the Ne3+-Ne6+ stages are low for all laser durations and intensities.

  6. Splash plasma channels produced by picosecond laser pulses in argon gas for laser wakefield acceleration

    NASA Astrophysics Data System (ADS)

    Mizuta, Y.; Hosokai, T.; Masuda, S.; Zhidkov, A.; Makito, K.; Nakanii, N.; Kajino, S.; Nishida, A.; Kando, M.; Mori, M.; Kotaki, H.; Hayashi, Y.; Bulanov, S. V.; Kodama, R.

    2012-12-01

    Short-lived, ˜10ps, deep plasma channels, with their lengths of ˜1mm and diameters of ˜20μm, are observed and characterized in Ar gas jets irradiated by moderate intensity, ˜1015-16W/cm2, laser pulses with a duration from subpicosecond to several picoseconds. The channels, upon 2D particle-in-cell simulations including ionization, fit well in the guiding of high intensity femtosecond laser pulses and, therefore, in laser wakefield acceleration with a controllable electron self-injection.

  7. Effect of dye laser pulse duration on selective cutaneous vascular injury

    SciTech Connect

    Garden, J.M.; Tan, O.T.; Kerschmann, R.; Boll, J.; Furumoto, H.; Anderson, R.R.; Parrish, J.A.

    1986-11-01

    The pulsed dye laser at 577 nm, a wavelength well absorbed by oxyhemoglobin, causes highly selective thermal injury to cutaneous blood vessels. Confinement of thermal damage to microvessels is, in theory, related to the laser exposure time (pulsewidth) on selective vascular injury. This study investigates the effect of 577 nm dye laser pulsewidth on selective vascular injury. Nine Caucasian, normal volunteers received 577 nm dye laser exposures at pulsewidths of 1.5-350 microseconds to their skin. Clinical purpura threshold exposure doses were determined in each volunteer, and biopsies of threshold and suprathreshold doses were examined in each volunteer. The laser exposure dose required to produce purpura increased as pulsewidth increased in all 9 subjects (p less than 0.001). This finding corresponds to laser pulsewidths equal to or exceeding the thermal relaxation times for dermal blood vessels. Histologically, vessel damage was selectively, but qualitatively, different for short vs long pulsewidths. Pulsewidths shorter than 20 microseconds caused vessel wall fragmentation and hemorrhage, whereas longer pulsewidths caused no significant hemorrhage. The purpura noted clinically appears to be due to a coagulum of intralumenal denatured erythrocytes. At 24 h, there was marked vessel wall necrosis at all pulsewidths. The short pulsewidths may cause erythrocyte vaporization, rapid thermal expansion, and mechanical vessel rupture with hemorrhage. Long pulsewidths appear to cause thermal denaturation with less mechanical vessel damage. The selective, nonhemorrhagic, vascular necrosis caused by the long-pulsewidth dye laser may lead to a more desirable clinical outcome in the therapy of blood vessel disease processes.

  8. Effect of coil orientation on strength–duration time constant and I-wave activation with controllable pulse parameter transcranial magnetic stimulation

    PubMed Central

    D’Ostilio, Kevin; Goetz, Stefan M.; Hannah, Ricci; Ciocca, Matteo; Chieffo, Raffaella; Chen, Jui-Cheng A.; Peterchev, Angel V.; Rothwell, John C.

    2016-01-01

    Objective To compare the strength–duration (S–D) time constants of motor cortex structures activated by current pulses oriented posterior–anterior (PA) or anterior–posterior (AP) across the central sulcus. Methods Motor threshold and input–output curve, along with motor evoked potential (MEP) latencies, of first dorsal interosseus were determined at pulse widths of 30, 60, and 120 μs using a controllable pulse parameter (cTMS) device, with the coil oriented PA or AP. These were used to estimate the S–D time constant and we compared with data for responses evoked by cTMS of the ulnar nerve at the elbow. Results The S–D time constant with PA was shorter than for AP stimulation (230.9 ± 97.2 vs. 294.2 ± 90.9 μs; p < 0.001). These values were similar to those calculated after stimulation of ulnar nerve (197 ± 47 μs). MEP latencies to AP, but not PA stimulation were affected by pulse width, showing longer latencies following short duration stimuli. Conclusion PA and AP stimuli appear to activate the axons of neurons with different time constants. Short duration AP pulses are more selective than longer pulses in recruiting longer latency corticospinal output. Significance More selective stimulation of neural elements may be achieved by manipulating pulse width and orientation. PMID:26077634

  9. Duration and frequency of a high temperature pulse affect survival of emergence-ready Megachile rotundata (Hymenoptera: Megachilidae) during low-temperature incubation.

    PubMed

    Yocum, George D; Rinehart, Joseph P; Kemp, William P

    2012-02-01

    Synchronizing Megachile rotundata (F.) nesting activity with alfalfa bloom is essential for ensuring optimal pollination for alfalfa seed production. This is achieved by timing the initiation of spring bee incubation so that adults will emerge -2 wk before peak bloom. If weather conditions change so as to delay the bloom, bee managers will commonly expose the developing bees to a period of low-temperature incubation to slow their development. We have previously demonstrated survival during low-temperature incubation can be significantly increased by using a fluctuating thermal regime (FTR) where the bees receive a daily pulse at 20 degrees C. A FTR incubation protocol is composed of a number of different components, such as the base and pulse temperatures, and the duration and frequency of the pulse. In this investigation, the effect of the duration of the pulse (5-120 min) and the frequency of a pulse (twice daily to weekly) on the survival of developing M. rotundata was examined. A pulse as short as 5 min at 20 degrees C increased survival of the developing bees as compared with the constant 6 degrees C controls. Increasing the pulse duration induced a further increase in tolerance to 6 degrees C. As with the pulse duration, increasing the pulse frequency from once weekly to twice daily had a significant effect on improving the bees tolerance to low-temperature incubation. This investigation further strengthens the argument that a FTR protocol is superior to using a constant low-temperature exposure for interrupting the spring incubation of M. rotundata. PMID:22420249

  10. Duration and frequency of a high temperature pulse affect survival of emergence-ready Megachile rotundata (Hymenoptera: Megachilidae) during low-temperature incubation.

    PubMed

    Yocum, George D; Rinehart, Joseph P; Kemp, William P

    2012-02-01

    Synchronizing Megachile rotundata (F.) nesting activity with alfalfa bloom is essential for ensuring optimal pollination for alfalfa seed production. This is achieved by timing the initiation of spring bee incubation so that adults will emerge -2 wk before peak bloom. If weather conditions change so as to delay the bloom, bee managers will commonly expose the developing bees to a period of low-temperature incubation to slow their development. We have previously demonstrated survival during low-temperature incubation can be significantly increased by using a fluctuating thermal regime (FTR) where the bees receive a daily pulse at 20 degrees C. A FTR incubation protocol is composed of a number of different components, such as the base and pulse temperatures, and the duration and frequency of the pulse. In this investigation, the effect of the duration of the pulse (5-120 min) and the frequency of a pulse (twice daily to weekly) on the survival of developing M. rotundata was examined. A pulse as short as 5 min at 20 degrees C increased survival of the developing bees as compared with the constant 6 degrees C controls. Increasing the pulse duration induced a further increase in tolerance to 6 degrees C. As with the pulse duration, increasing the pulse frequency from once weekly to twice daily had a significant effect on improving the bees tolerance to low-temperature incubation. This investigation further strengthens the argument that a FTR protocol is superior to using a constant low-temperature exposure for interrupting the spring incubation of M. rotundata.

  11. Yeast cell inactivation related to local heating induced by low-intensity electric fields with long-duration pulses.

    PubMed

    Guyot, Stéphane; Ferret, Eric; Boehm, Jean-Baptiste; Gervais, Patrick

    2007-01-25

    The effects of electric field (EF) treatments on Saccharomyces cerevisiae viability were investigated using a PG200 electroporator (Hoefer Scientific Instrument, San Fransisco, CA, USA) with specific attention to induced thermal effects on cell death. Lethal electric fields (1.5 kV cm(-1) for 5 s) were shown to cause heat variations in the cell suspension medium (water+glycerol), while corresponding classical thermal treatments at equivalent temperatures had no effect on the cells viability. Variations of the electrical conductivity of the intra- and extracellular matrix caused by ions and solutes transfer across the membrane were shown to be involved in the observed heating. The results permitted to build a theoretical model for the temperature variations induced by electric fields. Using this model and the electrical conductivity of the different media, a plausible explanation of the cell death induced by low-intensity electric fields with long-duration pulses has been proposed. Indeed, cell mortality could in part be caused by direct and indirect effects of electric fields. Direct effects are related to well known electromechanical phenomena, whereas indirect effects are related to secondary thermal stress caused by plasma membrane thermoporation. This thermoporation was attributed to electrical conductivity variations and the corresponding intracellular heating.

  12. Formation of laser-induced periodic surface structures on fused silica upon two-color double-pulse irradiation

    SciTech Connect

    Höhm, S.; Herzlieb, M.; Rosenfeld, A.; Krüger, J.; Bonse, J.

    2013-12-16

    The formation of laser-induced periodic surface structures (LIPSS) upon irradiation of fused silica with multiple irradiation sequences consisting of laser pulse pairs (50 fs single-pulse duration) of two different wavelengths (400 and 800 nm) is studied experimentally. Parallel polarized double-pulse sequences with a variable delay Δt between −10 and +10 ps and between the individual fs-laser pulses were used to investigate the LIPSS periods versus Δt. These two-color experiments reveal the importance of the ultrafast energy deposition to the silica surface by the first laser pulse for LIPSS formation. The second laser pulse subsequently reinforces the previously seeded spatial LIPSS frequencies.

  13. A chopper system for shortening the duration of pulsed supersonic beams seeded with NO or Br{sub 2} down to 13 μs

    SciTech Connect

    Lam, Jessica; Rennick, Christopher J.; Softley, Timothy P.

    2015-05-15

    A chopper wheel construct is used to shorten the duration of a molecular beam to 13 μs. Molecular beams seeded with NO or with Br{sub 2} and an initial pulse width of ≥200 μs were passed through a spinning chopper wheel, which was driven by a brushless DC in vacuo motor at a range of speeds, from 3000 rpm to 80 000 rpm. The resulting duration of the molecular-beam pulses measured at the laser detection volume ranged from 80 μs to 13 μs and was the same for both NO and Br{sub 2}. The duration is consistent with a simple analytical model, and the minimum pulse width measured is limited by the spreading of the beam between the chopper and the detection point as a consequence of the longitudinal velocity distribution of the beam. The setup adopted here effectively eliminates buildup of background gas without the use of a differential pumping stage, and a clean narrow pulse is obtained with low rotational temperature.

  14. Optical ablation by high-power short-pulse lasers

    SciTech Connect

    Stuart, B.C.; Feit, M.D.; Herman, S.; Rubenchik, A.M.; Shore, B.W.; Perry, M.D.

    1996-02-01

    Laser-induced damage threshold measurements were performed on homogeneous and multilayer dielectrics and gold-coated optics at 1053 and 526 nm for pulse durations {tau} ranging from 140 fs to 1 ns. Gold coatings were found, both experimentally and theoretically, to be limited to 0.6 J/cm{sup 2} in the subpicosecond range for 1053-nm pulses. In dielectrics, we find qualitative differences in the morphology of damage and a departure from the diffusion-dominated {tau}{sup 1/2} scaling that indicate that damage results from plasma formation and ablation for {tau}{le}10 ps and from conventional heating and melting for {tau}{approx_gt}50 ps. A theoretical model based on electron production by multiphoton ionization, joule heating, and collisional (avalanche) ionization is in quantitative agreement with both the pulse-width and the wavelength scaling of experimental results. {copyright} {ital 1996 Optical Society of America.}

  15. Resolution limitations and optimization of the ITT F4157 streak tube focus for fast (10 ps) operation

    SciTech Connect

    Lerche, R.A.; Grasz, E.L.; Griffith, R.L.; Simpson, R.A.; Posey, R.

    1987-11-01

    The ITT F4157 image tube is biased at voltages far from the original design for operation in an ultrafast (10 ps) streak camera. Its output resolution at streak camera operating potentials has been measured as a function of input slit width, incident-light wavelength, and focus-grid voltage. The results are similar to those reported for the RCA C73435 streak tube. Indeed, the two tubes can be substituted for each other with minor mechanical modifications. The temporal resolution is insensitive to focus-grid voltage for a narrow (50 ..mu..m) input slit, but is very sensitive to focus-grid voltage for a wide (500 ..mu..m) input slit. Spatial resolution is nearly independent of focus-grid voltage for values that give good temporal resolution. Both temporal and spatial resolution depend on the incident-light wavelength. Streak camera operation is simulated with a computer program that calculates photoelectron trajectories. Electron ray tracing describes the observed effects of slit width, incident-light wavelength, and focus-grid voltage on the output resolution. 6 refs., 10 figs., 1 tab.

  16. Ultrafast saturation of electronic-resonance-enhanced coherent anti-Stokes Raman scattering and comparison for pulse durations in the nanosecond to femtosecond regime

    NASA Astrophysics Data System (ADS)

    Patnaik, Anil K.; Roy, Sukesh; Gord, James R.

    2016-02-01

    The saturation threshold of a probe pulse in an ultrafast electronic-resonance-enhanced (ERE) coherent anti-Stokes Raman spectroscopy (CARS) configuration is calculated. We demonstrate that while the underdamping condition is a sufficient condition for saturation of ERE-CARS with the long-pulse excitations, a transient gain must be achieved to saturate the ERE-CARS signal for the ultrafast probe regime. We identify that the area under the probe pulse can be used as a definitive parameter to determine the criterion for a saturation threshold for ultrafast ERE-CARS. From a simplified analytical solution and a detailed numerical calculation based on density-matrix equations, the saturation threshold of ERE-CARS is compared for a wide range of probe-pulse durations from the 10-ns to the 10-fs regime. The theory explains both qualitatively and quantitatively the saturation thresholds of resonant transitions and also gives a predictive capability for other pulse duration regimes. The presented criterion for the saturation threshold will be useful in establishing the design parameters for ultrafast ERE-CARS.

  17. Influence of the Duration of Thermal Action on the Errors in Determining the Thermophysical Characteristics of Ceramic Materials by a Laser Pulse Method

    NASA Astrophysics Data System (ADS)

    Kuznetsov, G. V.; Kats, M. D.

    2016-05-01

    An analysis of the errors involved in determining the thermophysical characteristics of a special-purpose ceramic material — zirconium carbide — is made. It is shown that the errors of determining the heat capacity and thermal diffusivity of the indicated material under conditions corresponding to the implementation of the laser pulse method vary nonmonotonically depending on the pulse duration. The possibility of attaining minimum values of methodical errors by appropriately selecting the thickness of a sample and of the time of its heating is shown.

  18. Laser-induced damage in dielectrics with nanosecond to subpicosecond pulses. I. Experimental. Part 1

    SciTech Connect

    Stuart, B.C.; Herman, S.; Perry, M.D.

    1994-12-01

    The authors report extensive laser-induced damage threshold measurements on pure and multilayer dielectrics at 1053 and 526 mm for pulse durations, {tau}, ranging from 140 fs to 1 ns. Qualitative differences in the morphology of damage and a departure from the diffusion-dominated {tau}{sup 1/2} scaling indicate that damage results from plasma formation and ablation for {tau}{le}10 ps and from conventional melting and boiling for {tau}>50 ps. A theoretical model based on electron production via multiphoton ionization, Joule heating, and collisional (avalanche) ionization is in good agreement with both the pulsewidth and wavelength scaling of experimental results.

  19. 948 kHz repetition rate, picosecond pulse duration, all-PM 1.03 μm mode-locked fiber laser based on nonlinear polarization evolution

    NASA Astrophysics Data System (ADS)

    Boivinet, S.; Lecourt, J.-B.; Hernandez, Y.; Fotiadi, A.; Mégret, P.

    2014-05-01

    We present in this study a PM all-fiber laser oscillator passively mode-locked (ML) at 1.03 μm. The laser is based on Nonlinear Polarization Evolution (NPE) in polarization maintaining (PM) fibers. In order to obtain the mode-locking regime, a nonlinear reflective mirror including a fibered polarizer, a long fiber span and a fibered Faraday mirror (FM) is inserted in a Fabry-Perot laser cavity. In this work we explain the principles of operation of this original laser design that permits to generate ultrashort pulses at low repetition (lower that 1MHz) rate with a cavity length of 100 m of fiber. In this experiment, the measured pulse duration is about 6 ps. To our knowledge this is the first all-PM mode-locked laser based on the NPE with a cavity of 100m length fiber and a delivered pulse duration of few picosecondes. Furthermore, the different mode-locked regimes of the laser, i.e. multi-pulse, noise-like mode-locked and single pulse, are presented together with the ways of controlling the apparition of these regimes. When the single pulse mode-locking regime is achieved, the laser delivers linearly polarized pulses in a very stable way. Finally, this study includes numerical results which are obtained with the resolution of the NonLinear Schrodinger Equations (NLSE) with the Split-Step Fourier (SSF) algorithm. This modeling has led to the understanding of the different modes of operation of the laser. In particular, the influence of the peak power on the reflection of the nonlinear mirror and its operation are studied.

  20. Comparison of amplified spontaneous emission pulse cleaners for use in chirped pulse amplification front end lasers

    SciTech Connect

    Dawson, J; Siders, C; Phan, H; Kanz, V; Barty, C

    2007-07-02

    We compare various schemes for removing amplified spontaneous emission from seed laser pulses. We focus on compact schemes that are compatible with fiber laser front end systems with pulse energies in the 10nJ-1{micro}J range and pulse widths in the 100fs-10ps range. Pre-pulse contrast ratios greater than 10{sup 9} have been measured.

  1. Influence of wavelength and pulse duration on peripheral thermal and mechanical damage to dentin and alveolar bone during IR laser ablation

    NASA Astrophysics Data System (ADS)

    Lee, C.; Ragadio, Jerome N.; Fried, Daniel

    2000-03-01

    The objective of this study was to measure the peripheral thermal damage produced during the laser ablation of alveolar bone and dentin for clinically relevant IR laser systems. Previous studies have demonstrated that a char layer produced around the laser incision site can inhibit the wound healing process. Moreover, in the case of dentin, a char layer is unsightly and is difficult to bond to with restorative materials. Thermal damage was assessed using polarized light microscopy for laser pulse widths from 500 ns to 300 microseconds at 2.94 micrometer and 9.6 micrometer. Water- cooling was not employed to alleviate thermal damage during the laser irradiation. At 9.6 micrometer, minimal thermal damage was observed for pulse widths on the order of the thermal relaxation time of the deposited laser energy in the tissue, 3 - 4 microseconds, and peripheral thermal damage increased with increasing pulse duration. At 2.94 micrometer, thermal damage was minimal for the Q-switched (500 ns) laser system. This study shows that 9.6 micrometer CO2 laser pulses with pulse widths of 5 - 10 microseconds are well suited for the efficient ablation of dentin and bone with minimal peripheral damage. This work was supported by NIH/NIDCR R29DE12091.

  2. Construction of a magnetic bottle spectrometer and its application to pulse duration measurement of X-ray laser using a pump-probe method

    SciTech Connect

    Namba, S.; Hasegawa, N.; Kishimoto, M.; Nishikino, M.; Ishino, M.; Kawachi, T.

    2015-11-15

    To characterize the temporal evolution of ultrashort X-ray pulses emitted by laser plasmas using a pump-probe method, a magnetic bottle time-of-flight electron spectrometer is constructed. The design is determined by numerical calculations of a mirror magnetic field and of the electron trajectory in a flight tube. The performance of the spectrometer is characterized by measuring the electron spectra of xenon atoms irradiated with a laser-driven plasma X-ray pulse. In addition, two-color above-threshold ionization (ATI) experiment is conducted for measurement of the X-ray laser pulse duration, in which xenon atoms are simultaneously irradiated with an X-ray laser pump and an IR laser probe. The correlation in the intensity of the sideband spectra of the 4d inner-shell photoelectrons and in the time delay of the two laser pulses yields an X-ray pulse width of 5.7 ps, in good agreement with the value obtained using an X-ray streak camera.

  3. Construction of a magnetic bottle spectrometer and its application to pulse duration measurement of X-ray laser using a pump-probe method

    NASA Astrophysics Data System (ADS)

    Namba, S.; Hasegawa, N.; Kishimoto, M.; Nishikino, M.; Ishino, M.; Kawachi, T.

    2015-11-01

    To characterize the temporal evolution of ultrashort X-ray pulses emitted by laser plasmas using a pump-probe method, a magnetic bottle time-of-flight electron spectrometer is constructed. The design is determined by numerical calculations of a mirror magnetic field and of the electron trajectory in a flight tube. The performance of the spectrometer is characterized by measuring the electron spectra of xenon atoms irradiated with a laser-driven plasma X-ray pulse. In addition, two-color above-threshold ionization (ATI) experiment is conducted for measurement of the X-ray laser pulse duration, in which xenon atoms are simultaneously irradiated with an X-ray laser pump and an IR laser probe. The correlation in the intensity of the sideband spectra of the 4d inner-shell photoelectrons and in the time delay of the two laser pulses yields an X-ray pulse width of 5.7 ps, in good agreement with the value obtained using an X-ray streak camera.

  4. Effect of level, duration, and inter-pulse interval of 1-2 kHz sonar signal exposures on harbor porpoise hearing.

    PubMed

    Kastelein, Ronald A; Hoek, Lean; Gransier, Robin; Rambags, Martijn; Claeys, Naomi

    2014-07-01

    Safety criteria for underwater low-frequency active sonar sounds produced during naval exercises are needed to protect harbor porpoise hearing. As a first step toward defining criteria, a porpoise was exposed to sequences consisting of series of 1-s, 1-2 kHz sonar down-sweeps without harmonics (as fatiguing noise) at various combinations of average received sound pressure levels (SPLs; 144-179 dB re 1 μPa), exposure durations (1.9-240 min), and duty cycles (5%-100%). Hearing thresholds were determined for a narrow-band frequency-swept sine wave centered at 1.5 kHz before exposure to the fatiguing noise, and at 1-4, 4-8, 8-12, 48, 96, 144, and 1400 min after exposure, to quantify temporary threshold shifts (TTSs) and recovery of hearing. Results show that the inter-pulse interval of the fatiguing noise is an important parameter in determining the magnitude of noise-induced TTS. For the reported range of exposure combinations (duration and SPL), the energy of the exposure (i.e., cumulative sound exposure level; SELcum) can be used to predict the induced TTS, if the inter-pulse interval is known. Exposures with equal SELcum but with different inter-pulse intervals do not result in the same induced TTS.

  5. Hot-Electron Generation with Kilojoule Pulses on OMEGA EP

    NASA Astrophysics Data System (ADS)

    Nilson, P. M.; Myatt, J. F.; Stoeckl, C.; Jaanimagi, P. A.; Theobald, W.; Delettrez, J. A.; Zuegel, J. D.; Betti, R.; Meyerhofer, D. D.; Sangster, T. C.; Akli, K. U.; Patel, P. K.; MacKinnon, A. J.

    2009-11-01

    Intense laser--solid interactions generate high-current electron sources with relativistic energies that are important for advanced ignition experiments. Applications include rapid heating for fast ignition and energy deposition in solid material for flash radiography, isochoric heating, and x-ray scattering experiments. Results of laser-electron coupling experiments carried out on the OMEGA EP laser with up to 1.3-kJ, 10-ps-long pulses will be presented. Strong (˜20%) energy coupling to electrons is demonstrated with conversion efficiencies independent of the laser pulse duration. This work was supported by the U.S. D.O.E Office of Inertial Confinement Fusion under Cooperative Agreement Nos. DE-FC02-ER54789 and DE-FC52-08NA28302. (P.M. Nilson, R. Betti, and D.D. Meyerhofer also FSC.)

  6. Time- and frequency-dependent model of time-resolved coherent anti-Stokes Raman scattering (CARS) with a picosecond-duration probe pulse

    NASA Astrophysics Data System (ADS)

    Stauffer, Hans U.; Miller, Joseph D.; Slipchenko, Mikhail N.; Meyer, Terrence R.; Prince, Benjamin D.; Roy, Sukesh; Gord, James R.

    2014-01-01

    The hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering (fs/ps CARS) technique presents a promising alternative to either fs time-resolved or ps frequency-resolved CARS in both gas-phase thermometry and condensed-phase excited-state dynamics applications. A theoretical description of time-dependent CARS is used to examine this recently developed probe technique, and quantitative comparisons of the full time-frequency evolution show excellent accuracy in predicting the experimental vibrational CARS spectra obtained for two model systems. The interrelated time- and frequency-domain spectral signatures of gas-phase species produced by hybrid fs/ps CARS are explored with a focus on gas-phase N2 vibrational CARS, which is commonly used as a thermometric diagnostic of combusting flows. In particular, we discuss the merits of the simple top-hat spectral filter typically used to generate the ps-duration hybrid fs/ps CARS probe pulse, including strong discrimination against non-resonant background that often contaminates CARS signal. It is further demonstrated, via comparison with vibrational CARS results on a time-evolving solvated organic chromophore, that this top-hat probe-pulse configuration can provide improved spectral resolution, although the degree of improvement depends on the dephasing timescales of the observed molecular modes and the duration and timing of the narrowband final pulse. Additionally, we discuss the virtues of a frequency-domain Lorentzian probe-pulse lineshape and its potential for improving the hybrid fs/ps CARS technique as a diagnostic in high-pressure gas-phase thermometry applications.

  7. Time- and frequency-dependent model of time-resolved coherent anti-Stokes Raman scattering (CARS) with a picosecond-duration probe pulse.

    PubMed

    Stauffer, Hans U; Miller, Joseph D; Slipchenko, Mikhail N; Meyer, Terrence R; Prince, Benjamin D; Roy, Sukesh; Gord, James R

    2014-01-14

    The hybrid femtosecond∕picosecond coherent anti-Stokes Raman scattering (fs∕ps CARS) technique presents a promising alternative to either fs time-resolved or ps frequency-resolved CARS in both gas-phase thermometry and condensed-phase excited-state dynamics applications. A theoretical description of time-dependent CARS is used to examine this recently developed probe technique, and quantitative comparisons of the full time-frequency evolution show excellent accuracy in predicting the experimental vibrational CARS spectra obtained for two model systems. The interrelated time- and frequency-domain spectral signatures of gas-phase species produced by hybrid fs∕ps CARS are explored with a focus on gas-phase N2 vibrational CARS, which is commonly used as a thermometric diagnostic of combusting flows. In particular, we discuss the merits of the simple top-hat spectral filter typically used to generate the ps-duration hybrid fs∕ps CARS probe pulse, including strong discrimination against non-resonant background that often contaminates CARS signal. It is further demonstrated, via comparison with vibrational CARS results on a time-evolving solvated organic chromophore, that this top-hat probe-pulse configuration can provide improved spectral resolution, although the degree of improvement depends on the dephasing timescales of the observed molecular modes and the duration and timing of the narrowband final pulse. Additionally, we discuss the virtues of a frequency-domain Lorentzian probe-pulse lineshape and its potential for improving the hybrid fs∕ps CARS technique as a diagnostic in high-pressure gas-phase thermometry applications.

  8. Switchable dual-pulse-shape mode-locked figure-eight all-PM fibre master oscillator with 0.5 W-level average output

    NASA Astrophysics Data System (ADS)

    Kobtsev, Sergey; Ivanenko, Aleksey; Fedotov, Yurii; Smirnov, Sergey V.; Golubtsov, Artur; Khripunov, Sergey

    2016-03-01

    For the first time a method for switching between generation of single- and double-scale pulses has been demonstrated in a mode-locked figure-eight NALM-based all-PM-fibre Yb master oscillator by adjustment of two pumps power. Introduction into a F8 configuration of a non-linear amplifying loop mirror with two active media not only ensured relatively high average output power of the master oscillator (> 0.5 W at 22-MHz repetition rate), but also allowed switching laser operation from one pulse type (single-scale with duration of <10 ps) to another - femtosecond clusters with envelope width of 16 ps and sub-pulse duration <200 fs.

  9. Dependence of the absorption of pulsed CO{sub 2}-laser radiation by silane on wavenumber, fluence, pulse duration, temperature, optical path length, and pressure of absorbing and nonabsorbing gases

    SciTech Connect

    Blazejowski, J.; Gruzdiewa, L.; Rulewski, J.; Lampe, F.W.

    1995-05-15

    The absorption of three lines [{ital P}(20), 944.2 cm{sup {minus}1}; {ital P}(14), 949.2 cm{sup {minus}1}; and {ital R}(24), 978.5 cm{sup {minus}1}] of the pulsed CO{sub 2} laser (00{sup 0}1--10{sup 0}0 transition) by SiH{sub 4} was measured at various pulse energy, pulse duration, temperature, optical path length, and pressure of the compound and nonabsorbing foreign gases. In addition, low intensity infrared absorption spectrum of silane was compared with high intensity absorption characteristics for all lines of the pulsed CO{sub 2} laser. The experimental dependencies show deviations from the phenomenological Beer--Lambert law which can be considered as arising from the high intensity of an incident radiation and collisions of absorbing molecules with surroundings. These effects were included into the expression, being an extended form of the Beer--Lambert law, which reasonably approximates all experimental data. The results, except for extending knowledge on the interaction of a high power laser radiation with matter, can help understanding and planning processes leading to preparation of silicon-containing technologically important materials.

  10. Single-pulse laser ablation threshold of borosilicate, fused silica, sapphire, and soda-lime glass for pulse widths of 500  fs, 10  ps, 20  ns.

    PubMed

    Nieto, Daniel; Arines, Justo; O'Connor, Gerard M; Flores-Arias, María Teresa

    2015-10-10

    In this work, we report a comparative study of the laser ablation threshold of borosilicate, fused silica, sapphire, and soda-lime glass as a function of the pulse width and for IR laser wavelengths. We determine the ablation threshold for three different pulse durations: τ=500  fs, 10 ps, and 20 ns. Experiments have been performed using a single laser pulse per shot in an ambient (air) environment. The results show a significant difference, of two orders of magnitude, between the group of ablation thresholds obtained for femtosecond, picosecond, and nanosecond pulses. This difference is reduced to 1 order of magnitude in the soda-lime substrate with tin impurities, pointing out the importance of the incubation effect. The morphology of the marks generated over the different glass materials by one single pulse of different pulse durations has been analyzed using a scanning electron microscope (FESEM ULTRA Plus). Our results are important for practical purposes, providing the ablation threshold data of four commonly used substrates at three different pulse durations in the infrared regime (1030-1064 nm) and complete data for increasing the understanding of the differences in the mechanism's leading ablation in the nanosecond, picosecond, and femtosecond regimes.

  11. Theoretical study of electronic damage in single-particle imaging experiments at x-ray free-electron lasers for pulse durations from 0.1 to 10 fs

    NASA Astrophysics Data System (ADS)

    Gorobtsov, O. Yu.; Lorenz, U.; Kabachnik, N. M.; Vartanyants, I. A.

    2015-06-01

    X-ray free-electron lasers (XFELs) may allow us to employ the single-particle imaging (SPI) method to determine the structure of macromolecules that do not form stable crystals. Ultrashort pulses of 10 fs and less allow us to outrun complete disintegration by Coulomb explosion and minimize radiation damage due to nuclear motion, but electronic damage is still present. The major contribution to the electronic damage comes from the plasma generated in the sample that is strongly dependent on the amount of Auger ionization. Since the Auger process has a characteristic time scale on the order of femtoseconds, one may expect that its contribution will be significantly reduced for attosecond pulses. Here we study the effect of electronic damage on the SPI at pulse durations from 0.1 to 10 fs and in a large range of XFEL fluences to determine optimal conditions for imaging of biological samples. We analyzed the contribution of different electronic excitation processes and found that at fluences higher than 1013- 10 15 photons /μ m2 (depending on the photon energy and pulse duration) the diffracted signal saturates and does not increase further. A significant gain in the signal is obtained by reducing the pulse duration from 10 to 1 fs. Pulses below a duration of 1 fs do not give a significant gain in the scattering signal in comparison with 1-fs pulses. We also study the limits imposed on SPI by Compton scattering.

  12. Ultrashort-pulse laser machining

    SciTech Connect

    Banks, P S; Feit, M D; Nguyen, H T; Perry, M D; Rubenchik, A M; Sefcik, J A; Stuart, B C

    1998-09-01

    A new type of material processing is enabled with ultrashort (t < 10 ps) laser pulses. Cutting, drilling, sculpting of all materials (biologic materials, ceramics, sapphire, silicon carbide, diamond, metals) occurs by new mechanisms that eliminate thermal shock or collateral damage. High-precision machining to submicron tolerances is enabled resulting in high surface quality and negligible heat affected zone.

  13. Design of a pulse-type strain gauge balance for a long-test-duration hypersonic shock tunnel

    NASA Astrophysics Data System (ADS)

    Wang, Y.; Liu, Y.; Jiang, Z.

    2016-01-01

    When the measurement of aerodynamic forces is conducted in a hypersonic shock tunnel, the inertial forces lead to low-frequency vibrations of the model, and its motion cannot be addressed through digital filtering because a sufficient number of cycles cannot be obtained during a tunnel run. This finding implies restrictions on the model size and mass as the natural frequencies are inversely proportional to the length scale of the model. Therefore, the force measurement still has many problems, particularly for large and heavy models. Different structures of a strain gauge balance (SGB) are proposed and designed, and the measurement element is further optimized to overcome the difficulties encountered during the measurement of aerodynamic forces in a shock tunnel. The motivation for this study is to assess the structural performance of the SGB used in a long-test-duration JF12 hypersonic shock tunnel, which has more than 100 ms of test time. Force tests were conducted for a large-scale cone with a 10° semivertex angle and a length of 0.75 m in the JF12 long-test-duration shock tunnel. The finite element method was used for the analysis of the vibrational characteristics of the Model-Balance-Sting System (MBSS) to ensure a sufficient number of cycles, particularly for the axial force signal during a shock tunnel run. The higher-stiffness SGB used in the test shows good performance, wherein the frequency of the MBSS increases because of the stiff construction of the balance. The experimental results are compared with the data obtained in another wind tunnel and exhibit good agreement at M = 7 and α =5°.

  14. High Power Picosecond Laser Pulse Recirculation

    SciTech Connect

    Shverdin, M Y; Jovanovic, I; Semenov, V A; Betts, S M; Brown, C; Gibson, D J; Shuttlesworth, R M; Hartemann, F V; Siders, C W; Barty, C P

    2010-04-12

    We demonstrate a nonlinear crystal-based short pulse recirculation cavity for trapping the second harmonic of an incident high power laser pulse. This scheme aims to increase the efficiency and flux of Compton-scattering based light sources. We demonstrate up to 36x average power enhancement of frequency doubled sub-millijoule picosecond pulses, and 17x average power enhancement of 177 mJ, 10 ps, 10 Hz pulses.

  15. High-power picosecond laser pulse recirculation.

    PubMed

    Shverdin, M Y; Jovanovic, I; Semenov, V A; Betts, S M; Brown, C; Gibson, D J; Shuttlesworth, R M; Hartemann, F V; Siders, C W; Barty, C P J

    2010-07-01

    We demonstrate a nonlinear crystal-based short pulse recirculation cavity for trapping the second harmonic of an incident high-power laser pulse. This scheme aims to increase the efficiency and flux of Compton-scattering-based light sources. We demonstrate up to 40x average power enhancement of frequency-doubled submillijoule picosecond pulses, and 17x average power enhancement of 177 mJ, 10 ps, 10 Hz pulses.

  16. High-power picosecond laser pulse recirculation.

    PubMed

    Shverdin, M Y; Jovanovic, I; Semenov, V A; Betts, S M; Brown, C; Gibson, D J; Shuttlesworth, R M; Hartemann, F V; Siders, C W; Barty, C P J

    2010-07-01

    We demonstrate a nonlinear crystal-based short pulse recirculation cavity for trapping the second harmonic of an incident high-power laser pulse. This scheme aims to increase the efficiency and flux of Compton-scattering-based light sources. We demonstrate up to 40x average power enhancement of frequency-doubled submillijoule picosecond pulses, and 17x average power enhancement of 177 mJ, 10 ps, 10 Hz pulses. PMID:20596201

  17. 10 ps resolution, 160 ns full scale range and less than 1.5% differential non-linearity time-to-digital converter module for high performance timing measurements

    SciTech Connect

    Markovic, B.; Tamborini, D.; Villa, F.; Tisa, S.; Tosi, A.; Zappa, F.

    2012-07-15

    We present a compact high performance time-to-digital converter (TDC) module that provides 10 ps timing resolution, 160 ns dynamic range and a differential non-linearity better than 1.5% LSB{sub rms}. The TDC can be operated either as a general-purpose time-interval measurement device, when receiving external START and STOP pulses, or in photon-timing mode, when employing the on-chip SPAD (single photon avalanche diode) detector for detecting photons and time-tagging them. The instrument precision is 15 ps{sub rms} (i.e., 36 ps{sub FWHM}) and in photon timing mode it is still better than 70 ps{sub FWHM}. The USB link to the remote PC allows the easy setting of measurement parameters, the fast download of acquired data, and their visualization and storing via an user-friendly software interface. The module proves to be the best candidate for a wide variety of applications such as: fluorescence lifetime imaging, time-of-flight ranging measurements, time-resolved positron emission tomography, single-molecule spectroscopy, fluorescence correlation spectroscopy, diffuse optical tomography, optical time-domain reflectometry, quantum optics, etc.

  18. 10 ps resolution, 160 ns full scale range and less than 1.5% differential non-linearity time-to-digital converter module for high performance timing measurements

    NASA Astrophysics Data System (ADS)

    Markovic, B.; Tamborini, D.; Villa, F.; Tisa, S.; Tosi, A.; Zappa, F.

    2012-07-01

    We present a compact high performance time-to-digital converter (TDC) module that provides 10 ps timing resolution, 160 ns dynamic range and a differential non-linearity better than 1.5% LSBrms. The TDC can be operated either as a general-purpose time-interval measurement device, when receiving external START and STOP pulses, or in photon-timing mode, when employing the on-chip SPAD (single photon avalanche diode) detector for detecting photons and time-tagging them. The instrument precision is 15 psrms (i.e., 36 psFWHM) and in photon timing mode it is still better than 70 psFWHM. The USB link to the remote PC allows the easy setting of measurement parameters, the fast download of acquired data, and their visualization and storing via an user-friendly software interface. The module proves to be the best candidate for a wide variety of applications such as: fluorescence lifetime imaging, time-of-flight ranging measurements, time-resolved positron emission tomography, single-molecule spectroscopy, fluorescence correlation spectroscopy, diffuse optical tomography, optical time-domain reflectometry, quantum optics, etc.

  19. 10 ps resolution, 160 ns full scale range and less than 1.5% differential non-linearity time-to-digital converter module for high performance timing measurements.

    PubMed

    Markovic, B; Tamborini, D; Villa, F; Tisa, S; Tosi, A; Zappa, F

    2012-07-01

    We present a compact high performance time-to-digital converter (TDC) module that provides 10 ps timing resolution, 160 ns dynamic range and a differential non-linearity better than 1.5% LSB(rms). The TDC can be operated either as a general-purpose time-interval measurement device, when receiving external START and STOP pulses, or in photon-timing mode, when employing the on-chip SPAD (single photon avalanche diode) detector for detecting photons and time-tagging them. The instrument precision is 15 ps(rms) (i.e., 36 ps(FWHM)) and in photon timing mode it is still better than 70 ps(FWHM). The USB link to the remote PC allows the easy setting of measurement parameters, the fast download of acquired data, and their visualization and storing via an user-friendly software interface. The module proves to be the best candidate for a wide variety of applications such as: fluorescence lifetime imaging, time-of-flight ranging measurements, time-resolved positron emission tomography, single-molecule spectroscopy, fluorescence correlation spectroscopy, diffuse optical tomography, optical time-domain reflectometry, quantum optics, etc. PMID:22852708

  20. Pulse

    MedlinePlus

    ... resting for at least 10 minutes. Take the exercise heart rate while you are exercising. ... pulse rate can help determine if the patient's heart is pumping. ... rate gives information about your fitness level and health.

  1. Development of high damage threshold optics for petawatt-class short-pulse lasers

    SciTech Connect

    Stuart, B.C.; Perry, M.D.; Boyd, R.D.

    1995-02-22

    The authors report laser-induced damage threshold measurements on pure and multilayer dielectrics and gold-coated optics at 1053 and 526 nm for pulse durations, {tau}, ranging from 140 fs to 1 ns. Damage thresholds of gold coatings are limited to 500 mJ/cm{sup 2} in the subpicosecond range for 1053-nm pulses. In dielectrics, qualitative differences in the morphology of damage and a departure from the diffusion-dominated {tau}1/2 scaling indicate that damage results from plasma formation and ablation for {tau}{le}10 ps and from conventional melting and boiling for {tau}>50 ps. A theoretical model based on electron production via multiphoton ionization, Joule heating, and collisional (avalanche) ionization is in quantitative agreement with both the pulsewidth and wavelength scaling of experimental results.

  2. Development of high damage threshold optics for petawatt-class short-pulse lasers

    NASA Astrophysics Data System (ADS)

    Stuart, Brent C.; Perry, Michael D.; Boyd, Robert D.; Britten, Jerald A.; Shore, Bruce W.; Feit, Michael D.; Rubenchik, Alexander M.

    1995-04-01

    We report laser-induced damage threshold measurements on pure and multilayer dielectrics and gold-coated optics at 1053 and 526 nm for pulse durations, (tau) , ranging from 140 fs to 1 ns. Damage thresholds of gold coatings are limited to 500 mJ/cm2 in the subpicosecond range from 1053-nm pulses. In dielectrics, qualitative differences in the morphology of damage and a departure from the diffusion-dominated (tau) 1/2 scaling indicate that damage results from plasma formation and ablation for (tau) 10 ps and from conventional melting and boiling for (tau) > 50 ps. A theoretical model based on electron production via multiphoton ionization, Joule heating, and collisional (avalanche) ionization is in quantitative agreement with both the pulsewidth and wavelength scaling of experimental results.

  3. Synchronized ps fiber lasers with pulse durations (25, 50, 100-2000ps) and repetition rates (100kHz-150Mhz) continuously tunable over three orders of magnitude

    NASA Astrophysics Data System (ADS)

    Dupuis, Alexandre; Burgoyne, Bryan; Pena, Guido; Archambault, André; Lemieux, Dominic; Solomonean, Vasile; Duong, Maxime; Villeneuve, Alain

    2013-03-01

    Ultrafast lasers are enabling precision machining of a wide variety of materials. However, the optimal laser parameters for proper material processing can differ greatly from one material to another. In order to cut high aspect-ratio features at high processing speeds the laser parameters such as pulse energy, repetition rate, and cutting speed need to be optimized. In particular, a shorter pulse duration plays an important role in reducing the thermal damage in the Heat-Affected Zones. In this paper we present a novel ps fiber laser whose electronically tunable parameters aim to facilitate the search for optimal processing parameters. The 20W 1064nm Yb fiber laser is based on a Master Oscillator Power Amplifier (MOPA) architecture with a repetition rate that can be tuned continuously from 120kHz to 120MHz. More importantly, the integration of three different pulse generators enables the pulse duration to be switched from 25ps to 50ps, or to any value within the 55ps to 2000ps range. By reducing the pulse duration from the ns-regime down to 25ps, the laser approaches the transition from the thermal processing regime to the ablation regime of most materials. Moreover, in this paper we demonstrate the synchronization of the pulses from two such MOPA lasers. This enables more elaborate multipulse processing schemes where the pulses of each laser can be set to different parameter values, such as an initial etching pulse followed by a thermal annealing pulse. It should be noted that all the laser parameters are controlled electronically with no moving parts, including the synchronization.

  4. Particle Identification Using Cost Effective mRPC Technology for Time-of-Flight Measurements with Less than 10 ps Time Resolution

    NASA Astrophysics Data System (ADS)

    Shimek, Taylor

    2015-10-01

    This presentation will introduce the use of multi-gap Resistive Plate Chambers (mRPCs) for time of flight (TOF) based particle identification (PID) in nuclear and high-energy physics. The mRPC technology is developed for use in future experiments at the planned Electron Ion Collider, EIC. TOF PID using mRPCs with 10 ps timing resolution will make it possible to precisely determine the flavor content of valence- and sea-quarks in the proton through semi-inclusive deep inelastic scattering with identified pions and kaons. A first mRPC prototype using float glass resistive plates at UIUC has reached a timing resolution of 21 ps. In this presentation I discuss an effort to replace the float glass with cheaper Mylar-based resistive plates. I will also discuss the design and construction of a first prototype and present initial results on signal development, efficiencies and timing resolution of the mRPC prototype.

  5. Unraveling the roles of thermal annealing and off-time duration in magnetic properties of pulsed electrodeposited NiCu nanowire arrays

    NASA Astrophysics Data System (ADS)

    Haji jamali, Z.; Almasi Kashi, M.; Ramazani, A.; Montazer, A. H.

    2015-05-01

    Magnetic alloy nanowires (ANWs) have long been studied owing to both their fundamental aspects and possible applications in magnetic storage media and magnetoresistance devices. Here, we report on the roles of thermal annealing and duration of off-time between pulses (toff) in crystalline characteristics and magnetic properties of arrays of pulsed electrodeposited NiCu ANWs (35 nm in diameter and a length of 1.2 μm), embedded in porous anodic alumina template. Increasing toff enabled us to increase the Cu content thereby fabricating NiCu ANWs with different crystallinity and alloy compositions. Although major hysteresis curve measurements showed no considerable change in magnetic properties before and after annealing, the first-order reversal curve (FORC) analysis provided new insights into the roles of thermal annealing and toff. In other words, FORC diagrams indicated the presence of low and high coercive field regions in annealed Ni-rich ANWs, coinciding with the increase in toff in as-deposited ANWs. The former has a small coercivity with strong demagnetizing magnetostatic interactions from neighboring NWs and may correspond to a soft magnetic phase. The latter has a greater coercivity with weak interactions, corresponding to a hard magnetic phase. On the other hand, for as-deposited and annealed Cu-rich NiCu ANWs, a mixed phase of the soft and hard segments could be found. Furthermore, a transition from the interacting Ni-rich to non-interacting Cu-rich ANWs took place with a magnetic field applied parallel to the NW axis. Thus, these arrays of ANWs with tunable magnetic phases and interactions may have potential applications in the nanoscale devices.

  6. The effect of laser pulse duration and beam shape on the selective removal of novel thin film layers for flexible electronic devices

    NASA Astrophysics Data System (ADS)

    Moorhouse, C.; Karnakis, D. M.; Kapnopoulos, C.; Laskarakis, A.; Logothetidis, S.; Antonopoulos, G.; Mekeridis, E.

    2015-07-01

    Lightweight, flexible substrates coated with thin film layers <0.5μm thick are commonly utilized for modern electronic devices that are portable and constantly reducing in size, weight, power consumption and material cost. Patterning techniques for these thin films are required to provide device functionality and alternatives to photolithography such as direct write laser processes are particularly attractive. However, for complex devices with multiple thin layers, the quality requirements for laser scribing are extremely high, since each individual thin film layer must be patterned without damaging the underlying thin film layer(s) and also provide a suitable topography for subsequent layers to be deposited upon. Hence, the choice of the laser parameters is critical for a number of emerging thin film materials used in flexible electronic devices such as ITO, pedot:PSS, silver nanoparticle inks, amongst others. These thin films can be extremely sensitive to the thermal interaction with lasers and this report outlines the influence of laser pulse duration and beam shaping techniques on laser patterning of these thin films and the implications for laser system design.

  7. Effects of pulse phase duration and location of stimulation within the inferior colliculus on auditory cortical evoked potentials in a guinea pig model.

    PubMed

    Neuheiser, Anke; Lenarz, Minoo; Reuter, Guenter; Calixto, Roger; Nolte, Ingo; Lenarz, Thomas; Lim, Hubert H

    2010-12-01

    The auditory midbrain implant (AMI), which consists of a single shank array designed for stimulation within the central nucleus of the inferior colliculus (ICC), has been developed for deaf patients who cannot benefit from a cochlear implant. Currently, performance levels in clinical trials for the AMI are far from those achieved by the cochlear implant and vary dramatically across patients, in part due to stimulation location effects. As an initial step towards improving the AMI, we investigated how stimulation of different regions along the isofrequency domain of the ICC as well as varying pulse phase durations and levels affected auditory cortical activity in anesthetized guinea pigs. This study was motivated by the need to determine in which region to implant the single shank array within a three-dimensional ICC structure and what stimulus parameters to use in patients. Our findings indicate that complex and unfavorable cortical activation properties are elicited by stimulation of caudal-dorsal ICC regions with the AMI array. Our results also confirm the existence of different functional regions along the isofrequency domain of the ICC (i.e., a caudal-dorsal and a rostral-ventral region), which has been traditionally unclassified. Based on our study as well as previous animal and human AMI findings, we may need to deliver more complex stimuli than currently used in the AMI patients to effectively activate the caudal ICC or ensure that the single shank AMI is only implanted into a rostral-ventral ICC region in future patients.

  8. The effect of the diffusion time and pulse gradient duration ratio on the diffraction pattern and the structural information estimated from q-space diffusion MR: Experiments and simulations

    NASA Astrophysics Data System (ADS)

    Bar-Shir, Amnon; Avram, Liat; Özarslan, Evren; Basser, Peter J.; Cohen, Yoram

    2008-10-01

    q-Space diffusion MRI (QSI) provides a means of obtaining microstructural information about porous materials and neuronal tissues from diffusion data. However, the accuracy of this structural information depends on experimental parameters used to collect the MR data. q-Space diffusion MR performed on clinical scanners is generally collected with relatively long diffusion gradient pulses, in which the gradient pulse duration, δ, is comparable to the diffusion time, Δ. In this study, we used phantoms, consisting of ensembles of microtubes, and mathematical models to assess the effect of the ratio of the diffusion time and the duration of the diffusion pulse gradient, i.e., Δ/ δ, on the MR signal attenuation vs. q, and on the measured structural information extracted therefrom. We found that for Δ/ δ ˜ 1, the diffraction pattern obtained from q-space MR data are shallower than when the short gradient pulse (SGP) approximation is satisfied. For long δ the estimated compartment size is, as expected, smaller than the real size. Interestingly, for Δ/ δ ˜ 1 the diffraction peaks are shifted to even higher q-values, even when δ is kept constant, giving the impression that the restricted compartments are even smaller than they are. When phantoms composed of microtubes of different diameters are used, it is more difficult to estimate the diameter distribution in this regime. Excellent agreement is found between the experimental results and simulations that explicitly account for the use of long duration gradient pulses. Using such experimental data and this mathematical framework, one can estimate the true compartment dimensions when long and finite gradient pulses are used even when Δ/ δ ˜ 1.

  9. 180 mJ, long-pulse-duration, master-oscillator power amplifier with linewidth less than 25.6 kHz for laser guide stars.

    PubMed

    Wang, Chunhua; Zhang, Xiang; Ye, Zhibin; Liu, Chong; Chen, Jun

    2013-07-01

    A high-energy single-frequency hundred-microsecond long-pulse solid-state laser is demonstrated, which features an electro-optically modulated seed laser and two-stage double-passed pulse-pumped solid-state laser rod amplifier. Laser output with energy of 180 mJ, repetition rate of 50 Hz, and pulse width of 150 μs is achieved. The laser linewidth is measured to be less than 25.52 kHz by a fiber delay self-heterodyne method. In addition, a closed-loop controlling system is adopted to lock the center wavelength. No relaxation oscillation spikes appear in the pulse temporal profile, which is beneficial for further amplification.

  10. 180 mJ, long-pulse-duration, master-oscillator power amplifier with linewidth less than 25.6 kHz for laser guide stars.

    PubMed

    Wang, Chunhua; Zhang, Xiang; Ye, Zhibin; Liu, Chong; Chen, Jun

    2013-07-01

    A high-energy single-frequency hundred-microsecond long-pulse solid-state laser is demonstrated, which features an electro-optically modulated seed laser and two-stage double-passed pulse-pumped solid-state laser rod amplifier. Laser output with energy of 180 mJ, repetition rate of 50 Hz, and pulse width of 150 μs is achieved. The laser linewidth is measured to be less than 25.52 kHz by a fiber delay self-heterodyne method. In addition, a closed-loop controlling system is adopted to lock the center wavelength. No relaxation oscillation spikes appear in the pulse temporal profile, which is beneficial for further amplification. PMID:23842267

  11. Fiber Laser Front Ends for High Energy, Short Pulse Lasers

    SciTech Connect

    Dawson, J; Messerly, M; Phan, H; Siders, C; Beach, R; Barty, C

    2007-06-21

    We are developing a fiber laser system for short pulse (1-10ps), high energy ({approx}1kJ) glass laser systems. Fiber lasers are ideal for these systems as they are highly reliable and enable long term stable operation.

  12. Picosecond pulsed laser processing of polycrystalline diamond and cubic boron nitride composite materials

    NASA Astrophysics Data System (ADS)

    Warhanek, Maximilian G.; Pfaff, Josquin; Meier, Linus; Walter, Christian; Wegener, Konrad

    2016-03-01

    Capabilities and advantages of laser ablation processes utilizing ultrashort pulses have been demonstrated in various applications of scientific and industrial nature. Of particular interest are applications that require high geometrical accuracy, excellent surface integrity and thus tolerate only a negligible heat-affected zone in the processed area. In this context, this work presents a detailed study of the ablation characteristics of common ultrahard composite materials utilized in the cutting tool industry, namely polycrystalline diamond (PCD) and polycrystalline cubic boron nitride composite (PCBN). Due to the high hardness of these materials, conventional mechanical processing is time consuming and costly. Herein, laser ablation is an appealing solution, since no process forces and no wear have to be taken into consideration. However, an industrially viable process requires a detailed understanding of the ablation characteristics of each material. Therefore, the influence of various process parameters on material removal and processing quality at 10 ps pulse duration are investigated for several PCD and PCBN grades. The main focus of this study examines the effect of different laser energy input distributions, such as pulse frequency and burst pulses, on the processing conditions in deep cutting kerfs and the resulting processing speed. Based on these results, recommendations for efficient processing of such materials are derived.

  13. Interglacial Durations

    NASA Astrophysics Data System (ADS)

    Mangili, Clara; McManus, Jerry F.; Raynaud, Dominique

    2014-05-01

    In the context of future global warming induced by human activities, it is essential to assess the role of natural climatic variations. Precise knowledge of the duration of past interglacial periods is fundamental to the understanding of the potential future evolution of the Holocene. Past ice age cycles provide a natural laboratory for exploring the progression and duration of interglacial climate. Palaeorecords from ice, land and oceans extend over the last 800 ka, revealing eight glacial-interglacial cycles, with a range of insolation and greenhouse gas influences. The interglacials display a correspondingly large variety of intensity and duration, thus providing an opportunity for major insights into the mechanisms involved in the behaviour of interglacial climates. A comparison of the duration of these interglacials, however, is often difficult, as the definition of an interglacial depends on the archive that is considered. Therefore, to compare interglacial length and climate conditions from different archives, a consistent definition of interglacial conditions is required, ideally one that is not bound to the method nor to the archive under consideration. Here we present a method to identify interglacials and to calculate their length by mean of a simple statistical approach. We based our method on ~ 400 ka windows of time to determine mean climatic conditions while allowing for the possibility of long term evolution of the climatic baseline. For our study of interglacials of the past 800 ka, we used two windows that largely align with the pre- (800-430 ka ago) and post- (430-0 ka ago) mid-Brunhes event (MBE), although the resulting conclusions are not sensitive to this particular division. We applied this method to the last 800 ka of a few palaeoclimate records: the deuterium ice core (EDC) record as a climatic proxy, the benthic δ18O stack (LR04) as a proxy for sea level/ice volume, ice core (Vostok, EDC) atmospheric CO2 and additional records. Although

  14. Generation of runaway electrons and X-ray emission during breakdown of atmospheric-pressure air by voltage pulses with an ∼0.5-μs front duration

    SciTech Connect

    Kostyrya, I. D.; Tarasenko, V. F.

    2015-03-15

    Results are presented from experiments on the generation of runaway electron beams and X-ray emission in atmospheric-pressure air by using voltage pulses with an ∼0.5-μs front duration. It is shown that the use of small-curvature-radius spherical cathodes (or other cathodes with small curvature radii) decreases the intensity of the runaway electron beam and X-ray emission. It is found that, at sufficiently high voltages at the electrode gap (U{sub m} ∼ 100 kV), the gap breakdown, the formation of a spark channel, and the generation of a runaway electron beam occur over less than 10 ns. At high values of U{sub m} behind the anode that were reached by increasing the cathode size and the electrode gap length, a supershort avalanche electron beam with a full width at half-maximum (FWHM) of up to ∼100 ps was detected. At voltages of ∼50 kV, the second breakdown regime was revealed in which a runaway electron beam with an FWHM of ∼2 ns was generated, whereas the FWHM of the X-ray pulse increased to ∼100 ns. It is established that the energy of the bulk of runaway electrons decreases with increasing voltage front duration and is ⩽30 keV in the first regime and ⩽10 keV in the second regime.

  15. PULSE GENERATOR

    DOEpatents

    Roeschke, C.W.

    1957-09-24

    An improvement in pulse generators is described by which there are produced pulses of a duration from about 1 to 10 microseconds with a truly flat top and extremely rapid rise and fall. The pulses are produced by triggering from a separate input or by modifying the current to operate as a free-running pulse generator. In its broad aspect, the disclosed pulse generator comprises a first tube with an anode capacitor and grid circuit which controls the firing; a second tube series connected in the cathode circuit of the first tube such that discharge of the first tube places a voltage across it as the leading edge of the desired pulse; and an integrator circuit from the plate across the grid of the second tube to control the discharge time of the second tube, determining the pulse length.

  16. Two-photon double-ionization of the H2 molecule in light perpindicular to the internuclear axis: effects of pulse duration

    NASA Astrophysics Data System (ADS)

    Guan, Xiaoxu; Bartschat, Klaus; Schneider, Barry; Koesterke, Lars

    2014-05-01

    Earlier, we solved the time-dependent Schrödinger equation to calculate the two-photon double ionization of the hydrogen molecule induced by non-sequential absorption of photons with a central energy of 30 eV in a short laser pulse lasting for about 1.6 femtoseconds. The linear polarization of the radiation was aligned with the internuclear axis. At the equilibrium distance Req, several doubly excited 1Σg , u states, accessible through photon absorption,lie about 30 eV above the X1Σg ground state. These states are likely responsible for the significant disagreement seen in the literature for previous results on both angle-integrated and angle-differential cross sections. Here we continue to explore the fundamental role of doubly excited states on the two-photon break-up process,now for the even more difficult problem of laser polarization perpendicular to the internuclear axis. Such studies require relatively long laser pulses, thus making the calculations computationally very challenging.

  17. A prospective study analyzing the application of radiofrequency energy and high-voltage, ultrashort pulse duration electrical fields on the quantitative reduction of adipose tissue

    PubMed Central

    Duncan, Diane Irvine; Kim, Theresa H. M.; Temaat, Robbin

    2016-01-01

    Noninvasive fat reduction is claimed by many device manufacturers, but proof of efficacy has been difficult to establish. This prospective study was designed to measure the reduction of fat thickness and actual volume reduction in 20 female patients treated with an external radiofrequency (RF) device. This device combines RF heat, suction coupled vacuum, and oscillating electrical pulses that induce adipocyte death over time. Patients underwent pre- and post-treatment and intercurrent measurements of weight, body mass index, ultrasonic transcutaneous fat thickness, and 2D and 3D Vectra photography with independent calculation of circumferential and volumetric change. Mean transcutaneous ultrasound thickness at reproducible points was 2.78 cm; at 1-month post-treatment, the mean fat thickness was 1.71 cm. At 3-month post-treatment, the mean fat thickness reduction was 39.6%. Vectra circumference measurements were taken at 10-mm intervals, with postural and breathing cycle control. Independent analysis of serial measurements from + 60 to − 70 mm showed mean abdominal circumference measurement of 2.3 cm. Mean abdominal volume loss was 202.4 and 428.5 cc at 1- and 3-month post-treatment, respectively. Scanning electron microscopy confirmed that permanent cell destruction was caused by irreversible electroporation. Pyroptosis appears to be the mechanism of action. PMID:26962636

  18. Simultaneous compression of the passively mode-locked pulsewidth and pulse train

    NASA Technical Reports Server (NTRS)

    Yang, Xiang-Chun; Zhu, Xiao-Lei; Wu, Zhao-Qing; Sun, Zhan-Ao; Yang, Fu-Min; Tan, De-Tong; Chen, Wan-Zhen; Lu, Wen-Hu; Xiao, Chi-Kun

    1993-01-01

    Simultaneous compression of the passively mode-locked pulse width and pulse train have been achieved by using a plano-convex unstable resonator hybrided by a nonlinear Sagnac ring interferometer. The greater than 30 mJ single pulse energy of a lone oscillator and less than or equal to 10 ps pulsewidth have been obtained. Using this system, the LAGEOS and ETALON satellites' laser ranging have been performed successfully.

  19. Research on chirped pulse stimulated Raman scattering in ethanol

    NASA Astrophysics Data System (ADS)

    Guo, Xiao-Yang; Zou, Xiao; Xu, Yi; Lu, Xiao-Ming; Wang, Cheng; Liu, Yan-Qi; Li, Yan-Yan; Leng, Yu-Xin; Li, Ru-Xin

    2014-11-01

    We report a generation of 10.6% conversion efficiency near 1053 nm first order Stokes pulse in stimulated Raman scattering pumped using 800 nm Ti:sapphire based femtosecond pulses that are stretched to 460 ps, obtained by use of a single pass ethonal Raman shifter. The Stokes pulse almost maintains the bandwidth of the pump and is compressed to ~10 ps using a mismatched grating-pair. The spectral characteristic of the Raman pulse is calculated and the results explain the observed transient features.

  20. Laser fusion pulse shape controller

    DOEpatents

    Siebert, Larry D.

    1977-01-01

    An apparatus for controlling the pulse shape, i.e., the pulse duration and intensity pattern, of a pulsed laser system, and which is particularly well adapted for controlling the pellet ignition pulse in a laser-driven fusion reaction system. The apparatus comprises a laser generator for providing an optical control pulse of the shape desired, a pulsed laser triggered by the control pulse, and a plurality of optical Kerr-effect gates serially disposed at the output of the pulsed laser and selectively triggered by the control pulse to pass only a portion of the pulsed laser output generally corresponding in shape to the control pulse.

  1. Dependence of the phase-coherence time in CdS1-xSex on the laser pulse width

    NASA Astrophysics Data System (ADS)

    Schwab, H.; Klingshirn, C.

    1992-03-01

    We performed degenerate-four-wave-mixing (DFWM) experiments in CdS1-xSex mixed crystals with laser pulses of different duration. It was found that the measured phase-coherence times (T2) are critically dependent on the spectral width and by that on the temporal half-width (τlaser) of the exciting laser. In an experiment with 10-ps pulses we find values for T2 of up to 3 ns. Under the same conditions in the same sample, the maximum observed value for T2 is 100 ps for τlaser=1 ps. With even shorter pulses, the phase-coherence time drops below 80 fs, which is the temporal resolution of our experiment. In addition, the line shape of the dephasing curves as well as the density dependence of T2 are substantially changed. The reason for these findings is based on the structure of these crystals. The compositional disorder leads to the formation of localized states. Within the same spectral region, one also finds extended excitons. The interaction of carriers of both kinds is then responsible for the observed effects.

  2. Slow interfacial reamorphization of Ge films melted by ps laser pulses

    NASA Astrophysics Data System (ADS)

    Siegel, J.; Solis, J.; Afonso, C. N.

    1998-11-01

    Melting and rapid solidification is induced in 50-nm-thick amorphous Ge films on glass substrates by single laser pulses at 583 nm with a duration of 10 ps. The solidification process is followed by means of reflectivity measurements with ns time resolution both at the air/film (front) and the substrate/film (back) interfaces. Due to interference effects between the light reflected at the film-substrate and film-liquid interfaces, the back side reflectivity measurements turn out to be very sensitive to the melt depth induced by the laser pulse and their comparison to optical simulations enables the determination of the solidification dynamics. For low fluences, only a thin layer of the film is melted and solidification occurs interfacially leading to reamorphization of the molten material. The results provide a critical interface velocity for amorphization of ˜4 m/s, much slower than the one that has widely been reported for elementary semiconductors. For high fluences, the molten layer depth approaches the film thickness and the results are consistent with a bulk solidification process. In this case, recalescence effects upon solid phase nucleation become important and lead to the formation of crystallites distributed throughout the whole resolidified volume.

  3. Optically pulsed electron accelerator

    DOEpatents

    Fraser, John S.; Sheffield, Richard L.

    1987-01-01

    An optically pulsed electron accelerator can be used as an injector for a free electron laser and comprises a pulsed light source, such as a laser, for providing discrete incident light pulses. A photoemissive electron source emits electron bursts having the same duration as the incident light pulses when impinged upon by same. The photoemissive electron source is located on an inside wall of a radio frequency powered accelerator cell which accelerates the electron burst emitted by the photoemissive electron source.

  4. Optically pulsed electron accelerator

    DOEpatents

    Fraser, J.S.; Sheffield, R.L.

    1985-05-20

    An optically pulsed electron accelerator can be used as an injector for a free electron laser and comprises a pulsed light source, such as a laser, for providing discrete incident light pulses. A photoemissive electron source emits electron bursts having the same duration as the incident light pulses when impinged upon by same. The photoemissive electron source is located on an inside wall of a radiofrequency-powered accelerator cell which accelerates the electron burst emitted by the photoemissive electron source.

  5. Chirped-pulse amplification with narrowband pulses.

    PubMed

    Shverdin, M Y; Albert, F; Anderson, S G; Betts, S M; Gibson, D J; Messerly, M J; Hartemann, F V; Siders, C W; Barty, C P J

    2010-07-15

    We demonstrate a compact hyperdispersion stretcher and compressor pair that permit chirped-pulse amplification in Nd:YAG. We generate 750 mJ, 0.2 nm FWHM, 10 Hz pulses recompressed to an 8 ps near-transform-limited duration. The dispersion-matched pulse compressor and stretcher impart a chirp of 7300 ps/nm, in a 3 m x 1 m footprint.

  6. Chirped-pulse amplification with narrowband pulses.

    PubMed

    Shverdin, M Y; Albert, F; Anderson, S G; Betts, S M; Gibson, D J; Messerly, M J; Hartemann, F V; Siders, C W; Barty, C P J

    2010-07-15

    We demonstrate a compact hyperdispersion stretcher and compressor pair that permit chirped-pulse amplification in Nd:YAG. We generate 750 mJ, 0.2 nm FWHM, 10 Hz pulses recompressed to an 8 ps near-transform-limited duration. The dispersion-matched pulse compressor and stretcher impart a chirp of 7300 ps/nm, in a 3 m x 1 m footprint. PMID:20634869

  7. Template Reproduction of GRB Pulse Light Curves

    NASA Astrophysics Data System (ADS)

    Hakkila, Jon E.; Preece, R. D.; Loredo, T. J.; Wolpert, R. L.; Broadbent, M. E.

    2014-01-01

    A study of well-isolated pulses in gamma ray burst light curves indicates that simple models having smooth and monotonic pulse rises and decays are inadequate. Departures from the Norris et al. (2005) pulse shape are in the form of a wave-like pre-peak residual that is mirrored and stretched following the peak. Pulse shape departures are present in GRB pulses of all durations, but placement of the departures relative to pulse peaks correlates with asymmetry. This establishes an additional link between temporal structure and spectral evolution, as pulse asymmetry is related to initial hardness while pulse duration indicates the rate of hard-to-soft pulse evolution.

  8. Pulsed hall thruster system

    NASA Technical Reports Server (NTRS)

    Hruby, Vladimir J. (Inventor); Pote, Bruce M. (Inventor); Gamero-Castano, Manuel (Inventor)

    2004-01-01

    A pulsed Hall thruster system includes a Hall thruster having an electron source, a magnetic circuit, and a discharge chamber; a power processing unit for firing the Hall thruster to generate a discharge; a propellant storage and delivery system for providing propellant to the discharge chamber and a control unit for defining a pulse duration .tau.<0.1d.sup.3.rho./m, where d is the characteristic size of the thruster, .rho. is the propellant density at standard conditions, and m is the propellant mass flow rate for operating either the power processing unit to provide to the Hall thruster a power pulse of a pre-selected duration, .tau., or operating the propellant storage and delivery system to provide a propellant flow pulse of duration, .tau., or providing both as pulses, synchronized to arrive coincidentally at the discharge chamber to enable the Hall thruster to produce a discreet output impulse.

  9. Mechanisms subserving the physiological nocturnal relative hypoprolactinemia of healthy older men: dual decline in prolactin secretory burst mass and basal release with preservation of pulse duration, frequency, and interpulse interval--a General Clinical Research Center study.

    PubMed

    Iranmanesh, A; Mulligan, T; Veldhuis, J D

    1999-03-01

    Increasing age is accompanied by decrements in randomly obtained, fasting, or frequently sampled serum PRL concentrations. The precise neuroendocrine mechanisms underlying such relative hypoprolactinemia in aging are incompletely understood. In the present study, we sampled blood at 2.5-min intervals overnight in 11 young (aged 21-34 yr) and 8 older (aged 62-72 yr) healthy men for subsequent chemiluminescence-based assay of serum PRL concentrations. The mean (+/- SEM) serum PRL concentration was significantly reduced at 4.3 +/- 0.78 microg/L in older men compared with 9.5 +/- 1.2 microg/L in young volunteers (P = 0.0049). PRL concentrations correlated with serum testosterone (r = 0.473; P = 0.041), dehydroepiandrosteroen sulfate (r = +0.455, P = 0.05), and insulin-like growth factor I (r = 0.494; P = 0.032) levels. Deconvolution analysis was used to evaluate combined pulsatile and basal modes of PRL secretion. In older men, discrete PRL secretory bursts were marked by a significantly (2.4-fold) attenuated mass of hormone secreted per burst (amount of PRL secreted per unit distribution volume), viz. 1.6 +/- 0.23 (older) vs. 3.9 +/- 0.57 microg/L (young; P < 0.01). In contrast, PRL secretory burst frequency, interpulse interval, and pulse duration were invariant of age. Concomitantly, basal PRL secretion was reduced by 2-fold in older subjects, namely to 0.00030 +/- 0.00027 (older) vs. 0.00065 +/- 0.0002 microg/L/min (young; P < 0.01). The amount of total PRL secretion that was pulsatile averaged 82 +/- 5.3% in young and 99 +/- 0.13% in older men (P = 0.012), indicating preferential loss of the basal mode of PRL release in aging. Assuming that basal PRL secretion mirrors functional pituitary lactotroph cell secretory mass, whereas pulsatile PRL release reflects effective (net) intermittent hypothalamic drive to responsive lactotroph cells, then our results suggest both an attrition in lactotroph cell mass and an impoverishment of net positive hypothalamic (agonistic

  10. Long pulse production from short pulses

    DOEpatents

    Toeppen, John S.

    1994-01-01

    A method of producing a long output pulse (SA) from a short pump pulse (P), using an elongated amplified fiber (11) having a doped core (12) that provides an amplifying medium for light of one color when driven into an excited state by light of a shorter wavelength and a surrounding cladding 13. A seed beam (S) of the longer wavelength is injected into the core (12) at one end of the fiber (11) and a pump pulse (P) of the shorter wavelength is injected into the cladding (13) at the other end of the fiber (11). The counter-propagating seed beam (S) and pump pulse (P) will produce an amplified output pulse (SA) having a time duration equal to twice the transit time of the pump pulse (P) through the fiber (11) plus the length of the pump pulse (P).

  11. Long pulse production from short pulses

    DOEpatents

    Toeppen, J.S.

    1994-08-02

    A method of producing a long output pulse from a short pump pulse is disclosed, using an elongated amplified fiber having a doped core that provides an amplifying medium for light of one color when driven into an excited state by light of a shorter wavelength and a surrounding cladding. A seed beam of the longer wavelength is injected into the core at one end of the fiber and a pump pulse of the shorter wavelength is injected into the cladding at the other end of the fiber. The counter-propagating seed beam and pump pulse will produce an amplified output pulse having a time duration equal to twice the transit time of the pump pulse through the fiber plus the length of the pump pulse. 3 figs.

  12. Single-shot, high-resolution, fiber-based phase-diversity photodetection of optical pulses

    NASA Astrophysics Data System (ADS)

    Dorrer, C.; Waxer, L. J.; Kalb, A.; Hill, E. M.; Bromage, J.

    2016-03-01

    Temporally characterizing optical pulses is an important task when building, optimizing, and using optical sources. Direct photodetection with high-bandwidth photodiodes and real-time oscilloscopes is only adequate for optical pulses longer than ~10 ps; diagnostics based on indirect strategies are required to characterize femtosecond and sub-10-ps coherent sources. Most of these diagnostics are based on nonlinear optics and can be difficult to implement for the single-shot characterization of nonrepetitive events. A temporal diagnostic based on phase diversity is demonstrated in the context of picosecond high-energy laser systems, where single-shot pulse measurements are required for system safety and interpretation of experimental results. A plurality of ancillary optical pulses obtained by adding known amounts of chromatic dispersion to the pulse under test are directly measured by photodetection and processed to reconstruct the input pulse shape. This high-sensitivity (~50-pJ) diagnostic is based on a pulse replicator composed of fiber splitters and delay fibers, making it possible to operate with fiber sources and free-space sources after fiber coupling. Experimental data obtained with a high-bandwidth real-time oscilloscope demonstrate accurate characterization of pulses from a high-energy chirped-pulse amplification system, even for pulses shorter than the photodetection impulse response.

  13. Study of x-rays produced from debris-free sources with Ar, Kr and Kr/Ar mixture linear gas jets irradiated by UNR Leopard laser beam with fs and ns pulse duration

    NASA Astrophysics Data System (ADS)

    Kantsyrev, V. L.; Schultz, K. A.; Shlyaptseva, V. V.; Safronova, A. S.; Shrestha, I. K.; Petrov, G. M.; Moschella, J. J.; Petkov, E. E.; Stafford, A.; Cooper, M. C.; Weller, M. E.; Cline, W.; Wiewior, P.; Chalyy, O.

    2016-06-01

    Experiments of x-ray emission from Ar, Kr, and Ar/Kr gas jet mixture were performed at the UNR Leopard Laser Facility operated with 350 fs pulses at laser intensity of 2 × 1019 W/cm2 and 0.8 ns pulses at an intensity of 1016 W/cm2. Debris free x-ray source with supersonic linear nozzle generated clusters/monomer jet with an average density of ≥1019 cm-3 was compared to cylindrical tube subsonic nozzle, which produced only monomer jet with average density 1.5-2 times higher. The linear (elongated) cluster/gas jet provides the capability to study x-ray yield anisotropy and laser beam self-focusing with plasma channel formation that are interconnecting with efficient x-ray generation. Diagnostics include x-ray diodes, pinhole cameras and spectrometers. It was observed that the emission in the 1-9 keV spectral region was strongly anisotropic depending on the directions of laser beam polarization for sub-ps laser pulse and supersonic linear jet. The energy yield in the 1-3 keV region produced by a linear nozzle was an order of magnitude higher than from a tube nozzle. Non-LTE models and 3D molecular dynamic simulations of Ar and Kr clusters irradiated by sub-ps laser pulses have been implemented to analyze obtained data. A potential evidence of electron beam generation in jets' plasma was discussed. Note that the described debris-free gas-puff x-ray source can generate x-ray pulses in a high repetition regime. This is a great advantage compared to solid laser targets.

  14. Efficient optical pulse stacker system

    DOEpatents

    Seppala, Lynn G.; Haas, Roger A.

    1982-01-01

    Method and apparatus for spreading and angle-encoding each pulse of a multiplicity of small area, short pulses into several temporally staggered pulses by use of appropriate beam splitters, with the optical elements being arranged so that each staggered pulse is contiguous with one or two other such pulses, and the entire sequence of stacked pulses comprising a single, continuous long pulse. The single long pulse is expanded in area, and then doubly passed through a nonstorage laser amplifier such as KrF. After amplification, the physically separated, angle-encoded and temporally staggered pulses are recombined into a single pulse of short duration. This high intensity output beam is well collimated and may be propagated over long distance, or used for irradiating inertial confinement fusion targets.

  15. Neuromuscular disruption with ultrashort electrical pulses

    NASA Astrophysics Data System (ADS)

    Pakhomov, Andrei; Kolb, Juergen F.; Joshi, Ravindra P.; Schoenbach, Karl H.; Dayton, Thomas; Comeaux, James; Ashmore, John; Beason, Charles

    2006-05-01

    Experimental studies on single cells have shown that application of pulsed voltages, with submicrosecond pulse duration and an electric field on the order of 10 kV/cm, causes sudden alterations in the intracellular free calcium concentration, followed by immobilization of the cell. In order to examine electrical stimulation and incapacitation with such ultrashort pulses, experiments on anesthetized rats have been performed. The effect of single, 450 nanosecond monopolar pulses have been compared with that of single pulses with multi-microsecond duration (TASER pulses). Two conditions were explored: 1. the ability to elicit a muscle twitch, and, 2. the ability to suppress voluntary movement by using nanosecond pulses. The second condition is relevant for neuromuscular incapacitation. The preliminary results indicate that for stimulation microsecond pulses are advantageous over nanosecond pulses, whereas for incapacitation, the opposite seems to apply. The stimulation effects seem to scale with electrical charge, whereas the disruption effects don't follow a simple scaling law. The increase in intensity (time of incapacitation) for a given pulse duration, is increasing with electrical energy, but is more efficient for nanosecond than for microsecond pulses. This indicates different cellular mechanisms for incapacitation, most likely subcellular processes, which have been shown to become increasingly important when the pulse duration is shortened into the nanosecond range. If further studies can confirm these initial results, consequences of reduced pulse duration are a reduction in weight and volume of the pulse delivery system, and likely, because of the lower required energy for neuromuscular incapacitation, reduced safety risks.

  16. Pulse measurement apparatus and method

    DOEpatents

    Marciante, John R.; Donaldson, William R.; Roides, Richard G.

    2011-10-25

    An embodiment of the invention is directed to a pulse measuring system that measures a characteristic of an input pulse under test, particularly the pulse shape of a single-shot, nano-second duration, high shape-contrast optical or electrical pulse. An exemplary system includes a multi-stage, passive pulse replicator, wherein each successive stage introduces a fixed time delay to the input pulse under test, a repetitively-gated electronic sampling apparatus that acquires the pulse train including an entire waveform of each replica pulse, a processor that temporally aligns the replicated pulses, and an averager that temporally averages the replicated pulses to generate the pulse shape of the pulse under test. An embodiment of the invention is directed to a method for measuring an optical or an electrical pulse shape. The method includes the steps of passively replicating the pulse under test with a known time delay, temporally stacking the pulses, and temporally averaging the stacked pulses. An embodiment of the invention is directed to a method for increasing the dynamic range of a pulse measurement by a repetitively-gated electronic sampling device having a rated dynamic range capability, beyond the rated dynamic range of the sampling device; e.g., enhancing the dynamic range of an oscilloscope. The embodied technique can improve the SNR from about 300:1 to 1000:1. A dynamic range enhancement of four to seven bits may be achieved.

  17. Pulsed-neutron monochromator

    DOEpatents

    Mook, H.A. Jr.

    1984-01-01

    In one aspect, the invention is an improved pulsed-neutron monochromator of the vibrated-crystal type. The monochromator is designed to provide neutron pulses which are characterized both by short duration and high density. A row of neutron-reflecting crystals is disposed in a neutron beam to reflect neutrons onto a common target. The crystals in the row define progressively larger neutron-scattering angles and are vibrated sequentially in descending order with respect to the size of their scattering angles, thus generating neutron pulses which arrive simultaneously at the target. Transducers are coupled to one end of the crystals to vibrate them in an essentially non-resonant mode. The transducers propagate transverse waves in the crystal which progress longitudinally therein. The waves are absorbed at the undriven ends of the crystals by damping material mounted thereon. In another aspect, the invention is a method for generating neutron pulses characterized by high intensity and short duration.

  18. Pulsed-neutron monochromator

    DOEpatents

    Mook, Jr., Herbert A.

    1985-01-01

    In one aspect, the invention is an improved pulsed-neutron monochromator of the vibrated-crystal type. The monochromator is designed to provide neutron pulses which are characterized both by short duration and high density. A row of neutron-reflecting crystals is disposed in a neutron beam to reflect neutrons onto a common target. The crystals in the row define progressively larger neutron-scattering angles and are vibrated sequentially in descending order with respect to the size of their scattering angles, thus generating neutron pulses which arrive simultaneously at the target. Transducers are coupled to one end of the crystals to vibrate them in an essentially non-resonant mode. The transducers propagate transverse waves in the crystal which progress longitudinally therein. The wave are absorbed at the undriven ends of the crystals by damping material mounted thereon. In another aspect, the invention is a method for generating neutron pulses characterized by high intensity and short duration.

  19. [Sleep duration and metabolism].

    PubMed

    Viot-Blanc, V

    2015-12-01

    Sleep duration has gradually diminished during the last decade while obesity and type 2 diabetes have become epidemics. Experimental sleep curtailment leads to increased appetite, hormonal disturbances and, especially, insulin resistance. Numerous epidemiological studies have therefore examined whether habitual short sleep is associated with obesity and type 2 diabetes. A large majority of cross-sectional studies have confirmed an association between short, and also long sleep duration and obesity in adults more than in the elderly. Short sleep is strongly associated to obesity in children and adolescents. Prospective studies, including studies in children, are not conclusive with regard to the effect of short sleep on the incidence of obesity. Both short and long sleep durations are associated with diabetes, but only short sleep duration seems predictive of future diabetes. Insomnia seems to be a strong contributor to short sleep duration but the association of insomnia with obesity is not clear. Insomnia is associated with type 2 diabetes and also predictive of a higher incidence. Other studies have shown that short sleep duration and insomnia are associated with, and sometime predictive of, other components of the metabolic syndrome, especially hypertension and the risk of coronary disease. The treatment of short sleep duration and insomnia with regard to their effects on the metabolic syndrome merits further study. PMID:26603959

  20. PULSE RATE DIVIDER

    DOEpatents

    McDonald, H.C. Jr.

    1962-12-18

    A compact pulse-rate divider circuit affording low impedance output and high input pulse repetition rates is described. The circuit features a single secondary emission tube having a capacitor interposed between its dynode and its control grid. An output pulse is produced at the anode of the tube each time an incoming pulse at the control grid drives the tube above cutoff and the duration of each output pulse corresponds to the charging time of the capacitor. Pulses incoming during the time the grid bias established by the discharging capacitor is sufficiently negative that the pulses are unable to drive the tube above cutoff do not produce output pulses at the anode; these pulses are lost and a dividing action is thus produced by the circuit. The time constant of the discharge path may be vanied to vary in turn the division ratio of the circuit; the time constant of the charging circuit may be varied to vary the width of the output pulses. (AEC)

  1. SHORT PULSE STRETCHER

    DOEpatents

    Branum, D.R.; Cummins, W.F.

    1962-12-01

    >A short pulse stretching circuit capable of stretching a short puise to enable it to be displayed on a relatively slow sweeping oscilloscope is described. Moreover, the duration of the pulse is increased by charging a capacitor through a diode and thereafter discharging the capacitor at such time as is desired. In the circuit the trigger pulse alone passes through a delay line, whereas the main signal passes through the diode only, and results in over-all circuit losses which are proportional to the low losses of the diode only. (AEC)

  2. Short pulse free electron laser amplifier

    DOEpatents

    Schlitt, Leland G.; Szoke, Abraham

    1985-01-01

    Method and apparatus for amplification of a laser pulse in a free electron laser amplifier where the laser pulse duration may be a small fraction of the electron beam pulse duration used for amplification. An electron beam pulse is passed through a first wiggler magnet and a short laser pulse to be amplified is passed through the same wiggler so that only the energy of the last fraction, f, (f<1) of the electron beam pulse is consumed in amplifying the laser pulse. After suitable delay of the electron beam, the process is repeated in a second wiggler magnet, a third, . . . , where substantially the same fraction f of the remainder of the electron beam pulse is consumed in amplification of the given short laser pulse in each wiggler magnet region until the useful electron beam energy is substantially completely consumed by amplification of the laser pulse.

  3. Pulse distortion in single-mode fibers. 3: Chirped pulses.

    PubMed

    Marcuse, D

    1981-10-15

    The theory of pulse distortion in single-mode fibers is extended to include laser sources that suffer a linear wavelength sweep (chirp) during the duration of the pulse. The transmitted pulse is expressed as a Fourier integral whose spectral function is given by an analytical expression in closed form. The rms width of the transmitted pulse is also expressed in closed form. Numerical examples illustrate the influence of the chirp on the shape and rms width of the pulse. A somewhat paradoxical situation exists. A given input pulse can be made arbitrarily short by a sufficiently large amount of chirping, and, after a given fiber length, this chirped pulse returns to its original width. But at this particular distance an unchirped pulse would be only [equiation] times longer. Thus chirping can improve the rate of data transmission by only 40%.

  4. Resistor pulse-handling capability

    SciTech Connect

    Horner, L.E.

    1981-04-01

    Methods for calculating pulse-handling capabilities of various resistor types are described. The work represents a compilation of studies derived from various sources, as indicated in the bibliography. The results indicate that resistors may be subjected to short-duration pulses exceeding their rated powers without sustaining permanent damage.

  5. Subcycle Pulsed Focused Vector Beams

    SciTech Connect

    Lin Qiang; Zheng Jian; Becker, Wilhelm

    2006-12-22

    An accurate description of a subcycle pulsed beam (SCPB) is presented based on the complex-source model. The fields are exact solutions of Maxwell's equations and applicable to a focused pulsed beam with a pulse duration down to and below one cycle of the carrier wave and with arbitrary polarization state. Depending on the pulse duration, the pulse is blueshifted, and its wings are chirped. This effect, which we refer to as 'self-induced blueshift' goes beyond the carrier-envelope description. The corresponding phase is a temporal analog of the Gouy phase. The energy gain of a relativistic electron swept over by an SCPB is very sensitive to the proper form chosen to describe the pulse.

  6. Femtosecond pulsed laser processing of electronic materials: Fundamentals and micro/nano-scale applications

    NASA Astrophysics Data System (ADS)

    Choi, Tae-Youl

    ultrashort laser pulse accompanied by the pre-pulse induces air breakdown that can be detrimental to materials processing. A time-resolved pump-and-probe experiment provides distinct evidence for the occurrence of an air plasma and air breakdown. This highly nonlinear phenomenon takes place before the commencement of the ablation process, which is traced beyond elapsed time of the order of 10 ps with respect to the ablating pulse. The nonlinear refractive index of the generated air plasma is calculated as a function of electron density. The self-focusing of the main pulse is identified by the third order nonlinear susceptibility. A crystalline silicon sample is subjected to two optically separated ultra-fast laser pulses of full-width-half-maximum (FWHM) duration of about 80 femtoseconds. These pulses are delivered at wavelength, lambda = 800 nm. Femtosecond-resolved imaging pump-and-probe experiments in reflective and Schlieren configurations have been performed to investigate plasma dynamics and shock wave propagation during the sample ablation process. By using a diffractive optical element (DOE) for beam shaping, microchannels were fabricated. A super-long working distance objective lens was used to machine silicon materials in the sub-micrometer scale. As an extension of micro-machining, the finite difference time domain (FDTD) method is used to assess the feasibility of using near-field distribution of laser light. Gold coated films were machined with nano-scale dimensions and characterized with atomic force microscopy (AFM).

  7. LED flicker pulsing

    NASA Astrophysics Data System (ADS)

    Johnson, Mark A.; Cote, Paul J.

    2001-08-01

    There is need to replace hazardous radioluminescent light sources with a means of illumination that is environmentally friendly. This paper describes an electronic source that was developed as a potential candidate to replace low intensity tritium in a military system. It employs an LED for illumination and a 3-volt coin cell battery as a power source. This new light source is electronically invisible, requires minimal maintenance, and provides the lowest practical illumination to preclude detection by optical means. The low intensity requires that the LED be driven at DC current levels resulting in poor luminous efficiency. Therefore, in an effort to maximize battery life, the LED is pulsed into a more optically efficient mode of operation. However, conventional pulsing techniques are not employed because of concerns the electronics could be identified by conspicuous power spectral density (PSD) components in the electromagnetic spectrum generated by a pulsed LED. Therefore, flicker noise concepts have been employed to efficiently drive the LED while generating a virtually undetectable spectral signature. Although ideally the pulse durations, magnitudes, and spacings should be random, a significant reduction in conspicuous PSD components can be achieved when imposing practical constraints. The dominant components of the power spectrum are significantly reduced using fixed pulse durations and magnitudes while varying only the pulse spacing. The mean duty cycle is set to provide the same effective illumination as DC operation while generating a PSD normally associated with natural phenomena.

  8. Femtosecond pulse mode-locked VECSELs

    NASA Astrophysics Data System (ADS)

    Quarterman, A. H.; Wilcox, K. G.

    2014-03-01

    Femtosecond pulse mode-locked VECSELs have become a significant focus of research in the VECSEL community, with recent progress being made in several directions including power scaling. Power scaling advances in femtosecond VECSELs have included increasing the average power to over 5W [1], producing 3.3W average power with 400 fs pulses [2]. Here I report our recent work reducing the pulse duration of Watt-level VECSELs to 355 fs, and also developing approaches to reach sub-250-fs pulse durations using coherent broadening in photonic crystal fiber in the normal dispersion regime and a grating pulse compressor.

  9. MULTI-CHANNEL PULSE HEIGHT ANALYZER

    DOEpatents

    Boyer, K.; Johnstone, C.W.

    1958-11-25

    An improved multi-channel pulse height analyzer of the type where the device translates the amplitude of each pulse into a time duration electrical quantity which is utilized to control the length of a train of pulses forwarded to a scaler is described. The final state of the scaler for any one train of pulses selects the appropriate channel in a magnetic memory in which an additional count of one is placed. The improvement consists of a storage feature for storing a signal pulse so that in many instances when two signal pulses occur in rapid succession, the second pulse is preserved and processed at a later time.

  10. Coherent excitation with short electron pulses

    NASA Astrophysics Data System (ADS)

    Guertler, Andreas; Robicheaux, Francis; Noordam, Bart

    2000-06-01

    [1pt] The probability for a transition within an atom to be driven by a collision with a long pulse of electrons is proportional to the electron flux with the proportionality factor being the cross section for this transition. Recently it was shown [1] that for electron pulses shorter than the orbit time of the electron in the atom, a contribution of coherent scattering plays a role, which is proportional to the differential cross section in forward direction and the square of the electron flux. To investigate this effect, we are developing a picosecond electron gun [2]. Collision experiments will be done with Rydberg states in lithium around n=40 with Kepler orbit times in the order of 10 ps. For picosecond electron pulses, a quadratic dependance of the transition probability on the electron flux is expected in contrast to the linear dependance expected for nanosecond electron pulses. [1pt] References [1pt] [1] F. Robicheaux and L. D. Noordam, submitted to Phys. Rev. Lett. [1pt] [2] F. Robicheaux, G. M. Lankhuijzen, and L. D. Noordam, JOSA B 15, 1 (1998)

  11. HIGH POWER PULSED OSCILLATOR

    DOEpatents

    Singer, S.; Neher, L.K.

    1957-09-24

    A high powered, radio frequency pulse oscillator is described for generating trains of oscillations at the instant an input direct voltage is impressed, or immediately upon application of a light pulse. In one embodiment, the pulse oscillator comprises a photo-multiplier tube with the cathode connected to the first dynode by means of a resistor, and adjacent dynodes are connected to each other through adjustable resistors. The ohmage of the resistors progressively increases from a very low value for resistors adjacent the cathode to a high value adjacent the plate, the last dynode. Oscillation occurs with this circuit when a high negative voltage pulse is applied to the cathode and the photo cathode is bombarded. Another embodiment adds capacitors at the resistor connection points of the above circuit to increase the duration of the oscillator train.

  12. Means and method for characterizing high power, ultra short laser pulses in a real time, on line manner

    DOEpatents

    Veligdan, James T.

    1994-01-01

    An ultra short (<10 ps), high power laser pulse is temporally characterized by a system that uses a physical measurement of a wavefront that has been altered in a known manner. The system includes a first reflection switch to remove a portion of a pulse from a beam of pulses, then includes a second reflection switch, operating in a mode that is opposite to the first reflection switch, to slice off a portion of that removed portion. The sliced portion is then directed to a measuring device for physical measurement. The two reflection switches are arranged with respect to each other and with respect to the beam of ultra short pulses such that physical measurement of the sliced portion is related to the temporal measurement of the ultra short pulse by a geometric or trigonometric relationship. The reflection switches are operated by a control pulse that is directed to impinge on each of the reflection switches at a 90.degree. angle of incidence.

  13. Fast pulse nonthermal plasma reactor

    DOEpatents

    Rosocha, Louis A.

    2005-06-14

    A fast pulsed nonthermal plasma reactor includes a discharge cell and a charging assembly electrically connected thereto. The charging assembly provides plural high voltage pulses to the discharge cell. Each pulse has a rise time between one and ten nanoseconds and a duration of three to twenty nanoseconds. The pulses create nonthermal plasma discharge within the discharge cell. Accordingly, the nonthermal plasma discharge can be used to remove pollutants from gases or break the gases into smaller molecules so that they can be more efficiently combusted.

  14. Population inversion by chirped pulses

    SciTech Connect

    Lu Tianshi

    2011-09-15

    In this paper, we analyze the condition for complete population inversion by a chirped pulse over a finite duration. The nonadiabatic transition probability is mapped in the two-dimensional parameter space of coupling strength and detuning amplitude. Asymptotic forms of the probability are derived by the interference of nonadiabatic transitions for sinusoidal and triangular pulses. The qualitative difference between the maps for the two types of pulses is accounted for. The map is used for the design of stable inversion pulses under specific accuracy thresholds.

  15. Use of Additional Needle Pulses Using Electrical Discharge Machining

    NASA Astrophysics Data System (ADS)

    Schulze, Hans-Peter; Juhr, Henrik; Haas, Rüdiger

    2011-05-01

    The influence exerted by the longer rectangular pulses with additional Needle Pulses. Needle pulses for the spark erosion are the fundamental of the erosion pulses with pulse durations smaller 1 μs and high current-rise-velocity (ramp unit). In this shorter pulse-duration it is possible to use higher current densities; without composition of the thermal-affected zones. The technological advantage is a higher productivity because the higher pulse energy and parallel a better quality of the processing area exist; an additional factor for the higher productivity is the smaller number of back-cuts for the finish quality of the cut.

  16. Preference pulses without reinforcers.

    PubMed

    McLean, Anthony P; Grace, Randolph C; Pitts, Raymond C; Hughes, Christine E

    2014-05-01

    Preference pulses are thought to represent strong, short-term effects of reinforcers on preference in concurrent schedules. However, the general shape of preference pulses is substantially determined by the distributions of responses-per-visit (visit lengths) for the two choice alternatives. In several series of simulations, we varied the means and standard deviations of distributions describing visits to two concurrently available response alternatives, arranged "reinforcers" according to concurrent variable-interval schedules, and found a range of different preference pulses. Because characteristics of these distributions describe global aspects of behavior, and the simulations assumed no local effects of reinforcement, these preference pulses derive from the visit structure alone. This strongly questions whether preference pulses should continue to be interpreted as representing local effects of reinforcement. We suggest an alternative approach whereby local effects are assessed by subtracting the artifactual part, which derives from visit structure, from the observed preference pulses. This yields "residual" preference pulses. We illustrate this method in application to published data from mixed dependent concurrent schedules, revealing evidence that the delivery of reinforcers had modest lengthening effects on the duration of the current visit, a conclusion that is quantitatively consistent with early research on short-term effects of reinforcement.

  17. Cooperative pulses

    NASA Astrophysics Data System (ADS)

    Braun, Michael; Glaser, Steffen J.

    2010-11-01

    We introduce the concept of cooperative (COOP) pulses which are designed to compensate each other's imperfections. In multi-scan experiments, COOP pulses can cancel undesired signal contributions, complementing and generalizing phase cycles. COOP pulses can be efficiently optimized using an extended version of the optimal-control-based gradient ascent pulse engineering (GRAPE) algorithm. The advantage of the COOP approach is experimentally demonstrated for broadband and band-selective pulses.

  18. Intense isolated attosecond pulse generation from relativistic laser plasmas using few-cycle laser pulses

    SciTech Connect

    Ma, Guangjin; Dallari, William; Borot, Antonin; Tsakiris, George D.; Veisz, Laszlo; Krausz, Ferenc; Yu, Wei

    2015-03-15

    We have performed a systematic study through particle-in-cell simulations to investigate the generation of attosecond pulse from relativistic laser plasmas when laser pulse duration approaches the few-cycle regime. A significant enhancement of attosecond pulse energy has been found to depend on laser pulse duration, carrier envelope phase, and plasma scale length. Based on the results obtained in this work, the potential of attaining isolated attosecond pulses with ∼100 μJ energy for photons >16 eV using state-of-the-art laser technology appears to be within reach.

  19. Production of Picosecond, Kilojoule, and Petawatt Laser Pulses via Raman Amplification of Nanosecond Pulses

    SciTech Connect

    Trines, R. M. G. M.; Bingham, R.; Norreys, P. A.; Fiuza, F.; Fonseca, R. A.; Silva, L. O.

    2011-09-02

    Raman amplification in plasma has been promoted as a means of compressing picosecond optical laser pulses to femtosecond duration to explore the intensity frontier. Here we show for the first time that it can be used, with equal success, to compress laser pulses from nanosecond to picosecond duration. Simulations show up to 60% energy transfer from pump pulse to probe pulse, implying that multikilojoule ultraviolet petawatt laser pulses can be produced using this scheme. This has important consequences for the demonstration of fast-ignition inertial confinement fusion.

  20. 21 CFR 870.3600 - External pacemaker pulse generator.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... power supply and electronic circuits that produce a periodic electrical pulse to stimulate the heart... strength, duration, R-wave sensitivity, and other pacing variables. (b) Classification. Class...

  1. 21 CFR 870.3600 - External pacemaker pulse generator.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... power supply and electronic circuits that produce a periodic electrical pulse to stimulate the heart... strength, duration, R-wave sensitivity, and other pacing variables. (b) Classification. Class...

  2. 21 CFR 870.3600 - External pacemaker pulse generator.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... power supply and electronic circuits that produce a periodic electrical pulse to stimulate the heart... strength, duration, R-wave sensitivity, and other pacing variables. (b) Classification. Class...

  3. 21 CFR 870.3600 - External pacemaker pulse generator.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... power supply and electronic circuits that produce a periodic electrical pulse to stimulate the heart... strength, duration, R-wave sensitivity, and other pacing variables. (b) Classification. Class...

  4. Analysis of process parameter for the ablation of optical glasses with femto- and picosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Schindler, Christian; Friedrich, Maria; Bliedtner, Jens

    2016-03-01

    Experiments with an ultrashort pulsed laser system emitting pulses ranging from 350 fs to 10 ps and a maximum average power of 50 W at 1030 nm are presented. The laser beam gets deflected by a galvanometric scan-system with maximum scan speed of 2500 mm/s and focused by F-theta lenses onto the substrates. By experiments the influences of pulse energy, fluence, laser wavelength, pulse length and material conditions on the target figures is analyzed. These are represented by the material characteristics mean squared roughness, ablation depths as well as the microcrack distribution in depth. The experimental procedure is applied onto a series of fused silica and SF6 samples.

  5. Long Duration Sorbent Testbed

    NASA Technical Reports Server (NTRS)

    Howard, David F.; Knox, James C.; Long, David A.; Miller, Lee; Cmaric, Gregory; Thomas, John

    2016-01-01

    The Long Duration Sorbent Testbed (LDST) is a flight experiment demonstration designed to expose current and future candidate carbon dioxide removal system sorbents to an actual crewed space cabin environment to assess and compare sorption working capacity degradation resulting from long term operation. An analysis of sorbent materials returned to Earth after approximately one year of operation in the International Space Station's (ISS) Carbon Dioxide Removal Assembly (CDRA) indicated as much as a 70% loss of working capacity of the silica gel desiccant material at the extreme system inlet location, with a gradient of capacity loss down the bed. The primary science objective is to assess the degradation of potential sorbents for exploration class missions and ISS upgrades when operated in a true crewed space cabin environment. A secondary objective is to compare degradation of flight test to a ground test unit with contaminant dosing to determine applicability of ground testing.

  6. Downhole pulse radar

    DOEpatents

    Chang, Hsi-Tien

    1989-01-01

    A borehole logging tool generates a fast rise-time, short duration, high peak-power radar pulse having broad energy distribution between 30 MHz and 300 MHz through a directional transmitting and receiving antennas having barium titanate in the electromagnetically active region to reduce the wavelength to within an order of magnitude of the diameter of the antenna. Radar returns from geological discontinuities are sampled for transmission uphole.

  7. Downhole pulse radar

    DOEpatents

    Chang, Hsi-Tien

    1987-09-28

    A borehole logging tool generates a fast rise-time, short duration, high peak-power radar pulse having broad energy distribution between 30 MHz and 300 MHz through a directional transmitting and receiving antennas having barium titanate in the electromagnetically active region to reduce the wavelength to within an order of magnitude of the diameter of the antenna. Radar returns from geological discontinuities are sampled for transmission uphole. 7 figs.

  8. PULSE SORTER

    DOEpatents

    Wade, E.J.

    1958-07-29

    An apparatus is described for counting and recording the number of electrical pulses occurring in each of a timed sequence of groups of pulses. The particular feature of the invention resides in a novel timing circuit of the univibrator type which provides very accurately timed pulses for opening each of a series of coincidence channels in sequence. The univibrator is shown incorporated in a pulse analyzing system wherein a series of pulse counting channels are periodically opened in order, one at a time, for a predetermtned open time interval, so that only one channel will be open at the time of occurrence of any of the electrical pulses to be sorted.

  9. Long duration ash probe

    DOEpatents

    Hurley, J.P.; McCollor, D.P.; Selle, S.J.

    1994-07-26

    A long duration ash probe includes a pressure shell connected to a port in a combustor with a sample coupon mounted on a retractable carriage so as to retract the sample coupon within the pressure shell during soot blowing operation of the combustor. A valve mounted at the forward end of the pressure shell is selectively closeable to seal the sample coupon within the shell, and a heating element in the shell is operable to maintain the desired temperature of the sample coupon while retracted within the shell. The carriage is operably mounted on a pair of rails within the shell for longitudinal movement within the shell. A hollow carrier tube connects the hollow cylindrical sample coupon to the carriage, and extends through the carriage and out the rearward end thereof. Air lines are connected to the rearward end of the carrier tube and are operable to permit coolant to pass through the air lines and thence through the carrier tube to the sample coupon so as to cool the sample coupon. 8 figs.

  10. Long duration ash probe

    DOEpatents

    Hurley, John P.; McCollor, Don P.; Selle, Stanley J.

    1994-01-01

    A long duration ash probe includes a pressure shell connected to a port in a combustor with a sample coupon mounted on a retractable carriage so as to retract the sample coupon within the pressure shell during sootblowing operation of the combustor. A valve mounted at the forward end of the pressure shell is selectively closeable to seal the sample coupon within the shell, and a heating element in the shell is operable to maintain the desired temperature of the sample coupon while retracted within the shell. The carriage is operably mounted on a pair of rails within the shell for longitudinal movement within the shell. A hollow carrier tube connects the hollow cylindrical sample coupon to the carriage, and extends through the carriage and out the rearward end thereof. Air lines are connected to the rearward end of the carrier tube and are operable to permit coolant to pass through the air lines and thence through the carrier tube to the sample coupon so as to cool the sample coupon.

  11. Striatal dynamics explain duration judgments

    PubMed Central

    Gouvêa, Thiago S; Monteiro, Tiago; Motiwala, Asma; Soares, Sofia; Machens, Christian; Paton, Joseph J

    2015-01-01

    The striatum is an input structure of the basal ganglia implicated in several time-dependent functions including reinforcement learning, decision making, and interval timing. To determine whether striatal ensembles drive subjects' judgments of duration, we manipulated and recorded from striatal neurons in rats performing a duration categorization psychophysical task. We found that the dynamics of striatal neurons predicted duration judgments, and that simultaneously recorded ensembles could judge duration as well as the animal. Furthermore, striatal neurons were necessary for duration judgments, as muscimol infusions produced a specific impairment in animals' duration sensitivity. Lastly, we show that time as encoded by striatal populations ran faster or slower when rats judged a duration as longer or shorter, respectively. These results demonstrate that the speed with which striatal population state changes supports the fundamental ability of animals to judge the passage of time. DOI: http://dx.doi.org/10.7554/eLife.11386.001 PMID:26641377

  12. Pulse Oximetry

    MedlinePlus

    ... www.thoracic.org amount of gases (oxygen and carbon dioxide) that are in your blood. To get an ... Also, a pulse oximeter does not measure your carbon dioxide level. How accurate is the pulse oximeter? The ...

  13. Thresholds for cavitation produced in water by pulsed ultrasound.

    PubMed

    Atchley, A A; Frizzell, L A; Apfel, R E; Holland, C K; Madanshetty, S; Roy, R A

    1988-09-01

    The threshold for transient cavitation produced in water by pulsed ultrasound was measured as a function of pulse duration and pulse repetition frequency at both 0.98 and 2.30 MHz. The cavitation events were detected with a passive acoustic technique which relies upon the scattering of the irradiation field by the bubble clouds associated with the events. The results indicate that the threshold is independent of pulse duration and acoustic frequency for pulses longer than approximately 10 acoustic cycles. The threshold increases for shorter pulses. The cavitation events are likely to be associated with bubble clouds rather than single bubbles.

  14. Coiled transmission line pulse generators

    DOEpatents

    McDonald, Kenneth Fox

    2010-11-09

    Methods and apparatus are provided for fabricating and constructing solid dielectric "Coiled Transmission Line" pulse generators in radial or axial coiled geometries. The pour and cure fabrication process enables a wide variety of geometries and form factors. The volume between the conductors is filled with liquid blends of monomers, polymers, oligomers, and/or cross-linkers and dielectric powders; and then cured to form high field strength and high dielectric constant solid dielectric transmission lines that intrinsically produce ideal rectangular high voltage pulses when charged and switched into matched impedance loads. Voltage levels may be increased by Marx and/or Blumlein principles incorporating spark gap or, preferentially, solid state switches (such as optically triggered thyristors) which produce reliable, high repetition rate operation. Moreover, these Marxed pulse generators can be DC charged and do not require additional pulse forming circuitry, pulse forming lines, transformers, or an a high voltage spark gap output switch. The apparatus accommodates a wide range of voltages, impedances, pulse durations, pulse repetition rates, and duty cycles. The resulting mobile or flight platform friendly cylindrical geometric configuration is much more compact, light-weight, and robust than conventional linear geometries, or pulse generators constructed from conventional components. Installing additional circuitry may accommodate optional pulse shape improvements. The Coiled Transmission Lines can also be connected in parallel to decrease the impedance, or in series to increase the pulse length.

  15. Subcellular effects of nanosecond electrical pulses.

    PubMed

    Schoenbach, Karl H; Joshi, Ravindra; Kolb, J; Buescher, Stephen; Beebe, Stephen

    2004-01-01

    Electrical models for biological cells predict that reducing the duration of applied electrical pulses to values below the charging time of the outer membrane causes a strong increase in the probability for electric field interactions with intracellular structures. For electric field amplitudes exceeding MV/m such pulses are expected to cause electroporation of cell organelles, with the required electric field amplitude scaling linearly with the inverse of pulse duration. Experimental studies where human cells were exposed to pulsed electric field of up to 300 kV/cm amplitude with duration as short as 10 ns, have confirmed this hypothesis. The observed effects include the breaching of intracellular granule membranes without permanent damage to the cell membrane, abrupt rises in intracellular free calcium levels, and enhanced expression of genes. At increased electric fields, the application of nanosecond pulses induces apoptosis in biological cells, an effect that has been shown to reduce the growth of tumors.

  16. The Duration of Motor Responses Evoked with Intracortical Microstimulation in Rats Is Primarily Modulated by Stimulus Amplitude and Train Duration

    PubMed Central

    Watson, Meghan; Sawan, Mohamad

    2016-01-01

    Microstimulation of brain tissue plays a key role in a variety of sensory prosthetics, clinical therapies and research applications, however the effects of stimulation parameters on the responses they evoke remain widely unknown. In particular, the effects of parameters when delivered in the form of a stimulus train as opposed to a single pulse are not well understood despite the prevalence of stimulus train use. We aimed to investigate the contribution of each parameter of a stimulus train to the duration of the motor responses they evoke in forelimb muscles. We used constant-current, biphasic, square wave pulse trains in acute terminal experiments under ketamine anaesthesia. Stimulation parameters were systematically tested in a pair-wise fashion in the caudal forelimb region of the motor cortex in 7 Sprague-Dawley rats while motor evoked potential (MEP) recordings from the forelimb were used to quantify the influence of each parameter in the train. Stimulus amplitude and train duration were shown to be the dominant parameters responsible for increasing the total duration of the MEP, while interphase interval had no effect. Increasing stimulus frequency from 100–200 Hz or pulse duration from 0.18–0.34 ms were also effective methods of extending response durations. Response duration was strongly correlated with peak time and amplitude. Our findings suggest that motor cortex intracortical microstimulations are often conducted at a higher frequency rate and longer train duration than necessary to evoke maximal response duration. We demonstrated that the temporal properties of the evoked response can be both predicted by certain response metrics and modulated via alterations to the stimulation signal parameters. PMID:27442588

  17. Absorption of ultrashort electromagnetic pulses by metal nanospheres in a dielectric medium

    NASA Astrophysics Data System (ADS)

    Astapenko, V. A.; Svita, S. Yu

    2015-02-01

    The absorption of ultrashort electromagnetic pulses on silver nanosphere embedded into glass in vicinity of plasmon resonance is studied theoretically in the frame of perturbation theory. The calculations are made for corrected Gaussian shape of incident pulse which enables us to consider both the short duration and the long duration regimes. Analysis based on numerical calculations reveals the specific features of considered process so as the change of absorption spectra for different pulse length and nonlinear dependence of absorbed energy upon pulse duration.

  18. Programmable dispersion compensation and pulse shaping in a 26-fs chirped-pulse amplifier.

    PubMed

    Efimov, A; Reitze, D H

    1998-10-15

    We have constructed a 26-fs chirped-pulse amplifier that incorporates a programmable liquid-crystal spatial light modulator in the pulse stretcher. The modulator serves a dual purpose. First, we apply frequency-dependent phase shifts to compensate for cubic, quartic, and nonlinear phase dispersion in the amplifier, which results in a reduction in pulse duration from 32 to 26 fs, in agreement with the transform limit of the amplified pulse spectrum. Second, we are able to produce high-fidelity compressed amplified shaped pulses by applying phase masks directly within the stretcher. Shaped pulse energies of greater than 1 mJ are routinely obtained.

  19. Generation of intense 25-fsec pulses by a pulsed laser system

    SciTech Connect

    Angel, G.; Gagel, R.; Laubereau, A. )

    1989-09-15

    A pulsed femtosecond dye laser is demonstrated with relaxed stability requirements, improved output reproducibility, and significant pulse shortening. Starting with a sequence of {approx}350 pump pulses of a Nd:glass laser (repetition rate 6 Hz, duration 1.3 psec), pulses of 25 fsec and 10 nJ are generated at 566 nm. A non-colliding-pulse, mode-locked ring laser is used with dispersion compensation and the dyes Rhodamine 6G, DQOCI, and DTCI. The evolution of the pulse parameters as a function of cavity round trips is investigated.

  20. Programmable dispersion compensation and pulse shaping in a 26-fs chirped-pulse amplifier.

    PubMed

    Efimov, A; Reitze, D H

    1998-10-15

    We have constructed a 26-fs chirped-pulse amplifier that incorporates a programmable liquid-crystal spatial light modulator in the pulse stretcher. The modulator serves a dual purpose. First, we apply frequency-dependent phase shifts to compensate for cubic, quartic, and nonlinear phase dispersion in the amplifier, which results in a reduction in pulse duration from 32 to 26 fs, in agreement with the transform limit of the amplified pulse spectrum. Second, we are able to produce high-fidelity compressed amplified shaped pulses by applying phase masks directly within the stretcher. Shaped pulse energies of greater than 1 mJ are routinely obtained. PMID:18091861

  1. Pulse shortening of an ultrafast VECSEL

    NASA Astrophysics Data System (ADS)

    Waldburger, D.; Alfieri, C. G. E.; Link, S. M.; Gini, E.; Golling, M.; Mangold, M.; Tilma, B. W.; Keller, U.

    2016-03-01

    Ultrafast, optically pumped, passively modelocked vertical external-cavity surface-emitting lasers (VECSELs) are excellent sources for industrial and scientific applications that benefit from compact semiconductor based high-power ultrafast lasers with gigahertz repetition rates and excellent beam quality. Applications such as self-referenced frequency combs and multi-photon imaging require sub-200-fs pulse duration combined with high pulse peak power. Here, we present a semiconductor saturable absorber mirror (SESAM) modelocked VECSEL with a pulse duration of 147 fs and 328 W of pulse peak power. The average output power was 100 mW with a repetition rate of 1.82 GHz at a center wavelength of 1034 nm. The laser has optimal beam quality operating in a fundamental transverse mode with a M2 value of <1.05 in both orthogonal directions. The VECSEL was grown by metal-organic vapor phase epitaxy (MOVPE) with five pairs of strain-compensated InGaAs quantum wells (QWs). The QWs are placed symmetrical around the antinodes of the standing electric field at a reduced average field enhancement in the QWs of ≈ 0.5 (normalized to 4 outside the structure). These results overcome the trade-off between pulse duration and peak power of the state-of-the-art threshold values of 4.35 kW peak power for a pulse duration of 400 fs and 3.3 W peak power for a pulse duration of 107 fs.

  2. Ultralong optical-pulse corona preionized XeCl laser

    SciTech Connect

    Taylor, R.S.; Leopold, K.E.

    1989-01-01

    A simple corona preionization scheme together with magnetic spiker and pulse forming line technology has resulted in the production of 100-mJ, 1-..mu..s duration as well as 500-mJ, 0.5-..mu..s duration XeCl laser pulses.

  3. Dispersion compensation in chirped pulse amplification systems

    SciTech Connect

    Bayramian, Andrew James; Molander, William A.

    2014-07-15

    A chirped pulse amplification system includes a laser source providing an input laser pulse along an optical path. The input laser pulse is characterized by a first temporal duration. The system also includes a multi-pass pulse stretcher disposed along the optical path. The multi-pass pulse stretcher includes a first set of mirrors operable to receive input light in a first plane and output light in a second plane parallel to the first plane and a first diffraction grating. The pulse stretcher also includes a second set of mirrors operable to receive light diffracted from the first diffraction grating and a second diffraction grating. The pulse stretcher further includes a reflective element operable to reflect light diffracted from the second diffraction grating. The system further includes an amplifier, a pulse compressor, and a passive dispersion compensator disposed along the optical path.

  4. Peak holding circuit for extremely narrow pulses

    NASA Technical Reports Server (NTRS)

    Oneill, R. W. (Inventor)

    1975-01-01

    An improved pulse stretching circuit comprising: a high speed wide-band amplifier connected in a fast charge integrator configuration; a holding circuit including a capacitor connected in parallel with a discharging network which employs a resistor and an FET; and an output buffer amplifier. Input pulses of very short duration are applied to the integrator charging the capacitor to a value proportional to the input pulse amplitude. After a predetermined period of time, conventional circuitry generates a dump pulse which is applied to the gate of the FET making a low resistance path to ground which discharges the capacitor. When the dump pulse terminates, the circuit is ready to accept another pulse to be stretched. The very short input pulses are thus stretched in width so that they may be analyzed by conventional pulse height analyzers.

  5. Pulsed writing of solid state holograms.

    NASA Technical Reports Server (NTRS)

    Gaylord, T. K.; Rabson, T. A.; Tittel, F. K.; Quick, C. R.

    1973-01-01

    The pulsed writing of volume holograms in lithium niobate is reported, both with 200-nsec and 20-nsec duration pulses. This information is of particular interest in high capacity information storage applications since it indicates that writing times at least as short as 20-nsec are readily possible. A series of pulses was used in each case, and the diffraction efficiency was monitored using a He-Ne laser operating at 6328 A and aligned to its corresponding Bragg angle.

  6. Pulse stretcher

    DOEpatents

    Horton, J.A.

    1994-05-03

    Apparatus for increasing the length of a laser pulse to reduce its peak power without substantial loss in the average power of the pulse is disclosed. The apparatus uses a White cell having a plurality of optical delay paths of successively increasing number of passes between the field mirror and the objective mirrors. A pulse from a laser travels through a multi-leg reflective path between a beam splitter and a totally reflective mirror to the laser output. The laser pulse is also simultaneously injected through the beam splitter to the input mirrors of the optical delay paths. The pulses from the output mirrors of the optical delay paths go simultaneously to the laser output and to the input mirrors of the longer optical delay paths. The beam splitter is 50% reflective and 50% transmissive to provide equal attenuation of all of the pulses at the laser output. 6 figures.

  7. Pulse Voltammetry

    NASA Astrophysics Data System (ADS)

    Stojek, Zbigniew

    The idea of imposing potential pulses and measuring the currents at the end of each pulse was proposed by Barker in a little-known journal as early as in 1958 [1]. However, the first reliable trouble-free and affordable polarographs offering voltammetric pulse techniques appeared on the market only in the 1970s. This delay was due to some limitations on the electronic side. In the 1990s, again substantial progress in electrochemical pulse instrumentation took place. This was related to the introduction of microprocessors, computers, and advanced software.

  8. Giant-chirp oscillators for short-pulse fiber amplifiers.

    PubMed

    Renninger, William H; Chong, Andy; Wise, Frank W

    2008-12-15

    A new regime of pulse parameters in a normal-dispersion fiber laser is identified. Dissipative solitons exist with remarkably large pulse duration and chirp, along with large pulse energy. A low-repetition-rate oscillator that generates pulses with large and linear chirp can replace the standard oscillator, stretcher, pulse-picker, and preamplifier in a chirped-pulse fiber amplifier. The theoretical properties of such a giant-chirp oscillator are presented. A fiber laser designed to operate in the new regime generates approximately 150 ps pulses at a 3 MHz repetition rate. Amplification of these pulses to 1 microJ energy with pulse duration as short as 670 fs demonstrates the promise of this new approach.

  9. Simple ps microchip Nd:YVO4 laser with 3.3-ps pulses at 0.2 to 1.4 MHz and single-stage amplification to the microjoule level

    NASA Astrophysics Data System (ADS)

    Türkyilmaz, Erdal; Lohbreier, Jan; Günther, Christian; Mehner, Eva; Kopf, Daniel; Giessen, Harald; Braun, Bernd

    2016-06-01

    Commercial picosecond sources have found widespread applications. Typical system parameters are pulse widths below 20 ps, repetition rates between 0.1 and 2 MHz, and microjoule level pulse energies. Most systems are based on short pulse mode-locked oscillators, regenerative amplifiers, and pockel cells as active beam switches. In contrast, we present a completely passive system, consisting of a passively Q-switched microchip laser, a single-stage amplifier, and a pulse compressor. The Q-switched microchip laser has a 50-μm-long Nd:YVO4 gain material optically bonded to a 4.6-mm-thick undoped YVO4 crystal. It delivers pulse widths of 40 ps and repetition rates of 0.2 to 1.4 MHz at a wavelength of 1.064 μm. The pulse energy is a few nanojoule. These 40-ps pulses are spectrally broadened in a standard single-mode fiber and then compressed in a 24-mm-long chirped Bragg grating to as low as 3.3 ps. The repetition rate can be tuned from ˜0.2 to 1.4 MHz by changing the pump power, while the pulse width and the pulse energy from the microchip laser are unchanged. The spectral broadening in the fiber is observed throughout the pulse repetition rate, supporting sub-10-ps pulses. Finally, the pulses are amplified in a single-stage Nd:YVO4 amplifier up to the microjoule level (up to 4 μJ pulse energy). As a result, the system delivers sub-10-ps pulses at a microjoule level with about 1 MHz repetition rate, and thus fulfills the requirements for ps-micromachining. It does not contain any active switching elements and can be integrated in a very compact setup.

  10. Simple ps microchip Nd:YVO4 laser with 3.3-ps pulses at 0.2 to 1.4 MHz and single-stage amplification to the microjoule level

    NASA Astrophysics Data System (ADS)

    Türkyilmaz, Erdal; Lohbreier, Jan; Günther, Christian; Mehner, Eva; Kopf, Daniel; Giessen, Harald; Braun, Bernd

    2016-06-01

    Commercial picosecond sources have found widespread applications. Typical system parameters are pulse widths below 20 ps, repetition rates between 0.1 and 2 MHz, and microjoule level pulse energies. Most systems are based on short pulse mode-locked oscillators, regenerative amplifiers, and pockel cells as active beam switches. In contrast, we present a completely passive system, consisting of a passively Q-switched microchip laser, a single-stage amplifier, and a pulse compressor. The Q-switched microchip laser has a 50-μm-long Nd:YVO4 gain material optically bonded to a 4.6-mm-thick undoped YVO4 crystal. It delivers pulse widths of 40 ps and repetition rates of 0.2 to 1.4 MHz at a wavelength of 1.064 μm. The pulse energy is a few nanojoule. These 40-ps pulses are spectrally broadened in a standard single-mode fiber and then compressed in a 24-mm-long chirped Bragg grating to as low as 3.3 ps. The repetition rate can be tuned from ˜0.2 to 1.4 MHz by changing the pump power, while the pulse width and the pulse energy from the microchip laser are unchanged. The spectral broadening in the fiber is observed throughout the pulse repetition rate, supporting sub-10-ps pulses. Finally, the pulses are amplified in a single-stage Nd:YVO4 amplifier up to the microjoule level (up to 4 μJ pulse energy). As a result, the system delivers sub-10-ps pulses at a microjoule level with about 1 MHz repetition rate, and thus fulfills the requirements for ps-micromachining. It does not contain any active switching elements and can be integrated in a very compact setup.

  11. Simple ps microchip Nd:YVO4 laser with 3.3 ps pulses at 0.2 - 1.4 MHz and single-stage amplification to the microjoule level

    NASA Astrophysics Data System (ADS)

    Türkyilmaz, Erdal; Lohbreier, Jan; Günther, Christian; Mehner, Eva; Kopf, Daniel; Giessen, Harald; Braun, Bernd

    2016-03-01

    Commercial picosecond sources have found widespread applications. Typical system parameters are pulse widths below 20 ps, repetition rates between 0.1 to 2 MHz, and micro Joule level pulse energies. Most systems are based on short pulse modelocked oscillators, regenerative amplifiers, and pockel cells as active beam switches. In contrast we present a completely passive system, consisting of a passively Q-switched microchip laser, a single-stage amplifier, and a pulse compressor. The Q-switched microchip laser has a 50 μm long Nd:YVO4-gain material optically bonded to a 4.6 mm thick undoped YVO4-crystal. It delivers pulse widths of 40 ps and repetition rates of 0.2 - 1.4 MHz at a wavelength of 1.064 μm. The pulse energy is a few nJ. These 40-ps pulses are spectrally broadened in a standard single mode fibre and then compressed in a 24 mm long chirped Bragg grating to as low as 3.3 ps. The repetition rate can be tuned from app. 0.2 to 1.4 MHz by changing the pump power while the pulse width and the pulse energy from the microchip laser are unchanged. The spectral broadening in the fibre is observed throughout the pulse repetition rate, supporting sub-10- ps pulses. Finally, the pulses are amplified in a single-stage Nd:YVO4-amplifier up to the microjoule level (up to 4 μJ pulse energy). As a result the system delivers sub-10-ps pulses at a microjoule level with about 1 MHz repetition rate, and thus fulfills the requirements for ps-micromachining. It does not contain any active switching elements and can be integrated in a very compact setup.

  12. PULSE AMPLIFIER

    DOEpatents

    Johnstone, C.W.

    1958-06-17

    The improvement of pulse amplifiers used with scintillation detectors is described. The pulse amplifier circuit has the advantage of reducing the harmful effects of overloading cause by large signal inputs. In general the pulse amplifier circuit comprises two amplifier tubes with the input pulses applied to one amplifier grid and coupled to the second amplifier tube through a common cathode load. The output of the second amplifier is coupled from the plate circuit to a cathode follower tube grid and a diode tube in connected from grid to cathode of the cathode follower tube. Degenerative feedback is provided in the second amplifier by coupling a signal from the cathode follower cathode to the second amplifier grid. The circuit proqides moderate gain stability, and overload protection for subsequent pulse circuits.

  13. Fiber Laser Front Ends for High-Energy Short Pulse Lasers

    SciTech Connect

    Dawson, J W; Liao, Z M; Mitchell, S; Messerly, M; Beach, R; Jovanovic, I; Brown, C; Payne, S A; Barty, C J

    2005-01-18

    We are developing an all fiber laser system optimized for providing input pulses for short pulse (1-10ps), high energy ({approx}1kJ) glass laser systems. Fiber lasers are ideal solutions for these systems as they are highly reliable and once constructed they can be operated with ease. Furthermore, they offer an additional benefit of significantly reduced footprint. In most labs containing equivalent bulk laser systems, the system occupies two 4'x8' tables and would consist of 10's if not a 100 of optics which would need to be individually aligned and maintained. The design requirements for this application are very different those commonly seen in fiber lasers. High energy lasers often have low repetition rates (as low as one pulse every few hours) and thus high average power and efficiency are of little practical value. What is of high value is pulse energy, high signal to noise ratio (expressed as pre-pulse contrast), good beam quality, consistent output parameters and timing. Our system focuses on maximizing these parameters sometimes at the expense of efficient operation or average power. Our prototype system consists of a mode-locked fiber laser, a compressed pulse fiber amplifier, a ''pulse cleaner'', a chirped fiber Bragg grating, pulse selectors, a transport fiber system and a large flattened mode fiber amplifier. In our talk we will review the system in detail and present theoretical and experimental studies of critical components. We will also present experimental results from the integrated system.

  14. Progress of diagnostics for coherent beam combination on ultrashort pulse

    NASA Astrophysics Data System (ADS)

    Ouyang, Xiaoping; Wang, Yang; Zhu, Baoqiang; Zhu, Jian; Zhu, Jianqiang

    2015-08-01

    Ultrashort pulse is important to exploring laser acceleration in many areas, such as fast ignition, advanced radiography capability. Petawatt laser should not only improve output energy on a single beam, but also combine multi-beams coherently. Diagnostics of temporal and phase synchronization is developed for coherent beam combination on a 10ps laser pulse. When two pulses are guided into the diagnostics, one goes through a temporal delay unit and a lens with a focal length 500mm, then arrives at detector unit, the other goes through a phase delay unit and the same lens, and then arrives at detector unit, too. First, temporal synchronization is adjusted by temporal delay unit and monitored by a cross-correlation generator in the detector unit. Second, phase synchronization is adjusted by phase delay unit and monitored by a far field interferogram in the detector unit. In our design, temporal resolution is 6.7fs in temporal synchronization, and phase resolution is 0.007π in phase synchronization. Experiment has proved that this diagnostics is useful to realize synchronization between two ultrashort pulses both in temporal and in spatial.

  15. Long Duration Balloon Charge Controller Stack Integration

    NASA Astrophysics Data System (ADS)

    Clifford, Kyle

    NASA and the Columbia Scientific Balloon Facility are interested in updating the design of the charge controller on their long duration balloon (LDB) in order to enable the charge controllers to be directly interfaced via RS232 serial communication by a ground testing computers and the balloon's flight computer without the need to have an external electronics stack. The design involves creating a board that will interface with the existing boards in the charge controller in order to receive telemetry from and send commands to those boards, and interface with a computer through serial communication. The inputs to the board are digital status inputs indicating things like whether the photovoltaic panels are connected or disconnected; and analog inputs with information such as the battery voltage and temperature. The outputs of the board are 100ms duration command pulses that will switch relays that do things like connect the photovoltaic panels. The main component of this design is a PIC microcontroller which translates the outputs of the existing charge controller into serial data when interrogated by a ground testing or flight computer. Other components involved in the design are an AD7888 12-bit analog to digital converter, a MAX3232 serial transceiver, various other ICs, capacitors, resistors, and connectors.

  16. Pulsed laser irradiation of metal multilayers.

    SciTech Connect

    Adams, David Price; McDonald, Joel Patrick

    2010-11-01

    Vapor-deposited, exothermic metal-metal multilayer foils are an ideal class of materials for detailed investigations of pulsed laser-ignited chemical reactions. Created in a pristine vacuum environment by sputter deposition, these high purity materials have well-defined reactant layer thicknesses between 1 and 1000 nm, minimal void density and intimate contact between layers. Provided that layer thicknesses are made small, some reactive metal-metal multilayer foils can be ignited at a point by laser irradiation and exhibit subsequent high-temperature, self-propagating synthesis. With this presentation, we describe the pulsed laser-induced ignition characteristics of a single multilayer system (equiatomic Al/Pt) that exhibits self-propagating synthesis. We show that the thresholds for ignition are dependent on (i) multilayer design and (ii) laser pulse duration. With regard to multilayer design effects on ignition, there is a large range of multilayer periodicity over which ignition threshold decreases as layer thicknesses are made small. We attribute this trend of decreased ignition threshold to reduced mass transport diffusion lengths required for rapid exothermic mixing. With regard to pulse duration effects, we have determined how ignition threshold of a single Al/Pt multilayer varies with pulse duration from 10{sup -2} to {approx} 10{sup -13} sec (wavelength and spot size are held constant). A higher laser fluence is required for ignition when using a single laser pulse {approx} 100 fs or 1 ps compared with nanosecond or microsecond exposure, and we attribute this, in part, to the effects of reactive material being ablated when using the shorter pulse durations. To further understand these trends and other pulsed laser-based processes, our discussion concludes with an analysis of the heat-affected depths in multilayers as a function of pulse duration.

  17. 90 mJ parametric chirped pulse amplification of 10 fs pulses.

    PubMed

    Tavella, Franz; Marcinkevicius, Andrius; Krausz, Ferenc

    2006-12-25

    We demonstrate the amplification of broadband pulses from a Ti:Sapphire oscillator by non-collinear optical parametric chirped-pulse amplification technique in a type-I BBO crystal to energies of 90 mJ. Partial compression of the amplified pulses is demonstrated down to a 10 fs duration. These parameters come in combination with good spatial quality and focusability of the amplified beam.

  18. Pulse Data.

    ERIC Educational Resources Information Center

    Hands On!, 1998

    1998-01-01

    Presents an activity using computer software to investigate the role of the heart and blood, how the blood system responds to exercise, and how pulse rate is a good measure of physical condition. (ASK)

  19. Experimental study on double-pulse laser ablation of steel upon multiple parallel-polarized ultrashort-pulse irradiations

    NASA Astrophysics Data System (ADS)

    Schille, Joerg; Schneider, Lutz; Kraft, Sebastian; Hartwig, Lars; Loeschner, Udo

    2016-07-01

    In this paper, double-pulse laser processing is experimentally studied with the aim to explore the influence of ultrashort pulses with very short time intervals on ablation efficiency and quality. For this, sequences of 50 double pulses of varied energy and inter-pulse delay, as adjusted between 400 fs and 18 ns by splitting the laser beam into two optical paths of different length, were irradiated to technical-grade stainless steel. The depth and the volume of the craters produced were measured in order to evaluate the efficiency of the ablation process; the crater quality was analyzed by SEM micrographs. The results obtained were compared with craters produced with sequences of 50 single pulses and energies equal to the double pulse. It is demonstrated that double-pulse processing cannot exceed the ablation efficiency of single pulses of optimal fluence, but the ablation crater surface formed smoother if inter-pulse delay was in the range between 10 ns and 18 ns. In addition, the influence of pulse duration and energy distribution between the individual pulses of the double pulse on ablation was studied. For very short inter-pulse delay, no significant effect of energy variation within the double pulse on removal rate was found, indicating that the double pulse acts as a big single pulse of equal energy. Further, the higher removal efficiency was achieved when double-pulse processing using femtosecond pulses instead of picosecond pulses.

  20. Pulse stretcher

    DOEpatents

    Horton, James A.

    1994-01-01

    Apparatus (20) for increasing the length of a laser pulse to reduce its peak power without substantial loss in the average power of the pulse. The apparatus (20) uses a White cell (10) having a plurality of optical delay paths (18a-18d) of successively increasing number of passes between the field mirror (13) and the objective mirrors (11 and 12). A pulse (26) from a laser (27) travels through a multi-leg reflective path (28) between a beam splitter (21) and a totally reflective mirror (24) to the laser output (37). The laser pulse (26) is also simultaneously injected through the beam splitter (21) to the input mirrors (14a-14d) of the optical delay paths (18a-18d). The pulses from the output mirrors (16a-16d) of the optical delay paths (18a-18d) go simultaneously to the laser output (37) and to the input mirrors ( 14b-14d) of the longer optical delay paths. The beam splitter (21) is 50% reflective and 50% transmissive to provide equal attenuation of all of the pulses at the laser output (37).

  1. Wavelength effect on hole shapes and morphology evolution during ablation by picosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Zhao, Wanqin; Wang, Wenjun; Li, Ben Q.; Jiang, Gedong; Mei, Xuesong

    2016-10-01

    An experimental study is presented of the effect of wavelength on the shape and morphology evolution of micro holes ablated on stainless steel surface by a 10 ps Q-switched Nd:VAN pulsed laser. Two routes of hole development are associated with the visible (532 nm) and near-infrared (1064 nm) laser beams, respectively. The evolution of various geometric shapes and morphological characteristics of the micro holes ablated with the two different wavelengths is comparatively studied for other given processing conditions such as a laser power levels and the number of pulses applied. Plausible explanations, based on the light-materials interaction associated with laser micromachining, are also provided for the discernable paths of geometric and morphological development of holes under laser ablation.

  2. Saturation and pulsed FEL dynamics

    SciTech Connect

    Giannessi, L.; Mezi, L.

    1995-12-31

    The behavior of a FEL operating in the saturated pulsed regime, may be reproduced by the linear FEL integral equation, suitably modified to include saturation effects through a gain depression coefficient depending on the laser intensity. This simple method allows to evaluate several FEL parameters like gain, efficiency, band-width and optical pulse duration as functions of the optical cavity length, only with a numerical integration. The predictions have been compared with available experimental and numerical data, and the method has been applied to estimate the operating characteristics of some planned FEL experiments.

  3. Self-stabilizing optical clock pulse-train generator using SOA and saturable absorber for asynchronous optical packet processing.

    PubMed

    Nakahara, Tatsushi; Takahashi, Ryo

    2013-05-01

    We propose a novel, self-stabilizing optical clock pulse-train generator for processing preamble-free, asynchronous optical packets with variable lengths. The generator is based on an optical loop that includes a semiconductor optical amplifier (SOA) and a high-extinction spin-polarized saturable absorber (SA), with the loop being self-stabilized by balancing out the gain and absorption provided by the SOA and SA, respectively. The optical pulse train is generated by tapping out a small portion of a circulating seed pulse. The convergence of the generated pulse energy is enabled by the loop round-trip gain function that has a negative slope due to gain saturation in the SOA. The amplified spontaneous emission (ASE) of the SOA is effectively suppressed by the SA, and a backward optical pulse launched into the SOA enables overcoming the carrier-recovery speed mismatch between the SOA and SA. Without external control for the loop gain, a stable optical pulse train consisting of more than 50 pulses with low jitter is generated from a single 10-ps seed optical pulse even with a variation of 10 dB in the seed pulse intensity. PMID:23669927

  4. Autonomous portable pulsed-periodical generator of high-power radiofrequency-pulses based on gas discharge with hollow cathode.

    PubMed

    Bulychev, Sergey V; Dubinov, Alexander E; L'vov, Igor L; Popolev, Vyacheslav L; Sadovoy, Sergey A; Sadchikov, Eugeny A; Selemir, Victor D; Valiulina, Valeria K; Vyalykh, Dmitry V; Zhdanov, Victor S

    2016-05-01

    Portable autonomous generator of high-power RF-pulses based on the gas discharge with hollow cathode has been designed, fabricated, and tested. Input and output characteristics are the following: discharge current amplitude is 800 A, duration of generated RF-pulses is 350 ns, carrier frequency is ∼90 MHz, power in RF-pulse is 0.5 MW, pulse repetition rate is 0.5 kHz, and device efficiency is ∼25%.

  5. Autonomous portable pulsed-periodical generator of high-power radiofrequency-pulses based on gas discharge with hollow cathode

    NASA Astrophysics Data System (ADS)

    Bulychev, Sergey V.; Dubinov, Alexander E.; L'vov, Igor L.; Popolev, Vyacheslav L.; Sadovoy, Sergey A.; Sadchikov, Eugeny A.; Selemir, Victor D.; Valiulina, Valeria K.; Vyalykh, Dmitry V.; Zhdanov, Victor S.

    2016-05-01

    Portable autonomous generator of high-power RF-pulses based on the gas discharge with hollow cathode has been designed, fabricated, and tested. Input and output characteristics are the following: discharge current amplitude is 800 A, duration of generated RF-pulses is 350 ns, carrier frequency is ˜90 MHz, power in RF-pulse is 0.5 MW, pulse repetition rate is 0.5 kHz, and device efficiency is ˜25%.

  6. Bioelectric effects of intense ultrashort pulses.

    PubMed

    Joshi, R P; Schoenbach, K H

    2010-01-01

    Models for electric field interactions with biological cells predict that pulses with durations shorter than the charging time of the outer membrane can affect intracellular structures. Experimental studies in which human cells were exposed to pulsed electric fields of up to 300 kV/cm amplitude, with durations as short as 10 ns, have confirmed this hypothesis. The observed effects include the breaching of intracellular granule membranes without permanent damage to the cell membrane, abrupt rises in intracellular free calcium levels, enhanced expression of genes, cytochrome c release, and electroporation for gene transfer and drug delivery. At increased electric fields, the application of nanosecond pulses induces apoptosis (programmed cell death) in biological cells, an effect that has been shown to reduce the growth of tumors. Possible applications of the intracellular electroeffects are enhancing gene delivery to the nucleus, controlling cell functions that depend on calcium release (causing cell immobilization), and treating tumors. Such nanosecond electrical pulses have been shown to successfully treat melanoma tumors by using needle arrays as pulse delivery systems. Reducing the pulse duration of intense electric field pulses even further into the subnanosecond range will allow for the use of wideband antennas to deliver the electromagnetic fields into tissue with a spatial resolution in the centimeter range. This review carefully examines the above concepts, provides a theoretical basis, and modeling results based on both continuum approaches and atomistic molecular dynamics methods. Relevant experimental data are also presented, and some of the many potential bioengineering applications discussed.

  7. Extended Duration Orbiter Medical Project

    NASA Technical Reports Server (NTRS)

    Leach, C. S.; Pool, S. L.; Sawin, C. F.; Nicogossian, A. E.

    1990-01-01

    The Extended Duration Orbiter (EDO) program addresses a need for more time to perform experiments and other tasks during Space Shuttle missions. As a part of this program, the Extended Duration Orbiter Medical Project (EDOMP) has been instituted to obtain information about physiologic effects of extending mission duration and the effectiveness of countermeasures against factors that might compromise crew health, safety, or performance on extended-duration missions. Only those investigations that address and characterize operational problems, develop countermeasures, or evaluate the effectiveness of countermeasures will be pursued. The EDOMP investigations will include flight-associated Detailed Supplementary Objectives as well as ground-based studies simulating the influence of microgravity. Investigator teams have been formed in the following areas: biomedical physiology, cardiovascular and fluid/electrolyte physiology, environmental health, muscle and exercise physiology, and neurophysiology. Major operational questions must be answered in each of these areas, and investigations have been designed to answer them. The EDO program will proceed only after countermeasures have been shown to be effective in preventing or mitigating the adverse changes they have been designed to attenuate. The program is underway and will continue on each Shuttle flight as the manifest builds toward a 16-day orbital flight.

  8. Duration of an Elastic Collision

    ERIC Educational Resources Information Center

    de Izarra, Charles

    2012-01-01

    With a pedagogical goal, this paper deals with a study of the duration of an elastic collision of an inflatable spherical ball on a planar surface suitable for undergraduate studies. First, the force generated by the deformed spherical ball is obtained under assumptions that are discussed. The study of the motion of the spherical ball colliding…

  9. Study of filamentary damage in synthesized silica induced by chirped femtosecond laser pulses

    SciTech Connect

    Onda, Satoshi; Watanabe, Wataru; Yamada, Kazuhiro; Itoh, Kazuyoshi; Nishii, Junji

    2005-11-01

    Different filamentary tracks in synthesized silica were induced by varying both the pulse duration and the incident energy of chirped laser pulses under slow-focusing conditions. Short-duration pulses induced filamentary refractive-index change, whereas longer pulses produced scattering damage in filamentary tracks. We report a systematic study on the morphology and birefringence of filamentary refractive-index change and scattering damage.

  10. Heterodimer Autorepression Loop: A Robust and Flexible Pulse-Generating Genetic Module

    NASA Astrophysics Data System (ADS)

    Lannoo, B.; Carlon, E.; Lefranc, M.

    2016-07-01

    We investigate the dynamics of the heterodimer autorepression loop (HAL), a small genetic module in which a protein A acts as an autorepressor and binds to a second protein B to form an A B dimer. For suitable values of the rate constants, the HAL produces pulses of A alternating with pulses of B . By means of analytical and numerical calculations, we show that the duration of A pulses is extremely robust against variation of the rate constants while the duration of the B pulses can be flexibly adjusted. The HAL is thus a minimal genetic module generating robust pulses with a tunable duration, an interesting property for cellular signaling.

  11. The effect of temporal pulse shape on optical damage

    SciTech Connect

    Carr, C W; Trenholme, J B; Spaeth, M L

    2006-08-15

    The conditions under which optical materials are susceptible to laser-induced damage is a topic which has been the subject of considerable study. Laser parameters such as wavelength and temporal pulse duration have been studied extensively. Until this work the effect of temporal pulse shape has not been considered. We present here data from a simple single-parameter model and a supporting experiment which predicts that a Flat-In-Time-pulse will produce damage at approximately 80% of the fluence of a Gaussian pulse of the same FWHM duration.

  12. Studies of exposure of rabbits to electromagnetic pulsed fields

    SciTech Connect

    Cleary, S.F.; Nickless, F.; Liu, L.M.; Hoffman, R.

    1980-01-01

    Dutch rabbits were acutely exposed to electromagnetic pulsed (EMP) fields (pulse duration 0.4 mus, field strengths of 1--2 kV/cm and pulse repetition rates in the range of 10 to 38 Hz) for periods of up to two hours. The dependent variables investigated were pentobarbital-induced sleeping time and serum chemistry (including serum triglycerides, creatine phosphokinase (CPK) isoenzymes, and sodium and potassium). Core temperature measured immediately pre-exposure and postexposure revealed no exposure-related alterations. Over the range of field strengths and pulse durations investigated no consistent, statistically significant alterations were found in the end-points investigated.

  13. Cell electrofusion using nanosecond electric pulses

    PubMed Central

    Rems, Lea; Ušaj, Marko; Kandušer, Maša; Reberšek, Matej; Miklavčič, Damijan; Pucihar, Gorazd

    2013-01-01

    Electrofusion is an efficient method for fusing cells using short-duration high-voltage electric pulses. However, electrofusion yields are very low when fusion partner cells differ considerably in their size, since the extent of electroporation (consequently membrane fusogenic state) with conventionally used microsecond pulses depends proportionally on the cell radius. We here propose a new and innovative approach to fuse cells with shorter, nanosecond (ns) pulses. Using numerical calculations we demonstrate that ns pulses can induce selective electroporation of the contact areas between cells (i.e. the target areas), regardless of the cell size. We then confirm experimentally on B16-F1 and CHO cell lines that electrofusion of cells with either equal or different size by using ns pulses is indeed feasible. Based on our results we expect that ns pulses can improve fusion yields in electrofusion of cells with different size, such as myeloma cells and B lymphocytes in hybridoma technology. PMID:24287643

  14. Narrow-linewidth megahertz-rate pulse-burst laser for high-speed flow diagnostics.

    PubMed

    Thurow, Brian; Jiang, Naibo; Samimy, Mo; Lempert, Walter

    2004-09-10

    A second-generation pulse-burst laser system for high-speed flow diagnostics is described in detail. The laser can produce a burst of high-energy pulses (of the order of hundreds of millijoules per pulse) with individual pulse durations of less than 10 ns and pulse separations as short as 1 micros. A key improvement is the addition of a phase-conjugate mirror, which effectively isolates the high-intensity, short-duration pulses from the low-intensity, long-duration background illumination. It allows for more-efficient amplification and harmonic generation, with efficiencies exceeding 50% for second-harmonic and 40% for third-harmonic generation. Characteristics of the laser system, including gain narrowing, pulse-burst energy distribution, pulse narrowing, and overall pulse-burst energy, are described. In addition, the applicability of the laser for spectroscopic-based flow diagnostics is demonstrated through the presentation of megahertz-rate planar Doppler velocimetry results.

  15. Transverse emittance measurements from a photocathode RF gun with variable laser pulse length

    NASA Astrophysics Data System (ADS)

    Reis, D. A.; Hernandez, M.; Schmerge, J. F.; Winick, H.; Hogan, M. J.

    1999-06-01

    The gun test facility (GTF) at SSRL was started in 1996 to develop an appropriate injector for the proposed linac coherent light source (LCLS) at SLAC. The LCLS design requires the injector to produce a beam with at least 1 nC of charge in a 10 ps or shorter pulse with no greater than 1π mm mrad normalized rms emittance. The photoinjector at the GTF is 1.6 cell S-band symmetrized gun and emittance compensation solenoid. Emittance measurements, reported here, were made as function of laser pulse width using Gaussian longitudinal pulses. The lowest achieved emittance to date with 1 nC of charge is 5.6π mm mrad and was obtained with a pulse width of 5 ps (FWHM) and is in agreement with simulation. There are indications that the accelerator settings for these results may not have been optimal. Simulations also indicate that a normalized emittance meeting the LCLS requirement can be obtained using appropriately shaped transverse and temporal laser/electron beam pulses. Work has begun on producing temporal flat top laser pulses which combined with transverse clipping of the laser is expected to lower the emittance to approximately 1π mm mrad for 1 nC with optimal accelerator settings.

  16. Photocathode rf gun emittance measurements using variable-length laser pulses

    NASA Astrophysics Data System (ADS)

    Schmerge, John F.; Hernandez, Mike; Hogan, Mark J.; Reis, David A.; Winick, Herman

    1999-07-01

    The Gun Test Facility (GTF) at the Stanford Linear Accelerator Center (SLAC) was created to develop an appropriate injector for the proposed Linac Coherent Light Source (LCLS) at SLAC. The LCLS design requires the injector to produce a beam with at least 1 nC of charge in a 10 ps or shorter pulse with no greater than 1 (pi) mm-mrad normalized rms emittance. The first photoinjector under study at the GTF is a 1.6 cell S-band symmetrized gun with an emittance compensation solenoid. Emittance measurements, reported here, were made as function of the transverse laser pulse shape and the Gaussian longitudinal laser pulse length. The lowest achieved emittance to data with 1 nC of charge is 5.6 (pi) mm-mrad and was obtained with both a Gaussian longitudinal and transverse pulse shape with 5 ps FWHM and 2.4 mm FWHM respectively. The measurement is in agreement with a PARMELA simulation using measured beam parameters. There are indications that the accelerator settings used in the results presented here were not optimal. Simulations indicate that a normalized emittance meeting the LCLS requirement can be obtained using appropriately shaped transverse and temporal laser/electron beam pulses. Work has begun on producing temporal flat top laser pulses which combined with transverse clipping of the laser is expected to lower the emittance to approximately 1 (pi) mm-mrad for 1 nC beams with optimal accelerator settings.

  17. Divided-pulse nonlinear amplification and simultaneous compression

    SciTech Connect

    Hao, Qiang; Zhang, Qingshan; Sun, Tingting; Chen, Jie; Wang, Yuqing; Guo, Zhengru; Yang, Kangwen; Guo, Zhanhua; Zeng, Heping

    2015-03-09

    We report on a fiber laser system delivering 122 fs pulse duration and 600 mW average power at 1560 nm by the interplay between divided pulse amplification and nonlinear pulse compression. A small-core double-clad erbium-doped fiber with anomalous dispersion carries out the pulse amplification and simultaneously compresses the laser pulses such that a separate compressor is no longer necessary. A numeric simulation reveals the existence of an optimum fiber length for producing transform-limited pulses. Furthermore, frequency doubling to 780 nm with 240 mW average power and 98 fs pulse duration is achieved by using a periodically poled lithium niobate crystal at room temperature.

  18. Third-generation megahertz-rate pulse burst laser system.

    PubMed

    Thurow, Brian S; Satija, Aman; Lynch, Kyle

    2009-04-10

    The design and performance of a third-generation megahertz-rate pulse burst laser system is described. The third-generation system incorporates two distinct design changes that distinguish it from earlier-generation systems. The first is that pulse slicing is now achieved by using an economical acousto-optic modulator (AOM), and the second is the use of a variable pulse duration flashlamp driver that provides relatively uniform gain over a ~700 mus window. The use of an AOM for pulse slicing permits flexible operation such as pulse-on-demand operation with variable pulse durations ranging from 10 ns to DC. The laser described here is capable of producing a burst of laser pulses at repetition rates as high as 50 MHz and peak powers of 10 kW. Second-harmonic conversion efficiency using a type II KTP crystal is also demonstrated.

  19. PULSE COUNTER

    DOEpatents

    Trumbo, D.E.

    1959-02-10

    A transistorized pulse-counting circuit adapted for use with nuclear radiation detecting detecting devices to provide a small, light weight portable counter is reported. The small size and low power requirements of the transistor are of particular value in this instance. The circuit provides an adjustable count scale with a single transistor which is triggered by the accumulated charge on a storage capacitor.

  20. Expected endings and judged duration.

    PubMed

    Jones, M R; Boltz, M G; Klein, J M

    1993-09-01

    In four experiments, the predictions of an expectancy/contrast model (Jones & Boltz, 1989) for judged duration were evaluated. In Experiments 1 and 2, listeners estimated the relative durations of auditory pattern pairs that varied in contextual phrasing and temporal contrast. The results showed that when the second pattern of a pair either seems to (Experiments 1 and 2) or actually does (Experiment 2) end earlier (later) than the first, subjects judge it as being relatively shorter (longer). In Experiment 3, listeners heard single patterns in which notes immediately preceding the final one were omitted. Timing of the final (target) tone was varied such that it was one beat early, on time, or one beat late. Listeners' ratings of target tones revealed systematic effects of phrasing and target timing. In Experiment 4, listeners temporally completed (extrapolated) sequences of Experiment 3 that were modified to exclude the target tone. The results again showed that phrase context systematically influenced expectancies about "when" sequences should end. As a set, these studies demonstrate the effects of event structure and anticipatory attending upon experienced duration and are discussed in terms of the expectancy/contrast model.

  1. Pulsed discharge production Ar* metastables

    NASA Astrophysics Data System (ADS)

    Han, Jiande; Heaven, Michael C.; Emmons, Daniel; Perram, Glen P.; Weeks, David E.; Bailey, William F.

    2016-03-01

    The production of relatively high densities of Ar* metastables (>1012 cm-3) in Ar/He mixtures, at total pressures close to 1 atm, is essential for the efficient operation of an optically pumped Ar* laser. We have used emission spectroscopy and diode laser absorption spectroscopy measurements to observe the production and decay of Ar* in a parallel plate pulsed discharge. With discharge pulses of 1 μs duration we find that metastable production is dominated by processes occurring within the first 100 ns of the gas break-down. Application of multiple, closely spaced discharge pulses yields insights concerning conditions that favor metastable production. This information has been combined with time-resolved measurements of voltage and current. The experimental results and preliminary modeling of the discharge kinetics are presented.

  2. FEU-140 photomultipliers in pulsed plasma spectroscopy

    SciTech Connect

    Arteev, M.S.; Sulakshin, S.S.

    1987-12-01

    Special fast photomultipliers are usually employed in photoelectric spectroscopy of nonstationary plasmas. Measurements have been made on the pulse characteristics and spectral sensitivity for the FEU-140 photomultiplier, which enables one to record a light flux of about 10/sup -10/ W as pulses of duration down to 10 nsec in the range 200-650 nm with a fairly wide linearity range (10/sup -10/-10/sup -18/ W).

  3. Multiple laser pulse ignition method and apparatus

    DOEpatents

    Early, James W.

    1998-01-01

    Two or more laser light pulses with certain differing temporal lengths and peak pulse powers can be employed sequentially to regulate the rate and duration of laser energy delivery to fuel mixtures, thereby improving fuel ignition performance over a wide range of fuel parameters such as fuel/oxidizer ratios, fuel droplet size, number density and velocity within a fuel aerosol, and initial fuel temperatures.

  4. Note: Emittance measurements of intense pulsed proton beam for different pulse length and repetition rate

    SciTech Connect

    Miracoli, R.; Gammino, S.; Celona, L.; Mascali, D.; Castro, G.; Gobin, R.; Delferriere, O.; Adroit, G.; Senee, F.; Ciavola, G.

    2012-05-15

    The high intensity ion source (SILHI), in operation at CEA-Saclay, has been used to produce a 90 mA pulsed proton beam with pulse length and repetition rates suitable for the European Spallation Source (ESS) linac. Typical r-r{sup '} rms normalized emittance values smaller than 0.2{pi} mm mrad have been measured for operation in pulsed mode (0.01 < duty cycle < 0.15 and 1 ms < pulse duration < 10 ms) that are relevant for the design update of the Linac to be used at the ESS in Lund.

  5. Short-duration electrical immobilization of lake trout

    USGS Publications Warehouse

    Gaikowski, Mark P.; Gingerich, William H.; Gutreuter, Steve

    2001-01-01

    Chemical anesthetics induce stress responses, and most leave residues in fish tissues that require a certain withdrawal time before the animal can be released into the environment. Therefore, alternatives are needed in cases when fish must be released immediately, for example, during egg-collecting operations or after implanting elastomer tags. To evaluate pulsed direct current as an alternative method of immobilization, individual lake trout Salvelinus namaycush were electrically immobilized using various pulsed-DC voltage gradients and shock durations. Duration of opercular recovery and narcosis were measured for individual fish. Fish were euthanized 24 h after electrical immobilization and processed for lateral radiograph analysis and assessment of perivertebral hemorrhaging by dissection. Survival of lake trout after electrical immobilization at 0.6 V/cm for 30 or 40 s or 0.8 V/cm for 5 or 15 s was monitored for 81 or 84 d after immobilization. Mean narcosis duration increased with voltage gradient and shock duration. Larger fish had longer periods of narcosis at the same combination of voltage gradient and shock duration. Radiological evaluation indicated that 9 of 28 fish in the oldest age-class tested had detectable injuries of the vertebral column, but all but one were in the lowest injury category. Although vertebral column injuries were observed in most small fish, the majority of vertebral column injuries were minor compressions involving two to seven vertebrae. Of the 82 lake trout electrically immobilized to assess long-term survival, only 5 died (6%). Our data suggest that lake trout could be electrically immobilized for a sufficient period to allow field workers to collect length and weight data and implant visible implant tags or colored elastomer tags. The technique we used, however, is probably not appropriate for procedures that require immobilization for more than 2a??3 min.

  6. Ionization and pulse lethargy effects in inverse Cherenkov accelerators

    SciTech Connect

    Sprangle, P.; Hubbard, R.F.,; Hafizi, B.,

    1997-05-01

    Ionization processes limit the accelerating gradient and place an upper limit on the pulse duration of the electromagnetic driver in the inverse Cherenkov accelerator (ICA). Group velocity slippage, i.e., pulse lethargy, on the other hand, imposes a lower limit on the pulse duration. These limits are obtained for two ICA configurations in which the electromagnetic driver (e.g., laser or millimeter wave source) is propagated in a waveguide that is (i) lined with a dielectric material or (ii) filled with a neutral gas. In either configuration the electromagnetic driving field is guided and has an axial electric field with phase velocity equal to the speed of light in vacuum, c. The intensity of the driver in the ICA, and therefore the acceleration gradient, is limited by tunneling and collisional ionization effects. Partial ionization of the dielectric liner or gas can lead to significant modification of the dispersive properties of the waveguide, altering the phase velocity of the accelerating field and causing particle slippage, thus disrupting the acceleration process. An additional limitation on the pulse duration is imposed since the group velocity of the driving pulse is less than c and the pulse slips behind the accelerated electrons. Hence for sufficiently short pulses the electrons outrun the pulse, terminating the acceleration. Limitations on the driver pulse duration and accelerating gradient, due to ionization and pulse lethargy, are estimated for the two ICA configurations. Maximum accelerating gradients and pulse durations are presented for a 10 {mu}m, 1 mm, and 1 cm wavelength electromagnetic driver. The combination of ionization and pulse lethargy effects impose severe limitations on the maximum energy gain in inverse Cherenkov accelerators. {copyright} {ital 1997} {ital The American Physical Society}

  7. Pulsed hydrojet

    DOEpatents

    Bohachevsky, I.O.; Torrey, M.D.

    1986-06-10

    An underwater pulsed hydrojet propulsion system is provided for accelerating and propelling a projectile or other vessel. A reactant, such as lithium, is fluidized and injected into a water volume. The resulting reaction produces an energy density in a time effective to form a steam pocket. Thrust flaps or baffles direct the pressure from the steam pocket toward an exit nozzle for accelerating a water volume to create thrust. A control system regulates the dispersion of reactant to control thrust characteristics.

  8. Increasing laser intensity using pulse shaping method in fast ignitor research

    NASA Astrophysics Data System (ADS)

    Habara, H.; Kodama, R.; Mori, M.; Sawai, K.; Suzuki, K.; Kitagawa, Y.; Yamanaka, T.

    2004-03-01

    Pulse shaping in chirped pulse amplification laser system with large glass amplifier is demonstrated through the spectral control of the chirped pulse. Spectral shape is modified by changing the spatial dispersion with a spatially modulated transmission filter in pulse stretcher. Three different pulse shaping controls, prepulse control, pedestal reduction and pulse duration shortening, are performed in both experiments and calculations. A 70 TW/300 fs laser pulse was obtained without an increase of the laser energy in the system, which usually provides 40 TW/500 fs pulse.

  9. Slow light of subnanosecond pulses via stimulated Brillouin scattering in nonuniform fibers

    SciTech Connect

    Kalosha, V. P.; Chen, Liang; Bao, Xiaoyi

    2007-02-15

    We have proposed a way to obtain large optically controlled delay for subnanosecond pulses and simultaneously avoid the pulse distortions via stimulated Brillouin scattering (SBS) in optical fibers at cw pumping by the use of longitudinally nonuniform fibers with the Brillouin frequency linearly varying with distance. If the range of Brillouin frequency variation along the fiber covers the whole pulse spectrum, the delay of subnanosecond pulses is linearly proportional to the gain, could be larger than the pulse duration, and the pulse broadening is minimum. We have shown this by solving three-wave SBS equations for realistic fiber lengths, both single subnanosecond pulses and sequences of subnanosecond pulses.

  10. Effects of the shock duration on the response of CFRP composite laminates

    NASA Astrophysics Data System (ADS)

    Gay, Elise; Berthe, Laurent; Boustie, Michel; Arrigoni, Michel; Buzaud, Eric

    2014-11-01

    Shock loads induce a local tensile stress within a sample. The location and amplitude of this high strain rate stress can be monitored respectively by the duration and intensity of the shock. The process is applied to carbon fibre reinforced polymer (CFRP) composites, involved in aeronautic or defense industry. This paper describes the response of CFRP laminates of different thicknesses to a shock load normal to the fibres direction. The effects of the shock duration on the wave propagation are key issues of this work. Experiments have been performed on high power laser facilities and on a high power pulsed generator to get a wide range of pulse duration from fs to µs. Numerical simulation provides a comprehensive approach of the wave propagation and tensile stress generation within these complex materials. The main result concerns the relation between the load duration, the tensile stress and the induced delamination within 1, 4 and 8 ply composite laminates.

  11. Controlling output pulse and prepulse in a resonant microwave pulse compressor

    SciTech Connect

    Shlapakovski, A.; Artemenko, S.; Chumerin, P.; Yushkov, Yu.

    2013-02-07

    A resonant microwave pulse compressor with a waveguide H-plane-tee-based energy extraction unit was studied in terms of its capability to produce output pulses that comprise a low-power long-duration (prepulse) and a high-power short-duration part. The application of such combined pulses with widely variable prepulse and high-power pulse power and energy ratios is of interest in the research area of electronic hardware vulnerability. The characteristics of output radiation pulses are controlled by the variation of the H-plane tee transition attenuation at the stage of microwave energy storage in the compressor cavity. Results of theoretical estimations of the parameters tuning range and experimental investigations of the prototype S-band compressor (1.5 MW, 12 ns output pulse; {approx}13.2 dB gain) are presented. The achievable maximum in the prepulse power is found to be about half the power of the primary microwave source. It has been shown that the energy of the prepulse becomes comparable with that of the short-duration (nanosecond) pulse, while the power of the latter decreases insignificantly. The possible range of variation of the prepulse power and energy can be as wide as 40 dB. In the experiments, the prepulse level control within the range of {approx}10 dB was demonstrated.

  12. Apparatus and method for optical pulse measurement

    DOEpatents

    Trebino, Rick P.; Tsang, Thomas; Fittinghoff, David N.; Sweetser, John N.; Krumbuegel, Marco A.

    1999-12-28

    Practical third-order frequency-resolved optical grating (FROG) techniques for characterization of ultrashort optical pulses are disclosed. The techniques are particularly suited to the measurement of single and/or weak optical pulses having pulse durations in the picosecond and subpicosecond regime. The relative quantum inefficiency of third-order nonlinear optical effects is compensated for through i) use of phase-matched transient grating beam geometry to maximize interaction length, and ii) use of interface-enhanced third-harmonic generation.

  13. Laser pulse shaping for high gradient accelerators

    NASA Astrophysics Data System (ADS)

    Villa, F.; Anania, M. P.; Bellaveglia, M.; Bisesto, F.; Chiadroni, E.; Cianchi, A.; Curcio, A.; Galletti, M.; Di Giovenale, D.; Di Pirro, G.; Ferrario, M.; Gatti, G.; Moreno, M.; Petrarca, M.; Pompili, R.; Vaccarezza, C.

    2016-09-01

    In many high gradient accelerator schemes, i.e. with plasma or dielectric wakefield induced by particles, many electron pulses are required to drive the acceleration of one of them. Those electron bunches, that generally should have very short duration and low emittance, can be generated in photoinjectors driven by a train of laser pulses coming inside the same RF bucket. We present the system used to shape and characterize the laser pulses used in multibunch operations at Sparc_lab. Our system gives us control over the main parameter useful to produce a train of up to five high brightness bunches with tailored intensity and time distribution.

  14. Apparatus and method for optical pulse measurement

    SciTech Connect

    Trebino, R.P.; Tsang, T.; Fittinghoff, D.N.; Sweetser, J.N.; Krumbuegel, M.A.

    1999-12-28

    Practical third-order frequency-resolved optical grating (FROG) techniques for characterization of ultrashort optical pulses are disclosed. The techniques are particularly suited to the measurement of single and/or weak optical pulses having pulse durations in the picosecond and subpicosecond regime. The relative quantum inefficiency of third-order nonlinear optical effects is compensated for through (i) use of phase-matched transient grating beam geometry to maximize interaction length, and (ii) use of interface-enhanced third-harmonic generation.

  15. SWIFT OBSERVATIONS OF GAMMA-RAY BURST PULSE SHAPES: GRB PULSE SPECTRAL EVOLUTION CLARIFIED

    SciTech Connect

    Hakkila, Jon; Lien, Amy; Sakamoto, Takanori; Morris, David; Neff, James E.; Giblin, Timothy W.

    2015-12-20

    Isolated Swift gamma-ray burst (GRB) pulses, like their higher-energy BATSE counterparts, emit the bulk of their pulsed emission as a hard-to-soft component that can be fitted by the Norris et al. empirical pulse model. This signal is overlaid by a fainter, three-peaked signal that can be modeled by the residual fit of Hakkila and Preece: the two fits combine to reproduce GRB pulses with distinctive three-peaked shapes. The precursor peak appears on or before the pulse rise and is often the hardest component, the central peak is the brightest, and the decay peak converts exponentially decaying emission into a long, soft, power-law tail. Accounting for systematic instrumental differences, the general characteristics of the fitted pulses are remarkably similar. Isolated GRB pulses are dominated by hard-to-soft evolution; this is more pronounced for asymmetric pulses than for symmetric ones. Isolated GRB pulses can also exhibit intensity tracking behaviors that, when observed, are tied to the timing of the three peaks: pulses with the largest maximum hardnesses are hardest during the precursor, those with smaller maximum hardnesses are hardest during the central peak, and all pulses can re-harden during the central peak and/or during the decay peak. Since these behaviors are essentially seen in all isolated pulses, the distinction between “hard-to-soft and “intensity-tracking” pulses really no longer applies. Additionally, the triple-peaked nature of isolated GRB pulses seems to indicate that energy is injected on three separate occasions during the pulse duration: theoretical pulse models need to account for this.

  16. Swift Observations of Gamma-Ray Burst Pulse Shapes: GRB Pulse Spectral Evolution Clarified

    NASA Astrophysics Data System (ADS)

    Hakkila, Jon; Lien, Amy; Sakamoto, Takanori; Morris, David; Neff, James E.; Giblin, Timothy W.

    2015-12-01

    Isolated Swift gamma-ray burst (GRB) pulses, like their higher-energy BATSE counterparts, emit the bulk of their pulsed emission as a hard-to-soft component that can be fitted by the Norris et al. empirical pulse model. This signal is overlaid by a fainter, three-peaked signal that can be modeled by the residual fit of Hakkila & Preece: the two fits combine to reproduce GRB pulses with distinctive three-peaked shapes. The precursor peak appears on or before the pulse rise and is often the hardest component, the central peak is the brightest, and the decay peak converts exponentially decaying emission into a long, soft, power-law tail. Accounting for systematic instrumental differences, the general characteristics of the fitted pulses are remarkably similar. Isolated GRB pulses are dominated by hard-to-soft evolution; this is more pronounced for asymmetric pulses than for symmetric ones. Isolated GRB pulses can also exhibit intensity tracking behaviors that, when observed, are tied to the timing of the three peaks: pulses with the largest maximum hardnesses are hardest during the precursor, those with smaller maximum hardnesses are hardest during the central peak, and all pulses can re-harden during the central peak and/or during the decay peak. Since these behaviors are essentially seen in all isolated pulses, the distinction between “hard-to-soft and “intensity-tracking” pulses really no longer applies. Additionally, the triple-peaked nature of isolated GRB pulses seems to indicate that energy is injected on three separate occasions during the pulse duration: theoretical pulse models need to account for this.

  17. The Effects of Intense Submicrosecond Electrical Pulses on Cells

    PubMed Central

    Deng, Jingdong; Schoenbach, Karl H.; Buescher, E. Stephen; Hair, Pamela S.; Fox, Paula M.; Beebe, Stephen J.

    2003-01-01

    A simple electrical model for living cells predicts an increasing probability for electric field interactions with intracellular substructures of both prokaryotic and eukaryotic cells when the electric pulse duration is reduced into the sub-microsecond range. The validity of this hypothesis was verified experimentally by applying electrical pulses (durations 100 μs–60 ns, electric field intensities 3–150 kV/cm) to Jurkat cells suspended in physiologic buffer containing propidium iodide. Effects on Jurkat cells were assessed by means of temporally resolved fluorescence and light microscopy. For the longest applied pulses, immediate uptake of propidium iodide occurred consistent with electroporation as the cause of increased surface membrane permeability. For nanosecond pulses, more delayed propidium iodide uptake occurred with significantly later uptake of propidium iodide occurring after 60 ns pulses compared to 300 ns pulses. Cellular swelling occurred rapidly following 300 ns pulses, but was minimal following 60 ns pulses. These data indicate that submicrosecond pulses achieve temporally distinct effects on living cells compared to microsecond pulses. The longer pulses result in rapid permeability changes in the surface membrane that are relatively homogeneous across the cell population, consistent with electroporation, while shorter pulses cause surface membrane permeability changes that are temporally delayed and heterogeneous in their magnitude. PMID:12668479

  18. Simulations of spectral broadening by cross-phase modulation (XPM) with chaotic light pulses

    SciTech Connect

    Henesian, M.A.; Dixit, S.N.; Chen, C.J.; Wai, P.K.A.; Menyuk, C.R.

    1993-05-25

    Spectral broadening of single-frequency laser pulses by optical cross-phase modulation (XPM) with chaotic laser pulses in birefringent single-mode optical fibers is investigated numerically and results are compared with experiments. By this process we have generated laser pulses of variable bandwidth (1--25 {Angstrom}) at the fundamental wavelength (1053 nm) for amplification in high power solid-state Nd:glass lasers used for inertial confinement fusion research. Simulations indicate that a temporally smooth XPM pulse can be generated with intensity fluctuations of less than 10% and spectral width greater than 50 {Angstrom} using a short length ({approximately}5 m) of special low dispersion and low birefringence fiber, e.g. D = 10 ps/nm-km (normal dispersion) and {Delta}n = 2 {times} 10{sup {minus}5}. Readily available fibers of similar length, with parameters of D = 40 ps/nm-km and {Delta}n = 6 {times} 10{sup {minus}5}, can give spectral widths exceeding 25 {Angstrom}, but the noise will range from 25 to 60%. Broadband laser pulses generated by XPM are now routinely used at Lawrence Livermore National Laboratory for active smoothing of the laser irradiance on targets by the technique of smoothing-by-spectral dispersion.

  19. Human responses to bright light of different durations

    PubMed Central

    Chang, Anne-Marie; Santhi, Nayantara; St Hilaire, Melissa; Gronfier, Claude; Bradstreet, Dayna S; Duffy, Jeanne F; Lockley, Steven W; Kronauer, Richard E; Czeisler, Charles A

    2012-01-01

    Light exposure in the early night induces phase delays of the circadian rhythm in melatonin in humans. Previous studies have investigated the effect of timing, intensity, wavelength, history and pattern of light stimuli on the human circadian timing system. We present results from a study of the duration–response relationship to phase-delaying bright light. Thirty-nine young healthy participants (16 female; 22.18 ± 3.62 years) completed a 9-day inpatient study. Following three baseline days, participants underwent an initial circadian phase assessment procedure in dim light (<3 lux), and were then randomized for exposure to a bright light pulse (∼10,000 lux) of 0.2 h, 1.0 h, 2.5 h or 4.0 h duration during a 4.5 h controlled-posture episode centred in a 16 h wake episode. After another 8 h sleep episode, participants completed a second circadian phase assessment. Phase shifts were calculated from the difference in the clock time of the dim light melatonin onset (DLMO) between the initial and final phase assessments. Exposure to varying durations of bright light reset the circadian pacemaker in a dose-dependent, non-linear manner. Per minute of exposure, the 0.2 h duration was over 5 times more effective at phase delaying the circadian pacemaker (1.07 ± 0.36 h) as compared with the 4.0 h duration (2.65 ± 0.24 h). Acute melatonin suppression and subjective sleepiness also had a dose-dependent response to light exposure duration. These results provide strong evidence for a non-linear resetting response of the human circadian pacemaker to light duration. PMID:22526883

  20. Human responses to bright light of different durations.

    PubMed

    Chang, Anne-Marie; Santhi, Nayantara; St Hilaire, Melissa; Gronfier, Claude; Bradstreet, Dayna S; Duffy, Jeanne F; Lockley, Steven W; Kronauer, Richard E; Czeisler, Charles A

    2012-07-01

    Light exposure in the early night induces phase delays of the circadian rhythm in melatonin in humans. Previous studies have investigated the effect of timing, intensity, wavelength, history and pattern of light stimuli on the human circadian timing system. We present results from a study of the duration–response relationship to phase-delaying bright light. Thirty-nine young healthy participants (16 female; 22.18±3.62 years) completed a 9-day inpatient study. Following three baseline days, participants underwent an initial circadian phase assessment procedure in dim light (<3 lux), and were then randomized for exposure to a bright light pulse (∼10,000 lux) of 0.2 h, 1.0 h, 2.5 h or 4.0 h duration during a 4.5 h controlled-posture episode centred in a 16 h wake episode. After another 8 h sleep episode, participants completed a second circadian phase assessment. Phase shifts were calculated from the difference in the clock time of the dim light melatonin onset (DLMO) between the initial and final phase assessments. Exposure to varying durations of bright light reset the circadian pacemaker in a dose-dependent, non-linear manner. Per minute of exposure, the 0.2 h duration was over 5 times more effective at phase delaying the circadian pacemaker (1.07±0.36 h) as compared with the 4.0 h duration (2.65±0.24 h). Acute melatonin suppression and subjective sleepiness also had a dose-dependent response to light exposure duration. These results provide strong evidence for a non-linear resetting response of the human circadian pacemaker to light duration.

  1. Short pulse generation from a flashlamp-pumped rhodamine 6G ring dye laser using the colliding pulse mode-locking technique

    SciTech Connect

    Singh, S.

    1987-01-01

    The colliding pulse mode-locking (CPM) technique has been applied to a flashlamp-pumped rhodamine 6G dye laser to reliably generate pulses of <1.5 ps. Pulse evolution in the ring cavity has been studied by examining the pulse characteristics at various parts of the pulse train using a Photochron II streak camera. The measured pulse durations in the ring cavity were found to be detector-limited and were shorter than those generated in a linear cavity. The shortest pulses were observed to evolve toward the end of the --600-ns long mode-locked train.

  2. Diffraction limited amplification of picosecond pulses in 1170 microm2 effective area erbium fiber.

    PubMed

    Jasapara, J C; DeSantolo, A; Nicholson, J W; Yablon, A D; Várallyay, Z

    2008-11-10

    Robust fundamental mode propagation and amplification of picosecond pulses at 1.56 microm wavelength is demonstrated in a core-pumped Er fiber with 1170 microm2 effective area. Record peak power exceeding 120 kW, and 67 nJ pulse energy are achieved before the onset of pulse breakup. A small increase in input pulse energy results in a temporal collapse of the pulse center to 58 fs duration, with peak powers approaching 200 kW.

  3. Generation of unipolar optical pulses in a Raman-active medium

    NASA Astrophysics Data System (ADS)

    Arkhipov, R. M.; Arkhipov, M. V.; Belov, P. A.; Tolmachev, Yu A.; Babushkin, I.

    2016-04-01

    Response of a Raman-active media (RAM) to the excitation by a series of ultrashort (few-cycle) optical pulses propagating at a superluminal velocity is studied theoretically. It is shown that under certain conditions rectangular unipolar pulses (video-pulses) can be generated as the RAM response. The duration, shape and amplitude of these video-pulses can be widely tuned by modifying the pump pulse parameters.

  4. Bipolar nanosecond electric pulses are less efficient at electropermeabilization and killing cells than monopolar pulses

    PubMed Central

    Ibey, Bennett L.; Ullery, Jody; Pakhomova, Olga N.; Roth, Caleb C.; Semenov, Iurri; Beier, Hope T.; Tarango, Melissa; Xiao, Shu; Schoenbach, Karl; Pakhomov, Andrei G.

    2014-01-01

    Multiple studies have shown that bipolar (BP) electric pulses in the microsecond range are more effective at permeabilizing cells while maintaining similar cell survival rates as compared to monopolar (MP) pulse equivalents. In this paper, we investigated whether the same advantage existed for BP nanosecond-pulsed electric fields (nsPEF) as compared to MP nsPEF. To study permeabilization effectiveness, MP or BP pulses were delivered to single Chinese hamster ovary (CHO) cells and the response of three dyes, Calcium Green-1, Propidium Iodide (PI), and FM1-43, was measured by confocal microscopy. Results show that BP pulses were less effective at increasing intracellular calcium concentration or PI uptake and cause less membrane reorganization (FM1-43) than MP pulses. Twenty-four hour survival was measured in three cell lines (Jurkat, U937, CHO) and over ten times more BP pulses were required to induce death as compared to MP pulses of similar magnitude and duration. Flow cytometry analysis of CHO cells after exposure (15 minutes) revealed that to achieve positive FITC-Annexin V and PI expression, ten times more BP pulses were required than MP pulses. Overall, unlike longer pulse exposures, BP nsPEF exposures proved far less effective at both membrane permeabilization and cell killing than MP nsPEF. PMID:24332942

  5. Bipolar nanosecond electric pulses are less efficient at electropermeabilization and killing cells than monopolar pulses.

    PubMed

    Ibey, Bennett L; Ullery, Jody C; Pakhomova, Olga N; Roth, Caleb C; Semenov, Iurii; Beier, Hope T; Tarango, Melissa; Xiao, Shu; Schoenbach, Karl H; Pakhomov, Andrei G

    2014-01-10

    Multiple studies have shown that bipolar (BP) electric pulses in the microsecond range are more effective at permeabilizing cells while maintaining similar cell survival rates as compared to monopolar (MP) pulse equivalents. In this paper, we investigated whether the same advantage existed for BP nanosecond-pulsed electric fields (nsPEF) as compared to MP nsPEF. To study permeabilization effectiveness, MP or BP pulses were delivered to single Chinese hamster ovary (CHO) cells and the response of three dyes, Calcium Green-1, propidium iodide (PI), and FM1-43, was measured by confocal microscopy. Results show that BP pulses were less effective at increasing intracellular calcium concentration or PI uptake and cause less membrane reorganization (FM1-43) than MP pulses. Twenty-four hour survival was measured in three cell lines (Jurkat, U937, CHO) and over ten times more BP pulses were required to induce death as compared to MP pulses of similar magnitude and duration. Flow cytometry analysis of CHO cells after exposure (at 15 min) revealed that to achieve positive FITC-Annexin V and PI expression, ten times more BP pulses were required than MP pulses. Overall, unlike longer pulse exposures, BP nsPEF exposures proved far less effective at both membrane permeabilization and cell killing than MP nsPEF.

  6. High gain broadband amplification of ultraviolet pulses in optical parametric chirped pulse amplifier.

    PubMed

    Wnuk, Paweł; Stepanenko, Yuriy; Radzewicz, Czesław

    2010-04-12

    We report on a high gain amplification of broadband ultraviolet femtosecond pulses in an optical parametric chirped pulse amplifier. Broadband ultraviolet seed pulses were obtained by an achromatic frequency doubling of the output from a femtosecond Ti:Sapphire oscillator. Stretched seed pulses were amplified in a multipass parametric amplifier with a single BBO crystal pumped by a ns frequency quadrupled Nd:YAG laser. A noncollinear configuration was used for a broadband amplification. The total (after compression) amplification of 2.510(5) was achieved, with compressed pulse energy of 30 microJ and pulse duration of 24 fs. We found that the measured gain was limited by thermal effects induced by the absorption of the pump laser by color centers created in the BBO crystal.

  7. Pulse ignition characterization of mercury ion thruster hollow cathode using an improved pulse ignitor

    NASA Technical Reports Server (NTRS)

    Wintucky, E. G.; Gruber, R. P.

    1978-01-01

    An investigation of the high voltage pulse ignition characteristics of the 8 cm mercury ion thruster neutralizer cathode identified a low rate of voltage rise and long pulse duration as desirable factors for reliable cathode starting. Cathode starting breakdown voltages were measured over a range of mercury flow rates and tip heater powers for pulses with five different rates of voltage rise. Breakdown voltage requirements for the fastest rising pulse (2.5 to 3.0 kV/micro sec) were substantially higher (2 kV or more) than for the slowest rising pulse (0.3 to 0.5 kV/micro sec) for the same starting conditions. Also described is an improved, low impedance pulse ignitor circuit which reduces power losses and eliminates problems with control and packaging associated with earlier designs.

  8. Investigating the effects of stimulus duration and context on pitch perception by cochlear implant users

    PubMed Central

    Stohl, Joshua S.; Throckmorton, Chandra S.; Collins, Leslie M.

    2009-01-01

    Cochlear implant sound processing strategies that use time-varying pulse rates to transmit fine structure information are one proposed method for improving the spectral representation of a sound with the eventual goal of improving speech recognition in noisy conditions, speech recognition in tonal languages, and music identification and appreciation. However, many of the perceptual phenomena associated with time-varying rates are not well understood. In this study, the effects of stimulus duration on both the place and rate-pitch percepts were investigated via psychophysical experiments. Four Nucleus CI24 cochlear implant users participated in these experiments, which included a short-duration pitch ranking task and three adaptive pulse rate discrimination tasks. When duration was fixed from trial-to-trial and rate was varied adaptively, results suggested that both the place-pitch and rate-pitch percepts may be independent of duration for durations above 10 and 20 ms, respectively. When duration was varied and pulse rates were fixed, performance was highly variable within and across subjects. Implications for multi-rate sound processing strategies are discussed. PMID:19603888

  9. Pulse thermal processing of functional materials using directed plasma arc

    DOEpatents

    Ott, Ronald D.; Blue, Craig A.; Dudney, Nancy J.; Harper, David C.

    2007-05-22

    A method of thermally processing a material includes exposing the material to at least one pulse of infrared light emitted from a directed plasma arc to thermally process the material, the pulse having a duration of no more than 10 s.

  10. Femtosecond-Laser-Pulse Characterization and Optimization for CARS Microscopy.

    PubMed

    Piazza, Vincenzo; de Vito, Giuseppe; Farrokhtakin, Elmira; Ciofani, Gianni; Mattoli, Virgilio

    2016-01-01

    We present a simple method and its experimental implementation to determine the pulse durations and linear chirps of the pump-and-probe pulse and the Stokes pulse in a coherent anti-Stokes Raman scattering microscope at sample level without additional autocorrelators. Our approach exploits the delay line, ubiquitous in such microscopes, to perform a convolution of the pump-and-probe and Stokes pulses as a function of their relative delay and it is based on the detection of the photons emitted from an appropriate non-linear sample. The analysis of the non-resonant four-wave-mixing and sum-frequency-generation signals allows for the direct retrieval of the pulse duration on the sample and the linear chirp of each pulse. This knowledge is crucial in maximizing the spectral-resolution and contrast in CARS imaging. PMID:27224203

  11. Femtosecond-Laser-Pulse Characterization and Optimization for CARS Microscopy

    PubMed Central

    Piazza, Vincenzo; de Vito, Giuseppe; Farrokhtakin, Elmira; Ciofani, Gianni; Mattoli, Virgilio

    2016-01-01

    We present a simple method and its experimental implementation to determine the pulse durations and linear chirps of the pump-and-probe pulse and the Stokes pulse in a coherent anti-Stokes Raman scattering microscope at sample level without additional autocorrelators. Our approach exploits the delay line, ubiquitous in such microscopes, to perform a convolution of the pump-and-probe and Stokes pulses as a function of their relative delay and it is based on the detection of the photons emitted from an appropriate non-linear sample. The analysis of the non-resonant four-wave-mixing and sum-frequency-generation signals allows for the direct retrieval of the pulse duration on the sample and the linear chirp of each pulse. This knowledge is crucial in maximizing the spectral-resolution and contrast in CARS imaging. PMID:27224203

  12. Coherent propagation effects and pulse self-compression under the conditions of two-photon resonant difference-frequency generation

    NASA Astrophysics Data System (ADS)

    Nazarkin, A.; Korn, G.

    1997-12-01

    We predict the possibility of using two-photon coherent propagation effects for generating pulses at the difference frequency with duration significantly shorter and intensity higher than those of the input pump and injection pulse.

  13. PULSE COLUMN

    DOEpatents

    Grimmett, E.S.

    1964-01-01

    This patent covers a continuous countercurrent liquidsolids contactor column having a number of contactor states each comprising a perforated plate, a layer of balls, and a downcomer tube; a liquid-pulsing piston; and a solids discharger formed of a conical section at the bottom of the column, and a tubular extension on the lowest downcomer terminating in the conical section. Between the conical section and the downcomer extension is formed a small annular opening, through which solids fall coming through the perforated plate of the lowest contactor stage. This annular opening is small enough that the pressure drop thereacross is greater than the pressure drop upward through the lowest contactor stage. (AEC)

  14. Cohabitation Duration and Transient Domesticity.

    PubMed

    Golub, Andrew; Reid, Megan; Strickler, Jennifer; Dunlap, Eloise

    2013-01-01

    Research finds that many impoverished urban Black adults engage in a pattern of partnering and family formation involving a succession of short cohabitations yielding children, a paradigm referred to as transient domesticity. Researchers have identified socioeconomic status, cultural adaptations, and urbanicity as explanations for aspects of this pattern. We used longitudinal data from the 2001 Survey of Income and Program Participation to analyze variation in cohabitation and marriage duration by race/ethnicity, income, and urban residence. Proportional hazards regression indicated that separation risk is greater among couples that are cohabiting, below 200% of the federal poverty line, and Black but is not greater among urban dwellers. This provides empirical demographic evidence to support the emerging theory of transient domesticity and suggests that both socioeconomic status and race explain this pattern. We discuss the implications of these findings for understanding transient domesticity and make recommendations for using the Survey of Income and Program Participation to further study this family formation paradigm.

  15. Pulse-echo interaction in free-flying horseshoe bats, Rhinolophus ferrumequinum nippon.

    PubMed

    Shiori, Yu; Hiryu, Shizuko; Watanabe, Yu; Riquimaroux, Hiroshi; Watanabe, Yoshiaki

    2009-09-01

    Because horseshoe bats emit a long-duration pulse, the returning echo temporally overlaps with the emitted pulse during echolocation. Here, the pulse-echo interaction that horseshoe bats actually experience during flight was examined using onboard telemetry sound recordings. Doppler-shifted returning echoes produced beats in the amplitude patterns of constant-frequency components. Bats shortened the pulse duration with target distance, but the overlap duration was at least 8 ms within the approach phase. The computations suggest that the phase difference in slowly amplitude-modulated sound (the beat signal) provides a useful cue for target localization.

  16. Tapered pulse tube for pulse tube refrigerators

    DOEpatents

    Swift, Gregory W.; Olson, Jeffrey R.

    1999-01-01

    Thermal insulation of the pulse tube in a pulse-tube refrigerator is maintained by optimally varying the radius of the pulse tube to suppress convective heat loss from mass flux streaming in the pulse tube. A simple cone with an optimum taper angle will often provide sufficient improvement. Alternatively, the pulse tube radius r as a function of axial position x can be shaped with r(x) such that streaming is optimally suppressed at each x.

  17. Optimizing chirped laser pulse parameters for electron acceleration in vacuum

    SciTech Connect

    Akhyani, Mina; Jahangiri, Fazel; Niknam, Ali Reza; Massudi, Reza

    2015-11-14

    Electron dynamics in the field of a chirped linearly polarized laser pulse is investigated. Variations of electron energy gain versus chirp parameter, time duration, and initial phase of laser pulse are studied. Based on maximizing laser pulse asymmetry, a numerical optimization procedure is presented, which leads to the elimination of rapid fluctuations of gain versus the chirp parameter. Instead, a smooth variation is observed that considerably reduces the accuracy required for experimentally adjusting the chirp parameter.

  18. Pulse generation and preamplification for long pulse beamlines of Orion laser facility.

    PubMed

    Hillier, David I; Winter, David N; Hopps, Nicholas W

    2010-06-01

    We describe the pulse generation, shaping, and preamplification system for the nanosecond beamlines of the Orion laser facility. The system generates shaped laser pulses of up to approximately 1 J of 100 ps-5 ns duration with a programmable temporal profile. The laser has a 30th-power supergaussian spatial profile and is diffraction limited. The system is capable of imposing 2D smoothing by spectral dispersion upon the beam, which will produce a nonuniformity of 10% rms at the target.

  19. Free-electron-laser-induced shock-wave control and mechanistic analysis using pulse control

    SciTech Connect

    Kanai, Taizo; Yoshihashi-Suzuki, Sachiko; Awazu, Kunio

    2008-11-01

    The wavelength of the free electron laser (FEL) in Osaka University can be continuously varied in the range of 5.0-20.0 {mu}m. The FEL has a double-pulse structure, consisting of a train of macropulses of pulse duration 12 {mu}s. Each macropulse contains a train of 330 micropulses of pulse duration 5 ps. The tunability and picosecond pulses afford new medical and biological applications. However, a macropulse of long pulse duration leads to undesirable secondary effects. Precise control of the macropulse duration is essential for the high-precision applications of the FEL. An FEL pulse control system using acousto-optic modulators has been developed to investigate mechanical (shock-wave) effects of the FEL on living tissues. With this system, we have controlled photoinduced shock waves and determine the mechanism of interaction during FEL-induced tissue ablation.

  20. Neodymium glass laser with a pulse energy of 220 J and a pulse repetition rate of 0.02 Hz

    SciTech Connect

    Kuzmin, A A; Kulagin, O V; Khazanov, Efim A; Shaykin, A A

    2013-07-31

    A compact neodymium glass laser with a pulse energy of 220 J and a record-high pulse repetition rate of 0.02 Hz (pulse duration 30 ns) is developed. Thermally induced phase distortions are compensated using wave phase conjugation. The integral depolarisation of radiation is decreased to 0.4% by using linear compensation schemes. The second harmonic of laser radiation can be used for pumping Ti : sapphire multipetawatt complexes. (letters)

  1. Directly driven source of multi-gigahertz, sub-picosecond optical pulses

    DOEpatents

    Messerly, Michael J.; Dawson, Jay W.; Barty, Christopher P.J.; Gibson, David J.; Prantil, Matthew A.; Cormier, Eric

    2015-10-20

    A robust, compact optical pulse train source is described, with the capability of generating sub-picosecond micro-pulse sequences, which can be periodic as well as non-periodic, and at repetition rates tunable over decades of baseline frequencies, from MHz to multi-GHz regimes. The micro-pulses can be precisely controlled and formatted to be in the range of many ps in duration to as short as several fs in duration. The system output can be comprised of a continuous wave train of optical micro-pulses or can be programmed to provide gated bursts of macro-pulses, with each macro-pulse consisting of a specific number of micro-pulses or a single pulse picked from the higher frequency train at a repetition rate lower than the baseline frequency. These pulses could then be amplified in energy anywhere from the nJ to MJ range.

  2. Comparative investigation of three dose rate meters for their viability in pulsed radiation fields.

    PubMed

    Gotz, M; Karsch, L; Pawelke, J

    2015-06-01

    Pulsed radiation fields, characterized by microsecond pulse duration and correspondingly high pulse dose rates, are increasingly used in therapeutic, diagnostic and research applications. Yet, dose rate meters which are used to monitor radiation protection areas or to inspect radiation shielding are mostly designed, characterized and tested for continuous fields and show severe deficiencies in highly pulsed fields. Despite general awareness of the problem, knowledge of the specific limitations of individual instruments is very limited, complicating reliable measurements. We present here the results of testing three commercial dose rate meters, the RamION ionization chamber, the LB 1236-H proportional counter and the 6150AD-b scintillation counter, for their response in pulsed radiation fields of varied pulse dose and duration. Of these three the RamION proved reliable, operating in a pulsed radiation field within its specifications, while the other two instruments were only able to measure very limited pulse doses and pulse dose rates reliably. PMID:25978117

  3. System for generating shaped optical pulses and measuring optical pulses using spectral beam deflection (SBD)

    DOEpatents

    Skupsky, Stanley; Kessler, Terrance J.; Letzring, Samuel A.

    1993-01-01

    A temporally shaped or modified optical output pulse is generated from a bandwidth-encoded optical input pulse in a system in which the input pulse is in the form of a beam which is spectrally spread into components contained within the bandwidth, followed by deflection of the spectrally spread beam (SBD) thereby spatially mapping the components in correspondence with the temporal input pulse profile in the focal plane of a lens, and by spatially selective attenuation of selected components in that focal plane. The shaped or modified optical output pulse is then reconstructed from the attenuated spectral components. The pulse-shaping system is particularly useful for generating optical pulses of selected temporal shape over a wide range of pulse duration, such pulses finding application in the fields of optical communication, optical recording and data storage, atomic and molecular spectroscopy and laser fusion. An optical streak camera is also provided which uses SBD to display the beam intensity in the focal plane as a function of time during the input pulse.

  4. System for generating shaped optical pulses and measuring optical pulses using spectral beam deflection (SBD)

    DOEpatents

    Skupsky, S.; Kessler, T.J.; Letzring, S.A.

    1993-11-16

    A temporally shaped or modified optical output pulse is generated from a bandwidth-encoded optical input pulse in a system in which the input pulse is in the form of a beam which is spectrally spread into components contained within the bandwidth, followed by deflection of the spectrally spread beam (SBD) thereby spatially mapping the components in correspondence with the temporal input pulse profile in the focal plane of a lens, and by spatially selective attenuation of selected components in that focal plane. The shaped or modified optical output pulse is then reconstructed from the attenuated spectral components. The pulse-shaping system is particularly useful for generating optical pulses of selected temporal shape over a wide range of pulse duration, such pulses finding application in the fields of optical communication, optical recording and data storage, atomic and molecular spectroscopy and laser fusion. An optical streak camera is also provided which uses SBD to display the beam intensity in the focal plane as a function of time during the input pulse. 10 figures.

  5. H2 double ionization with few-cycle laser pulses

    NASA Astrophysics Data System (ADS)

    Saugout, S.; Charron, E.; Cornaggia, C.

    2008-02-01

    The temporal dynamics of double ionization of H2 has been investigated both experimentally and theoretically with few-cycle laser pulses. The main observables are the proton spectra associated with the H++H+ fragmentation channel. The model is based on the time-dependent Schrödinger equation and treats the electronic and nuclear coordinates on the same level. Therefore it allows the ultrafast nuclear dynamics to be followed as a function of the laser pulse duration, carrier-envelope phase offset, and peak intensity. We mainly report results in the sequential double-ionization regime above 2×1014Wcm-2 . The proton spectra are shifted to higher energies as the pulse duration is reduced from 40 down to 10 fs. The good agreement between the model predictions and the experimental data at 10 fs permits a theoretical study with pulse durations down to a few femtoseconds. We demonstrate the very fast nuclear dynamics of the H2+ ion for a pulse duration as short as 1 fs between the two ionization events, giving H2+ from H2 and H++H+ from H2+ . The carrier-envelope phase offset plays a significant role only for pulse durations shorter than 4 fs. At 10 fs, the laser intensity dependence of the proton spectra is fairly well reproduced by the model.

  6. A modeling approach to explain pulse design in bats.

    PubMed

    Boonman, Arjan; Ostwald, Joachim

    2007-08-01

    In this modeling study we wanted to find out why bats of the family Vespertilionidae (and probably also members of other families of bats) use pulses with a certain bandwidth and duration. Previous studies have only speculated on the function of bandwidth and pulse duration in bat echolocation or addressed this problem by assuming that bats optimize echolocation parameters to achieve very fine acuities in receiving single echoes. Here, we take a different approach by assuming that bats in nature rarely receive single echoes from each pulse emission, but rather many highly overlapping echoes. Some echolocation tasks require individual echoes to be separated to reconstruct reflection points in space. We used an established hearing model to investigate how the parameters bandwidth and pulse duration influence the separation of overlapping echoes. Our findings corroborate the following previously unknown or unsubstantiated facts: 1. Broadening the bandwidth improves the bat's lower resolution limit. 2. Increasing the sweep rate (defined by bandwidth and pulse duration) improves acuity of each extracted echo. 3. Decreasing the sweep rate improves the probability of frequency channels being activated. Since facts 2 and 3 affect sweep rate in an opposing fashion, an optimum sweep rate will exist, depending on the quality of the returning echoes and the requirements of the bat to improve acuity. The existence of an optimal sweep rate explains why bats are likely to use certain combinations of bandwidth and pulse duration to obtain such sweep rates.

  7. Excimer emission from pulsed microhollow cathode discharges in xenon

    SciTech Connect

    Lee, B.-J.; Nam, S. H.; Rahaman, H.; Iberler, M.; Jacoby, J.; Frank, K.

    2013-12-15

    Direct current (dc) microhollow cathode discharge (MHCD) is an intense source for excimer radiation in vacuum ultraviolet at a wavelength of 172 nm in a high pressure xenon (Xe) gas. The concentration of precursors for the excimer formation, i.e., excited and ionized gas atoms, increases significantly by applying high voltage pulse onto the dc MHCD over the pulse duration range from 20 to 100 ns. The intensity of the excimer emission for the voltage pulse of 20 ns duration exceeds that of the emission intensity obtained from the same MHCD operated only in the dc mode, by one order of magnitude. In addition, the emission intensity increases by one order of magnitude over the pulse duration range from 20 to 100 ns. It can be assumed that the emission intensity of the MHCD source increases as long as the duration of the high voltage pulse is shorter than the electron relaxation time. For the high voltage pulse of 100 ns duration, the emission intensity has been found to be further enhanced by a factor of three when the gas pressure is increased from 200 to 800 mbar.

  8. Excimer emission from pulsed microhollow cathode discharges in xenon

    NASA Astrophysics Data System (ADS)

    Lee, B.-J.; Rahaman, H.; Nam, S. H.; Iberler, M.; Jacoby, J.; Frank, K.

    2013-12-01

    Direct current (dc) microhollow cathode discharge (MHCD) is an intense source for excimer radiation in vacuum ultraviolet at a wavelength of 172 nm in a high pressure xenon (Xe) gas. The concentration of precursors for the excimer formation, i.e., excited and ionized gas atoms, increases significantly by applying high voltage pulse onto the dc MHCD over the pulse duration range from 20 to 100 ns. The intensity of the excimer emission for the voltage pulse of 20 ns duration exceeds that of the emission intensity obtained from the same MHCD operated only in the dc mode, by one order of magnitude. In addition, the emission intensity increases by one order of magnitude over the pulse duration range from 20 to 100 ns. It can be assumed that the emission intensity of the MHCD source increases as long as the duration of the high voltage pulse is shorter than the electron relaxation time. For the high voltage pulse of 100 ns duration, the emission intensity has been found to be further enhanced by a factor of three when the gas pressure is increased from 200 to 800 mbar.

  9. High-energy square pulses and burst-mode pulses in an all-normal dispersion double-clad mode-locked fiber laser

    NASA Astrophysics Data System (ADS)

    Qiao, Zhi; Wang, Xiaochao; Wang, Chao; Jing, Yuanyuan; Fan, Wei; Lin, Zunqi

    2016-05-01

    A double-clad Yb-doped mode-locked fiber laser that can operate in burst-mode and square-pulse states is experimentally investigated. In the burst-mode state, a burst train with 55 pulses of 500 ps duration is obtained. In the square-pulse state, which is similar to noiselike pulses, the maximum pulse energy is 820 nJ and the duration can be tuned from 15.8 to 546 ns. The square pulses have a narrow and multipeak spectrum, which is quite different from that of normal noiselike pulses. The fiber laser promises an alternative formation mechanism for burst-mode and square-pulse mode-locked fiber lasers.

  10. Extended Duration Orbiter Medical Project

    NASA Technical Reports Server (NTRS)

    Sawin, Charles F. (Editor); Taylor, Gerald R. (Editor); Smith, Wanda L. (Editor); Brown, J. Travis (Technical Monitor)

    1999-01-01

    Biomedical issues have presented a challenge to flight physicians, scientists, and engineers ever since the advent of high-speed, high-altitude airplane flight in the 1940s. In 1958, preparations began for the first manned space flights of Project Mercury. The medical data and flight experience gained through Mercury's six flights and the Gemini, Apollo, and Skylab projects, as well as subsequent space flights, comprised the knowledge base that was used to develop and implement the Extended Duration Orbiter Medical Project (EDOMP). The EDOMP yielded substantial amounts of data in six areas of space biomedical research. In addition, a significant amount of hardware was developed and tested under the EDOMP. This hardware was designed to improve data gathering capabilities and maintain crew physical fitness, while minimizing the overall impact to the microgravity environment. The biomedical findings as well as the hardware development results realized from the EDOMP have been important to the continuing success of extended Space Shuttle flights and have formed the basis for medical studies of crew members living for three to five months aboard the Russian space station, Mir. EDOMP data and hardware are also being used in preparation for the construction and habitation of International Space Station. All data sets were grouped to be non-attributable to individuals, and submitted to NASA s Life Sciences Data Archive.

  11. Icing Encounter Duration Sensitivity Study

    NASA Technical Reports Server (NTRS)

    Addy, Harold E., Jr.; Lee, Sam

    2011-01-01

    This paper describes a study performed to investigate how aerodynamic performance degradation progresses with time throughout an exposure to icing conditions. It is one of the first documented studies of the effects of ice contamination on aerodynamic performance at various points in time throughout an icing encounter. Both a 1.5 and 6 ft chord, two-dimensional, NACA-23012 airfoils were subjected to icing conditions in the NASA Icing Research Tunnel for varying lengths of time. At the end of each run, lift, drag, and pitching moment measurements were made. Measurements with the 1.5 ft chord model showed that maximum lift and pitching moment degraded more rapidly early in the exposure and degraded more slowly as time progressed. Drag for the 1.5 ft chord model degraded more linearly with time, although drag for very short exposure durations was slightly higher than expected. Only drag measurements were made with the 6 ft chord airfoil. Here, drag for the long exposures was higher than expected. Novel comparison of drag measurements versus an icing scaling parameter, accumulation parameter times collection efficiency was used to compare the data from the two different size model. The comparisons provided a means of assessing the level of fidelity needed for accurate icing simulation.

  12. Pulse compression using binary phase codes

    NASA Technical Reports Server (NTRS)

    Farley, D. T.

    1983-01-01

    In most MST applications pulsed radars are peak power limited and have excess average power capacity. Short pulses are required for good range resolution, but the problem of range ambiguity (signals received simultaneously from more than one altitude) sets a minimum limit on the interpulse period (IPP). Pulse compression is a technique which allows more of the transmitter average power capacity to be used without sacrificing range resolution. As the name implies, a pulse of power P and duration T is in a certain sense converted into one of power nP and duration T/n. In the frequency domain, compression involves manipulating the phases of the different frequency components of the pulse. One way to compress a pulse is via phase coding, especially binary phase coding, a technique which is particularly amenable to digital processing techniques. This method, which is used extensively in radar probing of the atmosphere and ionosphere is discussed. Barker codes, complementary and quasi-complementary code sets, and cyclic codes are addressed.

  13. Electrostatic Changes Observed with Narrow Bipolar Pulses

    NASA Astrophysics Data System (ADS)

    Karunarathne, S.; Marshall, T. C.; Stolzenburg, M.; Karunarathna, N.

    2015-12-01

    Narrow bipolar pulses (NBPs) or compact intracloud discharges are impulsive discharges that are considered to be the strongest natural emitters in the HF radio band; they usually occur at high altitudes in some thunderstorms. In the summer of 2011, we collected E-change data with wideband flat-plate antennas (0.16 Hz - 2.5 MHz) at ten stations covering an area of nearly 70 km x 100 km in and around Kennedy Space Center, Florida, USA. On one thunderstorm day, 14 August 2011, we detected 226 positive NBPs, and some observations of these pulses were published in Karunarathne et al. [2015, JGR-atmospheres]. Of these 226 NBPs, 50 (22.1 %) occurred within 10 km horizontally of at least one sensor. All of these closer sensors show electrostatic changes associated with corresponding NBPs, with a net electrostatic change in the main bipolar pulse and with a slower electrostatic change after the bipolar pulse that seems similar to short continuing current immediately after some cloud-to-ground return strokes. Although NBPs have been considered as short duration pulses (10 - 20 microseconds), the electrostatic changes after the main bipolar pulse ranged from 0.7 ms to 34 ms and associated charge moments were calculated. The total duration of the electrostatic E-change was strongly dependent on the distance to the sensors. In this presentation, we will present data for these electrostatic changes, some statistics, and physical background and reasoning for the electrostatic changes.

  14. Means and method for characterizing high power, ultra short laser pulses in a real time, on line manner

    DOEpatents

    Veligdan, J.T.

    1994-03-08

    An ultra short (<10 ps), high power laser pulse is temporally characterized by a system that uses a physical measurement of a wavefront that has been altered in a known manner. The system includes a first reflection switch to remove a portion of a pulse from a beam of pulses, then includes a second reflection switch, operating in a mode that is opposite to the first reflection switch, to slice off a portion of that removed portion. The sliced portion is then directed to a measuring device for physical measurement. The two reflection switches are arranged with respect to each other and with respect to the beam of ultra short pulses such that physical measurement of the sliced portion is related to the temporal measurement of the ultra short pulse by a geometric or trigonometric relationship. The reflection switches are operated by a control pulse that is directed to impinge on each of the reflection switches at a 90[degree] angle of incidence. 8 figures.

  15. Temporal compression of pulses from a 100-KHz-repetiton-rate femtosecond ytterbium laser

    NASA Astrophysics Data System (ADS)

    Didenko, N. V.; Konyashchenko, A. V.; Kostryukov, P. V.; Losev, L. L.; Pazyuk, V. S.; Tenyakov, S. Yu; Bryukhanov, V. V.

    2016-08-01

    We report the temporal compression a femtosecond ytterbium laser pulse at a pulse repetition rate of 100 kHz using the effect of nonlinear self-phase modulation in a gas-filled capillary. A 260-fs laser pulse is compressed down to 17 fs with an energy efficiency of 40%. An average radiation power at the compressor output is 2 W. At a second compression stage, the time contrast is increased and the pulse duration is reduced in the process of the second harmonic generation in a KDP crystal. The obtained pulses have a duration of 11 fs at an efficiency of 35%.

  16. Visual duration aftereffect is position invariant

    PubMed Central

    Li, Baolin; Yuan, Xiangyong; Chen, Youguo; Liu, Peiduo; Huang, Xiting

    2015-01-01

    Adaptation to relatively long or short sensory events leads to a negative aftereffect, such that the durations of the subsequent events within a certain range appear to be contracted or expanded. The distortion in perceived duration is presumed to arise from the adaptation of duration detectors. Here, we focus on the positional sensitivity of those visual duration detectors by exploring whether the duration aftereffect may be constrained by the visual location of stimuli. We adopted two different paradigms, one that tests for transfer across visual hemifields, and the other that tests for simultaneous selectivity between visual hemifields. By employing these experimental designs, we show that the duration aftereffect strongly transfers across visual hemifields and is not contingent on them. The lack of position specificity suggests that duration detectors in the visual system may operate at a relatively later stage of sensory processing. PMID:26500591

  17. Pulsed mid-infrared radiation from spectral broadening in laser wakefield simulations

    SciTech Connect

    Zhu, W.; Palastro, J. P.; Antonsen, T. M.

    2013-07-15

    Spectral red-shifting of high power laser pulses propagating through underdense plasma can be a source of ultrashort mid-infrared (MIR) radiation. During propagation, a high power laser pulse drives large amplitude plasma waves, depleting the pulse energy. At the same time, the large amplitude plasma wave provides a dynamic dielectric response that leads to spectral shifting. The loss of laser pulse energy and the approximate conservation of laser pulse action imply that spectral red-shifts accompany the depletion. In this paper, we investigate, through simulation, the parametric dependence of MIR generation on pulse energy, initial pulse duration, and plasma density.

  18. Three-wave mixing mediated femtosecond pulse compression in β-barium borate.

    PubMed

    Grün, A; Austin, Dane R; Cousin, Seth L; Biegert, J

    2015-10-15

    Nonlinear pulse compression mediated by three-wave mixing is demonstrated for ultrashort Ti:sapphire pulses in a type II phase-matched β-barium borate (BBO) crystal using noncollinear geometry. 170 μJ pulses at 800 nm with a pulse duration of 74 fs are compressed at their sum frequency to 32 fs with 55 μJ of pulse energy. Experiments and computer simulations demonstrate the potential of sum-frequency pulse compression to match the group velocities of the interacting waves to crystals that were initially not considered in the context of nonlinear pulse compression.

  19. High energy femtosecond pulse compression

    NASA Astrophysics Data System (ADS)

    Lassonde, Philippe; Mironov, Sergey; Fourmaux, Sylvain; Payeur, Stéphane; Khazanov, Efim; Sergeev, Alexander; Kieffer, Jean-Claude; Mourou, Gerard

    2016-07-01

    An original method for retrieving the Kerr nonlinear index was proposed and implemented for TF12 heavy flint glass. Then, a defocusing lens made of this highly nonlinear glass was used to generate an almost constant spectral broadening across a Gaussian beam profile. The lens was designed with spherical curvatures chosen in order to match the laser beam profile, such that the product of the thickness with intensity is constant. This solid-state optics in combination with chirped mirrors was used to decrease the pulse duration at the output of a terawatt-class femtosecond laser. We demonstrated compression of a 33 fs pulse to 16 fs with 170 mJ energy.

  20. An improved rolled strip pulse forming line

    NASA Astrophysics Data System (ADS)

    Li, Song; Qian, Bao-Liang; Yang, Han-Wu; Gao, Jing-Ming; Liu, Zhao-Xi

    2013-06-01

    The rolled strip pulse forming line (RSPFL) has advantages of compactness, portability, and long pulse achievability which could well meet the requirements of industrial application of the pulse power technology. In this paper, an improved RSPFL with an additional insulator between the grounded conductors is investigated numerically and experimentally. Results demonstrate that the jitter on the flat-top of the output voltage waveform is reduced to 3.8% due to the improved structure. Theoretical analysis shows that the electromagnetic coupling between the conductors of the RSPFL strongly influences the output voltage waveform. Therefore, the new structure was designed to minimize the detrimental effect of the electromagnetic coupling. Simulation results show that the electromagnetic coupling can be efficiently reduced in the improved RSPFL. Experimental results illustrate that the improved RSPFL, with dimensions and weight of Φ 290 × 250 mm and 16 kg, when used as a simple pulse forming line, could generate a well shaped quasi-square pulse with output power of hundreds of MW and pulse duration of 250 ns. Importantly, the improved RSPFL was successfully used as a Blumlein pulse forming line, and a 10.8 kV, 260 ns quasi-square pulse was obtained on a 2 Ω dummy load. Experiments show reasonable agreement with numerical analysis.

  1. Laser induced forward transfer of metals by temporally shaped femtosecond laser pulses.

    PubMed

    Klini, A; Loukakos, P A; Gray, D; Manousaki, A; Fotakis, C

    2008-07-21

    Temporally shaped, femtosecond laser pulses have been used for controlling the size and the morphology of micron-sized metallic structures obtained by using the Laser Induced Forward Transfer (LIFT) technique. We report the effect of pulse shaping on the size and morphology of the deposited structures of Au, Zn, Cr on a function of the pulse separation time ??t (from 0 to 10 ps) of double pulses of variable intensities generated by using a liquid crystal spatial light modulator (SLM). The observed differences in size and morphology are correlated with the outcome of pump-probe experiments for the study of electron-phonon scattering dynamics and subsequent energy transfer processes to the bulk in the different metals employed. We propose that in metals with weak electron-lattice coupling, the electron ballistic motion and the resulting fast electron scattering at the film surface, as well as the internal electron thermalization process are crucial to the morphology and size of the transferred material. Therefore, temporal shaping within the corresponding time scales of these processes may be used for tailoring the features of the metallic structures obtained by LIFT.

  2. High duty cycle pulses suppress orientation flights of crambid moths.

    PubMed

    Nakano, Ryo; Ihara, Fumio; Mishiro, Koji; Toyama, Masatoshi; Toda, Satoshi

    2015-12-01

    Bat-and-moth is a good model system for understanding predator-prey interactions resulting from interspecific coevolution. Night-flying insects have been under predation pressure from echolocating bats for 65Myr, pressuring vulnerable moths to evolve ultrasound detection and evasive maneuvers as counter tactics. Past studies of defensive behaviors against attacking bats have been biased toward noctuoid moth responses to short duration pulses of low-duty-cycle (LDC) bat calls. Depending on the region, however, moths have been exposed to predation pressure from high-duty-cycle (HDC) bats as well. Here, we reveal that long duration pulse of the sympatric HDC bat (e.g., greater horseshoe bat) is easily detected by the auditory nerve of Japanese crambid moths (yellow peach moth and Asian corn borer) and suppress both mate-finding flights of virgin males and host-finding flights of mated females. The hearing sensitivities for the duration of pulse stimuli significantly dropped non-linearly in both the two moth species as the pulse duration shortened. These hearing properties support the energy integrator model; however, the threshold reduction per doubling the duration has slightly larger than those of other moth species hitherto reported. And also, Asian corn borer showed a lower auditory sensitivity and a lower flight suppression to short duration pulse than yellow peach moth did. Therefore, flight disruption of moth might be more frequently achieved by the pulse structure of HDC calls. The combination of long pulses and inter-pulse intervals, which moths can readily continue detecting, will be useful for repelling moth pests.

  3. High duty cycle pulses suppress orientation flights of crambid moths.

    PubMed

    Nakano, Ryo; Ihara, Fumio; Mishiro, Koji; Toyama, Masatoshi; Toda, Satoshi

    2015-12-01

    Bat-and-moth is a good model system for understanding predator-prey interactions resulting from interspecific coevolution. Night-flying insects have been under predation pressure from echolocating bats for 65Myr, pressuring vulnerable moths to evolve ultrasound detection and evasive maneuvers as counter tactics. Past studies of defensive behaviors against attacking bats have been biased toward noctuoid moth responses to short duration pulses of low-duty-cycle (LDC) bat calls. Depending on the region, however, moths have been exposed to predation pressure from high-duty-cycle (HDC) bats as well. Here, we reveal that long duration pulse of the sympatric HDC bat (e.g., greater horseshoe bat) is easily detected by the auditory nerve of Japanese crambid moths (yellow peach moth and Asian corn borer) and suppress both mate-finding flights of virgin males and host-finding flights of mated females. The hearing sensitivities for the duration of pulse stimuli significantly dropped non-linearly in both the two moth species as the pulse duration shortened. These hearing properties support the energy integrator model; however, the threshold reduction per doubling the duration has slightly larger than those of other moth species hitherto reported. And also, Asian corn borer showed a lower auditory sensitivity and a lower flight suppression to short duration pulse than yellow peach moth did. Therefore, flight disruption of moth might be more frequently achieved by the pulse structure of HDC calls. The combination of long pulses and inter-pulse intervals, which moths can readily continue detecting, will be useful for repelling moth pests. PMID:26549128

  4. Duration perception in crossmodally-defined intervals.

    PubMed

    Mayer, Katja M; Di Luca, Massimiliano; Ernst, Marc O

    2014-03-01

    How humans perform duration judgments with multisensory stimuli is an ongoing debate. Here, we investigated how sub-second duration judgments are achieved by asking participants to compare the duration of a continuous sound to the duration of an empty interval in which onset and offset were marked by signals of different modalities using all combinations of visual, auditory and tactile stimuli. The pattern of perceived durations across five stimulus durations (ranging from 100 ms to 900 ms) follows the Vierordt Law. Furthermore, intervals with a sound as onset (audio-visual, audio-tactile) are perceived longer than intervals with a sound as offset. No modality ordering effect is found for visualtactile intervals. To infer whether a single modality-independent or multiple modality-dependent time-keeping mechanisms exist we tested whether perceived duration follows a summative or a multiplicative distortion pattern by fitting a model to all modality combinations and durations. The results confirm that perceived duration depends on sensory latency (summative distortion). Instead, we did not find evidence for multiplicative distortions. The results of the model and the behavioural data support the concept of a single time-keeping mechanism that allows for judgments of durations marked by multisensory stimuli. PMID:23953664

  5. Duration tuning in the mouse auditory midbrain.

    PubMed

    Brand, A; Urban, R; Grothe, B

    2000-10-01

    Temporal cues, including sound duration, are important for sound identification. Neurons tuned to the duration of pure tones were first discovered in the auditory system of frogs and bats and were discussed as specific adaptations in these animals. More recently duration sensitivity has also been described in the chinchilla midbrain and the cat auditory cortex, indicating that it might be a more general phenomenon than previously thought. However, it is unclear whether duration tuning in mammals is robust in face of changes of stimulus parameters other than duration. Using extracellular single-cell recordings in the mouse inferior colliculus, we found 55% of cells to be sensitive to stimulus duration showing long-pass, short-pass, or band-pass filter characteristics. For most neurons, a change in some other stimulus parameter, (e.g., intensity, frequency, binaural conditions, or using noise instead of pure tones) altered and sometimes abolished duration-tuning characteristics. Thus in many neurons duration tuning is interdependent with other stimulus parameters and, hence, might be context dependent. A small number of inferior colliculus neurons, in particular band-pass neurons, exhibited stable filter characteristics and could therefore be referred to as "duration selective." These findings support the idea that duration tuning is a general phenomenon in the mammalian auditory system.

  6. Standardization of Rocket Engine Pulse Time Parameters

    NASA Technical Reports Server (NTRS)

    Larin, Max E.; Lumpkin, Forrest E.; Rauer, Scott J.

    2001-01-01

    Plumes of bipropellant thrusters are a source of contamination. Small bipropellant thrusters are often used for spacecraft attitude control and orbit correction. Such thrusters typically operate in a pulse mode, at various pulse lengths. Quantifying their contamination effects onto spacecraft external surfaces is especially important for long-term complex-geometry vehicles, e.g. International Space Station. Plume contamination tests indicated the presence of liquid phase contaminant in the form of droplets. Their origin is attributed to incomplete combustion. Most of liquid-phase contaminant is generated during the startup and shutdown (unsteady) periods of thruster pulse. These periods are relatively short (typically 10-50 ms), and the amount of contaminant is determined by the thruster design (propellant valve response, combustion chamber size, thruster mass flow rate, film cooling percentage, dribble volume, etc.) and combustion process organization. Steady-state period of pulse is characterized by much lower contamination rates, but may be lengthy enough to significantly conh'ibute to the overall contamination effect. Because there was no standard methodology for thruster pulse time division, plume contamination tests were conducted at various pulse durations, and their results do not allow quantifying contaminant amounts from each portion of the pulse. At present, the ISS plume contamination model uses an assumption that all thrusters operate in a pulse mode with the pulse length being 100 ms. This assumption may lead to a large difference between the actual amounts of contaminant produced by the thruster and the model predictions. This paper suggests a way to standardize thruster startup and shutdown period definitions, and shows the usefulness of this approach to better quantify thruster plume contamination. Use of the suggested thruster pulse time-division technique will ensure methodological consistency of future thruster plume contamination test programs

  7. The effects of steep-front, short-duration impulses on power distribution components

    SciTech Connect

    Miller, D.B.; Lux, A.E.; Grzybowski, Stanislaw; Barnes, P.R.

    1989-07-01

    A line type pulser has been developed to test the effects of steep-front, short duration (SFSD) pulses on distribution components. Risetime is 50-100 ns, and pulse duration is on the order of 300 ns. Terminators often shattered or punctured rather than flashing over. Insulator flashover voltage is approximately 1.5 times CFO for standard lightning impulses. Arresters exhibit an inductive character, with SFSD peak voltage at 10 kA approximately 4--5 times the 8 /times/ 20 microsecond 10 kA discharge voltage. Polyethylene insulated cable has a characteristic degradation in which failure voltage decreases with number of SFSD pulses. 7 refs., 12 figs., 2 tabs.

  8. Short-duration galvanic vestibular stimulation evokes prolonged balance responses.

    PubMed

    Son, Gregory Martin Lee; Blouin, Jean-Sébastien; Inglis, John Timothy

    2008-10-01

    The application of galvanic vestibular stimulation (GVS) evokes distinct responses in lower limb muscles involved in the control of balance. The purpose of this study was to investigate the balance and lower limb muscle responses to short-duration GVS and to determine whether these responses are modulated by small changes in center of gravity (CoG) and baseline muscle activity occurring during quiet standing. Twelve subjects stood quietly on a force plate with their feet together and were instructed to look straight ahead. One thousand twenty-four GVS stimuli (4 mA, 20-ms pulses) were delivered bilaterally to the mastoid processes in a bipolar, binaural configuration. Bilateral surface electromyography (EMG) from soleus (Sol) and tibialis anterior (TA) and ground reaction forces were recorded. EMG and force responses were trigger averaged at the onset of the GVS pulse. Short-duration GVS applied during quiet standing with the head facing forward evoked characteristic balance responses and biphasic modulation of all muscles with the same polarity for ipsilateral Sol and TA. The amplitude of the GVS-evoked muscle responses was modulated by both the estimated position of the subject's CoG and the background activation of the recorded muscle. Muscle-dependent modulations of the GVS-evoked muscle responses were observed: the Sol responses decreased, while the TA responses increased when the CoG position shifted toward the heels. The well-defined balance responses evoked by short-duration GVS are important to acknowledge when studying the vestibulo-motor responses in healthy subjects and patient populations.

  9. ADJUSTABLE DOUBLE PULSE GENERATOR

    DOEpatents

    Gratian, J.W.; Gratian, A.C.

    1961-08-01

    >A modulator pulse source having adjustable pulse width and adjustable pulse spacing is described. The generator consists of a cross coupled multivibrator having adjustable time constant circuitry in each leg, an adjustable differentiating circuit in the output of each leg, a mixing and rectifying circuit for combining the differentiated pulses and generating in its output a resultant sequence of negative pulses, and a final amplifying circuit for inverting and square-topping the pulses. (AEC)

  10. [Experimental investigation of the collection efficiency of a PTW Roos ionization chamber irradiated with pulsed beams at high pulse dose with different pulse lengths].

    PubMed

    Karsch, Leonhard; Richter, Christian; Pawelke, Jörg

    2011-01-01

    In gas-filled ionization chambers as radiation detectors, the collection of the charge carriers is affected by the recombination effect. In dosimetry this effect must be accounted for by the saturation correction factor k(S). The physical description of the correction factor by Boag, Hochhäuser and Balk for pulsed radiation is well established. However, this description is only accurate when the pulse length is short compared to the collection time of the ionization chamber. In this work experimental investigations of the saturation correction factor have been made for pulses of 4 μ s up to pulse doses of about 230 mGy, and the theory of Boag, Hochhäuser and Balk was again confirmed. For longer pulses, however, the correction factor decreases and at a pulse duration of about 200μs reaches 75% of the value valid for short pulses. This reduced influence of the ion recombination is interpreted by the reaction kinetics of ion recombination as a second-order reaction. This effect is negligible for PTW Roos chambers at clinical linear accelerators with 4 μ s pulse duration for pulse doses up to 120 mGy.

  11. The ESRF Miniature Pulsed Magnetic Field System

    SciTech Connect

    Linden, Peter J. E. M. van der; Strohm, Cornelius; Roth, Thomas; Detlefs, Carsten; Mathon, Olivier

    2010-06-23

    We have developed a portable system to provide pulsed magnetic fields on the ESRF X-ray beamlines. The complete system consists of a power supply, liquid Helium and liquid Nitrogen dewars with a siphon each, control electronics and a double cryostat for separate coil and sample cooling. The liquid nitrogen cooled solenoids reach a maximum field of 30 Tesla for a total pulse duration of one milisecond. They are constructed for optimised cooling rate after the pulse to obtain a high duty cycle, the repetition rate is five pulses per minute at maximum field. The sample is cooled in an independent Helium flow cryostat which is inserted into the bore of the magnet. The flow cryostat has a temperature range from 5 to 250 Kelvin with a direct contact between the sample and Helium flow. This overview gives a general presentation of the system and we will show recent results.

  12. Passive imaging with pulsed ultrasound insonations.

    PubMed

    Haworth, Kevin J; Mast, T Douglas; Radhakrishnan, Kirthi; Burgess, Mark T; Kopechek, Jonathan A; Huang, Shao-Ling; McPherson, David D; Holland, Christy K

    2012-07-01

    Previously, passive cavitation imaging has been described in the context of continuous-wave high-intensity focused ultrasound thermal ablation. However, the technique has potential use as a feedback mechanism for pulsed-wave therapies, such as ultrasound-mediated drug delivery. In this paper, results of experiments and simulations are reported to demonstrate the feasibility of passive cavitation imaging using pulsed ultrasound insonations and how the images depend on pulsed ultrasound parameters. The passive cavitation images were formed from channel data that was beamformed in the frequency domain. Experiments were performed in an invitro flow phantom with an experimental echo contrast agent, echogenic liposomes, as cavitation nuclei. It was found that the pulse duration and envelope have minimal impact on the image resolution achieved. The passive cavitation image amplitude scales linearly with the cavitation emission energy. Cavitation images for both stable and inertial cavitation can be obtained from the same received data set.

  13. The ESRF Miniature Pulsed Magnetic Field System

    NASA Astrophysics Data System (ADS)

    van der Linden, Peter J. E. M.; Strohm, Cornelius; Roth, Thomas; Detlefs, Carsten; Mathon, Olivier

    2010-06-01

    We have developed a portable system to provide pulsed magnetic fields on the ESRF X-ray beamlines. The complete system consists of a power supply, liquid Helium and liquid Nitrogen dewars with a siphon each, control electronics and a double cryostat for separate coil and sample cooling. The liquid nitrogen cooled solenoids reach a maximum field of 30 Tesla for a total pulse duration of one milisecond. They are constructed for optimised cooling rate after the pulse to obtain a high duty cycle, the repetition rate is five pulses per minute at maximum field. The sample is cooled in an independent Helium flow cryostat which is inserted into the bore of the magnet. The flow cryostat has a temperature range from 5 to 250 Kelvin with a direct contact between the sample and Helium flow. This overview gives a general presentation of the system and we will show recent results.

  14. A pulsed cathodic arc spacecraft propulsion system

    NASA Astrophysics Data System (ADS)

    Neumann, P. R. C.; Bilek, M. M. M.; Tarrant, R. N.; McKenzie, D. R.

    2009-11-01

    We investigate the use of a centre-triggered cathodic arc as a spacecraft propulsion system that uses an inert solid as a source of plasma. The cathodic vacuum arc produces almost fully ionized plasma with a high exhaust velocity (>104 m s-1), giving a specific impulse competitive with other plasma or ion thrusters. A centre trigger design is employed that enables efficient use of cathode material and a high pulse-to-pulse repeatability. We compare three anode geometries, two pulse current profiles and two pulse durations for their effects on impulse generation, energy and cathode material usage efficiency. Impulse measurement is achieved through the use of a free-swinging pendulum target constructed from a polymer material. Measurements show that impulse is accurately controlled by varying cathode current. The cylindrical anode gave the highest energy efficiency. Cathode usage is optimized by choosing a sawtooth current profile. There is no requirement for an exhaust charge neutralization system.

  15. Ablation characteristics of quantum square pulse mode dental erbium laser

    NASA Astrophysics Data System (ADS)

    Lukač, Nejc; Suhovršnik, Tomaž; Lukač, Matjaž; Jezeršek, Matija

    2016-01-01

    Erbium lasers are by now an accepted tool for performing ablative medical procedures, especially when minimal invasiveness is desired. Ideally, a minimally invasive laser cutting procedure should be fast and precise, and with minimal pain and thermal side effects. All these characteristics are significantly influenced by laser pulse duration, albeit not in the same manner. For example, high cutting efficacy and low heat deposition are characteristics of short pulses, while vibrations and ejected debris screening are less pronounced at longer pulse durations. We report on a study of ablation characteristics on dental enamel and cementum, of a chopped-pulse Er:YAG [quantum square pulse (QSP)] mode, which was designed to reduce debris screening during an ablation process. It is shown that in comparison to other studied standard Er:YAG and Er,Cr:YSGG laser pulse duration modes, the QSP mode exhibits the highest ablation drilling efficacy with lowest heat deposition and reduced vibrations, demonstrating that debris screening has a considerable influence on the ablation process. By measuring single-pulse ablation depths, we also show that tissue desiccation during the consecutive delivery of laser pulses leads to a significant reduction of the intrinsic ablation efficacy that cannot be fully restored under clinical settings by rehydrating the tooth using an external water spray.

  16. Effects of nanosecond-duration laser prepulses on solid targets

    SciTech Connect

    Wharton, K.B.; Kim, J.M.; Stuart, B.C.

    2005-05-15

    A critical issue in high-intensity laser-solid interactions is the effect of the laser prepulse on the target, but the experimental details of these lower-intensity interactions are often difficult to measure due to the subsequent high-intensity pulse. We have performed target experiments using a 0.5-ns duration, 800-nm wavelength laser pulse, specifically designed to mimic the typical amplified spontaneous emission (ASE) prepulse from a high-power Ti:Sapphire laser. Using this ''artificial'' ASE prepulse, we find that the threshold for relevant changes to typical solid targets occurs at a fluence of {approx}0.1 J/cm{sup 2}, or {approx}10{sup 8} W/cm{sup 2}, well below the plasma formation threshold. Notably, the results are not consistent with simple surface vaporization, and suggest that the ASE prepulse causes multiatom clusters to be ejected from the target surface. In a full high-intensity experiment, this ablated material would then strongly interact with the subsequent primary laser pulse.

  17. Multiple Access in Ultra-Wideband Communications Using Multiple Pulses

    SciTech Connect

    Nekoogar, F; Dowla, F

    2003-04-11

    Multiple access (MA) in UWB communication is an area of active research. To date several time-division or code-division pulse amplitude modulation (PAM) or pulse position modulation (PPM) schemes have been proposed to separate multiple users in UWB communications. Conventionally, all users employ the same pulse shape and modulate the transmit pulse based on changing amplitude or position. One concern with using the same pulse for all channels is that the multiple access interference (MAI) increases as the number of users increase. This is due to increased cross-correlation between similar pulses of the different channels, raising thus the noise floor in such systems. In this paper we introduce and study the performance of a new MA scheme in the context of multiple orthogonal transmitted-reference (T-R) short duration (nsec) chirp pulses in the presence of multipath and additive white Gaussian noise (AWGN).

  18. Experimental verification and analysis of wavelength effect on pulse stretching and compressing in mid-IR chirped-pulse amplification

    NASA Astrophysics Data System (ADS)

    Zhong, Haizhe; Yuan, Peng; Zhao, Kun; Zhang, Lifu; Ma, Jingui; Li, Ying; Fan, Dianyuan

    2016-02-01

    As a consequence of the general experimental challenge to detect signals in mid-IR range, taking dispersive chirped near-IR laser pulses as the injected signal source seems to be an artistic route avoiding the daunting mid-IR stretcher and constantly was applied in moderate energy mid-IR optical parametric chirped-pulse amplifications (OPCPA) systems. In this paper we study the wavelength effect on pulse stretching and compressing in detail. Beginning with the theoretical analysis on each dispersion term of grating pairs, we evaluate the residual dispersions when pulse stretcher and compressor work at distinct wavelengths, which shows that this wavelength effect will result in poorly compressed pulses far from transform-limited. Via proof-of-principle experiments based on mid-IR OPCPAs and corresponding numerical simulations, we show that this artful configuration led to un-compressible pulses of ∼2 ps with a time-bandwidth product of ∼ 10 when the chirped-pulse duration is ∼400 ps. To overcome this effect, we demonstrate a simple design of pulse stretcher and compressor. The presented design consisted of a reflection grism-pair compressor can simultaneously cancel the quadric and cubic dispersions of conventional grating based stretcher, showing a potential ability of supporting high-contrast, sub-100-fs pulse-duration and 10,000× of pulse expansion.

  19. Investigation of Fe:ZnSe laser in pulsed and repetitively pulsed regimes

    SciTech Connect

    Velikanov, S D; Zaretskiy, N A; Zotov, E A; Maneshkin, A A; Chuvatkin, R S; Yutkin, I M; Kozlovsky, V I; Korostelin, Yu V; Krokhin, O N; Podmar'kov, Yu P; Savinova, S A; Skasyrsky, Ya K; Frolov, M P

    2015-01-31

    The characteristics of a Fe:ZnSe laser pumped by a single-pulse free-running Er : YAG laser and a repetitively pulsed HF laser are presented. An output energy of 4.9 J is achieved in the case of liquid-nitrogen cooling of the Fe{sup 2+}:ZnSe active laser element longitudinally pumped by an Er:YAG laser with a pulse duration of 1 ms and an energy up to 15 J. The laser efficiency with respect to the absorbed energy is 47%. The output pulse energy at room temperature is 53 mJ. The decrease in the output energy is explained by a strong temperature dependence of the upper laser level lifetime and by pulsed heating of the active element. The temperature dependence of the upper laser level lifetime is used to determine the pump parameters needed to achieve high pulse energies at room temperature. Stable repetitively-pulsed operation of the Fe{sup 2+}:ZnSe laser at room temperature with an average power of 2.4 W and a maximum pulse energy of 14 mJ is achieved upon pumping by a 1-s train of 100-ns HF laser pulses with a repetition rate of 200 Hz. (lasers)

  20. Colliding pulse mode-locked VECSEL

    NASA Astrophysics Data System (ADS)

    Marah, Declan; Laurain, Alexandre; Stolz, Wolfgang; Koch, Stephan; Ruiz Perez, Antje; McInerney, John; Moloney, Jerome

    2016-03-01

    Recent development of high power femtosecond pulse modelocked VECSEL with gigahertz pulse repetition rates sparked an increased interest from the scientific community due to the broad field of applications for such sources, such as frequency metrology, high-speed optical communication systems or high-resolution optical sampling. To the best of our knowledge, we report for the first time a colliding pulse modelocked VECSEL, where the VECSEL gain medium and a semiconductor saturable absorber (SESAM) are placed inside a ring cavity. This cavity geometry provides both a practical and an efficient way to get optimum performance from a modelocked laser system. The two counter propagating pulses in our ring cavity synchronize in the SESAM because the minimum energy is lost when they saturate the absorber together. This stronger saturation of the absorber increases the stability of the modelocking and reduces the overall losses of the laser for a given intra-cavity fluence, leading to a lower modelocking threshold. This also allows the generation of fundamental modelocking at a relatively low repetition rate (pulse repetition rate of 1GHz and a pulse duration ranging from 1ps to 3ps. The emitted spectrum was centered at 1007nm with a FWHM of 3.1nm, suggesting that shorter pulses can be obtained with adequate dispersion compensation. The laser characteristics such as the pulse duration and stability are studied in detail.

  1. An optimization principle for determining movement duration.

    PubMed

    Tanaka, Hirokazu; Krakauer, John W; Qian, Ning

    2006-06-01

    Movement duration is an integral component of motor control, but nearly all extant optimization models of motor planning prefix duration instead of explaining it. Here we propose a new optimization principle that predicts movement duration. The model assumes that the brain attempts to minimize movement duration under the constraint of meeting an accuracy criterion. The criterion is task and context dependent but is fixed for a given task and context. The model determines a unique duration as a trade-off between speed (time optimality) and accuracy (acceptable endpoint scatter). We analyzed the model for a linear motor plant, and obtained a closed-form equation for determining movement duration. By solving the equation numerically with specific plant parameters for the eye and arm, we found that the model can reproduce saccade duration as a function of amplitude (the main sequence), and arm-movement duration as a function of the ratio of target distance to size (Fitts's law). In addition, it explains the dependency of peak saccadic speed on amplitude and the dependency of saccadic duration on initial eye position. Furthermore, for arm movements, the model predicts a scaling relationship between peak velocity and distance and a reduction in movement duration with a moderate increase in viscosity. Finally, for a linear plant, our model predicts a neural control signal identical to that of the minimum-variance model set to the same movement duration. This control signal is a smooth function of time (except at the endpoint), in contrast to the discontinuous bang-bang control found in the time-optimal control literature. We suggest that one aspect of movement planning, as revealed by movement duration, may be to assign an endpoint accuracy criterion for a given task and context. PMID:16571740

  2. 5 CFR 890.1302 - Duration.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... EMPLOYEES HEALTH BENEFITS PROGRAM Department of Defense Federal Employees Health Benefits Program Demonstration Project § 890.1302 Duration. The demonstration project will run from January 1, 2000,...

  3. 5 CFR 330.1102 - Duration.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... PLACEMENT (GENERAL) Federal Employment Priority Consideration Program for Displaced Employees of the District of Columbia Department of Corrections § 330.1102 Duration. This program terminates 1 year...

  4. CO{sub 2} laser pulse shortening by laser ablation of a metal target

    SciTech Connect

    Donnelly, T.; Mazoyer, M.; Lynch, A.; O'Sullivan, G.; O'Reilly, F.; Dunne, P.; Cummins, T.

    2012-03-15

    A repeatable and flexible technique for pulse shortening of laser pulses has been applied to transversely excited atmospheric (TEA) CO{sub 2} laser pulses. The technique involves focusing the laser output onto a highly reflective metal target so that plasma is formed, which then operates as a shutter due to strong laser absorption and scattering. Precise control of the focused laser intensity allows for timing of the shutter so that different temporal portions of the pulse can be reflected from the target surface before plasma formation occurs. This type of shutter enables one to reduce the pulse duration down to {approx}2 ns and to remove the low power, long duration tails that are present in TEA CO{sub 2} pulses. The transmitted energy is reduced as the pulse duration is decreased but the reflected power is {approx}10 MW for all pulse durations. A simple laser heating model verifies that the pulse shortening depends directly on the plasma formation time, which in turn is dependent on the applied laser intensity. It is envisaged that this plasma shutter will be used as a tool for pulse shaping in the search for laser pulse conditions to optimize conversion efficiency from laser energy to useable extreme ultraviolet (EUV) radiation for EUV source development.

  5. Cooperative pulses for pseudo-pure state preparation

    NASA Astrophysics Data System (ADS)

    Wei, Daxiu; Chang, Yan; Glaser, Steffen J.; Yang, Xiaodong

    2014-06-01

    Using an extended version of the optimal-control-based gradient ascent pulse engineering algorithm, cooperative (COOP) pulses are designed for multi-scan experiments to prepare pseudo-pure states in quantum computation. COOP pulses can cancel undesired signal contributions, complementing and generalizing phase cycles. They also provide more flexibility and, in particular, eliminate the need to select specific individual target states and achieve the fidelity of theoretical limit by flexibly choosing appropriate number of scans and duration of pulses. The COOP approach is experimentally demonstrated for three-qubit and four-qubit systems.

  6. Cooperative pulses for pseudo-pure state preparation

    SciTech Connect

    Wei, Daxiu; Chang, Yan; Yang, Xiaodong E-mail: xiaodong.yang@sibet.ac.cn; Glaser, Steffen J. E-mail: xiaodong.yang@sibet.ac.cn

    2014-06-16

    Using an extended version of the optimal-control-based gradient ascent pulse engineering algorithm, cooperative (COOP) pulses are designed for multi-scan experiments to prepare pseudo-pure states in quantum computation. COOP pulses can cancel undesired signal contributions, complementing and generalizing phase cycles. They also provide more flexibility and, in particular, eliminate the need to select specific individual target states and achieve the fidelity of theoretical limit by flexibly choosing appropriate number of scans and duration of pulses. The COOP approach is experimentally demonstrated for three-qubit and four-qubit systems.

  7. Pulse Splitting in Short Wavelength Seeded Free Electron Lasers

    SciTech Connect

    Labat, M.; Couprie, M. E.; Joly, N.; Bruni, C.

    2009-12-31

    We investigate a fundamental limitation occurring in vacuum ultraviolet and extreme ultraviolet seeded free electron lasers (FELs). For a given electron beam and undulator configuration, an increase of the FEL output energy at saturation can be obtained via an increase of the seed pulse duration. We put in evidence a complex spatiotemporal deformation of the amplified pulse, leading ultimately to a pulse splitting effect. Numerical studies of the Colson-Bonifacio FEL equations reveal that slippage length and seed laser pulse wings are core ingredients of the dynamics.

  8. Towards attosecond X-ray pulses from the FEL

    SciTech Connect

    Zholents, Alexander A.; Fawley, William M.

    2004-07-01

    The ability to study ultrafast phenomena has been recently advanced by the demonstrated production and measurement of a single, 650-attosecond (10{sup 18} sec), VUV x-ray pulse[1] and, latter, a 250-attosecond pulse[2]. The next frontier is a production of the x-ray pulses with shorter wavelengths and in a broader spectral range. Several techniques for a generation of an isolated, attosecond duration, short-wavelength x-ray pulse based upon the ponderomotive laser acceleration [3], SASE and harmonic cascade FELs ([4] - [6]) had been already proposed. In this paper we briefly review a technique proposed in [5] and present some new results.

  9. Noncollinear gating for high-flux isolated-attosecond-pulse generation

    NASA Astrophysics Data System (ADS)

    Zhong, Shiyang; He, Xinkui; Jiang, Yujiao; Teng, Hao; He, Peng; Liu, Yangyang; Zhao, Kun; Wei, Zhiyi

    2016-03-01

    We propose an approach for producing high-flux isolated-attosecond pulses (IAPs) based on noncollinear geometry of high-order harmonic generation (HHG). By combining a main driving pulse and an ultrashort gating pulse in the interaction medium to form a tilt wave front in a very narrow overlapping time region, the attosecond pulses generated in this region are spatially separated from the original beam in the far field. It gives a way of extracting IAPs as well as fully characterizing an attosecond-pulse train (APT). Since this approach set no restriction on the pulse duration of the main driving pulse, it is particularly suitable for high-flux IAP generation by a high-energy laser which usually has multicycle pulse duration.

  10. Propagation of ultrashort laser pulses through water.

    PubMed

    Li, Jianchao; Alexander, Dennis R; Zhang, Haifeng; Parali, Ufuk; Doerr, David W; Bruce, John C; Wang, Hao

    2007-02-19

    In this paper, propagation of ultrashort pulses through a long 3.5 meter water channel was studied. Of particular interest was the attenuation of the beam at various lengths along the variable path length and to find an explanation of why the attenuation deviates from typical Beer Lambert law around 3 meters for ultrashort laser pulse transmission. Laser pulses of 10 fs at 75 MHz, 100 fs at 80 MHz and 300 fs at 1 KHz were employed to investigate the effects of pulse duration, spectrum and repetition rate on the attenuation after propagating through water up to 3 meters. Stretched pulse attenuation measurements produced from 10 fs at a frequency of 75 MHz were compared with the 10 fs attenuation measurements. Results indicate that the broad spectrum of the ultrashort pulse is the dominant reason for the observed decrease in attenuation after 3 meters of travel in a long water channel. The repetition rate is found not to play a significant role at least for the long pulse scenario in this reported attenuation studies. PMID:19532433

  11. Ultrashort pulse laser microsurgery on cell

    NASA Astrophysics Data System (ADS)

    Wang, He Z.; Huang, Xu G.; Zheng, Xiguang; Yu, Zhenxin; Gao, Zhaolan

    1995-05-01

    A laser microbeam system has been set up for microsurgery on cell. The relations of laser wavelength, pulse duration and pulse energy to punching effects and self-healing are studied. The experimental results demonstrate that picosecond pulse laser microbeam offers many advantages in cell microsurgery. The mechanism of punching by picosecond microbeam is high field puncture instead of heat effect, and is irrelevant to cell kinds and colors. The diameter and depth of microsurgery can therefore be easily controlled by adjusting the laser pulse energy. The diameter of the minimum aperture is about 0.1 micrometers , much smaller than the theoretical limit ((lambda) /2) for optical microscope due to self- focusing effect. With ultrashort pulse laser microbeam, we can easily cut off any part of a cell. An example is that eight nuclei in the center of unicellular parasite Pneumocystis Carinii can be destroyed one by one by ultrashort pulse laser microbeam without cell wall injury. The holes can also be punched by ultrashort pulse laser microbeam from cell wall to cell nucleus. In a fraction of a second to several seconds after punching, the hole on cell wall or cell membrane can self-heal. Exogenous DNA can be introduced into the cell before its self- healing.

  12. High current photoemission with 10 picosecond uv pulses

    SciTech Connect

    Fischer, J.; Srinivasan-Rao, T.; Tsang, T.

    1990-06-01

    The quantum efficiency and the optical damage threshold of various metals were explored with 10 ps, 266 nm, UV laser pulses. Efficiencies for Cu, Y, and Sm were: 1.4, 5, and 7 {times} 10{sup {minus}4}, with damage thresholds about 100, 10, and 30 mJ/cm{sup 2}. This would permit over 1 {mu}C/cm{sup 2} or current densities exceeding 100 kA/cm{sup 2}. High charge and current densities of up to 66 kA/cm{sup 2} were obtained on 0.25 mm diam cathodes, and 21 kA/cm{sup 2} on a 3 mm diam yttrium cathode. The maximum currents were limited by space charge and the dc field. The experiments with small area illumination indicate that the emitted electrons spread transversely due to Coulomb repulsion and their initial transverse velocity. This increases the effective area above the cathode, reduces the space charge effect and increases emission density on the cathode. The quantum efficiency can be increased substantially by enhancing the field on the surface by either a suitable electrode geometry or microstructures on it. 14 refs., 12 figs., 3 tabs.

  13. Ultrabroadband 50-130 THz pulses generated via phase-matcheddifference frequency mixing in LiIO3

    SciTech Connect

    Zentgraf, Thomas; Huber, Rupert; Nielsen, Nils C.; Chemla, DanielS.; Kaindl, Robert A.

    2006-10-10

    We report the generation of ultrabroadband pulses spanningthe 50-130 THz frequency range via phase-matched difference frequencymixing within the broad spectrum of sub-10 fs pulses in LiIO_3. Modelcalculations reproduce the octave-spanning spectra and predict few-cycleTHz pulse durations less than 20~;fs. The applicability of this scheme isdemonstrated with 9-fs pulses from a Ti:sapphire oscillator and with 7-fsamplified pulses from a hollow fiber compressor as pumpsources.

  14. A 100 microsec, reliable, 10 Hz pulsed supersonic molecular beam source

    NASA Technical Reports Server (NTRS)

    Byer, R. L.; Duncan, M. D.

    1981-01-01

    A 10-Hz repetition rate, 100-microsec duration, reliable pulsed supersonic molecular beam source is described. Mechanical and electrical design of the pulsed valve are given in detail. Characteristics of the supersonic expansion obtained using coherent anti-Stokes Raman spectroscopy in acetylene are presented. They include pulse shape, gas rotational and translational cooling as a function of distance from the nozzle, clustering effects, and shock heating at the leading edge of the pulse.

  15. Control of the electrode metal transfer by means of the welding current pulse generator

    NASA Astrophysics Data System (ADS)

    Knyaz'kov, A.; Pustovykh, O.; Verevkin, A.; Terekhin, V.; Shachek, A.; Knyaz'kov, S.; Tyasto, A.

    2016-04-01

    The paper presents a generator of welding current pulses to transfer an electrode metal into the molten pool. A homogeneous artificial line is used to produce near rectangular pulses. The homogeneous artificial line provides the minimum heat input with in the pulse to transfer the electrode metal, and it significantly decreases the impact of disturbances affecting this transfer. The pulse frequency does not exceed 300 Hz, and the duration is 0.6 ÷ 0.9 ms.

  16. Word Durations in Non-Native English

    PubMed Central

    Baker, Rachel E.; Baese-Berk, Melissa; Bonnasse-Gahot, Laurent; Kim, Midam; Van Engen, Kristin J.; Bradlow, Ann R.

    2010-01-01

    In this study, we compare the effects of English lexical features on word duration for native and non-native English speakers and for non-native speakers with different L1s and a range of L2 experience. We also examine whether non-native word durations lead to judgments of a stronger foreign accent. We measured word durations in English paragraphs read by 12 American English (AE), 20 Korean, and 20 Chinese speakers. We also had AE listeners rate the `accentedness' of these non-native speakers. AE speech had shorter durations, greater within-speaker word duration variance, greater reduction of function words, and less between-speaker variance than non-native speech. However, both AE and non-native speakers showed sensitivity to lexical predictability by reducing second mentions and high frequency words. Non-native speakers with more native-like word durations, greater within-speaker word duration variance, and greater function word reduction were perceived as less accented. Overall, these findings identify word duration as an important and complex feature of foreign-accented English. PMID:21516172

  17. 7 CFR 550.6 - Duration.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 7 Agriculture 6 2010-01-01 2010-01-01 false Duration. 550.6 Section 550.6 Agriculture Regulations of the Department of Agriculture (Continued) AGRICULTURAL RESEARCH SERVICE, DEPARTMENT OF AGRICULTURE GENERAL ADMINISTRATIVE POLICY FOR NON-ASSISTANCE COOPERATIVE AGREEMENTS General § 550.6 Duration. REE...

  18. 7 CFR 550.6 - Duration.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 7 Agriculture 6 2011-01-01 2011-01-01 false Duration. 550.6 Section 550.6 Agriculture Regulations of the Department of Agriculture (Continued) AGRICULTURAL RESEARCH SERVICE, DEPARTMENT OF AGRICULTURE GENERAL ADMINISTRATIVE POLICY FOR NON-ASSISTANCE COOPERATIVE AGREEMENTS General § 550.6 Duration. REE...

  19. Stimulus Intensity and the Perception of Duration

    ERIC Educational Resources Information Center

    Matthews, William J.; Stewart, Neil; Wearden, John H.

    2011-01-01

    This article explores the widely reported finding that the subjective duration of a stimulus is positively related to its magnitude. In Experiments 1 and 2 we show that, for both auditory and visual stimuli, the effect of stimulus magnitude on the perception of duration depends upon the background: Against a high intensity background, weak stimuli…

  20. Parabolic similariton Yb-fiber laser with triangular pulse evolution

    NASA Astrophysics Data System (ADS)

    Wang, Sijia; Wang, Lei

    2016-04-01

    We propose a novel mode-locked fiber laser design which features a passive nonlinear triangular pulse formation and self-similar parabolic pulse amplification intra cavity. Attribute to the nonlinear reshaping progress in the passive fiber, a triangular-profiled pulse with negative-chirp is generated and paved the way for rapid and efficient self-similar parabolic evolution in a following short-length high-gain fiber. In the meanwhile, the accompanied significantly compressed narrow spectrum from this passive nonlinear reshaping also gives the promise of pulse stabilization and gain-shaping robustness without strong filtering. The resulting short average intra-cavity pulse duration, low amplified spontaneous emission (ASE) and low intra-cavity power loss are essential for the low-noise operation. Simulations predict this modelocked fiber laser allows for high-energy ultra-short transform-limited pulse generation exceeding the gain bandwidth. The output pulse has a de-chirped duration (full-width at half maximum, FWHM) of 27 fs. In addition to the ultrafast laser applications, the proposed fiber laser scheme can support low-noise parabolic and triangular pulse trains at the same time, which are also attractive in optical pulse shaping, all-optical signal processing and high-speed communication applications.

  1. Emergence of a large pore subpopulation during electroporating pulses.

    PubMed

    Smith, Kyle C; Son, Reuben S; Gowrishankar, T R; Weaver, James C

    2014-12-01

    Electroporation increases ionic and molecular transport through cell membranes by creating transient aqueous pores. These pores cannot be directly observed experimentally, but cell system modeling with dynamic electroporation predicts pore populations that produce cellular responses consistent with experiments. We show a cell system model's response that illustrates the life cycle of a pore population in response to a widely used 1 kV/cm, 100 μs trapezoidal pulse. Rapid pore creation occurs early in the pulse, followed by the gradual emergence of a subpopulation of large pores reaching ~30 nm radius. After the pulse, pores rapidly contract to form a single thermally broadened distribution of small pores (~1 nm radius) that slowly decays. We also show the response of the same model to pulses of 100 ns to 1 ms duration, each with an applied field strength adjusted such that a total of 10,000±100 pores are created. As pulse duration is increased, the pore size distributions vary dramatically and a distinct subpopulation of large pores emerges for pulses of microsecond and longer duration. This subpopulation of transient large pores is relevant to understanding rapid transport of macromolecules into and out of cells during a pulse. PMID:24290730

  2. A PC-controlled voltage pulse generator for electroanalytical applications

    NASA Astrophysics Data System (ADS)

    Heredia-López, Francisco J.; Góngora-Alfaro, José L.; Alvarez-Cervera, Fernando J.; Bata-García, José Luis

    1997-04-01

    We present the design of a voltage pulse generator controlled by an IBM or compatible AT Personal Computer (PC) capable of synthesizing some of the voltage pulse wave forms commonly used in electrochemical studies. The included signals are: differential pulse voltametry, differential normal pulse voltametry, and differential pulse amperometry. Additionally, a triangular wave form and a constant-voltage signal, used in the pretreatment of carbon fiber microelectrodes for neurochemical analysis, are also available. Operating the generator imposes a minimum of restrictions on the specification of the duration, amplitude, and type of wave shapes. Low-cost PC-based design allows for compatibility, portability, and versatility. The operating ranges of the wave form parameters for the three voltametric signals are: initial voltage, -0.9-+0.9 V; step amplitude, 0.1-900 mV; period, 6 ms-60 s; measuring pulse amplitude, 0.1-900 mV; measuring pulse duration, 2 ms-20 s; prepulse duration, 2 ms-20 s. In the electrode pretreatment mode, the operating ranges are: amplitude, 0-±5 V; duration, unlimited; frequency, 15-240 Hz. The generator uses its own time base for the generation of all signals, thereby rendering it independent of processor clock speed or power-line frequency. The results of the experimental evaluation indicate that the system is accurate within ±10% of the expected values, taking into account the errors associated with the signal synthesis and the digitizing process. The maximum achievable scan rate is 500 V/s, and the highest frequency for the triangular wave form is 240 Hz. Therefore, the pulse generator could be used for fast cyclic voltametry (FCV). FCV and other wave forms could be added through software modules, without any hardware changes. We conclude that the PC-based electrochemistry pulse generator represents an economical and flexible alternative for electroanalytical applications.

  3. Generation of high-quality petawatt pulses

    SciTech Connect

    Mourou, G; Bado, Philippe

    1991-01-01

    CPA sources need a front-end capable of generating very short seed pulses. To meet this requirement, present CPA sources rely on actively modelocked solid-state oscillators used in conjunction with non-linear fiber stages. This approach generates pulses with a residual frequency chirp, resulting in a limited peak-to-background intensity contrast ratio. The availability of an oscillator capable of producing directly (i.e. without fiber stage) picosecond or sub-picosecond pulses would significantly improve the quality of CPA sources. We have pursued different approaches to replace the standard modelocked oscillator front-end. In an initial phase, we investigated the possible use of Additive Pulse Modelocking (APM) color-center lasers as oscillators for CPA Nd:glass sources. Lately we have developed a Ti:Sapphire modelocked oscillator operating in the one-micron range. In order to generate pulses with very high peak to background contrast ratio, we have built a non-linear coupled-cavity oscillator generating 200-fs pulses. This color-center laser operates in the 1.5--1.6 micron range. A diagram of the oscillator is shown in Fig. 1. The laser is pumped with a modelocked Nd:YAG source. Both KCl and NaCl crystals were tested as gain media. NaCl was found to have a larger tuning range and to generate a higher average power (up to 150 mW). When synchronously mode-locked, the color-center generates pulses in the 10--20 ps range. Once interferometrically coupled to non-linear external-cavity, this oscillator produces very short pulses (85 to 260 fs). This oscillator was first operated with a 2 mm birefringent plate. 85 fs, near transform-limited pulses were generated at 1.54 micron. As the laser was tuned to longer wavelength, the pulse duration increased, as well as the bandwidth-duration product. With a 4 mm birefringent plate, 125 fs, transform-limited pulses were generated over the full tuning range.

  4. Multi-pulse frequency shifted (MPFS) multiple access modulation for ultra wideband

    DOEpatents

    Nekoogar, Faranak; Dowla, Farid U.

    2012-01-24

    The multi-pulse frequency shifted technique uses mutually orthogonal short duration pulses o transmit and receive information in a UWB multiuser communication system. The multiuser system uses the same pulse shape with different frequencies for the reference and data for each user. Different users have a different pulse shape (mutually orthogonal to each other) and different transmit and reference frequencies. At the receiver, the reference pulse is frequency shifted to match the data pulse and a correlation scheme followed by a hard decision block detects the data.

  5. REVIEWS OF TOPICAL PROBLEMS: Laser excitation of ultrashort acoustic pulses: New possibilities in solid-state spectroscopy, diagnostics of fast processes, and nonlinear acoustics

    NASA Astrophysics Data System (ADS)

    Akhmanov, S. A.; Gusev, V. É.

    1992-03-01

    The experimental results in the field of laser generation of acoustic pulses of duration less than 1 ns are reviewed. The various physical mechanisms of optoacoustic conversion are analyzed theoretically. Possibilities are shown for shortening the duration of optoacoustic pulses by increasing the intensity of the laser exposure. The prospects of initiating ultrashort, strong shock pulses with high-power femtosecond light pulses, are discussed.

  6. On the applicability of arbitrarily shaped nanosecond laser pulses for high-quality, high-efficiency micromachining

    NASA Astrophysics Data System (ADS)

    Eiselen, Sasia; Riedel, Sebastian; Schmidt, Michael

    2014-05-01

    Progressive developments in temporal shaping of short laser pulses offer entirely new approaches at influence and investigate laser-matter-interactions. Commonly used parameters for describing the behavior of short or ultrashort pulses or pulse trains are fluence and intensity. However, fluence does not imply any information about the temporal behavior of energy input during specific pulse duration τ while using the pulse intensity as describing parameter is more meaningful. Nevertheless it still is an averaging over pulse duration and no change in intensity can be determined if the temporal pulse shape changes within a certain combination of pulse duration and pulse energy. Using a flexible programmable MOPA fiber laser experimental studies on the impact of temporal energy distribution within one single laser pulse in micro machining applications were therefore carried out. With this laser source a direct modulation of the temporal pulse shape in the nanosecond regime can easily be controlled. Experiments were carried out with moved as well as with un-moved beam resulting in areas and dimples respectively drilling holes. The presented results clearly show that any averaging over pulse duration results in missing information about time-dependent interactions but can at the same time lead to significant differences in ablation results. Thus, resulting surface roughness Sa can be decreased up to 25 % when changing the pulse shape at constant parameters of fluence and pulse peak power at a pulse duration of 30 ns. It can be observed that the combination of an intensity peak and a lower edge within one pulse can lead to increasing ablation efficiency as well as higher ablation quality compared to the commonly used Gaussian-like temporal pulse shape.

  7. Prognostic significance of QRS duration and morphology.

    PubMed

    Brenyo, Andrew; Zaręba, Wojciech

    2011-01-01

    QRS duration and morphology, evaluated via a standard 12-lead electrocardiogram (ECG), represent an opportunity to derive useful prognostic information regarding the risk of subsequent cardiac events or therapeutic outcomes. Prolonged QRS duration, and the presence of intraventricular conduction abnormalities, usually indicate the presence of changes in the myocardium due to underlying heart disease. Prolonged QRS duration is often associated with depressed ejection fraction or enlarged left ventricular volumes, but several studies have demonstrated that this simple ECG measure provides independent prognostic value, after adjusting for relevant clinical covariates. Post-infarction patients with prolonged QRS duration have a significantly increased risk of mortality, although data associating QRS prolongation specifically with sudden death is less supportive. In non-ischemic cardiomyopathy, there is no evidence that QRS duration has prognostic significance in predicting mortality or sudden death. Prolonged QRS duration, and especially presence of left bundle branch block, seems to predict a benefit from cardiac resynchronization therapy in both ischemic and non-ischemic cardiomyopathy patients. Therefore, QRS duration and morphology should not only be considered a predictor of death or sudden death in patients after myocardial infarction, and in those suspected of coronary artery disease, but also as a predictor of benefit from cardiac resynchronization therapy in patients with heart failure, whether of an ischemic or non-ischemic origin. PMID:21305480

  8. Repetition enhancement and memory effects for duration.

    PubMed

    Wiener, Martin; Thompson, James C

    2015-06-01

    A remarkable aspect of conscious perception is that moments carryover from one to the next, also known as temporal continuity. This ability is thus crucial for detecting regularities, such as in speech and music, and may rely on an accurate perception of time. Investigations of human time perception have detailed two electroencephalographic (EEG) components associated with timing, the contingent negative variation (CNV) and late positive component of timing (LPCt); however, the precise roles of these components in timing remain elusive. Recently, we demonstrated that the perception of duration is influenced by durations presented on prior trials, which we explained by the creation of an implicit memory standard that adapts to local changes in sequence presentation. Here, we turn to the neural basis of this effect. Human participants performed a temporal bisection task in which they were required to classify the duration of auditory stimuli into short and long duration categories; crucially, the presentation order was first-order counterbalanced, allowing us to measure the effect of each presented duration on the next. EEG recordings revealed that the CNV and LPCt signals both covaried with the duration presented on the current trial, with CNV predicting reaction time and LPCt predicting choice. Additionally, both signals covaried with the duration presented in the prior trial but in different ways, with the CNV amplitude reflecting the change in the memory standard and the LPCt reflecting decision uncertainty. Furthermore, we observed a repetition enhancement effect of duration only for the CNV, suggesting that this signal additionally indexes the similarity of successive durations. These findings demonstrate dissociable roles for the CNV and LPCt, and demonstrate that both signals are continuously updated on a trial-by-trial basis that reflects shifts in temporal decisions. PMID:25818689

  9. Repetition enhancement and memory effects for duration.

    PubMed

    Wiener, Martin; Thompson, James C

    2015-06-01

    A remarkable aspect of conscious perception is that moments carryover from one to the next, also known as temporal continuity. This ability is thus crucial for detecting regularities, such as in speech and music, and may rely on an accurate perception of time. Investigations of human time perception have detailed two electroencephalographic (EEG) components associated with timing, the contingent negative variation (CNV) and late positive component of timing (LPCt); however, the precise roles of these components in timing remain elusive. Recently, we demonstrated that the perception of duration is influenced by durations presented on prior trials, which we explained by the creation of an implicit memory standard that adapts to local changes in sequence presentation. Here, we turn to the neural basis of this effect. Human participants performed a temporal bisection task in which they were required to classify the duration of auditory stimuli into short and long duration categories; crucially, the presentation order was first-order counterbalanced, allowing us to measure the effect of each presented duration on the next. EEG recordings revealed that the CNV and LPCt signals both covaried with the duration presented on the current trial, with CNV predicting reaction time and LPCt predicting choice. Additionally, both signals covaried with the duration presented in the prior trial but in different ways, with the CNV amplitude reflecting the change in the memory standard and the LPCt reflecting decision uncertainty. Furthermore, we observed a repetition enhancement effect of duration only for the CNV, suggesting that this signal additionally indexes the similarity of successive durations. These findings demonstrate dissociable roles for the CNV and LPCt, and demonstrate that both signals are continuously updated on a trial-by-trial basis that reflects shifts in temporal decisions.

  10. Trident Pair Production in Strong Laser Pulses

    SciTech Connect

    Ilderton, Anton

    2011-01-14

    We calculate the trident pair production amplitude in a strong laser background. We allow for finite pulse durations, while still treating the laser fields nonperturbatively in strong-field QED. Our approach reveals explicitly the individual contributions of the one-step and two-step processes. We also expose the role gauge invariance plays in the amplitudes and discuss the relation between our results and the optical theorem.

  11. Analytical calculations of wake field generated by microwave pulses in a plasma filled waveguide for electron acceleration

    SciTech Connect

    Malik, Hitendra K.

    2008-09-01

    Analytical expressions are obtained for the longitudinal field (wake field), density perturbation, and the potential behind microwave pulse propagating in a plasma filled rectangular waveguide with the pulse duration half of the electron plasma period. A feasibility study on wake field is carried out with rectangular pulse and its combination with Gaussian and triangular pulses under the effects of microwave pulse parameters and waveguide dimensions. It is inferred that the wake field in the waveguide cannot be attained when the length of rectangular microwave pulse is exactly equal to the plasma wavelength. A 1 ns short rectangular pulse with intensity of 250 kW/cm{sup 2} at the frequency of 5.03 GHz can excite the wake field of 1.0 MV/m in a waveguide with width of 6 cm and height of 4 cm. However, enhanced field is obtained when rectangular-triangular pulse (combination of rectangular and triangular pulses) is used. The field of wake gets weakened at higher microwave frequency and larger dimensions of the waveguide for other fixed parameters. However, a larger field is achieved when the pulse length of the microwave pulses is made shorter and/or intensity of the pulses is increased. A comparative study of the pulses shows that better results can be obtained with rectangular pulse (rectangular-Gaussian pulse: combination of rectangular and Gaussian pulses) if the microwave of shorter pulse duration (higher intensity) is available.

  12. Enhancing High-Order Harmonic Generation in Light Molecules by Using Chirped Pulses.

    PubMed

    Lara-Astiaso, M; Silva, R E F; Gubaydullin, A; Rivière, P; Meier, C; Martín, F

    2016-08-26

    One of the current challenges in high-harmonic generation is to extend the harmonic cutoff to increasingly high energies while maintaining or even increasing the efficiency of the high-harmonic emission. Here we show that the combined effect of down-chirped pulses and nuclear dynamics in light molecules allows one to achieve this goal, provided that long enough IR pulses are used to allow the nuclei to move well outside the Franck-Condon region. We also show that, by varying the duration of the chirped pulse or by performing isotopic substitution while keeping the pulse duration constant, one can control the extension of the harmonic plateau. PMID:27610851

  13. Enhancing High-Order Harmonic Generation in Light Molecules by Using Chirped Pulses

    NASA Astrophysics Data System (ADS)

    Lara-Astiaso, M.; Silva, R. E. F.; Gubaydullin, A.; Rivière, P.; Meier, C.; Martín, F.

    2016-08-01

    One of the current challenges in high-harmonic generation is to extend the harmonic cutoff to increasingly high energies while maintaining or even increasing the efficiency of the high-harmonic emission. Here we show that the combined effect of down-chirped pulses and nuclear dynamics in light molecules allows one to achieve this goal, provided that long enough IR pulses are used to allow the nuclei to move well outside the Franck-Condon region. We also show that, by varying the duration of the chirped pulse or by performing isotopic substitution while keeping the pulse duration constant, one can control the extension of the harmonic plateau.

  14. Study of potassium DPAL operation in pulsed and CW mode

    NASA Astrophysics Data System (ADS)

    Zhdanov, Boris V.; Rotondaro, Matthew D.; Schaffer, Michael K.; Knize, Randall J.

    2014-10-01

    This paper presents the results of our experiments on development of the efficient hydrocarbon free Diode Pumped Alkali Laser based on potassium vapor buffered by He gas at 600 Torr. We studied the performance of this laser operating in pulsed mode with pulses up to 5 ms long at different pulse energies and cell temperatures. A slope efficiency of more than 50% was demonstrated with total optical efficiency about 30% for the pump pulses with duration about 30 μs. For the longer pump pulses the DPAL efficiency degraded in time with a characteristic time in the range from 0.5 ms to 4.5 ms depending on the pump pulse energy and cell temperature. The recorded spectrum of the side fluorescence indicates that multi-photon excitation, energy pooling collisions and ionization may be strong candidates for explaining the observed performance degradation.

  15. Femtosecond parabolic pulse shaping in normally dispersive optical fibers.

    PubMed

    Sukhoivanov, Igor A; Iakushev, Sergii O; Shulika, Oleksiy V; Díez, Antonio; Andrés, Miguel

    2013-07-29

    Formation of parabolic pulses at femtosecond time scale by means of passive nonlinear reshaping in normally dispersive optical fibers is analyzed. Two approaches are examined and compared: the parabolic waveform formation in transient propagation regime and parabolic waveform formation in the steady-state propagation regime. It is found that both approaches could produce parabolic pulses as short as few hundred femtoseconds applying commercially available fibers, specially designed all-normal dispersion photonic crystal fiber and modern femtosecond lasers for pumping. The ranges of parameters providing parabolic pulse formation at the femtosecond time scale are found depending on the initial pulse duration, chirp and energy. Applicability of different fibers for femtosecond pulse shaping is analyzed. Recommendation for shortest parabolic pulse formation is made based on the analysis presented.

  16. DIFFERENTIAL PULSE HEIGHT DISCRIMINATOR

    DOEpatents

    Test, L.D.

    1958-11-11

    Pulse-height discriminators are described, specifically a differential pulse-height discriminator which is adapted to respond to pulses of a band of amplitudes, but to reject pulses of amplitudes greater or less than tbe preselected band. In general, the discriminator includes a vacuum tube having a plurality of grids adapted to cut off plate current in the tube upon the application of sufficient negative voltage. One grid is held below cutoff, while a positive pulse proportional to the amplltude of each pulse is applled to this grid. Another grid has a negative pulse proportional to the amplitude of each pulse simultaneously applied to it. With this arrangement the tube will only pass pulses which are of sufficlent amplitude to counter the cutoff bias but not of sufficlent amplitude to cutoff the tube.

  17. Chirped Pulse Microwave Spectroscopy in Pulsed Uniform Supersonic Flows

    NASA Astrophysics Data System (ADS)

    Abeysekera, Chamara; Oldham, James; Prozument, Kirill; Joalland, Baptiste; Park, Barratt; Field, Robert W.; Sims, Ian; Suits, Arthur; Zack, Lindsay

    2014-06-01

    We present preliminary results describing the development of a new instrument that combines two powerful techniques: Chirped Pulse-Fourier Transform MicroWave (CP-FTMW) spectroscopy and pulsed uniform supersonic flows. It promises a nearly universal detection method that can deliver quantitative isomer, conformer, and vibrational level specific detection, characterization of unstable reaction products and intermediates and perform unique spectroscopic, kinetics and dynamics measurements. We have constructed a new high-power K_a-band, 26-40 GHz, chirped pulse spectrometer with sub-MHz resolution, analogous to the revolutionary CP-FTMW spectroscopic technique developed in the Pate group at University of Virginia. In order to study smaller molecules, the E-band, 60-90 GHz, CP capability was added to our spectrometer. A novel strategy for generating uniform supersonic flow through a Laval nozzle is introduced. High throughput pulsed piezo-valve is used to produce cold (30 K) uniform flow with large volumes of 150 cm^3 and densities of 1014 molecules/cm3 with modest pumping facilities. The uniform flow conditions for a variety of noble gases extend as far as 20 cm from the Laval nozzle and a single compound turbo-molecular pump maintains the operating pressure. Two competing design considerations are critical to the performance of the system: a low temperature flow is needed to maximize the population difference between rotational levels, and high gas number densities are needed to ensure rapid cooling to achieve the uniform flow conditions. At the same time, collision times shorter than the chirp duration will give inaccurate intensities and reduced signal levels due to collisional dephasing of free induction decay. Details of the instrument and future directions and challenges will be discussed.

  18. Electromagnetic Pulses at Short-Pulse Laser Facilities

    SciTech Connect

    Brown, Jr., C G; Throop, A; Eder, D; Kimbrough, J

    2007-08-28

    Electromagnetic Pulse (EMP) is a known issue for short-pulse laser facilities, and will also be an issue for experiments using the advanced radiographic capability (ARC) at the National Ignition Facility (NIF). The ARC diagnostic uses four NIF beams that are compressed to picosecond durations for backlighting ignition capsules and other applications. Consequently, we are working to understand the EMP due to high-energy (MeV) electrons escaping from targets heated by short-pulse lasers. Our approach is to measure EMP in the Titan short-pulse laser at Lawrence Livermore National Laboratory (LLNL) and to employ that data to establish analysis and simulation capabilities. We have installed a wide variety of probes inside and outside the Titan laser chamber. We have high-frequency B-dots and D-dots, a photodiode, and fast current-viewing and integrating current transformers. The probe outputs are digitized by 10 and 20 Gsample/s oscilloscopes. The cables and oscilloscopes are well shielded to reduce noise. Our initial measurement campaign has yielded data useful mainly from hundreds of MHz to several GHz. We currently are supplementing our high-frequency probes with lower-frequency ones to obtain better low-frequency data. In order to establish analysis and simulation capabilities we are modeling the Titan facility using various commercial and LLNL numerical electromagnetic codes. We have simulated EMP generation by having a specified number of electrons leave the target and strike the chamber wall and other components in the chamber. This short impulse of electrons has a corresponding broad spectrum, exciting high-frequency structure in the resulting EMP. In this paper, we present results of our initial measurement campaign and comparisons between the measurements and simulations.

  19. Electromagnetic Pulses at Short-Pulse Laser Facilities

    SciTech Connect

    Brown, C G; Throop, A; Eder, D; Kimbrough, J

    2008-02-04

    Electromagnetic Pulse (EMP) is a known issue for short-pulse laser facilities, and will also be an issue for experiments using the advanced radiographic capability (ARC) at the National Ignition Facility (NIF). The ARC diagnostic uses four NIF beams that are compressed to picosecond durations for backlighting ignition capsules and other applications. Consequently, we are working to understand the EMP due to high-energy (MeV) electrons escaping from targets heated by short-pulse lasers. Our approach is to measure EMP in the Titan short-pulse laser at Lawrence Livermore National Laboratory (LLNL) and to employ that data to establish analysis and simulation capabilities. We have installed a wide variety of probes inside and outside the Titan laser chamber. We have high-frequency B-dot and D-dot probes, a photodiode, and fast current-viewing and integrating current transformers. The probe outputs are digitized by 10 and 20 Gsample/s oscilloscopes. The cables and oscilloscopes are well shielded to reduce noise. Our initial measurement campaign has yielded data useful mainly from several hundreds of MHz to several GHz. We currently are supplementing our high-frequency probes with lower-frequency ones to obtain better low-frequency data. In order to establish analysis and simulation capabilities we are modeling the Titan facility using various commercial and LLNL numerical electromagnetics codes. We have simulated EMP generation by having a specified number of electrons leave the target and strike the chamber wall and other components in the chamber. This short impulse of electrons has a correspondingly broad spectrum, exciting high-frequency structure in the resulting EMP. In this paper, we present results of our initial measurement campaign and comparisons between the measurements and simulations.

  20. 30-fs pulses tunable across the visible with a 100-kHz Ti:sapphire regenerative amplifier

    SciTech Connect

    Reed, M.K.; Armas, M.S.; Steiner-Shepard, M.K.; Negus, D.K.

    1995-03-15

    A 100-kHz mode-locked Ti:sapphire-seeded regenerative amplifier pumping an optical parametric amplifier generates femtosecond pulses tunable from 470 to 710 nm. This output was compressed with a pair of prisms to bandwidth-limited pulses of 80- to 40-fs duration and more than 150 nJ of energy. These tunable pulses were then bandwidth expanded through self-phase modulation in bulk material and further compressed to less than 30-fs duration.

  1. Generation of attosecond pulse pair in polar media by chirped few-cycle pulses

    NASA Astrophysics Data System (ADS)

    Hu, Pidong; Niu, Yueping; Wang, Xiangxin; Gong, Shangqing; Liu, Chengpu

    2016-09-01

    The high-order harmonic generation in a polar medium driven by an initially chirped few-cycle laser pulse is investigated via numerically solving the nonlinear Bloch or Maxwell-Bloch equations based on whether propagation effects are taken into account or not. As a result of the reduction of quantum trajectories number due to the introduction of chirps, an attosecond pulse pair (APP) is generated instead of a general attosecond pulse train. Moreover, the time delay between the two attosecond pulses is tunable. When propagation effects take roles, the peak intensities of the APP can be enhanced at suitable propagation distances without observable duration broadening, and such an enhancement can be modulated by changing medium density.

  2. Strength-duration curve: a measure for assessing sensory deficit in peripheral neuropathy.

    PubMed Central

    Friedli, W G; Meyer, M

    1984-01-01

    By using an isolated constant current stimulator producing true square-wave pulses, sensory strength-duration curves were obtained at various sites by percutaneous electrical stimulation. Strength-duration curves derived from normal groups were compared to those of patients with peripheral neuropathy. Stimulus strength at sensory threshold was shown to be a reproducible measure of sensory deficit, increasing parallel to the degree of axonal failure found by conventional methods. This may be useful as a complementary method in assessing peripheral neuropathy. PMID:6323634

  3. Laser pulse stacking method

    DOEpatents

    Moses, E.I.

    1992-12-01

    A laser pulse stacking method is disclosed. A problem with the prior art has been the generation of a series of laser beam pulses where the outer and inner regions of the beams are generated so as to form radially non-synchronous pulses. Such pulses thus have a non-uniform cross-sectional area with respect to the outer and inner edges of the pulses. The present invention provides a solution by combining the temporally non-uniform pulses in a stacking effect to thus provide a more uniform temporal synchronism over the beam diameter. 2 figs.

  4. Nerve-pulse interactions

    SciTech Connect

    Scott, A.C.

    1982-01-01

    Some recent experimental and theoretical results on mechanisms through which individual nerve pulses can interact are reviewed. Three modes of interactions are considered: (1) interaction of pulses as they travel along a single fiber which leads to velocity dispersion; (2) propagation of pairs of pulses through a branching region leading to quantum pulse code transformations; and (3) interaction of pulses on parallel fibers through which they may form a pulse assembly. This notion is analogous to Hebb's concept of a cell assembly, but on a lower level of the neural hierarchy.

  5. Recycle Rate in a Pulsed, Optically Pumped Rubidium Laser

    SciTech Connect

    Miller, Wooddy S.; Sulham, Clifford V.; Holtgrave, Jeremy C.; Perram, Glen P.

    2010-10-08

    A pulsed, optically pumped rubidium laser operating in analogy to the diode pumped alkali laser (DPAL) system at pump intensities as high as 750 kW/cm{sup 2} has been demonstrated with output energies of up to 13 {mu}J/pulse. Output energy is dramatically limited by spin-orbit relaxation rates under these high intensity pump conditions. More than 250 photons are available for every rubidium atom in the pumped volume, requiring a high number of cycles per atom during the 2-8 ns duration of the pump pulse. At 550 Torr of ethane, the spin-orbit relaxation rate is too slow to effectively utilize all the incident pump photons. Indeed, a linear dependence of output energy on pump pulse duration for fixed pump energy is demonstrated.

  6. State dependent model predictive control for orbital rendezvous using pulse-width pulse-frequency modulated thrusters

    NASA Astrophysics Data System (ADS)

    Li, Peng; Zhu, Zheng H.; Meguid, S. A.

    2016-07-01

    This paper studies the pulse-width pulse-frequency modulation based trajectory planning for orbital rendezvous and proximity maneuvering near a non-cooperative spacecraft in an elliptical orbit. The problem is formulated by converting the continuous control input, output from the state dependent model predictive control, into a sequence of pulses of constant magnitude by controlling firing frequency and duration of constant-magnitude thrusters. The state dependent model predictive control is derived by minimizing the control error of states and control roughness of control input for a safe, smooth and fuel efficient approaching trajectory. The resulting nonlinear programming problem is converted into a series of quadratic programming problem and solved by numerical iteration using the receding horizon strategy. The numerical results show that the proposed state dependent model predictive control with the pulse-width pulse-frequency modulation is able to effectively generate optimized trajectories using equivalent control pulses for the proximity maneuvering with less energy consumption.

  7. Short pulse, high power microwave radiation source with a laser-induced sheet plasma mirror

    SciTech Connect

    Higashiguchi, Takeshi; Yugami, Noboru

    2009-05-01

    We have demonstrated the short pulse, high power microwave radiation source using an ultraviolet laser-induced sheet plasma mirror in a gas-filled x-band rectangular waveguide from the conventional microwave sources and components. A laser-induced sheet plasma with an overdense plasma acts as a plasma mirror. The long pulse propagating in the gas-filled waveguide was sliced by the sheet plasma mirror at two different points along the waveguide. We observed about twice the power of the pulse by adding the two sliced microwave pulses produced by this scheme. A maximum peak power of 200 kW with a pulse duration of 10 ns (full width at half maximum) from the long microwave pulse source with a pulse duration of 0.8 mus was observed.

  8. Tunable pulsed narrow bandwidth light source

    DOEpatents

    Powers, Peter E.; Kulp, Thomas J.

    2002-01-01

    A tunable pulsed narrow bandwidth light source and a method of operating a light source are provided. The light source includes a pump laser, first and second non-linear optical crystals, a tunable filter, and light pulse directing optics. The method includes the steps of operating the pump laser to generate a pulsed pump beam characterized by a nanosecond pulse duration and arranging the light pulse directing optics so as to (i) split the pulsed pump beam into primary and secondary pump beams; (ii) direct the primary pump beam through an input face of the first non-linear optical crystal such that a primary output beam exits from an output face of the first non-linear optical crystal; (iii) direct the primary output beam through the tunable filter to generate a sculpted seed beam; and direct the sculpted seed beam and the secondary pump beam through an input face of the second non-linear optical crystal such that a secondary output beam characterized by at least one spectral bandwidth on the order of about 0.1 cm.sup.-1 and below exits from an output face of the second non-linear optical crystal.

  9. Short-pulse laser materials processing

    SciTech Connect

    Stuart, B.C.; Perry, M.D.; Myers, B.R.; Banks, P.S.; Honea, E.C.

    1997-06-18

    While there is much that we have learned about materials processing in the ultrashort-pulse regime, there is an enormous amount that we don`t know. How short does the pulse have to be to achieve a particular cut (depth, material, quality)? How deep can you cut? What is the surface roughness? These questions are clearly dependent upon the properties of the material of interest along with the short-pulse interaction physics. From a technology standpoint, we are asked: Can you build a 100 W average power system ? A 1000 W average power system? This proposal seeks to address these questions with a combined experimental and theoretical program of study. Specifically, To develop an empirical database for both metals and dielectrics which can be used to determine the pulse duration and wavelength necessary to achieve a specific machining requirement. To investigate Yb:YAG as a potential laser material for high average power short-pulse systems both directly and in combination with titanium doped sapphire. To develop a conceptual design for a lOOW and eventually 5OOW average power short-pulse system.

  10. Cr4+ : YAG chirped-pulse oscillator

    PubMed Central

    Sorokin, Evgeni; Kalashnikov, Vladimir L; Mandon, Julien; Guelachvili, Guy; Picqué, Nathalie; Sorokina, Irina T

    2010-01-01

    We demonstrate chirped-pulse operation of a Cr : YAG passively mode-locked laser. Different operation regimes of the laser are extensively investigated in the vicinity of zero dispersion both experimentally and numerically. It is shown that for a given laser configuration, transition to the positive dispersion regime allows a 5-fold increase in the output pulse energy, which is otherwise limited by the onset of the multipulsing or ‘chaotic’ mode-locking. The output pulses have 1.4 ps duration and are compressible down to 120 fs in a 3 m piece of silica fiber, enabling supercontinuum generation in a nonlinear fiber. The spectrum shape and operation stability of the chirped-pulse regime depend strongly on the amount and shape of the intracavity dispersion. The numerical model predicts the existence of the minimum amount of the positive dispersion, above which the chirped-pulse regime can be realized. Once located, the chirped-pulse regime can be reliably reproduced and is sufficiently stable for applications. PMID:21151831

  11. A progressive-duration schedule of reinforcement.

    PubMed

    Gulotta, Kara B; Byrne, Tom

    2015-12-01

    We describe a schedule of reinforcement involving systematic, within-session increases in response-duration requirements. Rats received access to appetitive reinforcers for depressing and holding down a response lever. Duration requirements increased after each reinforcer delivery. Sessions ended when reinforcement criteria were unmet for a period of ten minutes. Breaking points, defined as the terminal duration requirement in effect prior to the end of the session, stabilized when environmental conditions were held constant. Breaking points were sensitive to manipulations of both food deprivation and reinforcer quality. Analogous to progressive-ratio schedules, progressive-duration schedules may provide an assay for measuring the amount of behavior an organism will emit for a given reinforcer under current motivational conditions.

  12. [Duration of antibiotic therapy in bacterial meningitis].

    PubMed

    Pereira, P Ricardo; Borges, Fernando; Mansinho, Kamal

    2013-01-01

    The duration of antibiotic therapy in bacterial meningitis is a controversial issue. Antibiotic regimens have changed over time along with the criteria used to determine the ideal antibiotic therapy duration. The authors aim to make an historical overview on this matter and simultaneously add the evidence of recent studies, pointing out some issues in results interpretation, namely, their design and the associated demographic and epidemiological questions. Clinical assays on this subject, with statistically significant results, are quite recent. Most of the scientific knowledge has been acquired empirically through the times. The actual investigation paradigm, in what concerns to antibiotic therapy in bacterial meningitis, lays on the dichotomy: "short versus long duration regimens". Nevertheless, so far, the existing studies have not completely cleared this doubt. Thus, despite some evidence suggests that short duration antibiotic regimens are effective for some patients, in patients with severe disease presentations or with other morbidities its use may be questioned.

  13. 1  MW peak-power subpicosecond optical pulse source based on a gain-switched laser diode.

    PubMed

    Fang, Yi-Cheng; Chaki, Tomohiro; Hung, Jui-Hung; Yamada, Hirohito; Yokoyama, Hiroyuki

    2016-09-01

    We have generated optical pulses of 1.2 MW peak power and 0.6 ps duration using a 1060 nm band gain-switched laser diode pulse oscillator. Optical pulses are amplified by three-stage ytterbium-doped fiber amplifiers, and remarkable reductions of amplified spontaneous emission noise and temporal duration have been accomplished based on self-phase modulation in the middle-stage amplifier. After the main amplifier, optical pulses were temporally compressed by a grating pair, and this enabled generation of subpicosecond optical pulses with over 1 MW peak power. PMID:27607964

  14. Pulsed Plasma Electron Sources

    NASA Astrophysics Data System (ADS)

    Krasik, Yakov

    2008-11-01

    Pulsed (˜10-7 s) electron beams with high current density (>10^2 A/cm^2) are generated in diodes with electric field of E > 10^6 V/cm. The source of electrons in these diodes is explosive emission plasma, which limits pulse duration; in the case E < 10^5 V/cm this plasma is not uniform and there is a time delay in its formation. Thus, there is a continuous interest in research of electron sources which can be used for generation of uniform electron beams produced at E <= 10^5 V/cm. In the present report, several types of plasma electron source (PES) will be considered. The first type of PES is fiber-based cathodes, with and without CsI coating. The operation of these cathodes is governed by the formation of the flashover plasma which serves as a source of electrons. The second type of PES is the ferroelectric plasma source (FPS). The operation of FPS, characterized by the formation of dense surface flashover plasma is accompanied also by the generation of fast microparticles and energetic neutrals. The latter was explained by Coulomb micro-explosions of the ferroelectric surface due to an large time-varying electric field at the front of the expanding plasma. A short review of recent achievements in the operation of a multi-FPS-assisted hollow anode to generate a large area electron beam will be presented as well. Finally, parameters of the plasma produced by a multi-capillary cathode with FPS and velvet igniters will be discussed. Ya. E. Krasik, J. Z. Gleizer, D. Yarmolich, A. Krokhmal, V. Ts. Gurovich, S.Efimov, J. Felsteiner V. Bernshtam, and Yu. M. Saveliev, J. Appl. Phys. 98, 093308 (2005). Ya. E. Krasik, A. Dunaevsky, and J. Felsteiner, Phys. Plasmas 8, 2466 (2001). D. Yarmolich, V. Vekselman, V. Tz. Gurovich, and Ya. E. Krasik, Phys. Rev. Lett. 100, 075004 (2008). J. Z. Gleizer, Y. Hadas and Ya. E. Krasik, Europhysics Lett. 82, 55001 (2008).

  15. Rainfall intensity-duration-frequency formulas.

    USGS Publications Warehouse

    Chen, C.-L.

    1983-01-01

    A new general rainfall intensity-duration-frequency formula is presented, utilizing a method similar to, but more accurate than one previously developed. The previously developed formula was based on the average depth-duration ratio of about 40% and the mean depth-frequency ratio of 1.48. It is shown that this formula is only a particular form of the writer's more general formulation. -from Author

  16. Optical parametric chirped pulse amplification and spectral shaping of a continuum generated in a photonic band gap fiber.

    PubMed

    Hugonnot, E; Somekh, M; Villate, D; Salin, F; Freysz, E

    2004-05-31

    A chirped pulse, spectrally broadened in a photonic bandgap optical fiber by 120 fs Ti:Sapphire laser pulses, is parametrically amplified in a BBO crystal pumped by a frequency doubled nanosecond Nd:YAG laser pulse. Without changing the frequency of the Ti:Sapphire, a spectral tunability of the amplified pulses is demonstrated. The possibility to achieve broader spectral range amplification is confirmed for a non-collinear pump-signal interaction geometry. For optimal non-collinear interaction geometry, the pulse duration of the original and amplified pulse are similar. Finally, we demonstrate that the combination of two BBO crystals makes it possible to spectrally shape the amplified pulses.

  17. Pulse to pulse klystron diagnosis system

    SciTech Connect

    Nowak, J.; Davidson, V.; Genova, L.; Johnson, R.; Reagan, D.

    1981-03-01

    This report describes a system used to study the behavior of SLAC high powered klystrons operating with a twice normal pulse width of 5 ..mu..s. At present, up to eight of the klystrons installed along the accelerator can be operated with long pulses and monitored by this system. The report will also discuss some of the recent findings and investigations.

  18. Dynamics of frequency-modulated soliton-like pulses in a longitudinally inhomogeneous, anomalous group velocity dispersion fibre amplifier

    SciTech Connect

    Zolotovskii, Igor' O; Korobko, D A; Okhotnikov, Oleg G; Sysolyatin, A A; Fotiadi, A A

    2012-09-30

    We examine conditions for the formation and amplification of frequency-modulated soliton-like pulses in longitudinally inhomogeneous, anomalous group velocity dispersion fibres. The group velocity dispersion profiles necessary for the existence and amplification of such pulses in active fibres are identified and the pulse duration and chirp are determined as functions of propagation distance. (optical fibres, lasers and amplifiers. properties and applications)

  19. Damage threshold and focusability of mid-infrared free-electron laser pulses gated by a plasma mirror with nanosecond switching pulses

    SciTech Connect

    Wang, Xiaolong; Nakajima, Takashi; Zen, Heishun; Kii, Toshiteru; Ohgaki, Hideaki

    2013-11-04

    The presence of a pulse train structure of an oscillator-type free-electron laser (FEL) results in the immediate damage of a solid target upon focusing. We demonstrate that the laser-induced damage threshold can be significantly improved by gating the mid-infrared FEL pulses with a plasma mirror. Although the switching pulses we employ have a nanosecond duration which does not guarantee the clean wavefront of the gated FEL pulses, the high focusability is experimentally confirmed through the observation of spectral broadening by a factor of 2.1 when we tightly focus the gated FEL pulses onto the Ge plate.

  20. Collective behaviors of book holding durations

    NASA Astrophysics Data System (ADS)

    Li, Ren-De; Guo, Qiang; Han, Jing-Ti; Liu, Jian-Guo

    2016-10-01

    Duration can directly reflect the collective reading behaviors of library user book holding. In this paper, by introducing the burstiness and memory coefficients, we empirically investigate the collective book holding behavior of three university libraries. The statistical results show that there are similar properties among the students with different backgrounds, presenting the burstiness < B > = - 0.2 and memory < M > = 0.5 for three datasets, which indicates that memory and random effects coexist in student book holding durations. In addition, we analyze the behavior patterns without duplicate durations by merging a series of books borrowed and returned at the same time. The results show the average burstiness B increases to -0.16 and memory M drops to 0.16 for three datasets, which indicates that both duplicate behavior and student's preference affect the memory effect. Furthermore, we present a model which assumes student's next book holding duration follows the previous one with probability p, and with probability 1 - p, the student would hold the book independently. The experimental results show that the presented model can reproduce the burstiness and memory effect of student book holding durations when p = 0.5 for empirical datasets and p = 0.2 for de-duplicate datasets, which indicate that the student's preferential holding behavior occurs with the probability p. This work helps in deeply understanding the regularity of duration-based human behaviors.

  1. High reflection mirrors for pulse compression gratings.

    PubMed

    Palmier, S; Neauport, J; Baclet, N; Lavastre, E; Dupuy, G

    2009-10-26

    We report an experimental investigation of high reflection mirrors used to fabricate gratings for pulse compression application at the wavelength of 1.053microm. Two kinds of mirrors are studied: the mixed Metal MultiLayer Dielectric (MMLD) mirrors which combine a gold metal layer with some e-beam evaporated dielectric bilayers on the top and the standard e-beam evaporated MultiLayer Dielectric (MLD) mirrors. Various samples were manufactured, damage tested at a pulse duration of 500fs. Damage sites were subsequently observed by means of Nomarski microscopy and white light interferometer microscopy. The comparison of the results evidences that if MMLD design can offer damage performances rather similar to MLD design, it also exhibits lower stresses; being thus an optimal mirror substrate for a pulse compression grating operating under vacuum.

  2. Pulsed power systems for the DARHT accelerators

    SciTech Connect

    Downing, J.N.; Parsons, W.M.; Earley, L.M.; Melton, J.G.; Moir, D.C.; Carlson, R.L.; Barnes, G.A.; Builta, L.A.; Eversole, S.A.; Keel, G.I.; Rader, D.C.; Romero, J.A.; Shurter, R.P.

    1991-01-01

    The Dual-Axis Radiographic Hydro Test (DARHT) Facility is being designed to produce high-resolution flash radiographs of hydrodynamics experiments. Two 16- to 20-MeV linear induction accelerators (LIA), with an included angle of 90{degree}, are used to produce intense bremsstrahlung x-ray pulses of short duration (60-ns flat-top). Each accelerator has a 4-MeV electron source that injects an electron beam into a series of 250-kV induction cells. The three major pulsed-power systems are the injectors, the induction-cell pulsed-power (ICPP) units, and the ICPP trigger systems, and are discussed in this paper. 11 refs., 5 figs, 3 tabs.

  3. Pulsed emission from an LaB6 thermionic cathode

    NASA Astrophysics Data System (ADS)

    Iremashvili, D. V.; Podgornyi, V. I.; Goncharuk, A. I.; Morozov, V. V.

    1988-06-01

    Experimental results are presented on the operation of an LaB6 thermionic cathode in the pulsed mode, and it is shown that a decline in emission current can occur which depends on temperature, operating mode, pulse duration, and degree of activity. It is suggested that this decline may be due to changes in the residual concentration of La atoms on the surface of LaB6 under the effect of the anodic electric field.

  4. Correlated states of a quantum oscillator acted by short pulses

    NASA Technical Reports Server (NTRS)

    Manko, O. V.

    1993-01-01

    Correlated squeezed states for a quantum oscillator are constructed based on the method of quantum integrals of motion. The quantum oscillator is acted upon by short duration pulses. Three delta-kickings of frequency are used to model the pulses' dependence upon the time aspects of the frequency of the oscillator. Additionally, the correlation coefficient and quantum variances of operations of coordinates and momenta are written in explicit form.

  5. Nonlinear pulse compression of picosecond parabolic-like pulses synthesized with a long period fiber grating filter.

    PubMed

    Krcmarík, David; Slavík, Radan; Park, Yongwoo; Azaña, José

    2009-04-27

    tract: We demonstrate high quality pulse compression at high repetition rates by use of spectral broadening of short parabolic-like pulses in a normally-dispersive highly nonlinear fiber (HNLF) followed by linear dispersion compensation with a conventional SMF-28 fiber. The key contribution of this work is on the use of a simple and efficient long-period fiber grating (LPFG) filter for synthesizing the desired parabolic-like pulses from sech(2)-like input optical pulses; this all-fiber low-loss filter enables reducing significantly the required input pulse power as compared with the use of previous all-fiber pulse re-shaping solutions (e.g. fiber Bragg gratings). A detailed numerical analysis has been performed in order to optimize the system's performance, including investigation of the optimal initial pulse shape to be launched into the HNLF fiber. We found that the pulse shape launched into the HNLF is critically important for suppressing the undesired wave breaking in the nonlinear spectral broadening process. The optimal shape is found to be independent on the parameters of normally dispersive HNLFs. In our experiments, 1.5-ps pulses emitted by a 10-GHz mode-locked laser are first reshaped into 3.2-ps parabolic-like pulses using our LPFG-based pulse reshaper. Flat spectrum broadening of the amplified initial parabolic-like pulses has been generated using propagation through a commercially-available HNLF. Pulses of 260 fs duration with satellite peak and pedestal suppression greater than 17 dB have been obtained after the linear dispersion compensation fiber. The generated pulses exhibit a 20-nm wide supercontinuum energy spectrum that has almost a square-like spectral profile with >85% of the pulse energy contained in its FWHM spectral bandwidth. PMID:19399083

  6. Nonlinear pulse compression of picosecond parabolic-like pulses synthesized with a long period fiber grating filter.

    PubMed

    Krcmarík, David; Slavík, Radan; Park, Yongwoo; Azaña, José

    2009-04-27

    tract: We demonstrate high quality pulse compression at high repetition rates by use of spectral broadening of short parabolic-like pulses in a normally-dispersive highly nonlinear fiber (HNLF) followed by linear dispersion compensation with a conventional SMF-28 fiber. The key contribution of this work is on the use of a simple and efficient long-period fiber grating (LPFG) filter for synthesizing the desired parabolic-like pulses from sech(2)-like input optical pulses; this all-fiber low-loss filter enables reducing significantly the required input pulse power as compared with the use of previous all-fiber pulse re-shaping solutions (e.g. fiber Bragg gratings). A detailed numerical analysis has been performed in order to optimize the system's performance, including investigation of the optimal initial pulse shape to be launched into the HNLF fiber. We found that the pulse shape launched into the HNLF is critically important for suppressing the undesired wave breaking in the nonlinear spectral broadening process. The optimal shape is found to be independent on the parameters of normally dispersive HNLFs. In our experiments, 1.5-ps pulses emitted by a 10-GHz mode-locked laser are first reshaped into 3.2-ps parabolic-like pulses using our LPFG-based pulse reshaper. Flat spectrum broadening of the amplified initial parabolic-like pulses has been generated using propagation through a commercially-available HNLF. Pulses of 260 fs duration with satellite peak and pedestal suppression greater than 17 dB have been obtained after the linear dispersion compensation fiber. The generated pulses exhibit a 20-nm wide supercontinuum energy spectrum that has almost a square-like spectral profile with >85% of the pulse energy contained in its FWHM spectral bandwidth.

  7. Reliability of High Power Laser Diode Arrays Operating in Long Pulse Mode

    NASA Technical Reports Server (NTRS)

    Amzajerdian, Farzin; Meadows, Byron L.; Barnes, Bruce W.; Lockard, George E.; Singh, Upendra N.; Kavaya, Michael J.; Baker, Nathaniel R.

    2006-01-01

    Reliability and lifetime of quasi-CW laser diode arrays are greatly influenced by their thermal characteristics. This paper examines the thermal properties of laser diode arrays operating in long pulse duration regime.

  8. Temporal Narrowing of Neutrons Produced by High-Intensity Short-Pulse Lasers.

    PubMed

    Higginson, D P; Vassura, L; Gugiu, M M; Antici, P; Borghesi, M; Brauckmann, S; Diouf, C; Green, A; Palumbo, L; Petrascu, H; Sofia, S; Stardubtsev, M; Willi, O; Kar, S; Negoita, F; Fuchs, J

    2015-07-31

    The production of neutron beams having short temporal duration is studied using ultraintense laser pulses. Laser-accelerated protons are spectrally filtered using a laser-triggered microlens to produce a short duration neutron pulse via nuclear reactions induced in a converter material (LiF). This produces a ∼3  ns duration neutron pulse with 10(4)  n/MeV/sr/shot at 0.56 m from the laser-irradiated proton source. The large spatial separation between the neutron production and the proton source allows for shielding from the copious and undesirable radiation resulting from the laser-plasma interaction. This neutron pulse compares favorably to the duration of conventional accelerator sources and should scale up with, present and future, higher energy laser facilities to produce brighter and shorter neutron beams for ultrafast probing of dense materials.

  9. Temporal Narrowing of Neutrons Produced by High-Intensity Short-Pulse Lasers

    NASA Astrophysics Data System (ADS)

    Higginson, D. P.; Vassura, L.; Gugiu, M. M.; Antici, P.; Borghesi, M.; Brauckmann, S.; Diouf, C.; Green, A.; Palumbo, L.; Petrascu, H.; Sofia, S.; Stardubtsev, M.; Willi, O.; Kar, S.; Negoita, F.; Fuchs, J.

    2015-07-01

    The production of neutron beams having short temporal duration is studied using ultraintense laser pulses. Laser-accelerated protons are spectrally filtered using a laser-triggered microlens to produce a short duration neutron pulse via nuclear reactions induced in a converter material (LiF). This produces a ˜3 ns duration neutron pulse with 104 n /MeV /sr /shot at 0.56 m from the laser-irradiated proton source. The large spatial separation between the neutron production and the proton source allows for shielding from the copious and undesirable radiation resulting from the laser-plasma interaction. This neutron pulse compares favorably to the duration of conventional accelerator sources and should scale up with, present and future, higher energy laser facilities to produce brighter and shorter neutron beams for ultrafast probing of dense materials.

  10. Improvement in the statistical operation of a Blumlein pulse forming line in bipolar pulse mode

    SciTech Connect

    Pushkarev, A. I. Isakova, Y. I.; Khaylov, I. P.

    2014-07-15

    The paper presents the results of studies on shot-to-shot performance of a water Blumlein pulse forming line of 1–1.2 kJ of stored energy. The experiments were carried using the TEMP-4M pulsed ion beam accelerator during its operation in both unipolar pulse mode (150 ns, 250–300 kV) and bipolar-pulse mode with the first negative (300–600 ns, 100–150 kV) followed by a second positive (120 ns, 250–300 kV) pulse. The analysis was carried out for two cases when the Blumlein was terminated with a resistive load and with a self-magnetically insulated ion diode. It was found that in bipolar pulse mode the shot-to-shot variation in breakdown voltage of a preliminary spark gap is small, the standard deviation (1σ) does not exceed 2%. At the same time, the shot-to-shot variation in the breakdown voltage of the main spark gap in both bipolar-pulse and unipolar pulse mode is 3–4 times higher than that for the preliminary spark gap. To improve the statistical performance of the main spark gap we changed the regime of its operation from a self-triggered mode to an externally triggered mode. In the new arrangement the first voltage pulse at the output of Blumlein was used to trigger the main spark gap. The new trigatron-type regime of the main spark gap operation showed a good stability of breakdown voltage and thus allowed to stabilize the duration of the first pulse. The standard deviation of the breakdown voltage and duration of the first pulse did not exceed 2% for a set of 50 pulses. The externally triggered mode of the main gap operation also allowed for a decrease in the charging voltage of the Blumlein to a 0.9–0.95 of self-breakdown voltage of the main spark gap while the energy stored in Marx generator was decreased from 4 kJ to 2.5 kJ. At the same time the energy stored in Blumlein remained the same.

  11. Constant potential pulse polarography

    USGS Publications Warehouse

    Christie, J.H.; Jackson, L.L.; Osteryoung, R.A.

    1976-01-01

    The new technique of constant potential pulse polarography, In which all pulses are to be the same potential, is presented theoretically and evaluated experimentally. The response obtained is in the form of a faradaic current wave superimposed on a constant capacitative component. Results obtained with a computer-controlled system exhibit a capillary response current similar to that observed In normal pulse polarography. Calibration curves for Pb obtained using a modified commercial pulse polarographic instrument are in good accord with theoretical predictions.

  12. Alternate drop pulse polarography

    USGS Publications Warehouse

    Christie, J.H.; Jackson, L.L.; Osteryoung, R.A.

    1976-01-01

    The new technique of alternate drop pulse polarography is presented. An experimental evaluation of alternate drop pulse polarography shows complete compensation of the capacitative background due to drop expansion. The capillary response phenomenon was studied in the absence of faradaic reaction and the capillary response current was found to depend on the pulse width to the -0.72 power. Increased signal-to-noise ratios were obtained using alternate drop pulse polarography at shorter drop times.

  13. Electrical pulse generator

    DOEpatents

    Norris, Neil J.

    1979-01-01

    A technique for generating high-voltage, wide dynamic range, shaped electrical pulses in the nanosecond range. Two transmission lines are coupled together by resistive elements distributed along the length of the lines. The conductance of each coupling resistive element as a function of its position along the line is selected to produce the desired pulse shape in the output line when an easily produced pulse, such as a step function pulse, is applied to the input line.

  14. Design of a Pulse Injector for DME Propellant

    NASA Astrophysics Data System (ADS)

    Fukunaga, Masato; Kakami, Akira; Tachibana, Takeshi

    Recently, a pulsed plasma thruster (PPT), which has advantages such as smallness, lightweight and low power consumption, has attracted attention again for the application to small satellites. Liquid propellant like water or alcohol provides higher specific impulse in comparison with conventional Teflon propellant. Nevertheless, water and alcohol propellants have problems: higher freezing point or contamination to satellites by the exhaust gas. In this study, we propose to apply DME (Di-methyl ether) to the PPT's propellant. DME can be stored as liquid, and requires no pressurant because DME has a vapor pressure of 0.6 MPa at 298 K. DME would also be potentially usable as heat transfer media, coolant, working fluid of heat pipe etc. We have designed and tested a prototyped pulse injector supplying liquid DME to discharge channels of the PPTs. Experimental results showed that the pulse injector successfully injected liquefied DME of 1.16 mg/shot, which is equivalent to the mass shot of a high power class PPT. The shape of injected liquid was dependent on the duration of the gating-pulse applied to the injector; a group of droplets were provided with a 20 ms gating-pulse duration, and a single stream with 25 ms or longer gating-pulse duration.

  15. Generation of individually modulated femtosecond pulse string by multilayer volume holographic gratings.

    PubMed

    Yan, Xiaona; Gao, Lirun; Yang, Xihua; Dai, Ye; Chen, Yuanyuan; Ma, Guohong

    2014-10-20

    A scheme to generate individually modulated femtosecond pulse string by multilayer volume holographic grating (MVHG) is proposed. Based on Kogelnik's coupled-wave theory and matrix optics, temporal and spectral expressions of diffracted field are given when a femtosecond pulse is diffracted by a MVHG. It is shown that the number of diffracted sub-pulses in the pulse string equals to the number of grating layers of the MVHG, peak intensity and duration of each diffracted sub-pulse depend on thickness of the corresponding grating layer, whereas pulse interval between adjacent sub-pulses is related to thickness of the corresponding buffer layer. Thus by modulating parameters of the MVHG, individually modulated femtosecond pulse string can be acquired. Based on Bragg selectivity of the volume grating and phase shift provided by the buffer layers, we give an explanation on these phenomena. The result is useful to design MVHG-based devices employed in optical communications, pulse shaping and processing. PMID:25401645

  16. Generation of intense coherent attosecond X-ray pulses using relativistic electron mirrors

    SciTech Connect

    Kulagin, V V; Kornienko, V N; Cherepenin, Vladimir A; Suk, Hyyong

    2013-05-31

    We analyse the steepening of the leading edge of femtosecond petawatt pulses with the use of plasma layers and show that, at an electron density several times higher than the critical one, an asymmetric (in time domain) pulse can be produced with an amplitude of the first half-wave differing little from the maximum pulse amplitude. Using numerical simulation, we have studied the interaction of such pulses with nanometre-thick films, including the generation of relativistic electron mirrors and the reflection of a counterpropagating probe pulse from such mirrors. The resulting coherent X-ray pulses have a duration of {approx}120 as and a power of {approx}600 GW at a wavelength of {approx}13 nm. Our results demonstrate that the reflectivity of a relativistic electron mirror situated in the accelerating pulse field is independent of the probe pulse amplitude when it increases up to the accelerating pulse amplitude. (interaction of laser radiation with matter. laser plasma)

  17. Generation of individually modulated femtosecond pulse string by multilayer volume holographic gratings.

    PubMed

    Yan, Xiaona; Gao, Lirun; Yang, Xihua; Dai, Ye; Chen, Yuanyuan; Ma, Guohong

    2014-10-20

    A scheme to generate individually modulated femtosecond pulse string by multilayer volume holographic grating (MVHG) is proposed. Based on Kogelnik's coupled-wave theory and matrix optics, temporal and spectral expressions of diffracted field are given when a femtosecond pulse is diffracted by a MVHG. It is shown that the number of diffracted sub-pulses in the pulse string equals to the number of grating layers of the MVHG, peak intensity and duration of each diffracted sub-pulse depend on thickness of the corresponding grating layer, whereas pulse interval between adjacent sub-pulses is related to thickness of the corresponding buffer layer. Thus by modulating parameters of the MVHG, individually modulated femtosecond pulse string can be acquired. Based on Bragg selectivity of the volume grating and phase shift provided by the buffer layers, we give an explanation on these phenomena. The result is useful to design MVHG-based devices employed in optical communications, pulse shaping and processing.

  18. A compact high-voltage pulse generator based on pulse transformer with closed magnetic core.

    PubMed

    Zhang, Yu; Liu, Jinliang; Cheng, Xinbing; Bai, Guoqiang; Zhang, Hongbo; Feng, Jiahuai; Liang, Bo

    2010-03-01

    A compact high-voltage nanosecond pulse generator, based on a pulse transformer with a closed magnetic core, is presented in this paper. The pulse generator consists of a miniaturized pulse transformer, a curled parallel strip pulse forming line (PFL), a spark gap, and a matched load. The innovative design is characterized by the compact structure of the transformer and the curled strip PFL. A new structure of transformer windings was designed to keep good insulation and decrease distributed capacitance between turns of windings. A three-copper-strip structure was adopted to avoid asymmetric coupling of the curled strip PFL. When the 31 microF primary capacitor is charged to 2 kV, the pulse transformer can charge the PFL to 165 kV, and the 3.5 ohm matched load can deliver a high-voltage pulse with a duration of 9 ns, amplitude of 84 kV, and rise time of 5.1 ns. When the load is changed to 50 ohms, the output peak voltage of the generator can be 165 kV, the full width at half maximum is 68 ns, and the rise time is 6.5 ns.

  19. Timing control of an intense picosecond pulse laser to the SPring-8 synchrotron radiation pulses

    NASA Astrophysics Data System (ADS)

    Tanaka, Yoshihito; Hara, Toru; Kitamura, Hideo; Ishikawa, Tetsuya

    2000-03-01

    We have developed a control system to synchronize intense picosecond laser pulses to the hard x-ray synchrotron radiation (SR) pulses of SPring-8. A regeneratively amplified mode-locked Ti:sapphire laser is synchronized to 40 ps SR pulses by locking the laser to the radio frequency of the ring. The synchronization of the pulses is monitored by detecting both beams simultaneously on a gold photocathode of a streak camera. This method enabled us to make a precise measurement of the time interval between the beams, even if the trigger of the streak camera drifts. Synchronization between the laser and the SR pulses has been achieved with a precision of ±2 ps for some hours. The stable timing control ensures the possibility of making two-photon excitation and pump-probe experiments with time resolution of a few tens of ps (limited by the pulse duration of the SR). We have used this system to show that closing undulator gaps in the storage ring shifts the arrival time of the SR pulses, in accord with expectations for the increased power loss.

  20. Millisecond measurement of transport during and after an electroporation pulse.

    PubMed Central

    Prausnitz, M R; Corbett, J D; Gimm, J A; Golan, D E; Langer, R; Weaver, J C

    1995-01-01

    Electroporation involves the application of an electric field pulse that creates transient aqueous pathways in lipid bilayer membranes. Transport through these pathways can occur by different mechanisms during and after a pulse. To determine the time scale of transport and the mechanism(s) by which it occurs, efflux of a fluorescent molecule, calcein, across erythrocyte ghost membranes was measured with a fluorescence microscope photometer with millisecond time resolution during and after electroporation pulses several milliseconds in duration. One of four outcomes was typically observed. Ghosts were: (1) partially emptied of calcein, involving efflux primarily after the pulse; (2) completely emptied of calcein, involving efflux primarily after the pulse; (3) completely emptied of calcein, involving efflux both during and after the pulse; or (4) completely emptied of calcein, involving efflux primarily during the pulse. Partial emptying, involving significant efflux during the pulse, was generally not observed. We conclude that under some conditions transport caused by electroporation occurs predominantly by electrophoresis and/or electroosmosis during a pulse, although under other conditions transport occurs in part or almost completely by diffusion within milliseconds to seconds after a pulse. PMID:7612828

  1. Pulse generation and preamplification for long pulse beamlines of Orion laser facility.

    PubMed

    Hillier, David I; Winter, David N; Hopps, Nicholas W

    2010-06-01

    We describe the pulse generation, shaping, and preamplification system for the nanosecond beamlines of the Orion laser facility. The system generates shaped laser pulses of up to approximately 1 J of 100 ps-5 ns duration with a programmable temporal profile. The laser has a 30th-power supergaussian spatial profile and is diffraction limited. The system is capable of imposing 2D smoothing by spectral dispersion upon the beam, which will produce a nonuniformity of 10% rms at the target. PMID:20517369

  2. Electron acceleration by few-cycle laser pulses with single-wavelength spot size.

    PubMed

    Dudnikova, G I; Bychenkov, V Yu; Maksimchuk, A; Mourou, G; Nees, J; Bochkarev, S G; Vshivkov, V A

    2003-02-01

    Generation of relativistic electrons from the interaction of a laser pulse with a high density plasma foil, accompanied by an underdense preplasma in front of it, has been studied with two-dimensional particle-in-cell (PIC) simulations for pulse durations comparable to a single cycle and for single-wavelength spot size. The electrons are accelerated predominantly in forward direction for a preplasma longer than the pulse length. Otherwise, both forward and backward electron accelerations occur. The primary mechanism responsible for electron acceleration is identified. Simulations show that the energy of the accelerated electrons has a maximum versus the pulse duration for relativistic laser intensities. The most effective electron acceleration takes place when the preplasma scale length is comparable to the pulse duration. Electron distribution functions have been found from PIC simulations. Their tails are well approximated by Maxwellian distributions with a hot temperature in the MeV range.

  3. Influence of consecutive picosecond pulses at 532 nm wavelength on laser ablation of human teeth

    NASA Astrophysics Data System (ADS)

    Mirdan, Balsam M.; Antonelli, Luca; Batani, Dimitri; Jafer, Rashida; Jakubowska, Katarzyna; Tarazi, Saad al; Villa, Anna Maria; Vodopivec, Bruno; Volpe, Luca

    2014-07-01

    The interaction of 40 ps pulse duration laser emitting at 532 nm wavelength with human dental tissue (enamel, dentin, and dentin-enamel junction) has been investigated. The crater profile and the surface morphology have been studied by using a confocal auto-fluorescence microscope (working in reflection mode) and a scanning electron microscope. Crater profile and crater morphology were studied after applying consecutive laser pulses and it was found that the ablation depth increases with the number of consecutive pulses, leaving the crater diameter unchanged. We found that the thermal damage is reduced by using short duration laser pulses, which implies an increased retention of restorative material. We observe carbonization of the irradiated samples, which does not imply changes in the chemical composition. Finally, the use of 40 ps pulse duration laser may become a state of art in conservative dentistry.

  4. Pulse width dependence of motor threshold and input–output curve characterized with controllable pulse parameter transcranial magnetic stimulation

    PubMed Central

    Peterchev, Angel V.; Goetz, Stefan M.; Westin, Gregory G.; Luber, Bruce; Lisanby, Sarah H.

    2013-01-01

    Objective To demonstrate the use of a novel controllable pulse parameter TMS (cTMS) device to characterize human corticospinal tract physiology. Methods Motor threshold and input-output (IO) curve of right first dorsal interosseus were determined in 26 and 12 healthy volunteers, respectively, at pulse widths of 30, 60, and 120 μs using a custom-built cTMS device. Strength–duration curve rheobase and time constant were estimated from the motor thresholds. IO slope was estimated from sigmoid functions fitted to the IO data. Results All procedures were well tolerated with no seizures or other serious adverse events. Increasing pulse width decreased the motor threshold and increased the pulse energy and IO slope. The average strength–duration curve time constant is estimated to be 196 μs, 95% CI [181 μs, 210 μs]. IO slope is inversely correlated with motor threshold both across and within pulse width. A simple quantitative model explains these dependencies. Conclusions Our strength–duration time constant estimate compares well to published values and may be more accurate given increased sample size and enhanced methodology. Multiplying the IO slope by the motor threshold may provide a sensitive measure of individual differences in corticospinal tract physiology. Significance Pulse parameter control offered by cTMS provides enhanced flexibility that can contribute novel insights in TMS studies. PMID:23434439

  5. Pulsed Laval nozzle with a large optical path length of 50 cm

    NASA Astrophysics Data System (ADS)

    Okada, Yoshiki; Isomura, Shohei; Satooka, Sakae; Takeuchi, Kazuo

    1994-07-01

    This note describes the design and performance of a pulsed valve developed as a gas source for a 500 mm long supersonic Laval nozzle with a 3 mm wide throat. The valve consists of a rotating drum with a slit, which allows an opening duration of approximately 14 ms. The duration of quasi-steady-state expansion is measured to be 10 ms at the nozzle throat when the pulsed valve is filled with 200 Torr of Ar gas.

  6. Cloning assay thresholds on cells exposed to ultrafast laser pulses

    NASA Astrophysics Data System (ADS)

    Koenig, Karsten; Riemann, Iris; Fischer, Peter; Becker, Thomas P.; Oehring, Hartmut; Halbhuber, Karl-Juergen

    1999-06-01

    The influence of the peak power, laser wavelength and the pulse duration of near infrared (NIR) ultrashort laser pulses on the reproduction behavior of Chinese hamster ovary (CHO) cells has been studied. In particular we determined the cloning efficiency of single cell pairs after exposure to ultrashort laser pulses with an intensity in the range of GW/cm2 and TW/cm2. A total of more than 3500 non- labeled cells were exposed to a highly focused scanning beam of a multiphoton laser microscope with 60 microsecond pixel dwell time per scan. The beam was provided by a tunable argon ion laser pumped mode-locked 76 MHz Titanium:Sapphire laser as well as by a compact solid-state laser based system (Vitesse) at a fixed wavelength of 800 nm. Pulse duration (tau) was varied in the range of 100 fs to 4 ps by out-of-cavity pulse- stretching units consisting of SF14 prisms and blazed gratings. Within an optical (laser power) window CHO cells could be scanned for hours without severe impact on reproduction behavior, morphology and vitality. Ultrastructural studies reveal that mitochondria are the major targets of intense destructive laser pulses. Above certain laser power P thresholds, CHO cells started to delay or failed to undergo cell division and, in part, to develop uncontrolled cell growth (giant cell formation). The damage followed a P2/(tau) relation which is typical for a two-photon excitation process. Therefore, cell damage was found to be more pronounced at shorter pulses. Due to the same P2/(tau) relation for the efficiency of fluorescence excitation, two- photon microscopy of living cells does not require extremely short femtosecond laser pulses nor pulse compression units. Picosecond as well as femtosecond layers can be used as efficient light sources in safe two photon fluorescence microscopy. Only in three photon fluorescence microscopy, femtosecond laser pulses are advantageous over picosecond pulses.

  7. Cloning assay thresholds on cells exposed to ultrafast laser pulses

    NASA Astrophysics Data System (ADS)

    Koenig, Karsten; Riemann, Iris; Fischer, Peter; Becker, Thomas P.; Oehring, Hartmut; Halbhuber, Karl-Juergen

    1999-06-01

    The influence of the peak power, laser wavelength and the pulse duration of near infrared ultrashort laser pulses on the reproduction behavior of Chinese hamster ovary (CHO) cells has been studied. In particular, we determined the cloning efficiency of single cell pairs after exposure to ultrashort laser pulses with an intensity in the range of GW/cm2 and TW/cm2. A total of more than 3500 non- labeled cells were exposed to a highly focused scanning beam of a multiphoton laser microscope with 60 microsecond(s) pixel dwell time per scan. The beam was provided by a tunable argon ion laser pumped mode-locked 76 MHz Titanium:Sapphire laser as well as by a compact solid-state laser based system (Vitesse) at a fixed wavelength of 800 nm. Pulse duration (tau) was varied in the range of 100 fs to 4 ps by out-of- cavity pulse-stretching units consisting of SF14 prisms and blazed gratings. Within an optical (laser power) window CHO cells could be scanned for hours without severe impact on reproduction behavior, morphology and vitality. Ultrastructural studies reveal that mitochondria are the major targets of intense destructive laser pulses. Above certain laser power P thresholds, CHO cells started to delay or failed to undergo cell division and, in part, to develop uncontrolled cell growth (giant cell formation). The damage followed a P2/(tau) relation which is typical for a two- photon excitation process. Therefore, cell damage was found to be more pronounced at shorter pulses. Due to the same P2/(tau) relation for the efficiency of fluorescence excitation, two-photon microscopy of living cells does not require extremely short femtosecond laser pulses nor pulse compression units. Picosecond as well as femtosecond lasers can be used as efficient light sources in safe two photon fluorescence microscopy. Only in three photon fluorescence microscopy, femtosecond laser pulses are advantageous over picosecond pulses.

  8. Estimating magnitude and duration of incident delays

    SciTech Connect

    Garib, A.; Radwan, A.E.; Al-Deek, H.

    1997-11-01

    Traffic congestion is a major operational problem on urban freeways. In the case of recurring congestion, travelers can plan their trips according to the expected occurrence and severity of recurring congestion. However, nonrecurring congestion cannot be managed without real-time prediction. Evaluating the efficiency of intelligent transportation systems (ITS) technologies in reducing incident effects requires developing models that can accurately predict incident duration along with the magnitude of nonrecurring congestion. This paper provides two statistical models for estimating incident delay and a model for predicting incident duration. The incident delay models showed that up to 85% of variation in incident delay can be explained by incident duration, number of lanes affected, number of vehicles involved, and traffic demand before the incident. The incident duration prediction model showed that 81% of variation in incident duration can be predicted by number of lanes affected, number of vehicles involved, truck involvement, time of day, police response time, and weather condition. These findings have implications for on-line applications within the context of advanced traveler information systems (ATIS).

  9. Duration expansion at low luminance levels.

    PubMed

    Bruno, Aurelio; Ayhan, Inci; Johnston, Alan

    2011-01-01

    Duration distortions have been shown to occur at the time of saccades and following high temporal frequency or contrast adaptation. Under all these conditions, changes in the temporal tuning of M neurons also occur, suggesting that there might be a link between the two phenomena. In order to explore this relationship further, we measured the apparent duration of visual stimuli in the dark, where the temporal impulse response has been reported to lengthen. We first measured a progressive shift and reduction of the occurrence of an apparent motion reversal as we decreased the luminance level, indicating a lengthening of the temporal impulse response. We then measured perceived duration at these luminance levels (0.75, 3, and 50 cd/m(2)) after matching for apparent contrast and temporal frequency. While perceived temporal frequency did not substantially differ across luminance levels, duration appeared expanded at the lowest luminance level relative to the highest by approximately 60 ms. Thus, we have shown that reduced luminance is associated with both a lengthening of the temporal impulse response and a duration expansion, linking the two and providing further evidence for a relationship between changes in the neuronal tuning in the early stages of the visual system and time perception.

  10. Hybrid chirped pulse amplification system

    DOEpatents

    Barty, Christopher P.; Jovanovic, Igor

    2005-03-29

    A hybrid chirped pulse amplification system wherein a short-pulse oscillator generates an oscillator pulse. The oscillator pulse is stretched to produce a stretched oscillator seed pulse. A pump laser generates a pump laser pulse. The stretched oscillator seed pulse and the pump laser pulse are directed into an optical parametric amplifier producing an optical parametric amplifier output amplified signal pulse and an optical parametric amplifier output unconverted pump pulse. The optical parametric amplifier output amplified signal pulse and the optical parametric amplifier output laser pulse are directed into a laser amplifier producing a laser amplifier output pulse. The laser amplifier output pulse is compressed to produce a recompressed hybrid chirped pulse amplification pulse.

  11. Stress pulse phenomena

    SciTech Connect

    McGlaun, M.

    1993-08-01

    This paper is an introductory discussion of stress pulse phenomena in simple solids and fluids. Stress pulse phenomena is a very rich and complex field that has been studied by many scientists and engineers. This paper describes the behavior of stress pulses in idealized materials. Inviscid fluids and simple solids are realistic enough to illustrate the basic behavior of stress pulses. Sections 2 through 8 deal with the behavior of pressure pulses. Pressure is best thought of as the average stress at a point. Section 9 deals with shear stresses which are most important in studying solids.

  12. Durations required to distinguish noise and tone: Effects of noise bandwidth and frequency.

    PubMed

    Taghipour, Armin; Moore, Brian C J; Edler, Bernd

    2016-05-01

    Perceptual audio coders exploit the masking properties of the human auditory system to reduce the bit rate in audio recording and transmission systems; it is intended that the quantization noise is just masked by the audio signal. The effectiveness of the audio signal as a masker depends on whether it is tone-like or noise-like. The determination of this, both physically and perceptually, depends on the duration of the stimuli. To gather information that might improve the efficiency of perceptual coders, the duration required to distinguish between a narrowband noise and a tone was measured as a function of center frequency and noise bandwidth. In experiment 1, duration thresholds were measured for isolated noise and tone bursts. In experiment 2, duration thresholds were measured for tone and noise segments embedded within longer tone pulses. In both experiments, center frequencies were 345, 754, 1456, and 2658 Hz and bandwidths were 0.25, 0.5, and 1 times the equivalent rectangular bandwidth of the auditory filter at each center frequency. The duration thresholds decreased with increasing bandwidth and with increasing center frequency up to 1456 Hz. It is argued that the duration thresholds depended mainly on the detection of amplitude fluctuations in the noise bursts. PMID:27250144

  13. Precipitation pulses and carbon fluxes in semiarid and arid ecosystems.

    PubMed

    Huxman, Travis E; Snyder, Keirith A; Tissue, David; Leffler, A Joshua; Ogle, Kiona; Pockman, William T; Sandquist, Darren R; Potts, Daniel L; Schwinning, Susan

    2004-10-01

    In the arid and semiarid regions of North America, discrete precipitation pulses are important triggers for biological activity. The timing and magnitude of these pulses may differentially affect the activity of plants and microbes, combining to influence the C balance of desert ecosystems. Here, we evaluate how a "pulse" of water influences physiological activity in plants, soils and ecosystems, and how characteristics, such as precipitation pulse size and frequency are important controllers of biological and physical processes in arid land ecosystems. We show that pulse size regulates C balance by determining the temporal duration of activity for different components of the biota. Microbial respiration responds to very small events, but the relationship between pulse size and duration of activity likely saturates at moderate event sizes. Photosynthetic activity of vascular plants generally increases following relatively larger pulses or a series of small pulses. In this case, the duration of physiological activity is an increasing function of pulse size up to events that are infrequent in these hydroclimatological regions. This differential responsiveness of photosynthesis and respiration results in arid ecosystems acting as immediate C sources to the atmosphere following rainfall, with subsequent periods of C accumulation should pulse size be sufficient to initiate vascular plant activity. Using the average pulse size distributions in the North American deserts, a simple modeling exercise shows that net ecosystem exchange of CO2 is sensitive to changes in the event size distribution representative of wet and dry years. An important regulator of the pulse response is initial soil and canopy conditions and the physical structuring of bare soil and beneath canopy patches on the landscape. Initial condition influences responses to pulses of varying magnitude, while bare soil/beneath canopy patches interact to introduce nonlinearity in the relationship between pulse

  14. Processing HIP-zirconia with ultra-short laser pulses

    NASA Astrophysics Data System (ADS)

    Werelius, Kristian; Weigl, Paul; Lubatschowski, Holger

    2003-11-01

    Creating individual complex three dimensional structures in HIP-zirconia by conventional mechanical machining, e.g. milling, is time consuming and subject to significant loss in bending strength due to microcracking during the milling process. Utilizing ultra-short laser pulses, individual complex three dimensional microstructures can be created very precisely without significant damage to the structure. This advantage is used to process HIP-zirconia in order to create dental restorations. To evaluate efficiency and quality, different laser parameters such as pulse duration, pulse energy and ablation strategies were studied. The maximum ablation rate was found at 400 fs.

  15. The recording and processing of pulsed laser diode spectra

    NASA Technical Reports Server (NTRS)

    Fuhr, Peter L.; Maufer, Thomas A.

    1987-01-01

    A system capable of measuring and statistically analyzing wavelength and intensity fluctuations in pulsed laser diode output beams has been developed. The snapshot wavelength-intensity performance of laser diodes emitting discrete short-duration optical pulse is determined by isolating and recording individual pulses. Statistical processing of the resultant data generates information about the magnitude and/or frequency of occurrence of power variations or wavelength fluctuations in narrow optical bands. The system configuration along with plots depicting results based on measurements taken for various laser diodes are presented.

  16. Isolated-attosecond-pulse generation with infrared double optical gating

    NASA Astrophysics Data System (ADS)

    Lan, Pengfei; Takahashi, Eiji J.; Midorikawa, Katsumi

    2011-06-01

    We propose and theoretically demonstrate an infrared two-color polarization gating scheme for generating an intense isolated attosecond pulse (IAP) in the multicycle regime. Our simulations show that an IAP can be produced using a multicycle two-color driving pulse with a duration up to 60 fs. Moreover, the carrier-envelope phase (CEP) of the driving laser is not required to be stabilized, although the IAP intensity changes with the CEP slip. Such a gating scheme significantly relaxes the requirements for driving lasers and opens the door to easily create intense IAPs with a high-power conventional multicycle laser pulse.

  17. Isolated-attosecond-pulse generation with infrared double optical gating

    SciTech Connect

    Lan Pengfei; Takahashi, Eiji J.; Midorikawa, Katsumi

    2011-06-15

    We propose and theoretically demonstrate an infrared two-color polarization gating scheme for generating an intense isolated attosecond pulse (IAP) in the multicycle regime. Our simulations show that an IAP can be produced using a multicycle two-color driving pulse with a duration up to 60 fs. Moreover, the carrier-envelope phase (CEP) of the driving laser is not required to be stabilized, although the IAP intensity changes with the CEP slip. Such a gating scheme significantly relaxes the requirements for driving lasers and opens the door to easily create intense IAPs with a high-power conventional multicycle laser pulse.

  18. Isolated Attosecond Pulses using a Detuned Second-harmonic Field

    SciTech Connect

    Merdji, Hamed; Auguste, Thierry; Boutu, Willem; Caumes, J.-Pascal; Carre, Bertrand; Pfeifer, Thomas; Jullien, Aurelie; Neumark, Daniel M.; Leone, Stephen R.; /UC, Berkeley /LBL, Berkeley

    2007-11-07

    Calculations are presented for the generation of an isolated attosecond pulse in a multicycle two-color strong-field regime. We show that the recollision of the electron wave packet can be confined to half an optical cycle using pulses of up to 40 fs in duration. The scheme is proven to be efficient using two intense beams, one producing a strong field at {omega} and the other a strong field detuned from 2{omega}. The slight detuning {delta}{omega} of the second harmonic is used to break the symmetry of the electric field over many optical cycles and provides a coherent control for the formation of an isolated attosecond pulse.

  19. LASERS: Laser stand for irradiation of targets by laser pulses from the Iskra-5 facility at a repetition rate of 100 MHz

    NASA Astrophysics Data System (ADS)

    Annenkov, V. I.; Garanin, Sergey G.; Eroshenko, V. A.; Zhidkov, N. V.; Zubkov, A. V.; Kalipanov, S. V.; Kalmykov, N. A.; Kovalenko, V. P.; Krotov, V. A.; Lapin, S. G.; Martynenko, S. P.; Pankratov, V. I.; Faizullin, V. S.; Khrustalev, V. A.; Khudikov, N. M.; Chebotar, V. S.

    2009-08-01

    A train of a few tens of high-power subnanosecond laser pulses with a repetition period of 10 ns is generated in the Iskra-5 facility. The laser pulse train has an energy of up to 300 J and contains up to 40 pulses (by the 0.15 intensity level), the single pulse duration in the train being ~0.5 ns. The results of experiments on conversion of a train of laser pulses to a train of X-ray pulses are presented. Upon irradiation of a tungsten target, a train of X-ray pulses is generated with the shape of an envelope in the spectral band from 0.18 to 0.28 keV similar to that of the envelope of the laser pulse train. The duration of a single X-ray pulse in the train is equal to that of a single laser pulse.

  20. STS mission duration enhancement study: (orbiter habitability)

    NASA Technical Reports Server (NTRS)

    Carlson, A. D.

    1979-01-01

    Habitability improvements for early flights that could be implemented with minimum impact were investigated. These included: (1) launching the water dispenser in the on-orbit position instead of in a locker; (2) the sleep pallet concept; and (3) suction cup foot restraints. Past studies that used volumetric terms and requirements for crew size versus mission duration were reviewed and common definitions of key habitability terms were established. An accurately dimensioned drawing of the orbiter mid-deck, locating all of the known major elements was developed. Finally, it was established that orbiter duration and crew size can be increased with minimum modification and impact to the crew module. Preliminary concepts of the aft med-deck, external versions of expanded tunnel adapters (ETA), and interior concepts of ETA-3 were developed and comparison charts showing the various factors of volume, weight, duration, size, impact to orbiter, and number of sleep stations were generated.

  1. Fluctuation behaviors of financial return volatility duration

    NASA Astrophysics Data System (ADS)

    Niu, Hongli; Wang, Jun; Lu, Yunfan

    2016-04-01

    It is of significantly crucial to understand the return volatility of financial markets because it helps to quantify the investment risk, optimize the portfolio, and provide a key input of option pricing models. The characteristics of isolated high volatility events above certain threshold in price fluctuations and the distributions of return intervals between these events arouse great interest in financial research. In the present work, we introduce a new concept of daily return volatility duration, which is defined as the shortest passage time when the future volatility intensity is above or below the current volatility intensity (without predefining a threshold). The statistical properties of the daily return volatility durations for seven representative stock indices from the world financial markets are investigated. Some useful and interesting empirical results of these volatility duration series about the probability distributions, memory effects and multifractal properties are obtained. These results also show that the proposed stock volatility series analysis is a meaningful and beneficial trial.

  2. Determinants of eye-fixation duration.

    PubMed

    Salthouse, T A; Ellis, C L

    1980-06-01

    Four variables that might be presumed to contribute to the duration of an eye fixation were investigated in a series of seven experiments. These variables were stimulus processing time, relative emphasis on speed or accuracy, sequential dependencies across successive fixations, and amplitude of the preceding and following saccades. The pattern of results suggested a two-component model to account for the duration of single eye-fixations. One component is the minimum pause time of the eye, estimated to be about 200 msec without any stimulus processing. The second component involves stimulus processing, estimated to require a minimum of 50 to 100 msec, but subject to a number of influences that can substantially increase or decrease this duration. Although the authors did not generate this model to account for eye movements in complex tasks such as reading, they speculate about how complications could be added.

  3. ELECTRICAL PULSE COUNTER APPARATUS

    DOEpatents

    Kaufman, W.M.; Jeeves, T.A.

    1962-09-01

    A progressive electrical pulse counter circuit rs designed for the counting of a chain of input pulses. The circuit employs a series of direct connected bistable counting stages simultaneously pulsed by each input pulse and a delay means connected between each of the stages. Each bistable stage has two d-c operative states, which stage, when in its initial state, prevents the next succeeding stage from changing its condition when the latter stage is pulsed. Since the delay circuits between the stages prevents the immediate decay of the d-c state of each stage when the stages are pulsed, only one stage will change its state for each input pulse, thereby providing progressive stage-by-stage counting. (AEC)

  4. Pulsed lasers in dentistry: sense or nonsense?

    NASA Astrophysics Data System (ADS)

    Koort, Hans J.; Frentzen, Matthias

    1991-05-01

    The great interest in the field of laser applications in dentistry provokes the question, if all these new techniques may really fulfill advantages, which are expected after initial in-vitro studies. Whereas laser surgery of soft oral tissues has been developed to a standard method, laser treatment of dental hard tissues and the bone are attended with many unsolved problems. Different laser types, especially pulsed lasers in a wide spectrum of wavelengths have been proofed for dental use. Today neither the excimer lasers, emitting in the far uv-range from 193 to 351 nm, nor the mid-infrared lasers like Nd:YAG (1,064 μm), Ho:YAG (2,1 μm) and Er:YAG (2,96 μm) or the C02-laser (10,6 μm) show mechanism of interaction more carefully and faster than a preparation of teeth with diamond drillers. The laser type with the most precise and considerate treatment effects in the moment is the short pulsed (15 ns) ArF-excimer laser with a wavelength of 193 nm. However this laser type has not yet the effectivity of mechanical instruments and it needs a mirror system to deliver the radiation. Histological results point out, that this laser shows no significant pathological alterations in the adjacent tissues. Another interesting excimer laser, filled with XeCI and emitting at a wavelength of 308 nm has the advantage to be good to deliver through quartz fibers. A little more thermal influence is to be seen according to the longer wavelength. Yet the energy density, necessary to cut dental hard tissues will not be reached with the laser systems available now. Both the pulsed Er:YAG- (2,94 μm, pulse duration 250 s) and the Ho:YAG -laser (2,1 μm, pulse duration 250 μs) have an effective coupling of the laser energy to hydrogeneous tissues, but they do not work sufficient on healthy enamel and dentine. The influence to adjacent healthy tissue is not tolerable, especially in regard of the thermal damage dentine and pulp tissues. Moreover, like the 193 nm ArF-excimer laser

  5. EDITORIAL: 10th anniversary of attosecond pulses 10th anniversary of attosecond pulses

    NASA Astrophysics Data System (ADS)

    Kienberger, Reinhard; Chang, Zenghu; Nam, Chang Hee

    2012-04-01

    Attosecond science is an emerging field prompted by the development of attosecond light sources during the last decade. Since shorter light sources can diagnose faster phenomena, the generation of very short light pulses is critical in ultrafast measurements. In 2001 two groups at Commissariat à l'Energie Atomique (CEA), Saclay, and Technische Universität Wien (TUW), Vienna, succeeded in proving the production of attosecond pulse trains and isolated attosecond pulses using high harmonic generation processes, respectively. For the temporal characterization, cross correlation techniques such as RABITT and FROG CRAB that make use of the photoionization of atoms by harmonic and infrared pulses have been demonstrated, in addition to autocorrelation techniques. Femtosecond laser technology has progressed so well that carrier envelope phase (CEP)-stabilized few cycle lasers are now widely used in the production of attosecond pulses. For the generation of isolated attosecond pulses the high-harmonic generation processes have been controlled: the amplitude gating method has been powerful with CEP-stabilized sub-two-cycle laser pulses and the temporal gating methods, including polarization gating and double optical gating, have been effective in accommodating multi-cycle laser pulses. In achieving near transform-limited attosecond pulses the compensation of the inherent attosecond chirp by material dispersion has been useful. The attosecond pulse duration has reached sub-100 attoseconds both for attosecond pulse trains and isolated attosecond pulses, and it is expected that attosecond pulses shorter than one atomic unit (24 as) will be obtained soon. With attosecond light sources, attosecond science has become an active research field. Ultrafast phenomena in atoms and molecules have been looked at in detail, especially in the time domain. The photoionization processes of atoms and molecules occurring in sub-optical cycles have been analyzed, and ultrafast characteristic

  6. Multiple noise-like pulsing of a figure-eight fibre laser

    NASA Astrophysics Data System (ADS)

    Pottiez, O.; Ibarra-Escamilla, B.; Kuzin, E. A.; Hernández-García, J. C.; González-García, A.; Durán-Sánchez, M.

    2014-01-01

    In this work we study multiple noise-like pulse generation in a 320 m long passively mode-locked erbium-doped figure-eight fibre laser in the normal net dispersion regime. The nonlinear optical loop mirror (NOLM) that is used as a mode locker operates through polarization asymmetry, which allows us to control its switching power by birefringence adjustments at the NOLM input, using a half-wave retarder (HWR). Over some range of the HWR orientation, a single noise-like pulse is observed in the cavity. Its peak power is adjustable as it remains clamped to the variable switching power, and its duration varies inversely between ˜5 and ˜22 ps. Beyond the HWR position, corresponding to the longest duration, the pulse splits into several noise-like pulses. These multiple pulses usually present a walkoff, however they can be synchronized through slight birefringence adjustments, although they are not evenly spaced in time. Up to 12 simultaneous noise-like pulses were observed experimentally, with a duration of ˜2 ns. Multiple pulsing and synchronization of the pulses are interpreted in terms of mechanisms of interaction between pulses. Multiple pulsing appears to be indirectly related to the peak power limiting effect of the NOLM.

  7. A compact repetitive high-voltage nanosecond pulse generator for the application of gas discharge.

    PubMed

    Pang, Lei; Zhang, Qiaogen; Ren, Baozhong; He, Kun

    2011-04-01

    Uniform and stable discharge plasma requires very short duration pulses with fast rise times. A repetitive high-voltage nanosecond pulse generator for the application of gas discharge is presented in this paper. It is constructed with all solid-state components. Two-stage magnetic compression is used to generate a short duration pulse. Unlike in some reported studies, common commercial fast recovery diodes instead of a semiconductor opening switch (SOS) are used in our experiment that plays the role of SOS. The SOS-like effects of four different kinds of diodes are studied experimentally to optimize the output performance. It is found that the output pulse voltage is higher with a shorter reverse recovery time, and the rise time of pulse becomes faster when the falling time of reverse recovery current is shorter. The SOS-like effect of the diodes can be adjusted by changing the external circuit parameters. Through optimization the pulse generator can provide a pulsed voltage of 40 kV with a 40 ns duration, 10 ns rise time, and pulse repetition frequency of up to 5 kHz. Diffuse plasma can be formed in air at standard atmospheric pressure using the developed pulse generator. With a light weight and small packaging the pulse generator is suitable for gas discharge application.

  8. Slow Wave Sleep and Long Duration Spaceflight

    NASA Technical Reports Server (NTRS)

    Whitmire, Alexandra; Orr, Martin; Arias, Diana; Rueger, Melanie; Johnston, Smith; Leveton, Lauren

    2012-01-01

    While ground research has clearly shown that preserving adequate quantities of sleep is essential for optimal health and performance, changes in the progression, order and /or duration of specific stages of sleep is also associated with deleterious outcomes. As seen in Figure 1, in healthy individuals, REM and Non-REM sleep alternate cyclically, with stages of Non-REM sleep structured chronologically. In the early parts of the night, for instance, Non-REM stages 3 and 4 (Slow Wave Sleep, or SWS) last longer while REM sleep spans shorter; as night progresses, the length of SWS is reduced as REM sleep lengthens. This process allows for SWS to establish precedence , with increases in SWS seen when recovering from sleep deprivation. SWS is indeed regarded as the most restorative portion of sleep. During SWS, physiological activities such as hormone secretion, muscle recovery, and immune responses are underway, while neurological processes required for long term learning and memory consolidation, also occur. The structure and duration of specific sleep stages may vary independent of total sleep duration, and changes in the structure and duration have been shown to be associated with deleterious outcomes. Individuals with narcolepsy enter sleep through REM as opposed to stage 1 of NREM. Disrupting slow wave sleep for several consecutive nights without reducing total sleep duration or sleep efficiency is associated with decreased pain threshold, increased discomfort, fatigue, and the inflammatory flare response in skin. Depression has been shown to be associated with a reduction of slow wave sleep and increased REM sleep. Given research that shows deleterious outcomes are associated with changes in sleep structure, it is essential to characterize and mitigate not only total sleep duration, but also changes in sleep stages.

  9. Effect of Paired-Pulse Electrical Stimulation on the Activity of Cortical Circuits

    PubMed Central

    Saito, Kei; Onishi, Hideaki; Miyaguchi, Shota; Kotan, Shinichi; Fujimoto, Shuhei

    2015-01-01

    Objective: We investigated the transient effect of short-duration paired-pulse electrical stimulation (ppES) on corticospinal excitability and the after-effect of long-duration ppES on excitability, short-latency afferent inhibition (SAI), and afferent facilitation (AF). Methods: A total of 28 healthy subjects participated in two different experiments. In Experiment 1, motor-evoked potentials (MEPs) were measured in the abductor pollicis brevis (APB) and abductor digiti minimi (ADM) muscles before and immediately after short-duration ppES (5 s) at various inter-pulse intervals (2, 3, 4, 5, 6, 7, 10, 15, 20, and 30 ms). In Experiment 2, MEPs, SAI, and AF were measured before, immediately, and 20 and 40 min after long-duration ppES (20 min, inter-pulse interval of 5 and 15 ms) and peripheral electrical stimulation (20 min, 10 and 20 Hz). Results: Short-duration ppES with inter-pulse intervals of 5 and 20 ms significantly increased MEP measured in APB but not in ADM. Long-duration ppES with an inter-pulse interval of 5 ms significantly decreased SAI but not MEPs in APB. In contrast, long-duration ppES did not affect ADM. Conclusion: The afferent inputs induced by ppES-5 ms were effective for transiently increasing MEP and sustaining SAI reduction. PMID:26733847

  10. Nanosecond, high-intensity pulsed electric fields induce apoptosis in human cells.

    PubMed

    Beebe, Stephen J; Fox, Paula M; Rec, Laura J; Willis, E Lauren K; Schoenbach, Karl H

    2003-08-01

    Electroporation by using pulsed electric fields with long durations compared with the charging time of the plasma membrane can induce cell fusion or introduce xenomolecules into cells. Nanosecond pulse power technology generates pulses with high-intensity electric fields, but with such short durations that the charging time of the plasma membrane is not reached, but intracellular membranes are affected. To determine more specifically their effects on cell structure and function, human cells were exposed to high intensity (up to 300 kV/cm) nanosecond (10-300 ns) pulsed electric fields (nsPEF) and were analyzed at the cellular and molecular levels. As the pulse duration decreased, plasma membrane electroporation decreased and appearances of apoptosis markers were delayed. NsPEF induced apoptosis within tens of minutes, depending on the pulse duration. Annexin-V binding, caspase activation, decreased forward light scatter, and cytochrome c release into the cytoplasm were coincident. Apoptosis was caspase- and mitochondria-dependent but independent of plasma membrane electroporation and thermal changes. The results suggest that with decreasing pulse durations, nsPEF modulate cell signaling from the plasma membrane to intracellular structures and functions. NsPEF technology provides a unique, high-power, energy-independent tool to recruit plasma membrane and/or intracellular signaling mechanisms that can delete aberrant cells by apoptosis.

  11. 20 CFR 336.3 - Duration of normal sickness benefits.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 20 Employees' Benefits 1 2011-04-01 2011-04-01 false Duration of normal sickness benefits. 336.3... INSURANCE ACT DURATION OF NORMAL AND EXTENDED BENEFITS Normal Benefits § 336.3 Duration of normal sickness benefits. The duration of normal sickness benefits is the same as the duration of normal...

  12. 20 CFR 336.3 - Duration of normal sickness benefits.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 20 Employees' Benefits 1 2010-04-01 2010-04-01 false Duration of normal sickness benefits. 336.3... INSURANCE ACT DURATION OF NORMAL AND EXTENDED BENEFITS Normal Benefits § 336.3 Duration of normal sickness benefits. The duration of normal sickness benefits is the same as the duration of normal...

  13. 20 CFR 336.3 - Duration of normal sickness benefits.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 20 Employees' Benefits 1 2013-04-01 2012-04-01 true Duration of normal sickness benefits. 336.3... INSURANCE ACT DURATION OF NORMAL AND EXTENDED BENEFITS Normal Benefits § 336.3 Duration of normal sickness benefits. The duration of normal sickness benefits is the same as the duration of normal...

  14. 20 CFR 336.3 - Duration of normal sickness benefits.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 20 Employees' Benefits 1 2012-04-01 2012-04-01 false Duration of normal sickness benefits. 336.3... INSURANCE ACT DURATION OF NORMAL AND EXTENDED BENEFITS Normal Benefits § 336.3 Duration of normal sickness benefits. The duration of normal sickness benefits is the same as the duration of normal...

  15. 20 CFR 336.3 - Duration of normal sickness benefits.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 20 Employees' Benefits 1 2014-04-01 2012-04-01 true Duration of normal sickness benefits. 336.3... INSURANCE ACT DURATION OF NORMAL AND EXTENDED BENEFITS Normal Benefits § 336.3 Duration of normal sickness benefits. The duration of normal sickness benefits is the same as the duration of normal...

  16. Slow Wave Sleep and Long Duration Spaceflight

    NASA Technical Reports Server (NTRS)

    Orr, M.; Whitmire, A.; Arias, D.; Leveton, L.

    2011-01-01

    To review the literature on slow wave sleep (SWS) in long duration space flight, and place this within the context of the broader literature on SWS particularly with respect to analogous environments such as the Antarctic. Explore how SWS could be measured within the International Space Station (ISS) context with the aim to utilize the ISS as an analog for future extra-orbital long duration missions. Discuss the potential use of emergent minimally intrusive wireless technologies like ZEO for integrated prelaunch, flight, and return to Earth analysis and optimization of SWS (and general quality of sleep).

  17. Retrograde amnesia produced by electron beam exposure: causal parameters and duration of memory loss. [Rats

    SciTech Connect

    Wheeler, T.G.; Hardy, K.A.

    1985-01-01

    The production of retrograde amnesia (RA) upon electron beam exposure has been investigated. RA production was evaluated using a single-trial avoidance task across a 10/sup 4/ dose range for 10-, 1-, and 0.1-..mu..sec pulsed exposures. The dose-response curve obtained at each pulse duration showed significant RA production. The most effective dose range was 0.1-10 rad at a dose rate of 10/sup 6/ rad/sec. By employing a 10 rad (10/sup 6/ rad/sec) pulse, a memory loss of the events occurring in the previous 4 sec was demonstrated. The conclusion was that the RA effect might be due to sensory activation which provided a novel stimulus that masked previous stimuli.

  18. Time-dependent radiolytic yield of OH• radical studied by picosecond pulse radiolysis.

    PubMed

    El Omar, Abdel Karim; Schmidhammer, Uli; Jeunesse, Pierre; Larbre, Jean-Philippe; Lin, Mingzhang; Muroya, Yusa; Katsumura, Yosuke; Pernot, Pascal; Mostafavi, Mehran

    2011-11-10

    Picosecond pulse radiolysis measurements using a pulse-probe method are performed to measure directly the time-dependent radiolytic yield of the OH(•) radical in pure water. The time-dependent absorbance of OH(•) radical at 263 nm is deduced from the observed signal by subtracting the contribution of the hydrated electron and that of the irradiated empty fused silica cell which presents also a transient absoption. The time-dependent radiolytic yield of OH(•) is obtained by assuming the yield of the hydrated electron at 20 ps equal to 4.2 × 10(-7) mol J(-1) and by assuming the values of the extinction coefficients of e(aq)(-) and OH(•) at 782 nm (ε(λ=782 nm) = 17025 M(-1) cm(-1)) and at 263 nm (ε(λ=263 nm) = 460 M(-1) cm(-1)), respectively. The value of the yield of OH(•) radical at 10 ps is found to be (4.80 ± 0.12) × 10(-7) mol J(-1). PMID:21970432

  19. Thyristor stack for pulsed inductive plasma generation.

    PubMed

    Teske, C; Jacoby, J; Schweizer, W; Wiechula, J

    2009-03-01

    A thyristor stack for pulsed inductive plasma generation has been developed and tested. The stack design includes a free wheeling diode assembly for current reversal. Triggering of the device is achieved by a high side biased, self supplied gate driver unit using gating energy derived from a local snubber network. The structure guarantees a hard firing gate pulse for the required high dI/dt application. A single fiber optic command is needed to achieve a simultaneous turn on of the thyristors. The stack assembly is used for switching a series resonant circuit with a ringing frequency of 30 kHz. In the prototype pulsed power system described here an inductive discharge has been generated with a pulse duration of 120 micros and a pulse energy of 50 J. A maximum power transfer efficiency of 84% and a peak power of 480 kW inside the discharge were achieved. System tests were performed with a purely inductive load and an inductively generated plasma acting as a load through transformer action at a voltage level of 4.1 kV, a peak current of 5 kA, and a current switching rate of 1 kA/micros. PMID:19334940

  20. Thyristor stack for pulsed inductive plasma generation.

    PubMed

    Teske, C; Jacoby, J; Schweizer, W; Wiechula, J

    2009-03-01

    A thyristor stack for pulsed inductive plasma generation has been developed and tested. The stack design includes a free wheeling diode assembly for current reversal. Triggering of the device is achieved by a high side biased, self supplied gate driver unit using gating energy derived from a local snubber network. The structure guarantees a hard firing gate pulse for the required high dI/dt application. A single fiber optic command is needed to achieve a simultaneous turn on of the thyristors. The stack assembly is used for switching a series resonant circuit with a ringing frequency of 30 kHz. In the prototype pulsed power system described here an inductive discharge has been generated with a pulse duration of 120 micros and a pulse energy of 50 J. A maximum power transfer efficiency of 84% and a peak power of 480 kW inside the discharge were achieved. System tests were performed with a purely inductive load and an inductively generated plasma acting as a load through transformer action at a voltage level of 4.1 kV, a peak current of 5 kA, and a current switching rate of 1 kA/micros.

  1. Time-Grating for the Generation of STUD Pulse Trains

    NASA Astrophysics Data System (ADS)

    Zheng, Jun; Wang, Shi-Wei; Xu, Jian-Qiu

    2013-04-01

    Spike train of uneven duration or delay (STUD) pulses hold potential for laser-plasma interaction (LPI) control in laser fusion. The technique based on time grating is applied to generate an STUD pulse train. Time grating, a temporal analogy of the diffraction grating, can control the pulse width, shape, and repetition rate easily through the use of electro-optical devices. The pulse width and repetition rate are given by the modulation frequency and depth of the phase modulation function in theory and numerical calculation. The zero-chirped phase modulation is good for the compression effect of the time grating. A principle experiment of two pulses interfering is shown to verify the time grating function.

  2. Experiments on light pulse communication and propagation through atmospheric clouds.

    PubMed

    Bucher, E A; Lerner, R M

    1973-10-01

    This paper describes the facilities and results in an experiment to investigate light pulse propagation through atmospheric clouds. The experiments were conducted with the transmitter and receiver located on two mountain peaks in a naturally cloudy area. The transmitter was a Q-switched ruby laser producing 30 nsec light pulses. The received pulses were 1-10 microsec in duration when there was a cloud in the propagation path. The multipath time lengthening of the received pulse resulted from multiple scattering inside the cloud. The extent of this multipath pulse spreading can be shown to be comparable to that predicted from computer simulation models. We also observed a number of effects in which relatively small changes in the gross cloud shape produced a change in the received signal intensity of an order of magnitude or so.

  3. Nonstationary scattering of electromagnetic pulses by spherical particles.

    PubMed

    Shifrin, K S; Zolotov, I G

    1995-01-20

    We have studied time variances of the shape of an electromagnetic pulse scattered by a spherical particle. General formulas are derived for a pulse with an arbitrary envelope, for momentary values of scattered-light fields and light intensity, and for efficiencies of extinction and scattering. It is possible, by the use of these formulas, to obtain by routine integration the sensitivity reaction of a receiver with any time dependence. The formulas are illustrated with examples of scattering of a Gaussian pulse with a carrier wave λ(0) = 0.6328 µm and of multisized water drops. Pulses of different durations are studied. However, only those pulses that have all significant values of the Fourier density in the domain of positive frequencies ω are considered. PMID:20963150

  4. Pulse-shaping assisted multidimensional coherent electronic spectroscopy

    SciTech Connect

    Rodriguez, Yuseff; Frei, Franziska; Cannizzo, Andrea Feurer, Thomas

    2015-06-07

    Understanding nuclear and electronic dynamics of molecular systems has advanced considerably by probing their nonlinear responses with a suitable sequence of pulses. Moreover, the ability to control crucial parameters of the excitation pulses, such as duration, sequence, frequency, polarization, slowly varying envelope, or carrier phase, has led to a variety of advanced time-resolved spectroscopic methodologies. Recently, two-dimensional electronic spectroscopy with ultrashort pulses has become a more and more popular tool since it allows to obtain information on energy and coherence transfer phenomena, line broadening mechanisms, or the presence of quantum coherences in molecular complexes. Here, we present a high fidelity two-dimensional electronic spectroscopy setup designed for molecular systems in solution. It incorporates the versatility of pulse-shaping methods to achieve full control on the amplitude and phase of the individual exciting and probing pulses. Selective and precise amplitude- and phase-modulation is shown and applied to investigate electronic dynamics in several reference molecular systems.

  5. Nonlinear pulse propagation: a time-transformation approach.

    PubMed

    Xiao, Yuzhe; Agrawal, Govind P; Maywar, Drew N

    2012-04-01

    We present a time-transformation approach for studying the propagation of optical pulses inside a nonlinear medium. Unlike the conventional way of solving for the slowly varying amplitude of an optical pulse, our new approach maps directly the input electric field to the output one, without making the slowly varying envelope approximation. Conceptually, the time-transformation approach shows that the effect of propagation through a nonlinear medium is to change the relative spacing and duration of various temporal slices of the pulse. These temporal changes manifest as self-phase modulation in the spectral domain and self-steepening in the temporal domain. Our approach agrees with the generalized nonlinear Schrödinger equation for 100 fs pulses and the finite-difference time-domain solution of Maxwell's equations for two-cycle pulses, while producing results 20 and 50 times faster, respectively.

  6. Spatio-temporal characteristics of Trichel pulse at low pressure

    SciTech Connect

    He, Shoujie; Jing, Ha

    2014-01-15

    Trichel pulses are investigated using a needle-to-plane electrode geometry at low pressure. The evolution of current and voltage, the spatio-temporal discharge images of Trichel pulse are measured. The rising time and duration time in a pulse are about 10 μs and several tens of microseconds, respectively. One period of pulse can be divided into three stages: the stage preceding cathode breakdown, cathode glow formation, and discharge decaying process. Besides a cathode glow and a dark space, an anode glow is also observed. The emission spectra mainly originate from the C{sup 3}Π{sub u} → B{sup 3}Π{sub g} transition for nitrogen. In addition, the capacitances in parallel connected with the discharge cell have important influence on the pulsing frequency.

  7. Optimization of femtosecond Yb-doped fiber amplifiers for high-quality pulse compression.

    PubMed

    Chen, Hung-Wen; Lim, JinKang; Huang, Shu-Wei; Schimpf, Damian N; Kärtner, Franz X; Chang, Guoqing

    2012-12-17

    We both theoretically and experimentally investigate the optimization of femtosecond Yb-doped fiber amplifiers (YDFAs) to achieve high-quality, high-power, compressed pulses. Ultrashort pulses amplified inside YDFAs are modeled by the generalized nonlinear Schrödinger equation coupled to the steady-state propagation-rate equations. We use this model to study the dependence of compressed-pulse quality on the YDFA parameters, such as the gain fiber's doping concentration and length, and input pulse pre-chirp, duration, and power. The modeling results confirmed by experiments show that an optimum negative pre-chirp for the input pulse exists to achieve the best compression.

  8. Femtosecond pulses generated from a synchronously pumped chromium-doped forsterite laser

    NASA Technical Reports Server (NTRS)

    Seas, A.; Petricevic, V.; Alfano, R. R.

    1993-01-01

    Kerr lens mode-locking (KLM) has become a standard method to produce femtosecond pulses from tunable solid state lasers. High power inside the laser resonator propagating through the laser-medium with nonlinear index of refraction, coupled with the stability conditions of the laser modes in the resonator, result in a passive amplitude modulation which explains the mechanism for pulse shortening. Recently, chromium doped forsterite was shown to exhibit similar pulse behavior. A successful attempt to generate femtosecond pulses from a synchronously pumped chromium-doped forsterite laser with intracavity dispersion compensation is reported. Stable, transform limited pulses with duration of 105 fs were routinely generated, tunable between 1240 to 1270 nm.

  9. Integrated pulse stretchers for high-energy CPA and OPCPA systems

    NASA Astrophysics Data System (ADS)

    Shah, Lawrence; Bodnar, Nathan; Roumayah, Patrick; Webb, Benjamin; Bradford, Joshua; Richardson, Martin

    2016-03-01

    Pulse stretchers are critical components in chirped pulse amplification (CPA) and optical parametric CPA (OPCPA) laser systems. In CPA systems, pulse stretching and compression is typical accomplished using bulk diffraction gratings; however integrated devices such volume or fiber Bragg gratings can provide similar optical performance with significantly smaller footprint and simplified alignment. In this work, we discuss the use of such integrated devices to stretch a 100 fs pulse to 400 ps with customized third order dispersion for use in a multi-TW Ti:Sapphire system as well as integrated optics to control the pulse duration in pump lasers for OPCPA systems.

  10. High-intensity terahertz pulses and their applications

    NASA Astrophysics Data System (ADS)

    Budiarto, Edward Wibowo

    1997-09-01

    A large aperture transmitter based on an electrically biased photoconductor has been constructed, which is capable of generating ultrashort high-intensity pulses operating in the far-infrared (terahertz) frequency regime. The terahertz pulse is a single-cycle freely propagating electrical pulse with a 600 femtosecond pulse duration and a pulse energy close to 200 nanojoules. A complete characterization of the transmitter and its output pulse has been conducted, resulting in new understandings of the pulse generation mechanism and propagation behavior. More specifically, it was revealed for the first time that near-field diffraction plays a significant role in the propagation behavior of the terahertz pulse from the large aperture transmitter. The pulse alters its temporal shape significantly as it travels away from the transmitter, especially when it is focused by a parabolic mirror. The high-intensity pulse is intended to be utilized as a probe of high-field transport properties of free carriers in semiconductors and superconductors. The transient dynamics of hot-electrons in silicon and gallium arsenide are of particular interest, as they relate to current issues in modern electronic devices. A simulation model has been developed which predicts a nonlinear absorption of the terahertz pulses by free-electrons in the semiconductors due to velocity saturation effects. The high-intensity terahertz pulse has also been used to probe the nonlinear electrodynamics of high-T c superconductors. The results confirm the ability of the pulse to break pairs of superconducting electrons and convert them to normal state electrons. This will allow further studies to be conducted to resolve the exact pair-breaking mechanism, which is ultimately linked to a better understanding of some of the failure mechanisms in today's superconducting microwave devices.

  11. Interspersion of fragmented fiber's splinters into tissue during pulsed alexandrite laser lithotripsy.

    PubMed

    Strunge, C; Brinkmann, R; Flemming, G; Engelhardt, R

    1991-01-01

    Laser induced shockwave lithotripsy (LISL) on artificially inserted human renal calculi was realized in explanted pig ureters. A pulse stretched Alexandrite solid state laser was used at 750nm. Pulses of 350ns and 1 microseconds duration were transmitted through a 250 microns all silica fiber onto a stone surface, keeping the fiber tip in contact with a stone close to the ureter wall. The high power density of the 350 ns pulses lead to an optical breakdown inside the distal fiber tip causing fiber fragmentation of about 28 mm/100 pulses. Deep penetration of the fiber fragments into the ureter wall was proven histologically. Fiber fragmentation was avoided by increasing the pulse duration up to 1 microseconds. Riks for patient treatment caused by short pulse lithotripsy are discussed.

  12. 34-fs, all-fiber all-polarization-maintaining single-mode pulse nonlinear amplifier.

    PubMed

    Yu, Jia; Feng, Ye; Cai, Yajun; Li, Xiaohui; Hu, Xiaohong; Zhang, Wei; Duan, Lina; Yang, Zhi; Wang, Yishan; Liu, Yuanshan; Zhao, Wei

    2016-07-25

    We present an all-fiber all-polarization-maintaining (PM) single mode (SM) fiber pulse nonlinear amplification system. The seed laser with a repetition rate of 200 MHz is amplified by two-section erbium-doped PM gain fibers with different peak-absorption rate. The amplified pulse duration can be compressed into 34-fs with 320-mW output power, which corresponds to 1.6-nJ pulse energy and approximate 23.5-kW peak power. In addition, the amplified and compressed pulse is further coupled into the high nonlinear fiber and an octave-spanning supercontinuum generation can be obtained. To the best of our knowledge, it is the highest peak power and the shortest pulse duration obtained in the field of all-fiber all-PM SM pulse-amplification systems. PMID:27464117

  13. Optimization of infrared two-color multicycle field synthesis for intense-isolated-attosecond-pulse generation

    NASA Astrophysics Data System (ADS)

    Lan, Pengfei; Takahashi, Eiji J.; Midorikawa, Katsumi

    2010-11-01

    We present the optimization of the two-color synthesis method for generating an intense isolated attosecond pulse (IAP) in the multicycle regime. By mixing an infrared assistant pulse with a Ti:sapphire main pulse, we show that an IAP can be produced using a multicycle two-color pulse with a duration longer than 30 fs. We also discuss the influence of the carrier-envelope phase (CEP) and the relative intensity on the generation of IAPs. By optimizing the wavelength of the assistant field, IAP generation becomes insensitive to the CEP slip. Therefore, the optimized two-color method enables us to relax the requirements of pulse duration and easily produce the IAP with a conventional multicycle laser pulse. In addition, it enables us to markedly suppress the ionization of the harmonic medium. This is a major advantage for efficiently generating intense IAPs from a neutral medium by applying the appropriate phase-matching and energy-scaling techniques.

  14. Optimization of infrared two-color multicycle field synthesis for intense-isolated-attosecond-pulse generation

    SciTech Connect

    Lan Pengfei; Takahashi, Eiji J.; Midorikawa, Katsumi

    2010-11-15

    We present the optimization of the two-color synthesis method for generating an intense isolated attosecond pulse (IAP) in the multicycle regime. By mixing an infrared assistant pulse with a Ti:sapphire main pulse, we show that an IAP can be produced using a multicycle two-color pulse with a duration longer than 30 fs. We also discuss the influence of the carrier-envelope phase (CEP) and the relative intensity on the generation of IAPs. By optimizing the wavelength of the assistant field, IAP generation becomes insensitive to the CEP slip. Therefore, the optimized two-color method enables us to relax the requirements of pulse duration and easily produce the IAP with a conventional multicycle laser pulse. In addition, it enables us to markedly suppress the ionization of the harmonic medium. This is a major advantage for efficiently generating intense IAPs from a neutral medium by applying the appropriate phase-matching and energy-scaling techniques.

  15. Single-beam Denisyuk holograms recording with pulsed 30Hz RGB laser

    NASA Astrophysics Data System (ADS)

    Zacharovas, Stanislovas; Bakanas, Ramūnas; Stankauskas, Algimantas

    2016-03-01

    It is well known fact that holograms can be recorded either by continuous wave (CW) laser, or by single pulse coming from pulsed laser. However, multi-pulse or multiple-exposure holograms were used only in interferometry as well as for information storage. We have used Geola's single longitudinal mode pulsed RGB laser to record Denisyuk type holograms. We successfully recorded objects situated at the distance of more than 30cm, employing the multi-pulse working regime of the laser. To record Denisyuk hologram we have used 50 ns duration 440, 660nm wavelength and 35ns duration 532nm wavelength laser pulses at the repetition rate of 30Hz. As photosensitive medium we have used Slavich-Geola PFG-03C glass photoplate. Radiations with different wavelengths were mixed into "white" beam, collimated and directed onto the photoplate. For further objects illumination an additional flat silver coated mirror was used.

  16. PULSE HEIGHT ANALYZER

    DOEpatents

    Goldsworthy, W.W.

    1958-06-01

    A differential pulse-height discriminator circuit is described which is readily adaptable for operation in a single-channel pulse-height analyzer. The novel aspect of the circuit lies in the specific arrangement of differential pulse-height discriminator which includes two pulse-height discriminators having a comnnon input and an anticoincidence circuit having two interconnected vacuum tubes with a common cathode resistor. Pulses from the output of one discriminator circuit are delayed and coupled to the grid of one of the anticoincidence tubes by a resistor. The output pulses from the other discriminator circuit are coupled through a cathode follower circuit, which has a cathode resistor of such value as to provide a long time constant with the interelectrode capacitance of the tube, to lenthen the output pulses. The pulses are then fed to the grid of the other anticoincidence tube. With such connections of the circuits, only when the incoming pulse has a pesk value between the operating levels of the two discriminators does an output pulse occur from the anticoincidence circuit.

  17. Sleep Duration and Breast Cancer Phenotype

    PubMed Central

    Khawaja, Ali; Rao, Santosh; Li, Li; Thompson, Cheryl L.

    2013-01-01

    Emerging evidence suggests that short sleep is associated with an increased risk of cancer; however, little has been done to study the role of sleep on tumor characteristics. In this study, we evaluated the relationship between sleep duration and tumor phenotype in 972 breast cancer patients. Sleep duration was inversely associated with tumor grade (univariate P = 0.032), particularly in postmenopausal women (univariate P = 0.018). This association did not reach statistical significance after adjustments for age, race, body mass index, hormone replacement therapy use, alcohol consumption, smoking, and physical activity in the entire study sample (P = 0.052), but it remained statistically significant (P = 0.049) among post-menopausal patients. We did not observe a statistically significant association between sleep duration and stage at diagnosis, ER, or HER2 receptor status. These results present a modest association between short duration of sleep and higher grade breast cancer in post-menopausal women. Further work needs to be done to validate these findings. PMID:24319459

  18. Duration and Intensity as Correlates of Fo.

    ERIC Educational Resources Information Center

    Zee, Eric

    1978-01-01

    The speech of two male Taiwanese speakers was analyzed to determine whether fundamental frequency (Fo) is correlated with both duration and intensity; five conclusions are drawn. The results are discussed in terms of theories of pitch production and speed of pitch change. (EJS)

  19. Breathhold duration and response to marijuana smoke.

    PubMed

    Zacny, J P; Chait, L D

    1989-06-01

    Marijuana smokers are frequently observed to hold the smoke in their lungs for prolonged periods (10-15 sec) apparently in the belief that prolonged breathholding intensifies the effects of the drug. The actual influence of breathhold duration on response to marijuana smoke has not been studied. The present study examined the effects of systematic manipulation of breathhold duration on the physiological, cognitive and subjective response to marijuana smoke in a group of eight regular marijuana smokers. Subjects were exposed to each of three breathhold duration conditions (0, 10 and 20 sec) on three occasions, scheduled according to a randomized block design. A controlled smoking procedure was used in which the number of puffs, puff volume and postpuff inhalation volume were held constant. Expired air carbon monoxide levels were measured before and after smoking to monitor smoke intake. Typical marijuana effects (increased heart rate, increased ratings of "high" and impaired memory performance) were observed under each of the breathhold conditions, but there was little evidence that response to marijuana was a function of breathhold duration.

  20. Developmental Aspects of English Segment Duration.

    ERIC Educational Resources Information Center

    Smith, Bruce L.

    The experiment reported here attempted to investigate the nature of both intrinsic, unlearned temporal parameters as well as learned, language-specific durational properties in the speech of young children. Developmental aspects of several temporal parameters were investigated in the speech of ten 2 1/2 to 3-year-old and ten 4 to 4 1/2-year-old…