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Sample records for 1-khz repetition rate

  1. Fast repetition rate (FRR) flasher

    DOEpatents

    Kolber, Zbigniew; Falkowski, Paul

    1997-02-11

    A fast repetition rate (FRR) flasher suitable for high flash photolysis including kinetic chemical and biological analysis. The flasher includes a power supply, a discharge capacitor operably connected to be charged by the power supply, and a flash lamp for producing a series of flashes in response to discharge of the discharge capacitor. A triggering circuit operably connected to the flash lamp initially ionizes the flash lamp. A current switch is operably connected between the flash lamp and the discharge capacitor. The current switch has at least one insulated gate bipolar transistor for switching current that is operable to initiate a controllable discharge of the discharge capacitor through the flash lamp. Control means connected to the current switch for controlling the rate of discharge of the discharge capacitor thereby to effectively keep the flash lamp in an ionized state between Successive discharges of the discharge capacitor. Advantageously, the control means is operable to discharge the discharge capacitor at a rate greater than 10,000 Hz and even up to a rate greater than about 250,000 Hz.

  2. Phosphor thermometry at high repetition rates

    NASA Astrophysics Data System (ADS)

    Fuhrmann, N.; Brübach, J.; Dreizler, A.

    2013-09-01

    Phosphor thermometry is a semi-invasive surface temperature measurement technique utilizing the luminescence properties of thermographic phosphors. Typically these ceramic materials are coated onto the object of interest and are excited by a short UV laser pulse. Photomultipliers and high-speed camera systems are used to transiently detect the subsequently emitted luminescence decay point wise or two-dimensionally resolved. Based on appropriate calibration measurements, the luminescence lifetime is converted to temperature. Up to now, primarily Q-switched laser systems with repetition rates of 10 Hz were employed for excitation. Accordingly, this diagnostic tool was not applicable to resolve correlated temperature transients at time scales shorter than 100 ms. For the first time, the authors realized a high-speed phosphor thermometry system combining a highly repetitive laser in the kHz regime and a fast decaying phosphor. A suitable material was characterized regarding its temperature lifetime characteristic and precision. Additionally, the influence of laser power on the phosphor coating in terms of heating effects has been investigated. A demonstration of this high-speed technique has been conducted inside the thermally highly transient system of an optically accessible internal combustion engine. Temperatures have been measured with a repetition rate of one sample per crank angle degree at an engine speed of 1000 rpm. This experiment has proven that high-speed phosphor thermometry is a promising diagnostic tool for the resolution of surface temperature transients.

  3. 1KHz high average power single-frequency Nd:YAG laser

    NASA Astrophysics Data System (ADS)

    Zhu, Xiaolei; Ma, Xiuhua; Li, Shiguang; Chen, Weibiao

    2015-02-01

    A laser-diode-pumped master oscillator and power amplifier was developed with high efficiency, high average power and high beam quality. The oscillator is an injection-seeding, fiber coupled diode-end-pumped E-O Q-switched Nd:YAG laser, producing single frequency pulse laser output with pulse energy of 8mJ and pulse width of 11ns at a pulse repetition rate of 1KHz,The 1KHz was divided into four chains with frequency of 250Hz, through E-O modulation technology, The power amplifier utilizes conductively-cooling Nd:YAG zigzag slab with two sides' pump architecture at bounce point. Pulse energy of more than 800mJ with pulse widths of 12.6ns was obtained at repetition rate of 250Hz in every amplifier chain, the frequency-doubled pulse energy of 360mJ when KTP crystal was used was obtained at a repetition of 250Hz.

  4. Properties of water surface discharge at different pulse repetition rates

    SciTech Connect

    Ruma,; Yoshihara, K.; Hosseini, S. H. R. Sakugawa, T.; Akiyama, H.; Akiyama, M.; Lukeš, P.

    2014-09-28

    The properties of water surface discharge plasma for variety of pulse repetition rates are investigated. A magnetic pulse compression (MPC) pulsed power modulator able to deliver pulse repetition rates up to 1000 Hz, with 0.5 J per pulse energy output at 25 kV, was used as the pulsed power source. Positive pulse with a point-to-plane electrode configuration was used for the experiments. The concentration and production yield of hydrogen peroxide (H₂O₂) were quantitatively measured and orange II organic dye was treated, to evaluate the chemical properties of the discharge reactor. Experimental results show that the physical and chemical properties of water surface discharge are not influenced by pulse repetition rate, very different from those observed for under water discharge. The production yield of H₂O₂ and degradation rate per pulse of the dye did not significantly vary at different pulse repetition rates under a constant discharge mode on water surface. In addition, the solution temperature, pH, and conductivity for both water surface and underwater discharge reactors were measured to compare their plasma properties for different pulse repetition rates. The results confirm that surface discharge can be employed at high pulse repetition rates as a reliable and advantageous method for industrial and environmental decontamination applications.

  5. Flexible high-repetition-rate ultrafast fiber laser

    PubMed Central

    Mao, Dong; Liu, Xueming; Sun, Zhipei; Lu, Hua; Han, Dongdong; Wang, Guoxi; Wang, Fengqiu

    2013-01-01

    High-repetition-rate pulses have widespread applications in the fields of fiber communications, frequency comb, and optical sensing. Here, we have demonstrated high-repetition-rate ultrashort pulses in an all-fiber laser by exploiting an intracavity Mach-Zehnder interferometer (MZI) as a comb filter. The repetition rate of the laser can be tuned flexibly from about 7 to 1100 GHz by controlling the optical path difference between the two arms of the MZI. The pulse duration can be reduced continuously from about 10.1 to 0.55 ps with the spectral width tunable from about 0.35 to 5.7 nm by manipulating the intracavity polarization controller. Numerical simulations well confirm the experimental observations and show that filter-driven four-wave mixing effect, induced by the MZI, is the main mechanism that governs the formation of the high-repetition-rate pulses. This all-fiber-based laser is a simple and low-cost source for various applications where high-repetition-rate pulses are necessary. PMID:24226153

  6. Medium Repetition Rate TEA Laser For Industrial Applications

    NASA Astrophysics Data System (ADS)

    Walter, Bruno

    1987-09-01

    The design and performance of an inexpensive compact repetitively pulsed TEA CO2 laser is described. The device uses a modified corona preionization technique and a fast transverse gas flow to achieve high repetition rates. An output energy of 500 mJ per pulse and an out-put power of 6.2W at 40Hz have been obtained. Due to the small energy needed for preionization, the efficiency of the device is high, whereas the gas dissociation is low when compared with commercial laser systems. This results in the relatively small fresh laser gas exchange of 20 ltr h-1 for long term operation.

  7. The Effect of Syllable Repetition Rate on Vocal Characteristics

    ERIC Educational Resources Information Center

    Topbas, Oya; Orlikoff, Robert F.; St. Louis, Kenneth O.

    2012-01-01

    This study examined whether mean vocal fundamental frequency ("F"[subscript 0]) or speech sound pressure level (SPL) varies with changes in syllable repetition rate. Twenty-four young adults (12 M and 12 F) repeated the syllables/p[inverted v]/,/p[inverted v]t[schwa]/, and/p[inverted v]t[schwa]k[schwa]/at a modeled "slow" rate of approximately one…

  8. High repetition rate plasma mirror device for attosecond science

    SciTech Connect

    Borot, A.; Douillet, D.; Iaquaniello, G.; Lefrou, T.; Lopez-Martens, R.; Audebert, P.; Geindre, J.-P.

    2014-01-15

    This report describes an active solid target positioning device for driving plasma mirrors with high repetition rate ultra-high intensity lasers. The position of the solid target surface with respect to the laser focus is optically monitored and mechanically controlled on the nm scale to ensure reproducible interaction conditions for each shot at arbitrary repetition rate. We demonstrate the target capabilities by driving high-order harmonic generation from plasma mirrors produced on glass targets with a near-relativistic intensity few-cycle pulse laser system operating at 1 kHz. During experiments, residual target surface motion can be actively stabilized down to 47 nm (root mean square), which ensures sub-300-as relative temporal stability of the plasma mirror as a secondary source of coherent attosecond extreme ultraviolet radiation in pump-probe experiments.

  9. Bipolar high-repetition-rate high-voltage nanosecond pulser

    SciTech Connect

    Tian Fuqiang; Wang Yi; Shi Hongsheng; Lei Qingquan

    2008-06-15

    The pulser designed is mainly used for producing corona plasma in waste water treatment system. Also its application in study of dielectric electrical properties will be discussed. The pulser consists of a variable dc power source for high-voltage supply, two graded capacitors for energy storage, and the rotating spark gap switch. The key part is the multielectrode rotating spark gap switch (MER-SGS), which can ensure wider range modulation of pulse repetition rate, longer pulse width, shorter pulse rise time, remarkable electrical field distortion, and greatly favors recovery of the gap insulation strength, insulation design, the life of the switch, etc. The voltage of the output pulses switched by the MER-SGS is in the order of 3-50 kV with pulse rise time of less than 10 ns and pulse repetition rate of 1-3 kHz. An energy of 1.25-125 J per pulse and an average power of up to 10-50 kW are attainable. The highest pulse repetition rate is determined by the driver motor revolution and the electrode number of MER-SGS. Even higher voltage and energy can be switched by adjusting the gas pressure or employing N{sub 2} as the insulation gas or enlarging the size of MER-SGS to guarantee enough insulation level.

  10. 1-kHz-repetition-rate femtosecond Raman laser

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

    A femtosecond Raman laser utilising compressed hydrogen is experimentally investigated under pumping by radiation from a 1-kHz-repetition-rate Ti : sapphire laser. In the regime of double-pulse pumping, the conditions are determined, which correspond to the minimal energy dispersion of Stokes pulses. The optical scheme is realised, which is capable of ensuring the long-term stability of the average power of the first Stokes component with a variation of less than 2%. The Stokes pulses are produced with a pulse duration of 60 fs and energy of 0.26 mJ at a conversion efficiency of 14%.

  11. Final Report, Photocathodes for High Repetition Rate Light Sources

    SciTech Connect

    Ben-Zvi, Ilan

    2014-04-20

    This proposal brought together teams at Brookhaven National Laboratory (BNL), Lawrence Berkeley National Laboratory (LBNL) and Stony Brook University (SBU) to study photocathodes for high repetition rate light sources such as Free Electron Lasers (FEL) and Energy Recovery Linacs (ERL). The work done under this grant comprises a comprehensive program on critical aspects of the production of the electron beams needed for future user facilities. Our program pioneered in situ and in operando diagnostics for alkali antimonide growth. The focus is on development of photocathodes for high repetition rate Free Electron Lasers (FELs) and Energy Recovery Linacs (ERLs), including testing SRF photoguns, both normal-conducting and superconducting. Teams from BNL, LBNL and Stony Brook University (SBU) led this research, and coordinated their work over a range of topics. The work leveraged a robust infrastructure of existing facilities and the support was used for carrying out the research at these facilities. The program concentrated in three areas: a) Physics and chemistry of alkali-antimonide cathodes b) Development and testing of a diamond amplifier for photocathodes c) Tests of both cathodes in superconducting RF photoguns and copper RF photoguns

  12. High repetition rate laser systems: targets, diagnostics and radiation protection

    SciTech Connect

    Gizzi, Leonida A.; Clark, Eugene; Neely, David; Tolley, Martin; Roso, Luis

    2010-02-02

    Accessing the high repetition regime of ultra intense laser-target interactions at small or moderate laser energies is now possible at a large number of facilities worldwide. New projects such as HiPER and ELI promise to extend this regime to the high energy realm at the multi-kJ level. This opportunity raises several issues on how best to approach this new regime of operation in a safe and efficient way. At the same time, a new class of experiments or a new generation of secondary sources of particles and radiation may become accessible, provided that target fabrication and diagnostics are capable of handling this rep-rated regime. In this paper, we explore this scenario and analyse existing and perspective techniques that promise to address some of the above issues.

  13. Resistive Wall Heating of the Undulator in High Repetition Rate

    SciTech Connect

    Qiang, J; Corlett, J; Emma, P; Wu, J

    2012-05-20

    In next generation high repetition rate FELs, beam energy loss due to resistive wall wakefields will produce significant amount of heat. The heat load for a superconducting undulator (operating at low temperature), must be removed and will be expensive to remove. In this paper, we study this effect in an undulator proposed for a Next Generation Light Source (NGLS) at LBNL. We benchmark our calculations with measurements at the LCLS and carry out detailed parameter studies using beam from a start-to-end simulation. Our preliminarym results suggest that the heat load in the undulator is about 2 W/m or lower with an aperture size of 6 mm for nominal NGLS preliminary design parameters.

  14. Fast repetition rate (FRR) fluorometer and method for measuring fluorescence and photosynthetic parameters

    DOEpatents

    Kolber, Z.; Falkowski, P.

    1995-06-20

    A fast repetition rate fluorometer device and method for measuring in vivo fluorescence of phytoplankton or higher plants chlorophyll and photosynthetic parameters of phytoplankton or higher plants is revealed. The phytoplankton or higher plants are illuminated with a series of fast repetition rate excitation flashes effective to bring about and measure resultant changes in fluorescence yield of their Photosystem II. The series of fast repetition rate excitation flashes has a predetermined energy per flash and a rate greater than 10,000 Hz. Also, disclosed is a flasher circuit for producing the series of fast repetition rate flashes. 14 figs.

  15. Fast repetition rate (FRR) fluorometer and method for measuring fluorescence and photosynthetic parameters

    DOEpatents

    Kolber, Zbigniew; Falkowski, Paul

    1995-06-20

    A fast repetition rate fluorometer device and method for measuring in vivo fluorescence of phytoplankton or higher plants chlorophyll and photosynthetic parameters of phytoplankton or higher plants by illuminating the phytoplankton or higher plants with a series of fast repetition rate excitation flashes effective to bring about and measure resultant changes in fluorescence yield of their Photosystem II. The series of fast repetition rate excitation flashes has a predetermined energy per flash and a rate greater than 10,000 Hz. Also, disclosed is a flasher circuit for producing the series of fast repetition rate flashes.

  16. Extreme-ultraviolet ultrafast ARPES at high repetition rates

    NASA Astrophysics Data System (ADS)

    Buss, Jan; Wang, He; Xu, Yiming; Stoll, Sebastian; Zeng, Lingkun; Ulonska, Stefan; Denlinger, Jonathan; Hussain, Zahid; Jozwiak, Chris; Lanzara, Alessandra; Kaindl, Robert

    Time- and angle-resolved photoemission spectroscopy (trARPES) represents a powerful approach to resolve the electronic structure and quasiparticle dynamics in complex materials, yet is often limited in either momentum space (incident photon energy), probe sensitivity (pulse repetition rate), or energy resolution. We demonstrate a novel table-top trARPES setup that combines a bright 50-kHz source of narrowband, extreme ultraviolet (XUV) pulses at 22.3 eV with UHV photoemission instrumentation to sensitively access dynamics for a large momentum space. The output of a high-power Ti:sapphire amplifier is split to provide the XUV probe and intense photoexcitation (up to mJ/cm2) . A vacuum beamline delivers spectral and flux characterization, differential pumping, as well as XUV beam steering and toroidal refocusing onto the sample with high incident flux of 3x1011 ph/s. Photoemission studies are carried out in a customized UHV chamber equipped with a hemispherical analyzer (R4000), six-axis sample cryostat, and side chambers for sample loading, storage and preparation. An ARPES energy resolution down to 70 meV with the direct XUV output is demonstrated. We will discuss initial applications of this setup including Fermi surface mapping and trARPES of complex materials.

  17. Method for generating high-energy and high repetition rate laser pulses from CW amplifiers

    DOEpatents

    Zhang, Shukui

    2013-06-18

    A method for obtaining high-energy, high repetition rate laser pulses simultaneously using continuous wave (CW) amplifiers is described. The method provides for generating micro-joule level energy in pico-second laser pulses at Mega-hertz repetition rates.

  18. Coherent quasi-CW 153-nm light source at high repetition rate

    NASA Astrophysics Data System (ADS)

    Nomura, Yutaka; Ito, Yoshiaki; Ozawa, Akira; Wang, Xiaoyang; Chen, Chuangtian; Shin, Shik; Watanabe, Shuntaro; Kobayashi, Yohei

    2012-02-01

    We present a quasi-cw laser in vacuum ultraviolet region at megahertz repetition rate. The narrowband pulses generated from an ytterbium-fiber laser system at 33 MHz repetition rate at the central wavelength of 1074 nm is frequency-converted by successive stages of LBO crystals and KBBF crystals. The generated radiation at 153 nm has the shortest wavelength achieved through phase-matched frequency conversion processes in nonlinear optical crystals to our knowledge.

  19. Diode-pumped passively Q-switched high-repetition-rate Yb microchip laser

    SciTech Connect

    Kisel', V E; Yasukevich, A S; Kondratyuk, N V; Kuleshov, N V

    2009-11-30

    The system of balance equations is modified for quasi-three-level passively Q-switched lasers with a slow saturable absorber. Optimal parameters of a Yb{sup 3+}:YAG microchip laser with a passive Cr{sup 4+}:YAG Q switch are calculated at a pulse repetition rate of {approx}100 kHz. The single-mode operation of the Yb:YAG-Cr:YAG laser with a pulse repetition rate above 100 kHz, the average output power 0.45 W and peak power 1.5 kW is experimentally demonstrated. In the multimode lasing regime, pulses with a peak power of 4.2 kW are obtained at an average output power of 0.8 W and a pulse repetition rate of 10 kHz. (lasers)

  20. 3.5-GHz intra-burst repetition rate ultrafast Yb-doped fiber laser

    NASA Astrophysics Data System (ADS)

    Kerse, Can; Kalaycıoğlu, Hamit; Elahi, Parviz; Akçaalan, Önder; Ilday, F. Ömer

    2016-05-01

    We report on an all-fiber Yb laser amplifier system with an intra-burst repetition rate of 3.5 GHz. The system is able to produce minimum of 15-ns long bursts containing approximately 50 pulses with a total energy of 215 μJ at a burst repetition rate of 1 kHz. The individual pulses are compressed down to the subpicosecond level. The seed signal from a 108 MHz fiber oscillator is converted to approximately 3.5 GHz by a multiplier consisting of six cascaded 50/50 couplers, and then amplified in ten stages. The highly cascaded amplification suppresses amplified spontaneous emission at low repetition rates. Nonlinear interactions between overlapping pulses within a burst is also discussed.

  1. Two-photon polymerization with variable repetition rate bursts of femtosecond laser pulses.

    PubMed

    Baldacchini, Tommaso; Snider, Scott; Zadoyan, Ruben

    2012-12-31

    We describe fabrication of microstructures by two-photon polymerization using bursts of femtosecond laser pulses. With the aid of an acousto-optic modulator driven by a function generator, two-photon polymerization is performed at variable burst repetition rates. We investigate how the time between the bursts of laser pulses influences the ultimate dimensions of lines written in a photosensitive resin. We observe that when using the same laser fluence, polymer lines fabricated at different burst repetition rates have different dimensions. In particular, the widths of two-photon polymerized lines become smaller with decreasing burst repetition rates. Based on the thermal properties of the resin and experimental writing conditions, we attribute this effect to localized heat accumulation. PMID:23388815

  2. Single Longitudinal Mode, High Repetition Rate, Q-switched Ho:YLF Laser for Remote Sensing

    NASA Technical Reports Server (NTRS)

    Bai, Yingxin; Yu, Jirong; Petzar, Paul; Petros, M.; Chen, Songsheng; Trieu, Bo; Lee, Nyung; Singh, U.

    2009-01-01

    Ho:YLF/LuLiF lasers have specific applications for remote sensing such as wind-speed measurement and carbon dioxide (CO2) concentration measurement in the atmosphere because the operating wavelength (around 2 m) is located in the eye-safe range and can be tuned to the characteristic lines of CO2 absorption and there is strong backward scattering signal from aerosol (Mie scattering). Experimentally, a diode pumped Ho:Tm:YLF laser has been successfully used as the transmitter of coherent differential absorption lidar for the measurement of with a repetition rate of 5 Hz and pulse energy of 75 mJ [1]. For highly precise CO2 measurements with coherent detection technique, a laser with high repetition rate is required to averaging out the speckle effect [2]. In addition, laser efficiency is critically important for the air/space borne lidar applications, because of the limited power supply. A diode pumped Ho:Tm:YLF laser is difficult to efficiently operate in high repetition rate due to the large heat loading and up-conversion. However, a Tm:fiber laser pumped Ho:YLF laser with low heat loading can be operated at high repetition rates efficiently [3]. No matter whether wind-speed or carbon dioxide (CO2) concentration measurement is the goal, a Ho:YLF/LuLiF laser as the transmitter should operate in a single longitudinal mode. Injection seeding is a valid technique for a Q-switched laser to obtain single longitudinal mode operation. In this paper, we will report the new results for a single longitudinal mode, high repetition rate, Q-switched Ho:YLF laser. In order to avoid spectral hole burning and make injection seeding easier, a four mirror ring cavity is designed for single longitudinal mode, high repetition rate Q-switched Ho:YLF laser. The ramp-fire technique is chosen for injection seeding.

  3. A contactless microwave-based diagnostic tool for high repetition rate laser systems

    SciTech Connect

    Braggio, C.; Borghesani, A. F.

    2014-02-15

    We report on a novel electro-optic device for the diagnostics of high repetition rate laser systems. It is composed of a microwave receiver and of a second order nonlinear crystal, whose irradiation with a train of short laser pulses produces a time-dependent polarization in the crystal itself as a consequence of optical rectification. This process gives rise to the emission of microwave radiation that is detected by a receiver and is analyzed to infer the repetition rate and intensity of the pulses. We believe that this new method may overcome some of the limitations of photodetection techniques.

  4. Repetitively rated plasma relativistic microwave oscillator with a controllable frequency in every pulse

    SciTech Connect

    Bogdankevich, I. L.; Grishin, D. M.; Gunin, A. V.; Ivanov, I. E.; Korovin, S. D.; Loza, O. T.; Mesyats, G. A.; Pavlov, D. A.; Rostov, V. V.; Strelkov, P. S.; Ul'yanov, D. K.

    2008-10-15

    A repetitively rated microwave oscillator whose frequency can be varied electronically from pulse to pulse in a predetermined manner is created for the first time. The microwave oscillator has a power on the order of 10{sup 8} W and is based on the Cherenkov interaction of a high-current relativistic electron beam with a plasma preformed before each pulse. Electronic control over the plasma properties allows one to arbitrarily vary the microwave frequency from pulse to pulse at a pulse repetition rate of up to 50 Hz.

  5. High power, high repetition rate, few picosecond Nd:LuVO₄ oscillator with cavity dumping.

    PubMed

    Gao, Peng; Guo, Jie; Li, Jinfeng; Lin, Hua; Yu, Haohai; Zhang, Huaijin; Liang, Xiaoyan

    2015-12-28

    We investigate the potential use of Nd:LuVO4 in high average power, high repetition rate ultrafast lasers. Maximum mode-locked average power of 28 W is obtained at the repetition rate of 58 MHz. The shortest pulse duration is achieved at 4 ps without dispersion compensation. With a cavity dumping technique, the pulse energy is scaling up to 40.7 μJ at 300 kHz and 14.3 μJ at 1.5 MHz. PMID:26831955

  6. High-order harmonic generation at a repetition rate of 100 kHz

    SciTech Connect

    Lindner, F.; Stremme, W.; Schaetzel, M. G.; Grasbon, F.; Paulus, G. G.; Walther, H.; Hartmann, R.; Strueder, L.

    2003-07-01

    We report high-order harmonic generation (HHG) in rare gases using a femtosecond laser system with a very high repetition rate (100 kHz) and low pulse energy (7 {mu}J). To our knowledge, this is the highest repetition rate reported to date for HHG. The tight focusing geometry required to reach sufficiently high intensities implies low efficiency of the process. Harmonics up to the 45th order are nevertheless generated and detected. We show evidence of clear separation and selection of quantum trajectories by moving the gas jet with respect to the focus, in agreement with the theoretical predictions of the semiclassical model of HHG.

  7. Injector Beam Dynamics for a High-Repetition Rate 4th-Generation Light Source

    SciTech Connect

    Papadopoulos, C. F.; Corlett, J.; Emma, P.; Filippetto, D.; Penn, G.; Qiang, J.; Reinsch, M.; Sannibale, F.; Steier, C.; Venturini, M.; Wells, R.

    2013-05-20

    We report on the beam dynamics studies and optimization methods for a high repetition rate (1 MHz) photoinjector based on a VHF normal conducting electron source. The simultaneous goals of beamcompression and reservation of 6-dimensional beam brightness have to be achieved in the injector, in order to accommodate a linac driven FEL light source. For this, a parallel, multiobjective optimization algorithm is used. We discuss the relative merits of different injector design points, as well as the constraints imposed on the beam dynamics by technical considerations such as the high repetition rate.

  8. Optical repetition rate stabilization of a mode-locked all-fiber laser.

    PubMed

    Rieger, Steffen; Hellwig, Tim; Walbaum, Till; Fallnich, Carsten

    2013-02-25

    We designed an all-fiber mode-locked Erbium laser with optically stabilized repetition rate of 31.4 MHz. The stabilization was achieved by changing the refractive index of an Ytterbium-doped fiber in the resonator via optical pumping at a wavelength of 978 nm; and for long-term stability the local temperature of the fiber was additionally controlled with a thermo-electric element. The repetition rate was stabilized over 12 hours, and an Allan deviation of 2.5 × 10⁻¹² for an averaging time of 1 s could be achieved.

  9. Advances in high repetition rate, ultra-short, gigawatt laser systems for time-resolved spectroscopy

    SciTech Connect

    DiMauro, L.F.

    1991-01-01

    The objective of this article is to emphasize the current advances in the development of high-repetition rate amplifier pumps. Although this review highlights amplifier pump development, any recent data from achieved outputs via the tunable amplifier section is also discussed. The first section describes desirable parameters attributable to the pump amplifier while the rest of the article deals with specific examples for various options. The pump amplifiers can be characterized into two distinct classes; those achieving operation in the hundred hertz regime and those performing at repetition rates {ge}1kHz. 23 refs., 4 figs.

  10. Advances in high repetition rate, ultra-short, gigawatt laser systems for time-resolved spectroscopy

    SciTech Connect

    DiMauro, L.F.

    1991-12-31

    The objective of this article is to emphasize the current advances in the development of high-repetition rate amplifier pumps. Although this review highlights amplifier pump development, any recent data from achieved outputs via the tunable amplifier section is also discussed. The first section describes desirable parameters attributable to the pump amplifier while the rest of the article deals with specific examples for various options. The pump amplifiers can be characterized into two distinct classes; those achieving operation in the hundred hertz regime and those performing at repetition rates {ge}1kHz. 23 refs., 4 figs.

  11. Picosecond supercontinuum laser with consistent emission parameters over variable repetition rates from 1 to 40 MHz

    NASA Astrophysics Data System (ADS)

    Schönau, Thomas; Siebert, Torsten; Härtel, Romano; Klemme, Dietmar; Lauritsen, Kristian; Erdmann, Rainer

    2013-02-01

    An freely triggerable picosecond visible supercontinuum laser source is presented that allows for a uniform spectral profile and equivalent pulse characteristics over variable repetition rates from 1 to 40MHz. The system features PM Yb3+-doped fiber amplification of a picosecond gain-switched seed diode at 1062 nm. The pump power in the multi-stage amplifier is actively adjusted by a microcontroller for a consistent peak power of the amplified signal in the full range of repetition rates. The length of the PCF is scaled to deliver a homogeneous spectrum and minimized distortion of the temporal pulse shape.

  12. Field Intensity Detection of Individual Terahertz Pulses at 80 MHz Repetition Rate

    NASA Astrophysics Data System (ADS)

    Rettich, F.; Vieweg, N.; Cojocari, O.; Deninger, A.

    2015-07-01

    We present a new approach to detect the intensity of individual terahertz pulses at repetition rates as high as 80 MHz. Our setup comprises a femtosecond fiber laser, an InGaAs-based terahertz emitter, a zero-bias Schottky detector, and a high-speed data acquisition unit. The detected pulses consist of two lobes with half-widths of 1-2 ns, which is much shorter than the inverse repetition rate of the laser. The system lends itself for high-speed terahertz transmission measurements, e.g., to study wetting dynamics in real time.

  13. Effect of the pulse repetition rate on fiber-assisted tissue ablation

    NASA Astrophysics Data System (ADS)

    Kang, Hyun Wook

    2016-07-01

    The effect of the pulse repetition rate on ablation performance was evaluated ex vivo at various fiber sweeping speeds for an effective 532-nm laser prostatectomy. Three pulse repetition rates (7.5, 15, and 30 kHz) at 100 W were delivered to bovine liver tissue at three sweeping speeds (2, 4, and 6 mm/s) to achieve bulky tissue removal. Ablation performance was quantitatively compared in terms of the ablation volume and the coagulation thickness. The lowest pulse repetition rate of 7.5 kHz attained the highest ablation volume (101.5 ± 12.0 mm3) and the thinnest coagulation (0.7 ± 0.1 mm) along with superficial carbonization. The highest pulse repetition rate of 30 kHz was associated with the least tissue removal (65.8 ± 5.0 mm3) and the deepest thermal denaturation (1.1 ± 0.2 mm). Quantitative evaluations of laser parameters can be instrumental in facilitating ablation efficiency and maintaining hemostatic coagulation during treatment of large-sized benign prostate hyperplasia.

  14. Multi-gigahertz repetition rate ultrafast waveguide lasers mode-locked with graphene saturable absorbers

    NASA Astrophysics Data System (ADS)

    Obraztsov, P. A.; Okhrimchuk, A. G.; Rybin, M. G.; Obraztsova, E. D.; Garnov, S. V.

    2016-08-01

    We report the development of an approach to build compact waveguide lasers that operate in the stable fundamental mode-locking regime with multigigahertz repetition rates. The approach is based on the use of depressed cladding multi- or single-mode waveguides fabricated directly in the active laser crystal using the femtosecond laser inscription method and a graphene saturable absorber. Using this approach we achieve the stable self-starting mode-locking operation of a diode-pumped waveguide Nd:YAG laser that delivers picosecond pulses at a repetition rate of up to 11.5 GHz with an average power of 12 mW at a central wavelength of 1064 nm. The saturable absorbers are formed through the chemical vapor deposition of single-layer graphene on the output coupler mirror or directly on the end facet of the laser crystal. The stable self-starting mode-locking operation is achieved by controlling the group delay dispersion in the laser cavity with an intracavity interferometer. The method developed for the creation of compact ultrashort pulse laser generators with gigahertz repetition rates can be extended further and applied for the development of compact high-repetition rate lasers that operate at a wide range of IR wavelengths.

  15. High Repetition Rate and Frequency Stabilized Ho:YLF Laser for CO2 Differential Absorption Lidar

    NASA Technical Reports Server (NTRS)

    Bai, Yingxin; Yu, Jirong; Petros, M.; Petzar, Pau; Trieu, Bo; Lee, Hyung; Singh, U.

    2009-01-01

    High repetition rate operation of an injection seeded Ho:YLF laser has been demonstrated. For 1 kHz operation, the output pulse energy reaches 5.8mJ and the optical-to-optical efficiency is 39% when the pump power is 14.5W.

  16. Estimation of Promotion, Repetition and Dropout Rates for Learners in South African Schools

    ERIC Educational Resources Information Center

    Uys, Daniël Wilhelm; Alant, Edward John Thomas

    2015-01-01

    A new procedure for estimating promotion, repetition and dropout rates for learners in South African schools is proposed. The procedure uses three different data sources: data from the South African General Household survey, data from the Education Management Information Systems, and data from yearly reports published by the Department of Basic…

  17. Spectral distortion of dual-comb spectrometry due to repetition rate fluctuation

    NASA Astrophysics Data System (ADS)

    Hong-Lei, Yang; Hao-Yun, Wei; Yan, Li

    2016-04-01

    Dual-comb spectrometry suffers the fluctuations of parameters in combs. We demonstrate that the repetition rate is more important than any other parameter, since the fluctuation of the repetition rate leads to a change of difference in the repetition rate between both combs, consequently causing the conversion factor variation and spectral frequency misalignment. The measured frequency noise power spectral density of the repetition rate exhibits an integrated residual frequency modulation of 1.4 Hz from 1 Hz to 100 kHz in our system. This value corresponds to the absorption peak fluctuation within a root mean square value of 0.19 cm‑1 that is verified by both simulation and experimental result. Further, we can also simulate spectrum degradation as the fluctuation varies. After modifying misaligned spectra and averaging, the measured result agrees well with the simulated spectrum based on the GEISA database. Project supported by the State Key Laboratory of Precision Measurement Technology & Instruments of Tsinghua University and the Young Scientists Fund of the National Natural Science Foundation of China (Grant No. 61205147).

  18. Multi-gigahertz repetition rate passively modelocked fiber lasers using carbon nanotubes.

    PubMed

    Martinez, Amos; Yamashita, Shinji

    2011-03-28

    There is an increasing demand for all-fiber passively mode-locked lasers with pulse repetition rates in the order of gigahertz for their potential applications in fields such as telecommunications and metrology. However, conventional mode-locked fiber lasers typically operate at fundamental repetition rates of only a few megahertz. In this paper, we report all-fiber laser operation with fundamental repetition rates of 4.24 GHz, 9.63 GHz and 19.45 GHz. This is, to date and to the best of our knowledge, the highest fundamental repetition rate reported for an all-fiber laser. The laser operation is based on the passive modelocking of a miniature all-fiber Fabry-Pérot laser (FFPL) by a carbon nanotube (CNT) saturable absorber. The key components for such device are a very high-gain Er:Yb phosphosilicate fiber and a fiber compatible saturable absorber with very small foot print and very low losses. The laser output of the three lasers was close to transform-limited with a pulsewidth of approximately 1 ps and low noise. As a demonstration of potential future applications for this laser, we also demonstrated supercontinuum generation with a longitudinal mode-spacing of 0.08 nm by launching the laser operating at 9.63 GHz into 30 m of a highly nonlinear dispersion shifted fiber.

  19. Spatial organization of repetition rate processing in cat anterior auditory field.

    PubMed

    Imaizumi, Kazuo; Priebe, Nicholas J; Cheung, Steven W; Schreiner, Christoph E

    2011-10-01

    Auditory cortex updates incoming information on a segment by segment basis for human speech and animal communication. Measuring repetition rate transfer functions (RRTFs) captures temporal responses to repetitive sounds. In this study, we used repetitive click trains to describe the spatial distribution of RRTF responses in cat anterior auditory field (AAF) and to discern potential variations in local temporal processing capacity. A majority of RRTF filters are band-pass. Temporal parameters estimated from RRTFs and corrected for characteristic frequency or latency dependencies are non-homogeneously distributed across AAF. Unlike the shallow global gradient observed in spectral receptive field parameters, transitions from loci with high to low temporal parameters are steep. Quantitative spatial analysis suggests non-uniform, circumscribed local organization for temporal pattern processing superimposed on global organization for spectral processing in cat AAF.

  20. Accurate modeling of high-repetition rate ultrashort pulse amplification in optical fibers

    NASA Astrophysics Data System (ADS)

    Lindberg, Robert; Zeil, Peter; Malmström, Mikael; Laurell, Fredrik; Pasiskevicius, Valdas

    2016-10-01

    A numerical model for amplification of ultrashort pulses with high repetition rates in fiber amplifiers is presented. The pulse propagation is modeled by jointly solving the steady-state rate equations and the generalized nonlinear Schrödinger equation, which allows accurate treatment of nonlinear and dispersive effects whilst considering arbitrary spatial and spectral gain dependencies. Comparison of data acquired by using the developed model and experimental results prove to be in good agreement.

  1. Accurate modeling of high-repetition rate ultrashort pulse amplification in optical fibers

    PubMed Central

    Lindberg, Robert; Zeil, Peter; Malmström, Mikael; Laurell, Fredrik; Pasiskevicius, Valdas

    2016-01-01

    A numerical model for amplification of ultrashort pulses with high repetition rates in fiber amplifiers is presented. The pulse propagation is modeled by jointly solving the steady-state rate equations and the generalized nonlinear Schrödinger equation, which allows accurate treatment of nonlinear and dispersive effects whilst considering arbitrary spatial and spectral gain dependencies. Comparison of data acquired by using the developed model and experimental results prove to be in good agreement. PMID:27713496

  2. A four kHz repetition rate compact TEA CO2 laser

    NASA Astrophysics Data System (ADS)

    Zheng, Yijun; Tan, Rongqing

    2013-09-01

    A compact transversely excited atmospheric (TEA) CO2 laser with high repetition-rate was reported. The size of the laser is 380 mm×300 mm×200 mm, and the discharge volume is 12×103 mm3. The laser cavity has a length of 320mm and consists of a totally reflective concave mirror with a radius of curvature of 4 m (Cu metal substrate coated with Au) and a partially reflecting mirror. The ultraviolet preionization makes the discharge even and stable,the output energy can be as high as 28 mJ under the circumstance of free oscillation, and the width of the light pulse is 60ns.To acquire the high wind velocity, a turbocharger is used in the system of the fast-gas flow cycle. When the wind speed is 100m/s, the repetition rate of the transversely excited atmospheric CO2 laser is up to 2 kHz. On this basis, a dual modular structure with two sets of the gas discharge unit is adopted to obtain a higher pulse repetition frequency output. The dual discharge unit composed two sets of electrodes and two sets of turbo fan. Alternate trigger technology is used to make the two sets of discharge module work in turn with repetition frequency of 2 kHz, the discharge interval of two sets of the gas discharge unit can be adjusted continuously from 20 microseconds to 250 microseconds. Under the conditions of maintaining the other parameters constant, the repetition frequency of the laser pulse is up to 4 kHz. The total size of laser with dual modular structure is 380mm×520mm×200mm, and the discharge volume is 24×103 mm3 with the cavity length of 520mm.

  3. Design and Development of High-Repetition-Rate Satellite Laser Ranging System

    NASA Astrophysics Data System (ADS)

    Choi, Eun-Jung; Bang, Seong-Cheol; Sung, Ki-Pyoung; Lim, Hyung-Chul; Jung, Chan-Gyu; Kim, In-Yeung; Choi, Jae-Seung

    2015-09-01

    The Accurate Ranging System for Geodetic Observation ? Mobile (ARGO-M) was successfully developed as the first Korean mobile Satellite Laser Ranging (SLR) system in 2012, and has joined in the International Laser Ranging Service (ILRS) tracking network, DAEdeoK (DAEK) station. The DAEK SLR station was approved as a validated station in April 2014, through the ILRS station ¡°data validation¡± process. The ARGO-M system is designed to enable 2 kHz laser ranging with millimeter-level precision for geodetic, remote sensing, navigation, and experimental satellites equipped with Laser Retroreflector Arrays (LRAs). In this paper, we present the design and development of a next generation high-repetition-rate SLR system for ARGO-M. The laser ranging rate up to 10 kHz is becoming an important issue in the SLR community to improve ranging precision. To implement high-repetition-rate SLR system, the High-repetition-rate SLR operation system (HSLR-10) was designed and developed using ARGO-M Range Gate Generator (A-RGG), so as to enable laser ranging from 50 Hz to 10 kHz. HSLR-10 includes both hardware controlling software and data post-processing software. This paper shows the design and development of key technologies of high-repetition-rate SLR system. The developed system was tested successfully at DAEK station and then moved to Sejong station, a new Korean SLR station, on July 1, 2015. HSLR-10 will begin normal operations at Sejong station in the near future.

  4. Continuous high-repetition-rate operation of collisional soft-x-ray lasers with solid targets.

    PubMed

    Weith, A; Larotonda, M A; Wang, Y; Luther, B M; Alessi, D; Marconi, M C; Rocca, J J; Dunn, J

    2006-07-01

    We have generated a laser average output power of 2 microW at a wavelength of 13.9 nm by operating a tabletop laser-pumped Ni-like Ag laser at a 5 Hz repetition rate, using a solid helicoidal target that is continuously rotated and advanced to renew the target surface between shots. More than 2 x 10(4) soft-x-ray laser shots were obtained by using a single target. Similar results were obtained at 13.2 nm in Ni-like Cd with a Cd-coated target. This scheme will allow uninterrupted operation of laser-pumped tabletop collisional soft-x-ray lasers at a repetition rate of 10 Hz for a period of hours, enabling the generation of continuous high average soft-x-ray powers for applications. PMID:16770410

  5. An optical parametric chirped-pulse amplifier for seeding high repetition rate free-electron lasers

    SciTech Connect

    Höppner, H.; Tanikawa, T.; Schulz, M.; Riedel, R.; Teubner, U.; Faatz, B.; Tavella, F.

    2015-05-15

    High repetition rate free-electron lasers (FEL), producing highly intense extreme ultraviolet and x-ray pulses, require new high power tunable femtosecond lasers for FEL seeding and FEL pump-probe experiments. A tunable, 112 W (burst mode) optical parametric chirped-pulse amplifier (OPCPA) is demonstrated with center frequencies ranging from 720–900 nm, pulse energies up to 1.12 mJ and a pulse duration of 30 fs at a repetition rate of 100 kHz. Since the power scalability of this OPCPA is limited by the OPCPA-pump amplifier, we also demonstrate a 6.7–13.7 kW (burst mode) thin-disk OPCPA-pump amplifier, increasing the possible OPCPA output power to many hundreds of watts. Furthermore, third and fourth harmonic generation experiments are performed and the results are used to simulate a seeded FEL with high-gain harmonic generation.

  6. A Dynamic Feedback Model for High Repetition Rate LINAC-Driven FELS

    SciTech Connect

    Mellado Munoz, M.; Doolittle, L.; Emma, P.; Huang, G.; Ratti, A.; Serrano, C.; Byrd, J. M.

    2012-05-20

    One of the concepts for the next generation of linacdriven FELs is a CW superconducting linac driving an electron beam with MHz repetition rates. One of the challenges for next generation FELs is improve the stability of the xray pulses by improving the shot-to-shot stability of the energy, charge, peak current, and timing jitter of the electron beam. A high repetition rate FEL with a CW linac presents an opportunity to use a variety of broadband feedbacks to stabilize the beam parameters. To understand the performance of such a feedback system, we are developing a dynamic model of the machine with a focus on the longitudinal beam properties. The model is being developed as an extension of the LITrack code and includes the dynamics of the beam-cavity interaction, RF feedback, beam-based feedback, and multibunch effects. In this paper, we present a detailed description of this model.

  7. A simple sub-nanosecond ultraviolet light pulse generator with high repetition rate and peak power.

    PubMed

    Binh, P H; Trong, V D; Renucci, P; Marie, X

    2013-08-01

    We present a simple ultraviolet sub-nanosecond pulse generator using commercial ultraviolet light-emitting diodes with peak emission wavelengths of 290 nm, 318 nm, 338 nm, and 405 nm. The generator is based on step recovery diode, short-circuited transmission line, and current-shaping circuit. The narrowest pulses achieved have 630 ps full width at half maximum at repetition rate of 80 MHz. Optical pulse power in the range of several hundreds of microwatts depends on the applied bias voltage. The bias voltage dependences of the output optical pulse width and peak power are analysed and discussed. Compared to commercial UV sub-nanosecond generators, the proposed generator can produce much higher pulse repetition rate and peak power.

  8. Group velocity locked vector dissipative solitons in a high repetition rate fiber laser.

    PubMed

    Luo, Yiyang; Li, Lei; Liu, Deming; Sun, Qizhen; Wu, Zhichao; Xu, Zhilin; Tang, Dingyuan; Fu, Songnian; Zhao, Luming

    2016-08-01

    Vectorial nature of dissipative solitons (DSs) with high repetition rate is studied for the first time in a normal-dispersion fiber laser. Despite the fact that the formed DSs are strongly chirped and the repetition rate is greater than 100 MHz, polarization locked and polarization rotating group velocity locked vector DSs can be formed under 129.3 MHz fundamental mode-locking and 258.6 MHz harmonic mode-locking of the fiber laser, respectively. The two orthogonally polarized components of these vector DSs possess distinctly different central wavelengths and travel together at the same group velocity in the laser cavity, resulting in a gradual spectral edge and small steps on the optical spectrum, which can be considered as an auxiliary indicator of the group velocity locked vector DSs. Moreover, numerical simulations well confirm the experimental observations and further reveal the impact of the net cavity birefringence on the properties of the formed vector DSs. PMID:27505834

  9. High-order harmonic generation using a high-repetition-rate turnkey laser

    SciTech Connect

    Lorek, E. Larsen, E. W.; Heyl, C. M.; Carlström, S.; Mauritsson, J.; Paleček, D.; Zigmantas, D.

    2014-12-15

    We generate high-order harmonics at high pulse repetition rates using a turnkey laser. High-order harmonics at 400 kHz are observed when argon is used as target gas. In neon, we achieve generation of photons with energies exceeding 90 eV (∼13 nm) at 20 kHz. We measure a photon flux of up to 4.4 × 10{sup 10} photons per second per harmonic in argon at 100 kHz. Many experiments employing high-order harmonics would benefit from higher repetition rates, and the user-friendly operation opens up for applications of coherent extreme ultra-violet pulses in new research areas.

  10. High-order harmonic generation using a high-repetition-rate turnkey laser.

    PubMed

    Lorek, E; Larsen, E W; Heyl, C M; Carlström, S; Paleček, D; Zigmantas, D; Mauritsson, J

    2014-12-01

    We generate high-order harmonics at high pulse repetition rates using a turnkey laser. High-order harmonics at 400 kHz are observed when argon is used as target gas. In neon, we achieve generation of photons with energies exceeding 90 eV (∼13 nm) at 20 kHz. We measure a photon flux of up to 4.4 × 10(10) photons per second per harmonic in argon at 100 kHz. Many experiments employing high-order harmonics would benefit from higher repetition rates, and the user-friendly operation opens up for applications of coherent extreme ultra-violet pulses in new research areas. PMID:25554271

  11. Frequency-agile kilohertz repetition-rate optical parametric oscillator based on periodically poled lithium niobate

    SciTech Connect

    Yang, S.T.; Velsko, S.P.

    1999-02-01

    We report kilohertz repetition-rate pulse-to-pulse wavelength tuning from 3.22 to 3.7 {mu}m in a periodically poled lithium niobate (PPLN) optical parametric oscillator (OPO). Rapid tuning over 400thinspcm{sup {minus}1} with random wavelength accessibility is achieved by rotation of the pump beam angle by no more than 24thinspthinspmrad in the PPLN crystal by use of an acousto-optic beam deflector. Over the entire tuning range, a near-transform-limited OPO bandwidth can be obtained by means of injection seeding with a single-frequency 1.5-{mu}m laser diode. The frequency agility, high repetition rate, and narrow bandwidth of this mid-IR PPLN OPO make it well suited as a lidar transmitter source. {copyright} {ital 1999} {ital Optical Society of America}

  12. Study of nanostructure growth with nanoscale apex induced by femtosecond laser irradiation at megahertz repetition rate

    PubMed Central

    2013-01-01

    Leaf-like nanostructures with nanoscale apex are induced on dielectric target surfaces by high-repetition-rate femtosecond laser irradiation in ambient conditions. We have recently developed this unique technique to grow leaf-like nanostructures with such interesting geometry without the use of any catalyst. It was found to be possible only in the presence of background nitrogen gas flow. In this synthesis method, the target serves as the source for building material as well as the substrate upon which these nanostructures can grow. In our investigation, it was found that there are three possible kinds of nanotips that can grow on target surfaces. In this report, we have presented the study of the growth mechanisms of such leaf-like nanostructures under various conditions such as different laser pulse widths, pulse repetition rates, dwell times, and laser polarizations. We observed a clear transformation in the kind of nanotips that grew for the given laser conditions. PMID:23607832

  13. Moderate repetition rate ultra-intense laser targets and optics using variable thickness liquid crystal films

    NASA Astrophysics Data System (ADS)

    Poole, P. L.; Willis, C.; Cochran, G. E.; Hanna, R. T.; Andereck, C. D.; Schumacher, D. W.

    2016-10-01

    Liquid crystal films are variable thickness, planar targets for ultra-intense laser matter experiments such as ion acceleration. Their target qualities also make them ideal for high-power laser optics such as plasma mirrors and waveplates. By controlling parameters of film formation, thickness can be varied on-demand from 10 nm to above 50 μm, enabling real-time optimization of laser interactions. Presented here are results using a device that draws films from a bulk liquid crystal source volume with any thickness in the aforementioned range. Films form within 2 μm of the same location each time, well within the Rayleigh range of even tight F / # systems, thus removing the necessity for realignment between shots. The repetition rate of the device exceeds 0.1 Hz for sub-100 nm films, facilitating higher repetition rate operation of modern laser facilities.

  14. Comparison of two high-repetition-rate pulsed CO/sub 2/ laser discharge geometries

    SciTech Connect

    Faszer, W.; Tulip, J.; Seguin, H.

    1980-11-01

    Two discharge geometries are commonly used for pumping high-repetition-rate transversely excited atmosphere (TEA) lasers. One uses solid electrodes with preionization provided by downstream spark pins. The other uses a solid electrode and a screen electrode with preionization provided by an auxiliary discharge behind the screen. In this study the performance of the two systems was compared. The repetition rate at which arcing occurs was found to increase linearly with flow velocity but decrease with increasing energy density. It was also dependent on system geometry and the spark pin preionized system performed better than the auxiliary discharge preionized system. Data are given for discharges in N/sub 2/, CO/sub 2/, He, and a CO/sub 2/ laser mixture.

  15. High Repetition Rate, LINAC-Based Nuclear Resonance Fluorescence FY 2008 Final Report

    SciTech Connect

    Scott M Watson; Mathew T Kinlaw; James L Jones; Alan W. Hunt; Glen A. Warren

    2008-12-01

    This summarizes the first year of a multi-laboratory/university, multi-year effort focusing on high repetition rate, pulsed LINAC-based nuclear resonance fluorescence (NRF) measurements. Specifically, this FY2008 effort centered on experimentally assessing NRF measurements using pulsed linear electron accelerators, operated at various repetition rates, and identifying specific detection requirements to optimize such measurements. Traditionally, interest in NRF as a detection technology, which continues to receive funding from DHS and DOE/NA-22, has been driven by continuous-wave (CW), Van de Graff-based bremsstrahlung sources. However, in addition to the relatively sparse present-day use of Van de Graff sources, only limited NRF data from special nuclear materials has been presented; there is even less data available regarding shielding effects and photon source optimization for NRF measurements on selected nuclear materials.

  16. Study of nanostructure growth with nanoscale apex induced by femtosecond laser irradiation at megahertz repetition rate

    NASA Astrophysics Data System (ADS)

    Patel, Nikunj B.; Tan, Bo; Venkatakrishnan, Krishnan

    2013-04-01

    Leaf-like nanostructures with nanoscale apex are induced on dielectric target surfaces by high-repetition-rate femtosecond laser irradiation in ambient conditions. We have recently developed this unique technique to grow leaf-like nanostructures with such interesting geometry without the use of any catalyst. It was found to be possible only in the presence of background nitrogen gas flow. In this synthesis method, the target serves as the source for building material as well as the substrate upon which these nanostructures can grow. In our investigation, it was found that there are three possible kinds of nanotips that can grow on target surfaces. In this report, we have presented the study of the growth mechanisms of such leaf-like nanostructures under various conditions such as different laser pulse widths, pulse repetition rates, dwell times, and laser polarizations. We observed a clear transformation in the kind of nanotips that grew for the given laser conditions.

  17. Study of nanostructure growth with nanoscale apex induced by femtosecond laser irradiation at megahertz repetition rate.

    PubMed

    Patel, Nikunj B; Tan, Bo; Venkatakrishnan, Krishnan

    2013-01-01

    Leaf-like nanostructures with nanoscale apex are induced on dielectric target surfaces by high-repetition-rate femtosecond laser irradiation in ambient conditions. We have recently developed this unique technique to grow leaf-like nanostructures with such interesting geometry without the use of any catalyst. It was found to be possible only in the presence of background nitrogen gas flow. In this synthesis method, the target serves as the source for building material as well as the substrate upon which these nanostructures can grow. In our investigation, it was found that there are three possible kinds of nanotips that can grow on target surfaces. In this report, we have presented the study of the growth mechanisms of such leaf-like nanostructures under various conditions such as different laser pulse widths, pulse repetition rates, dwell times, and laser polarizations. We observed a clear transformation in the kind of nanotips that grew for the given laser conditions. PMID:23607832

  18. High-repetition-rate high-power variable-bandwidth dye laser

    SciTech Connect

    Lavi, S.; Amit, M.; Bialolanker, G.; Miron, E.; Levin, L.A.

    1985-07-01

    An efficient high-repetition-rate dye laser is described which has a bandwidth that can be tailored to match typical atomic inhomogeneous linewidths. The dye laser is pumped by a 4-kHz 2--6 mJ/pulse copper vapor laser. The total efficiency of the dye laser (oscillator and amplifier) is 45% for rhodamine 6G and 30% for rhodamine B.

  19. High (1 GHz) repetition rate compact femtosecond laser: A powerful multiphoton tool for nanomedicine and nanobiotechnology

    NASA Astrophysics Data System (ADS)

    Ehlers, A.; Riemann, I.; Martin, S.; Le Harzic, R.; Bartels, A.; Janke, C.; König, K.

    2007-07-01

    Multiphoton tomography of human skin and nanosurgery of human chromosomes have been performed with a 1GHz repetition rate laser by the use of the commercially available femtosecond multiphoton laser tomograph DermaInspect as well as a compact galvoscanning microscope. We performed the autofluorescence tomography up to 100μm in the depth of human skin. Submicron cutting lines and hole drillings have been conducted on labeled human chromosomes.

  20. Studies of a Linac Driver for a High Repetition Rate X-Ray FEL

    SciTech Connect

    Venturini, M.; Corlett, J.; Doolittle, L.; Filippetto, D.; Papadopoulos, C.; Penn, G.; Prosnitz, D.; Qiang, J.; Reinsch, M.; Ryne, R.; Sannibale, F.; Staples, J.; Wells, R.; Wurtele, J.; Zolotorev, M.; Zholents, A.

    2011-06-01

    We report on on-going studies of a superconducting CW linac driver intended to support a high repetition rate FEL operating in the soft x-rays spectrum. We present a pointdesign for a 1.8 GeV machine tuned for 300 pC bunches and delivering low-emittance, low-energy spread beams as needed for the SASE and seeded beamlines.

  1. Steady State Microbunching for High Brilliance and High Repetition Rate Storage Ring-Based Light Sources

    SciTech Connect

    Chao, Alex; Ratner, Daniel; Jiao, Yi; /Beijing, Inst. High Energy Phys.

    2012-09-06

    Electron-based light sources have proven to be effective sources of high brilliance, high frequency radiation. Such sources are typically either linac-Free Electron Laser (FEL) or storage ring types. The linac-FEL type has high brilliance (because the beam is microbunched) but low repetition rate. The storage ring type has high repetition rate (rapid beam circulation) but comparatively low brilliance or coherence. We propose to explore the feasibility of a microbunched beam in a storage ring that promises high repetition rate and high brilliance. The steady-state-micro-bunch (SSMB) beam in storage ring could provide CW sources for THz, EUV, or soft X-rays. Several SSMB mechanisms have been suggested recently, and in this report, we review a number of these SSMB concepts as promising directions for high brilliance, high repetition rate light sources of the future. The trick of SSMB lies in the RF system, together with the associated synchrotron beam dynamics, of the storage ring. Considering various different RF arrangements, there could be considered a number of scenarios of the SSMB. In this report, we arrange these scenarios more or less in order of the envisioned degree of technical challenge to the RF system, and not in the chronological order of their original references. Once the stored beam is steady-state microbunched in a storage ring, it passes through a radiator repeatedly every turn (or few turns). The radiator extracts a small fraction of the beam energy as coherent radiation with a wavelength corresponding to the microbunched period of the beam. In contrast to an FEL, this radiator is not needed to generate the microbunching (as required e.g. by SASE FELs or seeded FELs), so the radiator can be comparatively simple and short.

  2. Dual-color three-dimensional STED microscopy with a single high-repetition-rate laser.

    PubMed

    Han, Kyu Young; Ha, Taekjip

    2015-06-01

    We describe a dual-color three-dimensional stimulated emission depletion (3D-STED) microscopy employing a single laser source with a repetition rate of 80 MHz. Multiple excitation pulses synchronized with a STED pulse were generated by a photonic crystal fiber, and the desired wavelengths were selected by an acousto-optic tunable filter with high spectral purity. Selective excitation at different wavelengths permits simultaneous imaging of two fluorescent markers at a nanoscale resolution in three dimensions. PMID:26030581

  3. High-Field High-Repetition-Rate Sources for the Coherent THz Control of Matter.

    PubMed

    Green, B; Kovalev, S; Asgekar, V; Geloni, G; Lehnert, U; Golz, T; Kuntzsch, M; Bauer, C; Hauser, J; Voigtlaender, J; Wustmann, B; Koesterke, I; Schwarz, M; Freitag, M; Arnold, A; Teichert, J; Justus, M; Seidel, W; Ilgner, C; Awari, N; Nicoletti, D; Kaiser, S; Laplace, Y; Rajasekaran, S; Zhang, L; Winnerl, S; Schneider, H; Schay, G; Lorincz, I; Rauscher, A A; Radu, I; Mährlein, S; Kim, T H; Lee, J S; Kampfrath, T; Wall, S; Heberle, J; Malnasi-Csizmadia, A; Steiger, A; Müller, A S; Helm, M; Schramm, U; Cowan, T; Michel, P; Cavalleri, A; Fisher, A S; Stojanovic, N; Gensch, M

    2016-01-01

    Ultrashort flashes of THz light with low photon energies of a few meV, but strong electric or magnetic field transients have recently been employed to prepare various fascinating nonequilibrium states in matter. Here we present a new class of sources based on superradiant enhancement of radiation from relativistic electron bunches in a compact electron accelerator that we believe will revolutionize experiments in this field. Our prototype source generates high-field THz pulses at unprecedented quasi-continuous-wave repetition rates up to the MHz regime. We demonstrate parameters that exceed state-of-the-art laser-based sources by more than 2 orders of magnitude. The peak fields and the repetition rates are highly scalable and once fully operational this type of sources will routinely provide 1 MV/cm electric fields and 0.3 T magnetic fields at repetition rates of few 100 kHz. We benchmark the unique properties by performing a resonant coherent THz control experiment with few 10 fs resolution. PMID:26924651

  4. High repetition rate (100 Hz), high peak power, high contrast femtosecond laser chain

    NASA Astrophysics Data System (ADS)

    Clady, R.; Tcheremiskine, V.; Azamoum, Y.; Ferré, A.; Charmasson, L.; Utéza, O.; Sentis, M.

    2016-03-01

    High intensity femtosecond laser are now routinely used to produce energetic particles and photons via interaction with solid targets. However, the relatively low conversion efficiency of such processes requires the use of high repetition rate laser to increase the average power of the laser-induced secondary source. Furthermore, for high intensity laser-matter interaction, a high temporal contrast is of primary importance as the presence of a ns ASE pedestal (Amplified Spontaneous Emission) and/or various prepulses may significantly affect the governing interaction processes by creating a pre-plasma on the target surface. We present the characterization of a laser chain based on Ti:Sa technology and CPA technique, which presents unique laser characteristics : a high repetition rate (100 Hz), a high peak power (>5 TW) and a high contrast ratio (ASE<10-10) obtained thanks to a specific design with 3 saturable absorbers inserted in the amplification chain. A deformable mirror placed before the focusing parabolic mirror should allow us to focus the beam almost at the limit of diffraction. In these conditions, peak intensity above 1019W.cm-2 on target could be achieved at 100 Hz, allowing the study of relativistic optics at a high repetition rate.

  5. High-Field High-Repetition-Rate Sources for the Coherent THz Control of Matter

    DOE PAGES

    Green, B.; Kovalev, S.; Asgekar, V.; Geloni, G.; Lehnert, U.; Golz, T.; Kuntzsch, M.; Bauer, C.; Hauser, J.; Voigtlaender, J.; et al

    2016-02-29

    Ultrashort flashes of THz light with low photon energies of a few meV, but strong electric or magnetic field transients have recently been employed to prepare various fascinating nonequilibrium states in matter. Here we present a new class of sources based on superradiant enhancement of radiation from relativistic electron bunches in a compact electron accelerator that we believe will revolutionize experiments in this field. Our prototype source generates high-field THz pulses at unprecedented quasi-continuous-wave repetition rates up to the MHz regime. We demonstrate parameters that exceed state-of-the-art laser-based sources by more than 2 orders of magnitude. The peak fields andmore » the repetition rates are highly scalable and once fully operational this type of sources will routinely provide 1 MV/cm electric fields and 0.3 T magnetic fields at repetition rates of few 100 kHz. In conclusion, we benchmark the unique properties by performing a resonant coherent THz control experiment with few 10 fs resolution.« less

  6. High-Field High-Repetition-Rate Sources for the Coherent THz Control of Matter

    PubMed Central

    Green, B.; Kovalev, S.; Asgekar, V.; Geloni, G.; Lehnert, U.; Golz, T.; Kuntzsch, M.; Bauer, C.; Hauser, J.; Voigtlaender, J.; Wustmann, B.; Koesterke, I.; Schwarz, M.; Freitag, M.; Arnold, A.; Teichert, J.; Justus, M.; Seidel, W.; Ilgner, C.; Awari, N.; Nicoletti, D.; Kaiser, S.; Laplace, Y.; Rajasekaran, S.; Zhang, L.; Winnerl, S.; Schneider, H.; Schay, G.; Lorincz, I.; Rauscher, A. A.; Radu, I.; Mährlein, S.; Kim, T. H.; Lee, J. S.; Kampfrath, T.; Wall, S.; Heberle, J.; Malnasi-Csizmadia, A.; Steiger, A.; Müller, A. S.; Helm, M.; Schramm, U.; Cowan, T.; Michel, P.; Cavalleri, A.; Fisher, A. S.; Stojanovic, N.; Gensch, M.

    2016-01-01

    Ultrashort flashes of THz light with low photon energies of a few meV, but strong electric or magnetic field transients have recently been employed to prepare various fascinating nonequilibrium states in matter. Here we present a new class of sources based on superradiant enhancement of radiation from relativistic electron bunches in a compact electron accelerator that we believe will revolutionize experiments in this field. Our prototype source generates high-field THz pulses at unprecedented quasi-continuous-wave repetition rates up to the MHz regime. We demonstrate parameters that exceed state-of-the-art laser-based sources by more than 2 orders of magnitude. The peak fields and the repetition rates are highly scalable and once fully operational this type of sources will routinely provide 1 MV/cm electric fields and 0.3 T magnetic fields at repetition rates of few 100 kHz. We benchmark the unique properties by performing a resonant coherent THz control experiment with few 10 fs resolution. PMID:26924651

  7. X-band linac technology for a high repetition rate light source

    NASA Astrophysics Data System (ADS)

    Christou, Chris

    2011-11-01

    Traditionally, the pulse-to-pulse charging and switching time for a thyratron-switched line-type modulator has limited the repetition rate of normal-conducting high-energy linacs; however the recent development of solid-state modulators employing IGBT switches has allowed the repetition rate of a high-power modulator to be increased by an order of magnitude. When combined with the high accelerating gradients that can be achieved in an X-band accelerating structure, this enables a relatively compact linear accelerator to be constructed that can operate with a pulse repetition rate in excess of 1 kHz. A study has been undertaken on the issues arising from the operation of an X-band linac in this mode, including a survey of availability and limitations of modulators, klystrons and structures. Close attention has been paid to the dissipation of power in critical parts of the high-power RF chain, both on average and transiently during the high-power RF pulse.

  8. All-optical repetition rate multiplication of pseudorandom bit sequences by employing power coupler and equalizer

    NASA Astrophysics Data System (ADS)

    Sun, Zhenchao; Wang, Zhi; Wu, Chongqing; Wang, Fu; Li, Qiang

    2015-10-01

    A scheme for all-optical repetition rate multiplication of pseudorandom bit sequences (PRBS) is demonstrated with a precision delay feedback loop cascaded with a terahertz optical asymmetric demultiplexer (TOAD)-based power equalizer. Its feasibility has been verified by experiments, which show a multiplication for PRBS at cycle 2^7-1 from 2.5 to 10 Gb/s. This scheme can be employed for the rate multiplication of a much longer cycle PRBS at a much higher bit rate over 40 Gb/s if the time-delay, the loss, and the dispersion of an optical delay line are all precisely managed.

  9. Effects of shifts in the rate of repetitive stimulation on sustained attention

    NASA Technical Reports Server (NTRS)

    Krulewitz, J. E.; Warm, J. S.; Wohl, T. H.

    1975-01-01

    The effects of shifts in the rate of presentation of repetitive neutral events (background event rate) were studied in a visual vigilance task. Four groups of subjects experienced either a high (21 events/min) or a low (6 events/min) event rate for 20 min and then experienced either the same or the alternate event rate for an additional 40 min. The temporal occurrence of critical target signals was identical for all groups, irrespective of event rate. The density of critical signals was 12 signals/20 min. By the end of the session, shifts in event rate were associated with changes in performance which resembled contrast effects found in other experimental situations in which shift paradigms were used. Relative to constant event rate control conditions, a shift from a low to a high event rate depressed the probability of signal detections, while a shift in the opposite direction enhanced the probability of signal detections.

  10. Characteristics of a velvet cathode under high repetition rate pulse operation

    SciTech Connect

    Xun Tao; Zhang Jiande; Yang Hanwu; Zhang Zicheng; Fan Yuwei

    2009-10-15

    As commonly used material for cold cathodes, velvet works well in single shot and low repetition rate (rep-rate) high-power microwave (HPM) sources. In order to determine the feasibility of velvet cathodes under high rep-rate operation, a series of experiments are carried out on a high-power diode, driven by a {approx}300 kV, {approx}6 ns, {approx}100 {omega}, and 1-300 Hz rep-rate pulser, Torch 02. Characteristics of vacuum compatibility and cathode lifetime under different pulse rep-rate are focused on in this paper. Results of time-resolved pressure history, diode performance, shot-to-shot reproducibility, and velvet microstructure changes are presented. As the rep-rate increases, the equilibrium pressure grows hyperlinearly and the velvet lifetime decreases sharply. At 300 Hz, the pressure in the given diode exceeded 1 Pa, and the utility shots decreased to 2000 pulses for nonstop mode. While, until the velvet begins to degrade, the pulse-to-pulse instability of diode voltage and current is quite small, even under high rep-rate conditions. Possible reasons for the operation limits are discussed, and methods to improve the performance of a rep-rate velvet cathode are also suggested. These results may be of interest to the repetitive HPM systems with cold cathodes.

  11. Acousto-optic pulse picking scheme with carrier-frequency-to-pulse-repetition-rate synchronization.

    PubMed

    de Vries, Oliver; Saule, Tobias; Plötner, Marco; Lücking, Fabian; Eidam, Tino; Hoffmann, Armin; Klenke, Arno; Hädrich, Steffen; Limpert, Jens; Holzberger, Simon; Schreiber, Thomas; Eberhardt, Ramona; Pupeza, Ioachim; Tünnermann, Andreas

    2015-07-27

    We introduce and experimentally validate a pulse picking technique based on a travelling-wave-type acousto-optic modulator (AOM) having the AOM carrier frequency synchronized to the repetition rate of the original pulse train. As a consequence, the phase noise characteristic of the original pulse train is largely preserved, rendering this technique suitable for applications requiring carrier-envelope phase stabilization. In a proof-of-principle experiment, the 1030-nm spectral part of an 74-MHz, carrier-envelope phase stable Ti:sapphire oscillator is amplified and reduced in pulse repetition frequency by a factor of two, maintaining an unprecedentedly low carrier-envelope phase noise spectral density of below 68 mrad. Furthermore, a comparative analysis reveals that the pulse-picking-induced additional amplitude noise is minimized, when the AOM is operated under synchronicity. The proposed scheme is particularly suitable when the down-picked repetition rate is still in the multi-MHz-range, where Pockels cells cannot be applied due to piezoelectric ringing. PMID:26367616

  12. Optimization of graffiti removal on natural stone by means of high repetition rate UV laser

    NASA Astrophysics Data System (ADS)

    Fiorucci, M. P.; López, A. J.; Ramil, A.; Pozo, S.; Rivas, T.

    2013-08-01

    The use of laser for graffiti removal is a promising alternative to conventional cleaning methods, though irradiation parameters must be carefully selected in order to achieve the effective cleaning without damaging the substrate, especially when referring to natural stone. From a practical point of view, once a safe working window is selected, it is necessary to determine the irradiation conditions to remove large paint areas, with minimal time consumption. The aim of this paper is to present a systematic procedure to select the optimum parameters for graffiti removal by means of the 3rd harmonic of a high repetition rate nanosecond Nd:YVO4 laser. Ablation thresholds of four spray paint colors were determined and the effect of pulse repetition frequency, beam diameter and line scan separation was analyzed, obtaining a set of values which optimize the ablation process.

  13. 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.

  14. Ultrashort pulse high repetition rate laser system for biological tissue processing

    DOEpatents

    Neev, Joseph; Da Silva, Luiz B.; Matthews, Dennis L.; Glinsky, Michael E.; Stuart, Brent C.; Perry, Michael D.; Feit, Michael D.; Rubenchik, Alexander M.

    1998-01-01

    A method and apparatus is disclosed for fast, efficient, precise and damage-free biological tissue removal using an ultrashort pulse duration laser system operating at high pulse repetition rates. The duration of each laser pulse is on the order of about 1 fs to less than 50 ps such that energy deposition is localized in a small depth and occurs before significant hydrodynamic motion and thermal conduction, leading to collateral damage, can take place. The depth of material removed per pulse is on the order of about 1 micrometer, and the minimal thermal and mechanical effects associated with this ablation method allows for high repetition rate operation, in the region 10 to over 1000 Hertz, which, in turn, achieves high material removal rates. The input laser energy per ablated volume of tissue is small, and the energy density required to ablate material decreases with decreasing pulse width. The ablation threshold and ablation rate are only weakly dependent on tissue type and condition, allowing for maximum flexibility of use in various biological tissue removal applications. The use of a chirped-pulse amplified Titanium-doped sapphire laser is disclosed as the source in one embodiment.

  15. Ultrashort pulse high repetition rate laser system for biological tissue processing

    DOEpatents

    Neev, J.; Da Silva, L.B.; Matthews, D.L.; Glinsky, M.E.; Stuart, B.C.; Perry, M.D.; Feit, M.D.; Rubenchik, A.M.

    1998-02-24

    A method and apparatus are disclosed for fast, efficient, precise and damage-free biological tissue removal using an ultrashort pulse duration laser system operating at high pulse repetition rates. The duration of each laser pulse is on the order of about 1 fs to less than 50 ps such that energy deposition is localized in a small depth and occurs before significant hydrodynamic motion and thermal conduction, leading to collateral damage, can take place. The depth of material removed per pulse is on the order of about 1 micrometer, and the minimal thermal and mechanical effects associated with this ablation method allows for high repetition rate operation, in the region 10 to over 1000 Hertz, which, in turn, achieves high material removal rates. The input laser energy per ablated volume of tissue is small, and the energy density required to ablate material decreases with decreasing pulse width. The ablation threshold and ablation rate are only weakly dependent on tissue type and condition, allowing for maximum flexibility of use in various biological tissue removal applications. The use of a chirped-pulse amplified Titanium-doped sapphire laser is disclosed as the source in one embodiment. 8 figs.

  16. Single-pass high harmonic generation at high repetition rate and photon flux

    NASA Astrophysics Data System (ADS)

    Hädrich, Steffen; Rothhardt, Jan; Krebs, Manuel; Demmler, Stefan; Klenke, Arno; Tünnermann, Andreas; Limpert, Jens

    2016-09-01

    Sources of short wavelength radiation with femtosecond to attosecond pulse durations, such as synchrotrons or free electron lasers, have already made possible numerous, and will facilitate more, seminal studies aimed at understanding atomic and molecular processes on fundamental length and time scales. Table-top sources of coherent extreme ultraviolet to soft x-ray radiation enabled by high harmonic generation (HHG) of ultrashort pulse lasers have also gained significant attention in the last few years due to their enormous potential for addressing a plethora of applications, therefore constituting a complementary source to large-scale facilities (synchrotrons and free electron lasers). Ti:sapphire based laser systems have been the workhorses for HHG for decades, but are limited in repetition rate and average power. On the other hand, it has been widely recognized that fostering applications in fields such as photoelectron spectroscopy and microscopy, coincidence detection, coherent diffractive imaging and frequency metrology requires a high repetition rate and high photon flux HHG sources. In this article we will review recent developments in realizing the demanding requirement of producing a high photon flux and repetition rate at the same time. Particular emphasis will be put on suitable ultrashort pulse and high average power lasers, which directly drive harmonic generation without the need for external enhancement cavities. To this end we describe two complementary schemes that have been successfully employed for high power fiber lasers, i.e. optical parametric chirped pulse amplifiers and nonlinear pulse compression. Moreover, the issue of phase-matching in tight focusing geometries will be discussed and connected to recent experiments. We will highlight the latest results in fiber laser driven high harmonic generation that currently produce the highest photon flux of all existing sources. In addition, we demonstrate the first promising applications and

  17. All-optical repetition rate multiplication of pseudorandom bit sequences based on cascaded TOADs

    NASA Astrophysics Data System (ADS)

    Sun, Zhenchao; Wang, Zhi; Wu, Chongqing; Wang, Fu; Li, Qiang

    2016-03-01

    A scheme for all-optical repetition rate multiplication of pseudorandom bit sequences (PRBS) is demonstrated with all-optical wavelength conversion and optical logic gate 'OR' based on cascaded Tera-Hertz Optical Asymmetric Demultiplexers (TOADs). Its feasibility is verified by multiplication experiments from 500 Mb/s to 4 Gb/s for 23-1 PRBS and from 1 Gb/s to 4 Gb/s for 27-1 PRBS. This scheme can be employed for rate multiplication for much longer cycle PRBS at much higher bit rate over 40 Gb/s when the time-delay, the loss and the dispersion of the optical delay line are all precisely managed. The upper limit of bit rate will be restricted by the recovery time of semiconductor optical amplifier (SOA) finally.

  18. Development of a cryogenic hydrogen microjet for high-intensity, high-repetition rate experiments

    NASA Astrophysics Data System (ADS)

    Kim, J. B.; Göde, S.; Glenzer, S. H.

    2016-11-01

    The advent of high-intensity, high-repetition-rate lasers has led to the need for replenishing targets of interest for high energy density sciences. We describe the design and characterization of a cryogenic microjet source, which can deliver a continuous stream of liquid hydrogen with a diameter of a few microns. The jet has been imaged at 1 μm resolution by shadowgraphy with a short pulse laser. The pointing stability has been measured at well below a mrad, for a stable free-standing filament of solid-density hydrogen.

  19. Adjustable high-repetition-rate pulse trains in a passively-mode-locked fiber laser

    NASA Astrophysics Data System (ADS)

    Si Fodil, Rachid; Amrani, Foued; Yang, Changxi; Kellou, Abdelhamid; Grelu, Ph.

    2016-07-01

    We experimentally investigate multipulse regimes obtained within a passively-mode-locked fiber laser that includes a Mach-Zehnder (MZ) interferometer. By adjusting the time delay imbalance of the MZ, ultrashort pulse trains at multi-GHz repetition rates are generated. We compare the observed dynamics with high-harmonic mode locking, and show that the multi-GHz pulse trains display an inherent instability, which has been overlooked. By using a recirculation loop containing the MZ, we demonstrate a significant improvement of the pulse train stability.

  20. Broadly tunable, low timing jitter, high repetition rate optoelectronic comb generator

    PubMed Central

    Metcalf, A. J.; Quinlan, F.; Fortier, T. M.; Diddams, S. A.; Weiner, A. M.

    2016-01-01

    We investigate the low timing jitter properties of a tunable single-pass optoelectronic frequency comb generator. The scheme is flexible in that both the repetition rate and center frequency can be continuously tuned. When operated with 10 GHz comb spacing, the integrated residual pulse-to-pulse timing jitter is 11.35 fs (1 Hz to 10 MHz) with no feedback stabilization. The corresponding phase noise at 1 Hz offset from the photodetected 10 GHz carrier is −100 dBc/Hz. PMID:26865734

  1. High repetition rate optical switch using an electroabsorption modulator in TOAD configuration

    NASA Astrophysics Data System (ADS)

    Huo, Li; Yang, Yanfu; Lou, Caiyun; Gao, Yizhi

    2007-07-01

    A novel optical switch featured with high repetition rate, short switching window width, and high contrast ratio is proposed and demonstrated for the first time by placing an electroabsorption modulator (EAM) in a terahertz optical asymmetric demultiplexer (TOAD) configuration. The feasibility and main characteristics of the switch are investigated by numerical simulations and experiments. With this EAM-based TOAD, an error-free return-to-zero signal wavelength conversion with 0.62 dB power penalty at 20 Gbit/s is demonstrated.

  2. Power scaling of supercontinuum seeded megahertz-repetition rate optical parametric chirped pulse amplifiers.

    PubMed

    Riedel, R; Stephanides, A; Prandolini, M J; Gronloh, B; Jungbluth, B; Mans, T; Tavella, F

    2014-03-15

    Optical parametric chirped-pulse amplifiers with high average power are possible with novel high-power Yb:YAG amplifiers with kW-level output powers. We demonstrate a compact wavelength-tunable sub-30-fs amplifier with 11.4 W average power with 20.7% pump-to-signal conversion efficiency. For parametric amplification, a beta-barium borate crystal is pumped by a 140 W, 1 ps Yb:YAG InnoSlab amplifier at 3.25 MHz repetition rate. The broadband seed is generated via supercontinuum generation in a YAG crystal.

  3. Power scaling of supercontinuum seeded megahertz-repetition rate optical parametric chirped pulse amplifiers.

    PubMed

    Riedel, R; Stephanides, A; Prandolini, M J; Gronloh, B; Jungbluth, B; Mans, T; Tavella, F

    2014-03-15

    Optical parametric chirped-pulse amplifiers with high average power are possible with novel high-power Yb:YAG amplifiers with kW-level output powers. We demonstrate a compact wavelength-tunable sub-30-fs amplifier with 11.4 W average power with 20.7% pump-to-signal conversion efficiency. For parametric amplification, a beta-barium borate crystal is pumped by a 140 W, 1 ps Yb:YAG InnoSlab amplifier at 3.25 MHz repetition rate. The broadband seed is generated via supercontinuum generation in a YAG crystal. PMID:24690803

  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. Application of the Repetitions in Reserve-Based Rating of Perceived Exertion Scale for Resistance Training

    PubMed Central

    Cronin, John; Storey, Adam; Zourdos, Michael C.

    2016-01-01

    ABSTRACT RATINGS OF PERCEIVED EXERTION ARE A VALID METHOD OF ESTIMATING THE INTENSITY OF A RESISTANCE TRAINING EXERCISE OR SESSION. SCORES ARE GIVEN AFTER COMPLETION OF AN EXERCISE OR TRAINING SESSION FOR THE PURPOSES OF ATHLETE MONITORING. HOWEVER, A NEWLY DEVELOPED SCALE BASED ON HOW MANY REPETITIONS ARE REMAINING AT THE COMPLETION OF A SET MAY BE A MORE PRECISE TOOL. THIS APPROACH ADJUSTS LOADS AUTOMATICALLY TO MATCH ATHLETE CAPABILITIES ON A SET-TO-SET BASIS AND MAY MORE ACCURATELY GAUGE INTENSITY AT NEAR-LIMIT LOADS. THIS ARTICLE OUTLINES HOW TO INCORPORATE THIS NOVEL SCALE INTO A TRAINING PLAN. PMID:27531969

  6. High time-bandwidth product and high repetition rate period signal generation based on spectral hole burning crystal.

    PubMed

    Ma, Xiurong; Wang, Song; Liang, Yuqing; Shan, Yunlong

    2015-04-01

    This paper proposes an approach for the generation of high time-bandwidth product (TBP) and high repetition rate pulse compression period signal. The complex spectral grating is created through a reference pulse and multiple programming pulses with different start frequencies. As the multiple probe chirped pulses with different start frequencies interact with the complex spectral gratings, a high TBP and repetition rate period signal is thus generated. This technique has the potential to generate a time-bandwidth product of 10⁵ when the repetition rate reaches up to tens of GHz. At the end of this paper, two simulation results of pulse compression period signal with 4×10⁵ TBP and 20 GHz repetition rate are presented.

  7. High Repetition Rate Pulsed 2-Micron Laser Transmitter for Coherent CO2 DIAL Measurement

    NASA Technical Reports Server (NTRS)

    Singh, Uprendra N.; Bai, Yingxin; Yu, Jirong; Petros, Mulugeta; Petzar, Paul J.; Trieu, Bo C.; Lee, Hyung

    2009-01-01

    A high repetition rate, highly efficient, Q-switched 2-micron laser system as the transmitter of a coherent differential absorption lidar for CO2 measurement has been developed at NASA Langley Research Center. Such a laser transmitter is a master-slave laser system. The master laser operates in a single frequency, either on-line or off-line of a selected CO2 absorption line. The slave laser is a Q-switched ring-cavity Ho:YLF laser which is pumped by a Tm:fiber laser. The repetition rate can be adjusted from a few hundred Hz to 10 kHz. The injection seeding success rate is from 99.4% to 99.95%. For 1 kHz operation, the output pulse energy is 5.5mJ with the pulse length of approximately 50 ns. The optical-to-optical efficiency is 39% when the pump power is 14.5W. The measured standard deviation of the laser frequency jitter is about 3 MHz.

  8. Experimental study on GaP surface damage threshold induced by a high repetition rate femtosecond laser

    SciTech Connect

    Li Yi; Liu Feng; Li Yanfeng; Chai Lu; Xing Qirong; Hu Minglie; Wang Chingyue

    2011-05-01

    The surface damage threshold of undoped bulk <110> GaP induced by a high repetition rate femtosecond pulse at 1040 nm with a duration of 61 fs was studied. The threshold value was obtained by a linear fit of the incident single pulse fluence and was confirmed with a breakdown test around the threshold level. The result will be useful in high intensity, high repetition rate laser applications and ultrafast processes.

  9. BEAM DYNAMICS STUDIES OF A HIGH-REPETITION RATE LINAC-DRIVER FOR A 4TH GENERATION LIGHT SOURCE

    SciTech Connect

    Ventturini, M.; Corlett, J.; Emma, P.; Papadopoulos, C.; Penn, G.; Placidi, M.; Qiang, J.; Reinsch, M.; Sannibale, F.; Steier, C.; Sun, C.; Wells, R.

    2012-05-18

    We present recent progress toward the design of a super-conducting linac driver for a high-repetition rate FEL-based soft x-ray light source. The machine is designed to accept beams generated by the APEX photo-cathode gun operating with MHz-range repetition rate and deliver them to an array of SASE and seeded FEL beamlines. We review the current baseline design and report results of beam dynamics studies.

  10. The effects of laser repetition rate on femtosecond laser ablation of dry bone: a thermal and LIBS study.

    PubMed

    Gill, Ruby K; Smith, Zachary J; Lee, Changwon; Wachsmann-Hogiu, Sebastian

    2016-01-01

    The aim of this study is to understand the effect of varying laser repetition rate on thermal energy accumulation and dissipation as well as femtosecond Laser Induced Breakdown Spectroscopy (fsLIBS) signals, which may help create the framework for clinical translation of femtosecond lasers for surgical procedures. We study the effect of repetition rates on ablation widths, sample temperature, and LIBS signal of bone. SEM images were acquired to quantify the morphology of the ablated volume and fsLIBS was performed to characterize changes in signal intensity and background. We also report for the first time experimentally measured temperature distributions of bone irradiated with femtosecond lasers at repetition rates below and above carbonization conditions. While high repetition rates would allow for faster cutting, heat accumulation exceeds heat dissipation and results in carbonization of the sample. At repetition rates where carbonization occurs, the sample temperature increases to a level that is well above the threshold for irreversible cellular damage. These results highlight the importance of the need for careful selection of the repetition rate for a femtosecond laser surgery procedure to minimize the extent of thermal damage to surrounding tissues and prevent misclassification of tissue by fsLIBS analysis.

  11. Diffusively cooled thin-sheath high-repetition-rate TEA and TEMA lasers

    NASA Astrophysics Data System (ADS)

    Yatsiv, Shaul; Gabay, Amnon; Sintov, Yoav

    1993-05-01

    Transverse electric atmospheric (TEA), or multi atmospheric (TEMA) lasers deliver intense short laser pulses of considerable energies. Recurrent high repetition rate pulse trains afford substantial average power levels. In a high rep-rate operation the gas flows across the cavity and is externally cooled to maintain a reasonably low temperature. The gas flow gear and heat exchanger are bulky and costly. In this work we present a repetitively pulsed TEA or TEMA laser that combines energy and peak power features in an individual pulse with the substantial average power levels of a pulse train in a thin layer of gas. Excess heat is disposed of, by conduction through the gas, to cooled enclosing walls. The gas does not flow. The method applies to vibrational transition molecular lasers in the infrared, where elevated temperatures are deleterious to the laser operation. The gist of the method draws on the law that heat conductivity in gases does not depend on their pressure. The fact lends unique operational flexibility and compactness, desirable for industrial and research purposes.

  12. An optical parametric chirped-pulse amplifier for seeding high repetition rate free-electron lasers

    DOE PAGES

    Höppner, H.; Hage, A.; Tanikawa, T.; Schulz, M.; Riedel, R.; Teubner, U.; Prandolini, M. J.; Faatz, B.; Tavella, F.

    2015-05-15

    High repetition rate free-electron lasers (FEL), producing highly intense extreme ultraviolet and x-ray pulses, require new high power tunable femtosecond lasers for FEL seeding and FEL pump-probe experiments. A tunable, 112 W (burst mode) optical parametric chirped-pulse amplifier (OPCPA) is demonstrated with center frequencies ranging from 720–900 nm, pulse energies up to 1.12 mJ and a pulse duration of 30 fs at a repetition rate of 100 kHz. Since the power scalability of this OPCPA is limited by the OPCPA-pump amplifier, we also demonstrate a 6.7–13.7 kW (burst mode) thin-disk OPCPA-pump amplifier, increasing the possible OPCPA output power to manymore » hundreds of watts. Furthermore, third and fourth harmonic generation experiments are performed and the results are used to simulate a seeded FEL with high-gain harmonic generation.« less

  13. Cellular response to high pulse repetition rate nanosecond pulses varies with fluorescent marker identity.

    PubMed

    Steelman, Zachary A; Tolstykh, Gleb P; Beier, Hope T; Ibey, Bennett L

    2016-09-23

    Nanosecond electric pulses (nsEP's) are a well-studied phenomena in biophysics that cause substantial alterations to cellular membrane dynamics, internal biochemistry, and cytoskeletal structure, and induce apoptotic and necrotic cell death. While several studies have attempted to measure the effects of multiple nanosecond pulses, the effect of pulse repetition rate (PRR) has received little attention, especially at frequencies greater than 100 Hz. In this study, uptake of Propidium Iodide, FM 1-43, and YO-PRO-1 fluorescent dyes in CHO-K1 cells was monitored across a wide range of PRRs (5 Hz-500 KHz) using a laser-scanning confocal microscope in order to better understand how high frequency repetition rates impact induced biophysical changes. We show that frequency trends depend on the identity of the dye under study, which could implicate transmembrane protein channels in the uptake response due to their chemical selectivity. Finally, YO-PRO-1 fluorescence was monitored in the presence of Gadolinium (Gd(3+)), Ruthenium Red, and in calcium-free solution to elucidate a mechanism for its unique frequency trend. PMID:27553279

  14. A high repetition rate laser-heavy water based neutron source

    NASA Astrophysics Data System (ADS)

    Hah, Jungmoo; He, Zhaohan; Nees, John; Krushelnick, Karl; Thomas, Alexander; CenterUltrafast Optical Science Team

    2015-11-01

    Neutrons have numerous applications in diverse areas, such as medicine, security, and material science. For example, sources of MeV neutrons may be used for active interrogation for nuclear security applications. Recently, alternative ways to generate neutron flux have been studied. Among them, ultrashort laser pulse interactions with dense plasma have attracted significant attention as compact, pulse sources of neutrons. To generate neutrons using a laser through fusion reactions, thin solid density targets have been used in a pitcher-catcher arrangement, using deuterated plastic for example. However, the use of solid targets is limited for high-repetition rate operation due to the need to refresh the target for every laser shot. Here, we use a free flowing heavy water target with a high repetition rate (500 Hz) laser without a catcher. From the interaction between a 10 micron scale diameter heavy water stream with the Lambda-cubed laser system at the Univ. of Michigan (12mJ, 800nm, 35fs), deuterons collide with each other resulting in D-D fusion reactions generating 2.45 MeV neutrons. Under best conditions a time average of ~ 105 n/s of neutrons are generated.

  15. Repetition rate multiplication of frequency comb using all-pass fiber resonator

    NASA Astrophysics Data System (ADS)

    Yang, Lijun; Yang, Honglei; Zhang, Hongyuan; Wei, Haoyun; Li, Yan

    2016-09-01

    We propose a stable method for repetition rate multiplication of a 250-MHz Er-fiber frequency comb by a phase-locked all-pass fiber ring resonator, whose phase-locking configuration is simple. The optical path length of the fiber ring resonator is automatically controlled to be accurately an odd multiple of half of the original cavity length using an electronical phase-locking unit with an optical delay line. As for shorter cavity length of the comb, high-order odd multiple is preferable. Because the power loss depends only on the net-attenuation of the fiber ring resonator, the energetic efficiency of the proposed method is high. The input and output optical spectrums show that the spectral width of the frequency comb is clearly preserved. Besides, experimental results show less pulse intensity fluctuation and 35 dB suppression ratio of side-modes while providing a good long-term and short-term frequency stability. Higher-order repetition rate multiplication to several GHz can be obtained by using several fiber ring resonators in cascade configuration.

  16. MHz repetition rate solid-state driver for high current induction accelerators

    SciTech Connect

    Brooksby, C; Caporaso, G; Goerz, D; Hanks, R; Hickman, B; Kirbie, H; Lee, B; Saethre, R

    1999-03-01

    A research team from the Lawrence Livermore National Laboratory and Bechtel Nevada Corporation is developing an all solid-state power source for high current induction accelerators. The original power system design, developed for heavy-ion fusion accelerators, is based on the simple idea of using an array of field effect transistors to switch energy from a pre-charged capacitor bank to an induction accelerator cell. Recently, that idea has been expanded to accommodate the greater power needs of a new class of high-current electron accelerators for advanced radiography. For this purpose, we developed a 3-stage induction adder that uses over 4,000 field effect transistors to switch peak voltages of 45 kV at currents up to 4.8 kA with pulse repetition rates of up to 2 MHz. This radically advanced power system can generate a burst of five or more pulses that vary from 200 ns to 2 µs at a duty cycle of up to 25%. Our new source is precise, robust, flexible, and exceeds all previous drivers for induction machines by a factor of 400 in repetition rate and a factor of 1000 in duty cycle.

  17. High repetition rate collisional soft x-ray lasers based on grazing incidence pumping

    SciTech Connect

    Luther, B M; Wang, Y; Larotonda, M A; Alessi, D; Berrill, M; Rocca, J J; Dunn, J; Keenan, R; Shlyaptsev, V N

    2005-11-18

    We discuss the demonstration of gain-saturated high repetition rate table-top soft x-ray lasers producing microwatt average powers at wavelengths ranging from 13.9 to 33 nm. The results were obtained heating a pre-created plasma with a picosecond optical laser pulse impinging at grazing incidence onto a pre-created plasma. This pumping geometry increases the energy deposition efficiency of the pump beam into the gain region, making it possible to saturate soft x-ray lasers in this wavelength range with a short pulse pump energy of only 1 J at 800 nm wavelength. Results corresponding to 5 Hz repetition rate operation of gain-saturated 14.7 nm Ni-like Pd and 32.6 nm line Ne-like Ti lasers pumped by a table-top Ti:sapphire laser are reported. We also discuss results obtained using a 1 {omega} 1054 nm pre-pulse and 2{omega} 527 nm short pulse from a Nd:glass pump laser. This work demonstrates the feasibility of producing compact high average power soft x-ray lasers for applications.

  18. Ultrafast XUV Pulses at High Repetition Rate for Time Resolved Photoelectron Spectroscopy of Surface Dynamics

    NASA Astrophysics Data System (ADS)

    Corder, Christopher; Zhao, Peng; Li, Xinlong; Muraca, Amanda R.; Kershis, Matthew D.; White, Michael G.; Allison, Thomas K.

    2016-05-01

    Ultrafast photoelectron studies of surface dynamics are often limited by low repetition rates. At Stony Brook we have built a cavity-enhanced high-harmonic generation XUV source that delivers ultrafast pulses to a surface science apparatus for photoelectron spectroscopy. We begin with a Ytterbium fiber laser at a repetition rate of 78 MHz and up to 90 W of average power. After compression the pulses have μJ's of energy with < 180 fs pulse width. We then use an enhancement cavity with a finesse of a few hundred to build up to the peak intensity required for high harmonic generation. The enhancement cavity is a six mirror double folded bow-tie geometry with a focus of 15 μm at a Krypton gas jet, followed by a Sapphire crystal at Brewster's angle for the fundamental to allow outcoupling of the harmonics. A single harmonic is selected using a time-preserving monochromator to maintain the short pulses, and is sent to an ultra high vacuum chamber with sample preparation and diagnostic tools as well as an electron energy spectrometer. This allows us to study the electronic dynamics of semiconductor surfaces and their interfaces with adsorbed molecules which enable various charge transfer effects. Supported by AFOSR.

  19. Diagnostic for a high-repetition rate electron photo-gun and first measurements

    NASA Astrophysics Data System (ADS)

    Filippetto, D.; Doolittle, L.; Huang, G.; Norum, E.; Portmann, G.; Qian, H.; Sannibale, F.

    2015-05-01

    The APEX electron source at LBNL combines the high-repetition-rate with the high beam brightness typical of photoguns, delivering low emittance electron pulses at MHz frequency. Proving the high beam quality of the beam is an essential step for the success of the experiment, opening the doors of the high average power to brightness-hungry applications as X-Ray FELs, MHz ultrafast electron diffraction etc.. As first step, a complete characterization of the beam parameters is foreseen at the Gun beam energy of 750 keV. Diagnostics for low and high current measurements have been installed and tested, and measurements of cathode lifetime and thermal emittance in a RF environment with mA current performed. The recent installation of a double slit system, a deflecting cavity and a high precision spectrometer, allow the exploration of the full 6D phase space. Here we discuss the present layout of the machine and future upgrades, showing the latest results at low and high repetition rate, together with the tools and techniques used.

  20. Characterization of MHz pulse repetition rate femtosecond laser-irradiated gold-coated silicon surfaces

    NASA Astrophysics Data System (ADS)

    Sivakumar, Manickam; Venkatakrishnan, Krishnan; Tan, Bo

    2011-12-01

    In this study, MHz pulse repetition rate femtosecond laser-irradiated gold-coated silicon surfaces under ambient condition were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), and X-ray photoelectron spectroscopy (XPS). The radiation fluence used was 0.5 J/cm2 at a pulse repetition rate of 25 MHz with 1 ms interaction time. SEM analysis of the irradiated surfaces showed self-assembled intermingled weblike nanofibrous structure in and around the laser-irradiated spots. Further TEM investigation on this nanostructure revealed that the nanofibrous structure is formed due to aggregation of Au-Si/Si nanoparticles. The XRD peaks at 32.2°, 39.7°, and 62.5° were identified as (200), (211), and (321) reflections, respectively, corresponding to gold silicide. In addition, the observed chemical shift of Au 4 f and Si 2 p lines in XPS spectrum of the irradiated surface illustrated the presence of gold silicide at the irradiated surface. The generation of Si/Au-Si alloy fibrous nanoparticles aggregate is explained by the nucleation and subsequent condensation of vapor in the plasma plume during irradiation and expulsion of molten material due to high plasma pressure.

  1. Characterization of MHz pulse repetition rate femtosecond laser-irradiated gold-coated silicon surfaces

    PubMed Central

    2011-01-01

    In this study, MHz pulse repetition rate femtosecond laser-irradiated gold-coated silicon surfaces under ambient condition were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), and X-ray photoelectron spectroscopy (XPS). The radiation fluence used was 0.5 J/cm2 at a pulse repetition rate of 25 MHz with 1 ms interaction time. SEM analysis of the irradiated surfaces showed self-assembled intermingled weblike nanofibrous structure in and around the laser-irradiated spots. Further TEM investigation on this nanostructure revealed that the nanofibrous structure is formed due to aggregation of Au-Si/Si nanoparticles. The XRD peaks at 32.2°, 39.7°, and 62.5° were identified as (200), (211), and (321) reflections, respectively, corresponding to gold silicide. In addition, the observed chemical shift of Au 4f and Si 2p lines in XPS spectrum of the irradiated surface illustrated the presence of gold silicide at the irradiated surface. The generation of Si/Au-Si alloy fibrous nanoparticles aggregate is explained by the nucleation and subsequent condensation of vapor in the plasma plume during irradiation and expulsion of molten material due to high plasma pressure. PMID:21711595

  2. Monitoring copper toxicity in natural phytoplankton assemblages: application of Fast Repetition Rate fluorometry.

    PubMed

    Pérez, Patricia; Beiras, Ricardo; Fernández, Emilio

    2010-09-01

    Four experiments were conducted with natural coastal phytoplankton assemblages exposed to [Cu] within the range 5-80 microg L(-1). The effect of Cu on several biological variables such as chlorophyll a concentration, particle size distribution, O2-production and fluorescence variables recorded by a Fast Repetition Rate fluorometer was monitored during 72 h. Variable fluorescence (Fv) was the most sensitive and rapid among all the variables tested. This work contributes to reinforce the use of fluorescence endpoints in ecotoxicological studies by proving their ecological relevance through relationships found between fluorescence and population-level responses as growth rate and gross O2 production. The lowest calculated EC10 was 2.65 microg L(-1), concentration commonly exceeded in polluted waters.

  3. Autonomic Nervous System Reactivity During Speech Repetition Tasks: Heart Rate Variability and Skin Conductance.

    PubMed

    Mackersie, Carol L; Calderon-Moultrie, Natalie

    2016-01-01

    Cognitive and emotional challenges may elicit a physiological stress response that can include arousal of the sympathetic nervous system (fight or flight response) and withdrawal of the parasympathetic nervous system (responsible for recovery and rest). This article reviews studies that have used measures of electrodermal activity (skin conductance) and heart rate variability (HRV) to index sympathetic and parasympathetic activity during auditory tasks. In addition, the authors present results from a new study with normal-hearing listeners examining the effects of speaking rate on changes in skin conductance and high-frequency HRV (HF-HRV). Sentence repetition accuracy for normal and fast speaking rates was measured in noise using signal to noise ratios that were adjusted to approximate 80% accuracy (+3 dB fast rate; 0 dB normal rate) while monitoring skin conductance and HF-HRV activity. A significant increase in skin conductance level (reflecting sympathetic nervous system arousal) and a decrease in HF-HRV (reflecting parasympathetic nervous system withdrawal) were observed with an increase in speaking rate indicating sensitivity of both measures to increased task demand. Changes in psychophysiological reactivity with increased auditory task demand may reflect differences in listening effort, but other person-related factors such as motivation and stress may also play a role. Further research is needed to understand how psychophysiological activity during listening tasks is influenced by the acoustic characteristics of stimuli, task demands, and by the characteristics and emotional responses of the individual. PMID:27355761

  4. Producing ultrashort Terahertz to UV photons at high repetition rates for research into materials

    SciTech Connect

    G. R. Neil; C. Behre; S. V. Benson; G. Biallas; J. Boyce; L.A. Dillon-Townes; D. Douglas; H. F. Dylla; R. Evans; A. Grippo; D. Gruber; J. Gubeli; C. Hernandez-Garcia; K. Jordan; M. J. Kelley; L. Merminga; J. Mammosser; N. Nishimori; J. Preble; R. Rimmer; Michelle D. Shinn; T. Siggins; R. Walker; G. P. Williams; and S. Zhang

    2005-11-01

    A new THz/IR/UV photon source at Jefferson Lab is the first of a new generation of light sources based on a Energy-Recovered, (superconducting) Linac (ERL). The machine has a 160 MeV electron beam and an average current of 10 mA in 75 MHz repetition rate hundred femtosecond bunches. These electron bunches pass through a magnetic chicane and therefore emit synchrotron radiation. For wavelengths longer than the electron bunch the electrons radiate coherently a broadband THz {approx} half cycle pulse whose average brightness is > 5 orders of magnitude higher than synchrotron IR sources. Previous measurements showed 20 W of average power extracted[1]. The new facility offers simultaneous synchrotron light from the visible through the FIR along with broadband THz production of 100 fs pulses with >200 W of average power (see G. P. Williams, this conference). The FELs also provide record-breaking laser power [2]: up to 10 kW of average power in the IR from 1 to 14 microns in 400 fs pulses at up to 74.85 MHz repetition rates and soon will produce similar pulses of 300-1000 nm light at up to 3 kW of average power from the UV FEL. These ultrashort pulses are ideal for maximizing the interaction with material surfaces. The optical beams are Gaussian with nearly perfect beam quality. See www.jlab.org/FEL for details of the operating characteristics; a wide variety of pulse train configurations are feasible from 10 microseconds long at high repetition rates to continuous operation. The THz and IR system has been commissioned. The UV system is to follow in 2005. The light is transported to user laboratories for basic and applied research. Additional lasers synchronized to the FEL are also available. Past activities have included production of carbon nanotubes, studies of vibrational relaxation of interstitial hydrogen in silicon, pulsed laser vapor deposition, nitriding of metals, and energy flow in proteins. This paper will present the status of the system and discuss some of

  5. Characteristics of a Saturated 18.9 nm Tabletop Laser Operating at 5 Hz Repetition Rate

    SciTech Connect

    Larotonda, M A; Luther, B M; Wang, Y; Liu, Y; Alessi, D; Berrill, M; Dummer, A; Brizuela, F; Menoni, C S; Marconi, M; Shlyaptsev, V N; Dunn, J; Rocca, J J

    2005-01-10

    We report the characteristics of a saturated high repetition rate Ni-like Mo laser at 18.9 nm. This table-top soft x-ray laser was pumped at 5 Hz repetition rate by 8 ps, 1 J optical laser pulses impinging at grazing incidence into a pre-created Mo plasma. The variation of the laser output intensity as a function of the grazing incidence angle of the main pump beam is reported. The maximum laser intensity was observed for an angle of 20 degrees, at which we measured a small signal gain of 65 cm{sup -1} and a gain-length product gxl > 15. Spatial coherence measurements resulting from a Young's double slit interference experiment show the equivalent incoherent source diameter is about 11 {micro}m. The peak spectral brightness is estimated to be of the order of 1 x 10{sup 24} photons s{sup -1} mm{sup -2} mrad{sup -2} within 0.01% spectral bandwidth. This type of practical, small scale, high repetition soft x-ray laser is of interest for many applications. This acts to reduce the sensitivity of burst properties to metallicity. Only the first anomalous burst in one model produces nuclei as heavy as A = 100. For the present choice of nuclear physics and accretion rates, other bursts and models make chiefly nuclei with A {approx} 64. The amount of carbon remaining after hydrogen-helium bursts is typically {approx}< 1% by mass, and decreases further as the ashes are periodically heated by subsequent bursts. For M = 3.5 x 10{sup -10} M{sub {circle_dot}} yr{sup -1} and solar metallicity, bursts are ignited in a hydrogen-free helium layer. At the base of this layer, up to 90% of the helium has already burned to carbon prior to the unstable ignition of the helium shell. These helium-ignited bursts have (a) briefer, brighter light curves with shorter tails; (b) very rapid rise times (< 0.1 s); and (c) ashes lighter than the iron group.

  6. Variable Thickness Liquid Crystal Films for High Repetition Rate Laser Applications

    NASA Astrophysics Data System (ADS)

    Poole, Patrick; Willis, Christopher; Cochran, Ginevra; Hanna, Randall; Andereck, C. David; Schumacher, Douglass

    2015-05-01

    The presentation of a clean target or target substrate at high repetition rates is of importance to a number of photoelectron spectroscopy and free electron laser applications, often in high vacuum environments. Additionally, high intensity laser facilities are approaching the 10 Hz shot rate at petawatt powers, but are currently unable to insert targets at these rates. We have developed liquid crystal films to address this need for high rep rate targets while preserving the planar geometry advantageous to many applications. The molecular ordering of liquid crystal is variable with temperature and can be manipulated to form a layered thin film. In this way temperature and volume control can be used to vary film thickness in vacuo and on-demand between 10 nm and over 10 μm. These techniques were previously applied to a single-shot ion acceleration experiment in, where target thickness critically determines the physics of the acceleration. Here we present an automatic film formation device that utilizes a linear sliding rail to form liquid crystal films within the aforementioned range at rates up to 0.1 Hz. The design ensures film formation location within 2 μm RMS, well within the Rayleigh range of even short f-number systems. Details of liquid crystal films and this target formation device will be shown as well as recent experimental data from the Scarlet laser facility at OSU. This work was supported by DARPA through a grant from AMRDEC.

  7. Repetition rate operation of an improved magnetically insulated transmission line oscillator

    SciTech Connect

    Fan Yuwei; Zhong Huihuang; Li Zhiqiang; Shu Ting; Yang Hanwu; Zhou Heng; Yuan Chengwei; Zhou Weihong; Luo Ling

    2008-08-15

    In order to investigate the performances of repetition rate (rep-rate) operation of an improved magnetically insulated transmission line oscillator (MILO), a series of experiments are carried out on the improved MILO device, which is driven by a 40 {omega}, 50 ns rep-rate pulser, TORCH-01. Polymer velvet and graphite cathodes are tested, respectively, in the experiments, whose diameters and lengths are the same. The results of experimental comparison between them are presented in the paper. Both cathodes are tested at electric field strengths of about 300 kV/cm. The applied voltage has 60 ns duration with a rise time of 10 ns. This paper focuses on the performance of the voltage and current characteristics, the shot-to-shot reproducibility, the pressure evolution of the diode, and the lifetime of the cathodes, not upon the radiated microwave power. The experimental results show that the graphite cathode is superior to the velvet cathode in the lifetime and the shot-to-shot reproducibility during the rep-rate operation, and it is a promising cathode for the MILO device under the rep-rate conditions.

  8. Design Studies for a High-Repetition-Rate FEL Facility at LBNL.

    SciTech Connect

    CORLETT, J.; BELKACEM, A.; BYRD, J. M.; FAWLEY, W.; KIRZ, J.; LIDIA, S.; MCCURDY, W.; PADMORE, H.; PENN, G.; POGORELOV, I.; QIANG, J.; ROBIN, D.; SANNIBALE, F.; SCHOENLEIN, R.; STAPLES, J.; STEIER, C.; VENTURINI, M.; WAN, W.; WILCOX, R.; ZHOLENTS, A.

    2007-10-04

    Lawrence Berkeley National Laboratory (LBNL) is working to address the needs of the primary scientific Grand Challenges now being considered by the U.S. Department of Energy, Office of Basic Energy Sciences: we are exploring scientific discovery opportunities, and new areas of science, to be unlocked with the use of advanced photon sources. A partnership of several divisions at LBNL is working to define the science and instruments needed in the future. To meet these needs, we propose a seeded, high-repetition-rate, free-electron laser (FEL) facility. Temporally and spatially coherent photon pulses, of controlled duration ranging from picosecond to sub-femtosecond, are within reach in the vacuum ultraviolet (VUV) to soft X-ray regime, and LBNL is developing critical accelerator physics and technologies toward this goal. We envision a facility with an array of FELs, each independently configurable and tunable, providing a range of photon-beam properties with high average and peak flux and brightness.

  9. Generation of Electron Bunches at Low Repetition Rates Using a Beat-Frequency Technique

    SciTech Connect

    Poelker, Matt; Grames, Joseph; Hansknecht, John; Kazimi, Reza; Musson, John

    2007-05-01

    Even at a continuous wave facility such as CEBAF at Jefferson Lab, an electron beam with long time intervals (tens of ns) between individual bunches can be useful, for example to isolate sources of background via time of flight detection or to measure the energy of neutral particles that cannot be separated with a magnetic field. This paper describes a demonstrated method to quickly and easily deliver bunches with repetition rates of 20 to 100 MHz corresponding to time intervals between 10 to 50 ns (respectively). This is accomplished by changing the ON/OFF frequency of the RF-pulsed drive laser by a small amount (f/f < 20%), resulting in a bunch frequency equal to the beat frequency between the radio frequencies of the drive laser and the photoinjector chopper system.

  10. Picosecond supercontinuum light source for stroboscopic white-light interferometry with freely adjustable pulse repetition rate.

    PubMed

    Novotny, Steffen; Durairaj, Vasuki; Shavrin, Igor; Lipiäinen, Lauri; Kokkonen, Kimmo; Kaivola, Matti; Ludvigsen, Hanne

    2014-06-01

    We present a picosecond supercontinuum light source designed for stroboscopic white-light interferometry. This source offers a potential for high-resolution characterization of vibrational fields in electromechanical components with frequencies up to the GHz range. The light source concept combines a gain-switched laser diode, the output of which is amplified in a two-stage fiber amplifier, with supercontinuum generation in a microstructured optical fiber. Implemented in our white-light interferometer setup, optical pulses with optimized spectral properties and below 310 ps duration are used for stroboscopic illumination at freely adjustable repetition rates. The performance of the source is demonstrated by characterizing the surface vibration field of a square-plate silicon MEMS resonator at 3.37 MHz. A minimum detectable vibration amplitude of less than 100 pm is reached.

  11. High-repetition-rate laser ignition of fuel-air mixtures.

    PubMed

    Hsu, Paul S; Roy, Sukesh; Zhang, Zhili; Sawyer, Jordan; Slipchenko, Mikhail N; Mance, Jason G; Gord, James R

    2016-04-01

    A laser-ignition (LI) method is presented that utilizes a high-repetition-rate (HRR) nanosecond laser to reduce minimal ignition energies of individual pulses by ∼10 times while maintaining comparable total energies. The most common LI employs a single nanosecond-laser pulse with energies on the order of tens of millijoules to ignite combustible gaseous mixtures. Because of the requirements of high energy per pulse, fiber coupling of traditional LI systems is difficult to implement in real-world systems with limited optical access. The HRR LI method demonstrated here has an order of magnitude lower per-pulse energy requirement than the traditional single-pulse LI technique, potentially allowing delivery through standard commercial optical fibers. Additionally, the HRR LI approach significantly increases the ignition probability of lean combustible mixtures in high-speed flows while maintaining low individual pulse energies. PMID:27192289

  12. Femtosecond-induced micostructures in Magnesium- doped Lithium Niobate crystals with high repetition rate

    NASA Astrophysics Data System (ADS)

    Kan, Hongli; Zhang, Shuanggen; Zhai, Kaili; Ma, Xiurong; Luo, Yiming; Hu, Minglie; Wang, Qingyue

    2016-02-01

    In this paper, heat accumulation effect of MgO: LN crystal irradiated by femtosecond pulses was analyzed by a developed thermal conduction model in terms of the spatial and temporal distribution of the absorbed laser energy. Using the focused femtosecond pulses about 61 fs at 1040 nm with a repetition rate of 52 MHz, ablation morphologies under different exposure time and average power were obtained experimentally. The measured laser-induced damage threshold of X-, Y- and Z-cut MgO: LN crystals are 0.82 mJ/cm2, 0.74 mJ/cm2 and 0.76 mJ/cm2, respectively, and based on the measurement achieved in the Lab the differences in the ablation morphologies were analyzed in detail.

  13. Thyratron characteristics under high di/dt and high-repetition-rate operation

    SciTech Connect

    Ball, D.; Hill, J.; Kan, T.

    1981-05-11

    Power conditioning systems for high peak and average power, high repetition rate discharge excited lasers involve operation of modulator components in unconventional regimes. Reliable operation of switches and energy storage elements under high voltage and high di/dt conditions is a pacing item for laser development at the present time. To test and evaluate these components a Modulator Component Test Facility (MCTF) was constructed. The MCTF consists of a command charge system, energy storage capacitors, thyratron switch with inverse thyratron protection, and a resistive load. The modulator has initially been operated at voltages up to 60 kV at 600 Hz. Voltage, current, and calorimetric diagnostics are provided for major modulator components. Measurements of thyratron characteristics under high di/dt operation are presented. Commutation energy loss and di/dt have been measured as functions of the tube hydrogen pressure.

  14. High-power high-repetition-rate copper-vapor-pumped dye laser

    SciTech Connect

    Singh, S.; Dasgupta, K.; Kumar, S.; Manohar, K.G.; Nair, L.G.; Chatterjee, U.K. . Laser and Plasma Technology Div.)

    1994-06-01

    The design and development of an efficient high average power dye laser oscillator-amplifier system developed at the Laser and Plasma Technology Division, Bhabha Atomic Research Centre, is reported. The dye laser is pumped by a 6.5-kHz repetition rate copper vapor laser. The signal beam to the dye amplifier is obtained from an efficient narrow-band grazing incidence grating (GIG) dye laser oscillator incorporating a multiple prism beam expander. Amplifier extraction efficiency up to 40% was obtained in a single amplifier stage, using rhodamine 6G (Rh6G) in ethanol. The authors have also demonstrated simultaneous amplification of two laser beams at different wavelengths in the same dye amplifier cell.

  15. Low-repetition rate femtosecond laser writing of optical waveguides in water-white glass slides.

    PubMed

    Lazcano, H E; Vázquez, G V

    2016-04-20

    Energy dose ranges for fabrication of subsurface and ablated ridge waveguides were defined using a low repetition rate femtosecond laser. The waveguides were written along the width of water-white glass slides. The buried waveguides written between 0.23 and 0.62  μJ/μm3 energy dose show strong guidance at 633 nm, reaching in the best cases propagation losses of 0.7 dB/cm. Meanwhile, the ridge waveguides were fabricated between 2.04 and 31.9  μJ/μm3, with a best case of 3.1 dB/cm. Outcomes of this study are promising for use in the manufacturing of sensing devices.

  16. High Repetition Rate Grazing Incidence Pumped X-ray Laser operating at 18.9 nm

    SciTech Connect

    Keenan, R; Dunn, J; Patel, P K; Price, D F; Smith, R F; Shlyaptsev, V N

    2004-05-11

    We have demonstrated a 10 Hz Ni-like Mo X-ray laser operating at 18.9 nm with 150 mJ total pump energy by employing a novel pumping scheme. The grazing incidence scheme is described, where a picosecond pulse is incident at a grazing angle to a Mo plasma column produced by a slab target irradiated by a 200 ps laser pulse. This scheme uses refraction of the short pulse at a pre-determined electron density to increase absorption to pump a specific gain region. The high efficiency inherent to this scheme allows a reduction in the pump energy where 70 mJ long pulse energy and 80 mJ short pulse energy are sufficient to produce lasing at a 10 Hz repetition rate. Under these conditions and by optimizing the delay between the pulses, we achieve strong amplification and saturation for 4 mm long targets.

  17. Role of the optical pulse repetition rate in the efficiency of terahertz emitters

    NASA Astrophysics Data System (ADS)

    Reklaitis, Antanas

    2016-07-01

    Excitation of n-GaAs and p-InAs terahertz emitters by the series of optical pulses is studied by ensemble Monte Carlo simulations. It is found that the spatial separation of photoexcited electrons and holes dramatically reduces the recombination intensity in n-GaAs emitter, the operation of which is based on the surface field effect. The spatial separation of carriers does not affect the recombination intensity in p-InAs emitter, the operation of which is based on the photo-Dember effect. Therefore, the recovery time of equilibrium state after optical pulse in n-GaAs emitter significantly exceeds the corresponding recovery time in p-InAs emitter. This fact leads to a substantial reduction of photocurrent amplitude in n-GaAs emitter excited by the optical pulse series at high repetition rate.

  18. High repetition rate tunable femtosecond pulses and broadband amplification from fiber laser pumped parametric amplifier.

    PubMed

    Andersen, T V; Schmidt, O; Bruchmann, C; Limpert, J; Aguergaray, C; Cormier, E; Tünnermann, A

    2006-05-29

    We report on the generation of high energy femtosecond pulses at 1 MHz repetition rate from a fiber laser pumped optical parametric amplifier (OPA). Nonlinear bandwidth enhancement in fibers provides the intrinsically synchronized signal for the parametric amplifier. We demonstrate large tunability extending from 700 nm to 1500 nm of femtosecond pulses with pulse energies as high as 1.2 muJ when the OPA is seeded by a supercontinuum generated in a photonic crystal fiber. Broadband amplification over more than 85 nm is achieved at a fixed wavelength. Subsequent compression in a prism sequence resulted in 46 fs pulses. With an average power of 0.5 W these pulses have a peak-power above 10 MW. In particular, the average power and pulse energy scalability of both involved concepts, the fiber laser and the parametric amplifier, will enable easy up-scaling to higher powers.

  19. A high repetition rate passively Q-switched microchip laser for controllable transverse laser modes

    NASA Astrophysics Data System (ADS)

    Dong, Jun; Bai, Sheng-Chuang; Liu, Sheng-Hui; Ueda, Ken-Ichi; Kaminskii, Alexander A.

    2016-05-01

    A Cr4+:YAG passively Q-switched Nd:YVO4 microchip laser for versatile controllable transverse laser modes has been demonstrated by adjusting the position of the Nd:YVO4 crystal along the tilted pump beam direction. The pump beam diameter-dependent asymmetric saturated inversion population inside the Nd:YVO4 crystal governs the oscillation of various Laguerre-Gaussian, Ince-Gaussian and Hermite-Gaussian modes. Controllable transverse laser modes with repetition rates over 25 kHz and up to 183 kHz, depending on the position of the Nd:YVO4 crystal, have been achieved. The controllable transverse laser beams with a nanosecond pulse width and peak power over hundreds of watts have been obtained for potential applications in optical trapping and quantum computation.

  20. Evaluating parallel architectures for two real-time applications with 100 kHz repetition rate

    SciTech Connect

    Baldier, J.; Busson, Ph.; Charlot, C. ); Centro, S.; Pascoli, D ); Davis, E.E.; Ni, P. ); Denes, E.; Odor, G.; Vesztergombi ); Gheorghe, A.; Legrand, I. ); Klefenz, F.; Maenner, R.; Noffz, K.H.; Zoz, R. ); Lourens, W.; Taal, A. ); Malecki, P.; Sobala, A. ); Thielmann, A. ); Vermeulen, J. )

    1993-02-01

    In the context of Research and Development (R and D) activities for future hadron colliders, competitive implementations of real-time algorithms for feature extraction have been made on various forms of commercial pipelined and parallel architectures. The algorithms used for benchmarking serve for decision making and are of relative complexity; they are required to run with a repetition rate of 1,000 kHz in data sets of kilobyte size. Results are reported and discussed in detail. Among the commercially available architectures, pipelined image processing systems can compete with custom-designed architectures. General-purpose processors with systolic mesh connectivity can also be used. Massively parallel systems of the SIMD type (many processors executing the same program on different data) are less suitable in the presently marketed form.

  1. High repetition rate Q-switched radially polarized laser with a graphene-based output coupler

    SciTech Connect

    Li, Lifei; Jin, Chenjie; Qi, Mei; Chen, Xiaoming; Ren, Zhaoyu E-mail: rzy@nwu.edu.cn; Zheng, Xinliang E-mail: rzy@nwu.edu.cn; Bai, Jintao; Sun, Zhipei

    2014-12-01

    We demonstrate a Q-switched radially polarized all-solid-state laser by transferring a graphene film directly onto an output coupler. The laser generates Q-switched radially polarized beam (QRPB) with a pulse width of 192 ns and 2.7 W average output power. The corresponding single pulse energy is up to 16.2 μJ with a high repetition rate of 167 kHz. The M{sup 2} factor and the polarization purity are ∼2.1 and 96%, respectively. Our QRPB source is a simple and low-cost source for a variety of applications, such as industrial material processing, optical trapping, and microscopy.

  2. Luminescence of black silicon fabricated by high-repetition rate femtosecond laser pulses

    SciTech Connect

    Chen Tao; Si Jinhai; Hou Xun; Kanehira, Shingo; Miura, Kiyotaka; Hirao, Kazuyuki

    2011-10-01

    We studied the photoluminescence (PL) from black silicon that was fabricated using an 800 nm, 250 kHz femtosecond laser in air. By changing the scan velocity and the fluence of the femtosecond laser, the formation of the PL band between the orange (600 nm) and red bands (near 680 nm) could be controlled. The red band PL from the photoinduced microstructures on the black silicon was observed even without annealing due to the thermal accumulation of high-repetition rate femtosecond laser pulses. The orange band PL was easily quenched under 532 nm cw laser irradiation, whereas the red band PL was more stable; this can be attributed to ''defect luminescence'' and ''quantum confinement'', respectively.

  3. Repetition rate switching in a passively mode-locked fibre laser

    NASA Astrophysics Data System (ADS)

    Tian, X. L.; Tang, M.; Gong, Y. D.; Shum, P.

    2006-09-01

    Here we demonstrated a dispersion stretched passively mode-locked fiber laser. The laser was mode-locked by nonlinear polarization rotation (NPR) technical. Both dispersion managed soliton and noise-like pulses were observed in the experiment. Harmonic mode-locked noise-like pulses were observed. By changing the pump power or rotating the waveplates, noise-like pulse could split and always form equally spaced pulse train, thus the repetition rate of the output pulse could be switched among different orders of harmonic frequency. The experiment results were analyzed. We found that peak power clamping caused by NPR module led to pulse splitting, the pulse interaction through the Raman light drives the pulse to space equally.

  4. Dentin bond strength after ablation using a CO2 laser operating at high pulse repetition rates

    NASA Astrophysics Data System (ADS)

    Hedayatollahnajafi, Saba; Staninec, Michal; Watanabe, Larry; Lee, Chulsung; Fried, Daniel

    2009-02-01

    Pulsed CO2 lasers show great promise for the rapid and efficient ablation of dental hard tissues. Our objective was to demonstrate that CO2 lasers operated at high repetition rates can be used for the rapid removal of dentin without excessive thermal damage and without compromising adhesion to restorative materials. Human dentin samples (3x3mm2) were rapidly ablated with a pulsed CO2 laser operating at a wavelength of 9.3-µm, pulse repetition rate of 300-Hz and an irradiation intensity of 18-J/cm2. The bond strength to composite was determined by the modified single plane shear test. There were 8 test groups each containing 10 blocks: negative control (non-irradiated non-etched), positive control (non-irradiated acid-etched), and six laser treated groups (three etched and three non-etched sets). The first and second etched and non-etched sets were ablated at a speed of 25 mm/sec and 50 mm/sec with water, respectively. The third set was also ablated at 50 mm/sec without application of water during laser irradiation. Minimal thermal damage was observed on the dentin surfaces for which water cooling was applied. Bond strengths exceeded 20 MPa for laser treated surfaces that were acid-etched after ablation (25-mm/sec: 29.9-MPa, 50-mm/sec: 21.3-MPa). The water-cooled etched laser groups all produced significantly stronger bonds than the negative control (p<0.001) and a lower bond strength than the positive control (p<0.05). These measurements demonstrate that dentin surfaces can be rapidly ablated by a CO2 lasers with minimal peripheral thermal damage. Additional studies are needed to determine if a lower bond strength than the acid-etched control samples is clinically significant where durability of these bonded restoration supersedes high bond strength.

  5. High repetition rate sealed CO2 TEA lasers using heterogeneous catalysts

    NASA Technical Reports Server (NTRS)

    Price, H. T.; Shaw, S. R.

    1987-01-01

    The significant operational advantages offered by CO2 lasers, operating in the 10.6 micron region of the spectrum, over current solid state lasers, emitting in the near IR region, have prompted increased interest in the development of compact, reliable, rugged CO2 laser sources. Perhaps the most critical aspect associated with achieving a laser compatible with military use is the development of lasers which require no gas replenishment. Sealed, single shot, CO2 TEA lasers have been available for a number of years. Stark et al were first to demonstrate reliable sealed operation in single shot CO2 TEA lasers in 1975 using gas catalysis. GEC Avionics reported the compact, environmentally qualified, MKIII CO2 TEA laser with a pulse life of greater than 10 to the 6th power pulses in 1980. A sealed laser lifetime of greater than 10 to the 6th power pulses is acceptable for single shot cases, such as direct detection rangefinders for tank laser sights. However, in many other applications, such as tracking of fast moving targets, it is essential that a repetition rate of typically 30Hz to 100Hz is employed. In such cases, a pulse lifetime of 10 to the 6th power pulses is no longer sufficient and a minimum pulse lifetime 10 to the 7th power pulses is essential to ensure a useful service life. In 1983 Stark el al described a sealed, 100Hz CO2 TEA laser, with a life of greater than 2.6 x 10 to the 6th power, which employed heterogeneous catalysis. Following this pioneering work, GEC Avionics has been engaged in the development of sealed high repetition rate lasers with a pulse lifetime of 20 million pulses.

  6. A study of high repetition rate pulse generation and all-optical add/drop multiplexing

    NASA Astrophysics Data System (ADS)

    Chen, Hongmin

    Ultra high-speed optical time-division-multiplexed (OTDM) transmission technologies are essential for the construction of ultra high-speed all-optical networks needed in the information era. In this Ph. D thesis dissertation, essential mechanisms associated with ultra high speed OTDM transmission systems, such as, high speed ultra short pulse generation, all optical demultiplexing and all optical add/drop multiplexing, have been studied. Both experimental demonstrations and numerical simulations have been performed. In order to realize high-speed optical TDM systems, high repetition rate, ultra short pulses are needed. A rational harmonic mode-locked ring fiber laser has been used to produce ultrashort pulses, the pulse jitter will be eliminated using a Phase-Locked-Loop (PLL), and the self-pulsation has been suppressed using a semiconductor optical amplifier (SOA). Sub pico-second pulses are very important for all optical sampling in the ultrahigh-speed OTDM transmission system. In this thesis, a two stage compression scheme utilizing the nonlinearity and dispersion of the optical fibers has been constructed and used to compress the gain switched DFB laser pulses. Also a nonlinear optical loop mirror has been constructed to suppress the wings associated with nonlinear compression. Pedestal free, transform-limited pulses with pulse widths in range of 0.2 to 0.4 ps have been generated. LiNbO3 modulators play a very important role in fiber optical communication systems. In this thesis, LiNbO3 modulators have been used to perform high repetition rate pulse generation, all optical demultiplexing and all optical add/drop for the TDM transmission system.

  7. 200 ps FWHM and 100 MHz repetition rate ultrafast gated camera for optical medical functional imaging

    NASA Astrophysics Data System (ADS)

    Uhring, Wilfried; Poulet, Patrick; Hanselmann, Walter; Glazenborg, René; Zint, Virginie; Nouizi, Farouk; Dubois, Benoit; Hirschi, Werner

    2012-04-01

    The paper describes the realization of a complete optical imaging device to clinical applications like brain functional imaging by time-resolved, spectroscopic diffuse optical tomography. The entire instrument is assembled in a unique setup that includes a light source, an ultrafast time-gated intensified camera and all the electronic control units. The light source is composed of four near infrared laser diodes driven by a nanosecond electrical pulse generator working in a sequential mode at a repetition rate of 100 MHz. The resulting light pulses, at four wavelengths, are less than 80 ps FWHM. They are injected in a four-furcated optical fiber ended with a frontal light distributor to obtain a uniform illumination spot directed towards the head of the patient. Photons back-scattered by the subject are detected by the intensified CCD camera; there are resolved according to their time of flight inside the head. The very core of the intensified camera system is the image intensifier tube and its associated electrical pulse generator. The ultrafast generator produces 50 V pulses, at a repetition rate of 100 MHz and a width corresponding to the 200 ps requested gate. The photocathode and the Micro-Channel-Plate of the intensifier have been specially designed to enhance the electromagnetic wave propagation and reduce the power loss and heat that are prejudicial to the quality of the image. The whole instrumentation system is controlled by an FPGA based module. The timing of the light pulses and the photocathode gating is precisely adjustable with a step of 9 ps. All the acquisition parameters are configurable via software through an USB plug and the image data are transferred to a PC via an Ethernet link. The compactness of the device makes it a perfect device for bedside clinical applications.

  8. Modeling and optimization of single-pass laser amplifiers for high-repetition-rate laser pulses

    SciTech Connect

    Ozawa, Akira; Udem, Thomas; Zeitner, Uwe D.; Haensch, Theodor W.; Hommelhoff, Peter

    2010-09-15

    We propose a model for a continuously pumped single-pass amplifier for continuous and pulsed laser beams. The model takes into account Gaussian shape and focusing geometry of pump and seed beam. As the full-wave simulation is complex we have developed a largely simplified numerical method that can be applied to rotationally symmetric geometries. With the tapered-shell model we treat (focused) propagation and amplification of an initially Gaussian beam in a gain crystal. The implementation can be done with a few lines of code that are given in this paper. With this code, a numerical parameter optimization is straightforward and example results are shown. We compare the results of our simple model with those of a full-wave simulation and show that they agree well. A comparison of model and experimental data also shows good agreement. We investigate in detail different regimes of amplification, namely the unsaturated, the fully saturated, and the intermediate regime. Because the amplification process is affected by spatially varying saturation and exhibits a nonlinear response against pump and seed power, no analytical expression for the expected output is available. For modeling of the amplification we employ a four-level system and show that if the fluorescence lifetime of the gain medium is larger than the inverse repetition rate of the seed beam, continuous-wave amplification can be employed to describe the amplification process of ultrashort pulse trains. We limit ourselves to this regime, which implies that if titanium:sapphire is chosen as gain medium the laser repetition rate has to be larger than a few megahertz. We show detailed simulation results for titanium:sapphire for a large parameter set.

  9. Indirect high-bandwidth stabilization of carrier-envelope phase of a high-energy, low-repetition-rate laser.

    PubMed

    Fu, Yuxi; Takahashi, Eiji J; Midorikawa, Katsumi

    2016-06-13

    We demonstrate a method of stabilizing the carrier-envelope phase (CEP) of low-repetition-rate, high-energy femtosecond laser systems such as TW-PW class lasers. A relatively weak high-repetition-rate (~1 kHz) reference pulse copropagates with a low-repetition-rate (10 Hz) high-energy pulse, which are s- and p-polarized, respectively. Using a Brewster angle window, the reference pulse is separated after the power amplifier and used for feedback to stabilize its CEP. The single-shot CEP of the high-energy pulse is indirectly stabilized to 550 mrad RMS, which is the highest CEP stability ever reported for a low-repetition-rate (10-Hz) high-energy laser system. In this novel method, the feedback frequency of the reference pulse from the front-end preamplifier can be almost preserved. Thus, higher CEP stability can be realized than for lower frequencies. Of course, a reference pulse with an even higher repetition rate (e.g., 10 kHz) can be easily employed to sample and feed back CEP jitter over a broader frequency bandwidth. PMID:27410345

  10. Continuous multigram nanoparticle synthesis by high-power, high-repetition-rate ultrafast laser ablation in liquids.

    PubMed

    Streubel, René; Barcikowski, Stephan; Gökce, Bilal

    2016-04-01

    Utilizing a novel laser system consisting of a 500 W, 10 MHz, 3 ps laser source which is fully synchronized with a polygon scanner reaching scanning speeds up to 500 m/s, we explore the possibilities to increase the productivity of nanoparticle synthesis by laser ablation in liquids. By exploiting the high scanning speed, laser-induced cavitation bubbles are spatially bypassed at high repetition rates and continuous multigram ablation rates up to 4 g/h are demonstrated for platinum, gold, silver, aluminum, copper, and titanium. Furthermore, the applicable, ablation-effective repetition rate is increased by two orders of magnitude. The ultrafast ablation mechanisms are investigated for different laser fluences, repetition rates, interpulse distances, and ablation times, while the resulting trends are successfully described by validating a model developed for ultrafast laser ablation in air to hold in liquids as well. PMID:27192268

  11. Assessing Sub-Antarctic Zone primary productivity from fast repetition rate fluorometry

    NASA Astrophysics Data System (ADS)

    Cheah, Wee; McMinn, Andrew; Griffiths, F. Brian; Westwood, Karen J.; Wright, Simon W.; Molina, Ernesto; Webb, Jason P.; van den Enden, Rick

    2011-11-01

    In situ primary productivity (PP) in the Sub-Antarctic Zone (SAZ) and the Polar Frontal Zone (PFZ) south of Australia was estimated using fast repetition rate fluorometry (FRRF). FRRF-derived PP at Process station 3 (P3) southeast of Tasmania (46°S, 153°E) were higher than P1 in the southwest of Tasmania (46°S, 140°E) and P2 in the Polar Frontal Zone (54°S, 146°E). The FRRF-derived PP rates were well correlated with 14C-uptake rates from one-hour incubations ( r2=0.85, slope=1.23±0.05, p<0.01, n=85) but the relationship between both methods differed vertically and spatially. There was a linear relationship between FRRF-based PP and 14C-based PP under light-limited conditions in deeper waters. Under light-saturated conditions near the surface (0-45 m), the relationship was less clear. This was likely associated with the effects of physiological processes such as cyclic electron flow and the Mehler reaction, which are stimulated at high irradiance. Our results indicate that FRRF can be used to estimate photosynthesis rates in the SAZ and PFZ but to derive an accurate estimation of C-fixation requires a detailed understanding of the physiological properties of the cells and their response to oceanographic parameters under different environmental conditions.

  12. Continuous hydroxyl radical planar laser imaging at 50 kHz repetition rate.

    PubMed

    Hammack, Stephen; Carter, Campbell; Wuensche, Clemens; Lee, Tonghun

    2014-08-10

    This study demonstrates high-repetition-rate planar laser-induced fluorescence (PLIF) imaging of hydroxyl radicals (OH) in flames at a continuous framing rate of 50 kHz. A frequency-doubled dye laser is pumped by the second harmonic of an Nd:YAG laser to generate laser radiation near 283 nm with a pulse width of 8 ns and rate of 50 kHz. Fluorescence is recorded by a two-stage image intensifier and complementary metal-oxide-semiconductor camera. The average power of the 283 nm beam reaches 7 W, yielding a pulse energy of 140 μJ. Both a Hencken burner and a DC transient-arc plasmatron are used to produce premixed CH4/air flames to evaluate the OH PLIF system. The average signal-to-noise ratio for the Hencken burner flame is greater than 20 near the flame front and greater than 10 further downstream in a region of the flame near equilibrium. Image sequences of the DC plasmatron discharge clearly illustrate development and evolution of flow features with signal levels comparable to those in the Hencken burner. The results are a demonstration of the ability to make high-fidelity OH PLIF measurements at 50 kHz using a Nd:YAG-pumped, frequency-doubled dye laser. PMID:25320935

  13. High-repetition rate industrial TEA CO2 laser with average output power of 1.5 kW

    NASA Astrophysics Data System (ADS)

    Wan, Chongyi; Liu, Shiming; Zhou, Jinwen; Qi, Jilan; Yang, Xiaola; Wu, Jin; Tan, Rongqing; Wang, Lichun; Mei, Qichu

    1995-03-01

    High power high repetition rate TEA CO2 laser has potential importance in material processing such as shock hardening, glazing, drilling, welding, and cutting for high damage threshold materials, as well as in chemical reaction and isotope separation. This paper describes a transverse-flow closed-cycle UV-preionized TEA CO2 laser with peak pulse power of 20 MW, maximum average power of 1.5 KW at repetition rate of 300 HZ. The laser has compact constructure of gas flow circulation system using tangential fans. With addition of small amounts of H2 and CO to the normal CO2-N2-He gas mixture, one filling sealed operating lifetime is up to millions of pulses. A novel spark gap switch has been developed for very high repetition rate laser discharge in the condition of high pulse power.

  14. Graphene-deposited microfiber photonic device for ultrahigh-repetition rate pulse generation in a fiber laser.

    PubMed

    Qi, You-Li; Liu, Hao; Cui, Hu; Huang, Yu-Qi; Ning, Qiu-Yi; Liu, Meng; Luo, Zhi-Chao; Luo, Ai-Ping; Xu, Wen-Cheng

    2015-07-13

    We report on the generation of a high-repetition-rate pulse in a fiber laser using a graphene-deposited microfiber photonic device (GMPD) and a Fabry-Perot filter. Taking advantage of the unique nonlinear optical properties of the GMPD, dissipative four-wave mixing effect (DFWM) could be induced at low pump power. Based on DFWM mode-locking mechanism, the fiber laser delivers a 100 GHz repetition rate pulse train. The results indicate that the small sized GMPD offers an alternative candidate of highly nonlinear optical component to achieve high-repetition rate pulses, and also opens up possibilities for the investigation of other abundant nonlinear effects or related fields of photonics. PMID:26191834

  15. Limits to the burster repetition rate as deduced from the 2nd catalog of the interplanetary network

    NASA Technical Reports Server (NTRS)

    Atteia, J. L.; Barat, C.; Hurley, K.; Niel, M.; Vedrenne, G.; Evans, W. D.; Fenimore, E. E.; Klebesadel, R. W.; Laros, J. G.; Cline, T. L.

    1985-01-01

    The burster repetition rate is an important parameter in many gamma ray burst models. The localizations of the interplanetary network, which have a relatively small combined surface area, may be used to estimate the average repetition rate. The method consists of (1) estimating the number of random overlaps between error boxes expected in the catalog and comparing this number to that actually observed; (2) modeling the response of the detectors in the network, so that the probability of detecting a burst can be estimated; and (3) simulating the arrival of bursts at the network assuming that burster repetition is governed by a Poisson process. The application of this method for many different burster luminosity functions shows that (1) the lower limit to the burster repetition rate depends strongly upon the assumed luminosity function; (2) the best lower limit to the repetition period obtainable from the data of the network is about 100 months; and (3) that a luminosity function for all bursters similar to that of the 1979 Mar 5 burster is inconsistent with the data.

  16. Study of filamentation with a high power high repetition rate ps laser at 1.03 µm.

    PubMed

    Houard, A; Jukna, V; Point, G; André, Y-B; Klingebiel, S; Schultze, M; Michel, K; Metzger, T; Mysyrowicz, A

    2016-04-01

    We study the propagation of intense, high repetition rate laser pulses of picosecond duration at 1.03 µm central wavelength through air. Evidence of filamentation is obtained from measurements of the beam profile as a function of distance, from photoemission imaging and from spatially resolved sonometric recordings. Good agreement is found with numerical simulations. Simulations reveal an important self shortening of the pulse duration, suggesting that laser pulses with few optical cycles could be obtained via double filamentation. An important lowering of the voltage required to induce guided electric discharges between charged electrodes is measured at high laser pulse repetition rate.

  17. A Real-Time Terahertz Time-Domain Polarization Analyzer with 80-MHz Repetition-Rate Femtosecond Laser Pulses

    PubMed Central

    Watanabe, Shinichi; Yasumatsu, Naoya; Oguchi, Kenichi; Takeda, Masatoshi; Suzuki, Takeshi; Tachizaki, Takehiro

    2013-01-01

    We have developed a real-time terahertz time-domain polarization analyzer by using 80-MHz repetition-rate femtosecond laser pulses. Our technique is based on the spinning electro-optic sensor method, which we recently proposed and demonstrated by using a regenerative amplifier laser system; here we improve the detection scheme in order to be able to use it with a femtosecond laser oscillator with laser pulses of a much higher repetition rate. This improvement brings great advantages for realizing broadband, compact and stable real-time terahertz time-domain polarization measurement systems for scientific and industrial applications. PMID:23478599

  18. Study of filamentation with a high power high repetition rate ps laser at 1.03 µm.

    PubMed

    Houard, A; Jukna, V; Point, G; André, Y-B; Klingebiel, S; Schultze, M; Michel, K; Metzger, T; Mysyrowicz, A

    2016-04-01

    We study the propagation of intense, high repetition rate laser pulses of picosecond duration at 1.03 µm central wavelength through air. Evidence of filamentation is obtained from measurements of the beam profile as a function of distance, from photoemission imaging and from spatially resolved sonometric recordings. Good agreement is found with numerical simulations. Simulations reveal an important self shortening of the pulse duration, suggesting that laser pulses with few optical cycles could be obtained via double filamentation. An important lowering of the voltage required to induce guided electric discharges between charged electrodes is measured at high laser pulse repetition rate. PMID:27137034

  19. Improved repetition rate mixed isotope CO{sub 2} TEA laser

    SciTech Connect

    Cohn, D. B.

    2014-09-15

    A compact CO{sub 2} TEA laser has been developed for remote chemical detection that operates at a repetition rate of 250 Hz. It emits 700 mJ/pulse at 10.6 μm in a multimode beam with the {sup 12}C{sup 16}O{sub 2} isotope. With mixed {sup 12}C{sup 16}O{sub 2} plus {sup 13}C{sup 16}O{sub 2} isotopes it emits multiple lines in both isotope manifolds to improve detection of a broad range of chemicals. In particular, output pulse energies are 110 mJ/pulse at 9.77 μm, 250 mJ/pulse at 10 μm, and 550 mJ/pulse at 11.15 μm, useful for detection of the chemical agents Sarin, Tabun, and VX. Related work shows capability for long term sealed operation with a catalyst and an agile tuner at a wavelength shift rate of 200 Hz.

  20. High-repetition rate relativistic electron beam generation from intense laser solid interactions

    NASA Astrophysics Data System (ADS)

    Batson, Thomas; Nees, John; Hou, Bixue; Thomas, A. G. R.; Krushelnick, Karl

    2015-05-01

    Relativistic electron beams have applications spanning materials science, medicine, and home- land security. Recent advances in short pulse laser technology have enabled the production of very high focused intensities at kHz rep rates. Consequently this has led to the generation of high ux sources of relativistic electrons- which is a necessary characteristic of these laser plasma sources for any potential application. In our experiments, through the generation of a plasma with the lambda cubed laser system at the University of Michigan (a 5 × 1018W=cm2, 500 Hz, Ti:Sapphire laser), we have measured electrons ejected from the surface of fused silica nd Cu targets having energies in excess of an MeV. The spectrum of these electrons was measured with respect to incident laser angle, prepulse timing, and focusing conditions. While taken at a high repetition rate, the pulse energy of the lambda cubed system was consistently on the order of 10 mJ. In order to predict scaling of the electron energy with laser pulse energy, simulations are underway which compare the spectrum generated with the lambda cubed system to the predicted spectrum generated on the petawatt scale HERCULES laser system at the University of Michigan.

  1. Laser ranging system and measurement analysis for space debris with high repetition rate

    NASA Astrophysics Data System (ADS)

    Wu, Zhibo; Zhang, Haifeng; Meng, Wendong; Li, Pu; Deng, Huarong; Tang, Kai; Ding, Renjie; Zhang, Zhongping

    2016-01-01

    Laser measurement technology is inherently high accurate and will play an important role in precise orbit determination, accurate catalog, surveillance to space debris. Shanghai Astronomical Observatory (SHAO) has been developing the technology of laser measurement to space debris for several years. Based on the first successful laser ranging measurement to space debris in country, by applying one new set of high power 532nm wavelength laser system with 200Hz repetition rate, and adopting low dark noise APD detector with high quantum efficiency and high transmissivity of narrow bandwidth spectral filter, SHAO have achieved hundreds of passes of laser data from space debris in 2014, and the measured objects with distance between 500km and 2200km, Radar Cross Section (RCS) of >10m2 to <0.5m2 at the precision of <1m RMS for small RCS targets ,and the success rate of measured passes of up to 80%. The results show that laser ranging technology in China can routinely measure space debris and provide enough measurement data with high accuracy to space debris applications and researches such as surveillance activities in the future.

  2. Fast repetition rate (FRR) fluorometer for making in situ measurements of primary productivity

    SciTech Connect

    Kolber, Z.S.; Falkowski, P.G.

    1992-01-01

    Understanding the ocean carbon cycle and predicting how climate-induced changes in ocean circulation will affect ocean productivity requires that (a) primary productivity be measured with high spatial and temporal resolution, and (b) natural variability in primary productivity be parameterized with regardto environmental factors such as nutrient availabuity, irradiance, and temperature. Instrumentation to measure primary productivity from the stimulated in vivo fluoresence of phytoplankton chlorophyll is currendy being developed at Brookhaven National Laboratory. The instrumentation is based on fast repetition rate (FRR) fluorometry, and provides a robust technique for deriving the photosynthetic rates in situ. Moreover, the FRR methodology directly measures several photosynthetic parameters such as effective absorption cross- section, photo-conversion efficiency, and turnover time of photosynthesis, and relate them to primary productivity. Since photosynthetic parameters are affected by environmental factors such as fight and nutrient availability, the relationship between these parameters and primary productivity can be established. By understanding such relationships, prognostic models of primary productivity can be developed and parameterized.

  3. Fast repetition rate (FRR) fluorometer for making in situ measurements of primary productivity

    SciTech Connect

    Kolber, Z.S.; Falkowski, P.G.

    1992-10-01

    Understanding the ocean carbon cycle and predicting how climate-induced changes in ocean circulation will affect ocean productivity requires that (a) primary productivity be measured with high spatial and temporal resolution, and (b) natural variability in primary productivity be parameterized with regardto environmental factors such as nutrient availabuity, irradiance, and temperature. Instrumentation to measure primary productivity from the stimulated in vivo fluoresence of phytoplankton chlorophyll is currendy being developed at Brookhaven National Laboratory. The instrumentation is based on fast repetition rate (FRR) fluorometry, and provides a robust technique for deriving the photosynthetic rates in situ. Moreover, the FRR methodology directly measures several photosynthetic parameters such as effective absorption cross- section, photo-conversion efficiency, and turnover time of photosynthesis, and relate them to primary productivity. Since photosynthetic parameters are affected by environmental factors such as fight and nutrient availability, the relationship between these parameters and primary productivity can be established. By understanding such relationships, prognostic models of primary productivity can be developed and parameterized.

  4. GHz repetition rate tabletop X-band photoinjector for free-electron laser applications

    SciTech Connect

    Le Sage, G.P.; Fochs, S.N.; Feng, H.X.C.

    1995-12-31

    A 1-1/2 cell {pi}-mode X-bend (8.568 GHz) photoinjector system capable of producing trains of up to one hundred, 1 nC, 1ps, 5 MeV, {epsilon}{sub n} < 2.5 {pi} mm-mrad photoelectron bunches, at a micropulse repetition rate of 1-10 Hz, is currently under development at LLNL, in the UC Davis DAS coherent millimeter-wave group. The system is powered by a 20 MW, 8.568 GHz SLAC development klystron. The system also uses a Cs{sub 2}Te (Cesium Telluride) photocathode which has a quantum efficiency > 5% in the UV (210 nm). The compact UV laser system is composed of a synchronously modelocked AlGaAs semiconductor laser oscillator which produces pulses with a duration of 250 fs and 100 pJ energy at 830 nm, at a repetion rate of 2.142 GHz with less 400 is jitter, a 5 GHz bandwidth Lithium Niobate Mach-Zender fiber modulator, an 8-pass, 10{sup 6} gain, TiAl{sub 2}O{sub 3} (Titanium:Sapphire) chirped pulse amplifier, and 2 BBO frequency doublers in series to quadruple the laser frequency into the UV (207 nm).

  5. A rapidly-tuned, short-pulse-length, high-repetition-rate CO{sub 2} laser for IR dial

    SciTech Connect

    Zaugg, T.; Thompson, D.; Leland, W.T.; Busch, G.

    1997-08-01

    Analysis of noise sources in Differential Absorption LIDAR (DIAL) in the infrared region of the spectrum indicates that the signal-to-noise ratio for direct detection can be improved if multiple-wavelength, short-pulse-length beams are transmitted and received at high repetition rates. Atmospheric effects can be minimized, albedo can be rapidly scanned, and uncorrelated speckle can be acquired at the maximum possible rate. A compact, rugged, RF-excited waveguide laser can produce 15 nanosecond pulses at a 100 kHz rate with sufficient energy per pulse to reach the speckle limit of the signal-to-noise ratio. A high-repetition-rate laser has been procured and will be used to verify these signal and noise scaling relationships at high repetition rates. Current line-tuning devices are mechanical and are capable of switching lines at a rate up to a few hundred Hertz. Acousto-optic modulators, deflectors or tunable filters can be substituted for these mechanical devices in the resonator of a CO{sub 2} laser and used to rapidly line-tune the laser across the 9 and 10 micron bands at a rate as high as 100 kHz. Several configurations for line tuning using acousto-optic and electro-optic devices with and without gratings are presented. The merits of and constraints on each design are also discussed. A pair of large aperture, acousto-optic deflectors has been purchased and the various line-tuning designs will be evaluated in a conventional, glass tube, CO{sub 2} laser, with a view to incorporation into the high-repetition-rate, waveguide laser. A computer model of the dynamics of an RF-excited, short-pulse-length, high-repetition-rate waveguide laser has been developed. The model will be used to test the consequences of various line-tuning designs.

  6. A high repetition rate multiwavelength polarized solid state laser source for long range lidar applications

    NASA Astrophysics Data System (ADS)

    Sudheer, S. K.; Pillai, V. P. Mahadevan; Nayar, V. U.

    2006-12-01

    Advances in Laser Technology and nonlinear Optical techniques can be effectively utilized for LIDAR applications in space and atmospheric sciences to achieve better flexibility and control of the available optical power. Using such devices, one can achieve highly accurate and resolved, measurement of the distribution for atmospheric scattering layers. In the present investigation a diode double end pumped high repetition rate, multi wavelength Nd:YAG laser is designed, fabricated and various laser beam parameters have been characterized for LIDAR applications. Nonlinear optical techniques have been employed to generate higher harmonics like 532nm, 355nm and 266nm for various spectral studies. The experimental setup mainly consists of two Fiber coupled pump laser diodes (Model FAP- 81-30C-800B, Coherent Inc, USA) with a maximum output power of 30Watt at a wavelength of 807-810nm at 30°C set temperature. A second harmonic LBO crystal cut for critical phase matching placed within the laser resonator is provided for converting a fraction of the fundamental beam to a second harmonic beam. A type II frequency tripling LBO nonlinear crystal (cut for critical phase matching) is also located inside the laser resonator. The third harmonic beam and the unconverted fundamental beam are then directed across a type I fourth harmonic LBO crystal cut for critical phase matching where a portion of the fundamental beam and a portion of the third harmonic beam are converted to a fourth harmonic frequency when both fundamental and third harmonic beams propagate through the frequency quadrupling crystal. The resulting beams which are the fundamental (1064nm), second harmonic (532nm), third harmonic (355nm) and fourth harmonic (266nm) are then directed to a fourth harmonic separator in which the fourth harmonic beam is separated from the fundamental beam. A maximum average power of 12W at 1064nm, 8W at 532nm, 5W at 355nm and 3W at 266nm have been measured at a repetition rate of 10KHz

  7. Evolution of polarization dependent microstructures induced by high repetition rate femtosecond laser irradiation in glass.

    PubMed

    Zhang, Fangteng; Gecevičius, Mindaugas; Chen, Qiuqun; Zhang, Hang; Dai, Ye; Qiu, Jianrong

    2016-09-19

    We report the observation of an anomalous polarization dependent process in an isotropic glass induced by long time stationary irradiation of a high repetition rate near-infrared femtosecond laser. Two distinctive types of polarization dependent microstructures were induced at different irradiation stages. At early stage (a few seconds), a dumbbell-shaped structure elongated perpendicularly to the laser polarization formed at the top of the modified region, which was later erased by further irradiation. At later stage (above 30 s), bubbles filled with O2 formed by the irradiation, which were distributed along the laser polarization at a distance far beyond the radius of the laser beam. Based on a simple modeling of light reflection on boundaries, a thermal accumulation process was proposed to explain the formation and evolution of the dumbbell-shaped microstructure. The possible factors responsible for polarization dependent distribution of bubbles are discussed, which needs further systematic investigations. The results may be helpful in the development of femtosecond laser microprocessing for various applications. PMID:27661877

  8. A HIGH REPETITION RATE VUV-SOFT X-RAY FEL CONCEPT

    SciTech Connect

    Corlett, J.; Byrd, J.; Fawley, W.M.; Gullans, M.; Li, D.; Lidia,S.M.; Padmore, H.; Penn, G.; Pogorelov, I.; Qiang, J.; Robin, D.; Sannibale, F.; Staples, J.W.; Steier, C.; Venturini, M.; Virostek, S.; Wan, W.; Wells, R.; Wilcox, R.; Wurtele, J.; Zholents, A.

    2007-06-24

    We report on design studies for a seeded FEL light source that is responsive to the scientific needs of the future. The FEL process increases radiation flux by several orders of magnitude above existing incoherent sources, and offers the additional enhancements attainable by optical manipulations of the electron beam: control of the temporal duration and bandwidth of the coherent output, reduced gain length in the FEL, utilization of harmonics to attain shorter wavelengths, and precise synchronization of the x-ray pulse with seed laser systems. We describe an FEL facility concept based on a high repetition rate RF photocathode gun, that would allow simultaneous operation of multiple independent FEL's, each producing high average brightness, tunable over the VUV-soft x-ray range, and each with individual performance characteristics determined by the configuration of the FEL. SASE, enhanced-SASE (ESASE), seeded, harmonic generation, and other configurations making use of optical manipulations of the electron beam may be employed, providing a wide range of photon beam properties to meet varied user demands.

  9. High energy, high repetition rate, second harmonic generation in large aperture DKDP, YCOB, and LBO crystals.

    PubMed

    Phillips, Jonathan P; Banerjee, Saumyabrata; Smith, Jodie; Fitton, Mike; Davenne, Tristan; Ertel, Klaus; Mason, Paul; Butcher, Thomas; De Vido, Mariastefania; Greenhalgh, Justin; Edwards, Chris; Hernandez-Gomez, Cristina; Collier, John

    2016-08-22

    We report on type-I phase-matched second harmonic generation (SHG) in three nonlinear crystals: DKDP (98% deuteration), YCOB (XZ plane), and LBO (XY plane), of 8 J, 10 Hz cryogenic gas cooled Yb:YAG laser operating at 1029.5 nm. DKDP exhibited an efficiency of 45% at a peak fundamental intensity of 0.24 GW/cm2 for 10 Hz operation at 10 ns. At the same intensity and repetition rate, YCOB and LBO showed 50% and 65% conversion efficiencies, respectively. Significant improvement in conversion efficiency, to a maximum of 82%, was demonstrated in LBO at 0.7 GW/cm2 and 10 Hz, generating output energy of 5.6 J at 514.75 nm, without damage or degradation. However, no improvement in conversion efficiency was recorded for YCOB at this increased intensity. Additionally, we present theoretically calculated temperature maps for both 10 J and 100 J operation at 10 Hz, and discuss the suitability of these three crystals for frequency conversion of a 100 J, 10 Hz diode pumped solid state laser (DPSSL). PMID:27557246

  10. Experiments and Simulations on Magnetically Driven Implosions in High Repetition Rate Dense Plasma Focus

    NASA Astrophysics Data System (ADS)

    Caballero Bendixsen, Luis; Bott-Suzuki, Simon; Cordaro, Samuel; Krishnan, Mahadevan; Chapman, Stephen; Coleman, Phil; Chittenden, Jeremy

    2015-11-01

    Results will be shown on coordinated experiments and MHD simulations on magnetically driven implosions, with an emphasis on current diffusion and heat transport. Experiments are run at a Mather-type dense plasma focus (DPF-3, Vc: 20 kV, Ip: 480 kA, E: 5.8 kJ). Typical experiments are run at 300 kA and 0.33 Hz repetition rate with different gas loads (Ar, Ne, and He) at pressures of ~ 1-3 Torr, usually gathering 1000 shots per day. Simulations are run at a 96-core HP blade server cluster using 3GHz processors with 4GB RAM per node.Preliminary results show axial and radial phase plasma sheath velocity of ~ 1x105 m/s. These are in agreement with the snow-plough model of DPFs. Peak magnetic field of ~ 1 Tesla in the radial compression phase are measured. Electron densities on the order of 1018 cm-3 anticipated. Comparison between 2D and 3D models with empirical results show a good agreement in the axial and radial phase.

  11. High energy, high repetition rate, second harmonic generation in large aperture DKDP, YCOB, and LBO crystals.

    PubMed

    Phillips, Jonathan P; Banerjee, Saumyabrata; Smith, Jodie; Fitton, Mike; Davenne, Tristan; Ertel, Klaus; Mason, Paul; Butcher, Thomas; De Vido, Mariastefania; Greenhalgh, Justin; Edwards, Chris; Hernandez-Gomez, Cristina; Collier, John

    2016-08-22

    We report on type-I phase-matched second harmonic generation (SHG) in three nonlinear crystals: DKDP (98% deuteration), YCOB (XZ plane), and LBO (XY plane), of 8 J, 10 Hz cryogenic gas cooled Yb:YAG laser operating at 1029.5 nm. DKDP exhibited an efficiency of 45% at a peak fundamental intensity of 0.24 GW/cm2 for 10 Hz operation at 10 ns. At the same intensity and repetition rate, YCOB and LBO showed 50% and 65% conversion efficiencies, respectively. Significant improvement in conversion efficiency, to a maximum of 82%, was demonstrated in LBO at 0.7 GW/cm2 and 10 Hz, generating output energy of 5.6 J at 514.75 nm, without damage or degradation. However, no improvement in conversion efficiency was recorded for YCOB at this increased intensity. Additionally, we present theoretically calculated temperature maps for both 10 J and 100 J operation at 10 Hz, and discuss the suitability of these three crystals for frequency conversion of a 100 J, 10 Hz diode pumped solid state laser (DPSSL).

  12. 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

  13. Effect of biofilm on fluorescence measurements derived from fast repetition rate fluorometers.

    PubMed

    Patil, Jagadish S; Saino, Toshiro

    2015-01-01

    This study evaluates, for the first time, the influence of biofilms on single and double optical window (SOW and DOW, respectively) fast repetition rate fluorometer (FRRF) measurements of microalgal photosystem-II initial fluorescence (F0), maximum fluorescence (Fm), variable fluorescence (Fv = Fm - F0), quantum yield (Fv/Fm) and functional absorption cross section (σPSII)]. Biofilms with chlorophyll > 0.1 μg cm(-2) and > 0.3 μgcm(-2) on SOW and DOW, respectively, produced a substantial increase in fluorescence. However, the relative magnitude of biofouling effects depended on sample chlorophyll concentrations, being more critical at concentrations < 1 mg m(-3). In DOW-FRRF, biofilms affected F0 (increased) and Fv/Fm (decreased) but not Fv and σPSII, whereas in SOW-FRRF, biofilms increased fluorescence and showed a variable effect on Fv/Fm and σPSII, because only biofilms on SOW attained actual Fm. As a result, the biofilm effect was substantial on SOW-FRRF measurements. On the other hand, the neutral-density filters (representing non-chlorophyll containing biofilms) with different transmission levels reduced the fluorescence signal. Correction procedures for the above photosystem-II parameters are proposed here.

  14. High-repetition rate laser ablation coupled to dielectric barrier discharge postionization for ambient mass spectrometry.

    PubMed

    Bierstedt, Andreas; Riedel, Jens

    2016-07-15

    Most ambient sample introduction and ionization techniques for native mass spectrometry are highly selective for polar agents. To achieve a more general sensitivity for a wider range of target analytes, a novel laser ablation dielectric barrier discharge (LA DBD) ionization scheme was developed. The approach employs a two-step mechanism with subsequent sample desorption and post-ionization. Effective ablation was achieved by the second harmonic output (λ=532nm) of a diode pumped Nd:YVO4 laser operating at a high-repetition rate of several kHz and pulse energies below 100μJ. The ejected analyte-containing aerosol was consecutively vaporized and ionized in the afterglow of a DBD plasma jet. Depending on their proton affinity the superexcited helium species in this afterglow produced analyte ions as protonated and ammoniated species, as well as radical cations. The optimization procedure could corroborate underlying conceptual consideration on the ablation, desorption and ionization mechanisms. A successful detection of a variety of target molecules could be shown from the pharmaceutical ibuprofen, urea, the amino acids l-arginine, l-lysine, the polymer polyethylene glycol, the organometallic compound ferrocene and the technical mixture wild mint oil. For a reliable evaluation of the introduced detection procedure spectra from the naturally abundant alkaloid capsaicin in dried capsicum fruits were recorded. PMID:26851554

  15. Direct writing of sub-wavelength ripples on silicon using femtosecond laser at high repetition rate

    NASA Astrophysics Data System (ADS)

    Xie, Changxin; Li, Xiaohong; Liu, Kaijun; Zhu, Min; Qiu, Rong; Zhou, Qiang

    2016-01-01

    The near sub-wavelength and deep sub-wavelength ripples on monocrystalline silicon were formed in air by using linearly polarized and high repetition rate femtosecond laser pulses (f = 76 MHz, λ = 800 nm, τ = 50 fs). The effects of laser pulse energy, direct writing speed and laser polarization on silicon surface morphology are studied. When the laser pulse energy is 2 nJ/pulse and the direct writing speed varies from 10 to 25 mm/s, the near sub-wavelength ripples (NSRs) with orientation perpendicular to the laser polarization are generated. While the direct writing speed reaches 30 mm/s, the direction of the obtained deep sub-wavelength ripples (DSRs) suddenly changes and becomes parallel to the laser polarization, rarely reported so far for femtosecond laser irradiation of silicon. Meanwhile, we extend the Sipe-Drude interference theory by considering the thermal excitation, and numerically calculate the efficacy factor for silicon irradiated by femtosecond laser pulses. The revised Sipe-Drude interference theoretical results show good agreement with the periods and orientations of sub-wavelength ripples.

  16. Choppers to optimise the repetition rate multiplication technique on a direct geometry neutron chopper spectrometer

    NASA Astrophysics Data System (ADS)

    Vickery, A.; Deen, P. P.

    2014-11-01

    In recent years the use of repetition rate multiplication (RRM) on direct geometry neutron spectrometers has been established and is the common mode of operation on a growing number of instruments. However, the chopper configurations are not ideally optimised for RRM with a resultant 100 fold flux difference across a broad wavelength band. This paper presents chopper configurations that will produce a relative constant (RC) energy resolution and a relative variable (RV) energy resolution for optimised use of RRM. The RC configuration provides an almost uniform ΔE/E for all incident wavelengths and enables an efficient use of time as the entire dynamic range is probed with equivalent statistics, ideal for single shot measurements of transient phenomena. The RV energy configuration provides an almost uniform opening time at the sample for all incident wavelengths with three orders of magnitude in time resolution probed for a single European Spallation Source (ESS) period, which is ideal to probe complex relaxational behaviour. These two chopper configurations have been simulated for the Versatile Optimal Resolution direct geometry spectrometer, VOR, that will be built at ESS.

  17. Advances in generation of high-repetition-rate burst mode laser output.

    PubMed

    Jiang, Naibo; Webster, Matthew C; Lempert, Walter R

    2009-02-01

    It is demonstrated that the incorporation of variable pulse duration flashlamp power supplies into an Nd:YAG burst mode laser system results in very substantial increases in the realizable energy per pulse, the total pulse train length, and uniformity of the intensity envelope. As an example, trains of 20 pulses at burst frequencies of 50 and 20 kHz are demonstrated with individual pulse energy at 1064 nm of 220 and 400 mJ, respectively. Conversion efficiency to the second- (532 nm) and third- (355 nm) harmonic wavelengths of approximately 50% and 35-40%, respectively, is also achieved. Use of the third-harmonic output of the burst mode laser as a pump source for a simple, home built optical parametric oscillator (OPO) produces pulse trains of broadly wavelength tunable output. Sum-frequency mixing of OPO signal output at 622 nm with residual output from the 355 nm pump beam is shown to produce uniform bursts of tunable output at approximately 226 nm, with individual pulse energy of approximately 0.5 mJ. Time-correlated NO planar laser induced fluorescence (PLIF) image sequences are obtained in a Mach 3 wind tunnel at 500 kHz, representing, to our knowledge, the first demonstration of NO PLIF imaging at repetition rates exceeding tens of hertz.

  18. Choppers to optimise the repetition rate multiplication technique on a direct geometry neutron chopper spectrometer

    SciTech Connect

    Vickery, A.; Deen, P. P.

    2014-11-15

    In recent years the use of repetition rate multiplication (RRM) on direct geometry neutron spectrometers has been established and is the common mode of operation on a growing number of instruments. However, the chopper configurations are not ideally optimised for RRM with a resultant 100 fold flux difference across a broad wavelength band. This paper presents chopper configurations that will produce a relative constant (RC) energy resolution and a relative variable (RV) energy resolution for optimised use of RRM. The RC configuration provides an almost uniform ΔE/E for all incident wavelengths and enables an efficient use of time as the entire dynamic range is probed with equivalent statistics, ideal for single shot measurements of transient phenomena. The RV energy configuration provides an almost uniform opening time at the sample for all incident wavelengths with three orders of magnitude in time resolution probed for a single European Spallation Source (ESS) period, which is ideal to probe complex relaxational behaviour. These two chopper configurations have been simulated for the Versatile Optimal Resolution direct geometry spectrometer, VOR, that will be built at ESS.

  19. A voltage-division-type low-jitter self-triggered repetition-rate switch

    NASA Astrophysics Data System (ADS)

    Su, Jian-cang; Zeng, Bo; Gao, Peng-cheng; Li, Rui; Wu, Xiao-long; Zhao, Liang

    2016-10-01

    A voltage-division-type (V/N) low-jitter self-triggered multi-stage switch is put forward. It comprises of a triggered corona gap, several quasi-uniform-field gaps, and an inversion inductor. When the corona gap is in the stage of self-breakdown, the multi-stage gaps are triggered and the switch is closed via an over-voltage. This type of V/N switch has the advantage of compact structure since the auxiliary components like the gas-blowing system and the triggered system are eliminated from the whole system. It also has advantages such as low breakdown jitter and high energy efficiency. The dependence of the self-triggered voltage on the over-voltage factor and the switch operating voltage is deduced. A switch of this type is designed and fabricated and experiments to research its characteristics are conducted. The results show that this switch can operate on a voltage of 1 MV at 50 Hz and can generate 1000 successive pulses with a jitter as low as 3% and an energy efficiency as high as 90%. This V/N switch can work under a high repetition rate with a long lifetime.

  20. [INVITED] Laser welding of glasses at high repetition rates - Fundamentals and prospects

    NASA Astrophysics Data System (ADS)

    Richter, Sören; Zimmermann, Felix; Tünnermann, Andreas; Nolte, Stefan

    2016-09-01

    We report on the welding of various glasses with ultrashort laser pulses. Femtosecond laser pulses at repetition rates in the MHz range are focused at the interface between two substrates, resulting in multiphoton absorption and heat accumulation from successive pulses. This leads to local melting and subsequent resolidification which can be used to weld the glasses. The fundamental interaction process was studied using an in-situ micro Raman setup to measure the laser induced temperature distribution and its temporal decay. The induced network changes were analyzed by Raman spectrocopy identifying an increase of three and four membered silicon rings within the laser irradiated area. In order to determine the stability of the laser welded samples a three point bending test was used. Thereby, we identified that the maximal achievable breaking strength is limited by laser induced stress surrounding the modified material. To minimize the amount of stress bursts of laser pulses or an post processing annealing step can be applied. Besides fused silica, we welded borosilicate glasses and glasses with a low thermal expansion coefficient. Even the welding of different glass combinations is possible demonstrating the versatility of ultrashort pulse induced laser welding.

  1. High-repetition-rate Q-modulation in solid-state laser using fast saturable absorber V:YAG

    NASA Astrophysics Data System (ADS)

    Ma, Jia-Sai; Wang, Feng; Li, Pei-Xin; Hu, Wei-Wei; Yin, Chun-Hao; Xu, Jin-Long

    2015-07-01

    A high-repetition-rate Q-modulation operation in a solid-state Nd:GdVO4 laser with a V3+:YAG saturable absorber has been demonstrated in this paper. The V3+:YAG crystal behaves as a fast saturable absorber in this laser because of its very short lifetime of 22 ns. Taking advantage of such fast bleaching recovery and effective cooling of the V:YAG by a home-made copper holder, we realized a pulse repetition rate of 2.4 MHz, which is, to our best knowledge, the maximum among the reported passively Q-switched lasers. The corresponding average output power and pulse width were 1.28 W and 170 ns, respectively, giving a slope efficiency of 15.9% and a pulse energy of 0.53 µJ. This compact high-repetition-rate Q-switched laser offers a potential application in the construction of low-cost, integrated and portable sensing detection equipment which needs a high laser pulse repetition rate.

  2. High-repetition-rate optical delay line using a micromirror array and galvanometer mirror for a terahertz system.

    PubMed

    Kitahara, Hideaki; Tani, Masahiko; Hangyo, Masanori

    2009-07-01

    We developed a high-repetition-rate optical delay line based on a micromirror array and galvanometer mirror for terahertz time-domain spectroscopy. The micromirror array is fabricated by using the x-ray lithographic technology. The measurement of terahertz time-domain waveforms with the new optical delay line is demonstrated successfully up to 25 Hz.

  3. Novel ultrafast sources on chip: filter driven four wave mixing lasers, from high repetition rate to burst mode operation

    NASA Astrophysics Data System (ADS)

    Pasquazi, Alessia; Peccianti, Marco; Chu, Sai T.; Moss, Dave J.; Morandotti, Roberto

    2016-03-01

    Passive fiber mode-locked lasers enable the excitation of multiple pulses per round trip representing a potential solutions for the increasing demand of practical optical sources with repetition rates of hundreds of GHz or higher. The control of such high repetition rate regimes is however a challenge. To this purpose, linear filters have been used in an "intracavity" configuration to force the repetition rate of the laser. This design is known as dissipative four wave mixing (DFWM) but it is usually unstable and hence marginally suitable for practical applications. We explore the use of nonlinear intracavity filters, such as integrated micro-ring resonators, capable of "driving" the FWM interaction in the laser. We term this approach as Filter-Driven FWM. With a proper choice of the filter properties in terms of free spectral range (FSR) and Q factor, we could observe stable regimes over a wide range of operating conditions, from high repetition rate oscillation at a 200GHz to the formation of two stable spectral comb replicas separated by the FSR of the main cavity (65MHz). High order filters, moreover, allow achieving nonlinear operation over large passbands. With an 11th order filter we achieve low-frequency mode-locking between the main cavity modes that oscillate within each resonance of the filter, producing burst pulsed operation. A stable mode-locked pulse train at 655GHz with an envelope of 42ps at 6.45MHz is achieved.

  4. High-repetition-rate optical delay line using a micromirror array and galvanometer mirror for a terahertz system.

    PubMed

    Kitahara, Hideaki; Tani, Masahiko; Hangyo, Masanori

    2009-07-01

    We developed a high-repetition-rate optical delay line based on a micromirror array and galvanometer mirror for terahertz time-domain spectroscopy. The micromirror array is fabricated by using the x-ray lithographic technology. The measurement of terahertz time-domain waveforms with the new optical delay line is demonstrated successfully up to 25 Hz. PMID:19655989

  5. Micro-processing of polymers and biological materials using high repetition rate femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Ding, Li

    High repetition rate femtosecond laser micro-processing has been applied to ophthalmological hydrogel polymers and ocular tissues to create novel refractive and diffractive structures. Through the optimization of laser irradiation conditions and material properties, this technology has become feasible for future industrial applications and clinical practices. A femtosecond laser micro-processing workstation has been designed and developed. Different experimental parameters of the workstation such as laser pulse duration, focusing lens, and translational stages have been described and discussed. Diffractive gratings and three-dimensional waveguides have been fabricated and characterized in hydrogel polymers, and refractive index modifications as large as + 0.06 have been observed within the laser-irradiated region. Raman spectroscopic studies have shown that our femtosecond laser micro-processing induces significant thermal accumulation, resulting in a densification of the polymer network and increasing the localized refractive index of polymers within the laser irradiated region. Different kinds of dye chromophores have been doped in hydrogel polymers to enhance the two-photon absorption during femtosecond laser micro-processing. As the result, laser scanning speed can be greatly increased while the large refractive index modifications remain. Femtosecond laser wavelength and pulse energy as well as water and dye concentration of the hydrogels are optimized. Lightly fixed ocular tissues such as corneas and lenses have been micro-processed by focused femtosecond laser pulses, and refractive index modifications without any tissue-breakdown are observed within the stromal layer of the corneas and the cortex of the lenses. Living corneas are doped with Sodium Fluorescein to increase the two-photon absorption during the laser micro-processing, and laser scanning speed can be greatly increased while inducing large refractive index modifications. No evidence of cell death

  6. Nonword Repetition by Children with Cochlear Implants: Accuracy Ratings from Normal-Hearing Listeners.

    ERIC Educational Resources Information Center

    Dillon, Caitlin M.; Burkholder, Rose A.; Cleary, Miranda; Pisoni, David B.

    2004-01-01

    Seventy-six children with cochlear implants completed a nonword repetition task. The children were presented with 20 nonword auditory patterns over a loudspeaker and were asked to repeat them aloud to the experimenter. The children's responses were recorded on digital audiotape and then played back to normal-hearing adult listeners to obtain…

  7. Low-pump-power, low-phase-noise, and microwave to millimeter-wave repetition rate operation in microcombs.

    PubMed

    Li, Jiang; Lee, Hansuek; Chen, Tong; Vahala, Kerry J

    2012-12-01

    Microresonator-based frequency combs (microcombs or Kerr combs) can potentially miniaturize the numerous applications of conventional frequency combs. A priority is the realization of broadband (ideally octave spanning) spectra at detectable repetition rates for comb self-referencing. However, access to these rates involves pumping larger mode volumes and hence higher threshold powers. Moreover, threshold power sets both the scale for power per comb tooth and also the optical pump. Along these lines, it is shown that a class of resonators having surface-loss-limited Q factors can operate over a wide range of repetition rates with minimal variation in threshold power. A new, surface-loss-limited resonator illustrates the idea. Comb generation on mode spacings ranging from 2.6 to 220 GHz with overall low threshold power (as low as 1 mW) is demonstrated. A record number of comb lines for a microcomb (around 1900) is also observed with pump power of 200 mW. The ability to engineer a wide range of repetition rates with these devices is also used to investigate a recently observed mechanism in microcombs associated with dispersion of subcomb offset frequencies. We observe high-coherence phase locking in cases where these offset frequencies are small enough so as to be tuned into coincidence. In these cases, a record-low microcomb phase noise is reported at a level comparable to an open-loop, high-performance microwave oscillator.

  8. Repetition rate stabilization of an erbium-doped all-fiber laser via opto-mechanical control of the intracavity group velocity

    SciTech Connect

    Shen, Xuling; He, Boqu; Zhao, Jian; Liu, Yang; Bai, Dongbi; Wang, Chao; Liu, Geping; Luo, Daping; Liu, Fengjiang; Li, Wenxue; Zeng, Heping; Yang, Kangwen; Hao, Qiang

    2015-01-19

    We present a method for stabilizing the repetition rate of an erbium-doped all-fiber laser by inserting an electronic polarization controller (EPC) in the fiber laser cavity. The device exhibited good integration, low cost, and convenient operation. Such a repetition rate stabilization may facilitate an all-fiber laser comb system with high integration. The repetition rate was phase-locked to a Rb reference more than 72 h with a low feedback voltage applied to one channel of the EPC. The repetition rate was 74.6 MHz. The standard deviation and the repetition rate linewidth were 1.4 and 1.7 mHz, respectively.

  9. 1  J, 0.5  kHz repetition rate picosecond laser.

    PubMed

    Baumgarten, Cory; Pedicone, Michael; Bravo, Herman; Wang, Hanchen; Yin, Liang; Menoni, Carmen S; Rocca, Jorge J; Reagan, Brendan A

    2016-07-15

    We report the demonstration of a diode-pumped chirped pulse amplification Yb:YAG laser that produces λ=1.03  μm pulses of up to 1.5 J energy compressible to sub-5 ps duration at a repetition rate of 500 Hz (750 W average power). Amplification to high energy takes place in cryogenically cooled Yb:YAG active mirrors designed for kilowatt average power laser operation. This compact laser system will enable new advances in high-average-power ultrashort-pulse lasers and high-repetition-rate tabletop soft x-ray lasers. As a first application, the laser was used to pump a 400 Hz λ=18.9  nm laser. PMID:27420530

  10. High-repetition-rate dual-signal intracavity optical parametric generator based on periodically-phase-reversal PPMgLN

    NASA Astrophysics Data System (ADS)

    Ji, Feng; Yao, Jianquan; Zheng, Fanghua; Li, Enbang; Zhang, Tieli; Zhao, Pu; Wang, Peng; Zhang, Baigang

    2007-10-01

    A high-repetition-rate dual-signal intracavity optical parametric generator (IOPG) inside a diode-end-pumped acousto-optically (AO) Q-switched Nd:YVO4 laser is presented. The nonlinear material is a periodically-phase-reversal periodically poled MgO-doped lithium niobate (ppr-PPMgLN). At an incident diode pump power of 6.1 W and a Q-switch repetition rate of 20 kHz, an average dual-signal output power of 0.44 W is achieved. The dual-signal wavelengths of 1477 and 1491 nm are obtained at a crystal temperature of 40 °C. The measurements of the beam quality factor of 1.4 and the pulse duration of 77 ns show good spatial and temporal overlaps for the dual-signal radiation.

  11. Ytterbium fiber-based, 270 fs, 100 W chirped pulse amplification laser system with 1 MHz repetition rate

    NASA Astrophysics Data System (ADS)

    Zhao, Zhigang; Kobayashi, Yohei

    2016-01-01

    A 100 W Yb-doped, fiber-based, femtosecond, chirped pulse amplification laser system was developed with a repetition rate of 1 MHz, corresponding to a pulse energy of 100 µJ. Large-scale, fused-silica transmission gratings were used for both the pulse stretcher and compressor, with a compression throughput efficiency of ∼85%. A pulse duration of 270 fs was measured by second harmonic generation frequency-resolved optical gating (SHG-FROG). To the best of our knowledge, this is the shortest pulse duration ever achieved by a 100-W-level fiber chirped pulse amplification laser system at a repetition rate of few megahertz, without any special post-compression manipulation.

  12. 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)

  13. The effect of laser repetition rate on the LASiS synthesis of biocompatible silver nanoparticles in aqueous starch solution

    PubMed Central

    Zamiri, Reza; Zakaria, Azmi; Ahangar, Hossein Abbastabar; Darroudi, Majid; Zamiri, Golnoosh; Rizwan, Zahid; Drummen, Gregor PC

    2013-01-01

    Laser ablation-based nanoparticle synthesis in solution is rapidly becoming popular, particularly for potential biomedical and life science applications. This method promises one pot synthesis and concomitant bio-functionalization, is devoid of toxic chemicals, does not require complicated apparatus, can be combined with natural stabilizers, is directly biocompatible, and has high particle size uniformity. Size control and reduction is generally determined by the laser settings; that the size and size distribution scales with laser fluence is well described. Conversely, the effect of the laser repetition rate on the final nanoparticle product in laser ablation is less well-documented, especially in the presence of stabilizers. Here, the influence of the laser repetition rate during laser ablation synthesis of silver nanoparticles in the presence of starch as a stabilizer was investigated. The increment of the repetition rate does not negatively influence the ablation efficiency, but rather shows increased productivity, causes a red-shift in the plasmon resonance peak of the silver–starch nanoparticles, an increase in mean particle size and size distribution, and a distinct lack of agglomerate formation. Optimal results were achieved at 10 Hz repetition rate, with a mean particle size of ~10 nm and a bandwidth of ~6 nm ‘full width at half maximum’ (FWHM). Stability measurements showed no significant changes in mean particle size or agglomeration or even flocculation. However, zeta potential measurements showed that optimal double layer charge is achieved at 30 Hz. Consequently, Ag–NP synthesis via the laser ablation synthesis in solution (LASiS) method in starch solution seems to be a trade-off between small size and narrow size distributions and inherent and long-term stability. PMID:23345971

  14. Self-mode-locked all-fibre erbium laser with a low repetition rate and high pulse energy

    SciTech Connect

    Denisov, Vladimir I; Nyushkov, B N; Pivtsov, V S

    2010-01-31

    Self-starting mode locking is demonstrated for the first time in an all-fibre erbium laser with a cavity length above 1 km and high positive (normal) intracavity dispersion. The unconventional cavity design, with polarisation instability compensation, ensures stable operation and good frequency stability. The laser generates pulses with a record low repetition rate (82.4 kHz) and record high energy (564.3 nJ). (lasers)

  15. The effect of laser repetition rate on the LASiS synthesis of biocompatible silver nanoparticles in aqueous starch solution.

    PubMed

    Zamiri, Reza; Zakaria, Azmi; Ahangar, Hossein Abbastabar; Darroudi, Majid; Zamiri, Golnoosh; Rizwan, Zahid; Drummen, Gregor P C

    2013-01-01

    Laser ablation-based nanoparticle synthesis in solution is rapidly becoming popular, particularly for potential biomedical and life science applications. This method promises one pot synthesis and concomitant bio-functionalization, is devoid of toxic chemicals, does not require complicated apparatus, can be combined with natural stabilizers, is directly biocompatible, and has high particle size uniformity. Size control and reduction is generally determined by the laser settings; that the size and size distribution scales with laser fluence is well described. Conversely, the effect of the laser repetition rate on the final nanoparticle product in laser ablation is less well-documented, especially in the presence of stabilizers. Here, the influence of the laser repetition rate during laser ablation synthesis of silver nanoparticles in the presence of starch as a stabilizer was investigated. The increment of the repetition rate does not negatively influence the ablation efficiency, but rather shows increased productivity, causes a red-shift in the plasmon resonance peak of the silver-starch nanoparticles, an increase in mean particle size and size distribution, and a distinct lack of agglomerate formation. Optimal results were achieved at 10 Hz repetition rate, with a mean particle size of ~10 nm and a bandwidth of ~6 nm 'full width at half maximum' (FWHM). Stability measurements showed no significant changes in mean particle size or agglomeration or even flocculation. However, zeta potential measurements showed that optimal double layer charge is achieved at 30 Hz. Consequently, Ag-NP synthesis via the laser ablation synthesis in solution (LASiS) method in starch solution seems to be a trade-off between small size and narrow size distributions and inherent and long-term stability.

  16. Generation of 16-fs, 10-TW pulses at a 10-Hz repetition rate with efficient Ti:sapphire amplifiers.

    PubMed

    Yamakawa, K; Aoyama, M; Matsuoka, S; Takuma, H; Barty, C P; Fittinghoff, D

    1998-04-01

    We describe a two-stage Ti:sapphire amplifier laser system that is capable of producing 16-fs pulses of 10-TW peak power at a 10-Hz repetition rate. Thin solid etalons were used to control gain narrowing and gain saturation during amplification. A cylindrical mirror expander was used to permit compensation of the dispersion of the system. An efficiency greater than 90% of the theoretical maximum for conversion of 532-nm pump light to 790-nm radiation is demonstrated.

  17. Breaking the trade-off: rainforest bats maximize bandwidth and repetition rate of echolocation calls as they approach prey

    PubMed Central

    Schmieder, Daniela A.; Kingston, Tigga; Hashim, Rosli; Siemers, Björn M.

    2010-01-01

    Both mammals and birds experience a performance trade-off between producing vocalizations with high bandwidths and at high repetition rate. Echolocating bats drastically increase repetition rate from 2–20 calls s−1 up to about 170 calls s−1 prior to intercepting airborne prey in order to accurately track prey movement. In turn, bandwidth drops to about 10–30 kHz for the calls of this ‘final buzz’. We have now discovered that Southeast Asian rainforest bats (in the vespertilionid subfamilies Kerivoulinae and Murininae) are able to maintain high call bandwidths at very high repetition rates throughout approach to prey. Five species of Kerivoula and Phoniscus produced call bandwidths of between 78 and 170 kHz at repetition rates of 140–200 calls s−1 and two of Murina at 80 calls s−1. The ‘typical’ and distinct drop in call frequency was present in none of the seven species. This stands in striking contrast to our present view of echolocation during approach to prey in insectivorous bats, which was established largely based on European and American members of the same bat family, the Vespertilionidae. Buzz calls of Kerivoula pellucida had mean bandwidths of 170 kHz and attained maximum starting frequencies of 250 kHz which makes them the most broadband and most highly pitched tonal animal vocalization known to date. We suggest that the extreme vocal performance of the Kerivoulinae and Murininae evolved as an adaptation to echolocating and tracking arthropods in the dense rainforest understorey. PMID:20356884

  18. MAPLE-deposited PFO films: influence of the laser fluence and repetition rate on the film emission and morphology

    NASA Astrophysics Data System (ADS)

    Caricato, A. P.; Anni, M.; Cesaria, M.; Lattante, S.; Leggieri, G.; Leo, C.; Martino, M.; Perulli, A.; Resta, V.

    2015-06-01

    The Matrix-Assisted Pulsed Laser Evaporation (MAPLE) technique is emerging as an alternative route to the conventional methods for depositing organic materials, although the MAPLE-deposited films very often present high surface roughness and characteristic morphological features. Films of the blue-emitting polymer, poly(9,9-dioctylfluorene)—PFO, have been deposited by MAPLE to investigate the influence of the laser fluence and repetition rate on both their topography and emission properties. The laser fluence has been changed from 150 up to 450 mJ/cm2, while laser repetition rates of 2 and 10 Hz have been considered. The interplay/relationship between the topography and the emission properties of the MAPLE-deposited films has been studied by confocal microscopy, photoluminescence spectrometry and atomic force microscopy. It has been found that under high irradiation (fluence of 450 mJ/cm2) conditions, the sample surface is characterized by bubbles presenting the intrinsic PFO blue emission. Instead, while improvements in the film morphology can be observed for lowered fluence and laser repetition rate, green emission becomes predominant in such conditions. Such result is very interesting to better understand the MAPLE ablation mechanism, which is discussed in this study.

  19. All-fiberized SBS-based high repetition rate sub-nanosecond Yb fiber laser for supercontinuum generation

    NASA Astrophysics Data System (ADS)

    Hua, Dacheng; Su, Jianjia; Cui, Wei; Yan, Yaxi; Jiang, Peipei

    2014-12-01

    We report an all-fiberized SBS-based high repetition rate sub-nanosecond Yb fiber laser for supercontinuum generation. The high repetition rate ns laser pulses were produced from a fiber Bragg grating (FBG)-constructed fiber laser cavity consisting of a piece of double cladding Yb fiber as the gain medium and a short piece of Bi/Cr-doped fiber as a saturable absorber (SA). By optimizing the fiber length of the Bi/Cr-doped fiber and the reflectivity of the FBG, the Q-switching state of the fiber laser can be adjusted so that the energy storing condition within the fiber cavity can assure the start of stimulated Brillouin scattering (SBS) and as a result, compress the laser pulse duration. The fiber laser had an average laser power output of 1.2 W at 1064 nm with pulse repetition rate of about 80 kHz, almost four times the reported results. The pulse duration was about 1 ns with peak power of about 15 kW. After one stage of amplification, the laser power was raised to about 3 W and was used to pump a 20 m long photonic crystal fiber (PCF). Supercontiuum (SC) laser output was obtained with average power up to 1.24 W and spectrum spanning from 550 to 2200 nm.

  20. Efficient high repetition rate electro-optic Q-switched laser with an optically active langasite crystal.

    PubMed

    Ma, Shihui; Yu, Haohai; Zhang, Huaijin; Han, Xuekun; Lu, Qingming; Ma, Changqin; Boughton, Robert I; Wang, Jiyang

    2016-01-01

    With an optically active langasite (LGS) crystal as the electro-optic Q-switch, we demonstrate an efficient Q-switched laser with a repetition rate of 200 kHz. Based on the theoretical analysis of the interaction between optical activity and electro-optic property, the optical activity of the crystal has no influence on the birefringence during Q-switching if the quarter wave plate used was rotated to align with the polarization direction. With a Nd:LuVO4 crystal possessing a large emission cross-section and a short fluorescence lifetime as the gain medium, a stable LGS Q-switched laser was designed with average output power of 4.39 W, corresponding to a slope efficiency of 29.4% and with a minimum pulse width of 5.1 ns. This work represents the highest repetition rate achieved so far in a LGS Q-switched laser and it can provide a practical Q-switched laser with a tunable high repetition rates for many applications, such as materials processing, laser ranging, medicine, military applications, biomacromolecule materials, remote sensing, etc.

  1. Efficient high repetition rate electro-optic Q-switched laser with an optically active langasite crystal

    PubMed Central

    Ma, Shihui; Yu, Haohai; Zhang, Huaijin; Han, Xuekun; Lu, Qingming; Ma, Changqin; Boughton, Robert I.; Wang, Jiyang

    2016-01-01

    With an optically active langasite (LGS) crystal as the electro-optic Q-switch, we demonstrate an efficient Q-switched laser with a repetition rate of 200 kHz. Based on the theoretical analysis of the interaction between optical activity and electro-optic property, the optical activity of the crystal has no influence on the birefringence during Q-switching if the quarter wave plate used was rotated to align with the polarization direction. With a Nd:LuVO4 crystal possessing a large emission cross-section and a short fluorescence lifetime as the gain medium, a stable LGS Q-switched laser was designed with average output power of 4.39 W, corresponding to a slope efficiency of 29.4% and with a minimum pulse width of 5.1 ns. This work represents the highest repetition rate achieved so far in a LGS Q-switched laser and it can provide a practical Q-switched laser with a tunable high repetition rates for many applications, such as materials processing, laser ranging, medicine, military applications, biomacromolecule materials, remote sensing, etc. PMID:27461819

  2. Efficient high repetition rate electro-optic Q-switched laser with an optically active langasite crystal

    NASA Astrophysics Data System (ADS)

    Ma, Shihui; Yu, Haohai; Zhang, Huaijin; Han, Xuekun; Lu, Qingming; Ma, Changqin; Boughton, Robert I.; Wang, Jiyang

    2016-07-01

    With an optically active langasite (LGS) crystal as the electro-optic Q-switch, we demonstrate an efficient Q-switched laser with a repetition rate of 200 kHz. Based on the theoretical analysis of the interaction between optical activity and electro-optic property, the optical activity of the crystal has no influence on the birefringence during Q-switching if the quarter wave plate used was rotated to align with the polarization direction. With a Nd:LuVO4 crystal possessing a large emission cross-section and a short fluorescence lifetime as the gain medium, a stable LGS Q-switched laser was designed with average output power of 4.39 W, corresponding to a slope efficiency of 29.4% and with a minimum pulse width of 5.1 ns. This work represents the highest repetition rate achieved so far in a LGS Q-switched laser and it can provide a practical Q-switched laser with a tunable high repetition rates for many applications, such as materials processing, laser ranging, medicine, military applications, biomacromolecule materials, remote sensing, etc.

  3. Efficient high repetition rate electro-optic Q-switched laser with an optically active langasite crystal.

    PubMed

    Ma, Shihui; Yu, Haohai; Zhang, Huaijin; Han, Xuekun; Lu, Qingming; Ma, Changqin; Boughton, Robert I; Wang, Jiyang

    2016-01-01

    With an optically active langasite (LGS) crystal as the electro-optic Q-switch, we demonstrate an efficient Q-switched laser with a repetition rate of 200 kHz. Based on the theoretical analysis of the interaction between optical activity and electro-optic property, the optical activity of the crystal has no influence on the birefringence during Q-switching if the quarter wave plate used was rotated to align with the polarization direction. With a Nd:LuVO4 crystal possessing a large emission cross-section and a short fluorescence lifetime as the gain medium, a stable LGS Q-switched laser was designed with average output power of 4.39 W, corresponding to a slope efficiency of 29.4% and with a minimum pulse width of 5.1 ns. This work represents the highest repetition rate achieved so far in a LGS Q-switched laser and it can provide a practical Q-switched laser with a tunable high repetition rates for many applications, such as materials processing, laser ranging, medicine, military applications, biomacromolecule materials, remote sensing, etc. PMID:27461819

  4. Performance of large aperture tapered fiber phase conjugate mirror with high pulse energy and 1-kHz repetition rate.

    PubMed

    Zhao, Zhigang; Dong, Yantao; Pan, Sunqiang; Liu, Chong; Chen, Jun; Tong, Lixin; Gao, Qingsong; Tang, Chun

    2012-01-16

    A large aperture fused silica tapered fiber phase conjugate mirror is presented with a maximum 70% stimulated Brillouin scattering (SBS) reflectivity, which is obtained with 1 kHz repetition rate, 15 ns pulse width and 38 mJ input pulse energy. To the best of our knowledge, this is the highest SBS reflectivity ever reported by using optical fiber as a phase conjugate mirror for such high pulse repetition rate (1 kHz) and several tens of millijoule (mJ) input pulse energy. The influences of fiber end surface quality and pump pulse widths on SBS reflectivity are investigated experimentally. The results show that finer fiber end surface quality and longer input pulse widths are preferred for obtaining higher SBS reflectivity with higher input pulse energy. Double passing amplification experiments are also performed. 52 mJ pulse energy is achieved at 1 kHz repetition rate, with a reflected SBS pulse width of 1.5 ns and a M(2) factor of 2.3. The corresponding peak power reaches 34.6 MW. Obvious beam quality improvement is observed. PMID:22274534

  5. Effects of high-repetition-rate femtosecond laser micromachining on the physical and chemical properties of polylactide (PLA).

    PubMed

    Jia, Wei; Luo, Yiming; Yu, Jian; Liu, Bowen; Hu, Minglie; Chai, Lu; Wang, Chingyue

    2015-10-19

    The effects of femtosecond laser ablation, with 115 fs pulses at 1040 nm wavelength and 57 MHz repetition-rate, on the physical and chemical properties of polylactide (PLA) were studied in air and in water. The surface of the PLA sample ablated by high-repetition-rate femtosecond laser was analysed using field emission scanning electron microscopy, infrared spectroscopy, raman spectroscopy, as well as X-ray photoelectron spectroscopy. Compared with the experiments in the air at ambient temperature, melting resolidification was negligible for the experiments conducted under water. Neither in air nor under water did oxidation and crystallization process take place in the laser ablated surface. In addition, the intensity of some oxygen related peaks increased for water experiments, probably due to the hydrolysis. Meantime, the chemical shift to higher energies appeared in C1s XPS spectrum of laser processing in water. Interestingly, a large amount of defects were observed after laser processing in air, while no significant change was shown under water experiments. This indicates that thermal and mechanical effects by high-repetition-rate femtosecond laser ablation in water are quite limited, which could be even ignored.

  6. Ultrafast, high repetition rate, ultraviolet, fiber-laser-based source: application towards Yb+ fast quantum-logic.

    PubMed

    Hussain, Mahmood Irtiza; Petrasiunas, Matthew Joseph; Bentley, Christopher D B; Taylor, Richard L; Carvalho, André R R; Hope, Joseph J; Streed, Erik W; Lobino, Mirko; Kielpinski, David

    2016-07-25

    Trapped ions are one of the most promising approaches for the realization of a universal quantum computer. Faster quantum logic gates could dramatically improve the performance of trapped-ion quantum computers, and require the development of suitable high repetition rate pulsed lasers. Here we report on a robust frequency upconverted fiber laser based source, able to deliver 2.5 ps ultraviolet (UV) pulses at a stabilized repetition rate of 300.00000 MHz with an average power of 190 mW. The laser wavelength is resonant with the strong transition in Ytterbium (Yb+) at 369.53 nm and its repetition rate can be scaled up using high harmonic mode locking. We show that our source can produce arbitrary pulse patterns using a programmable pulse pattern generator and fast modulating components. Finally, simulations demonstrate that our laser is capable of performing resonant, temperature-insensitive, two-qubit quantum logic gates on trapped Yb+ ions faster than the trap period and with fidelity above 99%. PMID:27464118

  7. A Simulation of the Effects of Varying Repetition Rate and Pulse Width of Nanosecond Discharges on Premixed Lean Methane-Air Combustion

    DOE PAGES

    Bak, Moon Soo; Cappelli, Mark A.

    2012-01-01

    Two-dimensional kinetic simulation has been carried out to investigate the effects of repetition rate and pulse width of nanosecond repetitively pulsed discharges on stabilizing premixed lean methane-air combustion. The repetition rate and pulse width are varied from 10 kHz to 50 kHz and from 9 ns to 2 ns while the total power is kept constant. The lower repetition rates provide larger amounts of radicals such as O, H, and OH. However, the effect on stabilization is found to be the same for all of the tested repetition rates. The shorter pulse width is found to favor the production of species in higher electronicmore » states, but the varying effects on stabilization are also found to be small. Our results indicate that the total deposited power is the critical element that determines the extent of stabilization over this range of discharge properties studied.« less

  8. Design concept and performance considerations for fast high power semiconductor switching for high repetition rate and high power excimer laser

    NASA Astrophysics Data System (ADS)

    Goto, Tatsumi; Kakizaki, Kouji; Takagi, Shigeyuki; Satoh, Saburoh; Shinohe, Takashi; Ohashi, Hiromichi; Endo, Fumihiko; Okamura, Katsuya; Ishii, Akira; Teranishi, Tsuneharu; Yasuoka, Koichi

    1997-07-01

    A semiconductor switching power supply has been developed, in which a novel structure semiconductor device, metal-oxide-semiconductor assisted gate-triggered thyristor (MAGT) was incorporated with a single stage magnetic pulse compression circuit (MPC). The MAGT was specially designed to directly replace thyratrons in a power supply for a high repetition rate laser. Compared with conventional high power semiconductor switching devices, it was designed to enable a fast switching, retaining a high blocking voltage and to extremely reduce the transient turn-on power losses, enduring a higher peak current. A maximum peak current density of 32 kA/cm2 and a current density risetime rate di/dt of 142 kA/(cm2×μs) were obtained at the chip area with an applied anode voltage of 1.5 kV. A MAGT switching unit connecting 32 MAGTs in series was capable of switching on more than 25 kV-300 A at a repetition rate of 5 kHz, which, coupled with the MPC, was equivalent to the capability of a high power thyratron. A high repetition rate and high power XeCl excimer laser was excited by the power supply. The results confirmed the stable laser operation of a repetition rate of up to 5 kHz, the world record to our knowledge. An average output power of 0.56 kW was obtained at 5 kHz where the shortage of the total discharge current was subjoined by a conventional power supply with seven parallel switching thyratrons, simultaneously working, for the MAGT power supply could not switch a greater current than that switched by one thyratron. It was confirmed by those excitations that the MAGT unit with the MPC could replace a high power commercial thyratron directly for excimer lasers. The switching stability was significantly superior to that of the thyratron in a high repetition rate region, judging from the discharge current wave forms. It should be possible for the MAGT unit, in the future, to directly switch the discharge current within a rise time of 0.1 μs with a magnetic assist.

  9. Rate-adaptive FSO links over atmospheric turbulence channels by jointly using repetition coding and silence periods.

    PubMed

    García-Zambrana, Antonio; Castillo-Vázquez, Carmen; Castillo-Vázquez, Beatriz

    2010-11-22

    In this paper, a new and simple rate-adaptive transmission scheme for free-space optical (FSO) communication systems with intensity modulation and direct detection (IM/DD) over atmospheric turbulence channels is analyzed. This scheme is based on the joint use of repetition coding and variable silence periods, exploiting the potential time-diversity order (TDO) available in the turbulent channel as well as allowing the increase of the peak-to-average optical power ratio (PAOPR). Here, repetition coding is firstly used in order to accommodate the transmission rate to the channel conditions until the whole time diversity order available in the turbulent channel by interleaving is exploited. Then, once no more diversity gain is available, the rate reduction can be increased by using variable silence periods in order to increase the PAOPR. Novel closed-form expressions for the average bit-error rate (BER) as well as their corresponding asymptotic expressions are presented when the irradiance of the transmitted optical beam follows negative exponential and gamma-gamma distributions, covering a wide range of atmospheric turbulence conditions. Obtained results show a diversity order as in the corresponding rate-adaptive transmission scheme only based on repetition codes but providing a relevant improvement in coding gain. Simulation results are further demonstrated to confirm the analytical results. Here, not only rectangular pulses are considered but also OOK formats with any pulse shape, corroborating the advantage of using pulses with high PAOPR, such as gaussian or squared hyperbolic secant pulses. We also determine the achievable information rate for the rate-adaptive transmission schemes here analyzed.

  10. Laser-diode pumped self-mode-locked praseodymium visible lasers with multi-gigahertz repetition rate.

    PubMed

    Zhang, Yuxia; Yu, Haohai; Zhang, Huaijin; Di Lieto, Alberto; Tonelli, Mauro; Wang, Jiyang

    2016-06-15

    We demonstrate efficient laser-diode pumped multi-gigahertz (GHz) self-mode-locked praseodymium (Pr3+) visible lasers with broadband spectra from green to deep red for the first time to our knowledge. With a Pr3+-doped GdLiF4 crystal, stable self-mode-locked visible pulsed lasers at the wavelengths of 522 nm, 607 nm, 639 nm, and 720 nm have been obtained with the repetition rates of 2.8 GHz, 3.1 GHz, 3.1 GHz, and 3.0 GHz, respectively. The maximum output power was 612 mW with the slope efficiency of 46.9% at 639 nm. The mode-locking mechanism was theoretically analyzed. The stable second-harmonic mode-locking with doubled repetition frequency was also realized based on the Fabry-Perot effect formed in the laser cavity. In addition, we find that the polarization directions were turned with lasing wavelengths. This work may provide a new way for generating efficient ultrafast pulses with high- and changeable-repetition rates in the visible range.

  11. Oral-diadochokinetic rates for Hebrew-speaking school-age children: real words vs. non-words repetition.

    PubMed

    Icht, Michal; Ben-David, Boaz M

    2015-02-01

    Oral-diadochokinesis (DDK) tasks are a common tool for evaluating speech disorders. Usually, these tasks involve repetitions of non-words. It has been suggested that repeating real words can be more suitable for preschool children. But, the impact of using real words with elementary school children has not been studied yet. This study evaluated oral-DDK rates for Hebrew-speaking elementary school children using non-words and real words. The participants were 60 children, 9-11 years old, with normal speech and language development, who were asked to repeat "pataka" (non-word) and "bodeket" (Hebrew real word). Data replicate the advantage generally found for real word repetition with preschoolers. Children produced real words faster than non-words for all age groups, and repetition rates were higher for the older children. The findings suggest that adding real words to the standard oral-DDK task with elementary school children may provide a more comprehensive picture of oro-motor function.

  12. Laser-diode pumped self-mode-locked praseodymium visible lasers with multi-gigahertz repetition rate.

    PubMed

    Zhang, Yuxia; Yu, Haohai; Zhang, Huaijin; Di Lieto, Alberto; Tonelli, Mauro; Wang, Jiyang

    2016-06-15

    We demonstrate efficient laser-diode pumped multi-gigahertz (GHz) self-mode-locked praseodymium (Pr3+) visible lasers with broadband spectra from green to deep red for the first time to our knowledge. With a Pr3+-doped GdLiF4 crystal, stable self-mode-locked visible pulsed lasers at the wavelengths of 522 nm, 607 nm, 639 nm, and 720 nm have been obtained with the repetition rates of 2.8 GHz, 3.1 GHz, 3.1 GHz, and 3.0 GHz, respectively. The maximum output power was 612 mW with the slope efficiency of 46.9% at 639 nm. The mode-locking mechanism was theoretically analyzed. The stable second-harmonic mode-locking with doubled repetition frequency was also realized based on the Fabry-Perot effect formed in the laser cavity. In addition, we find that the polarization directions were turned with lasing wavelengths. This work may provide a new way for generating efficient ultrafast pulses with high- and changeable-repetition rates in the visible range. PMID:27304265

  13. Multiple-circuit pulse generator for high repetition rate rare gas halide lasers.

    PubMed

    Wang, C P

    1978-10-01

    A multiple-circuit high pulse repetition frequency (PRF) pulse generator for the pumping of rare gas halide lasers is reported. With this multiple-circuit design, high PRF can be achieved by the use of existing low PRF thyratron switches and capacitors. A two-circuit pulse generator was constructed, and its performance is described. By means of this pulse generator and a blowdown-type fast transverse-flow system, high PRF laser action in XeF was obtained, typically, 6 mJ/pulse at 1 kHz or 6 W average power. High PRF laser action in N(2) was also observed.

  14. development of a medium repetition rate (10 Hz - 500 Hz) diode pumped laser transmitter for airborne scanning altimetry

    NASA Technical Reports Server (NTRS)

    Coyle, D. Barry; Lindauer, Steven J., II; Kay, Richard B.

    1998-01-01

    Since the late 1980's, NASA has developed several small, all-solid state lasers of low repetition rates for use as transmitters in prototype LIDAR and raster scanned altimetry retrieval systems. Our early laser transmitters were developed for high resolution airborne altimetry which employed cavity dumping techniques to produce a pulse shape with a 1 ns rise time. The first such laser was the SUMR (Sub-millimeter resolution) transmitter which used a side pumped, D-shaped half-rod of Nd:YAG for the oscillator active media and produced approximately 3 ns pulses of 100 micro-J energy at a 40 Hz repetition rate. (Coyle and Blair, 1993; Coyle et al., 1995) After several upgrades to improve rep rate and pulse energy, the final version produced 1.2 mJ pulses at 120 Hz with a 3.7 ns pulse width. The laser has become known as SPLT (Sharp Pulsed Laser Transmitter), and has flown successfully on a variety of airborne altimetry missions. (Coyle and Blair, 1995; Blair et al., 1994) From building these systems, we have accrued valuable experience in delivering field-deployable lasers and have become aware of the advantages and disadvantages of employing new technologies. For example, even though the laser's main operating environment is in a "cold" aircraft during flight, the laser must still operate in very warm temperatures. This is important if the mission is based in the desert or a tropical climate since ground calibration data from stationary targets must be gathered before and after each data flight. Because conductive cooling is much more convenient than closed loop water flow, achieving the highest possible laser efficiency is becoming a high priority when designing a flight laser. This is especially true for lasers with higher pulse energies and repetition rates which are needed for high altitude scanning altimeters and LIDARs.

  15. Filamentation effect in a gas attenuator for high-repetition-rate X-ray FELs.

    PubMed

    Feng, Yiping; Krzywinski, Jacek; Schafer, Donald W; Ortiz, Eliazar; Rowen, Michael; Raubenheimer, Tor O

    2016-01-01

    A sustained filamentation or density depression phenomenon in an argon gas attenuator servicing a high-repetition femtosecond X-ray free-electron laser has been studied using a finite-difference method applied to the thermal diffusion equation for an ideal gas. A steady-state solution was obtained by assuming continuous-wave input of an equivalent time-averaged beam power and that the pressure of the entire gas volume has reached equilibrium. Both radial and axial temperature/density gradients were found and describable as filamentation or density depression previously reported for a femtosecond optical laser of similar attributes. The effect exhibits complex dependence on the input power, the desired attenuation, and the geometries of the beam and the attenuator. Time-dependent simulations were carried out to further elucidate the evolution of the temperature/density gradients in between pulses, from which the actual attenuation received by any given pulse can be properly calculated. PMID:26698041

  16. A compact, transportable, microchip-based system for high repetition rate production of Bose-Einstein condensates

    NASA Astrophysics Data System (ADS)

    Farkas, Daniel M.; Hudek, Kai M.; Salim, Evan A.; Segal, Stephen R.; Squires, Matthew B.; Anderson, Dana Z.

    2010-03-01

    We present a compact, transportable system that produces Bose-Einstein condensates near the surface of an integrated atom microchip. The system occupies a volume of 0.4 m3, operates at a repetition rate as high as 0.3 Hz, and consumes an average power of 525 W. Evaporative cooling in a chip trap with trap frequencies of several kilohertz leads to nearly pure condensates containing 1.9×104 R87b atoms. Partial condensates are observed at a temperature of 1.58(8) μK, close to the theoretical transition temperature of 1.1 μK.

  17. High-repetition-rate widely tunable LiF : \\mathbf{\\mathsf{F}}_\\mathbf{\\mathsf{2}}^{-} color center lasers

    NASA Astrophysics Data System (ADS)

    Men, Shaojie; Liu, Zhaojun; Cong, Zhenhua; Rao, Han; Zhang, Sasa; Liu, Yang; Zverev, Petr G.; Konyushkin, Vasily A.; Zhang, Xingyu

    2016-02-01

    High-repetition-rate tunable LiF:\\text{F}2- color center lasers pumped by quasi-continuous-wave diode-side-pumped acousto-optically Q-switched Nd:YAG laser are demonstrated. Littrow-grating and Littman-grating tuning schemes are studied respectively. In the Littrow-grating scheme, the tuning range was 1085 nm to 1275 nm, and the maximal average output power was 275 mW. In the Littman-grating scheme, the tuning range was 1105.5 nm to 1215.5 nm, and the maximal average output power was 135 mW.

  18. Narrow-Bandwidth Tunable Infrared Difference-Frequency Generation at High Repetition Rates in LilO(3).

    PubMed

    Goldberg, L S

    1975-03-01

    Difference-frequency generation was studied in LiIO(3) with a narrow-bandwidth tunable dye laser pumped at high pulse-repetition rates by a frequency-doubled Nd:YAG laser. Tunable infrared radiation of 0.1, cm(-1) bandwidth was generated from 1.25 mum to 1.60 mum and from 3.40 mum to 5.65 mum by mixing rhodamine B dye laser cavity radiation with the 1.064-mum or 532-nm output of the Nd:YAG laser.

  19. >400 kHz repetition rate wavelength-swept laser and application to high-speed optical frequency domain imaging.

    PubMed

    Oh, Wang-Yuhl; Vakoc, Benjamin J; Shishkov, Milen; Tearney, Guillermo J; Bouma, Brett E

    2010-09-01

    We demonstrate a high-speed wavelength-swept laser with a tuning range of 104 nm (1228-1332 nm) and a repetition rate of 403 kHz. The design of the laser utilizes a high-finesse polygon-based wavelength-scanning filter and a short-length unidirectional ring resonator. Optical frequency domain imaging of the human skin in vivo is presented using this laser, and the system shows sensitivity of higher than 98 dB with single-side ranging depth of 1.7 mm over 4 dB sensitivity roll-off.

  20. Efficient intracavity frequency doubling of a high-repetition-rate diode-pumped Nd:YAG laser.

    PubMed

    Hanson, F; Poirier, P

    1994-10-01

    Efficient operation of a pulsed, high-repetition-rate diode-pumped and intracavity frequency-doubled Nd:YAG laser is reported. A 3-mm-diameter laser rod was side-pumped with a 5-bar stack of high-duty-cycle 1-cm diodearrays. The average Q-switched power at 1.06microum was 3.8 W at 1.33 kH(z), and more than 4 W at 0.532 ,microm wasobtained through intracavity frequency doubling with LiB(3)O(5).

  1. Output-stabilized high-repetition-rate 1. 545-. mu. m Q-switched Er:glass laser

    SciTech Connect

    Morishige, Y.; Kishida, S.; Washio, K.; Toratani, H.; Nakawawa, M.

    1984-05-01

    A newly developed Q-switched Er:glass laser with a long pulse length, suitable for fiber-fault location is described. A specially prepared athermal rod has made it possible to operate at a 5-Hz repetition rate. A feedback-stabilized Q-switched method involving fluorescence monitoring has been applied to this three-level laser system. A +- 3% power stability (standard deviation) has been obtained for a 2-..mu..sec pulse with a 1-mJ output energy.

  2. High-peak-power, high-repetition-rate LD end-pumped Nd:YVO4 burst mode laser

    NASA Astrophysics Data System (ADS)

    Pan, Hu; Yan, Renpeng; Fa, Xin; Yu, Xin; Ma, Yufei; Fan, Rongwei; Li, Xudong; Chen, Deying; Zhou, Zhongxiang

    2016-06-01

    A compact high-peak-power, high-repetition-rate burst mode laser is achieved by an acousto-optical Q-switched Nd:YVO4 1064 nm laser directly pumped at 878.6 nm. Pulse trains with 10-100 pulses are obtained using acousto-optical Q-switch at repetition rates of 10-100 kHz under a pulsed pumping with a 1 ms duration. At the maximum pump energy of 108.5 mJ, the pulse energy of 10 kHz burst mode laser reaches 44 mJ corresponding to a single pulse energy of 4.4 mJ and an optical-to-optical efficiency of 40.5 %.The maximum peak power of ~468.1 kW at 10 kHz is obtained with a pulse width of 9.4 ns. The beam quality factor is measured to be M 2 ~1.5 and the pulse jitter is estimated to be less than 1 % in both amplitude and time region.

  3. Bright high-repetition-rate source of narrowband extreme-ultraviolet harmonics beyond 22 eV

    SciTech Connect

    Wang, He; Xu, Yiming; Ulonska, Stefan; Robinson, Joseph S.; Ranitovic, Predrag; Kaindl, Robert A.

    2015-06-11

    Novel table-top sources of extreme-ultraviolet light based on high-harmonic generation yield unique insight into the fundamental properties of molecules, nanomaterials or correlated solids, and enable advanced applications in imaging or metrology. Extending high-harmonic generation to high repetition rates portends great experimental benefits, yet efficient extreme-ultraviolet conversion of correspondingly weak driving pulses is challenging. In this article, we demonstrate a highly-efficient source of femtosecond extreme-ultraviolet pulses at 50-kHz repetition rate, utilizing the ultraviolet second-harmonic focused tightly into Kr gas. In this cascaded scheme, a photon flux beyond ≈3 × 1013 s-1 is generated at 22.3 eV, with 5 × 10-5 conversion efficiency that surpasses similar harmonics directly driven by the fundamental by two orders-of-magnitude. The enhancement arises from both wavelength scaling of the atomic dipole and improved spatio-temporal phase matching, confirmed by simulations. Finally, spectral isolation of a single 72-meV-wide harmonic renders this bright, 50-kHz extreme-ultraviolet source a powerful tool for ultrafast photoemission, nanoscale imaging and other applications.

  4. Bright high-repetition-rate source of narrowband extreme-ultraviolet harmonics beyond 22 eV

    PubMed Central

    Wang, He; Xu, Yiming; Ulonska, Stefan; Robinson, Joseph S.; Ranitovic, Predrag; Kaindl, Robert A.

    2015-01-01

    Novel table-top sources of extreme-ultraviolet light based on high-harmonic generation yield unique insight into the fundamental properties of molecules, nanomaterials or correlated solids, and enable advanced applications in imaging or metrology. Extending high-harmonic generation to high repetition rates portends great experimental benefits, yet efficient extreme-ultraviolet conversion of correspondingly weak driving pulses is challenging. Here, we demonstrate a highly-efficient source of femtosecond extreme-ultraviolet pulses at 50-kHz repetition rate, utilizing the ultraviolet second-harmonic focused tightly into Kr gas. In this cascaded scheme, a photon flux beyond ≈3 × 1013 s−1 is generated at 22.3 eV, with 5 × 10−5 conversion efficiency that surpasses similar harmonics directly driven by the fundamental by two orders-of-magnitude. The enhancement arises from both wavelength scaling of the atomic dipole and improved spatio-temporal phase matching, confirmed by simulations. Spectral isolation of a single 72-meV-wide harmonic renders this bright, 50-kHz extreme-ultraviolet source a powerful tool for ultrafast photoemission, nanoscale imaging and other applications. PMID:26067922

  5. Tests of photocathodes for high repetition rate x-ray FELs at the APEX facility at LBNL

    NASA Astrophysics Data System (ADS)

    Sannibale, Fernando; Filippetto, Daniele; Qian, Houjun; Papadopoulos, Christos F.; Wells, Russell; Kramasz, Toby; Padmore, Howard; Feng, Jun; Nasiatka, James; Huang, Ruixuan; Zolotorev, Max; Staples, John W.

    2015-05-01

    After the formidable results of X-ray 4th generation light sources based on free electron lasers around the world, a new revolutionary step is undergoing to extend the FEL performance from the present few hundred Hz to MHz-class repetition rates. In such facilities, temporally equi-spaced pulses will allow for a wide range of previously non-accessible experiments. The Advanced Photo-injector EXperiment (APEX) at the Lawrence Berkeley National Laboratory (LBNL), is devoted to test the capability of a novel scheme electron source, the VHF-Gun, to generate the required electron beam brightness at MHz repetition rates. In linac-based FELs, the ultimate performance in terms of brightness is defined at the injector, and in particular, cathodes play a major role in the game. Part of the APEX program consists in testing high quantum efficiency photocathodes capable to operate at the conditions required by such challenging machines. Results and status of these tests at LBNL are presented.

  6. Stabilization and phase control of femtosecond Ti:sapphire laser with a repetition rate of 90MHz

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Han, Hainian; Wang, Peng; Wei, Zhiyi

    2007-01-01

    Carrier-enveloped phase controlled femtosecond laser has an important application in the absolute frequency measurement, which lead to a revolutionary progress in the frequency metrology. In this paper we will report a high stable optical frequency comb based on a 90MHz repetition rate Ti:sapphire laser, by using a photonic crystal fiber to broaden octave spanning spectrum and a self-reference technology to measure the offset frequency f ceo, both the repetition rate f rep and f ceo are locked simultaneously to a cesium clock with phase lock loop (PLL) technology. For simultaneous stabilization of f rep and f ceo, two sets of phase-locked loop electronics are introduced to control separately the laser cavity length for f rep with a PZT and the pump laser for f ceo with an acoustic optics modulation (AOM) respectively. As the result, we stabilized the f rep at a fluctuation within the order of μHz, and f ceo is in the order of mHz, which support a frequency comb with an uncertainty of 10 -14.

  7. Non-metal elemental analysis by a compact low-energy high-repetition rate laser-induced-breakdown spectrometer

    NASA Astrophysics Data System (ADS)

    Wagner, Christian; Ewald, Johannes; Ankerhold, Georg; Kohns, Peter

    2009-06-01

    A compact laser-induced-breakdown-spectroscopy (LIBS) system for surface elemental analysis using a low-energy, high-repetition rate Nd:YAG laser as excitation source has been developed. Elemental analyses were performed on various samples including non-metallic compounds and metal alloys. Fluorine and chlorine could be detected well qualitatively in different organic materials like Teflon FEP (fluorinated ethylene propylene) or PVC (polyvinyl chloride). Furthermore, low concentrations of silicon, magnesium and copper in aluminum have been measured and could be backed up by EDX and XPS analysis. Results were confirmed with a conventional LIBS system using a high-energy, low-repetition rate Nd:YAG SHG laser operating at 10 Hz with a pulse energy of 200 mJ. Especially the results with fluorine containing samples are very promising and show that LIBS measurements of non-metallic samples are possible even at very low pulse energies with a manageable trade-off in signal strength.

  8. Fourier-transform spectroscopy using an Er-doped fiber femtosecond laser by sweeping the pulse repetition rate

    PubMed Central

    Lee, Keunwoo; Lee, Joohyung; Jang, Yoon-Soo; Han, Seongheum; Jang, Heesuk; Kim, Young-Jin; Kim, Seung-Woo

    2015-01-01

    Femtosecond lasers allow for simultaneous detection of multiple absorption lines of a specimen over a broad spectral range of infrared or visible light with a single spectroscopic measurement. Here, we present an 8-THz bandwidth, 0.5-GHz resolution scheme of Fourier-transform spectroscopy using an Er-doped fiber femtosecond laser. A resolving power of 1.6 × 104 about a 1560-nm center wavelength is achieved by sweeping the pulse repetition rate of the light source on a fiber Mach-Zehnder interferometer configured to capture interferograms with a 0.02-fs temporal sampling accuracy through a well-stabilized 60-m unbalance arm length. A dual-servo mechanism is realized by combining a mechanical linear stage with an electro-optic modulator (EOM) within the fiber laser cavity, enabling stable sweeping control of the pulse repetition rate over a 1.0-MHz scan range with 0.4-Hz steps with reference to the Rb clock. Experimental results demonstrate that the P-branch lines of the H13CN reference cell can be observed with a signal-to-noise ratio reaching 350 for the most intense line. PMID:26503257

  9. Filamentation effect in a gas attenuator for high-repetition-rate X-ray FELs

    SciTech Connect

    Feng, Yiping; Krzywinski, Jacek; Schafer, Donald W.; Ortiz, Eliazar; Rowen, Michael; Raubenheimer, Tor O.

    2016-01-01

    A sustained filamentation or density depression phenomenon in an argon gas attenuator servicing a high-repetition femtosecond X-ray free-electron laser has been studied using a finite-difference method applied to the thermal diffusion equation for an ideal gas. A steady-state solution was obtained by assuming continuous-wave input of an equivalent time-averaged beam power and that the pressure of the entire gas volume has reached equilibrium. Both radial and axial temperature/density gradients were found and describable as filamentation or density depression previously reported for a femtosecond optical laser of similar attributes. The effect exhibits complex dependence on the input power, the desired attenuation, and the geometries of the beam and the attenuator. Time-dependent simulations were carried out to further elucidate the evolution of the temperature/density gradients in between pulses, from which the actual attenuation received by any given pulse can be properly calculated.

  10. The Role of Pulse Repetition Rate in nsPEF-Induced Electroporation: A Biological and Numerical Investigation.

    PubMed

    Lamberti, Patrizia; Romeo, Stefania; Sannino, Anna; Zeni, Luigi; Zeni, Olga

    2015-09-01

    The impact of pulse repetition rate (PRR) in modulating electroporation (EP) induced by nanosecond pulsed electric fields (nsPEFs) in mammalian cells was approached here by performing both biological and numerical analysis. Plasma membrane permeabilization and viability of Jurkat cells were analyzed after exposure to 500, 1.3 MV/m, 40 ns PEFs with variable PRR (2-30 Hz). A finite-element model was used to investigate EP dynamics in a single cell under the same pulsing conditions, by looking at the time course of transmembrane voltage and pore density on the ns time scale. The biological observations showed an increased EP and reduced viability of the exposed cells at lower PRR in the considered range. The numerical analysis resulted in different dynamics of plasma membrane response when ns pulses were delivered with different PRR, consistently with a phenomenon of electrodesensitization recently hypothesized by another research group. PMID:25850084

  11. Low drift cw-seeded high-repetition-rate optical parametric amplifier for fingerprint coherent Raman spectroscopy.

    PubMed

    Krauth, Joachim; Steinle, Tobias; Liu, Bowen; Floess, Moritz; Linnenbank, Heiko; Steinmann, Andy; Giessen, Harald

    2016-09-19

    We introduce a broadly tunable robust source for fingerprint (170 - 1620 cm-1) Raman spectroscopy. A cw thulium-doped fiber laser seeds an optical parametric amplifier, which is pumped by a 7-W, 450-fs Yb:KGW bulk mode-locked oscillator with 41 MHz repetition rate. The output radiation is frequency doubled in a MgO:PPLN crystal and generates 0.7 - 1.3-ps-long narrowband pump pulses that are tunable between 885 and 1015 nm with >80 mW average power. The Stokes beam is delivered by a part of the oscillator output, which is sent through an etalon to create pulses with 1.7 ps duration. We demonstrate a stimulated Raman gain measurement of toluene in the fingerprint spectral range. The cw seeding intrinsically ensures low spectral drift. PMID:27661963

  12. Application of a high-repetition-rate laser diagnostic system for single-cycle-resolved imaging in internal combustion engines.

    PubMed

    Hult, Johan; Richter, Mattias; Nygren, Jenny; Aldén, Marcus; Hultqvist, Anders; Christensen, Magnus; Johansson, Bengt

    2002-08-20

    High-repetition-rate laser-induced fluorescence measurements of fuel and OH concentrations in internal combustion engines are demonstrated. Series of as many as eight fluorescence images, with a temporal resolution ranging from 10 micros to 1 ms, are acquired within one engine cycle. A multiple-laser system in combination with a multiple-CCD camera is used for cycle-resolved imaging in spark-ignition, direct-injection stratified-charge, and homogeneous-charge compression-ignition engines. The recorded data reveal unique information on cycle-to-cycle variations in fuel transport and combustion. Moreover, the imaging system in combination with a scanning mirror is used to perform instantaneous three-dimensional fuel-concentration measurements.

  13. Time-gated single-photon detection module with 110 ps transition time and up to 80 MHz repetition rate

    SciTech Connect

    Buttafava, Mauro Boso, Gianluca; Ruggeri, Alessandro; Tosi, Alberto; Dalla Mora, Alberto

    2014-08-15

    We present the design and characterization of a complete single-photon counting module capable of time-gating a silicon single-photon avalanche diode with ON and OFF transition times down to 110 ps, at repetition rates up to 80 MHz. Thanks to this sharp temporal filtering of incoming photons, it is possible to reject undesired strong light pulses preceding (or following) the signal of interest, allowing to increase the dynamic range of optical acquisitions up to 7 decades. A complete experimental characterization of the module highlights its very flat temporal response, with a time resolution of the order of 30 ps. The instrument is fully user-configurable via a PC interface and can be easily integrated in any optical setup, thanks to its small and compact form factor.

  14. High repetition rate laser induced fluorescence applied to Surfatron Induced Plasmas

    NASA Astrophysics Data System (ADS)

    van der Mullen, J. J. A. M.; Palomares, J. M.; Carbone, E. A. D.; Graef, W.; Hübner, S.

    2012-05-01

    The reaction kinetics in the excitation space of Ar and the conversion space of Ar-molecule mixtures are explored using a combination of high rep-rate YAG-Dye laser systems with a well defined and easily controllable Surfatron Induced Plasma set-up. Applying the method of Saturation Time Resolved Laser Induced Fluorescence (SaTiRe-LIF), we could trace excitation and conversion channels and determine rates of electron and heavy particle excitation kinetics. The time resolved density disturbances observed in the Ar excitation space, which are initiated by the laser, reveal the excitation channels and corresponding rates; responses of the molecular radiation in Ar-molecule mixtures corresponds to the presence of conversion processes induced by heavy particle excitation kinetics.

  15. Generation of tunable, high repetition rate frequency combs with equalized spectra using carrier injection based silicon modulators

    NASA Astrophysics Data System (ADS)

    Nagarjun, K. P.; Selvaraja, Shankar Kumar; Supradeepa, V. R.

    2016-03-01

    High repetition-rate frequency combs with tunable repetition rate and carrier frequency are extensively used in areas like Optical communications, Microwave Photonics and Metrology. A common technique for their generation is strong phase modulation of a CW-laser. This is commonly implemented using Lithium-Niobate based modulators. With phase modulation alone, the combs have poor spectral flatness and significant number of missing lines. To overcome this, a complex cascade of multiple intensity and phase modulators are used. A comb generator on Silicon based on these principles is desirable to enable on-chip integration with other functionalities while reducing power consumption and footprint. In this work, we analyse frequency comb generation in carrier injection based Silicon modulators. We observe an interesting effect in these comb generators. Enhanced absorption accompanying carrier injection, an undesirable effect in data modulators, shapes the amplitude here to enable high quality combs from a single modulator. Thus, along with reduced power consumption to generate a specific number of lines, the complexity has also been significantly reduced. We use a drift-diffusion solver and mode solver (Silvaco TCAD) along with Soref-Bennett relations to calculate the variations in refractive indices and absorption of an optimized Silicon PIN - waveguide modulator driven by an unbiased high frequency (10 Ghz) voltage signal. Our simulations demonstrate that with a device length of 1 cm, a driving voltage of 2V and minor shaping with a passive ring-resonator filter, we obtain 37 lines with a flatness better than 5-dB across the band and power consumption an order of magnitude smaller than Lithium-Niobate modulators.

  16. Scattering-type scanning near-field optical microscopy with low-repetition-rate pulsed light source through phase-domain sampling

    NASA Astrophysics Data System (ADS)

    Wang, Haomin; Wang, Le; Xu, Xiaoji G.

    2016-10-01

    Scattering-type scanning near-field optical microscopy (s-SNOM) allows spectroscopic imaging with spatial resolution below the diffraction limit. With suitable light sources, s-SNOM is instrumental in numerous discoveries at the nanoscale. So far, the light sources have been limited to continuous wave or high-repetition-rate pulsed lasers. Low-repetition-rate pulsed sources cannot be used, due to the limitation of the lock-in detection mechanism that is required for current s-SNOM techniques. Here, we report a near-field signal extraction method that enables low-repetition-rate pulsed light sources. The method correlates scattering signals from pulses with the mechanical phases of the oscillating s-SNOM probe to obtain near-field signal, by-passing the apparent restriction imposed by the Nyquist-Shannon sampling theorem on the repetition rate. The method shall enable s-SNOM with low-repetition-rate pulses with high-peak-powers, such as femtosecond laser amplifiers, to facilitate investigations of strong light-matter interactions and nonlinear processes at the nanoscale.

  17. Effect of laser annealing using high repetition rate pulsed laser on optical properties of phosphorus-ion-implanted ZnO nanorods

    NASA Astrophysics Data System (ADS)

    Shimogaki, Tetsuya; Ofuji, Taihei; Tetsuyama, Norihiro; Okazaki, Kota; Higashihata, Mitsuhiro; Nakamura, Daisuke; Ikenoue, Hiroshi; Asano, Tanemasa; Okada, Tatsuo

    2013-03-01

    The effect of high repetition rate pulsed laser annealing with a KrF excimer laser on the optical properties of phosphorus-ion-implanted zinc oxide nanorods has been investigated. The recovery levels of phosphorus-ion-implanted zinc oxide nanorods have been measured by photoluminescence spectra and cathode luminescence images. Cathode luminescence disappeared over 300 nm below the surface due to the damage caused by ion implantation with an acceleration voltage of 25 kV. When the annealing was performed at a low repetition rate of the KrF excimer laser, cathode luminescence was recovered only in a shallow area below the surface. The depth of the annealed area was increased along with the repetition rate of the annealing laser. By optimizing the annealing conditions such as the repetition rate, the irradiation fluence and so on, we have succeeded in annealing the whole damaged area of over 300 nm in depth and in observing cathode luminescence. Thus, the effectiveness of high repetition rate pulsed laser annealing on phosphorus-ion-implanted zinc oxide nanorods was demonstrated.

  18. Effect of laser annealing using high repetition rate pulsed laser on optical properties of phosphorus-ion-implanted ZnO nanorods

    NASA Astrophysics Data System (ADS)

    Shimogaki, Tetsuya; Ofuji, Taihei; Tetsuyama, Norihiro; Okazaki, Kota; Higashihata, Mitsuhiro; Nakamura, Daisuke; Ikenoue, Hiroshi; Asano, Tanemasa; Okada, Tatsuo

    2014-02-01

    The effect of high repetition rate pulsed laser annealing with a KrF excimer laser on the optical properties of phosphorus-ion-implanted zinc oxide nanorods has been investigated. The recovery levels of phosphorus-ion-implanted zinc oxide nanorods have been measured by photoluminescence spectra and cathode luminescence images. Cathode luminescence disappeared over 300 nm below the surface due to the damage caused by ion implantation with an acceleration voltage of 25 kV. When the annealing was performed at a low repetition rate of the KrF excimer laser, cathode luminescence was recovered only in a shallow area below the surface. The depth of the annealed area was increased along with the repetition rate of the annealing laser. By optimizing the annealing conditions such as the repetition rate, the irradiation fluence and so on, we have succeeded in annealing the whole damaged area of over 300 nm in depth and in observing cathode luminescence. Thus, the effectiveness of high repetition rate pulsed laser annealing on phosphorus-ion-implanted zinc oxide nanorods was demonstrated.

  19. Scattering-type scanning near-field optical microscopy with low-repetition-rate pulsed light source through phase-domain sampling

    PubMed Central

    Wang, Haomin; Wang, Le; Xu, Xiaoji G.

    2016-01-01

    Scattering-type scanning near-field optical microscopy (s-SNOM) allows spectroscopic imaging with spatial resolution below the diffraction limit. With suitable light sources, s-SNOM is instrumental in numerous discoveries at the nanoscale. So far, the light sources have been limited to continuous wave or high-repetition-rate pulsed lasers. Low-repetition-rate pulsed sources cannot be used, due to the limitation of the lock-in detection mechanism that is required for current s-SNOM techniques. Here, we report a near-field signal extraction method that enables low-repetition-rate pulsed light sources. The method correlates scattering signals from pulses with the mechanical phases of the oscillating s-SNOM probe to obtain near-field signal, by-passing the apparent restriction imposed by the Nyquist–Shannon sampling theorem on the repetition rate. The method shall enable s-SNOM with low-repetition-rate pulses with high-peak-powers, such as femtosecond laser amplifiers, to facilitate investigations of strong light–matter interactions and nonlinear processes at the nanoscale. PMID:27748360

  20. Implementation of time-resolved step-scan fourier transform infrared (FT-IR) spectroscopy using a kHz repetition rate pump laser.

    PubMed

    Magana, Donny; Parul, Dzmitry; Dyer, R Brian; Shreve, Andrew P

    2011-05-01

    Time-resolved step-scan Fourier transform infrared (FT-IR) spectroscopy has been shown to be invaluable for studying excited-state structures and dynamics in both biological and inorganic systems. Despite the established utility of this method, technical challenges continue to limit the data quality and more wide ranging applications. A critical problem has been the low laser repetition rate and interferometer stepping rate (both are typically 10 Hz) used for data acquisition. Here we demonstrate significant improvement in the quality of time-resolved spectra through the use of a kHz repetition rate laser to achieve kHz excitation and data collection rates while stepping the spectrometer at 200 Hz. We have studied the metal-to-ligand charge transfer excited state of Ru(bipyridine)(3)Cl(2) in deuterated acetonitrile to test and optimize high repetition rate data collection. Comparison of different interferometer stepping rates reveals an optimum rate of 200 Hz due to minimization of long-term baseline drift. With the improved collection efficiency and signal-to-noise ratio, better assignments of the MLCT excited-state bands can be made. Using optimized parameters, carbonmonoxy myoglobin in deuterated buffer is also studied by observing the infrared signatures of carbon monoxide photolysis upon excitation of the heme. We conclude from these studies that a substantial increase in performance of ss-FT-IR instrumentation is achieved by coupling commercial infrared benches with kHz repetition rate lasers.

  1. Efficient generation of twin photons at telecom wavelengths with 2.5 GHz repetition-rate-tunable comb laser.

    PubMed

    Jin, Rui-Bo; Shimizu, Ryosuke; Morohashi, Isao; Wakui, Kentaro; Takeoka, Masahiro; Izumi, Shuro; Sakamoto, Takahide; Fujiwara, Mikio; Yamashita, Taro; Miki, Shigehito; Terai, Hirotaka; Wang, Zhen; Sasaki, Masahide

    2014-01-01

    Efficient generation and detection of indistinguishable twin photons are at the core of quantum information and communications technology (Q-ICT). These photons are conventionally generated by spontaneous parametric down conversion (SPDC), which is a probabilistic process, and hence occurs at a limited rate, which restricts wider applications of Q-ICT. To increase the rate, one had to excite SPDC by higher pump power, while it inevitably produced more unwanted multi-photon components, harmfully degrading quantum interference visibility. Here we solve this problem by using recently developed 10 GHz repetition-rate-tunable comb laser, combined with a group-velocity-matched nonlinear crystal, and superconducting nanowire single photon detectors. They operate at telecom wavelengths more efficiently with less noises than conventional schemes, those typically operate at visible and near infrared wavelengths generated by a 76 MHz Ti Sapphire laser and detected by Si detectors. We could show high interference visibilities, which are free from the pump-power induced degradation. Our laser, nonlinear crystal, and detectors constitute a powerful tool box, which will pave a way to implementing quantum photonics circuits with variety of good and low-cost telecom components, and will eventually realize scalable Q-ICT in optical infra-structures. PMID:25524646

  2. Dynamic absorption and scattering of water and hydrogel during high-repetition-rate (>100 MHz) burst-mode ultrafast-pulse laser ablation.

    PubMed

    Qian, Zuoming; Covarrubias, Andrés; Grindal, Alexander W; Akens, Margarete K; Lilge, Lothar; Marjoribanks, Robin S

    2016-06-01

    High-repetition-rate burst-mode ultrafast-laser ablation and disruption of biological tissues depends on interaction of each pulse with the sample, but under those particular conditions which persist from previous pulses. This work characterizes and compares the dynamics of absorption and scattering of a 133-MHz repetition-rate, burst-mode ultrafast-pulse laser, in agar hydrogel targets and distilled water. The differences in energy partition are quantified, pulse-by-pulse, using a time-resolving integrating-sphere-based device. These measurements reveal that high-repetition-rate burst-mode ultrafast-laser ablation is a highly dynamical process affected by the persistence of ionization, dissipation of plasma plume, neutral material flow, tissue tensile strength, and the hydrodynamic oscillation of cavitation bubbles. PMID:27375948

  3. Dynamic absorption and scattering of water and hydrogel during high-repetition-rate (>100 MHz) burst-mode ultrafast-pulse laser ablation

    PubMed Central

    Qian, Zuoming; Covarrubias, Andrés; Grindal, Alexander W.; Akens, Margarete K.; Lilge, Lothar; Marjoribanks, Robin S.

    2016-01-01

    High-repetition-rate burst-mode ultrafast-laser ablation and disruption of biological tissues depends on interaction of each pulse with the sample, but under those particular conditions which persist from previous pulses. This work characterizes and compares the dynamics of absorption and scattering of a 133-MHz repetition-rate, burst-mode ultrafast-pulse laser, in agar hydrogel targets and distilled water. The differences in energy partition are quantified, pulse-by-pulse, using a time-resolving integrating-sphere-based device. These measurements reveal that high-repetition-rate burst-mode ultrafast-laser ablation is a highly dynamical process affected by the persistence of ionization, dissipation of plasma plume, neutral material flow, tissue tensile strength, and the hydrodynamic oscillation of cavitation bubbles. PMID:27375948

  4. Femtosecond laser bone ablation with a high repetition rate fiber laser source

    PubMed Central

    Mortensen, Luke J.; Alt, Clemens; Turcotte, Raphaël; Masek, Marissa; Liu, Tzu-Ming; Côté, Daniel C.; Xu, Chris; Intini, Giuseppe; Lin, Charles P.

    2014-01-01

    Femtosecond laser pulses can be used to perform very precise cutting of material, including biological samples from subcellular organelles to large areas of bone, through plasma-mediated ablation. The use of a kilohertz regenerative amplifier is usually needed to obtain the pulse energy required for ablation. This work investigates a 5 megahertz compact fiber laser for near-video rate imaging and ablation in bone. After optimization of ablation efficiency and reduction in autofluorescence, the system is demonstrated for the in vivo study of bone regeneration. Image-guided creation of a bone defect and longitudinal evaluation of cellular injury response in the defect provides insight into the bone regeneration process. PMID:25657872

  5. High repetition rate relativistic electron beam generation from intense laser solid interactions

    NASA Astrophysics Data System (ADS)

    Batson, Thomas; Nees, John; Hou, Bixue; Thomas, Alexander; Krushelnick, Karl

    2014-10-01

    Relativistic electron beams have wide-ranging applications in medicine, materials science, and homeland security. Recent advances in short pulse laser technology have enabled the production of very high focused intensities at kHz rep rates. Consequently this has led to the generation of high flux sources of relativistic electrons - which is a necessary characteristic of these laser plasma sources for any potential application. In our experiments, through the generation of a plasma by focusing a 5 × 1018 W/cm2, 500 Hz, Ti:Sapphire laser pulse onto a fused silica target, we have measured electrons ejected from the target surface having energies in excess of an MeV. The spectrum of these electrons, as well as the spatial divergence of the resulting beam, was also measured with respect to incident laser angle, prepulse timing and focusing conditions. The experimental results are compared to particle in cell simulations.

  6. High-average-power 2 μm few-cycle optical parametric chirped pulse amplifier at 100 kHz repetition rate.

    PubMed

    Shamir, Yariv; Rothhardt, Jan; Hädrich, Steffen; Demmler, Stefan; Tschernajew, Maxim; Limpert, Jens; Tünnermann, Andreas

    2015-12-01

    Sources of long wavelengths few-cycle high repetition rate pulses are becoming increasingly important for a plethora of applications, e.g., in high-field physics. Here, we report on the realization of a tunable optical parametric chirped pulse amplifier at 100 kHz repetition rate. At a central wavelength of 2 μm, the system delivered 33 fs pulses and a 6 W average power corresponding to 60 μJ pulse energy with gigawatt-level peak powers. Idler absorption and its crystal heating is experimentally investigated for a BBO. Strategies for further power scaling to several tens of watts of average power are discussed.

  7. High-average-power 2 μm few-cycle optical parametric chirped pulse amplifier at 100 kHz repetition rate.

    PubMed

    Shamir, Yariv; Rothhardt, Jan; Hädrich, Steffen; Demmler, Stefan; Tschernajew, Maxim; Limpert, Jens; Tünnermann, Andreas

    2015-12-01

    Sources of long wavelengths few-cycle high repetition rate pulses are becoming increasingly important for a plethora of applications, e.g., in high-field physics. Here, we report on the realization of a tunable optical parametric chirped pulse amplifier at 100 kHz repetition rate. At a central wavelength of 2 μm, the system delivered 33 fs pulses and a 6 W average power corresponding to 60 μJ pulse energy with gigawatt-level peak powers. Idler absorption and its crystal heating is experimentally investigated for a BBO. Strategies for further power scaling to several tens of watts of average power are discussed. PMID:26625047

  8. Multi-GHz bandpass, high-repetition rate single channel mobile diagnostic system for ultra-wideband applications

    NASA Astrophysics Data System (ADS)

    Miner, Lynn M.; Voss, Donald E.

    1993-01-01

    Characterizing radiated ultra-wideband (UWB) signals poses challenges due to requirements for (1) multi-GHz bandpass recording of the signal's leading edge; (2) GHz-bandpass recording of long record lengths (10s-100s of ns); and (3) determining shot-to-shot reproducibility at rep-rates exceeding 10 kHz. The System Verification Apparatus (SVA) is a novel diagnostic system which can measure 60-ps rise-time signals on a single-shot basis, while monitoring pulse-to-pulse variation. The fully-integrated SVA includes a broadband sensor, signal and trigger conditioning electronics, multiple parallel digitizers with deep local storge, and automated software for acquiring, archiving, and analyzing waveform data with rapid (secs-minute) turnaround time. The instruments are housed in a portable 100-dB shielded aluminum enclosure. The SVA utilizes a 6-GHz bandpass free-field D-dot sensor to measure the incident electric field. Three separate digitizers together meet the requirements of high bandwidth, long record length, and high repetition rate. A 6-GHz bandpass scan converter digitizer captures the leading edge (few ns) of the radiated signal. 1-GHz and 600 MHz bandwidth solid-state digitizers supporting long record lengths (greater than 2 micrometers) record the balance of the signal, which typically contains negligible content above 1 GHz. These solid-state digitizers can store greater than 900 waveforms locally at rep-rates exceeding 65 Hz and 100 kHz, respectively. Data management and instrument control use an 80486-based PC, operating in a user-friendly Windows environment. All waveform and system configuration data are automatically stored in a built-in database. A fiber-optic link, up to 2 km long, provides electromagnetic isolation of the computer.

  9. Synthesis, characterization and evaluation of CO-oxidation catalysts for high repetition rate CO2 TEA lasers

    NASA Technical Reports Server (NTRS)

    Moser, Thomas P.

    1990-01-01

    An extremely active class of noble metal catalysts supported on titania was developed and fabricated at Hughes for the recombination of oxygen (O2) and carbon monoxide (CO) in closed-cycle CO2 TEA lasers. The incipient wetness technique was used to impregnate titania and alumina pellets with precious metals including platinum and palladium. In particular, the addition of cerium (used as an oxygen storage promoter) produced an extremely active Pt/Ce/TiO2 catalyst. By comparison, the complementary Pt/Ce/ gamma-Al2O3 catalyst was considerably less active. In general, chloride-free catalyst precursors proved critical in obtaining an active catalyst while also providing uniform metal distributions throughout the support structure. Detailed characterization of the Pt/Ce/TiO2 catalyst demonstrated uniform dendritic crystal growth of the metals throughout the support. Electron spectroscopy for Chemical Analysis (ESCA) analysis was used to characterize the oxidation states of Pt, Ce and Ti. The performance of the catalysts was evaluated with an integral flow reactor system incorporating real time analysis of O2 and CO. With this system, the transient and steady-state behavior of the catalysts were evaluated. The kinetic evaluation was complemented by tests in a compact, closed-cycle Hughes CO2 TEA laser operating at a pulse repetition rate of 100 Hz with a catalyst temperature of 75 to 95 C. The Pt/Ce/TiO2 catalyst was compatible with a C(13)O(16)2 gas fill.

  10. Reduction of edge-localized mode intensity using high-repetition-rate pellet injection in tokamak H-mode plasmas.

    PubMed

    Baylor, L R; Commaux, N; Jernigan, T C; Brooks, N H; Combs, S K; Evans, T E; Fenstermacher, M E; Isler, R C; Lasnier, C J; Meitner, S J; Moyer, R A; Osborne, T H; Parks, P B; Snyder, P B; Strait, E J; Unterberg, E A; Loarte, A

    2013-06-14

    High repetition rate injection of deuterium pellets from the low-field side (LFS) of the DIII-D tokamak is shown to trigger high-frequency edge-localized modes (ELMs) at up to 12× the low natural ELM frequency in H-mode deuterium plasmas designed to match the ITER baseline configuration in shape, normalized beta, and input power just above the H-mode threshold. The pellet size, velocity, and injection location were chosen to limit penetration to the outer 10% of the plasma. The resulting perturbations to the plasma density and energy confinement time are thus minimal (<10%). The triggered ELMs occur at much lower normalized pedestal pressure than the natural ELMs, suggesting that the pellet injection excites a localized high-n instability. Triggered ELMs produce up to 12× lower energy and particle fluxes to the divertor, and result in a strong decrease in plasma core impurity density. These results show for the first time that shallow, LFS pellet injection can dramatically accelerate the ELM cycle and reduce ELM energy fluxes on plasma facing components, and is a viable technique for real-time control of ELMs in ITER.

  11. A Compact, Transportable, Microchip-Based System for High Repetition Rate Production of Bose-Einstein Condensates

    NASA Astrophysics Data System (ADS)

    Farkas, Daniel; Hudek, Kai; Salim, Evan; Segal, Stephen; Anderson, Dana

    2010-03-01

    We present a compact, transportable system that produces Bose-Einstein condensates (BECs) near the surface of an integrated atom microchip. Occupying a volume of 0.4 m^3 and consuming an average power of 525 W, the system contains all of the components needed to produce and image BECs, including an ultra-high vacuum system, lasers, data acquisition hardware, electronics, and imaging equipment. RF evaporative cooling forms nearly-pure condensates containing 1.9x10^4 ^87Rb atoms in the |F=2,mF=+2> ground hyperfine state. With trap frequencies of several kHz, evaporative cooling times as short as 1.5 s have been used to create BECs, resulting in production repetition rates as high as 0.3 Hz. The system can be easily reconfigured for use with atom chips having wire patterns designed for different applications. As such, it can serve as a standardized platform for a variety of portable experiments that utilize ultracold matter.

  12. Power, pulse width, and repetition rate agile low-cost multi-spectral semi-active laser simulator

    NASA Astrophysics Data System (ADS)

    O'Daniel, Jason K.; Young, Preston; Golden, Eric; Barton, Robert; Snyder, Donald

    2010-04-01

    The emergence of spectrally multimode smart missiles requires hardware-in-the-loop (HWIL) facilities to simulate multiple spectral signatures simultaneously. While traditional diode-pumped solid-state (DPSS) sources provide a great basic testing source for smart missiles, they typically are bulky and provide substantially more power peak power than what is required for laboratory simulation, have fixed pulse widths, and require some external means to attenuate the output power. HWIL facilities require systems capable of high speed variability of the angular divergence and optical intensity over several orders of magnitude, which is not typically provided by basic DPSS systems. In order to meet the needs of HWIL facilities, we present a low-cost semi-active laser (SAL) simulator source using laser diode sources that emits laser light at the critical wavelengths of 1064 nm and 1550 nm, along with light in the visible for alignment, from a single fiber aperture. Fiber delivery of the multi-spectral output can provide several advantages depending on the testing setup. The SAL simulator source presented is capable of providing attenuation of greater than 70 dB with a response time of a few milliseconds and provides a means to change the angular divergence over an entire dynamic range of 0.02- 6º in less than 400 ms. Further, the SAL simulator is pulse width and pulse repetition rate agile making it capable of producing both current and any future coding format necessary.

  13. Low-repetition rate femtosecond laser writing of optical waveguides in KTP crystals: analysis of anisotropic refractive index changes.

    PubMed

    Butt, Muhammad Ali; Nguyen, Huu-Dat; Ródenas, Airán; Romero, Carolina; Moreno, Pablo; Vázquez de Aldana, Javier R; Aguiló, Magdalena; Solé, Rosa Maria; Pujol, Maria Cinta; Díaz, Francesc

    2015-06-15

    We report on the direct low-repetition rate femtosecond pulse laser microfabrication of optical waveguides in KTP crystals and the characterization of refractive index changes after the thermal annealing of the sample, with the focus on studying the potential for direct laser fabricating Mach-Zehnder optical modulators. We have fabricated square cladding waveguides by means of stacking damage tracks, and found that the refractive index decrease is large for vertically polarized light (c-axis; TM polarized) but rather weak for horizontally polarized light (a-axis; TE polarized), this leading to good near-infrared light confinement for TM modes but poor for TE modes. However, after performing a sample thermal annealing we have found that the thermal process enables a refractive index increment of around 1.5x10(-3) for TE polarized light, while maintaining the negative index change of around -1x10(-2) for TM polarized light. In order to evaluate the local refractive index changes we have followed a multistep procedure: We have first characterized the waveguide cross-sections by means of Raman micro-mapping to access the lattice micro-modifications and their spatial extent. Secondly we have modeled the waveguides following the modified region sizes obtained by micro-Raman with finite element method software to obtain a best match between the experimental propagation modes and the simulated ones. Furthermore we also report the fabrication of Mach-Zehnder structures and the evaluation of propagation losses. PMID:26193514

  14. Thermoelastic study of nanolayered structures using time-resolved X-ray diffraction at high repetition rate

    SciTech Connect

    Navirian, H. A.; Schick, D. Leitenberger, W.; Bargheer, M.; Gaal, P.; Shayduk, R.

    2014-01-13

    We investigate the thermoelastic response of a nanolayered sample composed of a metallic SrRuO{sub 3} electrode sandwiched between a ferroelectric Pb(Zr{sub 0.2}Ti{sub 0.8})O{sub 3} film with negative thermal expansion and a SrTiO{sub 3} substrate. SrRuO{sub 3} is rapidly heated by fs-laser pulses with 208 kHz repetition rate. Diffraction of X-ray pulses derived from a synchrotron measures the transient out-of-plane lattice constant c of all three materials simultaneously from 120 ps to 5 μs with a relative accuracy up to Δc/c = 10{sup −6}. The in-plane propagation of sound is essential for understanding the delayed out-of-plane compression of Pb(Zr{sub 0.2}Ti{sub 0.8})O{sub 3}.

  15. Low-repetition rate femtosecond laser writing of optical waveguides in KTP crystals: analysis of anisotropic refractive index changes.

    PubMed

    Butt, Muhammad Ali; Nguyen, Huu-Dat; Ródenas, Airán; Romero, Carolina; Moreno, Pablo; Vázquez de Aldana, Javier R; Aguiló, Magdalena; Solé, Rosa Maria; Pujol, Maria Cinta; Díaz, Francesc

    2015-06-15

    We report on the direct low-repetition rate femtosecond pulse laser microfabrication of optical waveguides in KTP crystals and the characterization of refractive index changes after the thermal annealing of the sample, with the focus on studying the potential for direct laser fabricating Mach-Zehnder optical modulators. We have fabricated square cladding waveguides by means of stacking damage tracks, and found that the refractive index decrease is large for vertically polarized light (c-axis; TM polarized) but rather weak for horizontally polarized light (a-axis; TE polarized), this leading to good near-infrared light confinement for TM modes but poor for TE modes. However, after performing a sample thermal annealing we have found that the thermal process enables a refractive index increment of around 1.5x10(-3) for TE polarized light, while maintaining the negative index change of around -1x10(-2) for TM polarized light. In order to evaluate the local refractive index changes we have followed a multistep procedure: We have first characterized the waveguide cross-sections by means of Raman micro-mapping to access the lattice micro-modifications and their spatial extent. Secondly we have modeled the waveguides following the modified region sizes obtained by micro-Raman with finite element method software to obtain a best match between the experimental propagation modes and the simulated ones. Furthermore we also report the fabrication of Mach-Zehnder structures and the evaluation of propagation losses.

  16. Intense high repetition rate Mo Kα x-ray source generated from laser solid interaction for imaging application

    SciTech Connect

    Huang, K.; Li, M. H.; Yan, W. C.; Ma, Y.; Zhao, J. R.; Li, Y. F.; Chen, L. M.; Guo, X.; Li, D. Z.; Chen, Y. P.; Zhang, J.

    2014-11-15

    We report an efficient Mo Kα x-ray source produced by interaction of femtosecond Ti: sapphire laser pulses with a solid Molybdenum target working at 1 kHz repetition rate. The generated Mo Kα x-ray intensity reaches to 4.7 × 10{sup 10} photons sr{sup −1} s{sup −1}, corresponding to an average power of 0.8 mW into 2π solid angle. The spatial resolution of this x-ray source is measured to be 26 lp/mm. With the high flux and high spatial resolution characteristics, high resolving in-line x-ray radiography was realized on test objects and large size biological samples within merely half a minute. This experiment shows the possibility of laser plasma hard x-ray source as a new low cost and high resolution system for radiography and its ability of ultrafast x-ray pump-probe study of matter.

  17. Synthesis, characterization and evaluation of CO-oxidation catalysts for high repetition rate CO2 TEA lasers

    NASA Astrophysics Data System (ADS)

    Moser, Thomas P.

    1990-06-01

    An extremely active class of noble metal catalysts supported on titania was developed and fabricated at Hughes for the recombination of oxygen (O2) and carbon monoxide (CO) in closed-cycle CO2 TEA lasers. The incipient wetness technique was used to impregnate titania and alumina pellets with precious metals including platinum and palladium. In particular, the addition of cerium (used as an oxygen storage promoter) produced an extremely active Pt/Ce/TiO2 catalyst. By comparison, the complementary Pt/Ce/ gamma-Al2O3 catalyst was considerably less active. In general, chloride-free catalyst precursors proved critical in obtaining an active catalyst while also providing uniform metal distributions throughout the support structure. Detailed characterization of the Pt/Ce/TiO2 catalyst demonstrated uniform dendritic crystal growth of the metals throughout the support. Electron spectroscopy for Chemical Analysis (ESCA) analysis was used to characterize the oxidation states of Pt, Ce and Ti. The performance of the catalysts was evaluated with an integral flow reactor system incorporating real time analysis of O2 and CO. With this system, the transient and steady-state behavior of the catalysts were evaluated. The kinetic evaluation was complemented by tests in a compact, closed-cycle Hughes CO2 TEA laser operating at a pulse repetition rate of 100 Hz with a catalyst temperature of 75 to 95 C. The Pt/Ce/TiO2 catalyst was compatible with a C(13)O(16)2 gas fill.

  18. Laser driven nuclear science and applications: The need of high efficiency, high power and high repetition rate Laser beams

    NASA Astrophysics Data System (ADS)

    Gales, S.

    2015-10-01

    Extreme Light Infrastructure (ELI) is a pan European research initiative selected on the European Strategy Forum on Research Infrastructures Roadmap that aims to close the gap between the existing laboratory-based laser driven research and international facility-grade research centre. The ELI-NP facility, one of the three ELI pillars under construction, placed in Romania and to be operational in 2018, has as core elements a couple of new generation 10 PW laser systems and a narrow bandwidth Compton backscattering gamma source with photon energies up to 19 MeV. ELI-NP will address nuclear photonics, nuclear astrophysics and quantum electrodynamics involving extreme photon fields. Prospective applications of high power laser in nuclear astrophysics, accelerator physics, in particular towards future Accelerator Driven System, as well as in nuclear photonics, for detection and characterization of nuclear material, and for nuclear medicine, will be discussed. Key issues in these research areas will be at reach with significant increase of the repetition rates and of the efficiency at the plug of the high power laser systems as proposed by the ICAN collaboration.

  19. 500 MW peak power degenerated optical parametric amplifier delivering 52 fs pulses at 97 kHz repetition rate.

    PubMed

    Rothhardt, J; Hädrich, S; Röser, F; Limpert, J; Tünnermann, A

    2008-06-01

    We present a high peak power degenerated parametric amplifier operating at 1030 nm and 97 kHz repetition rate. Pulses of a state-of-the art fiber chirped-pulse amplification (FCPA) system with 840 fs pulse duration and 410 microJ pulse energy are used as pump and seed source for a two stage optical parametric amplifier. Additional spectral broadening of the seed signal in a photonic crystal fiber creates enough bandwidth for ultrashort pulse generation. Subsequent amplification of the broadband seed signal in two 1 mm BBO crystals results in 41 microJ output pulse energy. Compression in a SF 11 prism compressor yields 37 microJ pulses as short as 52 fs. Thus, pulse shortening of more than one order of magnitude is achieved. Further scaling in terms of average power and pulse energy seems possible and will be discussed, since both concepts involved, the fiber laser and the parametric amplifier have the reputation to be immune against thermo-optical effects.

  20. 100 Repetitions

    ERIC Educational Resources Information Center

    Benson, Jeffrey

    2012-01-01

    One hundred repetitions--100 "useful" repetitions. This notion has guided the author's work in alternative education programs for almost 20 years, dealing with the most challenging students, from addicts to conduct-disordered adolescents to traumatized 5th graders. There are no magic tricks. The role of educators is to align with the healthy…

  1. Confirmation of gravitationally induced attitude drift of spinning satellite Ajisai with Graz high repetition rate SLR data

    NASA Astrophysics Data System (ADS)

    Kucharski, Daniel; Kirchner, Georg; Otsubo, Toshimichi; Lim, Hyung-Chul; Bennett, James; Koidl, Franz; Kim, Young-Rok; Hwang, Joo-Yeon

    2016-02-01

    The high repetition rate Satellite Laser Ranging system Graz delivers the millimeter precision range measurements to the corner cube reflector panels of Ajisai. The analysis of 4599 passes measured from October 2003 until November 2014 reveals the secular precession and nutation of Ajisai spin axis due to the gravitational forces as predicted by Kubo (1987) with the periods of 35.6 years and 116.5 days respectively. The observed precession cone is oriented at RA = 88.9°, Dec = -88.85° (J2000) and has a radius of 1.08°. The radius of the nutation cone increases from 1.32° to 1.57° over the 11 years of the measurements. We also detect a draconitic wobbling of Ajisai orientation due to the 'motion' of the Sun about the satellite's orbit. The observed spin period of Ajisai increases exponentially over the investigated time span according to the trend function: T = 1.492277·exp(0.0148388·Y) [s], where Y is in years since launch (1986.6133), RMS = 0.412 ms. The physical simulation model fitted to the observed spin parameters proves a very low interaction between Ajisai and the Earth's magnetic field, what assures that the satellite's angular momentum vector will remain in the vicinity of the south celestial pole for the coming decades. The developed empirical model of the spin axis orientation can improve the accuracy of the range determination between the ground SLR systems and the satellite's center-of-mass (Kucharski et al., 2015) and enable the accurate attitude prediction of Ajisai for the laser time-transfer experiments (Kunimori et al., 1992).

  2. Parameters of a trigatron-driven low-pulse-repetition-rate TEA CO{sub 2} laser preionised by a surface corona discharge

    SciTech Connect

    Aram, M; Shabanzadeh, M; Mansori, F; Behjat, A

    2007-01-31

    The design of a TEA CO{sub 2} laser with UV preionisation by a surface corona discharge is described and the dependences of its average output energy on the gas-flow rate, discharge voltage and pulse repetition rate are presented. The scheme of the electric circuit and the geometry of the pre-ionisation system are considered. The electric circuit is designed to produce only impulse voltage difference between the laser electrodes. The triggering system of the trigatron is used to prevent the appearance of the arc. The dependences of the current, voltage and average output energy on the gas-mixture composition and applied voltages at a low pulse repetition rate are presented. The central output wavelength of the laser was measured with an IR spectrometer. Lasing at two adjacent vibrational-rotational transitions of the CO{sub 2} molecule was observed, which demonstrates the possibility of simultaneous lasing at several lines. (lasers)

  3. Derivation of a formula describing the saturation correction of plane-parallel ionization chambers in pulsed fields with arbitrary repetition rate

    NASA Astrophysics Data System (ADS)

    Karsch, Leonhard

    2016-04-01

    Gas-filled ionization chambers are widely used radiation detectors in radiotherapy. A quantitative description and correction of the recombination effects exists for two cases, for continuous radiation exposure and for pulsed radiation fields with short single pulses. This work gives a derivation of a formula for pulsed beams with arbitrary pulse rate for which the prerequisites of the two existing descriptions are not fulfilled. Furthermore, an extension of the validity of the two known cases is investigated. The temporal evolution of idealized charge density distributions within a plane parallel chamber volume is described for pulsed beams of vanishing pulse duration and arbitrary pulse repetition rate. First, the radiation induced release, movement and collection of the charge carriers without recombination are considered. Then, charge recombination is calculated basing on these simplified charge distributions and the time dependent spatial overlap of positive and negative charge carrier distributions. Finally, a formula for the calculation of the saturation correction factor is derived by calculation and simplification of the first two terms of a Taylor expansion for small recombination. The new formula of saturation correction contains the two existing cases, descriptions for exposure by single pulses and continuous irradiation, as limiting cases. Furthermore, it is possible to determine the pulse rate range for which each of the three descriptions is applicable by comparing the dependencies of the new formula with the two existing cases. As long as the time between two pulses is lower than one third of the collection time of the chamber, the formalism for a continuous exposure can be used. The known description for single pulse irradiation is only valid if the repetition rate is less than 1.2 times the inverse collection time. For all other repetition rates in between the new formula should be used. The experimental determination by Jaffe diagrams can be

  4. Cryogenic disk Yb : YAG laser with 120-mJ energy at 500-Hz pulse repetition rate

    SciTech Connect

    Perevezentsev, E A; Mukhin, I B; Kuznetsov, I I; Palashov, O V; Khazanov, Efim A

    2013-03-31

    A repetitively pulsed laser system based on cryogenically cooled Yb : YAG disks is developed. The creation of Yb : YAG/YAG composites and the use of an active liquid nitrogen cooling system made it possible to significantly decrease the effect of amplified spontaneous emission. The average output power of the system is 60 W. (extreme light fields and their applications)

  5. Optimizing Stimulus Repetition Rate for Recording Ocular Vestibular Evoked Myogenic Potential Elicited by Air-Conduction Tone Bursts of 500 Hz

    PubMed Central

    Singh, Niraj Kumar; Kadisonga, Peter; Ashitha, Palliyath

    2014-01-01

    Amidst several publications reporting the effects of stimulus-related parameters on ocular vestibular evoked myogenic potential (oVEMP), the effect of the repetition rate on oVEMP responses has largely gone unexplored. Studies have used a repetition rate of ~5.1 Hz mainly due to a presumption that oVEMP, like cervical VEMP, should produce best responses for ~5 Hz, although there is paucity of experimental evidence to support this hypothesis. 52 healthy individuals in the age range of 17-35 years underwent air-conduction oVEMP elicited by 500 Hz tone-bursts using seven different repetition rates (3.1, 5.1, 10.1, 15.1, 20.1, 25.1 and 30.1 Hz). The results revealed a tendency for prolongation of latencies and reduction in amplitude with increasing repetition rate. However, significantly longer latencies were observed only for 20.1 Hz and larger amplitudes for 3.1 and 5.1 Hz (P<0.05). There was no significant difference between the rates of 3.1 Hz and 5.1 Hz. However 3.1 Hz produced poorer signal-to-noise ratio and required considerably longer time and thereby had lesser efficiency than 5.1 Hz (P<0.05). This would also result in higher fatigue and irritation levels considering the physical act of maintaining a supero-medial gaze. Thus the use of 5.1 Hz is recommended for clinical recording of oVEMP. PMID:26557349

  6. Narrow-band, near-uv, high-repetition-rate laser-induced fluorescence system for use as an edge diagnostic in fusion machines

    SciTech Connect

    Young, C.E.; Gruen, D.M.; Pellin, M.J.; Calaway, W.F.

    1983-01-01

    A laser system for impurity diagnostics in the edge region of fusion devices is described, representing a substantial advance in repetition rate and capacity for velocity distribution measurements. A single mode cw dye laser with scan capability of 30 GHz in 100 msec is amplified by 3 fast flow dye cells, pumped by a high repetition rate excimer laser (60 mJ/pulse at 130 Hz at 308 rm). Average power during the 8 ns pulses of about 0.8 MW for amplified narrowband output at 604 rm, and 80 kW after frequency doubling in KD*P was achieved, with spectral bandwidth in the tenths of GHz regime. The usefulness of such high resolution is demonstrated by a model calculation for Fe velocity spectra involving the presence of thermal and sputtered flux, and spatial averaging. Laboratory velocity spectra are presented for Fe atoms, sputtered in the a/sup 5/D/sub 4/ ground state.

  7. A high-repetition rate scheme for synchrotron-based picosecond laser pump/x-ray probe experiments on chemical and biological systems in solution

    SciTech Connect

    Lima, Frederico A.; Milne, Christopher J.; Amarasinghe, Dimali C. V.; Rittmann-Frank, Mercedes Hannelore; Veen, Renske M. van der; Reinhard, Marco; Pham, Van-Thai; Karlsson, Susanne; Mourik, Frank van; Chergui, Majed; Johnson, Steven L.; Grolimund, Daniel; Borca, Camelia; Huthwelker, Thomas; Janousch, Markus; Abela, Rafael

    2011-06-15

    We present the extension of time-resolved optical pump/x-ray absorption spectroscopy (XAS) probe experiments towards data collection at MHz repetition rates. The use of a high-power picosecond laser operating at an integer fraction of the repetition rate of the storage ring allows exploitation of up to two orders of magnitude more x-ray photons than in previous schemes based on the use of kHz lasers. Consequently, we demonstrate an order of magnitude increase in the signal-to-noise of time-resolved XAS of molecular systems in solution. This makes it possible to investigate highly dilute samples at concentrations approaching physiological conditions for biological systems. The simplicity and compactness of the scheme allows for straightforward implementation at any synchrotron beamline and for a wide range of x-ray probe techniques, such as time-resolved diffraction or x-ray emission studies.

  8. Dual-frequency comb generation with differing GHz repetition rates by parallel Fabry-Perot cavity filtering of a single broadband frequency comb source

    NASA Astrophysics Data System (ADS)

    Mildner, Jutta; Meiners-Hagen, Karl; Pollinger, Florian

    2016-07-01

    We present a dual-comb-generator based on a coupled Fabry-Perot filtering cavity doublet and a single seed laser source. By filtering a commercial erbium-doped fiber-based optical frequency comb with CEO-stabilisation and 250 MHz repetition rate, two broadband coherent combs of different repetition rates in the GHz range are generated. The filtering doublet consists of two Fabry-Perot cavities with a tunable spacing and Pound-Drever-Hall stabilisation scheme. As a prerequisite for the development of such a filtering unit, we present a method to determine the actual free spectral range and transmission bandwidth of a Fabry-Perot cavity in situ. The transmitted beat signal of two diode lasers is measured as a function of their tunable frequency difference. Finally, the filtering performance and resulting beat signals of the heterodyned combs are discussed as well as the optimisation measures of the whole system.

  9. High-repetition-rate quasi-CW side-pumped mJ eye-safe laser with a monolithic KTP crystal for intracavity optical parametric oscillator.

    PubMed

    Cho, C Y; Chen, Y C; Huang, Y P; Huang, Y J; Su, K W; Chen, Y F

    2014-04-01

    We demonstrate a high-repetition-rate millijoule passively Q-switched eye-safe Nd:YVO(4) laser pumped by a quasi-CW diode stack. A theoretical analysis has been explored for the design criteria of generating TEM(n,0) mode in the diode-stack directly side-pumping configuration. We successfully generate TEM(n,0) modes at 1064 nm by adjusting the gain medium with respected to the laser axis. We further observe the spatial cleaning ability for generating an nearly TEM(0,0) mode output at 1573 nm with a monolithic OPO cavity. At the repetition rate up to 200 Hz, the output pulse energy reaches 1.21 mJ with the threshold pump energy of 17.9 mJ.

  10. High-repetition-rate single-frequency electro-optic Q-switched Nd:YAG laser with feedback controlled prelase

    NASA Astrophysics Data System (ADS)

    Dai, Shutao; Shi, Fei; Huang, Jianhong; Deng, Jing; Zheng, Hui; Liu, Huagang; Wu, Hongchun; Weng, Wen; Ge, Yan; Li, Jinhui; Lin, Wenxiong

    2015-10-01

    A stable high-repetition-rate, high pulse energy and single-frequency electro-optic Q-switched laser has been developed and demonstrated in this paper. The prelase technique has been used in this single-frequency laser. And a PID feedback control electronics is applied to stabilize the prelase. Meanwhile, a two-plate resonant reflector take the place of traditional dielectric output coupler mirror to enhance the single-axial-mode selection. And a Cr:YAG saturable absorber is also inserted in the cavity to improve single-axial-mode selection. Output laser power over 2 W with 10 ns pulse duration has been obtained at a repetition rate of 1 kHz. And the single-axial-mode probability was 100% in one hour without any manual adjustments. The experimental results show that the prelase technique is reliable to attain single-frequency operation.

  11. Supercontinuum generation at 1.55 μm in an all-normal dispersion photonic crystal fiber with high-repetition-rate picosecond pulses

    NASA Astrophysics Data System (ADS)

    Xu, Yong-zhao; Han, Tao; Song, Jian-xun; Ling, Dong-xiong; Li, Hong-tao

    2014-11-01

    We demonstrate the generation of supercontinuum (SC) spectrum covering S+C+L band of optical communication by injecting 1.4 ps optical pulses with center wavelength of 1 552 nm and repetition rate of 10 GHz into an all-normal dispersion photonic crystal fiber (PCF) with length of 80 m. The experimental results are in good agreement with the numerical simulations, which are used to illustrate the SC generation dynamics by self-phase modulation and optical wave breaking (WB).

  12. 1 W average-power 100 MHz repetition-rate 259 nm femtosecond deep ultraviolet pulse generation from ytterbium fiber amplifier.

    PubMed

    Zhou, Xiangyu; Yoshitomi, Dai; Kobayashi, Yohei; Torizuka, Kenji

    2010-05-15

    We demonstrate 1W average-power ultraviolet (UV) femtosecond (fs) ultrashort pulse generation at a wavelength of 259 nm and a repetition rate as high as 100 MHz by quadrupling a fs ytterbium-fiber laser. A cavity-enhanced design is employed for efficient frequency doubling to the UV region. The optical-to-optical efficiency of UV output to the pump diode is 2.6%.

  13. Highly efficient, versatile, self-Q-switched, high-repetition-rate microchip laser generating Ince–Gaussian modes for optical trapping

    NASA Astrophysics Data System (ADS)

    Dong, Jun; He, Yu; Zhou, Xiao; Bai, Shengchuang

    2016-03-01

    Lasers operating in the Ince-Gaussian (IG) mode have potential applications for optical manipulation of microparticles and formation of optical vortices, as well as for optical trapping and optical tweezers. Versatile, self-Q-switched, high-peak-power, high-repetition-rate Cr, Nd:YAG microchip lasers operating in the IG mode are implemented under tilted, tightly focused laser-diode pumping. An average output power of over 2 W is obtained at an absorbed pump power of 6.4 W. The highest optical-to-optical efficiency of 33.2% is achieved at an absorbed pump power of 3.9 W. Laser pulses with a pulse energy of 7.5 μJ, pulse width of 3.5 ns and peak power of over 2 kW are obtained. A repetition rate up to 335 kHz is reached at an absorbed pump power of 5.8 W. Highly efficient, versatile, IG-mode lasers with a high repetition rate and a high peak power ensure a better flexibility in particle manipulation and optical trapping.

  14. Demonstration of saturated tabletop soft x-ray lasers at 5 Hz repetition rate in transitions of Ne-like ions with wavelengths near 30 nm

    NASA Astrophysics Data System (ADS)

    Wang, Yong; Shlyaptsev, Vyacheslav N.; Rocca, Jorge J.

    2005-10-01

    Recent experiments have demonstrated that the laser pump energy required to operate collisional soft x-ray lasers in the gain saturated regime can be significantly reduced by directing the heating pulse into the plasma at grazing incidence for a more efficient energy deposition [1-2]. Optimization of the incidence angle led to gain-saturated operation at 5Hz repetition rate in several transitions of Ni-like ions at wavelengths ranging from 18.9nm to 13.2nm [3]. We report saturated high repetition rate laser-pumped table-top soft x-ray lasers in Ne-like ions at wavelengths near 30nm. Gain-saturated lasers operating at 5Hz repetition rate were obtained in Ne-like Ti at 32.6nm and in Ne-like V at 30.4nm heating plasmas with laser pulses of ˜1J and 8ps impinging at 20^o grazing incidence. Average powers > 1μW were measured. Strong lasing was also observed in Ne-like Cr at 28.6nm. 1. R. Keenan et al, Phys. Rev. Lett., 94, 103901, (2005). 2. B. M. Luther et al, Opt. Lett., 30, 165, (2005). 3. Y. Wang et al, submitted to Phys. Rev. A, (2005).

  15. Compact High-Repetition-Rate Monochromatic Terahertz Source Based on Difference Frequency Generation from a Dual-Wavelength Nd:YAG Laser and DAST Crystal

    NASA Astrophysics Data System (ADS)

    Zhong, Kai; Mei, Jialin; Wang, Maorong; Liu, Pengxiang; Xu, Degang; Wang, Yuye; Shi, Wei; Yao, Jianquan; Teng, Bing; Xiao, Yong

    2016-10-01

    Although high-repetition-rate dual-wavelength Nd:YAG lasers at 1319 and 1338 nm have been realized for quite a long time, we have employed it in generating monochromatic terahertz (THz) wave in this paper for the first time. The dual-wavelength laser was LD-end-pumped and acousto-optically (AO) Q-switched with the output power of watt level operating at different repetition rates from 5.5 to 30 kHz. Using a 0.6-mm-thick organic nonlinear crystal DAST for difference frequency generation (DFG), a compact terahertz source was achieved at 3.28 THz. The maximum average output power was about 0.58 μW obtained at a repetition rate of 5.5 kHz, corresponding to the conversion efficiency of about 6.4 × 10-7. The output power scaling is still feasible with higher pump power and a longer nonlinear DFG crystal. Owing to the compactness of the dual-wavelength laser and the nonlinear crystal, a palm-top terahertz source is expected for portable applications such as imaging and so on.

  16. Highly efficient, versatile, self-Q-switched, high-repetition-rate microchip laser generating Ince-Gaussian modes for optical trapping

    NASA Astrophysics Data System (ADS)

    Dong, Jun; He, Yu; Zhou, Xiao; Bai, Shengchuang

    2016-03-01

    Lasers operating in the Ince-Gaussian (IG) mode have potential applications for optical manipulation of microparticles and formation of optical vortices, as well as for optical trapping and optical tweezers. Versatile, self-Q-switched, high-peak-power, high-repetition-rate Cr, Nd:YAG microchip lasers operating in the IG mode are implemented under tilted, tightly focused laser-diode pumping. An average output power of over 2 W is obtained at an absorbed pump power of 6.4 W. The highest optical-to-optical efficiency of 33.2% is achieved at an absorbed pump power of 3.9 W. Laser pulses with a pulse energy of 7.5 μJ, pulse width of 3.5 ns and peak power of over 2 kW are obtained. A repetition rate up to 335 kHz is reached at an absorbed pump power of 5.8 W. Highly efficient, versatile, IG-mode lasers with a high repetition rate and a high peak power ensure a better flexibility in particle manipulation and optical trapping.

  17. A frequency-locked and frequency-doubled, hybrid Q-switched Yb:KYW laser at 515 nm with a widely adjustable repetition rate

    NASA Astrophysics Data System (ADS)

    Tjörnhammar, S.; Zukauskas, A.; Canalias, C.; Pasiskevicius, V.; Laurell, F.

    2015-09-01

    We demonstrate a compact wavelength-stabilized, frequency-doubled Yb-doped double-tungstate laser with widely tunable repetition rate, spanning from 35 Hz to 3 kHz obtained by hybrid Q-switching. The Q-switching unit consisted of a combination of a passive Cr:YAG crystal and an opto-mechanical active intensity modulator. The fundamental wavelength was locked at 1029 nm with a volume Bragg grating, and the pulse length and energy were 42 ns and 250 µJ, respectively. As the laser was stabilized with the VBG and the opto-mechanical modulator, the frequency instability was reduced six times from free running down to 0.29 %. Frequency doubling was done extra-cavity in PPKTP, and a repetition rate-independent conversion efficiency of 63 % was obtained. The controllable repetition rate together with stable temporal and spatial characteristics makes this laser a suitable candidate in many biology-related experiments, as a pump source for in vivo excitation of fluorophores, e.g., pumping of "living lasers" and matrix-assisted laser desorption/ionization mass spectroscopy.

  18. Bandwidth and repetition rate programmable Nyquist sinc-shaped pulse train source based on intensity modulators and four-wave mixing.

    PubMed

    Cordette, S; Vedadi, A; Shoaie, M A; Brès, C-S

    2014-12-01

    We propose and experimentally demonstrate an all-optical Nyquist sinc-shaped pulse train source based on intensity modulation and four-wave mixing. The proposed scheme allows for the tunability of the bandwidth and the full flexibility of the repetition rate in the limit of the electronic bandwidth of the modulators used through the flexible synthesis of rectangular frequency combs. Bandwidth up to 360 GHz at 40 GHz rate and up to 45 frequency lines at 5 GHz rate are demonstrated with 40 GHz modulators.

  19. Single-pulse picking at kHz repetition rates using a Ge plasma switch at the free-electron laser FELBE

    SciTech Connect

    Schmidt, J. Helm, M.; Winnerl, S.; Seidel, W.; Schneider, H.; Bauer, C.; Gensch, M.

    2015-06-15

    We demonstrate a system for picking of mid-infrared and terahertz (THz) radiation pulses from the free-electron laser (FEL) FELBE operating at a repetition rate of 13 MHz. Single pulses are reflected by a dense electron-hole plasma in a Ge slab that is photoexcited by amplified near-infrared (NIR) laser systems operating at repetition rates of 1 kHz and 100 kHz, respectively. The peak intensity of picked pulses is up to 400 times larger than the peak intensity of residual pulses. The required NIR fluence for picking pulses at wavelengths in the range from 5 μm to 30 μm is discussed. In addition, we show that the reflectivity of the plasma decays on a time scale from 100 ps to 1 ns dependent on the wavelengths of the FEL and the NIR laser. The plasma switch enables experiments with the FEL that require high peak power but lower average power. Furthermore, the system is well suited to investigate processes with decay times in the μs to ms regime, i.e., much longer than the 77 ns long pulse repetition period of FELBE.

  20. The effect of pulse repetition rate on the delay sensitivity of neurons in the auditory cortex of the FM bat, Myotis lucifugus.

    PubMed

    Wong, D; Maekawa, M; Tanaka, H

    1992-04-01

    1. Echo delay is the primary cue used by echolocating bats to determine target range. During target-directed flight, the repetition rate of pulse emission increases systematically as range decreases. Thus, we examined the delay tuning of 120 neurons in the auditory cortex of the bat, Myotis lucifugus, as repetition rate was varied. 2. Delay sensitivity was exhibited in 77% of the neurons over different ranges of pulse repetition rates (PRRs). Delay tuning typically narrowed and eventually disappeared at higher PRRs. 3. Two major types of delay-sensitive neurons were found: i) delay-tuned neurons (59%) had a single fixed best delay, while ii) tracking neurons (22%) changed their best delay with PRR. 4. PRRs from 1-100/s were represented by the population of delay-sensitive neurons, with the majority of neurons delay-sensitive at PRRs of at least 10-20/s. Thus, delay-dependent neurons in Myotis are most active during the search phase of echolocation. 5. Delay-sensitive neurons that also responded to single sounds were common. At PRRs where delay sensitivity was found, the responses to single sounds were reduced and the responses to pulse-echo pairs at particular delays were greater than the single-sound responses. In facilitated neurons (53%), the maximal delay-dependent response was always larger than the best single-sound responses, whereas in enhanced neurons (47%), these responses were comparable. The presence of neurons that respond maximally to single sounds at one PRR and to pulse-echo pairs with particular echo delays at other PRRs suggests that these neurons perform echo-ranging in conjunction with other biosonar functions during target pursuit. PMID:1625215

  1. High-power, high-repetition-rate performance characteristics of β-BaB₂O₄ for single-pass picosecond ultraviolet generation at 266 nm.

    PubMed

    Kumar, S Chaitanya; Casals, J Canals; Wei, Junxiong; Ebrahim-Zadeh, M

    2015-10-19

    We report a systematic study on the performance characteristics of a high-power, high-repetition-rate, picosecond ultraviolet (UV) source at 266 nm based on β-BaB2O4 (BBO). The source, based on single-pass fourth harmonic generation (FHG) of a compact Yb-fiber laser in a two-crystal spatial walk-off compensation scheme, generates up to 2.9 W of average power at 266 nm at a pulse repetition rate of ~80 MHz with a single-pass FHG efficiency of 35% from the green to UV. Detrimental issues such as thermal effects have been studied and confirmed by performing relevant measurements. Angular and temperature acceptance bandwidths in BBO for FHG to 266 nm are experimentally determined, indicating that the effective interaction length is limited by spatial walk-off and thermal gradients under high-power operation. The origin of dynamic color center formation due to two-photon absorption in BBO is investigated by measurements of intensity-dependent transmission at 266 nm. Using a suitable theoretical model, two-photon absorption coefficients as well as the color center densities have been estimated at different temperatures. The measurements show that the two-photon absorption coefficient in BBO at 266 nm is ~3.5 times lower at 200°C compared to that at room temperature. The long-term power stability as well as beam pointing stability is analyzed at different output power levels and focusing conditions. Using cylindrical optics, we have circularized the generated elliptic UV beam to a circularity of >90%. To our knowledge, this is the first time such high average powers and temperature-dependent two-photon absorption measurements at 266 nm are reported at repetition rates as high as ~80 MHz.

  2. High-power, high-repetition-rate performance characteristics of β-BaB₂O₄ for single-pass picosecond ultraviolet generation at 266 nm.

    PubMed

    Kumar, S Chaitanya; Casals, J Canals; Wei, Junxiong; Ebrahim-Zadeh, M

    2015-10-19

    We report a systematic study on the performance characteristics of a high-power, high-repetition-rate, picosecond ultraviolet (UV) source at 266 nm based on β-BaB2O4 (BBO). The source, based on single-pass fourth harmonic generation (FHG) of a compact Yb-fiber laser in a two-crystal spatial walk-off compensation scheme, generates up to 2.9 W of average power at 266 nm at a pulse repetition rate of ~80 MHz with a single-pass FHG efficiency of 35% from the green to UV. Detrimental issues such as thermal effects have been studied and confirmed by performing relevant measurements. Angular and temperature acceptance bandwidths in BBO for FHG to 266 nm are experimentally determined, indicating that the effective interaction length is limited by spatial walk-off and thermal gradients under high-power operation. The origin of dynamic color center formation due to two-photon absorption in BBO is investigated by measurements of intensity-dependent transmission at 266 nm. Using a suitable theoretical model, two-photon absorption coefficients as well as the color center densities have been estimated at different temperatures. The measurements show that the two-photon absorption coefficient in BBO at 266 nm is ~3.5 times lower at 200°C compared to that at room temperature. The long-term power stability as well as beam pointing stability is analyzed at different output power levels and focusing conditions. Using cylindrical optics, we have circularized the generated elliptic UV beam to a circularity of >90%. To our knowledge, this is the first time such high average powers and temperature-dependent two-photon absorption measurements at 266 nm are reported at repetition rates as high as ~80 MHz. PMID:26480467

  3. High repetition rate passive Q-switching of diode-pumped Nd:GdVO4 laser at 912 nm with V3+:YAG as the saturable absorber

    NASA Astrophysics Data System (ADS)

    Yang, H. W.; Huang, H. T.; He, J. L.; Liu, S. D.; Liu, F. Q.; Yang, X. Q.; Xu, J. L.; Yang, J. F.; Zhang, B. T.

    2011-01-01

    The character of a diode-pumped passively Q-switched Nd:GdVO4/V3+:YAG 912 nm laser was demonstrated for the first time to our knowledge. With an absorbed pump power of 7.4 W, an average output power of 360 mW with a Q-switched pulse width of 328 ns at a pulse repetition rate of 163 kHz was obtained. The Q-switching efficiency was found to be 32.7%. Our work further indicated V3+:YAG could be an effective fast passive Q-switch for 0.9 μm radiation.

  4. Optimized spatial overlap in optical pump-X-ray probe experiments with high repetition rate using laser-induced surface distortions.

    PubMed

    Reinhardt, Matthias; Koc, Azize; Leitenberger, Wolfram; Gaal, Peter; Bargheer, Matias

    2016-03-01

    Ultrafast X-ray diffraction experiments require careful adjustment of the spatial overlap between the optical excitation and the X-ray probe pulse. This is especially challenging at high laser repetition rates. Sample distortions caused by the large heat load on the sample and the relatively low optical energy per pulse lead to only tiny signal changes. In consequence, this results in small footprints of the optical excitation on the sample, which turns the adjustment of the overlap difficult. Here a method for reliable overlap adjustment based on reciprocal space mapping of a laser excited thin film is presented. PMID:26917135

  5. Optimized spatial overlap in optical pump-X-ray probe experiments with high repetition rate using laser-induced surface distortions.

    PubMed

    Reinhardt, Matthias; Koc, Azize; Leitenberger, Wolfram; Gaal, Peter; Bargheer, Matias

    2016-03-01

    Ultrafast X-ray diffraction experiments require careful adjustment of the spatial overlap between the optical excitation and the X-ray probe pulse. This is especially challenging at high laser repetition rates. Sample distortions caused by the large heat load on the sample and the relatively low optical energy per pulse lead to only tiny signal changes. In consequence, this results in small footprints of the optical excitation on the sample, which turns the adjustment of the overlap difficult. Here a method for reliable overlap adjustment based on reciprocal space mapping of a laser excited thin film is presented.

  6. 615 fs pulses with 17 mJ energy generated by an Yb:thin-disk amplifier at 3 kHz repetition rate.

    PubMed

    Fischer, Jonathan; Heinrich, Alexander-Cornelius; Maier, Simon; Jungwirth, Julian; Brida, Daniele; Leitenstorfer, Alfred

    2016-01-15

    A combination of Er/Yb:fiber and Yb:thin-disk technology produces 615 fs pulses at 1030 nm with an average output power of 72 W. The regenerative amplifier allows variation of the repetition rate between 3 and 5 kHz with pulse energies from 13 to 17 mJ. A broadband and intense seed provided by the compact and versatile fiber front-end minimizes gain narrowing. The resulting sub-ps performance is ideal for nonlinear frequency conversion and pulse compression. Operating in the upper branch of a bifurcated pulse train, the system exhibits exceptional noise performance and stability.

  7. Dispersion-compensation-free femtosecond Tm-doped all-fiber laser with a 248  MHz repetition rate.

    PubMed

    Sun, Biao; Luo, Jiaqi; Ng, Boon Ping; Yu, Xia

    2016-09-01

    In this Letter, we report a dispersion-compensation-free ultrafast thulium-doped all-fiber laser based on nonlinear polarization evolution (NPE) mode locking, delivering 330 fs soliton pulses at 1950 nm. A multifunctional hybrid fiberized device was applied in the oscillator to minimize the physical cavity length to ∼80  cm with a total dispersion of -0.045  ps2, enabling a state-of-the-art fundamental mode-locking repetition rate of 248 MHz in an NPE-based oscillator at ∼2  μm. PMID:27607970

  8. 1-J operation of monolithic composite ceramics with Yb:YAG thin layers: multi-TRAM at 10-Hz repetition rate and prospects for 100-Hz operation.

    PubMed

    Divoky, Martin; Tokita, Shigeki; Hwang, Sungin; Kawashima, Toshiyuki; Kan, Hirofumi; Lucianetti, Antonio; Mocek, Tomas; Kawanaka, Junji

    2015-03-15

    Experimental amplification of 10-ns pulses to energy of 1 J at repetition rate of 10-100 Hz in cryogenic multipass total-reflection active-mirror (TRAM) amplifier is reported for the first time. By using a monolithic multi-TRAM, which is a YAG ceramic composite with three thin Yb:YAG active layers, efficient energy extraction was achieved without parasitic lasing. A detailed measurement of output characteristics of the laser amplifier is presented; results are discussed and compared with numerical calculations.

  9. Octave-spanning OPCPA system delivering CEP-stable few-cycle pulses and 22 W of average power at 1 MHz repetition rate.

    PubMed

    Rothhardt, Jan; Demmler, Stefan; Hädrich, Steffen; Limpert, Jens; Tünnermann, Andreas

    2012-05-01

    We report on an OPCPA system delivering CEP-stable pulses with a pulse duration of only 1.7 optical cycles at 880 nm wavelength. This pulse duration is achieved by the generation, optical parametric amplification and compression of a full optical octave of bandwidth. The system is pumped by a high average power Yb-fiber laser system, which allows for operation of the OPCPA at up to 1 MHz repetition rate and 22 W of average output power. Further scaling towards single-cycle pulses, higher energy and output power is discussed. PMID:22565712

  10. Modeling and optimizing of low-repetition-rate high-energy pulse amplification in high-concentration erbium-doped fiber amplifiers

    NASA Astrophysics Data System (ADS)

    Li, Jianfeng; Dai, Zhiyong; Ou, Zhonghua; Zhang, Lixun; Liu, Yongzhi; Liu, Yong

    2009-09-01

    Starting from the modeling of isolated ions and ion-pairs, a closed form rate and power evolution equations for pulse amplification in high-concentration erbium-doped fiber amplifiers (EDFAs) are constructed. According to the equations, the effects of ion-pairs on the performance of a high-concentration EDFA in steady state including upper-state population, ASE powers without input signal are analyzed numerically. Furthermore, the effects of ion-pairs on the dynamic characteristics of low-repetition-rate pulse amplification in the EDFA including the storied energy, output pulse energy and evolution of pulse waveform distortion are systematically studied by using the finite-difference method. The results show that the presence of the ion-pairs deteriorates amplifier performance, such as the upper-state population, ASE power, storied energy, output pulse energy, and saturated gain, etc. For the high-concentration EDFA, the optimum fiber length should be modified to achieve a better performance. The relations between the evolution of pulse waveform distortion or output pulse energy and the input pulse peak power are also discussed. The results can provide important guide for the design and optimization of the low-repetition-rate pulse amplification in high-concentration EDFAs.

  11. 1.55 µm InAs/GaAs quantum dots and high repetition rate quantum dot SESAM mode-locked laser.

    PubMed

    Zhang, Z Y; Oehler, A E H; Resan, B; Kurmulis, S; Zhou, K J; Wang, Q; Mangold, M; Süedmeyer, T; Keller, U; Weingarten, K J; Hogg, R A

    2012-01-01

    High pulse repetition rate (≥ 10 GHz) diode-pumped solid-state lasers, modelocked using semiconductor saturable absorber mirrors (SESAMs) are emerging as an enabling technology for high data rate coherent communication systems owing to their low noise and pulse-to-pulse optical phase-coherence. Quantum dot (QD) based SESAMs offer potential advantages to such laser systems in terms of reduced saturation fluence, broader bandwidth, and wavelength flexibility. Here, we describe the development of an epitaxial process for the realization of high optical quality 1.55 µm In(Ga)As QDs on GaAs substrates, their incorporation into a SESAM, and the realization of the first 10 GHz repetition rate QD-SESAM modelocked laser at 1.55 µm, exhibiting ∼2 ps pulse width from an Er-doped glass oscillator (ERGO). With a high areal dot density and strong light emission, this QD structure is a very promising candidate for many other applications, such as laser diodes, optical amplifiers, non-linear and photonic crystal based devices.

  12. 1.55 µm InAs/GaAs Quantum Dots and High Repetition Rate Quantum Dot SESAM Mode-locked Laser

    PubMed Central

    Zhang, Z. Y.; Oehler, A. E. H.; Resan, B.; Kurmulis, S.; Zhou, K. J.; Wang, Q.; Mangold, M.; Süedmeyer, T.; Keller, U.; Weingarten, K. J.; Hogg, R. A.

    2012-01-01

    High pulse repetition rate (≥10 GHz) diode-pumped solid-state lasers, modelocked using semiconductor saturable absorber mirrors (SESAMs) are emerging as an enabling technology for high data rate coherent communication systems owing to their low noise and pulse-to-pulse optical phase-coherence. Quantum dot (QD) based SESAMs offer potential advantages to such laser systems in terms of reduced saturation fluence, broader bandwidth, and wavelength flexibility. Here, we describe the development of an epitaxial process for the realization of high optical quality 1.55 µm In(Ga)As QDs on GaAs substrates, their incorporation into a SESAM, and the realization of the first 10 GHz repetition rate QD-SESAM modelocked laser at 1.55 µm, exhibiting ∼2 ps pulse width from an Er-doped glass oscillator (ERGO). With a high areal dot density and strong light emission, this QD structure is a very promising candidate for many other applications, such as laser diodes, optical amplifiers, non-linear and photonic crystal based devices. PMID:22745898

  13. Gain-switched laser diode seeded Yb-doped fiber amplifier delivering 11-ps pulses at repetition rates up to 40-MHz

    NASA Astrophysics Data System (ADS)

    Ryser, Manuel; Neff, Martin; Pilz, Soenke; Burn, Andreas; Romano, Valerio

    2012-02-01

    Here, we demonstrate all-fiber direct amplification of 11 picosecond pulses from a gain-switched laser diode at 1063 nm. The diode was driven at a repetition rate of 40 MHz and delivered 13 μW of fiber-coupled average output power. For the low output pulse energy of 0.33 pJ we have designed a multi-stage core pumped preamplifier based on single clad Yb-doped fibers in order to keep the contribution of undesired amplified spontaneous emission as low as possible and to minimize temporal and spectral broadening. After the preamplifier we reduced the 40 MHz repetition rate to 1 MHz using a fiber coupled pulse-picker. The final amplification was done with a cladding pumped Yb-doped large mode area fiber and a subsequent Yb-doped rod-type fiber. With our setup we achieved amplification of 72 dBs to an output pulse energy of 5.7 μJ, pulse duration of 11 ps and peak power of >0.6 MW.

  14. High repetition rate tabletop soft x-ray lasers at wavelengths down to 11.9 nm in Nickel-like ions

    NASA Astrophysics Data System (ADS)

    Luther, Bradley M.; Shlyaptsev, Vyacheslav N.; Rocca, Jorge J.

    2005-10-01

    There is significant interest in the development of high average power table-top soft x-ray lasers (SXL) for applications. The repetition rate of gain-saturated collisional SXL operating at wavelengths of less than 30nm has been limited to one shot every several minutes by the large laser pump energy required to heat the plasma. Recent experiments have demonstrated a large pump energy reduction by directing the heating pulse into the plasma at grazing incidence [1-3]. This pumping geometry takes advantage of the refraction of the pump beam in the plasma to deposit a large fraction of its energy into the gain region. Here we report 5Hz repetition rate operation of gain-saturated table-top lasers with 1-2μW average power in transitions of Ni-like ions (Mo, Ru, Pd, Ag and Cd) at wavelengths between 18.9nm and 13.2nm, using a 1J, 8 ps heating pulse from a Ti:Sa laser. Strong amplification was also observed at 11.9 nm in Ni-like Sn. 1. R. Keenan et al, Phys. Rev. Lett., 94, 103901, (2005). 2. B. M. Luther et al, Opt. Lett., 30, 165, (2005). 3. D. Alessi et al, Opt. Express, 13, 2093, (2005).

  15. High-repetition-rate and high-photon-flux 70 eV high-harmonic source for coincidence ion imaging of gas-phase molecules.

    PubMed

    Rothhardt, Jan; Hädrich, Steffen; Shamir, Yariv; Tschnernajew, Maxim; Klas, Robert; Hoffmann, Armin; Tadesse, Getnet K; Klenke, Arno; Gottschall, Thomas; Eidam, Tino; Limpert, Jens; Tünnermann, Andreas; Boll, Rebecca; Bomme, Cedric; Dachraoui, Hatem; Erk, Benjamin; Di Fraia, Michele; Horke, Daniel A; Kierspel, Thomas; Mullins, Terence; Przystawik, Andreas; Savelyev, Evgeny; Wiese, Joss; Laarmann, Tim; Küpper, Jochen; Rolles, Daniel

    2016-08-01

    Unraveling and controlling chemical dynamics requires techniques to image structural changes of molecules with femtosecond temporal and picometer spatial resolution. Ultrashort-pulse x-ray free-electron lasers have significantly advanced the field by enabling advanced pump-probe schemes. There is an increasing interest in using table-top photon sources enabled by high-harmonic generation of ultrashort-pulse lasers for such studies. We present a novel high-harmonic source driven by a 100 kHz fiber laser system, which delivers 1011 photons/s in a single 1.3 eV bandwidth harmonic at 68.6 eV. The combination of record-high photon flux and high repetition rate paves the way for time-resolved studies of the dissociation dynamics of inner-shell ionized molecules in a coincidence detection scheme. First coincidence measurements on CH3I are shown and it is outlined how the anticipated advancement of fiber laser technology and improved sample delivery will, in the next step, allow pump-probe studies of ultrafast molecular dynamics with table-top XUV-photon sources. These table-top sources can provide significantly higher repetition rates than the currently operating free-electron lasers and they offer very high temporal resolution due to the intrinsically small timing jitter between pump and probe pulses. PMID:27505779

  16. Repetition reduction: Lexical repetition in the absence of referent repetition

    PubMed Central

    Lam, Tuan Q.; Watson, Duane G.

    2014-01-01

    Repeated words are produced with reduced acoustic prominence compared to words that are new to a discourse. Although these effects are often attributed to priming in the production system, the locus of the effect within the production system remains unresolved because in natural speech, repetition often involves repetition of referents and lexical items simultaneously. Therefore, repetition reduction could be due to repeated mention of a referent, or repetition of a word or referring expression. In our study, we test whether repetition reduction is due to repetition of lexical items or repeated mention of referents using an event description task. The results show that repeated lexical items lead to reduced duration and intensity even in the absence of referent repetition whereas repeated referents lead to reduced intensity alone. The general pattern suggests that repetition reduction is due most strongly to repetition of the lexical item, rather than repeated mention of the referent. PMID:24548320

  17. Human sensory-evoked responses differ coincident with either "fusion-memory" or "flash-memory", as shown by stimulus repetition-rate effects

    PubMed Central

    Jewett, Don L; Hart, Toryalai; Larson-Prior, Linda J; Baird, Bill; Olson, Marram; Trumpis, Michael; Makayed, Katherine; Bavafa, Payam

    2006-01-01

    Background: A new method has been used to obtain human sensory evoked-responses whose time-domain waveforms have been undetectable by previous methods. These newly discovered evoked-responses have durations that exceed the time between the stimuli in a continuous stream, thus causing an overlap which, up to now, has prevented their detection. We have named them "A-waves", and added a prefix to show the sensory system from which the responses were obtained (visA-waves, audA-waves, somA-waves). Results: When A-waves were studied as a function of stimulus repetition-rate, it was found that there were systematic differences in waveshape at repetition-rates above and below the psychophysical region in which the sensation of individual stimuli fuse into a continuity. The fusion phenomena is sometimes measured by a "Critical Fusion Frequency", but for this research we can only identify a frequency-region [which we call the STZ (Sensation-Transition Zone)]. Thus, the A-waves above the STZ differed from those below the STZ, as did the sensations. Study of the psychophysical differences in auditory and visual stimuli, as shown in this paper, suggest that different stimulus features are detected, and remembered, at stimulation rates above and below STZ. Conclusion: The results motivate us to speculate that: 1) Stimulus repetition-rates above the STZ generate waveforms which underlie "fusion-memory" whereas rates below the STZ show neuronal processing in which "flash-memory" occurs. 2) These two memories differ in both duration and mechanism, though they may occur in the same cell groups. 3) The differences in neuronal processing may be related to "figure" and "ground" differentiation. We conclude that A-waves provide a novel measure of neural processes that can be detected on the human scalp, and speculate that they may extend clinical applications of evoked response recordings. If A-waves also occur in animals, it is likely that A-waves will provide new methods for

  18. The effect of stimulus repetition rate on the diagnostic efficacy of the auditory nerve-brain-stem evoked response.

    PubMed

    Freeman, S; Sohmer, H; Silver, S

    1991-04-01

    This study investigates the hypothesis that an increase in the click presentation rate during diagnostic testing with the auditory nerve-brain-stem response (ABR) will increase the efficiency with which lesions may be detected in the nervous system. Cats were exposed to conditions of hypoxia, hypercapnia and acidemia, and hypoglycemia was induced in rats. ABR was recorded using the standard 10/sec click rate and also a higher (55/sec) rate during both the control state and experimental state. Various parameters of the ABR were compared at the two click rates in the control and experimental states to see if the higher click rate was more effective in detecting pathology in the nervous system. It was found that in only a very few cases was the higher stimulus presentation rate more effective, and that in general ABR recordings at one stimulus rate only is quite sufficient for work in a clinical setting. PMID:1706249

  19. Diode-pumped short pulse passively Q-switched 912 nm Nd:GdVO4/Cr:YAG laser at high repetition rate operation

    NASA Astrophysics Data System (ADS)

    Chen, F.; Yu, X.; Wang, C.; Yan, R. P.; Li, X. D.; Gao, J.; Zhang, Z. H.; Yu, J. H.

    2010-06-01

    A diode-end-pumped passively Q-switched 912 nm Nd:GdVO4/Cr:YAG laser is demonstrated for the first time. In a concave-piano cavity, pulsed 912 nm laser performance is investigated using two kinds of Cr:YAG crystal with different unsaturated transmission ( T U) of 95% and 90% at 912 nm as the saturable absorbers. When the T U = 90% Cr:YAG is used, as much as 2.6 W average output power for short pulsed 912 nm laser is achieved at an absorbed pump power of 34.0 W, corresponding to an optical efficiency of 7.6% and a slope efficiency of 20.3%. Moreover, 10.5 ns duration pulses and up to 2.3 kW peak power is obtained at the repetition rate around 81.6 kHz.

  20. Nanosecond pulsed power generator for a voltage amplitude up to 300 kV and a repetition rate up to 16 Hz for fine disintegration of quartz

    NASA Astrophysics Data System (ADS)

    Krastelev, E. G.; Sedin, A. A.; Tugushev, V. I.

    2015-12-01

    A generator of high-power high-voltage nanosecond pulses is intended for electrical discharge disintegration of mineral quartz and other nonconducting minerals. It includes a 320 kV Marx pulsed voltage generator, a high-voltage glycerin-insulated coaxial peaking capacitor, and an output gas spark switch followed by a load, an electric discharge disintegration chamber. The main parameters of the generator are as follows: a voltage pulse amplitude of up to 300 kV, an output impedance of ≈10 Ω, a discharge current amplitude of up to 25 kA for a half-period of 80-90 ns, and a pulse repetition rate of up to 16 Hz.

  1. Frequency and duty cycle modulation optimization in minimizing thermal accumulation effect in Z-scan measurement with high-repetition-rate laser

    NASA Astrophysics Data System (ADS)

    Shahnan Zainal Abidin, Mohd; Noor, Ahmad Shukri Muhammad; Rashid, Suraya Abdul; Adzir Mahdi, Mohd

    2014-11-01

    In this study, we demonstrate the optimization of the chopper frequency and duty cycle in a Z-scan measurement with a 250 MHz high-repetition-rate (HRR) femtosecond laser to minimize the thermal lensing effect due to cumulative heating of the sample. The result shows that such minimization can be achieved by keeping the modulated exposure time on the sample shorter than the thermal diffusivity decay time tc. The minimum chopper frequency fmin is predicted by relating the duty cycle factor F with tc, while maintaining stable peak and valley transmittances, i.e., ΔTp and ΔTv, respectively. Furthermore, a lower fmin is obtained by taking a stable range of the peak-valley difference ΔTpv into consideration. The optimization allows for the low operational modulation frequency of Z-scan measurement with reduced thermal influence, thus enabling simple management of the thermal lensing effect.

  2. Nanosecond pulsed power generator for a voltage amplitude up to 300 kV and a repetition rate up to 16 Hz for fine disintegration of quartz

    SciTech Connect

    Krastelev, E. G. Sedin, A. A.; Tugushev, V. I.

    2015-12-15

    A generator of high-power high-voltage nanosecond pulses is intended for electrical discharge disintegration of mineral quartz and other nonconducting minerals. It includes a 320 kV Marx pulsed voltage generator, a high-voltage glycerin-insulated coaxial peaking capacitor, and an output gas spark switch followed by a load, an electric discharge disintegration chamber. The main parameters of the generator are as follows: a voltage pulse amplitude of up to 300 kV, an output impedance of ≈10 Ω, a discharge current amplitude of up to 25 kA for a half-period of 80–90 ns, and a pulse repetition rate of up to 16 Hz.

  3. PULSAR: A High-Repetition-Rate, High-Power, CE Phase-Locked Laser for the J.R. Macdonald Laboratory at Kansas State University

    SciTech Connect

    Ben-Itzhak, Itzik; Carnes, Kevin D.; Cocke, C. Lew; Fehrenbach, Charles W.; Kumarappan, Vinod; Rudenko, Artem; Trallero, Carlos

    2014-05-09

    This instrumentation grant funded the development and installation of a state-of-the-art laser system to be used for the DOE funded research at the J.R. Macdonald Laboratory at Kansas State University. Specifically, we purchased a laser based on the KMLABs Red-Dragon design, which has a high repetition rate of 10-20 kHz crucial for multi-parameter coincidence measurements conducted in our lab. This laser system is carrier-envelope phase (CEP) locked and provides pulses as short as 21 fs directly from the amplifier (see details below). In addition, we have developed a pulse compression setup that provides sub 5 fs pulses and a CEP tagging capability that allows for long measurements of CEP dependent processes.

  4. High energy pulses generation with giant spectrum bandwidth and submegahertz repetition rate from a passively mode-locked Yb-doped fiber laser in all normal dispersion cavity

    NASA Astrophysics Data System (ADS)

    Lin, J.-H.; Wang, D.; Lin, K.-H.

    2011-01-01

    Robust passively mode-locked pulse generation with low pulse repetition rate and giant spectrum bandwidth in an all-fiber, all-normal-dispersion ytterbium-doped fiber laser has been experimentally demonstrated using nonlinear polarization evolution technique. The highest pulse energy over 20 nJ with spectrum bandwidth over 50 nm can be experimentally obtained at 175 mW pump power. The mode-locked pulses reveal broadened 3-dB pulsewidth about several nanosecond and widened pedestal in time trace that is resulted from enormous dispersion in laser cavity and gain dynamics. At certain mode-locking state, a spectrum gap around 1056 nm are observed between the three and four energy levels of Yb-doped fiber laser. By properly rotating the polarization controller, the gap can be eliminated due to four-wave mixing to produce more flattened spectrum output.

  5. Laser ablation efficiency during the production of Ag nanoparticles in ethanol at a low pulse repetition rate (1-10 Hz)

    NASA Astrophysics Data System (ADS)

    Valverde-Alva, M. A.; García-Fernández, T.; Esparza-Alegría, E.; Villagrán-Muniz, M.; Sánchez-Aké, C.; Castañeda-Guzmán, R.; de la Mora, M. B.; Márquez-Herrera, C. E.; Sánchez Llamazares, J. L.

    2016-10-01

    We studied the effect of the repetition rate of laser pulses (RRLP) in the range from 1-10 Hz in the production of silver nanoparticles (Ag-NPs) by laser ablation in ethanol. Laser pulses with a duration of 7 ns, a wavelength of 1064 nm and an energy of 60 mJ were used to ablate a 99.99% pure silver target immersed in 10 ml of ethanol. Transmittance analysis and atomic absorption spectroscopy were used to study the silver concentration in the colloidal solutions. The ablation process was studied by measuring the transmission of the laser pulses through the colloid. It is shown that for a fixed number of laser pulses (NLP) the ablation efficiency, in terms of the ablated silver mass per laser pulse, increases with the RRLP. This result contradicts what had previously been established in the literature.

  6. Temperature scaling of hot electrons produced by a tightly focused relativistic-intensity laser at 0.5 kHz repetition rate

    SciTech Connect

    Mordovanakis, Aghapi G.; Masson-Laborde, Paul-Edouard; Easter, James; Hou Bixue; Nees, John; Krushelnick, Karl; Popov, Konstantin; Rozmus, Wojciech; Mourou, Gerard; Haines, Malcolm G.

    2010-02-15

    The energy spectrum of hot electrons emitted from the interaction of a relativistically intense laser with an Al plasma is measured at a repetition rate of 0.5 kHz by accumulating approx10{sup 3} highly reproducible laser shots. In the 10{sup 17}-2x10{sup 18} W/cm{sup 2} range, the temperature of electrons escaping the plasma along the specular direction scales as (Ilambda{sup 2}){sup 0.64+}-{sup 0.05} for p-polarized pulses incident at 45 deg. This scaling is in good agreement with three-dimensional particle-in-cell simulations and a simple model that estimates the hot-electron temperature by considering the balance between the deposited laser intensity and the energy carried away by those electrons.

  7. Generation of 1.5 W average power, 18 kHz repetition rate coherent mid-ultraviolet radiation at 271.2 nm.

    PubMed

    Biswal, Ramakanta; Agrawal, Praveen K; Dixit, Sudhir K; Nakhe, Shankar V

    2015-11-10

    This paper presents to our knowledge a first time study on the generation of 1.5 W average power, 18 kHz repetition rate coherent mid-ultraviolet (UV) radiation at 271.2 nm. The work is based on frequency summing of coherent green (G: 510.6 nm) and yellow (Y: 578.2 nm) radiations of a copper-HBr laser in a β-barium borate crystal. Average and peak sum frequency conversion efficiencies of about 13% and 16%, respectively, are obtained. The sum frequency results are experimentally analyzed in terms of the extent of matching of green and yellow pump radiations in space, time, and frequency domains. The result is of high significance for many applications in photonics components fabrication, semiconductor technology, and spectroscopy. PMID:26560794

  8. Ultrafast laser with an average power of 120 W at 515 nm and a highly dynamic repetition rate in the MHz range for novel applications in micromachining

    NASA Astrophysics Data System (ADS)

    Harth, F.; Piontek, M. C.; Herrmann, T.; L'huillier, J. A.

    2016-03-01

    A new generation of resonant scanners in the kHz-range shows ultra-high deflection speeds of more than 1000m/s but suffer from an inherent nonlinear mirror oscillation. If this oscillation is not compensated, a typical bitmap, written point by point, would be strongly distorted because of the decreasing spot distance at the turning point of the scanning mirror. However, this can be avoided by a dynamic adaption of the repetition rate (RR) of the ultrafast laser. Since resonant scanners are operated in the 10 kHz-range, this means that the RR has to be continuously swept up to several 10 000 times per second between e.g. 5MHz and 10 MHz. High-speed continuous adaption of the RR could also optimize laser micromachining of narrow curved geometries, where nowadays a time consuming approximation with numerous vectors is required. We present a laser system, which is capable of sweeping the RR more than 32 000 times per second between 5MHz and 10MHz at an average output power of more than 120W at 515nm with a pulse duration of about 40 ps. The laser consists of a semiconductor oscillator, a 3-stage fiber pre-amplifier, a solid state InnoSlab power amplifier and a SHG stage. We systematically analyzed the dynamic of the laser system as well as the spectral and temporal behavior of the optical pulses. Switching the repetition rate typically causes a varying pulse energy, which could affect the machining quality over one scanning line. This effect will be analyzed and discussed. Possible techniques to compensate or avoid this effect will be considered.

  9. Demonstration of a time-resolved x-ray scattering instrument utilizing the full-repetition rate of x-ray pulses at the Pohang Light Source

    NASA Astrophysics Data System (ADS)

    Jo, Wonhyuk; Eom, Intae; Landahl, Eric C.; Lee, Sooheyong; Yu, Chung-Jong

    2016-03-01

    We report on the development of a new experimental instrument for time-resolved x-ray scattering (TRXS) at the Pohang Light Source (PLS-II). It operates with a photon energy ranging from 5 to 18 keV. It is equipped with an amplified Ti:sappahire femtosecond laser, optical diagnostics, and laser beam delivery for pump-probe experiments. A high-speed single-element detector and high trigger-rate oscilloscope are used for rapid data acquisition. While this instrument is capable of measuring sub-nanosecond dynamics using standard laser pump/x-ray probe techniques, it also takes advantage of the dense 500 MHz standard fill pattern in the PLS-II storage ring to efficiently record nano-to-micro-second dynamics simultaneously. We demonstrate this capability by measuring both the (fast) impulsive strain and (slower) thermal recovery dynamics of a crystalline InSb sample following intense ultrafast laser excitation. Exploiting the full repetition rate of the storage ring results in a significant improvement in data collection rates compared to conventional bunch-tagging methods.

  10. Demonstration of a time-resolved x-ray scattering instrument utilizing the full-repetition rate of x-ray pulses at the Pohang Light Source.

    PubMed

    Jo, Wonhyuk; Eom, Intae; Landahl, Eric C; Lee, Sooheyong; Yu, Chung-Jong

    2016-03-01

    We report on the development of a new experimental instrument for time-resolved x-ray scattering (TRXS) at the Pohang Light Source (PLS-II). It operates with a photon energy ranging from 5 to 18 keV. It is equipped with an amplified Ti:sappahire femtosecond laser, optical diagnostics, and laser beam delivery for pump-probe experiments. A high-speed single-element detector and high trigger-rate oscilloscope are used for rapid data acquisition. While this instrument is capable of measuring sub-nanosecond dynamics using standard laser pump/x-ray probe techniques, it also takes advantage of the dense 500 MHz standard fill pattern in the PLS-II storage ring to efficiently record nano-to-micro-second dynamics simultaneously. We demonstrate this capability by measuring both the (fast) impulsive strain and (slower) thermal recovery dynamics of a crystalline InSb sample following intense ultrafast laser excitation. Exploiting the full repetition rate of the storage ring results in a significant improvement in data collection rates compared to conventional bunch-tagging methods. PMID:27036819

  11. Efficient generation of twin photons at telecom wavelengths with 2.5 GHz repetition-rate-tunable comb laser

    PubMed Central

    Jin, Rui-Bo; Shimizu, Ryosuke; Morohashi, Isao; Wakui, Kentaro; Takeoka, Masahiro; Izumi, Shuro; Sakamoto, Takahide; Fujiwara, Mikio; Yamashita, Taro; Miki, Shigehito; Terai, Hirotaka; Wang, Zhen; Sasaki, Masahide

    2014-01-01

    Efficient generation and detection of indistinguishable twin photons are at the core of quantum information and communications technology (Q-ICT). These photons are conventionally generated by spontaneous parametric down conversion (SPDC), which is a probabilistic process, and hence occurs at a limited rate, which restricts wider applications of Q-ICT. To increase the rate, one had to excite SPDC by higher pump power, while it inevitably produced more unwanted multi-photon components, harmfully degrading quantum interference visibility. Here we solve this problem by using recently developed 10 GHz repetition-rate-tunable comb laser, combined with a group-velocity-matched nonlinear crystal, and superconducting nanowire single photon detectors. They operate at telecom wavelengths more efficiently with less noises than conventional schemes, those typically operate at visible and near infrared wavelengths generated by a 76 MHz Ti Sapphire laser and detected by Si detectors. We could show high interference visibilities, which are free from the pump-power induced degradation. Our laser, nonlinear crystal, and detectors constitute a powerful tool box, which will pave a way to implementing quantum photonics circuits with variety of good and low-cost telecom components, and will eventually realize scalable Q-ICT in optical infra-structures. PMID:25524646

  12. Efficient generation of twin photons at telecom wavelengths with 2.5 GHz repetition-rate-tunable comb laser

    NASA Astrophysics Data System (ADS)

    Jin, Rui-Bo; Shimizu, Ryosuke; Morohashi, Isao; Wakui, Kentaro; Takeoka, Masahiro; Izumi, Shuro; Sakamoto, Takahide; Fujiwara, Mikio; Yamashita, Taro; Miki, Shigehito; Terai, Hirotaka; Wang, Zhen; Sasaki, Masahide

    2014-12-01

    Efficient generation and detection of indistinguishable twin photons are at the core of quantum information and communications technology (Q-ICT). These photons are conventionally generated by spontaneous parametric down conversion (SPDC), which is a probabilistic process, and hence occurs at a limited rate, which restricts wider applications of Q-ICT. To increase the rate, one had to excite SPDC by higher pump power, while it inevitably produced more unwanted multi-photon components, harmfully degrading quantum interference visibility. Here we solve this problem by using recently developed 10 GHz repetition-rate-tunable comb laser, combined with a group-velocity-matched nonlinear crystal, and superconducting nanowire single photon detectors. They operate at telecom wavelengths more efficiently with less noises than conventional schemes, those typically operate at visible and near infrared wavelengths generated by a 76 MHz Ti Sapphire laser and detected by Si detectors. We could show high interference visibilities, which are free from the pump-power induced degradation. Our laser, nonlinear crystal, and detectors constitute a powerful tool box, which will pave a way to implementing quantum photonics circuits with variety of good and low-cost telecom components, and will eventually realize scalable Q-ICT in optical infra-structures.

  13. Demonstration of a time-resolved x-ray scattering instrument utilizing the full-repetition rate of x-ray pulses at the Pohang Light Source.

    PubMed

    Jo, Wonhyuk; Eom, Intae; Landahl, Eric C; Lee, Sooheyong; Yu, Chung-Jong

    2016-03-01

    We report on the development of a new experimental instrument for time-resolved x-ray scattering (TRXS) at the Pohang Light Source (PLS-II). It operates with a photon energy ranging from 5 to 18 keV. It is equipped with an amplified Ti:sappahire femtosecond laser, optical diagnostics, and laser beam delivery for pump-probe experiments. A high-speed single-element detector and high trigger-rate oscilloscope are used for rapid data acquisition. While this instrument is capable of measuring sub-nanosecond dynamics using standard laser pump/x-ray probe techniques, it also takes advantage of the dense 500 MHz standard fill pattern in the PLS-II storage ring to efficiently record nano-to-micro-second dynamics simultaneously. We demonstrate this capability by measuring both the (fast) impulsive strain and (slower) thermal recovery dynamics of a crystalline InSb sample following intense ultrafast laser excitation. Exploiting the full repetition rate of the storage ring results in a significant improvement in data collection rates compared to conventional bunch-tagging methods.

  14. Controlled generation of single photons in a coupled atom-cavity system at a fast repetition-rate.

    PubMed

    Kang, Sungsam; Lim, Sooin; Hwang, Myounggyu; Kim, Wookrae; Kim, Jung-Ryul; An, Kyungwon

    2011-01-31

    We have demonstrated high-speed controlled generation of single photons in a coupled atom-cavity system. A single 85Rb atom, pumped with a nanosecond-pulse laser, generates a single photon into the cavity mode, and the photon is then emitted out the cavity rapidly. By employing cavity parameters for a moderate coupling regime, the single-photon emission process was optimized for both high efficiency and fast bit rates up to 10 MHz. The temporal single-photon wave packet was studied by means of the photon-arrival-time distribution relative to the pump pulse and the efficiency of the single-photon generation was investigated as the pump power. The single-photon nature of the emission was confirmed by the second-order correlation of emitted photons.

  15. A Perceptual Repetition Blindness Effect

    NASA Technical Reports Server (NTRS)

    Hochhaus, Larry; Johnston, James C.; Null, Cynthia H. (Technical Monitor)

    1994-01-01

    Before concluding Repetition Blindness is a perceptual phenomenon, alternative explanations based on memory retrieval problems and report bias must be rejected. Memory problems were minimized by requiring a judgment about only a single briefly displayed field. Bias and sensitivity effects were empirically measured with an ROC-curve analysis method based on confidence ratings. Results from five experiments support the hypothesis that Repetition Blindness can be a perceptual phenomenon.

  16. Handheld nonlinear microscope system comprising a 2 MHz repetition rate, mode-locked Yb-fiber laser for in vivo biomedical imaging

    PubMed Central

    Krolopp, Ádám; Csákányi, Attila; Haluszka, Dóra; Csáti, Dániel; Vass, Lajos; Kolonics, Attila; Wikonkál, Norbert; Szipőcs, Róbert

    2016-01-01

    A novel, Yb-fiber laser based, handheld 2PEF/SHG microscope imaging system is introduced. It is suitable for in vivo imaging of murine skin at an average power level as low as 5 mW at 200 kHz sampling rate. Amplified and compressed laser pulses having a spectral bandwidth of 8 to 12 nm at around 1030 nm excite the biological samples at a ~1.89 MHz repetition rate, which explains how the high quality two-photon excitation fluorescence (2PEF) and second harmonic generation (SHG) images are obtained at the average power level of a laser pointer. The scanning, imaging and detection head, which comprises a conventional microscope objective for beam focusing, has a physical length of ~180 mm owing to the custom designed imaging telescope system between the laser scanner mirrors and the entrance aperture of the microscope objective. Operation of the all-fiber, all-normal dispersion Yb-fiber ring laser oscillator is electronically controlled by a two-channel polarization controller for Q-switching free mode-locked operation. The whole nonlinear microscope imaging system has the main advantages of the low price of the fs laser applied, fiber optics flexibility, a relatively small, light-weight scanning and detection head, and a very low risk of thermal or photochemical damage of the skin samples. PMID:27699118

  17. Deception rate in a "lying game": different effects of excitatory repetitive transcranial magnetic stimulation of right and left dorsolateral prefrontal cortex not found with inhibitory stimulation.

    PubMed

    Karton, Inga; Palu, Annegrete; Jõks, Kerli; Bachmann, Talis

    2014-11-01

    Knowing the brain processes involved in lying is the key point in today's deception detection studies. We have previously found that stimulating the dorsolateral prefrontal cortex (DLPFC) with repetitive transcranial magnetic stimulation (rTMS) affects the rate of spontaneous lying in simple behavioural tasks. The main idea of this study was to examine the role of rTMS applied to the DLPFC in the behavioural conditions where subjects were better motivated to lie compared to our earlier studies and where all possible conditions (inhibition of left and right DLPFC with 1-Hz and sham; excitation of left and right DLPFC with 10-Hz and sham) were administered to the same subjects. It was expected that excitation of the left DLPFC with rTMS decreases and excitation of the right DLPFC increases the rate of lying and that inhibitory stimulation reverses the effects. As was expected, excitation of the left DLPFC decreased lying compared to excitation of the right DLPFC, but contrary to the expectation, inhibition had no different effects. These findings suggest that propensity to lie can be manipulated by non-invasive excitatory brain stimulation by TMS targeted at DLPFC and the direction of the effect depends on the cortical target locus. PMID:25233864

  18. Handheld nonlinear microscope system comprising a 2 MHz repetition rate, mode-locked Yb-fiber laser for in vivo biomedical imaging

    PubMed Central

    Krolopp, Ádám; Csákányi, Attila; Haluszka, Dóra; Csáti, Dániel; Vass, Lajos; Kolonics, Attila; Wikonkál, Norbert; Szipőcs, Róbert

    2016-01-01

    A novel, Yb-fiber laser based, handheld 2PEF/SHG microscope imaging system is introduced. It is suitable for in vivo imaging of murine skin at an average power level as low as 5 mW at 200 kHz sampling rate. Amplified and compressed laser pulses having a spectral bandwidth of 8 to 12 nm at around 1030 nm excite the biological samples at a ~1.89 MHz repetition rate, which explains how the high quality two-photon excitation fluorescence (2PEF) and second harmonic generation (SHG) images are obtained at the average power level of a laser pointer. The scanning, imaging and detection head, which comprises a conventional microscope objective for beam focusing, has a physical length of ~180 mm owing to the custom designed imaging telescope system between the laser scanner mirrors and the entrance aperture of the microscope objective. Operation of the all-fiber, all-normal dispersion Yb-fiber ring laser oscillator is electronically controlled by a two-channel polarization controller for Q-switching free mode-locked operation. The whole nonlinear microscope imaging system has the main advantages of the low price of the fs laser applied, fiber optics flexibility, a relatively small, light-weight scanning and detection head, and a very low risk of thermal or photochemical damage of the skin samples.

  19. Repetition Reduction: Lexical Repetition in the Absence of Referent Repetition

    ERIC Educational Resources Information Center

    Lam, Tuan Q.; Watson, Duane G.

    2014-01-01

    Compared to words that are new to a discourse, repeated words are produced with reduced acoustic prominence. Although these effects are often attributed to priming in the production system, the locus of the effect within the production system remains unresolved because, in natural speech, repetition often involves repetition of referents and…

  20. Dual crystal x-ray spectrometer at 1.8 keV for high repetition-rate single-photon counting spectroscopy experiments

    NASA Astrophysics Data System (ADS)

    Gamboa, E. J.; Bachmann, B.; Kraus, D.; MacDonald, M. J.; Bucher, M.; Carron, S.; Coffee, R. N.; Drake, R. P.; Emig, J.; Ferguson, K. R.; Fletcher, L. B.; Glenzer, S. H.; Gorkhover, T.; Hau-Riege, S. P.; Krzywinski, J.; Levitan, A. L.; Meiwes-Broer, K.-H.; Osipov, T.; Pardini, T.; Peltz, C.; Skruszewicz, S.; Bostedt, C.; Fennel, T.; Döppner, T.

    2016-08-01

    With the recent development of high-repetition rate x-ray free electron lasers (FEL), it is now possible to perform x-ray scattering and emission spectroscopy measurements from thin foils or gasses heated to high-energy density conditions by integrating over many experimental shots. Since the expected signal may be weaker than the typical CCD readout noise over the region-of-interest, it is critical to the success of this approach to use a detector with high-energy resolution so that single x-ray photons may be isolated. Here we describe a dual channel x-ray spectrometer developed for the Atomic and Molecular Optics endstation at the Linac Coherent Light Source (LCLS) for x-ray spectroscopy near the K-edge of aluminum. The spectrometer is based on a pair of curved PET (002) crystals coupled to a single pnCCD detector which simultaneously measures x-ray scattering and emission in the forward and backward directions. The signals from single x-ray photons are accumulated permitting continuous single-shot acquisition at 120 Hz.

  1. Versatile high-repetition-rate phase-locked chopper system for fast timing experiments in the vacuum ultraviolet and x-ray spectral region.

    PubMed

    Plogmaker, Stefan; Linusson, Per; Eland, John H D; Baker, Neville; Johansson, Erik M J; Rensmo, Håkan; Feifel, Raimund; Siegbahn, Hans

    2012-01-01

    A novel light chopper system for fast timing experiments in the vacuum-ultraviolet (VUV) and x-ray spectral region has been developed. It can be phase-locked and synchronized with a synchrotron radiation storage ring, accommodating repetition rates in the range of ~8 to ~120 kHz by choosing different sets of apertures and subharmonics of the ring frequency (MHz range). Also the opening time of the system can be varied from some nanoseconds to several microseconds to meet the needs of a broad range of applications. Adjusting these parameters, the device can be used either for the generation of single light pulses or pulse packages from a microwave driven, continuous He gas discharge lamp or from storage rings which are otherwise often considered as quasi-continuous light sources. This chopper can be utilized for many different kinds of experiments enabling, for example, unambiguous time-of-flight (TOF) multi-electron coincidence studies of atoms and molecules excited by a single light pulse as well as time-resolved visible laser pump x-ray probe electron spectroscopy of condensed matter in the valence and core level region.

  2. Three-dimensional polymer nanostructures for applications in cell biology generated by high-repetition rate sub-15 fs near-infrared laser pulses

    NASA Astrophysics Data System (ADS)

    Licht, Martin; Straub, Martin; König, Karsten; Afshar, Maziar; Feili, Dara; Seidel, Helmut

    2011-03-01

    In recent years two-photon photopolymerization has emerged as a novel and extremely powerful technique of three-dimensional nanostructure formation. Complex-shaped structures can be generated using appropriate beam steering or nanopositioning systems. Here, we report on the fabrication of three-dimensional arrangements made of biocompatible polymer material, which can be used as templates for cell growth. Using three-dimensional cell cages as cell culture substrates is advantageous, as cells may develop in a more natural environment as compared to conventional planar growth methods. The two-photon fabrication experiments were carried out on a commercial microscope setup. Sub-15 fs pulsed Ti:Sapphire laser light (centre wavelength 800 nm, bandwidth 120 nm, repetition rate 85 MHz) was focused into the polymer material by a high-numerical aperture oil immersion objective. Due to the high peak intensities picojoule pulse energies in the focal spot are sufficient to polymerize the material at sub-100 nm structural element dimensions. Therefore, cell cages of sophisticated architecture can be constructed involving very fine features which take into account the specific needs of various types of cells. Ultimately, our research aims at three-dimensional assemblies of photopolymerized structural elements involving sub-100 nm features, which provide cell culture substrates far superior to those currently existing.

  3. Resonance ionization spectroscopy of sodium Rydberg levels using difference frequency generation of high-repetition-rate pulsed Ti:sapphire lasers

    NASA Astrophysics Data System (ADS)

    Naubereit, P.; Marín-Sáez, J.; Schneider, F.; Hakimi, A.; Franzmann, M.; Kron, T.; Richter, S.; Wendt, K.

    2016-05-01

    The generation of tunable laser light in the green to orange spectral range has generally been a deficiency of solid-state lasers. Hence, the formalisms of difference frequency generation (DFG) and optical parametric processes are well known, but the DFG of pulsed solid-state lasers was rarely efficient enough for its use in resonance ionization spectroscopy. Difference frequency generation of high-repetition-rate Ti:sapphire lasers was demonstrated for resonance ionization of sodium by efficiently exciting the well-known D1 and D2 lines in the orange spectral range (both ≈589 nm). In order to prove the applicability of the laser system for its use at resonance ionization laser ion sources of radioactive ion beam facilities, the first ionization potential of Na was remeasured by three-step resonance ionization into Rydberg levels and investigating Rydberg convergences. A result of EIP=41449.455 (6) stat(7) syscm-1 was obtained, which is in perfect agreement with the literature value of EIPlit =41449.451(2)cm-1 . A total of 41 level positions for the odd-parity Rydberg series n f 2F5/2,7/2o for principal quantum numbers of 10 ≤n ≤60 were determined experimentally.

  4. High repetition-rate neutron generation by several-mJ, 35 fs pulses interacting with free-flowing D2O

    NASA Astrophysics Data System (ADS)

    Hah, J.; Petrov, G. M.; Nees, J. A.; He, Z.-H.; Hammig, M. D.; Krushelnick, K.; Thomas, A. G. R.

    2016-10-01

    Using several-mJ energy pulses from a high-repetition rate (1/2 kHz), ultrashort (35 fs) pulsed laser interacting with a ˜ 10 μm diameter stream of free-flowing heavy water (D2O), we demonstrate a 2.45 MeV neutron flux of 105/s. Operating at high intensity (of order 1019 W/cm2), laser pulse energy is efficiently absorbed in the pre-plasma, generating energetic deuterons. These collide with deuterium nuclei in both the bulk target and the large volume of low density D2O vapor surrounding the target to generate neutrons through d ( d , n ) 3 He reactions. The neutron flux, as measured by a calibrated neutron bubble detector, increases as the laser pulse energy is increased from 6 mJ to 12 mJ. A quantitative comparison between the measured flux and the results derived from 2D-particle-in-cell simulations shows comparable neutron fluxes for laser characteristics similar to the experiment. The simulations reveal that there are two groups of deuterons. Forward moving deuterons generate deuterium-deuterium fusion reactions in the D2O stream and act as a point source of neutrons, while backward moving deuterons propagate through the low-density D2O vapor filled chamber and yield a volumetric source of neutrons.

  5. High-power LD side-pump Nd: YAG regenerative amplifier at 1 kHz repetition rate with volume Bragg gratings (VBG) for broadening and compressor

    NASA Astrophysics Data System (ADS)

    Long, Ming-Liang; Chen, Li-Yuan; Chen, Meng; Li, Gang

    2016-05-01

    Pulse width of 8.7 ps was broadened to 102.2, 198 ps with single and double pass the VBG respectively. When the 102.2 ps pulse was injected into 1 kHz repetition rate of LD side-pump Nd: YAG regenerative amplifier (RA), pulse width of 87.5 ps at 1 kHz was obtained with the pulse energy of 9.4 mJ, the beam quality of M^2 factor was 1.2. The pulse width was compressed to 32.7 ps with a single pass VBG and the pulse energy reduced to 8.8 mJ, and the power density was up to 15.2 GW/cm2, the stability for pulse to pulse rms is about 0.6 %, beam pointing was about 35 μrad. In addition, when 198 ps pulse was injected into RA, pulse width of 156 ps was obtained which energy was 9.6 mJ, the pulse width was compressed to 38 ps by double passing the VBG, the pulse energy decreased to 8.5 mJ. Chirped VBG is a new way to obtain high-intensity picosecond pulse laser system simple and smaller.

  6. High-energy femtosecond Yb-doped all-fiber monolithic chirped-pulse amplifier at repetition rate of 1 MHz

    NASA Astrophysics Data System (ADS)

    Lv, Zhi-Guo; Teng, Hao; Wang, Li-Na; Wang, Jun-Li; Wei, Zhi-Yi

    2016-09-01

    A high-energy femtosecond all ytterbium fiber amplifier based on a chirped-pulse amplification (CPA) technique at a repetition rate of 1 MHz seeded by a dispersion-management mode-locked picosecond broadband oscillator is studied. We find that the compressed pulse duration is dependent on the amplified energy, the pulse duration of 804 fs corresponds to the maximum amplified energy of 10.5 μJ, while the shortest pulse duration of 424 fs corresponds to the amplified energy of 6.75 μJ. The measured energy fluctuation is approximately 0.46% root mean square (RMS) over 2 h. The low-cost femtosecond fiber laser source with super-stability will be widely used in industrial micromachines, medical therapy, and scientific studies. Project supported by the National Key Technology Research and Development Program of the Ministry of Science and Technology of China (Grant No. 2012BAC23B03), the National Key Basic Research Program of China (Grant No. 2013CB922401), and the National Natural Science Foundation of China (Grant No. 11474002).

  7. Versatile high-repetition-rate phase-locked chopper system for fast timing experiments in the vacuum ultraviolet and x-ray spectral region

    SciTech Connect

    Plogmaker, Stefan; Johansson, Erik M. J.; Rensmo, Haakan; Feifel, Raimund; Siegbahn, Hans; Linusson, Per; Eland, John H. D.; Baker, Neville

    2012-01-15

    A novel light chopper system for fast timing experiments in the vacuum-ultraviolet (VUV) and x-ray spectral region has been developed. It can be phase-locked and synchronized with a synchrotron radiation storage ring, accommodating repetition rates in the range of {approx}8 to {approx}120 kHz by choosing different sets of apertures and subharmonics of the ring frequency (MHz range). Also the opening time of the system can be varied from some nanoseconds to several microseconds to meet the needs of a broad range of applications. Adjusting these parameters, the device can be used either for the generation of single light pulses or pulse packages from a microwave driven, continuous He gas discharge lamp or from storage rings which are otherwise often considered as quasi-continuous light sources. This chopper can be utilized for many different kinds of experiments enabling, for example, unambiguous time-of-flight (TOF) multi-electron coincidence studies of atoms and molecules excited by a single light pulse as well as time-resolved visible laser pump x-ray probe electron spectroscopy of condensed matter in the valence and core level region.

  8. A short pulse (7 μs FWHM) and high repetition rate (dc-5kHz) cantilever piezovalve for pulsed atomic and molecular beams

    NASA Astrophysics Data System (ADS)

    Irimia, Daniel; Dobrikov, Dimitar; Kortekaas, Rob; Voet, Han; van den Ende, Daan A.; Groen, Wilhelm A.; Janssen, Maurice H. M.

    2009-11-01

    In this paper we report on the design and operation of a novel piezovalve for the production of short pulsed atomic or molecular beams. The high speed valve operates on the principle of a cantilever piezo. The only moving part, besides the cantilever piezo itself, is a very small O-ring that forms the vacuum seal. The valve can operate continuous (dc) and in pulsed mode with the same drive electronics. Pulsed operation has been tested at repetition frequencies up to 5 kHz. The static deflection of the cantilever, as mounted in the valve body, was measured as a function of driving field strength with a confocal microscope. The deflection and high speed dynamical response of the cantilever can be easily changed and optimized for a particular nozzle diameter or repetition rate by a simple adjustment of the free cantilever length. Pulsed molecular beams with a full width at half maximum pulse width as low as 7 μs have been measured at a position 10 cm downstream of the nozzle exit. This represents a gas pulse with a length of only 10 mm making it well matched to for instance experiments using laser beams. Such a short pulse with 6 bar backing pressure behind a 150 μm nozzle releases about 1016 particles/pulse and the beam brightness was estimated to be 4×1022 particles/(s str). The short pulses of the cantilever piezovalve result in a much reduced gas load in the vacuum system. We demonstrate operation of the pulsed valve with skimmer in a single vacuum chamber pumped by a 520 l/s turbomolecular pump maintaining a pressure of 5×10-6 Torr, which is an excellent vacuum to have the strong and cold skimmed molecular beam interact with laser beams only 10 cm downstream of the nozzle to do velocity map slice imaging with a microchannel-plate imaging detector in a single chamber. The piezovalve produces cold and narrow (Δv /v=2%-3%) velocity distributions of molecules seeded in helium or neon at modest backing pressures of only 6 bar. The low gas load of the cantilever

  9. A short pulse (7 {mu}s FWHM) and high repetition rate (dc-5kHz) cantilever piezovalve for pulsed atomic and molecular beams

    SciTech Connect

    Irimia, Daniel; Dobrikov, Dimitar; Kortekaas, Rob; Voet, Han; Janssen, Maurice H. M.; Ende, Daan A. van den; Groen, Wilhelm A.

    2009-11-15

    In this paper we report on the design and operation of a novel piezovalve for the production of short pulsed atomic or molecular beams. The high speed valve operates on the principle of a cantilever piezo. The only moving part, besides the cantilever piezo itself, is a very small O-ring that forms the vacuum seal. The valve can operate continuous (dc) and in pulsed mode with the same drive electronics. Pulsed operation has been tested at repetition frequencies up to 5 kHz. The static deflection of the cantilever, as mounted in the valve body, was measured as a function of driving field strength with a confocal microscope. The deflection and high speed dynamical response of the cantilever can be easily changed and optimized for a particular nozzle diameter or repetition rate by a simple adjustment of the free cantilever length. Pulsed molecular beams with a full width at half maximum pulse width as low as 7 {mu}s have been measured at a position 10 cm downstream of the nozzle exit. This represents a gas pulse with a length of only 10 mm making it well matched to for instance experiments using laser beams. Such a short pulse with 6 bar backing pressure behind a 150 {mu}m nozzle releases about 10{sup 16} particles/pulse and the beam brightness was estimated to be 4x10{sup 22} particles/(s str). The short pulses of the cantilever piezovalve result in a much reduced gas load in the vacuum system. We demonstrate operation of the pulsed valve with skimmer in a single vacuum chamber pumped by a 520 l/s turbomolecular pump maintaining a pressure of 5x10{sup -6} Torr, which is an excellent vacuum to have the strong and cold skimmed molecular beam interact with laser beams only 10 cm downstream of the nozzle to do velocity map slice imaging with a microchannel-plate imaging detector in a single chamber. The piezovalve produces cold and narrow ({Delta}v/v=2%-3%) velocity distributions of molecules seeded in helium or neon at modest backing pressures of only 6 bar. The low gas

  10. A short pulse (7 micros FWHM) and high repetition rate (dc-5 kHz) cantilever piezovalve for pulsed atomic and molecular beams.

    PubMed

    Irimia, Daniel; Dobrikov, Dimitar; Kortekaas, Rob; Voet, Han; van den Ende, Daan A; Groen, Wilhelm A; Janssen, Maurice H M

    2009-11-01

    In this paper we report on the design and operation of a novel piezovalve for the production of short pulsed atomic or molecular beams. The high speed valve operates on the principle of a cantilever piezo. The only moving part, besides the cantilever piezo itself, is a very small O-ring that forms the vacuum seal. The valve can operate continuous (dc) and in pulsed mode with the same drive electronics. Pulsed operation has been tested at repetition frequencies up to 5 kHz. The static deflection of the cantilever, as mounted in the valve body, was measured as a function of driving field strength with a confocal microscope. The deflection and high speed dynamical response of the cantilever can be easily changed and optimized for a particular nozzle diameter or repetition rate by a simple adjustment of the free cantilever length. Pulsed molecular beams with a full width at half maximum pulse width as low as 7 micros have been measured at a position 10 cm downstream of the nozzle exit. This represents a gas pulse with a length of only 10 mm making it well matched to for instance experiments using laser beams. Such a short pulse with 6 bar backing pressure behind a 150 microm nozzle releases about 10(16) particles/pulse and the beam brightness was estimated to be 4x10(22) particles/(s str). The short pulses of the cantilever piezovalve result in a much reduced gas load in the vacuum system. We demonstrate operation of the pulsed valve with skimmer in a single vacuum chamber pumped by a 520 l/s turbomolecular pump maintaining a pressure of 5x10(-6) Torr, which is an excellent vacuum to have the strong and cold skimmed molecular beam interact with laser beams only 10 cm downstream of the nozzle to do velocity map slice imaging with a microchannel-plate imaging detector in a single chamber. The piezovalve produces cold and narrow (Delta v/v=2%-3%) velocity distributions of molecules seeded in helium or neon at modest backing pressures of only 6 bar. The low gas load of the

  11. 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.

  12. Development of a high time resolution measurement of NO2 and HCHO concentration in the atmosphere using high repetition rate cavity ring-down spectroscopy

    NASA Astrophysics Data System (ADS)

    Ida, A.; Nakamura, K.; Kajii, Y. J.

    2013-12-01

    Many chemical species with light absorption band at 300 ~ 350 nm are contained in the atmosphere, however these trace gases have important role in the atmosphere. The sun light is absorbed by these trace gases then free radicals cause the photochemistry in the atmosphere are formed by photolysis of these trace gases. Both hydrogen and formylradicals which will be converted into HO2 radicals in the atmosphere are generated in the photolysis of formaldehyde in the atmosphere. NO2 is important precursor for O3 in the troposphere that strongly control oxidation capacity of the air because OH radicals are formed in the photolysis of ozone. It is important to measure concentrations of these photoactive species precisely to reveal the atmospheric chemistry. These trace gases have short lifetimes and the forming process are complicated then these trace gases have wide fluctuations of concentrations. In this study, we developed a measurement system of NO2 and H2CO with high time resolution and high sensitivity using UV laser absorption system. The Cavity ring-down system was employed with high repetition rate laser system (10kHz). The ring-down time of N2 was measured to be 2.9×0.9, 3.0×0.1, 2.90×0.01 μs with the averaging time of 1 (0.1 ms), 50 (5ms) and 100000 (1s) shots, respectively. The uncertainty was decreasing to increase average times and the limit of detection was drastically decreasing. For example of NO2, the limit of detection was improved from 1.4 ppm to 3 ppb. The intercomparison measurement of the sample gases containing NO2 was performed under the several NO2 concentrations with this CRDS system and NOx analyser (MODEL 42i: Thermo Electron Corporation) employed cemiluminescense. The correlation factor was calculated to be 0.975. Measurement values from CRDS system was ensured. H2CO absorbs the UV light around 350~360 nm. The concentration was determined using the absorption band. The limit of detection was about 10 ppb of H2CO. In January 2012, ambient

  13. Grade Repetition in Queensland State Prep Classes

    ERIC Educational Resources Information Center

    Anderson, Robyn

    2012-01-01

    The current study considers grade repetition rates in the early years of schooling in Queensland state schools with specific focus on the pre-schooling year, Prep. In particular, it provides empirical evidence of grade repetition in Queensland state schools along with groups of students who are more often repeated. At the same time, much of the…

  14. 5.2-W high-repetition-rate eye-safe laser at 1525 nm generated by Nd:YVO₄₋YVO₄stimulated Raman conversion.

    PubMed

    Ding, Xin; Fan, Chen; Sheng, Quan; Li, Bin; Yu, Xuanyi; Zhang, Guizhong; Sun, Bing; Wu, Liang; Zhang, Haiyong; Liu, Jian; Jiang, Pengbo; Zhang, Wei; Zhao, Cen; Yao, Jianquan

    2014-11-17

    We report herein an efficient eye-safe Raman laser, which is based upon Nd:YVO₄₋YVO₄ and in-band pumped by a wavelength-locked laser diode array at 878.6 nm. By virtue of mitigated thermal load and improved pump absorption, a maximum average output power of 5.2 W at 1525 nm is obtained under the incident pump power of 30.6 W with the pulse repetition frequency of 140 kHz, corresponding to an optical efficiency of 17.0%. PMID:25402149

  15. A high repetition rate TEA CO II laser operating at λ=9.3-μm for the rapid and conservative ablation and modification of dental hard tissues

    NASA Astrophysics Data System (ADS)

    Fan, Kenneth; Fried, Daniel

    2006-02-01

    TEA CO II lasers tuned to the strong mineral absorption of hydroxyapatite near λ=9-μm are ideally suited for the efficient ablation of dental hard tissues if the laser-pulse is stretched to greater than 5-10-μs to avoid plasma shielding phenomena. Such CO II lasers are capable of operating at high repetition rates for the rapid removal of dental hard tissues. An Impact 2500 TEA CO II laser system from GSI Lumonics (Rugby, UK) custom modified by LightMachinery (Ottawa, Canada) with a repetition rate of 0-500 Hz was used for rapid tissue removal. The single pulse ablation rates through enamel were determined for incident fluence ranging from (1-160 J/cm2). Lateral incisions using a computer controlled scanning stage and water spray were produced and the crater morphology and chemical composition were measured using optical microscopy and high-resolution synchrotron radiation infrared spectromicroscopy. The transmission through 2-meter length 300, 500, 750 and 1000-μm silica hollow waveguides was measured and 80% transmission was achieved with 40-mJ per pulse. The λ=9.3-μm laser pulses efficiently removed dental enamel at rates exceeding 15-μm per pulses with minimal heat accumulation. The residual energy remaining in tooth samples was measured to be 30-40% without water cooling, significantly lower than for longer CO II laser pulses. These results suggest that high repetition rate TEA CO II laser systems operating at λ=9.3-μm with pulse durations of 10-20-μs are ideally suited for dental application.

  16. Grammatical Change through Repetition.

    ERIC Educational Resources Information Center

    Arevart, Supot

    1989-01-01

    The effect of repetition on grammatical change in an unrehearsed talk is examined based on a case study of a single learner. It was found that repetition allows for accuracy monitoring in that errors committed in repeated contexts undergo correction. Implications for teaching are discussed. (23 references) (LB)

  17. Replicating repetitive DNA.

    PubMed

    Tognetti, Silvia; Speck, Christian

    2016-05-27

    The function and regulation of repetitive DNA, the 'dark matter' of the genome, is still only rudimentarily understood. Now a study investigating DNA replication of repetitive centromeric chromosome segments has started to expose a fascinating replication program that involves suppression of ATR signalling, in particular during replication stress. PMID:27230530

  18. The Negative Repetition Effect

    ERIC Educational Resources Information Center

    Mulligan, Neil W.; Peterson, Daniel J.

    2013-01-01

    A fundamental property of human memory is that repetition enhances memory. Peterson and Mulligan (2012) recently documented a surprising "negative repetition effect," in which participants who studied a list of cue-target pairs twice recalled fewer targets than a group who studied the pairs only once. Words within a pair rhymed, and…

  19. Repetitive Stress Injuries

    MedlinePlus

    ... any problems since. What Are Repetitive Stress Injuries? Repetitive stress injuries (RSIs) are injuries that happen when too much stress is placed on a part of the body, resulting in inflammation (pain and swelling), muscle strain, or tissue damage. This stress generally occurs from ...

  20. Repetitive stereotyped behaviors.

    PubMed

    Berkson, G

    1983-11-01

    This paper points to factors that determine whether repetitive stereotyped behavior occur in the behavior repertoire. The analysis pits an "intrinsic oscillator" mechanism against a "self-stimulation" theory and chooses to emphasize the latter. The paper accounts for the repetitive and rhythmic nature of stereotypy by suggesting that repetition in a rhythmic way is the most efficient way of self-stimulation. It proposes that rhythm may be a reinforcement in at least some cases. It raises the question of whether control of stimulation by the person is a necessary condition for maintaining stereotypy. The paper recognizes the possibility that stereotyped behaviors may have their origin in the common repetitive behaviors of infancy but emphasizes that pathological stereotypy may involve more than immature repetition. It suggests that there is reason to believe that early intervention to prevent pathological stereotyped behavior might be effective but that we do not know much about how stereotypies get started.

  1. Roles of repetitive sequences

    SciTech Connect

    Bell, G.I.

    1991-12-31

    The DNA of higher eukaryotes contains many repetitive sequences. The study of repetitive sequences is important, not only because many have important biological function, but also because they provide information on genome organization, evolution and dynamics. In this paper, I will first discuss some generic effects that repetitive sequences will have upon genome dynamics and evolution. In particular, it will be shown that repetitive sequences foster recombination among, and turnover of, the elements of a genome. I will then consider some examples of repetitive sequences, notably minisatellite sequences and telomere sequences as examples of tandem repeats, without and with respectively known function, and Alu sequences as an example of interspersed repeats. Some other examples will also be considered in less detail.

  2. 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.

  3. High-power, high-repetition-rate mid-infrared generation with PE-SRO based on a fan-out periodically poled MgO-doped lithium niobate

    NASA Astrophysics Data System (ADS)

    Xiong, Bo; Ma, Jian-Li; Chen, Ran; Wang, Bao-Hua; Cui, Qian-Jin; Zhang, Ling; Guo, Lin; Hou, Wei; Lin, Xue-Chun; Li, Jin-Min

    2011-03-01

    We present a high-average-power, pulsed mid-infrared pump-enhanced singly-resonant optical parametric oscillator (PE-SRO) using a fan-out periodically poled MgO-doped lithium niobate (MgO:PPLN). The pump laser is a Q-switched Nd:YAG laser with a repetition rate of 10 kHz. When the pump power was 22.0 W, a maximum idler output power of 3.4 W at 3781.4 nm was obtained. The thermal guiding effect caused by signal absorption was observed and the crystal heating power was measured with a new method.

  4. Perceptual Repetition Blindness Effects

    NASA Technical Reports Server (NTRS)

    Hochhaus, Larry; Johnston, James C.; Null, Cynthia H. (Technical Monitor)

    1994-01-01

    The phenomenon of repetition blindness (RB) may reveal a new limitation on human perceptual processing. Recently, however, researchers have attributed RB to post-perceptual processes such as memory retrieval and/or reporting biases. The standard rapid serial visual presentation (RSVP) paradigm used in most RB studies is, indeed, open to such objections. Here we investigate RB using a "single-frame" paradigm introduced by Johnston and Hale (1984) in which memory demands are minimal. Subjects made only a single judgement about whether one masked target word was the same or different than a post-target probe. Confidence ratings permitted use of signal detection methods to assess sensitivity and bias effects. In the critical condition for RB a precue of the post-target word was provided prior to the target stimulus (identity precue), so that the required judgement amounted to whether the target did or did not repeat the precue word. In control treatments, the precue was either an unrelated word or a dummy.

  5. Repetition priming in music.

    PubMed

    Hutchins, Sean; Palmer, Caroline

    2008-06-01

    The authors explore priming effects of pitch repetition in music in 3 experiments. Musically untrained participants heard a short melody and sang the last pitch of the melody as quickly as possible. Each experiment manipulated (a) whether or not the tone to be sung (target) was heard earlier in the melody (primed) and (b) the prime-target distance (measured in events). Experiment 1 used variable-length melodies, whereas Experiments 2 and 3 used fixed-length melodies. Experiment 3 changed the timbre of the target tone. In all experiments, fast-responding participants produced repeated tones faster than nonrepeated tones, and this repetition benefit decreased as prime-target distances increased. All participants produced expected tonic endings faster than less expected nontonic endings. Repetition and tonal priming effects are compared with harmonic priming effects in music and with repetition priming effects in language. PMID:18505332

  6. Repetition priming in music.

    PubMed

    Hutchins, Sean; Palmer, Caroline

    2008-06-01

    The authors explore priming effects of pitch repetition in music in 3 experiments. Musically untrained participants heard a short melody and sang the last pitch of the melody as quickly as possible. Each experiment manipulated (a) whether or not the tone to be sung (target) was heard earlier in the melody (primed) and (b) the prime-target distance (measured in events). Experiment 1 used variable-length melodies, whereas Experiments 2 and 3 used fixed-length melodies. Experiment 3 changed the timbre of the target tone. In all experiments, fast-responding participants produced repeated tones faster than nonrepeated tones, and this repetition benefit decreased as prime-target distances increased. All participants produced expected tonic endings faster than less expected nontonic endings. Repetition and tonal priming effects are compared with harmonic priming effects in music and with repetition priming effects in language.

  7. Characterizing temporal repetition

    SciTech Connect

    Cukierman, D.; Delgrande, J.

    1996-12-31

    We are investigating the representation and reasoning about schedulable, repeated activities, specified using calendars. Examples of such activities include meeting every Tuesday and Thursday during a semester and attending a seminar every first day of a month. This research provides for a valuable framework for scheduling systems, financial systems and, in general, date-based systems. Very recently work has been done related to reasoning about repetition in the Artificial Intelligence community and others. A partial reference list is provided here. However, to our knowledge no extensive taxonomy of repetition has been proposed in the literature. We believe that reasoning about repeated activities calls for a study and precise definition of the topological characteristics in a repetitive series. In this abstract we summarize a proposal to classify types of repetition according to parameters. The combination of all possible values of these parameters provides a complete taxonomy of repetitive classes with respect to the proposed parameters. Several notions of repetition are considered, some are extremely general, some are very specific.

  8. Indirect decentralized repetitive control

    NASA Technical Reports Server (NTRS)

    Lee, Soo Cheol; Longman, Richard W.

    1993-01-01

    Learning control refers to controllers that learn to improve their performance at executing a given task, based on experience performing this specific task. In a previous work, the authors presented a theory of indirect decentralized learning control based on use of indirect adaptive control concepts employing simultaneous identification and control. This paper extends these results to apply to the indirect repetitive control problem in which a periodic (i.e., repetitive) command is given to a control system. Decentralized indirect repetitive control algorithms are presented that have guaranteed convergence to zero tracking error under very general conditions. The original motivation of the repetitive control and learning control fields was learning in robots doing repetitive tasks such as on an assembly line. This paper starts with decentralized discrete time systems, and progresses to the robot application, modeling the robot as a time varying linear system in the neighborhood of the desired trajectory. Decentralized repetitive control is natural for this application because the feedback control for link rotations is normally implemented in a decentralized manner, treating each link as if it is independent of the other links.

  9. Pulsed UV-C disinfection of Escherichia coli with light-emitting diodes, emitted at various repetition rates and duty cycles.

    PubMed

    Wengraitis, Stephen; McCubbin, Patrick; Wade, Mary Margaret; Biggs, Tracey D; Hall, Shane; Williams, Leslie I; Zulich, Alan W

    2013-01-01

    A 2010 study exposed Staphylococcus aureus to ultraviolet (UV) radiation and thermal heating from pulsed xenon flash lamps. The results suggested that disinfection could be caused not only by photochemical changes from UV radiation, but also by photophysical stress damage caused by the disturbance from incoming pulses. The study called for more research in this area. The recent advances in light-emitting diode (LED) technology include the development of LEDs that emit in narrow bands in the ultraviolet-C (UV-C) range (100-280 nm), which is highly effective for UV disinfection of organisms. Further, LEDs would use less power, and allow more flexibility than other sources of UV energy in that the user may select various pulse repetition frequencies (PRFs), pulse irradiances, pulse widths, duty cycles and types of waveform output (e.g. square waves, sine waves, triangular waves, etc.). Our study exposed Escherichia coli samples to square pulses of 272 nm radiation at various PRFs and duty cycles. A statistically significant correlation was found between E. coli's disinfection sensitivity and these parameters. Although our sample size was small, these results show promise and are worthy of further investigation. Comparisons are also made with pulsed disinfection by LEDs emitting at 365 nm, and pulsed disinfection by xenon flash lamps.

  10. Repetitive strain injury: causes, treatment and prevention.

    PubMed

    Shuttleworth, Ann

    Repetitive strain injury (RSI) has become increasingly prevalent with the growth of computer-based and automated occupations. While environmental factors such as work stations and repetitive tasks are primary causes, a number of secondary causes can increase a person's risk of RSI. Various treatments provide relief but the rate of recovery varies widely. Prevention involves adopting a range of measures that will also promote recovery in those with RSI.

  11. Continuous-wave and high repetition rate Q-switched operation of Ho:YLF laser in-band pumped by a linearly polarized Tm:fiber laser

    NASA Astrophysics Data System (ADS)

    Kwiatkowski, Jacek; Zendzian, Waldemar; Jabczynski, Jan Karol; Swiderski, Jacek

    2014-11-01

    A study of Ho:YLF laser in continuous-wave (CW) and Q-switched operation, single-pass end-pumped by a Tm:fiber laser is presented. The research was made for two crystals of the same length and with different Ho dopant concentrations (0.5 at%, 3×3×30 mm3 and 1.0 at%, 5×5×30 mm3). The lasers operated on π-polarization. The lasers based on both crystals were examined under the same experimental circumstances. At room temperature, for an output coupling transmission of 40%, the maximum CW output powers of 11.5 W (0.5 at%) and 14.5 W (1.0 at%) were achieved, corresponding to slope efficiencies of 40.9% and 53.4% and optical-to-optical efficiencies of 35.4% and 44.6% with respect to the incident pump power, respectively. For a Q-switched operation, in a CW pumping regime, the pulse repetition frequency (PRF) was changed from 1 to 10 kHz. For this case, the maximum average output power of 14.2 W at the PRF of 10 kHz was obtained for a higher holmium-doping concentration crystal. For 1 kHz PRF, pulse energies of 5.7 mJ with a 11 ns FWHM pulse width corresponding to almost 520 kW peak power were recorded. The laser operated at the wavelength of 2050.08 nm with the FWHM line width of 0.86 nm delivering a near-diffraction-limited beam with M2 values of 1.05 and 1.09 in the horizontal and vertical directions, respectively.

  12. The negative repetition effect.

    PubMed

    Mulligan, Neil W; Peterson, Daniel J

    2013-09-01

    A fundamental property of human memory is that repetition enhances memory. Peterson and Mulligan (2012) recently documented a surprising negative repetition effect, in which participants who studied a list of cue-target pairs twice recalled fewer targets than a group who studied the pairs only once. Words within a pair rhymed, and across pairs, the target words were drawn from a small set of categories. In the repetition condition, the pairs were initially presented in a random order and then presented a 2nd time blocked by the category of the target words. In the single presentation condition, the pairs were presented only in the blocked order. Participants in the former condition recalled fewer target words on a free recall test despite having seen the word pairs twice (the negative repetition effect). This phenomenon is explored in a series of 5 experiments assessing 3 theoretical accounts of the effect. The experiments demonstrate that the negative repetition effect generalizes over multiple encoding conditions (reading and generative encoding), over different memory tests (free and cued recall), and over delay (5 min and 2 days). The results argue against a retrieval account and a levels-of-processing account but are consistent with the item-specific-relational account, the account upon which the effect was initially predicated. PMID:23421508

  13. Repetitive strain injury.

    PubMed

    Al-Otaibi, S T

    2001-05-01

    Repetitive strain injury is a group of musculoskeletal disorders affecting muscles, tendons, nerves and blood vessels. These disorders could be attributed to occupational causes; however non-occupational causes should be excluded. The management of these cases required a multidisciplinary team approach.

  14. Repetition Priming in Music

    ERIC Educational Resources Information Center

    Hutchins, Sean; Palmer, Caroline

    2008-01-01

    The authors explore priming effects of pitch repetition in music in 3 experiments. Musically untrained participants heard a short melody and sang the last pitch of the melody as quickly as possible. Each experiment manipulated (a) whether or not the tone to be sung (target) was heard earlier in the melody (primed) and (b) the prime-target distance…

  15. 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.

  16. Multi-purpose two- and three-dimensional momentum imaging of charged particles for attosecond experiments at 1 kHz repetition rate

    SciTech Connect

    Månsson, Erik P. Sorensen, Stacey L.; Gisselbrecht, Mathieu; Arnold, Cord L.; Kroon, David; Guénot, Diego; Fordell, Thomas; Johnsson, Per; L’Huillier, Anne; Lépine, Franck

    2014-12-15

    We report on the versatile design and operation of a two-sided spectrometer for the imaging of charged-particle momenta in two dimensions (2D) and three dimensions (3D). The benefits of 3D detection are to discern particles of different mass and to study correlations between fragments from multi-ionization processes, while 2D detectors are more efficient for single-ionization applications. Combining these detector types in one instrument allows us to detect positive and negative particles simultaneously and to reduce acquisition times by using the 2D detector at a higher ionization rate when the third dimension is not required. The combined access to electronic and nuclear dynamics available when both sides are used together is important for studying photoreactions in samples of increasing complexity. The possibilities and limitations of 3D momentum imaging of electrons or ions in the same spectrometer geometry are investigated analytically and three different modes of operation demonstrated experimentally, with infrared or extreme ultraviolet light and an atomic/molecular beam.

  17. Multi-purpose two- and three-dimensional momentum imaging of charged particles for attosecond experiments at 1 kHz repetition rate.

    PubMed

    Månsson, Erik P; Sorensen, Stacey L; Arnold, Cord L; Kroon, David; Guénot, Diego; Fordell, Thomas; Lépine, Franck; Johnsson, Per; L'Huillier, Anne; Gisselbrecht, Mathieu

    2014-12-01

    We report on the versatile design and operation of a two-sided spectrometer for the imaging of charged-particle momenta in two dimensions (2D) and three dimensions (3D). The benefits of 3D detection are to discern particles of different mass and to study correlations between fragments from multi-ionization processes, while 2D detectors are more efficient for single-ionization applications. Combining these detector types in one instrument allows us to detect positive and negative particles simultaneously and to reduce acquisition times by using the 2D detector at a higher ionization rate when the third dimension is not required. The combined access to electronic and nuclear dynamics available when both sides are used together is important for studying photoreactions in samples of increasing complexity. The possibilities and limitations of 3D momentum imaging of electrons or ions in the same spectrometer geometry are investigated analytically and three different modes of operation demonstrated experimentally, with infrared or extreme ultraviolet light and an atomic/molecular beam.

  18. Multi-purpose two- and three-dimensional momentum imaging of charged particles for attosecond experiments at 1 kHz repetition rate.

    PubMed

    Månsson, Erik P; Sorensen, Stacey L; Arnold, Cord L; Kroon, David; Guénot, Diego; Fordell, Thomas; Lépine, Franck; Johnsson, Per; L'Huillier, Anne; Gisselbrecht, Mathieu

    2014-12-01

    We report on the versatile design and operation of a two-sided spectrometer for the imaging of charged-particle momenta in two dimensions (2D) and three dimensions (3D). The benefits of 3D detection are to discern particles of different mass and to study correlations between fragments from multi-ionization processes, while 2D detectors are more efficient for single-ionization applications. Combining these detector types in one instrument allows us to detect positive and negative particles simultaneously and to reduce acquisition times by using the 2D detector at a higher ionization rate when the third dimension is not required. The combined access to electronic and nuclear dynamics available when both sides are used together is important for studying photoreactions in samples of increasing complexity. The possibilities and limitations of 3D momentum imaging of electrons or ions in the same spectrometer geometry are investigated analytically and three different modes of operation demonstrated experimentally, with infrared or extreme ultraviolet light and an atomic/molecular beam. PMID:25554286

  19. FRB repetition and non-Poissonian statistics

    NASA Astrophysics Data System (ADS)

    Connor, Liam; Pen, Ue-Li; Oppermann, Niels

    2016-05-01

    We discuss some of the claims that have been made regarding the statistics of fast radio bursts (FRBs). In an earlier Letter, we conjectured that flicker noise associated with FRB repetition could show up in non-cataclysmic neutron star emission models, like supergiant pulses. We show how the current limits of repetition would be significantly weakened if their repeat rate really were non-Poissonian and had a pink or red spectrum. Repetition and its statistics have implications for observing strategy, generally favouring shallow wide-field surveys, since in the non-repeating scenario survey depth is unimportant. We also discuss the statistics of the apparent latitudinal dependence of FRBs, and offer a simple method for calculating the significance of this effect. We provide a generalized Bayesian framework for addressing this problem, which allows for direct model comparison. It is shown how the evidence for a steep latitudinal gradient of the FRB rate is less strong than initially suggested and simple explanations like increased scattering and sky temperature in the plane are sufficient to decrease the low-latitude burst rate, given current data. The reported dearth of bursts near the plane is further complicated if FRBs have non-Poissonian repetition, since in that case the event rate inferred from observation depends on observing strategy.

  20. Characterizing caregiver responses to restricted and repetitive behaviors in toddlers with autism spectrum disorder.

    PubMed

    Harrop, Clare; Gulsrud, Amanda; Shih, Wendy; Hovsepyan, Lilit; Kasari, Connie

    2016-04-01

    Restricted and repetitive behaviors are a core feature of autism spectrum disorder. This descriptive study documented the presence of restricted and repetitive behaviors in 85 toddlers with autism spectrum disorder as they interacted with their caregiver in a play interaction. For each child restricted and repetitive behavior, a caregiver response/non-response was coded. Caregiver responses were rated as successful or unsuccessful. In all, 83 toddlers demonstrated at least one restricted and repetitive behavior in 10 min. The most common child restricted and repetitive behavior was repetitive object use with 72 children displaying at least one instance of this category of restricted and repetitive behavior. Overall, caregivers responded to fewer than half of their child's restricted and repetitive behaviors, and caregiver response varied by child restricted and repetitive behavior type. The most common response was redirection. Success varied by child restricted and repetitive behavior type and caregiver response--redirections were most successful for child verbal and motor restricted and repetitive behaviors, whereas physical or verbal responses were rated more successful for repetitive object use and visual restricted and repetitive behaviors. This study represents the first attempt to characterize how caregivers respond to restricted and repetitive behaviors. Toddlers with autism spectrum disorder are already demonstrating a variety of restricted and repetitive behaviors within the context of a free play sessions, and caregivers differentially and naturally respond to them.

  1. Repetitive strain injury.

    PubMed

    van Tulder, Maurits; Malmivaara, Antti; Koes, Bart

    2007-05-26

    Repetitive strain injury remains a controversial topic. The term repetitive strain injury includes specific disorders such as carpal tunnel syndrome, cubital tunnel syndrome, Guyon canal syndrome, lateral epicondylitis, and tendonitis of the wrist or hand. The diagnosis is usually made on the basis of history and clinical examination. Large high-quality studies using newer imaging techniques, such as MRI and ultrasonography are few. Consequently, the role of such imaging in diagnosis of upper limb disorders remains unclear. In many cases, no specific diagnosis can be established and complaints are labelled as non-specific. Little is known about the effectiveness of treatment options for upper limb disorders. Strong evidence for any intervention is scarce and the effect, if any, is mainly short-term pain relief. Exercise is beneficial for non-specific upper limb disorders. Immobilising hand braces and open carpal tunnel surgery release are beneficial for carpal tunnel syndrome, and topical and oral non-steroidal anti-inflammatory drugs, and corticosteroid injections are helpful for lateral epicondylitis. Exercise is probably beneficial for neck pain, as are corticosteroid injections and exercise for shoulder pain. Although upper limb disorders occur frequently in the working population, most trials have not exclusively included a working population or assessed effects on work-related outcomes. Further high-quality trials should aim to include sufficient sample sizes, working populations, and work-related outcomes.

  2. A single-pulse shock tube coupled with high-repetition-rate time-of-flight mass spectrometry and gas chromatography for high-temperature gas-phase kinetics studies

    NASA Astrophysics Data System (ADS)

    Sela, P.; Shu, B.; Aghsaee, M.; Herzler, J.; Welz, O.; Fikri, M.; Schulz, C.

    2016-10-01

    Shock tubes are frequently used to investigate the kinetics of chemical reactions in the gas phase at high temperatures. Conventionally, two complementary arrangements are used where either time-resolved intermediate species measurements are conducted after the initiation of the reaction or where the product composition is determined after rapid initiation and quenching of the reaction through gas-dynamic processes. This paper presents a facility that combines both approaches to determine comprehensive information. A single-pulse shock tube is combined with high-sensitivity gas chromatography/mass spectrometry for product composition and concentration measurement as well as high-repetition-rate time-of-flight mass spectrometry for time-dependent intermediate concentration determination with 10 μs time resolution. Both methods can be applied simultaneously. The arrangement is validated with investigations of the well-documented thermal unimolecular decomposition of cyclohexene towards ethylene and 1,3-butadiene at temperatures between 1000 and 1500 K and pressures ranging from 0.8 to 2.4 bars. The comparison shows that the experimental results for both detections are in very good agreement with each other and with literature data.

  3. Repetitively pulsed plasma illumination source improvements

    NASA Astrophysics Data System (ADS)

    Root, Robert G.; Falkos, Paul

    1999-05-01

    A repetitively pulsed broad band visible illumination system has been developed that is suitable for capturing images of high speed motion over sizable areas. At full pulse energy, a two lamp system can illuminate 60 square feet for movies at f/4 with 400 ASA color film and framing rates as high as 1700 fps. At reduced energy, for smaller area applications, the framing rate can be doubled. The short pulse length (4.5 microsecond(s) at full energy, 1.5 microsecond(s) at reduced energy) produces sharp images of high speed objects. This paper reports developments since the last presentation, including: (1) higher pulse repetition rates (a few kilohertz), (2) synchronization with high speed camera, (3) full scale burst of several thousand pulses, (4) characteristics of a compact demonstration system, and (5) demonstration of the ability of the short pulse to freeze motion.

  4. Repetitive resonant railgun power supply

    DOEpatents

    Honig, E.M.; Nunnally, W.C.

    1985-06-19

    A repetitive resonant railgun power supply provides energy for repetitively propelling projectiles from a pair of parallel rails. The supply comprises an energy storage capacitor, a storage inductor to form a resonant circuit with the energy storage capacitor and a magnetic switch to transfer energy between the resonant circuit and the pair of parallel rails for the propelling of projectiles.

  5. Repetitive resonant railgun power supply

    DOEpatents

    Honig, Emanuel M.; Nunnally, William C.

    1988-01-01

    A repetitive resonant railgun power supply provides energy for repetitively propelling projectiles from a pair of parallel rails. The supply comprises an energy storage capacitor, a storage inductor to form a resonant circuit with the energy storage capacitor and a magnetic switch to transfer energy between the resonant circuit and the pair of parallel rails for the propelling of projectiles.

  6. Repetitive strain injury.

    PubMed

    Helliwell, P S; Taylor, W J

    2004-08-01

    Pain in the forearm is relatively common in the community. In the workplace forearm pain is associated with work involving frequent repetition, high forces, and prolonged abnormal postures. Nevertheless, other factors are involved in the presentation and the continuation of the pain. Notable among these factors are psychosocial issues and the workplace environment-the attitude to workers and their welfare, the physical conditions, and design of the job. Primary prevention may be effective but active surveillance is important with early intervention and an active management approach. Physical treatments have not been extensively evaluated. In the established case, management should be multidisciplinary, addressing physical aspects of the job but also addressing the "yellow, blue, and black flags" which should be viewed as obstacles to recovery. For the worker "on sick" a dialogue should be established between the worker, the primary care physician, and the workplace. Return to work should be encouraged and facilitated by medical interventions and light duty options. Rehabilitation programmes may be of use in chronic cases.

  7. Neural Basis of Repetition Priming during Mathematical Cognition: Repetition Suppression or Repetition Enhancement?

    ERIC Educational Resources Information Center

    Salimpoor, Valorie N.; Chang, Catie; Menon, Vinod

    2010-01-01

    We investigated the neural basis of repetition priming (RP) during mathematical cognition. Previous studies of RP have focused on repetition suppression as the basis of behavioral facilitation, primarily using word and object identification and classification tasks. More recently, researchers have suggested associative stimulus-response learning…

  8. Neural repetition suppression reflects fulfilled perceptual expectations

    PubMed Central

    Summerfield, Christopher; Monti, Jim M.P.; Trittschuh, Emily H.; Mesulam, M.-Marsel; Egner, Tobias

    2009-01-01

    Stimulus-evoked neural activity is attenuated upon stimulus repetition (‘repetition suppression’), a phenomenon attributed to largely automatic processes in sensory neurons. By manipulating the likelihood of stimulus repetition, we show that repetition suppression in the human brain is reduced when stimulus repetitions are improbable (and thus, unexpected). These data suggest that repetition suppression reflects a relative reduction in top-down perceptual ‘prediction error’ when processing an expected compared to an unexpected stimulus. PMID:19160497

  9. Paucity of moderately repetitive sequences

    SciTech Connect

    Schmid, C.W.

    1991-01-01

    We examined clones of renatured repetitive human DNA to find novel repetitive DNAs. After eliminating known repeats, the remaining clones were subjected to sequence analysis. These clones also corresponded to known repeats, but with greater sequence diversity. This indicates that either these libraries were depleted of short interspersed repeats in construction, or these repeats are much less prevalent in the human genome than is indicated by data from {und Xenopus} or sea urchin studies. We directly investigated the sequence composition of human DNA through traditional renaturation techniques with the goal of estimating the limits of abundance of repetitive sequence classes in human DNA. Our results sharply limit the maximum possible abundance to 1--2% of the human genome. Our estimate, minus the known repeats in this fraction, leaves about 1% (3 {times} 10{sup 7} nucleotides) of the human genome for novel repetitive elements. 2 refs. (MHB)

  10. Software reliability: Repetitive run experimentation and modeling

    NASA Technical Reports Server (NTRS)

    Nagel, P. M.; Skrivan, J. A.

    1982-01-01

    A software experiment conducted with repetitive run sampling is reported. Independently generated input data was used to verify that interfailure times are very nearly exponentially distributed and to obtain good estimates of the failure rates of individual errors and demonstrate how widely they vary. This fact invalidates many of the popular software reliability models now in use. The log failure rate of interfailure time was nearly linear as a function of the number of errors corrected. A new model of software reliability is proposed that incorporates these observations.

  11. Chronic occupational repetitive strain injury.

    PubMed Central

    O'Neil, B. A.; Forsythe, M. E.; Stanish, W. D.

    2001-01-01

    OBJECTIVE: To review common repetitive strain injuries (RSIs) that occur in the workplace, emphasizing diagnosis, treatment, and etiology of these conditions. QUALITY OF EVIDENCE: A MEDLINE search from January 1966 to June 1999 focused on articles published since 1990 because RSIs are relatively new diagnoses. MeSH headings that were explored using the thesaurus included "cumulative trauma disorder," "overuse injury," and "repetitive strain injury." The search was limited to English articles only, and preference was given to randomized controlled trials. MAIN MESSAGE: Repetitive strain injuries result from repeated stress to the body's soft tissue structures including muscles, tendons, and nerves. They often occur in patients who perform repetitive movements either in their jobs or in extracurricular activities. Common RSIs include tendon-related disorders, such as rotator cuff tendonitis, and peripheral nerve entrapment disorders, such as carpal tunnel syndrome. A careful history and physical examination often lead to the diagnosis, but newer imaging techniques, such as magnetic resonance imaging and ultrasound, can help in refractory cases. Conservative management with medication, physiotherapy, or bracing is the mainstay of treatment. Surgery is reserved for cases that do not respond to treatment. CONCLUSION: Repetitive strain injury is common; primary care physicians must establish a diagnosis and, more importantly, its relationship to occupation. Treatment can be offered by family physicians who refer to specialists for cases refractory to conservative management. PMID:11228032

  12. Between memory and destiny: repetition.

    PubMed

    Marucco, Norberto Carlos

    2007-04-01

    This essay focuses mainly on the topic of repetition (agieren)-on its metapsychological, clinical, and technical conceptions. It contains a core problem, that is, the question of the represented, the nonrepresented, and the unrepresentable in the psyche. This problem, in turn, brings to light the dialectical relation between drive and object and its specific articulation with the traumatic. The author attributes special significance to its clinical expression as 'destiny.' He points out a shift in the theory of the cure from recollection and the unveiling of unconscious desire, to the possibility of understanding 'pure' repetition, which would constitute the very essence of the drive. The author highlights three types of repetition, namely, 'representative' (oedipal) repetition, the repetition of the 'nonrepresented' (narcissistic), which may gain representation, and that of the 'unrepresentable' (sensory impressions, 'lived experiences from primal times,' 'prelinguistic signifiers,' 'ungovernable mnemic traces'). The concept-the metaphor-drive embryo brings the author close to the question of the archaic in psychoanalysis, where the repetition in the act would express itself. 'Another unconscious' would zealously conceal the entombed (verschüttet) that we are not yet able to describe-the 'innermost' rather than the 'buried' (untergegangen) or the 'annihilated' (zugrunde gegangen)-through a mechanism whose way of expression is repetition in the act. With 'Constructions in analysis' as its starting point, this paper suggests a different technical implementation from that of the Freudian construction; its main material is what emerges in the present of the transference as the repetition of 'something' lacking as history. The memory of the analytic process offers a historical diachrony whereby a temporality freed from repetition and utterly unique might unfold in the analysis. This diachrony would no longer be the historical reconstruction of material truth, but the

  13. Between memory and destiny: repetition.

    PubMed

    Marucco, Norberto Carlos

    2007-04-01

    This essay focuses mainly on the topic of repetition (agieren)-on its metapsychological, clinical, and technical conceptions. It contains a core problem, that is, the question of the represented, the nonrepresented, and the unrepresentable in the psyche. This problem, in turn, brings to light the dialectical relation between drive and object and its specific articulation with the traumatic. The author attributes special significance to its clinical expression as 'destiny.' He points out a shift in the theory of the cure from recollection and the unveiling of unconscious desire, to the possibility of understanding 'pure' repetition, which would constitute the very essence of the drive. The author highlights three types of repetition, namely, 'representative' (oedipal) repetition, the repetition of the 'nonrepresented' (narcissistic), which may gain representation, and that of the 'unrepresentable' (sensory impressions, 'lived experiences from primal times,' 'prelinguistic signifiers,' 'ungovernable mnemic traces'). The concept-the metaphor-drive embryo brings the author close to the question of the archaic in psychoanalysis, where the repetition in the act would express itself. 'Another unconscious' would zealously conceal the entombed (verschüttet) that we are not yet able to describe-the 'innermost' rather than the 'buried' (untergegangen) or the 'annihilated' (zugrunde gegangen)-through a mechanism whose way of expression is repetition in the act. With 'Constructions in analysis' as its starting point, this paper suggests a different technical implementation from that of the Freudian construction; its main material is what emerges in the present of the transference as the repetition of 'something' lacking as history. The memory of the analytic process offers a historical diachrony whereby a temporality freed from repetition and utterly unique might unfold in the analysis. This diachrony would no longer be the historical reconstruction of material truth, but the

  14. Repetitively Q-switched Nd:BeL lasers

    NASA Technical Reports Server (NTRS)

    Degnan, J.; Birnbaum, M.; Deshazer, L. G.

    1979-01-01

    The thermal and mechanical characteristics which will ultimately limit the performance of Nd:BeL at high average power levels were investigated. The output beam characteristics (pulse width, peak power, beam dimensions and collimation) were determined at high repetition rates for both Nd:BeL and Nd:YAG. The output of Nd:BeL was shown to exceed that of Nd:YAG by a factor of 2.7 at low Q-switched repetition rates (1 Hz). This result follows from the smaller stimulated emission cross section of x-axis Nb:BeL compared to that of NdYAG by the same factor. At high repetition rates (10 Hz) the output of Nd:Bel falls to a level of three-fifths of its low repetition rate value while under similar tests the output of Nd:YAG remains essentially constant. A comparison of the measured values of the elasto-optic coefficients, the dn/dT values and the linear expansion coefficients for BeL and YAG failed to provide an explanation for the performance of BeL; however, thermal lensing was observed in Nd:BeL. Results imply that the output of a high repetition rate Q-switched Nd:BeL laser (high thermal loading) could be dramatically increased by utilization of a resonator design to compensate for the thermal lensing effects.

  15. Constructive and Unconstructive Repetitive Thought

    ERIC Educational Resources Information Center

    Watkins, Edward R.

    2008-01-01

    The author reviews research showing that repetitive thought (RT) can have constructive or unconstructive consequences. The main unconstructive consequences of RT are (a) depression, (b) anxiety, and (c) difficulties in physical health. The main constructive consequences of RT are (a) recovery from upsetting and traumatic events, (b) adaptive…

  16. Unintended Imitation in Nonword Repetition

    ERIC Educational Resources Information Center

    Kappes, Juliane; Baumgaertner, Annette; Peschke, Claudia; Ziegler, Wolfram

    2009-01-01

    Verbal repetition is conventionally considered to require motor-reproduction of only the phonologically relevant content of a perceived linguistic stimulus, while imitation of incidental acoustic properties of the stimulus is not an explicit part of this task. Exemplar-based theories of speech processing, however, would predict that imitation…

  17. Repetitive elements in parasitic protozoa.

    PubMed

    Clayton, Christine

    2010-01-01

    A recent paper published in BMC Genomics suggests that retrotransposition may be active in the human gut parasite Entamoeba histolytica. This adds to our knowledge of the various types of repetitive elements in parasitic protists and the potential influence of such elements on pathogenicity.

  18. Repetitive DNA in eukaryotic genomes.

    PubMed

    Biscotti, Maria Assunta; Olmo, Ettore; Heslop-Harrison, J S Pat

    2015-09-01

    Repetitive DNA--sequence motifs repeated hundreds or thousands of times in the genome--makes up the major proportion of all the nuclear DNA in most eukaryotic genomes. However, the significance of repetitive DNA in the genome is not completely understood, and it has been considered to have both structural and functional roles, or perhaps even no essential role. High-throughput DNA sequencing reveals huge numbers of repetitive sequences. Most bioinformatic studies focus on low-copy DNA including genes, and hence, the analyses collapse repeats in assemblies presenting only one or a few copies, often masking out and ignoring them in both DNA and RNA read data. Chromosomal studies are proving vital to examine the distribution and evolution of sequences because of the challenges of analysis of sequence data. Many questions are open about the origin, evolutionary mode and functions that repetitive sequences might have in the genome. Some, the satellite DNAs, are present in long arrays of similar motifs at a small number of sites, while others, particularly the transposable elements (DNA transposons and retrotranposons), are dispersed over regions of the genome; in both cases, sequence motifs may be located at relatively specific chromosome domains such as centromeres or subtelomeric regions. Here, we overview a range of works involving detailed characterization of the nature of all types of repetitive sequences, in particular their organization, abundance, chromosome localization, variation in sequence within and between chromosomes, and, importantly, the investigation of their transcription or expression activity. Comparison of the nature and locations of sequences between more, and less, related species is providing extensive information about their evolution and amplification. Some repetitive sequences are extremely well conserved between species, while others are among the most variable, defining differences between even closely relative species. These data suggest

  19. Repetition blindness for pseudoobject pictures.

    PubMed

    Arnell, K M; Jolicoeur, P

    1997-08-01

    In this study the nature of type activations that underlie repetition blindness (RB) was addressed. According to the token individuation hypothesis put forward to explain RB, both instances of a repeated stimulus make contact with the mental representation, or type, for that stimulus. In the resulting confusion only the first stimulus is encoded as an episodic instance or token. Type representations have traditionally been thought of as preexisting and are often linked within a network of nodes. The authors developed and tested a picture frequency task, which does not require stimulus naming, and used it to examine repetition performance for unfamiliar nonobject pictures. RB was found for these stimuli, despite the fact that they had no prior phonological or semantic representation. These results suggest that the reactivation of a newly formed visual type is sufficient to produce RB. Implications for the role of types in the token individuation hypothesis are discussed.

  20. Workshop on Repetitive Opening Switches

    NASA Astrophysics Data System (ADS)

    Kristiansen, M.; Schoenbach, K. H.

    1981-04-01

    A workshop on Repetitive Opening Switches was conducted by Texas Tech University for the U.S. Army Research Office. Several papers on a wide range of innovative opening switch concepts were presented. Discussions about the research needs to advance the state-of-the-art in this important, emerging field are summarized. A concensus on research topics and their importance is summarized and a suggested research priority list given.

  1. Chromosome specific repetitive DNA sequences

    DOEpatents

    Moyzis, Robert K.; Meyne, Julianne

    1991-01-01

    A method is provided for determining specific nucleotide sequences useful in forming a probe which can identify specific chromosomes, preferably through in situ hybridization within the cell itself. In one embodiment, chromosome preferential nucleotide sequences are first determined from a library of recombinant DNA clones having families of repetitive sequences. Library clones are identified with a low homology with a sequence of repetitive DNA families to which the first clones respectively belong and variant sequences are then identified by selecting clones having a pattern of hybridization with genomic DNA dissimilar to the hybridization pattern shown by the respective families. In another embodiment, variant sequences are selected from a sequence of a known repetitive DNA family. The selected variant sequence is classified as chromosome specific, chromosome preferential, or chromosome nonspecific. Sequences which are classified as chromosome preferential are further sequenced and regions are identified having a low homology with other regions of the chromosome preferential sequence or with known sequences of other family me This invention is the result of a contract with the Department of Energy (Contract No. W-7405-ENG-36).

  2. Characterizing exploration behavior in spatial neglect: omissions and repetitive search.

    PubMed

    Olk, Bettina; Harvey, Monika

    2006-11-01

    In search tasks, patients with spatial neglect typically fail to respond to stimuli on the contralesional side. Such behavior has been associated with hyperattention to the ipsilesional side and a deficit in disengaging from attended stimuli. The present study investigated whether such explanations can also account for a further kind of behavior frequently shown by neglect patients: repetitive returns to previously indicated stimuli, particularly on the ipsilesional side. A group of neglect patients was tested along with a group of healthy participants and a patient control group without neglect. Participants performed an exploration task in which they searched for targets defined by their shape or for all stimuli either with the aid of vision or blindfolded. The results showed differential effects of reducing the salience of visual stimuli by blindfolding. For a subgroup of patients, detection rate improved, while for others the percentage of omissions increased. However, contrary to the control groups, blindfolding had no effect on repetitive search in the neglect group, inconsistent with hyperattention, a disengage or impaired working memory deficits. The rate of repetitive returns to previously indicated locations did not seem to be associated with the percentage of omitted stimuli, suggesting that repetitive returns may be best explained by a disruption of systematic search and lack of volitional control in spatial neglect. The results further underline the importance of considering repetitive search behavior in addition to omissions in standard neglect assessments. PMID:16979143

  3. Characterizing exploration behavior in spatial neglect: omissions and repetitive search.

    PubMed

    Olk, Bettina; Harvey, Monika

    2006-11-01

    In search tasks, patients with spatial neglect typically fail to respond to stimuli on the contralesional side. Such behavior has been associated with hyperattention to the ipsilesional side and a deficit in disengaging from attended stimuli. The present study investigated whether such explanations can also account for a further kind of behavior frequently shown by neglect patients: repetitive returns to previously indicated stimuli, particularly on the ipsilesional side. A group of neglect patients was tested along with a group of healthy participants and a patient control group without neglect. Participants performed an exploration task in which they searched for targets defined by their shape or for all stimuli either with the aid of vision or blindfolded. The results showed differential effects of reducing the salience of visual stimuli by blindfolding. For a subgroup of patients, detection rate improved, while for others the percentage of omissions increased. However, contrary to the control groups, blindfolding had no effect on repetitive search in the neglect group, inconsistent with hyperattention, a disengage or impaired working memory deficits. The rate of repetitive returns to previously indicated locations did not seem to be associated with the percentage of omitted stimuli, suggesting that repetitive returns may be best explained by a disruption of systematic search and lack of volitional control in spatial neglect. The results further underline the importance of considering repetitive search behavior in addition to omissions in standard neglect assessments.

  4. Nanosecond repetitively pulsed discharge control of premixed lean methane-air combustion

    NASA Astrophysics Data System (ADS)

    Bak, Moon Soo; Cappelli, Mark A.

    2012-10-01

    Two-dimensional kinetic simulations are carried out to investigate the effects of the discharge repetition rate and pulse width of nanosecond repetitively pulsed discharges on stabilizing premixed lean methane-air combustion. The repetition rate and pulse widths are varied from 10 kHz to 50 kHz and from 9 ns to 2 ns respectively, while the total power is held constant. The lower repetition rates, because of their higher pulse energies, produce a larger fraction of radicals such as O, H, and OH. Surprisingly, however, the effect on flame stabilization is found to be essentially the same for all of the tested repetition rates. The shorter pulse width is found to favor the production of species in higher electronic states, but the varying effects on stabilization is also found to be small. Our results indicate that the total deposited power is the critical element that determines the extent of stabilization over this range of discharge properties studied.

  5. Investigation of a repetitive pulsed electrothermal thruster

    NASA Technical Reports Server (NTRS)

    Burton, R. L.; Fleischer, D.; Goldstein, S. A.; Tidman, D. A.; Winsor, N. K.

    1986-01-01

    A pulsed electrothermal (PET) thruster with 1000:1 ratio nozzle is tested in a repetitive mode on water propellant. The thruster is driven by a 60J pulse forming network at repetition rates up to 10 Hz (600W). The pulse forming network has a .31 ohm impedance, well matched to the capillary discharge resistance of .40 ohm, and is directly coupled to the thruster electrodes without a switch. The discharge is initiated by high voltage breakdown, typically at 2500V, through the water vapor in the interelectrode gap. Water is injected as a jet through a .37 mm orifice on the thruster axis. Thruster voltage, current and impulse bit are recorded for several seconds at various power supply currents. Thruster to power ratio is typically T/P = .07 N/kW. Tank background pressure precludes direct measurement of exhaust velocity which is inferred from calculated pressure and temperature in the discharge to be about 14 km/sec. Efficiency, based on this velocity and measured T/P is .54 + or - .07. Thruster ablation is zero at the throat and becomes measurable further upstream, indicating that radiative ablation is occurring late in the pulse.

  6. Masked repetition priming and proportion effects under cognitive load.

    PubMed

    Bodner, Glen E; Stalinski, Stephanie M

    2008-06-01

    The authors used a cognitive load manipulation (rehearsing a string of digits during the trial) to test the automaticity of (a) masked repetition priming and (b) the masked repetition proportion (RP) effect (i.e., greater priming when the proportion of repetition-prime trials is higher) in the lexical decision task. The RP (.2 vs. .8) was varied across blocks. Masked priming was not reduced under load compared with a no-load group. Surprisingly, only the load group showed an RP effect in response latencies, although the no-load group showed an RP effect in the error rates. Our results show that masked priming is automatic, yet the influence of masked primes can nonetheless be adjusted at an unconscious level. Implications for accounts of masked priming are discussed. PMID:18572990

  7. Nonword Repetition with Spectrally Reduced Speech: Some Developmental and Clinical Findings from Pediatric Cochlear Implantation

    ERIC Educational Resources Information Center

    Burkholder-Juhasz, Rose A.; Levi, Susannah V.; Dillon, Caitlin M.; Pisoni, David B.

    2007-01-01

    Nonword repetition skills were examined in 24 pediatric cochlear implant (CI) users and 18 normal-hearing (NH) adult listeners listening through a CI simulator. Two separate groups of NH adult listeners assigned accuracy ratings to the nonword responses of the pediatric CI users and the NH adult speakers. Overall, the nonword repetitions of…

  8. Pressure rig for repetitive casting

    SciTech Connect

    Vasquez, P.; Hutto, W.R.; Philips, A.R.

    1989-09-12

    This patent describes a pressure rig for repetitive casting. It comprises: a hollow ceramic inner shell: an outer steel housing disposed around the outside of the ceramic inner shell. The housing having a pressure end at the lower end thereof and a mold end at the upper end thereof; a rubber diaphragm attached to the pressure end of the outer steel housing; a slideable transit plate located above the rubber diaphragm; a layer of blanket insulating material lining the remaining portion of the hollow ceramic inner shell, thereby defining an inner cavity wherein a casing material is located; a pressure means located at the lower end of the pressure rig for applying pressure to the lower end of the rubber diaphragm; whereby the casting material in the inner cavity is forced out of the pressure rig into a mold when pressure is applied to the lower end of the rubber diaphragm.

  9. Constructive and Unconstructive Repetitive Thought

    PubMed Central

    Watkins, Edward R.

    2008-01-01

    The author reviews research showing that repetitive thought (RT) can have constructive or unconstructive consequences. The main unconstructive consequences of RT are (a) depression, (b) anxiety, and (c) difficulties in physical health. The main constructive consequences of RT are (a) recovery from upsetting and traumatic events, (b) adaptive preparation and anticipatory planning, (c) recovery from depression, and (d) uptake of health-promoting behaviors. Several potential principles accounting for these distinct consequences of RT are identified within this review: (a) the valence of thought content, (b) the intrapersonal and situational context in which RT occurs, and (c) the level of construal (abstract vs. concrete processing) adopted during RT. Of the existing models of RT, it is proposed that an elaborated version of the control theory account provides the best theoretical framework to account for its distinct consequences. PMID:18298268

  10. Pressure rig for repetitive casting

    NASA Technical Reports Server (NTRS)

    Vasquez, Peter (Inventor); Hutto, William R. (Inventor); Philips, Albert R. (Inventor)

    1989-01-01

    The invention is a pressure rig for repetitive casting of metal. The pressure rig performs like a piston for feeding molten metal into a mold. Pressure is applied to an expandable rubber diaphragm which expands like a balloon to force the metal into the mold. A ceramic cavity which holds molten metal is lined with blanket-type insulating material, necessitating only a relining for subsequent use and eliminating the lengthy cavity preparation inherent in previous rigs. In addition, the expandable rubber diaphragm is protected by the insulating material thereby decreasing its vulnerability to heat damage. As a result of the improved design the life expectancy of the pressure rig contemplated by the present invention is more than doubled. Moreover, the improved heat protection has allowed the casting of brass and other alloys with higher melting temperatures than possible in the conventional pressure rigs.

  11. A repetitive 0.14 THz relativistic surface wave oscillator

    SciTech Connect

    Wang Guangqiang; Tong Changjiang; Li Xiaoze; Wang Xuefeng; Li Shuang; Lu Xicheng; Wang Jianguo

    2013-04-15

    Preliminary experimental results of a repetitive 0.14 THz overmoded relativistic surface wave oscillator (RSWO) are presented in this paper. The repetitive RSWO is developed by using a rectangularly corrugated slow-wave structure with overmoded ratio of 3 and a foilless diode emitting annular electron beam with thickness of 0.5 mm. The high quality electron beams at the repetition rate of 10 are obtained over a wide range of diode voltage (180 kV < U < 240 kV) and current (700 A < I < 1.2 kA). The generation experiments of RSWO are conducted at an axial pulsed magnetic field whose maximum strength and duration can reach about 2.7 T and 1 s, respectively. The experimental results show that the RSWO successfully produces reasonable uniform terahertz pulses at repetition rate of 10, and the pulse duration, frequency, and power of a single pulse are about 1.5 ns, 0.154 THz, and 2.6 MW, respectively, whereas the dominated radiation mode of the RSWO is TM{sub 02}.

  12. A Nonword Repetition Task for Speakers with Misarticulations: The Syllable Repetition Task (SRT)

    ERIC Educational Resources Information Center

    Shriberg, Lawrence D.; Lohmeier, Heather L.; Campbell, Thomas F.; Dollaghan, Christine A.; Green, Jordan R.; Moore, Christopher A.

    2009-01-01

    Purpose: Conceptual and methodological confounds occur when non(sense) word repetition tasks are administered to speakers who do not have the target speech sounds in their phonetic inventories or who habitually misarticulate targeted speech sounds. In this article, the authors (a) describe a nonword repetition task, the Syllable Repetition Task…

  13. Serial Position Effects in Nonword Repetition

    ERIC Educational Resources Information Center

    Gupta, P.; Lipinski, J.; Abbs, B.; Lin, P.H.

    2005-01-01

    A growing body of research has emphasized the linkage between performance in immediate serial recall of lists, nonword repetition, and word learning. Recently, it has been reported that primacy and recency effects are obtained in repetition of individual syllables within nonwords (Gupta, in press). Five experiments examined whether such…

  14. Development and evaluation of an observational method for assessing repetition in hand tasks.

    PubMed

    Latko, W A; Armstrong, T J; Foulke, J A; Herrin, G D; Rabourn, R A; Ulin, S S

    1997-04-01

    Several physical stressors, including repetitive, sustained, and forceful exertions, awkward postures, localized mechanical stress, highly dynamic movements, exposures to low temperatures, and vibration have been linked to increased risk of work-related musculoskeletal disorders. Repetitive exertions have been among the most widely studied of these stressors, but there is no single metric for assessing exposure to repetitive work. A new methodology enables repetitive hand activity to be rated based on observable characteristics of manual work. This method uses a series of 10-cm visual-analog scales with verbal anchors and benchmark examples. Ratings for repetition reflect both the dynamic aspect of hand movements and the amount of recovery or idle hand time. Trained job analysis experts rate the jobs individually and then agree on ratings. For a group of 33 jobs, repetition ratings using this system were compared to measurements of recovery time within the cycle, exertion counts, and cycle time. Amount of recovery time within the job cycle was found to be significantly correlated with the analysis ratings (r2 = 0.58), as were the number of exertions per second (r2 = 0.53). Cycle time was not related to the analyst ratings. Repeated analyses using the new method were performed 1 1/2 to 2 years apart on the same jobs with the same group of raters. Ratings for repetition differed less than 1 point (on the 10-cm scale), on average, among the different sessions. These results indicate that the method is sensitive to exertion level and recovery time, and that the decision criteria and benchmark examples allow for a consistent application of these methods over a period of time. This method of rating repetition can be combined with similar scales for other physical stressors. PMID:9115085

  15. Repetition priming results in sensitivity attenuation

    PubMed Central

    Allenmark, Fredrik; Hsu, Yi-Fang; Roussel, Cedric; Waszak, Florian

    2015-01-01

    Repetition priming refers to the change in the ability to perform a task on a stimulus as a consequence of a former encounter with that very same item. Usually, repetition results in faster and more accurate performance. In the present study, we used a contrast discrimination protocol to assess perceptual sensitivity and response bias of Gabor gratings that are either repeated (same orientation) or alternated (different orientation). We observed that contrast discrimination performance is worse, not better, for repeated than for alternated stimuli. In a second experiment, we varied the probability of stimulus repetition, thus testing whether the repetition effect is due to bottom-up or top-down factors. We found that it is top-down expectation that determines the effect. We discuss the implication of these findings for repetition priming and related phenomena as sensory attenuation. This article is part of a Special Issue entitled SI: Prediction and Attention. PMID:25819554

  16. Strategies for Using Repetition as a Powerful Teaching Tool

    ERIC Educational Resources Information Center

    Saville, Kirt

    2011-01-01

    Brain research indicates that repetition is of vital importance in the learning process. Repetition is an especially useful tool in the area of music education. The success of repetition can be enhanced by accurate and timely feedback. From "simple repetition" to "repetition with the addition or subtraction of degrees of freedom," there are many…

  17. Environmental conditions associated with repetitive behavior in a group of African elephants.

    PubMed

    Hasenjager, Matthew J; Bergl, Richard A

    2015-01-01

    Repetitive movement patterns are commonly observed in zoo elephants. The extent to which these behaviors constitute a welfare concern varies, as their expression ranges from stereotypies to potentially beneficial anticipatory behaviors. Nevertheless, their occurrence in zoo animals is often viewed negatively. To better identify conditions that prompt their performance, observations were conducted on six African elephants (Loxodonta africana) at the North Carolina Zoo. Individuals spent most of their time engaged in feeding, locomotion, resting, and repetitive behavior. Both generalized estimating equation and zero-inflated negative binomial models were used to identify factors associated with increased rates of repetitive behavior. Time of day in conjunction with location on- or off-exhibit best explained patterns of repetitive behavior. Repetitive behaviors occurred at a lower rate in the morning when on-exhibit, as compared to afternoons on-exhibit or at any time of day off-exhibit. Increased repetitive behavior rates observed on-exhibit in the afternoon prior to the evening transfer and feeding were possibly anticipatory responses towards those events. In contrast, consistently elevated frequencies of repetitive behavior off-exhibit at all times of day could be related to differences in exhibit complexity between off-exhibit and on-exhibit areas, as well as a lack of additional foraging opportunities. Our study contributes valuable information on captive elephant behavior and represents a good example of how behavioral research can be employed to improve management of zoo animals.

  18. Environmental conditions associated with repetitive behavior in a group of African elephants.

    PubMed

    Hasenjager, Matthew J; Bergl, Richard A

    2015-01-01

    Repetitive movement patterns are commonly observed in zoo elephants. The extent to which these behaviors constitute a welfare concern varies, as their expression ranges from stereotypies to potentially beneficial anticipatory behaviors. Nevertheless, their occurrence in zoo animals is often viewed negatively. To better identify conditions that prompt their performance, observations were conducted on six African elephants (Loxodonta africana) at the North Carolina Zoo. Individuals spent most of their time engaged in feeding, locomotion, resting, and repetitive behavior. Both generalized estimating equation and zero-inflated negative binomial models were used to identify factors associated with increased rates of repetitive behavior. Time of day in conjunction with location on- or off-exhibit best explained patterns of repetitive behavior. Repetitive behaviors occurred at a lower rate in the morning when on-exhibit, as compared to afternoons on-exhibit or at any time of day off-exhibit. Increased repetitive behavior rates observed on-exhibit in the afternoon prior to the evening transfer and feeding were possibly anticipatory responses towards those events. In contrast, consistently elevated frequencies of repetitive behavior off-exhibit at all times of day could be related to differences in exhibit complexity between off-exhibit and on-exhibit areas, as well as a lack of additional foraging opportunities. Our study contributes valuable information on captive elephant behavior and represents a good example of how behavioral research can be employed to improve management of zoo animals. PMID:25919392

  19. Repetitively pulsed Cr:LiSAF laser for lidar applications

    SciTech Connect

    Shimada, Tsutomu; Early, J.W.; Lester, C.S.; Cockroft, N.J.

    1994-03-01

    A Cr:LiSAF laser has been successfully operated at time averaged powers up to 11 W and at pulse repetition rates to 12 Hz. During Q-switch operation, output energy as high as 450 mJ (32 ns FWHM) was obtained. Finally, line narrowed Q-switched pulses (< 0.1 nm) from the Cr:LiSAF laser were successfully used as a tunable light source for lidar to measure atmospheric water content.

  20. Repetitively pulsed regime of Nd : glass large-aperture laser amplifiers

    SciTech Connect

    Kuzmin, A A; Khazanov, Efim A; Shaykin, A A

    2012-04-30

    A repetitively pulsed operation regime of neodymium glass rod laser amplifiers with apertures of 4.5, 6, 8.5, and 10 cm is analysed using experimental data. The limits of an increase in the pulse repetition rates are determined. Universal dependences are obtained, which help finding a compromise between increasing the repetition rate and enhancing the gain for each particular case. In particular, it is shown that an amplifier 4.5-cm in diameter exhibits a five-fold safety factor with respect to a thermo-mechanical breakdown at a repetition rate of 1 pulse min{sup -1} and stored energy of above 100 J. A strong thermally induced birefringence in two such amplifiers is experimentally reduced to a 'cold' level by employing a 90 Degree-Sign optical rotator.

  1. A compact, repetitive accelerator for military and industrial applications

    SciTech Connect

    Zutavern, F.J.; O`Malley, M.W.; Ruebush, M.H.; Rinehart, L.F.; Loubriel, G.M.; Babcock, S.R.; Denison, G.J.

    1998-04-01

    A compact, short pulse, repetitive accelerator has many useful military and commercial applications in biological counter proliferation, materials processing, radiography, and sterilization (medical instruments, waste, and food). The goal of this project was to develop and demonstrate a small, 700 kV accelerator, which can produce 7 kA particle beams with pulse lengths of 10--30 ns at rates up to 50 Hz. At reduced power levels, longer pulses or higher repetition rates (up to 10 kHz) could be achieved. Two switching technologies were tested: (1) spark gaps, which have been used to build low repetition rate accelerators for many years; and (2) high gain photoconductive semiconductor switches (PCSS), a new solid state switching technology. This plan was economical, because it used existing hardware for the accelerator, and the PCSS material and fabrication for one module was relatively inexpensive. It was research oriented, because it provided a test bed to examine the utility of other emerging switching technologies, such as magnetic switches. At full power, the accelerator will produce 700 kV and 7 kA with either the spark gap or PCSS pulser.

  2. Dispersed repetitive DNA sequence of Mucor racemosus.

    PubMed Central

    Dewar, R; Katayama, C; Sypherd, P S; Cihlar, R L

    1985-01-01

    A dispersed repetitive DNA sequence has been identified within the genome of the fungus Mucor racemosus. Recombinant phage clones, as well as a plasmid harboring the sequence, have been isolated. Examination of cloned fragments comprising part of the repetitive sequence has led to a partial characterization of the element. The sequence has been detected in other Mucor species, and although the apparent number and chromosomal position of the repetitive sequence vary from strain to strain, it is clear that at least portions of the element have been conserved. Images PMID:3980442

  3. Minor and repetitive head injury.

    PubMed

    Buki, Andras; Kovacs, Noemi; Czeiter, Endre; Schmid, Kara; Berger, Rachel P; Kobeissy, Firas; Italiano, Domenico; Hayes, Ronald L; Tortella, Frank C; Mezosi, Emese; Schwarcz, Attila; Toth, Arnold; Nemes, Orsolya; Mondello, Stefania

    2015-01-01

    Traumatic brain injury (TBI) is the leading cause of death and disability in the young, active population and expected to be the third leading cause of death in the whole world until 2020. The disease is frequently referred to as the silent epidemic, and many authors highlight the "unmet medical need" associated with TBI.The term traumatically evoked brain injury covers a heterogeneous group ranging from mild/minor/minimal to severe/non-salvageable damages. Severe TBI has long been recognized to be a major socioeconomical health-care issue as saving young lives and sometimes entirely restituting health with a timely intervention can indeed be extremely cost efficient.Recently it has been recognized that mild or minor TBI should be considered similarly important because of the magnitude of the patient population affected. Other reasons behind this recognition are the association of mild head injury with transient cognitive disturbances as well as long-term sequelae primarily linked to repeat (sport-related) injuries.The incidence of TBI in developed countries can be as high as 2-300/100,000 inhabitants; however, if we consider the injury pyramid, it turns out that severe and moderate TBI represents only 25-30 % of all cases, while the overwhelming majority of TBI cases consists of mild head injury. On top of that, or at the base of the pyramid, are the cases that never show up at the ER - the unreported injuries.Special attention is turned to mild TBI as in recent military conflicts it is recognized as "signature injury."This chapter aims to summarize the most important features of mild and repetitive traumatic brain injury providing definitions, stratifications, and triage options while also focusing on contemporary knowledge gathered by imaging and biomarker research.Mild traumatic brain injury is an enigmatic lesion; the classification, significance, and its consequences are all far less defined and explored than in more severe forms of brain injury

  4. Resistance to change of operant variation and repetition.

    PubMed

    Doughty, A H; Lattal, K A

    2001-09-01

    A multiple chained schedule was used to compare the relative resistance to change of variable and fixed four-peck response sequences in pigeons. In one terminal link, a response sequence produced food only if it occurred infrequently relative to 15 other response sequences (vary). In the other terminal link, a single response sequence produced food (repeat). Identical variable-interval schedules operated in the initial links. During baseline, lower response rates generally occurred in the vary initial link, and similar response and reinforcement rates occurred in each terminal link. Resistance of responding to prefeeding and three rates of response-independent food delivered during the intercomponent intervals then was compared between components. During each disruption condition, initial- and terminal-link response rates generally were more resistant in the vary component than in the repeat component. During the response-independent food conditions, terminal-link response rates were more resistant than initial-link response rates in each component, but this did not occur during prefeeding. Variation (in vary) and repetition (in repeat) both decreased during the response-independent food conditions in the respective components, but with relatively greater disruption in repeat. These results extend earlier findings demonstrating that operant variation is more resistant to disruption than is operant repetition and suggest that theories of response strength, such as behavioral momentum theory, must consider factors other than reinforcement rate. The implications of the results for understanding operant response classes are discussed.

  5. Reversing-counterpulse repetitive-pulse inductive storage circuit

    DOEpatents

    Honig, E.M.

    1987-02-10

    A high-power reversing-counterpulse repetitive-pulse inductive storage and transfer circuit includes an opening switch, a main energy storage coil, a counterpulse capacitor and a small inductor. After counterpulsing the opening switch off, the counterpulse capacitor is recharged by the main energy storage coil before the load pulse is initiated. This gives the counterpulse capacitor sufficient energy for the next counterpulse operation, although the polarity of the capacitor's voltage must be reversed before that can occur. By using a current-zero switch as the counterpulse start switch, the capacitor is disconnected from the circuit (with a full charge) when the load pulse is initiated, preventing the capacitor from depleting its energy store by discharging through the load. After the load pulse is terminated by reclosing the main opening switch, the polarity of the counterpulse capacitor voltage is reversed by discharging the capacitor through a small inductor and interrupting the discharge current oscillation at zero current and peak reversed voltage. The circuit enables high-power, high-repetition-rate operation with reusable switches and features total control (pulse-to-pulse) over output pulse initiation, duration, repetition rate, and, to some extent, risetime. 10 figs.

  6. Reversing-counterpulse repetitive-pulse inductive storage circuit

    DOEpatents

    Honig, Emanuel M.

    1987-01-01

    A high-power reversing-counterpulse repetitive-pulse inductive storage and transfer circuit includes an opening switch, a main energy storage coil, a counterpulse capacitor and a small inductor. After counterpulsing the opening switch off, the counterpulse capacitor is recharged by the main energy storage coil before the load pulse is initiated. This gives the counterpulse capacitor sufficient energy for the next counterpulse operation, although the polarity of the capacitor's voltage must be reversed before that can occur. By using a current-zero switch as the counterpulse start switch, the capacitor is disconnected from the circuit (with a full charge) when the load pulse is initiated, preventing the capacitor from depleting its energy store by discharging through the load. After the load pulse is terminated by reclosing the main opening switch, the polarity of the counterpulse capacitor voltage is reversed by discharging the capacitor through a small inductor and interrupting the discharge current oscillation at zero current and peak reversed voltage. The circuit enables high-power, high-repetition-rate operation with reusable switches and features total control (pulse-to-pulse) over output pulse initiation, duration, repetition rate, and, to some extent, risetime.

  7. Reversing-counterpulse repetitive-pulse inductive storage circuit

    DOEpatents

    Honig, E.M.

    1984-06-05

    A high power reversing-counterpulse repetitive-pulse inductive storage and transfer circuit includes an opening switch, a main energy storage coil, a counterpulse capacitor and a small inductor. After counterpulsing the opening switch off, the counterpulse capacitor is recharged by the main energy storage coil before the load pulse is initiated. This gives the counterpulse capacitor sufficient energy for the next counterpulse operation, although the polarity of the capacitor's voltage must be reversed before that can occur. By using a current-zero switch as the counterpulse start switch, the capacitor is disconnected from the circuit (with a full charge) when the load pulse is initiated, preventing the capacitor from depleting its energy store by discharging through the load. After the load pulse is terminated by reclosing the main opening switch, the polarity of the counterpulse capacitor voltage is reversed by discharging the capacitor through a small inductor and interrupting the discharge current oscillation at zero current and peak reversed voltage. The circuit enables high-power, high-repetition-rate operation with reusable switches and features total control (pulse-to-pulse) over output pulse initiation, duration, repetition rate, and, to some extent, risetime.

  8. Bubble Phenomena caused by High Repetitive Plasmas in Water

    NASA Astrophysics Data System (ADS)

    Akiyama, Masahiro; Oikawa, Takuma; Fue, Masatoshi; Ogata, Ryoma; Takaki, Koich; Akiyama, Hidenori; Iwate Univ Team; Kumamoto Univ Collaboration

    2015-09-01

    Streamer discharges in water were generated by a pulsed power generator. The streamer shape changed depending on pulse repetition rate. Streamer discharges at 500 pulses per second (pps) resulted in a ball shape. Under this formation, small bubbles gather near the electrode tip. Our aims are the analysis and discussion of the bubble phenomena caused by high repetitive plasmas produced in water. Pulsed power with a maximum output of 1 J/pulse was applied to an electrode of 0.8 mm in diameter covered by an insulator of 2 mm thickness. The electrode was inserted into tap water with conductivity of 170 uS/cm. The polarity was positive. Phenomena, in which the resulting gas bubbles oscillate and gather, were found to have an important role in producing ball shape streamer discharges.

  9. Global familiarity of visual stimuli affects repetition-related neural plasticity but not repetition priming

    PubMed Central

    Soldan, Anja; Zarahn, Eric; Hilton, H. John; Stern, Yaakov

    2007-01-01

    In this study we tested the prediction of the component process model of priming (Henson, 2003) that repetition priming of familiar and unfamiliar objects produces qualitatively different neural repetition effects. In an fMRI study, subjects viewed four repetitions of familiar objects and globally unfamiliar objects with familiar components. Reliable behavioral priming occurred for both item types across the four presentations and was of a similar magnitude for both stimulus types. The imaging data was analyzed using multivariate linear modeling, which permits explicit testing of the hypothesis that the repetition effects for familiar and unfamiliar objects are qualitatively different (i.e., non-scaled versions of one another). The results showed the presence of two qualitatively different latent spatial patterns of repetition effects from presenation one to presentation four for familiar and unfamilar objects, indicating that familiarity with an object’s global structural, semantic, or lexical features is an important factor in priming-related neural plasticity. The first latent spatial pattern strongly weighted regions with a similar repetition effect for both item types. The second pattern strongly weighted regions contributing a repetition suppression effect for the familiar objects and repetition enhancement for the unfamiliar objects, particularly the posterior insula, superior temporal gyrus, precentral gyrus, and cingulate cortex. This differential repetition effect might reflect the formation of novel memory representations for the unfamiliar items, which already exist for the familiar objects, consistent with the component-process model of priming. PMID:17913513

  10. A high repetition rate plasma focus for neutron interrogation applications

    NASA Astrophysics Data System (ADS)

    Bures, Brian; Krishnan, Mahadevan; James, Colt; Madden, Robert; Hennig, Wolfgang; Breus, Dimitry; Asztalos, Stephen; Sabourov, Konstantin; Lane, Stephen

    2011-10-01

    A fast pulsed neutron source enables identification and ranging of contraband nuclear material using time-of-flight separation of the probe neutron pulse from the fission induced emission quanta. Alameda Applied Sciences Corporation has demonstrated a 1 Hz plasma focus neutron source that uses an impedance matching transformer to better couple the power from the driver to the dynamic pinch load. For a 24 kV primary charge, the system produces a 61 kA peak current with a neutron yield up to 5 ×105 neutrons/pulse at 1 Hz. Experiments are described in which induced 845 keV gamma emission from iron targets (by 2.45 MeV DD neutrons) was separated (by time of flight) from the 20-30 ns probe neutron pulses. Monte Carlo simulations are used to optimize the concept for a fieldable system. Work supported by US Department of Homeland Security (DNDO) and by the US Air Force (KAFB).

  11. A compact high repetition rate CO2 coherent Doppler lidar

    NASA Technical Reports Server (NTRS)

    Alejandro, S.; Frelin, R.; Dix, B.; Mcnicholl, P.

    1992-01-01

    As part of its program to develop coherent heterodyne detection lidar technology for space, airborne, and ground based applications, the Optical Environment Division of the USAF's Phillips Laboratory developed a compact coherent CO2 TEA lidar system. Although originally conceived as a high altitude balloon borne system, the lidar is presently integrated into a trailer for ground based field measurements of aerosols and wind fields. In this role, it will also serve as a testbed for signal acquisition and processing development for planned future airborne and space based solid state lidar systems. The system has also found significance in new areas of interest to the Air Force such as cloud studies and coherent Differential Absorption Lidar (DIAL) systems.

  12. Word Recognition during Reading: The Interaction between Lexical Repetition and Frequency

    PubMed Central

    Lowder, Matthew W.; Choi, Wonil; Gordon, Peter C.

    2013-01-01

    Memory studies utilizing long-term repetition priming have generally demonstrated that priming is greater for low-frequency words than for high-frequency words and that this effect persists if words intervene between the prime and the target. In contrast, word-recognition studies utilizing masked short-term repetition priming typically show that the magnitude of repetition priming does not differ as a function of word frequency and does not persist across intervening words. We conducted an eye-tracking while reading experiment to determine which of these patterns more closely resembles the relationship between frequency and repetition during the natural reading of a text. Frequency was manipulated using proper names that were high-frequency (e.g., Stephen) or low-frequency (e.g., Dominic). The critical name was later repeated in the sentence, or a new name was introduced. First-pass reading times and skipping rates on the critical name revealed robust repetition-by-frequency interactions such that the magnitude of the repetition-priming effect was greater for low-frequency names than for high-frequency names. In contrast, measures of later processing showed effects of repetition that did not depend on lexical frequency. These results are interpreted within a framework that conceptualizes eye-movement control as being influenced in different ways by lexical- and discourse-level factors. PMID:23283808

  13. The Prevalence and Phenomenology of Repetitive Behavior in Genetic Syndromes

    ERIC Educational Resources Information Center

    Moss, Joanna; Oliver, Chris; Arron, Kate; Burbidge, Cheryl; Berg, Katy

    2009-01-01

    We investigated the prevalence and phenomenology of repetitive behavior in genetic syndromes to detail profiles of behavior. The Repetitive Behaviour Questionnaire (RBQ) provides fine-grained identification of repetitive behaviors. The RBQ was employed to examine repetitive behavior in Angelman (N = 104), Cornelia de Lange (N = 101), Cri-du-Chat…

  14. The infogram: Entropic evidence of the signature of repetitive transients

    NASA Astrophysics Data System (ADS)

    Antoni, Jerome

    2016-06-01

    A classical symptom of rotating machines faults in vibration signals is the presence of repetitive transients, whose distinctive signature is both impulsive and cyclostationary. Typical approaches for their detection proceed in the time or frequency domains, with tools such as the spectral kurtosis, the kurtogram, or the envelope spectrum. The object of this paper is to extend and somehow connect these concepts in order to capture the signature of repetitive transients in both domains. Motivated by ideas borrowed from the field of thermodynamics where transients are seen as departures from a state of equilibrium, it is proposed to measure the negentropy of the squared envelope (SE) and of the squared envelope spectrum (SES) of the signal. This defines the SE infogram, the SES infogram, and their average which is theoretically maximum for a Dirac comb according to Hirschman's uncertainty principle. It is demonstrated that the joint consideration of the infograms significantly extends the domain of applicability of the kurtogram, in particular to situations corrupted with impulsive noise or when the relaxation time of the transients is low as compared to their rate of repetition. This is illustrated on both synthetic and actual vibration signals. This paper is part of a special issue in honor of Professor Simon Braun and pays tribute to his early contribution to the field of mechanical signature analysis.

  15. Repetition Priming and Repetition Suppression: A Case for Enhanced Efficiency Through Neural Synchronization

    PubMed Central

    Gotts, Stephen J.; Chow, Carson C.; Martin, Alex

    2012-01-01

    Stimulus repetition in identification tasks leads to improved behavioral performance ("repetition priming") but attenuated neural responses ("repetition suppression") throughout task-engaged cortical regions. While it's clear that this pervasive brain-behavior relationship reflects some form of improved processing efficiency, the exact form that it takes remains elusive. In this Discussion Paper, we review four different theoretical proposals that have the potential to link repetition suppression and priming, with a particular focus on a proposal that stimulus repetition affects improved efficiency through enhanced neural synchronization. We argue that despite exciting recent work on the role of neural synchronization in cognitive processes such as attention and perception, similar studies in the domain of learning and memory - and priming, in particular - have been lacking. We emphasize the need for new studies with adequate spatiotemporal resolution, formulate several novel predictions, and discuss our ongoing efforts to disentangle the current proposals. PMID:23144664

  16. Chromatin diminution in the copepod Mesocyclops edax: elimination of both highly repetitive and nonhighly repetitive DNA.

    PubMed

    McKinnon, Christian; Drouin, Guy

    2013-01-01

    Chromatin diminution, a developmentally regulated process of DNA elimination, is found in numerous eukaryotic species. In the copepod Mesocyclops edax, some 90% of its genomic DNA is eliminated during the differentiation of embryonic cells into somatic cells. Previous studies have shown that the eliminated DNA contains highly repetitive sequences. Here, we sequenced DNA fragments from pre- and postdiminution cells to determine whether nonhighly repetitive sequences are also eliminated during the process of chromatin diminution. Comparative analyses of these sequences, as well as the sequences eliminated from the genome of the copepod Cyclops kolensis, show that they all share similar abundances of tandem repeats, dispersed repeats, transposable elements, and various coding and noncoding sequences. This suggests that, in the chromatin diminution observed in M. edax, both highly repetitive and nonhighly repetitive sequences are eliminated and that there is no bias in the type of nonhighly repetitive DNA being eliminated.

  17. Conservative treatment for repetitive strain injury.

    PubMed

    Konijnenberg, H S; de Wilde, N S; Gerritsen, A A; van Tulder, M W; de Vet, H C

    2001-10-01

    Various conservative treatment options for repetitive strain injury are widely used, despite questionable evidence of their effectiveness. This systematic review evaluates the effectiveness of these treatment options for relieving symptoms of repetitive strain injury and improving activities of daily living. Searches in Medline and Embase, with additional reference checking resulted in 15 eligible trials for this review. Methodological quality was assessed, and data-extraction was performed. With the use of a "best-evidence synthesis", no strong evidence was found for the effectiveness of any of the treatment options. There is limited evidence that multidisciplinary rehabilitation, ergonomic intervention measures, exercises, and spinal manipulation combined with soft tissue therapy are effective in providing symptom relief or improving activities of daily living. There is conflicting evidence for the effectiveness of behavioral therapy. In conclusion, little is known about the effectiveness of conservative treatment options for repetitive strain injury. To establish strong evidence, more high-quality trials are needed.

  18. Physiological and biomechanical responses to a prolonged repetitive asymmetric lifting activity.

    PubMed

    Mehta, Jay P; Lavender, Steven A; Jagacinski, Richard J

    2014-01-01

    This study investigated the effects of a prolonged repetitive asymmetric lifting task on behavioural adaptations during repetitive lifting activity, measures of tissue oxygenation and spine kinematics. Seventeen volunteers repeatedly lifted a box, normalised to 15% of the participant's maximum lifting strength, at the rate of 10 lifts/min for a period of 60 min. The lifts originated in front of the participants at ankle level and terminated on their left side at waist level. Overall, perceived workload increased during the repetitive lifting task. Erector spinae oxygenation levels, assessed using near-infrared spectroscopy, decreased significantly over time. Behavioural changes observed during the repetitive lifting task included increases in the amount of forward bending, the extension velocity and the lateral bending velocity, and a reduced lateral bending moment on the spine. These changes, with the exception of the reduced lateral bending moment, are associated with increased risk of low back disorder.

  19. The discharge characteristics of surface dielectric barrier discharge sustained by repetitive nanosecond pulses in open air

    NASA Astrophysics Data System (ADS)

    Lei, Pang; Kun, He; Qiaogen, Zhang

    2016-09-01

    A nanosecond pulsed surface dielectric barrier discharge (NPSDBD) is a promising method for flow control and combustion. We systematically investigated the influence of pulse parameters on the discharge characteristics of NPSDBD, especially on the conduction current of discharge and the energy deposition curves. Meanwhile, the differences of the characteristics of the discharge generated by positive pulses and negative pulses are focused in this paper. The underlying physics is also discussed. Four different discharge regimes of NPSDBD are presented, which can be distinguished by the temporal emission behaviors of discharge and the conduction current of discharge. The transitions of four discharge regimes were also investigated by changing the pulse amplitude, repetitive rate, and voltage polarity. It was found that it is easier to translate quasi-uniform discharge to filamentary discharge or transition mode for the repetitive pulses with a negative polarity. A phenomenological model was proposed to explain the differences between a positive repetitive pulse discharge and a negative repetitive pulse discharge.

  20. Pathophysiological Tissue Changes Associated With Repetitive Movement: A Review of the Evidence

    PubMed Central

    Barr, Ann E; Barbe, Mary F

    2006-01-01

    Work-related musculoskeletal disorders (WMSDs) represent approximately one third of workers’ compensation costs in US private industry, yet estimates of acceptable exposure levels for forceful and repetitive tasks are imprecise, in part, due to lack of measures of tissue injury in humans. In this review, the authors discuss the scope of upper-extremity WMSDs, the relationship between repetition rate and forcefulness of reaching tasks and WMSDs, cellular responses to injury in vivo and in vitro, and animal injury models of repetitive, forceful tasks. The authors describe a model using albino rats and present evidence related to tissue injury and inflammation due to a highly repetitive reaching task. A conceptual schematic for WMSD development and suggestions for further research are presented. Animal models can enhance our ability to predict risk and to manage WMSDs in humans because such models permit the direct observation of exposed tissues as well as motor behavior. PMID:11856068

  1. An Experiment on Repetitive Pulse Operation of Microwave Rocket

    SciTech Connect

    Oda, Yasuhisa; Shibata, Teppei; Komurasaki, Kimiya; Takahashi, Koji; Kasugai, Atsushi; Sakamoto, Keishi

    2008-04-28

    Microwave Rocket was operated with repetitive pulses. The microwave rocket model with forced breathing system was used. The pressure history in the thruster was measured and the thrust impulse was deduced. As a result, the impulse decreased at second pulse and impulses at latter pulses were constant. The dependence of the thrust performance on the partial filling rate of the thruster was compared to the thrust generation model based on the shock wave driven by microwave plasma. The experimental results showed good agreement to the predicted dependency.

  2. Temporal Processing Capabilities in Repetition Conduction Aphasia

    ERIC Educational Resources Information Center

    Sidiropoulos, Kyriakos; Ackermann, Hermann; Wannke, Michael; Hertrich, Ingo

    2010-01-01

    This study investigates the temporal resolution capacities of the central-auditory system in a subject (NP) suffering from repetition conduction aphasia. More specifically, the patient was asked to detect brief gaps between two stretches of broadband noise (gap detection task) and to evaluate the duration of two biphasic (WN-3) continuous noise…

  3. Assessment of anomalous sentences repetition test

    PubMed Central

    Rai, G S; Stewart, K; Scott, L C

    1990-01-01

    Use of Anomalous Sentences Repetition Test (ASRT) in 16 patients with diagnosis of dementia of Alzheimer's type, 16 normal elderly and 18 patients with depression revealed no difference in the age adjusted scores between the three groups, suggesting that it is not a good test for diagnosing dementia or differentiating dementia from depression. PMID:2391527

  4. Social Interaction and Repetitive Motor Behaviors

    ERIC Educational Resources Information Center

    Loftin, Rachel L.; Odom, Samuel L.; Lantz, Johanna F.

    2008-01-01

    Students with autism have difficulty initiating social interactions and may exhibit repetitive motor behavior (e.g., body rocking, hand flapping). Increasing social interaction by teaching new skills may lead to reductions in problem behavior, such as motor stereotypies. Additionally, self-monitoring strategies can increase the maintenance of…

  5. Large-scale detection of repetitions.

    PubMed

    Smyth, W F

    2014-05-28

    Combinatorics on words began more than a century ago with a demonstration that an infinitely long string with no repetitions could be constructed on an alphabet of only three letters. Computing all the repetitions (such as ∙∙∙TTT ∙∙∙ or ∙∙∙ CGACGA ∙∙∙ ) in a given string x of length n is one of the oldest and most important problems of computational stringology, requiring time in the worst case. About a dozen years ago, it was discovered that repetitions can be computed as a by-product of the Θ(n)-time computation of all the maximal periodicities or runs in x. However, even though the computation is linear, it is also brute force: global data structures, such as the suffix array, the longest common prefix array and the Lempel-Ziv factorization, need to be computed in a preprocessing phase. Furthermore, all of this effort is required despite the fact that the expected number of runs in a string is generally a small fraction of the string length. In this paper, I explore the possibility that repetitions (perhaps also other regularities in strings) can be computed in a manner commensurate with the size of the output.

  6. Using Repetition to Make Ideas Stick

    ERIC Educational Resources Information Center

    Lykins, Alicia N.

    2015-01-01

    In elementary school, the use of repetitive songs to help children remember concepts is commonplace and is usually very effective. Unfortunately for many students, this strategy is generally not used in later grades. A group of mathematics teachers at Westerville South High School in Westerville, Ohio, have taken this approach to a new creative…

  7. A repetitive elements perspective in Polycomb epigenetics.

    PubMed

    Casa, Valentina; Gabellini, Davide

    2012-01-01

    Repetitive elements comprise over two-thirds of the human genome. For a long time, these elements have received little attention since they were considered non-functional. On the contrary, recent evidence indicates that they play central roles in genome integrity, gene expression, and disease. Indeed, repeats display meiotic instability associated with disease and are located within common fragile sites, which are hotspots of chromosome re-arrangements in tumors. Moreover, a variety of diseases have been associated with aberrant transcription of repetitive elements. Overall this indicates that appropriate regulation of repetitive elements' activity is fundamental. Polycomb group (PcG) proteins are epigenetic regulators that are essential for the normal development of multicellular organisms. Mammalian PcG proteins are involved in fundamental processes, such as cellular memory, cell proliferation, genomic imprinting, X-inactivation, and cancer development. PcG proteins can convey their activity through long-distance interactions also on different chromosomes. This indicates that the 3D organization of PcG proteins contributes significantly to their function. However, it is still unclear how these complex mechanisms are orchestrated and which role PcG proteins play in the multi-level organization of gene regulation. Intriguingly, the greatest proportion of Polycomb-mediated chromatin modifications is located in genomic repeats and it has been suggested that they could provide a binding platform for Polycomb proteins. Here, these lines of evidence are woven together to discuss how repetitive elements could contribute to chromatin organization in the 3D nuclear space.

  8. Large-scale detection of repetitions.

    PubMed

    Smyth, W F

    2014-05-28

    Combinatorics on words began more than a century ago with a demonstration that an infinitely long string with no repetitions could be constructed on an alphabet of only three letters. Computing all the repetitions (such as ∙∙∙TTT ∙∙∙ or ∙∙∙ CGACGA ∙∙∙ ) in a given string x of length n is one of the oldest and most important problems of computational stringology, requiring time in the worst case. About a dozen years ago, it was discovered that repetitions can be computed as a by-product of the Θ(n)-time computation of all the maximal periodicities or runs in x. However, even though the computation is linear, it is also brute force: global data structures, such as the suffix array, the longest common prefix array and the Lempel-Ziv factorization, need to be computed in a preprocessing phase. Furthermore, all of this effort is required despite the fact that the expected number of runs in a string is generally a small fraction of the string length. In this paper, I explore the possibility that repetitions (perhaps also other regularities in strings) can be computed in a manner commensurate with the size of the output. PMID:24751872

  9. Repetition effects in human ERPs to faces.

    PubMed

    Schweinberger, Stefan R; Neumann, Markus F

    2016-07-01

    In the present paper, we review research conducted over the past 25 years addressing the effects of repeating various kinds of information in faces (e.g., pictorial, spatial configural, identity, semantic) on different components in human event-related brain potentials (ERPs). This body of evidence suggests that several ERP components are systematically linked to different functional components of face identity processing. Specifically, we argue (1) that repetition of the category of faces (categorical adaptation) strongly affects the occipitotemporal N170 amplitude, which is systematically suppressed when a face is preceded by another face, irrespective of its identity, whereas (2) the prototypicality of a face's second order spatial configuration has a prominent effect on the subsequent occipitotemporal P200. Longer-latency repetition effects are related to the processing of individual facial identities. These include (3) an ERP correlate of the transient activation of individual representations of repeated faces in the form of an enhanced occipitotemporal N250r as seen in repetition priming experiments, and (4) a correlate of the acquisition of individual face identity representations during learning as seen in a topographically similar long-lasting N250 effect. Finally, (5) the repetition of semantic information in familiar person recognition elicits a central-parietal N400 ERP effect. We hope that this overview will encourage researchers to further exploit the potential of ERPs to provide a continuous time window to neuronal correlates of multiple processes in face perception under comparatively natural viewing conditions. PMID:26672902

  10. Verbal Repetitions and Echolalia in Alzheimer's Discourse

    ERIC Educational Resources Information Center

    Da Cruz, Fernanda Miranda

    2010-01-01

    This article reports on an investigation of echolalic repetition in Alzheimer's disease (AD). A qualitative analysis of data from spontaneous conversations with MHI, a woman with AD, is presented. The data come from the DALI Corpus, a corpus of spontaneous conversations involving subjects with AD. This study argues that echolalic effects can be…

  11. Sentence Repetition: What Does the Task Measure?

    ERIC Educational Resources Information Center

    Polišenská, Kamila; Chiat, Shula; Roy, Penny

    2015-01-01

    Background: Sentence repetition is gaining increasing attention as a source of information about children's sentence-level abilities in clinical assessment, and as a clinical marker of specific language impairment. However, it is widely debated what the task is testing and therefore how informative it is. Aims: (1) To evaluate the effects of…

  12. Improving Child Compliance on a Computer-Administered Nonword Repetition Task

    ERIC Educational Resources Information Center

    Polišenská, Kamila; Kapalková, Svetlana

    2014-01-01

    Purpose: A range of nonword repetition (NWR) tasks are used in research and clinical applications, but compliance rates among young children remain low. Live presentation is usually used to improve compliance rates, but this lacks the consistency of recorded stimuli. In this study, the authors examined whether a novel delivery of NWR stimuli based…

  13. [Relationship to Carcinogenesis of Repetitive Low-Dose Radiation Exposure].

    PubMed

    Ootsuyama, Akira

    2016-06-01

    We studied the carcinogenic effects caused by repetitive irradiation at a low dose, which has received attention in recent years, and examined the experimental methods used to evaluate radiation-induced carcinogenesis. For this experiment, we selected a mouse with as few autochthonous cancers as possible. Skin cancer was selected as the target for analysis, because it is a rare cancer in mice. Beta-rays were selected as the radiation source. The advantage of using beta-rays is weaker penetration power into tissues, thus protecting organs, such as the digestive and hematogenous organs. The benefit of our experimental method is that only skin cancer requires monitoring, and it is possible to perform long-term experiments. The back skin of mice was exposed repetitively to beta-rays three times a week until the occurrence of cancer or death, and the dose per exposure ranged from 0.5 to 11.8 Gy. With the high-dose range (2.5-11.8 Gy), the latency period and carcinogenic rate were almost the same in each experimental group. When the dose was reduced to 1-1.5 Gy, the latency period increased, but the carcinogenic rate remained. When the dose was further reduced to 0.5 Gy, skin cancer never happened, even though we continued irradiation until death of the last mouse in this group. The lifespan of 0.5 Gy group mice was the same as that of the controls. We showed that the 0.5 Gy dose did not cause cancer, even in mice exposed repetitively throughout their life span, and thus refer to 0.5 Gy as the threshold-like dose. PMID:27302731

  14. [Relationship to Carcinogenesis of Repetitive Low-Dose Radiation Exposure].

    PubMed

    Ootsuyama, Akira

    2016-06-01

    We studied the carcinogenic effects caused by repetitive irradiation at a low dose, which has received attention in recent years, and examined the experimental methods used to evaluate radiation-induced carcinogenesis. For this experiment, we selected a mouse with as few autochthonous cancers as possible. Skin cancer was selected as the target for analysis, because it is a rare cancer in mice. Beta-rays were selected as the radiation source. The advantage of using beta-rays is weaker penetration power into tissues, thus protecting organs, such as the digestive and hematogenous organs. The benefit of our experimental method is that only skin cancer requires monitoring, and it is possible to perform long-term experiments. The back skin of mice was exposed repetitively to beta-rays three times a week until the occurrence of cancer or death, and the dose per exposure ranged from 0.5 to 11.8 Gy. With the high-dose range (2.5-11.8 Gy), the latency period and carcinogenic rate were almost the same in each experimental group. When the dose was reduced to 1-1.5 Gy, the latency period increased, but the carcinogenic rate remained. When the dose was further reduced to 0.5 Gy, skin cancer never happened, even though we continued irradiation until death of the last mouse in this group. The lifespan of 0.5 Gy group mice was the same as that of the controls. We showed that the 0.5 Gy dose did not cause cancer, even in mice exposed repetitively throughout their life span, and thus refer to 0.5 Gy as the threshold-like dose.

  15. [Repetitive strain injuries. Forearm pain caused by tissue responses to repetitive strain].

    PubMed

    Sorgatz, H

    2002-10-01

    According to the National Research Council, painful work-related upper limb disorders are caused by different pathophysiological mechanisms, one of which is repetitive strain injury (RSI). Forearm pain, tenderness, and paresthesias are thought to result from a continual risk of exceeding limits of "cumulative trauma load tolerance" (CTLT, cf. NRC 2001) in soft tissue by thousands of high-frequency, repetitive movements. On the other hand, repetitive painful stimulations also produce neuroplastic changes in the spinal and supraspinal nociceptive systems. Thus, repetitive motor and nociceptive impulses become part of the same motor programs, which are also responsible for high-frequency movements and tissue damage. In this way RSI pain may be felt as a task-related response, even after all injuries are completely healed. Consequences of this neuroplastic CTLT model for RSI prevention and therapy are discussed.

  16. Development of Silver Tape Target System for High Repetition X-ray Laser

    NASA Astrophysics Data System (ADS)

    Nishikino, Masaharu; Ochi, Yoshihiro; Hasegawa, Noboru; Kawachi, Tetsuya; Ohba, Toshiyuki; Kaihori, Takeshi; Nagashima, Keisuke

    The development of continuous pumping to the target system is an important issue for realizing an x-ray laser (XRL) with the high repetition rate. We have developed a 13.9 nm XRL using a silver tape target and demonstrated a highly coherent XRL with an oscillator-amplifier configuration using two tape target systems and the TOPAZ laser system with a 10-J and a 0.1-Hz repetition rate. The output energy is comparable to the x-ray laser generated with a silver-deposited slab target, and the pointing stability using the new tape target system is better than conventional slab target.

  17. A Nonword Repetition Task for Speakers with Misarticulations: The Syllable Repetition Task (SRT)

    PubMed Central

    Shriberg, Lawrence D.; Lohmeier, Heather L.; Campbell, Thomas F.; Dollaghan, Christine A.; Green, Jordan R.; Moore, Christopher A.

    2010-01-01

    Purpose Conceptual and methodological confounds occur when non(sense) repetition tasks are administered to speakers who do not have the target speech sounds in their phonetic inventories or who habitually misarticulate targeted speech sounds. We describe a nonword repetition task, the Syllable Repetiton Task (SRT) that eliminates this confound and report findings from three validity studies. Method Ninety-five preschool children with Speech Delay and 63 with Typical Speech, completed an assessment battery that included the Nonword Repetition Task (NRT: Dollaghan & Campbell, 1998) and the SRT. SRT stimuli include only four of the earliest occurring consonants and one early occurring vowel. Results Study 1 findings indicated that the SRT eliminated the speech confound in nonword testing with speakers who misarticulate. Study 2 findings indicated that the accuracy of the SRT to identify expressive language impairment was comparable to findings for the NRT. Study 3 findings illustrated the SRT’s potential to interrogate speech processing constraints underlying poor nonword repetition accuracy. Results supported both memorial and auditory-perceptual encoding constraints underlying nonword repetition errors in children with speech-language impairment. Conclusion The SRT appears to be a psychometrically stable and substantively informative nonword repetition task for emerging genetic and other research with speakers who misarticulate. PMID:19635944

  18. If you negate, you may forget: negated repetitions impair memory compared with affirmative repetitions.

    PubMed

    Mayo, Ruth; Schul, Yaacov; Rosenthal, Meytal

    2014-08-01

    One of the most robust laws of memory is that repeated activation improves memory. Our study shows that the nature of repetition matters. Specifically, although both negated repetition and affirmative repetition improve memory compared with no repetition, negated repetition hinders memory compared with affirmative repetition. After showing participants different entities, we asked them about features of these entities, leading to either "yes" or "no" responses. Our findings show that correctly negating an incorrect feature of an entity elicits an active forgetting effect compared with correctly affirming its true features. For example, after seeing someone drink a glass of white wine, answering "no" to "was it red wine?" may lead one to greater memory loss of the individual drinking wine at all compared with answering "yes" to "was it white wine?" We find this negation-induced forgetting effect in 4 experiments that differ in (a) the meaning given for the negation, (b) the type of stimuli (visual or verbal), and (c) the memory measure (recognition or free recall). We discuss possible underlying mechanisms and offer theoretical and applied implications of the negation-induced forgetting effect in relation to other known inhibition effects. PMID:24635186

  19. High-repetition CO{sub 2} laser for collective Thomson scattering diagnostic of {alpha} particles in burning plasmas

    SciTech Connect

    Kondoh, T.; Hayashi, T.; Kawano, Y.; Kusama, Y.; Sugie, T.; Miura, Y.; Koseki, R.; Kawahara, Y.

    2006-10-15

    A high-repetition and high-energy transversely excited atmospheric carbon dioxide (CO{sub 2}) laser for a collective Thomson scattering (CTS) diagnostic has been developed to establish a diagnostic method of confined {alpha} particles in burning plasmas. To excite a single-transverse and single-longitudinal mode, a continuous wave seed laser was injected to an unstable resonator with a cavity length of {approx}4.4 m. Pulse energy of 10 J with a repetition rate of 10 Hz has been achieved in the single-mode operation. Pulse energies of 18 J with a repetition rate of 10 Hz and 36 J with single shot operation have also been achieved in the multimode operation. These results give a prospect for the CTS diagnostic on International Thermonuclear Experimental Reactor (ITER), which requires single-mode energy of 20 J with repetition rate of 40 Hz.

  20. Repetition probability effects for inverted faces.

    PubMed

    Grotheer, Mareike; Hermann, Petra; Vidnyánszky, Zoltán; Kovács, Gyula

    2014-11-15

    It has been shown, that the repetition related reduction of the blood-oxygen level dependent (BOLD) signal is modulated by the probability of repetitions (P(rep)) for faces (Summerfield et al., 2008), providing support for the predictive coding (PC) model of visual perception (Rao and Ballard, 1999). However, the stage of face processing where repetition suppression (RS) is modulated by P(rep) is still unclear. Face inversion is known to interrupt higher level configural/holistic face processing steps and if modulation of RS by P(rep) takes place at these stages of face processing, P(rep) effects are expected to be reduced for inverted when compared to upright faces. Therefore, here we aimed at investigating whether P(rep) effects on RS observed for face stimuli originate at the higher-level configural/holistic stages of face processing by comparing these effects for upright and inverted faces. Similarly to previous studies, we manipulated P(rep) for pairs of stimuli in individual blocks of fMRI recordings. This manipulation significantly influenced repetition suppression in the posterior FFA, the OFA and the LO, independently of stimulus orientation. Our results thus reveal that RS in the ventral visual stream is modulated by P(rep) even in the case of face inversion and hence strongly compromised configural/holistic face processing. An additional whole-brain analysis could not identify any areas where the modulatory effect of probability was orientation specific either. These findings imply that P(rep) effects on RS might originate from the earlier stages of face processing.

  1. Modeling repetitive motions using structured light.

    PubMed

    Xu, Yi; Aliaga, Daniel G

    2010-01-01

    Obtaining models of dynamic 3D objects is an important part of content generation for computer graphics. Numerous methods have been extended from static scenarios to model dynamic scenes. If the states or poses of the dynamic object repeat often during a sequence (but not necessarily periodically), we call such a repetitive motion. There are many objects, such as toys, machines, and humans, undergoing repetitive motions. Our key observation is that when a motion-state repeats, we can sample the scene under the same motion state again but using a different set of parameters; thus, providing more information of each motion state. This enables robustly acquiring dense 3D information difficult for objects with repetitive motions using only simple hardware. After the motion sequence, we group temporally disjoint observations of the same motion state together and produce a smooth space-time reconstruction of the scene. Effectively, the dynamic scene modeling problem is converted to a series of static scene reconstructions, which are easier to tackle. The varying sampling parameters can be, for example, structured-light patterns, illumination directions, and viewpoints resulting in different modeling techniques. Based on this observation, we present an image-based motion-state framework and demonstrate our paradigm using either a synchronized or an unsynchronized structured-light acquisition method.

  2. The Dfam database of repetitive DNA families

    PubMed Central

    Hubley, Robert; Finn, Robert D.; Clements, Jody; Eddy, Sean R.; Jones, Thomas A.; Bao, Weidong; Smit, Arian F.A.; Wheeler, Travis J.

    2016-01-01

    Repetitive DNA, especially that due to transposable elements (TEs), makes up a large fraction of many genomes. Dfam is an open access database of families of repetitive DNA elements, in which each family is represented by a multiple sequence alignment and a profile hidden Markov model (HMM). The initial release of Dfam, featured in the 2013 NAR Database Issue, contained 1143 families of repetitive elements found in humans, and was used to produce more than 100 Mb of additional annotation of TE-derived regions in the human genome, with improved speed. Here, we describe recent advances, most notably expansion to 4150 total families including a comprehensive set of known repeat families from four new organisms (mouse, zebrafish, fly and nematode). We describe improvements to coverage, and to our methods for identifying and reducing false annotation. We also describe updates to the website interface. The Dfam website has moved to http://dfam.org. Seed alignments, profile HMMs, hit lists and other underlying data are available for download. PMID:26612867

  3. The Dfam database of repetitive DNA families.

    PubMed

    Hubley, Robert; Finn, Robert D; Clements, Jody; Eddy, Sean R; Jones, Thomas A; Bao, Weidong; Smit, Arian F A; Wheeler, Travis J

    2016-01-01

    Repetitive DNA, especially that due to transposable elements (TEs), makes up a large fraction of many genomes. Dfam is an open access database of families of repetitive DNA elements, in which each family is represented by a multiple sequence alignment and a profile hidden Markov model (HMM). The initial release of Dfam, featured in the 2013 NAR Database Issue, contained 1143 families of repetitive elements found in humans, and was used to produce more than 100 Mb of additional annotation of TE-derived regions in the human genome, with improved speed. Here, we describe recent advances, most notably expansion to 4150 total families including a comprehensive set of known repeat families from four new organisms (mouse, zebrafish, fly and nematode). We describe improvements to coverage, and to our methods for identifying and reducing false annotation. We also describe updates to the website interface. The Dfam website has moved to http://dfam.org. Seed alignments, profile HMMs, hit lists and other underlying data are available for download.

  4. The Dfam database of repetitive DNA families.

    PubMed

    Hubley, Robert; Finn, Robert D; Clements, Jody; Eddy, Sean R; Jones, Thomas A; Bao, Weidong; Smit, Arian F A; Wheeler, Travis J

    2016-01-01

    Repetitive DNA, especially that due to transposable elements (TEs), makes up a large fraction of many genomes. Dfam is an open access database of families of repetitive DNA elements, in which each family is represented by a multiple sequence alignment and a profile hidden Markov model (HMM). The initial release of Dfam, featured in the 2013 NAR Database Issue, contained 1143 families of repetitive elements found in humans, and was used to produce more than 100 Mb of additional annotation of TE-derived regions in the human genome, with improved speed. Here, we describe recent advances, most notably expansion to 4150 total families including a comprehensive set of known repeat families from four new organisms (mouse, zebrafish, fly and nematode). We describe improvements to coverage, and to our methods for identifying and reducing false annotation. We also describe updates to the website interface. The Dfam website has moved to http://dfam.org. Seed alignments, profile HMMs, hit lists and other underlying data are available for download. PMID:26612867

  5. Lingual Kinematics during Rapid Syllable Repetition in Parkinson's Disease

    ERIC Educational Resources Information Center

    Wong, Min Ney; Murdoch, Bruce E.; Whelan, Brooke-Mai

    2012-01-01

    Background: Rapid syllable repetition tasks are commonly used in the assessment of motor speech disorders. However, little is known about the articulatory kinematics during rapid syllable repetition in individuals with Parkinson's disease (PD). Aims: To investigate and compare lingual kinematics during rapid syllable repetition in dysarthric…

  6. Repetition Blindness: An Emergent Property of Inter-Item Competition

    ERIC Educational Resources Information Center

    Morris, Alison L.; Still, Mary L.; Caldwell-Harris, Catherine L.

    2009-01-01

    Repeating an item in a brief or rapid display usually produces faster or more accurate identification of the item (repetition priming), but sometimes produces the opposite effect (repetition blindness). We present a theory of short-term repetition effects, the "competition hypothesis," which explains these paradoxical outcomes. The central tenet…

  7. Repetitive Behaviours in Typically Developing 2-Year-Olds

    ERIC Educational Resources Information Center

    Leekam, Susan; Tandos, Jonathan; McConachie, Helen; Meins, Elizabeth; Parkinson, Kathryn; Wright, Charlotte; Turner, Michelle; Arnott, Bronia; Vittorini, Lucia; Le Couteur, Ann

    2007-01-01

    Background: Repetitive behaviours are an essential part of the diagnosis of autism but are also commonly seen in typically developing children. The current study investigated the frequency and factor structure of repetitive behaviours in a large community sample of 2-year-olds. Methods: A new measure, the Repetitive Behaviour Questionnaire (RBQ-2)…

  8. Experimental models of repetitive brain injuries.

    PubMed

    Weber, John T

    2007-01-01

    Repetitive traumatic brain injury (TBI) occurs in a significant portion of trauma patients, especially in specific populations, such as child abuse victims or athletes involved in contact sports (e.g. boxing, football, hockey, and soccer). A continually emerging hypothesis is that repeated mild injuries may cause cumulative damage to the brain, resulting in long-term cognitive dysfunction. The growing attention to this hypothesis is reflected in several recent experimental studies of repeated mild TBI in vivo. These reports generally demonstrate cellular and cognitive dysfunction after repetitive injury using rodent TBI models. In some cases, data suggests that the effects of a second mild TBI may be synergistic, rather than additive. In addition, some studies have found increases in cellular markers associated with Alzheimer's disease after repeated mild injuries, which demonstrates a direct experimental link between repetitive TBI and neurodegenerative disease. To complement the findings from humans and in vivo experimentation, my laboratory group has investigated the effects of repeated trauma in cultured brain cells using a model of stretch-induced mechanical injury in vitro. In these studies, hippocampal cells exhibited cumulative damage when mild stretch injuries were repeated at either 1-h or 24-h intervals. Interestingly, the extent of damage to the cells was dependent on the time between repeated injuries. Also, a very low level of stretch, which produced no cell damage on its own, induced cell damage when it was repeated several times at a short interval (every 2 min). Although direct comparisons to the clinical situation are difficult, these types of repetitive, low-level, mechanical stresses may be similar to the insults received by certain athletes, such as boxers, or hockey and soccer players. This type of in vitro model could provide a reliable system in which to study the mechanisms underlying cellular dysfunction following repeated injuries. As

  9. The Adult Repetitive Behaviours Questionnaire-2 (RBQ-2A): A Self-Report Measure of Restricted and Repetitive Behaviours

    ERIC Educational Resources Information Center

    Barrett, Sarah L.; Uljarevic, Mirko; Baker, Emma K.; Richdale, Amanda L.; Jones, Catherine R. G.; Leekam, Susan R.

    2015-01-01

    In two studies we developed and tested a new self-report measure of restricted and repetitive behaviours (RRB) suitable for adults. In Study 1, The Repetitive Behaviours Questionnaire-2 for adults (RBQ-2A) was completed by a sample of 163 neurotypical adults. Principal components analysis revealed two components: Repetitive Motor Behaviours and…

  10. Further characterization of repetitive behavior in C58 mice: developmental trajectory and effects of environmental enrichment.

    PubMed

    Muehlmann, A M; Edington, G; Mihalik, A C; Buchwald, Z; Koppuzha, D; Korah, M; Lewis, M H

    2012-12-01

    Aberrant repetitive behaviors are commonly observed in a variety of neurodevelopmental, neurological, and neuropsychiatric disorders. Little is known about the specific neurobiological mechanisms that underlie such behaviors, however, and effective treatments are lacking. Valid animal models can aid substantially in identifying pathophysiological factors mediating aberrant repetitive behavior and aid in treatment development. The C58 inbred mouse strain is a particularly promising model, and we have further characterized its repetitive behavior phenotype. Compared to C57BL/6 mice, C58 mice exhibit high rates of spontaneous hindlimb jumping and backward somersaulting reaching adult frequencies by 5 weeks post-weaning and adult temporal organization by 2 weeks post-weaning. The development of repetitive behavior in C58 mice was markedly attenuated by rearing these mice in larger, more complex environments. In addition to characterizing repetitive motor behavior, we also assessed related forms of inflexible behavior that reflect restricted and perseverative responding. Contrary to our hypothesis, C58 mice did not exhibit increased marble burying nor did they display reduced exploratory behavior in the holeboard task. The C58 strain appears to be a very useful model for the repetitive motor behavior characteristic of a number of clinical disorders. As an inbred mouse strain, studies using the C58 model can take full advantage of the tool kit of modern genetics and molecular neuroscience. This technical advantage makes the model a compelling choice for use in studies designed to elucidate the etiology and pathophysiology of aberrant repetitive behavior. Such findings should, in turn, translate into effective new treatments.

  11. Liking and wanting pleasant odors: different effects of repetitive exposure in men and women

    PubMed Central

    Triscoli, Chantal; Croy, Ilona; Olausson, Håkan; Sailer, Uta

    2014-01-01

    Odors can enrich the perception of our environment and are commonly used to attract people in marketing situations. However, the perception of an odor changes over repetitions. This study investigated whether repetitive exposition to olfactory stimuli leads to a change in the perceived pleasantness (“liking”) or in the wish to be further exposed to the same olfactory stimulus (“wanting”), and whether these two mechanisms show gender differences. Three different pleasant odors were each repeatedly presented for 40 times in random order with a mean inter-stimulus interval of 18 s. Eighteen participants rated both “liking” and “wanting” for each of the 120 olfactory stimuli. Wanting ratings decreased significantly over repetitions in women and men, with a steeper decrease for men during the initial trials before plateauing. In contrast, liking ratings decreased significantly over repetitions only in men, with a steeper decrease after the initial ratings, but not in women. Additionally, women scored higher in a questionnaire on reward responsiveness than men. We conclude that positive evaluation (liking) and the wish to experience more of the same (wanting) are different concepts even in the domain of olfaction. The persistence of perceived pleasantness in women may be due to the attribution of a greater subjective value to odors. PMID:24910630

  12. Development of a picosecond CO2 laser system for a high-repetition γ-source

    SciTech Connect

    Polyanskiy, M.N.; Pogorelsky, I.V.; Yakimenko, V.E.; Platonenko, V.T.

    2009-04-17

    The concept of a high-repetition-rate, high-average power {gamma}-source is based on Compton backscattering from the relativistic electron beam inside a picosecond CO{sub 2} laser cavity. Proof-of-principle experiments combined with computer simulations allow evaluating the promise of this approach for novel applications in science and technology.

  13. High-power pulse repetitive HF(DF) laser with a solid-state pump generator

    NASA Astrophysics Data System (ADS)

    Velikanov, S. D.; Domazhirov, A. P.; Zaretskiy, N. A.; Kazantsev, S. Yu; Kononov, I. G.; Kromin, A. A.; Podlesnykh, S. V.; Sivachev, A. A.; Firsov, K. N.; Kharitonov, S. V.; Tsykin, V. S.; Shchurov, V. V.; Yutkin, I. M.

    2015-11-01

    Operation of a repetitively pulsed electric-discharge HF(DF) laser with an all-solid-state pump generator based on FID switches is demonstrated. The energy stored in the pump generator capacitors was 880 J at an open-circuit voltage of 240 kV and a discharge pulse repetition rate of 25 Hz. The specific energy extractions were 3.8 and 3.4 J L-1 for the HF and DF lasers, respectively. The possibilities of improving the output laser characteristics are discussed.

  14. [Guidelines for redesigning jobs with repetitive tasks].

    PubMed

    Colombini, D; Occhipinti, E; Meroni, M; Menoni, O; Bergamasco, R; Girola, C; Grea, V; Vendola, D

    1996-01-01

    Preventive measures aimed at minimising the occurrence of work-related musculo-skeletal disorders of the upper limbs (WMSDs) associated with repetitive tasks can be divided into 3 categories: structural, organisational and educational. Whenever specific risk and injury assessments have shown the need for preventive action, this is most often implemented within the framework of a range of assorted measures. In particular, structural measures pertain to optimising the layout of the work area and furnishings, and the "ergonomic" properties of work tools and equipment. Such measures serve to alleviate the problems caused by the use of excessive force and improper postures. The authors refer to the principles guiding such structural measures, in the light of the extensive literature that has been published on the subject. Organisational (or re-organisational) measures essentially relate to job design (i.e. distribution of tasks, speeds and pauses). They serve to alleviate problems connected with highly repetitive and frequent actions, excessively lengthy tasks and inadequate recovery periods. Very few relevant findings are available: the authors therefore illustrate in some detail a practical trial conducted in a major engineering firm. The objective was to lower to acceptable limits the frequency of certain repetitive tasks performed by workers using their upper limbs. The trial made it possible to identify a suitable plan and schedule of measures taking into due consideration the impact of the plan on production levels (and costs). The fundamental principles guiding the adoption of specific educational and training programmes for the workers and their supervisors are presented and discussed.

  15. Repetitive DNA alterations in human skin cancers.

    PubMed

    Ribeiro, Gil R H; Francisco, Guilherme; Teixeira, Lúcia V S; Romão-Correia, Rosana F; Sanches, José A; Neto, Cyro Festa; Ruiz, Itamar R G

    2004-11-01

    Repetitive sequences constitute landmarks for genome regulation, evolution, and chromatin architecture. Patterns of specific and non-specific repetitive sequences change in many types and stages of tumor cells, characterized by band loss, gain, and (de) increased staining of pre-existing bands. In this work, repetitive DNA was studied in search of genome instability of skin cancers: basal and squamous cell carcinomas (BCC and SCC), malignant melanoma (MM), melanocytic nevus (MN), and actinic keratosis (AK) lesions. DNAs were extracted from blood and tumor samples from 21 BCC, 7 SCC, 11 MM and 7 lesions. Banding patterns were obtained by random amplification of polymorphic DNA (RAPD), and specific D9S50 and D9S52 microsatellites (9p21). D9S50 patterns revealed microsatellite instability (MSI) and/or loss of heterozygosity (LOH) in 36% BCC, 25% SCC, and 57% MM tumors. D9S52 microsatellite showed 28.5%; 42.8%; and 71.4% altered tumors, respectively. No microsatellite alterations were found in MN and AK. On the other hand, genomic rearrangements detected by RAPD were present in 100% tumors. In BCC, the mean number of tumor DNA alterations showed predominant gain of bands. On the contrary, MM samples presented loss, or decreased intensity signal of RAPD bands. Genome alterations in skin cancers would result from chromosomal rearrangements, aneuploidy and/or polysomies. The low-cost and quick RAPD technique may reveal unknown genes or DNA sequences associated with tumor development and progression, and may be easily implemented in clinical diagnosis.

  16. Repetitive Head Impacts and Chronic Traumatic Encephalopathy.

    PubMed

    McKee, Ann C; Alosco, Michael L; Huber, Bertrand R

    2016-10-01

    Chronic traumatic encephalopathy (CTE) is a distinctive neurodegenerative disease that occurs as a result of repetitive head impacts. CTE can only be diagnosed by postmortem neuropathologic examination of brain tissue. CTE is a unique disorder with a pathognomonic lesion that can be reliably distinguished from other neurodegenerative diseases. CTE is associated with violent behaviors, explosivity, loss of control, depression, suicide, memory loss and cognitive changes. There is increasing evidence that CTE affects amateur athletes as well as professional athletes and military veterans. CTE has become a major public health concern.

  17. AUTOSIM: An automated repetitive software testing tool

    NASA Technical Reports Server (NTRS)

    Dunham, J. R.; Mcbride, S. E.

    1985-01-01

    AUTOSIM is a software tool which automates the repetitive run testing of software. This tool executes programming tasks previously performed by a programmer with one year of programming experience. Use of the AUTOSIM tool requires a knowledge base containing information about known faults, code fixes, and the fault diagnosis-correction process. AUTOSIM can be considered as an expert system which replaces a low level of programming expertise. Reference information about the design and implementation of the AUTOSIM software test tool provides flowcharts to assist in maintaining the software code and a description of how to use the tool.

  18. Repetitive Head Impacts and Chronic Traumatic Encephalopathy.

    PubMed

    McKee, Ann C; Alosco, Michael L; Huber, Bertrand R

    2016-10-01

    Chronic traumatic encephalopathy (CTE) is a distinctive neurodegenerative disease that occurs as a result of repetitive head impacts. CTE can only be diagnosed by postmortem neuropathologic examination of brain tissue. CTE is a unique disorder with a pathognomonic lesion that can be reliably distinguished from other neurodegenerative diseases. CTE is associated with violent behaviors, explosivity, loss of control, depression, suicide, memory loss and cognitive changes. There is increasing evidence that CTE affects amateur athletes as well as professional athletes and military veterans. CTE has become a major public health concern. PMID:27637402

  19. From N400 to N300: variations in the timing of semantic processing with repetition.

    PubMed

    Renoult, Louis; Wang, Xiaoxiao; Calcagno, Vincent; Prévost, Marie; Debruille, J Bruno

    2012-05-15

    The present study aimed to explore the variations of semantic processing according to the number of target words (i.e., 4, 12 and 24) and according to the number of repetitions (i.e, 1 to 15). The number of targets had no impact on the N400 brain potential, the index of semantic processing, nor on the late positive component (LPC), an index of episodic encoding and retrieval. Analyses of the effects of the number of repetitions showed that the duration of semantic processes--assessed by measuring N400 latency--was linearly shortened along repetitions while their extent--as indexed by N400 amplitude--remained constant after the second presentation. In contrast, the extent of episodic processes--as indexed by LPC amplitude--was found to increase linearly with repetition. By showing that N400 latency may be much less stable than previously thought, these results bring new constraints on the functional correlates of this key stage in the processing of semantic information. They also suggest that semantic processes can be studied at high repetition rates whatever the number of target stimuli. Finally, our findings show that each episode of prior presentation has an impact on the late processing of a stimulus despite the absence of an explicit memory task.

  20. An educational approach to an epidemic of repetitive motion injuries among office workers

    SciTech Connect

    Halunen, L.J.

    1988-09-23

    Among office workers, repetitive motion injuries such as tendonitis, muscle fatigue, and nerve irritation (caused by poor posture and arm/hand positioning while performing repetitive tasks) are a fairly new phenomenon. Office workers and their managers are not prepared to respond properly to the identification and treatment of these injuries. We found an unusually high incidence within one department at a large research facility--the Lawrence Livermore National Laboratory--and developed an educational approach to reduce the frequency and severity of these injuries. Our approach was to inform the workers and managers about the origins and severity of repetitive motion injuries and their effect on the work force. Classes in ergonomic adjustment of video workstations were scheduled for all personnel who had jobs that required heavy keyboard use. The individual's responsibility in reporting any symptoms of repetitive motion injury was emphasized. We stressed to management the seriousness of the problem, the desirability of obtaining improved equipment workers may need, or the possibility of arranging a lighter workload for those showing symptoms of repetitive motion injuries. We followed these classes and briefings with additional videotaped material and written guidelines, pamphlets, and articles for further study and discussion. Early results indicate that informed workers in a supportive environment detect symptoms earlier, and therefore recover more quickly; managers who understand the problem and are able to respond positively gain better labor relations as well as lower injury rates. 4 refs., 2 figs.

  1. Peripheral neuritis and increased spinal cord neurochemicals are induced in a model of repetitive motion injury with low force and repetition exposure.

    PubMed

    Elliott, Melanie B; Barr, Ann E; Kietrys, David M; Al-Shatti, Talal; Amin, Mamta; Barbe, Mary F

    2008-07-01

    Performance of high repetition tasks with or without force is associated with peripheral tissue inflammation, decreased nerve function and motor dysfunction. Here, we examined whether a low repetition task with negligible force (LRNF) produces fewer tissue and behavioral pathologies than previously observed with high repetition tasks using our rat model of repetitive motion injury (RMI). Thirty-seven rats were randomized into control or LRNF groups, the latter reaching and grasping a 45 mg food pellet at a rate of 3 reaches/min. This task was performed in 4, 0.5 5 h sessions with 1.5 5 h rest periods for 3 days/week for up to 12 weeks. Examination of distal median nerve, forelimb flexor tendons and bones for ED1-positive cells (macrophages and osteoclasts) revealed increases in nerve and bone in week 12. The nerve also contained increased TNF-alpha expressing cells in week 12. Examination of spinal cord dorsal horns revealed increased immunoexpression of Substance P in week 8 and neurokinin-1 in weeks 8 and 12 in the superficial lamina. Motor behavioral analyses showed no changes in reach rate across weeks, slightly reduced task duration (a measurement of voluntary task participation) in week 12, but significantly increased extra arm movement reversals during reaching in week 8. These extra movement reversals were corrections for missed food pellets during a reach. Thus, performance of even a low repetition, negligible force upper extremity task for 3 months can induce mild peripheral tissue inflammation, neurochemical increases in spinal cord dorsal horns, and declines in fine motor control.

  2. The Effects of Repetition on Children’s True and False Reports

    PubMed Central

    Evans, Angela D.; Brunet, Megan K.; Talwar, Victoria; Bala, Nicholas; Lindsay, Rod C.L.; Lee, Kang

    2013-01-01

    As children are often called upon to provide testimony in court proceedings, determining the veracity of their statements is an important issue. In the course of investigation by police and social workers, children are often repeatedly interviewed about their experiences, though the impact of this repetition on children’s true and false statements remains largely unexamined. The current study analysed semantic differences in children’s truthful and fabricated statements about an event they had or had not participated in. Results revealed that children’s truthful and fabricated reports differed in linguistic content, and that their language also varied with repetition. Discriminant analyses revealed that with repetition, children’s true and false reports became increasingly difficult to differentiate using linguistic markers, though true reports were consistently classified correctly at higher rates than false reports. The implications of these findings for legal procedures concerning child witnesses are discussed. PMID:24265592

  3. Relationship between redistribution on exercise thallium-201 scintigraphy and repetitive ventricular premature beats in patients with recent myocardial infarction

    SciTech Connect

    Tsuji, H.; Iwasaka, T.; Sugiura, T.; Shimada, T.; Nakamori, H.; Kimura, Y.; Inada, M. )

    1991-06-01

    The relationship between myocardial ischemia detected by exercise thallium-201 scintigraphy and repetitive ventricular premature beats (VPBs) during ambulatory monitoring was evaluated in 57 patients with recent myocardial infarction. Multivariate analysis was performed to obtain the relatively important factor related to repetitive VPBs with the use of the following variables: age, redistribution, left ventricular ejection fraction, serum potassium and magnesium concentration, QRS score, left ventricular aneurysm, and the number of diseased vessels. Thirty-five patients had redistribution, but only three of them had repetitive VPBs during exercise testing. The average heart rate before 79% of 398 episodes of repetitive VPBs during ambulatory monitoring was in the range of 56 to 70/min. These data indicate that most of repetitive VPBs during ambulatory monitoring were not provoked by exercise-induced acute myocardial ischemia. However, redistribution was found to be an important factor associated with repetitive VPBs. The electrical abnormality relating to a substrate characterized by chronic reversible ischemia may explain the association between redistribution and repetitive VPBs.

  4. Pull-production in repetitive remanufacturing

    SciTech Connect

    McCaskey, D.W. Jr.

    1992-09-01

    In the past, production activity control practices in most repetitive remanufacturing facilities resembled those used in intermittent production operations. These operations were characterized by large amounts of work-in-process (WIP), frequent work stoppages due to part shortages, excessive overtime, low product velocity, informal scheduling between dependent operations, low employee and management moral, and a lot of wasted time, material, labor, and space. Improvement in production activity control (PAC) methods for repetitive remanufactures has been hampered by uncertainty in: supply of incoming assets, configuration of assets, process times to refurbish assets, and yields in reclamation processes. collectively these uncertainties make shop floor operations seem uncontrollable. However, one United States Army depot has taken on the challenge. Through management supported, cross-functional teams, the Tooele Army Depot has designed and implemented pull-production systems for two of its major products, with several others to follow. This article presents a generalized version of Tooele's pull-production system and highlights design characteristics which are specific to remanufacturing applications.

  5. Pull-production in repetitive remanufacturing

    SciTech Connect

    McCaskey, D.W. Jr.

    1992-09-01

    In the past, production activity control practices in most repetitive remanufacturing facilities resembled those used in intermittent production operations. These operations were characterized by large amounts of work-in-process (WIP), frequent work stoppages due to part shortages, excessive overtime, low product velocity, informal scheduling between dependent operations, low employee and management moral, and a lot of wasted time, material, labor, and space. Improvement in production activity control (PAC) methods for repetitive remanufactures has been hampered by uncertainty in: supply of incoming assets, configuration of assets, process times to refurbish assets, and yields in reclamation processes. collectively these uncertainties make shop floor operations seem uncontrollable. However, one United States Army depot has taken on the challenge. Through management supported, cross-functional teams, the Tooele Army Depot has designed and implemented pull-production systems for two of its major products, with several others to follow. This article presents a generalized version of Tooele`s pull-production system and highlights design characteristics which are specific to remanufacturing applications.

  6. RN-BSN curricula: designed for transition, not repetition.

    PubMed

    Allen, Patricia E; Armstrong, Myrna L

    2013-01-01

    Combined efforts of professional mandates, employer preferences for increased educational levels of staff registered nurses (RNs), Magnet's higher environmental ratings, the Institute of Medicine report, and Aiken's (2003, 2008, & 2011) clinical research outcomes have spawn renewed attention for RN-baccalaureate degree of science in nursing (BSN) education. Yet, nationally, only 21.6% of associate degree nurses are continuing their education (Health Resources and Services Administration, 2010). Designing programs with the student as the center, where student/faculty engagement is the goal, has enabled one school of nursing to develop a quality on-line RN-to-BSN program. Core values of the program reveal a faculty who is committed to development of education to transition the associate degree and/or diploma graduate to professional nursing practice without repetition of content and learning activities.

  7. Exposure to Repetitive Tasks Induces Motor Changes Related to Skill Acquisition and Inflammation in Rats

    PubMed Central

    Kietrys, David M.; Barr, Ann E; Barbe, Mary F

    2013-01-01

    This study elucidates exposure-response relationships between repetitive tasks, inflammation and motor changes with work-related musculoskeletal disorders. Using a rat model of reaching and handle-pulling, we examined effects of performing a high repetition low force (HRLF), low repetition high force (LRHF), or high repetition high force (HRHF) task (2 h/day, 3 days/wk, 12 wks) on reach rate and force, percent success, duration of participation and grip strength. Reach rate and reach force improved with HRLF, and percent success increased in all groups in week 9, and HRLF and HRHF in week 12, indicative of skill acquisition. Duration and grip strength showed force-dependent declines with task performance. A subset of HRHF rats received ibuprofen in weeks 5–12. Ibuprofen significantly improved reach rate, reach force and duration in treated rats, indicative of an inflammatory influence on reach performance. Ibuprofen improved percent successful reaches in week 9, although this increase was not sustained. However, declines in grip strength, a nocifensive behavior, were not prevented by ibuprofen. Examination of cervical spinal cords of untreated and ibuprofen treated HRHF rats showed increased IL-1beta, an inflammatory cytokine, in neurons. These findings suggest that only a preventive intervention could have addressed all motor declines. PMID:22087754

  8. A long-pulse repetitive operation magnetically insulated transmission line oscillator

    SciTech Connect

    Fan, Yu-Wei; Zhong, Hui-Huang; Zhang, Jian-De; Shu, Ting; Liu, Jin Liang

    2014-05-15

    The improved magnetically insulated transmission line oscillator (MILO) is a gigawatt-class L-band high power microwave tube. It has allowed us to generate 3.1 GW pulse of 40 ns duration in the single-pulse operation and 500 MW pulse of 25 ns duration in the repetition rate operation. However, because of the severe impedance mismatch, the power conversion efficiency is only about 4% in the repetition rate operation. In order to eliminate the impedance mismatch and obtain repetitive long-pulse high-power microwave (HPM), a series of experiments are carried out and the recent progress is presented in this paper. In the single-pulse operation, when the diode voltage is 466 kV and current is 41.6 kA, the radiated microwave power is above 2.2 GW, the pulse duration is above 102 ns, the microwave frequency is about 1.74 GHz, and the power conversion efficiency is about 11.5%. In the repetition rate operation, under the condition of the diode voltage about 400 kV, beam current about 38 kA, the radiated microwave power is about 1.0 GW, the pulse duration is about 85 ns. Moreover, the radiated microwave power and the pulse duration decline little by little when the shot numbers increase gradually. The experimental results show that the impedance matching is a vital factor for HPM systems and one of the major technical challenges is to improve the cathode for the repetition rate operation MILO.

  9. A long-pulse repetitive operation magnetically insulated transmission line oscillator.

    PubMed

    Fan, Yu-Wei; Zhong, Hui-Huang; Zhang, Jian-De; Shu, Ting; Liu, Jin Liang

    2014-05-01

    The improved magnetically insulated transmission line oscillator (MILO) is a gigawatt-class L-band high power microwave tube. It has allowed us to generate 3.1 GW pulse of 40 ns duration in the single-pulse operation and 500 MW pulse of 25 ns duration in the repetition rate operation. However, because of the severe impedance mismatch, the power conversion efficiency is only about 4% in the repetition rate operation. In order to eliminate the impedance mismatch and obtain repetitive long-pulse high-power microwave (HPM), a series of experiments are carried out and the recent progress is presented in this paper. In the single-pulse operation, when the diode voltage is 466 kV and current is 41.6 kA, the radiated microwave power is above 2.2 GW, the pulse duration is above 102 ns, the microwave frequency is about 1.74 GHz, and the power conversion efficiency is about 11.5%. In the repetition rate operation, under the condition of the diode voltage about 400 kV, beam current about 38 kA, the radiated microwave power is about 1.0 GW, the pulse duration is about 85 ns. Moreover, the radiated microwave power and the pulse duration decline little by little when the shot numbers increase gradually. The experimental results show that the impedance matching is a vital factor for HPM systems and one of the major technical challenges is to improve the cathode for the repetition rate operation MILO.

  10. Context and repetition in word learning

    PubMed Central

    Horst, Jessica S.

    2013-01-01

    Young children learn words from a variety of situations, including shared storybook reading. A recent study by Horst et al. (2011a) demonstrates that children learned more new words during shared storybook reading if they were read the same stories repeatedly than if they were read different stories that had the same number of target words. The current paper reviews this study and further examines the effect of contextual repetition on children's word learning in both shared storybook reading and other situations, including fast mapping by mutual exclusivity. The studies reviewed here suggest that the same cognitive mechanisms support word learning in a variety of situations. Both practical considerations for experimental design and directions for future research are discussed. PMID:23580347

  11. Context and repetition in word learning.

    PubMed

    Horst, Jessica S

    2013-01-01

    Young children learn words from a variety of situations, including shared storybook reading. A recent study by Horst et al. (2011a) demonstrates that children learned more new words during shared storybook reading if they were read the same stories repeatedly than if they were read different stories that had the same number of target words. The current paper reviews this study and further examines the effect of contextual repetition on children's word learning in both shared storybook reading and other situations, including fast mapping by mutual exclusivity. The studies reviewed here suggest that the same cognitive mechanisms support word learning in a variety of situations. Both practical considerations for experimental design and directions for future research are discussed.

  12. A review of neuroimaging findings in repetitive brain trauma.

    PubMed

    Koerte, Inga K; Lin, Alexander P; Willems, Anna; Muehlmann, Marc; Hufschmidt, Jakob; Coleman, Michael J; Green, Isobel; Liao, Huijun; Tate, David F; Wilde, Elisabeth A; Pasternak, Ofer; Bouix, Sylvain; Rathi, Yogesh; Bigler, Erin D; Stern, Robert A; Shenton, Martha E

    2015-05-01

    Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease confirmed at postmortem. Those at highest risk are professional athletes who participate in contact sports and military personnel who are exposed to repetitive blast events. All neuropathologically confirmed CTE cases, to date, have had a history of repetitive head impacts. This suggests that repetitive head impacts may be necessary for the initiation of the pathogenetic cascade that, in some cases, leads to CTE. Importantly, while all CTE appears to result from repetitive brain trauma, not all repetitive brain trauma results in CTE. Magnetic resonance imaging has great potential for understanding better the underlying mechanisms of repetitive brain trauma. In this review, we provide an overview of advanced imaging techniques currently used to investigate brain anomalies. We also provide an overview of neuroimaging findings in those exposed to repetitive head impacts in the acute/subacute and chronic phase of injury and in more neurodegenerative phases of injury, as well as in military personnel exposed to repetitive head impacts. Finally, we discuss future directions for research that will likely lead to a better understanding of the underlying mechanisms separating those who recover from repetitive brain trauma vs. those who go on to develop CTE. PMID:25904047

  13. A review of neuroimaging findings in repetitive brain trauma.

    PubMed

    Koerte, Inga K; Lin, Alexander P; Willems, Anna; Muehlmann, Marc; Hufschmidt, Jakob; Coleman, Michael J; Green, Isobel; Liao, Huijun; Tate, David F; Wilde, Elisabeth A; Pasternak, Ofer; Bouix, Sylvain; Rathi, Yogesh; Bigler, Erin D; Stern, Robert A; Shenton, Martha E

    2015-05-01

    Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease confirmed at postmortem. Those at highest risk are professional athletes who participate in contact sports and military personnel who are exposed to repetitive blast events. All neuropathologically confirmed CTE cases, to date, have had a history of repetitive head impacts. This suggests that repetitive head impacts may be necessary for the initiation of the pathogenetic cascade that, in some cases, leads to CTE. Importantly, while all CTE appears to result from repetitive brain trauma, not all repetitive brain trauma results in CTE. Magnetic resonance imaging has great potential for understanding better the underlying mechanisms of repetitive brain trauma. In this review, we provide an overview of advanced imaging techniques currently used to investigate brain anomalies. We also provide an overview of neuroimaging findings in those exposed to repetitive head impacts in the acute/subacute and chronic phase of injury and in more neurodegenerative phases of injury, as well as in military personnel exposed to repetitive head impacts. Finally, we discuss future directions for research that will likely lead to a better understanding of the underlying mechanisms separating those who recover from repetitive brain trauma vs. those who go on to develop CTE.

  14. The use of repetition suppression paradigms in developmental cognitive neuroscience.

    PubMed

    Nordt, Marisa; Hoehl, Stefanie; Weigelt, Sarah

    2016-07-01

    Repetition suppression paradigms allow a more detailed look at brain functioning than classical paradigms and have been applied vigorously in adult cognitive neuroscience. These paradigms are well suited for studies in the field of developmental cognitive neuroscience as they can be applied without collecting a behavioral response and across all age groups. Furthermore, repetition suppression paradigms can be employed in various neuroscience techniques, such as functional magnetic resonance imaging (fMRI), functional near-infrared spectroscopy (fNIRS), electroencephalography (EEG) and magnetoencephalography (MEG). In the present article we review studies using repetition suppression paradigms in developmental cognitive neuroscience covering the age range from infancy to adolescence. Our first goal is to point out characteristics of developmental repetition suppression effects. In doing so, we discuss the relationship of the direction of repetition effects (suppression vs enhancement) with developmental factors, and address the question how the direction of repetition effects might be related to looking-time effects in behavioral infant paradigms, the most prominently used behavioral measure in infant research. To highlight the potential of repetition suppression paradigms, our second goal is to provide an overview on the insights recently obtained by applying repetition paradigms in neurodevelopmental studies, including research on children with autism spectrum disorders (ASDs). We conclude that repetition suppression paradigms are valuable tools for investigating neurodevelopmental processes, while at the same time we highlight the necessity for further studies that disentangle methodological and developmental factors.

  15. The golden ratio of gait harmony: repetitive proportions of repetitive gait phases.

    PubMed

    Iosa, Marco; Fusco, Augusto; Marchetti, Fabio; Morone, Giovanni; Caltagirone, Carlo; Paolucci, Stefano; Peppe, Antonella

    2013-01-01

    In nature, many physical and biological systems have structures showing harmonic properties. Some of them were found related to the irrational number φ known as the golden ratio that has important symmetric and harmonic properties. In this study, the spatiotemporal gait parameters of 25 healthy subjects were analyzed using a stereophotogrammetric system with 25 retroreflective markers located on their skin. The proportions of gait phases were compared with φ, the value of which is about 1.6180. The ratio between the entire gait cycle and stance phase resulted in 1.620 ± 0.058, that between stance and the swing phase was 1.629 ± 0.173, and that between swing and the double support phase was 1.684 ± 0.357. All these ratios did not differ significantly from each other (F = 0.870, P = 0.422, repeated measure analysis of variance) or from φ (P = 0.670, 0.820, 0.422, resp., t-tests). The repetitive gait phases of physiological walking were found in turn in repetitive proportions with each other, revealing an intrinsic harmonic structure. Harmony could be the key for facilitating the control of repetitive walking. Harmony is a powerful unifying factor between seemingly disparate fields of nature, including human gait.

  16. GRAPE - GIS Repetition Using Audio-Visual Repetition Units and its Leanring Effectiveness

    NASA Astrophysics Data System (ADS)

    Niederhuber, M.; Brugger, S.

    2011-09-01

    A new audio-visual learning medium has been developed at the Department of Environmental Sciences at ETH Zurich (Switzerland), for use in geographical information sciences (GIS) courses. This new medium, presented in the form of Repetition Units, allows students to review and consolidate the most important learning concepts on an individual basis. The new material consists of: a) a short enhanced podcast (recorded and spoken slide show) with a maximum duration of 5 minutes, which focuses on only one important aspect of a lecture's theme; b) one or two relevant exercises, covering different cognitive levels of learning, with a maximum duration of 10 minutes; and c), solutions for the exercises. During a pilot phase in 2010, six Repetition Units were produced by the lecturers. Twenty more Repetition Units will be produced by our students during the fall semester of 2011 and 2012. The project is accompanied by a 5-year study (2009 - 2013) that investigates learning success using the new material, focussing on the question, whether or not the new material help to consolidate and refresh basic GIS knowledge. It will be analysed based on longitudinal studies. Initial results indicate that the new medium helps to refresh knowledge as the test groups scored higher than the control group. These results are encouraging and suggest that the new material with its combination of short audio-visual podcasts and relevant exercises help to consolidate students' knowledge.

  17. Early Grade Repetition and Inattention Associated with Neurofibromatosis Type 1

    ERIC Educational Resources Information Center

    Coude, Francois X.; Mignot, Claire; Lyonnet, Stanislas; Munnich, Arnold

    2007-01-01

    Objective: The authors analyze the occurrence of grade repetition and inattention in children diagnosed with neurofibromatosis type 1 (NF1). Method: The participant group consisted of 310 patients with NF1 and a control group of 242 individuals. The number of grade repetitions for each participant during his or her time in elementary, middle, and…

  18. Pre-Lexical Disorders in Repetition Conduction Aphasia

    ERIC Educational Resources Information Center

    Sidiropoulos, Kyriakos; de Bleser, Ria; Ackermann, Hermann; Preilowski, Bruno

    2008-01-01

    At the level of clinical speech/language evaluation, the repetition type of conduction aphasia is characterized by repetition difficulties concomitant with reduced short-term memory capacities, in the presence of fluent spontaneous speech as well as unimpaired naming and reading abilities. It is still unsettled which dysfunctions of the…

  19. Conversational Characteristics of Children with Fragile X Syndrome: Repetitive Speech.

    ERIC Educational Resources Information Center

    Belser, Richard C.; Sudhalter, Vicki

    2001-01-01

    Comparison of the production of repetitive speech during conversations in 30 people with either fragile X syndrome, autistic disorder, or mental retardation not caused by fragile X found repetitive speech more prevalent among those with fragile X. Results support the hypothesis that such speech dysfluency reflects the effects of physiological…

  20. A Negative Effect of Repetition in Episodic Memory

    ERIC Educational Resources Information Center

    Peterson, Daniel J.; Mulligan, Neil W.

    2012-01-01

    One of the foundational principles of human memory is that repetition (i.e., being presented with a stimulus multiple times) improves recall. In the current study a group of participants who studied a list of cue-target pairs twice recalled fewer targets than a group who studied the pairs only once, a negative repetition effect. Such a…

  1. 10 CFR 63.23 - Elimination of repetition.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 10 Energy 2 2010-01-01 2010-01-01 false Elimination of repetition. 63.23 Section 63.23 Energy NUCLEAR REGULATORY COMMISSION (CONTINUED) DISPOSAL OF HIGH-LEVEL RADIOACTIVE WASTES IN A GEOLOGIC REPOSITORY AT YUCCA MOUNTAIN, NEVADA Licenses License Application § 63.23 Elimination of repetition. In...

  2. 10 CFR 63.23 - Elimination of repetition.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 10 Energy 2 2012-01-01 2012-01-01 false Elimination of repetition. 63.23 Section 63.23 Energy NUCLEAR REGULATORY COMMISSION (CONTINUED) DISPOSAL OF HIGH-LEVEL RADIOACTIVE WASTES IN A GEOLOGIC REPOSITORY AT YUCCA MOUNTAIN, NEVADA Licenses License Application § 63.23 Elimination of repetition. In...

  3. 10 CFR 63.23 - Elimination of repetition.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 10 Energy 2 2013-01-01 2013-01-01 false Elimination of repetition. 63.23 Section 63.23 Energy NUCLEAR REGULATORY COMMISSION (CONTINUED) DISPOSAL OF HIGH-LEVEL RADIOACTIVE WASTES IN A GEOLOGIC REPOSITORY AT YUCCA MOUNTAIN, NEVADA Licenses License Application § 63.23 Elimination of repetition. In...

  4. 10 CFR 63.23 - Elimination of repetition.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 10 Energy 2 2011-01-01 2011-01-01 false Elimination of repetition. 63.23 Section 63.23 Energy NUCLEAR REGULATORY COMMISSION (CONTINUED) DISPOSAL OF HIGH-LEVEL RADIOACTIVE WASTES IN A GEOLOGIC REPOSITORY AT YUCCA MOUNTAIN, NEVADA Licenses License Application § 63.23 Elimination of repetition. In...

  5. 10 CFR 63.23 - Elimination of repetition.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 10 Energy 2 2014-01-01 2014-01-01 false Elimination of repetition. 63.23 Section 63.23 Energy NUCLEAR REGULATORY COMMISSION (CONTINUED) DISPOSAL OF HIGH-LEVEL RADIOACTIVE WASTES IN A GEOLOGIC REPOSITORY AT YUCCA MOUNTAIN, NEVADA Licenses License Application § 63.23 Elimination of repetition. In...

  6. 10 CFR 61.21 - Elimination of repetition.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 10 Energy 2 2012-01-01 2012-01-01 false Elimination of repetition. 61.21 Section 61.21 Energy NUCLEAR REGULATORY COMMISSION (CONTINUED) LICENSING REQUIREMENTS FOR LAND DISPOSAL OF RADIOACTIVE WASTE Licenses § 61.21 Elimination of repetition. In its application, the applicant may incorporate by...

  7. 10 CFR 60.23 - Elimination of repetition.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 10 Energy 2 2010-01-01 2010-01-01 false Elimination of repetition. 60.23 Section 60.23 Energy NUCLEAR REGULATORY COMMISSION (CONTINUED) DISPOSAL OF HIGH-LEVEL RADIOACTIVE WASTES IN GEOLOGIC REPOSITORIES Licenses License Applications § 60.23 Elimination of repetition. In its application,...

  8. 10 CFR 60.23 - Elimination of repetition.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 10 Energy 2 2011-01-01 2011-01-01 false Elimination of repetition. 60.23 Section 60.23 Energy NUCLEAR REGULATORY COMMISSION (CONTINUED) DISPOSAL OF HIGH-LEVEL RADIOACTIVE WASTES IN GEOLOGIC REPOSITORIES Licenses License Applications § 60.23 Elimination of repetition. In its application,...

  9. 10 CFR 60.23 - Elimination of repetition.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 10 Energy 2 2014-01-01 2014-01-01 false Elimination of repetition. 60.23 Section 60.23 Energy NUCLEAR REGULATORY COMMISSION (CONTINUED) DISPOSAL OF HIGH-LEVEL RADIOACTIVE WASTES IN GEOLOGIC REPOSITORIES Licenses License Applications § 60.23 Elimination of repetition. In its application,...

  10. 10 CFR 60.23 - Elimination of repetition.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 10 Energy 2 2013-01-01 2013-01-01 false Elimination of repetition. 60.23 Section 60.23 Energy NUCLEAR REGULATORY COMMISSION (CONTINUED) DISPOSAL OF HIGH-LEVEL RADIOACTIVE WASTES IN GEOLOGIC REPOSITORIES Licenses License Applications § 60.23 Elimination of repetition. In its application,...

  11. 10 CFR 60.23 - Elimination of repetition.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 10 Energy 2 2012-01-01 2012-01-01 false Elimination of repetition. 60.23 Section 60.23 Energy NUCLEAR REGULATORY COMMISSION (CONTINUED) DISPOSAL OF HIGH-LEVEL RADIOACTIVE WASTES IN GEOLOGIC REPOSITORIES Licenses License Applications § 60.23 Elimination of repetition. In its application,...

  12. 10 CFR 61.21 - Elimination of repetition.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 10 Energy 2 2010-01-01 2010-01-01 false Elimination of repetition. 61.21 Section 61.21 Energy NUCLEAR REGULATORY COMMISSION (CONTINUED) LICENSING REQUIREMENTS FOR LAND DISPOSAL OF RADIOACTIVE WASTE Licenses § 61.21 Elimination of repetition. In its application, the applicant may incorporate by...

  13. 10 CFR 61.21 - Elimination of repetition.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 10 Energy 2 2014-01-01 2014-01-01 false Elimination of repetition. 61.21 Section 61.21 Energy NUCLEAR REGULATORY COMMISSION (CONTINUED) LICENSING REQUIREMENTS FOR LAND DISPOSAL OF RADIOACTIVE WASTE Licenses § 61.21 Elimination of repetition. In its application, the applicant may incorporate by...

  14. 10 CFR 61.21 - Elimination of repetition.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 10 Energy 2 2013-01-01 2013-01-01 false Elimination of repetition. 61.21 Section 61.21 Energy NUCLEAR REGULATORY COMMISSION (CONTINUED) LICENSING REQUIREMENTS FOR LAND DISPOSAL OF RADIOACTIVE WASTE Licenses § 61.21 Elimination of repetition. In its application, the applicant may incorporate by...

  15. 10 CFR 61.21 - Elimination of repetition.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 10 Energy 2 2011-01-01 2011-01-01 false Elimination of repetition. 61.21 Section 61.21 Energy NUCLEAR REGULATORY COMMISSION (CONTINUED) LICENSING REQUIREMENTS FOR LAND DISPOSAL OF RADIOACTIVE WASTE Licenses § 61.21 Elimination of repetition. In its application, the applicant may incorporate by...

  16. Varieties of Repetitive Behavior in Autism: Comparisons to Mental Retardation.

    ERIC Educational Resources Information Center

    Bodfish, James W.; Symons, Frank J.; Parker, Dawn E.; Lewis, Mark H.

    2000-01-01

    A study compared specific repetitive behaviors in 32 adults with autism with 34 controls with mental retardation. The occurrence of each behavior category, except dyskinesias, was higher in individuals with autism and they showed a greater number of topographies of stereotypy and compulsions. Repetitive behavior severity also predicated autism…

  17. Repetition Blindness: Out of Sight or Out of Mind?

    ERIC Educational Resources Information Center

    Morris, Alison L.; Harris, Catherine L.

    2004-01-01

    Does repetition blindness represent a failure of perception or of memory? In Experiment 1, participants viewed rapid serial visual presentation (RSVP) sentences. When critical words (C1 and C2) were orthographically similar, C2 was frequently omitted from serial report; however, repetition priming for C2 on a postsentence lexical decision task was…

  18. 10 CFR 52.8 - Combining licenses; elimination of repetition.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 10 Energy 2 2014-01-01 2014-01-01 false Combining licenses; elimination of repetition. 52.8 Section 52.8 Energy NUCLEAR REGULATORY COMMISSION (CONTINUED) LICENSES, CERTIFICATIONS, AND APPROVALS FOR NUCLEAR POWER PLANTS General Provisions § 52.8 Combining licenses; elimination of repetition. (a)...

  19. 10 CFR 52.8 - Combining licenses; elimination of repetition.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 10 Energy 2 2012-01-01 2012-01-01 false Combining licenses; elimination of repetition. 52.8 Section 52.8 Energy NUCLEAR REGULATORY COMMISSION (CONTINUED) LICENSES, CERTIFICATIONS, AND APPROVALS FOR NUCLEAR POWER PLANTS General Provisions § 52.8 Combining licenses; elimination of repetition. (a)...

  20. 10 CFR 52.8 - Combining licenses; elimination of repetition.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 10 Energy 2 2013-01-01 2013-01-01 false Combining licenses; elimination of repetition. 52.8 Section 52.8 Energy NUCLEAR REGULATORY COMMISSION (CONTINUED) LICENSES, CERTIFICATIONS, AND APPROVALS FOR NUCLEAR POWER PLANTS General Provisions § 52.8 Combining licenses; elimination of repetition. (a)...

  1. 10 CFR 52.8 - Combining licenses; elimination of repetition.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 10 Energy 2 2011-01-01 2011-01-01 false Combining licenses; elimination of repetition. 52.8 Section 52.8 Energy NUCLEAR REGULATORY COMMISSION (CONTINUED) LICENSES, CERTIFICATIONS, AND APPROVALS FOR NUCLEAR POWER PLANTS General Provisions § 52.8 Combining licenses; elimination of repetition. (a)...

  2. 10 CFR 52.8 - Combining licenses; elimination of repetition.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 10 Energy 2 2010-01-01 2010-01-01 false Combining licenses; elimination of repetition. 52.8 Section 52.8 Energy NUCLEAR REGULATORY COMMISSION (CONTINUED) LICENSES, CERTIFICATIONS, AND APPROVALS FOR NUCLEAR POWER PLANTS General Provisions § 52.8 Combining licenses; elimination of repetition. (a)...

  3. Repetitive sequence families in Alces alces americana.

    PubMed

    Blake, R D; Wang, J Z; Beauregard, L

    1997-05-01

    High-resolution derivative melting was used to obtain detailed distributions of local (G + C) contents in a number of ruminant DNAs. Profiles over low (G + C) regions [20-36% (G + C)] are congruent for all ruminants. This region represents 45-50% of the nuclear DNA content and primarily contains intergenic and intron sequences. The high (G + C) region, where most coding sequences are found [38-68% (G + C)], is marked by satellite bands denoting the presence of transcriptionally inert, tandemly repetitive sequence families. These bands can be analyzed for the abundance, base composition, and sequence divergence of satellite families with relatively high precision. Band patterns are unique to each species; even closely related species can be readily distinguished by their base distribution profiles. Variations in nuclear DNA contents in ruminants, determined by flow cytometry, are primarily due to variations in abundances of these repetitive sequence families. Thus, A. alces (moose) is found to have 8.85 +/- 0.2 pg DNA/cell, 25% more than the average in ruminants, while the base distribution curve indicates the presence of an unusually abundant satellite of 52.6% (G + C). The size (1 kb) and sequence of this satellite corresponds to satellite-I of other cervids, and in consequence it is designated Alces-I. The sequence of a cloned repeat of Alces-I has a length of 968 bp, a (G + C) content of 52.6%, and contributes 35%, or almost 3 million copies to the nuclear DNA, exceeding by approximately 300% the average array size of this repeat family in related cervids. In situ hybridization indicates the repeat is distributed throughout centromeric regions of all 62 acrocentric autosomes. Alces-I has much greater-than-expected numbers of GG, GA, and AG and far fewer numbers of TA and CG duplets, characteristics of all tandem repeats. The sequence is judged to be orthologous with satellite-I sequences from Rangifer tarandus (caribou), Capreolus capreolus (roe deer), Muntiacus

  4. The Effect of Task Instructions on Students' Use of Repetition in Argumentative Discourse

    NASA Astrophysics Data System (ADS)

    Gilabert, Sandra; Garcia-Mila, Merce; Felton, Mark K.

    2013-11-01

    The reasoning belief of argumentum ad nauseam assumes that when someone repeats something often enough, he or she becomes more convincing. The present paper analyses the use of this strategy by seventh-grade students in an argumentation task. Sixty-five students (mean age: 12.2, SD = 0.4) from a public school in a mid-sized urban environment took part in the study. The students were asked to either argue to convince an opposing partner or argue to reach consensus with an opposing partner on three dilemmas that dealt with energy sources. Data were gathered according to a between-groups design that included one independent variable (argumentative goal: to convince vs. to reach consensus) and one dependent variable (the degree of argumentative repetitions). We predicted that in the condition to convince their partner, the students would use the repetition strategy more often in their attempts to be persuasive. Our findings show that the mean number of argumentative repetitions was significantly higher for the persuasion group for both of the most frequent argumentative structures (claim and claim data). The mean percentage of repeated claims for the persuasion condition was 86.2 vs. 69.0 for the consensus condition. For the claim data, the mean percentage for the persuasion group was 35.2 vs. 24.3 for the consensus group. Also, students in the persuasion group tended to repeat one idea many times rather than repeating many ideas a few times within the same argumentative structure. The results of our study support the hypothesis that the goal of the argumentative task mediates argumentative discourse and, more concretely, the rate of repetitions and the conceptual diversity of the statements. These differences in rates of repetition and conceptual diversity are related to the amount of learning produced by the instructional goal. We apply Mercer's idea that not all classroom argumentation tasks promote learning equally.

  5. Compact repetitively Q-switched Yb:YCa4O(BO3)3 laser with an acousto-optic modulator

    NASA Astrophysics Data System (ADS)

    Chen, Xiaowen; Xu, Honghao; Han, Wenjuan; Yi, Hongying; Yu, Haohai; Zhang, Huaijin; Liu, Junhai

    2015-07-01

    Repetitively Q-switched operation was achieved with a Yb:YCa4O(BO3)3 laser in a wide repetition rate range from 20 down to 0.1 kHz. An output power of 6.81 W at 20 kHz was generated with pulse duration of 42 ns; while operated at a low repetition rate of 0.1 kHz, the laser produced 0.53 W of output power with pulse width of 21 ns, the resulting pulse energy and peak power amounted respectively to 5.3 mJ and 252.4 kW.

  6. Transgenerational effects of environmental enrichment on repetitive motor behavior development.

    PubMed

    Bechard, Allison R; Lewis, Mark H

    2016-07-01

    The favorable consequences of environmental enrichment (EE) on brain and behavior development are well documented. Much less is known, however, about transgenerational benefits of EE on non-enriched offspring. We explored whether transgenerational effects of EE might extend to the development of repetitive motor behaviors in deer mice. Repetitive motor behaviors are invariant patterns of movement that, across species, can be reduced by EE. We found that EE not only attenuated the development of repetitive behavior in dams, but also in their non-enriched offspring. Moreover, maternal behavior did not seem to mediate the transgenerational effect we found, although repetitive behavior was affected by reproductive experience. These data support a beneficial transgenerational effect of EE on repetitive behavior development and suggest a novel benefit of reproductive experience.

  7. Transgenerational effects of environmental enrichment on repetitive motor behavior development.

    PubMed

    Bechard, Allison R; Lewis, Mark H

    2016-07-01

    The favorable consequences of environmental enrichment (EE) on brain and behavior development are well documented. Much less is known, however, about transgenerational benefits of EE on non-enriched offspring. We explored whether transgenerational effects of EE might extend to the development of repetitive motor behaviors in deer mice. Repetitive motor behaviors are invariant patterns of movement that, across species, can be reduced by EE. We found that EE not only attenuated the development of repetitive behavior in dams, but also in their non-enriched offspring. Moreover, maternal behavior did not seem to mediate the transgenerational effect we found, although repetitive behavior was affected by reproductive experience. These data support a beneficial transgenerational effect of EE on repetitive behavior development and suggest a novel benefit of reproductive experience. PMID:27059336

  8. Repetition is easy: Why repeated referents have reduced prominence

    PubMed Central

    Lam, Tuan Q.; Watson, Duane G.

    2011-01-01

    The repetition and predictability of a word in a conversation are two factors that are believed to affect whether or not it is emphasized: predictable, repeated words are less acoustically prominent than unpredictable, new words. However, because predictability and repetition are correlated, it is unclear whether speakers lengthen unpredictable words to facilitate comprehension or whether this lengthening is the result of difficulties in accessing a new (non-repeated) lexical item. In this paper, we investigate the relationship between acoustic prominence, repetition, and predictability in a description task. In Experiment 1, we find that repeated referents are produced with reduced prominence, even when these referents are unexpected. In Experiment 2, we find that predictability and repetition both have independent effects on duration and intensity. However, word duration was primarily determined by repetition, and intensity was primarily determined by predictability. The data are most consistent with an account in which multiple cognitive factors influence the acoustic prominence of a word. PMID:21156876

  9. Repetition and Emotive Communication in Music Versus Speech

    PubMed Central

    Margulis, Elizabeth Hellmuth

    2013-01-01

    Music and speech are often placed alongside one another as comparative cases. Their relative overlaps and disassociations have been well explored (e.g., Patel, 2008). But one key attribute distinguishing these two domains has often been overlooked: the greater preponderance of repetition in music in comparison to speech. Recent fMRI studies have shown that familiarity – achieved through repetition – is a critical component of emotional engagement with music (Pereira et al., 2011). If repetition is fundamental to emotional responses to music, and repetition is a key distinguisher between the domains of music and speech, then close examination of the phenomenon of repetition might help clarify the ways that music elicits emotion differently than speech. PMID:23576998

  10. Self-controlled KR schedules: does repetition order matter?

    PubMed

    Patterson, Jae T; Carter, Michael J; Hansen, Steve

    2013-08-01

    The impact of an experimenter-defined repetition schedule on the utility of a self-controlled KR context during motor skill acquisition was examined. Participants were required to learn three novel spatial-temporal tasks in either a random or blocked repetition schedule with or without the opportunity to control their KR. Results from the retention period showed that participants provided control over their KR schedule in a random repetition schedule demonstrated superior learning. However, performance measures from the transfer test showed that, independent of repetition schedule, learners provided the opportunity to control their KR schedule demonstrated superior transfer performance compared to their yoked counterparts. The dissociated impact of repetition schedule and self-controlled KR schedules on retention and transfer is discussed.

  11. Repetitive Transcranial Magnetic Stimulation to Supplementary Motor Area in Refractory Obsessive-Compulsive Disorder Treatment: a Sham-Controlled Trial

    PubMed Central

    Harika-Germaneau, Ghina; Rachid, Fady; Gaudeau-Bosma, Christian; Tanguy, Marie-Laure; BenAdhira, Rene; Bouaziz, Noomane; Popa, Traian; Wassouf, Issa; Saba, Ghassen; Januel, Dominique; Jaafari, Nematollah

    2016-01-01

    Background: Repetitive transcranial magnetic stimulation has been explored in patients with obsessive-compulsive disorder, but with negative or conflicting results. This randomized double-blind study was designed to assess the efficacy of 1-Hz repetitive transcranial magnetic stimulation over the presupplementary area. Methods: Forty medication-resistant patients were assigned to 4 weeks of either active or sham repetitive transcranial magnetic stimulation targeting the presupplementary area with the help of a neuronavigation system. Results: According to the Yale-Brown obsessive-compulsive scale, the baseline-week 4 evolution showed no significant differences between groups. Responder rates at week 4 were not different between groups (repetitive transcranial magnetic stimulation 10.5% vs sham 20%; P=.63). Conclusion: Low-frequency repetitive transcranial magnetic stimulation applied to the presupplementary area seems ineffective for the treatment of obsessive-compulsive disorder patients, at least in severe and drug-refractory cases such as those included in this study. Further research is required to determine profiles of responder patients and appropriate repetitive transcranial magnetic stimulation parameters for obsessive-compulsive disorder. PMID:27207923

  12. On the Dissociation of Word/Nonword Repetition Effects in Lexical Decision: An Evidence Accumulation Account.

    PubMed

    Perea, Manuel; Marcet, Ana; Vergara-Martínez, Marta; Gomez, Pablo

    2016-01-01

    A number of models of visual-word recognition assume that the repetition of an item in a lexical decision experiment increases that item's familiarity/wordness. This would produce not only a facilitative repetition effect for words, but also an inhibitory effect for nonwords (i.e., more familiarity/wordness makes the negative decision slower). We conducted a two-block lexical decision experiment to examine word/nonword repetition effects in the framework of a leading "familiarity/wordness" model of the lexical decision task, namely, the diffusion model (Ratcliff et al., 2004). Results showed that while repeated words were responded to faster than the unrepeated words, repeated nonwords were responded to more slowly than the nonrepeated nonwords. Fits from the diffusion model revealed that the repetition effect for words/nonwords was mainly due to differences in the familiarity/wordness (drift rate) parameter. This word/nonword dissociation favors those accounts that posit that the previous presentation of an item increases its degree of familiarity/wordness.

  13. Exploring the effects of seated whole body vibration exposure on repetitive asymmetric lifting tasks.

    PubMed

    Mehta, Jay P; Lavender, Steven A; Jagacinski, Richard J; Sommerich, Carolyn M

    2015-01-01

    This study investigated changes in the physiological and behavioral responses to repetitive asymmetric lifting activity after exposure to whole body vibrations. Seventeen healthy volunteers repeatedly lifted a box (15% of lifter's capacity) positioned in front of them at ankle level to a location on their left side at waist level at the rate of 10 lifts/min for a period of 60 minutes. Prior to lifting, participants were seated on a vibrating platform for 60 minutes; in one of the two sessions the platform did not vibrate. Overall, the physiological responses assessed using near-infrared spectroscopy signals for the erector spinae muscles decreased significantly over time during the seating and the lifting tasks (p < 0.001). During repetitive asymmetric lifting, behavioral changes included increases in peak forward bending motion, twisting movement, and three-dimensional movement velocities of the spine. The lateral bending movement of the spine and the duration of each lift decreased significantly over the 60 minutes of repetitive lifting. With exposure to whole body vibration, participants twisted farther (p = 0.046) and twisted faster (p = 0.025). These behavioral changes would suggest an increase in back injury risk when repetitive lifting tasks are preceded by whole body vibration exposure.

  14. On the Dissociation of Word/Nonword Repetition Effects in Lexical Decision: An Evidence Accumulation Account

    PubMed Central

    Perea, Manuel; Marcet, Ana; Vergara-Martínez, Marta; Gomez, Pablo

    2016-01-01

    A number of models of visual-word recognition assume that the repetition of an item in a lexical decision experiment increases that item's familiarity/wordness. This would produce not only a facilitative repetition effect for words, but also an inhibitory effect for nonwords (i.e., more familiarity/wordness makes the negative decision slower). We conducted a two-block lexical decision experiment to examine word/nonword repetition effects in the framework of a leading “familiarity/wordness” model of the lexical decision task, namely, the diffusion model (Ratcliff et al., 2004). Results showed that while repeated words were responded to faster than the unrepeated words, repeated nonwords were responded to more slowly than the nonrepeated nonwords. Fits from the diffusion model revealed that the repetition effect for words/nonwords was mainly due to differences in the familiarity/wordness (drift rate) parameter. This word/nonword dissociation favors those accounts that posit that the previous presentation of an item increases its degree of familiarity/wordness. PMID:26925021

  15. Exploring the effects of seated whole body vibration exposure on repetitive asymmetric lifting tasks.

    PubMed

    Mehta, Jay P; Lavender, Steven A; Jagacinski, Richard J; Sommerich, Carolyn M

    2015-01-01

    This study investigated changes in the physiological and behavioral responses to repetitive asymmetric lifting activity after exposure to whole body vibrations. Seventeen healthy volunteers repeatedly lifted a box (15% of lifter's capacity) positioned in front of them at ankle level to a location on their left side at waist level at the rate of 10 lifts/min for a period of 60 minutes. Prior to lifting, participants were seated on a vibrating platform for 60 minutes; in one of the two sessions the platform did not vibrate. Overall, the physiological responses assessed using near-infrared spectroscopy signals for the erector spinae muscles decreased significantly over time during the seating and the lifting tasks (p < 0.001). During repetitive asymmetric lifting, behavioral changes included increases in peak forward bending motion, twisting movement, and three-dimensional movement velocities of the spine. The lateral bending movement of the spine and the duration of each lift decreased significantly over the 60 minutes of repetitive lifting. With exposure to whole body vibration, participants twisted farther (p = 0.046) and twisted faster (p = 0.025). These behavioral changes would suggest an increase in back injury risk when repetitive lifting tasks are preceded by whole body vibration exposure. PMID:25264920

  16. On the Dissociation of Word/Nonword Repetition Effects in Lexical Decision: An Evidence Accumulation Account.

    PubMed

    Perea, Manuel; Marcet, Ana; Vergara-Martínez, Marta; Gomez, Pablo

    2016-01-01

    A number of models of visual-word recognition assume that the repetition of an item in a lexical decision experiment increases that item's familiarity/wordness. This would produce not only a facilitative repetition effect for words, but also an inhibitory effect for nonwords (i.e., more familiarity/wordness makes the negative decision slower). We conducted a two-block lexical decision experiment to examine word/nonword repetition effects in the framework of a leading "familiarity/wordness" model of the lexical decision task, namely, the diffusion model (Ratcliff et al., 2004). Results showed that while repeated words were responded to faster than the unrepeated words, repeated nonwords were responded to more slowly than the nonrepeated nonwords. Fits from the diffusion model revealed that the repetition effect for words/nonwords was mainly due to differences in the familiarity/wordness (drift rate) parameter. This word/nonword dissociation favors those accounts that posit that the previous presentation of an item increases its degree of familiarity/wordness. PMID:26925021

  17. Basis function repetitive and feedback control with application to a particle accelerator

    NASA Astrophysics Data System (ADS)

    Akogyeram, Raphael Akuete

    2002-09-01

    The thesis addresses three problem areas within repetitive control. Firstly, it addresses issues concerning the ability of repetitive control and feedback control systems to eliminate periodic disturbances occurring above the Nyquist frequency of the hardware. Methods are developed for decomposing and unfolding notch filter or comb filter feedback control so that disturbances above Nyquist frequency can be canceled. Phenomena affecting final error levels are discussed, including error in unfolding, coarseness of zero-order hold cancellation, and waterbed effects in the feedback control system frequency response for different sample rates. Secondly, matched basis function repetitive control laws are developed for batch mode and real time implementation to converge to zero tracking error in the presence of periodic disturbances. For both control methods, conditions are given that guarantee asymptotic and monotonic convergence. Stability tests are formulated to examine stability when the period of a disturbance is not an integer number of sample times, and when there are multiple unrelated periods whose common period is too long to use. Thirdly, an understanding is developed of the optimum division of labor between the objectives accomplished by feedback and the objectives accomplished by repetitive control action. Some experimental results of the particle accelerator testbed at Thomas Jefferson National Accelerator Facility, Newport News, Virginia, are reported.

  18. The repetition of large-earthquake ruptures.

    PubMed Central

    Sieh, K

    1996-01-01

    This survey of well-documented repeated fault rupture confirms that some faults have exhibited a "characteristic" behavior during repeated large earthquakes--that is, the magnitude, distribution, and style of slip on the fault has repeated during two or more consecutive events. In two cases faults exhibit slip functions that vary little from earthquake to earthquake. In one other well-documented case, however, fault lengths contrast markedly for two consecutive ruptures, but the amount of offset at individual sites was similar. Adjacent individual patches, 10 km or more in length, failed singly during one event and in tandem during the other. More complex cases of repetition may also represent the failure of several distinct patches. The faults of the 1992 Landers earthquake provide an instructive example of such complexity. Together, these examples suggest that large earthquakes commonly result from the failure of one or more patches, each characterized by a slip function that is roughly invariant through consecutive earthquake cycles. The persistence of these slip-patches through two or more large earthquakes indicates that some quasi-invariant physical property controls the pattern and magnitude of slip. These data seem incompatible with theoretical models that produce slip distributions that are highly variable in consecutive large events. Images Fig. 3 Fig. 7 Fig. 9 PMID:11607662

  19. A chenopod extensin lacks repetitive tetrahydroxyproline blocks

    SciTech Connect

    Li, Xiongbiao; Kieliszewski, M.; Lamport, D.T.A. )

    1990-02-01

    An extensin isolated from sugar beet (Beta vulgaris) cell suspension cultures fulfills all criteria for membership of the extensin family save one, notably, lack of the diagnostic pentamer Ser-Hyp-Hyp-Hyp-Hyp. However, sequence analysis of the major tryptic peptides shows that sugar beet extensin shares a motif in common with tomato extensin P1 but differs by the position of an insertion sequence (X) or (Y) which, in sugar beet, splits the tetrahydroxyproline block: Ser-Hyp-Hyp-(X)-Hyp-Hyp-Thr-Hyp-Val-Tyr-Lys, where (X) is (Val-His-Glu/Lys-Tyr-Pro), while in tomato the insertion sequence (Y) = (Val-Lys-Pro-Tyr-His-Pro) and, when it occurs, immediately follows the tetrahydroxyproline block: Ser-Hyp-Hyp-Hyp-Hyp-(Y)-Thr-Hyp-Val-Tyr-Lys. Based on these data were reinterpret three highly repetitive cDNA sequences, including nodulin N75 from soybean and wound-induced P33 of carrot, as extensins with split tetra(hydroxy)proline blocks.

  20. Understanding communicative actions: a repetitive TMS study.

    PubMed

    Stolk, Arjen; Noordzij, Matthijs L; Volman, Inge; Verhagen, Lennart; Overeem, Sebastiaan; van Elswijk, Gijs; Bloem, Bas; Hagoort, Peter; Toni, Ivan

    2014-02-01

    Despite the ambiguity inherent in human communication, people are remarkably efficient in establishing mutual understanding. Studying how people communicate in novel settings provides a window into the mechanisms supporting the human competence to rapidly generate and understand novel shared symbols, a fundamental property of human communication. Previous work indicates that the right posterior superior temporal sulcus (pSTS) is involved when people understand the intended meaning of novel communicative actions. Here, we set out to test whether normal functioning of this cerebral structure is required for understanding novel communicative actions using inhibitory low-frequency repetitive transcranial magnetic stimulation (rTMS). A factorial experimental design contrasted two tightly matched stimulation sites (right pSTS vs left MT+, i.e., a contiguous homotopic task-relevant region) and tasks (a communicative task vs a visual tracking task that used the same sequences of stimuli). Overall task performance was not affected by rTMS, whereas changes in task performance over time were disrupted according to TMS site and task combinations. Namely, rTMS over pSTS led to a diminished ability to improve action understanding on the basis of recent communicative history, while rTMS over MT+ perturbed improvement in visual tracking over trials. These findings qualify the contributions of the right pSTS to human communicative abilities, showing that this region might be necessary for incorporating previous knowledge, accumulated during interactions with a communicative partner, to constrain the inferential process that leads to action understanding. PMID:24268321