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Sample records for absolute frequency stabilization

  1. Absolute frequency stabilization of an injection-seeded optical parametric oscillator

    SciTech Connect

    Plusquellic, D.F.; Votava, O.; Nesbitt, D.J.

    1996-03-01

    A method is described that provides absolute frequency stabilization and calibration of the signal and idler waves generated by an injection-seeded optical parametric oscillator (OPO). The method makes use of a He{endash}Ne stabilized transfer cavity (TC) to control the frequencies of the cw sources used to seed both the pump laser and OPO cavity. The TC serves as a stable calibration source for the signal and idler waves by providing marker fringes as the seed laser is scanned. Additionally, an acoustic-optic modulator (AOM) is used to shift the OPO seed laser{close_quote}s frequency before locking it onto the TC. The sidebands of the AOM are tunable over more than one free spectral range of the TC, thereby permitting stabilization of the signal and idler waves at any frequency. A {plus_minus}25-MHz residual error in the absolute frequency stabilities of the pump, signal, and idler waves is experimentally demonstrated, which is roughly 30{percent} of the 160-MHz near-transform-limited linewidths of the signal and idler pulses. {copyright} {ital 1996 Optical Society of America.}

  2. Monolithically integrated absolute frequency comb laser system

    DOEpatents

    Wanke, Michael C.

    2016-07-12

    Rather than down-convert optical frequencies, a QCL laser system directly generates a THz frequency comb in a compact monolithically integrated chip that can be locked to an absolute frequency without the need of a frequency-comb synthesizer. The monolithic, absolute frequency comb can provide a THz frequency reference and tool for high-resolution broad band spectroscopy.

  3. Absolute distance measurement by multi-heterodyne interferometry using a frequency comb and a cavity-stabilized tunable laser.

    PubMed

    Wu, Hanzhong; Zhang, Fumin; Liu, Tingyang; Balling, Petr; Qu, Xinghua

    2016-05-20

    In this paper, we develop a multi-heterodyne system capable of absolute distance measurement using a frequency comb and a tunable diode laser locked to a Fabry-Perot cavity. In a series of subsequent measurements, numerous beat components can be obtained by downconverting the optical frequency into the RF region with multi-heterodyne interferometry. The distances can be measured via the mode phases with a series of synthetic wavelengths. The comparison with the reference interferometer shows an agreement within 1.5 μm for the averages of five measurements and 2.5 μm for the single measurement, which is at the 10-8 relative precision level. PMID:27411152

  4. Molecular iodine absolute frequencies. Final report

    SciTech Connect

    Sansonetti, C.J.

    1990-06-25

    Fifty specified lines of {sup 127}I{sub 2} were studied by Doppler-free frequency modulation spectroscopy. For each line the classification of the molecular transition was determined, hyperfine components were identified, and one well-resolved component was selected for precise determination of its absolute frequency. In 3 cases, a nearby alternate line was selected for measurement because no well-resolved component was found for the specified line. Absolute frequency determinations were made with an estimated uncertainty of 1.1 MHz by locking a dye laser to the selected hyperfine component and measuring its wave number with a high-precision Fabry-Perot wavemeter. For each line results of the absolute measurement, the line classification, and a Doppler-free spectrum are given.

  5. Stabilized radio frequency quadrupole

    DOEpatents

    Lancaster, Henry D.; Fugitt, Jock A.; Howard, Donald R.

    1984-01-01

    A long-vane stabilized radio frequency resonator for accelerating charged particles and including means defining a radio frequency resonator cavity, a plurality of long vanes mounted in the defining means for dividing the cavity into sections, and means interconnecting opposing ones of the plurality of vanes for stabilizing the resonator.

  6. Stabilized radio frequency quadrupole

    DOEpatents

    Lancaster, H.D.; Fugitt, J.A.; Howard, D.R.

    1984-12-25

    Disclosed is a long-vane stabilized radio frequency resonator for accelerating charged particles and including means defining a radio frequency resonator cavity, a plurality of long vanes mounted in the defining means for dividing the cavity into sections, and means interconnecting opposing ones of the plurality of vanes for stabilizing the resonator. 5 figs.

  7. Absolute Stability Analysis of a Phase Plane Controlled Spacecraft

    NASA Technical Reports Server (NTRS)

    Jang, Jiann-Woei; Plummer, Michael; Bedrossian, Nazareth; Hall, Charles; Jackson, Mark; Spanos, Pol

    2010-01-01

    Many aerospace attitude control systems utilize phase plane control schemes that include nonlinear elements such as dead zone and ideal relay. To evaluate phase plane control robustness, stability margin prediction methods must be developed. Absolute stability is extended to predict stability margins and to define an abort condition. A constrained optimization approach is also used to design flex filters for roll control. The design goal is to optimize vehicle tracking performance while maintaining adequate stability margins. Absolute stability is shown to provide satisfactory stability constraints for the optimization.

  8. Electroweak absolute, meta-, and thermal stability in neutrino mass models

    NASA Astrophysics Data System (ADS)

    Lindner, Manfred; Patel, Hiren H.; Radovčić, Branimir

    2016-04-01

    We analyze the stability of the electroweak vacuum in neutrino mass models containing right-handed neutrinos or fermionic isotriplets. In addition to considering absolute stability, we place limits on the Yukawa couplings of new fermions based on metastability and thermal stability in the early Universe. Our results reveal that the upper limits on the neutrino Yukawa couplings can change significantly when the top quark mass is allowed to vary within the experimental range of uncertainty in its determination.

  9. The correction of vibration in frequency scanning interferometry based absolute distance measurement system for dynamic measurements

    NASA Astrophysics Data System (ADS)

    Lu, Cheng; Liu, Guodong; Liu, Bingguo; Chen, Fengdong; Zhuang, Zhitao; Xu, Xinke; Gan, Yu

    2015-10-01

    Absolute distance measurement systems are of significant interest in the field of metrology, which could improve the manufacturing efficiency and accuracy of large assemblies in fields such as aircraft construction, automotive engineering, and the production of modern windmill blades. Frequency scanning interferometry demonstrates noticeable advantages as an absolute distance measurement system which has a high precision and doesn't depend on a cooperative target. In this paper , the influence of inevitable vibration in the frequency scanning interferometry based absolute distance measurement system is analyzed. The distance spectrum is broadened as the existence of Doppler effect caused by vibration, which will bring in a measurement error more than 103 times bigger than the changes of optical path difference. In order to decrease the influence of vibration, the changes of the optical path difference are monitored by a frequency stabilized laser, which runs parallel to the frequency scanning interferometry. The experiment has verified the effectiveness of this method.

  10. The absolute frequency of the 87Sr optical clock transition

    NASA Astrophysics Data System (ADS)

    Campbell, Gretchen K.; Ludlow, Andrew D.; Blatt, Sebastian; Thomsen, Jan W.; Martin, Michael J.; de Miranda, Marcio H. G.; Zelevinsky, Tanya; Boyd, Martin M.; Ye, Jun; Diddams, Scott A.; Heavner, Thomas P.; Parker, Thomas E.; Jefferts, Steven R.

    2008-10-01

    The absolute frequency of the 1S0-3P0 clock transition of 87Sr has been measured to be 429 228 004 229 873.65 (37) Hz using lattice-confined atoms, where the fractional uncertainty of 8.6 × 10-16 represents one of the most accurate measurements of an atomic transition frequency to date. After a detailed study of systematic effects, which reduced the total systematic uncertainty of the Sr lattice clock to 1.5 × 10-16, the clock frequency is measured against a hydrogen maser which is simultaneously calibrated to the US primary frequency standard, the NIST Cs fountain clock, NIST-F1. The comparison is made possible using a femtosecond laser based optical frequency comb to phase coherently connect the optical and microwave spectral regions and by a 3.5 km fibre transfer scheme to compare the remotely located clock signals.

  11. Absolute Frequency Measurements of the D1 and D2 Transitions in Aatomic Li

    NASA Astrophysics Data System (ADS)

    Sheets, Donal; Almaguer, Jose; Baron, Jacob; Elgee, Peter; Rowan, Michael; Stalnaker, Jason

    2014-05-01

    We present preliminary results from our measurements of the D1 and D2 transitions in Li. The data were obtained from a collimated atomic beam excited by light from an extended cavity diode laser. The frequency of the diode laser was stabilized to an optical frequency comb, providing absolute frequency measurement and control of the excitation laser frequency. These measurements will provide a stringent test of atomic structure calculations and yield information about the nuclear structure. We also discuss plans to extend the technique to other high-lying states in lithium. Funded by the NIST Precision Measurements Grant and NSF Award #1305591.

  12. Stability of array spectroradiometers and their suitability for absolute calibrations

    NASA Astrophysics Data System (ADS)

    Nevas, Saulius; Teuber, Annette; Sperling, Armin; Lindemann, Matthias

    2012-04-01

    An investigation of the short- and long-term stability of various low-end and high-end array spectroradiometers is presented. Potentially weak points of array spectroradiometers with respect to their suitability for absolute calibrations are pointed out. The influence of ambient conditions on relevant instrumental characteristics and their temporal stability is discussed. It is shown that the temporal stability of some instruments can be significantly affected by high ambient humidity. Most important ambient temperature effects on instrument properties are also discussed.

  13. Femtosecond frequency comb measurement of absolute frequencies and hyperfine coupling constants in cesium vapor

    SciTech Connect

    Stalnaker, Jason E.; Mbele, Vela; Gerginov, Vladislav; Fortier, Tara M.; Diddams, Scott A.; Hollberg, Leo; Tanner, Carol E.

    2010-04-15

    We report measurements of absolute transition frequencies and hyperfine coupling constants for the 8S{sub 1/2}, 9S{sub 1/2}, 7D{sub 3/2}, and 7D{sub 5/2} states in {sup 133}Cs vapor. The stepwise excitation through either the 6P{sub 1/2} or 6P{sub 3/2} intermediate state is performed directly with broadband laser light from a stabilized femtosecond laser optical-frequency comb. The laser beam is split, counterpropagated, and focused into a room-temperature Cs vapor cell. The repetition rate of the frequency comb is scanned and we detect the fluorescence on the 7P{sub 1/2,3/2{yields}}6S{sub 1/2} branches of the decay of the excited states. The excitations to the different states are isolated by the introduction of narrow-bandwidth interference filters in the laser beam paths. Using a nonlinear least-squares method we find measurements of transition frequencies and hyperfine coupling constants that are in agreement with other recent measurements for the 8S state and provide improvement by 2 orders of magnitude over previously published results for the 9S and 7D states.

  14. Stabilized radio-frequency quadrupole

    DOEpatents

    Lancaster, H.D.; Fugitt, J.A.; Howard, D.R.

    1982-09-29

    A long-vane stabilized radio frequency resonator for accelerating charged particles and including means defining a radio frequency resonator cavity, a plurality of long vanes mounted in the defining means for dividing the cavity into sections, and means interconnecting opposing ones of the plurality of vanes for stabilizing the resonator.

  15. Robust control design with real parameter uncertainty using absolute stability theory. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    How, Jonathan P.; Hall, Steven R.

    1993-01-01

    The purpose of this thesis is to investigate an extension of mu theory for robust control design by considering systems with linear and nonlinear real parameter uncertainties. In the process, explicit connections are made between mixed mu and absolute stability theory. In particular, it is shown that the upper bounds for mixed mu are a generalization of results from absolute stability theory. Both state space and frequency domain criteria are developed for several nonlinearities and stability multipliers using the wealth of literature on absolute stability theory and the concepts of supply rates and storage functions. The state space conditions are expressed in terms of Riccati equations and parameter-dependent Lyapunov functions. For controller synthesis, these stability conditions are used to form an overbound of the H2 performance objective. A geometric interpretation of the equivalent frequency domain criteria in terms of off-axis circles clarifies the important role of the multiplier and shows that both the magnitude and phase of the uncertainty are considered. A numerical algorithm is developed to design robust controllers that minimize the bound on an H2 cost functional and satisfy an analysis test based on the Popov stability multiplier. The controller and multiplier coefficients are optimized simultaneously, which avoids the iteration and curve-fitting procedures required by the D-K procedure of mu synthesis. Several benchmark problems and experiments on the Middeck Active Control Experiment at M.I.T. demonstrate that these controllers achieve good robust performance and guaranteed stability bounds.

  16. Frequency stabilized laser

    NASA Astrophysics Data System (ADS)

    Mongeon, R. J.; Henschke, R. W.

    1984-08-01

    The document describes a frequency control system for a laser for compensating for thermally-induced laser resonator length changes. The frequency control loop comprises a frequency reference for producing an error signal and electrical means to move a length-controlling transducer in response thereto. The transducer has one of the laser mirrors attached thereto. The effective travel of the transducer is multiplied severalfold by circuitry for sensing when the transducer is running out of extension and in response thereto rapidly moving the transducer and its attached mirror toward its midrange position.

  17. Laser frequency stabilization for LISA

    NASA Technical Reports Server (NTRS)

    Mueller, Guido; McNamara, Paul; Thorpe, Ira; Camp, Jordan

    2005-01-01

    The requirement on laser frequency noise in the Laser Interferometer Space Antenna (LISA) depends on the velocity and our knowledge of the position of each spacecraft of the interferometer. Currently it is assumed that the lasers must have a pre-stabilized frequency stability of 30Hz/square root of Hz over LISA'S most sensitive frequency band (3 mHz - 30 mHz). The intrinsic frequency stability of even the most stable com- mercial lasers is several orders of magnitude above this level. Therefore it is necessary to stabilize the laser frequency to an ultra-stable frequency reference which meets the LISA requirements. The baseline frequency reference for the LISA lasers are high finesse optical cavities based on ULE spacers. We measured the stability of two ULE spacer cavities with respect to each other. Our current best results show a noise floor at, or below, 30 Hz/square root of Hz above 3 mHz. In this report we describe the experimental layout of the entire experiment and discuss the limiting noise sources.

  18. Absolute frequency measurement of the neutral 40Ca optical frequency standard at 657 nm based on microkelvin atoms

    NASA Astrophysics Data System (ADS)

    Wilpers, G.; Oates, C. W.; Diddams, S. A.; Bartels, A.; Fortier, T. M.; Oskay, W. H.; Bergquist, J. C.; Jefferts, S. R.; Heavner, T. P.; Parker, T. E.; Hollberg, L.

    2007-04-01

    We report an absolute frequency measurement of the optical clock transition at 657 nm in 40Ca with a relative uncertainty of 7.5 × 10-15, one of the most accurate frequency measurements of a neutral atom optical transition to date. The frequency (455 986 240 494 135.8 ± 3.4) Hz was measured by stabilizing a diode laser system to a spectroscopic signal derived from an ensemble of 106 atoms cooled in two stages to a temperature of 10 µK. The measurement used a femtosecond-laser-based frequency comb to compare the Ca transition frequency with that of the single-ion 199Hg+ optical frequency standard at NIST. The Hg+ frequency was simultaneously calibrated relative to the NIST Cs fountain via the NIST time scale to yield an absolute value for the Ca transition frequency. The relative fractional instability between the two optical standards was 2 × 10-15 for 10 s of averaging time and 2 × 10-16 for 2000 s.

  19. FREQUENCY STABILIZING SYSTEM

    DOEpatents

    Kerns, Q.A.; Anderson, O.A.

    1960-05-01

    An electronic control circuit is described in which a first signal frequency is held in synchronization with a second varying reference signal. The circuit receives the first and second signals as inputs and produces an output signal having an amplitude dependent upon rate of phase change between the two signals and a polarity dependent on direction of the phase change. The output may thus serve as a correction signal for maintaining the desired synchronization. The response of the system is not dependent on relative phase angle between the two compared signals. By having practically no capacitance in the circuit, there is minimum delay between occurrence of a phase shift and a response in the output signal and therefore very fast synchronization is effected.

  20. DSS 13 frequency stability tests

    NASA Technical Reports Server (NTRS)

    Otoshi, T. Y.; Franco, M. M.

    1987-01-01

    In a previous article, the results of frequency stability tests at DSS 13 were presented in table form for tau = 1000 s for the test period May 1985 through March 1986. This article is a continuation of that initial report and presents specially selected Allan sigma (square root of variance) plots of each of the subsystem test previously reported. An additional result obtained from tests performed during July 1986 was included for completeness. The Allan sigma plots are useful in that frequency stability information is not only given for tau = 1000 s, but for tau values in the regions of 1, 100, 500, and 2000 s as well.

  1. Landsat-7 ETM+ radiometric stability and absolute calibration

    USGS Publications Warehouse

    Markham, B.L.; Barker, J.L.; Barsi, J.A.; Kaita, E.; Thome, K.J.; Helder, D.L.; Palluconi, Frank Don; Schott, J.R.; Scaramuzza, P.

    2002-01-01

    Launched in April 1999, the Landsat-7 ETM+ instrument is in its fourth year of operation. The quality of the acquired calibrated imagery continues to be high, especially with respect to its three most important radiometric performance parameters: reflective band instrument stability to better than ??1%, reflective band absolute calibration to better than ??5%, and thermal band absolute calibration to better than ??0.6 K. The ETM+ instrument has been the most stable of any of the Landsat instruments, in both the reflective and thermal channels. To date, the best on-board calibration source for the reflective bands has been the Full Aperture Solar Calibrator, which has indicated changes of at most -1.8% to -2.0% (95% C.I.) change per year in the ETM+ gain (band 4). However, this change is believed to be caused by changes in the solar diffuser panel, as opposed to a change in the instrument's gain. This belief is based partially on ground observations, which bound the changes in gain in band 4 at -0.7% to +1.5%. Also, ETM+ stability is indicated by the monitoring of desert targets. These image-based results for four Saharan and Arabian sites, for a collection of 35 scenes over the three years since launch, bound the gain change at -0.7% to +0.5% in band 4. Thermal calibration from ground observations revealed an offset error of +0.31 W/m 2 sr um soon after launch. This offset was corrected within the U. S. ground processing system at EROS Data Center on 21-Dec-00, and since then, the band 6 on-board calibration has indicated changes of at most +0.02% to +0.04% (95% C.I.) per year. The latest ground observations have detected no remaining offset error with an RMS error of ??0.6 K. The stability and absolute calibration of the Landsat-7 ETM+ sensor make it an ideal candidate to be used as a reference source for radiometric cross-calibrating to other land remote sensing satellite systems.

  2. Low-pressure line-shape study in molecular oxygen with absolute frequency reference

    NASA Astrophysics Data System (ADS)

    Domysławska, J.; Wójtewicz, S.; Cygan, A.; Bielska, K.; Lisak, D.; Masłowski, P.; Trawiński, R. S.; Ciuryło, R.

    2013-11-01

    We present a line-shape analysis of the rovibronic R1 Q2 transition of the oxygen B band resolved by the Pound-Drever-Hall-locked frequency-stabilized cavity ring-down spectroscopy technique in the low pressure range. The frequency axis of the spectra is linked by the ultra-narrow diode laser to the optical frequency comb in order to measure the absolute frequency at each point of the recorded spectra. Experimental spectra are fitted with various line-shape models: the Voigt profile, the Galatry profile, the Nelkin-Ghatak profile, the speed-dependent Voigt profile, and the speed-dependent Nelkin-Ghatak profile with quadratic and hypergeometric approximations for the speed dependence of collisional broadening and shifting. The influences of Dicke narrowing, speed-dependent effects, and correlation between phase- and velocity-changing collisions on the line shape are investigated. Values of line-shape parameters, including the absolute frequency of the transition 435685.24828(46) GHz, are reported.

  3. 47 CFR 24.135 - Frequency stability.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 2 2010-10-01 2010-10-01 false Frequency stability. 24.135 Section 24.135... SERVICES Narrowband PCS § 24.135 Frequency stability. (a) The frequency stability of the transmitter shall be maintained within ±0.0001 percent (±1 ppm) of the center frequency over a temperature variation...

  4. 47 CFR 24.235 - Frequency stability.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 2 2013-10-01 2013-10-01 false Frequency stability. 24.235 Section 24.235... SERVICES Broadband PCS § 24.235 Frequency stability. The frequency stability shall be sufficient to ensure that the fundamental emission stays within the authorized frequency block....

  5. 47 CFR 101.507 - Frequency stability.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 5 2012-10-01 2012-10-01 false Frequency stability. 101.507 Section 101.507... SERVICES 24 GHz Service and Digital Electronic Message Service § 101.507 Frequency stability. The frequency...% for each DEMS User Station transmitter. The frequency stability in the 24,250-25,250 MHz bands must...

  6. 47 CFR 24.235 - Frequency stability.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 2 2010-10-01 2010-10-01 false Frequency stability. 24.235 Section 24.235... SERVICES Broadband PCS § 24.235 Frequency stability. The frequency stability shall be sufficient to ensure that the fundamental emission stays within the authorized frequency block....

  7. 47 CFR 24.135 - Frequency stability.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 2 2014-10-01 2014-10-01 false Frequency stability. 24.135 Section 24.135... SERVICES Narrowband PCS § 24.135 Frequency stability. (a) The frequency stability of the transmitter shall be maintained within ±0.0001 percent (±1 ppm) of the center frequency over a temperature variation...

  8. 47 CFR 24.135 - Frequency stability.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 2 2011-10-01 2011-10-01 false Frequency stability. 24.135 Section 24.135... SERVICES Narrowband PCS § 24.135 Frequency stability. (a) The frequency stability of the transmitter shall be maintained within ±0.0001 percent (±1 ppm) of the center frequency over a temperature variation...

  9. 47 CFR 24.135 - Frequency stability.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 2 2012-10-01 2012-10-01 false Frequency stability. 24.135 Section 24.135... SERVICES Narrowband PCS § 24.135 Frequency stability. (a) The frequency stability of the transmitter shall be maintained within ±0.0001 percent (±1 ppm) of the center frequency over a temperature variation...

  10. 47 CFR 24.135 - Frequency stability.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 2 2013-10-01 2013-10-01 false Frequency stability. 24.135 Section 24.135... SERVICES Narrowband PCS § 24.135 Frequency stability. (a) The frequency stability of the transmitter shall be maintained within ±0.0001 percent (±1 ppm) of the center frequency over a temperature variation...

  11. 47 CFR 101.507 - Frequency stability.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 5 2014-10-01 2014-10-01 false Frequency stability. 101.507 Section 101.507... SERVICES 24 GHz Service and Digital Electronic Message Service § 101.507 Frequency stability. The frequency...% for each DEMS User Station transmitter. The frequency stability in the 24,250-25,250 MHz bands must...

  12. 47 CFR 101.507 - Frequency stability.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 5 2013-10-01 2013-10-01 false Frequency stability. 101.507 Section 101.507... SERVICES 24 GHz Service and Digital Electronic Message Service § 101.507 Frequency stability. The frequency...% for each DEMS User Station transmitter. The frequency stability in the 24,250-25,250 MHz bands must...

  13. 47 CFR 24.235 - Frequency stability.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 2 2012-10-01 2012-10-01 false Frequency stability. 24.235 Section 24.235... SERVICES Broadband PCS § 24.235 Frequency stability. The frequency stability shall be sufficient to ensure that the fundamental emission stays within the authorized frequency block....

  14. 47 CFR 24.235 - Frequency stability.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 2 2014-10-01 2014-10-01 false Frequency stability. 24.235 Section 24.235... SERVICES Broadband PCS § 24.235 Frequency stability. The frequency stability shall be sufficient to ensure that the fundamental emission stays within the authorized frequency block....

  15. 47 CFR 101.507 - Frequency stability.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 5 2011-10-01 2011-10-01 false Frequency stability. 101.507 Section 101.507... SERVICES 24 GHz Service and Digital Electronic Message Service § 101.507 Frequency stability. The frequency...% for each DEMS User Station transmitter. The frequency stability in the 24,250-25,250 MHz bands must...

  16. 47 CFR 24.235 - Frequency stability.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 2 2011-10-01 2011-10-01 false Frequency stability. 24.235 Section 24.235... SERVICES Broadband PCS § 24.235 Frequency stability. The frequency stability shall be sufficient to ensure that the fundamental emission stays within the authorized frequency block....

  17. 47 CFR 101.507 - Frequency stability.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 5 2010-10-01 2010-10-01 false Frequency stability. 101.507 Section 101.507... SERVICES 24 GHz Service and Digital Electronic Message Service § 101.507 Frequency stability. The frequency...% for each DEMS User Station transmitter. The frequency stability in the 24,250-25,250 MHz bands must...

  18. Coupled Resonance Laser Frequency Stabilization

    NASA Astrophysics Data System (ADS)

    Burd, Shaun; Uys, Hermann; MAQClab Team

    2013-05-01

    We have demonstrated simultaneous laser frequency stabilization of a UV and IR laser, to the same photodiode signal derived from the UV laser only. For trapping and cooling Yb+ ions, a frequency stabilized laser is required at 369.9 nm to drive the S1/2-P1/2 cooling cycle. Since that cycle is not closed, a repump beam is needed at 935.18 nm to drive the D3/2-D[ 3 / 2 ] transition, which rapidly decays back to the S1/2 state. Our 369 nm laser is locked using Doppler free polarization spectroscopy of Yb+ ions, generated in a hollow cathode discharge lamp. Without pumping, the metastable D3/2 level is only sparsely populated, making direct absorption of 935 nm light difficult to detect. A resonant 369 nm pump laser can populate the D3/2 state, and fast repumping to the S1/2 ground state by on resonant 935 nm light, can be detected via the change in absorption of the 369 nm laser. This is accomplished using lock-in detection on the same photodiode signal to which the 369 nm laser is locked. In this way, simultaneous locking of two frequencies in very different spectral regimes is accomplished, while exploiting only the photodiode signal from one of the lasers. A rate equation model gives good qualitative agreement with experimental observation. This work was partially funded by the South African National Research Foundation.

  19. 47 CFR 27.54 - Frequency stability.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 2 2013-10-01 2013-10-01 false Frequency stability. 27.54 Section 27.54 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) COMMON CARRIER SERVICES MISCELLANEOUS WIRELESS COMMUNICATIONS SERVICES Technical Standards § 27.54 Frequency stability. The frequency stability shall...

  20. 47 CFR 22.863 - Frequency stability.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 2 2010-10-01 2010-10-01 false Frequency stability. 22.863 Section 22.863...-Ground Radiotelephone Service Commercial Aviation Air-Ground Systems § 22.863 Frequency stability. The frequency stability of equipment used under this subpart shall be sufficient to ensure that,...

  1. 47 CFR 22.863 - Frequency stability.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 2 2013-10-01 2013-10-01 false Frequency stability. 22.863 Section 22.863...-Ground Radiotelephone Service Commercial Aviation Air-Ground Systems § 22.863 Frequency stability. The frequency stability of equipment used under this subpart shall be sufficient to ensure that,...

  2. 47 CFR 27.54 - Frequency stability.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 2 2014-10-01 2014-10-01 false Frequency stability. 27.54 Section 27.54 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) COMMON CARRIER SERVICES MISCELLANEOUS WIRELESS COMMUNICATIONS SERVICES Technical Standards § 27.54 Frequency stability. The frequency stability shall...

  3. 47 CFR 22.863 - Frequency stability.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 2 2011-10-01 2011-10-01 false Frequency stability. 22.863 Section 22.863...-Ground Radiotelephone Service Commercial Aviation Air-Ground Systems § 22.863 Frequency stability. The frequency stability of equipment used under this subpart shall be sufficient to ensure that,...

  4. 47 CFR 22.863 - Frequency stability.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 2 2014-10-01 2014-10-01 false Frequency stability. 22.863 Section 22.863...-Ground Radiotelephone Service Commercial Aviation Air-Ground Systems § 22.863 Frequency stability. The frequency stability of equipment used under this subpart shall be sufficient to ensure that,...

  5. 47 CFR 22.863 - Frequency stability.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 2 2012-10-01 2012-10-01 false Frequency stability. 22.863 Section 22.863...-Ground Radiotelephone Service Commercial Aviation Air-Ground Systems § 22.863 Frequency stability. The frequency stability of equipment used under this subpart shall be sufficient to ensure that,...

  6. 47 CFR 27.54 - Frequency stability.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 2 2012-10-01 2012-10-01 false Frequency stability. 27.54 Section 27.54 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) COMMON CARRIER SERVICES MISCELLANEOUS WIRELESS COMMUNICATIONS SERVICES Technical Standards § 27.54 Frequency stability. The frequency stability shall...

  7. 47 CFR 27.54 - Frequency stability.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 2 2010-10-01 2010-10-01 false Frequency stability. 27.54 Section 27.54 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) COMMON CARRIER SERVICES MISCELLANEOUS WIRELESS COMMUNICATIONS SERVICES Technical Standards § 27.54 Frequency stability. The frequency stability shall...

  8. 47 CFR 27.54 - Frequency stability.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 2 2011-10-01 2011-10-01 false Frequency stability. 27.54 Section 27.54 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) COMMON CARRIER SERVICES MISCELLANEOUS WIRELESS COMMUNICATIONS SERVICES Technical Standards § 27.54 Frequency stability. The frequency stability shall...

  9. Absolute molecular transition frequencies measured by three cavity-enhanced spectroscopy techniques.

    PubMed

    Cygan, A; Wójtewicz, S; Kowzan, G; Zaborowski, M; Wcisło, P; Nawrocki, J; Krehlik, P; Śliwczyński, Ł; Lipiński, M; Masłowski, P; Ciuryło, R; Lisak, D

    2016-06-01

    Absolute frequencies of unperturbed (12)C(16)O transitions from the near-infrared (3-0) band were measured with uncertainties five-fold lower than previously available data. The frequency axis of spectra was linked to the primary frequency standard. Three different cavity enhanced absorption and dispersion spectroscopic methods and various approaches to data analysis were used to estimate potential systematic instrumental errors. Except for a well established frequency-stabilized cavity ring-down spectroscopy, we applied the cavity mode-width spectroscopy and the one-dimensional cavity mode-dispersion spectroscopy for measurement of absorption and dispersion spectra, respectively. We demonstrated the highest quality of the dispersion line shape measured in optical spectroscopy so far. We obtained line positions of the Doppler-broadened R24 and R28 transitions with relative uncertainties at the level of 10(-10). The pressure shifting coefficients were measured and the influence of the line asymmetry on unperturbed line positions was analyzed. Our dispersion spectra are the first demonstration of molecular spectroscopy with both axes of the spectra directly linked to the primary frequency standard, which is particularly desirable for the future reference-grade measurements of molecular spectra. PMID:27276950

  10. Absolute molecular transition frequencies measured by three cavity-enhanced spectroscopy techniques

    NASA Astrophysics Data System (ADS)

    Cygan, A.; Wójtewicz, S.; Kowzan, G.; Zaborowski, M.; Wcisło, P.; Nawrocki, J.; Krehlik, P.; Śliwczyński, Ł.; Lipiński, M.; Masłowski, P.; Ciuryło, R.; Lisak, D.

    2016-06-01

    Absolute frequencies of unperturbed 12C16O transitions from the near-infrared (3-0) band were measured with uncertainties five-fold lower than previously available data. The frequency axis of spectra was linked to the primary frequency standard. Three different cavity enhanced absorption and dispersion spectroscopic methods and various approaches to data analysis were used to estimate potential systematic instrumental errors. Except for a well established frequency-stabilized cavity ring-down spectroscopy, we applied the cavity mode-width spectroscopy and the one-dimensional cavity mode-dispersion spectroscopy for measurement of absorption and dispersion spectra, respectively. We demonstrated the highest quality of the dispersion line shape measured in optical spectroscopy so far. We obtained line positions of the Doppler-broadened R24 and R28 transitions with relative uncertainties at the level of 10-10. The pressure shifting coefficients were measured and the influence of the line asymmetry on unperturbed line positions was analyzed. Our dispersion spectra are the first demonstration of molecular spectroscopy with both axes of the spectra directly linked to the primary frequency standard, which is particularly desirable for the future reference-grade measurements of molecular spectra.

  11. Real-Time Determination of Absolute Frequency in Continuous-Wave Terahertz Radiation with a Photocarrier Terahertz Frequency Comb Induced by an Unstabilized Femtosecond Laser

    NASA Astrophysics Data System (ADS)

    Minamikawa, Takeo; Hayashi, Kenta; Mizuguchi, Tatsuya; Hsieh, Yi-Da; Abdelsalam, Dahi Ghareab; Mizutani, Yasuhiro; Yamamoto, Hirotsugu; Iwata, Tetsuo; Yasui, Takeshi

    2016-05-01

    A practical method for the absolute frequency measurement of continuous-wave terahertz (CW-THz) radiation uses a photocarrier terahertz frequency comb (PC-THz comb) because of its ability to realize real-time, precise measurement without the need for cryogenic cooling. However, the requirement for precise stabilization of the repetition frequency ( f rep) and/or use of dual femtosecond lasers hinders its practical use. In this article, based on the fact that an equal interval between PC-THz comb modes is always maintained regardless of the fluctuation in f rep, the PC-THz comb induced by an unstabilized laser was used to determine the absolute frequency f THz of CW-THz radiation. Using an f rep-free-running PC-THz comb, the f THz of the frequency-fixed or frequency-fluctuated active frequency multiplier chain CW-THz source was determined at a measurement rate of 10 Hz with a relative accuracy of 8.2 × 10-13 and a relative precision of 8.8 × 10-12 to a rubidium frequency standard. Furthermore, f THz was correctly determined even when fluctuating over a range of 20 GHz. The proposed method enables the use of any commercial femtosecond laser for the absolute frequency measurement of CW-THz radiation.

  12. Frequency stabilized lasers for space applications

    NASA Astrophysics Data System (ADS)

    Lieber, Mike; Adkins, Mike; Pierce, Robert; Warden, Robert; Wallace, Cynthia; Weimer, Carl

    2014-09-01

    metrology, spectroscopy, atomic clocks and geodesy. This technology will be a key enabler to several proposed NASA science missions. Although lasers such as Q-switched Nd-YAG are now commonly used in space, other types of lasers - especially those with narrow linewidth - are still few in number and more development is required to advance their technology readiness. In this paper we discuss a reconfigurable laser frequency stabilization testbed, and end-to-end modeling to support system development. Two important features enabling testbed flexibility are that the controller, signal processing and interfaces are hosted on a field programmable gate array (FPGA) which has spacequalified equivalent parts, and secondly, fiber optic relay of the beam paths. Given the nonlinear behavior of lasers, FPGA implementation is a key system reliability aspect allowing on-orbit retuning of the control system and initial frequency acquisition. The testbed features a dual sensor system, one based upon a high finesse resonator cavity which provides relative stability through Pound-Drever-Hall (PDH) modulation and secondly an absolute frequency reference by dither locking to an acetylene gas cell (GC). To provide for differences between ground and space implementation, we have developed an end-to-end Simulink/ Matlab®-based control system model of the testbed components including the important noise sources. This model is in the process of being correlated to the testbed data which then can be used for trade studies, and estimation of space-based performance and sensitivities. A 1530 nm wavelength semiconductor laser is used for this initial work.

  13. 47 CFR 87.133 - Frequency stability.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 5 2012-10-01 2012-10-01 false Frequency stability. 87.133 Section 87.133... Technical Requirements § 87.133 Frequency stability. (a) Except as provided in paragraphs (c), (d), (f), and (g) of this section, the carrier frequency of each station must be maintained within these...

  14. 47 CFR 90.213 - Frequency stability.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 5 2014-10-01 2014-10-01 false Frequency stability. 90.213 Section 90.213... MOBILE RADIO SERVICES General Technical Standards § 90.213 Frequency stability. (a) Unless noted elsewhere, transmitters used in the services governed by this part must have a minimum frequency...

  15. 47 CFR 90.539 - Frequency stability.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 5 2013-10-01 2013-10-01 false Frequency stability. 90.539 Section 90.539... MOBILE RADIO SERVICES Regulations Governing the Licensing and Use of Frequencies in the 758-775 and 788-805 MHz Bands § 90.539 Frequency stability. Transmitters designed to operate in 769-775 MHz and...

  16. 47 CFR 90.213 - Frequency stability.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 5 2012-10-01 2012-10-01 false Frequency stability. 90.213 Section 90.213... MOBILE RADIO SERVICES General Technical Standards § 90.213 Frequency stability. (a) Unless noted elsewhere, transmitters used in the services governed by this part must have a minimum frequency...

  17. 47 CFR 90.539 - Frequency stability.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 5 2014-10-01 2014-10-01 false Frequency stability. 90.539 Section 90.539... MOBILE RADIO SERVICES Regulations Governing the Licensing and Use of Frequencies in the 763-775 and 793-805 MHz Bands § 90.539 Frequency stability. Transmitters designed to operate in 769-775 MHz and...

  18. 47 CFR 87.133 - Frequency stability.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 5 2010-10-01 2010-10-01 false Frequency stability. 87.133 Section 87.133... Technical Requirements § 87.133 Frequency stability. (a) Except as provided in paragraphs (c), (d), and (f) of this section, the carrier frequency of each station must be maintained within these...

  19. 47 CFR 5.101 - Frequency stability.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 1 2010-10-01 2010-10-01 false Frequency stability. 5.101 Section 5.101...) Technical Standards and Operating Requirements § 5.101 Frequency stability. An applicant must propose to use a frequency tolerance that would confine emissions within the band of operation, unless...

  20. 47 CFR 5.101 - Frequency stability.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 1 2014-10-01 2014-10-01 false Frequency stability. 5.101 Section 5.101... Operating Requirements § 5.101 Frequency stability. Experimental Radio Service licensees shall ensure that transmitted emissions remain within the authorized frequency band under normal operating conditions:...

  1. 47 CFR 5.101 - Frequency stability.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 1 2012-10-01 2012-10-01 false Frequency stability. 5.101 Section 5.101...) Technical Standards and Operating Requirements § 5.101 Frequency stability. An applicant must propose to use a frequency tolerance that would confine emissions within the band of operation, unless...

  2. 47 CFR 87.133 - Frequency stability.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 5 2011-10-01 2011-10-01 false Frequency stability. 87.133 Section 87.133... Technical Requirements § 87.133 Frequency stability. (a) Except as provided in paragraphs (c), (d), (f), and (g) of this section, the carrier frequency of each station must be maintained within these...

  3. 47 CFR 90.539 - Frequency stability.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 5 2012-10-01 2012-10-01 false Frequency stability. 90.539 Section 90.539... MOBILE RADIO SERVICES Regulations Governing the Licensing and Use of Frequencies in the 763-775 and 793-805 MHz Bands § 90.539 Frequency stability. Transmitters designed to operate in 769-775 MHz and...

  4. 47 CFR 90.539 - Frequency stability.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 5 2010-10-01 2010-10-01 false Frequency stability. 90.539 Section 90.539... MOBILE RADIO SERVICES Regulations Governing the Licensing and Use of Frequencies in the 763-775 and 793-805 MHz Bands § 90.539 Frequency stability. Transmitters designed to operate in 769-775 MHz and...

  5. 47 CFR 5.101 - Frequency stability.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 1 2011-10-01 2011-10-01 false Frequency stability. 5.101 Section 5.101...) Technical Standards and Operating Requirements § 5.101 Frequency stability. An applicant must propose to use a frequency tolerance that would confine emissions within the band of operation, unless...

  6. 47 CFR 87.133 - Frequency stability.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 5 2013-10-01 2013-10-01 false Frequency stability. 87.133 Section 87.133... Technical Requirements § 87.133 Frequency stability. (a) Except as provided in paragraphs (c), (d), (f), and (g) of this section, the carrier frequency of each station must be maintained within these...

  7. 47 CFR 5.101 - Frequency stability.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 1 2013-10-01 2013-10-01 false Frequency stability. 5.101 Section 5.101... Operating Requirements § 5.101 Frequency stability. Experimental Radio Service licensees shall ensure that transmitted emissions remain within the authorized frequency band under normal operating conditions:...

  8. 47 CFR 90.213 - Frequency stability.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 5 2010-10-01 2010-10-01 false Frequency stability. 90.213 Section 90.213... MOBILE RADIO SERVICES General Technical Standards § 90.213 Frequency stability. (a) Unless noted elsewhere, transmitters used in the services governed by this part must have a minimum frequency...

  9. 47 CFR 90.539 - Frequency stability.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 5 2011-10-01 2011-10-01 false Frequency stability. 90.539 Section 90.539... MOBILE RADIO SERVICES Regulations Governing the Licensing and Use of Frequencies in the 763-775 and 793-805 MHz Bands § 90.539 Frequency stability. Transmitters designed to operate in 769-775 MHz and...

  10. 47 CFR 87.133 - Frequency stability.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 5 2014-10-01 2014-10-01 false Frequency stability. 87.133 Section 87.133... Technical Requirements § 87.133 Frequency stability. (a) Except as provided in paragraphs (c), (d), (f), and (g) of this section, the carrier frequency of each station must be maintained within these...

  11. 47 CFR 90.213 - Frequency stability.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 5 2011-10-01 2011-10-01 false Frequency stability. 90.213 Section 90.213... MOBILE RADIO SERVICES General Technical Standards § 90.213 Frequency stability. (a) Unless noted elsewhere, transmitters used in the services governed by this part must have a minimum frequency...

  12. 47 CFR 90.213 - Frequency stability.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 5 2013-10-01 2013-10-01 false Frequency stability. 90.213 Section 90.213... MOBILE RADIO SERVICES General Technical Standards § 90.213 Frequency stability. (a) Unless noted elsewhere, transmitters used in the services governed by this part must have a minimum frequency...

  13. Absolute frequency of an atomic hydrogen maser clock

    NASA Technical Reports Server (NTRS)

    Peters, H. E.; Hall, R. G.; Percival, D. B.

    1972-01-01

    An accurate determination was made of the unperturbed atomic hydrogen ground state hyperfine transition frequency (F=1,m=0 - F=0,m=0) in reference to present world wide realizations of internationally defined time interval. In relation to the international atomic time system, the composite value is 1,420,405,751.7755 plus or minus 0.0031 HZ.

  14. Operational frequency stability of rubidium and cesium frequency standards

    NASA Technical Reports Server (NTRS)

    Lavery, J. E.

    1973-01-01

    The frequency stabilities under operational conditions of several commercially available rubidium and cesium frequency standards were determined from experimental data for frequency averaging times from 10 to the 7th power s and are presented in table and graph form. For frequency averaging times between 10 to the 5th power and 10 to the 7th power s, the rubidium standards tested have a stability of between 10 to the minus 12th power and 5 x 10 to the minus 12th power, while the cesium standards have a stability of between 2 x 10 to the minus 13th power and 5 x 10 to the minus 13th power.

  15. Relative and absolute stability in perceived parenting behaviour: a longitudinal study with children and adolescents.

    PubMed

    Carrasco, M A; Rodríguez, M A; Del Barrio, M V; Holgado, F P

    2011-02-01

    Patterns of relative and absolute stability in parental behaviour with children and adolescents are reported. The sample comprised 523 youth (58.7% girls). Data were collected at three time periods: T1 (M age = 11.1 yr.), T2 (M age = 12.2 yr.), and T3 (M age = 13.2 yr.), each separated by one year. According to children's reports, relative consistency was moderate in both mothers and fathers, particularly as regards communication and strict control. In contrast, as children got older, parental rearing practices related to strict control and hostility decreased. There was a similarity between fathers and mothers in terms of relative and absolute stability. Relative stability was affected by the child's sex, the parenting variable, and the time period; however, the patterns of absolute stability reveal no differences by sex. PMID:21526601

  16. Frequency-scanning interferometry for dynamic absolute distance measurement using Kalman filter.

    PubMed

    Tao, Long; Liu, Zhigang; Zhang, Weibo; Zhou, Yangli

    2014-12-15

    We propose a frequency-scanning interferometry using the Kalman filtering technique for dynamic absolute distance measurement. Frequency-scanning interferometry only uses a single tunable laser driven by a triangle waveform signal for forward and backward optical frequency scanning. The absolute distance and moving speed of a target can be estimated by the present input measurement of frequency-scanning interferometry and the previously calculated state based on the Kalman filter algorithm. This method not only compensates for movement errors in conventional frequency-scanning interferometry, but also achieves high-precision and low-complexity dynamic measurements. Experimental results of dynamic measurements under static state, vibration and one-dimensional movement are presented. PMID:25503050

  17. Viscous linear stability of axisymmetric low-density jets: Parameters influencing absolute instability

    NASA Astrophysics Data System (ADS)

    Srinivasan, V.; Hallberg, M. P.; Strykowski, P. J.

    2010-02-01

    Viscous linear stability calculations are presented for model low-density axisymmetric jet flows. Absolute growth transitions for the jet column mode are mapped out in a parametric space including velocity ratio, density ratio, Reynolds number, momentum thickness, and subtle differences between velocity and density profiles. Strictly speaking, the profiles used in most jet stability studies to date are only applicable to unity Prandtl numbers and zero pressure gradient flows—the present work relaxes this requirement. Results reveal how subtle differences between the velocity and density profiles generally used in jet stability theory can dramatically alter the absolute growth rate of the jet column mode in these low-density flows. The results suggest heating/cooling or mass diffusion at the outer nozzle surface can suppress absolute instability and potentially global instability in low-density jets.

  18. Quantifying discipline practices using absolute versus relative frequencies: clinical and research implications for child welfare.

    PubMed

    Lindhiem, Oliver; Shaffer, Anne; Kolko, David J

    2014-01-01

    In the parent intervention outcome literatures, discipline practices are generally quantified as absolute frequencies or, less commonly, as relative frequencies. These differences in methodology warrant direct comparison as they have critical implications for study results and conclusions among treatments targeted at reducing parental aggression and harsh discipline. In this study, we directly compared the absolute frequency method and the relative frequency method for quantifying physically aggressive, psychologically aggressive, and nonaggressive discipline practices. Longitudinal data over a 3-year period came from an existing data set of a clinical trial examining the effectiveness of a psychosocial treatment in reducing parental physical and psychological aggression and improving child behavior (N = 139). Discipline practices (aggressive and nonaggressive) were assessed using the Conflict Tactics Scale. The two methods yielded different patterns of results, particularly for nonaggressive discipline strategies. We suggest that each method makes its own unique contribution to a more complete understanding of the association between parental aggression and intervention effects. PMID:24106146

  19. Absolute frequency measurement at 10-16 level based on the international atomic time

    NASA Astrophysics Data System (ADS)

    Hachisu, H.; Fujieda, M.; Kumagai, M.; Ido, T.

    2016-06-01

    Referring to International Atomic Time (TAI), we measured the absolute frequency of the 87Sr lattice clock with its uncertainty of 1.1 x 10-15. Unless an optical clock is continuously operated for the five days of the TAI grid, it is required to evaluate dead time uncertainty in order to use the available five-day average of the local frequency reference. We homogeneously distributed intermittent measurements over the five-day grid of TAI, by which the dead time uncertainty was reduced to low 10-16 level. Three campaigns of the five (or four)-day consecutive measurements have resulted in the absolute frequency of the 87Sr clock transition of 429 228 004 229 872.85 (47) Hz, where the systematic uncertainty of the 87Sr optical frequency standard amounts to 8.6 x 10-17.

  20. Absolute frequency measurements and hyperfine structures of the molecular iodine transitions at 578 nm

    NASA Astrophysics Data System (ADS)

    Kobayashi, Takumi; Akamatsu, Daisuke; Hosaka, Kazumoto; Inaba, Hajime; Okubo, Sho; Tanabe, Takehiko; Yasuda, Masami; Onae, Atsushi; Hong, Feng-Lei

    2016-04-01

    We report absolute frequency measurements of 81 hyperfine components of the rovibrational transitions of molecular iodine at 578 nm using the second harmonic generation of an 1156-nm external-cavity diode laser and a fiber-based optical frequency comb. The relative uncertainties of the measured absolute frequencies are typically $1.4\\times10^{-11}$. Accurate hyperfine constants of four rovibrational transitions are obtained by fitting the measured hyperfine splittings to a four-term effective Hamiltonian including the electric quadrupole, spin-rotation, tensor spin-spin, and scalar spin-spin interactions. The observed transitions can be good frequency references at 578 nm, and are especially useful for research using atomic ytterbium since the transitions are close to the $^{1}S_{0}-^{3}P_{0}$ clock transition of ytterbium.

  1. Precise Stabilization of the Optical Frequency of WGMRs

    NASA Technical Reports Server (NTRS)

    Savchenkov, Anatoliy; Matsko, Andrey; Matsko, Andrey; Yu, Nan; Maleki, Lute; Iltchenko, Vladimir

    2009-01-01

    Crystalline whispering gallery mode resonators (CWGMRs) made of crystals with axial symmetry have ordinary and extraordinary families of optical modes. These modes have substantially different thermo-refractive constants. This results in a very sharp dependence of differential detuning of optical frequency on effective temperature. This frequency difference compared with clock gives an error signal for precise compensation of the random fluctuations of optical frequency. Certain crystals, like MgF2, have turnover points where the thermo-refractive effect is completely nullified. An advantage for applications using WGMRs for frequency stabilization is in the possibility of manufacturing resonators out of practically any optically transparent crystal. It is known that there are crystals with negative and zero thermal expansion at some specific temperatures. Doping changes properties of the crystals and it is possible to create an optically transparent crystal with zero thermal expansion at room temperature. With this innovation s stabilization technique, the resultant WGMR will have absolute frequency stability The expansion of the resonator s body can be completely compensated for by nonlinear elements. This results in compensation of linear thermal expansion (see figure). In three-mode, the MgF2 resonator, if tuned at the turnover thermal point, can compensate for all types of random thermal-related frequency drift. Simplified dual-mode method is also available. This creates miniature optical resonators with good short- and long-term stability for passive secondary frequency ethalon and an active resonator for active secondary frequency standard (a narrowband laser with long-term stability).

  2. Metrology with AN Optical Feedback Frequency Stabilized Crds

    NASA Astrophysics Data System (ADS)

    Kassi, Samir; Burkart, Johannes

    2015-06-01

    We will present a metrological application of our recently developed Optical Feedback Frequency Stabilized - Cavity Ring Down Spectrometer (OFFS-CRDS). This instrument, which ideally fits with an optical frequency comb for absolute frequency calibration, relies on the robust lock of a steady cavity ring down resonator against a highly stable, radiofrequency tuned optical source. At 1.6 μm, over 7 nm, we demonstrate Lamb dip spectroscopy of CO_2 with line frequency retrieval at the kHz level, a dynamic in excess of 700,000 on the absorption scale and a detectivity of 4x10-13cm-1Hz-1/2. Such an instrument nicely meets the requirements for the most demanding spectroscopy spanning from accurate isotopic ratio determination and very precise lineshape recordings to Boltzmann constant redefinition.

  3. Radio frequency controlled synthetic wavelength sweep for absolute distance measurement by optical interferometry

    SciTech Connect

    Le Floch, Sebastien; Salvade, Yves; Mitouassiwou, Rostand; Favre, Patrick

    2008-06-01

    We present a new technique applied to the variable optical synthetic wavelength generation in optical interferometry. It consists of a chain of optical injection locking among three lasers: first a distributed-feedback laser is used as a master to injection lock an intensity-modulated laser that is directly modulated around 15 GHz by a radio frequency generator on a sideband. A second distributed-feedback laser is injection locked on another sideband of the intensity-modulated laser. The variable synthetic wavelength for absolute distance measurement is simply generated by sweeping the radio frequency over a range of several hundred megahertz, which corresponds to the locking range of the two slave lasers. In this condition, the uncertainty of the variable synthetic wavelength is equivalent to the radio frequency uncertainty. This latter has a relative accuracy of 10{sup -7} or better, resulting in a resolution of {+-}25 {mu}m for distances exceeding tens of meters. The radio frequency generator produces a linear frequency sweep of 1 ms duration (i.e., exactly equal to one absolute distance measurement acquisition time), with frequency steps of about 1 MHz. Finally, results of absolute distance measurements for ranges up to 10 m are presented.

  4. Radio frequency controlled synthetic wavelength sweep for absolute distance measurement by optical interferometry.

    PubMed

    Le Floch, Sébastien; Salvadé, Yves; Mitouassiwou, Rostand; Favre, Patrick

    2008-06-01

    We present a new technique applied to the variable optical synthetic wavelength generation in optical interferometry. It consists of a chain of optical injection locking among three lasers: first a distributed-feedback laser is used as a master to injection lock an intensity-modulated laser that is directly modulated around 15 GHz by a radio frequency generator on a sideband. A second distributed-feedback laser is injection locked on another sideband of the intensity-modulated laser. The variable synthetic wavelength for absolute distance measurement is simply generated by sweeping the radio frequency over a range of several hundred megahertz, which corresponds to the locking range of the two slave lasers. In this condition, the uncertainty of the variable synthetic wavelength is equivalent to the radio frequency uncertainty. This latter has a relative accuracy of 10(-7) or better, resulting in a resolution of +/-25 microm for distances exceeding tens of meters. The radio frequency generator produces a linear frequency sweep of 1 ms duration (i.e., exactly equal to one absolute distance measurement acquisition time), with frequency steps of about 1 MHz. Finally, results of absolute distance measurements for ranges up to 10 m are presented. PMID:18516123

  5. Improved low frequency stability of bolometric detectors

    NASA Technical Reports Server (NTRS)

    Wilbanks, T.; Devlin, M.; Lange, A. E.; Beeman, J. W.; Sato, S.

    1990-01-01

    An ac bridge readout system has been developed that greatly improves the low-frequency stability of bolometric detectors. The readout can be implemented with a simple circuit appropriate for use in space applications. A matched pair of detectors was used in the readout to achieve system noise within a factor of two of the fundamental noise limit of the detectors at frequencies as low as 10 mHz. The low-frequency stability of the readout system allows slower, more sensitive detectors to be used in many applications, and it facilitates observing strategies that are well suited to spaceborne observations.

  6. Dynamic frequency-domain interferometer for absolute distance measurements with high resolution

    SciTech Connect

    Weng, Jidong; Liu, Shenggang; Ma, Heli; Tao, Tianjiong; Wang, Xiang; Liu, Cangli; Tan, Hua

    2014-11-15

    A unique dynamic frequency-domain interferometer for absolute distance measurement has been developed recently. This paper presents the working principle of the new interferometric system, which uses a photonic crystal fiber to transmit the wide-spectrum light beams and a high-speed streak camera or frame camera to record the interference stripes. Preliminary measurements of harmonic vibrations of a speaker, driven by a radio, and the changes in the tip clearance of a rotating gear wheel show that this new type of interferometer has the ability to perform absolute distance measurements both with high time- and distance-resolution.

  7. Simplified absolute phase retrieval of dual-frequency fringe patterns in fringe projection profilometry

    NASA Astrophysics Data System (ADS)

    Lu, Jin; Mo, Rong; Sun, Huibin; Chang, Zhiyong; Zhao, Xiaxia

    2016-04-01

    In fringe projection profilometry, a simplified method is proposed to recover absolute phase maps of two-frequency fringe patterns by using a unique mapping rule. The mapping rule is designed from the rounded phase values to the fringe order of each pixel. Absolute phase can be recovered by the fringe order maps. Unlike the existing techniques, where the lowest frequency of dual- or multiple-frequency fringe patterns must be single, the presented method breaks the limitation and simplifies the procedure of phase unwrapping. Additionally, due to many issues including ambient light, shadow, sharp edges, step height boundaries and surface reflectivity variations, a novel framework of automatically identifying and removing invalid phase values is also proposed. Simulations and experiments have been carried out to validate the performances of the proposed method.

  8. High-resolution optical frequency metrology with stabilized femtosecond lasers

    NASA Astrophysics Data System (ADS)

    Jones, Ronald Jason

    is analyzed in this work. A fractional frequency instability below 4 x 10-13 in only 100 milliseconds of averaging time was measured between the fs comb and the reference cavity. These initial results show great potential as higher finesse reference cavities and increased servo bandwidths can be used to further reduce the short term instability of the laser to unprecedented levels. Two experiments demonstrating the unique properties of the cavity stabilized mode-locked laser are performed. First., the equally spaced modes of the KLM laser are used as a, "frequency ruler" to characterize the dispersion in the Fabry-Perot reference cavity as a result of frequency dependent phase shifts in the cavity mirrors. This technique is then applied to measure the dispersion of air by characterizing the reference cavity dispersion in vacuum and at atmospheric pressure. The fs laser is also used to directly measure optical frequencies. The absolute optical frequency of the reference cavity modes were measured with a precision of better than 1 kHz (˜2 parts in 1012) for averaging times less than one second, limited by instabilities in the radio frequency counters used. A two-photon optical transition frequency in atomic rubidium was also measured directly with the mode-locked laser. The measurement demonstrates the high short term stability and potential accuracy of optical frequency measurements based on the cavity stabilized femtosecond laser. The stability of this measurement (˜10-11 ) was limited primarily by that of the cw laser locked to the atomic transition.

  9. Radio frequency cavity analysis, measurement, and calibration of absolute Dee voltage for K-500 superconducting cyclotron at VECC, Kolkata

    NASA Astrophysics Data System (ADS)

    Som, Sumit; Seth, Sudeshna; Mandal, Aditya; Paul, Saikat; Duttagupta, Anjan

    2013-02-01

    Variable Energy Cyclotron Centre has commissioned a K-500 superconducting cyclotron for various types of nuclear physics experiments. The 3-phase radio-frequency system of superconducting cyclotron has been developed in the frequency range 9-27 MHz with amplitude and phase stability of 100 ppm and ±0.20, respectively. The analysis of the RF cavity has been carried out using 3D Computer Simulation Technology (CST) Microwave Studio code and various RF parameters and accelerating voltages ("Dee" voltage) are calculated from simulation. During the RF system commissioning, measurement of different RF parameters has been done and absolute Dee voltage has been calibrated using a CdTe X-ray detector along with its accessories and known X-ray source. The present paper discusses about the measured data and the simulation result.

  10. Radio frequency cavity analysis, measurement, and calibration of absolute Dee voltage for K-500 superconducting cyclotron at VECC, Kolkata.

    PubMed

    Som, Sumit; Seth, Sudeshna; Mandal, Aditya; Paul, Saikat; Duttagupta, Anjan

    2013-02-01

    Variable Energy Cyclotron Centre has commissioned a K-500 superconducting cyclotron for various types of nuclear physics experiments. The 3-phase radio-frequency system of superconducting cyclotron has been developed in the frequency range 9-27 MHz with amplitude and phase stability of 100 ppm and ±0.2(0), respectively. The analysis of the RF cavity has been carried out using 3D Computer Simulation Technology (CST) Microwave Studio code and various RF parameters and accelerating voltages ("Dee" voltage) are calculated from simulation. During the RF system commissioning, measurement of different RF parameters has been done and absolute Dee voltage has been calibrated using a CdTe X-ray detector along with its accessories and known X-ray source. The present paper discusses about the measured data and the simulation result. PMID:23464200

  11. Radio frequency cavity analysis, measurement, and calibration of absolute Dee voltage for K-500 superconducting cyclotron at VECC, Kolkata

    SciTech Connect

    Som, Sumit; Seth, Sudeshna; Mandal, Aditya; Paul, Saikat; Duttagupta, Anjan

    2013-02-15

    Variable Energy Cyclotron Centre has commissioned a K-500 superconducting cyclotron for various types of nuclear physics experiments. The 3-phase radio-frequency system of superconducting cyclotron has been developed in the frequency range 9-27 MHz with amplitude and phase stability of 100 ppm and {+-}0.2{sup 0}, respectively. The analysis of the RF cavity has been carried out using 3D Computer Simulation Technology (CST) Microwave Studio code and various RF parameters and accelerating voltages ('Dee' voltage) are calculated from simulation. During the RF system commissioning, measurement of different RF parameters has been done and absolute Dee voltage has been calibrated using a CdTe X-ray detector along with its accessories and known X-ray source. The present paper discusses about the measured data and the simulation result.

  12. The onset of absolute instability of rotating Hagen-Poiseuille flow: A spatial stability analysis

    NASA Astrophysics Data System (ADS)

    Fernandez-Feria, R.; del Pino, C.

    2002-09-01

    A spatial, viscous stability analysis of Poiseuille pipe flow with superimposed solid body rotation is considered. For each value of the swirl parameter (inverse Rossby number) L>0, there exists a critical Reynolds number Rec)(L above which the flow first becomes convectively unstable to nonaxisymmetric disturbances with azimuthal wave number n=-1. This neutral stability curve confirms previous temporal stability analyses. From this spatial stability analysis, we propose here a relatively simple procedure to look for the onset of absolute instability that satisfies the so-called Briggs-Bers criterion. We find that, for perturbations with n=-1, the flow first becomes absolutely unstable above another critical Reynolds number Ret)(L>Rec)(L, provided that L>0.38, with Ret[right arrow]Rec as L[right arrow]infinity. Other values of the azimuthal wave number n are also considered. For Re>Ret)(L, the disturbances grow both upstream and downstream of the source, and the spatial stability analysis becomes inappropriate. However, for Ret, the spatial analysis provides a useful description on how convectively unstable perturbations become absolutely unstable in this kind of flow.

  13. A Laser Frequency Comb System for Absolute Calibration of the VTT Echelle Spectrograph

    NASA Astrophysics Data System (ADS)

    Doerr, H.-P.; Steinmetz, T.; Holzwarth, R.; Kentischer, T.; Schmidt, W.

    2012-10-01

    A wavelength calibration system based on a laser frequency comb (LFC) was developed in a co-operation between the Kiepenheuer-Institut für Sonnenphysik, Freiburg, Germany and the Max-Planck-Institut für Quantenoptik, Garching, Germany for permanent installation at the German Vacuum Tower Telescope (VTT) on Tenerife, Canary Islands. The system was installed successfully in October 2011. By simultaneously recording the spectra from the Sun and the LFC, for each exposure a calibration curve can be derived from the known frequencies of the comb modes that is suitable for absolute calibration at the meters per second level. We briefly summarize some topics in solar physics that benefit from absolute spectroscopy and point out the advantages of LFC compared to traditional calibration techniques. We also sketch the basic setup of the VTT calibration system and its integration with the existing echelle spectrograph.

  14. Effects of relative and absolute frequency in the spectral weighting of loudness.

    PubMed

    Joshi, Suyash Narendra; Wróblewski, Marcin; Schmid, Kendra K; Jesteadt, Walt

    2016-01-01

    The loudness of broadband sound is often modeled as a linear sum of specific loudness across frequency bands. In contrast, recent studies using molecular psychophysical methods suggest that low and high frequency components contribute more to the overall loudness than mid frequencies. In a series of experiments, the contribution of individual components to the overall loudness of a tone complex was assessed using the molecular psychophysical method as well as a loudness matching task. The stimuli were two spectrally overlapping ten-tone complexes with two equivalent rectangular bandwidth spacing between the tones, making it possible to separate effects of relative and absolute frequency. The lowest frequency components of the "low-frequency" and the "high-frequency" complexes were 208 and 808 Hz, respectively. Perceptual-weights data showed emphasis on lowest and highest frequencies of both the complexes, suggesting spectral-edge related effects. Loudness matching data in the same listeners confirmed the greater contribution of low and high frequency components to the overall loudness of the ten-tone complexes. Masked detection thresholds of the individual components within the tone complex were not correlated with perceptual weights. The results show that perceptual weights provide reliable behavioral correlates of relative contributions of the individual frequency components to overall loudness of broadband sounds. PMID:26827032

  15. Noninvasive absolute cerebral oximetry with frequency-domain near-infrared spectroscopy

    NASA Astrophysics Data System (ADS)

    Hallacoglu, Bertan

    Near-infrared spectroscopy (NIRS) measurements of absolute concentrations of oxy-hemoglobin and deoxy-hemoglobin in the human brain can provide critical information about cerebral physiology in terms of cerebral blood volume, blood flow, oxygen delivery, and metabolic rate of oxygen. We developed several frequency domain NIRS data acquisition and analysis methods aimed at absolute measurements of hemoglobin concentration and saturation in cerebral tissue of adult human subjects. Extensive experimental investigations were carried out in various homogenous and two-layered tissue-mimicking phantoms, and biological tissues. The advantages and limitations of commonly used homogenous models and inversion strategies were thoroughly investigated. Prior to human subjects, extensive studies were carried out in in vivo animal models. In rabbits, absolute hemoglobin oxygen desaturation was shown to depend strongly on surgically induced testicular torsion. Methods developed in this study were then adapted for measurements in the rat brain. Absolute values were demonstrated to discern cerebrovascular impairment in a rat model of diet-induced vascular cognitive impairment. These results facilitated the development of clinically useful optical measures of cerebrovascular health. In a large group of human subjects, employing a homogeneous model for absolute measurements was shown to be reliable and robust. However, it was also shown to be limited due to the relatively thick extracerebral tissue. The procedure we develop in this work and the thesis thereof performs a nonlinear inversion procedure with six unknown parameters with no other prior knowledge for the retrieval of the optical coefficients and top layer thickness with high accuracy on two-layered media. Our absolute measurements of cerebral hemoglobin concentration and saturation are based on the discrimination of extracerebral and cerebral tissue layers, and they can enhance the impact of NIRS for cerebral hemodynamics and

  16. Comb-calibrated frequency-modulated continuous-wave ladar for absolute distance measurements.

    PubMed

    Baumann, Esther; Giorgetta, Fabrizio R; Coddington, Ian; Sinclair, Laura C; Knabe, Kevin; Swann, William C; Newbury, Nathan R

    2013-06-15

    We demonstrate a comb-calibrated frequency-modulated continuous-wave laser detection and ranging (FMCW ladar) system for absolute distance measurements. The FMCW ladar uses a compact external cavity laser that is swept quasi-sinusoidally over 1 THz at a 1 kHz rate. The system simultaneously records the heterodyne FMCW ladar signal and the instantaneous laser frequency at sweep rates up to 3400 THz/s, as measured against a free-running frequency comb (femtosecond fiber laser). Demodulation of the ladar signal against the instantaneous laser frequency yields the range to the target with 1 ms update rates, bandwidth-limited 130 μm resolution and a ~100 nm accuracy that is directly linked to the counted repetition rate of the comb. The precision is <100 nm at the 1 ms update rate and reaches ~6 nm for a 100 ms average. PMID:23938965

  17. Acousto-optical spectrometers' frequency performance stability

    NASA Astrophysics Data System (ADS)

    Ivanov, Sergei I.; Lavrov, Aleksandr P.; Molodyakov, Sergey A.; Saenko, Igor I.

    2004-02-01

    Performance characteristics of the acoutsto-optical spectrometers for some radioastronomical applications are discussed. The main attention is given to the long-term stability of the acousto-optical spectrometer's frequency characteristics. It is shown that a problem of the frequency scale thermal instabilities can be overcome by using the suitable correction, based on the proposed model of the frequency scale drifts. For the acousto-optical spectrometers under consideration a simple method of the frequency scale drifts correction by using the data from measuring of a single reference signal's frequency was developed and applied for correction of molecular lines observations data. More careful procedure for more exigent applications, such as pulsar timing, is considered.

  18. Stabilizing Microwave Frequency of a Photonic Oscillator

    NASA Technical Reports Server (NTRS)

    Maleki, Lute; Yu, Nan; Tu, Meirong

    2006-01-01

    A scheme for stabilizing the frequency of a microwave signal is proposed that exploits the operational characteristics of a coupled optoelectronic oscillator (COEO) and related optoelectronic equipment. An essential element in the scheme is a fiber mode-locked laser (MLL), the optical frequency of which is locked to an atomic transition. In this scheme, the optical frequency stability of the mode-locked laser is transferred to that of the microwave in the same device. Relative to prior schemes for using wideband optical frequency comb to stabilize microwave signals, this scheme is simpler and lends itself more readily to implementation in relatively compact, rugged equipment. The anticipated development of small, low-power, lightweight, highly stable microwave oscillators based on this scheme would afford great benefits in communication, navigation, metrology, and fundamental sciences. COEOs of various designs, at various stages of development, in some cases called by different names, have been described in a number of prior NASA Tech Briefs articles. A COEO is an optoelectronic apparatus that generates both short (picosecond) optical pulses and a steady microwave signal having an ultrahigh degree of spectral purity. The term "coupled optoelectronic" in the full name of such an apparatus signifies that its optical and electronic oscillations are coupled to each other in a single device. The present frequency-stabilization scheme is best described indirectly by describing the laboratory apparatus used to demonstrate it. The apparatus (see figure) includes a COEO that generates a comb-like optical spectrum, the various frequency components of which interfere, producing short optical pulses. This spectrum is centered at a nominal wavelength of 1,560 nm. The spectrum separation of this comb is about 10 GHz, as determined primarily by the length of an optical loop and the bandpass filter in the microwave feedback loop. The optical loop serves as microwave resonator

  19. Quantifying Discipline Practices Using Absolute vs. Relative Frequencies: Clinical and Research Implications for Child Welfare

    PubMed Central

    Lindhiem, Oliver; Shaffer, Anne; Kolko, David J.

    2014-01-01

    In the parent intervention outcome literatures, discipline practices are generally quantified as absolute frequencies or, less commonly, as relative frequencies. These differences in methodology warrant direct comparison as they have critical implications for study results and conclusions among treatments targeted at reducing parental aggression and harsh discipline. In this study, we directly compared the absolute frequency method and the relative frequency method for quantifying physically aggressive, psychologically aggressive, and nonaggressive discipline practices. Longitudinal data over a 3-year period came from an existing data set of a clinical trial examining the effectiveness of a psychosocial treatment in reducing parental physical and psychological aggression and improving child behavior (N = 139; Kolko et al., 2009). Discipline practices (both aggressive and nonaggressive) were assessed using the Conflict Tactics Scale (CTS; Straus et al., 1998). The two methods yielded different patterns of results, particularly for nonaggressive discipline strategies. We suggest that each method makes its own unique contribution to a more complete understanding of the association between parental aggression and intervention effects. PMID:24106146

  20. Measuring absolute frequencies beyond the GPS limit via long-haul optical frequency dissemination.

    PubMed

    Clivati, Cecilia; Cappellini, Giacomo; Livi, Lorenzo F; Poggiali, Francesco; de Cumis, Mario Siciliani; Mancini, Marco; Pagano, Guido; Frittelli, Matteo; Mura, Alberto; Costanzo, Giovanni A; Levi, Filippo; Calonico, Davide; Fallani, Leonardo; Catani, Jacopo; Inguscio, Massimo

    2016-05-30

    Global Positioning System (GPS) dissemination of frequency standards is ubiquitous at present, providing the most widespread time and frequency reference for the majority of industrial and research applications worldwide. On the other hand, the ultimate limits of the GPS presently curb further advances in high-precision, scientific and industrial applications relying on this dissemination scheme. Here, we demonstrate that these limits can be reliably overcome even in laboratories without a local atomic clock by replacing the GPS with a 642-km-long optical fiber link to a remote primary caesium frequency standard. Through this configuration we stably address the 1S0-3P0 clock transition in an ultracold gas of 173Yb, with a precision that exceeds the possibilities of a GPS-based measurement, dismissing the need for a local clock infrastructure to perform beyond-GPS high-precision tasks. We also report an improvement of two orders of magnitude in the accuracy on the transition frequency reported in literature. PMID:27410109

  1. Laser Frequency Stabilization for GRACE-II

    NASA Technical Reports Server (NTRS)

    Folkner, W. M.; deVine, G.; Klipstein, W. M.; McKenzie, K.; Shaddock, D.; Spero, R.; Thompson, R.; Wuchenich, D.; Yu, N.; Stephens, M.; Leitch, J.; Davis, M.; deCino, J.; Pace, C.; Pierce, R.

    2010-01-01

    The GRACE mission monitors changes in the Earth's gravity field by measuring changes in the distance between spacecraft induced by that changing field. The distance variation is measured with a microwave ranging system with sub-micron accuracy. The ranging measurement accuracy is limited by the signal-to-noise ratio and by the frequency stability of the microwave signal referenced to an ultra-stable oscillator (USO). For GRACE-2 a laser ranging system is envisioned with accuracy better than the GRACE microwave ranging system. A laser ranging system easily provides an improved signal-to-noise ratio over the microwave system. Laser frequency stability better than the GRACE USO stability has been demonstrated in several laboratories using thermally stabilized optical cavities. We are developing a space-qualifiable optical cavity and associated optics and electronics for use on GRACE-2 to provide a stable frequency reference for the laser ranging system. Two breadboard units have been developed and tested for performance and ability to survive launch and orbit environments. A prototype unit is being designed using lessons learned from tests of the breadboard units.

  2. Precision absolute frequency laser spectroscopy of argon II in parallel and antiparallel geometry using a frequency comb for calibration

    NASA Astrophysics Data System (ADS)

    Lioubimov, Vladimir

    A collinear fast ion beam laser apparatus was constructed and tested. It will be used on-line to the SLOW RI radioactive beam facility in RIKEN (Japan) and as in the present experiment for precision absolute frequency measurements of astrophysically important reference lines. In the current work we conducted absolute measurements of spectral lines of Ar+ ions using parallel and antiparallel geometries. To provide a reference for the laser wavelength iodine saturation spectroscopy was used. The precision of this reference was enhanced by simultaneously observing the beat node between the spectroscopy laser and the corresponding mode of a femtosecond laser frequency comb. When performing collinear and anticollinear measurements simultaneously for the laser induced fluorescence, the exact relativistic formula for the transition frequency n0=ncoll˙n anticoll can be applied. In this geometry ion source instabilities due to pressure and anode voltage fluctuation are minimized. The procedure of fluorescence lineshapes fitting is discussed and the errors in the measurements are estimated. The result is n0 = 485, 573, 619.7 +/- 0.3MHz corresponding to Dnn = 6 x 10-10 and is an improvement of two orders of magnitude over the NIST published value.

  3. Absolute frequency measurement of the 7s2 1S0-7s7p 1P1 transition in Ra225

    NASA Astrophysics Data System (ADS)

    Santra, B.; Dammalapati, U.; Groot, A.; Jungmann, K.; Willmann, L.

    2014-10-01

    Transition frequencies were determined for transitions in Ra in an atomic beam and for reference lines in Te2 molecules in a vapor cell. The absolute frequencies were calibrated against a GPS stabilized Rb clock by means of an optical frequency comb. The 7s21S0(F=1/2)-7s7p1P1(F =3/2) transition in Ra225 was determined to be 621042124(2)MHz. The measurements provide input for designing efficient and robust laser cooling of Ra atoms in preparation of a search for a permanent electric dipole moment in Ra isotopes.

  4. Dual-frequency-moiré based absolute position sensing for lens focusing

    NASA Astrophysics Data System (ADS)

    Yin, Didi; Wang, Yahui; Di, Chengliang

    2015-10-01

    Micro motor, a typical equipment to adjust the zoom lens, together with a position feedback sensor constitute the closed position loop, which is the key factor to perform successfully accurate lens focusing. Traditionally, the incremental grating ruler tends to be adopted as the position sensor, which continues counting the number of grating pitches on a dynamic one-dimensional moving platform. Instead of incremental counting, this paper proposes a dual-frequency-moiré based absolute position sensing method for reading immediate position at static environment. According to the relative positions of two kind of moiré, the absolute position of the measurement point can be retrieve at nano-meters level through look-up table. By the way, the measurement range can be expanded to millimeters level satisfying the demands of lens focusing, and furthermore the measurement efficiency is improved greatly without dynamic moving. In order to verify the performances of proposed method, a model of dual-frequency-moiré is built, and theological principles are deduced. Finally, the simulation results indicate that, with established configurations, dual-frequency-moiré could measure position within 0~5000μm. At the same time, the measurement accuracy achieves nano-meters level.

  5. Use of the absolute phase in frequency modulated continuous wave plasma reflectometry

    SciTech Connect

    Cunningham, G.

    2008-08-15

    In frequency modulated continuous wave reflectometry, used for density profile measurement in fusion plasmas, it is usual to measure the beat frequency between the launched wave and the reflected wave, and from this to calculate the position of the reflecting layer in the plasma. The absolute phase of the beat signal is usually neglected. The reason is that the phase shift between sweeps is usually comparable with or more than 2{pi}, leading to an ambiguity that is impossible to resolve. However, recent observations on the MAST tokamak have shown that, under quiet plasma conditions (this term has to be defined), the phase shift between sweeps is small compared with 2{pi} and the phase ambiguity can be readily resolved. The reflectometer signal is then being analyzed as an interferometer signal would normally be, and there is a substantial improvement in spatial resolution. The method is illustrated by application to small edge localized mode precursor and allows what is believed to be the first quantitative measurement of the displacement of the plasma boundary by such a precursor mode. The errors in both the absolute phase measurement and the more conventional frequency measurement are also estimated.

  6. A dedicated pistonphone for absolute calibration of infrasound sensors at very low frequencies

    NASA Astrophysics Data System (ADS)

    He, Wen; He, Longbiao; Zhang, Fan; Rong, Zuochao; Jia, Shushi

    2016-02-01

    Aimed at the absolute calibration of infrasound sensors at very low frequencies, an upgraded and improved infrasonic pistonphone has been developed. The pistonphone was designed such that a very narrow clearance between the piston and its guide was realized based on an automatically-centered clearance-sealing structure, and a large volume rigid-walled chamber was also adopted, which improved the leakage time-constant of the chamber. A composite feedback control system was applied to the electromagnetic vibrator to control the precise motion of the piston. Performance tests and uncertainty analysis show that the leakage time-constant is so large, and the distortion of the sound pressure is so small, that the pistonphone can be used as a standard infrasound source in the frequency range from 0.001 Hz to 20 Hz. The low frequency property of the pistonphone has been verified through calibrating low frequency microphones. Comparison tests with the reciprocity method have shown that the pressure sensitivities from the pistonphone are not only reliable at common frequencies but also have smaller uncertainties at low frequencies.

  7. Absolute frequency measurements of the lithium D lines using an optical frequency comb

    NASA Astrophysics Data System (ADS)

    Simien, Clayton; Brewer, Samuel; Tan, Joseph; Gillaspy, John; Sansonetti, Craig

    2010-03-01

    High precision spectroscopic measurements of the isotope shift of low-lying lithium transitions can be combined with precise theory to probe the relative nuclear charge radii of various lithium isotopes. This technique is of particular interest for exotic isotopes for which scattering experiments are not feasible. But recently measured isotope shifts for the D1 and D2 lines of the stable isotopes ^6Li and ^7Li remain in strong disagreement with each other and with theory. Experimental values for the splitting isotope shift (SIS), believed to be the most reliable prediction, are not even consistent as to sign and disagree with theory by as much as 16 standard deviations. We will report results from a new experiment in progress at the NIST. We observe the D lines by crossing a highly collimated lithium beam with a very stable tunable laser. Unlike previous experiments, we directly measure the optical frequency of the laser at every data point by using an optical frequency comb referenced to a cesium clock. Initial results suggest that fully resolved lithium hyperfine components will be determined with an uncertainty of a few tens of kilohertz. We expect to obtain precise new values for the fine structure, hyperfine structure, and isotope shifts of the lithium D lines and a definitive test of the calculated SIS.

  8. Using AIRS and IASI Data to Evaluate Absolute Radiometric Accuracy and Stability for Climate Applications

    NASA Technical Reports Server (NTRS)

    Aumann, Hartmut H.; Pagano, Thomas S.

    2008-01-01

    The creation of multi-decadal data sets for climate research requires better than 100 mK absolute calibration accuracy for the full range of spectral temperatures encountered under global conditions. Validation that this accuracy is achieved by the operational hyperspectral sounders from polar orbit is facilitated by comparing data from two instruments. Extreme radiometric calibration stability is critical to allow a long time series of noisy, but presumably long-term accurate truth measurements to be used for the validation of absolute accuracy at the 100 mK level. We use the RTGSST in the tropical oceans as ground truth. The difference between the AIRS derived sst2616 and the RTGSST based on six years of data shows a systematic cold bias of about 250 mK, but better than 4 mK/year stability. The double difference between AIRS and the RTGSST and IASI and the RTGSST with less than one year of data already allows statements at the 100 mK absolute level. It shows a 60 mK difference between the AIRS and the IASI calibration at 2616 cm-(sup 1) and 300 K, with a statistically insignificant 20 mK shift in six months.

  9. Laser frequency stabilization using bichromatic crossover spectroscopy

    SciTech Connect

    Jeong, Taek; Seb Moon, Han

    2015-03-07

    We propose a Doppler-free spectroscopic method named bichromatic crossover spectroscopy (BCS), which we then use for the frequency stabilization of an off-resonant frequency that does not correspond to an atomic transition. The observed BCS in the 5S{sub 1/2} → 5P{sub 1/2} transition of {sup 87}Rb is related to the hyperfine structure of the conventional saturated absorption spectrum of this transition. Furthermore, the Doppler-free BCS is numerically calculated by considering all of the degenerate magnetic sublevels of the 5S{sub 1/2} → 5P{sub 1/2} transition in an atomic vapor cell, and is found to be in good agreement with the experimental results. Finally, we successfully achieve modulation-free off-resonant locking at the center frequency between the two 5S{sub 1/2}(F = 1 and 2) → 5P{sub 1/2}(F′ = 1) transitions using a polarization rotation of the BCS. The laser frequency stability was estimated to be the Allan variance of 2.1 × 10{sup −10} at 1 s.

  10. 47 CFR 2.1055 - Measurements required: Frequency stability.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 1 2012-10-01 2012-10-01 false Measurements required: Frequency stability. 2... Certification § 2.1055 Measurements required: Frequency stability. (a) The frequency stability shall be measured...) Frequency measurements shall be made at the extremes of the specified temperature range and at intervals...

  11. Measurement of absolute transition frequencies of {sup 87}Rb to nS and nD Rydberg states by means of electromagnetically induced transparency

    SciTech Connect

    Mack, Markus; Karlewski, Florian; Hattermann, Helge; Hoeckh, Simone; Jessen, Florian; Cano, Daniel; Fortagh, Jozsef

    2011-05-15

    We report the measurement of absolute excitation frequencies of {sup 87}Rb to nS and nD Rydberg states. The Rydberg transition frequencies are obtained by observing electromagnetically induced transparency on a rubidium vapor cell. The accuracy of the measurement of each state is < or approx. 1 MHz, which is achieved by frequency stabilizing the two diode lasers employed for the spectroscopy to a frequency comb and a frequency comb calibrated wavelength meter, respectively. Based on the spectroscopic data we determine the quantum defects of {sup 87}Rb, and compare it with previous measurements on {sup 85}Rb. We determine the ionization frequency from the 5S{sub 1/2}(F=1) ground state of {sup 87}Rb to 1010.029 164 6(3)THz, providing the binding energy of the ground state with an accuracy improved by two orders of magnitude.

  12. Absolute stability and synchronization in neural field models with transmission delays

    NASA Astrophysics Data System (ADS)

    Kao, Chiu-Yen; Shih, Chih-Wen; Wu, Chang-Hong

    2016-08-01

    Neural fields model macroscopic parts of the cortex which involve several populations of neurons. We consider a class of neural field models which are represented by integro-differential equations with transmission time delays which are space-dependent. The considered domains underlying the systems can be bounded or unbounded. A new approach, called sequential contracting, instead of the conventional Lyapunov functional technique, is employed to investigate the global dynamics of such systems. Sufficient conditions for the absolute stability and synchronization of the systems are established. Several numerical examples are presented to demonstrate the theoretical results.

  13. Absolute stability in a collisionless electron-heat-conducting plasma in strong magnetic fields

    NASA Astrophysics Data System (ADS)

    de la Torre, A.; Duhau, S.

    1989-02-01

    The dispersion relation obtained from a linear analysis of the hydrodynamic system of equations of Duhau is used to study the behaviour of the fast and slow magnetosonic and entropy modes in an electron-heat-flux-conducting plasma. The evolution of the hydrodynamic modes different from the Alfvén mode are studied as the electron heat flux is increased from zero as well as around the borders of overstable regions, for any anisotropy condition of the ions. The development of the domains of mirror and electron-heat-flux overstabilities are established and the regions of absolute stability are shown

  14. Accurate absolute frequencies of the {nu}{sub 1}+{nu}{sub 3} band of {sup 13}C{sub 2}H{sub 2} determined using an infrared mode-locked Cr:YAG laser frequency comb

    SciTech Connect

    Madej, Alan A.; Bernard, John E.; John Alcock, A.; Czajkowski, Andrzej; Chepurov, Sergei

    2006-04-15

    Absolute frequency measurements, with up to 1x10{sup -11} level accuracies, are presented for 60 lines of the P and R branches for the {nu}{sub 1}+{nu}{sub 3} band of {sup 13}C{sub 2}H{sub 2} at 1.5 {mu}m (194 THz). The measurements were made using cavity-enhanced, diode-laser-based saturation spectroscopy. With one laser system stabilized to the P(16) line and a second laser system stabilized to the line whose frequency was to be determined, a Cr:YAG frequency comb was employed to accurately measure the tetrahertz level frequency intervals. The results are compared with recent work from other groups and indicate that these lines would form a basis for a high-quality atlas of reference frequencies for this region of the spectrum.

  15. Design concepts using ring lasers for frequency stabilization

    NASA Technical Reports Server (NTRS)

    Mocker, H.

    1967-01-01

    Laser frequency stabilization methods are based on a frequency discriminant which generates an unambiguous deviation signal used for automatic stabilization. Closed-loop control stabilizes cavity length at a null point. Some systems have a stabilized ring laser using a piezoelectric dither and others use a Doppler gain tube.

  16. Improved Absolute Frequency Measurement of the 171Yb Optical Lattice Clock towards a Candidate for the Redefinition of the Second

    NASA Astrophysics Data System (ADS)

    Yasuda, Masami; Inaba, Hajime; Kohno, Takuya; Tanabe, Takehiko; Nakajima, Yoshiaki; Hosaka, Kazumoto; Akamatsu, Daisuke; Onae, Atsushi; Suzuyama, Tomonari; Amemiya, Masaki; Hong, Feng-Lei

    2012-10-01

    We demonstrate an improved absolute frequency measurement of the 1S0–3P0 clock transition at 578 nm in 171Yb atoms in a one-dimensional optical lattice. The clock laser linewidth is reduced to ≈2 Hz by phase-locking the laser to an ultrastable neodymium-doped yttrium aluminum garnet (Nd:YAG) laser at 1064 nm through an optical frequency comb with an intracavity electrooptic modulator to achieve a high servo bandwidth. The absolute frequency is determined as 518 295 836 590 863.1(2.0) Hz relative to the SI second, and will be reported to the International Committee for Weights and Measures.

  17. Correlation of symptom clusters of schizophrenia with absolute powers of main frequency bands in quantitative EEG

    PubMed Central

    Gross, Andres; Joutsiniemi, Sirkka-Liisa; Rimon, Ranan; Appelberg, Björn

    2006-01-01

    Background Research of QEEG activity power spectra has shown intriguing results in patients with schizophrenia. Different symptom clusters have been correlated to QEEG frequency bands. The findings have been to some extent inconsistent. Replication of the findings of previous research is thus an important task. In the current study we investigated the correlations between the absolute powers of delta, theta, alpha, and beta frequency bands over the fronto-central scalp area (FC) with the PANSS subscales and the Liddle's factors in 16 patients with schizophrenia. The authors hypothesised a priori the correlations reported by Harris et al (1999) of PANSS negative subscale with delta power, Liddle's psychomotor poverty with delta and beta powers, disorganisation with delta power and reality distortion with alpha power on the midline FC. Methods The sample consisted of 16 patients with chronic schizophrenia considered as having insufficient clinical response to conventional antipsychotic treatment and evidencing a relapse. The correlations between quantitative electroencephalography (QEEG) absolute powers of delta (1.5–3.0 Hz), theta (3.0–7.5 Hz), alpha (7.5–12.5 Hz), and beta (12.5–20.0 Hz) frequency bands over the fronto-central scalp area (FC) with PANSS subscales and Liddle's factors (reality distortion, disorganisation, psychomotor poverty) were investigated. Results Significant positive correlations were found between the beta and psychomotor poverty (p < 0.05). Trends towards positive correlations (p < 0.1) were observed between delta and PANSS negative subscale and psychomotor poverty. Alpha did not correlate with reality distortion and delta did not correlate with disorganisation. Post hoc analysis revealed correlations of the same magnitude between beta and psychopathology generally over FC. Conclusion The a priori hypothesis was partly supported by the correlation of the beta and psychomotor poverty. Liddle's factors showed correlations of the same

  18. Absolute photometric calibration of detectors to 0.3 mmag using amplitude-stabilized lasers and a helium-cooled absolute radiometer

    NASA Technical Reports Server (NTRS)

    Miller, Peter J.

    1988-01-01

    Laser sources whose intensity is determined with a cryogenic electrical substitution radiometer are described. Detectors are then calibrated against this known flux, with an overall error of 0.028 percent (0.3 mmag). Ongoing research has produced laser intensity stabilizers with flicker and drift of less than 0.01 percent. Recently, the useful wavelength limit of these stabilizers have been extended to 1.65 microns by using a new modular technology and InGaAs detector systems. Data from Si photodiode calibration using the method of Zalewski and Geist are compared against an absolute cavity radiometer calibration as an internal check on the calibration system.

  19. Frequency stability of a wavelength meter and applications to laser frequency stabilization.

    PubMed

    Saleh, Khaldoun; Millo, Jacques; Didier, Alexandre; Kersalé, Yann; Lacroûte, Clément

    2015-11-10

    Interferometric wavelength meters have attained frequency resolutions down to the megahertz range. In particular, Fizeau interferometers, which have no moving parts, are becoming a popular tool for laser characterization and stabilization. In this paper, we characterize such a wavelength meter using an ultrastable laser in terms of relative frequency instability σ(y)(τ) and demonstrate that it can achieve a short-term instability σ(y)(1s)≈2×10(-10) and a frequency drift of order 10 MHz/day. We use this apparatus to demonstrate frequency control of a near-infrared laser, where a frequency instability below 3×10(-10) from 1 to 2000 s is achieved. Such performance is, for example, adequate for ion trapping and atom cooling experiments. PMID:26560771

  20. A system for measuring absolute frequencies of up to 4.25 THz using a Josephson point contact

    NASA Astrophysics Data System (ADS)

    Mild, Yukinobu; Onae, Atsushi; Kurosawa, Tomizo; Sakuma, Eiichi

    1993-11-01

    A system for measuring the absolute frequency of a far-infrared (FIR) laser is described. Josephson point contacts have been utilized in the system as a frequency harmonic mixer connecting microwaves and optically pumped CH3OH laser lines. The Josephson point contacts are capable of generating beat signals of 90 GHz microwaves and FIR waves of up to 4.25 THz. To measure the frequency of the beat signals from the Josephson junction with a frequency counter, tracking oscillators have been developed, which tracks the beat signals by phase locking and regenerate clean signals for frequency counting. It is shown that the absolute frequency can be measured to an accuracy of about 100 Hz by using the tracking oscillators.

  1. Accurate absolute reference frequencies from 1511 to 1545 nm of the {nu}{sub 1}+{nu}{sub 3} band of {sup 12}C{sub 2}H{sub 2} determined with laser frequency comb interval measurements

    SciTech Connect

    Madej, Alan A.; Alcock, A. John; Czajkowski, Andrzej; Bernard, John E.; Chepurov, Sergei

    2006-10-15

    Absolute frequency measurements, with uncertainties as low as 2 kHz (1x10{sup -11}), are presented for the {nu}{sub 1}+{nu}{sub 3} band of {sup 12}C{sub 2}H{sub 2} at 1.5 {mu}m (194-198 THz). The measurements were made using cavity-enhanced, diode-laser-based saturation spectroscopy. With one laser system stabilized to the P(16) line of {sup 13}C{sub 2}H{sub 2} and a system stabilized to the line in {sup 12}C{sub 2}H{sub 2} whose frequency was to be determined, a Cr:YAG laser-based frequency comb was employed to measure the frequency intervals. The systematic uncertainty is notably reduced relative to that of previous studies, and the region of measured lines has been extended. Improved molecular constants are obtained.

  2. Absolutely Exponential Stability and Temperature Control for Gas Chromatograph System Under Dwell Time Switching Techniques.

    PubMed

    Sun, Xi-Ming; Wang, Xue-Fang; Tan, Ying; Wang, Xiao-Liang; Wang, Wei

    2016-06-01

    This paper provides a design strategy for temperature control of the gas chromatograph. Usually gas chromatograph is modeled by a simple first order system with a time-delay, and a proportion integration (PI) controller is widely used to regulate the output of the gas chromatograph to the desired temperature. As the characteristics of the gas chromatograph varies at the different temperature range, the single-model based PI controller cannot work well when output temperature varies from one range to another. Moreover, the presence of various disturbance will further deteriorate the performance. In order to improve the accuracy of the temperature control, multiple models are used at the different temperature ranges. With a PI controller designed for each model accordingly, a delay-dependent switching control scheme using the dwell time technique is proposed to ensure the absolute exponential stability of the closed loop. Experiment results demonstrate the effectiveness of the proposed switching technique. PMID:26316283

  3. Absolute Hydration Free Energies of Blocked Amino Acids: Implications for Protein Solvation and Stability

    PubMed Central

    König, Gerhard; Bruckner, Stefan; Boresch, Stefan

    2013-01-01

    Most proteins perform their function in aqueous solution. The interactions with water determine the stability of proteins and the desolvation costs of ligand binding or membrane insertion. However, because of experimental restrictions, absolute solvation free energies of proteins or amino acids are not available. Instead, solvation free energies are estimated based on side chain analog data. This approach implies that the contributions to free energy differences are additive, and it has often been employed for estimating folding or binding free energies. However, it is not clear how much the additivity assumption affects the reliability of the resulting data. Here, we use molecular dynamics–based free energy simulations to calculate absolute hydration free energies for 15 N-acetyl-methylamide amino acids with neutral side chains. By comparing our results with solvation free energies for side chain analogs, we demonstrate that estimates of solvation free energies of full amino acids based on group-additive methods are systematically too negative and completely overestimate the hydrophobicity of glycine. The largest deviation of additive protocols using side chain analog data was 6.7 kcal/mol; on average, the deviation was 4 kcal/mol. We briefly discuss a simple way to alleviate the errors incurred by using side chain analog data and point out the implications of our findings for the field of biophysics and implicit solvent models. To support our results and conclusions, we calculate relative protein stabilities for selected point mutations, yielding a root-mean-square deviation from experimental results of 0.8 kcal/mol. PMID:23442867

  4. Design of digital Pound-Drever-Hall frequency stabilizing system for two-cavity dual-frequency Nd:YAG laser

    NASA Astrophysics Data System (ADS)

    Xing, Junhong; Jiao, Mingxing; Zheng, Yi; Zheng, Lingling

    2013-01-01

    Two-cavity dual-frequency Nd:YAG laser with large frequency difference can be used as an ideal light source for synthetic-wave absolute-distance interferometric system. The operation principle of the two-cavity dual-frequency Nd:YAG laser with large frequency difference has been introduced, and the frequency locking principle of the Pound-Drever-Hall (PDH) method has been analyzed. A FPGA-based digital PDH frequency stabilizing system for the two-cavity dual-frequency Nd:YAG laser has been designed, in which the same frequency reference of a high finesse Fabry-Perot cavity is used and two separate heterodyne interference sub-systems are employed so that two electrical error signals can be obtained. Having been processed through FPGA, the output signals are applied to drive the PZT frequency actuators attached on the two-cavity dual-frequency Nd:YAG laser, as a result both operating frequencies of the two-cavity dual-frequency Nd:YAG laser can be simultaneously frequency-locked to two resonant frequencies of the Fabry-Perot cavity. A frequency stability of better than 10-10 will be obtained by use of the digital PDH frequency locking system, which can meet the needs of synthetic-wave absolute-distance interferometry.

  5. Long-term laser frequency stabilization using fiber interferometers.

    PubMed

    Kong, Jia; Lucivero, Vito Giovanni; Jiménez-Martínez, Ricardo; Mitchell, Morgan W

    2015-07-01

    We report long-term laser frequency stabilization using only the target laser and a pair of 5 m fiber interferometers, one as a frequency reference and the second as a sensitive thermometer to stabilize the frequency reference. When used to stabilize a distributed feedback laser at 795 nm, the frequency Allan deviation at 1000 s drops from 5.6 × 10(-8) to 6.9 × 10(-10). The performance equals that of an offset lock employing a second, atom-stabilized laser in the temperature control. PMID:26233353

  6. Long-term laser frequency stabilization using fiber interferometers

    SciTech Connect

    Kong, Jia; Lucivero, Vito Giovanni; Jiménez-Martínez, Ricardo; Mitchell, Morgan W.

    2015-07-15

    We report long-term laser frequency stabilization using only the target laser and a pair of 5 m fiber interferometers, one as a frequency reference and the second as a sensitive thermometer to stabilize the frequency reference. When used to stabilize a distributed feedback laser at 795 nm, the frequency Allan deviation at 1000 s drops from 5.6 × 10{sup −8} to 6.9 × 10{sup −10}. The performance equals that of an offset lock employing a second, atom-stabilized laser in the temperature control.

  7. Stabilization of a self-referenced, prism-based, Cr:forsterite laser frequency comb using an intracavity prism

    SciTech Connect

    Tillman, Karl A.; Thapa, Rajesh; Knabe, Kevin; Wu Shun; Lim, Jinkang; Washburn, Brian R.; Corwin, Kristan L.

    2009-12-20

    The frequency comb from a prism-based Cr:forsterite laser has been frequency stabilized using intracavity prism insertion and pump power modulation. Absolute frequency measurements of a CW fiber laser stabilized to the P(13) transition of acetylene demonstrate a fractional instability of {approx}2x10{sup -11} at a 1 s gate time, limited by a commercial Global Positioning System (GPS)-disciplined rubidium oscillator. Additionally, absolute frequency measurements made simultaneously using a second frequency comb indicate relative instabilities of 3x10{sup -12} for both combs for a 1 s gate time. Estimations of the carrier-envelope offset frequency linewidth based on relative intensity noise and the response dynamics of the carrier-envelope offset to pump power changes confirm the observed linewidths.

  8. Frequency standard stability for Doppler measurements on-board the shuttle

    NASA Technical Reports Server (NTRS)

    Harton, P. L.

    1974-01-01

    The short and long term stability characteristics of crystal and atomic standards are described. Emphasis is placed on crystal oscillators because of the selection which was made for the shuttle baseline and the complexities which are introduced by the shuttle environment. Attention is given, first, to the definitions of stability and the application of these definitions to the shuttle system and its mission. Data from time domain measurements are used to illustrate the definitions. Results of a literature survey to determine environmental effects on frequency reference sources are then presented. Finally, methods of standard frequency dissemination over radio frequency carriers are noted as a possible means of measuring absolute accuracy and long term stability characteristics during on one way Doppler equipment.

  9. Atomic frequency standards for ultra-high-frequency stability

    NASA Technical Reports Server (NTRS)

    Maleki, L.; Prestage, J. D.; Dick, G. J.

    1987-01-01

    The general features of the Hg-199(+) trapped-ion frequency standard are outlined and compared to other atomic frequency standards, especially the hydrogen maser. The points discussed are those which make the trapped Hg-199(+) standard attractive: high line Q, reduced sensitivity to external magnetic fields, and simplicity of state selection, among others.

  10. Methods and apparatus for broadband frequency comb stabilization

    SciTech Connect

    Cox, Jonathan A; Kaertner, Franz X

    2015-03-17

    Feedback loops can be used to shift and stabilize the carrier-envelope phase of a frequency comb from a mode-locked fibers laser or other optical source. Compared to other frequency shifting and stabilization techniques, feedback-based techniques provide a wideband closed-loop servo bandwidth without optical filtering, beam pointing errors, or group velocity dispersion. It also enables phase locking to a stable reference, such as a Ti:Sapphire laser, continuous-wave microwave or optical source, or self-referencing interferometer, e.g., to within 200 mrad rms from DC to 5 MHz. In addition, stabilized frequency combs can be coherently combined with other stable signals, including other stabilized frequency combs, to synthesize optical pulse trains with pulse durations of as little as a single optical cycle. Such a coherent combination can be achieved via orthogonal control, using balanced optical cross-correlation for timing stabilization and balanced homodyne detection for phase stabilization.

  11. Frequency response characteristics of the fuzzy polar power system stabilizer

    SciTech Connect

    Ortmeyer, T.H.; Hiyama, Takashi

    1995-06-01

    The fuzzy polar power system stabilizer (FPPSS) which has been recently developed is analyzed using frequency domain methods. the frequency domain approach allows the PSS designer to compare the new FPPSS with more conventional controllers. The significance of the three FPPSS design parameters are readily seen from the frequency response data, and their relationship to the conventional lead-lag design approach can be evaluated. Furthermore, the frequency response data for the FPPSS allows an alternate design approach for this stabilizer, and can be used to develop information concerning the small signal stability of the resulting system.

  12. The High Frequency Stabilization of a Magnetoplasmadynamic Thruster

    NASA Astrophysics Data System (ADS)

    Kirdyashev, K.

    2004-10-01

    Experimental data on the high-frequency stabilization of the MPD thruster and the suppression of low-frequency oscillations in the frequency range from 20 to 100 kHz are presented. Conditions for the stabilizing effect of a high-frequency magnetic field at the frequency of 40 MHz on the plasma jet produced by the thruster are determined, and the efficiency of this action is evaluated. The action of high frequency field on the MPD thruster consists in the contention of two processes - the stabilization of the plasma drift instability by the magnetic component of high frequency field and the energy conversion of natural plasma oscillations excited by the external field to the ion-sound wave energy.

  13. Optical frequency measurements with the global positioning system: tests with an iodine-stabilized He-Ne laser.

    PubMed

    Fox, Richard W; Diddams, Scott A; Bartels, Albrecht; Hollberg, Leo

    2005-01-01

    Global positioning system- (GPS-) referenced optical frequency combs based on mode-locked lasers offer calibrations for length metrology traceable to international length standards through the SI second and the speed of light. The absolute frequency of an iodine-stabilized He-Ne laser [127I2 R(127) 11-5 f component] was measured with a femtosecond comb referenced to a multichannel GPS timing receiver. The expected performance and limitations of GPS-referenced comb measurements are discussed. PMID:15662892

  14. 3D absolute shape measurement of live rabbit hearts with a superfast two-frequency phase-shifting technique.

    PubMed

    Wang, Yajun; Laughner, Jacob I; Efimov, Igor R; Zhang, Song

    2013-03-11

    This paper presents a two-frequency binary phase-shifting technique to measure three-dimensional (3D) absolute shape of beating rabbit hearts. Due to the low contrast of the cardiac surface, the projector and the camera must remain focused, which poses challenges for any existing binary method where the measurement accuracy is low. To conquer this challenge, this paper proposes to utilize the optimal pulse width modulation (OPWM) technique to generate high-frequency fringe patterns, and the error-diffusion dithering technique to produce low-frequency fringe patterns. Furthermore, this paper will show that fringe patterns produced with blue light provide the best quality measurements compared to fringe patterns generated with red or green light; and the minimum data acquisition speed for high quality measurements is around 800 Hz for a rabbit heart beating at 180 beats per minute. PMID:23482151

  15. 47 CFR 2.1055 - Measurements required: Frequency stability.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 1 2010-10-01 2010-10-01 false Measurements required: Frequency stability. 2.1055 Section 2.1055 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL FREQUENCY ALLOCATIONS AND RADIO TREATY MATTERS; GENERAL RULES AND REGULATIONS Equipment Authorization Procedures Certification § 2.1055 Measurements required:...

  16. Gyrotron Frequency Stabilization by a Weak Reflected Wave

    NASA Astrophysics Data System (ADS)

    Glyavin, M. Yu.; Denisov, G. G.; Kulygin, M. L.; Mel'nikova, M. M.; Novozhilova, Yu. V.; Ryskin, N. M.

    2016-02-01

    The possibility of reducing the radiation frequency fluctuations by a factor of 3-5 using a nonresonant or highly resonant weakly reflecting load for the gyrotrons employed in controlled-fusion facilities is shown. The ranges of system parameters where the frequency stabilization is most effective were identified both analytically and numerically.

  17. Laser frequency stabilization and shifting by using modulation transfer spectroscopy

    NASA Astrophysics Data System (ADS)

    Cheng, Bing; Wang, Zhao-Ying; Wu, Bin; Xu, Ao-Peng; Wang, Qi-Yu; Xu, Yun-Fei; Lin, Qiang

    2014-10-01

    The stabilizing and shifting of laser frequency are very important for the interaction between the laser and atoms. The modulation transfer spectroscopy for the 87Rb atom with D2 line transition F = 2 → F' = 3 is used for stabilizing and shifting the frequency of the external cavity grating feedback diode laser. The resonant phase modulator with electro—optical effect is used to generate frequency sideband to lock the laser frequency. In the locking scheme, circularly polarized pump- and probe-beams are used. By optimizing the temperature of the vapor, the pump- and probe-beam intensity, the laser linewidth of 280 kHz is obtained. Furthermore, the magnetic field generated by a solenoid is added into the system. Therefore the system can achieve the frequency locking at any point in a range of hundreds of megahertz frequency shifting with very low power loss.

  18. Characterization of a partially-stabilized frequency comb

    NASA Astrophysics Data System (ADS)

    Gold Dahl, M. E.; Erikson, Alex; Woodbury, Daniel; Bergeson, Scott

    2015-05-01

    We present measurements of well-known frequency intervals in Cs, Rb, and Ca. These measurements are used to determine the accuracy of a partially-stabilized ti:sapphire frequency comb. One mode of our frequency comb is offset-locked to a Rb-stabilized diode laser. The comb's repetition rate is counted but not locked. A second laser is used to probe well-known atomic transitions in Cs, Rb, and Ca. We describe our offset locking and scanning techniques and demonstrate a frequency precision of 10 kHz in a 30 second measurement time. The accuracy of our laser frequency interval measurements is approximately 40 kHz. However, cell-based frequency references can be off by several hundred kHz. Research supported by the National Science Foundation (Grant No. PHY-0969856) and the Air Force (Grant No. FA9950-12-1-0308).

  19. Third-order chromatic dispersion stabilizes Kerr frequency combs.

    PubMed

    Parra-Rivas, Pedro; Gomila, Damià; Leo, François; Coen, Stéphane; Gelens, Lendert

    2014-05-15

    Using numerical simulations of an extended Lugiato-Lefever equation we analyze the stability and nonlinear dynamics of Kerr frequency combs generated in microresonators and fiber resonators, taking into account third-order dispersion effects. We show that cavity solitons underlying Kerr frequency combs, normally sensitive to oscillatory and chaotic instabilities, are stabilized in a wide range of parameter space by third-order dispersion. Moreover, we demonstrate how the snaking structure organizing compound states of multiple cavity solitons is qualitatively changed by third-order dispersion, promoting an increased stability of Kerr combs underlined by a single cavity soliton. PMID:24978250

  20. Frequency domain stability analysis of nonlinear active disturbance rejection control system.

    PubMed

    Li, Jie; Qi, Xiaohui; Xia, Yuanqing; Pu, Fan; Chang, Kai

    2015-05-01

    This paper applies three methods (i.e., root locus analysis, describing function method and extended circle criterion) to approach the frequency domain stability analysis of the fast tool servo system using nonlinear active disturbance rejection control (ADRC) algorithm. Root locus qualitative analysis shows that limit cycle is generated because the gain of the nonlinear function used in ADRC varies with its input. The parameters in the nonlinear function are adjustable to suppress limit cycle. In the process of root locus analysis, the nonlinear function is transformed based on the concept of equivalent gain. Then, frequency domain description of the nonlinear function via describing function is presented and limit cycle quantitative analysis including estimating prediction error is presented, which virtually and theoretically demonstrates that the describing function method cannot guarantee enough precision in this case. Furthermore, absolute stability analysis based on extended circle criterion is investigated as a complement. PMID:25532936

  1. Stability and noise spectra of relative Loran-C frequency comparisons

    NASA Technical Reports Server (NTRS)

    Proverbio, E.; Quesada, V.; Simoncini, A.

    1973-01-01

    Relative comparisons of Loran-C frequency transmissions between the master station of Catanzaro (Simeri Crichi) and the X, Z slave stations of Estartit (Spain) and Lampedusa (Italy) are carrying out by the GG LORSTA monitor station of the Mediterranean Sea Loran-C chain. These comparisons are able to emphasize the relative and, under certain conditions, the absolute rate of the emitting standard frequencies of the slave stations and some relevant statistical properties of the Loran-C Method for frequency transmission and time synchronization. The stability of each Loran-C frequency standard transmission is subject to perturbations, more or less known, due to the propagation medium and other causes. Following the Allan (1966) method for data processing, the performance of the relative rate of frequency of the transmissions of the X, Z slave stations are described calculating the standard deviation of a set of N frequency measurements from its mean averaged during sampling times. This standard deviation is designated as the measure of the stability of the Loran-C frequency transmission.

  2. Absolute measurement of the 1S0 − 3P0 clock transition in neutral 88Sr over the 330 km-long stabilized fibre optic link

    PubMed Central

    Morzyński, Piotr; Bober, Marcin; Bartoszek-Bober, Dobrosława; Nawrocki, Jerzy; Krehlik, Przemysław; Śliwczyński, Łukasz; Lipiński, Marcin; Masłowski, Piotr; Cygan, Agata; Dunst, Piotr; Garus, Michał; Lisak, Daniel; Zachorowski, Jerzy; Gawlik, Wojciech; Radzewicz, Czesław; Ciuryło, Roman; Zawada, Michał

    2015-01-01

    We report a stability below 7 × 10−17 of two independent optical lattice clocks operating with bosonic 88Sr isotope. The value (429 228 066 418 008.3(1.9)syst (0.9)stat Hz) of the absolute frequency of the 1S0 – 3P0 transition was measured with an optical frequency comb referenced to the local representation of the UTC by the 330 km-long stabilized fibre optical link. The result was verified by series of measurements on two independent optical lattice clocks and agrees with recommendation of Bureau International des Poids et Mesures. PMID:26639347

  3. Stabilization of the potential multi-steady-state absolute instabilities in a gyrotron traveling-wave amplifier

    SciTech Connect

    Du Chaohai; Liu Pukun

    2009-10-15

    The problem of spurious oscillations induced by absolute instabilities is the most challenging one that hinders the development of the millimeter-wave gyrotron traveling-wave amplifiers (gyro-TWTs). A spurious oscillation exists as a high order axial mode (HOAM) in the interaction circuit. This paper is devoted to demonstrating the complicated steady states of these HOAMs and exploring corresponding techniques to stabilize these potential multi-steady-state absolute instabilities. The stability-oriented design principle is conveyed in a start-to-end design flow of a Ka-band TE{sub 11} mode gyro-TWT. Strong magnetic tapering near the downstream port, which is capable of cutting short the effective interaction circuit of a spurious oscillation and simultaneously boosting the amplification performance, is for the first time proposed to further improve the system stability. It is also found that an ideal prebunched electron beam in the linear stage is the necessary condition to efficient amplification in the nonlinear stage, suggesting that it is feasible to design a stable prebunching stage to replace the distributed-loss-loaded linear stage. The stability-oriented design principle provides more explicit reference for future design of a zero-drive stable gyro-TWT.

  4. Absolute and relative stability of alexithymia in alcoholic inpatients undergoing alcohol withdrawal: relationship to depression and anxiety.

    PubMed

    de Timary, Philippe; Luts, Alain; Hers, Denis; Luminet, Olivier

    2008-01-15

    To evaluate whether alexithymia in alcohol-dependent patients is a personality trait or a state-dependent phenomenon related to depression and anxiety, we evaluated absolute stability (the extent to which alexithymia scores change over time) and relative stability (the extent to which relative differences among individuals remain the same over time) of alexithymia during alcohol withdrawal. Seventy alcohol-dependent inpatients were assessed for alexithymia, depression and anxiety with the 20-item Toronto Alexithymia Scale, the Beck Depression Inventory and the State-Trait Anxiety Inventory at the onset of withdrawal, after 2 days and 2 weeks. Paired t-tests and correlational analyses were performed to evaluate absolute and relative stability of alexithymia and hierarchical regression analyses to assess whether alexithymia was related to anxiety and depression. Alexithymia decreased significantly from onset to end of withdrawal, but two of its three subfactors remained stable. Alexithymia scores at onset correlated significantly with scores at end, after partialling out the effects of depression and anxiety. In conclusion, the relative stability of alexithymia contrasting with large decreases in depression and anxiety during alcohol withdrawal supports the view that alexithymia is a stable personality trait rather than a state-dependent phenomenon. PMID:17884180

  5. Fast scanning cavity offset lock for laser frequency drift stabilization

    NASA Astrophysics Data System (ADS)

    Seymour-Smith, Nicolas; Blythe, Peter; Keller, Matthias; Lange, Wolfgang

    2010-07-01

    We have implemented a compact setup for long-term laser frequency stabilization. Light from a stable reference laser and several slave lasers is coupled into a confocal Fabry-Pérot resonator. By stabilizing the position of the transmission peaks of the slave lasers relative to successive peaks of the master laser as the length of the cavity is scanned over one free spectral range, the long-term stability of the master laser is transferred to the slave lasers. By using fast analog peak detection and low-latency microcontroller-based digital feedback, with a scanning frequency of 3 kHz, we obtain a feedback bandwidth of 380 Hz and a relative stability of better than 10 kHz at timescales longer than 1 s, a significant improvement on previous scanning-cavity stabilization systems.

  6. Laser Frequency Stabilization by Using Arm-Locking

    NASA Astrophysics Data System (ADS)

    Schulte, Hans Reiner; Gath, Peter F.; Herz, Markus

    2006-11-01

    In order to achieve the required measurement performance on LISA, the laser frequency must be stabilized to approximately 30 Hz/√Hz ×[1+(1mHz/f)4]1/2 in the LISA measurement bandwidth from 0.03 mHz up to 1 Hz for the master laser in the constellation. All other lasers are offset locked to the master laser such that the Doppler shifts are taken into account and beat signals between 3 MHz and 18 MHz are produced on all detectors in the constellation. Ensuring sufficient frequency stability can be established by different methods. A straight forward approach is to use an optical cavity. It turns out that a cavity alone significantly drives the thermal stability requirements at low frequencies. Therefore, different versions of arm-locking are considered in order to provide both, frequency stabilization at low frequencies as well as at high frequencies. While it is obvious how a stable feedback loop at low frequencies can be achieved, a stable control system with noise suppression also at high frequencies can only be achieved when at least two arms are combined in the overall control approach. In the framework of this paper, the Sagnac and the Michelson locking scheme are described and it is shown that the resulting system is stable and achieves significant noise suppression at frequencies up to around 100 Hz. The theoretical results are supported by frequency and time-domain simulations. Results from the time-domain simulation are currently being used for an end-to-end simulation of the LISA measurement data chain that involves the Synthetic LISA simulator, the laser frequency noise generated from the arm-locking simulation, the digital part of the phasemeter, and the TDI data post-processing. This effort will result in a detailed understanding and quantization of additional error sources introduced at the various level of data processing.

  7. A linewidth-narrowed and frequency-stabilized dye laser for application in laser cooling of molecules.

    PubMed

    Dai, D P; Xia, Y; Yin, Y N; Yang, X X; Fang, Y F; Li, X J; Yin, J P

    2014-11-17

    We demonstrate a robust and versatile solution for locking the continuous-wave dye laser for applications in laser cooling of molecules which need linewidth-narrowed and frequency-stabilized lasers. The dye laser is first stabilized with respect to a reference cavity by Pound-Drever-Hall (PDH) technique which results in a single frequency with the linewidth 200 kHz and short-term stabilization, by stabilizing the length of the reference cavity to a stabilized helium-neon laser we simultaneously transfer the ± 2 MHz absolute frequency stability of the helium-neon laser to the dye laser with long-term stabilization. This allows the dye laser to be frequency chirped with the maximum 60 GHz scan range while its frequency remains locked. It also offers the advantages of locking at arbitrary dye laser frequencies, having a larger locking capture range and frequency scanning range to be implemented via software. This laser has been developed for the purpose of laser cooling a molecular magnesium fluoride beam. PMID:25402105

  8. High-resolution absolute frequency referenced fiber optic sensor for quasi-static strain sensing

    SciTech Connect

    Lam, Timothy T.-Y.; Chow, Jong H.; Shaddock, Daniel A.; Littler, Ian C. M.; Gagliardi, Gianluca; Gray, Malcolm B.; McClelland, David E.

    2010-07-20

    We present a quasi-static fiber optic strain sensing system capable of resolving signals below nanostrain from 20 mHz. A telecom-grade distributed feedback CW diode laser is locked to a fiber Fabry-Perot sensor, transferring the detected signals onto the laser. An H{sup 13}C{sup 14}N absorption line is then used as a frequency reference to extract accurate low-frequency strain signals from the locked system.

  9. Scientific applications of frequency-stabilized laser technology in space

    NASA Technical Reports Server (NTRS)

    Schumaker, Bonny L.

    1990-01-01

    A synoptic investigation of the uses of frequency-stabilized lasers for scientific applications in space is presented. It begins by summarizing properties of lasers, characterizing their frequency stability, and describing limitations and techniques to achieve certain levels of frequency stability. Limits to precision set by laser frequency stability for various kinds of measurements are investigated and compared with other sources of error. These other sources include photon-counting statistics, scattered laser light, fluctuations in laser power, and intensity distribution across the beam, propagation effects, mechanical and thermal noise, and radiation pressure. Methods are explored to improve the sensitivity of laser-based interferometric and range-rate measurements. Several specific types of science experiments that rely on highly precise measurements made with lasers are analyzed, and anticipated errors and overall performance are discussed. Qualitative descriptions are given of a number of other possible science applications involving frequency-stabilized lasers and related laser technology in space. These applications will warrant more careful analysis as technology develops.

  10. Tunable cw UV laser with <35 kHz absolute frequency instability for precision spectroscopy of Sr Rydberg states.

    PubMed

    Bridge, Elizabeth M; Keegan, Niamh C; Bounds, Alistair D; Boddy, Danielle; Sadler, Daniel P; Jones, Matthew P A

    2016-02-01

    We present a solid-state laser system that generates over 200 mW of continuous-wave, narrowband light, tunable from 316.3 nm - 317.7 nm and 318.0 nm - 319.3 nm. The laser is based on commercially available fiber amplifiers and optical frequency doubling technology, along with sum frequency generation in a periodically poled stoichiometric lithium tantalate crystal. The laser frequency is stabilized to an atomic-referenced high finesse optical transfer cavity. Using a GPS-referenced optical frequency comb we measure a long term frequency instability of < 35 kHz for timescales between 10(-3) s and 10(3) s. As an application we perform spectroscopy of Sr Rydberg states from n = 37 - 81, demonstrating mode-hop-free scans of 24 GHz. In a cold atomic sample we measure Doppler-limited linewidths of 350 kHz. PMID:26906804

  11. Precise Frequency Measurements Using a Superconducting Cavity Stabilized Oscillator

    NASA Technical Reports Server (NTRS)

    Strayer, D. M.; Yeh, N.-C.; Jiang, W.; Anderson, V. L.; Asplund, N.

    1999-01-01

    Many physics experiments call on improved resolution to better define the experimental results, thus improving tests of theories. Modern microwave technology combined with high-Q resonators can achieve frequency readout and control with resolutions up to a part in 10(exp 18). When the physical quantity in question in the experiment can be converted to a frequency or a change in frequency, a high-stability microwave oscillator can be applied to obtain state-of-the-art precision. In this work we describe the overall physical concepts and the required experimental procedures for optimizing a high-resolution frequency measurement system that employs a high-Q superconducting microwave cavity and a low-noise frequency synthesizer. The basic approach is to resolve the resonant frequencies of a high-Q (Q > 10(exp 10)) cavity to extremely high precision (one part in 10(exp 17)- 10(exp 18)). Techniques for locking the synthesizer frequency to a resonant frequency of the superconducting cavity to form an ultra-stable oscillator are described. We have recently set up an ultra-high-vacuum high-temperature annealing system to process superconducting niobium cavities, and have been able to consistently achieve Q > 10(exp 9). We have integrated high-Q superconducting cavities with a low-noise microwave synthesizer in a phase-locked-loop to verify the frequency stability of the system. Effects that disturb the cavity resonant frequency (such as the temperature fluctuations and mechanical vibrations) and methods to mitigate those effects are also considered. Applicability of these techniques to experiments will be discussed, and our latest experimental progress in achieving high-resolution frequency measurements using the superconducting-cavity-stabilized-oscillator will be presented.

  12. Frequency stabilization of laser diodes in an aggressive thermal environment

    NASA Astrophysics Data System (ADS)

    Minch, J. R.; Walther, F. G.; Savage, S.; Plante, A.; Scalesse, V.

    2015-03-01

    Mobile free-space laser communication systems must reconcile the requirements of low size, weight, and power with the ability to both survive and operate in harsh thermal and mechanical environments. In order to minimize the aperture size and amplifier power requirements of such systems, communication links must exhibit performance near theoretical limits. Such performance requires laser transmitters and receiver filters and interferometers to maintain frequency accuracy to within a couple hundred MHz of the design frequency. We demonstrate an approach to achieving high frequency stability over wide temperature ranges by using conventional DFB lasers, tuned with TEC and current settings, referenced to an HCN molecular frequency standard. A HCN cell absorption line is scanned across the TEC set-point to adjust the DFB laser frequency. Once the center of the line is determined, the TEC set-point is offset as required to obtain frequency agility. To obtain large frequency offsets from an HCN absorption line, as well as continuous laser source operation, a second laser is offset from the reference laser and the resulting beat tone is detected in a photoreceiver and set to the desired offset using a digital frequency-locked loop. Using this arrangement we have demonstrated frequency accuracy and stability of better than 8 MHz RMS over an operational temperature range of 0ºC to 50º C, with operation within minutes following 8 hour soaks at -40º C and 70º C.

  13. Frequency stabilized optical comb source with high finesse intracavity etalon

    NASA Astrophysics Data System (ADS)

    Ozdur, Ibrahim; Ozharar, Sarper; Akbulut, Mehmetcan; Mandridis, Dimitrios; Quinlan, Franklyn; Delfyett, Peter J.

    2009-05-01

    Mode-locked lasers have applications in signal processing and communications such as analog to digital conversion, arbitrary waveform generation and wavelength division multiplexing. For such applications low noise and phase coherent frequency stabilized optical combs are needed. In this work we report a low noise, Pound-Drever Hall frequency stabilized, semiconductor mode-locked laser at 10.287GHz centered at 1550nm with 1000-Finesse sealed, ultralow insertion loss intracavity etalon. The output optical power of the mode locked laser is ~5mW.

  14. Short-term frequency stability of the Rb-87 maser.

    NASA Technical Reports Server (NTRS)

    Tetu, M.; Busca, G.; Vanier, J.

    1973-01-01

    Measurements of the short-term stability of the Rb-87 maser as a function of the maser power output and the receiver cutoff frequency are reported. The experimental data are compared to theoretical results obtained from an approximate theory. In this theory the transfer function of the maser for thermal noise is derived, and the spectral density of the phase fluctuations is calculated. An analytical expression for the 'Allan variance' is also given. A comparison of the stability of the Rb-87 maser with existing frequency standards shows its superiority for averaging times less than 1 sec.

  15. Laser frequency stabilization using regenerative spectral hole burning

    NASA Astrophysics Data System (ADS)

    Strickland, N. M.; Sellin, P. B.; Sun, Y.; Carlsten, J. L.; Cone, R. L.

    2000-07-01

    We demonstrate laser frequency stabilization using a continuously regenerated transient spectral hole in an inhomogeneously broadened resonance of a solid. Regenerative transient holes provide extreme stabilization for time scales appropriate for spectroscopy, signal processing, ranging, and interferometry. Stabilization to 20 Hz on a 10-ms time scale using spectral holes at 793 nm in Tm3+:Y3Al5O12 gives substantial improvement in the reliability of stimulated photon echoes in the same material and enables the observation of a third population storage mechanism for hole burning in Tm3+:Y3Al5O12.

  16. Absolute stability and spatiotemporal long-range order in Floquet systems

    NASA Astrophysics Data System (ADS)

    von Keyserlingk, C. W.; Khemani, Vedika; Sondhi, S. L.

    2016-08-01

    Recent work has shown that a variety of novel phases of matter arise in periodically driven Floquet systems. Among these are many-body localized phases which spontaneously break global symmetries and exhibit novel multiplets of Floquet eigenstates separated by quantized quasienergies. Here we show that these properties are stable to all weak local deformations of the underlying Floquet drives—including those that explicitly break the defining symmetries—and that the models considered until now occupy submanifolds within these larger "absolutely stable" phases. While these absolutely stable phases have no explicit global symmetries, they spontaneously break Hamiltonian-dependent emergent symmetries, and thus continue to exhibit the novel multiplet structure. The multiplet structure in turn encodes characteristic oscillations of the emergent order parameter at multiples of the fundamental period. Altogether these phases exhibit a form of simultaneous long-range order in space and time which is new to quantum systems. We describe how this spatiotemporal order can be detected in experiments involving quenches from a broad class of initial states.

  17. Stray-field-induced quadrupole shift and absolute frequency of the 688-THz {sup 171}Yb{sup +} single-ion optical frequency standard

    SciTech Connect

    Tamm, Chr.; Weyers, S.; Lipphardt, B.; Peik, E.

    2009-10-15

    We report experimental investigations of a single-ion optical frequency standard based on {sup 171}Yb{sup +}. The ion is confined in a cylindrically symmetric radiofrequency Paul trap. The reference transition is the {sup 2}S{sub 1/2}(F=0)-{sup 2}D{sub 3/2}(F{sup '}=2) electric quadrupole transition at 688 THz. Using a differential measurement scheme, we determine the shift of the reference transition frequency that occurs due to the interaction of the electric quadrupole moment of the {sup 2}D{sub 3/2} state with the gradient of the electrostatic stray field in the trap. We determine an upper limit for the instability of the quadrupole shift over times between 100 s to 20 h. We also observe the variations in the shift and in the applied stray-field compensation voltages that result from loading a new ion into the trap and during a subsequent storage period of 74 days. This information is utilized to measure the absolute frequency of the reference transition with an uncertainty that is a factor of 3 smaller than that of the previous measurement. Using a fiber laser based optical frequency comb generator and the cesium fountain clock CSF1 of PTB (Physikalisch-Technische Bundesanstalt), the frequency at 300 K temperature is determined as 688 358 979 309 306.62{+-}0.73 Hz.

  18. Stabilized Fiber-Optic Distribution of Reference Frequency

    NASA Technical Reports Server (NTRS)

    Calhoun, Malcolm; Tjoelker, Robert; Diener, William; Dick, G. John; Wang, Rabi; Kirk, Albert

    2003-01-01

    An optoelectronic system distributes a reference signal of low noise and highly stabilized phase and frequency (100 MHz) from an atomic frequency standard to a remote facility at a distance up to tens of kilometers. The reference signal is transmitted to the remote station as amplitude modulation of an optical carrier signal propagating in an optical fiber. The stabilization scheme implemented in this system is intended particularly to suppress phase and frequency fluctuations caused by vibrations and by expansion and contraction of the optical fiber and other components in diurnal and seasonal heating and cooling cycles. The system (see figure) comprises several subsystems, the main one being (1) a hydrogen-maser or linear-ion-trap frequency standard in an environmentally controlled room in a signal-processing center (SPC), (2) a stabilized fiber-optic distribution assembly (SFODA), (3) a compensated sapphire oscillator (CSO) in an environmentally controlled room in the remote facility, (4) thermally stabilized distribution amplifiers and cabling from the environmentally controlled room to end users, and (5) performance- measuring equipment.

  19. Time domain measurement of frequency stability: A tutorial introduction

    NASA Technical Reports Server (NTRS)

    Vanier, J.; Tetu, M.

    1978-01-01

    The theoretical basis behind the definition of frequency stability in the time domain is outlined. Various types of variances were examined. Their differences and interrelation are pointed out. Systems that are generally used in the measurement of these variances are described.

  20. Physics characterization and frequency stability of the pulsed rubidium maser

    SciTech Connect

    Godone, Aldo; Micalizio, Salvatore; Levi, Filippo; Calosso, Claudio

    2006-10-15

    In this paper we report the theoretical and experimental characterization of a pulsed optically pumped vapor-cell frequency standard based on the detection of the free-induction decay microwave signal. The features that make this standard similar to a pulsed passive maser are presented. In order to predict and optimize the frequency stability, thermal and shot noise sources are analyzed, as well as the conversions of the laser and microwave fluctuations into the output frequency. The experimental results obtained with a clock prototype based on {sup 87}Rb in buffer gas are compared with the theoretical predictions, showing the practical possibility to implement a frequency standard limited in the medium term only by thermal drift. The achieved frequency stability is {sigma}{sub y}({tau})=1.2x10{sup -12}{tau}{sup -1/2} for measurement times up to {tau}{approx_equal}10{sup 5} s. It represents one of the best results reported in literature for gas cell frequency standards and is compliant with the present day requirements for on board space applications.

  1. Landsat-7 ETM+ on-orbit reflective-band radiometric stability and absolute calibration

    USGS Publications Warehouse

    Markham, B.L.; Thome, K.J.; Barsi, J.A.; Kaita, E.; Helder, Dennis L.; Barker, J. L.; Scaramuzza, Pat

    2004-01-01

    Launched in April 1999, the Landsat-7 Enhanced Thematic Mapper Plus (ETM+) instrument is in its sixth year of operation. The ETM+ instrument has been the most stable of any of the Landsat instruments. To date, the best onboard calibration source for the reflective bands has been the Full Aperture Solar Calibrator, a solar-diffuser-based system, which has indicated changes of between 1% to 2% per year in the ETM+ gain for bands 1-4 and 8 and less than 0.5%/year for bands 5 and 7. However, most of this change is believed to be caused by changes in the solar diffuser panel, as opposed to a change in the instrument's gain. This belief is based partially on vicarious calibrations and observations of "invariant sites", hyperarid sites of the Sahara and Arabia. Weighted average slopes determined from these datasets suggest changes of 0.0% to 0.4% per year for bands 1-4 and 8 and 0.4% to 0.5% per year for bands 5 and 7. Absolute calibration of the reflective bands of the ETM+ is consistent with vicarious observations and other sensors generally at the 5% level, though there appear to be some systematic differences.

  2. Drug Treated Schizophrenia, Schizoaffective and Bipolar Disorder Patients Evaluated by qEEG Absolute Spectral Power and Mean Frequency Analysis

    PubMed Central

    Wix-Ramos, Richard; Moreno, Xiomara; Capote, Eduardo; González, Gilbert; Uribe, Ezequiel

    2014-01-01

    Objective Research of electroencephalograph (EEG) power spectrum and mean frequency has shown inconsistent results in patients with schizophrenic, schizoaffective and bipolar disorders during medication when compared to normal subjects thus; the characterization of these parameters is an important task. Methods We applied quantitative EEG (qEEG) to investigate 38 control, 15 schizophrenic, 7 schizoaffective and 11 bipolar disorder subjects which remaine under the administration of psychotropic drugs (except control group). Absolute spectral power (ASP), mean frequency and hemispheric electrical asymmetry were measured by 19 derivation qEEG. Group mean values were compared with non parametrical Mann-Whitney test and spectral EEG maps with z-score method at p < 0.05. Results Most frequent drug treatments for schizophrenic patients were neuroleptic+antiepileptic (40% of cases) or 2 neuroleptics (33.3%). Schizoaffective patients received neuroleptic+benzodiazepine (71.4%) and for bipolar disorder patients neuroleptic+antiepileptic (81.8%). Schizophrenic (at all derivations except for Fp1, Fp2, F8 and T6) and schizoaffective (only at C3) show higher values of ASP (+57.7% and +86.1% respectively) compared to control group. ASP of bipolar disorder patients did not show differences against control group. The mean frequency was higher at Fp1 (+14.2%) and Fp2 (+17.4%) in bipolar disorder patients than control group, but no differences were found in frequencies between schizophrenic or schizoaffective patients against the control group. Majority of spectral differences were found at the left hemisphere in schizophrenic and schizoaffective but not in bipolar disorder subjects. Conclusion The present report contributes to characterize quantitatively the qEEG in drug treated schizophrenic, schizoaffective or bipolar disorder patients. PMID:24851121

  3. Confocal Fabry-Perot interferometer for frequency stabilization of laser

    NASA Astrophysics Data System (ADS)

    Pan, H.-J.; Ruan, P.; Wang, H.-W.; Li, F.

    2011-02-01

    The frequency shift of laser source of Doppler lidar is required in the range of a few megahertzs. To satisfy this demand, a confocal Fabry-Perot (F-P) interferometer was manufactured as the frequency standard for frequency stabilization. After analyzing and contrasting the center frequency shift of confocal Fabry-Perot interferometers that are made of three different types of material with the change of temperature, the zerodur material was selected to fabricate the interferometer, and the cavity mirrors were optically contacted onto the end of spacer. The confocal Fabry-Perot interferometer was situated within a double-walled chamber, and the change of temperature in the chamber was less than 0.01 K. The experimental results indicate that the free spectral range is 500 MHz, the full-width at half maximum is 3.33 MHz, and the finesse is 150.

  4. Low Frequency Vibration Energy Harvesting using Diamagnetically Stabilized Magnet Levitation

    NASA Astrophysics Data System (ADS)

    Palagummi, Sri Vikram

    Over the last decade, vibration-based energy harvesting has provided a technology push on the feasibility of self-powered portable small electronic devices and wireless sensor nodes. Vibration energy harvesters in general transduce energy by damping out the environmentally induced relative emotion through either a cantilever beam or an equivalent suspension mechanism with one of the transduction mechanisms, like, piezoelectric, electrostatic, electromagnetic or magnetostrictive. Two major challenges face the present harvesters in literature, one, they suffer from the unavoidable mechanical damping due to internal friction present in the systems, second, they cannot operate efficiently in the low frequency range (< 10 Hz), when most of the ambient vibrational energy is in this low frequency broadband range. Passive and friction free diamagnetically stabilized magnet levitation mechanisms which can work efficiently as a vibration energy harvester in the low frequency range are discussed in this work. First, a mono-stable vertical diamagnetic levitation (VDL) based vibration energy harvester (VEH) is discussed. The harvester consists of a lifting magnet (LM), a floating magnet (FM) and two diamagnetic plates (DPs). The LM balances out the weight of the FM and stability is brought about by the repulsive effect of the DPs, made of pyrolytic graphite. Two thick cylindrical coils, placed in grooves which are engraved in the DPs, are used to convert the mechanical energy into electrical energy. Experimental frequency response of the system is validated by the theoretical analysis which showed that the VEH works in a low frequency range but sufficient levitation gap was not achieved and the frequency response characteristic of the system was effectively linear. To overcome these challenges, the influence of the geometry of the FM, the LM, and the DP were parametrically studied to assess their effects on the levitation gap, size of the system and the natural frequency. For

  5. Frequency stabilized near-IR laser system for optical communications

    NASA Astrophysics Data System (ADS)

    Růžička, B.; Číp, O.; Lazar, J.

    2005-08-01

    We present a design of a stabilized laser system, an etalon of the optical frequency at the 1.5 μm band following the demands of the telecommunication industry in the Czech Republic. Our laser system employs a DFB laser diode in a two stage stabilizing scheme. The linear absorption arrangement with an acetylene filled absorption cell of a pressure about 1 kPa is used to lock the laser to the Doppler-broadened lines. To achieve a reliable and robust stabilization of the laser frequency we arranged a two-loop digital servo-system overcoming the problem of a narrow locking range of the detected transition. The wavelength of the laser is modulated by current and the servo-control and tuning is performed by a fast and precise thermal control. To achieve the resolution of the weak sub-Doppler transitions we assembled a locking scheme via frequency-modulation spectroscopy to the high finesse cavity. The system is assembled using predominantly fibre-optic components. A technology of acetylene absorption cells with AR coated windows is presented as well.

  6. B-chromosome frequency stability in Prochilodus lineatus (Characiformes, Prochilodontidae).

    PubMed

    Voltolin, Tatiana Aparecida; Senhorini, José Augusto; Oliveira, Claudio; Foresti, Fausto; Bortolozzi, Jehud; Porto-Foresti, Fabio

    2010-03-01

    The genus Prochilodus includes individuals ranging in size from medium to large, being highly relevant for commercial and subsistence fishing. Prochilodus species have a diploid number of 2n = 54 chromosomes and up to seven supernumerary (B) microchromosomes. Previous research has shown that B frequency increased drastically in the Mogi-Guaçu river population of Prochilodus lineatus in the early 1980s, whereas it remained about constant in the 1990s. Here we analyses B frequency in this population during the 2003-2007 period and have found that frequency has not changed significantly since 1987, and that these B chromosomes do not show the intra-individual variation in number that characterized them in the 1980s. This indicates that these B chromosomes have been neutralized, after their invasion, through their mitotic stabilization. PMID:19882308

  7. Laser frequency stabilization using folded cavity and mirror reflectivity tuning

    NASA Astrophysics Data System (ADS)

    Liu, X.; Cassou, K.; Chiche, R.; Dupraz, K.; Favier, P.; Flaminio, R.; Honda, Y.; Huang, W. H.; Martens, A.; Michel, C.; Pinard, L.; Sassolas, B.; Soskov, V.; Tang, C. X.; Zomer, F.

    2016-06-01

    A new method of laser frequency stabilization using polarization property of an optical cavity is proposed. In a standard Fabry-Perot cavity, the coating layers thickness of cavity mirrors is calculated to obtain the same phase shift for s- and p-wave but a slight detuning from the nominal thickness can produce s- and p-wave phase detuning. As a result, each wave accumulates a different round-trip phase shift and resonates at a different frequency. Using this polarization property, an error signal is generated by a simple setup consisting of a quarter wave-plate rotated at 45°, a polarizing beam splitter and two photodiodes. This method exhibits similar error signal as the Pound-Drever-Hall technique but without need for any frequency modulation. Lock theory and experimental results are presented in this paper.

  8. Frequency stabilization of diode-laser-pumped solid state lasers

    NASA Technical Reports Server (NTRS)

    Byer, Robert L.

    1988-01-01

    The goal of the NASA Sunlite program is to fly two diode-laser-pumped solid-state lasers on the space shuttle and while doing so to perform a measurement of their frequency stability and temporal coherence. These measurements will be made by combining the outputs of the two lasers on an optical radiation detector and spectrally analyzing the beat note. Diode-laser-pumped solid-state lasers have several characteristics that will make them useful in space borne experiments. First, this laser has high electrical efficiency. Second, it is of a technology that enables scaling to higher powers in the future. Third, the laser can be made extremely reliable, which is crucial for many space based applications. Fourth, they are frequency and amplitude stable and have high temporal coherence. Diode-laser-pumped solid-state lasers are inherently efficient. Recent results have shown 59 percent slope efficiency for a diode-laser-pumped solid-state laser. As for reliability, the laser proposed should be capable of continuous operation. This is possible because the diode lasers can be remote from the solid state gain medium by coupling through optical fibers. Diode lasers are constructed with optical detectors for monitoring their output power built into their mounting case. A computer can actively monitor the output of each diode laser. If it sees any variation in the output power that might indicate a problem, the computer can turn off that diode laser and turn on a backup diode laser. As for stability requirements, it is now generally believed that any laser can be stabilized if the laser has a frequency actuator capable of tuning the laser frequency as far as it is likely to drift in a measurement time.

  9. Absolute and relative emission spectroscopy study of 3 cm wide planar radio frequency atmospheric pressure bio-plasma source

    NASA Astrophysics Data System (ADS)

    Deng, Xiaolong; Nikiforov, Anton Yu; Ionita, Eusebiu-Rosini; Dinescu, Gheorghe; Leys, Christophe

    2015-08-01

    The dynamics of low power atmospheric pressure radio frequency discharge generated in Ar gas in long gap of 3 cm is investigated. This plasma source is characterized and analyzed for possible large scale biomedical applications where low gas temperature and potential-less effluent are required. The discharge forms a homogenous glow-like afterglow in ambient air at input power of 30 W with low gas temperature of 330 K, which is desirable in biomedical applications. With absolute calibrated spectroscopy of the discharge, electron density of 0.4 × 1018 m-3 and electron temperature of 1.5 eV are obtained from continuum Bremsstrahlung radiation of the source. Time and spatial resolved emission spectroscopy is used to analyze discharge generation mechanism and active species formation. It is found that discharge dynamics strongly correlates with the discharge current waveform. Strong Ar(2p) excited states emission is observed nearby the electrodes surface on a distance up to 200 μm in the plasma sheath region at 10 ns after the current peak, whereas OH(A) emission is uniform along of the interelectrode gap.

  10. Nonlinear Trivelpiece-Gould Waves: Frequency, Functional Form, and Stability

    NASA Astrophysics Data System (ADS)

    Dubin, Daniel H. E.

    2015-11-01

    This poster considers the frequency, spatial form, and stability, of nonlinear Trivelpiece- Gould (TG) waves on a cylindrical plasma column of length L and radius rp, treating both traveling and standing waves, and focussing on the regime of experimental interest in which L/rp >> 1. In this regime TG waves are weakly dispersive, allowing strong mode-coupling between Fourier harmonics. The mode coupling implies that linear theory for such waves is a poor approximation even at fairly small amplitudes, and nonlinear theories that include only a small number of harmonics (such as 3-wave parametric resonance theory) fail to fully capture the stability properties of the system. We find that nonlinear standing waves suffer jumps in their functional form as their amplitude is varied continuously. The jumps are caused by nonlinear resonances between the standing wave and nearly linear waves whose frequencies and wave numbers are harmonics of the standing wave. Also, the standing waves are found to be unstable to a multi-wave version of 3-wave parametric resonance, with an amplitude required for instability onset that is much larger than expected from three wave theory. For traveling wave, linearly stability is found for all amplitudes that could be studied, in contradiction to 3-wave theory. Supported by National Science Foundation Grant PHY-1414570, Department of Energy Grants DE-SC0002451and DE-SC0008693.

  11. Easy Absolute Values? Absolutely

    ERIC Educational Resources Information Center

    Taylor, Sharon E.; Mittag, Kathleen Cage

    2015-01-01

    The authors teach a problem-solving course for preservice middle-grades education majors that includes concepts dealing with absolute-value computations, equations, and inequalities. Many of these students like mathematics and plan to teach it, so they are adept at symbolic manipulations. Getting them to think differently about a concept that they…

  12. Heterodyne laser frequency stabilization for long baseline optical interferometry in space-based gravitational wave detectors

    NASA Astrophysics Data System (ADS)

    Eichholz, Johannes; Tanner, David B.; Mueller, Guido

    2015-07-01

    The European Space Agency (ESA) selected the gravitational universe as the science theme for L3, a large space mission with a planned launch in 2034. NASA expressed a strong interest in joining ESA as a junior partner. The goal of the mission is the detection of gravitational waves of frequencies between 0.1 mHz and 0.1 Hz, where many long-lived sources are expected to be steady emitters of gravitational waves. Most likely, the mission design will evolve out of the earlier Laser Interferometer Space Antenna (LISA) concept. The interferometric heterodyne phase readout in LISA is performed by phase meters developed specifically to handle the low light powers and Doppler-drift of laser frequencies that appear as complications in the mission baseline. LISA requires the frequency noise of its seed lasers to be below 300 Hz /√{Hz } throughout the measurement band due to uncertainties in the absolute interferometer arm lengths. We have developed and successfully demonstrated Heterodyne Stabilization (HS), a novel cavity-laser frequency stabilization method that integrates well into the LISA mission baseline due to similar component demand. The cavities for the test setup were assembled with Clearceram-Z spacers, an ultralow thermal expansion coefficient material with potential applicability in interferometric space missions. Using HS, we were able to suppress the frequency noise of two lasers in a bench-top experiment to a level that meets the LISA requirement, suggesting both HS and Clearceram-Z can be considered in future mission concepts.

  13. Characterizing DSN System Frequency Stability with Spacecraft Tracking Data

    NASA Technical Reports Server (NTRS)

    Pham, T.; Machuzak, R.; Bedrossian, A.

    2010-01-01

    This paper describes a recent effort in characterizing frequency stability performance of the ground system in the NASA Deep Space Network (DSN). Unlike the traditional approach where performance is obtained from special calibration sessions that are both time consuming and require manual setup, the new method taps into the daily spacecraft tracking data. This method significantly increases the amount of data available for analysis, roughly by two orders of magnitude; making it possible to conduct trend analysis with reasonable confidence. Since the system is monitored daily, any significant variation in performance can be detected timely. This helps the DSN maintain its performance commitment to customers.

  14. Frequency stabilization in nonlinear MEMS and NEMS oscillators

    SciTech Connect

    Lopez, Omar Daniel; Antonio, Dario

    2014-09-16

    An illustrative system includes an amplifier operably connected to a phase shifter. The amplifier is configured to amplify a voltage from an oscillator. The phase shifter is operably connected to a driving amplitude control, wherein the phase shifter is configured to phase shift the amplified voltage and is configured to set an amplitude of the phase shifted voltage. The oscillator is operably connected to the driving amplitude control. The phase shifted voltage drives the oscillator. The oscillator is at an internal resonance condition, based at least on the amplitude of the phase shifted voltage, that stabilizes frequency oscillations in the oscillator.

  15. Dynamics of microresonator frequency comb generation: models and stability

    NASA Astrophysics Data System (ADS)

    Hansson, Tobias; Wabnitz, Stefan

    2016-06-01

    Microresonator frequency combs hold promise for enabling a new class of light sources that are simultaneously both broadband and coherent, and that could allow for a profusion of potential applications. In this article, we review various theoretical models for describing the temporal dynamics and formation of optical frequency combs. These models form the basis for performing numerical simulations that can be used in order to better understand the comb generation process, for example helping to identify the universal combcharacteristics and their different associated physical phenomena. Moreover, models allow for the study, design and optimization of comb properties prior to the fabrication of actual devices. We consider and derive theoretical formalisms based on the Ikeda map, the modal expansion approach, and the Lugiato-Lefever equation. We further discuss the generation of frequency combs in silicon resonators featuring multiphoton absorption and free-carrier effects. Additionally, we review comb stability properties and consider the role of modulational instability as well as of parametric instabilities due to the boundary conditions of the cavity. These instability mechanisms are the basis for comprehending the process of frequency comb formation, for identifying the different dynamical regimes and the associated dependence on the comb parameters. Finally, we also discuss the phenomena of continuous wave bi- and multistability and its relation to the observation of mode-locked cavity solitons.

  16. Frequency stability of maser oscillators operated with cavity Q. [hydrogen and rubidium masers

    NASA Technical Reports Server (NTRS)

    Tetu, M.; Tremblay, P.; Lesage, P.; Petit, P.; Audoin, C.

    1982-01-01

    The short term frequency stability of masers equipped with an external feedback loop to increase the cavity quality factor was studied. The frequency stability of a hydrogen and a rubidium maser were measured and compared with theoretical evaluation. It is shown that the frequency stability passes through an optimum when the cavity Q is varied. Long term fluctuations are discussed and the optimum mid term frequency stability achievably by small size active and passive H-masers is considered.

  17. Earth Observing-1 Advanced Land Imager Flight Performance Assessment: Absolute Radiometry and Stability During the First Year

    NASA Technical Reports Server (NTRS)

    Mendenhall, J. A.; Lencioni, D. E.

    2002-01-01

    The absolute radiometry of the Advanced Land Imager during the first year on orbit (November 21,2000 - November 21, 2001) is presented. Results derived from solar, lunar, ground truth, and internal reference lamp measurements are presented. An 18% drop in the radiometric response of the Band 1p data since preflight calibration at Lincoln Laboratory is observed using all techniques. This decrease cannot be accounted for by preflight calibration errors, stray light, or contamination of the focal plane. A slight drooping of the VNIR response toward the blue and a 5-12% increase in the Band 5 response is also apparent in all the data. Radiometric response correction factors have been calculated and preflight calibration coefficients have been updated in order to provide +/- 5% agreement between the measured solar, lunar, and ground truth data and the expected values. The radiometric stability of the ALI during the first year of operation is also presented for each spectral band. Internal reference lamp data indicate the focal plane has been stable to within 1% for bands 1p, 1, 2, 5p, 5, 7, pan and 3% for Bands 3,4, 4p since launch. Solar, lunar, and ground truth measurements indicate the optical train and solar diffuser of the instrument has been stable to within 1% since initial measurements on orbit in late December 2000.

  18. Spiral resonators for on-chip laser frequency stabilization

    NASA Astrophysics Data System (ADS)

    Lee, Hansuek; Suh, Myoung-Gyun; Chen, Tong; Li, Jiang; Diddams, Scott A.; Vahala, Kerry J.

    2013-09-01

    Frequency references are indispensable to radio, microwave and time keeping systems, with far reaching applications in navigation, communication, remote sensing and basic science. Over the past decade, there has been an optical revolution in time keeping and microwave generation that promises to ultimately impact all of these areas. Indeed, the most precise clocks and lowest noise microwave signals are now based on a laser with short-term stability derived from a reference cavity. In spite of the tremendous progress, these systems remain essentially laboratory devices and there is interest in their miniaturization, even towards on-chip systems. Here we describe a chip-based optical reference cavity that uses spatial averaging of thermorefractive noise to enhance resonator stability. Stabilized fibre lasers exhibit relative Allan deviation of 3.9 × 10-13 at 400 μs averaging time and an effective linewidth <100 Hz by achieving over 26 dB of phase-noise reduction.

  19. Spiral resonators for on-chip laser frequency stabilization

    PubMed Central

    Lee, Hansuek; Suh, Myoung-Gyun; Chen, Tong; Li, Jiang; Diddams, Scott A.; Vahala, Kerry J.

    2013-01-01

    Frequency references are indispensable to radio, microwave and time keeping systems, with far reaching applications in navigation, communication, remote sensing and basic science. Over the past decade, there has been an optical revolution in time keeping and microwave generation that promises to ultimately impact all of these areas. Indeed, the most precise clocks and lowest noise microwave signals are now based on a laser with short-term stability derived from a reference cavity. In spite of the tremendous progress, these systems remain essentially laboratory devices and there is interest in their miniaturization, even towards on-chip systems. Here we describe a chip-based optical reference cavity that uses spatial averaging of thermorefractive noise to enhance resonator stability. Stabilized fibre lasers exhibit relative Allan deviation of 3.9 × 10−13 at 400 μs averaging time and an effective linewidth <100 Hz by achieving over 26 dB of phase-noise reduction. PMID:24043134

  20. Design of Pound-Drever-Hall laser frequency stabilization system without phase shifter

    NASA Astrophysics Data System (ADS)

    Su, Juan; Jiao, Mingxing; Xing, Junhong; Li, Zhe

    2015-02-01

    The Pound-Drever-Hall (PDH) laser frequency stabilization is a wide spread adopted technique for narrow linewidth and ultra-stable lasers, and a phase shifter is an important part in a traditional PDH frequency stabilization system. A PDH laser frequency stabilization system without phase shifter was proposed, in which quadrature coherent detection method was used to extract the frequency drifts. Orthogonal reference signals are generated using direct digital frequency synthesizer (DDS) and mixed with the output of a photo-detector. Over-sampling technique and cumulative average algorithm were used to improve the detection resolution and SNR, orthogonal phase sensitive detection algorithm was adopted to obtain the frequency drifts. Both the quadrature demodulation system structure and the signal processing methods were adopted, the systematic detection error is reduced, the anti-noise performance is raised and long term frequency stability is improved with the PDH laser frequency stabilization system without phase shifter.

  1. Developing Stabilized Lasers, Measuring their Frequencies, demoting the Metre, inventing the Comb, and further consequences

    NASA Astrophysics Data System (ADS)

    Hall, John L.

    2010-02-01

    Michelson's 1907 proposal to define the SI Metre in terms of an optical wavelength was realized only in 1960, based on a ^86Krypton discharge lamp. The same year saw the cw HeNe laser arrive and a future redefinition based on laser technology assured. Separation in the late 60's of the laser's gain and spectral-reference-gas functions led to unprecedented levels of laser frequency stability and reproducibility. In addition to HeNe:CH4 system at 3392 nm and HeNe:I2 at 633 nm, systems at 514 nm and 10600 nm were studied. Absolute frequency measurement became the holy grail and some NBS team experiences will be shared. We measured both frequency and wavelength in 1972, and so obtained a speed of light value, improved 100-fold in accuracy. During the next decade, the NBS value of c was confirmed by other national labs, and frequency metrology was extended to the 473 THz (633 nm) Iodine-based wavelength standard. This frequency to ˜10 digit accuracy was obtained in 1983, thus setting the stage for redefining the SI Metre. By consensus choice the value 299 792 458 m/s was adopted for the speed of light, effectively reducing the Metre to a derived SI quantity. Knowledge of the frequency of the particular laser being utilized was controlled by International intercomparisons, but the need for a fast and accurate means to make these laser frequency measurements was obvious. Creative proposals by H"ansch and by Chebotayev were to use ultra-fast repetitive pulses to create an ``Optical Comb,'' but it was years before any technical basis existed to implement their Fourier dreams. Finally, in 1999 the last needed capability was demonstrated -- continuum production at 100 MHz rates and non-destructive power levels. By May 2000 phase-locked combs were operational in both Garching and Boulder, substantially accelerated by their collaborative interactions. Within 18 months all the known proposed ``optical frequency standards'' had been accurately measured via Comb techniques. )

  2. Measurement of carrier envelope offset frequency for a 10 GHz etalon-stabilized semiconductor optical frequency comb

    NASA Astrophysics Data System (ADS)

    Akbulut, M.; Davila-Rodriguez, J.; Ozdur, I.; Quinlan, F.; Ozharar, S.; Hoghooghi, N.; Delfyett, P. J.

    2011-08-01

    We report Carrier Envelope Offset (CEO) frequency measurements of a 10 GHz harmonically mode-locked, Fabry-Perot etalon-stabilized, semiconductor optical frequency comb source. A modified multi-heterodyne mixing technique with a reference frequency comb was utilized for the measurement. Also, preliminary results from an attempt at f-2f self-referencing measurement are presented. The CEO frequency was found to be ~1.47 GHz for the particular etalon that was used.

  3. Frequency conversion in field stabilization system for application in SC cavity of linear accelerator

    NASA Astrophysics Data System (ADS)

    Filipek, Tomasz A.

    2005-09-01

    The paper concerns frequency conversion circuits of electromagnetic field stabilization system in superconductive cavity of linear accelerator. The stabilization system consists of digital part (based on FPGA) and analog part (frequency conversions, ADC/DAC, filters). Frequency conversion circuit is analyzed. The main problem in the frequency conversion for the stabilization system are: linearity of conversion and stability. Also, second order problems are subject of analysis: control of local oscillator parameters and fluctuation of actuated signal (exposing conversion). The following work was done: analysis of individual stage parameters on field stability and external influence, simulation. The work was closed with conclusions of the major frequency conversion parameters for field stabilization. The results have been applied for field stabilization system (RF Feedback System) in TESLA Test Facility 2 and preliminary research on X-Ray Free Electron Laser.

  4. Absolute frequency measurement of the ^1S0<->^3P0 clock transition at 578.4 nm in ytterbium

    NASA Astrophysics Data System (ADS)

    Hoyt, Chad; Barber, Zeb; Oates, Chris; Fortier, Tara; Diddams, Scott

    2005-05-01

    We report the first precision absolute frequency measurements of the highly forbidden (6s^2)^1S0<->(6s6p)^3P0 optical clock transition at 578.4 nm in two odd isotopes of ytterbium. Atoms are cooled to tens of microkelvins in two successive stages of laser cooling and magneto-optical trapping that use transitions at 398.9 nm and 555.8 nm, respectively. The resulting trapped atomic cloud is irradiated with excitation light at 578.4 nm and absorption is detected by monitoring trapped atom depletion. With the laser on resonance, we demonstrate trap depletions of more than 80 % relative to the off-resonance case. Absolute frequency measurements are made for ^171Yb (I=1/2) and ^173Yb (I=5/2) with an uncertainty of 4.4 kHz using a femtosecond-laser frequency comb calibrated by the NIST cesium fountain clock. The natural linewidth of these J=0 to J=0 transitions is ˜10 mHz, making them well-suited to support a new generation of optical atomic clocks based on confinement in an optical lattice. Lattice-based optical clocks have the potential to surpass the performance of the best current atomic clocks by orders of magnitude. The accurate ytterbium frequency knowledge presented here (nearly a million-fold reduction in uncertainty) will greatly expedite Doppler- and recoil-free lattice spectroscopy.

  5. Absolute frequency and isotope shift of the magnesium (3 s2) 1S0→(3 s 3 d ) 1D2 two-photon transition by direct frequency-comb spectroscopy

    NASA Astrophysics Data System (ADS)

    Peters, E.; Reinhardt, S.; Hänsch, Th. W.; Udem, Th.

    2015-12-01

    We use a picosecond frequency-doubled mode-locked titanium sapphire laser to generate a frequency comb at 431 nm in order to probe the (3 s2) 1S0 →(3 s 3 d ) 1D2 transition in atomic magnesium. Using a second, self-referenced femtosecond frequency comb, the absolute transition frequency and the 24Mg and 26Mg isotope shift is determined relative to a global-positioning-system-referenced hydrogen maser. Our result for the transition frequency of the main isotope 24Mg of 1 391 128 606.14 (12 ) MHz agrees with previous measurements and reduces its uncertainty by four orders of magnitude. For the isotope shift we find δ ν26 ,24=3915.13 (39 ) MHz. Accurate values for transition frequencies in Mg are relevant in astrophysics and to test atomic structure calculations.

  6. Optical Frequency Metrology of an Iodine-Stabilized He-Ne Laser Using the Frequency Comb of a Quantum-Interference-Stabilized Mode-Locked Laser

    PubMed Central

    Smith, Ryan P.; Roos, Peter A.; Wahlstrand, Jared K.; Pipis, Jessica A.; Rivas, Maria Belmonte; Cundiff, Steven T.

    2007-01-01

    We perform optical frequency metrology of an iodine-stabilized He-Ne laser using a mode-locked Ti:sapphire laser frequency comb that is stabilized using quantum interference of photocurrents in a semiconductor. Using this technique, we demonstrate carrier-envelope offset frequency fluctuations of less than 5 mHz using a 1 s gate time. With the resulting stable frequency comb, we measure the optical frequency of the iodine transition [127I2 R(127) 11-5 i component] to be 473 612 214 712.96 ± 0.66 kHz, well within the uncertainty of the CIPM recommended value. The stability of the quantum interference technique is high enough such that it does not limit the measurements. PMID:27110472

  7. Frequency Stabilization of High-Power 3.3 μm CW Laser with a Frequency Comb System

    NASA Astrophysics Data System (ADS)

    Kuma, Susumu; Momose, Takamasa

    2010-06-01

    %TEXT OF YOUR ABSTRACT The development of optical frequency combs has enabled a broad range of lasers to be stabilized. In this study, we have developed a system to stabilize high-power CW mid-infrared (MIR) radiation at 3.3 μm using a NIR-VIS frequency comb. The mid-infrared radiation at 3.3 μm were generated as an idler of a CW OPO laser pumped by a 1.064 μm fibre laser. To stabilize the MIR radiation with a frequency comb system in 450 nm to 1.25 μm range, the pump frequency at 1.064 μm and the sum frequency of the MIR radiation and the pump radiation were locked simultaneously to the comb laser. The sum frequency of the MIR and pump radiations was generated in a PPLN crystal. With this technique, we have successfully obtained a width of better than 50 kHz at 3.3 μm with a power of more than 1 W. The stability is currently limited by the response of the PZT in an OPO cavity. Further improvement is underway. The stabilized MIR radiation at 3.3 μm can be used as a source for ultra-high-resolution spectroscopy of vibration-rotation transitions of molecules. Especially, it may be used to decrease the frequency uncertainty of the ν_3 F_2(2) component of the P(7) transition of CH_4, which is one of the optical frequency standards recommended by CIPM. Another application of frequency stabilized MIR radiation is to build-up MIR radiation in a cavity for optical manipulation and trapping of cold molecules we have proposed in New. J. Phys. 11. 055023 (2009).

  8. The JPL Hg(sup +) Extended Linear Ion Trap Frequency Standard: Status, Stability, and Accuracy Prospects

    NASA Technical Reports Server (NTRS)

    Tjoelker, R. L.; Prestage, J. D.; Maleki, L.

    1996-01-01

    Microwave frequency standards based on room temperature (sup 199)Hg(sup +) ions in a Linear Ion Trap (LITS) presently achieve a Signal to Noise and line Q inferred short frequency stability. Long term stability has been measured for averaging intervals up to 5 months with apparent sensitivity to variations in ion number/temperature limiting the flicker floor.

  9. Enabling coherent control of trapped ions with economical multi-laser frequency stabilization technology

    NASA Astrophysics Data System (ADS)

    Lybarger, Warren Emanuel, Jr.

    A phase-locked scanning stability transfer cavity (SSTC) for transferring the absolute frequency stability of an iodine referenced He-Ne (master) laser to three otherwise uncalibrated (slave) lasers (at 844, 1033, & 1092 nm) of a trapped-Sr+ quantum information processing (QIP) apparatus is described. When locked, the 422 nm frequency-doubled Doppler-cooling laser exhibits an error of <1 MHz RMS for several hours, and similar stability is achieved with the other slave lasers. When unlocked, each slave laser drifts by a large fraction (or more) of the corresponding transition linewidth in minutes, thus making reliable laser cooling, ion state readout, and execution of QIP algorithms practically infeasible. The SSTC makes coherent control of Sr+ possible by addressing this problem, and the QIP apparatus is now sufficiently stable for single user operation. New single-ion experimental capabilities include ground state cooling, high-fidelity Rabi flopping, Ramsey interferometry, and sympathetic cooling of 88Sr+( 86Sr+) with 86Sr+( 88Sr+). A 2.5 msec coherence time has been achieved with the optical quoit encoded in a |5 2S 1/2> ↔ |4 2D5/2> quadrupole transition, a precision measurement of the isotope shift of the qubit transition in 86Sr+ relative to 88Sr+ is reported, and a single-ion heating rate consistent with results throughout the trapped-ion community is reported. The SSTC is simple to implement, uses no custom optics, and it has a higher scanning rate than previously demonstrated SSTC's. Phase-locked SSTC's are shown to have an advantage over the more common displacement-locked SSTC in the low finesse regime, and they are an attractive alternative to passively stable but complex optical references and diode lasers designed to address the same problem. The SSTC is useful in spectroscopic applications with other ion species, atoms, and molecules, in general. An appendix is dedicated to describing in detail an advanced trapped-ion quantum processor concept

  10. Effects of increased anterior-posterior voluntary sway frequency on mechanical and perceived postural stability.

    PubMed

    Martin Lorenzo, Teresa; Vanrenterghem, Jos

    2015-02-01

    Despite a substantial number of studies, the interaction between mechanical indicators of stability and perception of instability remains unclear. The purpose of this study was to determine the effect of sway frequency and verbal restraint on mechanical and perceived postural stability. Fourteen participants underwent a series of standing voluntary anterior-posterior swaying trials at three frequencies (20, 40, and 60bpm) and two levels of restraint (non restraint and verbally restraint to swaying at the ankle). Repeated measures ANOVA tests revealed greater mechanical stability defined though the margin of stability, and greater horizontal ground reaction forces, while the center of pressure excursions remained unchanged with increasing frequency. Furthermore, ground reaction forces were greater in the non-restraint condition. Moreover, a tendency toward greater perceived instability with increasing voluntary sway frequency was observed. Our results indicate that variations in sway frequency and verbal restraint resulted in noticeable alterations in mechanical indicators of stability, with no clear effect on perceived instability. PMID:25498287

  11. Diode laser frequency stabilization using a low cost, low finesse Fabry-Perot cavity

    NASA Astrophysics Data System (ADS)

    Hastings, Hannah; Jaber, Noura B.; Piatt, Georgia; Gregoric, Vincent C.; Carroll, Thomas J.; Noel, Michael W.

    2016-05-01

    Our lab employs low cost, low finesse Fabry-Perot cavities to stabilize the frequency of diode lasers used in ultra-cold Rydberg atom experiments. To characterize the stability of this technique, we perform a self-heterodyne linewidth measurement. For comparison, we also measure the linewidth when using a saturated absorption spectrometer to provide frequency stability. This work is supported by the National Science Foundation under Grants No. 1205895 and No. 1205897.

  12. Frequency-Tunable Pre-stabilized lasers for LISA via Stabilized Lasers for LISA via Sideband Locking

    NASA Technical Reports Server (NTRS)

    Livas, Jeffrey; Thorpe, James Ira; Numata, K.

    2008-01-01

    This viewgraph presentation discusses a major potential source of noise for the Laser Interferometer Space Antenna (LISA) that is the laser frequency noise and the proposed mechanism to suppress the unstabilized frequency fluctuations. These fluctuations must be suppresed by about 12 orders of magnitude to achieve a stability that is sufficient for the detection of gravitational waves. This presentation reviews present a modification to the traditional cavity locking technique that allows the laser to be locked to a cavity resonance with an adjustable frequency offset. This presentation also discusses measurements of the system stability, demonstrating that the pre-stabilization level satisfies LISA requirements and a demonstration of a phase-lock loop which utilizes the tunable sideband locking technique as a pre-stabilization stage.

  13. Observation and absolute frequency measurements of the 1S0-3P0 optical clock transition in neutral ytterbium.

    PubMed

    Hoyt, C W; Barber, Z W; Oates, C W; Fortier, T M; Diddams, S A; Hollberg, L

    2005-08-19

    We report the direct excitation of the highly forbidden (6s2) 1S0 <--> (6s6p) 3P0 optical transition in two odd isotopes of neutral ytterbium. As the excitation laser frequency is scanned, absorption is detected by monitoring the depletion from an atomic cloud at approximately 70 microK in a magneto-optical trap. The measured frequency in 171Yb (F=1/2) is 518,295,836,591.6 +/- 4.4 kHz. The measured frequency in 173Yb (F=5/2) is 518,294,576,847.6 +/- 4.4 kHz. Measurements are made with a femtosecond-laser frequency comb calibrated by the National Institute of Standards and Technology cesium fountain clock and represent nearly a 10(6)-fold reduction in uncertainty. The natural linewidth of these J=0 to J=0 transitions is calculated to be approximately 10 mHz, making them well suited to support a new generation of optical atomic clocks based on confinement in an optical lattice. PMID:16196856

  14. Absolute optical frequency measurements of the cesium D1 transitions and their effect on alpha, the fine-structured constant

    NASA Astrophysics Data System (ADS)

    Calkins, Keith Gordon

    The fine-structure constant or electromagnetic coupling constant, alpha e, is a dimensionless ratio which unites many physics subfields. Although known precisely via experiments in each subfield, there is disagreement within and between subfields. In particular, precise values obtained via electron ge - 2 experiments which depend heavily on QED calculations have not always been in agreement with those obtained via muon g mu - 2 experiments. Also, solid state measurements (quantum hall effect and AC Josephson effect) often disagree with neutronic hmn measurements. alphae is often said to vary with energy but the question remains as to whether or not its low energy value is stable now or has been stable over the history of the universe. Improved precision helps resolve these issues as they relate to physics, possibly beyond the standard model. The Optical Frequency Measurements group in the Time and Frequency Division at the National Institute of Science and Technology (NIST, Boulder, CO) developed and maintains a femtosecond laser frequency comb which is calibrated with respect to the cesium fountain clock implementation of the second. A single frequency component of the femtosecond laser comb is used together with a solid state diode laser and cesium thermal beam to precisely measure the cesium D1 F ∈ {3,4} transition frequencies. The value of fD1centroid = 335 116 048 748.1(2.4) kHz obtained for the transition centroid is over fifteen times more precise than the most recent previous measurement. A precise value for the cesium D1 hyperfine splitting fHFe = 1 167 723.6(4.7) kHz is reported as well. This value is also over fifteen times more precise than the most recent previous measurement. These new neutral 133Cs 6s 2 S½ → 6p 2 P½ transition (D1) frequencies, when combined with the 2002 CODATA values of the Rydberg, proton/electron mass ratio, cesium atomic mass, and cesium recoil frequency, provide an almost QED-free value of alpha: alphae = 1/137.036 0000

  15. Sexual Frequency and the Stability of Marital and Cohabiting Unions

    ERIC Educational Resources Information Center

    Yabiku, Scott T.; Gager, Constance T.

    2009-01-01

    Prior research found that lower sexual frequency and satisfaction were associated with higher rates of divorce, but little research had examined the role of sexual activity in the dissolution of cohabiting unions. We drew upon social exchange theory to hypothesize why sexual frequency is more important in cohabitation: (a) cohabitors' lower costs…

  16. Stabilized frequency comb with a self-referenced femtosecond Cr:forsterite laser.

    PubMed

    Kim, K; Washburn, B R; Wilpers, G; Oates, C W; Hollberg, L; Newbury, N R; Diddams, S A; Nicholson, J W; Yan, M F

    2005-04-15

    A frequency comb is generated with a Cr:forsterite femtosecond laser, spectrally broadened through a highly nonlinear optical fiber to span from 1.0 to 2.2 ,m, and stabilized using the f-to-2f self-referencing technique. The repetition rate and the carrier-envelope offset frequency are stabilized to a hydrogen maser, calibrated by a cesium atomic fountain clock. Simultaneous frequency measurement of a 657-nm cw laser by use of the stabilized frequency combs from this Cr:forsterite system and a Ti:sapphire laser agree at the 10(-13) level. The frequency noise of the comb components is observed at 1064, 1314, and 1550 nm by comparing the measured beat frequencies between cw lasers and the supercontinuum frequency combs. PMID:15865403

  17. Phase Stabilization of a Frequency Comb using Multipulse Quantum Interferometry

    NASA Astrophysics Data System (ADS)

    Cadarso, Andrea; Mur-Petit, Jordi; García-Ripoll, Juan José

    2014-02-01

    From the interaction between a frequency comb and an atomic qubit, we derive quantum protocols for the determination of the carrier-envelope offset phase, using the qubit coherence as a reference, and without the need of frequency doubling or an octave spanning comb. Compared with a trivial interference protocol, the multipulse protocol results in a polynomial enhancement of the sensitivity O(N-2) with the number N of laser pulses involved. We specialize the protocols using optical or hyperfine qubits, Λ schemes, and Raman transitions, and introduce methods where the reference is another phase-stable cw laser or frequency comb.

  18. Phase stabilization of a frequency comb using multipulse quantum interferometry.

    PubMed

    Cadarso, Andrea; Mur-Petit, Jordi; García-Ripoll, Juan José

    2014-02-21

    From the interaction between a frequency comb and an atomic qubit, we derive quantum protocols for the determination of the carrier-envelope offset phase, using the qubit coherence as a reference, and without the need of frequency doubling or an octave spanning comb. Compared with a trivial interference protocol, the multipulse protocol results in a polynomial enhancement of the sensitivity O(N-2) with the number N of laser pulses involved. We specialize the protocols using optical or hyperfine qubits, Λ schemes, and Raman transitions, and introduce methods where the reference is another phase-stable cw laser or frequency comb. PMID:24579598

  19. Frequency-tunable Pre-stabilized Lasers for LISA via Sideband-locking

    NASA Technical Reports Server (NTRS)

    Livas, Jeffrey C.; Thorpe, James I.; Numata, Kenji; Mitryk, Shawn; Mueller, Guido; Wand, Vinzenz

    2008-01-01

    Laser frequency noise mitigation is one of the most challenging aspects of the LISA interferometric measurement system. The unstabilized frequency fluctuations must be suppressed by roughly twelve orders of magnitude in order to achieve stability sufficient for gravitational wave detection. This enormous suppression will be achieved through a combination of stabilization and common-mode rejection. The stabilization component will itself be achieved in two stages: pre-stabilization to a local optical cavity followed by arm-locking to some combination of the inter-spacecraft distances. In order for these two stabilization stages to work simultaneously, the lock-point of the pre-stabilization loop must be frequency tunable. The current baseline stabilization technique, locking to an optical cavity, does not provide tunability between cavity resonances, which are typically spaced by 100s of MHz. Here we present a modification to the traditional Pound-Drever-Hall cavity locking technique that allows the laser to be locked to a cavity resonance with an adjustable frequency offset. This technique requires no modifications to the optical cavity itself, thus preserving the stability of the frequency reference. We present measurements of the system performance and demonstrate that we can meet implement the first two stages of stabilization.

  20. A digital frequency stabilization system of external cavity diode laser based on LabVIEW FPGA

    NASA Astrophysics Data System (ADS)

    Liu, Zhuohuan; Hu, Zhaohui; Qi, Lu; Wang, Tao

    2015-10-01

    Frequency stabilization for external cavity diode laser has played an important role in physics research. Many laser frequency locking solutions have been proposed by researchers. Traditionally, the locking process was accomplished by analog system, which has fast feedback control response speed. However, analog system is susceptible to the effects of environment. In order to improve the automation level and reliability of the frequency stabilization system, we take a grating-feedback external cavity diode laser as the laser source and set up a digital frequency stabilization system based on National Instrument's FPGA (NI FPGA). The system consists of a saturated absorption frequency stabilization of beam path, a differential photoelectric detector, a NI FPGA board and a host computer. Many functions, such as piezoelectric transducer (PZT) sweeping, atomic saturation absorption signal acquisition, signal peak identification, error signal obtaining and laser PZT voltage feedback controlling, are totally completed by LabVIEW FPGA program. Compared with the analog system, the system built by the logic gate circuits, performs stable and reliable. User interface programmed by LabVIEW is friendly. Besides, benefited from the characteristics of reconfiguration, the LabVIEW program is good at transplanting in other NI FPGA boards. Most of all, the system periodically checks the error signal. Once the abnormal error signal is detected, FPGA will restart frequency stabilization process without manual control. Through detecting the fluctuation of error signal of the atomic saturation absorption spectrum line in the frequency locking state, we can infer that the laser frequency stability can reach 1MHz.

  1. System and method for tuning adjusting the central frequency of a laser while maintaining frequency stabilization to an external reference

    NASA Technical Reports Server (NTRS)

    Livas, Jeffrey (Inventor); Thorpe, James I. (Inventor); Numata, Kenji (Inventor)

    2011-01-01

    A method and system for stabilizing a laser to a frequency reference with an adjustable offset. The method locks a sideband signal generated by passing an incoming laser beam through the phase modulator to a frequency reference, and adjusts a carrier frequency relative to the locked sideband signal by changing a phase modulation frequency input to the phase modulator. The sideband signal can be a single sideband (SSB), dual sideband (DSB), or an electronic sideband (ESB) signal. Two separate electro-optic modulators can produce the DSB signal. The two electro-optic modulators can be a broadband modulator and a resonant modulator. With a DSB signal, the method can introduce two sinusoidal phase modulations at the phase modulator. With ESB signals, the method can further drive the optical phase modulator with an electrical signal with nominal frequency OMEGA(sub 1) that is phase modulated at a frequency OMEGA(sub 2)

  2. Photonic radio-frequency dissemination via optical fiber with high-phase stability.

    PubMed

    Wang, Xiaocheng; Liu, Zhangweiyi; Wang, Siwei; Sun, Dongning; Dong, Yi; Hu, Weisheng

    2015-06-01

    We demonstrate a photonic radio-frequency transmission system via optical fiber. Optical radio-frequency signal is generated utilizing a Mach-Zehnder modulator based on double-side-band with carrier suppression modulation scheme. The phase error induced by optical fiber transmission is transferred to an intermediate frequency signal by the dual-heterodyne phase error transfer scheme, and then canceled by a phase locked loop. With precise phase compensation, a radio frequency with high-phase stability can be obtained at the remote end. We performed 20.07-GHz radio-frequency transfer over 100-km optical fiber, and achieved residual phase noise of -65  dBc/Hz at 1-Hz offset frequency, and the RMS timing jitter in the frequency range from 0.01 Hz to 1 MHz reaches 110 fs. The long-term frequency stability also achieves 8×10(-17) at 10,000 s averaging time. PMID:26030572

  3. Thermal-noise limit in the frequency stabilization of lasers with rigid cavities.

    PubMed

    Numata, Kenji; Kemery, Amy; Camp, Jordan

    2004-12-17

    We evaluate thermal noise (Brownian motion) in a rigid reference cavity used for frequency stabilization of lasers, based on the mechanical loss of cavity materials and the numerical analysis of the mirror-spacer mechanics with the direct application of the fluctuation dissipation theorem. This noise sets a fundamental limit for the frequency stability achieved with a rigid frequency-reference cavity of order 1 Hz/ square root Hz (0.01 Hz/ square root Hz) at 10 mHz (100 Hz) at room temperature. This level coincides with the world-highest level stabilization results. PMID:15697887

  4. Spectral line-shapes investigation with Pound-Drever-Hall-locked frequency-stabilized cavity ring-down spectroscopy

    NASA Astrophysics Data System (ADS)

    Cygan, A.; Wójtewicz, S.; Domysławska, J.; Masłowski, P.; Bielska, K.; Piwiński, M.; Stec, K.; Trawiński, R. S.; Ozimek, F.; Radzewicz, C.; Abe, H.; Ido, T.; Hodges, J. T.; Lisak, D.; Ciuryło, R.

    2013-10-01

    A review of recent experiments involving a newly developed Pound-Drever-Hall-locked frequency-stabilized cavity ring-down spectroscopy (PDH-locked FS-CRDS) system is presented. By comparison to standard FS-CRDS, the PDH lock of the probe laser to the ring-down cavity optimized coupling into the cavity, thus increasing the ring-down signal acquisition rate nearly 300-fold to 14 kHz and reducing the noise-equivalent absorption coefficient by more than an order of magnitude to 7 × 10-11 cm-1. We discuss how averaging approximately 1000 spectra yielded a signal-to-noise ratio of 220000. We also discuss how the spectrum frequency axis was linked to an optical frequency comb, thus enabling absolute frequency measurements of molecular optical transitions at sub-MHz levels. Applications of the spectrometer to molecular line-shape studies are also presented. For these investigations, we use semi-classical line-shape models that consider the influence of Dicke narrowing as well as the speed dependence of the pressure broadening and shifting to fit spectra. We show that the improved precision and spectrum fidelity of the spectrometer enable precise determinations of line-shape parameters. We also discuss the importance of line-shape analysis with regard to the development of new spectroscopic databases as well as in the optical determination of the Boltzmann constant.

  5. Low-frequency rTMS over the Parieto-frontal network during a sensorimotor task: The role of absolute beta power in the sensorimotor integration.

    PubMed

    Gongora, Mariana; Bittencourt, Juliana; Teixeira, Silmar; Basile, Luis F; Pompeu, Fernando; Droguett, Enrique López; Arias-Carrion, Oscar; Budde, Henning; Cagy, Mauricio; Velasques, Bruna; Nardi, Antonio Egídio; Ribeiro, Pedro

    2016-01-12

    Several studies have demonstrated that Repetitive Transcranial Magnetic Stimulation (rTMS) promotes alterations in the Central Nervous System circuits and networks. The focus of the present study is to examine the absolute beta power patterns in the Parieto-frontal network. We hypothesize that rTMS alters the mechanisms of the sensorimotor integration process during a visuomotor task. Twelve young healthy volunteers performed a visuomotor task involving decision making recorded (Catch a ball in a free fall) by Electroencephalography. rTMS was applied on the Superior Parietal Cortex (SPC; Brodmann area [BA] 7) with low-frequency (1 Hz - 15 min - 80% Resting Motor Threshold). For each Frontal and Parietal region, a two-way ANOVA was used to compare the absolute beta power before and after TMS for each condition of the study (Rest 1, Task and Rest 2). The results demonstrated interactions (TMS vs. Condition) for the Frontal electrodes: Fp1, Fp2 and F7 and an effect of TMS (before and after) for F4.The results for the Parietal region showed a main effect of Condition for the P3, PZ and P4 electrodes. Thus, our paradigm was useful to better understand the reorganization and neural plasticity mechanisms in the parieto-frontal network during the sensorimotor integration process. PMID:26608023

  6. Monolithic device for modelocking and stabilization of frequency combs.

    PubMed

    Lee, C-C; Hayashi, Y; Silverman, K L; Feldman, A; Harvey, T; Mirin, R P; Schibli, T R

    2015-12-28

    We demonstrate a device that integrates a III-V semiconductor saturable absorber mirror with a graphene electro-optic modulator, which provides a monolithic solution to modelocking and noise suppression in a frequency comb. The device offers a pure loss modulation bandwidth exceeding 5 MHz and only requires a low voltage driver. This hybrid device provides not only compactness and simplicity in laser cavity design, but also small insertion loss, compared to the previous metallic-mirror-based modulators. We believe this work paves the way to portable and fieldable phase-coherent frequency combs. PMID:26831973

  7. Stabilization of Gyrotron Frequency by PID Feedback Control on the Acceleration Voltage

    NASA Astrophysics Data System (ADS)

    Khutoryan, E. M.; Idehara, T.; Kuleshov, A. N.; Tatematsu, Y.; Yamaguchi, Y.; Matsuki, Y.; Fujiwara, T.

    2015-12-01

    The results of frequency stabilization by proportional-integral-derivative (PID) feedback control of acceleration voltage in the 460-GHz Gyrotron FU CW GVI (the official name in Osaka University is Gyrotron FU CW GOI) are presented. The experiment was organized on the basis of the frequency modulation by modulation of acceleration voltage of beam electrons. The frequency stabilization during 10 h experiment was better than 10-6, which is compared with the results of the frequency deviation in free-running gyrotron operation.

  8. Laser frequency stabilization using a dispersive line shape induced by Doppler Effect.

    PubMed

    Wang, Qing; Qi, Xianghui; Liu, Shuyong; Yu, Jiachen; Chen, Xuzong

    2015-02-01

    We report a simple and robust Doppler-free spectroscopic technique to stabilize a laser frequency to the atomic transition. By employing Doppler Effect on the atomic beam, we obtained a very stable dispersive signal with a high signal-to-noise ratio and no Doppler-background, which served as an error signal to electronically stabilize a laser frequency without modulation. For validating the performance of this technique, we locked a DFB laser to the (133)Cs D2 line and observed an efficient suppression of the frequency noise and a long-term reduction of the frequency drifts in a laboratory environment. PMID:25836158

  9. Frequency-Tuneable Pre-Stabilized Lasers for LISA via Sideband Locking

    NASA Technical Reports Server (NTRS)

    Thorpe, James Ira; Numata, Kenji; Livas, jeffery

    2008-01-01

    Laser frequency noise mitigation is one of the most challenging aspects of the LISA interferometric measurement system. The unstabilized frequency fluctuations must be suppressed by roughly twelve orders of magnitude in order to achieve a stability sufficient for gravitational wave detection. This enormous suppression will be achieved through a combination of stabilization and common-mode rejection. The stabilization component will itself be achieved in two stages: pre-stabilization to a local optical cavity followed by arm-locking to some combination of the inter-spacecraft distances. In order for these two stabilization stages to work simultaneously, the lock-point of the pre-stabilization loop must be frequency tunable. The current baseline stabilization technique, locking to an optical cavity, does not provide tunability between cavity resonance, which are typically spaced by 100s of MHz. Here we present a modification to the traditional Pound-Drever-Hall cavity locking technique that allows the laser to be locked to a cavity resonance with an adjustable frequency offset. This technique requires no modifications to the optical cavity itself, thus preserving the stability of the frequency reference. We present measurements of the system stability, demonstrating that the pre-stabilization level satisfies LISA requirements. We also present a demonstration of a phase-lock loop which utilizes the tunable sideband locking technique as a pre-stabilizations tage. The performance of the pre-stabilized phase-lock-loop indicates that the tunable sideband technique will meet the requirements as an actuator for arm-locking in LISA.

  10. 47 CFR 2.1055 - Measurements required: Frequency stability.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... with variation of ambient temperature as follows: (1) From −30° to +50° centigrade for all equipment...) Frequency measurements shall be made at the extremes of the specified temperature range and at intervals of... components of the oscillator circuit at each temperature level shall be allowed prior to...

  11. 47 CFR 2.1055 - Measurements required: Frequency stability.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... with variation of ambient temperature as follows: (1) From −30° to +50° centigrade for all equipment...) Frequency measurements shall be made at the extremes of the specified temperature range and at intervals of... components of the oscillator circuit at each temperature level shall be allowed prior to...

  12. Absolute atomic oxygen and nitrogen densities in radio-frequency driven atmospheric pressure cold plasmas: Synchrotron vacuum ultra-violet high-resolution Fourier-transform absorption measurements

    SciTech Connect

    Niemi, K.; O'Connell, D.; Gans, T.; Oliveira, N. de; Joyeux, D.; Nahon, L.; Booth, J. P.

    2013-07-15

    Reactive atomic species play a key role in emerging cold atmospheric pressure plasma applications, in particular, in plasma medicine. Absolute densities of atomic oxygen and atomic nitrogen were measured in a radio-frequency driven non-equilibrium plasma operated at atmospheric pressure using vacuum ultra-violet (VUV) absorption spectroscopy. The experiment was conducted on the DESIRS synchrotron beamline using a unique VUV Fourier-transform spectrometer. Measurements were carried out in plasmas operated in helium with air-like N{sub 2}/O{sub 2} (4:1) admixtures. A maximum in the O-atom concentration of (9.1 {+-} 0.7) Multiplication-Sign 10{sup 20} m{sup -3} was found at admixtures of 0.35 vol. %, while the N-atom concentration exhibits a maximum of (5.7 {+-} 0.4) Multiplication-Sign 10{sup 19} m{sup -3} at 0.1 vol. %.

  13. Total Variance: A Progress Report on a New Frequency Stability Characterization

    NASA Technical Reports Server (NTRS)

    Howe, D. A.; Greenhall, C. A.

    1997-01-01

    We give results of recent work on a newly developed frequency stability characterization, called Total variance, whose main advantages are improved confidence at and near the longest averaging time of half the data duration, and lower sensitivity to drift removal.

  14. A Miniaturized Plasma Impedance Probe For Ionospheric Absolute Electron Density and Electron-Neutral Collision Frequency Measurements

    NASA Astrophysics Data System (ADS)

    Patra, S.; Rao, A. J.; Jayaram, M.; Hamoui, M. E.; Spencer, E. A.; Winstead, C.

    2008-12-01

    A fully integrated, low power, miniaturized Plasma Impedance Probe (PIP) is developed for small satellite constellation missions to create a map of electron density in the ionosphere. Two alternative methods for deriving plasma parameters from impedance measurements are discussed. The first method employs a frequency sweep technique, while the second employs a pulse based technique. The pulse based technique is a new method that leads to faster measurements. The two techniques necessitate different specifications for the front end analog circuit design. Unlike previous PIP designs, the integrated PIP performs direct voltage/current sampling at the probe's terminal. The signal processing tasks are performed by an off-chip FPGA to compute the impedance of the probe in the surrounding plasma. The new design includes self- calibration algorithms in order to increase the accuracy and reliability of the probe for small satellite constellation missions. A new feature included in this instrument is that the plasma parameters are derived from impedance measurements directly on the FPGA, significantly reducing the bandwith of telemetered data down to ground.

  15. Diode-pumped Yb:KYW femtosecond laser frequency comb with stabilized carrier-envelope offset frequency

    NASA Astrophysics Data System (ADS)

    Meyer, S. A.; Squier, J. A.; Diddams, S. A.

    2008-06-01

    We describe the detection and stabilization of the carrier envelope offset (CEO) frequency of a diode-pumped Yb:KYW (ytterbium-doped potassium yttrium tungstate) femtosecond oscillator that is spectrally centered at 1033 nm. The system consists of a diode-pumped, passively mode-locked femtosecond laser that produces 290 fs pulses at a repetition rate of 160 MHz. These pulses are first amplified, spectrally broadened and temporally compressed to 80 fs, and then launched into microstructured fiber to produce an octave-spanning spectrum. An f-2f nonlinear interferometer is employed with the broadened spectrum to detect and stabilize the CEO frequency through feedback to the pump laser current. These results demonstrate that such a Yb-doped tungstate laser can provide an efficient, compact, high-repetition-rate optical frequency comb with coverage from 650-1450 nm.

  16. Review of the frequency stabilization of TEA CO2 laser oscillators

    NASA Technical Reports Server (NTRS)

    Willetts, David V.

    1987-01-01

    Most applications of TEA CO2 lasers in heterodyne radar systems require that the transmitter has a high degree of frequency stability. This ensures good Doppler resolution and maximizes receiver sensitivity. However, the environment within the device is far from benign with fast acoustic and electrical transients being present. Consequently the phenomena which govern the frequency stability of pulsed lasers are quite different from those operative in their CW counterparts. This review concentrates on the mechanisms of chirping within the output pulse; pulse to pulse frequency drift may be eliminated by frequency measurement and correction on successive pulses. It emerges that good stability hinges on correct cavity design. The energy-dependent laser-induced frequency sweep falls dramatically as mode diameter is increased. Thus, it is necessary to construct resonators with good selectivity for single mode operation while having a large spot size.

  17. A long-term frequency stabilized deep ultraviolet laser for Mg+ ions trapping experiments

    NASA Astrophysics Data System (ADS)

    Zhang, J.; Yuan, W. H.; Deng, K.; Deng, A.; Xu, Z. T.; Qin, C. B.; Lu, Z. H.; Luo, J.

    2013-12-01

    As many precision laser spectroscopy experiments require frequency stabilized lasers, development of long-term stabilized lasers is of great interest. In this work, we report long-term frequency stabilization of a 280 nm deep ultraviolet laser to a high precision wavemeter with digital servo control such that the long-term drift of the laser frequency was greatly reduced. Long-term laser frequency drift was measured with a fiber frequency comb system over 8 h. After locking, the maximum drift rate of the 280 nm laser was lowered from 576 MHz/h to 6.4 MHz/h. With proper environment control of the wavemeter, the maximum drift rate of the 280 nm laser was further lowered to less than 480 kHz/h. The locked laser system was successfully used in a Mg+ ions trapping experiment, which was also discussed in this work.

  18. Stabilization of femtosecond laser frequency combs with subhertz residual linewidths.

    PubMed

    Bartels, A; Oates, C W; Hollberg, L; Diddams, S A

    2004-05-15

    We demonstrate that femtosecond laser frequency combs (FLFCs) can have a subhertz linewidth across their entire emission spectra when they are phase locked to a reference laser with a similarly narrow linewidth. Correspondingly, the coherence time of the comb components relative to the reference laser can be of the order of a few seconds. Thus we are able to detect high-contrast spectral interferograms at up to 10-s integration time between two FLFCs locked to a common optical reference. PMID:15181992

  19. Diode-laser frequency stabilization based on the resonant Faraday effect

    NASA Technical Reports Server (NTRS)

    Wanninger, P.; Valdez, E. C.; Shay, T. M.

    1992-01-01

    The authors present the results of a method for frequency stabilizing laser diodes based on the resonant Faraday effects. A Faraday cell in conjunction with a polarizer crossed with respect to the polarization of the laser diode comprises the intracavity frequency selective element. In this arrangement, a laser pull-in range of 9 A was measured, and the laser operated at a single frequency with a linewidth less than 6 MHz.

  20. An atomic magnetometer with autonomous frequency stabilization and large dynamic range.

    PubMed

    Pradhan, S; Mishra, S; Behera, R; Poornima; Dasgupta, K

    2015-06-01

    The operation of a highly sensitive atomic magnetometer using elliptically polarized resonant light is demonstrated. It is based on measurement of zero magnetic field resonance in degenerate two level systems using polarimetric detection. The transmitted light through the polarimeter is used for laser frequency stabilization, whereas reflected light is used for magnetic field measurement. Thus, the experimental geometry allows autonomous frequency stabilization of the laser frequency leading to compact operation of the overall device and has a preliminary sensitivity of <10 pT/Hz(1/2) @ 1 Hz. Additionally, the dynamic range of the device is improved by feedback controlling the bias magnetic field without compromising on its sensitivity. PMID:26133825

  1. Exploring the Frequency Stability Limits of Whispering Gallery Mode Resonators for Metrological Applications

    NASA Technical Reports Server (NTRS)

    Chembo, Yanne K.; Baumgartel, Lukas; Grudinin, Ivan; Strekalov, Dmitry; Thompson, Robert; Yu, Nan

    2012-01-01

    Whispering gallery mode resonators are attracting increasing interest as promising frequency reference cavities. Unlike commonly used Fabry-Perot cavities, however, they are filled with a bulk medium whose properties have a significant impact on the stability of its resonance frequencies. In this context that has to be reduced to a minimum. On the other hand, a small monolithic resonator provides opportunity for better stability against vibration and acceleration. this feature is essential when the cavity operates in a non-laboratory environment. In this paper, we report a case study for a crystalline resonator, and discuss the a pathway towards the inhibition of vibration-and acceleration-induced frequency fluctuations.

  2. An atomic magnetometer with autonomous frequency stabilization and large dynamic range

    SciTech Connect

    Pradhan, S. E-mail: pradhans75@gmail.com; Poornima,; Dasgupta, K.; Mishra, S.; Behera, R.

    2015-06-15

    The operation of a highly sensitive atomic magnetometer using elliptically polarized resonant light is demonstrated. It is based on measurement of zero magnetic field resonance in degenerate two level systems using polarimetric detection. The transmitted light through the polarimeter is used for laser frequency stabilization, whereas reflected light is used for magnetic field measurement. Thus, the experimental geometry allows autonomous frequency stabilization of the laser frequency leading to compact operation of the overall device and has a preliminary sensitivity of <10 pT/Hz{sup 1/2} @ 1 Hz. Additionally, the dynamic range of the device is improved by feedback controlling the bias magnetic field without compromising on its sensitivity.

  3. A compact laser head with high-frequency stability for Rb atomic clocks and optical instrumentation

    SciTech Connect

    Affolderbach, Christoph; Mileti, Gaetano

    2005-07-15

    We present a compact and frequency-stabilized laser head based on an extended-cavity diode laser. The laser head occupies a volume of 200 cm{sup 3} and includes frequency stabilization to Doppler-free saturated absorption resonances on the hyperfine components of the {sup 87}Rb D{sub 2} lines at 780 nm, obtained from a simple and compact spectroscopic setup using a 2 cm{sup 3} vapor cell. The measured frequency stability is {<=}2x10{sup -12} over integration times from 1 s to 1 day and shows the potential to reach 2x10{sup -13} over 10{sup 2}-10{sup 5} s. Compact laser sources with these performances are of great interest for applications in gas-cell atomic frequency standards, atomic magnetometers, interferometers and other instruments requiring stable and narrow-band optical sources.

  4. Improvement in medium long-term frequency stability of the integrating sphere cold atom clock

    NASA Astrophysics Data System (ADS)

    Liu, Peng; Cheng, Huadong; Meng, Yanling; Wan, Jinyin; Xiao, Ling; Wang, Xiumei; Wang, Yaning; Liu, Liang

    2016-07-01

    The medium-long term frequency stability of the integrating sphere cold atom clock was improved.During the clock operation, Rb atoms were cooled and manipulated using cooling light diffusely reflected by the inner surface of a microwave cavity in the clock. This light heated the cavity and caused a frequency drift from the resonant frequency of the cavity. Power fluctuations of the cooling light led to atomic density variations in the cavity's central area, which increased the clock frequency instability through a cavity pulling effect. We overcame these limitations with appropriate solutions. A frequency stability of 3.5E-15 was achieved when the integrating time ? increased to 2E4 s.

  5. Absolute Zero

    NASA Astrophysics Data System (ADS)

    Donnelly, Russell J.; Sheibley, D.; Belloni, M.; Stamper-Kurn, D.; Vinen, W. F.

    2006-12-01

    Absolute Zero is a two hour PBS special attempting to bring to the general public some of the advances made in 400 years of thermodynamics. It is based on the book “Absolute Zero and the Conquest of Cold” by Tom Shachtman. Absolute Zero will call long-overdue attention to the remarkable strides that have been made in low-temperature physics, a field that has produced 27 Nobel Prizes. It will explore the ongoing interplay between science and technology through historical examples including refrigerators, ice machines, frozen foods, liquid oxygen and nitrogen as well as much colder fluids such as liquid hydrogen and liquid helium. A website has been established to promote the series: www.absolutezerocampaign.org. It contains information on the series, aimed primarily at students at the middle school level. There is a wealth of material here and we hope interested teachers will draw their student’s attention to this website and its substantial contents, which have been carefully vetted for accuracy.

  6. Using Frequency Noise Feedback to Improve Stability in Extended Cavity Diode Lasers

    NASA Astrophysics Data System (ADS)

    Pugh, Mckinley; Durfee, Dallin

    2016-03-01

    We are developing a feedback system to stabilize extended cavity diode lasers using frequency noise. In other literature, amplitude noise has been used to predict and prevent mode hops. We've found, however, that amplitude noise only correlates to an impending mode hop when the laser is locked to a frequency reference. We have found evidence that the amplitude noise is generated from more fundamental frequency noise by the lock feedback. We therefore propose a way to use frequency noise directly to generate a signal to predict and prevent mode hops.

  7. Absolute and relative emission spectroscopy study of 3 cm wide planar radio frequency atmospheric pressure bio-plasma source

    SciTech Connect

    Deng, Xiaolong; Nikiforov, Anton Yu Leys, Christophe; Ionita, Eusebiu-Rosini; Dinescu, Gheorghe

    2015-08-03

    The dynamics of low power atmospheric pressure radio frequency discharge generated in Ar gas in long gap of 3 cm is investigated. This plasma source is characterized and analyzed for possible large scale biomedical applications where low gas temperature and potential-less effluent are required. The discharge forms a homogenous glow-like afterglow in ambient air at input power of 30 W with low gas temperature of 330 K, which is desirable in biomedical applications. With absolute calibrated spectroscopy of the discharge, electron density of 0.4 × 10{sup 18} m{sup −3} and electron temperature of 1.5 eV are obtained from continuum Bremsstrahlung radiation of the source. Time and spatial resolved emission spectroscopy is used to analyze discharge generation mechanism and active species formation. It is found that discharge dynamics strongly correlates with the discharge current waveform. Strong Ar(2p) excited states emission is observed nearby the electrodes surface on a distance up to 200 μm in the plasma sheath region at 10 ns after the current peak, whereas OH(A) emission is uniform along of the interelectrode gap.

  8. Particle simulation on radio frequency stabilization of flute modes in a tandem mirror. I. Parallel antenna

    SciTech Connect

    Kadoya, Y.; Abe, H.

    1988-04-01

    A two- and one-half-dimensional electromagnetic particle code (PS2M) (H. Abe and S. Nakajima, J. Phys. Soc. Jpn. 53, xxx (1987)) is used to study how an electric field applied parallel to the magnetic field affects the radio frequency stabilization of flute modes in a tandem mirror plasma. The parallel electric field E/sub parallel/ perturbs the electron velocity v/sub parallel/ parallel to the magnetic field and also induces a perpendicular magnetic field perturbation B/sub perpendicular/. The unstable growth of the flute mode in the absence of such a radio frequency electric field is first studied as a basis for comparison. The ponderomotive force originating from the time-averaged product is then shown to stabilize the flute modes. The stabilizing wave power threshold, the frequency dependency, and the dependence on delchemically bondE/sub parallel/chemically bond all agree with the theoretical predictions.

  9. A high-performance frequency stability compact CPT clock based on a Cs-Ne microcell.

    PubMed

    Boudot, Rodolphe; Liu, Xiaochi; Abbé, Philippe; Chutani, Ravinder; Passilly, Nicolas; Galliou, Serge; Gorecki, Christophe; Giordano, Vincent

    2012-11-01

    This paper reports on a compact table-top Cs clock based on coherent population trapping (CPT) with advanced frequency stability performance. The heart of the clock is a single buffer gas Cs-Ne microfabricated cell. Using a distributed feedback (DFB) laser resonant with the Cs D1 line, the contrast of the CPT signal is found to be maximized around 80°C, a value for which the temperature dependence of the Cs clock frequency is canceled. Advanced techniques are implemented to actively stabilize the clock operation on a zero-light-shift point. The clock frequency stability is measured to be 3.8 × 10(-11) at 1 s and well below 10(-11) until 50,000 s. These results demonstrate the possibility to develop high-performance chip-scale atomic clocks using vapor cells containing a single buffer gas. PMID:23192824

  10. Stabilizing soliton-based multichannel transmission with frequency dependent linear gain-loss

    NASA Astrophysics Data System (ADS)

    Chakraborty, Debananda; Peleg, Avner; Nguyen, Quan M.

    2016-07-01

    We report several major theoretical steps towards realizing stable long-distance multichannel soliton transmission in Kerr nonlinear waveguide loops. We find that transmission destabilization in a single waveguide is caused by resonant formation of radiative sidebands and investigate the possibility to increase transmission stability by optimization with respect to the Kerr nonlinearity coefficient γ. Moreover, we develop a general method for transmission stabilization, based on frequency dependent linear gain-loss in Kerr nonlinear waveguide couplers, and implement it in two-channel and three-channel transmission. We show that the introduction of frequency dependent loss leads to significant enhancement of transmission stability even for non-optimal γ values via decay of radiative sidebands, which takes place as a dynamic phase transition. For waveguide couplers with frequency dependent linear gain-loss, we observe stable oscillations of soliton amplitudes due to decay and regeneration of the radiative sidebands.

  11. Measurement and analysis of the frequency stability of GPS Navstar clocks

    SciTech Connect

    McCaskill, T.B.; Largay, M.M.; Oaks, O.J.

    1994-12-31

    Analysis of the frequency stability of Global Positioning System (GPS) on-orbit Navstar clocks Z`s performed by the Naval Research Laboratory (NRL). Clock offsets for each Navstar clock are derived from smoothed pseudorange measurements collected as the Navstar space vehicle passes over the tracking station. The clock offsets are further smoothed and estimated at the time of closest approach (TCA) of the space vehicle over the tracking station. Analysis of more than 50 Navstar clocks by NRL shows that the majority of these clocks provide performance that exceeds the GPS frequency stability specification. This precision measurement technique is capable of determining one-day frequency stabilities of the Navstar GPS clocks to an accuracy of better than 1 x 10-13.

  12. Long-term frequency stabilization system for external cavity diode laser based on mode boundary detection

    NASA Astrophysics Data System (ADS)

    Xu, Zhouxiang; Huang, Kaikai; Jiang, Yunfeng; Lu, Xuanhui

    2011-12-01

    We have realized a long-term frequency stabilization system for external cavity diode laser (ECDL) based on mode boundary detection method. In this system, the saturated absorption spectroscopy was used. The current and the grating of the ECDL were controlled by a computer-based feedback control system. By checking if there are mode boundaries in the spectrum, the control system determined how to adjust current to avoid mode hopping. This procedure was executed periodically to ensure the long-term stabilization of ECDL in the absence of mode hops. This diode laser system with non-antireflection coating had operated in the condition of long-term mode-hop-free stabilization for almost 400 h, which is a significant improvement of ECDL frequency stabilization system.

  13. Comparison of Implant Stability Using Resonance Frequency Analysis: Osteotome Versus Conventional Drilling

    PubMed Central

    Sadeghi, Rokhsareh; Miremadi, Asghar

    2015-01-01

    Objectives: Implant primary stability is one of the important factors in achieving implant success. The osteotome technique may improve primary stability in patients with poor bone quality. The aim of this study was to compare implant stability using two different techniques namely osteotome versus conventional drilling in the posterior maxilla. Materials and Methods: In this controlled randomized clinical trial, 54 dental implants were placed in 32 patients; 29 implants were placed in the osteotome group and 25 in the conventional drilling group. Implant stability was assessed at four time intervals namely at baseline, one, two and three months after implant placement using resonance frequency analysis (RFA). Results: Primary stability based on implant stability quotient (ISQ) units was 71.4±7 for the osteotome group and 67.4±10 for the control group. There was no statistically significant difference between the two groups in implant stability at any of the measurement times. In each group, changes in implant stability from baseline to one month and also from two months to three months post-operatively were not significant but from one month to two months after implant placement, implant stability showed a significant increase in both groups. Conclusion: The results of this study revealed that in both techniques, good implant stability was achieved and osteotome technique did not have any advantage compared to conventional drilling in this regard. PMID:27148375

  14. Improvement in the control aspect of laser frequency stabilization for SUNLITE project

    NASA Technical Reports Server (NTRS)

    Zia, Omar

    1992-01-01

    Flight Electronics Division of Langley Research Center is developing a spaceflight experiment called the Stanford University and NASA Laser In-Space Technology (SUNLITE). The objective of the project is to explore the fundamental limits on frequency stability using an FM laser locking technique on a Nd:YAG non-planar ring (free-running linewidth of 5 KHz) oscillator in the vibration free, microgravity environment of space. Compact and automated actively stabilized terahertz laser oscillators will operate in space with an expected linewidth of less than 3 Hz. To implement and verify this experiment, NASA engineers have designed and built a state of the art, space qualified high speed data acquisition system for measuring the linewidth and stability limits of a laser oscillator. In order to achieve greater stability and better performance, an active frequency control scheme requiring the use of a feedback control loop has been applied. In the summer of 1991, the application of control theory in active frequency control as a frequency stabilization technique was investigated. The results and findings were presented in 1992 at the American Control Conference in Chicago, and have been published in Conference Proceedings. The main focus was to seek further improvement in the overall performance of the system by replacing the analogue controller by a digital algorithm.

  15. Wavemeter measurements of frequency stability of an injection seeded alexandrite laser for pressure and temperature lidar

    NASA Technical Reports Server (NTRS)

    Prasad, C. R.; Schwemmer, G. K.; Korb, C. L.

    1992-01-01

    The GSFC pressure-temperature lidar is a differential absorption lidar operating in the oxygen A band absorption region (760 to 770 nm), and utilizes two tunable pulsed alexandrite lasers. For obtaining temperature measurements with an accuracy of less than or = 1 K, it has been determined that the stability of the online laser frequency over a period of time corresponding to a set of measurements, 0.1 to 30 min, has to be better than +/- 0.002/cm. In addition, the requirements on laser spectral bandwidth and spectral purity are less than or = 0.02/cm and greater than or = 99.9 percent, respectively. Injection seeding with a stabilized AlGaAs diode laser was used to achieve the required frequency stability and spectral bandwidth. A high resolution Fizeau wavemeter was employed to determine the frequency stability of the pulsed alexandrite laser and determine its bandwidth, mode structure. We present the results of measurements of the frequency stability and the spectrum of the injection seeded alexandrite laser.

  16. Frequency stability of InP HBT over 0.2 to 220 GHz

    NASA Astrophysics Data System (ADS)

    Zhijiang, Zhou; Kun, Ren; Jun, Liu; Wei, Cheng; Haiyan, Lu; Lingling, Sun

    2015-02-01

    The frequency stabilities of InP DHBTs in a broadband over 1 to 220 GHz are investigated. A hybrid π-topology small-signal model is used to accurately capture the parasitics of devices. The model parameters are extracted from measurements analytically. The investigation results show that the excellent agreement between the measured and simulated data is obtained in the frequency range 200 MHz to 220 GHz. The dominant parameters of the π-topology model, bias conditions and emitter area have significant effects on the stability factor K. The HBT model can be unconditionally stable by reasonable selection of the proper bias condition and the physical layout of the device.

  17. Stabilization of a laser on a large-detuned atomic-reference frequency by resonant interferometry

    NASA Astrophysics Data System (ADS)

    Barboza, Priscila M. T.; Nascimento, Guilherme G.; Araújo, Michelle O.; da Silva, Cícero M.; Cavalcante, Hugo L. D. de S.; Oriá, Marcos; Chevrollier, Martine; Passerat de Silans, Thierry

    2016-04-01

    We report a simple technique for stabilization of a laser frequency at the wings of an atomic resonance. The reference signal used for stabilization issues from interference effects obtained in a low-quality cavity filled with a resonant atomic vapour. For a frequency detuned 2.6 GHz from the 133Cs D2 6S{}1/2 F = 4 to 6P{}3/2 F’ = 5 transition, the fractional frequency Allan deviation is 10-8 for averaging times of 300 s, corresponding to a frequency deviation of 4 MHz. Adequate choice of the atomic density and of the cell thickness allows locking the laser at detunings larger than 10 GHz. Such a simple technique does not require magnetic fields or signal modulation.

  18. Atomic fountain clock with very high frequency stability employing a pulse-tube-cryocooled sapphire oscillator.

    PubMed

    Takamizawa, Akifumi; Yanagimachi, Shinya; Tanabe, Takehiko; Hagimoto, Ken; Hirano, Iku; Watabe, Ken-ichi; Ikegami, Takeshi; Hartnett, John G

    2014-09-01

    The frequency stability of an atomic fountain clock was significantly improved by employing an ultra-stable local oscillator and increasing the number of atoms detected after the Ramsey interrogation, resulting in a measured Allan deviation of 8.3 × 10(-14)τ(-1/2)). A cryogenic sapphire oscillator using an ultra-low-vibration pulse-tube cryocooler and cryostat, without the need for refilling with liquid helium, was applied as a local oscillator and a frequency reference. High atom number was achieved by the high power of the cooling laser beams and optical pumping to the Zeeman sublevel m(F) = 0 employed for a frequency measurement, although vapor-loaded optical molasses with the simple (001) configuration was used for the atomic fountain clock. The resulting stability is not limited by the Dick effect as it is when a BVA quartz oscillator is used as the local oscillator. The stability reached the quantum projection noise limit to within 11%. Using a combination of a cryocooled sapphire oscillator and techniques to enhance the atom number, the frequency stability of any atomic fountain clock, already established as primary frequency standard, may be improved without opening its vacuum chamber. PMID:25167146

  19. Chip Scale Atomic Resonator Frequency Stabilization System With Ultra-Low Power Consumption for Optoelectronic Oscillators.

    PubMed

    Zhao, Jianye; Zhang, Yaolin; Lu, Haoyuan; Hou, Dong; Zhang, Shuangyou; Wang, Zhong

    2016-07-01

    We present a long-term chip scale stabilization scheme for optoelectronic oscillators (OEOs) based on a rubidium coherent population trapping (CPT) atomic resonator. By locking a single mode of an OEO to the (85)Rb 3.035-GHz CPT resonance utilizing an improved phase-locked loop (PLL) with a PID regulator, we achieved a chip scale frequency stabilization system for the OEO. The fractional frequency stability of the stabilized OEO by overlapping Allan deviation reaches 6.2 ×10(-11) (1 s) and  ∼ 1.45 ×10 (-11) (1000 s). This scheme avoids a decrease in the extra phase noise performance induced by the electronic connection between the OEO and the microwave reference in common injection locking schemes. The total physical package of the stabilization system is [Formula: see text] and the total power consumption is 400 mW, which provides a chip scale and portable frequency stabilization approach with ultra-low power consumption for OEOs. PMID:26529751

  20. Absolute Summ

    NASA Astrophysics Data System (ADS)

    Phillips, Alfred, Jr.

    Summ means the entirety of the multiverse. It seems clear, from the inflation theories of A. Guth and others, that the creation of many universes is plausible. We argue that Absolute cosmological ideas, not unlike those of I. Newton, may be consistent with dynamic multiverse creations. As suggested in W. Heisenberg's uncertainty principle, and with the Anthropic Principle defended by S. Hawking, et al., human consciousness, buttressed by findings of neuroscience, may have to be considered in our models. Predictability, as A. Einstein realized with Invariants and General Relativity, may be required for new ideas to be part of physics. We present here a two postulate model geared to an Absolute Summ. The seedbed of this work is part of Akhnaton's philosophy (see S. Freud, Moses and Monotheism). Most important, however, is that the structure of human consciousness, manifest in Kenya's Rift Valley 200,000 years ago as Homo sapiens, who were the culmination of the six million year co-creation process of Hominins and Nature in Africa, allows us to do the physics that we do. .

  1. An Auto-Lock Laser System for Long Term Frequency Stabilization

    NASA Astrophysics Data System (ADS)

    Berthiaume, Robert; Vorozcovs, Andrew; Kumarakrishnan, A.

    2010-03-01

    We have developed a compact, digitally controlled system to automatically stabilize the frequency of an external cavity diode laser to an atomic resonance. The key component of the system is a low-cost single-board computer with A/D and D/A capability that acts as a specialized lock-in amplifier. The system performs pattern matching between Doppler-free peaks obtained by scanning the laser frequency and reference peaks stored in the processor's memory. The incoming spectral signals are compared with the reference waveforms using a sliding correlation algorithm, which determines the control voltage required for adjusting the laser frequency to the desired lock point. The system has a scan amplitude of less than 1MHz when locked and it can re-lock for frequency drifts up to 10 GHz without human intervention. The dependence of laser frequency stability on ambient temperature, humidity, and pressure has been investigated. The performance of the system is suitable for experiments in atom trapping and atom interferometry that require long-term laser frequency stabilization.

  2. UHF FM receiver having improved frequency stability and low RFI emission

    DOEpatents

    Lupinetti, Francesco

    1990-02-27

    A UHF receiver which converts UHF modulated carrier signals to baseband video signals without any heterodyne or frequency conversion stages. A bandpass filter having a fixed frequency first filters the signals. A low noise amplifier amplifies the filtered signal and applies the signal through further amplification stages to a limited FM demodulator circuit. The UHF signal is directly converted to a baseband video signal. The baseband video signal is clamped by a clamping circuit before driving a monitor. Frequency stability for the receivers is at a theoretical maximum, and interference to adjacent receivers is eliminated due to the absence of a local oscillator.

  3. Multipoint dissemination of RF frequency in fiber optic link with stabilized propagation delay.

    PubMed

    Krehlik, Przemyslaw; Sliwczyński, Łukasz; Buczek, Łukasz; Lipiński, Marcin

    2013-09-01

    In this paper, we present the concept of accessing the signal at some midpoint of a frequency dissemination system with stabilized propagation delay, which allows building the point-to-multipoint frequency dissemination network. In the first experiments with a 160 km-long fiber link composed of a field-deployed optical cable and fibers spooled in the lab, exposed to both diurnal and seasonal temperature variations, in the access node, we obtained the Allan deviation of a 10- MHz frequency signal of about 3 × 10(-17) and the time deviation not greater than 2 ps for 10(5) s averaging. PMID:24658713

  4. Surface-polymer stabilized liquid crystals with dual-frequency control.

    PubMed

    Minasyan, Amalya; Galstian, Tigran

    2013-08-01

    Dual-frequency control liquid crystal (LC) and thin reactive mesogen (RM) films, cast on internal surfaces of cell substrate, are used to build surface polymer stabilized structures. Electric field of high frequency is used to orient the LC molecules by the negative dielectric torque prior to the photopolymerization of RM films. Electro-optic characterization results show that the contrasts of light scatter modulation and polarization dependence are noticeably improved by the dual-frequency control. However, there is no significant shortening in the full cycle duration of excitation-relaxation-excitation. PMID:23913090

  5. Frequency stability of an RF oscillator with an MEMS-based encapsulated resonator

    NASA Astrophysics Data System (ADS)

    Bohua, Peng; Wei, Luo; Jicong, Zhao; Quan, Yuan; Jinling, Yang; Fuhua, Yang

    2015-07-01

    This paper presents a high-Q RF MEMS oscillator consisting of a micro-disk resonator and low noise feedback circuits. The oscillator has high frequency stability and low phase noise. The two-port resonator was hermetically encapsulated using low-cost Sn-rich Au-Sn solder bonding, which significantly improves the frequency stability. A low noise oscillator circuit was designed with a two-stage amplifying architecture which effectively improves both the frequency stability and phase noise performance. The measured phase noise is -96 dBc/Hz at 1 kHz offset and -128 dBc/Hz at far-from-carrier offsets. Moreover, the medium-term frequency stability and Allan deviation of the oscillator are ±4 ppm and 10 ppb, respectively. The oscillator is a promising component in future wireless communication application. Project supported by the National Natural Science Foundation of China (Nos. 61234007, 61404136) and the State Key Development Program for Basic Research of China (Nos. 2011CB933102, 2013YQ16055103).

  6. Frequency stabilization of a mode-locked waveguide laser using the Pound-Drever-Hall technique

    NASA Astrophysics Data System (ADS)

    Fanto, M. L.; Malowicki, J. E.; Bussjager, R. J.; Repak, P. L.; Kramer, K. A.; Casimir, D.; Hayduk, M. J.

    2005-05-01

    The generation of stable mode-locked pulses in the 1550 nm regime is required for high resolution signal processing used in transient probes, optical clocks, and optical A-D converters. More recently the frequency combs comprising these pulses have been applied to innovative methods of arbitrary waveform generation (AWG) in the optical domain. Temporal stability, however, limits the performance in some of those applications. We show here that a Pound-Drever-Hall (PDH) technique applied to a mode-locked Erbium Doped Waveguide Laser (EDWL) effectively stabilizes the frequency comb for extended time intervals. The ultra-compact waveguide configuration offers greater packaging flexibility. The system performance in terms of temporal stability is also found to compare favorably with those of a high grade commercial erbium-doped fiber laser (EDFL).

  7. Frequency stabilization of spin-torque-driven oscillations by coupling with a magnetic nonlinear resonator

    SciTech Connect

    Kudo, Kiwamu Suto, Hirofumi; Nagasawa, Tazumi; Mizushima, Koichi; Sato, Rie

    2014-10-28

    The fundamental function of any oscillator is to produce a waveform with a stable frequency. Here, we show a method of frequency stabilization for spin-torque nano-oscillators (STNOs) that relies on coupling with an adjacent nanomagnet through the magnetic dipole–dipole interaction. It is numerically demonstrated that highly stable oscillations occur as a result of mutual feedback between an STNO and a nanomagnet. The nanomagnet acts as a nonlinear resonator for the STNO. This method is based on the nonlinear behavior of the resonator and can be considered as a magnetic analogue of an optimization scheme in nanoelectromechanical systems. The oscillation frequency is most stabilized when the nanomagnet is driven at a special feedback point at which the feedback noise between the STNO and resonator is completely eliminated.

  8. Absolute frequency spectroscopy of CO2 lines at around 2.09 μm by combined use of an Er:fiber comb and a Ho:YLF amplifier.

    PubMed

    Gatti, D; Coluccelli, N; Gambetta, A; Di Lieto, A; Tonelli, M; Galzerano, G; Laporta, P; Marangoni, M

    2011-10-01

    The low-frequency tail of an octave-spanning supercontinuum (SC) generated by an Er:fiber comb is enhanced by a multipass Ho:YLF amplifier and used in a sum-frequency-generation scheme to obtain absolute referencing of a single-mode Tm-Ho:YAG laser tunable around 2.09 μm. By tuning the comb repetition frequency, the probing laser is scanned across the absorption lines of a CO(2) gas sample and highly accurate absorption profiles are measured. This approach can be readily scaled to any wavelength above ~2 μm. PMID:21964142

  9. A novel single frequency stabilized Fabry-Perot laser diode at 1590 nm for gas sensing

    NASA Astrophysics Data System (ADS)

    Weldon, Vincent; Boylan, Karl; Corbett, Brian; McDonald, David; O'Gorman, James

    2002-09-01

    A novel single frequency stabilized Fabry-Perot (SFP) laser diode with an emission wavelength of λ=1590 nm for H 2S gas sensing is reported. Sculpting of the multi-mode spectral distribution of a FP laser to achieve single frequency emission is carried out using post growth photolitographic processing of the device. The resulting longitudinal-mode controlled FP laser has a stabilized single frequency emission with a side mode suppression ratio (SMSR) of 40 dB. The application of this device to spectroscopic based H 2S sensing is demonstrated by targeting absorption lines in the wavelength range 1588≤ λ≤1591 nm. Using wavelength modulation spectroscopy (WMS), a low detection limit of 120 ppm.m.Hz -1/2 was estimated while targeting the absorption line at 1590.08 nm. These initial results demonstrate the potential of the stabilized FP laser diode at this wavelength as a tunable, single frequency source for spectroscopic based gas sensing.

  10. Operational stability of rubidium and cesium frequency standards. [analysis of equipment performance at NASA tracking stations

    NASA Technical Reports Server (NTRS)

    Lavery, J. E.

    1972-01-01

    In the course of testing various rubidium and cesium frequency standards under operational conditions for use in NASA tracking stations, about 55 unit-years of relative frequency measurements for averaging times from 10 to 10 to the 7th power have been accumulated at Goddard Space Flight Center (GSFC). Statistics on the behavior of rubidium and cesium standards under controlled laboratory conditions have been published, but it was not known to what extent the lesser controlled environments of NASA tracking stations affected the performance of the standards. The purpose of this report is to present estimates of the frequency stability of rubidium and cesium frequency standards under operational conditions based on the data accumulated at GSFC.

  11. Stabilized operation of the improvement of the Spallation Neutron Source (SNS) radio-frequency quadrupole (RFQ)

    SciTech Connect

    Kim, Sang-Ho; Aleksandrov, Alexander V; Crofford, Mark T; Galambos, John D; Gibson, Paul E; Hardek, Thomas W; Henderson, Stuart D; Kang, Yoon W; Kasemir, Kay; Peters, Charles C; Thompson, David H; Stockli, Martin P; Williams, Derrick C

    2010-01-01

    The Spallation Neutron Source (SNS) radio-frequency quadrupole (RFQ) had resonance control instabilities at duty factors higher than approximately four percent. Systematic investigations have been carried out to understand the cause of the instability and to ensure the operational stability of the RFQ. The most critical source of the instability is revealed to be an interaction between hydrogen released by beam bombardments and the RFQ RF field resulting in a discharge, which consumes additional RF power and could cause the RFQ to operate in an unstable region. This paper reports improvement of the SNS RFQ operational stability based on the findings during the SNS operation.

  12. High-bandwidth transfer of phase stability through a fiber frequency comb.

    PubMed

    Scharnhorst, Nils; Wübbena, Jannes B; Hannig, Stephan; Jakobsen, Kornelius; Kramer, Johannes; Leroux, Ian D; Schmidt, Piet O

    2015-07-27

    We demonstrate phase locking of a 729 nm diode laser to a 1542 nm master laser via an erbium-doped-fiber frequency comb, using a transfer-oscillator feedforward scheme which suppresses the effect of comb noise in an unprecedented 1.8 MHz bandwidth. We illustrate its performance by carrying out coherent manipulations of a trapped calcium ion with 99 % fidelity even at few-μs timescales. We thus demonstrate that transfer-oscillator locking can provide sufficient phase stability for high-fidelity quantum logic manipulation even without pre-stabilization of the slave diode laser. PMID:26367634

  13. Fast phase stabilization of a low frequency beat note for atom interferometry

    NASA Astrophysics Data System (ADS)

    Oh, E.; Horne, R. A.; Sackett, C. A.

    2016-06-01

    Atom interferometry experiments rely on the ability to obtain a stable signal that corresponds to an atomic phase. For interferometers that use laser beams to manipulate the atoms, noise in the lasers can lead to errors in the atomic measurement. In particular, it is often necessary to actively stabilize the optical phase between two frequency components of the beams. Typically this is achieved using a time-domain measurement of a beat note between the two frequencies. This becomes challenging when the frequency difference is small and the phase measurement must be made quickly. The method presented here instead uses a spatial interference detection to rapidly measure the optical phase for arbitrary frequency differences. A feedback system operating at a bandwidth of about 10 MHz could then correct the phase in about 3 μs. This time is short enough that the phase correction could be applied at the start of a laser pulse without appreciably degrading the fidelity of the atom interferometer operation. The phase stabilization system was demonstrated in a simple atom interferometer measurement of the 87Rb recoil frequency.

  14. Fast phase stabilization of a low frequency beat note for atom interferometry.

    PubMed

    Oh, E; Horne, R A; Sackett, C A

    2016-06-01

    Atom interferometry experiments rely on the ability to obtain a stable signal that corresponds to an atomic phase. For interferometers that use laser beams to manipulate the atoms, noise in the lasers can lead to errors in the atomic measurement. In particular, it is often necessary to actively stabilize the optical phase between two frequency components of the beams. Typically this is achieved using a time-domain measurement of a beat note between the two frequencies. This becomes challenging when the frequency difference is small and the phase measurement must be made quickly. The method presented here instead uses a spatial interference detection to rapidly measure the optical phase for arbitrary frequency differences. A feedback system operating at a bandwidth of about 10 MHz could then correct the phase in about 3 μs. This time is short enough that the phase correction could be applied at the start of a laser pulse without appreciably degrading the fidelity of the atom interferometer operation. The phase stabilization system was demonstrated in a simple atom interferometer measurement of the (87)Rb recoil frequency. PMID:27370424

  15. Single frequency and wavelength stabilized near infrared laser source for water vapor DIAL remote sensing application

    NASA Astrophysics Data System (ADS)

    Chuang, Ti; Walters, Brooke; Shuman, Tim; Losee, Andrew; Schum, Tom; Puffenberger, Kent; Burnham, Ralph

    2015-02-01

    Fibertek has demonstrated a single frequency, wavelength stabilized near infrared laser transmitter for NASA airborne water vapor DIAL application. The application required a single-frequency laser transmitter operating at 935 nm near infrared (NIR) region of the water vapor absorption spectrum, capable of being wavelength seeded and locked to a reference laser source and being tuned at least 100 pm across the water absorption spectrum for DIAL on/off measurements. Fibertek is building a laser transmitter system based on the demonstrated results. The laser system will be deployed in a high altitude aircraft (ER-2 or UAV) to autonomously perform remote, long duration and high altitude water vapor measurements.

  16. Highly precise stabilization of intracavity prism-based Er:fiber frequency comb using optical-microwave phase detector.

    PubMed

    Zhang, Shuangyou; Wu, Jiutao; Leng, Jianxiao; Lai, Shunnan; Zhao, Jianye

    2014-11-15

    In this Letter, we demonstrate a fully stabilized Er:fiber frequency comb by using a fiber-based, high-precision optical-microwave phase detector. To achieve high-precision and long-term phase locking of the repetition rate to a microwave reference, frequency control techniques (tuning pump power and cavity length) are combined together as its feedback. Since the pump power has been used for stabilization of the repetition rate, we introduce a pair of intracavity prisms as a regulator for carrier-envelope offset frequency, thereby phase locking one mode of the comb to the rubidium saturated absorption transition line. The stabilized comb performs the same high stability as the reference for the repetition rate and provides a residual frequency instability of 3.6×10(-13) for each comb mode. The demonstrated stabilization scheme could provide a high-precision comb for optical communication, direct frequency comb spectroscopy. PMID:25490492

  17. Stability Diagrams for Paul Ion Traps Driven by Two-Frequencies.

    PubMed

    Possa, Gabriela C; Roncaratti, Luiz F

    2016-07-14

    In this paper, we present and discuss stability diagrams for Paul traps driven by two ac voltages. In contrast to a typical Paul trap, here we suggest a secondary ac voltage whose frequency is twice the frequency of the primary one. The ratio between their amplitudes can be used to expand the region of stability and to access different states of motion of trapped ions. This provides a further mechanism to trap, cool, and manipulate single ions and also to improve the experimental framework where ion clouds and crystals can be prepared and controlled. Such approach opens the possibility of designing more sophisticated trapping architectures, leading to a wide variety of applications on ion trap research and mass analysis techniques. PMID:26881458

  18. Local vs. global redundancy - trade-offs between resilience against cascading failures and frequency stability

    NASA Astrophysics Data System (ADS)

    Plietzsch, A.; Schultz, P.; Heitzig, J.; Kurths, J.

    2016-05-01

    When designing or extending electricity grids, both frequency stability and resilience against cascading failures have to be considered amongst other aspects of energy security and economics such as construction costs due to total line length. Here, we compare an improved simulation model for cascading failures with state-of-the-art simulation models for short-term grid dynamics. Random ensembles of realistic power grid topologies are generated using a recent model that allows for a tuning of global vs local redundancy. The former can be measured by the algebraic connectivity of the network, whereas the latter can be measured by the networks transitivity. We show that, while frequency stability of an electricity grid benefits from a global form of redundancy, resilience against cascading failures rather requires a more local form of redundancy and further analyse the corresponding trade-off.

  19. Frequency Locking and Stabilization Regimes in High-Power Gyrotrons with Low-Q Resonators

    NASA Astrophysics Data System (ADS)

    Zotova, I. V.; Ginzburg, N. S.; Denisov, G. G.; Rozental', R. M.; Sergeev, A. S.

    2016-02-01

    Using a nonstationary self-consistent model, we analyze the frequency locking and stabilization regimes arising in gyrotrons with low-Q resonators under the action of an external signal or when reflections from a remote nonresonant load are introduced. In the simulations, we used the parameters of high-power gyrotrons designed for controlled thermonuclear fusion with optimized resonator profile. This approach makes it possible to determine output characteristics of the gyrotrons operated in considered regimes taking into account the effect of the incident wave (external or reflected) on the longitudinal field structure with greater precision compared with the earlier results based on the fixed RF-field structure approximation, while qualitative results of the two approaches coincide. Analysis of the effect of reflections from a remote load has demonstrated a substantial dependence of the efficiency of the gyrotron frequency stabilization on the ratio between the characteristic time scale of the synchronism detuning fluctuations and the signal delay time.

  20. Monolithic CEO-stabilization scheme-based frequency comb from an octave-spanning laser

    NASA Astrophysics Data System (ADS)

    Zi-Jiao, Yu; Hai-Nian, Han; Yang, Xie; Hao, Teng; Zhao-Hua, Wang; Zhi-Yi, Wei

    2016-04-01

    We demonstrate a carrier-envelope phase-stabilized octave-spanning oscillator based on the monolithic scheme. A wide output spectrum extending from 480 nm to 1050 nm was generated directly from an all-chirped mirror Ti:sapphire laser. After several improvements, the carrier-envelope offset (CEO) beat frequency accessed nearly 60 dB under a resolution of 100 kHz. Using a feedback system with 50-kHz bandwidth, we compressed the residual phase noise to 55 mrad (integrated from 1 Hz to 1 MHz) for the stabilized CEO, corresponding to 23-as timing jitter at the central wavelength of 790 nm. This is, to the best of our knowledge, the smallest timing jitter achieved among the existing octave-spanning laser based frequency combs. Project supported by the National Basic Research Program of China (Grant No. 2012CB821304) and the National Natural Science Foundation of China (Grant Nos. 11078022 and 61378040).

  1. Stabilized chip-scale Kerr frequency comb via a high-Q reference photonic microresonator

    NASA Astrophysics Data System (ADS)

    Lim, Jinkang; Huang, Shu-Wei; Vinod, Abhinav K.; Mortazavian, Parastou; Yu, Mingbin; Kwong, Dim-Lee; Savchenkov, Anatoliy A.; Matsko, Andrey B.; Maleki, Lute; Wong, Chee Wei

    2016-08-01

    We stabilize a chip-scale Si3N4 phase-locked Kerr frequency comb via locking the pump laser to an independent stable high-Q reference microresonator and locking the comb spacing to an external microwave oscillator. In this comb, the pump laser shift induces negligible impact on the comb spacing change. This scheme is a step towards miniaturization of the stabilized Kerr comb system as the microresonator reference can potentially be integrated on-chip. Fractional instability of the optical harmonics of the stabilized comb is limited by the microwave oscillator used for comb spacing lock below 1 s averaging time and coincides with the pump laser drift in the long term.

  2. Lysogen stability is determined by the frequency of activity bursts from the fate-determining gene

    PubMed Central

    Zong, Chenghang; So, Lok-hang; Sepúlveda, Leonardo A; Skinner, Samuel O; Golding, Ido

    2010-01-01

    The ability of living cells to maintain an inheritable memory of their gene-expression state is key to cellular differentiation. Bacterial lysogeny serves as a simple paradigm for long-term cellular memory. In this study, we address the following question: in the absence of external perturbation, how long will a cell stay in the lysogenic state before spontaneously switching away from that state? We show by direct measurement that lysogen stability exhibits a simple exponential dependence on the frequency of activity bursts from the fate-determining gene, cI. We quantify these gene-activity bursts using single-molecule-resolution mRNA measurements in individual cells, analyzed using a stochastic mathematical model of the gene-network kinetics. The quantitative relation between stability and gene activity is independent of the fine details of gene regulation, suggesting that a quantitative prediction of cell-state stability may also be possible in more complex systems. PMID:21119634

  3. Laser frequency stabilization to excited state transitions using electromagnetically induced transparency in a cascade system

    SciTech Connect

    Abel, R. P.; Mohapatra, A. K.; Bason, M. G.; Pritchard, J. D.; Weatherill, K. J.; Raitzsch, U.; Adams, C. S.

    2009-02-16

    We demonstrate laser frequency stabilization to excited state transitions using cascade electromagnetically induced transparency. Using a room temperature Rb vapor cell as a reference, we stabilize a first diode laser to the D{sub 2} transition and a second laser to a transition from the intermediate 5P{sub 3/2} state to a highly excited state with principal quantum number n=19-70. A combined laser linewidth of 280{+-}50 kHz over a 100 {mu}s time period is achieved. This method may be applied generally to any cascade system and allows laser stabilization to an atomic reference in the absence of a direct absorption signal.

  4. Lysogen stability is determined by the frequency of activity bursts from the fate-determining gene.

    PubMed

    Zong, Chenghang; So, Lok-hang; Sepúlveda, Leonardo A; Skinner, Samuel O; Golding, Ido

    2010-11-30

    The ability of living cells to maintain an inheritable memory of their gene-expression state is key to cellular differentiation. Bacterial lysogeny serves as a simple paradigm for long-term cellular memory. In this study, we address the following question: in the absence of external perturbation, how long will a cell stay in the lysogenic state before spontaneously switching away from that state? We show by direct measurement that lysogen stability exhibits a simple exponential dependence on the frequency of activity bursts from the fate-determining gene, cI. We quantify these gene-activity bursts using single-molecule-resolution mRNA measurements in individual cells, analyzed using a stochastic mathematical model of the gene-network kinetics. The quantitative relation between stability and gene activity is independent of the fine details of gene regulation, suggesting that a quantitative prediction of cell-state stability may also be possible in more complex systems. PMID:21119634

  5. Influence of Speed Governors of Hydropower Stations on Frequency Stabilization of Fixed-Speed Wind Farm

    NASA Astrophysics Data System (ADS)

    AL Jowder, Fawzi A. Rahman

    2013-05-01

    This paper uses a small power system, consisting of two hydropower stations and a fixed-speed wind farm as sources of power, to study the influence of type of speed governor of hydropower stations on the frequency stabilization of the fixed-speed wind farm. As an example, two types of speed governors are selected which are (1) mechanical-hydraulic speed governor and (2) electrical-hydraulic speed governor. Rest of the speed governors can be also examined following the same methodology presented in the research. Two transfer functions, which correspond to the two speed governors, are developed for each hydropower station. The overall transfer function of the test power system is developed, and different study cases are presented. The frequency response analysis of the different transfer functions is used to compare the two speed governors based on their ability to stabilize the frequency deviation of the fixed-speed wind resulting from electrical or mechanical disturbances in the power systems. Time-domain simulations under a mechanical disturbance, represented by a wind gust, and an electrical disturbance, represented by three-phase to ground fault, are performed to validate the results of the frequency response analysis.

  6. Maximum likelihood method for estimating airplane stability and control parameters from flight data in frequency domain

    NASA Technical Reports Server (NTRS)

    Klein, V.

    1980-01-01

    A frequency domain maximum likelihood method is developed for the estimation of airplane stability and control parameters from measured data. The model of an airplane is represented by a discrete-type steady state Kalman filter with time variables replaced by their Fourier series expansions. The likelihood function of innovations is formulated, and by its maximization with respect to unknown parameters the estimation algorithm is obtained. This algorithm is then simplified to the output error estimation method with the data in the form of transformed time histories, frequency response curves, or spectral and cross-spectral densities. The development is followed by a discussion on the equivalence of the cost function in the time and frequency domains, and on advantages and disadvantages of the frequency domain approach. The algorithm developed is applied in four examples to the estimation of longitudinal parameters of a general aviation airplane using computer generated and measured data in turbulent and still air. The cost functions in the time and frequency domains are shown to be equivalent; therefore, both approaches are complementary and not contradictory. Despite some computational advantages of parameter estimation in the frequency domain, this approach is limited to linear equations of motion with constant coefficients.

  7. A tunable Doppler-free dichroic lock for laser frequency stabilization

    NASA Astrophysics Data System (ADS)

    Singh, Vivek; Tiwari, V. B.; Mishra, S. R.; Rawat, H. S.

    2016-08-01

    We propose and demonstrate a laser frequency stabilization scheme which generates a dispersion-like tunable Doppler-free dichroic lock (TDFDL) signal. This signal offers a wide tuning range for lock point (i.e. zero-crossing) without compromising on the slope of the locking signal. The method involves measurement of magnetically induced dichroism in an atomic vapour for a weak probe laser beam in the presence of a counter-propagating strong pump laser beam. A simple model is presented to explain the basic principles of this method to generate the TDFDL signal. The spectral shift in the locking signal is achieved by tuning the frequency of the pump beam. The TDFDL signal is shown to be useful for locking the frequency of a cooling laser used for magneto-optical trap (MOT) for 87 Rb atoms.

  8. Frequency effects on the stability of a journal bearing for periodic loading

    NASA Technical Reports Server (NTRS)

    Vijayaraghavan, D.; Brewe, D. E.

    1991-01-01

    The stability of a journal bearing is numerically predicted when a unidirectional periodic external load is applied. The analysis is performed using a cavitation algorithm, which mimics the Jakobsson-Floberg and Olsson (JFO) theory by accounting for the mass balance through the complete bearing. Hence, the history of the film is taken into consideration. The loading pattern is taken to be sinusoidal and the frequency of the load cycle is varied. The results are compared with the predictions using Reynolds boundary conditions for both film rupture and reformation. With such comparisons, the need for accurately predicting the cavitation regions for complex loading patterns is clearly demonstrated. For a particular frequency of loading, the effects of mass, amplitude of load variation and frequency of journal speed are also investigated. The journal trajectories, transient variations in fluid film forces, net surface velocity and minimum film thickness, and pressure profiles are also presented.

  9. Long term frequency stability analysis of the GPS NAVSTAR 6 Cesium clock

    NASA Technical Reports Server (NTRS)

    Mccaskill, T. B.; Stebbins, S.; Carson, C.; Buisson, J.

    1982-01-01

    Time domain measurements, taken between the NAVSTAR 6 Spacecraft Vehicle (SV) and the Vandenberg Global Positioning System (GPS) Monitor Site, by a pseudo random noise receiver, were collected over an extended period of time and analyzed to estimate the long term frequency stability of the NAVSTAR 6 onboard frequency standard, referenced to the Vandenberg MS frequency standard. The technique employed separates the clock offset from the composite signal by first applying corrections for equipment delays, ionospheric delay, tropospheric delay, Earth rotation and the relativistic effect. The data are edited and smoothed using the predicted SV ephemeris to calculate the geometric delay. Then all available passes from each of the four GPS monitor stations, are collected at 1-week intervals and used to calculate the NAVSTAR orbital elements. The procedure is then completed by subtracting the corrections and the geometric delay, using the final orbital elements, from the composite signal, thus leaving the clock offset and random error.

  10. Absolute Quantitation of Met Using Mass Spectrometry for Clinical Application: Assay Precision, Stability, and Correlation with MET Gene Amplification in FFPE Tumor Tissue

    PubMed Central

    Catenacci, Daniel V. T.; Liao, Wei-Li; Thyparambil, Sheeno; Henderson, Les; Xu, Peng; Zhao, Lei; Rambo, Brittany; Hart, John; Xiao, Shu-Yuan; Bengali, Kathleen; Uzzell, Jamar; Darfler, Marlene; Krizman, David B.; Cecchi, Fabiola; Bottaro, Donald P.; Karrison, Theodore; Veenstra, Timothy D.; Hembrough, Todd; Burrows, Jon

    2014-01-01

    Background Overexpression of Met tyrosine kinase receptor is associated with poor prognosis. Overexpression, and particularly MET amplification, are predictive of response to Met-specific therapy in preclinical models. Immunohistochemistry (IHC) of formalin-fixed paraffin-embedded (FFPE) tissues is currently used to select for ‘high Met’ expressing tumors for Met inhibitor trials. IHC suffers from antibody non-specificity, lack of quantitative resolution, and, when quantifying multiple proteins, inefficient use of scarce tissue. Methods After describing the development of the Liquid-Tissue-Selected Reaction Monitoring-mass spectrometry (LT-SRM-MS) Met assay, we evaluated the expression level of Met in 130 FFPE gastroesophageal cancer (GEC) tissues. We assessed the correlation of SRM Met expression to IHC and mean MET gene copy number (GCN)/nucleus or MET/CEP7 ratio by fluorescence in situ hybridization (FISH). Results Proteomic mapping of recombinant Met identified 418TEFTTALQR426 as the optimal SRM peptide. Limits of detection (LOD) and quantitation (LOQ) for this peptide were 150 and 200 amol/µg tumor protein, respectively. The assay demonstrated excellent precision and temporal stability of measurements in serial sections analyzed one year apart. Expression levels of 130 GEC tissues ranged (<150 amol/µg to 4669.5 amol/µg. High correlation was observed between SRM Met expression and both MET GCN and MET/CEP7 ratio as determined by FISH (n = 30; R2 = 0.898). IHC did not correlate well with SRM (n = 44; R2 = 0.537) nor FISH GCN (n = 31; R2 = 0.509). A Met SRM level of ≥1500 amol/µg was 100% sensitive (95% CI 0.69–1) and 100% specific (95% CI 0.92–1) for MET amplification. Conclusions The Met SRM assay measured the absolute Met levels in clinical tissues with high precision. Compared to IHC, SRM provided a quantitative and linear measurement of Met expression, reliably distinguishing between non-amplified and amplified MET

  11. Absolute frequency measurement of 1S0(F = 1/2)-3P0(F = 1/2) transition of 171Yb atoms in a one-dimensional optical lattice at KRISS

    NASA Astrophysics Data System (ADS)

    Park, Chang Yong; Yu, Dai-Hyuk; Lee, Won-Kyu; Eon Park, Sang; Kim, Eok Bong; Lee, Sun Kyung; Cho, Jun Woo; Yoon, Tai Hyun; Mun, Jongchul; Jong Park, Sung; Kwon, Taeg Yong; Lee, Sang-Bum

    2013-04-01

    We measured the absolute frequency of the optical clock transition 1S0(F = 1/2)-3P0(F = 1/2) of 171Yb atoms confined in a one-dimensional optical lattice and it was determined to be 518 295 836 590 863.5(8.1) Hz. The frequency was measured against Terrestrial Time (TT; the SI second on the geoid) using an optical frequency comb of which the frequency was phase-locked to an H-maser as a flywheel oscillator traceable to TT. The magic wavelength was also measured as 394 798.48(79) GHz. The results are in good agreement with two previous measurements of other institutes within the specified uncertainty of this work.

  12. Integrated wideband optical frequency combs with high stability and their application in microwave photonic filters

    NASA Astrophysics Data System (ADS)

    Sun, Wenhui; Wang, Sunlong; Zhong, Xin; Liu, Jianguo; Wang, Wenting; Tong, Youwan; Chen, Wei; Yuan, Haiqing; Yu, Lijuan; Zhu, Ninghua

    2016-08-01

    An integrated wideband optical frequency comb (OFC) based on a semiconductor quantum dot laser is realized with high stability. The OFC module is packaged in our lab. A circuit which is designed to provide a low-ripple current and control the temperature regards as a servo system to enhance the stability of the OFC. The frequency stability of the OFC is 2.7×10-9 (Allan Variance). The free spectral range (FSR) of the OFC is 40 GHz and the number of comb lines is up to 55. The flatness of the OFC over span of 4 nm can be limited to 0.5 dB. Negative coefficients microwave photonic filters with multiple taps are generated based on the proposed OFC. For the 10 taps microwave photonic filter, the pass-band at 8.74 GHz has a 3 dB bandwidth of 630 MHz with 16.58 dB side-lobe suppression. Compared with the published microwave photonic filters, the proposed system is more stable, of more compact structures, and of less power consumption.

  13. Experimental Investigation of Hexagon Stability in Two Frequency Forced Faraday Waves

    NASA Astrophysics Data System (ADS)

    Ding, Yu; Umbanhowar, Paul

    2003-03-01

    We have conducted experiments on a deep layer of silicone oil vertically oscillated with an acceleration a(t) = Am sin(m ω t + φ_m) + An sin(n ω t + φ_n). The stability of hexagonal surface wave patterns is investigated as a function of the overall acceleration, the ratio m:n, and the phase of the two rationally related driving frequencies. When the ratio A_m/An is chosen so the system is near a co-dimension two point, the stability of hexagons above onset is determined by the acceleration amplitude and the relative phase. Recent results by Porter and Silver (J. Porter and M. Silber, Phys. Rev. Lett. 084501, 2002) predicts that the range of pattern stability above onset as a function of acceleration is determined by cos(Φ), where Φ = π/4 - m φn / 2- n φm /2. We have tested this prediction for a number of m:n ratios and for various values of the dimensionless damping coefficient γ. We find that the patterns exhibit the predicted functional dependence on s(Φ) but with an additional phase offset. We measure the phase offset as a function of m:n and γ for varying frequency ω and fluid viscosity 5 cS <= ν <= 30 cS.

  14. Improving the frequency stability of microwave oscillators by utilizing the dual-mode sapphire-loaded cavity resonator

    NASA Astrophysics Data System (ADS)

    Tobar, Michael E.; Ivanov, Eugene N.; Locke, Clayton R.; Hartnett, John G.; Cros, Dominique

    2002-08-01

    The design and experimental testing of a novel control circuit to stabilize the temperature of a sapphire-loaded cavity whispering gallery resonator-oscillator and improve its medium-term frequency stability is presented. Finite-element software was used to predict frequencies and quality factors of WGE7,0,0 and the WGH9,0,0 modes near 9 GHz, and separated in frequency by approximately 80 MHz. Calculations show that the novel temperature control circuits from the difference frequency can result in a frequency stability of better than one part in 1013 at 270 K. Also, we present details on the best way to couple orthogonally to two modes of similar frequency but different polarization.

  15. Stability of the human upright stance depending on the frequency of external disturbances.

    PubMed

    Ishida, Akimasa; Masuda, Tadashi; Inaoka, Hidenori; Fukuoka, Yutaka

    2008-03-01

    During an upright stance of humans, it is usually assumed that a stiffer ankle joint contributes to stabilize the stance. To show that under certain conditions a stiffer ankle joint can reduce the stability, the frequency responses of the moment and the angle of the ankle joint against external disturbances caused by random horizontal translations of the support surface were evaluated in ten healthy adult subjects by varying the difficulty of the task at four levels. When it was difficult to keep the upright stance, the subject tended to make the ankle joint stiffer. The transfer function relating the external disturbance moment to the ankle joint moment showed a larger gain in the high frequency range (>0.3 Hz) compared with the gains obtained under easier conditions. A simulation analysis based on a simple inverted pendulum model also reproduced this tendency. These results indicate that the stiffer ankle joint and the resulting higher ankle moment for high frequency external disturbances enhance the possibility that the center of pressure exceeds the limit arising from the size of the feet and can make the upright stance unstable. PMID:17929068

  16. Dynamics of suspended microchannel resonators conveying opposite internal fluid flow: Stability, frequency shift and energy dissipation

    NASA Astrophysics Data System (ADS)

    Zhang, Wen-Ming; Yan, Han; Jiang, Hui-Ming; Hu, Kai-Ming; Peng, Zhi-Ke; Meng, Guang

    2016-04-01

    In this paper, the dynamics of suspended microchannel resonators which convey internal flows with opposite directions are investigated. The fluid-structure interactions between the laminar fluid flow and oscillating cantilever are analyzed by comprehensively considering the effects of velocity profile, flow viscosity and added flowing particle. A new model is developed to characterize the dynamic behavior of suspended microchannel resonators with the fluid-structure interactions. The stability, frequency shift and energy dissipation of suspended microchannel resonators are analyzed and discussed. The results demonstrate that the frequency shifts induced by the added flowing particle which are obtained from the new model have a good agreement with the experimental data. The steady mean flow can cause the frequency shift and influence the stability of the dynamic system. As the flow velocity reaches the critical value, the coupled-mode flutter occurs via a Hamiltonian Hopf bifurcation. The perturbation flow resulted from the vibration of the microcantilever leads to energy dissipation, while the steady flow does not directly cause the damping which increases with the increasing of the flow velocity predicted by the classical model. It can also be found that the steady flow firstly changes the mode shape of the cantilever and consequently affects the energy dissipation.

  17. Stability and natural frequency of nonspherical mode of an encapsulated microbubble in a viscous liquid

    NASA Astrophysics Data System (ADS)

    Liu, Yunqiao; Wang, Qianxi

    2016-06-01

    The dynamics of encapsulated microbubbles (EMBs) subject to an ultrasound wave have wide and important medical applications, including sonography, drug delivery, and sonoporation. The nonspherical shape oscillation of an EMB, termed as shape modes, is one of the core mechanisms of these applications and therefore its natural frequency is a fundamentally important parameter. Based on the linear stability theory, we show that shape modes of an EMB in a viscous Newtonian liquid are stable. We derive an explicit expression for the natural frequency of shape modes, in terms of the equilibrium radius of an EMB, and the parameters of the external liquid, coating, and internal gases. The expression is validated by comparing to the numerical results obtained from the dynamic equations of shape modes of an EMB. The natural frequency of shape modes shifts appreciably due to the viscosity of the liquid, and this trend increases with the mode number. The significant viscous effects are due to the no-slip condition for the liquid flow at the surface of an EMB. Our results show that when subject to an acoustic wave, the shape instability for an EMB is prone to appear if 2ωk/ωd = n, where ωk is the natural frequency of shape modes, ωd is the driving frequency of the acoustic wave, and n is a natural number. The effects of viscosity on the natural frequency is thus critical in setting the driving frequency of ultrasound to avoid or activate shape modes of EMBs, which should be considered in the applications of medical ultrasound.

  18. Low frequency azimuthal stability of the ionization region of the Hall thruster discharge. II. Global analysis

    SciTech Connect

    Escobar, D.; Ahedo, E.

    2015-10-15

    The linear stability of the Hall thruster discharge is analysed against axial-azimuthal perturbations in the low frequency range using a time-dependent 2D code of the discharge. This azimuthal stability analysis is spatially global, as opposed to the more common local stability analyses, already afforded previously (D. Escobar and E. Ahedo, Phys. Plasmas 21(4), 043505 (2014)). The study covers both axial and axial-azimuthal oscillations, known as breathing mode and spoke, respectively. The influence on the spoke instability of different operation parameters such as discharge voltage, mass flow, and thruster size is assessed by means of different parametric variations and compared against experimental results. Additionally, simplified models are used to unveil and characterize the mechanisms driving the spoke. The results indicate that the spoke is linked to azimuthal oscillations of the ionization process and to the Bohm condition in the transition to the anode sheath. Finally, results obtained from local and global stability analyses are compared in order to explain the discrepancies between both methods.

  19. Stabilization of Neoclassical Tearing Modes in Tokamaks by Radio Frequency Current Drive

    SciTech Connect

    La Haye, R. J.

    2007-09-28

    Resistive neoclassical tearing modes (NTMs) will be the principal limit on stability and performance in the ITER standard scenario as the resulting islands break up the magnetic surfaces that confine the plasma. Drag from rotating island-induced eddy current in the resistive wall can also slow the plasma rotation, produce locking to the wall, and cause loss of high confinement H-mode and disruption. The NTMs are maintained by helical perturbations to the pressure-gradient driven 'bootstrap' current. Thus, this is a high beta instability even at the modest beta for ITER. A major line of research on NTM stabilization is the use of radio frequency (rf) current drive at the island rational surface. While large, broad current drive from lower hybrid waves has been shown to be stabilizing (COMPASS-D), most research is directed to small, narrow current drive from electron cyclotron waves (ECCD); ECCD stabilization and/or preemptive prevention is successful in ASDEX Upgrade, DIII-D and JT-60U, for example, with as little as a few percent of the total plasma current if the ECCD is kept sufficiently narrow so that the peak off-axis ECCD is comparable to the local bootstrap current.

  20. Low frequency azimuthal stability of the ionization region of the Hall thruster discharge. II. Global analysis

    NASA Astrophysics Data System (ADS)

    Escobar, D.; Ahedo, E.

    2015-10-01

    The linear stability of the Hall thruster discharge is analysed against axial-azimuthal perturbations in the low frequency range using a time-dependent 2D code of the discharge. This azimuthal stability analysis is spatially global, as opposed to the more common local stability analyses, already afforded previously (D. Escobar and E. Ahedo, Phys. Plasmas 21(4), 043505 (2014)). The study covers both axial and axial-azimuthal oscillations, known as breathing mode and spoke, respectively. The influence on the spoke instability of different operation parameters such as discharge voltage, mass flow, and thruster size is assessed by means of different parametric variations and compared against experimental results. Additionally, simplified models are used to unveil and characterize the mechanisms driving the spoke. The results indicate that the spoke is linked to azimuthal oscillations of the ionization process and to the Bohm condition in the transition to the anode sheath. Finally, results obtained from local and global stability analyses are compared in order to explain the discrepancies between both methods.

  1. Using BD Vacutainer CD4 Stabilization Tubes for Absolute Cluster of Differentiation Type 4 Cell Count Measurement on BD FacsCount and Partec Cyflow Cytometers: A Method Comparison Study from Zimbabwe

    PubMed Central

    Vogt, Florian; Van den Bergh, Rafael; Bernasconi, Andrea; Moyo, Buhlebenkosi; Havazvidi, Liberty; Bastard, Mathieu; Flevaud, Laurence; Taziwa, Fabian; Makondo, Eliphas; Mtapuri-Zinyowera, Sekesai

    2015-01-01

    Background Blood collected in conventional EDTA tubes requires laboratory analysis within 48 hours to provide valid CD4 cell count results. This restricts access to HIV care for patients from rural areas in resource-constraint settings due to sample transportation problems. Stabilization Tubes with extended storage duration have been developed but not yet evaluated comprehensively. Objective To investigate stability of absolute CD4 cell count measurement of samples in BD Vacutainer CD4 Stabilization Tubes over the course of 30 days. Methods This was a laboratory-based method comparison study conducted at a rural district hospital in Beitbridge, Zimbabwe. Whole peripheral blood from 88 HIV positive adults was drawn into BD Vacutainer CD4 Stabilization Tubes and re-tested 1, 2, 3, 5, 7, 14 and 30 days after collection on BD FacsCount and Partec Cyflow cytometers in parallel. Absolute CD4 cell levels were compared to results from paired samples in EDTA tubes analysed on BD FacsCount at the day of sample collection (references methodology). Bland-Altman analysis based on ratios of the median CD4 counts was used, with acceptable variation ranges for Limits of Agreements of +/-20%. Results Differences in ratios of the medians remained below 10% until day 21 on BD FacsCount and until day 5 on Partec Cyflow. Variations of Limits of Agreement were beyond 20% after day 1 on both cytometers. Specimen quality decreased steadily after day 5, with only 68% and 40% of samples yielding results on BD FacsCount and Partec Cyflow at day 21, respectively. Conclusions We do not recommend the use of BD Vacutainer CD4 Stabilization Tubes for absolute CD4 cell count measurement on BD FacsCount or Partec Cyflow due to large variation of results and decay of specimen quality. Alternative technologies for enhanced CD4 testing in settings with limited laboratory and sample transportation capacity still need to be developed. PMID:26295802

  2. Injection seeding of a Q-switched alexandrite laser: Study of frequency stabilization

    NASA Technical Reports Server (NTRS)

    Brown, Lamarr A.

    1992-01-01

    AlGaAs diode lasers were used to injection seed a pulsed Q-switched alexandrite laser which produces a narrowband of radiation. Injection seeding is a method for achieving linewidths of less than 500 mega-Hz in the output of the broadband, tunable solid state laser. When the laser was set at a current of 59.8 milli-A and a temperature of 14.04 C, the wavelength was 767.6 nano-m. The Q-switched alexandrite laser was injection seeded and frequency stabilization was studied. The linewidth requirement was met, but the stability requirement was not due to drifting in the feedback voltage. Improvements on injection seeding should focus on increasing the feedback voltage to the laser diode, filtering the laser diode by using temperature controlled narrowband filters, and the use of diamond (SiC) grating placed inside the alexandrite laser's resonator cavity.

  3. High-frequency vibration effect on the stability of a horizontal layer of ternary fluid.

    PubMed

    Lyubimova, Tatyana

    2015-05-01

    The effect of small-amplitude high-frequency longitudinal vibrations on the stability of a horizontal layer of ternary fluid is studied in the framework of average approach. Long-wave instability is studied analytically and instability to the perturbations with finite wave numbers is studied numerically. It is found that, similar to the case when vibrations are absent, for ternary fluids there exist monotonic and oscillatory long-wave instability modes. The calculations show that the vibrations lead to destabilization in the case of heating from below and to stabilization in the case of heating from above. Additionally, vibrations influence on the parameter range where long-wave instability is most dangerous. New, vibrational, instability modes are found which leads to the existence of convection in zero-gravity conditions. PMID:25998169

  4. Effect of high power low frequency ultrasound processing on the stability of lycopene.

    PubMed

    Oliveira, Valéria S; Rodrigues, Sueli; Fernandes, Fabiano A N

    2015-11-01

    The stability of lycopene was evaluated after application of high power low frequency ultrasound. The study was carried out on a solution containing pure lycopene to evaluate the direct effect of ultrasound on lycopene and on tomato purée to evaluate the direct and indirect effects of ultrasound application within a food matrix. Power densities ranging from 55 to 5000 W/L and temperatures ranging from 23°C (ambient) to 60°C were evaluated. The experiments on pure lycopene showed that the application of ultrasound did not have any direct effect over lycopene. However, the retention of lycopene in tomato puree has decreased indicating an indirect effect on lycopene stability caused by high concentration of hydrogen peroxide and the activation of peroxidase enzymes leading to the reduction of ascorbic acid and its regenerative action towards lycopene. PMID:25921608

  5. Frequency Stability of 1X10(sup -13) in a compensated Saphirre Oscillator Operating Above 77K

    NASA Technical Reports Server (NTRS)

    Dick, G. John; Santiago, David G.; Wang, Rabi T.

    1996-01-01

    We report on tests of a compensated saphirre oscillator (CS) which shows frequency-stable operation at temperatures above 77k.The frequency stability for this oscillator shows an apparent flicker floor of 7.5X10(sup -14) for measuring times between 3 and 10 seconds, and stability is better than 2X10(sup -13) for all measuring times between 10 and 100 seconds... Frequency sensitivities os the microwave sapphire resonator to temperature and temperature rate have been characterized, and a careful analysis of several aspects of the ac frequency-lock.

  6. Gain, phase and frequency stability of DSS-42 and DSS-43 vor Voyage Uranus encounter

    NASA Technical Reports Server (NTRS)

    Cha, A. G.; Levy, R.

    1986-01-01

    Theoretically rigorous definitions are derived of such parameters as RF signal path length, phase delay, and phase/frequency stability in a Cassegrainian antenna applicable to a narrow bandwidth channel, as well as algorithms for evaluating these parameters. This work was performed in support of the Voyager spacecraft encounter with Uranus in January 1986. The information was needed to provide Voyager/Uranus radio science researchers with a rotational basis for deciding the best strategy to operate the three antennas involved during the crucial 5-hour occultation period of the encounter. Such recommendations are made at the end of the article.

  7. Frequency Stability of 1X10(sup -13) in a Compensated Sapphire Oscillator Operating Above 77 K

    NASA Technical Reports Server (NTRS)

    Santiago, D. G.; Dick, G. J.; Wang, R. T.

    1996-01-01

    We report on a frequency-stable temperature compensated sapphire oscillator (CSO) at temperatures above 77 K. Previously, high stability in sapphire oscillators had only been obtained with liquid helium cooling.

  8. Stability of the translocation frequency following whole-body irradiation measured in rhesus monkeys

    NASA Technical Reports Server (NTRS)

    Lucas, J. N.; Hill, F. S.; Burk, C. E.; Cox, A. B.; Straume, T.

    1996-01-01

    Chromosome translocations are persistent indicators of prior exposure to ionizing radiation and the development of 'chromosome painting' to efficiently detect translocations has resulted in a powerful biological dosimetry tool for radiation dose reconstruction. However, the actual stability of the translocation frequency with time after exposure must be measured before it can be used reliably to obtain doses for individuals exposed years or decades previously. Human chromosome painting probes were used here to measure reciprocal translocation frequencies in cells from two tissues of 8 rhesus monkeys (Macaca mulatta) irradiated almost three decades previously. Six of the monkeys were exposed in 1965 to whole-body (fully penetrating) radiation and two were unexposed controls. The primates were irradiated as juveniles to single doses of 0.56, 1.13, 2.00, or 2.25 Gy. Blood lymphocytes (and skin fibroblasts from one individual) were obtained for cytogenetic analysis in 1993, near the end of the animals' lifespans. Results show identical dose-response relationships 28 y after exposure in vivo and immediately after exposure in vitro. Because chromosome aberrations are induced with identical frequencies in vivo and in vitro, these results demonstrate that the translocation frequencies induced in 1965 have not changed significantly during the almost three decades since exposure. Finally, our emerging biodosimetry data for individual radiation workers are now confirming the utility of reciprocal translocations measured by FISH in radiation dose reconstruction.

  9. A self-analyzing double-loop digital controller in laser frequency stabilization for inter-satellite laser ranging.

    PubMed

    Luo, Yingxin; Li, Hongyin; Yeh, Hsien-Chi; Luo, Jun

    2015-04-01

    We present a digital controller specially designed for laser frequency stabilization in the application of inter-satellite laser ranging. The prototype of controller is developed using field programmable gate arrays programmed with National Instruments LabVIEW software. The controller is flexible, self-analyzing, and easily optimized with build-in system analysis. Application and performance of the controller to a laser frequency stabilization system designed for spaceborne scientific missions are demonstrated. PMID:25933873

  10. Characterization of the Individual Short-Term Frequency Stability of Cryogenic Sapphire Oscillators at the 10(-16) Level.

    PubMed

    Fluhr, Christophe; Grop, Serge; Dubois, Benoit; Kersale, Yann; Rubiola, Enrico; Giordano, Vincent

    2016-06-01

    We present the characterization of three cryogenic sapphire oscillators (CSOs) using the three-cornered-hat method. Easily implemented with commercial components and instruments, this method reveals itself very useful to analyze the fractional frequency stability limitations of these state-of-the-art ultrastable oscillators. The best unit presents a fractional frequency stability better than 5 ×10(-16) at 1 s and below 2 ×10(-16) for [Formula: see text]. PMID:27076408

  11. Implant stability evaluation by resonance frequency analysis in the fit lock technique. A clinical study.

    PubMed

    Falisi, Giovanni; Galli, Massimo; Velasquez, Pedro Vittorini; Rivera, Juan Carlos Gallegos; Di Paolo, Carlo

    2013-01-01

    Surgical procedures for the application of implants in the lateral-superior sectors are affected by the availability of the residual bone. When this condition is lower than 5 mm it is recommended that techniques involving two therapeutic phases, a reconstructive and an applicative one, as reported in the international literature, are adopted. The authors propose here a new method with the potential to apply implants simultaneously with the reconstructive phase. The aim of this longitudinal retrospective study was to evaluate the stability of implants applied with the fit lock technique in the upper maxillarys in us with bone availability lower than 4 mm by measuring resonance frequency at different follow-up periods The seme as urements, carried out on 30 implants, were analysed with specific statistical procedures. The results indicate that the stability of the implants inserted with the fit lock method increases progressively over time in a statistically significant manner. The stability recorded after one year from the insertion (ISQ T2) is significantly higher than that recorded after six months (ISQ T1), and this is significantly higher than that recorded at the time of implant placement (ISQ T0). The implants inserted in the maxillary zones with scarce bone availability and applied with this technique showed a similar stability as reported with other techniques. In light of the results, the authors confirm that the primary stability represents the basic requirement to guarantee a correct healing of the implant and demonstrate that the fit lock technique also all ows reaching this condition when bone availability is minimal. PMID:23991271

  12. The Autonomous Cryocooled Sapphire Oscillator: A Reference for Frequency Stability and Phase Noise Measurements

    NASA Astrophysics Data System (ADS)

    Giordano, V.; Grop, S.; Fluhr, C.; Dubois, B.; Kersalé, Y.; Rubiola, E.

    2016-06-01

    The Cryogenic Sapphire Oscillator (CSO) is the microwave oscillator which feature the highest short-term stability. Our best units exhibit Allan deviation σy (τ) of 4.5x10-16 at 1s, ≈ 1.5x10-16 at 100 s ≤ t ≤ 5,000 s (floor), and ≤ 5x10-15 at one day. The use of a Pulse-Tube cryocooler enables full two year operation with virtually no maintenance. Starting with a short history of the CSO in our lab, we go through the architecture and we provide more details about the resonator, the cryostat, the oscillator loop, and the servo electronics. We implemented three similar oscillators, which enable the evaluation of each with the three- cornered hat method, and provide the potential for Allan deviation measurements at parts of 10-17 level. One of our CSOs (ULISS) is transportable, and goes with a small customized truck. The unique feature of ULISS is that its σy (τ) can be validated at destination by measuring before and after the roundtrip. To this extent, ULISS can be regarded as a traveling standard of frequency stability. The CSOs are a part of the Oscillator IMP project, a platform dedicated to the measurement of noise and short-term stability of oscillators and devices in the whole radio spectrum (from MHz to THz), including microwave photonics. The scope spans from routine measurements to the research on new oscillators, components, and measurement methods.

  13. Stability improvement of an operational two-way satellite time and frequency transfer system

    NASA Astrophysics Data System (ADS)

    Huang, Yi-Jiun; Fujieda, Miho; Takiguchi, Hiroshi; Tseng, Wen-Hung; Tsao, Hen-Wai

    2016-04-01

    To keep national time accurately coherent with coordinated universal time, many national metrology institutes (NMIs) use two-way satellite time and frequency transfer (TWSTFT) to continuously measure the time difference with other NMIs over an international baseline. Some NMIs have ultra-stable clocks with stability better than 10-16. However, current operational TWSTFT can only provide frequency uncertainty of 10-15 and time uncertainty of 1 ns, which is inadequate. The uncertainty is dominated by the short-term stability and the diurnals, i.e. the measurement variation with a period of one day. The aim of this work is to improve the stability of operational TWSTFT systems without additional transmission, bandwidth or increase in signal power. A software-defined receiver (SDR) comprising a high-resolution correlator and successive interference cancellation associated with open-loop configuration as the TWSTFT receiver reduces the time deviation from 140 ps to 73 ps at averaging time of 1 h, and occasionally suppresses diurnals. To study the source of the diurnals, TWSTFT is performed using a 2  ×  2 earth station (ES) array. Consequently, some ESs sensitive to temperature variation are identified, and the diurnals are significantly reduced by employing insensitive ESs. Hence, the operational TWSTFT using the proposed SDR with insensitive ESs achieves time deviation to 41 ps at 1 h, and 80 ps for averaging times from 1 h to 20 h.

  14. Fast stabilization of a CO{sub 2} laser for a frequency standard at 10 {mu}m

    SciTech Connect

    Pisani, M.Q.; Sassi, M.P.; Zucco, M.

    1994-12-31

    A CO{sub 2} laser has been frequency stabilized to an OsO{sub 4} transition with a control bandwidth of 10 kHz. The obtained spectral purity of the laser is 100 Hz. The realization of very accurate frequency standards and experiments of high resolution spectroscopy in the 10 {mu}m region are made possible by this source.

  15. Frequency stabilization of a 2.05 μm laser using hollow-core fiber CO2 frequency reference cell

    NASA Astrophysics Data System (ADS)

    Meras, Patrick; Poberezhskiy, Ilya Y.; Chang, Daniel H.; Spiers, Gary D.

    2010-04-01

    We have designed and built a hollow-core fiber frequency reference cell, filled it with CO2, and used it to demonstrate frequency stabilization of a 2.05 μm Tm:Ho:YLF laser using frequency modulation (FM) spectroscopy technique. The frequency reference cell is housed in a compact and robust hermetic package that contains a several meter long hollow-core photonic crystal fiber optically coupled to index-guiding fibers with a fusion splice on one end and a mechanical splice on the other end. The package has connectorized fiber pigtails and a valve used to evacuate, refill it, or adjust the gas pressure. We have demonstrated laser frequency standard deviation decreasing from >450MHz (free-running) to <2.4MHz (stabilized). The 2.05 μm laser wavelength is of particular interest for spectroscopic instruments due to the presence of many CO2 and H20 absorption lines in its vicinity. To our knowledge, this is the first reported demonstration of laser frequency stabilization at this wavelength using a hollow-core fiber reference cell. This approach enables all-fiber implementation of the optical portion of laser frequency stabilization system, thus making it dramatically more lightweight, compact, and robust than the traditional free-space version that utilizes glass or metal gas cells. It can also provide much longer interaction length of light with gas and does not require any alignment. The demonstrated frequency reference cell is particularly attractive for use in aircraft and space coherent lidar instruments for measuring atmospheric CO2 profile.

  16. Teaching Absolute Value Meaningfully

    ERIC Educational Resources Information Center

    Wade, Angela

    2012-01-01

    What is the meaning of absolute value? And why do teachers teach students how to solve absolute value equations? Absolute value is a concept introduced in first-year algebra and then reinforced in later courses. Various authors have suggested instructional methods for teaching absolute value to high school students (Wei 2005; Stallings-Roberts…

  17. Optimization of A 2-Micron Laser Frequency Stabilization System for a Double-Pulse CO2 Differential Absorption Lidar

    NASA Technical Reports Server (NTRS)

    Chen, Songsheng; Yu, Jirong; Bai, Yingsin; Koch, Grady; Petros, Mulugeta; Trieu, Bo; Petzar, Paul; Singh, Upendra N.; Kavaya, Michael J.; Beyon, Jeffrey

    2010-01-01

    A carbon dioxide (CO2) Differential Absorption Lidar (DIAL) for accurate CO2 concentration measurement requires a frequency locking system to achieve high frequency locking precision and stability. We describe the frequency locking system utilizing Frequency Modulation (FM), Phase Sensitive Detection (PSD), and Proportional Integration Derivative (PID) feedback servo loop, and report the optimization of the sensitivity of the system for the feed back loop based on the characteristics of a variable path-length CO2 gas cell. The CO2 gas cell is characterized with HITRAN database (2004). The method can be applied for any other frequency locking systems referring to gas absorption line.

  18. 0. 04 Hz relative optical-frequency stability in a 1. 5. mu. m distributed-Bragg-reflector (DBR) laser

    SciTech Connect

    Ishida, O.; Toba, H. ); Tohmori, Y. )

    1989-12-01

    The optical frequency of a 1.5 {mu}m distributed-Bragg-reflector (DBR) laser is stabilized against that of a master laser by heterodyne-type frequency locking with a phase-locked loop (PLL). Despite its wide linewidth of 16 MHz, stable PLL operation with an optical hold-in range of 26 GHz is realized, and residual frequency fluctuations are reduced to 0.04 Hz at an averaging time of 500 s. The combination of DBR laser and PLL is, therefore, suitable for future frequency-controlled light sources. The offset error from the settled frequency caused by the band-limited beat spectrum is also discussed.

  19. Chronic alcohol self-administration in monkeys shows long-term quantity/frequency categorical stability

    PubMed Central

    Baker, Erich J.; Farro, Jonathan; Gonzales, Steven; Helms, Christa; Grant, Kathleen A.

    2014-01-01

    Background The current criteria for alcohol use disorders (AUD) do not include consumption (quantity/frequency) measures of alcohol intake, in part due to the difficulty of these measures in humans. Animal models of ethanol self-administration have been fundamental in advancing our understanding of the neurobiological basis of (AUD) and can address quantity/frequency measures with accurate measurements over prolonged periods of time. The non-human primate (NHP) model of voluntary oral alcohol self-administration has documented both binge drinking and drinking to dependence and can be used to test the stability of consumption measures over time. Methods and Results Here, an extensive set of alcohol intakes (g/kg/day) was analyzed from a large multi-cohort population of Rhesus (Macaca mulatta) monkeys (n=31). Daily ethanol intake was uniformly distributed over chronic (12 months) access for all animals. Underlying this distribution of intakes were subpopulations of monkeys that exhibited distinctive clustering of drinking patterns, allowing us to categorically define very heavy drinking (VHD), heavy drinking (HD), binge drinking (BD), and low drinking (LD). These categories were stable across the 12-month assessed by the protocol, but exhibited fluctuations when examined at shorter intervals. Conclusions The establishment of persistent drinking categories based on quantity/frequency suggests that consumption variables can be used to track long-term changes in behavioral, molecular or physiochemical mechanisms related to our understanding of diagnosis, prevention, intervention and treatment efficacies. PMID:25421519

  20. High frequency stability oscillator for surface acoustic wave-based gas sensor

    NASA Astrophysics Data System (ADS)

    Wang, Wen; He, Shitang; Li, Shunzhou; Pan, Yong

    2006-12-01

    This paper presents a 158 MHz surface acoustic wave (SAW) oscillator used for a gas sensor. As the oscillator element, a SAW delay line on ST-X quartz substrate with low insertion loss (<8 dB) and single mode selection capability was developed. Low insertion loss was achieved by an electrode width control single phase unidirectional transducer (EWC/SPUDT) configuration. Single mode selection was simply accomplished by a comb transducer which is a means of combining the frequency selectivity of two interdigital transducers (IDTs). Coupling of modes (COM) simulation was performed to predict device performance prior to fabrication. The measured frequency response S12 showed a good agreement with simulated results. The effect of the oscillator circuit system temperature shift upon frequency stability was observed in detail. The experimental results showed that the baseline noise was typically up to ~0.7 × 10-7 in a laboratory environment with temperature control. The oscillator was successfully applied to a gas sensor coated self-assembled composite monolayer as a sensor material for dimethyl-methyl-phosphonate (DMMP). The sensitivity for low DMMP concentration detection was evaluated as ~25 Hz mg-1 m-3, and the threshold detection limit was up to 0.5 mg m-3.

  1. Short-term stability improvements of an optical frequency standard based on free Ca atoms

    NASA Astrophysics Data System (ADS)

    Sherman, Jeff; Oates, Chris

    2010-03-01

    Compared to optical frequency standards featuring trapped ions or atoms in optical lattices, the strength of a standard using freely expanding neutral calcium atoms is not ultimate accuracy but rather short-term stability and experimental simplicity. Recently, a fractional frequency instability of 4 x10-15 at 1 second was demonstrated for the Ca standard at 657 nm [1]. The short cycle time (˜2 ms) combined with only a moderate interrogation duty cycle (˜15 %) is thought to introduce excess, and potentially critically limiting technical noise due to the Dick effect---high-frequency noise on the laser oscillator is not averaged away but is instead down-sampled by aliasing. We will present results of two strategies employed to minimize this effect: the reduction of clock laser noise by filtering the master clock oscillator through a high-finesse optical cavity [2], and an optimization of the interrogation cycle to match our laser's noise spectrum.[4pt] [1] Oates et al., Optics Letters, 25(21), 1603--5 (2000)[0pt] [2] Nazarova et al., J. Opt. Soc. Am. B, 5(10), 1632--8 (2008)

  2. Gigahertz frequency comb offset stabilization based on supercontinuum generation in silicon nitride waveguides.

    PubMed

    Klenner, Alexander; Mayer, Aline S; Johnson, Adrea R; Luke, Kevin; Lamont, Michael R E; Okawachi, Yoshitomo; Lipson, Michal; Gaeta, Alexander L; Keller, Ursula

    2016-05-16

    Silicon nitride (Si3N4) waveguides represent a novel photonic platform that is ideally suited for energy efficient and ultrabroadband nonlinear interactions from the visible to the mid-infrared. Chip-based supercontinuum generation in Si3N4 offers a path towards a fully-integrated and highly compact comb source for sensing and time-and-frequency metrology applications. We demonstrate the first successful frequency comb offset stabilization that utilizes a Si3N4 waveguide for octave-spanning supercontinuum generation and achieve the lowest integrated residual phase noise of any diode-pumped gigahertz laser comb to date. In addition, we perform a direct comparison to a standard silica photonic crystal fiber (PCF) using the same ultrafast solid-state laser oscillator operating at 1 µm. We identify the minimal role of Raman scattering in Si3N4 as a key benefit that allows to overcome the fundamental limitations of silica fibers set by Raman-induced self-frequency shift. PMID:27409927

  3. Optical Frequency Stabilization and Optical Phase Locked Loops: Golden Threads of Precision Measurement

    SciTech Connect

    Taubman, Matthew S.

    2013-07-01

    Stabilization of lasers through locking to optical cavities, atomic transitions, and molecular transitions has enabled the field of precision optical measurement since shortly after the invention of the laser. Recent advances in the field have produced an optical clock that is orders of magnitude more stable than those of just a few years prior. Phase locking of one laser to another, or to a frequency offset from another, formed the basis for linking stable lasers across the optical spectrum, such frequency chains exhibiting progressively finer precision through the years. Phase locking between the modes within a femtosecond pulsed laser has yielded the optical frequency comb, one of the most beautiful and useful instruments of our time. This talk gives an overview of these topics, from early work through to the latest 1E-16 thermal noise-limited precision recently attained for a stable laser, and the ongoing quest for ever finer precision and accuracy. The issues of understanding and measuring line widths and shapes are also studied in some depth, highlighting implications for servo design for sub-Hz line widths.

  4. Transient Stability and Frequency Response of the US Western Interconnection under conditions of High Wind and Solar Generation

    SciTech Connect

    Clark, Kara; Miller, Nicholas W.; Shao, Miaolei; Pajic, Slobodan; D'Aquila, Robert

    2015-04-15

    Adding large amounts of wind and solar generation to bulk power systems that are traditionally subject to operating constraints set by transient stability and frequency response limitations is the subject of considerable concern in the industry. The US Western Interconnection (WI) is expected to experience substantial additional growth in both wind and solar generation. These plants will, to some extent, displace large central station thermal generation, both coal and gas-fired, which have traditionally helped maintain stability. Our paper reports the results of a study that investigated the transient stability and frequency response of the WI with high penetrations of wind and solar generation. Moreover, the main goals of this work were to (1) create a realistic, baseline model of the WI, (2) test selected transient stability and frequency events, (3) investigate the impact of large amounts of wind and solar generation, and (4) examine means to improve performance.

  5. Modulation-free laser frequency stabilization to a saturated sub-Doppler spectral line in a transversal magnetic field

    NASA Astrophysics Data System (ADS)

    Okubo, Sho; Iwakuni, Kana; Hasegawa, Taro

    2012-09-01

    We demonstrate frequency stabilization of a modulation-free laser to a saturated absorption spectral line of atoms in a transversal magnetic field. This stabilization scheme has been proposed for wide capture range in comparison with the dichroic atomic vapor laser lock (DAVLL) scheme and demonstrated for a Doppler-broadened spectral line in J. Opt. Soc. Am. B, 26, 1216 (2009). In this paper, a 1083-nm external-cavity laser diode is frequency-stabilized to the sub-Doppler spectral line of helium transition (23S1,mJ=0↔23P0). Even though the error signal shape strongly depends on the pump beam polarization, the stabilized frequency is expected to be insensitive to the pump beam polarization.

  6. Frequency stabilization of a 1083 nm fiber laser to ⁴He transition lines with optical heterodyne saturation spectroscopies.

    PubMed

    Gong, W; Peng, X; Li, W; Guo, H

    2014-07-01

    Two kinds of optical heterodyne saturation spectroscopies, namely, frequency modulation spectroscopy (FMS) and modulation transfer spectroscopy (MTS), are demonstrated for locking a fiber laser to the transition lines of metastable (4)He atoms around 1083 nm. The servo-loop error signals of FMS and MTS for stabilizing laser frequency are optimized by studying the dependence of the peak-to-peak amplitude and slope on the optical power of pump and probe beams. A comparison of the stabilization performances of FMS/MTS and polarization spectroscopy (PS) is presented, which shows that MTS exhibits relatively superior performance with the least laser frequency fluctuation due to its flat-background dispersive signal, originated from the four-wave mixing process. The Allan deviation of the stabilized laser frequency is 5.4 × 10(-12)@100 s with MTS for data acquired in 1000 s, which is sufficiently applicable for fields like laser cooling, optical pumping, and optical magnetometry. PMID:25085123

  7. Frequency stabilization of a 1083 nm fiber laser to {sup 4}He transition lines with optical heterodyne saturation spectroscopies

    SciTech Connect

    Gong, W.; Peng, X. Li, W.; Guo, H.

    2014-07-15

    Two kinds of optical heterodyne saturation spectroscopies, namely, frequency modulation spectroscopy (FMS) and modulation transfer spectroscopy (MTS), are demonstrated for locking a fiber laser to the transition lines of metastable {sup 4}He atoms around 1083 nm. The servo-loop error signals of FMS and MTS for stabilizing laser frequency are optimized by studying the dependence of the peak-to-peak amplitude and slope on the optical power of pump and probe beams. A comparison of the stabilization performances of FMS/MTS and polarization spectroscopy (PS) is presented, which shows that MTS exhibits relatively superior performance with the least laser frequency fluctuation due to its flat-background dispersive signal, originated from the four-wave mixing process. The Allan deviation of the stabilized laser frequency is 5.4 × 10{sup −12}@100 s with MTS for data acquired in 1000 s, which is sufficiently applicable for fields like laser cooling, optical pumping, and optical magnetometry.

  8. Frequency stabilization of a 1083 nm fiber laser to 4He transition lines with optical heterodyne saturation spectroscopies

    NASA Astrophysics Data System (ADS)

    Gong, W.; Peng, X.; Li, W.; Guo, H.

    2014-07-01

    Two kinds of optical heterodyne saturation spectroscopies, namely, frequency modulation spectroscopy (FMS) and modulation transfer spectroscopy (MTS), are demonstrated for locking a fiber laser to the transition lines of metastable 4He atoms around 1083 nm. The servo-loop error signals of FMS and MTS for stabilizing laser frequency are optimized by studying the dependence of the peak-to-peak amplitude and slope on the optical power of pump and probe beams. A comparison of the stabilization performances of FMS/MTS and polarization spectroscopy (PS) is presented, which shows that MTS exhibits relatively superior performance with the least laser frequency fluctuation due to its flat-background dispersive signal, originated from the four-wave mixing process. The Allan deviation of the stabilized laser frequency is 5.4 × 10-12@100 s with MTS for data acquired in 1000 s, which is sufficiently applicable for fields like laser cooling, optical pumping, and optical magnetometry.

  9. Frequency stabilization of the zero-phonon line of a quantum dot via phonon-assisted active feedback

    SciTech Connect

    Hansom, Jack; Schulte, Carsten H. H.; Matthiesen, Clemens; Stanley, Megan J.; Atatüre, Mete

    2014-10-27

    We report on the feedback stabilization of the zero-phonon emission frequency of a single InAs quantum dot. The spectral separation of the phonon-assisted component of the resonance fluorescence provides a probe of the detuning between the zero-phonon transition and the resonant driving laser. Using this probe in combination with active feedback, we stabilize the zero-phonon transition frequency against environmental fluctuations. This protocol reduces the zero-phonon fluorescence intensity noise by a factor of 22 by correcting for environmental noise with a bandwidth of 191 Hz, limited by the experimental collection efficiency. The associated sub-Hz fluctuations in the zero-phonon central frequency are reduced by a factor of 7. This technique provides a means of stabilizing the quantum dot emission frequency without requiring access to the zero-phonon emission.

  10. Power-Stabilization of High Frequency Gyrotrons Using a Double PID Feedback Control for Applications to High Power THz Spectroscopy

    NASA Astrophysics Data System (ADS)

    Idehara, Toshitaka; Kuleshov, Alexei; Ueda, Keisuke; Khutoryan, Eduard

    2013-11-01

    High stabilization of the output power of high frequency gyrotrons for high power THz spectroscopy is an important issue in order to extend the applications of gyrotrons to wider subjects. For this objective, we tried a PID feedback control on a heater current of a triode magnetron injection gun (MIG) for stabilization of an electron beam current and an additional PID control of an anode voltage of the gun for direct stabilization of output power. This double PID control achieved effective responses for the stabilization of output power in both slow (from several tens seconds to several minutes) and fast (from milliseconds to seconds) time scales.

  11. Stabilization and Low-Frequency Oscillation of Capillary Bridges with Modulated Acoustic Radiation Pressure

    NASA Technical Reports Server (NTRS)

    Marston, Philip L.; Marr-Lyon, Mark J.; Morse, S. F.; Thiessen, David B.

    1996-01-01

    In the work reported here it is demonstrated that acoustic radiation pressure may be used in simulated low gravity to produce stable bridges significantly beyond the Rayleigh limit with S as large as 3.6. The bridge (PDMS mixed with a dense liquid) has the same density as the surrounding water bath containing an ultrasonic standing wave. Modulation was first used to excite specific bridge modes. In the most recent work reported here the shape of the bridge is optically sensed and the ultrasonic drive is electronically adjusted such that the radiation stress distribution dynamically quenches the most unstable mode. This active control simulates passive stabilization suggested for low gravity. Feedback increases the mode frequency in the naturally stable region since the effective stiffness of the mode is increased.

  12. Observation and Absolute Frequency Measurements of the {sup 1}S{sub 0}-{sup 3}P{sub 0} Optical Clock Transition in Neutral Ytterbium

    SciTech Connect

    Hoyt, C.W.; Barber, Z.W.; Oates, C.W.; Fortier, T.M.; Diddams, S.A.; Hollberg, L.

    2005-08-19

    We report the direct excitation of the highly forbidden (6s{sup 2}){sup 1}S{sub 0}{r_reversible}(6s6p){sup 3}P{sub 0} optical transition in two odd isotopes of neutral ytterbium. As the excitation laser frequency is scanned, absorption is detected by monitoring the depletion from an atomic cloud at {approx}70 {mu}K in a magneto-optical trap. The measured frequency in {sup 171}Yb (F=1/2) is 518 295 836 591.6{+-}4.4 kHz. The measured frequency in {sup 173}Yb (F=5/2) is 518 294 576 847.6{+-}4.4 kHz. Measurements are made with a femtosecond-laser frequency comb calibrated by the National Institute of Standards and Technology cesium fountain clock and represent nearly a 10{sup 6}-fold reduction in uncertainty. The natural linewidth of these J=0 to J=0 transitions is calculated to be {approx}10 mHz, making them well suited to support a new generation of optical atomic clocks based on confinement in an optical lattice.

  13. Emulsification by high frequency ultrasound using piezoelectric transducer: formation and stability of emulsifier free emulsion.

    PubMed

    Kaci, Messaouda; Meziani, Smail; Arab-Tehrany, Elmira; Gillet, Guillaume; Desjardins-Lavisse, Isabelle; Desobry, Stephane

    2014-05-01

    Emulsifier free emulsion was developed with a new patented technique for food and cosmetic applications. This emulsification process dispersed oil droplets in water without any emulsifier. Emulsions were prepared with different vegetable oil ratios 5%, 10% and 15% (v/v) using high frequency ultrasounds generated by piezoelectric ceramic transducer vibrating at 1.7 MHz. The emulsion was prepared with various emulsification times between 0 and 10h. Oil droplets size was measured by laser granulometry. The pH variation was monitored; electrophoretic mobility and conductivity variation were measured using Zêtasizer equipment during emulsification process. The results revealed that oil droplets average size decreased significantly (p<0.05) during the first 6h of emulsification process and that from 160 to 1 μm for emulsions with 5%, 10% and from 400 to 29 μm for emulsion with 15% of initial oil ratio. For all tested oil ratios, pH measurement showed significant decrease and negative electrophoretic mobility showed the accumulation of OH(-) at oil/water interface leading to droplets stability in the emulsion. The conductivity of emulsions showed a decrease of the ions quantity in solution, which indicated formation of positive charge layer around OH(-) structure. They constitute a double ionic layer around oil particles providing emulsion stability. This study showed a strong correlation between turbidity measurement and proportion of emulsified oil. PMID:24315670

  14. On-chip multi spectral frequency standard replication by stabilizing a microring resonator to a molecular line

    NASA Astrophysics Data System (ADS)

    Zektzer, Roy; Stern, Liron; Mazurski, Noa; Levy, Uriel

    2016-07-01

    Stabilized laser lines are highly desired for myriad of applications ranging from precise measurements to optical communications. While stabilization can be obtained by using molecular or atomic absorption references, these are limited to specific frequencies. On the other hand, resonators can be used as wide band frequency references. Unfortunately, such resonators are unstable and inaccurate. Here, we propose and experimentally demonstrate a chip-scale multispectral frequency standard replication operating in the spectral range of the near IR. This is obtained by frequency locking a microring resonator (MRR) to an acetylene absorption line. The MRR consists of a Si3N4 waveguides with microheater on top of it. The thermo-optic effect is utilized to lock one of the MRR resonances to an acetylene line. This locked MRR is then used to stabilize other laser sources at 980 nm and 1550 nm wavelength. By beating the stabilized laser to another stabilized laser, we obtained frequency instability floor of 4 ×10-9 at around 100 s in terms of Allan deviation. Such stable and accurate chip scale sources are expected to serve as important building block in diverse fields such as communication and metrology.

  15. The Interannual Stability of Cumulative Frequency Distributions for Convective System Size and Intensity

    NASA Technical Reports Server (NTRS)

    Mohr, Karen I.; Molinari, John; Thorncroft, Chris D,

    2010-01-01

    The characteristics of convective system populations in West Africa and the western Pacific tropical cyclone basin were analyzed to investigate whether interannual variability in convective activity in tropical continental and oceanic environments is driven by variations in the number of events during the wet season or by favoring large and/or intense convective systems. Convective systems were defined from TRMM data as a cluster of pixels with an 85 GHz polarization-corrected brightness temperature below 255 K and with an area at least 64 km 2. The study database consisted of convective systems in West Africa from May Sep for 1998-2007 and in the western Pacific from May Nov 1998-2007. Annual cumulative frequency distributions for system minimum brightness temperature and system area were constructed for both regions. For both regions, there were no statistically significant differences among the annual curves for system minimum brightness temperature. There were two groups of system area curves, split by the TRMM altitude boost in 2001. Within each set, there was no statistically significant interannual variability. Sub-setting the database revealed some sensitivity in distribution shape to the size of the sampling area, length of sample period, and climate zone. From a regional perspective, the stability of the cumulative frequency distributions implied that the probability that a convective system would attain a particular size or intensity does not change interannually. Variability in the number of convective events appeared to be more important in determining whether a year is wetter or drier than normal.

  16. Multipoint joint time and frequency dissemination in delay-stabilized fiber optic links.

    PubMed

    Śliwczyński, Ł; Krehlik, P

    2015-03-01

    This paper presents the system for dissemination of both the RF frequency (e.g., 5, 10, or 100 MHz) and time (pulse per second) signals using an actively tapped fiber-optic link with electronic stabilization of the propagation delay. In principle several nodes for accessing the time/frequency signals may be added without the degradation of the dissemination in the main link. We are discussing the algorithm of determining the propagation delay from the local end of the link to the access node that is required for calibration of the time dissemination. Performed analysis shows that the uncertainty of the time calibration at the access node may in practice be dominated by the dependence of the propagation delay of the receivers on impinging optical powers and is only weakly affected by the distance between the local and access modules. The uncertainty is, however, still low, being only about two times higher compared with the calibration uncertainty of the main link. Experimental results performed on several spooled fibers show that the accuracy of described calibration procedures, expressed as a difference from the results of direct measurement, is not worse than 35 ps. PMID:25768810

  17. Far off-resonance laser frequency stabilization using multipass cells in Faraday rotation spectroscopy.

    PubMed

    Quan, Wei; Li, Yang; Li, Rujie; Shang, Huining; Fang, Zishan; Qin, Jie; Wan, Shuangai

    2016-04-01

    We propose a far off-resonance laser frequency stabilization method by using multipass cells in Rb Faraday rotation spectroscopy. Based on the detuning equation, if multipass cells with several meters optical path length are used in the conventional Faraday spectroscopy, the detuning of the lock point can be extended much further from the alkali metal resonance. A plate beam splitter was used to generate two different Faraday signals at the same time. The transmitted optical path length was L=50  mm and the reflected optical path length was 2L=100  mm. When the optical path length doubled, the detuning of the lock points moved further away from the atomic resonance. The temperature dependence of the detuning of the lock point was also analyzed. A temperature-insensitive lock point was found near resonance when the cell temperature was between 110°C and 130°C. We achieved an rms fluctuation of 0.9 MHz/23 h at a detuning of 0.5 GHz. A frequency drift of 16 MHz/h at a detuning of -5.6  GHz and 4 MHz/h at a detuning of -5.2  GHz were also obtained for the transmitted and reflected light Faraday signal. PMID:27139650

  18. Absorption line metrology by optical feedback frequency-stabilized cavity ring-down spectroscopy

    NASA Astrophysics Data System (ADS)

    Burkart, Johannes; Kassi, Samir

    2015-04-01

    Optical feedback frequency-stabilized cavity ring-down spectroscopy (OFFS-CRDS) is a near-shot-noise-limited technique combining a sensitivity of with a highly linear frequency axis and sub-kHz resolution. Here, we give an in-depth review of the key elements of the experimental setup encompassing a highly stable V-shaped reference cavity, an integrated Mach-Zehnder modulator and a tightly locked ring-down cavity with a finesse of 450,000. Carrying out a detailed analysis of the spectrometer performance and its limitations, we revisit the photo-electron shot-noise limit in CRDS and discuss the impact of optical fringes. We demonstrate different active schemes for fringe cancelation by varying the phase of parasitic reflections. The proof-of-principle experiments reported here include a broadband high-resolution spectrum of carbon dioxide at 1.6 µm and an isolated line-shape measurement with a signal-to-noise ratio of 80,000. Beyond laboratory-based absorption line metrology for fundamental research, OFFS-CRDS holds a considerable potential for field laser measurements of trace gas concentrations and isotopic ratios by virtue of its small sample volume and footprint, the robust cavity-locking scheme and supreme precision.

  19. Frequency, stability and differentiation of self-reported school fear and truancy in a community sample

    PubMed Central

    Steinhausen, Hans-Christoph; Müller, Nora; Metzke, Christa Winkler

    2008-01-01

    Background Surprisingly little is known about the frequency, stability, and correlates of school fear and truancy based on self-reported data of adolescents. Methods Self-reported school fear and truancy were studied in a total of N = 834 subjects of the community-based Zurich Adolescent Psychology and Psychopathology Study (ZAPPS) at two times with an average age of thirteen and sixteen years. Group definitions were based on two behavioural items of the Youth Self-Report (YSR). Comparisons included a control group without indicators of school fear or truancy. The three groups were compared across questionnaires measuring emotional and behavioural problems, life-events, self-related cognitions, perceived parental behaviour, and perceived school environment. Results The frequency of self-reported school fear decreased over time (6.9 vs. 3.6%) whereas there was an increase in truancy (5.0 vs. 18.4%). Subjects with school fear displayed a pattern of associated internalizing problems and truants were characterized by associated delinquent behaviour. Among other associated psychosocial features, the distress coming from the perceived school environment in students with school fear is most noteworthy. Conclusion These findings from a community study show that school fear and truancy are frequent and display different developmental trajectories. Furthermore, previous results are corroborated which are based on smaller and selected clinical samples indicating that the two groups display distinct types of school-related behaviour. PMID:18625042

  20. Eosinophil count - absolute

    MedlinePlus

    Eosinophils; Absolute eosinophil count ... the white blood cell count to give the absolute eosinophil count. ... than 500 cells per microliter (cells/mcL). Normal value ranges may vary slightly among different laboratories. Talk ...

  1. Stabilization and time resolved measurement of the frequency evolution of a modulated diode laser for chirped pulse generation

    NASA Astrophysics Data System (ADS)

    Varga-Umbrich, K.; Bakos, J. S.; Djotyan, G. P.; Ignácz, P. N.; Ráczkevi, B.; Sörlei, Zs; Szigeti, J.; Kedves, M. Á.

    2016-05-01

    We have developed experimental methods for the generation of chirped laser pulses of controlled frequency evolution in the nanosecond pulse length range for coherent atomic interaction studies. The pulses are sliced from the radiation of a cw external cavity diode laser while its drive current, and consequently its frequency, are sinusoidally modulated. By the proper choice of the modulation parameters, as well as of the timing of pulse slicing, we can produce a wide variety of frequency sweep ranges during the pulse. In order to obtain the required frequency chirp, we need to stabilize the center frequency of the modulated laser and to measure the resulting frequency evolution with appropriate temporal resolution. These tasks have been solved by creating a beat signal with a reference laser locked to an atomic transition frequency. The beat signal is then analyzed, as well as its spectral sideband peaks are fed back to the electronics of the frequency stabilization of the modulated laser. This method is simple and it has the possibility for high speed frequency sweep with narrow linewidth that is appropriate, for example, for selective manipulation of atomic states in a magneto-optical trap.

  2. Simple digital system for tuning and long-term frequency stabilization of a CW Ti:Sapphire laser

    NASA Astrophysics Data System (ADS)

    Beterov, Ilya I.; Markovski, Asparuh G.; Kobtsev, Sergey M.; Yakshina, Elena A.; Entin, Vasily M.; Tretyakov, Denis B.; Baraulya, Vladimir I.; Ryabtsev, Igor I.

    2015-03-01

    We have implemented a simple digital system for long-term frequency stabilization and locking to an arbitrary wavelength of the single-frequency ring CW Ti:Sapphire laser. This system is built using two confocal Fabry-Pérot cavities, one of which is used to narrow the short-term linewidth of the laser and the other to improve the long-term stability of the laser frequency. The length of the second cavity is stabilized using the radiation from an external-cavity diode laser locked to an atomic transition. Our system is an improvement of a commercial Tekhnoscan laser lock. This system has been successfully used in our experiments on high-resolution laser spectroscopy of ultracold rubidium Rydberg atoms.

  3. Active laser frequency stabilization and resolution enhancement of interferometers for the measurement of gravitational waves in space

    NASA Astrophysics Data System (ADS)

    Herz, Markus

    2005-09-01

    Laser frequency stabilization is notably one of the major challenges on the way to a space-borne gravitational wave observatory. The proposed Laser Interferometer Space Antenna (LISA) is presently under development in an ESA, NASA collaboration. We present a novel method for active laser stabilization and phase noise suppression in such a gravitational wave detector. The proposed approach is a further evolution of the "arm-locking" method, which in essence consists of using an interferometer arm as an optical cavity, exploiting the extreme long-run stability of the cavity size in the frequency band of interest. We extend this method by using the natural interferometer arm length differences and existing interferometer signals as additional information sources for the reconstruction and active suppression of the quasi-periodic laser frequency noise, enhancing the resolution power of space-borne gravitational wave detectors.

  4. A frequency-stabilized Yb:KYW femtosecond laser frequency comb and its application to low-phase-noise microwave generation

    NASA Astrophysics Data System (ADS)

    Meyer, Stephanie A.; Fortier, Tara M.; Lecomte, Steve; Diddams, Scott A.

    2013-09-01

    We present an optically stabilized Yb:KYW fs-laser frequency comb. We use an f-2 f nonlinear interferometer to measure the carrier envelope offset frequency ( f 0) and the heterodyne beatnote between the comb and a stable CW laser at 1068 nm to detect fluctuations in the comb repetition rate (). Both of these degrees of freedom of the comb are then controlled using phase-locked loops. As a demonstration of the frequency-stabilized comb, we generate low-phase-noise 10 GHz microwaves through detection of the pulse train on a high bandwidth photodiode. The phase noise of the resulting 10 GHz microwaves was -99 dBc/Hz at 1 Hz and the corresponding Allen deviation was <2.6 × 10-15 at 1 s, measured by comparison to an independently stabilized Ti:sapphire frequency comb. This room-temperature, optically based source of microwaves has close-to-carrier phase noise comparable to the very best cryogenic microwave oscillators.

  5. Linearized blade row compression component model. Stability and frequency response analysis of a J85-3 compressor

    NASA Technical Reports Server (NTRS)

    Tesch, W. A.; Moszee, R. H.; Steenken, W. G.

    1976-01-01

    NASA developed stability and frequency response analysis techniques were applied to a dynamic blade row compression component stability model to provide a more economic approach to surge line and frequency response determination than that provided by time-dependent methods. This blade row model was linearized and the Jacobian matrix was formed. The clean-inlet-flow stability characteristics of the compressors of two J85-13 engines were predicted by applying the alternate Routh-Hurwitz stability criterion to the Jacobian matrix. The predicted surge line agreed with the clean-inlet-flow surge line predicted by the time-dependent method to a high degree except for one engine at 94% corrected speed. No satisfactory explanation of this discrepancy was found. The frequency response of the linearized system was determined by evaluating its Laplace transfer function. The results of the linearized-frequency-response analysis agree with the time-dependent results when the time-dependent inlet total-pressure and exit-flow function amplitude boundary conditions are less than 1 percent and 3 percent, respectively. The stability analysis technique was extended to a two-sector parallel compressor model with and without interstage crossflow and predictions were carried out for total-pressure distortion extents of 180 deg, 90 deg, 60 deg, and 30 deg.

  6. Absolute CF{sub 2} density and gas temperature measurements by absorption spectroscopy in dual-frequency capacitively coupled CF{sub 4}/Ar plasmas

    SciTech Connect

    Liu, Wen-Yao; Xu, Yong Peng, Fei; Gong, Fa-Ping; Li, Xiao-Song; Zhu, Ai-Min; Liu, Yong-Xin; Wang, You-Nian

    2014-10-15

    Broadband ultraviolet absorption spectroscopy has been used to determine the CF{sub 2} radical density in dual-frequency capacitively coupled CF{sub 4}/Ar plasmas, using the CF{sub 2} A{sup ~1}B{sub 1}←X{sup ~1}A{sub 1} system of absorption spectrum. The rotational temperature of ground state CF{sub 2} and excited state CF was also estimated by using A{sup ~1}B{sub 1}←X{sup ~1}A{sub 1} system and B{sup 2}Δ−X{sup 2}Π system, respectively. The translational gas temperature was deduced from the Doppler width of the Ar{sup *}({sup 3}P{sub 2}) and Ar{sup *}({sup 3}P{sub 0}) metastable atoms absorption line by using the tunable diode laser absorption spectroscopy. The rotational temperatures of the excited state CF are about 100 K higher than those of ground state CF{sub 2}, and about 200 K higher than the translational gas temperatures. The dependences of the radical CF{sub 2} density, electron density, electron temperature, rotational temperature, and gas temperature on the high frequency power and pressure have been analyzed. Furthermore, the production and loss mechanisms of CF{sub 2} radical and the gas heating mechanisms have also been discussed.

  7. Laser Frequency Stabilization for Coherent Lidar Applications using Novel All-Fiber Gas Reference Cell Fabrication Technique

    NASA Technical Reports Server (NTRS)

    Meras, Patrick, Jr.; Poberezhskiy, Ilya Y.; Chang, Daniel H.; Levin, Jason; Spiers, Gary D.

    2008-01-01

    Compact hollow-core photonic crystal fiber (HC-PCF)gas frequency reference cell was constructed using a novel packaging technique that relies on torch-sealing a quartz filling tube connected to a mechanical splice between regular and hollow-core fibers. The use of this gas cell for laser frequency stabilization was demonstrated by locking a tunable diode laser to the center of the P9 line from the (nu)1+(nu)3 band of acetylene with RMS frequency error of 2.06 MHz over 2 hours. This effort was performed in support of a task to miniaturize the laser frequency stabilization subsystem of JPL/LMCT Laser Absorption Spectrometer (LAS) instrument.

  8. Theoretical and experimental analysis of high-power frequency-stabilized semiconductor master oscillator power-amplifier system.

    PubMed

    Ji, Encai; Liu, Qiang; Nie, Mingming; Fu, Xing; Gong, Mali

    2016-04-10

    We present a compact high-power 780 nm frequency-stabilized diode laser with a power of as high as 2.825 W, corresponding to an estimated overall efficiency of 38.5%. The tapered amplifier (TPA) gain was about 24.5 dB, which was basically consistent with the simulation results. The beam quality factor was M2<1.72. The core feature of the system was stabilizing the frequency of the narrowband semiconductor TPA system with the matured saturated absorption spectrum technique. The laser frequency was stabilized against mode hops for a period of >4200  s with a frequency fluctuation around 6.7×10-10 within 1 s of the observation period, and the linewidth was no more than 0.95 MHz. The laser performance indicates that the current frequency-stabilized semiconductor laser has great potential in certain conditions that require several watts of output power. PMID:27139853

  9. Design of laser system for absolute gravimeter based on 87Rb atom interferometer

    NASA Astrophysics Data System (ADS)

    Zhao, Yang; Wang, Shaokai; Zhuang, Wei; Fang, Fang; Li, Tianchu

    2015-08-01

    We present a laser system design for an absolute gravimeter based on 87Rb atom interferometer. By skillful design, lasers with 9 different frequencies are based on two diode lasers including tapered amplifier. Two electrical feedback systems are used for laser frequency stabilization and the Raman lasers generation respectively. All other lasers are based on two Raman lasers and realized with frequency shift by acoustic optical modulators. This laser system not only has the compact and simple construction, but meets all requirements for laser power and frequency controlling for the atom interferometer. It has the characteristic of reliability and integrity.

  10. Dynamic characterization and single-frequency cancellation performance of SMASH (SMA actuated stabilizing handgrip)

    NASA Astrophysics Data System (ADS)

    Pathak, Anupam; Brei, Diann; Luntz, Jonathan; LaVigna, Chris; Kwatny, Harry

    2008-03-01

    In urban combat environments where it is common to have unsupported firing positions, wobble significantly decreases shooting accuracy reducing mission effectiveness and soldier survivability. The SMASH (SMA Stabilizing Handgrip) has been developed to cancel wobble using antagonistic SMA actuators which reduce weight and size relative to conventional actuation, but lead to interesting control challenges. This paper presents the specification and design of the SMA actuation system for the SMASH platform along with experimental validation of the actuation and cancellation authority on the benchtop and on an M16 platform. Analytical dynamic weapon models and shooter experiments were conducted to define actuation frequency and amplitude specifications. The SMASH, designed to meet these, was experimentally characterized from the bounding quasi-static case up to the 3 Hz range, successfully generating the +/-2 mm amplitude requirement. To effectively cancel wobble it is critical to produce the proper output functional shape which is difficult for SMA due to inherent nonlinearities, hysteresis, etc. Three distinct electrical heating input functions (square, ramp, and preheat) were investigated to shape the actuator output to produce smooth sinusoidal motion. The effect of each of these functions on the cancellation response of the SMASH applied to the M16 platform was experimentally studied across the wobble range (1-3 Hz) demonstrating significant cancellation, between 50-97% depending on the smoothing function and frequency. These results demonstrate the feasibility of a hand-held wobble cancellation device providing an important foundation for future work in overall system optimization and the development of physically based feed-forward signals for closed-loop control.

  11. The Interannual Stability of Cumulative Frequency Distributions for Convective System Size and Intensity

    NASA Technical Reports Server (NTRS)

    Mohr, Karen I.; Molinari, John; Thorncroft, Chris

    2009-01-01

    The characteristics of convective system populations in West Africa and the western Pacific tropical cyclone basin were analyzed to investigate whether interannual variability in convective activity in tropical continental and oceanic environments is driven by variations in the number of events during the wet season or by favoring large and/or intense convective systems. Convective systems were defined from Tropical Rainfall Measuring Mission (TRMM) data as a cluster of pixels with an 85-GHz polarization-corrected brightness temperature below 255 K and with an area of at least 64 square kilometers. The study database consisted of convective systems in West Africa from May to September 1998-2007, and in the western Pacific from May to November 1998-2007. Annual cumulative frequency distributions for system minimum brightness temperature and system area were constructed for both regions. For both regions, there were no statistically significant differences between the annual curves for system minimum brightness temperature. There were two groups of system area curves, split by the TRMM altitude boost in 2001. Within each set, there was no statistically significant interannual variability. Subsetting the database revealed some sensitivity in distribution shape to the size of the sampling area, the length of the sample period, and the climate zone. From a regional perspective, the stability of the cumulative frequency distributions implied that the probability that a convective system would attain a particular size or intensity does not change interannually. Variability in the number of convective events appeared to be more important in determining whether a year is either wetter or drier than normal.

  12. Optomechanics for absolute rotation detection

    NASA Astrophysics Data System (ADS)

    Davuluri, Sankar

    2016-07-01

    In this article, we present an application of optomechanical cavity for the absolute rotation detection. The optomechanical cavity is arranged in a Michelson interferometer in such a way that the classical centrifugal force due to rotation changes the length of the optomechanical cavity. The change in the cavity length induces a shift in the frequency of the cavity mode. The phase shift corresponding to the frequency shift in the cavity mode is measured at the interferometer output to estimate the angular velocity of absolute rotation. We derived an analytic expression to estimate the minimum detectable rotation rate in our scheme for a given optomechanical cavity. Temperature dependence of the rotation detection sensitivity is studied.

  13. Apparatus for using a time interval counter to measure frequency stability

    NASA Technical Reports Server (NTRS)

    Greenhall, Charles A. (Inventor)

    1989-01-01

    An apparatus for measuring the relative stability of two signals is disclosed comprising a means for mixing the two signals down to a beat note sine wave and for producing a beat note square wave whose upcrossings are the same as the sine wave. A source of reference frequency is supplied to a clock divider and interval counter to synchronize them and to generate a picket fence for providing a time reference grid of period shorter than the beat period. An interval counter is employed to make a preliminary measurement between successive upcrossings of the beat note square wave for providing an approximate time interval therebetween as a reference. The beat note square wave and the picket fence are then provided to the interval counter to provide an output consisting of the time difference between the upcrossing of each beat note square wave cycle and the next picket fence pulse such that the counter is ready for each upcrossing and dead time is avoided. A computer containing an algorithm for calculating the exact times of the beat note upcrossings then computes the upcrossing times.

  14. Motion correction and frequency stabilization for MRS of the human spinal cord.

    PubMed

    Hock, Andreas; Henning, Anke

    2016-04-01

    Subject motion is challenging for MRS, because it can falsify results. For spinal cord MRS in particular, subject movement is critical, since even a small movement > 1 mm) can lead to a voxel shift out of the desired measurement region. Therefore, the identification of motion corrupted MRS scans is essential. In this investigation, MR navigators acquired simultaneously with the MRS data are used to identify a displacement of the spinal cord due to subject motion. It is shown that navigators are able to recognize substantial subject motion (>1 mm) without impairing the MRS measurement. In addition, navigators are easy to apply to the measurement, because no additional hardware and just a minor additional user effort are needed. Moreover, no additional scan time is required, because navigators can be applied in the deadtime of the MRS sequence. Furthermore, in this work, retrospective motion correction combined with frequency stabilization is presented by combining navigators with non-water-suppressed (1) H-MRS, resulting in an improved spectral quality of the spinal cord measurements. Copyright © 2016 John Wiley & Sons, Ltd. PMID:26867133

  15. Frequency stabilization of single layer graphene oscillators through optical injection locking

    NASA Astrophysics Data System (ADS)

    Houri, Samer; Cartamil Bueno, Santiago; Venstra, Warner

    Single layer graphene (SLG) drum resonators offer exciting prospects as experimental testbeds for nonlinear dynamics. Recently, photo-thermal induced feedback effects leading to self-oscillations in graphene have been demonstrated. In this paper we examine the phase jitter of self-oscillating SLG, and the means to improve the frequency stability through optical injection locking. The resonator consists of an SLG on top of a 10 micron diameter circular cavity with a cavity depth of 750 nm. By shining a 10 mW He-Ne laser the drum enters a regime of photo-thermally induced self-oscillation. The oscillating SLG suffers from a significant phase noise that can be directly observed in the time domain as random walk of the oscillation period. By applying a lock tone to the oscillator through the application of a modulated blue laser (405 nm), the SLG motion is then phase locked to the applied tone with more than an order of magnitude improvement in its coherence time. The injection locking is also studied as a function of lock signal detuning and power. Presenting author.

  16. Western Wind and Solar Integration Study Phase 3 -- Frequency Response and Transient Stability (Report and Executive Summary)

    SciTech Connect

    Miller, N. W.; Shao, M.; Pajic, S.; D'Aquila, R.

    2014-12-01

    The primary objectives of Phase 3 of the Western Wind and Solar Integration Study (WWSIS-3) were to examine the large-scale transient stability and frequency response of the Western Interconnection with high wind and solar penetration, and to identify means to mitigate any adverse performance impacts via transmission reinforcements, storage, advanced control capabilities, or other alternatives.

  17. Tunable frequency stabilized diode-laser-pumped Tm,Ho:YLiF4 laser at room temperature

    NASA Technical Reports Server (NTRS)

    Mcguckin, Brendan T.; Menzies, Robert T.; Esproles, Carlos

    1993-01-01

    A diode-laser-pumped single-frequency thulium holmium yttrium lithium fluoride laser that exhibits a closed-loop stability of a few megahertz and a continuous single-mode tuning range of 800 MHz is described. The laser output power is 25 mW, and is tunable over about 8/cm at 25 C.

  18. Characterization of the frequency stability of an optical frequency standard at 1.39 µm based upon noise-immune cavity-enhanced optical heterodyne molecular spectroscopy.

    PubMed

    Dinesan, H; Fasci, E; D'Addio, A; Castrillo, A; Gianfrani, L

    2015-01-26

    Frequency fluctuations of an optical frequency standard at 1.39 µm have been measured by means of a highly-sensitive optical frequency discriminator based on the fringe-side transmission of a high finesse optical resonator. Built on a Zerodur spacer, the optical resonator exhibits a finesse of 5500 and a cavity-mode width of about 120 kHz. The optical frequency standard consists of an extended-cavity diode laser that is tightly stabilized against the center of a sub-Doppler H(2) (18)O line, this latter being detected by means of noise-immune cavity-enhanced optical heterodyne molecular spectroscopy. The emission linewidth has been carefully determined from the frequency-noise power spectral density by using a rather simple approximation, known as β-line approach, as well as the exact method based on the autocorrelation function of the laser light field. It turns out that the linewidth of the optical frequency standard amounts to about 7 kHz (full width at half maximum) for an observation time of 1 ms. Compared to the free-running laser, the measured width corresponds to a line narrowing by a factor of ~220. PMID:25835931

  19. Matrix method of determining the longitudinal-stability coefficients and frequency response of an aircraft from transient flight data

    NASA Technical Reports Server (NTRS)

    Donegan, James J; Pearson, Henry A

    1952-01-01

    A matrix method is presented for determining the longitudinal-stability coefficients and frequency response of an aircraft from arbitrary maneuvers. The method is devised so that it can be applied to time-history measurements of combinations of such simple quantities as angle of attack, pitching velocity, load factor, elevator angle, and hinge moment to obtain the over-all coefficients. Although the method has been devised primarily for the evaluation of stability coefficients which are of primary interest in most aircraft loads and stability studies, it can be used also, with a simple additional computation, to determine the frequency-response characteristics. The entire procedure can be applied or extended to other problems which can be expressed by linear differential equations.

  20. Stability of the Free and Bound Microstates of a Mobile Loop of α-Amylase Obtained from the Absolute Entropy and Free Energy.

    PubMed

    Cheluvaraja, Srinath; Meirovitch, Hagai

    2008-01-01

    The hypothetical scanning molecular dynamics (HSMD) method is a relatively new technique for calculating the absolute entropy, S, and free energy, F, from a given sample generated by any simulation procedure. Thus, each sample conformation, i, is reconstructed by calculating transition probabilities that their product leads to the probability of i, hence to the entropy. HSMD is an exact method where all interactions are considered, and the only approximation is due to insufficient sampling. In previous studies HSMD (and HS Monte Carlo - HSMC) has been applied very successfully to liquid argon, TIP3P water, self-avoiding walks, and peptides in a α-helix, extended, and hairpin microstates. In this paper HSMD is developed further as applied to the flexible 7-residue surface loop, 304-310 (Gly-His-Gly-Ala-Gly-Gly-Ser) of the enzyme porcine pancreatic α-amylase. We are mainly interested in entropy and free energy differences ΔS = Sfree - Sbound (and ΔF=Ffree-Fbound) between the free and bound microstates of the loop, which are obtained from two separate MD samples of these microstates without the need to carry out thermodynamic integration. As for peptides, we find that relatively large systematic errors in Sfree and Sbound (and Ffree and Fbound) are cancelled in ΔS (ΔF) which is thus obtained efficiently with high accuracy, i.e., with a statistical error of 0.1-0.2 kcal/mol (T=300 K) using the AMBER force field and AMBER with the implicit solvation GB/SA. We provide theoretical arguments in support of this cancellation, discuss in detail the problems involved in the computational definition of a microstate in conformational space, suggest potential ways for enhancing efficiency further, and describe the next development where explicit water will replace implicit solvation. PMID:26619992

  1. Biomechanical evaluation of oversized drilling technique on primary implant stability measured by insertion torque and resonance frequency analysis

    PubMed Central

    Santamaría-Arrieta, Gorka; Brizuela-Velasco, Aritza; Fernández-González, Felipe J.; Chávarri-Prado, David; Chento-Valiente, Yelko; Solaberrieta, Eneko; Diéguez-Pereira, Markel; Yurrebaso-Asúa, Jaime

    2016-01-01

    Background This study evaluated the influence of implant site preparation depth on primary stability measured by insertion torque and resonance frequency analysis (RFA). Material and Methods Thirty-two implant sites were prepared in eight veal rib blocks. Sixteen sites were prepared using the conventional drilling sequence recommended by the manufacturer to a working depth of 10mm. The remaining 16 sites were prepared using an oversize drilling technique (overpreparation) to a working depth of 12mm. Bone density was determined using cone beam computerized tomography (CBCT). The implants were placed and primary stability was measured by two methods: insertion torque (Ncm), and RFA (implant stability quotient [ISQ]). Results The highest torque values were achieved by the conventional drilling technique (10mm). The ANOVA test confirmed that there was a significant correlation between torque and drilling depth (p<0.05). However, no statistically significant differences were obtained between ISQ values at 10 or 12 mm drilling depths (p>0.05) at either measurement direction (cortical and medullar). No statistical relation between torque and ISQ values was identified, or between bone density and primary stability (p >0.05). Conclusions Vertical overpreparation of the implant bed will obtain lower insertion torque values, but does not produce statistically significant differences in ISQ values. Key words:Implant stability quotient, overdrilling, primary stability, resonance frequency analysis, torque. PMID:27398182

  2. Absolute nuclear material assay

    DOEpatents

    Prasad, Manoj K.; Snyderman, Neal J.; Rowland, Mark S.

    2012-05-15

    A method of absolute nuclear material assay of an unknown source comprising counting neutrons from the unknown source and providing an absolute nuclear material assay utilizing a model to optimally compare to the measured count distributions. In one embodiment, the step of providing an absolute nuclear material assay comprises utilizing a random sampling of analytically computed fission chain distributions to generate a continuous time-evolving sequence of event-counts by spreading the fission chain distribution in time.

  3. Absolute nuclear material assay

    DOEpatents

    Prasad, Manoj K.; Snyderman, Neal J.; Rowland, Mark S.

    2010-07-13

    A method of absolute nuclear material assay of an unknown source comprising counting neutrons from the unknown source and providing an absolute nuclear material assay utilizing a model to optimally compare to the measured count distributions. In one embodiment, the step of providing an absolute nuclear material assay comprises utilizing a random sampling of analytically computed fission chain distributions to generate a continuous time-evolving sequence of event-counts by spreading the fission chain distribution in time.

  4. Absolute distance measurements by variable wavelength interferometry

    NASA Astrophysics Data System (ADS)

    Bien, F.; Camac, M.; Caulfield, H. J.; Ezekiel, S.

    1981-02-01

    This paper describes a laser interferometer which provides absolute distance measurements using tunable lasers. An active feedback loop system, in which the laser frequency is locked to the optical path length difference of the interferometer, is used to tune the laser wavelengths. If the two wavelengths are very close, electronic frequency counters can be used to measure the beat frequency between the two laser frequencies and thus to determine the optical path difference between the two legs of the interferometer.

  5. Automated Performance Characterization of DSN System Frequency Stability Using Spacecraft Tracking Data

    NASA Technical Reports Server (NTRS)

    Pham, Timothy T.; Machuzak, Richard J.; Bedrossian, Alina; Kelly, Richard M.; Liao, Jason C.

    2012-01-01

    This software provides an automated capability to measure and qualify the frequency stability performance of the Deep Space Network (DSN) ground system, using daily spacecraft tracking data. The results help to verify if the DSN performance is meeting its specification, therefore ensuring commitments to flight missions; in particular, the radio science investigations. The rich set of data also helps the DSN Operations and Maintenance team to identify the trends and patterns, allowing them to identify the antennas of lower performance and implement corrective action in a timely manner. Unlike the traditional approach where the performance can only be obtained from special calibration sessions that are both time-consuming and require manual setup, the new method taps into the daily spacecraft tracking data. This new approach significantly increases the amount of data available for analysis, roughly by two orders of magnitude, making it possible to conduct trend analysis with good confidence. The software is built with automation in mind for end-to-end processing. From the inputs gathering to computation analysis and later data visualization of the results, all steps are done automatically, making the data production at near zero cost. This allows the limited engineering resource to focus on high-level assessment and to follow up with the exceptions/deviations. To make it possible to process the continual stream of daily incoming data without much effort, and to understand the results quickly, the processing needs to be automated and the data summarized at a high level. Special attention needs to be given to data gathering, input validation, handling anomalous conditions, computation, and presenting the results in a visual form that makes it easy to spot items of exception/deviation so that further analysis can be directed and corrective actions followed.

  6. Automated Performance Characterization of DSN System Frequency Stability Using Spacecraft Tracking Data

    NASA Technical Reports Server (NTRS)

    Pham, Timothy T.; Machuzak, Richard J.; Bedrossian, Alina; Kelly, Richard M.; Liao, Jason C.

    2012-01-01

    This software provides an automated capability to measure and qualify the frequency stability performance of the Deep Space Network (DSN) ground system, using daily spacecraft tracking data. The results help to verify if the DSN performance is meeting its specification, therefore ensuring commitments to flight missions; in particular, the radio science investigations. The rich set of data also helps the DSN Operations and Maintenance team to identify the trends and patterns, allowing them to identify the antennas of lower performance and implement corrective action in a timely manner. Unlike the traditional approach where the performance can only be obtained from special calibration sessions that are both time-consuming and require manual setup, the new method taps into the daily spacecraft tracking data. This new approach significantly increases the amount of data available for analysis, roughly by two orders of magnitude, making it possible to conduct trend analysis with good confidence. The software is built with automation in mind for end-to-end processing. From the inputs gathering to computation analysis and later data visualization of the results, all steps are done automatically, making the data production at near zero cost. This allows the limited engineering resource to focus on high-level assessment and to follow up with the exceptions/deviations. To make it possible to process the continual stream of daily incoming data without much effort, and to understand the results quickly, the processing needs to be automated and the data summarized at a high level. Special attention needs to be given to data gathering, input validation, handling anomalous conditions, computation, and presenting the results in a visual form that makes it easy to spot items of exception/ deviation so that further analysis can be directed and corrective actions followed.

  7. Control strategy for stabilizing force with goal-equivalent joint torques is frequency-dependent during human hopping.

    PubMed

    Yen, Jasper T; Chang, Young-Hui

    2009-01-01

    Normal human locomotion requires the ability to control a complex, redundant neuromechanical system to repetitively cycle the legs in a stable manner. In a reduced paradigm of locomotion, hopping, we investigated the ability of human subjects to exploit motor redundancy in the legs to coordinate joint torques fluctuations to minimize force fluctuations generated against the ground. Although we saw invariant performance in terms of force stabilization across frequencies, we found that the role of joint torque coordination in stabilizing force was most important at slow hopping frequencies. Notably, the role of this coordinated variation strategy decreased as hopping frequency increased, giving way to an independent joint variation strategy. At high frequencies, the control strategy to stabilize force was more dependent on a direct reduction in ankle torque fluctuations. Through the systematic study of how joint-level variances affect task-level end-point function, we can gain insight into the underlying control strategies in place for automatically counteracting cycle-to-cycle deviations during normal human locomotion. PMID:19964783

  8. Absolute instability of the Gaussian wake profile

    NASA Technical Reports Server (NTRS)

    Hultgren, Lennart S.; Aggarwal, Arun K.

    1987-01-01

    Linear parallel-flow stability theory has been used to investigate the effect of viscosity on the local absolute instability of a family of wake profiles with a Gaussian velocity distribution. The type of local instability, i.e., convective or absolute, is determined by the location of a branch-point singularity with zero group velocity of the complex dispersion relation for the instability waves. The effects of viscosity were found to be weak for values of the wake Reynolds number, based on the center-line velocity defect and the wake half-width, larger than about 400. Absolute instability occurs only for sufficiently large values of the center-line wake defect. The critical value of this parameter increases with decreasing wake Reynolds number, thereby indicating a shrinking region of absolute instability with decreasing wake Reynolds number. If backflow is not allowed, absolute instability does not occur for wake Reynolds numbers smaller than about 38.

  9. Generation of a 20 GHz train of subpicosecond pulses with a stabilized optical-frequency-comb generator.

    PubMed

    Xiao, Shijun; Hollberg, Leo; Diddams, Scott A

    2009-01-01

    With a modulator-based 10 GHz optical-frequency-comb generator at 1.55 microm, we report a 20 GHz repetitive train of optical pulses as short as 450 fs. The timing stability of the 20 GHz pulses, in addition to the phase for optical-comb modes, shows a strong dependence on the relative frequency detuning between the comb generator's cavity and the seed cw laser. With a new and simple scheme, the comb generator's cavity resonance was locked to a narrow-linewidth seed laser within an estimated optical-frequency range < or = 6 MHz, enabling high-fidelity 20 GHz subpicosecond pulses and stable optical-frequency-comb generation for indefinite periods. PMID:19109648

  10. Reaching 5.0×10-13 τ -1/2 short term frequency stability of the integrating sphere cold atom clock

    NASA Astrophysics Data System (ADS)

    Liu, P.; Meng, Y. L.; Wan, J. Y.; Wang, X. M.; Wang, Y. N.; Xiao, L.; Cheng, H. D.; Liu, L.

    2016-06-01

    We present an improvement of short term frequency stability of the integrating sphere cold atom clock after increasing the intensities of clock signals and optimizing the feedback loop of the clock. A short term frequency stability of 5.0×10-13 τ -1/2 has been achieved and the limiting factors have been analyzed.

  11. Arbitrary frequency stabilization of a diode laser based on visual Labview PID VI and sound card output

    NASA Astrophysics Data System (ADS)

    Feng, Guo-Sheng; Wu, Ji-Zhou; Wang, Xiao-Feng; Zheng, Ning-Xuan; Li, Yu-Qing; Ma, Jie; Xiao, Lian-Tuan; Jia, Suo-Tang

    2015-10-01

    We report a robust method of directly stabilizing a grating feedback diode laser to an arbitrary frequency in a large range. The error signal, induced from the difference between the frequency measured by a wavelength meter and the preset target frequency, is fed back to the piezoelectric transducer module of the diode laser via a sound card in the computer. A visual Labview procedure is developed to realize a feedback system. In our experiment the frequency drift of the diode laser is reduced to 8 MHz within 25 min. The robust scheme can be adapted to realize the arbitrary frequency stabilization for many other kinds of lasers. Project supported by the National Basic Research Program of China (Grant No. 2012CB921603), the Program for Changjiang Scholars and Innovative Research Team in University of Ministry of Education of China (Grant No. IRT13076), the Major Research Plan of the National Natural Science Foundation of China (Grant No. 91436108), the National Natural Science Foundation of China (Grant Nos. 61378014, 61308023, 61378015, and 11434007), the Fund for Fostering Talents in Basic Science of the National Natural Science Foundation of China (Grant No. J1103210), the New Teacher Fund of the Ministry of Education of China (Grant No. 20131401120012), and the Natural Science Foundation for Young Scientists of Shanxi Province, China (Grant No. 2013021005-1).

  12. Particle simulation of radio frequency stabilization of the flute mode in a tandem mirror. II. Perpendicular antenna

    SciTech Connect

    Abe, H.; Kadoya, Y.

    1988-10-01

    A two-and-a-half-dimensional electromagnetic particle code PS2M (J. Phys. Soc. Jpn. 56, 3899 (1987)) is used to study how an electric field applied perpendicularly to the magnetic field affects the radio frequency stabilization of flute modes in a tandem mirror plasma. The electric field perpendicular to the magnetic field stabilizes or destabilizes the flute mode through the mechanism of the ponderomotive force acting on electrons and ions and through the mechanism of sideband coupling. In the simulations two typical examples have been shown: (i) when the sideband coupling effects (in which the electron terms are dominant) stabilize the flute modes and (ii) when the perpendicular ponderomotive force acting on the electrons destabilizes the flute modes.

  13. Method for wavelength stabilization of pulsed difference frequency laser at 1572 nm for CO(2) detection lidar.

    PubMed

    Gong, Wei; Ma, Xin; Han, Ge; Xiang, Chengzhi; Liang, Ailin; Fu, Weidong

    2015-03-01

    High-accuracy on-line wavelength stabilization is required for differential absorption lidar (DIAL), which is ideal for precisely measuring atmospheric CO(2) concentration. Using a difference-frequency laser, we developed a ground-based 1.57-μm pulsed DIAL for performing atmospheric CO(2) measurements. Owing to the system complexity, lacking phase, and intensity instability, the stabilization method was divided into two parts-wavelength calibration and locking-based on saturated absorption. After obtaining the on-line laser position, accuracy verification using statistical theory and locking stabilization using a one-dimensional template matching method, namely least-squares matching (LSM), were adopted to achieve wavelength locking. The resulting system is capable of generating a stable wavelength. PMID:25836838

  14. Sub-kilohertz linewidth narrowing of a mid-infrared optical parametric oscillator idler frequency by direct cavity stabilization.

    PubMed

    Ricciardi, I; Mosca, S; Parisi, M; Maddaloni, P; Santamaria, L; De Natale, P; De Rosa, M

    2015-10-15

    We stabilize the idler frequency of a singly resonant optical parametric oscillator directly to the resonance of a mid-infrared Fabry-Perot reference cavity. This is accomplished by the Pound-Drever-Hall locking scheme, controlling either the pump laser or the resonant signal frequency. A residual relative frequency noise power spectral density below 10(3)  Hz(2)/Hz is reached on average, with a Gaussian linewidth of 920 Hz over 100 ms, which reveals the potential for reaching spectral purity down to the hertz level by locking the optical parametric oscillator against a mid-infrared cavity with state-of-the-art superior performance. PMID:26469609

  15. Absolute biological needs.

    PubMed

    McLeod, Stephen

    2014-07-01

    Absolute needs (as against instrumental needs) are independent of the ends, goals and purposes of personal agents. Against the view that the only needs are instrumental needs, David Wiggins and Garrett Thomson have defended absolute needs on the grounds that the verb 'need' has instrumental and absolute senses. While remaining neutral about it, this article does not adopt that approach. Instead, it suggests that there are absolute biological needs. The absolute nature of these needs is defended by appeal to: their objectivity (as against mind-dependence); the universality of the phenomenon of needing across the plant and animal kingdoms; the impossibility that biological needs depend wholly upon the exercise of the abilities characteristic of personal agency; the contention that the possession of biological needs is prior to the possession of the abilities characteristic of personal agency. Finally, three philosophical usages of 'normative' are distinguished. On two of these, to describe a phenomenon or claim as 'normative' is to describe it as value-dependent. A description of a phenomenon or claim as 'normative' in the third sense does not entail such value-dependency, though it leaves open the possibility that value depends upon the phenomenon or upon the truth of the claim. It is argued that while survival needs (or claims about them) may well be normative in this third sense, they are normative in neither of the first two. Thus, the idea of absolute need is not inherently normative in either of the first two senses. PMID:23586876

  16. Characterization of Low-Frequency Combustion Stability of the Fastrac Engine

    NASA Technical Reports Server (NTRS)

    Rocker, Marvin; Jones, Preston (Technical Monitor)

    2002-01-01

    A series of tests were conducted to measure the combustion performance of the Fastrac engine thrust chamber. During mainstage, the thrust chamber exhibited no large-amplitude chamber pressure oscillations that could be identified as low-frequency combustion instability or 'chug'. However, during start-up and shutdown, the thrust chamber very briefly exhibited large-amplitude chamber pressure oscillations that were identified as chug. These instabilities during start-up and shutdown were regarded as benign due to their brevity. Linear models of the thrust chamber and the propellant feed systems were formulated for both the thrust chamber component tests and the flight engine tests. These linear models determined the frequency and decay rate of chamber pressure oscillations given the design and operating conditions of the thrust chamber and feed system. The frequency of chamber pressure oscillations determined from the model closely matched the frequency of low-amplitude, low-frequency chamber pressure oscillations exhibited in some of the later thrust chamber mainstage tests. The decay rate of the chamber pressure oscillations determined from the models indicated that these low-frequency oscillations were stable. Likewise, the decay rate, determined from the model of the flight engine tests indicated that the low-frequency chamber pressure oscillations would be stable.

  17. Frequency-response method for determination of dynamic stability characteristics of airplanes with automatic controls

    NASA Technical Reports Server (NTRS)

    Greenberg, Harry

    1947-01-01

    A frequency-response method for determining the critical control-gearing and hunting oscillations of airplanes with automatic pilots is presented. The method is graphical and has several advantages over the standard numerical procedure based on Routh's discriminant. The chief advantage of the method is that direct use can be made of the measured response characteristics of the automatic pilot. This feature is especially useful in determining the existence, amplitude, and frequency of the hunting oscillations that may be present when the automatic pilot has nonlinear dynamic characteristics. Several examples are worked out to illustrate the application of the frequency-response method in determining the effect of automatic-pilot lag or lead on critical control gearing and in determining the amplitude and frequency hunting. It is shown that the method may be applied to the case of a control geared to airplane motions about two axes.

  18. Simultaneous stabilization of frequency and magnetic field with the tilted 0-0 state

    NASA Astrophysics Data System (ADS)

    Jau, Y.-Y.; Happer, W.

    2005-11-01

    "Tilted" versions of axially symmetric states of alkali-metal atoms can be readily generated by pumping with D1 light of appropriate modulation format. Of particular interest is the tilted 0-0 state, that can be generated by push-pull pumping with additional pulse modulation at the Zeeman frequency. The tilted 0-0 state can be used to simultaneously lock a magnetic field and a clock frequency.

  19. Frequency and phase stabilization of a multimode gyrotron with megawatt power by an external signal

    NASA Astrophysics Data System (ADS)

    Bakunin, V. L.; Denisov, G. G.; Novozhilova, Yu. V.

    2014-05-01

    We have numerically studied capturing of the oscillation frequency and phase of the TE28.12 operating mode by an external monochromatic signal for a multimode gyrotron with a close to real regime of activation. It is shown that, even at a low external-signal power, in a wide range of the magnetic field and voltage, a highly efficient single-mode generating is set at the frequency of the external signal.

  20. Transportable cavity-stabilized laser system for optical carrier frequency transmission experiments.

    PubMed

    Parker, B; Marra, G; Johnson, L A M; Margolis, H S; Webster, S A; Wright, L; Lea, S N; Gill, P; Bayvel, P

    2014-12-10

    We report the design and performance of a transportable laser system at 1543 nm, together with its application as the source for a demonstration of optical carrier frequency transmission over 118 km of an installed dark fiber network. The laser system is based around an optical reference cavity featuring an elastic mounting that bonds the cavity to its support, enabling the cavity to be transported without additional clamping. The cavity exhibits passive fractional frequency insensitivity to vibration along the optical axis of 2.0×10(-11)  m(-1) s(2). With active fiber noise cancellation, the optical carrier frequency transmission achieves a fractional frequency instability, measured at the user end, of 2.6×10(-16) at 1 s, averaging down to below 3×10(-18) after 20,000 s. The fractional frequency accuracy of the transfer is better than 3×10(-18). This level of performance is sufficient for comparison of state-of-the-art optical frequency standards and is achieved in an urban fiber environment. PMID:25608055

  1. High Conversion Efficiency and Power Stability of 532 nm Generation from an External Frequency Doubling Cavity

    NASA Astrophysics Data System (ADS)

    Zhao, Yang; Lin, Bai-Ke; Li, Ye; Zhang, Hong-Xi; Cao, Jian-Ping; Fang, Zhan-Jun; Li, Tian-Chu; Zang, Er-Jun

    2012-09-01

    We present a high-efficiency 532 nm green light conversion from an external cavity-enhanced second harmonic generation (SHG) with a periodically poled KTP crystal (PPKTP). The cavity is a bow-tie ring configuration with a unitized structure. When the impedance matching is optimized, the coupling efficiency of the fundamental is as high as 95%. Taking into account both the high power output of the second harmonic and the stability of the system, we obtain over 500 mW green passing through the output cavity mirror, corresponding to a net conversion efficiency higher than 75.2%. Under these operating conditions, the power stability is better than ±0.25% during 5 h. It is the highest conversion efficiency and power stability ever produced in the bow-tie ring cavity with PPKTP for 532 nm generation.

  2. Quasi-laminar stability and sensitivity analyses for turbulent flows: Prediction of low-frequency unsteadiness and passive control

    NASA Astrophysics Data System (ADS)

    Mettot, Clément; Sipp, Denis; Bézard, Hervé

    2014-04-01

    This article presents a quasi-laminar stability approach to identify in high-Reynolds number flows the dominant low-frequencies and to design passive control means to shift these frequencies. The approach is based on a global linear stability analysis of mean-flows, which correspond to the time-average of the unsteady flows. Contrary to the previous work by Meliga et al. ["Sensitivity of 2-D turbulent flow past a D-shaped cylinder using global stability," Phys. Fluids 24, 061701 (2012)], we use the linearized Navier-Stokes equations based solely on the molecular viscosity (leaving aside any turbulence model and any eddy viscosity) to extract the least stable direct and adjoint global modes of the flow. Then, we compute the frequency sensitivity maps of these modes, so as to predict before hand where a small control cylinder optimally shifts the frequency of the flow. In the case of the D-shaped cylinder studied by Parezanović and Cadot [J. Fluid Mech. 693, 115 (2012)], we show that the present approach well captures the frequency of the flow and recovers accurately the frequency control maps obtained experimentally. The results are close to those already obtained by Meliga et al., who used a more complex approach in which turbulence models played a central role. The present approach is simpler and may be applied to a broader range of flows since it is tractable as soon as mean-flows — which can be obtained either numerically from simulations (Direct Numerical Simulation (DNS), Large Eddy Simulation (LES), unsteady Reynolds-Averaged-Navier-Stokes (RANS), steady RANS) or from experimental measurements (Particle Image Velocimetry - PIV) — are available. We also discuss how the influence of the control cylinder on the mean-flow may be more accurately predicted by determining an eddy-viscosity from numerical simulations or experimental measurements. From a technical point of view, we finally show how an existing compressible numerical simulation code may be used in

  3. Measurement of laser quantum frequency fluctuations using a Pound-Drever stabilization system

    SciTech Connect

    Cheng, Y.J.; Mussche, P.L.; Siegman, A.E. . Edward L. Ginzton Lab.)

    1994-06-01

    The authors describe a method for measuring the frequency fluctuation spectrum of a laser oscillator, especially the weak noise contributions in the wings of the spectrum, and apply this method to confirm the existence of large excess quantum frequency fluctuations in a laser oscillator using an unstable optical resonator. The measurement apparatus uses the Pound-Drever technique, which employs an RF phase modulator and a Fabry-Perot cavity to produce a sensitive high-speed frequency discrimination signal. The authors show that this signal can also be used to measure the quantum noise contributions to the frequency spectrum of a laser oscillator. Experimental measurements on a miniature diode-pumped Nd:YAG laser using a stable optical cavity closely match the predictions of the usual Schawlow-Townes theory, while the frequency fluctuations in a nearly identical laser employing an unstable optical resonator are approximately 1,300 times larger. These much larger fluctuations arise in part from the larger output coupling and cavity bandwidth of the unstable cavity, but they also appear to confirm a predicted excess spontaneous emission factor (Petermann excess noise factor) of [approx]180 times arising from the nonorthogonal transverse mode properties of the unstable cavity.

  4. Atomic clock using coherent population trapping in a cesium cell: frequency stability and limitations

    NASA Astrophysics Data System (ADS)

    Mejri, Sinda; Tricot, Francois; Danet, Jean-Marie; Yun, Peter; De Clercq, Emeric; Guerandel, Stephane

    2016-06-01

    Toward the next generation of compact devices, atomic clocks based on coherent population trapping (CPT) offer a very interesting alternative. We present a review of our studies on the short and mid term stability of a compact high performance atomic clock based on CPT in view of portable applications.

  5. Atomic frequency standards at NICT

    NASA Astrophysics Data System (ADS)

    Ido, T.; Fujieda, M.; Hachisu, H.; Hayasaka, K.; Kajita, M.; Kojima, R.; Kumagai, M.; Locke, C.; Li, Y.; Matsubara, K.; Nogami, A.; Shiga, N.; Yamaguchi, A.; Koyama, Y.; Hosokawa, M.; Hanado, Y.

    2011-10-01

    Various activities of atomic frequency standards studied in National Institute of Information and Communications Technology (NICT) are briefly reviewed. After BIPM accepted the first cesium fountain clock in NICT as a reference to determine International Atomic Time (TAI), efforts to further reduce the uncertainty of collision shifts are ongoing. A second fountain clock using atomic molasses is being built to enable the operation with less atomic density. Single ion clock using calcium has been pursued for several years in NICT. The absolute frequency measured in 2008 has CIPM to adopt the Ca+ clock transition as a part of the list of radiation (LoR) to realize the meter. Sr lattice clock has started its operation last year. The absolute frequency agreed well with those obtained in other institutes. Study of stable cavities to stabilize clock lasers are also introduced.

  6. Determination of lateral-stability derivatives and transfer-function coefficients from frequency-response data for lateral motions

    NASA Technical Reports Server (NTRS)

    Donegan, James J; Robinson, Samuel W , Jr; Gates, Ordway, B , jr

    1955-01-01

    A method is presented for determining the lateral-stability derivatives, transfer-function coefficients, and the modes for lateral motion from frequency-response data for a rigid aircraft. The method is based on the application of the vector technique to the equations of lateral motion, so that the three equations of lateral motion can be separated into six equations. The method of least squares is then applied to the data for each of these equations to yield the coefficients of the equations of lateral motion from which the lateral-stability derivatives and lateral transfer-function coefficients are computed. Two numerical examples are given to demonstrate the use of the method.

  7. The absolute path command

    2012-05-11

    The ap command traveres all symlinks in a given file, directory, or executable name to identify the final absolute path. It can print just the final path, each intermediate link along with the symlink chan, and the permissions and ownership of each directory component in the final path. It has functionality similar to "which", except that it shows the final path instead of the first path. It is also similar to "pwd", but it canmore » provide the absolute path to a relative directory from the current working directory.« less

  8. The absolute path command

    SciTech Connect

    Moody, A.

    2012-05-11

    The ap command traveres all symlinks in a given file, directory, or executable name to identify the final absolute path. It can print just the final path, each intermediate link along with the symlink chan, and the permissions and ownership of each directory component in the final path. It has functionality similar to "which", except that it shows the final path instead of the first path. It is also similar to "pwd", but it can provide the absolute path to a relative directory from the current working directory.

  9. Flight-Like Optical Reference Cavity for GRACE Follow-On Laser Frequency Stabilization

    NASA Technical Reports Server (NTRS)

    Folkner, W. M.; deVine, G.; Klipstein, W. M.; McKenzie, K.; Spero, R.; Thompson, R.; Yu, N.; Stephens, M.; Leitch, J.; Pierce, R.; Shaddock, D.; Lam, T.

    2011-01-01

    We describe a prototype optical cavity and associated optics that has been developed to provide a stable frequency reference for a future space-based laser ranging system. This instrument is being considered for inclusion as a technology demonstration on the recently announced GRACE follow-on mission, which will monitor variations in the Earth's gravity field.

  10. Evaluation of the Temperature Stability of a Low-Frequency a0 Mode Transducer Developed for Shm Applications

    NASA Astrophysics Data System (ADS)

    Clarke, T.; Simonetti, F.; Rokhlin, S.; Cawley, P.

    2008-02-01

    A piezoelectric-based transducer generating high purity A0 mode guided waves at low frequencies (around 20 kHz) was developed. Parametric studies were undertaken by varying the backing mass length, the transducer diameter and the thickness of a soft front layer. Results obtained by FEM were validated by experimental measurements and showed that signals with A0/S0 energy ratios substantially above 40 dB can be obtained. The amplitude, phase and frequency stability of signals produced by these transducers and the general robustness of an experimental pitch-catch system were evaluated in an environment subjected to 10 °C temperature shifts. Temperature compensation and baseline subtraction methods were applied to the signals and residual signal amplitude of -38 dB in relation to the amplitude of the first arrival was obtained. Reflections from a weak reflector attached to the plate were identifiable even with a 10 °C temperate change.

  11. Two-frequency acousto-optic modulator driver to improve the beam pointing stability during intensity ramps

    SciTech Connect

    Froehlich, B.; Lahaye, T.; Kaltenhaeuser, B.; Kuebler, H.; Mueller, S.; Koch, T.; Fattori, M.; Pfau, T.

    2007-04-15

    We report on a scheme to improve the pointing stability of the first order beam diffracted by an acousto-optic modulator (AOM). Due to thermal effects inside the crystal, the angular position of the beam can change by as much as 1 mrad when the radio-frequency power in the AOM is reduced to decrease the first order beam intensity. This is done, for example, to perform forced evaporative cooling in ultracold atom experiments using far-off-resonant optical traps. We solve this problem by driving the AOM with two radio frequencies f{sub 1} and f{sub 2}. The power of f{sub 2} is adjusted relative to the power of f{sub 1} to keep the total power constant. Using this, the beam displacement is decreased by a factor of 20. The method is simple to implement in existing experimental setups, without any modification of the optics.

  12. Radio frequency induced hyperthermia mediated by dextran stabilized LSMO nanoparticles: in vitro evaluation of heat shock protein response

    NASA Astrophysics Data System (ADS)

    Bhayani, K. R.; Rajwade, J. M.; Paknikar, K. M.

    2013-01-01

    Dextran stabilized La0.7Sr0.3MnO3 (Dex-LSMO) is an alternative cancer hyperthermia agent holding considerable promise. Here, we have carried out a comparative study on radio frequency (˜264 kHz) induced Dex-LSMO mediated heating and extraneous heating (mimicking generalized hyperthermia) in terms of changes in the morphology, proliferation pattern and induction of heat shock proteins in a human melanoma cell line (A375). Our results clearly show that the cellular effects seen with extraneous heating (60 min at 43 °C) could be reproduced by just six minutes of radio frequency induced Dex-LSMO mediated heating. More importantly, the observed enhanced levels of HSP 70 and 90 (molecular markers of heat shock that trigger favorable immunological reactions) seen with Dex-LSMO mediated heating were comparable to extraneous heating. These results suggest the possible utility of Dex-LSMO as a cancer hyperthermia agent.

  13. Active frequency stabilization of a 1.062-micron, Nd:GGG, diode-laser-pumped nonplanar ring oscillator to less than 3 Hz of relative linewidth

    NASA Technical Reports Server (NTRS)

    Day, T.; Gustafson, E. K.; Byer, R. L.

    1990-01-01

    Results are presented on the frequency stabilization of two diode-laser-pumped ring lasers that are independently locked to the same high-finesse interferometer. The relative frequency stability is measured by locking the lasers one free spectral range apart and observing the heterodyne beat note. The resultant beat note width of 2.9 Hz is consistent with the theoretical system noise-limited linewidth and is approximately 20 times that expected for shot-noise-limited performance.

  14. Improved stabilization of a 1.3 microm femtosecond optical frequency comb by use of a spectrally tailored continuum from a nonlinear fiber grating.

    PubMed

    Kim, K; Diddams, S A; Westbrook, P S; Nicholson, J W; Feder, K S

    2006-01-15

    We report significant enhancement (+24 dB) of the optical beat note between a 657 nm cw laser and the second-harmonic generation of the tailored continuum at 1314 nm generated with a femtosecond Cr:forsterite laser and a nonlinear fiber Bragg grating. The same continuum is used to stabilize the carrier-envelope offset frequency of the Cr:forsterite femtosecond laser and permits improved optical stabilization of the frequency comb from 1.0 to 2.2 microm. Using a common optical reference at 657 nm, a relative fractional frequency instability of 2.0 x 10(-15) is achieved between the repetition rates of Cr:forsterite and Ti:sapphire laser systems in 10 s averaging time. The fractional frequency offset between the optically stabilized frequency combs of the Cr:forsterite and Ti:sapphire lasers is +/-(0.024 +/- 6.1) x 10(-17). PMID:16441055

  15. Frequency stabilization and transverse mode discrimination in injection-seeded unstable resonator TEA CO2 lasers

    NASA Technical Reports Server (NTRS)

    Ancellet, G. M.; Menzies, R. T.; Brothers, A. M.

    1987-01-01

    Longitudinal mode selection by injection has been demonstrated as a viable technique for TEA-CO2 lasers with pulse energies of a Joule or greater. Once reliable generation of single-longitudinal-mode (SLM) pulses is obtained, the characteristics and the causes of intrapulse frequency variation can be studied. These include the effect of the decaying plasma, the thermal gradient due to the energy dissipation associated with the laser mechanism itself, and the pressure shift of the center frequency of the laser transition. The use of the positive-branch unstable resonator as an efficient means of coupling a discharge with large spatial dimensions to an optical cavity mode introduces another concern: namely, what can be done to emphasize transverse mode discrimination in an unstable resonator cavity while maintaining high coupling efficiency. These issues are discussed in this paper, and relevant experimental results are included.

  16. Frequency-stabilized Yb:fiber comb with a tapered single-mode fiber

    NASA Astrophysics Data System (ADS)

    Yang, Xie; Hai-Nian, Han; Long, Zhang; Zi-Jiao, Yu; Zheng, Zhu; Lei, Hou; Li-Hui, Pang; Zhi-Yi, Wei

    2016-04-01

    We demonstrate a stable Yb:fiber frequency comb with supercontinuum generation by using a specially designed tapered single-mode fiber, in which a spectrum spanning from 500 nm to 1500 nm is produced. The carrier-envelope offset signal of the Yb:fiber comb is measured with a signal-to-noise ratio of more than 40 dB and a linewidth narrower than 120 kHz. The repetition rate and carrier-envelope offset signals are simultaneously phase locked to a microwave reference frequency. Project supported by the National Basic Research Program of China (973 Program) (Grant No. 2012CB821304) and the National Natural Science Foundation of China (Grant No. 61378040).

  17. Systematic and quantitative analysis of residual amplitude modulation in Pound-Drever-Hall frequency stabilization

    NASA Astrophysics Data System (ADS)

    Shen, Hui; Li, Liufeng; Bi, Jin; Wang, Jia; Chen, Lisheng

    2015-12-01

    We theoretically analyze the effects of two primary mechanisms of residual amplitude modulation, estimate the resulting frequency instabilities, and discuss relevant experimental countermeasures, providing useful information that are beneficial for the development of ultrastable optical oscillators as well as many precision experiments relying on stable lasers. A Pound-Drever-Hall signal comprising contributions from the birefringence of the electro-optic crystal is derived and used to examine the birefringence-related amplitude modulation and the resultant frequency offset in terms of various experimental parameters. The combined effect of the crystal birefringence and pararsitic étalons is further investigated by dividing the étalons into three representative categories according to their locations in the optical path. The analysis shows that introducing a resonant optical cavity only scales the birefringence-generated amplitude modulation by a constant, thereby lending strong support to the active control scheme using a separate detection path. When a parasitic étalon is added, the active control scheme can still suppress the resultant instability except for the parasitic étalon that is located closely in front of the optical cavity. In this case the étalon produces rather large frequency instability and therefore should be avoided. In addition, numerical calculations are performed to assess the impact of a special situation where the front and end surfaces of an ultrastable optical cavity are potential sources of the parasitic étalon that can strongly couple with the cavity.

  18. A new readout system for bolometers with improved low frequency stability

    NASA Astrophysics Data System (ADS)

    Gaertner, S.; Benoit, A.; Lamarre, J.-M.; Giard, M.; Bret, J.-L.; Chabaud, J.-P.; Desert, F.-X.; Faure, J.-P.; Jegoudez, G.; Lande, J.; Leblanc, J.; Lepeltier, J.-P.; Narbonne, J.; Piat, M.; Pons, R.; Serra, G.; Simiand, G.

    1997-11-01

    A new readout electronic system for bolometers is presented in this paper. The bolometer resistance is measured in a bridge with a capacitive load, using a periodic square wave bias current. The bias voltages at both ends of the bridge are balanced in order to keep the middle point around zero. Only changes around this zero value are amplified and detected synchronously with the bias signal. These features shift the measurement frequency out of the electrical low frequency noises (JFETs), and reduces the dynamics required from the amplification chain. The bias voltages are fully controlled by computer, and the lock-in detection is digital. This readout electronic has many advantages over previous ones. In particular, it proved to be able to read the total power of the radiation reaching the bolometer, and to perform measurements down to low frequencies (<= 0.1 Hz) without significant additional noise. These features open new observation strategies such as full sky scanning to bolometer instruments on board future submillimetre space projects having high thermal background levels (warm telescope). The different steps of the development of this new readout electronics on the ground-based Diabolo experiment are described, the performances reached are discussed, and a version suitable for the readout of the arrays of bolometers on the COBRAS/SAMBA satellite mission is presented.

  19. Low frequency azimuthal stability of the ionization region of the Hall thruster discharge. I. Local analysis

    SciTech Connect

    Escobar, D.; Ahedo, E.

    2014-04-15

    Results based on a local linear stability analysis of the Hall thruster discharge are presented. A one-dimensional azimuthal framework is used including three species: neutrals, singly charged ions, and electrons. A simplified linear model is developed with the aim of deriving analytical expressions to characterize the stability of the ionization region. The results from the local analysis presented here indicate the existence of an instability that gives rise to an azimuthal oscillation in the +E × B direction with a long wavelength. According to the model, the instability seems to appear only in regions where the ionization and the electric field make it possible to have positive gradients of plasma density and ion velocity at the same time. A more complex model is also solved numerically to validate the analytical results. Additionally, parametric variations are carried out with respect to the main parameters of the model to identify the trends of the instability. As the temperature increases and the neutral-to-plasma density ratio decreases, the growth rate of the instability decreases down to a limit where azimuthal perturbations are no longer unstable.

  20. Stabilization of Homoserine-O-Succinyltransferase (MetA) Decreases the Frequency of Persisters in Escherichia coli under Stressful Conditions

    PubMed Central

    Mordukhova, Elena A.; Pan, Jae-Gu

    2014-01-01

    Bacterial persisters are a small subpopulation of cells that exhibit multi-drug tolerance without genetic changes. Generally, persistence is associated with a dormant state in which the microbial cells are metabolically inactive. The bacterial response to unfavorable environmental conditions (heat, oxidative, acidic stress) induces the accumulation of aggregated proteins and enhances formation of persister cells in Escherichia coli cultures. We have found that methionine supplementation reduced the frequency of persisters at mild (37°C) and elevated (42°C) temperatures, as well as in the presence of acetate. Homoserine-o-succinyltransferase (MetA), the first enzyme in the methionine biosynthetic pathway, is prone to aggregation under many stress conditions, resulting in a methionine limitation in E. coli growth. Overexpression of MetA induced the greatest number of persisters at 42°C, which is correlated to an increased level of aggregated MetA. Substitution of the native metA gene on the E. coli K-12 WE chromosome by a mutant gene encoding the stabilized MetA led to reduction in persisters at the elevated temperature and in the presence of acetate, as well as lower aggregation of the mutated MetA. Decreased persister formation at 42°C was confirmed also in E. coli K-12 W3110 and a fast-growing WErph+ mutant harboring the stabilized MetA. Thus, this is the first study to demonstrate manipulation of persister frequency under stressful conditions by stabilization of a single aggregation-prone protein, MetA. PMID:25329174

  1. Stabilization of homoserine-O-succinyltransferase (MetA) decreases the frequency of persisters in Escherichia coli under stressful conditions.

    PubMed

    Mordukhova, Elena A; Pan, Jae-Gu

    2014-01-01

    Bacterial persisters are a small subpopulation of cells that exhibit multi-drug tolerance without genetic changes. Generally, persistence is associated with a dormant state in which the microbial cells are metabolically inactive. The bacterial response to unfavorable environmental conditions (heat, oxidative, acidic stress) induces the accumulation of aggregated proteins and enhances formation of persister cells in Escherichia coli cultures. We have found that methionine supplementation reduced the frequency of persisters at mild (37°C) and elevated (42°C) temperatures, as well as in the presence of acetate. Homoserine-o-succinyltransferase (MetA), the first enzyme in the methionine biosynthetic pathway, is prone to aggregation under many stress conditions, resulting in a methionine limitation in E. coli growth. Overexpression of MetA induced the greatest number of persisters at 42°C, which is correlated to an increased level of aggregated MetA. Substitution of the native metA gene on the E. coli K-12 WE chromosome by a mutant gene encoding the stabilized MetA led to reduction in persisters at the elevated temperature and in the presence of acetate, as well as lower aggregation of the mutated MetA. Decreased persister formation at 42°C was confirmed also in E. coli K-12 W3110 and a fast-growing WErph+ mutant harboring the stabilized MetA. Thus, this is the first study to demonstrate manipulation of persister frequency under stressful conditions by stabilization of a single aggregation-prone protein, MetA. PMID:25329174

  2. An overview of DREV's activities on pulsed CO2 laser transmitters: Frequency stability and lifetime aspects

    NASA Technical Reports Server (NTRS)

    Cruickshank, James; Pace, Paul; Mathieu, Pierre

    1987-01-01

    After introducing the desired features in a transmitter for laser radar applications, the output characteristics of several configurations of frequency-stable TEA-CO2 lasers are reviewed. Based on work carried out at the Defence Research Establishment Valcartier (DREV), output pulses are examined from short cavity lasers, CW-TEA hybrid lasers, and amplifiers for low power pulses. It is concluded that the technique of injecting a low-power laser beam into a TEA laser resonator with Gaussian reflectivity mirrors should be investigated because it appears well adapted to producing high energy, single mode, low chirp pulses. Finally, a brief report on tests carried out on catalysts composed of stannic oxide and noble metals demonstrates the potential of these catalysts, operating at close to room temperature, to provide complete closed-cycle laser operation.

  3. Inertially Stabilized Microfluidic Crystals: Self-assembly and Spatial Frequency Tuning

    NASA Astrophysics Data System (ADS)

    Lee, Wonhee; Amini, Hamed; Stone, Howard; di Carlo, Dino

    2010-11-01

    Dynamic self-assembly can be found over a wide range of scales originating from different fundamental opposing forces. By taking advantage of inertial effects we demonstrate controllable self-assembling particle systems at the microscale. Inertially focused particles in confined high-speed microfluidic channel flows dynamically self-assemble into uniformly spaced lattices through purely hydrodynamic interactions with no external force fields. Focusing on the dynamics of the particle-particle interactions reveals a mechanism for the dynamic self-assembly process; inertial lift forces and a parabolic flow field act together to stabilize interparticle spacings that otherwise would diverge to infinity due to viscous wakes. The interplay of the repulsive viscous interaction and inertial lift also allow us to design and implement microfluidic structures that irreversibly change interparticle spacing, similar to a low-pass filter. Although often not considered at the microscale, nonlinearity due to inertia can provide a platform for high-throughput passive control of particle positions in all directions, which will be useful for applications in flow cytometry, tissue engineering, and synthesis of metamaterials.

  4. Frequency-Downconversion Stability of PMMA Coatings in Hybrid White Light-Emitting Diodes

    NASA Astrophysics Data System (ADS)

    Caruso, Fulvio; Mosca, Mauro; Rinella, Salvatore; Macaluso, Roberto; Calì, Claudio; Saiano, Filippo; Feltin, Eric

    2016-01-01

    We report on the properties of a poly(methyl methacrylate)-based coating used as a host for an organic dye in hybrid white light-emitting diodes. The device is composed by a pump source, which is a standard inorganic GaN/InGaN blue light-emitting diode (LED) emitting at around 450 nm, and a spin-coated conversion layer making use of Lumogen® F Yellow 083. Under prolonged irradiation, the coating exhibits significant bleaching, thus degrading the color rendering performance of the LED. We present experimental results that confirm that the local temperature rise of the operating diode does not affect the conversion layer. It is also proven that, during the test, the photostability of the organic dye is compromised, resulting in a chromatic shift from Commission Internationale de l'Eclairage (CIE) ( x; y) coordinates (0.30;0.39) towards the color of the pump (0.15;0.04). Besides photodegradation of the dye, we address a phenomenon attributed to modification of the polymer matrix activated by the LED's blue light energy as confirmed by ultraviolet-visible and Fourier-transform infrared spectroscopic analyses. Three methods for improving the overall stability of the organic coating are presented.

  5. Experimental Determination of Effects of Frequency and Amplitude on the Lateral Stability Derivatives for a Delta, a Swept, and Unswept Wing Oscillating in Yaw

    NASA Technical Reports Server (NTRS)

    Fisher, Lewis R

    1958-01-01

    Three wing models were oscillated in yaw about their vertical axes to determine the effects of systematic variations of frequency and amplitude of oscillation on the in-phase and out-of-phase combination lateral stability derivatives resulting from this motion. The tests were made at low speeds for a 60 degree delta wing, a 45 degree swept wing, and an unswept wing; the swept and unswept wings had aspect ratios of 4. The results indicate that large changes in the magnitude of the stability derivatives due to the variation of frequency occur at high angles of attack, particularly for the delta wing. The greatest variations of the derivatives with frequency take place for the lowest frequencies of oscillation; at the higher frequencies, the effects of frequency are smaller and the derivatives become more linear with angle of attack. Effects of amplitude of oscillation on the stability derivatives for delta wings were evident for certain high angles of attack and for the lowest frequencies of oscillation. As the frequency became high, the amplitude effects tended to disappear.

  6. Electronic Absolute Cartesian Autocollimator

    NASA Technical Reports Server (NTRS)

    Leviton, Douglas B.

    2006-01-01

    An electronic absolute Cartesian autocollimator performs the same basic optical function as does a conventional all-optical or a conventional electronic autocollimator but differs in the nature of its optical target and the manner in which the position of the image of the target is measured. The term absolute in the name of this apparatus reflects the nature of the position measurement, which, unlike in a conventional electronic autocollimator, is based absolutely on the position of the image rather than on an assumed proportionality between the position and the levels of processed analog electronic signals. The term Cartesian in the name of this apparatus reflects the nature of its optical target. Figure 1 depicts the electronic functional blocks of an electronic absolute Cartesian autocollimator along with its basic optical layout, which is the same as that of a conventional autocollimator. Referring first to the optical layout and functions only, this or any autocollimator is used to measure the compound angular deviation of a flat datum mirror with respect to the optical axis of the autocollimator itself. The optical components include an illuminated target, a beam splitter, an objective or collimating lens, and a viewer or detector (described in more detail below) at a viewing plane. The target and the viewing planes are focal planes of the lens. Target light reflected by the datum mirror is imaged on the viewing plane at unit magnification by the collimating lens. If the normal to the datum mirror is parallel to the optical axis of the autocollimator, then the target image is centered on the viewing plane. Any angular deviation of the normal from the optical axis manifests itself as a lateral displacement of the target image from the center. The magnitude of the displacement is proportional to the focal length and to the magnitude (assumed to be small) of the angular deviation. The direction of the displacement is perpendicular to the axis about which the

  7. A Frequency Transfer and Cleanup System for Ultra-High Stability at Both Long and Short Times for the Cassini Ka-Band Experiment

    NASA Technical Reports Server (NTRS)

    Calhoun, M. D.; Dick, G. J.; Wang, R. T.

    1999-01-01

    New radio science experiments, including a gravitational wave search and several atmospheric occultation studies, are planned for the Cassini Ka-band experiment. These experiments are made possible by reduced solar-induced phase fluctuations at the high-frequency (32 GHZ) of the radio link between the earth and the spacecraft. In order to match the improved link performance, a significant upgrade is under way to improve the frequency stability capabilities of NASA's Deep Space Network (DSN). Significant improvements are being undertaken in many areas, including antenna vibration and (wet) tropospheric calibration, in addition to frequency generation and distribution. We describe here the design and development of a system to provide a reference signal with the highest possible frequency stability for both long-term, short-term, and phase noise, at an antenna (DSS 25) that is remote from the frequency standards room at SPC-10 at the Goldstone site. The new technologies were developed in order to meet the very tight requirements. They are: 1) a Stabilized Fiber-Optic Distribution Assembly (SFODA) that includes active compensation of thermal variations to transfer long-term stability over 16 km of ordinary fiber-optic cable, and 2) a Compensated Sapphire Oscillator (CSO) that provides short-term performance in a cryocooled sapphire oscillator with ultra-high short-term stability and low phase noise.

  8. Dissemination of time and RF frequency via a stabilized fibre optic link over a distance of 420 km

    NASA Astrophysics Data System (ADS)

    Śliwczyński, Łukasz; Krehlik, Przemysław; Czubla, Albin; Buczek, Łukasz; Lipiński, Marcin

    2013-04-01

    In this paper we present the results of our work concerning the long-distance fibre optic dissemination of time (1 PPS) and frequency (10 MHz) signals generated by atomic sources, such as caesium clocks, hydrogen masers or caesium fountains. For these purposes we developed dedicated hardware (a fibre optic system with active stabilization of the propagation delay and bidirectional fibre optic amplifiers) together with a procedure to enable calibration of the time transfer. Our laboratory measurements performed over fibre lengths of up to 480 km showed an Allan deviation of the order of 4 × 10-17, time deviation below 1 ps (both at one-day averaging) and the possibility of calibration with picosecond accuracy even for the longest from evaluated links. After successful laboratory evaluation the system was next installed on a 421.4 km long route between the Central Office of Measures (GUM) in Warsaw, Poland, and the Astrogeodynamic Observatory (AOS) in Borowiec near Poznań, Poland. Experiments comparing the UTC(PL) and UTC(AOS) atomic timescales using the fibre optic link and TTS-4 dual-frequency GNSS time transfer receivers showed that the consistency of the results is within the calibration accuracy of the GPS receivers and with much better noise performance. The field operation of the system proved its full functionality and confirmed our previous laboratory evaluation to the maximum extent possible using the methods for comparing distant clocks available at GUM and AOS.

  9. ABSOLUTE POLARIMETRY AT RHIC.

    SciTech Connect

    OKADA; BRAVAR, A.; BUNCE, G.; GILL, R.; HUANG, H.; MAKDISI, Y.; NASS, A.; WOOD, J.; ZELENSKI, Z.; ET AL.

    2007-09-10

    Precise and absolute beam polarization measurements are critical for the RHIC spin physics program. Because all experimental spin-dependent results are normalized by beam polarization, the normalization uncertainty contributes directly to final physics uncertainties. We aimed to perform the beam polarization measurement to an accuracy Of {Delta}P{sub beam}/P{sub beam} < 5%. The absolute polarimeter consists of Polarized Atomic Hydrogen Gas Jet Target and left-right pairs of silicon strip detectors and was installed in the RHIC-ring in 2004. This system features proton-proton elastic scattering in the Coulomb nuclear interference (CNI) region. Precise measurements of the analyzing power A{sub N} of this process has allowed us to achieve {Delta}P{sub beam}/P{sub beam} = 4.2% in 2005 for the first long spin-physics run. In this report, we describe the entire set up and performance of the system. The procedure of beam polarization measurement and analysis results from 2004-2005 are described. Physics topics of AN in the CNI region (four-momentum transfer squared 0.001 < -t < 0.032 (GeV/c){sup 2}) are also discussed. We point out the current issues and expected optimum accuracy in 2006 and the future.

  10. Laser-Frequency Stabilization Based on Steady-State Spectral-Hole Burning in Eu(3+)∶Y(2)SiO(5).

    PubMed

    Cook, Shon; Rosenband, Till; Leibrandt, David R

    2015-06-26

    We present and analyze a method of laser-frequency stabilization via steady-state patterns of spectral holes in Eu(3+)∶Y(2)SiO(5). Three regions of spectral holes are created, spaced in frequency by the ground-state hyperfine splittings of (151)Eu(3+). The absorption pattern is shown not to degrade after days of laser-frequency stabilization. An optical frequency comparison of a laser locked to such a steady-state spectral-hole pattern with an independent cavity-stabilized laser and a Yb optical lattice clock demonstrates a spectral-hole fractional frequency instability of 1.0×10(-15)τ(-1/2) that averages to 8.5(-1.8)(+4.8)×10(-17) at τ=73  s. Residual amplitude modulation at the frequency of the rf drive applied to the fiber-coupled electro-optic modulator is reduced to less than 1×10(-6) fractional amplitude modulation at τ>1  s by an active servo. The contribution of residual amplitude modulation to the laser-frequency instability is further reduced by digital division of the transmission and incident photodetector signals to less than 1×10(-16) at τ>1  s. PMID:26197127

  11. Laser-Frequency Stabilization Based on Steady-State Spectral-Hole Burning in Eu3 +∶Y2SiO5

    NASA Astrophysics Data System (ADS)

    Cook, Shon; Rosenband, Till; Leibrandt, David R.

    2015-06-01

    We present and analyze a method of laser-frequency stabilization via steady-state patterns of spectral holes in Eu3 +∶Y2SiO5 . Three regions of spectral holes are created, spaced in frequency by the ground-state hyperfine splittings of 151Eu 3+. The absorption pattern is shown not to degrade after days of laser-frequency stabilization. An optical frequency comparison of a laser locked to such a steady-state spectral-hole pattern with an independent cavity-stabilized laser and a Yb optical lattice clock demonstrates a spectral-hole fractional frequency instability of 1.0 ×10-15τ-1 / 2 that averages to 8. 5-1.8+4.8×10-17 at τ =73 s . Residual amplitude modulation at the frequency of the rf drive applied to the fiber-coupled electro-optic modulator is reduced to less than 1 ×10-6 fractional amplitude modulation at τ >1 s by an active servo. The contribution of residual amplitude modulation to the laser-frequency instability is further reduced by digital division of the transmission and incident photodetector signals to less than 1 ×10-16 at τ >1 s .

  12. A CPT-based Cs vapor cell atomic clock with a short-term fractional frequency stability of 3 x 10-13 τ-1/2

    NASA Astrophysics Data System (ADS)

    Abdel Hafiz, Moustafa; Liu, Xiaochi; Guérandel, Stéphane; De Clercq, Emeric; Boudot, Rodolphe

    2016-06-01

    This article reports on the development and short-term fractional frequency stability of a continuous-regime (CW) Cs vapor cell atomic clock based on coherent population trapping (CPT). The push-pull optical pumping technique is used to increase the number of atoms that participate to the clock transition, yielding a typical CPT resonance contrast of 25% for a CPT linewidth of about 450 Hz. The clock short-term fractional frequency stability is measured to be 3 x 10-13 τ-1/2 up to 100 seconds averaging time, in correct agreement with the signal-to-noise ratio limit. The mid-term frequency stability results are currently mainly limited by laser power effects. The detection of high-contrast narrow Raman-Ramsey fringes is demonstrated with this setup by making the atoms interact with a light pulse sequence.

  13. Frequency stabilization of an Er-doped fiber laser with a collinear 2f-to-3f self-referencing interferometer

    SciTech Connect

    Hitachi, K. Ishizawa, A.; Mashiko, H.; Sogawa, T.; Gotoh, H.; Tadanaga, O.; Nishikawa, T.

    2015-06-08

    We report the stabilization of the carrier-envelope offset (CEO) frequency of an Er-doped fiber laser with a collinear 2f-to-3f self-referencing interferometer. The interferometer is implemented by a dual-pitch periodically poled lithium niobate ridge waveguide with two different quasi-phase matching pitch sizes. We obtain a 52-dB signal-to-noise ratio in the 100-kHz resolution bandwidth of a heterodyne beat signal, which is sufficient for frequency stabilization. We also demonstrate that the collinear geometry is robust against environmental perturbation by comparing in-loop and out-of-loop Allan deviations when the in-loop CEO frequency is stabilized with a phase-locked loop circuit.

  14. Frequency stabilization of an Er-doped fiber laser with a collinear 2f-to-3f self-referencing interferometer

    NASA Astrophysics Data System (ADS)

    Hitachi, K.; Ishizawa, A.; Tadanaga, O.; Nishikawa, T.; Mashiko, H.; Sogawa, T.; Gotoh, H.

    2015-06-01

    We report the stabilization of the carrier-envelope offset (CEO) frequency of an Er-doped fiber laser with a collinear 2f-to-3f self-referencing interferometer. The interferometer is implemented by a dual-pitch periodically poled lithium niobate ridge waveguide with two different quasi-phase matching pitch sizes. We obtain a 52-dB signal-to-noise ratio in the 100-kHz resolution bandwidth of a heterodyne beat signal, which is sufficient for frequency stabilization. We also demonstrate that the collinear geometry is robust against environmental perturbation by comparing in-loop and out-of-loop Allan deviations when the in-loop CEO frequency is stabilized with a phase-locked loop circuit.

  15. Absolute determination of local tropospheric OH concentrations

    NASA Technical Reports Server (NTRS)

    Armerding, Wolfgang; Comes, Franz-Josef

    1994-01-01

    Long path absorption (LPA) according to Lambert Beer's law is a method to determine absolute concentrations of trace gases such as tropospheric OH. We have developed a LPA instrument which is based on a rapid tuning of the light source which is a frequency doubled dye laser. The laser is tuned across two or three OH absorption features around 308 nm with a scanning speed of 0.07 cm(exp -1)/microsecond and a repetition rate of 1.3 kHz. This high scanning speed greatly reduces the fluctuation of the light intensity caused by the atmosphere. To obtain the required high sensitivity the laser output power is additionally made constant and stabilized by an electro-optical modulator. The present sensitivity is of the order of a few times 10(exp 5) OH per cm(exp 3) for an acquisition time of a minute and an absorption path length of only 1200 meters so that a folding of the optical path in a multireflection cell was possible leading to a lateral dimension of the cell of a few meters. This allows local measurements to be made. Tropospheric measurements have been carried out in 1991 resulting in the determination of OH diurnal variation at specific days in late summer. Comparison with model calculations have been made. Interferences are mainly due to SO2 absorption. The problem of OH self generation in the multireflection cell is of minor extent. This could be shown by using different experimental methods. The minimum-maximum signal to noise ratio is about 8 x 10(exp -4) for a single scan. Due to the small size of the absorption cell the realization of an open air laboratory is possible in which by use of an additional UV light source or by additional fluxes of trace gases the chemistry can be changed under controlled conditions allowing kinetic studies of tropospheric photochemistry to be made in open air.

  16. In situ high-frequency UV-Vis spectrometer probes for investigating runoff processes and end member stability.

    NASA Astrophysics Data System (ADS)

    Schwab, Michael; Weiler, Markus; Pfister, Laurent; Klaus, Julian

    2014-05-01

    In recent years, several limitations as to the application of end member mixing analysis with isotope and geochemical tracers have been revealed: unstable end member solutions, inputs varying in space and time, and unrealistic mixing assumptions. In addition, the necessary high-frequency sampling using conventional methods is time and resources consuming, and hence most sampling rates are not suitable for capturing the response times of the majority of observed headwater catchments. However, high-frequency observations are considered fundamental for gaining new insights into hydrological systems. In our study, we have used two portable, in situ, high-frequency UV-Vis spectrometers (spectro::lyser; scan Messtechnik GmbH) to investigate the variability of several signatures in streamflow and end member stability. The spectro::lyser measures TOC, DOC, nitrate and the light absorption spectrum from 220 to 720 nm with 2.5 nm increment. The Weierbach catchment (0.45 km2) in the Attert basin (297 km2) in Luxemburg is a small headwater research catchment (operated by the CRP Gabriel Lippmann), which is completely forested and underlain by schist bedrock. The catchment is equipped with a dense network of hydrological instruments and for this study, the outlet of the Weierbach catchment was equipped with one spectro::lyser, permanently sensing stream water at a 15 minutes time step over several months. Hydrometric and meteorologic data was compared with the high-frequency spectro::lyser time series of TOC, DOC, nitrate and the light absorption spectrum, to get a first insight into the behaviour of the catchment under different environmental conditions. As a preliminary step for a successful end member mixing analysis, the stability of rainfall, soil water, and groundwater was tested with one spectro::lyser, both temporally and spatially. Thereby, we focused on the investigation of changes and patterns of the light absorption spectrum of the different end members and the

  17. Frequency characteristics of an inherently stable Nd:YAG laser operated at liquid helium temperature

    SciTech Connect

    Scholz, Matthias; Kovalchuk, Evgeny; Peters, Achim

    2009-07-10

    We report on frequency measurements of a free-running Nd:YAG laser operating at temperatures down to 6.5 K using a femtosecond laser frequency comb. Due to lower thermal expansion and thermo-optic effects as well as reduced electron-phonon interactions in Nd:YAG at cryogenic temperatures, a laser frequency stability on the order of 10{sup -11} at {tau} < or = 30s has been achieved. Within a one-week measurement period, absolute frequency deviations were lower than 1.85 MHz. This is up to a 100-fold improvement of frequency stability compared to any existing free-running solid-state laser.

  18. Implants as absolute anchorage.

    PubMed

    Rungcharassaeng, Kitichai; Kan, Joseph Y K; Caruso, Joseph M

    2005-11-01

    Anchorage control is essential for successful orthodontic treatment. Each tooth has its own anchorage potential as well as propensity to move when force is applied. When teeth are used as anchorage, the untoward movements of the anchoring units may result in the prolonged treatment time, and unpredictable or less-than-ideal outcome. To maximize tooth-related anchorage, techniques such as differential torque, placing roots into the cortex of the bone, the use of various intraoral devices and/or extraoral appliances have been implemented. Implants, as they are in direct contact with bone, do not possess a periodontal ligament. As a result, they do not move when orthodontic/orthopedic force is applied, and therefore can be used as "absolute anchorage." This article describes different types of implants that have been used as orthodontic anchorage. Their clinical applications and limitations are also discussed. PMID:16463910

  19. Absolute Equilibrium Entropy

    NASA Technical Reports Server (NTRS)

    Shebalin, John V.

    1997-01-01

    The entropy associated with absolute equilibrium ensemble theories of ideal, homogeneous, fluid and magneto-fluid turbulence is discussed and the three-dimensional fluid case is examined in detail. A sigma-function is defined, whose minimum value with respect to global parameters is the entropy. A comparison is made between the use of global functions sigma and phase functions H (associated with the development of various H-theorems of ideal turbulence). It is shown that the two approaches are complimentary though conceptually different: H-theorems show that an isolated system tends to equilibrium while sigma-functions allow the demonstration that entropy never decreases when two previously isolated systems are combined. This provides a more complete picture of entropy in the statistical mechanics of ideal fluids.

  20. Frequency-stabilized 1 W optical comb at 2.2-2.6 μm by Cr2+:ZnSe multipass amplification.

    PubMed

    Coluccelli, Nicola; Gambetta, Alessio; Sala, Tommaso; Gatti, Davide; Marangoni, Marco; Laporta, Paolo; Galzerano, Gianluca

    2012-11-01

    We present a frequency comb source with power level up to 150 μW per comb mode, tunable in the 2.2-2.6 μm wavelength region, based on a Cr(2+):ZnSe multipass solid-state amplifier seeded by the output of an actively stabilized optical parametric oscillator, synchronously pumped by a commercial 250 MHz Er:fiber laser. Phase relationship between idler, signal, and pump waves is exploited to perform frequency comb stabilization in the whole 2.2-2.6 μm mid-infrared spectral region. PMID:23114322

  1. Frequency stabilization based on high finesse glass-ceramic Fabry-Perot cavity for a 632.8-nm He-Ne laser

    NASA Astrophysics Data System (ADS)

    Fu, Tingting; Yang, Kaiyong; Tan, Zhongqi; Luo, Zhifu; Wu, Suyong

    2014-12-01

    A frequency stabilization technique for a 632.8nm He-Ne laser with a high finesse Fabry-Perot cavity is introduced in this paper. The resonant frequency of the cavity is taken as the frequency standard .In this system the Fabry-Perot cavity is composed of a glass-ceramic spacer, with thermal expansion coefficient smaller than 2×10-8/°C , which means an excellent thermal stabilization which greatly decreases the thermal impacts on the cavity length in the desired constant-temperature environment.The intra-cavity spherical mirror is specially designed, which makes the Fabry-cavity a sensor element in our subsequent experiments for a new practical optical accelerometer .Both cavity mirrors were custom made in our laboratory which have reflectivities greater than 99.995% at 632.8nm, so the Fabry-Perot cavity has a finesse of about 62830. The half-maximum transmission line width is about 55.48 KHz and the free spectral range is 3.5GHz .In the experimental setup, we adopt the frequency stabilization circuit with small dithering .With proper dithering voltage, the laser can be precisely locked to the Fabry-Perot cavity minimum reflection point. Theoretically the frequency stability can reach 10-10 order.

  2. Low frequency AC waveform generator

    DOEpatents

    Bilharz, Oscar W.

    1986-01-01

    Low frequency sine, cosine, triangle and square waves are synthesized in circuitry which allows variation in the waveform amplitude and frequency while exhibiting good stability and without requiring significant stabilization time. A triangle waveform is formed by a ramped integration process controlled by a saturation amplifier circuit which produces the necessary hysteresis for the triangle waveform. The output of the saturation circuit is tapped to produce the square waveform. The sine waveform is synthesized by taking the absolute value of the triangular waveform, raising this absolute value to a predetermined power, multiplying the raised absolute value of the triangle wave with the triangle wave itself and properly scaling the resultant waveform and subtracting it from the triangular waveform itself. The cosine is synthesized by squaring the triangular waveform, raising the triangular waveform to a predetermined power and adding the squared waveform raised to the predetermined power with a DC reference and subtracting the squared waveform therefrom, with all waveforms properly scaled. The resultant waveform is then multiplied with a square wave in order to correct the polarity and produce the resultant cosine waveform.

  3. Absolute neutrino mass measurements

    NASA Astrophysics Data System (ADS)

    Wolf, Joachim

    2011-10-01

    The neutrino mass plays an important role in particle physics, astrophysics and cosmology. In recent years the detection of neutrino flavour oscillations proved that neutrinos carry mass. However, oscillation experiments are only sensitive to the mass-squared difference of the mass eigenvalues. In contrast to cosmological observations and neutrino-less double beta decay (0v2β) searches, single β-decay experiments provide a direct, model-independent way to determine the absolute neutrino mass by measuring the energy spectrum of decay electrons at the endpoint region with high accuracy. Currently the best kinematic upper limits on the neutrino mass of 2.2eV have been set by two experiments in Mainz and Troitsk, using tritium as beta emitter. The next generation tritium β-experiment KATRIN is currently under construction in Karlsruhe/Germany by an international collaboration. KATRIN intends to improve the sensitivity by one order of magnitude to 0.2eV. The investigation of a second isotope (137Rh) is being pursued by the international MARE collaboration using micro-calorimeters to measure the beta spectrum. The technology needed to reach 0.2eV sensitivity is still in the R&D phase. This paper reviews the present status of neutrino-mass measurements with cosmological data, 0v2β decay and single β-decay.

  4. Absolute neutrino mass measurements

    SciTech Connect

    Wolf, Joachim

    2011-10-06

    The neutrino mass plays an important role in particle physics, astrophysics and cosmology. In recent years the detection of neutrino flavour oscillations proved that neutrinos carry mass. However, oscillation experiments are only sensitive to the mass-squared difference of the mass eigenvalues. In contrast to cosmological observations and neutrino-less double beta decay (0v2{beta}) searches, single {beta}-decay experiments provide a direct, model-independent way to determine the absolute neutrino mass by measuring the energy spectrum of decay electrons at the endpoint region with high accuracy.Currently the best kinematic upper limits on the neutrino mass of 2.2eV have been set by two experiments in Mainz and Troitsk, using tritium as beta emitter. The next generation tritium {beta}-experiment KATRIN is currently under construction in Karlsruhe/Germany by an international collaboration. KATRIN intends to improve the sensitivity by one order of magnitude to 0.2eV. The investigation of a second isotope ({sup 137}Rh) is being pursued by the international MARE collaboration using micro-calorimeters to measure the beta spectrum. The technology needed to reach 0.2eV sensitivity is still in the R and D phase. This paper reviews the present status of neutrino-mass measurements with cosmological data, 0v2{beta} decay and single {beta}-decay.

  5. On-orbit frequency stability analysis of the GPS NAVSTAR-1 quartz clock and the NAVSTARs-6 and -8 rubidium clocks

    NASA Technical Reports Server (NTRS)

    Mccaskill, T. B.; Buisson, J. A.; Reid, W. G.

    1984-01-01

    An on-orbit frequency stability performance analysis of the GPS NAVSTAR-1 quartz clock and the NAVSTARs-6 and -8 rubidium clocks is presented. The clock offsets were obtained from measurements taken at the GPS monitor stations which use high performance cesium standards as a reference. Clock performance is characterized through the use of the Allan variance, which is evaluated for sample times of 15 minutes to two hours, and from one day to 10 days. The quartz and rubidium clocks' offsets were corrected for aging rate before computing the frequency stability. The effect of small errors in aging rate is presented for the NAVSTAR-8 rubidium clock's stability analysis. The analysis includes presentation of time and frequency residuals with respect to linear and quadratic models, which aid in obtaining aging rate values and identifying systematic and random effects. The frequency stability values were further processed with a time domain noise process analysis, which is used to classify random noise process and modulation type.

  6. Absolute Identification by Relative Judgment

    ERIC Educational Resources Information Center

    Stewart, Neil; Brown, Gordon D. A.; Chater, Nick

    2005-01-01

    In unidimensional absolute identification tasks, participants identify stimuli that vary along a single dimension. Performance is surprisingly poor compared with discrimination of the same stimuli. Existing models assume that identification is achieved using long-term representations of absolute magnitudes. The authors propose an alternative…

  7. Be Resolute about Absolute Value

    ERIC Educational Resources Information Center

    Kidd, Margaret L.

    2007-01-01

    This article explores how conceptualization of absolute value can start long before it is introduced. The manner in which absolute value is introduced to students in middle school has far-reaching consequences for their future mathematical understanding. It begins to lay the foundation for students' understanding of algebra, which can change…

  8. An Ex Vivo Model in Human Femoral Heads for Histopathological Study and Resonance Frequency Analysis of Dental Implant Primary Stability

    PubMed Central

    Hernández-Cortés, Pedro; Galindo-Moreno, Pablo; Catena, Andrés; Ortega-Oller, Inmaculada; Salas-Pérez, José; Gómez-Sánchez, Rafael; Aguilar, Mariano; Aguilar, David

    2014-01-01

    Objective. This study was designed to explore relationships of resonance frequency analysis (RFA)—assessed implant stability (ISQ values) with bone morphometric parameters and bone quality in an ex vivo model of dental implants placed in human femoral heads and to evaluate the usefulness of this model for dental implant studies. Material and Methods. This ex vivo study included femoral heads from 17 patients undergoing surgery for femoral neck fracture due to osteoporosis (OP) (n = 7) or for total prosthesis joint replacement due to severe hip osteoarthrosis (OA) (n = 10). Sixty 4.5 × 13 mm Dentsply Astra implants were placed, followed by RFA. CD44 immunohistochemical analysis for osteocytes was also carried out. Results. As expected, the analysis yielded significant effects of femoral head type (OA versus OA) (P < 0.001), but not of the implants (P = 0.455) or of the interaction of the two factors (P = 0.848). Bonferroni post hoc comparisons showed a lower mean ISQ for implants in decalcified (50.33 ± 2.92) heads than in fresh (66.93 ± 1.10) or fixated (70.77 ± 1.32) heads (both P < 0.001). The ISQ score (fresh) was significantly higher for those in OA (73.52 ± 1.92) versus OP (67.13 ± 1.09) heads. However, mixed linear analysis showed no significant association between ISQ scores and morphologic or histomorphometric results (P > 0.5 in all cases), and no significant differences in ISQ values were found as a function of the length or area of the cortical layer (both P > 0.08). Conclusion. Although RFA-determined ISQ values are not correlated with morphometric parameters, they can discriminate bone quality (OP versus OA). This ex vivo model is useful for dental implant studies. PMID:24995307

  9. Asteroid absolute magnitudes and slope parameters

    NASA Technical Reports Server (NTRS)

    Tedesco, Edward F.

    1991-01-01

    A new listing of absolute magnitudes (H) and slope parameters (G) has been created and published in the Minor Planet Circulars; this same listing will appear in the 1992 Ephemerides of Minor Planets. Unlike previous listings, the values of the current list were derived from fits of data at the V band. All observations were reduced in the same fashion using, where appropriate, a single basis default value of 0.15 for the slope parameter. Distances and phase angles were computed for each observation. The data for 113 asteroids was of sufficiently high quality to permit derivation of their H and G. These improved absolute magnitudes and slope parameters will be used to deduce the most reliable bias-corrected asteroid size-frequency distribution yet made.

  10. A 99nW 70.4kHz Resistive Frequency Locking On-Chip Oscillator with 27.4ppm/°C Temperature Stability

    PubMed Central

    Choi, Myungjoon; Bang, Suyoung; Jang, Tae-Kwang; Blaauw, David; Sylvester, Dennis

    2015-01-01

    We present a low power on-chip oscillator for system-on-chip designs. The oscillator introduces a resistive frequency locking loop topology where the equivalent resistance of a switched-capacitor is matched to a temperature-compensated resistor. The approach eliminates the traditional comparator from the oscillation loop, which consumes significant power and limits temperature stability in conventional relaxation oscillators. The oscillator is fabricated in 0.18μm CMOS and exhibits 27.4ppm/°C and <7ppm long-term stability while consuming 99.4nW at 70.4 kHz. PMID:26855849

  11. Positional stability and radial dynamics of sonoluminescent bubbles under bi-harmonic driving: Effect of the high-frequency component and its relative phase.

    PubMed

    Rosselló, J M; Dellavale, D; Bonetto, F J

    2016-07-01

    The use of bi-frequency driving in sonoluminescence has proved to be an effective way to avoid the spatial instability (pseudo-orbits) developed by bubbles in systems with high viscous liquids like sulfuric or phosphoric acids. In this work, we present extensive experimental and numerical evidence in order to assess the effect of the high frequency component (PAc(HF)) of a bi-harmonic acoustic pressure field on the dynamic of sonoluminescent bubbles in an aqueous solution of sulfuric acid. The present study is mainly focused on the role of the harmonic frequency (Nf0) and the relative phase between the two frequency components (φb) of the acoustic field on the spatial, positional and diffusive stability of the bubbles. The results presented in this work were analyzed by means of three different approaches. First, we discussed some qualitative considerations about the changes observed in the radial dynamics, and the stability of similar bubbles under distinct bi-harmonic drivings. Later, we have investigated, through a series of numerical simulations, how the use of high frequency harmonic components of different order N, affects the positional stability of the SL bubbles. Furthermore, the influence of φb in their radius temporal evolution is systematically explored for harmonics ranging from the second to the fifteenth harmonic (N=2-15). Finally, a multivariate analysis based on the covariance method is performed to study the dependences among the parameters characterizing the SL bubble. Both experimental and numerical results indicate that the impact of PAc(HF) on the positional instability and the radial dynamics turns to be progressively negligible as the order of the high frequency harmonic component grows (i.e. N ≫ 1), however its effectiveness on the reduction of the spatial instability remains unaltered or even improved. PMID:26964988

  12. Two-Stage System Based on a Software-Defined Radio for Stabilizing of Optical Frequency Combs in Long-Term Experiments

    PubMed Central

    Čížek, Martin; Hucl, Václav; Hrabina, Jan; Šmíd, Radek; Mikel, Břetislav; Lazar, Josef; Číp, Ondřej

    2014-01-01

    A passive optical resonator is a special sensor used for measurement of lengths on the nanometer and sub-nanometer scale. Astabilized optical frequency comb can provide an ultimate reference for measuring the wavelength of a tunable laser locked to the optical resonator. If we lock the repetition and offset frequencies of the comb to a high-grade radiofrequency (RF) oscillator its relative frequency stability is transferred from the RF to the optical frequency domain. Experiments in the field of precise length metrology of low-expansion materials are usually of long-term nature so it is required that the optical frequency comb stay in operation for an extended period of time. The optoelectronic closed-loop systems used for stabilization of combs are usually based on traditional analog electronic circuits processing signals from photodetectors. From an experimental point of view, these setups are very complicated and sensitive to ambient conditions, especially in the optical part, therefore maintaining long-time operation is not easy. The research presented in this paper deals with a novel approach based on digital signal processing and a software-defined radio. We describe digital signal processing algorithms intended for keeping the femtosecond optical comb in a long-time stable operation. This need arose during specialized experiments involving measurements of optical frequencies of tunable continuous-wave lasers. The resulting system is capable of keeping the comb in lock for an extensive period of time (8 days or more) with the relative stability better than 1.6 × 10−11. PMID:24448169

  13. Low frequency ac waveform generator

    DOEpatents

    Bilharz, O.W.

    1983-11-22

    Low frequency sine, cosine, triangle and square waves are synthesized in circuitry which allows variation in the waveform amplitude and frequency while exhibiting good stability and without requiring significant stablization time. A triangle waveform is formed by a ramped integration process controlled by a saturation amplifier circuit which produces the necessary hysteresis for the triangle waveform. The output of the saturation circuit is tapped to produce the square waveform. The sine waveform is synthesized by taking the absolute value of the triangular waveform, raising this absolute value to a predetermined power, multiplying the raised absolute value of the triangle wave with the triangle wave itself and properly scaling the resultant waveform and subtracting it from the triangular waveform to a predetermined power and adding the squared waveform raised to the predetermined power with a DC reference and subtracting the squared waveform therefrom, with all waveforms properly scaled. The resultant waveform is then multiplied with a square wave in order to correct the polarity and produce the resultant cosine waveform.

  14. Frequency-Stabilized Cavity Ring-Down Spectroscopy of Oxygen and Carbon Dioxide to Support Atmospheric Remote Sensing

    NASA Astrophysics Data System (ADS)

    Long, David Alexander

    Recent remote-sensing satellite missions have aimed to measure global greenhouse gas concentrations with precisions as demanding as 0.25%. These high-resolution measurements should allow for the quantification of carbon sources and sinks, thus, allowing for a considerable reduction in present carbon cycle uncertainties. To achieve these unprecedented measurement goals will require the most precise body of spectroscopic reference data (i.e., laboratory measurements) ever assembled. In order to aid these missions, we have measured ultraprecise spectroscopic parameters for the (30012)←(00001) CO2 band at 1.57 microm and the O2 A-band at 0.76 microm. These near-infrared transitions are utilized in recent greenhouse gas monitoring missions, with the A-band being employed to derive pressure and temperature profiles. In these investigations we have employed frequency-stabilized cavity ring-down spectroscopy (FS-CRDS), a novel ultrasensitive spectroscopic technique. In the O2 A-band we have measured magnetic dipole line parameters for 16O 2 as well as each of the rare isotopologues and have produced calculated, HITRAN-style line lists. Due to the clear presence of collisional narrowing in the spectra, we have utilized the Galatry line profile in these studies and have reported narrowing parameters under self- and air-broadened conditions. We anticipate that the use of these spectral parameters will greatly reduce the uncertainties of atmospheric remote-sensing retrievals. In addition, the spectral fidelity of FS-CRDS allowed us to observe and quantify unresolved hyperfine structure for the 17O-containing isotopologues. Furthermore, the high sensitivity of FS-CRDS enabled measurements of ultraweak (S˜10 -30 cm molec.-1) electric quadrupole transitions in the A-band, many of which had not previously been observed. Recently we have begun a series of studies of the near-infrared CO2 transitions. Measurements at low pressures (<40 kPa) have revealed the simultaneous presence

  15. Vertical stability and the Brunt-Väisäla frequency of deep natural waters by the example of Lake Baikal, Lake Tanganyika, and the World Ocean

    NASA Astrophysics Data System (ADS)

    Sherstyankin, P. P.; Kuimova, L. N.

    2009-12-01

    Theoretical analysis, calculations, and comparison with the results of observations in Lake Baikal, Lake Tanganyika, and the World Ocean are performed for the vertical stability E and the Brunt-Väisäla frequency N in the form of N 2 with regard to all components (at the constant temperature T and the salinity S, the common adiabatic form at T, S Const). The adiabatic stability E ad and the Väisäla frequency N in the form of N {/ad 2} are always positive; at a change from the inverse to the direct temperature stratification, they have deep minimums reaching 10-16 m-1 and 10-15 s-2 and less; the minimums have the form of a special point, a reversal point of the first kind called a “cusp.” The reality of these reversal points is confirmed by the analysis of the investigation procedure, comparison with the results of previous theoretical (Sherstyankin, et al., 2007), and experimental (observations in Baikal, Shimaraev et al., 1994) works. The features of vertical profiles of E ad , E and N {/ad 2}, N 2, as well as the layers where the Brunt-Väisäla frequency is less than the inertial frequency, are studied. The analysis with regard to all components of the stability E ad and the Brunt-Väisäla frequency N makes a great contribution to understanding of mixing processes in theoretical and experimental investigations; it is valid in all reservoirs of the Earth with inverse and direct temperature stratification, including Lake Baikal, Lake Tanganyika, and the World Ocean.

  16. Absolute instability of a viscous hollow jet

    NASA Astrophysics Data System (ADS)

    Gañán-Calvo, Alfonso M.

    2007-02-01

    An investigation of the spatiotemporal stability of hollow jets in unbounded coflowing liquids, using a general dispersion relation previously derived, shows them to be absolutely unstable for all physical values of the Reynolds and Weber numbers. The roots of the symmetry breakdown with respect to the liquid jet case, and the validity of asymptotic models are here studied in detail. Asymptotic analyses for low and high Reynolds numbers are provided, showing that old and well-established limiting dispersion relations [J. W. S. Rayleigh, The Theory of Sound (Dover, New York, 1945); S. Chandrasekhar, Hydrodynamic and Hydromagnetic Stability (Dover, New York, 1961)] should be used with caution. In the creeping flow limit, the analysis shows that, if the hollow jet is filled with any finite density and viscosity fluid, a steady jet could be made arbitrarily small (compatible with the continuum hypothesis) if the coflowing liquid moves faster than a critical velocity.

  17. Transferring the Rb+ hyperfine-structure stability to a Fabry-Perot resonator used as a frequency standard for astronomical spectrographs

    NASA Astrophysics Data System (ADS)

    Huke, Philipp; Holzhüter, Hanno; Reiners, Ansgar

    2015-06-01

    We report on the experimental realization of locking a Fabry-Perot interferometer (FPI) onto a stabilized diode laser for the calibration of astronomical spectrographs. The external cavity diode laser (ECDL) is stabilized to the 85Rb+ F* = 2 --> F = 3 transition with a pump-probe setup. The stability of the 85Rb+ reached between optical clocks is on the order of 10-13.1 and can be used to reduce the linewidth / drift of the ECDL to a few kHz.2 The measured linewidth of the transition is around 20 MHz due to unavoidable misalignment between pump- and probe-beam, power- and Doppler-broadening at room temperature.2 The aim is to transfer this stability to a FPI that can be used as optical frequency standard: Therefore the phase of the light reflected from the FPI is observed using the Pound-Drever-Hall method. The theoretically reachable stability of a few mHz/Hz3 is limited by different noise factors. In order to identify these noise factors we a) follow the calculation of noise factors given by, 4 b) calculate the contribution of misalignment and insufficient mode matching by applying the generalized matrix-formalism, 5 and c) estimate the contribution of the initial laser linewidth and the present electronic noise sources.

  18. Clock time is absolute and universal

    NASA Astrophysics Data System (ADS)

    Shen, Xinhang

    2015-09-01

    A critical error is found in the Special Theory of Relativity (STR): mixing up the concepts of the STR abstract time of a reference frame and the displayed time of a physical clock, which leads to use the properties of the abstract time to predict time dilation on physical clocks and all other physical processes. Actually, a clock can never directly measure the abstract time, but can only record the result of a physical process during a period of the abstract time such as the number of cycles of oscillation which is the multiplication of the abstract time and the frequency of oscillation. After Lorentz Transformation, the abstract time of a reference frame expands by a factor gamma, but the frequency of a clock decreases by the same factor gamma, and the resulting multiplication i.e. the displayed time of a moving clock remains unchanged. That is, the displayed time of any physical clock is an invariant of Lorentz Transformation. The Lorentz invariance of the displayed times of clocks can further prove within the framework of STR our earth based standard physical time is absolute, universal and independent of inertial reference frames as confirmed by both the physical fact of the universal synchronization of clocks on the GPS satellites and clocks on the earth, and the theoretical existence of the absolute and universal Galilean time in STR which has proved that time dilation and space contraction are pure illusions of STR. The existence of the absolute and universal time in STR has directly denied that the reference frame dependent abstract time of STR is the physical time, and therefore, STR is wrong and all its predictions can never happen in the physical world.

  19. Providing hydrogen maser timing stability to orbiting VLBI radio telescope observations by post-measurement compensation of linked frequency standard imperfections

    NASA Technical Reports Server (NTRS)

    Springett, James C.

    1994-01-01

    Orbiting VLBI (OVLBI) astronomical observations are based upon measurements acquired simultaneously from ground-based and earth-orbiting radio telescopes. By the mid-1990s, two orbiting VLBI observatories, Russia's Radioastron and Japan's VSOP, will augment the worldwide VLBI network, providing baselines to earth radio telescopes as large as 80,000 km. The challenge for OVLBI is to effectuate space to ground radio telescope data cross-correlation (the observation) to a level of integrity currently achieved between ground radio telescopes. VLBI radio telescopes require ultrastable frequency and timing references in order that long term observations may be made without serious cross-correlation loss due to frequency source drift and phase noise. For this reason, such instruments make use of hydrogen maser frequency standards. Unfortunately, space-qualified hydrogen maser oscillators are currently not available for use on OVLBI satellites. Thus, the necessary long-term stability needed by the orbiting radio telescope may only be obtained by microwave uplinking a ground-based hydrogen maser derived frequency to the satellite. Although the idea of uplinking the frequency standard intrinsically seems simple, there are many 'contaminations' which degrade both the long and short term stability of the transmitted reference. Factors which corrupt frequency and timing accuracy include additive radio and electronic circuit thermal noise, slow or systematic phase migration due to changes of electronic circuit temporal operating conditions (especially temperature), ionosphere and troposphere induced scintillations, residual Doppler-incited components, and microwave signal multipath propagation. What is important, though, is to realize that ultimate stability does not have to be achieved in real-time. Instead, information needed to produce a high degree of coherence in the subsequent cross-correlation operation may be derived from a two-way coherent radio link, recorded and later

  20. Absolute and Convective Instability in Fluid-Conveying Flexible Pipes

    NASA Astrophysics Data System (ADS)

    de Langre, E.; Ouvrard, A. E.

    1998-11-01

    The effect of internal plug flow on the lateral stability of fluid conveying flexible pipes is investigated by determining the absolute/convective nature of the instability from the analytically derived linear dispersion relation. The fluid-structure interaction is modeled following the work of Gregory and Paidoussis (1966). The different domains of stability, convective instability, and absolute instability are explicitly derived in parameter space. The effect of flow velocity, mass ratio between the fluid and the structure, stiffness of the elastic foundation and axial tension is considered. Absolute instability prevails over a wide range of parameters. Convective instability only takes place at very high mass ratio, small stiffness and small axial tension. Relation is made with previous work of Brazier-Smith & Scott (1984) and Crighton (1991), considered here as a short wave approximation.

  1. Noise properties of an optical frequency comb from a SESAM-mode-locked 1.5-μm solid-state laser stabilized to the 10-13 level

    NASA Astrophysics Data System (ADS)

    Schilt, S.; Dolgovskiy, V.; Bucalovic, N.; Schori, C.; Stumpf, M. C.; Di Domenico, G.; Pekarek, S.; Oehler, A. E. H.; Südmeyer, T.; Keller, U.; Thomann, P.

    2012-11-01

    We present a detailed investigation of the noise properties of an optical frequency comb generated from a femtosecond diode-pumped solid-state laser operating in the 1.5-μm spectral region. The stabilization of the passively mode-locked Er:Yb:glass laser oscillator, referred to as ERGO, is achieved using pump power modulation for the control of the carrier envelope offset (CEO) frequency and by adjusting the laser cavity length for the control of the repetition rate. The stability and the noise of the ERGO comb are characterized in free-running and in phase-locked operation by measuring the noise properties of the CEO, of the repetition rate, and of a comb line at 1558 nm. The comb line is analyzed from the heterodyne beat signal with a cavity-stabilized ultra-narrow-linewidth laser using a frequency discriminator. Two different schemes to stabilize the comb to a radio-frequency (RF) reference are compared. The comb properties (phase noise, frequency stability) are limited in both cases by the RF oscillator used to stabilize the repetition rate, while the contribution of the CEO is negligible at all Fourier frequencies, as a consequence of the low-noise characteristics of the CEO-beat. A linewidth of ≈150 kHz and a fractional frequency instability of 4.2×10-13 at 1 s are obtained for an optical comb line at 1558 nm. Improved performance is obtained by stabilizing the comb to an optical reference, which is a cavity-stabilized ultra-narrow linewidth laser at 1558 nm. The fractional frequency stability of 8×10-14 at 1 s, measured in preliminary experiments, is limited by the reference oscillator used in the frequency comparison.

  2. On the Absolutely Continuous Spectrum of Stark Operators

    NASA Astrophysics Data System (ADS)

    Perelman, Galina

    The stability of the absolutely continuous spectrum of the one-dimensional Stark operator under perturbations of the potential is discussed. The focus is on proving this stability under minimal assumptions on smoothness of the perturbation. A general criterion is presented together with some applications. These include the case of periodic perturbations where we show that any perturbation vL1()∩H-1/2() preserves the a.c. spectrum.

  3. Continuously tunable wavelength output from an Er-doped fiber femtosecond optical frequency comb with single-point frequency-doubling technique

    NASA Astrophysics Data System (ADS)

    Liu, H.; Cao, S. Y.; Meng, F.; Lin, B. K.; Fang, Z. J.

    2015-07-01

    Femtosecond optical frequency combs (FOFCs) with wavelengths covering the visible range have potential applications in the absolute frequency measurement of iodine-stabilized lasers and optical clock lasers. In this paper, an Er-FOFC with a tunable wavelength output from 689 to 813 nm based on the single-point frequency-doubling technique is demonstrated. Meanwhile, a beat frequency signal between the Er-FOFC and a tested laser at 729 nm with a signal-to-noise ratio of 30 dB at a resolution bandwidth of 100 kHz is obtained.

  4. Absolute transition probabilities of phosphorus.

    NASA Technical Reports Server (NTRS)

    Miller, M. H.; Roig, R. A.; Bengtson, R. D.

    1971-01-01

    Use of a gas-driven shock tube to measure the absolute strengths of 21 P I lines and 126 P II lines (from 3300 to 6900 A). Accuracy for prominent, isolated neutral and ionic lines is estimated to be 28 to 40% and 18 to 30%, respectively. The data and the corresponding theoretical predictions are examined for conformity with the sum rules.-

  5. SUNLITE program. Sub-Hertz relative frequency stabilization of two diode laser pumped Nd:YAG lasers locked to a Fabry-Perot interferometer

    NASA Technical Reports Server (NTRS)

    Byer, R. L.

    1990-01-01

    Two laser pumped Nd:YAG lasers were frequency stabilized to a commercial 6.327 GHz free spectral range Fabry-Perot interferometer yielding a best case beatnote linewidth of 330 MHz. In addition, a Fabry-Perot interferometer with a free spectral range of 680 MHz, a linewidth of 25 kHz, and a finesse of 27,500 was built, and when it was substituted in place of the commercial interferometer, it produced a robust and easily repeatable beatnote linewidth of 700 MHz.

  6. Theoretical Investigation on the Substituent Effect of Halogen Atoms at the C8 Position of Adenine: Relative Stability, Vibrational Frequencies, and Raman Spectra of Tautomers.

    PubMed

    Chen, Yan-Li; Wu, De-Yin; Tian, Zhong-Qun

    2016-06-16

    We have theoretically investigated the substituent effect of adenine at the C8 position with a substituent X = H, F, Cl, and Br by using the density functional theory (DFT) at the B3LYP/6-311+G(d, p) level. The aim is to study the substituent effect of halogen atoms on the relative stability, vibrational frequencies, and solvation effect of tautomers. Our calculated results show that for substituted adenine molecules the N9H8X tautomer to be the most stable structure in gas phase at the present theoretical level. Here N9H8X denotes the hydrogen atom binds to the N9 position of imidazole ring and X denotes H, F, Cl, and Br atoms. The influence of the induced attraction of the fluorine substituent is significantly larger than chlorine and bromine ones. The halogen substituent effect has a significant influence on changes of vibrational frequencies and Raman intensities. PMID:27243104

  7. A microrod-resonator Brillouin laser with 240 Hz absolute linewidth

    NASA Astrophysics Data System (ADS)

    Loh, William; Becker, Joe; Cole, Daniel C.; Coillet, Aurelien; Baynes, Fred N.; Papp, Scott B.; Diddams, Scott A.

    2016-04-01

    We demonstrate an ultralow-noise microrod-resonator based laser that oscillates on the gain supplied by the stimulated Brillouin scattering optical nonlinearity. Microresonator Brillouin lasers are known to offer an outstanding frequency noise floor, which is limited by fundamental thermal fluctuations. Here, we show experimental evidence that thermal effects also dominate the close-to-carrier frequency fluctuations. The 6 mm diameter microrod resonator used in our experiments has a large optical mode area of ∼100 μm2, and hence its 10 ms thermal time constant filters the close-to-carrier optical frequency noise. The result is an absolute laser linewidth of 240 Hz with a corresponding white-frequency noise floor of 0.1 Hz2 Hz‑1. We explain the steady-state performance of this laser by measurements of its operation state and of its mode detuning and lineshape. Our results highlight a mechanism for noise that is common to many microresonator devices due to the inherent coupling between intracavity power and mode frequency. We demonstrate the ability to reduce this noise through a feedback loop that stabilizes the intracavity power.

  8. High-frequency detection of the formation and stabilization of a radiation-induced defect cluster in semiconductor structures

    SciTech Connect

    Puzanov, A. S.; Obolenskiy, S. V. Kozlov, V. A.; Volkova, E. V.; Paveliev, D. G.

    2015-12-15

    The processes of the formation and stabilization of a radiation-induced defect cluster upon the arrival of a fast neutron to the space-charge region of a semiconductor diode are analyzed. The current pulse formed by secondary electrons is calculated and the spectrum of the signal generated by the diode (detector) under the action of an instantaneous neutron flux of the fission spectrum is determined. The possibility of experimental detection of the picosecond radiation-induced transition processes is discussed.

  9. Multifrequency continuous wave terahertz spectroscopy for absolute thickness determination

    SciTech Connect

    Scheller, Maik; Baaske, Kai; Koch, Martin

    2010-04-12

    We present a tunable multifrequency continuous wave terahertz spectrometer based on two laser diodes, photoconductive antennas, and a coherent detection scheme. The system is employed to determine the absolute thickness of samples utilizing a proposed synthetic difference frequency method to circumvent the 2pi uncertainty known from conventional photomixing systems while preserving a high spatial resolution.

  10. Global absolut gravity reference system as replacement of IGSN 71

    NASA Astrophysics Data System (ADS)

    Wilmes, Herbert; Wziontek, Hartmut; Falk, Reinhard

    2015-04-01

    The determination of precise gravity field parameters is of great importance in a period in which earth sciences are achieving the necessary accuracy to monitor and document global change processes. This is the reason why experts from geodesy and metrology joined in a successful cooperation to make absolute gravity observations traceable to SI quantities, to improve the metrological kilogram definition and to monitor mass movements and smallest height changes for geodetic and geophysical applications. The international gravity datum is still defined by the International Gravity Standardization Net adopted in 1971 (IGSN 71). The network is based upon pendulum and spring gravimeter observations taken in the 1950s and 60s supported by the early free fall absolute gravimeters. Its gravity values agreed in every case to better than 0.1 mGal. Today, more than 100 absolute gravimeters are in use worldwide. The series of repeated international comparisons confirms the traceability of absolute gravity measurements to SI quantities and confirm the degree of equivalence of the gravimeters in the order of a few µGal. For applications in geosciences where e.g. gravity changes over time need to be analyzed, the temporal stability of an absolute gravimeter is most important. Therefore, the proposition is made to replace the IGSN 71 by an up-to-date gravity reference system which is based upon repeated absolute gravimeter comparisons and a global network of well controlled gravity reference stations.

  11. High-power dense wavelength division multiplexing (HP-DWDM) of frequency stabilized 9xx diode laser bars with a channel spacing of 1.5 nm

    NASA Astrophysics Data System (ADS)

    Hengesbach, Stefan; Holly, Carlo; Krauch, Niels; Witte, Ulrich; Westphalen, Thomas; Traub, Martin; Hoffmann, Dieter

    2014-03-01

    We present a compact High-Power DenseWavelength Division Multiplexer (HP-DWDM) based on Volume Bragg Gratings (VBGs) for spectrally stabilized diode lasers with a low average beam quality M2 <=50. The center wavelengths of the five input channels with a spectral spacing of 1.5 nm are 973 nm, 974.5 nm, 976 nm, 977.5 nm and 979 nm. Multiplexing efficiencies of 97%+/-2% have been demonstrated with single mode, frequency stabilized laser radiation. Since the diffraction efficiency strongly depends on the beam quality, the multiplexing efficiency decreases to 94% (M2 = 25) and 85%+/-3% (M2 = 45) if multimode radiation is overlaid. Besides, the calculated multiplexing efficiency of the radiation with M2 = 45 amounts to 87:5 %. Thus, calculations and measurements are in good agreement. In addition, we developed a dynamic temperature control for the multiplexing VBGs which adapts the Bragg wavelengths to the diode laser center wavelengths. In short, the prototype with a radiance of 70GWm-2 sr-1 consists of five spectrally stabilized and passively cooled diode laser bars with 40Woutput after beam transformation. To achieve a good stabilization performance ELOD (Extreme LOw Divergence) diode laser bars have been chosen in combination with an external resonator based on VBGs. As a result, the spectral width defined by 95% power inclusion is < 120pm for each beam source across the entire operating range from 30 A to 120 A. Due to the spectral stabilization, the output power of each bar decreases in the range of < 5 %.

  12. Absolute Antenna Calibration at the US National Geodetic Survey

    NASA Astrophysics Data System (ADS)

    Mader, G. L.; Bilich, A. L.

    2012-12-01

    format. The NGS absolute system is located in Corbin, Virginia, and uses field measurements and actual GNSS satellite signals to quantitatively determine the carrier phase advance/delay introduced by the antenna element. NGS is interested in providing calibrations for a wide variety of dual-frequency, geodetic-grade antennas, from types in use at IGS and CORS reference stations to rover antennas not normally seen in those networks. In this presentation, we describe the NGS absolute calibration facility, and discuss the observation models and strategy used to generate NGS absolute calibrations. We also demonstrate that NGS absolute phase center variation (PCV) patterns are consistent with published values determined by other absolute antenna calibration facilities.

  13. Frequency Stability of 1x10(sup -13) in a Compensated Sapphire Oscillator Operating Above 77K

    NASA Technical Reports Server (NTRS)

    Dick, G. J.; Santiago, D. G.; Wang, R. T.

    1996-01-01

    We report on the design and test of a whispering gallery sapphire resonator for which the dominant (WGH(sub n11)) microwave mode family shows frequency-stable, compensated operation for temperatures above 77 kelvin. The resonator makes possible a new ultra-stable oscillator (USO) capability that promises performance improvements over the best available crystal quartz oscillators in a compact cryogenic package.

  14. A combined wave distribution function and stability analysis of Viking particle and low-frequency wave data

    SciTech Connect

    Oscarsson, T.E.; Roennmark, K.G. )

    1990-12-01

    In this paper the authors present an investigation of low-frequency waves observed on auroral field lines below the acceleration region by the Swedish satellite Viking. The measured frequency spectra are peaked at half the local proton gyrofrequency, and the waves are observed in close connection with precipitating electrons. In order to obtain information about the distribution of wave energy in wave vector space, they reconstruct the wave distribution function (WDF) from observed spectral densities. They use a new scheme that allows them to reconstruct simultaneously the WDF over a broad frequency band. The method also makes it possible to take into account available particle observations as well as Doppler shifts caused by the relative motion between the plasma and the satellite. The distribution of energy in wave vector space suggested by the reconstructed WDF is found to be consistent with what is expected from a plasma instability driven by the observed precipitating electrons. Furthermore, by using UV images obtained on Viking, they demonstrate that the wave propagation directions indicated by the reconstructed WDFs are consistent with a simple model of the presumed wave source in the electron precipitation region.

  15. United time-frequency spectroscopy for dynamics and global structure.

    PubMed

    Marian, Adela; Stowe, Matthew C; Lawall, John R; Felinto, Daniel; Ye, Jun

    2004-12-17

    Ultrashort laser pulses have thus far been used in two distinct modes. In the time domain, the pulses have allowed probing and manipulation of dynamics on a subpicosecond time scale. More recently, phase stabilization has produced optical frequency combs with absolute frequency reference across a broad bandwidth. Here we combine these two applications in a spectroscopic study of rubidium atoms. A wide-bandwidth, phase-stabilized femtosecond laser is used to monitor the real-time dynamic evolution of population transfer. Coherent pulse accumulation and quantum interference effects are observed and well modeled by theory. At the same time, the narrow linewidth of individual comb lines permits a precise and efficient determination of the global energy-level structure, providing a direct connection among the optical, terahertz, and radio-frequency domains. The mechanical action of the optical frequency comb on the atomic sample is explored and controlled, leading to precision spectroscopy with an appreciable reduction in systematic errors. PMID:15550622

  16. Optimization of a Frequency-Stabilized Laser Reference at 1.57μM for AN Active Laser Remote Sensing of CO2 from Space

    NASA Astrophysics Data System (ADS)

    Chen, S.; Petway, L. B.; Lee, H. R.; Harrison, F. W.; Browell, E. V.

    2011-12-01

    Several airborne flight campaigns have shown that active remote sensing of carbon dioxide mixing ratio (XCO2) in the atmosphere using either an Intensity Modulated-Continuous Wave (IM-CW) Laser Absorption Spectrometer (LAS) at 1.57 μm or a pulsed laser CO2 sounder at 1.57 μm is a promising technique for an accurate space measurement approach for the Active Sensing of CO2 over Nights, Days, and Seasons mission [1, 2]. In order to achieve a measurement accuracy of one part per million (ppmv) for CO2 column density and associated mixing ratio by volume, the frequency stability (frequency or wavelength variance) of the lasers at 1.57 μm for a space-borne active remote sensing system should be greater than 1.5e-9 (less than 300 kHz or less than 2.5e-3 pm) is required for most moderate-size instruments [3]. In this paper, we report a design and optimization of a frequency-locking laser reference with an integration of Frequency Modulation (FM), Phase Sensitive Detection (PSD) and Proportional Integration Derivation (PID) feed-back control techniques to stabilize laser frequency associated to one of CO or CO2 absorption lines at 1.57 μm. The optimized sensitivity based on PSD signals in terms of the modulation frequency, the length of the gas cell, and the pressure of the gas will be provided. The design and optimization has been demonstrated at a 2-μm CO2 absorption line and is applicable to the active remote sensing systems at 1.57 μm. [1] E. V. Browell, J. Dobler, F. W. Harrison, and B. Moore III, "Development and Validation of CO2 and O2 Laser Measurements for Future Active XCO2 Space Mission", Geophysical Research Abstracts, Vol. 13, EGU2011-12598, 2011 [2] J. B. Abshire, H. Riris, G. R. Allen, C. J. Weaver, J. Mao, X. Sun, W. E. Hasselbrack, S. R. Kawa, S. Biraud, "Pulsed Airborne Lidar Measurements of Atmospheric CO2 column Absorption", Tellus (2010), 62B, 770-783 [3] E. Ehret, C. Kiemle, M. Wirth, A. Amediek, A. Fix, and S. Houweling, 2008: Space

  17. Absolute/convective instability of planar viscoelastic jets

    NASA Astrophysics Data System (ADS)

    Ray, Prasun K.; Zaki, Tamer A.

    2015-01-01

    Spatiotemporal linear stability analysis is used to investigate the onset of local absolute instability in planar viscoelastic jets. The influence of viscoelasticity in dilute polymer solutions is modeled with the FENE-P constitutive equation which requires the specification of a non-dimensional polymer relaxation time (the Weissenberg number, We), the maximum polymer extensibility, L, and the ratio of solvent and solution viscosities, β. A two-parameter family of velocity profiles is used as the base state with the parameter, S, controlling the amount of co- or counter-flow while N-1 sets the thickness of the jet shear layer. We examine how the variation of these fluid and flow parameters affects the minimum value of S at which the flow becomes locally absolutely unstable. Initially setting the Reynolds number to Re = 500, we find that the first varicose jet-column mode dictates the presence of absolute instability, and increasing the Weissenberg number produces important changes in the nature of the instability. The region of absolute instability shifts towards thin shear layers, and the amount of back-flow needed for absolute instability decreases (i.e., the influence of viscoelasticity is destabilizing). Additionally, when We is sufficiently large and N-1 is sufficiently small, single-stream jets become absolutely unstable. Numerical experiments with approximate equations show that both the polymer and solvent contributions to the stress become destabilizing when the scaled shear rate, η = /W e dU¯1/dx 2L ( /d U ¯ 1 d x 2 is the base-state velocity gradient), is sufficiently large. These qualitative trends are largely unchanged when the Reynolds number is reduced; however, the relative importance of the destabilizing stresses increases tangibly. Consequently, absolute instability is substantially enhanced, and single-stream jets become absolutely unstable over a sizable portion of the parameter space.

  18. The Absolute Spectrum Polarimeter (ASP)

    NASA Technical Reports Server (NTRS)

    Kogut, A. J.

    2010-01-01

    The Absolute Spectrum Polarimeter (ASP) is an Explorer-class mission to map the absolute intensity and linear polarization of the cosmic microwave background and diffuse astrophysical foregrounds over the full sky from 30 GHz to 5 THz. The principal science goal is the detection and characterization of linear polarization from an inflationary epoch in the early universe, with tensor-to-scalar ratio r much greater than 1O(raised to the power of { -3}) and Compton distortion y < 10 (raised to the power of{-6}). We describe the ASP instrument and mission architecture needed to detect the signature of an inflationary epoch in the early universe using only 4 semiconductor bolometers.

  19. Absolute calibration of optical flats

    DOEpatents

    Sommargren, Gary E.

    2005-04-05

    The invention uses the phase shifting diffraction interferometer (PSDI) to provide a true point-by-point measurement of absolute flatness over the surface of optical flats. Beams exiting the fiber optics in a PSDI have perfect spherical wavefronts. The measurement beam is reflected from the optical flat and passed through an auxiliary optic to then be combined with the reference beam on a CCD. The combined beams include phase errors due to both the optic under test and the auxiliary optic. Standard phase extraction algorithms are used to calculate this combined phase error. The optical flat is then removed from the system and the measurement fiber is moved to recombine the two beams. The newly combined beams include only the phase errors due to the auxiliary optic. When the second phase measurement is subtracted from the first phase measurement, the absolute phase error of the optical flat is obtained.

  20. The influence of genetic drift on the formation and stability of polymorphisms arising from negative frequency-dependent selection.

    PubMed

    Zhao, Lei; Waxman, David

    2016-02-21

    We consider the simplest form of negative frequency-dependent selection in a biallelic haploid population, where the selection coefficient of a mutant allele is a linear function of the allele's frequency, and changes from positive to negative as the frequency is increased. In an effectively infinite population this behaviour leads to a stable polymorphism. We present a theoretical investigation of what occurs in a finite population, where a long-lived polymorphism may be formed, but which fluctuates and ultimately disappears due to random genetic drift. We model the dynamics as a branching process and explicitly take into account differences between the census population size and the effective population size, which play different roles in the dynamics. We characterise the behaviour of the population in terms of three distinct timescales associated with: (i) early loss of mutant alleles, (ii) achievement of the long-lived polymorphism, (iii) disappearance of the polymorphism. Timescales (i) and (iii) depend on the effective population size and are, as a consequence, affected by random genetic drift, while timescale (ii) depends primarily on the census size and is relatively insensitive to genetic drift. Analysis and simulations of the branching process clarify the different influences of the census and effective population sizes. One substantial quantitative difference, between populations where the effective and census population sizes coincide and where they differ, lies in the number of mutant alleles in the long-lived polymorphism. This number is approximately proportional to the census size. Thus assuming the census size equals a much smaller effective population size predicts a much smaller number of mutants in the long-lived polymorphism. PMID:26656188

  1. Computer programs for calculation of matrix stability and frequency response from a state-space system description

    NASA Technical Reports Server (NTRS)

    Seidel, R. C.

    1974-01-01

    FORTRAN computer subroutines stemming from requirements to process state variable system equations for systems of high order are presented. They find the characteristic equation of a matrix using the method of Danilevsky, the number of roots with positive real parts using the Routh-Horwitz alternate formulation, convert a state variable system description to a Laplace transfer function using the method of Bollinger, and evaluate that transfer function and obtain its frequency response. A sample problem is presented to demonstrate use of the subroutines.

  2. Stability, Bistability, and Critical Thresholds in Fire-prone Forested Landscapes: How Frequency and Intensity of Disturbance Interact and Influence Forest Cover

    NASA Astrophysics Data System (ADS)

    Miller, A. D.

    2015-12-01

    Many aspects of disturbance processes can have large impacts on the composition of plant communities, and associated changes in land cover type in turn have biogeochemical feedbacks to climate. In particular, changes to disturbance regimes can potentially change the number and stability of equilibrial states, and plant community states can differ dramatically in their carbon (C) dynamics, energy balance, and hydrology. Using the Klamath region of northern California as a model system, we present a theoretical analysis of how changes to climate and associated fire dynamics can disrupt high-carbon, long-lived conifer forests and replace them with shrub-chaparral communities that have much lower biomass and are more pyrogenic. Specifically, we develop a tractable model of plant community dynamics, structured by size class, life-history traits, lottery-type competition, and species-specific responses to disturbance. We assess the stability of different states in terms of disturbance frequency and intensity, and quantitatively partition long-term low-density population growth rates into mechanisms that influence critical transitions from stable to bistable behavior. Our findings show how different aspects of disturbance act and interact to control competitive outcomes and stable states, hence ecosystem-atmosphere C exchange. Forests tend to dominate in low frequency and intensity regimes, while shrubs dominate at high fire frequency and intensity. In other regimes, the system is bistable, and the fate of the system depends both on initial conditions and random chance. Importantly, the system can cross a critical threshold where hysteresis prevents easy return to the prior forested state. We conclude that changes in disturbance-recovery dynamics driven by projected climate change can shift this system away from forest dominated in the direction of shrub-dominated landscape. This will result in a large net C release from the landscape, and alter biophysical ecosystem

  3. Extension of the absolute flux density scale to 22.285 GHz. [radio astronomy

    NASA Technical Reports Server (NTRS)

    Janssen, M. A.; Golden, L. M.; Welch, W. J.

    1974-01-01

    Extending the absolute flux density scale at microwave wavelengths, the absolute flux densities at 22.285 GHz of several standard sources were determined using the absolute calibrations of the 6.1 meter antenna of the Hat Creek Observatory. Interpolation formulas for each nonthermal standard source have been derived by combining these data with those determined at lower frequencies. The suitability of employing the standard sources for calibrating other antennas is discussed.

  4. Effect of the carrier-envelope-offset dynamics on the stabilization of a diode-pumped solid-state frequency comb.

    PubMed

    Bucalovic, N; Dolgovskiy, V; Stumpf, M C; Schori, C; Di Domenico, G; Keller, U; Schilt, S; Südmeyer, T

    2012-11-01

    We investigate the dynamics of the carrier-envelope-offset (CEO) frequency, f(CEO), controlled by a pump current on the self-referencing of an optical frequency comb generated from a diode-pumped solid-state laser at 1.56 μm. We observe a reversal point in the tuning of f(CEO) with the pump current. Between the low- and high-frequency region in the dynamic response of f(CEO) to pump current modulation, we observe a significant phase shift of ≈180 deg in the transfer function. As a result, it is impossible to stabilize f(CEO) at a pump current above the reversal point, although the free-running CEO beat at this point has a higher signal-to-noise ratio than underneath the reversal point at which the locking is straightforward. Our results indicate that a high signal-to-noise ratio and a low-noise CEO beat are not sufficient indicators for the feasibility of comb self-referencing in cases for which CEO dynamics play a dominant role. PMID:23114318

  5. CEO stabilized frequency comb from a 1-μm Kerr-lens mode-locked bulk Yb:CYA laser.

    PubMed

    Yu, Zijiao; Han, Hainian; Xie, Yang; Peng, Yingnan; Xu, Xiaodong; Wei, Zhiyi

    2016-02-01

    We report the first Kerr-lens mode-locked (KLM) bulk frequency comb in the 1-μm spectral regime. The fundamental KLM Yb:CYA laser is pumped by a low-noise, high-bright 976-nm fiber laser and typically provides 250-mW output power and 57-fs pulse duration. Only 58-mW output pulses were launched into a 1.3-m photonic crystal fiber (PCF) for one octave-spanning supercontinuum generation. Using a simplified collinear f-2f interferometer, the free-running carrier-envelope offset (CEO) frequency was measured to be 42-dB signal-to-noise ratio (SNR) for a 100-kHz resolution and 9.6-kHz full width at half maximum (FWHM) under a 100-Hz resolution. A long-term CEO control at 23 MHz was ultimately realized by feeding the phase error signal to the pump power of the oscillator. The integrated phase noise (IPN) of the locked CEO was measured to be 316 mrad with an integrated range from 1 Hz to 10 MHz. The standard deviation and Allan deviation for more than 4-hour recording are 1.6 mHz and 5.6 × 10(-18) (for 1-s gate time), respectively. This is, to the best of our knowledge, the best stability achieved among the 1-μm solid-state frequency combs. PMID:26906875

  6. Low-loss smile-insensitive external frequency-stabilization of high power diode lasers enabled by vertical designs with extremely low divergence angle and high efficiency

    NASA Astrophysics Data System (ADS)

    Crump, Paul; Knigge, Steffen; Maaßdorf, Andre; Bugge, Frank; Hengesbach, Stefan; Witte, Ulrich; Hoffmann, Hans-Dieter; Köhler, Bernd; Hubrich, Ralf; Kissel, Heiko; Biesenbach, Jens; Erbert, Götz; Traenkle, Guenther

    2013-02-01

    Broad area lasers with narrow spectra are required for many pumping applications and for wavelength beam combination. Although monolithically stabilized lasers show high performance, some applications can only be addressed with external frequency stabilization, for example when very narrow spectra are required. When conventional diode lasers with vertical far field angle, ΘV 95% ~ 45° (95% power) are stabilized using volume holographic gratings (VHGs), optical losses are introduced, limiting both efficiency and reliable output power, with the presence of any bar smile compounding the challenge. Diode lasers with designs optimized for extremely low vertical divergence (ELOD lasers) directly address these challenges. The vertical far field angle in conventional laser designs is limited by the waveguiding of the active region itself. In ELOD designs, quantum barriers are used that have low refractive index, enabling the influence of the active region to be suppressed, leading to narrow far field operation from thin vertical structures, for minimal electrical resistance and maximum power conversion efficiency. We review the design process, and show that 975 nm diode lasers with 90 μm stripes that use ELOD designs operate with ΘV 95% = 26° and reach 58% power conversion efficiency at a CW output power of 10 W. We demonstrate directly that VHG stabilized ELOD lasers have significantly lower loss and larger operation windows than conventional lasers in the collimated feedback regimes, even in the presence of significant (≥ 1 μm) bar smile. We also discuss the potential influence of ELOD designs on reliable output power and options for further performance improvement.

  7. Frequency comb metrology with an optical parametric oscillator.

    PubMed

    Balskus, K; Schilt, S; Wittwer, V J; Brochard, P; Ploetzing, T; Jornod, N; McCracken, R A; Zhang, Z; Bartels, A; Reid, D T; Südmeyer, T

    2016-04-18

    We report on the first demonstration of absolute frequency comb metrology with an optical parametric oscillator (OPO) frequency comb. The synchronously-pumped OPO operated in the 1.5-µm spectral region and was referenced to an H-maser atomic clock. Using different techniques, we thoroughly characterized the frequency noise power spectral density (PSD) of the repetition rate frep, of the carrier-envelope offset frequency fCEO, and of an optical comb line νN. The comb mode optical linewidth at 1557 nm was determined to be ~70 kHz for an observation time of 1 s from the measured frequency noise PSD, and was limited by the stability of the microwave frequency standard available for the stabilization of the comb repetition rate. We achieved a tight lock of the carrier envelope offset frequency with only ~300 mrad residual integrated phase noise, which makes its contribution to the optical linewidth negligible. The OPO comb was used to measure the absolute optical frequency of a near-infrared laser whose second-harmonic component was locked to the F = 2→3 transition of the 87Rb D2 line at 780 nm, leading to a measured transition frequency of νRb = 384,228,115,346 ± 16 kHz. We performed the same measurement with a commercial fiber-laser comb operating in the 1.5-µm region. Both the OPO comb and the commercial fiber comb achieved similar performance. The measurement accuracy was limited by interferometric noise in the fibered setup of the Rb-stabilized laser. PMID:27137274

  8. The AFGL absolute gravity program

    NASA Technical Reports Server (NTRS)

    Hammond, J. A.; Iliff, R. L.

    1978-01-01

    A brief discussion of the AFGL's (Air Force Geophysics Laboratory) program in absolute gravity is presented. Support of outside work and in-house studies relating to gravity instrumentation are discussed. A description of the current transportable system is included and the latest results are presented. These results show good agreement with measurements at the AFGL site by an Italian system. The accuracy obtained by the transportable apparatus is better than 0.1 microns sq sec 10 microgal and agreement with previous measurements is within the combined uncertainties of the measurements.

  9. Mathematical Model for Absolute Magnetic Measuring Systems in Industrial Applications

    NASA Astrophysics Data System (ADS)

    Fügenschuh, Armin; Fügenschuh, Marzena; Ludszuweit, Marina; Mojsic, Aleksandar; Sokół, Joanna

    2015-09-01

    Scales for measuring systems are either based on incremental or absolute measuring methods. Incremental scales need to initialize a measurement cycle at a reference point. From there, the position is computed by counting increments of a periodic graduation. Absolute methods do not need reference points, since the position can be read directly from the scale. The positions on the complete scales are encoded using two incremental tracks with different graduation. We present a new method for absolute measuring using only one track for position encoding up to micrometre range. Instead of the common perpendicular magnetic areas, we use a pattern of trapezoidal magnetic areas, to store more complex information. For positioning, we use the magnetic field where every position is characterized by a set of values measured by a hall sensor array. We implement a method for reconstruction of absolute positions from the set of unique measured values. We compare two patterns with respect to uniqueness, accuracy, stability and robustness of positioning. We discuss how stability and robustness are influenced by different errors during the measurement in real applications and how those errors can be compensated.

  10. Absolute Radiometer for Reproducing the Solar Irradiance Unit

    NASA Astrophysics Data System (ADS)

    Sapritskii, V. I.; Pavlovich, M. N.

    1989-01-01

    A high-precision absolute radiometer with a thermally stabilized cavity as receiving element has been designed for use in solar irradiance measurements. The State Special Standard of the Solar Irradiance Unit has been built on the basis of the developed absolute radiometer. The Standard also includes the sun tracking system and the system for automatic thermal stabilization and information processing, comprising a built-in microcalculator which calculates the irradiance according to the input program. During metrological certification of the Standard, main error sources have been analysed and the non-excluded systematic and accidental errors of the irradiance-unit realization have been determined. The total error of the Standard does not exceed 0.3%. Beginning in 1984 the Standard has been taking part in a comparison with the Å 212 pyrheliometer and other Soviet and foreign standards. In 1986 it took part in the international comparison of absolute radiometers and standard pyrheliometers of socialist countries. The results of the comparisons proved the high metrological quality of this Standard based on an absolute radiometer.

  11. Increasing frequency of low summer precipitation synchronizes dynamics and compromises metapopulation stability in the Glanville fritillary butterfly.

    PubMed

    Tack, Ayco J M; Mononen, Tommi; Hanski, Ilkka

    2015-05-01

    Climate change is known to shift species' geographical ranges, phenologies and abundances, but less is known about other population dynamic consequences. Here, we analyse spatio-temporal dynamics of the Glanville fritillary butterfly (Melitaea cinxia) in a network of 4000 dry meadows during 21 years. The results demonstrate two strong, related patterns: the amplitude of year-to-year fluctuations in the size of the metapopulation as a whole has increased, though there is no long-term trend in average abundance; and there is a highly significant increase in the level of spatial synchrony in population dynamics. The increased synchrony cannot be explained by increasing within-year spatial correlation in precipitation, the key environmental driver of population change, or in per capita growth rate. On the other hand, the frequency of drought during a critical life-history stage (early larval instars) has increased over the years, which is sufficient to explain the increasing amplitude and the expanding spatial synchrony in metapopulation dynamics. Increased spatial synchrony has the general effect of reducing long-term metapopulation viability even if there is no change in average metapopulation size. This study demonstrates how temporal changes in weather conditions can lead to striking changes in spatio-temporal population dynamics. PMID:25854888

  12. Increasing frequency of low summer precipitation synchronizes dynamics and compromises metapopulation stability in the Glanville fritillary butterfly

    PubMed Central

    Tack, Ayco J. M.; Mononen, Tommi; Hanski, Ilkka

    2015-01-01

    Climate change is known to shift species' geographical ranges, phenologies and abundances, but less is known about other population dynamic consequences. Here, we analyse spatio-temporal dynamics of the Glanville fritillary butterfly (Melitaea cinxia) in a network of 4000 dry meadows during 21 years. The results demonstrate two strong, related patterns: the amplitude of year-to-year fluctuations in the size of the metapopulation as a whole has increased, though there is no long-term trend in average abundance; and there is a highly significant increase in the level of spatial synchrony in population dynamics. The increased synchrony cannot be explained by increasing within-year spatial correlation in precipitation, the key environmental driver of population change, or in per capita growth rate. On the other hand, the frequency of drought during a critical life-history stage (early larval instars) has increased over the years, which is sufficient to explain the increasing amplitude and the expanding spatial synchrony in metapopulation dynamics. Increased spatial synchrony has the general effect of reducing long-term metapopulation viability even if there is no change in average metapopulation size. This study demonstrates how temporal changes in weather conditions can lead to striking changes in spatio-temporal population dynamics. PMID:25854888

  13. Spectral and temporal characterization of a fused-quartz-microresonator optical frequency comb

    NASA Astrophysics Data System (ADS)

    Papp, Scott B.; Diddams, Scott A.

    2011-11-01

    We report on the fabrication of high-Q, fused-quartz microresonators and the parametric generation of a frequency comb with 36-GHz line spacing using them. We have characterized the intrinsic stability of the comb in both the time and frequency domains to assess its suitability for future precision metrology applications. Intensity autocorrelation measurements and line-by-line comb control reveal near-transform-limited picosecond pulse trains that are associated with good relative phase and amplitude stability of the comb lines. The comb's 36-GHz line spacing can be readily photodetected, which enables measurements of its intrinsic and absolute phase fluctuations.

  14. Design and simulation of a biconic multipass absorption cell for the frequency stabilization of the reference seeder laser in IPDA lidar.

    PubMed

    Mu, Yongji; Du, Juan; Yang, Zhongguo; Sun, Yanguang; Liu, Jiqiao; Hou, Xia; Chen, Weibiao

    2016-09-01

    The design process and simulation method of a multipass absorption cell used for the frequency stabilization of the reference seeder laser in integrated path differential absorption (IPDA) lidar are presented. On the basis of the fundamental theory of the Herriott multipass cell comprising two spherical mirrors, the initial parameters of the multipass cell, which has an optical path greater than 10 m and consists of two biconic mirrors, were calculated. More than 30 light spots were distributed on each mirror, and the distance between adjacent spots was mostly optimized to greater than six times the beam waist. After optimization, the simulated transmittance spectrum and associated differential signal were obtained. The interference induced by surface scattering was also simulated, and its influence on the differential signal was analyzed. A correspondence between the simulated results and the testing data was observed. PMID:27607288

  15. Stability analysis of the spatiotemporal Lugiato-Lefever model for Kerr optical frequency combs in the anomalous and normal dispersion regimes

    NASA Astrophysics Data System (ADS)

    Godey, Cyril; Balakireva, Irina V.; Coillet, Aurélien; Chembo, Yanne K.

    2014-06-01

    We propose a detailed stability analysis of the Lugiato-Lefever model for Kerr optical frequency combs in whispering-gallery-mode resonators when they are pumped in either the anomalous- or normal-dispersion regime. We analyze the spatial bifurcation structure of the stationary states depending on two parameters that are experimentally tunable; namely, the pump power and the cavity detuning. Our study demonstrates that, in both the anomalous- and normal-dispersion cases, nontrivial equilibria play an important role in this bifurcation map because their associated eigenvalues undergo critical bifurcations that are actually foreshadowing the existence of localized and extended spatial dissipative structures. The corresponding bifurcation maps are evidence of a considerable richness from a dynamical standpoint. The case of anomalous dispersion is indeed the most interesting from the theoretical point of view because of the considerable variety of dynamical behavior that can be observed. For this case we study the emergence of super- and subcritical Turing patterns (or primary combs) in the system via modulational instability. We determine the areas where bright isolated cavity solitons emerge, and we show that soliton molecules can emerge as well. Very complex temporal patterns can actually be observed in the system, where solitons (or soliton complexes) coexist with or without mutual interactions. Our investigations also unveil the mechanism leading to the phenomenon of breathing solitons. Two routes to chaos in the system are identified; namely, a route via the destabilization of a primary comb, and another via the destabilization of solitons. For the case of normal dispersion, we unveil the mechanism leading to the emergence of weakly stable Turing patterns. We demonstrate that this weak stability is justified by the distribution of stable and unstable fixed points in the parameter space (flat states). We show that dark cavity solitons can emerge in the system, and

  16. Cosmology with negative absolute temperatures

    NASA Astrophysics Data System (ADS)

    Vieira, J. P. P.; Byrnes, Christian T.; Lewis, Antony

    2016-08-01

    Negative absolute temperatures (NAT) are an exotic thermodynamical consequence of quantum physics which has been known since the 1950's (having been achieved in the lab on a number of occasions). Recently, the work of Braun et al. [1] has rekindled interest in negative temperatures and hinted at a possibility of using NAT systems in the lab as dark energy analogues. This paper goes one step further, looking into the cosmological consequences of the existence of a NAT component in the Universe. NAT-dominated expanding Universes experience a borderline phantom expansion (w < ‑1) with no Big Rip, and their contracting counterparts are forced to bounce after the energy density becomes sufficiently large. Both scenarios might be used to solve horizon and flatness problems analogously to standard inflation and bouncing cosmologies. We discuss the difficulties in obtaining and ending a NAT-dominated epoch, and possible ways of obtaining density perturbations with an acceptable spectrum.

  17. Precise frequency measurements of {sup 127}I{sub 2} lines in the wavelength region 750-780 nm

    SciTech Connect

    Liao, Chun-Chieh; Wu, Kuo-Yu; Lien, Yu-Hung; Shy, Jow-Tsong; Knoeckel, Horst; Tiemann, Eberhard; Chui, Hsiang-Chen

    2010-06-15

    High precision frequency measurements of {sup 127}I{sub 2} hyperfine transitions in the wavelength range between 750 and 780 nm were performed employing an optical frequency comb. A Ti:sapphire laser is frequency stabilized to a hyperfine component of I{sub 2} using a Doppler-free frequency modulation technique, and an optical frequency comb is used to measure its frequency precisely. Improved absolute frequencies of 27 hyperfine transitions between 750 and 780 nm of the bands (0-12) and (0-13) of B {sup 3}{Pi}{sub 0{sub u{sup +}}}-X {sup 1}{Sigma}{sub g}{sup +} system of I{sub 2} are presented. The relative uncertainty of the measurement is a few times 10{sup -10}, limited by the frequency instability of the iodine-stabilized laser. The frequencies are compared to the predicted frequencies using the model description of [Eur. Phys. J. D 28, 199 (2004)], which yields differences larger than expected. An improved model is developed for the range from 755 to 815 nm for the prediction of lines with an error limit of the absolute frequency less than 0.2 MHz.

  18. Absolute phase effects on CPMG-type pulse sequences

    NASA Astrophysics Data System (ADS)

    Mandal, Soumyajit; Oh, Sangwon; Hürlimann, Martin D.

    2015-12-01

    We describe and analyze the effects of transients within radio-frequency (RF) pulses on multiple-pulse NMR measurements such as the well-known Carr-Purcell-Meiboom-Gill (CPMG) sequence. These transients are functions of the absolute RF phases at the beginning and end of the pulse, and are thus affected by the timing of the pulse sequence with respect to the period of the RF waveform. Changes in transients between refocusing pulses in CPMG-type sequences can result in signal decay, persistent oscillations, changes in echo shape, and other effects. We have explored such effects by performing experiments in two different low-frequency NMR systems. The first uses a conventional tuned-and-matched probe circuit, while the second uses an ultra-broadband un-tuned or non-resonant probe circuit. We show that there are distinct differences between the absolute phase effects in these two systems, and present simple models that explain these differences.

  19. Laser Stabilization

    SciTech Connect

    Hall, John L.; Taubman, Matthew S.; Ye, Jun

    2010-01-01

    This book chapter covers the basics of the field of stabilizing lasers to optical frequency references such as optical cavities and molecular transitions via the application of servo control systems. These discussions are given with reference to the real-life frequency metrology experienced in Hall-Labs (now Ye-Labs), JILA, University of Colorado. The subjects covered include: the basics of control system stability, a discussion of both the theoretical and experimental limitations, an outline of optical cavity susceptibility to environmental noise, and a brief introduction to the use and limitations of molecular transitions as frequency references.

  20. Improving HST Pointing & Absolute Astrometry

    NASA Astrophysics Data System (ADS)

    Lallo, Matthew; Nelan, E.; Kimmer, E.; Cox, C.; Casertano, S.

    2007-05-01

    Accurate absolute astrometry is becoming increasingly important in an era of multi-mission archives and virtual observatories. Hubble Space Telescope's (HST's) Guidestar Catalog II (GSC2) has reduced coordinate error to around 0.25 arcsecond, a factor 2 or more compared with GSC1. With this reduced catalog error, special attention must be given to calibrate and maintain the Fine Guidance Sensors (FGSs) and Science Instruments (SIs) alignments in HST to a level well below this in order to ensure that the accuracy of science product's astrometry keywords and target positioning are limited only by the catalog errors. After HST Servicing Mission 4, such calibrations' improvement in "blind" pointing accuracy will allow for more efficient COS acquisitions. Multiple SIs and FGSs each have their own footprints in the spatially shared HST focal plane. It is the small changes over time in primarily the whole-body positions & orientations of these instruments & guiders relative to one another that is addressed by this work. We describe the HST Cycle 15 program CAL/OTA 11021 which, along with future variants of it, determines and maintains positions and orientations of the SIs and FGSs to better than 50 milli- arcseconds and 0.04 to 0.004 degrees of roll, putting errors associated with the alignment sufficiently below GSC2 errors. We present recent alignment results and assess their errors, illustrate trends, and describe where and how the observer sees benefit from these calibrations when using HST.

  1. Absolute oral bioavailability of ciprofloxacin.

    PubMed

    Drusano, G L; Standiford, H C; Plaisance, K; Forrest, A; Leslie, J; Caldwell, J

    1986-09-01

    We evaluated the absolute bioavailability of ciprofloxacin, a new quinoline carboxylic acid, in 12 healthy male volunteers. Doses of 200 mg were given to each of the volunteers in a randomized, crossover manner 1 week apart orally and as a 10-min intravenous infusion. Half-lives (mean +/- standard deviation) for the intravenous and oral administration arms were 4.2 +/- 0.77 and 4.11 +/- 0.74 h, respectively. The serum clearance rate averaged 28.5 +/- 4.7 liters/h per 1.73 m2 for the intravenous administration arm. The renal clearance rate accounted for approximately 60% of the corresponding serum clearance rate and was 16.9 +/- 3.0 liters/h per 1.73 m2 for the intravenous arm and 17.0 +/- 2.86 liters/h per 1.73 m2 for the oral administration arm. Absorption was rapid, with peak concentrations in serum occurring at 0.71 +/- 0.15 h. Bioavailability, defined as the ratio of the area under the curve from 0 h to infinity for the oral to the intravenous dose, was 69 +/- 7%. We conclude that ciprofloxacin is rapidly absorbed and reliably bioavailable in these healthy volunteers. Further studies with ciprofloxacin should be undertaken in target patient populations under actual clinical circumstances. PMID:3777908

  2. Absolute Instability in Coupled-Cavity TWTs

    NASA Astrophysics Data System (ADS)

    Hung, D. M. H.; Rittersdorf, I. M.; Zhang, Peng; Lau, Y. Y.; Simon, D. H.; Gilgenbach, R. M.; Chernin, D.; Antonsen, T. M., Jr.

    2014-10-01

    This paper will present results of our analysis of absolute instability in a coupled-cavity traveling wave tube (TWT). The structure mode at the lower and upper band edges are respectively approximated by a hyperbola in the (omega, k) plane. When the Briggs-Bers criterion is applied, a threshold current for onset of absolute instability is observed at the upper band edge, but not the lower band edge. The nonexistence of absolute instability at the lower band edge is mathematically similar to the nonexistence of absolute instability that we recently demonstrated for a dielectric TWT. The existence of absolute instability at the upper band edge is mathematically similar to the existence of absolute instability in a gyroton traveling wave amplifier. These interesting observations will be discussed, and the practical implications will be explored. This work was supported by AFOSR, ONR, and L-3 Communications Electron Devices.

  3. The High-Pathogenicity Island of Yersinia enterocolitica Ye8081 Undergoes Low-Frequency Deletion but Not Precise Excision, Suggesting Recent Stabilization in the Genome

    PubMed Central

    Bach, Sandrine; Buchrieser, Carmen; Prentice, Michael; Guiyoule, Annie; Msadek, Tarek; Carniel, Elisabeth

    1999-01-01

    Highly pathogenic strains of Yersinia pestis, Y. pseudotuberculosis, and Y. enterocolitica are characterized by the possession of a pathogenicity island designated the high-pathogenicity island (HPI). This 35- to 45-kb island carries an iron uptake system named the yersiniabactin locus. While the HPIs of Y. pestis and Y. pseudotuberculosis are subject to high-frequency spontaneous deletion from the chromosome, we were initially unable to obtain HPI-deleted Y. enterocolitica 1B isolates. In the present study, using a positive selection strategy, we identified three HPI-deleted mutants of Y. enterocolitica strain Ye8081. In these three independent clones, the chromosomal deletion was not limited to the HPI but encompassed a larger DNA fragment of approximately 140 kb. Loss of this fragment, which occurred at a frequency of approximately 5 × 10−7, resulted in the disappearance of several phenotypic traits, such as growth in a minimal medium, hydrolysis of o-nitrophenyl-β-d-thiogalactopyranoside, Tween esterase activity, and motility, and in a decreased virulence for mice. However, no precise excision of the Ye8081 HPI was observed. To gain more insight into the molecular basis for this phenomenon, the putative machinery of HPI excision in Y. enterocolitica was analyzed and compared to that in Y. pseudotuberculosis. We show that the probable reasons for failure of precise excision of the HPI of Y. enterocolitica Ye8081 are (i) the interruption of the P4-like integrase gene located close to its right-hand boundary by a premature stop codon and (ii) lack of conservation of 17-bp att-like sequences at both extremities of the HPI. These mutations may represent a process of HPI stabilization in the species Y. enterocolitica. PMID:10496882

  4. The PiggyBac transposon enhances the frequency of CHO stable cell line generation and yields recombinant lines with superior productivity and stability.

    PubMed

    Matasci, Mattia; Baldi, Lucia; Hacker, David L; Wurm, Florian M

    2011-09-01

    Generating stable, high-producing mammalian cell lines is a major bottleneck in the manufacture of recombinant therapeutic proteins. Conventional gene transfer methods for cell line generation rely on random plasmid integration, resulting in unpredictable and highly variable levels of transgene expression. As a consequence, a large number of stably transfected cells must be analyzed to recover a few high-producing clones. Here we present an alternative gene transfer method for cell line generation based on transgene integration mediated by the piggyBac (PB) transposon. Recombinant Chinese hamster ovary (CHO) cell lines expressing a tumor necrosis factor receptor:Fc fusion protein were generated either by PB transposition or by conventional transfection. Polyclonal populations and isolated clonal cell lines were characterized for the level and stability of transgene expression for up to 3 months in serum-free suspension culture. Pools of transposed cells produced up to fourfold more recombinant protein than did the pools generated by standard transfection. For clonal cell lines, the frequency of high-producers was greater following transposition as compared to standard transfection, and these clones had a higher volumetric productivity and a greater number of integrated transgenes than did those generated by standard transfection. In general, the volumetric productivity of the cell pools and individual cell lines generated by transposition was stable for up to 3 months in the absence of selection. Our results indicate that the PB transposon supports the generation of cell lines with high and stable transgene expression at an elevated frequency relative to conventional transfection. Thus, PB-mediated gene delivery is expected to reduce the extent of recombinant cell line screening. PMID:21495018

  5. Absolute negative mobility of interacting Brownian particles

    NASA Astrophysics Data System (ADS)

    Ou, Ya-li; Hu, Cai-tian; Wu, Jian-chun; Ai, Bao-quan

    2015-12-01

    Transport of interacting Brownian particles in a periodic potential is investigated in the presence of an ac force and a dc force. From Brownian dynamic simulations, we find that both the interaction between particles and the thermal fluctuations play key roles in the absolute negative mobility (the particle noisily moves backwards against a small constant bias). When no the interaction acts, there is only one region where the absolute negative mobility occurs. In the presence of the interaction, the absolute negative mobility may appear in multiple regions. The weak interaction can be helpful for the absolute negative mobility, while the strong interaction has a destructive impact on it.

  6. Intelligent Systems for Stabilizing Mode-Locked Lasers and Frequency Combs: Machine Learning and Equation-Free Control Paradigms for Self-Tuning Optics

    NASA Astrophysics Data System (ADS)

    Kutz, J. Nathan; Brunton, Steven L.

    2015-12-01

    We demonstrate that a software architecture using innovations in machine learning and adaptive control provides an ideal integration platform for self-tuning optics. For mode-locked lasers, commercially available optical telecom components can be integrated with servocontrollers to enact a training and execution software module capable of self-tuning the laser cavity even in the presence of mechanical and/or environmental perturbations, thus potentially stabilizing a frequency comb. The algorithm training stage uses an exhaustive search of parameter space to discover best regions of performance for one or more objective functions of interest. The execution stage first uses a sparse sensing procedure to recognize the parameter space before quickly moving to the near optimal solution and maintaining it using the extremum seeking control protocol. The method is robust and equationfree, thus requiring no detailed or quantitatively accurate model of the physics. It can also be executed on a broad range of problems provided only that suitable objective functions can be found and experimentally measured.

  7. Simultaneous frequency stabilization and high-power dense wavelength division multiplexing (HP-DWDM) using an external cavity based on volume Bragg gratings (VBGs)

    NASA Astrophysics Data System (ADS)

    Hengesbach, Stefan; Klein, Sarah; Holly, Carlo; Witte, Ulrich; Traub, Martin; Hoffmann, Dieter

    2016-03-01

    Multiplexing technologies enable the development of high-brightness diode lasers for direct industrial applications. We present a High-Power Dense Wavelength Division Multiplexer (HP-DWDM) with an average channel spacing of 1.7 (1.5) nm and a subsequent external cavity mirror to provide feedback for frequency stabilization and multiplexing in one step. The "self-optimizing" multiplexing unit consists of four reflective Volume Bragg Gratings (VBGs) with 99% diffraction efficiency and seven dielectric mirrors to overlay the radiation of five input channels with an adjustable channel spacing of 1-2 nm. In detail, we focus on the analysis of the overall optical efficiency, the change of the beam parameter product and the spectral width. The performance is demonstrated using five 90 μm multimode 9xx single emitters with M2<=17. Because of the feedback the lateral (multimodal) spatial and angular intensity distribution changes strongly and the beam parameter product decreases by a factor of 1.2 to 1.9. Thereby the angular intensity distribution is more affected than the width of the beam waist. The spectral width per emitter decreases to 3-200 pm (FWHM) depending on the injection current and the reflectance of the feedback mirror (0.75%, 1.5%, 4%, 6% or 8%). The overall optical multiplexing efficiency ranges between 77% and 86%. With some modifications (e.g. enhanced AR-coatings) we expect 90-95%.

  8. Frequency comb transferred by surface plasmon resonance.

    PubMed

    Geng, Xiao Tao; Chun, Byung Jae; Seo, Ji Hoon; Seo, Kwanyong; Yoon, Hana; Kim, Dong-Eon; Kim, Young-Jin; Kim, Seungchul

    2016-01-01

    Frequency combs, millions of narrow-linewidth optical modes referenced to an atomic clock, have shown remarkable potential in time/frequency metrology, atomic/molecular spectroscopy and precision LIDARs. Applications have extended to coherent nonlinear Raman spectroscopy of molecules and quantum metrology for entangled atomic qubits. Frequency combs will create novel possibilities in nano-photonics and plasmonics; however, its interrelation with surface plasmons is unexplored despite the important role that plasmonics plays in nonlinear spectroscopy and quantum optics through the manipulation of light on a subwavelength scale. Here, we demonstrate that a frequency comb can be transformed to a plasmonic comb in plasmonic nanostructures and reverted to the original frequency comb without noticeable degradation of <6.51 × 10(-19) in absolute position, 2.92 × 10(-19) in stability and 1 Hz in linewidth. The results indicate that the superior performance of a well-defined frequency comb can be applied to nanoplasmonic spectroscopy, quantum metrology and subwavelength photonic circuits. PMID:26898307

  9. Frequency comb transferred by surface plasmon resonance

    NASA Astrophysics Data System (ADS)

    Geng, Xiao Tao; Chun, Byung Jae; Seo, Ji Hoon; Seo, Kwanyong; Yoon, Hana; Kim, Dong-Eon; Kim, Young-Jin; Kim, Seungchul

    2016-02-01

    Frequency combs, millions of narrow-linewidth optical modes referenced to an atomic clock, have shown remarkable potential in time/frequency metrology, atomic/molecular spectroscopy and precision LIDARs. Applications have extended to coherent nonlinear Raman spectroscopy of molecules and quantum metrology for entangled atomic qubits. Frequency combs will create novel possibilities in nano-photonics and plasmonics; however, its interrelation with surface plasmons is unexplored despite the important role that plasmonics plays in nonlinear spectroscopy and quantum optics through the manipulation of light on a subwavelength scale. Here, we demonstrate that a frequency comb can be transformed to a plasmonic comb in plasmonic nanostructures and reverted to the original frequency comb without noticeable degradation of <6.51 × 10-19 in absolute position, 2.92 × 10-19 in stability and 1 Hz in linewidth. The results indicate that the superior performance of a well-defined frequency comb can be applied to nanoplasmonic spectroscopy, quantum metrology and subwavelength photonic circuits.

  10. Frequency comb transferred by surface plasmon resonance

    PubMed Central

    Geng, Xiao Tao; Chun, Byung Jae; Seo, Ji Hoon; Seo, Kwanyong; Yoon, Hana; Kim, Dong-Eon; Kim, Young-Jin; Kim, Seungchul

    2016-01-01

    Frequency combs, millions of narrow-linewidth optical modes referenced to an atomic clock, have shown remarkable potential in time/frequency metrology, atomic/molecular spectroscopy and precision LIDARs. Applications have extended to coherent nonlinear Raman spectroscopy of molecules and quantum metrology for entangled atomic qubits. Frequency combs will create novel possibilities in nano-photonics and plasmonics; however, its interrelation with surface plasmons is unexplored despite the important role that plasmonics plays in nonlinear spectroscopy and quantum optics through the manipulation of light on a subwavelength scale. Here, we demonstrate that a frequency comb can be transformed to a plasmonic comb in plasmonic nanostructures and reverted to the original frequency comb without noticeable degradation of <6.51 × 10−19 in absolute position, 2.92 × 10−19 in stability and 1 Hz in linewidth. The results indicate that the superior performance of a well-defined frequency comb can be applied to nanoplasmonic spectroscopy, quantum metrology and subwavelength photonic circuits. PMID:26898307

  11. Laser interferometer for absolute distance measurement based on a tunable VCSEL laser

    NASA Astrophysics Data System (ADS)

    Cip, Ondrej; Mikel, Bretislav; Lazar, Josef

    2005-02-01

    In the work, we present the absolute distance interferometer with a narrow-linewidth tunable VCSEL laser (Vertical-Cavity Surface-Emitting Laser) working at &lambda ~760 nm. As a detection technique, we use a fast wavelength-scanning interferometry improved by an amplitude division of the interference fringe with using two signals in quadrature. Used VCSEL laser is wide tunable with the mod-hop free tuning range more than 1.2 nm by means of the amplitude modulation of the injection current. We control the stabilization and tuning process of the laser wavelength with using the frequency lock to a Fabry-Perot resonator. We build that resonator as a glass plan-parallel etalon with high-fines. Except the frequency lock, the etalon helps us to measure a wavelength-tuning interval of VCSEL laser during the scanning process. We have stabilized an operating temperature of the VCSEL laser by means of a fast digital temperature controller. The optical set-up of the interferometer begins with a polarizing beam-splitter. It splits the laser beam into the measuring and reference arm of the Michelson interferometer. Two cubic corner cubes reflect beams back to this beam-splitter. It collects reflected beams to the same axis of propagation. Then a detection unit produces the combination of two perpendicularly polarized laser beams with production of two electronic signals that are in the quadrature. A fast analog-to-digital card equipped with the digital signal processor (DSP) samples these signals. DSP also controls the course of the scanning process. After Δλ ~ 1 nm scan of the wavelength of VCSEL laser we obtain a record of passed interference fringes and passed Fabry-Perot resonance modes at the same time. On basis of these measured quantities we are able to calculate with high precision the instantaneous value of the optical path length difference between the measuring and reference arm of the Michelson interferometer. We experimentally compared the developed absolute

  12. Absolute Gravity Datum in the Age of Cold Atom Gravimeters

    NASA Astrophysics Data System (ADS)

    Childers, V. A.; Eckl, M. C.

    2014-12-01

    increase in accuracy. Our presentation will also explore the impact of such an instrument on our theory of how to constrain the gravity datum and on how to ensure stability, repeatability, and reproducibility across different absolute gravimeter systems.

  13. Inequalities, Absolute Value, and Logical Connectives.

    ERIC Educational Resources Information Center

    Parish, Charles R.

    1992-01-01

    Presents an approach to the concept of absolute value that alleviates students' problems with the traditional definition and the use of logical connectives in solving related problems. Uses a model that maps numbers from a horizontal number line to a vertical ray originating from the origin. Provides examples solving absolute value equations and…

  14. Absolute optical metrology : nanometers to kilometers

    NASA Technical Reports Server (NTRS)

    Dubovitsky, Serge; Lay, O. P.; Peters, R. D.; Liebe, C. C.

    2005-01-01

    We provide and overview of the developments in the field of high-accuracy absolute optical metrology with emphasis on space-based applications. Specific work on the Modulation Sideband Technology for Absolute Ranging (MSTAR) sensor is described along with novel applications of the sensor.

  15. Introducing the Mean Absolute Deviation "Effect" Size

    ERIC Educational Resources Information Center

    Gorard, Stephen

    2015-01-01

    This paper revisits the use of effect sizes in the analysis of experimental and similar results, and reminds readers of the relative advantages of the mean absolute deviation as a measure of variation, as opposed to the more complex standard deviation. The mean absolute deviation is easier to use and understand, and more tolerant of extreme…

  16. Investigating Absolute Value: A Real World Application

    ERIC Educational Resources Information Center

    Kidd, Margaret; Pagni, David

    2009-01-01

    Making connections between various representations is important in mathematics. In this article, the authors discuss the numeric, algebraic, and graphical representations of sums of absolute values of linear functions. The initial explanations are accessible to all students who have experience graphing and who understand that absolute value simply…

  17. Absolute Income, Relative Income, and Happiness

    ERIC Educational Resources Information Center

    Ball, Richard; Chernova, Kateryna

    2008-01-01

    This paper uses data from the World Values Survey to investigate how an individual's self-reported happiness is related to (i) the level of her income in absolute terms, and (ii) the level of her income relative to other people in her country. The main findings are that (i) both absolute and relative income are positively and significantly…

  18. Absolute Pitch in Boreal Chickadees and Humans: Exceptions that Test a Phylogenetic Rule

    ERIC Educational Resources Information Center

    Weisman, Ronald G.; Balkwill, Laura-Lee; Hoeschele, Marisa; Moscicki, Michele K.; Bloomfield, Laurie L.; Sturdy, Christopher B.

    2010-01-01

    This research examined generality of the phylogenetic rule that birds discriminate frequency ranges more accurately than mammals. Human absolute pitch chroma possessors accurately tracked transitions between frequency ranges. Independent tests showed that they used note naming (pitch chroma) to remap the tones into ranges; neither possessors nor…

  19. Absolute calibration for a broad range single shot electron spectrometer

    SciTech Connect

    Glinec, Y.; Faure, J.; Guemnie-Tafo, A.; Malka, V.; Monard, H.; Larbre, J. P.; De Waele, V.; Marignier, J. L.; Mostafavi, M.

    2006-10-15

    This article gives a detailed description of a single shot electron spectrometer which was used to characterize electron beams produced by laser-plasma interaction. Contrary to conventional electron sources, electron beams from laser-plasma accelerators can produce a broad range of energies. Therefore, diagnosing these electron spectra requires specific attention and experimental development. Here, we provide an absolute calibration of the Lanex Kodak Fine screen on a laser-triggered radio frequency picosecond electron accelerator. The efficiency of scintillating screens irradiated by electron beams has never been investigated so far. This absolute calibration is then compared to charge measurements from an integrating current transformer for quasimonoenergetic electron spectra from laser-plasma interaction.

  20. Proposal for an absolute, atomic definition of mass

    NASA Astrophysics Data System (ADS)

    Wignall, J. W. G.

    1991-11-01

    It is proposed that the mass of a particle be defined absolutely as its de Broglie frequency, measured as the mean de Broglie wavelength of the particle when it has a mean speed (v) and Lorentz factor (gamma); the masses of systems too large to have a measurable de Broglie wavelength mean are then to be derived by specifying the usual inertial and additive properties of mass. This definition avoids the use of an arbitrary macroscopic standard such as the prototype kilogram, and, if present theory is correct, does not even require the choice of a specific particle as a mass standard. Suggestions are made as to how this absolute mass can be realized and measured at the macroscopic level and, finally, some comments are made on the effect of the new definition on the form of the equations of physics.

  1. Absolute calibration for a broad range single shot electron spectrometer

    NASA Astrophysics Data System (ADS)

    Glinec, Y.; Faure, J.; Guemnie-Tafo, A.; Malka, V.; Monard, H.; Larbre, J. P.; De Waele, V.; Marignier, J. L.; Mostafavi, M.

    2006-10-01

    This article gives a detailed description of a single shot electron spectrometer which was used to characterize electron beams produced by laser-plasma interaction. Contrary to conventional electron sources, electron beams from laser-plasma accelerators can produce a broad range of energies. Therefore, diagnosing these electron spectra requires specific attention and experimental development. Here, we provide an absolute calibration of the Lanex Kodak Fine screen on a laser-triggered radio frequency picosecond electron accelerator. The efficiency of scintillating screens irradiated by electron beams has never been investigated so far. This absolute calibration is then compared to charge measurements from an integrating current transformer for quasimonoenergetic electron spectra from laser-plasma interaction.

  2. The Spatiotemporal Stability of Dominant Frequency Sites in In-Silico Modeling of 3-Dimensional Left Atrial Mapping of Atrial Fibrillation

    PubMed Central

    Hwang, Minki; Song, Jun-Seop; Lee, Young-Seon; Joung, Boyoung; Pak, Hui-Nam

    2016-01-01

    Background We previously reported that stable rotors were observed in in-silico human atrial fibrillation (AF) models, and were well represented by dominant frequency (DF). We explored the spatiotemporal stability of DF sites in 3D-AF models imported from patient CT images of the left atrium (LA). Methods We integrated 3-D CT images of the LA obtained from ten patients with persistent AF (male 80%, 61.8 ± 13.5 years old) into an in-silico AF model. After induction, we obtained 6 seconds of AF simulation data for DF analyses in 30 second intervals (T1–T9). The LA was divided into ten sections. Spatiotemporal changes and variations in the temporal consistency of DF were evaluated at each section of the LA. The high DF area was defined as the area with the highest 10% DF. Results 1. There was no spatial consistency in the high DF distribution at each LA section during T1–T9 except in one patient (p = 0.027). 2. Coefficients of variation for the high DF area were highly different among the ten LA sections (p < 0.001), and they were significantly higher in the four pulmonary vein (PV) areas, the LA appendage, and the peri-mitral area than in the other LA sections (p < 0.001). 3. When we conducted virtual ablation of 10%, 15%, and 20% of the highest DF areas (n = 270 cases), AF was changed to atrial tachycardia (AT) or terminated at a rate of 40%, 57%, and 76%, respectively. Conclusions Spatiotemporal consistency of the DF area was observed in 10% of AF patients, and high DF areas were temporally variable. Virtual ablation of DF is moderately effective in AF termination and AF changing into AT. PMID:27459377

  3. Frequency Standards and Metrology

    NASA Astrophysics Data System (ADS)

    Maleki, Lute

    2009-04-01

    Preface / Lute Maleki -- Symposium history / Jacques Vanier -- Symposium photos -- pt. I. Fundamental physics. Variation of fundamental constants from the big bang to atomic clocks: theory and observations (Invited) / V. V. Flambaum and J. C. Berengut. Alpha-dot or not: comparison of two single atom optical clocks (Invited) / T. Rosenband ... [et al.]. Variation of the fine-structure constant and laser cooling of atomic dysprosium (Invited) / N. A. Leefer ... [et al.]. Measurement of short range forces using cold atoms (Invited) / F. Pereira Dos Santos ... [et al.]. Atom interferometry experiments in fundamental physics (Invited) / S. W. Chiow ... [et al.]. Space science applications of frequency standards and metrology (Invited) / M. Tinto -- pt. II. Frequency & metrology. Quantum metrology with lattice-confined ultracold Sr atoms (Invited) / A. D. Ludlow ... [et al.]. LNE-SYRTE clock ensemble: new [symbol]Rb hyperfine frequency measurement - spectroscopy of [symbol]Hg optical clock transition (Invited) / M. Petersen ... [et al.]. Precise measurements of S-wave scattering phase shifts with a juggling atomic clock (Invited) / S. Gensemer ... [et al.]. Absolute frequency measurement of the [symbol] clock transition (Invited) / M. Chwalla ... [et al.]. The semiclassical stochastic-field/atom interaction problem (Invited) / J. Camparo. Phase and frequency noise metrology (Invited) / E. Rubiola ... [et al.]. Optical spectroscopy of atomic hydrogen for an improved determination of the Rydberg constant / J. L. Flowers ... [et al.] -- pt. III. Clock applications in space. Recent progress on the ACES mission (Invited) / L. Cacciapuoti and C. Salomon. The SAGAS mission (Invited) / P. Wolf. Small mercury microwave ion clock for navigation and radioScience (Invited) / J. D. Prestage ... [et al.]. Astro-comb: revolutionizing precision spectroscopy in astrophysics (Invited) / C. E. Kramer ... [et al.]. High frequency very long baseline interferometry: frequency standards and

  4. Cosmic backgrounds of relic gravitons and their absolute normalization

    NASA Astrophysics Data System (ADS)

    Giovannini, Massimo

    2014-11-01

    Provided the consistency relations are not violated, the recent BICEP2 observations pin down the absolute normalization, the spectral slope and the maximal frequency of the cosmic graviton background produced during inflation. The properly normalized spectra are hereby computed from the lowest frequencies (of the order of the present Hubble rate) up to the highest frequency range in the GHz region. Deviations from the conventional paradigm cannot be excluded and are examined by allowing for different physical possibilities including, in particular, a running of the tensor spectral index, an explicit breaking of the consistency relations and a spike in the high-frequency tail of the spectrum coming either from a post-inflationary phase dominated by a stiff fluid or from the contribution of waterfall fields in a hybrid inflationary context. The direct determinations of the tensor to scalar ratio at low frequencies, if confirmed by the forthcoming observations, will also affect and constrain the high-frequency uncertainties. The limits on the cosmic graviton backgrounds coming from wide-band interferometers (such as LIGO/Virgo, LISA and BBO/DECIGO) together with a more accurate scrutiny of the tensor B-mode polarization at low frequencies will set direct bounds on the post-inflationary evolution and on other unconventional completions of the standard lore.

  5. Parametric seeding of a microresonator optical frequency comb.

    PubMed

    Papp, Scott B; Del'Haye, Pascal; Diddams, Scott A

    2013-07-29

    We have investigated parametric seeding of a microresonator frequency comb (microcomb) by way of a pump laser with two electro-optic-modulation sidebands. We show that the pump-sideband spacing is precisely replicated throughout the microcomb's optical spectrum, and we demonstrate a record absolute line-spacing stability for microcombs of 1.6 × 10(-13) at 1 s. The spectrum of a microcomb is complex, and often non-equidistant subcombs are observed. Our results demonstrate that parametric seeding can not only control the subcombs, but can lead to the generation of a strictly equidistant microcomb spectrum. PMID:23938634

  6. Frequency ratios and the discrimination of pure tone sequences.

    PubMed

    Schellenberg, E G; Trehub, S E

    1994-10-01

    We examined the effect of frequency ratios on the discrimination of patterns of alternating pure tones (ABABA). Listeners heard a repeating pattern presented in transposition (same frequency ratios between successive tones, different absolute frequencies) and were required to indicate when the pattern changed (different frequency ratios and absolute frequencies). Changes from patterns with simple frequency ratios to those with more complex ratios were more readily detected than were changes from complex ratios to simpler ratios. PMID:7984402

  7. Low-Speed Investigation of the Effects of Frequency and Amplitude of Oscillation in Sideslip on the Lateral Stability Derivatives of a 60 deg Delta Wing, a 45 deg Sweptback Wing and an Unswept Wing

    NASA Technical Reports Server (NTRS)

    Lichtenstein, Jacob H.; Williams, James L.

    1961-01-01

    A low-speed investigation has been conducted in the Langley stability tunnel to study the effects of frequency and amplitude of sideslipping motion on the lateral stability derivatives of a 60 deg. delta wing, a 45 deg. sweptback wing, and an unswept wing. The investigation was made for values of the reduced-frequency parameter of 0.066 and 0.218 and for a range of amplitudes from +/- 2 to +/- 6 deg. The results of the investigation indicated that increasing the frequency of the oscillation generally produced an appreciable change in magnitude of the lateral oscillatory stability derivatives in the higher angle-of-attack range. This effect was greatest for the 60 deg. delta wing and smallest for the unswept wing and generally resulted in a more linear variation of these derivatives with angle of attack. For the relatively high frequency at which the amplitude was varied, there appeared to be little effect on the measured derivatives as a result of the change in amplitude of the oscillation.

  8. Absolute optical instruments without spherical symmetry

    NASA Astrophysics Data System (ADS)

    Tyc, Tomáš; Dao, H. L.; Danner, Aaron J.

    2015-11-01

    Until now, the known set of absolute optical instruments has been limited to those containing high levels of symmetry. Here, we demonstrate a method of mathematically constructing refractive index profiles that result in asymmetric absolute optical instruments. The method is based on the analogy between geometrical optics and classical mechanics and employs Lagrangians that separate in Cartesian coordinates. In addition, our method can be used to construct the index profiles of most previously known absolute optical instruments, as well as infinitely many different ones.

  9. Methods to calibrate the absolute receive sensitivity of single-element, focused transducers

    PubMed Central

    Rich, Kyle T.; Mast, T. Douglas

    2015-01-01

    Absolute pressure measurements of acoustic emissions by single-element, focused passive cavitation detectors would be facilitated by improved wideband receive calibration techniques. Here, calibration methods were developed to characterize the absolute, frequency-dependent receive sensitivity of a spherically focused, single-element transducer using pulse-echo and pitch-catch techniques. Validation of these calibration methods on a focused receiver were made by generating a pulse from a small diameter source at the focus of the transducer and comparing the absolute pressure measured by a calibrated hydrophone to that of the focused transducer using the receive sensitivities determined here. PMID:26428812

  10. Methods to calibrate the absolute receive sensitivity of single-element, focused transducers.

    PubMed

    Rich, Kyle T; Mast, T Douglas

    2015-09-01

    Absolute pressure measurements of acoustic emissions by single-element, focused passive cavitation detectors would be facilitated by improved wideband receive calibration techniques. Here, calibration methods were developed to characterize the absolute, frequency-dependent receive sensitivity of a spherically focused, single-element transducer using pulse-echo and pitch-catch techniques. Validation of these calibration methods on a focused receiver were made by generating a pulse from a small diameter source at the focus of the transducer and comparing the absolute pressure measured by a calibrated hydrophone to that of the focused transducer using the receive sensitivities determined here. PMID:26428812

  11. The Physical Origin of Severe Low-Frequency Pressure Fluctuations in Giant Francis Turbines

    NASA Astrophysics Data System (ADS)

    Zhang, R.-K.; Cai, Q.-D.; Wu, J.-Z.; Wu, Y.-L.; Liu, S.-H.; Zhang, L.

    The physical origin of severe low-frequency pressure fluctuation frequently observed in Francis hydraulic turbines under off-design conditions, which greatly damages the structural stability of turbines and even power stations, is analyzed based on the hydrodynamic stability theory and our Reynolds-averaged Navier-Stokes equation simulation (RANS) of the flow in the entire passage of a Francis turbine. We find that spontaneous unsteady vortex ropes, which induce severe pressure fluctuations, are formed due to the absolute instability of the swirling flow at the conical inlet of the turbine's draft tube.

  12. Absolute magnitudes of trans-neptunian objects

    NASA Astrophysics Data System (ADS)

    Duffard, R.; Alvarez-candal, A.; Pinilla-Alonso, N.; Ortiz, J. L.; Morales, N.; Santos-Sanz, P.; Thirouin, A.

    2015-10-01

    Accurate measurements of diameters of trans- Neptunian objects are extremely complicated to obtain. Radiomatric techniques applied to thermal measurements can provide good results, but precise absolute magnitudes are needed to constrain diameters and albedos. Our objective is to measure accurate absolute magnitudes for a sample of trans- Neptunian objects, many of which have been observed, and modelled, by the "TNOs are cool" team, one of Herschel Space Observatory key projects grantes with ~ 400 hours of observing time. We observed 56 objects in filters V and R, if possible. These data, along with data available in the literature, was used to obtain phase curves and to measure absolute magnitudes by assuming a linear trend of the phase curves and considering magnitude variability due to rotational light-curve. In total we obtained 234 new magnitudes for the 56 objects, 6 of them with no reported previous measurements. Including the data from the literature we report a total of 109 absolute magnitudes.

  13. A New Gimmick for Assigning Absolute Configuration.

    ERIC Educational Resources Information Center

    Ayorinde, F. O.

    1983-01-01

    A five-step procedure is provided to help students in making the assignment absolute configuration less bothersome. Examples for both single (2-butanol) and multi-chiral carbon (3-chloro-2-butanol) molecules are included. (JN)

  14. Method of differential-phase/absolute-amplitude QAM

    DOEpatents

    Dimsdle, Jeffrey William

    2007-07-03

    A method of quadrature amplitude modulation involving encoding phase differentially and amplitude absolutely, allowing for a high data rate and spectral efficiency in data transmission and other communication applications, and allowing for amplitude scaling to facilitate data recovery; amplitude scale tracking to track-out rapid and severe scale variations and facilitate successful demodulation and data retrieval; 2.sup.N power carrier recovery; incoherent demodulation where coherent carrier recovery is not possible or practical due to signal degradation; coherent demodulation; multipath equalization to equalize frequency dependent multipath; and demodulation filtering.

  15. Method of differential-phase/absolute-amplitude QAM

    DOEpatents

    Dimsdle, Jeffrey William

    2008-10-21

    A method of quadrature amplitude modulation involving encoding phase differentially and amplitude absolutely, allowing for a high data rate and spectral efficiency in data transmission and other communication applications, and allowing for amplitude scaling to facilitate data recovery; amplitude scale tracking to track-out rapid and severe scale variations and facilitate successful demodulation and data retrieval; 2.sup.N power carrier recovery; incoherent demodulation where coherent carrier recovery is not possible or practical due to signal degradation; coherent demodulation; multipath equalization to equalize frequency dependent multipath; and demodulation filtering.

  16. Method of differential-phase/absolute-amplitude QAM

    DOEpatents

    Dimsdle, Jeffrey William

    2007-07-17

    A method of quadrature amplitude modulation involving encoding phase differentially and amplitude absolutely, allowing for a high data rate and spectral efficiency in data transmission and other communication applications, and allowing for amplitude scaling to facilitate data recovery; amplitude scale tracking to track-out rapid and severe scale variations and facilitate successful demodulation and data retrieval; 2.sup.N power carrier recovery; incoherent demodulation where coherent carrier recovery is not possible or practical due to signal degradation; coherent demodulation; multipath equalization to equalize frequency dependent multipath; and demodulation filtering.

  17. Method of differential-phase/absolute-amplitude QAM

    DOEpatents

    Dimsdle, Jeffrey William

    2007-10-02

    A method of quadrature amplitude modulation involving encoding phase differentially and amplitude absolutely, allowing for a high data rate and spectral efficiency in data transmission and other communication applications, and allowing for amplitude scaling to facilitate data recovery; amplitude scale tracking to track-out rapid and severe scale variations and facilitate successful demodulation and data retrieval; 2.sup.N power carrier recovery; incoherent demodulation where coherent carrier recovery is not possible or practical due to signal degradation; coherent demodulation; multipath equalization to equalize frequency dependent multipath; and demodulation filtering.

  18. Method of differential-phase/absolute-amplitude QAM

    DOEpatents

    Dimsdle, Jeffrey William

    2009-09-01

    A method of quadrature amplitude modulation involving encoding phase differentially and amplitude absolutely, allowing for a high data rate and spectral efficiency in data transmission and other communication applications, and allowing for amplitude scaling to facilitate data recovery; amplitude scale tracking to track-out rapid and severe scale variations and facilitate successful demodulation and data retrieval; 2.sup.N power carrier recovery; incoherent demodulation where coherent carrier recovery is not possible or practical due to signal degradation; coherent demodulation; multipath equalization to equalize frequency dependent multipath; and demodulation filtering.

  19. METHOD FOR STABILIZING KLYSTRONS

    DOEpatents

    Magnuson, D.W.; Smith, D.F.

    1959-04-14

    High-frequency oscillators for the generation of microwaves, particularly a system for stabilizing frequency-modulated klystron oscillators of the reflex type, are described. The system takos advantage of the fact that a change in oscillator frequency will alter the normal phase displacement between the cavity and its modulator, creating an error voltage which is utilized to regulate the frequency of the oscillator and stabilize it.

  20. Absolute wind measurements in the lower thermosphere of Venus using infrared heterodyne spectroscopy

    NASA Technical Reports Server (NTRS)

    Goldstein, Jeffrey J.

    1990-01-01

    The first absolute wind velocities above the Venusian cloud-tops were obtained using NASA/Goddard infrared heterodyne spectrometers at the NASA Infrared Telescope Facility (IRTF) and the McMath Solar Telescope. Beam-integrated Doppler displacements in the non-thermal emission core of (12)C(16)O2 10.33 micron R(8) sampled the line of sight projection of the lower thermospheric wind field (100 to 120 km). A field-usable Lamb-dip laser stabilization system, developed for spectrometer absolute frequency calibration to less than + or - 0.1 MHz, allowed S/N-limited line of sight velocity resolution at the 1 m/s level. The spectrometer's diffraction-limited beam (1.7 arc-second HPBW at McMath, 0.9 arc-second HPBW at IRTF), and 1 to 2 arc-second seeing, provided the spatial resolution necessary for circulation model discrimination. Qualitative analysis of beam-integrated winds provided definitive evidence of a dominant subsolar-antisolar circulation in the lower thermosphere. Beam-integrated winds were modelled with a 100x100 grid over the beam, incorporating beam spatial rolloff and across-the-beam gradients in non-thermal emission intensity, line of sight projection geometry, and horizontal wind velocity. Horizontal wind velocity was derived from a 2-parameter model wind field comprised of subsolar-antisolar and zonal components. Best-fit models indicated a dominant subsolar-antisolar flow with 120 m/s cross-terminator winds and a retrograde zonal component with a 25 m/s equatorial velocity. A review of all dynamical indicators above the cloud-tops allowed development of an integrated and self-consistent picture of circulation in the 70 to 200 km range.