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Showing papers by "James Taylor published in 1986"


Journal ArticleDOI
01 Aug 1986-Nature
TL;DR: The pulsar has a small dispersion measure (13.3 cm−3 pc), suggesting a distance of only ∼350 pc as discussed by the authors, and its location within 25 pc of the galactic plane argues that millisecond pulsars form a significant fraction of the pulsar population, leaving many detectable ones undiscovered.
Abstract: Recent observations1,2 at the Arecibo Observatory have resulted in the discovery of PSR1855+09, a pulsar with period P=5.362 ms, moving in a nearly circular orbit of period 12.3 days. The pulsar is only the third one known with P < 10 ms, and the sixth known radio pulsar in a binary system. (Discovery of a seventh binary pulsar is announced in an accompanying paper3.) Three of the seven binaries are among the fastest five of more than 400 pulsars—a fact that provides strong support for the conclusion that fast pulsars are ‘recycled’ neutron stars, spun up during a phase of mass accretion from an evolving companion star. The pulsar has a small dispersion measure (13.3 cm−3 pc), suggesting a distance of only ∼350 pc. The proximity of this pulsar and its location within 25 pc of the galactic plane argue that millisecond pulsars form a significant fraction (∼10%) of the pulsar population, leaving many detectable ones undiscovered4,5. Its signal is strong enough to permit pulse-arrival-time measurements with single-day uncertainties of <3µs. Timing observations already suggest that PSR1855+09, like the 1.5-ms pulsar PS R1937+21, will prove to be a natural clock of extremely high stability6. The existence of a second pulsar with extremely small timing uncertainties will greatly aid the search for background gravitational waves using millisecond pulsars as detectors.

59 citations


Journal ArticleDOI
01 Aug 1986-Nature
TL;DR: In this article, it was shown that PSR2303+46 was a binary pulsar and PSR1831+00 was a member of a binary system, the seventh such radio pulsar known.
Abstract: Much of the interesting physics concerning neutron stars and their evolution depends for its experimental foundation on observations of the rotation rates of pulsars. To continue recent efforts of our group in this area1–3, we began a series of pulse-arrival-time observations of ∼70 pulsars in January 1985. Most of the pulsars in this study were discovered in the Princeton/NRAO pulsar survey of the preceding two years4,5. Soon after we began these observations it became clear that PSR2303+46 was a binary pulsar2; it is now evident that PSR1831–00 is also a member of a binary system, the seventh such radio pulsar known. It moves in an orbit with a period of 1.81 days, a small eccentricity, and an unusually small mass function of 0.00012 M⊙ (where M⊙ is the mass of the Sun). With a period P = 0.521 s and period derivative P≲ 10−17 s s−1, PSR1831–00, like the other known binary pulsars, has a relatively weak magnetic field. We discuss the features of this system that provide clues to its evolutionary history and outline possible models for its formation.

26 citations


Journal ArticleDOI
TL;DR: In this article, the power-dependent pulsewidth variations for input 85 ps pulses from a cw mode-locked Nd: YAG laser propagating through 125 m of single-mode optical fibre have been examined using a Synchroscan streak camera.
Abstract: The power-dependent pulsewidth variations for input 85 ps pulses from a cw mode-locked Nd: YAG laser propagating through 125 m of single-mode optical fibre have been examined using a Synchroscan streak camera. Simultaneous spectral and temporal measurements provide information as to the optimum parameters for pulse compression in fibres.

24 citations


Journal ArticleDOI
TL;DR: In this article, an extra-cavity pulse narrowing technique is demonstrated in which a frequency-swept optical pulse is compressed by the application of a spectral window, in a regime where self-phase modulation was the dominant nonlinear mechanism and group velocity dispersion and stimulated Raman scattering were negligible.

23 citations


Journal ArticleDOI
TL;DR: In this paper, the passive mode locking of the laser dyes DCM and Rhodamine 101, which operate in similar spectral regions, has been carried out in a simple flashlamp-pumped system.

22 citations


Journal ArticleDOI
01 Jan 1986-Nature
TL;DR: The second fastest pulsar, PSR1953+29, has a period of 6.133 ms and is a member of a binary system with an orbital period of 117.35 days as mentioned in this paper.
Abstract: PSR1953+29, the second fastest of more than 400 known pulsars1, has a period of 6.133 ms and is a member of a binary system with an orbital period of 117.35 days. The system is of great interest because of what it can reveal about the evolution of pulsars and close binary stars2–4. Recently we have carried out observations to determine two of the most important parameters of the system, the pulsar period derivative Ṗ and the orbital eccentricity e. We find a small but non-zero eccentricity, e =(330.3±0.4) × 10−6, and a spindown rate of Ṗ = (1±6)×10−20 s s−1, smaller than that measured for any other pulsar. These values are consistent with an evolutionary history involving spin-up during a mass accretion phase, but are difficult to reconcile with a recent report of periodically pulsed γ rays from this object5.

22 citations


Journal ArticleDOI
TL;DR: In this paper, the authors examined pump pulse depletion for high peak power (∼ 100 kW) 90 ps pulses from a Q-switched and mode-locked Nd:YAG laser in 4 m of single-mode optical fiber.
Abstract: Pump pulse depletion has been examined for high peak power (∼ 100 kW) 90 ps pulses from a Q -switched and mode-locked Nd:YAG laser in 4 m of single-mode optical fiber. Fragmentation of the fundamental and low Stokes Raman orders has been observed for this cascading process. Pulse compression using an interferometric technique has been carried out, obtaining compression ratios of up to times five, on these fragments which exhibited a negative frequency chirp.

20 citations


Proceedings ArticleDOI
18 Jun 1986
TL;DR: In essence, SIDF input/output (I/O) models of the compensated nonlinear system are exploited to directly synthesize a compensator nonlinearity that eliminates or reduces the amplitude dependence of the open-loop I/O relation.
Abstract: A nonlinear autotuning regulator algorithm is obtained via a direct combination of the Astrom-Hagglund algorithm for the linear case [1] with the sinusoidal-input describing function (SIDEF) approach to nonlinear compensator synthesis of Taylor and Strobel [2]. The basic approach for linear autotuning proceeds as follows: a. install a relay with hysteresis in series with the unknown plant to be controlled; close a unitygain feedback loop around this combination; b. choose several values of hysteresis so that this system exhibits limit cycles; the frequencies and amplitudes of the oscillation at the output of the plant determine points on the plant Nyquist plot; and c. given points on the plant Nyquist plot, set the PID controller gains using an appropriate tuning algorithm (e.g., Ziegler-Nichols). This approach produces good results if the plant is liner or nearly so; however, if the plant behavior is strongly amplitude-dependent, there are likely to be problems with implementing this algorithm. The nonlinear autotuning regulator algorithm which extends the above approach to handle situations where the plant behavior is strongly amplitude-dependent is based on the SIDF approach. In essence, SIDF input/output (I/O) models of the compensated nonlinear system are exploited to directly synthesize a compensator nonlinearity that eliminates or reduces the amplitude dependence of the open-loop I/O relation. The nonlinear synthesis portion of this algorithm is reasonably simple to implement, has been shown to be effective [2], and should be of practical utility. An example application to a precision position control system is provided as an illustration.

18 citations


Journal ArticleDOI
TL;DR: The passive mode locking of a cw Rhodamine 110 dye laser is reported, in a simple uncompensated linear cavity, subpicosecond pulse generation was achieved over the spectral range 553–570 nm.
Abstract: The passive mode locking of a cw Rhodamine 110 dye laser is reported. In a simple uncompensated linear cavity, subpicosecond pulse generation was achieved over the spectral range 553–570 nm. Pulses as short as 150 fsec were recorded using standard second-harmonic autocorrelation measurement techniques. Two saturable-absorbing species were found to operate successfully in this region.

17 citations


Journal ArticleDOI
TL;DR: In this article, the green and red components generated in a nonpolarization preserving optical fiber using a Q-switched and mode-locked cw Nd: YAG laser have been examined spectrally and temporally with picosecond resolution.
Abstract: Intense green and red components generated in a non-polarization preserving optical fibre using a Q-switched and mode-locked cw Nd: YAG laser have been examined spectrally and temporally with picosecond resolution. In addition to the red (four-photon interaction) and green (second-harmonic) components, many other frequency mixing processes were detected. From theoretical considerations, the red component (anti-Stokes) which is generated through parametric four photon mixing should be in the same propagation mode as the Stokes component (ir) and this was confirmed experimentally.

16 citations


Journal ArticleDOI
TL;DR: In this paper, the passive modelocking of a cw rhodamine B dye laser was reported, and a simple linear cavity with no dispersion correction was achieved over the spectral range 616-658 nm using 1,3'-diethyl-4,2'-quinolylthiacarbocyanine iodide (DQTCI) as the saturable absorber.

Journal ArticleDOI
TL;DR: In this article, the passive modelocking of a cw rhodamine 6G dye laser over the spectral range 570 to 600 nm using 2-(p-dimethylaminostyryl)- benzthiazolylethyliodide (DASBTI) as the saturable absorber is reported.

Journal ArticleDOI
TL;DR: In this article, the first passive mode locking of a continuous-wave energy transfer dye laser was reported using an argon ion laser-pumped mixture of rhodamine 6G and sulphur rhodamines 101 as the active medium, pulses of less than 500 fs duration were generated over the spectral range 652-694 nm using two different saturable absorbers in a simple linear cavity without dispersion optimization.
Abstract: The first passive mode locking of a continuous-wave energy transfer dye laser is reported. Using an argon ion laser-pumped mixture of rhodamine 6G and sulphur rhodamine 101 as the active medium, pulses of less than 500 fs duration have been generated over the spectral range 652-694 nm using two different saturable absorbers in a simple linear cavity without dispersion optimization. Pulses as short as 120 fs have been measured using standard second-harmonic generation autocorrelation techniques.

Journal ArticleDOI
TL;DR: Using a synchronously operating streak camera in conjunction with a 1 m monochromator, the induced frequency chirp of an optical pulse on propagation over 2.2 km of singlemode optical fibre has been directly measured with picosecond resolution as discussed by the authors.
Abstract: Using a synchronously operating streak camera in conjunction with a 1 m monochromator the induced frequency chirp of an optical pulse on propagation over 2.2 km of single-mode optical fibre has been directly measured with picosecond resolution.

Journal ArticleDOI
TL;DR: In this article, the authors describe the use of a laser YAG with a generation of 1.4 ps and an impulsive force of 85 ps in the presence of 60 ps compression.
Abstract: Compression par un facteur de 60. Utilisation d'un laser YAG: Nd. Generation d'impulsions de 1,4 ps a partir d'impulsion de 85 ps

Journal ArticleDOI
TL;DR: In this paper, the authors used a laser-based camera operated in stroboscopic mode to measure the variation in the compressed pulsed duration through the pulse train with a circularly scanning streak camera.

Journal ArticleDOI
TL;DR: In this paper, the flourescence decay of the J aggregates of 1,1′-diethyl-2,2′-cyanine (pseudoisocyanine) iodide was measured with picosecond resolution to be 24 ps.

Journal ArticleDOI
TL;DR: The hybrid modelocking of the Rhodamine B dye laser for the first time was reported in this paper, where pulses as short as ∼430 fs were generated from a simple linear cavity with a single dye jet.

Journal ArticleDOI
TL;DR: In this article, the first passive mode locking of the continuous wave (cw) DCM dye laser was reported, where subpicosecond pulses as short as 0.68 ps were obtained over the spectral region from 655 to 673 nm.
Abstract: The first passive mode locking of the continuous wave (cw) DCM dye laser is reported. Subpicosecond pulses as short as 0.68 ps were obtained over the spectral region from 655 to 673 nm from a simple linear cavity with no dispersion optimisation. The dye 1,3′ Diethyl 4,2′ quinolythiacarbocyanine iodide (DQTCI) was used as the saturable absorber.

Journal ArticleDOI
TL;DR: Two saturable absorber dye solutions, HITCI and DOTCI, have been employed to provide hybrid mode-locking of a cw dye-aser operating over the 770-781 nm and 710-718 nm spectral ranges respectively as discussed by the authors.

Journal ArticleDOI
TL;DR: In this paper, a Photochron IIA Synchrosan streak camera with picosecond resolution was used to give time resolved detection of the first four order Stokes-Raman pulses at 1.12, 1.18,1.24, and 1.31 μm.
Abstract: Stimulated Raman scattering of Q -switched and mode-locked Nd:YAG laser pulses at 1.06 μm in a 120-m-long single-mode fiber has been investigated experimentally. A Photochron IIA Synchrosan streak camera with picosecond resolution was used to give time resolved detection of the first four order Stokes-Raman pulses at 1.12, 1.18, 1.24, and 1.31 μm. It has been shown that in traversing the fiber the fundamental and the first two order Stokes were substantially shortened and that the Stokes pulses were asymmetrical with sharper leading edges.

Journal ArticleDOI
TL;DR: In this article, the spectrum and dispersion parameters of a synchronously mode-locked Rhodamine B dye laser were optimized to generate pulses as short as ∼270 fs without using any saturable absorber or pulse compressor.

Book ChapterDOI
James Taylor1
01 Jan 1986
TL;DR: Taylor as discussed by the authors is a simulation-based nonlinear control system analysis and design environment based on sinusoidal-input describing function (SIDF) methods, which can treat general nonlinear systems, with no restrictions as to system order, number of nonlinearities, configuration, or nonlinearity type.
Abstract: We report on recent progress in developing a computer-aided nonlinear control system analysis and design environment based on sinusoidal-input describing function (SIDF) methods. In particular, two major additions have been made to our CAD software for nonlinear controls during 1984: a simulation-based program for generating amplitude-dependent SIDF input/output models for nonlinear plants, and a frequency-domain nonlinear compensator design package. Both of these are described in detail. This software can treat very general nonlinear systems, with no restrictions as to system order, number of nonlinearities, configuration, or nonlinearity type. An overview of the application of this software to the design of controllers for a realistic, nonlinear model of an industrial robot is presented in Taylor (1984). which serves to illustrate the use of these tools. Based on the software presented here, the use of SIDF-based nonlinear control system analysis and design methods is substantially easier to carry out.

Journal ArticleDOI
TL;DR: In this article, the authors used four interferometers (d = 0.5 mm, corresponding to ~ 850 m of quartz) to compress negatively chirped fragments of a high-power pulse depleted by Raman scattering in a fibre.
Abstract: We have previously used four of the interferometers (d = 0.5 mm, corresponding to ~ 850 m of quartz) to compress negatively chirped fragments of a high-power pulse depleted by Raman scattering in a fibre [6]. Compression factors of x 4 were obtained. The dispersion equivalent of 850 m quartz agrees well with the theoretical estimate by Dianov et al. [7] which showed that ~ 1 km of fibre would be required for compression of the fragments as described in [6]. For the experimental results presented here, the pulse durations were monitored in real time using a synchronously operated streak camera. A schematic of the experiment is shown in Fig. (2) m = 0, 1,2, ... wto = 2mn ± f3

Book ChapterDOI
01 Jan 1986
TL;DR: In this paper, an architecture for an expert system to assist a control engineer in coping with the complexity of computer-aided control engineering, with major emphasis placed on implementation, is discussed.
Abstract: We discuss an architecture for an expert system to assist a control engineer in coping with the complexity of computer-aided control engineering, with major emphasis placed on implementation. Issues to be treated include: rule base organization, knowledge to be contained in various rule bases, a mechanism to switch between rule bases as the problem solution proceeds, a protocol to coordinate the symbolic computations of the inference engine with the numeric computations of conventional analysis and design software, support of non-monotonic reasoning to permit retracting and revising steps in the design process, and conversion between numeric and symbolic data. We present our approach to these issues, and give examples of rules used to represent operational knowledge and to guide the solution of the problem.

Journal ArticleDOI
TL;DR: In this paper, the pump source for a novel optically biased synchronously excited dye laser and a high-power dye laser respectively were used as the pump sources for a Q-switched and mode-locked system.
Abstract: Temporally compressed pulses from a c.w. mode-locked Nd: YAG laser or Q-switched and mode-locked system have been used as the pump source for a novel optically biased synchronously excited dye laser and a high-power dye laser respectively. The former dye laser produced pulses of 1·5 ps and an average power of ~ 10 mW, while the latter generated 4 ps pulses with peak powers of 20 kW in an unoptimized cavity.


Journal ArticleDOI
TL;DR: In this paper, the amplified output from a GaAs photoconductive device was used to drive a synchronously operated Photochron IIA streak camera at 300MHz sweep rates with a temporal jitter of ±6 ps.
Abstract: Excited by the frequency doubled optically compressed 10‐ps pulses from a cw mode‐locked Nd:YAG laser, the amplified output from a GaAs photoconductive device was used to drive a synchronously operated Photochron IIA streak camera at 300‐MHz sweep rates. A temporal jitter of ±6 ps was measured which was limited by the driving laser pulse width and amplitude stability.

Journal ArticleDOI
TL;DR: In this paper, a Monte Carlo simulation method is presented for calculating line shapes for charged-particle analyzers with cylindrical symmetry, which can be used for the design of any analyzer having axial symmetry.
Abstract: A Monte Carlo simulation method is presented for calculating line shapes for charged‐particle analyzers with cylindrical symmetry. Either isotropic or cosine angular distributions of charged‐particle emission can be simulated. Application of this technique is demonstrated by simulation of the line shape exhibited by the Helmer planar‐retarding‐grid analyzer. Ray tracing is used to determine the origin of line‐shape asymmetry, new entrance optics are designed, and subsequently, a simulation is used to optimize the dimensions of the analyzer apertures and beam stop to produce a symmetric nearly Gaussian line shape. This result is then verified experimentally. Although the simulation method is applied to a specific problem, it should prove to be of value for the design of any analyzer having axial symmetry.

Journal ArticleDOI
TL;DR: In this article, the authors reported the first continuous output trains of subpicosecond pulses with two saturable absorber dyes, DOTCI and HITCI, in the 727-740 nm and 762-778 nm spectral regions respectively.
Abstract: Passive mode-locking of a c.w. rhodamine 700 dye laser is reported for the first time. Continuous output trains of subpicosecond pulses have been obtained with two saturable absorber dyes, DOTCI and HITCI, in the 727–740 nm and 762–778 nm spectral regions respectively. By the addition of a fast recovery time dye (DCI) to the DOTCI saturable absorber solution, pulses as short as 350 fs at 740 nm have been generated in a linear cavity configuration.