Showing papers on "Ultrashort pulse published in 1972"

Fluctuation mechanism of ultrashort pulse generation by laser with saturable absorber

Abstract: This paper presents a theoretical treatment of the fluctuation mechanism involved in the generation of picosecond laser pulses with saturable absorbers. The processes responsible for the shortening of the pulsewidth and for selection of the most intense pulse are treated. Some experimental results that confirmed the treatment are presented. The influence of inertia of saturable absorber and nonlinear losses (self-focusing and self-modulation) is discussed.

Experimental study of single picosecond light pulses

Abstract: Single picosecond light pulses from a mode-locked Nd:glass laser are investigated by several methods. Their temporal structure is studied by two-photon fluorescence. The frequency spectra are measured quantitatively. The energy distribution is simultaneously investigated by three-photon fluorescence, photoelectric measurements, and quantitative studies of the contrast ratio of the two-photon fluorescence. The pulse shape is measured using a method based on the stimulated Raman effect. It is observed that the pulses are weakly asymmetric-the pulse decay is slower (exponential) than the pulse rise (Gaussian). Bandwidth-limited pulses of 4-8 ps are present in the leading part of the pulse train. Substantial frequency broadening develops as the pulse train reaches its maximum and a subpicosecond structure is formed in the trailing part of the pulse train.

Method and apparatus for distance measurement

Abstract: There is disclosed a range finder operating on the principle of finding the range of an object by measuring the time between transmission of a pulse towards an object and the reception of the reflected pulse. Errors in the range measurement caused by the different half-rise times of reflected pulses of different amplitudes are avoided by using only a reflected pulse of a predetermined constant magnitude as a measuring pulse for range determination. The desired magnitude of the measuring pulse is obtained by altering the power of the transmitter and/or by changing the amplification of the receiver. The use of pulsed laser range finders operating in the infra-red region of the spectrum is referred to for generating pulses as well as other sources of pulsed energy.

Optical pulsewidth measurement using self-phase modulation

Abstract: Simple expressions are given that relate the duration of a self-phase modulated ultrashort optical laser pulse to the number of minima (or maxima) and the maximum Stokes (or anti-Stokes) frequency shift of its spectrum.

Method of and apparatus for generating ultra-short time-duration laser pulses

Abstract: Both a method and an apparatus are disclosed for generating laser pulses having a time duration on the order of subnanoseconds. These light pulses also have a high output power. They are generated by causing a laser to lase and removing the bulk of the radiation contained in the laser cavity. The remaining radiation or light extends over only a short length of the cavity. This light pulse is mode locked, that is it consists of individual Fourier components of the proper phase so that the short light pulse retains its shape while being amplified again in the laser cavity. This short-duration light pulse may then be made to issue from the cavity. Alternatively, the amplified light may be made to issue as a pulse train or set of pulses. Finally, a single pulse may be utilized for mode locking another laser where the ultra-short time-duration pulse may be amplified again. This may be considered priming and subsequent mode locking of the second laser.

Variable Ultrafast Photographic Shutter

Abstract: We propose an ultrafast shutter, based on the saturable properties of polymethine cyanide dyes, with a variable shutter speed of 10–40 psec and more. With this, one can measure the pulse duration of the mode‐locked ruby laser pulse. We can also deduce the fluorescence decay time of these solutions employed.

Generation of single l-ns pulses at 10.6 µ

Abstract: Single pulses of 1-ns duration have been generated at 106-μ wavelength using a pulse-selection scheme in conjunction with an actively mode-locked CO 2 TEA oscillator The experimental setup and its operating characteristics are presented A technique is described, which yields pulse extinction ratios of approximately 900:1

Passage of an ultrashort coherent light pulse through a semiconductor

Abstract: A theory is given of the resonant interaction between an ultrashort coherent light pulse and a semiconductor, which occurs when the pulse duration is less than the polarization or phase memory relaxation time. It is shown that, under certain conditions, a stationary 2? pulse can form. Numerical estimates of the velocity of propagation of a stable pulse are obtained for a typical semiconductor.

An RF Time-Domain Reflectometer Not in Real Time (Short Papers)

Abstract: A nanosecond RADAR system was developed, in which each line of the pulse spectrum was radiated in turn, their reflections measured and stored in a computer, and finally added up to compute the echo.

Double pulse laser

Abstract: Double pulses are produced from a single laser by generating two successive optical pumping pulses from the same flash lamp and Qswitching once after each pumping pulse prior to the next pumping pulse.

The effect of dispersion on pulse distortion in optical filaments

Abstract: It is shown theoretically that short intense light pulses of optical filaments can form an optical shock at the leading edge in the usual Kerr liquids. Under certain conditions an extremely sharp spike occurs at the front of the pulse.

Pulse processing system

Abstract: A pulse counting system with improved energy resolution is disclosed having dual channels for pulse processing at different rates and a pulse pileup detector to select which channel is utilized. Pulse input is delayed until the pileup detector can determine if any pulse is so closely followed in time by a second pulse to constitute pulse pileup. If no pulse pileup is detected, the slower channel is selected. The slow channel clips the pulse to a relatively wide pulse width to retain good energy resolution. If pulse pileup is predicted, the fast channel with correspondingly shorter pulse width is selected to improve resolution in respect to time. The output of the two channels are transmitted to a pulse height analyzer for interpretation.

A versatile pulse programmer for pulse nuclear magnetic resonance spectroscopy

Abstract: A digital pulse programmer producing the standard pulse sequences required for pulse nuclear magnetic resonance spectroscopy is described. In addition, a 'saturation burst' sequence, useful in the measurement of long relaxation times in solids, is provided. Both positive and negative 4 V trigger pulses are produced that are fully synchronous with a crystal-controlled time base, and the pulse programmer may be phase-locked with a maximum pulse jitter of 3ns to the oscillator of a coherent pulse spectrometer. Medium speed TTL integrated circuits are used throughout.

Optical generation of intense picosecond electrical pulses

Abstract: Electrical pulses, 4 A in 10 psec, have been generated by rectification of 1.06‐μm pulses in LiTaO3: Cu++. Their amplitude and duration were measured by photographing the birefringence induced by the pulses propagating along an electro‐optic transmission line illuminated transversely in a Pockel's cell arrangement. The principal mechanism responsible for the generation is the macroscopic polarization resulting from the difference in dipole moment between the ground and excited states of the absorbing Cu++ impurities.

Frequency Modulation and Transient Effects in the Resonant Propagation of Coherent Light Pulses

Abstract: A theoretical analysis of the propagation of near resonant and linearly chirped light pulses through a resonant medium is presented under the restriction that the pulses are far enough off resonance or weak enough so that they do not significantly alter the atomic populations. If the pulses are of duration comparable to or less than the phase memory time T2 of the atoms, it is found that the transient response of the medium gives rise to amplitude- and phase-modulating effects. Analytic solutions are presented to describe the propagation of an off-resonant pulse which is very short compared with T2 and an off-resonant rectangular pulse. The evolution of a Gaussian pulse having a positive linear chirp is studied numerically.

Laser arrangement for creating a stable pulse with short pulse spacings

Abstract: A laser arrangement for creating a stable pulse with short pulse spacings, comprising an active laser medium, a modulator, a mode selector and an optical resonator, wherein the mode selector is an optical filter for a mode group.

Dynamic spectroscopy of picosecond pulses

Abstract: A device for producing a dynamic spectrogram of a picosecond pulse of electromagnetic radiation is described. A technique for recording the component wavelengths and their relative intensity as a function of time for the pulse is also discussed.

Shaping Fast Rise-Time Pulses with Tapered Transmission Lines

Abstract: For the purpose of checking very fast time-domain reflectometer (TDR) systems it is desirable to have a fast rise-time pulse whose parameters are known. A means for obtaining pulses meeting these requirements has been achieved by suitably tapering the inner conductor of a rigid coaxial transmission line having air dielectric, commonly referred to as an air line. The air line is driven with a pulse that has a very fast rise time compared to the rise time of the expected output pulse. A reflected pulse will be generated whose shape is dependent upon the taper of the inner conductor. A procedure is outlined for determining the proper taper to shape the leading edge of the reflected pulse to match any continuous single-valued function. Air lines that were designed and built for producing a pulse whose leading edge is a linear ramp, a truncated Gaussian function, and the integral of a truncated Gaussian function are discussed and traces of these pulses are shown. The problem of re-reflections due to the multiple discontinuities along the air line was analyzed by means of a computer. This program is described. The effect of the driving-pulse parameters on the reflected pulse is analyzed on a theoretical basis. Rise time, pulse shape, and aberrations such as overshoot and ringing of the driving pulse are considered in this analysis.

A time domain method for producing pulse compression in a plasma

Abstract: The propagation of a rectangular envelope RF pulse in a lossless homogeneous isotropic plasma is considered. It is desired to produce pulse enhancement by an appropriate choice of the phase variation. A time domain technique is developed for choosing the phase. The resulting enhancement is greater than that reported previously.

Observation of transient behavior of picosecond laser pulses

Abstract: Dynamic behavior of picosecond pulses from a Q‐switched ruby laser is observed by using a high‐speed oscilloscope and a silicon photodiode. At the early portion of the Q‐switched pulse envelope, the mode locking is not perfect and the picosecond pulse has a few peaks. On the other hand, at the end of the Q‐switched pulse envelope, the background pulses are completely suppressed, so that the mode‐locked pulse has a single peak. The temporal compression of the picosecond optical pulse by passing through an optically active Kerr liquid is also observed.

Description of laser pulses using Fourier analysis

Abstract: The output of lasers in various modes of operation is described in a unified way, using Fourier analysis. A novel model for treating an active Fabry-Perot cavity, including the case of high gain, is developed resulting in a more exact expression for the spectral width of the cavity modes. Simple mathematical tools are given to relate the observed pulse length with the average gain and with the initial population inversion in the laser medium. It is shown that lasers with homogeneously broadened spectral lines have cavity modes of equal width and that if the modes are locked together the resulting ultrashort pulses are of equal duration. For lasers with inhomogeneously broadened spectral lines the cavity modes vary in width along the gain curve and, when mode-locked, the ultrashort pulses increase monotonically in duration along the emitted pulse train.

Pulse train processing system with discrimination against noise for use with pulse width modulation

Abstract: System for separating pulses containing information in a pulse width modulated pulse train, wherein the leading edges of the pulses occur at a fixed repetition rate. Noise which occurs on the leading edge of the pulses is reduced by slicing the fixed position leading edges. A gating wave stabilized by the received pulse train, and which is insensitive to wide band noise, opens a gate for the pulses after the leading edge of each pulse, and closes the gate before the leading edge of the next pulse. A plurality of gates can be provided to separate pulse trains which are multiplexed to form a composite pulse train. The gates do not affect the pulse width modulation represented by the position of the lagging edges of the pulses and reduces the noise accompanying the demodulated signals.

GHz-rate, hundred-V pulse generator

Abstract: A high-efficiency microwave avalanche diode has been used to generate high-power GHz-rate pulses. Pulse amplitude is 125 V into a 50-ohm load. Pulsewidth is 400 ps, risetime 100 ps, and falltime 200 ps.