Showing papers on "Ultrashort pulse published in 1973"

Solitons in nonlinear optics. I. A more accurate description of the 2π pulse in self-induced transparency

Abstract: A more accurate description of the 2 pi pulse of self-induced transparency is obtained. This is an exact solution of an approximate form of the Maxwell-Bloch equations in which only backscattering is neglected; the equations are valid at densities less than about 1018 atoms cm-3. At such densities the 2 pi sech pulse of McCall and Hahn (1967, 1969) remains a good approximate well into the picosecond range. The more accurate solution is chirped by a factor proportional to the square of the ratio of the spectral width of the pulse to its carrier wave frequency. The stability of this pulse solution and other N soliton solutions of the approximate Maxwell-Bloch equations is demonstrated.

Radio Frequency Pulsewidth Modulation

Abstract: The width of a train of square pulses can be varied to produce a modulated carrier at the pulse repetition frequency. When the pulse train is generated by switching (class D) transistors, highefficiency operation is possible. The efficiency of this type of amplifier can be significantly higher than that of conventional pulsewidth modulation amplifiers, since the switching rate is reduced. In addition, the spectrum of a bipolar pulse train so modulated has the highly desirable property of all spurious products being band limited near the odd harmonics of the carrier.

The role of linear dispersion in plane‐wave self‐phase modulation

Abstract: It is shown by computer calculation that linear dispersion and self‐phase modulation can strongly couple to influence pulse propagation phenomena. Pulses become distorted temporally as they propagate, and, under certain circumstances, optical shocks can form on the leading edge (in time) of a pulse. Some interesting cases are considered for pulse propagation in CS2. The pulse compression scheme of Fisher, Kelley, and Gustafson is modified to take self‐dispersive effects into consideration.

A new approach to picosecond laser pulse analysis shaping and coding

Abstract: An optical device exhibiting both a time versus frequency and a space versus frequency dispersion has made possible the performance of 1) the pulse by pulse spectrum analysis of mode-locked Nd-glass laser trains and 2) the shaping of these pulses by a completely passive process. The relatively poor performance of this spectrum analyzer (7 spectral lines resolved) is essentially due to the rise time of the photodetection setup utilized in the experiments. The shaping consists in a preliminary pulse expansion (from picoseconds to nanoseconds), which gives linear FM long pulses whose envelopes are then modulated with a rise time of 50 ps by a spectral filtering simply obtained by diaphragms and neutral filters.

The length dependence of pulse spreading in the CGW-Bell-10 optical fiber

Abstract: Previous measurements of pulse broadening in the CGW-Bell-10 optical fiber showed very low dispersion ( 550 m) which are of practical significance.

Investigation of the characterstics of a mode-locked Nd:Glass laser with the aid of a picosecond streak camera

Abstract: An infrared-sensitive streak camera, capable of resolving optical pulses of durations of ∼3 ps, has been used to analyze the temporal development of the individual picosecond pulses in a mode-locked pulse train. A progressive increase in the duration of the individual pulses throughout the pulse train is observed, the rate of increase in the pulse duration being an approximate quadratic function of the optical field. In addition, temporal analysis of the laser output signal, dispersively delayed with the aid of a grating pair, confirms the existence of phase-modulation effects during the development of the mode-locked pulse train.

Study of Self-Focusing and Self-Phase-Modulation in the Picosecond-Time Regime

Abstract: Study of the propagation of a single picosecond pulse of a mode-locked Nd-glass laser in CS2 nitrobenzene and toluene by observations of the birefringence and spectral changes in self-focused laser light. Multiple second-harmonic probing beams are used for birefringence measurements in a single IR pulse in various portions of the active cell. The orientational Kerr effect is found to be the prime factor of induced birefringence in nitrobenzene and toluene. The results for CS2 are also consistent with this mechanism and show that the duration of an IR pulse in the focal volume is less than that of the incident pulse. The properties of beams which are focused within the cell by an external lens are also investigated.

Apparatus and systems using broad band radiation pulse source

Abstract: Picosecond pulses produced from mode-locked lasers are passed through high Raman coefficient media in which a variety of Stokes and anti-Stokes frequency transitions result. The exiting pulse, which may have an envelope of the same order of magnitude time duration, contains a virtual continuum of wavelengths. The "white" pulse so produced is then spatially and/or phase divided into a series of "component" pulses each containing distinct spectral portions of that contained within the white pulse. Component pulses are then processed, for example, by passage through a sample or by passage through a modulator. Information so imparted, generally taking the form of an amplitude change, may serve to spectrally identify the nature of the sample or may serve a communications function.

Influence of saturable-absorber transmission and optical pumping on the reproducibility of passive mode locking

Abstract: Following the Letokhov model for passive mode locking, which describes the buildup of ultrashort light pulses from noise, the statistical behavior of passive mode locking and the discrimination characteristics of the nonlinear absorber are examined. The probability W of having a second ultrashort pulse of a certain intensity within the resonator round-trip time 2t_{L} is described. This probability is essentially a function of the initial dye absorption coefficient x 0 and a pumping parameter t p that is a measure for the excitation rate of the optical pump. Experimental results are reported that confirm these theoretical considerations.

Ultrafast optical Kerr effect in CS2 at 10.6 μm

Abstract: This letter reports experiments that used a mode‐locked TEA CO2 laser to modulate a cw He–Ne laser. This technique uses the optical Kerr effect in CS2. The optical Kerr coefficient, n2, at 10.6 μm is estimated from our data to be approximately 10−20 m2/V2.

Improved apparatus for lengthening laser output pulse duration

Abstract: A system for lengthening the pulse output of a relatively short duration of laser radiation from a pulse laser oscillator of high spectral purity without loss of the spectral purity. The laser system employs a regenerative laser amplifier and a pulse output configuration which provides isolation from the pulse input. The configuration of the laser amplifier permits multiple traversals of the laser amplifier to provide more efficient amplification for each oscillator pulse.

Effect of rotational level coupling on pulse sharpening in CO 2 amplifiers

Abstract: The linear (small-signal) and nonlinear temporal response of CO 2 laser media was studied. Experimental results of the amplification of optical pulses whose duration is comparable to the inverse gain-bandwidth of the amplifying medium are described. Pulse narrowing, a consequence of nonlinear amplification, was observed. Computer calculations based upon a two-level model incorporating phenomenologically CO 2 rotational level coupling are compared with experimental observations.

Driver circuit for pulse modulation of a semiconductor laser

Abstract: A pulse modulation driver circuit for a semiconductor laser is disclosed which discriminates among input pulse signals composed of binary codes to detect the occurrence of a pulse having a code of '''' 1'''' following a pulse having a code of ''''0''''. Detection of this pattern is used to control the driver to increase either or both the width or peak value of the pulse having a code of 1. The effect of this is to eliminate a pattern effect in the light emitted by the semiconductor laser caused by an attenuation of the population inversion in the laser.

Ionospheric dispersion of electromagnetic pulses

Abstract: When an electromagnetic pulse having a Gaussian envelope is passed through the ionosphere it remains a Gaussian pulse; however, its amplitude is reduced and its pulsewidth is increased with respect to what these parameters would be for free space propagation. It is pointed out that if this Gaussian pulse is chirped (i.e., if it is given a linear FM), then after passing through the ionosphere and following the pulse compression in the receiver, the signals envelope is still Gaussian. Furthermore, when the bandwidths for both signals are the same (or equivalently, when the pulsewidth of the compressed transmitted chirped pulse is the same as that of the transmitted unchirped Gaussian pulse) the amplitude degradation and pulsewidth spreading are identical for both signals. This not too surprising result applies as long as the time-bandwidth product is large enough for the chirped signal. The results obtained for chirped Gaussian pulse are compared, as to the pulse distortion introduced by the ionosphere and available bandwidth of the ionosphere, with the results obtained in the literature for other waveforms. It is pointed out that the amplitude degradation and pulsewidth spreading for a chirped signal having a 40 dB Taylor or Hamming weighting is about the same as obtained with the chirped pulse having a Gaussian envelope as long as the compressed pulsewidths of the transmitted signals are identical. Finally, the numerical results obtained previously in the literature are presented in a more convenient form.

Electron-beam-semiconductor application to laser pulsing

Abstract: A high-current electron-beam-semiconductor pulse amplifier was used to modulate an injection laser. Results show the capability of infrared output having faster rise time and shorter duration than can be obtained with commonly used types of pulse drivers.

A computational theory of short pulse generation

Abstract: The semi-classical equations for the electric field and population inversion in a two-level medium are simplified for the case of a saturable absorber cell which is shorter than the length of fluctuations in the optical-pulse envelope. The spatial coordinates in the cell are effectively lumped, and the integration is reduced to the one dimension of time. The pulse is passed through an amplifying medium and frequency selective elements by a fast Fourier transform into its spectral components. The case of pulse formation in a ruby laser, starting from a noise fluctuation is computed for the parameters of a recently reported accurate measurement of pulse duration. Good agreement is obtained with experiment. Finally, a pulse length is predicted for a cavity containing an etalon which cancels gain narrowing.

Characterization of large-aperture CO 2 amplifier

Abstract: Detailed, spatially resolved gain measurements have been made on a UV preionized 9 \times 9 \times 50 -cm atmospheric pressure discharge

Compression and shaping of pulses from high power solid state lasers

Abstract: Pulse compression is discussed as one possible means to overcome the pulse energy limitations imposed by self focusing in high power solid laser systems. Linear and nonlinear processing techniques are compared. In linear systems, a short oscillator pulse is expanded, chirped, and shaped entirely by linear dispersive and filter elements. It is then re-compressed after being amplified. In nonlinear systems, the oscillator pulse is long, and the chirp is created by self phase modulation in a Kerr liquid. A comparison is made between the Gires-Tournois interferometer and the grating pair for use in high energy pulse compression.

Propagation of an intense Gaussian laser pulse in air

Abstract: A numerical solution of the nonlinear macroscopic laser‐fluid equations for propagation of a Gaussian laser pulse in air is described The concept of ``utility analysis'' of numerical differencing schemes is introduced With the computation scheme used, the laser pulse could be followed for only 10−5 sec; so enormous energy was put into the pulse to enhance the interaction with the fluid Thus the initial pulse distortion could be observed Analytical evaluation of the computer results produces a detailed quantitative check and suggests that a combination of analytic and numerical methods would allow a pulse to be conveniently followed for much longer periods of time The preceding paper by the same authors describes various types of instabilities to be anticipated for propagation over long periods of time or with large powers

Gigahertz-rate 100-V pulse generator

Abstract: A high-density electron-hole plasma generated within a high-efficiency avalanche diode induces a sharp, high-voltage pulse on a transmission line. A novel gigahertz-rate pulse generator has been constructed utilizing the high- efficiency microwave avalanche diode. An impedance discontinuity within the circuit gives rise to a sharp pulse with undistorted waveform, which keeps retriggering the diode for a self-excited pulse generation. The peak- to-peak amplitude of the pulse is 125 V into a 50-/spl Omega/ load. The pulsewidth is 400 ps, the rise time 100 ps, and the fall time 200 ps.

Pulse broadening in multimode fibres excited by GaAs lasers

Abstract: Pulse dispersion in multimode fibres depends strongly on mode excitation at the input and mode coupling in the fibre. Measurements on fibres of up to 160 m in length are given: pulse dispersion seems to follow a square-root law with the lengths of the fibres.

Gas breakdown laser pulse selector

Abstract: A single pulse or a selected number of pulses from a mode-locked laser may be isolated from the laser pulse train. A gas breakdown cell is positioned in the path of the laser pulse train and the laser pulses are focused within the cell. When the intensity of the pulses exceeds the gas breakdown threshold, a plasma is generated which acts as a highly reflecting mirror. In the preferred embodiment using a ring cavity geometry, the laser pulse train travels through the cell in one direction and the gas pressure in the cell is adjusted so that breakdown of the gas occurs near the peak intensity of the traveling pulse. The breakdown plasma reflects a portion of the breakdown pulse which propagates in the opposite direction from the original pulse train. A single nonmode-locked laser pulse may be shaped by using the reflection capabilities of the breakdown plasma formed in a gas cell.

On the generation of short light pulses with reference to the ruby laser

Abstract: The results are presented of an experimental and theoretical study of short light pulse generation in a ruby laser. Initial work on the construction of a 'mode-locked' ruby laser led to the invention of a new type of laser reflector based on the non-resonant interference of components of the laser beam. An accurate measurement was made of pulse lengths using the two-photon fluorescence technique. An automated apparatus then allowed a wide range of accurate measurements to be made under various conditions of general-ion, showing that a compound solution of saturable absorbers, or a suitable etalon, could lead to a substantial reduction in pulse length. The shortest pulse generated had a duration or 15ps. A threshold intensity for pulse substructure was observed. Below this intensity, the shape and duration of the pulse were accurately described by a computational theory of pulse generation from spontaneous emission noise. The important role of the laser linewidth was brought out, and further evidence adduced for excited state absorption in the saturable absorber, DDI. The effects of the fast nonlinear refractive index of sapphire were included, at first in a model for plane waves, and finally, a model which included a limited degree of self-focussing. It was shown that the spectrum rapidly evolved until its width was of the order of the laser linewidth, when parts of the pulse became strongly attenuated and substructure formed in the pulse on the scale of the inverse of the linewidth. It was found that the model with self-focussing gave a sharp 'threshold' for the formation of substructure, and also gave an integrated pulse spectrum in excellent agreement with experiment. The value of nonlinear index which best fitted the experimental threshold was n2 = 0.7 x 10-13 e.s.u., on the assumption of an electronic distortion mechanism for the O-ray polarisation in sapphire. Some general guidelines for the construction of short pulse lasers are given.