Showing papers on "Femtosecond pulse shaping published in 1986"

Characterization of the noise in continuously operating mode-locked lasers

Abstract: An experimental and theoretical investigation of the fluctuations of the pulses from continuous-wave mode-locked lasers is presented. It is shown that these fluctuations can be detected and quantitatively characterized from measurements of the power spectrum of the light intensity. Such power spectra can be measured with great accuracy by shining the laser output on a suitable photodetector and by processing the detector signal with the use of an electronic spectrum analyzer. Different types of noise such as fluctuations of the pulse energy, pulse repetition time, and pulse duration, can be readily recognized from their characteristic spectral signature. Experimental results of noise measurements are presented for a synchronously mode-locked dye laser pumped by an acousto-optically mode-locked argon ion laser, and also for a colliding pulse passively mode-locked dye laser.

Femtosecond optical ranging in biological systems.

Abstract: Optical ranging using femtosecond laser pulses and nonlinear-optical cross correlation is demonstrated for the investigation of the microstructure of biological systems. By using pulses of 65-fsec duration generated by a colliding-pulse mode-locked ring dye laser, a spatial resolution of less than 15 μm is achieved with a detection sensitivity to remitted signals as small as 10−7 of the incident pulse energy. This technique is applied to measure the cornea in rabbit eyes in vivo as well as to investigate the epidermal structure of human skin in vitro.

Observation of high-order solitons directly produced by a femtosecond ring laser.

Abstract: We report here the first experimental observation of $N=3$ solitonlike pulses generated by a passively mode-locked ring laser at 620 nm. The evolution of the pulse shape is recorded along the soliton period corresponding to about 2400 cavity round trips. Experimental indications of the soliton character of any pulse produced by this type of laser are also obtained. Properties of high-order solitons could offer new possibilities of intracavity pulse compression.

Compression of femtosecond optical pulses with dielectric multilayer interferometers

Abstract: The group velocity dispersion of a multilayer thin film Gires-Tournois interferometer used for reflection of ultrashort optical pulses can be continuously tuned from positive to negative values at an extremely low loss in pulse energy. Thus, this device can be applied for compression of femtosecond pulses independent of the sign of the frequency chirp by simple angle tuning of the interferometer. This has been demonstrated with up-chirped 210 fs pulses which have been compressed to an almost transform-limited duration of 115 fs.

Spectral extent and pulse shape of the supercontinuum for ultrashort laser pulse

Abstract: The pulse shape and the generated supercontinuum spectral distribution associated with the propagation of an ultrashort intense pulse in a cubic ( X^(3) ) nonlinear medium are obtained by solving the electromagnetic field wave equation using the method of multiple scales. New forms for the set of quasi-linear partial differential equations describing the system, pulse distortion, and the spectral extent of the supercontinuum are the focus of this paper.

Self-action of wave packets in a nonlinear medium and femtosecond laser pulse generation

Abstract: The review describes the present status of the physics of optical pulse self-action phenomenon. A brief analysis of linear propagation of ultrashort laser pulses in dispersive media and optical elements is given. Results on self-phase-modulation and on profile shock waves in media with various group velocity dispersion are presented. The problems of optical pulse compression and the possibilities to control their shape are discussed in detail. Particular attention is paid to the physical aspects of formation and interaction of optical solitons. Stochastic problems of temporal self-action are also discussed. In conclusion the promising directions in nonlinear optics of femtosecond laser pulses are discussed.

Subpicosecond pulse generation by a tandem-type AlGaAs DH laser with colliding pulse mode locking

Abstract: Experimental results of colliding pulse mode locking (CPM) of a double-contact AlGaAs DH injection laser with an external cavity are presented. The laser has two amplifying sections and a passive umpumped segment located between them which exhibited saturable absorption action. Ultrashort pulses propagating in opposite directions collided in the absorber and pulse shortening occurred. Bursts of 0.8 ps (FWHM) pulses at a 710 MHz repetition rate are obtained by means of CPM. The pulse duration is measured by a second harmonic generation correlation method and an ultrafast streak camera.

Optically biased tunable femtosecond dye laser and spectral windowing of the compressed second harmonic of Nd:YAG

Abstract: We describe a technique for enhancing tunable ultrashort pulse pumped dye laser performance based on the use of "long" pump pulses to optically bias the cavity toward minimal losses. Increases in dye laser output power of 155 percent and powers as high as 125 mW have been measured with pulse durations under 300 fs. Optical pulses as short as 180 fs are reported for this ultrashort pulse pumped dye laser oscillator. We also report the first measurements of the spectral windowing of compressed 532 nm pulses for temporal pulse shaping, in the optimal group velocity dispersion limit. Temporal pulse shaping is demonstrated with small losses in power and minimal pulse broadening.

Reflection of femtosecond optical pulses from multiple-layer dielectric mirrors--Analysis

Abstract: We present an analytical treatment of the reflection of femtosecond pulses from broad-band multiple-layer dielectric mirrors. In particular, closed-form expressions are given for the reflected pulse amplitude which includes the dispersive effect of the cubic phase term. It is shown that this term is still insufficient to accurately describe certain experimental results obtained with 20-fs optical pulses. We introduce an alternative technique which describes the phase branches analytically and yields accurate closed-form expressions for the reflected pulse amplitude in terms of complementary error functions having real or complex arguments.

Method and apparatus for editing particle produced electrical pulses

Abstract: Particle produced pulses (10, 12, 14) are evaluated on an individual basis for shape symmetry, with significantly asymmetric pulses, becoming subject to editing, ie exclusion Pulse symmetry is determined by measuring the areas (A, B) under the pulse before and after the first pulse before and after the first pulse amplitude peak (16, 20, 24) and then by comparing those pulse areas with respect to pre-established limits which are not based upon any of the pulses then being evaluted

Reduction of transient laser chirp in 1.5 µm dfb lasers by shaping the modulation pulse

Abstract: It is shown that the dynamic linewidth of 1.5µm ridge-waveguide distributed-feedback lasers can be reduced by appropriate shaping of the modulating current waveform. A theoretical model is used to predict the result of two different shaping techniques, both in terms of the optical pulse and spectral outputs, with the optimum conditions being derived for each shaping method. Experimental results confirm the theoretical predictions and demonstrate between 40% and 60% dynamic linewidth reduction with optimum shaped modulating pulses.

Suppression of the second intracavity pulse in a synchronously pumped dye laser

Abstract: The subject invention relates to method of suppressing one of the counterpropagating intracavity pulses generated in a dye laser synchronously pumped by the output of a mode locked Q-switched pump laser. The method includes extracting a portion of one of the pulses generated in the cavity such that the other pulse experiences a greater effective gain. The pulse with the highest effective gain will dominate the other pulse and at the steady state only one pulse will exist in the cavity. In the preferred embodiment, a double pass acousto-optic cell is used to extract the both the unwanted pulse and, at a later time, the high energy, useful pulse. In this case, maximum efficiency is achieved by placing the dye cell at one of a number of well defined locations within the optical cavity.

Device and method for signal transmission and optical communications

Abstract: An optical pulse having time-dependent spectral variation is modulated by a time-dependent signal so that, upon determination of the spectral content of the modulated pulse, a representation of the signal can be obtained. Frequency in the optical pulse preferably varies essentially unidirectionally, i.e., aside from noise, each frequency is encountered just once as, e.g., in a linear relationship. Such an optical pulse can be produced by passing a short laser pulse through a dispersive medium such as, e.g., an optical fiber whose zero-dispersion wavelength is away from wavelengths to be dispersed. Modulation of the optical pulse may be by electrooptic interaction. The technique can be used for the characterization of device and material responses; envisaged also are communications applications.

Generation of single short tunable UV pulses using a simple short-cavity dye laser.

Abstract: Generation of single, short, tunable UV pulses using a short-cavity dye laser (SCDL) with a novel simple cavity structure is described. A single 80-ps pulse has been obtained at the 616-nm wavelength from a rhodamine 640 dye laser pumped with a 2-ns N2 laser pulse. By amplifying and subsequent frequency-doubling, a 90-ps 308-nm pulse was generated, which can be used as a short-duration XeCl excimer laser source. The temporal characteristics coupled rate equations.

Semiconductor laser light pulse generator

Abstract: PURPOSE:To reduce the influence of relaxation oscillation and obtain a nearly flat light pulse by a method wherein a light pulse which is emitted from a semiconductor laser and contains the relaxation oscillation is divided into a plurality of light pulses and, after a required time difference is provided between the respective divided light pulses in accordance with the relaxation oscillation frequency of the semiconductor laser, the respective pulses are synthesized. CONSTITUTION:A light delay means 15 is, for instance, an optical fiber or an optical waveguide. A semiconductor laser 11 for modulation is driven by a modulating semiconductor laser driving pulse 12 and emits a light pulse 13 containing relaxation oscillation. The light pulse 13 is divided into two components by an optical divider 14. One component is delayed by about a half of the relaxation oscillation period by the light delay means 15 to become a light pulse 18 and the other is not delayed and becomes a light pulse 17. The light pulse 17 and the light pulse 18 are synthesized by a photocoupler and outputted as a light pulse 19. By superposing the respective divided light pulses with the time difference so as to cancel the oscillations of each other, i.e. by superposing the oscillations with the phases opposite to each other, the influence of the relaxation oscillation can be reduced.

Generation of controlled-duration ultrashort pulses in a passively mode-locked YAG:Nd3+ laser

Abstract: The results are given of an investigation of a simple method for generating controlled-duration ultrashort pulses in a YAG:Nd3+ laser, passively mode-locked by a nonlinear filter with saturable absorption. The physical basis of the duration control is a variable initial transmission of the filter and the predominance of the action of temporal pulse compression by the nonlinear filter over the pulse broadening factor during the linear amplification stage in the active medium and corresponding spectral narrowing. The technical realization of the method of controlling the duration of ultrashort pulses is based on the use of a polymer switch utilizing dye No. 4363, an analog of No. 3274, and made in the form of a wedge. A service life was achieved in which ~104 pulses were generated at a single point in the switch when the pulsetrain energy was ~2 mJ. The range in which the duration of ultrashort pulses from the YAG:Nd3+ laser could be controlled was 15–100 psec, with practically 100% reproducibility of lasing of a single pulse per axial period. The 100% probability of isolating a single ultrashort pulse per period was due to the mode self-locking in the free-lasing regime.

Microbubble Response to Finite Amplitude Waveforms

Abstract: Prediction of the response of gaseous micronuclei to ultrasonic waves is complicated by the finite amplitude distortion associated with high intensity acoustic outputs. Typical finite amplitude pulses consist of a sharp positive spike followed by a comparatively small, slowly varying negative pressure. This paper computes the response of microbubbles to acoustic fields which have these temporal characteristics. The reaults show that (a) neither the instantaneous intensity nor the maximum intensity of the distorted pulse are good predictors of bubble response, (b) the shape of bubble response is more influenced by the negative extreme than the positive spike of the distorted pulse, (c) the harmonics components appearing in the distorted pulse have little effect on the bubble respome.

Arbitrary pulse shapes in the near-resonance Kapitza-Dirac effect.

Abstract: In a recent Letter Gould, Ruff, and Pritchard reported the first quantitative comparison between theory and experiment for Kapitza-Dirac scattering of an atomic beam from a standing wave of light. Their discussion was based on an educated guess concerning the effect of laser beam cross-sectional shape. They concluded that the observed fractions of the atoms that had received even multiples of the photon momentum could be brought in agreement with the theory only if half of the actually measured light intensity was employed in the calculations. In this Comment we point out that their guess, in fact, produces the exact result, and argue that the assumptions of their theory cannot be responsible for such a discrepancy. When the center-of-mass motion in the direction of the laser beams is included, in the notation of Ref. 1 the Schrodinger equation for the amplitudes of the ground (1) and excited (2) states reads

Shaping of the laser pulse time profile by saturable filters

Abstract: A study was made of the possibility of altering the time profile of laser radiation pulses in neodymium-glass amplifying systems by the use of saturable LiF filters. The use of these filters in an UMI-35 unit made it possible to reduce the peaking of a laser pulse which was observed on saturation of the active-element gain.

Frequency Spectrum of Optical Free Induction Decay Ultrashort CO 2 Laser Pulses

Abstract: The optical free induction decay (OFID) method has been quite successful in generating high power picosecond CO2 laser pulses with continuously variable pulse durations. Recently, these OFID pulses have been applied to the study of free electron absorption in semiconductors, pulse width dependence of the absorption spectra of polyatomic mole­ cules such as C3F7I, and in the measurement of multiphoton absorption in InSb. In the interpretation of the data in these experiments, a laser linewidth of ~ l cm was always assumed. For a quantitative interpretation of the pulse width dependence of many coherent interaction phenomena, it is important to calculate the laser line shape accurately. We have recently analyzed the OFID laser system in terms of its pulse width characteristics. It was shown that a FWHM of 22-150 ps could be obtained by varying the CO2 gas pressure in the hot resonant absorber. In this letter, we shall present calculations of the OFID pulse spectrum for various laser pulse durations. As discussed in Ref. 5, the truncated CO2 pulse can be regarded as a half Gaussian due to the T E M 0 0 Gaussian spatial profile: