Showing papers on "Ultrashort pulse published in 1987"

Ultrashort pulse propagation, pulse breakup, and fundamental soliton formation in a single-mode optical fiber

Abstract: The propagation of ultrashort (0.83 ps), intense dye laser pulses through a single-mode optical fiber is investigated. The input wavelength is tuned in the vicinity of the zero dispersion wavelength of the fiber. Although the input power is sufficient to generate solitons of up to the tenth order we do not observe the formation of high-order solitons. Instead, the input pulse breaks up temporally and spectrally after an initial stage of narrowing, and an ultrashort Stokes pulse is formed which shifts continuously to lower frequencies with increasing fiber length. The parameters of this pulse closely correspond to those of the fundamental soliton solution of the nonlinear Schroedinger equation. Using fiber lengths from a few meters up to 1 km the resulting pulse durations lie between 55 and 410 fs and the corresponding wavelengths between 1.36 and 1.54 μm. Numerical simulations solving a modified nonlinear Schroedinger equation including higher order dispersion and the Raman effect are in good agreement with the experimental results. It is shown that the principal soliton pulse shaping mechanisms are pulse narrowing and the soliton self-frequency shift.

Subpicosecond gain dynamics in GaAlAs laser diodes

Abstract: Ultrafast gain dynamics in GaAlAs diode amplifiers have been studied using 100 fs optical pulses. Pulse propagation through the amplifier resulted in temporal broadening and pulse shaping due to both gain saturation and material dispersion. Pump‐probe experiments indicate the presence of two processes contributing to the gain dynamics but give no evidence of spectral hole burning. A dynamic carrier heating model is presented to explain all of the observed gain nonlinearities, and the implications of our results on the dynamic response of laser diodes are discussed.

Cross-phase modulation in optical fibers

Abstract: When pulse pairs copropagate in a fiber, each pulse chirps the other through cross-phase modulation (XPM). In particular, XPM causes spectral broadening of signal pulses during Raman or parametric optical pulse amplification. We have studied XPM experimentally in the fiber Raman amplification soliton laser. We show that experimentally observed spectra can be explained by a simple model that concentrates on the phase change as a function of pulse walk-off.

Ablation and etching of polymethylmethacrylate by very short (160 fs) ultraviolet (308 nm) laser pulses

Abstract: The effect of pulse width on the ablation of polymers has been extended to ultrashort pulses (160 fs) of 308 nm wavelength. Polymethylmethacrylate has negligible absorption at this wavelength for one‐photon excitation. With the ultrashort pulse clean etching without any sign of thermal damage can be achieved at fluences as little as 0.2–0.3 J/cm2. This is the first demonstration that the high power of ultrashort pulses of ultraviolet light can produce photochemical etching by taking advantage of multiphoton excitation to dissociative states.

Design of high-power ultrashort pulse amplifiers by expansion and recompression

Abstract: A system that expands and recompresses an ultrashort pulse by means of diffraction gratings is described. The expansion can be large enough to broaden the pulse to several nanoseconds. In this manner, as the signal and pump pulses have similar lengths, high-efficiency amplifiers can be designed. The expansion avoids inefficient energy storage in high-gain amplifiers and nonlinear effects in the amplifier medium, and the amplified spontaneous emission is drastically reduced by working in a saturated amplifier regime.

Generation of high-peak-power tunable infrared femtosecond pulses in an organic crystal: application to time resolution of weak infrared signals

Abstract: High-intensity femtosecond pulses tunable in the 0.8–1.6-μm range have been generated by parametric amplification of a continuum white light in a new organic crystal, N-(4-nitrophenyl)-L-prolinol (NPP). The traditional concept of noncritical phase matching was revised in view of requirements linked to the observation of ultrafast subpicosecond nonlinear phenomena. The notions of θ (noncritical) and λ (noncritical) phase matching are introduced together with their applications. An experimental determination of phase-matching curves for both second-harmonic generation and three-wave mixing has been carried out. A θ noncritical phase-matching configuration for second-harmonic generation at 1.15 μm and a quasi-λ noncritical phase-matching configuration in the near IR for three-wave mixing were evidenced. Frequency and pump-intensity dependences of the gain have also been studied. Parametric emission at degeneracy was observed, with the emitted bandwidth extending from 1.0 to 1.4 μm. Time resolution of the amplified signal has been carried out by cross correlating the pump with the incoming signal, evidencing a reduced time broadening of the interacting pulses; a new spectroscopic method with subpicosecond time resolution is derived from the previous nonlinear optical characterization experiments by replacing the IR continuum from the water cell by any sample emitting in the same frequency range. This method, termed parametric amplification and sampling spectroscopy, was used for temporal analysis of amplified and emitted infrared signals generated in an NPP crystal.

Ultrashort pulses from the soliton laser.

Abstract: We report the production of 50-fsec FWHM pulses directly from the soliton laser and 19-fsec pulses with compression in an external fiber. The 19-fsec FWHM corresponds to just under four optical cycles at the laser wavelength of 1.5 μm. We argue that these limits are set by dispersion properties of the control and compression fibers.

Intensity effects on the stimulated four photon spectra generated by picosecond pulses in optical fibers

Abstract: The intensity dependence of stimulated four photon mixing (SFPM) spectra generated in 15 m of a 4-mode optical fiber by 25- ps pulses has been investigated. Despite the shortness of pulses, the SFPM conversion was highly efficient due to the intrinsic phase matching condition. In addition to usual features of SFPM spectra generated by nanosecond pump pulses, picosecond SFPM spectra were broadened by self phase modulation (SPM) and cross phase modulation (XPM). At the highest pump powers, intensity saturated frequency continua, arising from the combined effects of SFPM, stimulated Raman scattering (SRS), SPM, and XPM were generated all over the visible spectrum.

Lasers for ultrashort light pulses

Abstract: The present rapid expansion of research work on picosecond lasers and their application makes it difficult to survey and comprehend the large number of publications in this field. This book aims to provide an introduction to the field starting with the very basic and moving on to an advanced level. Contents: Fundamentals of the interaction between light pulses and matter; Fundamentals of lasers for ultrashort light pulses; Methods of measurement; Active modelocking; Synchronously pumped lasers; Passive modelocking of dye lasers; Passive modelocking of solid state lasers; Nonstationary nonlinear optical processes; Ultrafast spectroscopy.

Picosecond and femtosecond Fourier pulse shape synthesis

Abstract: 2014 We review our work on the synthesis of arbitrarily shaped, coherent optical pulses, by spatial filtering in a grating pulse compressor. We describe picosecond pulses shaped using a fiber and grating pulse compressor and femtosecond pulses shaped using a nondispersive grating compressor. The discussion includes generation of coherent square pulses and abruptly phase-modulated « odd » pulses, two slit temporal interference measurements of the optical phase spectrum, and ultrashort pulse encryption and decoding by phase scrambling. We conclude with a proposal for an ultrafast optical self-routing switch based upon frequency domain phase coding of ultrashort pulses. Revue Phys. Appl. 22 (1987) -1628 DÉCEMBRE 1987, PAGE 1619

Soliton processing element for all-optical switching and logic

Abstract: A new type of all-optical processing element is proposed, based on nonlinear fiber waveguides. The device utilizes soliton propagation in the two arms of a Mach–Zehnder configuration. The device displays excellent switching characteristics for envelope pulses of the sech form and illustrates the necessity for using solitons as the essential bits in ultrafast optical switching and logic.

High-speed picosecond optical pulse compression from gain-switched 1.3-µm distributed feedback-laser diode (DFB-LD) through highly dispersive single-mode fiber

Abstract: Picosecond optical pulse compression characteristics of chirped pulses from gain-switched distributed feedback-laser diodes (DFB-LD) transmitting through highly dispersive media are studied theoretically and experimentally. It is clarified theoretically that gain-switched chirped pulses can be compressed to about a 0.7-time bandwidth product by normal dispersion of the dispersive media and that the optimum dispersion value to obtain a minimum compressed pulse is proportional to the square of original pulsewidth. Through a dispersion, shifted single-mode fiber with -48-ps/nm normal dispersion at a 1.3-μm wavelength, gain-switched 30-ps (FWHM) pulses from a directly modulated 1.3-μm DFB-LD at a 4.4-GHz repetition rate have been successfully compressed to 6.4-ps optical pulses with a 0.86-time bandwidth product. Experimental results agree with the theoretical analysis.

Ultrafast optical multi/demultiplexer utilising optical kerb effect in polarisation-maintaining single-mode fibres

Abstract: An ultrafast time-domain optical multi/demultiplexer utilising the optical Kerr effect in two birefringent fibres concatenated with each fast axis crossed is proposed. Stable demultiplexing of an ultrashort 30 ps optical pulse train at 1.97 GHz from a gain-switched DFB LD has been successfully demonstrated using CW mode-locked Nd:YAG laser control pulses.

Decay of femtosecond higher-order solitons in an optical fiber induced by Raman self-pumping.

Abstract: We have numerically solved an extended version of the nonlinear Schrodinger equation, taking into account higher-order dispersion, the shock (self-steepening) term, and a term describing the Raman self-pumping of an ultrashort pulse. It is shown that the Raman effect is dominant on a femtosecond time scale and leads to the decay of higher-order solitons. For the case of the N = 2 soliton an intense pulse at a distinctly Stokes-shifted frequency is created. This pulse eventually shapes into a fundamental soliton, and its further evolution is governed by the combination of dispersion, self-phase modulation, and the soliton self-frequency shift.

Optical systems using volume holographic elements to provide arbitrary space-time characteristics, including frequency-and/or spatially-dependent delay lines, chirped pulse compressors, pulse hirpers, pulse shapers, and laser resonators

Abstract: Optical systems, using volume holographic elements (gratings) having geometries which tailor the spatio-temporal dispersion of the optical pulses for the system. The input optical pulse is characterized by a frequency variation across the temporal profile of the pulse. The various frequency components of this pulse are first dispersed by at least one grating which may be of the blazed reflection or holographic volume transmission type. The resultant dispersed light is then diffracted by a holographic volume grating which imparts the desired temporal dispersion characteristics to the pulse. The shape of the holographic element will vary according to the input pulse frequency profile as formed by varied chirping techniques. A grating stage may then be repeated, preferably with additional elements in mirror symmetry to the first or by retro-reflection, in order to recombine the spatially dispersed pulse components into an exiting pulse which may be of vastly compressed temporal profile. In optical dispersive delay lines, the grating geometry provides temporal dispersion which is a desired function of wavelength of the optical pulses.

Ultrafast light‐controlled optical‐fiber modulator

Abstract: We report the ultrafast operation of a light‐controlled optical‐fiber modulator, driven by subpicosecond, compressed, and amplified (6000 A) dye laser pulses, controlling frequency‐doubled (5320 A) yttrium aluminum garnet laser pulses The operation of the modulator is based on the optical Kerr effect, and its main component is 7 mm of single‐mode optical fiber Using this system as a light‐controlled shutter, we produced either 04 ps green light pulses or 05 ps holes on the much longer duration second harmonic pulses

Induced spectral broadening about a second harmonic generated by an intense primary ultrashort laser pulse in ZnSe crystals.

Abstract: The induced spectral broadening about a weak non-phase-matched 530-nm second-harmonic pulse is observed by propagating an intense primary 1060-nm picosecond laser pulse through ZnSe crystals. This broadening is attributed to the induced phase modulation of excitation states.

Generation of short pulses from CW light by influence of crossphase modulation (CPM) in optical fibres

Abstract: We demonstrate that crossphase modulation, imposed by a train of pulses on a weak CW signal in the wavelength region of anomalous fibre dispersion, can induce the generation of short pulses (~1 ps) at the signal wavelength

Nonlinear optical devices

Abstract: This invention provides optical devices with an organic nonlinear optical component which is a transparent medium of a wholly aromatic polymer which exhibits a third order nonlinear optical susceptibility χ.sup.(3) of at least about 1×10-12 esu. Illustrative of an invention embodiment is an ultrafast all-optical gate device with a transparent poly([benzo(1,2-d:4,5-d')bisthiazole-2,6-diyl]-1,4-phenylene) optical component which exhibits a third order nonlinear optical susceptibility χ.sup.(3) of 10×10-12 esu.

Picosecond pulse generation (<1.8 ps) in a quantum well laser by a gain switching method

Abstract: A picosecond pulse (<1.8 ps) at 8570 A is successfully generated by a gain switching method in an optically pumped GaAs/AlGaAs multiquantum well laser with a cavity length of 155 μm. This is the narrowest pulse width so far achieved in semiconductor lasers without the external cavity. We believe that this short pulse generation results from the enhanced differential gain due to the two‐dimensional properties of the carriers in the quantum wells.

Generation of 33-fsec pulses at 1.32 μm through a high-order soliton effect in a single-mode optical fiber

Abstract: Pulse shortening by a factor of 2700× at 1.32 μm has been realized by means of a two-stage pulse compression. In the first stage, 90-psec pulses from a cw mode-locked Nd:YAG laser were compressed to ∼1.5 psec by using a standard fiber–grating-pair configuration. Subsequent propagation of these pulses through ∼20 m of single-mode optical fiber with a minimum dispersion at 1.27 μm led to a final pulse width of 33 fsec. This represents the shortest reported pulse generated at 1.32 μm by using the technique described above as well as the largest overall compression factor using optical fibers yet reported.

Picosecond photoelectron scanning electron microscope for noncontact testing of integrated circuits

Abstract: A scanning electron microscope which uses an ultrashort pulsed laser/photocathode combination as an electron source produces electron pulses of order 1 ps in duration at a 100‐MHz repetition rate and with a peak brightness of 3×108 A/cm2 steradian at 1.8 keV. By using this instrument in the voltage contrast mode, without contact with the samples, we have been able to measure electrical pulses propagating on coplanar transmission lines with, simultaneously, a temporal resolution of 5 ps, a voltage resolution of 3 mV/(Hz)1/2, and a spatial resolution of 0.1 μm. These measurements are achieved with extraction fields above the sample of about 1 kV/mm.

Analytic study of pulse broadening in dispersive optical fibers

Abstract: It is demonstrated that for an optical pulse propagating along an optical fiber the rms pulse width varies parabolically with distance, irrespective of initial pulse form and frequency chirp variation. Furthermore, the result is true to arbitrary dispersive order and should prove a very useful tool in determining the information-carrying capability of long-distance optical-fiber transmission systems.

Photomultiplier tube having a transmission strip line photocathode and system for use therewith

Abstract: A photomultiplier tube which may be used in time resolving a luminiscence profile emitted from a sample with picosecond resolution using short (picosecond) electrical pulses as a probe and in time resolving an electrical pulse profile produced by fast electronic or optoelectronic devices with femtosecond resolution, using short (femtosecond) laser pulses as the probe is disclosed. The photomultiplier tube includes a photocathode for receiving light and producing emission of electrons in proportion to the intensity of the light, said photocathode having a transmission strip line configuration, accellerating means for accellerating electrons emitted by said photocathode, electron multiplication means for performing electron multiplication on the electrons emitted from the accellerating means, anode means for receiving electrons from the electron multiplication means and producing an analog electrical signal output, means for causing electrons emitted by the photocathode to move through the accellerating means and the electron multiplication means and then impinge on the anode means, and means connected to said photocathode for receiving an ultrafast voltage signal.

Method and apparatus for measuring ultrashort optical pulses

Abstract: A method and apparatus for measuring ultrashort optical pulses is described. Pulse waveforms to be measured are the type which vary at high speed in a time close to or less than the response time of an optical detector. Changes of optical wavelength or frequency are measured at various sections of that pulse. The light to be measured is split into two beams, and recombined after provided with different delay times, respectively. The combined light is caused to enter a doubling crystal to generate a second-harmonic light, and the second-harmonic light component, or both the second-harmonic and fundamental components, is measured. The intensity shape and chirping of the pulses is obtained from the changes in the intensity of these components as a function of delay time difference by Fourier analysis including iterative arithmetic operations.

Generalized multiple-prism dispersion theory for pulse compression in ultrafast dye lasers

Abstract: A generalized multiple-prism dispersion theory, applicable to pulse compression schemes in femtosecond dye lasers, is described. The equations can be utilized to determine the dispersive characteristics of any multiple-prism arrangement. Also, the difference in dispersive values resulting in the use of various prism materials, including ZnSe, is compared.

Time-delayed four-wave mixing using incoherent light for observation of ultrafast population relaxation

Abstract: Time-delayed four-wave mixing using incoherent light has been proposed as a new method to measure the ultrafast population relaxation time T1. Assuming three input beams of incoherent light with much longer duration than T1, the theoretical calculation has shown that the decay curve by T1 appears in the signal profile and that the time resolution is determined by the correlation time of the light. The decay time to be observed is twice that of the transient four-wave mixing with short pulses. We have experimentally confirmed the prediction by observing picosecond population relaxations of organic dye solutions, using nanosecond pulses from a normal broadband dye laser. An advantage of the present method over the pump-probe method using incoherent light is also discussed.

Limits of fiber-grating optical pulse compression

Abstract: It is shown that the fiber and grating-pair pulse-compression technique is limited by higher-order terms in the response of the grating-pair compressor and that these terms also limit the usefulness of the compressor for canceling the effects of group-velocity dispersion on the propagation of ultrashort optical pulses. Numerical evaluations of these limits are in good agreement with the minimum experimentally observed compressed pulse width of 8 fsec. Approaches for achieving shorter pulses are discussed.