Showing papers on "Femtosecond pulse shaping 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.

Single-shot measurement of a 52-fs pulse.

Abstract: We demonstrate the possibility of a 52-fs pulse single-shot measurement by using the spatial analysis of the second harmonic beam produced in an optical autocorrelator. We show that this method gives a reliable means of optimizing low repetition rate femtosecond amplifiers. Since the introduction of femtosecond laser systems in 19811 much progress has been made toward reducing the duration of the produced pulses. These lasers are able to produce pulses shorter than 70 fs and with a peak power up to 10 GW. 2 3 Moreover, one always uses the classical background-free autocorrelation scheme 4 (modified Michelson interferometer with a scanning arm) to measure the pulses. There have not been significant advances in obtaining a real time measurement (i.e., made with a single pulse) of femtosecond pulses. In the picosecond domain, streak cameras with 0.4-ps rise time exist, but they cannot be used for 100-fs pulses. At this time, there is much theorizing about new measurement systems for femtosecond pulses 5 - 7 but few experimental demonstrations of their capabilities. The problem is to transform the temporal information (shape of the pulse) into a more convenient form (spatial or slowly varying signal). In a classical autocorrelator the delay between the two pulses is slowly swept, and the autocorrelation function is built from a large number of successive pulses. In the picosecond domain, single-shot measurements have been demonstrated using two-photon fluorescence (TPF) 8 or second harmonic generation. 9 In a recent paper, Sperber and Penzkofer 8 show that TPF traces could be decorrelated to determine the approximate temporal shape of modulated pulses. Nevertheless, the continuous background signal produced by each individual beam gives a maximum contrast ratio of 3:1 between the maximum value of the autocorrelation function and the background level. In 1981, Wyatt and Marinero 9

Femtosecond laser-tissue interactions: Retinal injury studies

Abstract: We report the first study of laser-tissue interaction in the femtosecond time regime. Retinal damage thresholds and mechanisms produced by exposure to high-intensity femtosecond laser pulses were investigated in chinchilla grey rabbits. Exposures were performed using single laser pulses of 80 fs duration at 625 nm. ED 50 injury thresholds of 0.75 and 4.5 μJ were measured using fluorescein angiographic and ophthalmoscopic visibility criteria evaluating 204 laser exposures. Ultrastructural studies including light and electron microscopy were performed on selected lesions. Results suggest that the primary energy deposition in the retina occurs in melanin, However, in contrast to laser injuries produced by longer pulses, exposures of more than 100 × threshold in the 50-100 \mu J range did not produce significantly more severe lesions or hemorrhage. This suggests the presence of a nonlinear damage limiting mechanics in tissue exposed to femtosecond laser pulses.

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

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.

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.

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.

Subpicosecond fiber laser

Abstract: A fiber laser for producing subpicosecond pulses is formed by placing a laser fiber in a resonant cavity, in either a linear or closed loop configuration. The laser fiber is formed of two different types of fibers joined in series, a gain fiber which contains the laser gain medium followed by a pulse shaping fiber which uses the phenomenon of solution pulse shaping to shorten the pulses. An initially formed pulse recirculates many times in the resonator; on each pass the pulse is both amplified and shortened until steady state is reached. The zero dispersion wavelength of the pulse shaping fiber is chosen to be slightly less than the laser wavelength. The fiber is pumped by a continuous source, particularly CW laser diodes. The initial pulse can be formed by a self starting technique produced by selecting the proper length of the laser fiber, or else a mode locker/acousto-optic shutter can be placed in the cavity.

Generation of programmable, picosecond-resolution shaped laser pulses by fiber-grating pulse compression.

Abstract: We demonstrate that fiber-optic compression can be sufficiently well characterized to permit generation of an arbitrarily shaped, 1-psec-resolution laser pulse from a predistorted, much longer pulse. Coupled with our previously demonstrated capability to generate an arbitrary shape with 10-psec resolution and software control, this technique provides significant advantages over conventional mode-locked, cavity-dumped, synchronously pumped laser systems.

Implementation of a phase and amplitude modulated π pulse for coherent optical spectroscopy

Abstract: We have implemented an amplitude and phase modulated laser pulse of the form [sech(αt)]1+3i. Such a pulse shape creates uniform population inversion within a selected bandwidth, compensates for Rabi frequency inhomogeneity, and leaves transitions outside the bandwidth unaffected. The unique features of this pulse shape are verified by measuring total fluorescence in iodine vapor as a function of laser power.

Precision laser system useful for ophthalmic surgery.

Abstract: A laser system is capable of producing a plasma in a target irrespective of whether the target (18) is absorbing or non-absorbing for the laser pulses. This system is particularly useful for making precise cuts in animal tissue for laser surgery such as for opthamological procedures. The system including a generation zone (24) for generating a principal lasing radiation pulse (44), an shortening zone (56) for shortening the duration of the principal pulse, a pulse multiplier (102) that multiplies the shortened pulse to a plurality of temporally, and preferably spatially, spaced apart pulses, and a beam delivery system (28) that focuses the spaced apart pulses into a sufficiently small spot size to achieve an irradiance of at least about 10 watts/cm in the target. A pulse shortener achieves substantial pulse shortening using amplified spontaneous emission.

Investigation of controlled ultrashort pulse dye laser for femtosecond nonlinear spectroscopy

Abstract: Characteristics of a simple but practical ultrashort pulse laser system for transient nonlinear spectroscopy around and below 100 fs are described. The system is based on a hybridly mode-locked, cavitydumped cw dye laser, with high stability, broad tunability and specific phase properties, producing both clean transform-limited and chirped pulses. The laser system is applied to demonstrate the feasibility of using chirped pulses in high time-resolution measurement of relaxation times in condensed matter by means of degenerate transient four-wave mixing.

Compression and Shaping of a Short Light Pulse by a Monochromator

Abstract: A simple technique to shape a short light pulse to an arbitrary temporal pattern using a monochromator is described. Operational conditions of the pulse shaping by Fourier transformation are discussed.

Fiber-grating pulse compressor: Performance with initially chirped pulses

Abstract: Numerical simulation of a fiber-grating pulse compressor is performed assuming incident frequency chirped pulses. Characteristic fiber lengths are defined to explain qualitatively the behavior of the compression ratio curves. High compression ratios are not particularly sensitive to the input pulse chirp even for pulses of up to twice the bandwidth limit. The results are presented in normalized form with the help of optical soliton theory and can be used for a wide range of initial pulse widths.

Observation of periodical short pulse trains in free-electron laser oscillations

Abstract: Periodical short pulse trains were observed in a long pulse, low current, low voltage waveguide mode free‐electron laser. The pulse width and the pulse train intervals of the periodical short pulse trains were about a few ns and about 23 ns, respectively. These pulse trains can be explained as self‐mode‐locked oscillations of a free‐electron laser.

CPM pulse laser device having a feedback means

Abstract: A CPM pulse laser device is provided which has a means for emitting pulses in two separate directions. A return system is provided for returning one of the pulses to the laser resonator in such a manner that the returned pulse is superposed on the other pulse which was propagated in the other direction. The return system preferably includes a total reflecting mirror or a nonlinear crystal. The position of the total reflecting mirror or nonlinear crystal is precisely adjusted to create the superposition.

Generation of Ultrashort Optical Pulses

Abstract: Two processes which are essential to generate ultrashort optical pulses are described. They are 1) producing/providing the broad-band optical spectra and 2) controlling the phase relation between the optical frequency components.Additionally, typical methods of ultrashort optical pulse generation, i. e. modelocking, electrooptic gates, an optical pulse synthesizer, and…, are summarized.

Short pulse generation from a flashlamp-pumped rhodamine 6G ring dye laser using the colliding pulse mode-locking technique.

Abstract: The colliding pulse mode-locking (CPM) technique has been applied to a flashlamp-pumped rhodamine 6G dye laser to reliably generate pulses of <1.5 ps. Pulse evolution in the ring cavity has been studied by examining the pulse characteristics at various parts of the pulse train using a Photochron II streak camera. The measured pulse durations in the ring cavity were found to be detector-limited and were shorter than those generated in a linear cavity. The shortest pulses were observed to evolve toward the end of the ~600-ns long mode-locked train.

Generalized interferometric technique for ultrashort pulse characterization.

Abstract: A direct Young interferometric technique as a tool to determine ultrashort chirped Gaussian pulses characteristics is described: the intensity as a function of the order of the minima of the interference pattern depends on a function of the pulse characteristics. Effects related to modification of the functional forms of the shape and phase are computed, and the modulation in the intensity due to the finite size of the slits is deduced. A generalization of this technique, through measuring the minima intensity for an appropriately generated second harmonic pulse, permits the individual determination of the pulse width and chirp rate.

Measurements of Ultrashort Light Pulses Using Nonlinear Correlation Methods

Abstract: Recent progress of ultrashort pulse lasers and pulse compression techniques has allowed us to generate pulses with duration of the order of 10 fs or less.The development of measurement techniques is also necessary for characterizing the ultrashort pulses. Linear direct measurement combined with photodetectors and oscilloscopes or ultrafast streak camera is no longer adequate to temporally resolve these pulses. Instead, various nonlinear correlation methods based on the nonlinear optical processes with time resolution of subpicosecond or femtosecond are proposed and demonstrated.The basic concept, advantages and limitations of the methods including the recent development are discussed here.

Pulse to Pulse Instabilities in a Multimode Q-Switched Nd: YAG-Laser

Abstract: Sometimes problems arise in high volume production with Q-switched lasers. In high speed resistor trimming, for instance, reasonable peak powers at 30 kHz repetition rate would be desirable in some cases. This can no longer be provided by means of a conventional TEMoo laser. To increase the peak power, the aperture is increased and one tries to work with a low order mode. The poorer beam quality does not usually present a problem. The poor and unpredictable pulse-to-pulse stability, however, does; see Fig. 1.

An Ultrashort-Pulse Laser Technology

Abstract: The present status of ultrashort-pulse lasers and pulse-compression techniques in the femtosecond-time region is reviewed. In addition, the future problems to be solved for generation of shorter pulses are described.

The Soliton Laser: A Simplified Model

Abstract: The soliton laser oscillation, as described by Mollenauer and Stolenl, is achieved by reinjecting into the main cavity a pulse that has been compressed after its passage through an optical fiber. This pulse, being extracted from the preceding mode locked pulse, is thus coherent with the existing pulse in the laser cavity. Moreover, the parameters are adjusted in order that the reinjected pulse coincides precisely with the laser pulse.

Laser pulse radiation sensing system and pulse envelope detectors.

Abstract: Pulse Doppler laser rangefinder systems operate on the detection of the leading of the envelope of the return pulse from a target, the leading edge being determined after the pulse has been demodulated. Demodulation is presently achieved by mixing a local oscillator signal with the pulse but the frequency of the pulse may not be known and the local oscillator frequency would need to be ramped within the duration of a return pulse to match the two frequencies for demodulation. This ramping may cause unsynchronised demodulation of the pulse or even cause the pulse to be missed. Described herein is a laser rangefinder system in which demodulation is achieved by dividing and self-mixing an electrical signal which corresponds to a modulated beam comprising the envelopes of the return pulses from a target.

Effects of Pulse Shaping in Laser Spectroscopy

Abstract: We have shown theoretically and experimentally that specially shaped laser pulses can give enhanced excitation selectivity, compensate for experimental complications such as inhomogeneities and pulse amplitude jitter, and cleanly pump forbidden transitions. A new approach to generating picosecond pulses, which does not require modelocking, permits software controlled, arbitrarily shaped (phase and amplitude modulated) pulses with roughly 1 ps resolution.