Showing papers by "Gerard Mourou published in 1995"

Self-channeling of high-peak-power femtosecond laser pulses in air

Abstract: The self-channeling of ultrashort laser pulses through 20 m of air was demonstrated. The channeled pulse was measured to have 0.75 mJ of energy, a diameter of 80 microm FWHM, and a modulated spectrum. All these values were measured to be fairly constant during the propagation of the pulse. A preliminary model is shown to explain these results.

Method for controlling configuration of laser induced breakdown and ablation

Abstract: In one aspect the invention provides a method for laser induced breakdown of a material with a pulsed laser beam where the material is characterized by a relationship of fluence breakdown threshold (Fth) versus laser beam pulse width (T) that exhibits an abrupt, rapid, and distinct change or at least a clearly detectable and distinct change in slope at a predetermined laser pulse width value. The method comprises generating a beam of laser pulses in which each pulse has a pulse width equal to or less than the predetermined laser pulse width value. The beam is focused to a point at or beneath the surface of a material where laser induced breakdown is desired. The beam may be used in combination with a mask in the beam path. The beam or mask may be moved in the X, Y and Z directions to produce desired features. The technique can produce features smaller than the spot size and Rayleigh range due to enhanced damage threshold accuracy in the short pulse regime.

X‐ray spectroscopy of hot solid density plasmas produced by subpicosecond high contrast laser pulses at 1018–1019 W/cm2

Abstract: Analysis is presented of K‐shell spectra obtained from solid density plasmas produced by a high contrast (1010:1) subpicosecond laser pulse (0.5 μm) at 1018–1019 W/cm2. Stark broadening measurements of He‐like and Li‐like lines are used to infer the mean electron density at which emission takes place. The measurements indicate that there is an optimum condition to produce x‐ray emission at solid density for a given isoelectronic sequence, and that the window of optimum conditions to obtain simultaneously the shortest and the brightest x‐ray pulse at a given wavelength is relatively narrow. Lower intensity produces a short x‐ray pulse but low brightness. The x‐ray yield (and also the energy fraction in hot electrons) increases with the laser intensity, but above some laser intensity (1018 W/cm2 for Al) the plasma is overdriven: during the expansion, the plasma is still hot enough to emit, so that emission occurs at lower density and lasts much longer. Energy transport measurements indicate that approximate...

Highly efficient second-harmonic generation of ultraintense Nd:glass laser pulses

Abstract: Second-harmonic conversion efficiencies of 80% for type I KDP crystals and 70% for type II have been demonstrated with 500-fs, 1.053-μm laser pulses at intensities as high as 400 GW/cm2. The results are generally in good agreement with simulations and indicate that self-phase modulation and cross-phase modulation may be significant. For type II conversion with a predelay between the input o and e waves, some evidence is obtained of pulse shortening to ~100 fs.

Apparatus and method for enabling the creation of multiple extended conduction paths in the atmosphere

Abstract: An apparatus and method for enabling the creation of multiple extended conduction paths in the atmosphere including a chirped-pulse amplification laser system having a high peak-power laser capable of transmitting through the atmosphere a high-peak power ultrashort laser pulse. The laser pulse is configured to have a rough spacial profile and is of sufficient energy to create multiple electrically conductive ionized channels in the atmosphere.

Terawatt Ti:sapphire laser with a spherical reflective-optic pulse expander

Abstract: We have developed a novel stretcher–compressor system to produce 45-fs, 75-mJ pulses at a 10-Hz repetition rate.

Characterization of short-pulse oscillators by means of a high-dynamic-range autocorrelation measurement.

Abstract: A high-dynamic-range autocorrelation technique was used to characterize the temporal pulse shape of ultrashort laser pulses produced from four separate oscillators. These lasers included two Kerr-lens mode-locked Ti:sapphire oscillators as well as a Nd:glass and a Ti:sapphire oscillator, each passively mode locked by an antiresonant Fabry–Perot semiconductor saturable absorber. It was shown that the Nd:glass oscillator supported a pulse that was temporally clean over 8 orders of magnitude.

Chirped-pulse amplification of ultrashort pulses with a multimode Tm:ZBLAN fiber upconversion amplifier

Abstract: Microjoule pulse energies are achieved from a single-stage upconversion fiber amplifier for the first time, to our knowledge, in this demonstration of chirped-pulse amplification with a multimode Tm:ZBLAN fiber. A Ti:sapphire laser system provides the seed pulse for the fiber upconversion amplifier that produces picosecond pulse trains with energies as great as 16 μJ at a repetition rate of 4.4 kHz.

Upconversion chirped-pulse amplification of ultrashort pulses using a multimode Tm:ZBLAN fiber

Abstract: Microjoule pulse energies are achieved from a single stage upconversion fiber amplifier for the first time in this demonstration of chirped pulse amplification using a multimode Tm:ZBLAN fiber. A Ti:sapphire laser system provides the seed pulse for the upconversion fiber amplifier which produces subpicosecond pulse trains with energies as great as 16 (mu) J at repetition rate of 4.4 kHz. The compressed pulse peak power is more than 1 MW, and the pulse is characterized both temporally and spatially.

Laser-induced breakdown as a function of pulse duration: from 7 ns to 150 fs

Abstract: Single-shot laser induced breakdown, in wide band gap materials such as SiO2 and MgF2, has been studied over almost 5 orders of magnitude in duration from 150 fs to 7 ns. A Ti:sapphire chirped pulse amplification system was used in this experiement, so the pulse duration could be continuously adjusted without changing any other parameters. The damage threshold was detected by looking at the plasma formation and the change of material transmission coefficient. The avalanche mechanism was found to dominate over the entire pulse-width range even for 150 fs pulses where we would expect multi-photon processes to take over. A strong departure from the conventional fluence threshold scaling law is observed for pulses shorter than 10 ps, where beyond this point the fluence threshold increases. Also, it is observed for the first time that for short pulses the damage threshold becomes very accurate and less statistical than that for longer pulses.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

High-efficiency frequency doubling of ultra-intense Nd:glass laser pulses

Abstract: Efficient second harmonic conversion (70 - 80%) using Type II and Type I crystals is demonstrated with 400-fs, 1.053-micrometers laser pulses at intensities up to several hundreds of GW/cm2. The experimental results generally agree with the predictions of the code MIXER. For the Type II predelay scheme, evidence is obtained of pulse shortening down to approximately 100 fs.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.