Showing papers by "Gerard Mourou published in 1998"
TL;DR: In this article, the optical breakdown threshold and ablation depth in dielectrics with different band gaps for laser pulse durations ranging from 5 ps to 5 fs at a carrier wavelength of 780 nm.
Abstract: We report measurements of the optical breakdown threshold and ablation depth in dielectrics with different band gaps for laser pulse durations ranging from 5 ps to 5 fs at a carrier wavelength of 780 nm. For t, 100 fs, the dominant channel for free electron generation is found to be either impact or multiphoton ionization (MPI) depending on the size of the band gap. The observed MPI rates are substantially lower than those predicted by the Keldysh theory. We demonstrate that sub-10-fs laser pulses open up the way to reversible nonperturbative nonlinear optics (at intensities greater than 10 14 Wycm 2 slightly below damage threshold) and to nanometer-precision laser ablation (slightly above threshold) in dielectric materials. [S0031-9007(98)05969-9]
805 citations
TL;DR: In this paper, it was shown that at these intensities, the light pressure, P = I/c, is extreme, on the order of giga-to-terabars.
Abstract: Over the past ten years, laser intensities have increased by more than four orders of magnitude to reach enormous intensities of 1020 W/cm2. The field strength at these intensities is on the order of a teravolt per centimeter, or a hundred times the Coulombic field binding the ground state electron in the hydrogen atom. The electrons driven by such a field are relativistic, with an oscillatory energy of 10 MeV. At these intensities, the light pressure, P = I/c, is extreme, on the order of giga‐ to terabars. The laser interacting with matter—solid, gas, plasma—generates high‐order harmonics of the incident beam up to the 3 nm wavelength range, energetic ions or electrons with mega‐electron‐volt energies (figure 1), gigagauss magnetic fields and violent accelerations of 1021 g (g is Earth's gravity). Finally, the interaction of an ultraintense beam with superrelativistic particles can produce fields approaching the critical field in which an electron gains in one Compton wavelength an energy equal to twice ...
483 citations
TL;DR: In this paper, a femtosecond terawatt Ti:sapphire chirped-pulse-amplification (CPA) laser was suppressed by injecting clean microjoule seed pulses into the regenerative amplifier.
163 citations
TL;DR: In this paper, experimental evidence is presented demonstrating that avalanche ionization is the dominant mechanism for dielectric breakdown in silicon with ultrafast laser pulses at above-gap photon energies.
Abstract: Experimental evidence is presented demonstrating avalanche ionization as the dominant mechanism for dielectric breakdown in silicon with ultrafast laser pulses at above-gap photon energies. Data are presented for pulses between 80 fs and 9 ns at 786 nm and 1.06 \ensuremath{\mu}m. Associated electric fields range from 0.3 to 40 MV/cm. Avalanche ionization coefficients range from ${10}^{10}$ to ${10}^{14} {\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$ and are discussed in relation to semiempirical dc ionization theory and recent ac Monte Carlo calculations. Correlation is obtained between electron collision times and associated ionization rates.
153 citations
TL;DR: Wave-front correction and focal spot improvement of femtosecond laser beams have been achieved with a deformable mirror with an on-line single-shot three-wave lateral shearing interferometer diagnostic and it is demonstrated that having a focal spot close to the diffraction limit does not constitute a good criterion for the quality of the laser in terms of peak intensity.
Abstract: Wave-front correction and focal spot improvement of femtosecond laser beams have been achieved, for the first time to our knowledge, with a deformable mirror with an on-line single-shot three-wave lateral shearing interferometer diagnostic. Wave-front distortions of a 100-fs laser that are due to third-order nonlinear effects have been compensated for. This technique, which permits correction in a straightforward process that requires no feedback loop, is also used on a 10-TW Ti:sapphire-Nd:phosphate glass laser in the subpicosecond regime. We also demonstrate that having a focal spot close to the diffraction limit does not constitute a good criterion for the quality of the laser in terms of peak intensity.
115 citations
TL;DR: In this article, the authors present a technique of high-dynamic-range plasma-shuttered streak camera contrast measurement, as well as two efficient and relatively inexpensive ways of improving the contrast of short pulse lasers without sacrificing on the output energy: a double-pass Pockels cell (PC) and clean high-energy pulse seeding of the regenerative amplifier.
Abstract: As ultrafast lasers achieve ever higher focused intensities on target, the problem of ensuring a clean laser-solid interaction becomes more pressing. In this paper, we give concrete examples of the deleterious effects of low-contrast interactions, and address the problem of subpicosecond laser intensity contrast ratio on both characterization and control fronts. We present the new technique of high-dynamic-range plasma-shuttered streak camera contrast measurement, as well as two efficient and relatively inexpensive ways of improving the contrast of short pulse lasers without sacrificing on the output energy: a double-pass Pockels cell (PC), and clean high-energy-pulse seeding of the regenerative amplifier.
85 citations
TL;DR: Wave-front distortions of a terawatt-class laser system are measured with good accuracy (lambda/50) and discussed, emphasizing the necessity of implementing adaptive optics in ultrahigh-intensity chirped-pulse amplification lasers.
Abstract: A simple new three-wave interferometric technique is used to measure, for what is believed to be the first time, the wave front of femtosecond ultrahigh-peak-power pulses carrying a strong B integral (B = 5.26+/-0.15) in a single shot. Wave-front distortions of a terawatt-class laser system are measured with good accuracy (lambda/50) and discussed. These distortions can significantly reduce the focused peak intensity, emphasizing the necessity of implementing adaptive optics in ultrahigh-intensity chirped-pulse amplification lasers.
57 citations
Patent•
02 Dec 1998TL;DR: In this article, a method for transscleral photodisruption of tissue on the interior surface of the sclera includes selecting a wavelength for a laser beam, which can be either from a first range of wavelengths (0.4-1.4 μm) which is normally strongly scattered as it is transmitted through the Sclera, or from a second range of longer wavelengths (1.5-2.5 μm).
Abstract: An ab interno method for transscleral photodisruption of tissue on the interior surface of the sclera includes selecting a wavelength for a laser beam. The selected wavelength may be either from a first range of wavelengths (0.4-1.4 μm) which is normally strongly scattered as it is transmitted through the sclera, or from a second range of longer wavelengths (1.5-2.5 μm) which is less scattered as it is transmitted through the sclera. If the first range of wavelengths is selected, a chemical agent may be applied to the sclera to make it effectively transparent, but this may not be necessary. In either case, the laser beam is focused directly through the sclera to a focal point on the interior surface of the sclera. Once focused, the laser beam is activated to photodisrupt scleral tissue at the focal point. The laser beam is then moved in a pattern and refocused at successive focal points to photodisrupt scleral tissue at each of the focal points. This continues until the desired volume of scleral tissue has be photodisrupted, and thereby removed, from the interior surface of the sclera. The use of ultrashort laser pulses (in the femtosecond or picosecond range) is advantageous in order to achieve high precision and avoid collateral tissue damage. Such collateral damage is known to cause unwanted healing effects which are known to result in surgical failure.
55 citations
TL;DR: In this paper, the choice of high-saturation-fluence gain material and the measurement and active control of temporal and spatial phase distortions for compact chirped-pulse amplification (CPA) systems of the future are discussed.
Abstract: If further developments in high-field lasers are to be accessible to universities and institutes, new laser materials and phase control techniques, which will result in compact, reliable systems with higher peak power, must be adopted. The choice of high-saturation-fluence gain material and the measurement and active control of temporal and spatial phase distortions for compact chirped-pulse amplification (CPA) systems of the future are discussed. Using the proper material and phase control a focused intensity of 10/sup 25/ W/cm/sup 2/ is theoretically possible.
40 citations
TL;DR: Experimental results with strongly aberrated beams focused close to the diffraction limit are presented for the cw regime and it is shown that this approach is relevant for spatial phase correction of ultraintense laser pulses.
Abstract: We demonstrate correction of laser wavefront distortions by use of an adaptive-optical technique based on a light valve. The setup consists of an achromatic and adjustable-sensitivity wavefront sensor and a wavefront corrector relying on an optically addressed liquid-crystal spatial light modulator. Experimental results with strongly aberrated beams focused close to the diffraction limit are presented for the cw regime. Additional experiments with pulses and measurement of damage thresholds show that this approach is relevant for spatial phase correction of ultraintense laser pulses.
39 citations
18 May 1998
TL;DR: In this article, the wavelength dependence of the minimum spot size of a laser beam focused through human sclera was determined to evaluate the potential for transcleral glaucoma surgical techniques using ultrashort-pulsed lasers.
Abstract: We determined the wavelength dependence of the minimum spot size of a laser beam focused through human sclera to evaluate the potential for transcleral glaucoma surgical techniques using ultrashort-pulsed lasers The spectrum of the forward scattered light was measured by collimating the incident and transmitted beam in a spectrophotometer This spectrum shows that sclera is highly scattering until 1100 nm, after which, the transmission spectrum is similar to water To measure the minimal spot size, a laser beam was focused on the back surface of sclera of differing thickness The minimum spot at 800 nm, 1060 nm, 1301 nm, and 1557 nm was imaged At 800 nm, the spot size was invariant upon focal lens position, being a thousand fold larger than the incident beam spot size As the wavelength increased, the area of the spot decreased, so that at 1557 nm, the minimal spot size was on the order of the incident beam spot size© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering Downloading of the abstract is permitted for personal use only
TL;DR: In this paper, simulations of chirped-pulse amplification (CPA) in a quasi-three-level laser are presented which illustrate how depletion of the inversion can occur at ten times below the saturation fluence in a regenerative amplifier.
Abstract: Simulations of chirped-pulse amplification (CPA) in a quasi-three-level laser are presented which illustrate how depletion of the inversion can occur at ten times below the saturation fluence in a regenerative amplifier. The simulations are applied to Yb:glass, a promising laser medium for a directly diode-pumped high-peak power laser. Virtually stretching a pulse to a portion of the buildup time of a regenerative amplifier allows for efficient energy extraction from a laser medium that has a saturation fluence greater than the damage threshold. Experimental results from a Yb:glass regenerative amplifier produced 12-mJ pulses at a peak fluence of 9 J/cm/sup 2/ without damage.
TL;DR: By driving electrons in the relativistic regime, the table-top terawatt (T3) laser has given nonlinear optics a second wind, with applications in particle beam, nuclear, astrophysics, and nonlinear quantum electrodynamics as discussed by the authors.
Abstract: By driving electrons in the relativistic regime, the table-top terawatt (T3) laser has given nonlinear optics a second wind, with applications in particle beam, nuclear, astrophysics, and nonlinear quantum electrodynamics.
01 Jan 1998
TL;DR: Refractive corneal surgical procedures utilizing amplified femtosecond laser pulses from a reliable and compact femtosescond laser system suited for medical applications are investigated.
Abstract: We investigated refractive corneal surgical procedures utilizing amplified femtosecond laser pulses from a reliable and compact femtosecond laser system suited for medical applications. Procedures such as corneal flap cutting and laser keratomileusis have been demonstrated in vivo and in vitro. Cutting was found to be well confined and highly precise.
TL;DR: In this article, an intragrating-pair parallel plate is demonstrated as a simple, low-alignment-tolerance device for third-order dispersion control in chirped-pulse amplification.
Abstract: An intragrating-pair parallel plate is demonstrated as a simple, low-alignment-tolerance device for third-order dispersion control in chirped-pulse amplification. We have demonstrated a simple and alignment insensitive device to eliminate third-order phase errors. Instead of needing arc-minute accuracies (as is the case of third-order tuning using the gratings themselves), the plate requires only degree accuracies, easily obtained experimentally. Further, using the numerical simulation, it is shown how different plate configurations can be used in response to changes in the system parameters.
03 May 1998
TL;DR: In this paper, the authors demonstrate electron production by avalanche ionization as the dominant mechanism for laser breakdown, and subsequent surface damage in silicon, for laser pulse durations in the range of 80 fs to 9 ns.
Abstract: Summary form only given. Data are presented that demonstrate electron production by avalanche ionization as the dominant mechanism for laser breakdown, and subsequent surface damage in silicon, for laser pulse durations in the range of 80 fs to 9 ns. Experiments are performed at 786 nm and 1.06 /spl mu/m exhibiting the correct wavelength dependence for an avalanche process.
14 Sep 1998
TL;DR: In this article, a GaAsP photodiode was used to recover the temporal profile and phase from autocorrelation trace and the pulse spectrum for ultrashort laser pulses by using two-photon induced photocurrent in semiconductors.
Abstract: Second-order autocorrelation of ultrashort laser pulses by using two-photon-induced photocurrent in semiconductors offers several advantages compared with baditionally employed combination o f a second harmonic (SH) c y t a l and B photomultiplier tube. A low-priced commercially available photodiode [I] sllows to overcome principal drawback of SH-based amcomelation: limited phaos matching bandwidth and wavelength.dependent sensitivity o f the light detector leading to B spectral filtering effect, pulse brmdening due to crystal bulk dispersion, low conversion efficiency which decrease9 with increase o f SH bandwidth, high cost and manufacturing problems associated with thin SH crystals. A siaificant advantage o f incorporating a semiconductor photodiode into autocorrel&tioa measurements i E that the desired two-photon reoponre and ihe transformation of light into electric current are combined into a single nolid-stste device. I t has been shown recently that for the vast majority of practically realisable pulses the complete phase and amplitude information could be rapidly recovered fmm the autocorrelation trace and the pulse spectrum by means of a two-stage iteratiw algorithm [Z]. In this convihurion we demonstrate that due to absence of spectrsl filtering effect and high dynamic range of quadratic response to the incident intensity in a GaAsP photodiode [I], correct retrieval of temporal profile and phase from autocorrelation and spectrum c m be achieved for ultrashort l a w pulses with bandwidths as large BS 130 nm and pulse energies as IOW BS
TL;DR: In this article, a high energy flashlamp pumped Ti:sapphire laser was developed for the pumping source of Yb:glass chirped pulse amplification, and the free running oscillator generated 12 Joule/pulse at 793 nm at 1 Hz repetition.
Abstract: A high energy flashlamp pumped Ti:sapphire laser has been developed for the pumping source of Yb:glass chirped pulse amplification. The free running oscillator generates 12 Joule/pulse at 793 nm at 1 Hz repetition. The output energy of 6 Joule/pulse at 920 nm has been obtained.
03 May 1998
TL;DR: In this paper, the wave-front correction of femtosecond pulses distorted by third-order nonlinearities was studied using an achromatic three-wave lateral shearing interferometer (ATWLSI).
Abstract: Chirped pulse amplification allowed the development of ultrashort, high-intensity lasers. At this high-intensity level, the third-order nonlinear effect can cause wave-front distortions in even a small amount of material. Although often neglected, this effect can significantly reduce the spatial quality and thus the focusability of the beam, thereby severely reducing the attainable focused intensity. To quantify this decrease in the peak focused intensity, we use the normalized Strehl intensity, which is the ratio of the peak intensity at focus ofa beam with a distorted wave front to that of the same beam without distortions. We present, in this paper, the wave-front correction of femtosecond pulses distorted by third-order nonlinearities. To measure with a good accuracy this wave-front distortion, we use an achromatic three-wave lateral shearing interferometer (ATWLSI), which has been shown to be particularly suitable for single-shot measurements of both phase and intensity for femtosecond pulses.
TL;DR: In this article, an adaptive and programmable module allowing the spatial control of the beam amplitude and the correction of the phase distortions due to the optical components and the gain media of the laser chain is presented.
Abstract: Space aberration effects which arise in high energy or in high average power laser chains are important parameters to control in order to emit a beam quality close to the diffraction limit. For that purpose we present recent experiments using an original adaptive and programmable module allowing the spatial control of the beam amplitude and the correction of the phase distortions due to the optical components and the gain media of the laser chain. Beam shaping is achieved by an optically addressed photoconductor-liquid crystal light valve. The light valve is addressed in the blue-green spectral range by incoherent projection of a VGA liquid crystal display. This adaptive optics module controls either the amplitude or the phase of near infrared laser beams depending on the liquid crystal operating mode. The other specific characteristics of the module will be detailed: no spurious diffraction effects, up to 10(pi) phase excursion and tri-lateral wavefront sensor. Experimental results of compensation of aberrations introduced on different laser beams will also be presented.
01 Feb 1998
TL;DR: In this paper, a focused intensity of 1025 W/cm2 is theoretically possible using the proper material and phase control, which will result in compact, reliable systems with higher peak power.
Abstract: Over the past ten years, we have seen a revolution in the generation of ultraintense pulses, now well in the 1019 W/cm2 range. If further developments in high-field lasers are to be accessible to universities and institutes, new laser materials and phase control techniques, which will result in compact, reliable systems with higher peak power, must be adopted. The choice of high-saturation-fluence gain material and the measurement and active control of temporal and spatial phase distortions for compact CPA systems of the future will be essential. Using the proper material and phase control, a focused intensity of 1025 W/cm2 is theoretically possible.
01 Dec 1998
TL;DR: In this paper, the authors present the results of the characterization tests performed on their sub-picosecond x-ray streak camera at the University of Michigan and at the European Synchrotron Radiation Facility.
Abstract: The advent of CPA femtosecond lasers has opened the way to a new regime of interaction with atoms and molecules. In some experiments like time-resolved x-ray diffraction of laser- excited samples, the signal to be measured can contain very few photons and repetition rates up to 1 kHz are required. The laser-triggered x-ray streak camera system is therefore a promising tool for the study ultrashort x-ray events. We present the results of the characterization tests performed on our subpicosecond x-ray streak camera at the University of Michigan and at the European Synchrotron Radiation Facility. This new ultrafast diagnostic is triggered by a short laser pulse and can acquire images at rates up to 1 kHz and features a subpicosecond time resolution along with a 40 micrometer spatial resolution. We discuss the different issues related to the interaction between the laser pulse and photo-conductive switches, the synchronization of the detector.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
03 May 1998
TL;DR: In this article, the scaling of chirped-pulse amplification (CPA) in a Yb:glass large-mode amplifier operating under low-gain, low-loss conditions is demonstrated.
Abstract: The use of a simple free-running pump laser to store high energy density in Yb-doped material is demonstrated. We report on scaling of chirped-pulse amplification (CPA) in a Yb:glass large-mode amplifier operating under low-gain, low-loss conditions. Further improvement in compactness and efficiency can be obtained by direct diode pumping of Yb:glass.
TL;DR: In this article, the wavefront correction of high intensity laser beam using deformable mirror is described and compensated, and the B-integral and the thermal lensing wavefront distortions are characterized and compensated.
Abstract: We report the wavefront correction of high intensity laser beam, using deformable mirror. The B-integral and the thermal lensing wave-front distortions are characterized and compensated.
14 Sep 1998
03 May 1998
TL;DR: In this article, a Yb:glass laser was side-pumped by two 20-W diode bars with negligible thermal effects, which were combined together by using a polarizer and a halfwave plate.
Abstract: We demonstrated a Yb:glass laser directly side-pumped by two 20-W diode bars with negligible thermal effects. The experimental setup has two cw 20-W, l-cm InGaAs laser-diode bars from Thomson-CSF, France, which were combined together by using a polarizer and a halfwave plate.
03 May 1998
TL;DR: This work presents, for the first time, chirped pulse amplification (CPA) in a directly diode pumped Yb:glass laser.
Abstract: Summary form only given. We present, for the first time, chirped pulse amplification (CPA) in a directly diode pumped Yb:glass laser. The injected pulses were obtained from a mode-locked Ti:sapphire laser (coherent) tuned to 1040 nm with a pulse width of 200 fs. The pulses were then stretched in a fibre.