Showing papers by "Gerard Mourou published in 1999"
TL;DR: In this article, a single-shot damage threshold measurement and modeling for fused silica at 800 nm as a function of pulse duration down to 20 fs was presented, and the respective roles of multiphoton ionization, tunnel ionization and impact ionization in laser damage were examined.
Abstract: We present a single-shot damage threshold measurement and modeling for fused silica at 800 nm as a function of pulse duration down to 20 fs. We examine the respective roles of multiphoton ionization, tunnel ionization, and impact ionization in laser damage. We find that avalanche predominates even in the case of sub-100-fs pulses.
525 citations
TL;DR: It is concluded that femtosecond laser technology may be able to perform a variety of corneal refractive procedures with high precision, offering advantages over current mechanical and laser devices and techniques.
Abstract: We investigated the use of ultrashort pulsed (femtosecond) laser technology in corneal refractive surgery. When compared to longer pulsewidth nanosecond or picosecond laser pulses, femtosecond laser-tissue interactions are characterized by significantly smaller and more deterministic photodisruptive energy thresholds, as well as reduced shock waves and smaller cavitation bubbles. We utilized a highly reliable all-solid-state femtosecond laser system for all studies to demonstrate practicality in real-world operating conditions. Contiguous tissue effects were achieved by scanning a 5-/spl mu/m focused laser spot below the corneal surface at pulse energies of approximately 2-4 /spl mu/J. A variety of scanning patterns was used to perform three prototype procedures in animal eyes; corneal flap cutting, keratomileusis, and intrastromal vision correction. Superior dissection and surface quality results were obtained for lamellar procedures (corneal flap cutting and keratornileusis). Preliminary in vivo studies of intrastromal vision correction suggest that consistent refractive changes can also be achieved with this method. We conclude that femtosecond laser technology may be able to perform a variety of corneal refractive procedures with high precision, offering advantages over current mechanical and laser devices and techniques.
405 citations
TL;DR: In this paper, the authors review recent achievements with ultrafast bulk lasers and amplifiers based on Yb:YAG and yb:glass and pay attention to those aspects of the quasi-three-level nature of gain media that are important for short-pulse generation.
Abstract: We review recent achievements with ultrafast bulk lasers and amplifiers based on Yb:YAG and Yb:glass. Spe- cial attention is paid to those aspects of the quasi-three-level nature of these gain media that are important for short-pulse generation. The potential of Yb-doped media for efficient short-pulse generation and amplification is compared to their Nd-doped counterparts.
318 citations
TL;DR: An electrostatically deformable, gold-coated, silicon nitride membrane mirror was used as a phase modulator to compress pulses from 92 to 15 fs to test the range of the deformable-mirror-based compressor.
Abstract: An electrostatically deformable, gold-coated, silicon nitride membrane mirror was used as a phase modulator to compress pulses from 92 to 15 fs. Both an iterative genetic algorithm and single-step dispersion compensation based on frequency-resolved optical gating calibration of the mirror were used to compress pulses to within 10% of the transform limit. Frequency-resolved optical gating was used to characterize the pulses and to test the range of the deformable-mirror-based compressor.
287 citations
TL;DR: A kinetic model is developed which describes the plasma channel formation and the subsequent ambient gas excitation and ionization and the axial profile of laser channel and on-axis laser intensity is reconstructed.
Abstract: Using interferometry, we investigate the dynamics of interaction of a relativistically intense 4-TW, 400-fs laser pulse with a He gas jet. We observe a stable plasma channel 1 mm long and less than 30 $\ensuremath{\mu}$m in diameter, with a radial gradient of electron density $\ensuremath{\sim}5\ifmmode\times\else\texttimes\fi{}{10}^{22}$ ${\mathrm{cm}}^{\ensuremath{-}4}$ and with an on-axis electron density approximately ten times less than its maximum value of $8\ifmmode\times\else\texttimes\fi{}{10}^{19}$ ${\mathrm{cm}}^{\ensuremath{-}3}.$ A high radial velocity of the surrounding gas ionization of $\ensuremath{\sim}3.8\ifmmode\times\else\texttimes\fi{}{10}^{8}$ cm/s has been observed after the channel formation, and it is attributed to the fast ions expelled from the laser channel and propagating radially outward. We developed a kinetic model which describes the plasma channel formation and the subsequent ambient gas excitation and ionization. Comparing the model predictions with the interferometric data, we reconstructed the axial profile of laser channel and on-axis laser intensity. The estimated maximum energy of accelerated ions is about 500 keV, and the total energy of the fast ions is 5% of the laser pulse energy.
175 citations
TL;DR: An Yb:glass regenerative amplifier directly side pumped by four 20-W diodes is demonstrated and a free-running average output power as great as 4 W with a TEM(00) -like mode was achieved from the bare cavity, with a 0.56 pump duty cycle.
Abstract: An Yb:glass regenerative amplifier directly side pumped by four 20-W diodes is demonstrated. By use of a novel pumping scheme and introduction of cylindrical optics into the cavity, a free-running average output power as great as 4 W with a TEM(00) -like mode was achieved from the bare cavity, with a 0.56 pump duty cycle. When the regenerative amplifier injected, 1-mJ 200-fs FWHM pulses were obtained following compression by use of 2-ms pump pulses and up to a 150-Hz repetition rate.
42 citations
TL;DR: In this article, chirped-pulse amplification in a Yb3+-doped phosphate glass regenerative amplifier pumped by a free-running Ti:sapphire laser was demonstrated.
30 citations
TL;DR: In this paper, the use of a spatially dispersive laser cavity as a regenerative amplifier of ultrashort pulses has been reported, and an energy of 1.6 mJ was obtained with a spectrum of 81 nm at full width at half-maximum (FWHM).
28 citations
04 Mar 1999
TL;DR: Two methods are identified, using pulses centered at 1700 nm and a transparency inducing drug, to produce the spatial and temporal confinement of the pulse necessary to produce photodisruption in the highly scattering sclera.
Abstract: To evaluate transscleral glaucoma surgery techniques using ultrashort pulsed lasers, we attempted to produce photodisruption on the inner surface of the sclera without damaging the overlying tissue. We identified two methods, using pulses centered at 1700 nm and a transparency inducing drug, to produce the spatial and temporal confinement of the pulse necessary to produce photodisruption in the highly scattering sclera. When fully developed these concepts may help address the longstanding limitations of current glaucoma surgical techniques.
18 citations
TL;DR: In this article, a new technique based on the addition of laser sub-harmonic, ALS, was proposed, which allows the production of a single-cycle pulse with single-femtosecond pulse duration.
Abstract: Since the inception of the laser, pulse duration has been continuously decreased by the use of a variety of techniques: Q-switching, mode-locking, and pulse compression. We would like to present a new technique based on the addition of laser sub-harmonic, ALS, that allows the production of a single-cycle pulse with single-femtosecond pulse duration. This simple technique takes advantage of the recent progress made in the generation of a few optical cycles and in optical parametric amplification.
18 citations
04 Mar 1999
TL;DR: In this paper, the spatial confinement of laser beams focused through human cornea and sclera using long near infrared wavelengths was investigated using a 0.4 numerical aperture lens, which measured the spatial transmission of the smallest emergent beam on the back surface of the tissue.
Abstract: We investigated the spatial confinement of laser beams focused through human cornea and sclera using long near infrared wavelengths. Using a 0.4 numerical aperture lens, we measured the spatial transmission of the smallest emergent beam on the back surface of the tissue. We found that standard axial transmission measurements over estimate the amount of unscattered light for the sclera and that 1600 nm to 1700 nm had the maximum unscattered transmission through cornea and sclera. The light confinement may be useful in producing localized subsurface linear and nonlinear optical processes.
04 Feb 1999
TL;DR: The technology is capable to perform a variety of corneal refractive procedures at high precision, offering advantages over current mechanical and laser devices and enabling entirely new approaches for refractive surgery.
Abstract: We investigated refractive corneal surgery in vivo and in vitro by intrastromal photodisruption using a compact ultrafast femtosecond laser system. Ultrashort-pulsed lasers operating in the femtosecond time regime are associated with significantly smaller and deterministic threshold energies for photodisruption, as well as reduced shock waves and smaller cavitation bubbles than the nanosecond or picosecond lasers. Our reliable all-solid-state laser system was specifically designed for real world medical applications. By scanning the 5 micron focus spot of the laser below the corneal surface, the overlapping small ablation volumes of single pulses resulted in contiguous tissue cutting and vaporization. Pulse energies were typically in the order of a few microjoules. Combination of different scanning patterns enabled us to perform corneal flap cutting, femtosecond-LASIK, and femtosecond intrastromal keratectomy in porcine, rabbit, and primate eyes. The cuts proved to be highly precise and possessed superior dissection and surface quality. Preliminary studies show consistent refractive changes in the in vivo studies. We conclude that the technology is capable to perform a variety of corneal refractive procedures at high precision, offering advantages over current mechanical and laser devices and enabling entirely new approaches for refractive surgery.
11 Dec 1999-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this paper, the properties of an electron beam trapped and accelerated in a laser wake have been investigated and the number of electrons detected per bunch was determined to be (2.6$0.3) MeV/c.
Abstract: The properties of an electron beam trapped and accelerated in a laser wake"eld have been investigated. Plastic scintillating "bers were employed together with position sensitive photomultiplier tubes (PMT) and a series of dipole electro-magnets to study the beam. The measured momentum spectrum peaks around 7 MeV/c with an exponential fall-o! at high momenta up to (70.3$19.9) MeV/c. The number of electrons detected per bunch is determined to be (2.6$0.3)]1011. ( 1999 Elsevier Science B.V. All rights reserved.
28 May 1999
TL;DR: In this paper, a deformable mirror is used to correct the distortion of the output beam caused by thermal effects in the gain medium, imperfections of the optics, compressor misalignment and B-integral.
Abstract: Summary form only given. High power lasers using the chirped pulsed amplification (CPA) technique now frequently achieve terawatt peak power level. During the amplification of the pulse, the wavefront is distorted due to thermal effects in the gain medium, imperfections of the optics, compressor misalignment and B-integral. This leads to a bigger focal spot and thus to a decrease of the peak focused intensity. We present, in this paper, a direct correction of the output beam. The wavefront is measured with an achromatic three wave lateral shearing interferometer (ATWLSI). ATWLSI presents several advantages such as a tunable sensitivity, a self-estimation of the error on the phase measurement and its achromaticity. The correction is achieved with a deformable mirror.
28 May 1999
TL;DR: In this paper, a deformable mirror was used to adaptively optimize the focusing of a 10-fs pulse in an imaging geometry, and the second harmonic generation or two-photon fluorescence signal was optimized using a feedback loop based on a genetic algorithm.
Abstract: Summary form only given. Multiphoton confocal microscopy with extremely short (10 fs) optical pulses requires reflective optics, and ultimately requires control of the spatial wavefront in order to achieve diffraction-limited performance. We have demonstrated the use of a deformable mirror to adaptively optimize the focusing of a 10-fs pulse in an imaging geometry. We optimize the second harmonic generation or two-photon fluorescence signal from our sample using a feedback loop based on a genetic algorithm. To improve the speed of the convergence of our algorithm we use a Zernike orthogonal basis to control the deformable mirror.
18 Jun 1999
TL;DR: Substantial subsurface photodisruption was achieved in vitro without damaging overlying tissues with three techniques: use of long laser wavelengths, application of pressure, and application of a dehydrating agent.
Abstract: Transcleral photodisruption may provide a noninvasive method for creating partial thickness scleral channels to reduce elevated intraocular pressure associated with glaucoma. We achieved subsurface photodisruption in vitro without damaging overlying tissues with three techniques: (1) use of long laser wavelengths, (2) application of pressure, and (3) application of a dehydrating agent. Using 1 and 3, we were able to photodisrupt the internal surface of a full thickness block of sclera by focusing through the tissue.
28 May 1999
TL;DR: In this article, a single-shot measurement of the intrinsic laser damage in the sub-50 fs regime was performed under single shot conditions, and to exclude the complexity of cumulative effects.
Abstract: Summary form only given. The availability of ultrafast sub-50 fs lasers and the technology of chirped-pulse amplification have extended the study of the pulsewidth dependence of damage to ultrashort time scales. Various groups have reported two remarkable features of ultrashort pulse damage. First, short pulse damage exhibits a deterministic nature as opposed to the statistical behavior for long-pulse damage. Second, damage threshold fluence is higher than the prediction from the /spl radic//spl tau/ scaling rule for pulsewidth /spl tau/<10 ps. However, these measurements display different pulsewidth dependence of damage threshold in the subpicosecond regime. None of the theoretical models proposed before can explain this dissimilarity. The discrepancy among observations was thought to arise from different experimental conditions for instance, the number of laser shots. The sample may suffer a cumulative change in material properties as it is subjected to a series of subthreshold pulses. In order to study intrinsic laser damage, and to exclude the complexity of cumulative effects, our recent measurement was done under single-shot conditions.
28 May 1999
TL;DR: Using a KDP type II crystal with a predelay, the authors was able to generate high contrast laser pulses with a duration as short as 75 fs at /spl lambda/=0.53 /spl mu/m.
Abstract: Summary form only given. Using a KDP type II crystal with a predelay we were able to generate high contrast laser pulses with a duration as short as 75 fs at /spl lambda/=0.53 /spl mu/m. At the crystals output we have used a deformable mirror to correct for accumulated B-integral to focus laser pulses to the intensity of 2.10/sup 19/ W/cm/sup 2/. Second harmonic generation in this system was studied.
23 Jul 1999
TL;DR: In this paper, the theoretical limits for the generation of high focused intensity laser are presented and the important role of high saturation-fluence materials is established and the use of regenerative chirped pulsed amplification is discussed.
Abstract: We present the theoretical limits for generation of high focused intensity laser. The important role of high- saturation-fluence materials is established and the use of regenerative chirped pulsed amplification to achieve high energy extraction from such materials is discussed. A regenerative chirped pulse amplification model and related experiments support the view that the surface damage threshold does not limit the range of useful laser materials to those with saturation fluence below the surface damage threshold. In addition the importance of phase measurement and control in providing well-defined conditions for experiments are noted.
28 May 1999
TL;DR: In this paper, a linear pre-compensation of self phase modulation (SPM) was demonstrated using a mode-locked Ti:sapphire laser and a pulse shaper using a linear deformable mirror in the Fourier plane of the pulseShaper.
Abstract: Summary form only given. We have implemented a demonstration on the linear pre-compensation of self phase modulation (SPM), using a mode-locked Ti:sapphire laser and a pulse shaper using a linear deformable mirror in the Fourier plane of the pulse shaper. The pulses were first stretched in 3.2 cm of glass, sent through the pulse shaper, and injected into 38 cm of single-mode fiber as the nonlinear element. The pulses were then recompressed using a grating pair (400 l/mm), and measured using interferometric autocorrelation.
28 May 1999
TL;DR: In this paper, an interaction of ultra-high intensity short laser pulses with underdense plasma is of considerable interest from the standpoint of basic physics and potential application for advanced inertial confinement fusion, X-ray lasers and particle accelerators.
Abstract: Summary form only given. An interaction of ultra-high intensity short laser pulses with underdense plasma is of considerable interest from the standpoint of basic physics and potential application for advanced inertial confinement fusion, X-ray lasers and particle accelerators. The ultra-high electromagnetic fields in the laser focus produce an extremely high pondermotive force that expels free electrons from the laser axis and relativistically modify the electron mass, plasma frequency and the plasma refractive index so that the plasma acts as a positive lens. If the laser pulse duration is long enough, the charge separation produces strong electrostatic field /spl sim/1 GV/cm that can accelerate ions to MeV energies. All these effects lead to a relativistic self-focusing and self-guiding of the laser beam that can further increase the laser intensity and maintain it over distances much longer than a Rayleigh range.