Showing papers on "Femtosecond published in 1995"
TL;DR: The self-channeling of ultrashort laser pulses through 20 m of air was demonstrated and a preliminary model is shown to explain these results.
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.
1,205 citations
TL;DR: In this article, dual-quadrature spectral interferometry and Fourier transform (FT) were used to obtain a complete measurement of the complex electric field, E(ω), as a continuous function of frequency.
Abstract: Although nonlinear methods can provide only the amplitude and the phase of an isolated ultrashort pulse, linear techniques can yield such measurements with a much better sensitivity and reliability when a reference pulse is available. We demonstrate two such methods, dual-quadrature spectral interferometry and Fourier-transform spectral interferometry. These techniques are simple to implement, very sensitive, and provide a complete measurement of the complex electric field, E(ω), as a continuous function of frequency.
942 citations
TL;DR: In this article, the authors proposed an active and passive pulse shaping method based on phase-only filtering and an alternate Fourier synthesis pulse shaping technique, as well as additional passive and active pulse shaping methods.
482 citations
TL;DR: In this article, a Ti:sapphire laser was used to ablate holes with a diameter of 300 nm and a depth of 52 nm to produce very small features in materials.
457 citations
TL;DR: It is shown that during the first 100 fs the changes of the optical constants and of the nonlinear optical susceptibility are determined by the various electronic excitation processes and only to a lesser extent by the process of disordering.
Abstract: Laser-induced ultrafast order-disorder transitions in silicon and gallium arsenide are studied by means of femtosecond time-resolved linear and nonlinear optical spectroscopy. Detailed measurements of the reflectivity and of the reflected second harmonic over a wide range of fluences reveal a complex picture of the phase transformation. We show that during the first 100 fs the changes of the optical constants and of the nonlinear optical susceptibility ${\mathrm{\ensuremath{\chi}}}^{(2)}$ are determined by the various electronic excitation processes and only to a lesser extent by the process of disordering. On the other hand, time-resolved measurements of reflectivity spectra indicate that the development of a Drude-like metallic spectrum takes a few hundred femtoseconds. Our data show that the laser-induced structural changes develop slower than previously believed, occurring on a time scale of a few hundred femtoseconds.
296 citations
TL;DR: In this paper, the authors reported the observation of a gain of approximately Ω(exp{exp{left(11\right)$ at 41.8 nm in 8-times ionized xenon.
Abstract: We report the observation of a gain of approximately $\mathrm{exp}\left(11\right)$ at 41.8 nm in 8-times-ionized xenon. This extreme ultraviolet (XUV) laser is driven by a 10-Hz, 70-mJ circularly polarized femtosecond laser pulse. The laser is focused into Xe at pressures ranging from 5 to 12 torr. The laser is collisionally excited, with both the ions and electrons produced by field induced tunneling.
275 citations
TL;DR: Using theory to guide the choice of pulse shape, frequency-chirped laser pulses are synthesized and used to control the evolution of vibrational wave packets on the 8 excited state of iodine.
Abstract: Using theory to guide the choice of pulse shape, we have synthesized frequency-chirped laser pulses and used them to control the evolution of vibrational wave packets on the $B$ excited state of iodine. A negatively chirped pulse produces a wave packet at the target time localized about an internuclear position and momentum of our choice. An approximately time-reversed pulse, however, produces a delocalized wave packet. The experimental results are in very good qualitative agreement with quantum simulations.
270 citations
TL;DR: In this article, a complete theoretical model is presented to simulate the electron seeding and the evolution of the plasma of electron-ion in the applied field, and the results of the theory verified by small scale experiments are used to simulate lightning in atmosphere, and helps to define the parameters of a laser system for lightning protection.
Abstract: Ultraviolet pulses of 200 fs duration and low energy (/spl ap/0.2 mJ) have a sufficiently high peak power to ionize oxygen and nitrogen by three- and four-photon ionization, respectively. It is shown that the resultant ionization channel induces a lightning like discharge at half of the natural self-breakdown voltage in nitrogen or air. The laser triggered discharging process is studied by monitoring the voltage between two planar electrodes. The effects of oxygen on the induced breakdown is investigated. A complete theoretical model is presented to simulate: (1) the electron seeding; and (2) the evolution of the plasma of electron-ion in the applied field. The results of the theory verified by small scale experiments-are used to simulate the process of laser triggered lightning in atmosphere, and helps to define the parameters of a laser system for lightning protection. >
255 citations
TL;DR: In this paper, the thermalization of copper nanoparticles embedded in glass was investigated using femtosecond pump-probe spectroscopy, where the time dependent induced transmission was enhanced near the surface plasmon resonance of the nanoparticles, as opposed to the static one obtained with thermomodulation measurements.
Abstract: The thermalization of electrons in copper nanoparticles embedded in glass is investigated using femtosecond pump-probe spectroscopy. The time dependent induced transmission is enhanced near the surface plasmon resonance of the nanoparticles, as opposed to the static one obtained with thermomodulation measurements. In addition, a slowing of the process of electron cooling to the lattice temperature is observed at the plasmon resonance. These observations show the importance of quasiparticle collisions in confined metallic structures.
250 citations
IBM1
TL;DR: The physics of electron dynamics at surfaces and interfaces encompasses a rich variety of processes ranging from electron scattering and diffusion to electron-hole recombination and surface state and defect trapping.
242 citations
TL;DR: In this article, the authors compared the threshold energies of ablation in gold as a function of pulse width from 10 ns to 100 fs, and further numerically computed results for gold and silicon on ablation rates, threshold surface temperatures, liquid thicknesses, and vaporization rates.
Abstract: Application of picosecond and femtosecond laser pulses to the controlled ablation of materials represents a relatively unexplored yet important topic in laser processing. Such ultrashort pulses are of potential value in areas of thin‐film deposition, micromachining, and surgical procedures. We report here some early results of systematic studies being done from the femtosecond to the nanosecond regime, as an assessment of the problems and benefits associated with various laser pulse durations and their use in processing optically absorbing media. Experimental data and theoretical results of computer simulations are presented and compared for the threshold energies of ablation in gold as a function of pulse width from 10 ns to 100 fs. This work is then extended to include further numerically computed results for gold and silicon on ablation rates, threshold surface temperatures, liquid thicknesses, and vaporization rates as a function of pulse duration throughout the ultrafast regime from tens of femtoseco...
TL;DR: In this paper, the Fabry-Perot saturable absorber has been used to predict the dynamic behavior of a solid state laser in the important regimes of Q-switching, mode-locked Qswitching and continuous-wave mode locking.
Abstract: We have successfully demonstrated that an appropriately designed semiconductor saturable absorber device, the antiresonant Fabry-Perot saturable absorber, can reliably start and sustain stable mode locking of solid state lasers such as Nd:YAG, Nd:YLF, Nd:Glass, Cr:LiSAF, and Ti:sapphire lasers. Especially for solid state lasers with long upper-state lifetimes, previous attempts to produce self-starting passive mode locking with saturable absorbers was always accompanied by self-Q-switching. We derive criteria that characterize the dynamic behavior of solid state lasers in the important regimes of Q-switching, mode-locked Q-switching, and continuous-wave mode locking in the picosecond and femtosecond range for the pulsewidth. We demonstrate that semiconductor absorbers can be designed to predetermine the dynamic behavior of a laser for a given solid state laser material and present an experimental verification. This allows for the development and design of robust, compact pico- and femtosecond solid state laser sources for scientific and industrial applications.
TL;DR: In this article, a quasi-single-cycle near-infrared light pulses with a measured spectrum extending from 7 to 15 μm have been generated, opening up new perspectives in IR spectroscopy.
Abstract: Quasi‐single‐cycle near‐infrared light pulses with a measured spectrum extending from 7 to 15 μm have been generated, opening up new perspectives in IR spectroscopy. The method is based on the rectification of 0.8 μm 10–15 fs light pulses from a 100 MHz oscillator, using the instantaneous second‐order polarizability of bulk semiconductors such as GaAs.
TL;DR: The femtosecond optical heterodyne detected optical Kerr effect/Raman-induced Kerr effect (OHD OKE/RIKE) is described in detail with emphasis on the utility for investigating the intermolecular spectra and dynamics of liquids as mentioned in this paper.
Abstract: The femtosecond optical heterodyne detected optical Kerr effect/Raman-induced Kerr effect (OHD OKE/RIKE) is described in detail with emphasis on the utility for investigating the intermolecular spectra and dynamics of liquids. The femtosecond dynamics of the liquids CS2, benzene and CCI4 are addressed through a combination of conventional time-domain kinetic and Fourier-transform analyses, and the physical origin of the intermolecular intensity is addressed for each. The distinctions between the excitation mechanisms of the femtosecond OKE/RIKE and other continuous-wave and picosecond Raman techniques are described. The distinctions between the dephasing mechanisms of intramolecular and intermolecular vibrational modes are discussed.
TL;DR: In this article, a model is presented describing the perturbed free induction decay effect for the general situation, where a complex molecule containing many overlapping vibrational modes is investigated, leading to an efficient linear least square fit algorithm allowing the analysis of huge data sets.
TL;DR: A new low-loss semiconductor structure for femtosecond intracavity mode locking in low-gain solidstate lasers is introduced and mode-locking mechanisms in quantum-well passively mode-locked solid-state lasers are discussed.
Abstract: We introduce a new low-loss semiconductor structure for femtosecond intracavity mode locking in low-gain solid-state lasers. This monolithic device can be engineered to exhibit specific saturation characteristics desirable for mode locking solid-state lasers. Self-starting 90-fs pulses are obtained with Ti:sapphire and diode-pumped Cr:LiSAF lasers. We discuss mode-locking mechanisms in quantum-well passively mode-locked solid-state lasers.
TL;DR: In this article, the authors compared the femtosecond transient dichroism signals observed for I2 in hexane reported by Scherer, Jonas, and Fleming (J. Chem. Phys. 1993,99, 153-168) and found that the pump-probe signal converges toward the classical limit as temperature is increased.
Abstract: quantum and classical pictures of the change in the ground state vibrational density operator, Computations of the iodine ground state contribution to the pump-probe signal agree with the classical predictions and show that deg can be narrower than the zero point level probability distribution. These computations are compared to the femtosecond transient dichroism signals observed for I2 in hexane reported by Scherer, Jonas, and Fleming (J. Chem. Phys. 1993,99, 153-168) and found to agree within experimental error. The quantum calculations also show the thermal simplification of the pump-probe signal toward the classical limit as temperature is increased. We show quantitatively that for an electronically resonant pump-pulse, deg tends toward a negative operator (a “pure ground state hole”) with increasing temperature, implying that certain types of pump-probe signals (e.g. photon-detected transient absorption) have signed ground state signals which do not oscillate through zero.
TL;DR: A passively mode-locked femtosecond Yb:YAG laser is demonstrated using different semiconductor saturable absorber devices, a high-finesse and a low- finesse antiresonant Fabry–Perot saturative absorber and mode locked the laser at either 1.03 or 1.05 μm.
Abstract: We demonstrate a passively mode-locked femtosecond Yb:YAG laser using different semiconductor saturable absorber devices, a high-finesse and a low-finesse antiresonant Fabry–Perot saturable absorber. We achieved pulses as short as 540 fs with dispersion compensation and 1.7-ps pulses without dispersion compensation. We also mode locked the laser at either 1.03 or 1.05 μm by adjusting the band gap and antiresonance wavelength design of the antiresonant Fabry–Perot saturable absorber.
TL;DR: In this paper, the S1→S0 transition energy distribution for the solvents methanol and acetonitrile at several temperatures is described by the dependence of the mean (first moment), width, and asymmetry (second and third central moments) of the distribution on time.
Abstract: Spectra of transient absorption and stimulated emission are recorded for the styryl dye DASPI, after excitation at 470 nm, with experimental resolution of 100 fs. The evolution of the S1→S0 transition energy distribution is obtained for the solvents methanol and acetonitrile at several temperatures. It is described by the dependence of the mean (first moment), width, and asymmetry (second and third central moments) of the distribution on time. The observed time‐dependence of the mean transition energy is simulated by appropriate models for the solvation dynamics. In both methanol and acetonitrile an ultrafast component is observed. Width and asymmetry change most rapidly and characteristically during this initial part of solvation. In the evolution of the higher moments, different relaxation contributions apparently are better distinguished than in the evolution of the first moment. For methanol at 50 °C, an oscillatory evolution is observed mainly in the higher moments which may indicate underdamped coherent solvent motion.
TL;DR: The frequency-dependent group delay of dielectric mirrors was measured by spectrally resolved white-light interferometry and thin-film Gires-Tournois interferometers designed for dispersion control in a femtosecond Ti:sapphire laser oscillator-amplifier system were tested.
Abstract: The frequency-dependent group delay of dielectric mirrors was measured by spectrally resolved white-light interferometry. Chirped mirrors and thin-film Gires-Tournois interferometers designed for dispersion control in a femtosecond Ti:sapphire laser oscillator-amplifier system were tested with a group-delay resolution of +/-0.2 fs and a spectral resolution of ~1 nm over the spectral range of 670-870 nm.
TL;DR: In this paper, femtosecond measurements of the dynamics of photoinduced electrons at the liquid-metal interface produced by exciting the surface plasmon band of aqueous silver colloidal particles are reported.
Abstract: We report direct femtosecond measurements of the dynamics of photoinduced electrons at the liquid–metal interface produced by exciting the surface plasmon band of aqueous silver colloidal particles. The electron plasma resonance created initially dephases into individually excited electrons in less than 150 fs. This is followed by a large component, fast exponential decay with a time constant of 2 ps, which is attributed to electronic energy relaxation through electron–phonon coupling. A slower 40 ps decay is also observed and attributed to subsequent cooling of the excited phonons due to phonon–solvent interaction. The decay dynamics, especially the 2 ps decay, are relatively insensitive to the solvent environment, indicating that the early time decay is dominated by the properties of the silver particles. The solvent molecules play an important role in the phonon cooling process following the electronic energy relaxation. The results show that the majority of the electrons created through photoexcitatio...
TL;DR: A review is presented of femtosecond pulse-shaping methods and their application to spectroscopy of atoms, molecules, and condensed materials and theoretical predictions and qualitative discussions of optical control possibilities involving complex ultrafast waveforms.
Abstract: A review is presented of femtosecond pulse-shaping methods and their application to spectroscopy of atoms, molecules, and condensed materials. Pulse shaping can be used to generate femtosecond pulse sequences and other optical waveforms whose time-dependent amplitude, phase, frequency, and polarization profiles are all specified precisely. The lightmatter interaction mechanisms through which such waveforms can be used for optical control over molecular and material responses are discussed. Most of the spectroscopic experiments conducted to date that involve shaped femtosecond waveforms are reviewed. These have involved control over coherent electronic responses of atoms, small molecules, and multiple quantum wells and control over coherent molecular and lattice vibrations. A selective review is presented of theoretical predictions and qualitative discussions of optical control possibilities involving complex ultrafast waveforms
TL;DR: In this paper, the authors studied the time-resolved fluorescence spectra of the DCM dye molecule in methanol and chloroform using the fluorescence upconversion technique with femtosecond time resolution.
TL;DR: W wavelength-division multiplexing with a single broadband femtosecond source is demonstrated by slicing the 3.7-THz spectral bandwidth of 85-fs laser pulses into 16 channels that are modulated individually.
Abstract: We demonstrate wavelength-division multiplexing with a single broadband femtosecond source by slicing the 3.7-THz spectral bandwidth of 85-fs laser pulses into 16 channels that are modulated individually.
TL;DR: It is demonstrated that coherent phonons allow monitoring the pathway to nonthermal laser-induced melting of crystalline materials and the observed frequency shift is of purely electronic origin.
Abstract: We investigate the dynamics of coherent optical phonons in tellurium after high-density excitation with femtosecond laser pulses. The data show a continuous redshift of the phonon frequency with increasing excitation density. Experiments with double-pulse excitation prove that the observed frequency shift is of purely electronic origin. We demonstrate that coherent phonons allow monitoring the pathway to nonthermal laser-induced melting of crystalline materials.
TL;DR: It is shown that the temporal profile of the photon echo allows separation of the homogeneous from the inhomogeneous contribution to the optical spectrum.
Abstract: We report on time-resolved femtosecond photon echo experiments of a dye molecule in a polar solution. The photon echo is time resolved by mixing the echo with a femtosecond gate pulse in a nonlinear crystal. It is shown that the temporal profile of the photon echo allows separation of the homogeneous from the inhomogeneous contribution to the optical spectrum. A biexponential correlation function for frequency fluctuations is used to simulate the echo.
TL;DR: For the first time, it is confirmed experimentally that the material responses obtained by these time- and frequency-domain measurements completely agree with each other in a frequency region extending over 3 orders of magnitudes.
Abstract: The dynamical response of matter measured by femtosecond optical Kerr effect spectroscopy is directly compared with the high-resolution light scattering spectrum obtained by a tandem Fabry-P\'erot interferometer. Using simple liquids as samples, we have for the first time confirmed experimentally that the material responses obtained by these time- and frequency-domain measurements completely agree with each other in a frequency region extending over 3 orders of magnitudes.
TL;DR: In this paper, the connection between dephasing of optical coherence and the measured spectral density of the pure solvent is made through measurements and calculations of photon echo signals, and two approaches that employ the response function description of nonlinear spectroscopy; (i) a single Brownian oscillator line shape model and (ii) the line shape obtained using the solvent spectral density.
Abstract: The connection between dephasing of optical coherence and the measured spectral density of the pure solvent is made through measurements and calculations of photon echo signals. 2‐pulse photon echo measurements of a cyanine dye in polar solvents are presented. Signals are recorded for both phase matched directions enabling accurate determination of the echo signal time shift. Echo signals are calculated by two approaches that employ the response function description of nonlinear spectroscopy; (i) a single Brownian oscillator line shape model, and (ii) the line shape obtained using the solvent spectral density. The strongly overdamped Brownian oscillator model incorporates only a single adjustable parameter while the experimental data present two fitting constraints. The second model incorporates the measured solvent spectral density. Both give very good agreement with the experimental results. The significance of the second method lies in this being a new approach to calculate nonlinear spectroscopic sign...