Showing papers on "Femtosecond published in 1993"
TL;DR: The frequency-resolved optical gating (FROG) technique as discussed by the authors was proposed to measure the spectrum of the signal pulse as a function of the delay between two input pulses and the resulting trace of intensity versus frequency and delay is related to the pulse's spectrogram a visually intuitive transform containing time and frequency information.
Abstract: The frequency-resolved optical gating (FROG) technique for characterizing and displaying arbitrary femtosecond pulses is presented. The method is simple, general, broadband, and does not require a reference pulse. Using virtually any instantaneous nonlinear-optical effect, FROG involves measuring the spectrum of the signal pulse as a function of the delay between two input pulses. The resulting trace of intensity versus frequency and delay is related to the pulse's spectrogram a visually intuitive transform containing time and frequency information. It is proven using phase retrieval concepts that the FROG trace yields the full intensity I(t) and phase phi (t) of an arbitrary ultrashort pulse with no physically significant ambiguities. FROG appears to have temporal resolution limited only by the response of the nonlinear medium. The method is demonstrated by using self-diffraction through the electronic Kerr effect in BK-7 glass and 620-nm, linearly chirped, approximately 200-fs pulses of a few microjoules. >
846 citations
TL;DR: In this article, the nonlinear optical response of liquids subjected to a series of femtosecond laser pulses is calculated using a multimode harmonic model for nuclear motions, with nonlinear coupling to the radiation field through the coordinate dependence of the electronic polarizability.
Abstract: The nonlinear optical response of liquids subjected to a series of N femtosecond laser pulses is calculated using a multimode harmonic model for nuclear motions, with nonlinear coupling to the radiation field through the coordinate dependence of the electronic polarizability. Using electronically off‐resonant optical fields, this multidimensional spectroscopy is shown to provide direct information regarding the homogeneous or the inhomogeneous nature of the spectral density obtained from optical birefringence measurements. Complementary information can be obtained using infrared pulses where the multiple time correlation functions of the nuclear dipole moment (rather than the electronic polarizability) are being probed.
520 citations
TL;DR: In this paper, the phase of two excited-state vibrational modes is conserved for a period of picoseconds over a large range of temperatures in a genetically modified bacterial reaction centre.
Abstract: Multicolour near-infrared femtosecond experiments of a genetically modified bacterial reaction centre show that the phase of two excited-state vibrational modes is conserved for a period of picoseconds over a large range of temperatures. The direct visualization of low-frequency nuclear vibrations in this protein, which is embedded in its natural membrane, implicates coherent nuclear motion in the primary electron transfer reaction in functional reaction centres.
506 citations
TL;DR: Ultrafast relaxation processes in poly(p-phenylenevinylene) and its oligomers are investigated using femtosecond luminescence spectroscopy and a quasi-instantaneous luminecence rise and the absence of luminescent near the excitation energy indicate very rapid vibronic relaxation.
Abstract: Ultrafast relaxation processes in poly(p-phenylenevinylene) and its oligomers are investigated using femtosecond luminescence spectroscopy. A quasi-instantaneous luminescence rise and the absence of luminescence near the excitation energy indicate very rapid vibronic relaxation. The subsequent transient redshift of the spectra is attributed to ultrafast energy relaxation of optical excitations within an inhomogeneously broadened density of states.
365 citations
TL;DR: A new technique, femtosecond transillumination optical coherence tomography, for time-gated imaging of objects embedded in scattering media, derives a fundamental limit on ballistic imaging thickness based on quantum noise considerations.
Abstract: We describe a new technique, femtosecond transillumination optical coherence tomography, for time-gated imaging of objects embedded in scattering media. Time gating is performed with a fiber-optic interferometer with femtosecond pulses and coherent heterodyne detection to achieve a 130-dB dynamic range. A confocal imaging arrangement provides additional spatial discrimination against multiply scattered light. By time gating ballistic photons, we achieve 125-microm-resolution images of absorbing objects in media 27 scattering mean free paths thick. We derive a fundamental limit on ballistic imaging thickness based on quantum noise considerations.
286 citations
TL;DR: Measurements performed in a thin gold film in the very low perturbation limit yield evidence for the existence of a non-Fermi electron distribution with an electron thermalization time of ∼500 fs and an electron-lattice interaction time of 1 ps.
Abstract: Electron-electron and electron-phonon thermalization processes are investigated in gold films using a high-sensitivity multiple-wavelength femtosecond pump-probe technique. A nonequilibrium electron distribution is excited by free-carrier absorption of an infrared femtosecond pulse and its relaxation dynamics followed by measuring the transient reflectivity and transmissivity with a visible probe pulse. Measurements performed in a thin gold film in the very low perturbation limit (\ensuremath{\Delta}${\mathit{T}}_{\mathit{e}}$\ensuremath{\sim}20 K) yield evidence for the existence of a non-Fermi electron distribution with an electron thermalization time of \ensuremath{\sim}500 fs and an electron-lattice interaction time of 1 ps. The apparent thermalization dynamics of the electron gas is much faster in optically thick samples and is shown to be dominated by transport effects.
221 citations
TL;DR: In this paper, Gruebele et al. presented a formalism for extracting highly resolved spectral information and the potential of bound isolated systems from coherent ultrafast laser experiments, using I2 as a model system.
Abstract: Recently, we presented a formalism for extracting highly resolved spectral information and the potential of bound isolated systems from coherent ultrafast laser experiments, using I2 as a model system [Gruebele et al., Chem. Phys. Lett. 166, 459 (1990)]. The key to this approach is the formation of coherent wave packets on the potential energy curve (or surface) of interest, and the measurement of their scalar and vector properties. Here we give a full account of the method by analyzing the coherences of the wave packet in the temporal transients of molecules excited by ultrashort laser pulses, either at room temperature, or in a molecular beam. From this, some general considerations for properly treating temporal data can be derived. We also present a direct inversion to the potential and quantum and classical calculations for comparison with the experiments.
208 citations
TL;DR: In this paper, the authors developed a simple, high-speed, nearly vibration-free, mechanically scanned, optical delay line suitable for femtosecond time-resolved signal-averaging measurements.
Abstract: We have developed a simple, high-speed, nearly vibration-free, mechanically scanned, optical delay line suitable for femtosecond time-resolved signal-averaging measurements. We demonstrate a 2-ps time window autocorrelator with a display updated at 400 Hz. The delay line uses a dithering planar mirror as a time-varying linear phase ramp in the spectral plane of a modified grating-lens femtosecond pulse shaper. The time delay is linearly proportional to the angular deviation of the mirror. The high speed and low vibration are a result of the extremely small angular changes required to generate a large time delay.
205 citations
TL;DR: In this article, a femtosecond traveling-wave parametric generator with a parametric superfluorescence seed source and parametric amplifier was proposed. But the performance of the generator was limited to 1-ps and 200-fs pulses at wavelengths of 0.53 and 0.6 μm, respectively.
Abstract: We report on the generation of ultrashort tunable pulses with a cavityless traveling-wave scheme consisting of a parametric superfluorescence seed source and a parametric amplifier. We show that the traveling-wave approach, with its advantages of simplicity and direct generation of tunable energetic single pulses, can be used in the femtosecond regime, and to this end we discuss the performances that were obtained with pump pulses of ≈1-ps and 200-fs duration at wavelengths of 0.53 and 0.6 μm, respectively. Of particular interest is the β-barium borate-based traveling-wave parametric generator (type-II phase matching), since it offers the possibility of generating nearly transform-limited pulses that are continuously tunable within a wide spectral range to as high as 3 μm in the IR. With a diffraction-limited pump at 0.53 μm. we obtained tunable pulses in a 1.2× diffraction-limited beam, which could be focused, with an f/20 optics lens, to an intensity of 1013 GW/cm2. A temperature-tuned lithium triborate-based femtosecond parametric generator, with its smaller group-velocity dispersion and absence of walk-off, can operate at a pump energy of as low as 30 μJ in a 200-fs pulse.
203 citations
TL;DR: The advent of lasers powerful enough to generate a measurable effect, and which can be pulsed on femtosecond time scales, has made the optical Kerr effect into a practical technology for investigating the molecular structure and interactions of condensed systems.
Abstract: In the optical Kerr effect, the electric field of light incident on a transparent sample induces an anisotropic refractive index, which is measured by its effect on the passage of a second light beam. The advent of lasers powerful enough to generate a measurable effect, and which can be pulsed on femtosecond time scales, has made the optical Kerr effect into a practical technology for investigating the molecular structure and interactions of condensed systems such as pure liquids, liquid solutions, and plastic crystals.
199 citations
TL;DR: In this article, the femtosecond nonlinear optical response of ethylene glycol is quite similar to that of water, and the pure nuclear solvent response is transformed into a dipolar solvation correlation function for comparison with ultrafast electron transfer reaction rates.
Abstract: We have measured the ultrafast solvent relaxation of liquid ethylene glycol, triacetin, and water by means of femtosecond polarization spectroscopy, using optical‐heterodyne‐detected Raman‐induced Kerr‐effect spectroscopy. In the viscous liquids triacetin and ethylene glycol, femtosecond relaxation processes were resolved. Not surprisingly, the femtosecond nonlinear optical response of ethylene glycol is quite similar to that of water. Using the theory of Maroncelli, Kumar, and Papazyan, we transform the pure‐nuclear solvent response into a dipolar‐solvation correlation function for comparison with ultrafast electron‐transfer reaction rates.
Proceedings Article•
02 May 1993TL;DR: In this article, the possibility of creating and probing a transient nonequilibrium electron population in metals with ultrashort laser pulses has been demonstrated by different groups, including the possibility to create and probe a transient electron population.
Abstract: The possibility of creating and probing a transient nonequilibrium electron population in metals with ultrashort laser pulses has been demonstrated by different groups.1,2 Because of the large electron densities, electron-electron interactions were assumed to be sufficiently fast to instantaneously thermalize the electron gas, although some deviations from Fermi-distribution behavior were observed dose to the Fermi surface.2 Recently, by using a photoemission technique, thermalization times as long as 600 fs were measured in gold films for large changes of the electron temperature (of the order of 400 K).3
TL;DR: In this article, the anisotropies in ultrashort pulse pump-probe experiments were calculated and the original results, well known from the theory of resonance Raman, were recovered for zero delay times.
TL;DR: A broadly tunable femtosecond optical parametric oscillator (OPO) based on KTiOPO(4) that is externally pumped by a self-mode-locked Ti:sapphire laser is described.
Abstract: A broadly tunable femtosecond optical parametric oscillator (OPO) based on KTiOPO4 is externally pumped by a self-mode-locked Ti:sapphire laser. The laser is capable of continuous tuning from 1.2 micrometers to 1.37 micrometers in the signal branch and 1.8 to 2.15 micrometers in the idler branch, when using one set of OPO optics. Other optics expand the tuning range of the OPO from 1.0 micrometers to 2.75 micrometers, for example, by using three sets of mirrors and two different crystals. Without prisms in the OPO cavity, 215 mW of chirped pulses is generated in the signal branch, while 235 mW is generated in the idler branch. The total conversion efficiency, as measured by pump depletion, is 50%. With prisms in the cavity, nearly transform-limited pulses of 135 femtoseconds are generated, which can be shortened to 75 fs by increasing the output coupling.
TL;DR: In this article, a comprehensive study of the UV photolysis of I3− in ethanol solution, using femtosecond time resolved transient transmission experiments, is presented, which indicates that with high probability, photoexcitation leads to direct formation of diiodide ions within 300 fs, which are vibrating coherently.
Abstract: We report a comprehensive study of the UV photolysis of I3− in ethanol solution, using femtosecond time resolved transient transmission experiments. We interpret our results to indicate that with high probability, photoexcitation leads to direct formation of di‐iodide ions within 300 fs, which are vibrating coherently. Through our experiments we have been able to determine that the time scales for vibrational dephasing, vibrational relaxation, and reorientation of the fragment ions are 400 fs, 4 ps, and 5 ps, respectively. Transmission signals at 620 nm and at 880 nm, which are above and below the λmax of the known absorption of I2−, oscillate at a precisely opposite phase. This and other results presented indicate that through the oscillations we are observing coherent vibration of the I2− photofragment. UV transient transmission experiments have been conducted in order to characterize the time scales for recombination. Preliminary results show that recombination takes place on several time scales. A fas...
TL;DR: This work reports programmable femtosecond pulseshaping using two commercially avaliable liquid crystal spatial light modulators (SLM) that allows generation of waveforms with arbitrary temporal phase and amplitude profiles within a 2.9 picosecond time window with features of less than 100 femToseconds.
Abstract: We report programmable femtosecond pulseshaping using two commercially avaliable liquid crystal spatial light modulators (SLM). This allows generation of waveforms with arbitrary temporal phase and amplitude profiles within a 2.9 picosecond time window with features of less than 100 femtoseconds. Such waveforms suggest exciting prospects for the control of chemical behaviour.
TL;DR: In this article, one-and two-color time-domain probing of the resonant dichroic response of iodine in n−hexane following femtosecond B•X excitation at 580 nm is described.
Abstract: One‐ and two‐color time‐domain probing of the resonant dichroic response of iodine in n‐hexane following femtosecond B‐X excitation at 580 nm is described. The detected signals contain both ground and excited state vibrational coherence contributions to the third‐order polarization. The dichroic response can be separated into positive and negative amplitude contributions: B‐X absorption and stimulated emission are positive but absorption from the B‐state can yield either positive or negative signals depending on the direction of the transition moment. Wave packet motion on both the ground and excited states of iodine is studied with a frequency tunable femtosecond probe. It is shown that the positive signals can be interpreted as B‐X dichroic response using the classical Franck principle. The classical Franck principle also provides information about the potential probed in absorption from the B state. From the probe wavelength dependent delay in the signal appearance, it is concluded that the absorptive signal for blue probe wavelengths arises from a repulsive state reached by solvent‐induced predissociation of the B state. Dephasing of B state vibrational coherence results from this solvent‐induced predissociation of iodine. We discuss the evolving reaction in terms of possible dissociative potential energy curves a1g(3Π) and a’0g+(3Σ−). The time evolution of the bluest probe dichroism signals is representative of continuing atom separation; the experiments have not yet probed large enough internuclear separations to evidence a buildup of dissociated product or momentum reversal, i.e., caging.
TL;DR: In this paper, the authors demonstrate that femtosecond laser pulses can be spectrally narrowed by self-phase modulation in optical fibers and obtain a reduction of the spectral linewidth from 10.6 nm to 2.7 nm, limited only by the laser power in the fiber.
Abstract: We demonstrate experimentally and theoretically that frequency‐modulated femtosecond laser pulses can be spectrally narrowed by self‐phase modulation in optical fibers. We obtain a reduction of the spectral linewidth from 10.6 down to 2.7 nm, limited only by the laser power in the fiber. Applications for extracavity conversion of femtosecond lasers to narrow‐linewidth picosecond sources are discussed.
TL;DR: The first femtosecond electronic dephasing in CdSe nanocrystals using three-pulse photon echoes and a novel mode-suppression technique was reported in this article.
Abstract: We report the first direct measurements of femtosecond electronic dephasing in CdSe nanocrystals using three-pulse photon echoes and a novel mode-suppression technique. We are able to separate the dynamics of the coherently excited LO phonons from the underlying electron-hole dephasing by suppressing the quantum beats. The homogeneous linewidth of these materials at 15 K results from electronic dephasing in \ensuremath{\sim}85 fs, approximately half of which is due to acoustic phonon modes. Contributions from acoustic phonons dominate the homogeneous linewidth at room temperature.
TL;DR: The oscillator presented has the potential for producing sub-10-fs pulses in the 800-nm wavelength region, and the position of the dispersive resonance is used to determine the ratio of the net second- and third-order intracavity dispersions.
Abstract: We report the operating characteristics of a self-mode-locked Ti:sapphire solitary laser at reduced group-delay dispersion. The generation of ≈12.3 fs near-sech2 optical pulses at 775 nm is reported, together with experimental evidence for the dominant role of third-order dispersion (TOD) as a limiting factor to further pulse shortening in the oscillator. At reduced second-order dispersion excessive residual TOD is shown to lead to dispersive wave generation, and the position of the dispersive resonance is used to determine the ratio of the net second- and third-order intracavity dispersions. Since the magnitude of TOD rapidly decreases with increasing wavelength in prism-pair dispersion-compensated resonators, the oscillator presented has the potential for producing sub-10-fs pulses in the 800-nm wavelength region.
Proceedings Article•
02 May 1993TL;DR: In this article, femtosecond optical spectroscopy was used to observe the vacuum Rabi oscillations associated with the coupled exciton-photon mode splitting in a semiconductor quantum microcavity.
Abstract: We have used femtosecond optical spectroscopy to observe directly the vacuum Rabi oscillations associated with the coupled exciton-photon mode splitting in a semiconductor quantum microcavity. When the microcavity is impulsively excited by a coherent short optical pulse, the time-resolved emission from the cavity shows beats corresponding to the oscillation between cavity and exciton modes, with a decay corresponding to approximately twice the cavity lifetime. Interferometric pump-probe measurements clearly show the coherent evolution of the cavity polarization.
TL;DR: The transmission of 100-fs ultrafast laser pulses through biological tissues was measured by using femtosecond and picosecond time-resolved detection techniques and the broadening of transmitted pulses was found to increase as the thickness of the biological tissue increases.
Abstract: The transmission of 100-fs ultrafast laser pulses through biological tissues was measured by using femtosecond and picosecond time-resolved detection techniques. The broadening of transmitted pulses was found to increase as the thickness of the biological tissue increases. The absence of a distinct ballistic pulse transmitted through a relatively thin tissue is in sharp contrast with the pulse transmission through a random medium of discrete scatterers. Because of the continuous variation of the dielectric constant in tissue, the photons undergo scattering through the tissue, travel in various small zigzag least optical paths, and form a broadened early-arriving portion of the transmitted pulse. Even in the absence of a well-defined ballistic pulse, we can image an opaque object hidden inside a tissue as thick as 6.5 mm with submillimeter resolution by selecting the early-arriving portion of the transmitted pulse.
TL;DR: In this paper, diffuse-light time-gated imaging with transillumination optical coherence tomography was proposed to obtain submillimeter-resolution imaging of objects hidden in biological tissue.
Abstract: We describe diffuse-light time-gated imaging with transillumination optical coherence tomography. Submillimeter-resolution imaging of objects hidden in thick biological tissue is achieved in cases in which ballistic light is absent by selecting only the early-arriving coherent portion of the diffuse transmitted light. By using a femtosecond laser as a high-power low-coherence light source, we perform high-sensitivity (130-dB dynamic range) optical gating with interferometric heterodyne detection. The dependence of image resolution on coherent photon arrival time is investigated in model scattering media.
TL;DR: In this article, the authors reported the simultaneous generation of two collinear synchronous mode-locked pulse trains, with central wavelength separations of 60 to 80 nm, from a single-cavity modelocked Ti:sapphire laser.
Abstract: We report the simultaneous generation of two collinear synchronous mode-locked pulse trains, with central wavelength separations of 60 to 80 nm, from a single-cavity mode-locked Ti:sapphire laser. Near-transform-limited pulses of duration 50 to 70 fs were generated at each wavelength, with jitter of less than 20 fs between the two-color pulses. These pulses were directly used to generate infrared pulses centered at 9 μm, by difference-frequency mixing in an AgGaS2 crystal.
01 Oct 1993
TL;DR: In this paper, the electronic dephasing of two oxazine dyes dissolved in ethylene glycol at room temperature was investigated by femtosecond degenerate four wave mixing (DFWM) experiments.
Abstract: The electronic dephasing of two oxazine dyes dissolved in ethylene glycol at room temperature is investigated by femtosecond degenerate four wave mixing (DFWM) experiments. Both two-pulse and three-pulse DFWM with simultaneous detection of the signals at two distinct phase-matching directions permits detailed investigation of dephasing dynamics in a room temperature liquid. At least two stochastic processes are responsible for the observed electronic dephasing: one is treated empirically as an exponential decay; the second is regarded in the full analytic form of the Kubo relaxation function. Both fast and slow (inhomogeneous) dynamics are recovered. The slow dynamics is found to bring about spectral diffusion over the inhomogeneous distribution on the time scale around a picosecond.
TL;DR: In this paper, the spectral gain narrowing was identified as one of the main issues, and a solution was proposed to solve it. But it was only applied to a Ti:sapphire/Nd:silicate glass power chain.
Abstract: Femtosecond pulses in the 50–60-TW power range have been generated at 1064 nm by using the chirped-pulse-amplification technique applied to a Ti:sapphire/Nd:silicate glass (90-mm output aperture) power chain. We have identified the spectral gain narrowing to be one of the main issues, and we show how to solve it.
TL;DR: In this article, the authors describe the generation of femtosecond waveforms by using frequency-domain phase-only filters designed by numerical optimization techniques and demonstrate the ability to generate high-quality terahertz-repetition-rate sequences of femto-cond pulses by means of low-loss phase only filtering.
Abstract: We describe generation of shaped femtosecond waveforms by using frequency-domain phase-only filters designed by numerical optimization techniques. The task of filter design for pulse shaping in the time domain is directly analogous to the design of phase-only filters for beam shaping and array generation in the spatial domain. We experimentally tested phase filters that were designed to produce ultrafast square and triangle pulses and femtosecond pulse sequences. Our results demonstrate the ability to generate high-quality terahertz-repetition-rate sequences of femtosecond pulses by means of low-loss phase-only filtering. On the other hand, experiments that tested generation of individual shaped pulses, such as square pulses, were less successful than previous experiments that used simultaneous phase and amplitude filtering. Our results indicate the importance of building increased robustness against variations in the input pulse shape into the phase-only filter design.
TL;DR: In this paper, the ABCD law is extended to resonators of femtosecond self-mode-locked solid-state lasers containing a self-focusing Kerr medium, and simple closed-form results valid for arbitrary resonator configurations are obtained and criteria for designing and optimizing resonators for selfmode locked lasers are discussed.
TL;DR: Frequency transformation of high-power Ti:sapphire laser pulses in three β-barium borate crystals resulted in 180-fs optical pulses tunable from 189 to 200 nm.
Abstract: Frequency transformation of high-power Ti:sapphire laser pulses in three β-barium borate crystals resulted in 180-fs optical pulses tunable from 189 to 200 nm. UV pulses with energies of as much as 4 μJ at 200 nm with a 1-kHz repetition rate and pulses with energies of more than 2 μJ at 193 nm with a 20-Hz repetition rate were produced.