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Showing papers on "Pulse duration published in 1993"


Journal ArticleDOI
TL;DR: By incorporating a section of large positive-dispersion fiber in an all-fiber erbium ring laser, a fully self-starting source of 77-fs pulse with 90 pJ of energy and greater than 1 kW of peak power at a 45-MHz repetition rate is obtained.
Abstract: By incorporating a section of large positive-dispersion fiber in an all-fiber erbium ring laser, we obtain high-energy pulses with spectral widths of 56 nm. The chirp on these pulses is highly linear and can be compensated for with dispersion in the output coupling fiber lead. The result is a fully self-starting source of 77-fs pulse with 90 pJ of energy and greater than 1 kW of peak power at a 45-MHz repetition rate.

912 citations


Journal ArticleDOI
TL;DR: In this article, the frequency-resolved optical gating (FOSG) technique was introduced for measuring the intensity and phase of an arbitrary ultrashort pulse using an instantaneous nonlinear-optical interaction of two variably delayed replicas.
Abstract: We introduce a new technique, frequency-resolved optical gating, for measuring the intensity I(t) and the phase ϕ(t) of an individual arbitrary ultrashort pulse. Using an instantaneous nonlinear-optical interaction of two variably delayed replicas of the pulse, frequency-resolved optical gating involves measuring the spectrum of the signal pulse versus relative delay. The resulting trace, a spectrogram, yields an intuitive full-information display of the pulse. Inversion of this trace to obtain the pulse intensity and phase is equivalent to the well-known two-dimensional phase-retrieval problem and thus yields essentially unambiguous results for I(t) and ϕ(t).

484 citations


Journal ArticleDOI
TL;DR: The initial optical zone may be altered by the formation of char during high-irradiance laser exposure, and a spectrum of char absorbance is presented.
Abstract: The primary zone of deposition of optical energy is called here the optical zone. The tissue absorption, tissue scattering, laser-beam diameter, or size of pigmented structures can specify the size of the optical zone. The initial optical zone may be altered by the formation of char during high-irradiance laser exposure, and a spectrum of char absorbance is presented. The relationship between the optical zone and the pulse duration specifies the type of laser-tissue interaction that may occur. Short laser pulses can confine thermal energy and/or stress energy within the optical zone, which maximizes photothermal and photomechanical mechanisms of interaction.

264 citations


Journal ArticleDOI
TL;DR: Temporal phase coherence in a double-barrier tunneling structure produces ``ringing'' in the response of the current to a voltage pulse, which can be observed experimentally in the dc current by varying the pulse length in a train of voltage pulses.
Abstract: A general formulation is presented of the nonlinear, time-dependent current through a small interacting region, where electron energies are changed by time-dependent voltages. An exact solution is obtained for the noninteracting case when the elastic coupling to the leads is independent of energy. Temporal phase coherence in a double-barrier tunneling structure produces ``ringing'' in the response of the current to a voltage pulse, which can be observed experimentally in the dc current by varying the pulse length in a train of voltage pulses. The nonlinear current due to an ac bias also shows complex time dependence.

239 citations


Journal ArticleDOI
TL;DR: A minimal model of the defibrillation capability of a monophasic capacitive discharge pulse derived from the Weiss‐Lapicque strength duration model suggests that present, empirically derived values of pulse durations and tilts are close to optimum for presently used values of capacitors and electrode resistances.
Abstract: A minimal model of the defibrillation capability of a monophasic capacitive discharge pulse is derived from the Weiss-Lapicque strength duration model. The model suggests that present, empirically derived values of pulse durations and tilts are close to optimum for presently used values of capacitors and electrode resistances. The model suggests that neither the tilt nor fixed duration specification is universally superior to the other for dealing with electrode resistance changes. A tilt specification would appear to best handle resistance decreases while a fixed duration specification would best handle resistance increases. The model was used to study the effect of capacitance changes. It appears that the optimum tilt and pulse duration vary with the capacitance value. The model further suggests that decreasing the capacitance from presently used values may lower defibrillation thresholds.

130 citations


Journal ArticleDOI
TL;DR: An alternative configuration of the laser wake-field accelerator is proposed in which enhanced acceleration is achieved via resonant self-modulation of the lasers pulse, which requires laser power in excess of the critical power for relativistic guiding and a plasma wavelength short compared to the laser pulse length.
Abstract: An alternative configuration of the laser wake-field accelerator is proposed in which enhanced acceleration is achieved via resonant self-modulation of the laser pulse. This requires laser power in excess of the critical power for relativistic guiding and a plasma wavelength short compared to the laser pulse length. Relativistic and density wake effects strongly modulate the laser pulse at the plasma wavelength, resonantly exciting the plasma wave and leading to enhanced acceleration.

122 citations


Journal ArticleDOI
Seiji Samukawa1, Shuichi Furuoya1
TL;DR: In this paper, the authors examined modulated electron cyclotron resonance (ECR) plasma discharge occurring within a few tens of μs and found a good correlation between the density ratio of CF2 radicals and F atoms in the CHF3 plasma, and the combination of the pulse duration and pulse intervals.
Abstract: This study examines modulated electron cyclotron resonance (ECR) plasma discharge occurring within a few tens of μs. It can control the generation of reactive species in plasmas. Reactive species are measured by an actinometric optical emission spectroscopy in the pulsed plasma. Good correlation is found between the density ratio of CF2 radicals and F atoms in the CHF3 plasma, and the combination of the pulse duration and pulse intervals. These characteristics are explained by the dependence of reactive species generation in ECR plasma on a time within a few tens of μs. This method provides for controlling the polymerization during SiO2 etching.

100 citations


Journal ArticleDOI
TL;DR: This work reports the first dual operation comprising laser action and Q switching of Cr(4+):YAG pumped intracavity by a Nd:YAG laser, which produced dual 1.06- and 1.44-microm pulses with 35- and 200-ns pulse widths.
Abstract: We report what is to our knowledge the first dual operation comprising laser action and Q switching of Cr(4+):YAG pumped intracavity by a Nd:YAG laser. This technique produced dual 1.06- and 1.44-microm pulses with 35- and 200-ns pulse widths, respectively. The Nd:YAG rod was pumped by a 1-ms flash-lamp pulse, resulting in a train of 1.06- and 1.44-microm pulse pairs at approximately a 30-kHz rate.

98 citations


Journal ArticleDOI
TL;DR: In this paper, a general axisymmetric formulation based on relativistic fluid equations is proposed for the laser wake-field acceleration concept, which is valid for arbitrary laser intensities and allows the laser-plasma interaction to be simulated over long propagation distances.
Abstract: The laser wake‐field acceleration concept is studied using a general axisymmetric formulation based on relativistic fluid equations This formalism is valid for arbitrary laser intensities and allows the laser–plasma interaction to be simulated over long propagation distances (many Rayleigh lengths) Several methods for optically guiding the laser pulse are examined, including relativistic guiding, preformed plasma density channels and tailored pulse profiles Self‐modulation of the laser, which occurs when the pulse length is long compared to the plasma wavelength and the power exceeds the critical power, is also examined Simulations of three possible laser wake‐field accelerator (LWFA) configurations are performed and discussed: (i) a channel‐guided LWFA, (ii) a tailored‐pulse LWFA, and (iii) a self‐modulated LWFA

97 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used light and electron-microscopy at short laser-pulse durations of 0.9 and 1.8 μs and a long pulse of 250 μs.
Abstract: Bone ablation using different pulse parameters and four emission lines of 9.3, 9.6, 10.3, and 10.6 μm of the CO2 laser exhibits effects which are caused by the thermal properties and the absorption spectrum of bone material. The ablation mechanism was investigated with light- and electron-microscopy at short laser-pulse durations of 0.9 and 1.8 μs and a long pulse of 250 μs. It is shown that different processes are responsible for the ablation mechanism either using the short or the long pulse durations. In the case of short pulse durations it is shown that, although the mineral components are the main absorber for CO2 radiation, water is the driving force for the ablation process. The destruction of material is based on explosive evaporation of water with an ablation energy of 1.3 kJ/cm3. Histological examination revealed a minimal zone of 10–15 μm of thermally altered material at the bottom of the laser drilled hole. Within the investigated spectral range we found that the ablation threshold at 9.3 and 9.6 μm is lower than at 10.3 and 10.6 μm. In comparison the ablation with a long pulse duration is determined by two processes. On the one side, the heat lost by heat conduction leads to carbonization of a surface layer, and the absorption of the CO2 radiation in this carbonized layer is the driving force of the ablation process. On the other side, it is shown that up to 60% of the pulse energy is absorbed in the ablation plume. Therefore, a long pulse duration results in an eight-times higher specific ablation energy of 10 kJ/cm3.

90 citations


Patent
18 Nov 1993
TL;DR: In this paper, a method for fabricating polycrystalline thin films on low-temperature (or high temperature) substrates which uses processing temperatures that are low enough to avoid damage to the substrate, and then transiently heating select layers of the thin films with at least one pulse of a laser or other homogenized beam source is presented.
Abstract: A method for fabricating polycrystalline thin films on low-temperature (or high-temperature) substrates which uses processing temperatures that are low enough to avoid damage to the substrate, and then transiently heating select layers of the thin films with at least one pulse of a laser or other homogenized beam source. The pulse length is selected so that the layers of interest are transiently heated to a temperature which allows recrystallization and/or dopant activation while maintaining the substrate at a temperature which is sufficiently low to avoid damage to the substrate. This method is particularly applicable in the fabrication of solar cells.

Journal ArticleDOI
TL;DR: A cw-pumping, repetitively Q-switched, InGaAs-diode-pumped Yb:YAG laser has been demonstrated at room temperature and no optical damage was observed despite the high saturation fluence and the short pulse length.
Abstract: A cw-pumped, repetitively Q-switched, InGaAs-diode-pumped Yb:YAG laser has been demonstrated at room temperature. An output energy of as much as 72 microJ/pulse at 1.03 microm with a pulse length as short as 11 ns (FWHM) was attained. No optical damage was observed despite the high saturation fluence (~10 J/cm(2)) of the Yb:YAG laser and the short pulse length.

Journal ArticleDOI
TL;DR: The effect of third-order dispersion on the width of mode-locked pulses is investigated analytically and numerically and computer simulations show the appearance of a resonant sideband that also taxes the gain.
Abstract: The effect of third-order dispersion on the width of mode-locked pulses is investigated analytically and numerically. The pulse width increases monotonically with increasing third-order dispersion as a consequence of the symmetric chirp introduced by it. The chirp broadens the bandwidth and lowers the gain. Computer simulations show the appearance of a resonant sideband that also taxes the gain. Reducing the filter bandwidth partially suppresses the sideband and narrows the pulse.

Journal ArticleDOI
TL;DR: A cw room-temperature Cr(4+):YAG laser, tuning from 1.37 to 1.51 microm, is described and mode locking of this novel laser is reported for what is to the authors' knowledge the first time.
Abstract: A cw room-temperature Cr4+:YAG laser, tuning from 1.37 to 1.51 μm, is described. Mode locking of this novel laser is reported for what is to our knowledge the first time.

Patent
26 Feb 1993
TL;DR: In this article, a more favorable energy and current distribution is obtained by introducing lossy elements in one or more paths, or by capacitor-switching methods, where RVA is given one polarity, and at least two of the other electrodes are given opposite polarity yielding at least 2 pathways.
Abstract: A more favorable energy and current distribution is obtained by introducing lossy elements in one or more paths, or by capacitor-switching methods, where RVA is given one polarity, and at least two of the other electrodes are given opposite polarity, yielding at least two pathways. A current and energy steering by means of differing pulse durations in different paths is described. Further, it derives a rectangular current waveform from a capacitor discharge by using a current limiter. This pulse-shaping method is equally applicable to single-path and multiple-path situations. A rectangular pulse delivers a maximum of energy for a given peak-field value with a particular electrode combination and pulse duration. Peak field is a measure of the tissue-damage potentiality of a particular discharge.

Journal ArticleDOI
TL;DR: In this paper, a high-power source of coherent picosecond light pulses based on optical parametric generation and amplification in LiB3O5 and AgGaS2 crystals is reported.
Abstract: We report a high-power source of coherent picosecond light pulses based on optical parametric generation and amplification in LiB3O5 and AgGaS2 crystals. The spectral range of this continuously tunable source covers the visible, near-infrared and medium-infrared spectrum from 0.41 to 12.9 μm. An optical parametric generator and amplifier, consisting of two type-I phase-matched LiB3O5 crystals and a diffraction grating, is pumped by the third harmonic of a picosecond Nd:YAG laser and provides spectrally narrow, high-power pulses from 0.41 to 2.4 μm. Energy conversion efficiencies up to 16 percent are achieved. The pulse duration is about 14 ps, the bandwidth between 10 and 30 cm−1. The tuning range is extended to 12.9 μm by mixing the infrared output between 1.16 and 2.13 μm with the fundamental of the Nd:YAG laser in type-I-phase-matched AgGaS2 crystals. Up to 25 percent of the pulse energy at 1.064 μm is converted into parametric infrared pulses. Bandwidths between 3 and 8 cm−1 and a pulse duration of approximately 19 ps are measured for these pulses. We also observe a retracing behaviour in the tuning curve of AgGaS2 not reported before.

Journal ArticleDOI
TL;DR: In this paper, the authors analyzed the robustness of the optimal electric field with respect to variations in the field parameters (chirp rates, pulse duration, and carrier frequency).
Abstract: Theory and experiments are currently being developed in our laboratory to use tailored light fields to control the dynamics of molecular reactions. We have recently shown theoretically that a properly chirped light pulse can be used to overcome the natural tendency of wave packets to spread on anharmonic molecular potential energy surfaces. The optimal chirp rate can be readily obtained by solving a linear optimal control equation. In this paper we analyze a number of aspects crucial to the success of the experiments. We test the robustness of the optimal electric field with respect to variations in the field parameters (chirp rates, pulse duration, and carrier frequency). We also study the effects of finite temperature by using a thermal vibrational distribution as the initial in the dynamics

Journal ArticleDOI
TL;DR: A compact flash-lamp-pumped Cr:LiSrAlF(6) (Cr:LiSAF) laser system capable of producing peak powers in excess of 1 TW is developed.
Abstract: We have developed a compact flash-lamp-pumped Cr:LiSrAlF(6) (Cr:LiSAF) laser system capable of producing peak powers in excess of 1 TW. Chirped-pulse amplification in a Cr:LiSAF regenerative amplifier produces 8-mJ pulses at a 5-Hz repetition rate. Further amplification in Cr:LiSAF yields recompressed pulse energies of 150 mJ and a pulse duration <135 fs at a 0.5-Hz repetition rate.

Journal ArticleDOI
TL;DR: In this article, the authors used the Taguchi technique of experimental design in optimizing the process parameters for drilling deep-holes in nickel-based superalloy, Inconel 718.

Journal ArticleDOI
TL;DR: Intensity scaling suggests that laser spot size and two-dimensional expansion are important for optimizing x-ray production at these low-irradiation intensities.
Abstract: X-ray production in the region ~ 13 nm from laser-produced plasmas has been investigated as a source for projection x-ray lithography. The dependence of x-ray conversion efficiency on target material, intensity, and pulse length has been studied by using a 0.53-μm laser with a maximum of 0.3 J. A conversion efficiency of 1% into a 0.3-nm bandwidth has been demonstrated for Sn targets at intensities of ~ 1011 W/cm2 by using a 7.5-ns pulse. Intensity scaling suggests that laser spot size and two-dimensional expansion are important for optimizing x-ray production at these low-irradiation intensities.

Journal ArticleDOI
TL;DR: In this paper, the phase conjugate reflectivity and diffraction efficiency were measured for both the reflection and transmission grating cases for a Nd:YAG amplifier using orthogonally polarised pump beams of pulse duration 16 ns.

Journal ArticleDOI
TL;DR: The first experimental observation of limit-cycle power oscillations in a short-pulse free-electron laser is presented, due to a nonlinear modulation of the optical micropulse shape and phase by the electrons, which leads to the formation of a train of subpulses.
Abstract: The first experimental observation of limit-cycle power oscillations in a short-pulse free-electron laser is presented. These are due to a nonlinear modulation of the optical micropulse shape and phase by the electrons, which leads to the formation of a train of subpulses. Experimentally, the oscillations have been found to depend on the slippage distance and on the desynchronism between optical pulses and electron bunches, comparing well with theoretical predictions.

Journal ArticleDOI
TL;DR: In this paper, a 1.9mm-thick nonlinear molecular crystal of N-(4-nitrophenyl)-l-prolinol was pumped at a wavelength of 0.5927 μm and a pulse duration of 1 ns (FWHM).
Abstract: Tunable near-infrared optical parametric oscillation in an organic crystal has been achieved for the first time to our knowledge. A 1.9-mm-thick nonlinear molecular crystal of N-(4-nitrophenyl)-l-prolinol was pumped at a wavelength of 0.5927 μm and a pulse duration of 1 ns (FWHM). Tunability from 0.9 to 1.7 μm and a maximum but nonoptimized total conversion efficiency of ~5% were obtained with considerable improvement in performance still available. In addition, the optical parametric oscillation threshold estimation method and the importance of a high nonlinearity for optical parametric oscillation operation at the 1-ns time scale are discussed.

Patent
29 Apr 1993
TL;DR: In this paper, the transponder response signal indicates that it has received enough power from the interrogation signal, represented as a voltage stored on a capacitor located in the Transponder.
Abstract: Since the distance from the interrogator to the transponder cannot be controlled in many RF-ID applications, a time or power control over the interrogation pulse is provided to eliminate transponder heat-up. The RF_ID system transmits a narrow interrogation pulse, for example of 5 msec duration and then monitors for an even shorter duration, for example 1 msec, for a transponders response signal. The monitoring duration is maintained a minimum to create the most efficient charge-up system. Upon the absence of the transponders response signal, the interrogator increases the interrogation pulse duration in steps, until the receiver in the interrogator detects a response signal. A response signal indicates that the transponder has received enough power from the interrogation signal, represented as a voltage stored on a capacitor located in the transponder. This system can be supported by transponders which have no discharge function, to allow the transponders to achieve the final charge-up voltage level with a series of combined short duration power pulses, or by transponders which have discharge functions and which must wait for an adequate duration interrogation pulse to receive enough voltage. Alternatively, instead of increasing the duration of the interrogation pulses, the amplitude of the interrogation pulses can be increased to produce a similar increase in the amount of interrogation power transmitted.

Journal ArticleDOI
TL;DR: In this paper, the authors relate the generation of spectral sidebands to a loss mechanism dependent on the pulse duration and total cavity dispersion, and confirm experimentally using an erbium figure eight laser that the minimum pulse duration is therefore limited by the total dispersion.
Abstract: Generation of spectral sidebands is characteristic of ultrashort soliton all‐fiber lasers. We relate the generation of these sidebands to a loss mechanism dependent on the pulse duration and total cavity dispersion. We confirm experimentally using an erbium figure eight laser that the minimum pulse duration is therefore limited by the total dispersion. Short cavities constructed from low‐dispersion components allow shorter pulses to be obtained, and we demonstrate pulse durations as short as 160 fs.

Journal ArticleDOI
TL;DR: In this article, it was shown that for a sufficiently short high-current pulse, the wire, encapsulated in oxide, will not reach thermal equilibrium and the currentinduced heating can be modeled as being adiabatic.
Abstract: It is pointed out that voltage programmable link (VPL) technologies impose a new criterion on the reliability of metal interconnect. Lines of metallization must support the full programming current, which can be many times larger than the signal level current, for very short periods of time. For a sufficiently short high-current pulse, the wire, encapsulated in oxide, will not reach thermal equilibrium and the current-induced heating can be modeled as being adiabatic. Energy conservation predicts a relationship between maximum current density that can be carried by a wire before it fuses, and the pulse duration time, J/sup 2/t=10/sup 8/ A/sup 2/-s/cm/sup 4/. This relationship is based on a temperature rise in the metal line at failure of theta /sub f/*=300 degrees C. The time required for the metal to reach thermal equilibrium at a given current density is shown to be proportional to the square of the oxide thickness. These predictions are experimentally verified with layered AlSi/Ti metallization on thermal oxide on silicon substrates. >

Journal ArticleDOI
TL;DR: In this article, a pulsed optical parametric oscillator that has a wide tuning range from 0.7 to 1.8 μm, a conversion efficiency of a few percent, and a minimum pulse duration of as low as 65 fs was presented.
Abstract: Parametric three-photon interaction provides continuously tunable ultrashort pulses in extended spectral regions from the UV to the mid-IR. We focus on parametric systems operating in the pulsed mode. Optical parametric oscillators pumped by intense microsecond trains of subpicosecond pulses exhibit favorable properties. We present data on a pulsed optical parametric oscillator that has a wide tuning range from 0.7 to 1.8 μm, a conversion efficiency of a few percent, and a minimum pulse duration of as low as 65 fs. Larger tuning ranges are covered by subsequent downconversion or parametric amplification. We discuss the generation of ≲1-ps pulses at wavelengths between 2 and 18 μm. Finally, the potential of parametrically generated IR pulses is demonstrated by several applications.

Journal ArticleDOI
TL;DR: In this paper, a detailed theoretical treatment of spin-lattice and spin-spin relaxation effects which occur during the application of long selective pulses is presented, and the effects of T1 and T2 on the degradation of the frequency-domain profile are discussed for a wide variety of pulse shapes.

Journal ArticleDOI
TL;DR: In this article, the phase control achievable in a sub-picosecond self-mode-locked pulse-compressed Ti:Al2O3 system permits the production of a seed beam for a KrF* (248-nm) system operating near the power limit determined by self-phase modulation in the optical window material used.
Abstract: The phase control achievable in a subpicosecond self-mode-locked pulse-compressed Ti:Al2O3 system permits the production of a seed beam for a KrF* (248-nm) system operating near the power limit determined by self-phase modulation in the optical window material used. These limits are ~14 and ~30 GW/cm2 for CaF2 and MgF2 optics, respectively. We show experimental results for CaF2, which at 248 nm demonstrate a pulse length of ~270 fs, a pulse energy of ~240 mJ, and a resulting brightness of ~2.9 × 1021 W cm−2 sr−1.

Journal ArticleDOI
TL;DR: In this paper, the effects of self-phase modulation, stimulated Raman scattering, and parametric four-photon interaction in an 8-μm core fibre of 4 m length with the effect of selective spectral attenuation in a ruby rod resulted in a rather smooth spectra extending from 685 nm to 830 nm (spectral width ≈ 2300 cm-1).
Abstract: Picosecond light pulses of a passively mode-locked ruby laser (pulse duration Δt L≈35 ps) are spectrally broadened in optical fibres of core diameters from 4 μm to 600 μm. Combining the effects of self-phase modulation, stimulated Raman scattering, and parametric four-photon interaction in an 8-μm core fibre of 4 m length with the effect of selective spectral attenuation in a ruby rod resulted in rather smooth spectra extending from 685 nm to 830 nm (spectral width ≈2300 cm-1).