Simple generation of high-power,picosecond, tunable excimer laser pulses

A single excimer laser (a modified commercial oscillation-amplifier combination) is used to pump a dye laser generating a single ps pulse at twice the excimer wavelength and to amplify the frequency-doubled pulse to high peak powers. With XeCl at 308 nm an output pulse energy of 10 mJ with <5 ps pulse width was achieved with <5% ASE energy.     

Generation of short high-power pulses in excimer lasers by fast pulseQ-switching

The possibility of generation of short high-power pulses by pulse electroopticQ-switching in a high-gain excimer system was investigated numerically. Two methods of short-pulse generation were considered. In the first the electroopticQ-switch is controlled by two half-wave voltage gates. The method normally enables pulses from several hundreds of picoseconds to a few nanoseconds duration to be obtained. In the second method the Q-switch is controlled by a train of voltage gates of amplitude equal to the double half-wave voltage. In this case, even at short times of laser pumping ( 50 ns), it is possible to generate high-power pulses of duration from tens to several hundreds of picoseconds. The influence of various system parameters on the generation process and the parameters of the generated pulses was analysed in detail.     

Interaction of high-power laser pulses with glasses containing implanted metallic nanoparticles

Sodium calcium silicate glasses with Ag⁺ implanted ions are studied. The ion implantation conditions are as follows: the energy is 60 keV, the dose is 7×10¹⁶ cm⁻², and the ion current density is 10 μA/cm². Ion implantation provides the formation of a composite layer that incorporates silver nanoparticles in the surface region of glass. The size distribution of nanoparticles over the depth in the composite layer is strongly nonuniform. The effect of a high-power pulsed excimer laser on the composite layer is investigated. It is found that, under laser irradiation, the size of silver nanoparticles in the implanted layer decreases but the size distribution of nanoparticles over the depth remains nonuniform, even though it becomes slightly narrower compared to that observed prior to irradiation. The experimental results are interpreted in terms of the effects of the melting of glass and metallic particles on a nanosecond scale. __________ Translated from Fizika Tverdogo Tela, Vol. 43, No. 11, 2001, pp. 2100–2106. Original Russian Text Copyright ? 2001 by Stepanov, Popok, Hole, Bukharaev.     

Atmospheric propagation of high-power laser pulses by self-channelling

The atmospheric propagation of a sequence of short, intense laser pulses is considered. The pulses propagate in a self-induced low-density channel, the effectiveness of which depends on a set of three variables. Using a simple model for the laser-atmosphere interaction, the range of successive pulses is determined by numerical solutions to the paraxial wave equation. The dependence of the length, width, and depth of the created channel on the important variables is explored.     

Ion acceleration by superintense laser pulses in plasmas

Ion acceleration by petawatt laser radiation in underdense and overdense plasmas is studied with 2D3V-PIC (Particle in Cell) numerical simulations. These simulations show that the laser pulse drills a channel through the plasma slab, and electrons and ions expand in vacuum. Fast electrons escape first from the electron-ion cloud. Later, ions gain a high energy on account of the Coulomb explosion of the cloud and the inductive electric field which appears due to fast change of the magnetic field generated by the laser pulse. Similarly, when a superintense laser pulse interacts with a thin slab of overdense plasma, its ponderomotive pressure blows all the electrons away from a finite-diameter spot on the slab. Then, due to the Coulomb explosion, ions gain an energy as high as 1 GeV. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 2, 80–86 (25 July 1999) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Change in the resonance frequency of surface plasmons in copper nanoparticles excited by femtosecond laser pulses

Changes in the optical density ΔD(t), halfwidth ΔH/2(t), and spectral position of the maximum Δλ_SP(t) of the surface plasmon band in Cu nanoparticles after their excitation by femtosecond laser pulses have been investigated. The Δλ_SP(t) dependence appears to be alternating and is accompanied by a nonmonotonic variation in ΔH/2(t) in the time interval 0–5 ps. The results are explained in a model based on the evolution of the dielectric response of such a composite medium excited by intense laser pulses.     

Filaments in high-speed counter-streaming plasma interactions driven by high-power laser pulses

Interactions of two counter-streaming plasmas driven by high power laser pulses are studied on Shenguang II laser facility.Filamentary structures were observed in the interaction region after the electrostatic shockwave decay.Theoretical analysis and observations indicate that the filaments are because of collisionless mechanisms,which are caused by the electromagnetic instability,such as the beam-Weibel instability.Collision experiments were also carried out for comparison and no filaments were generated.     

Generation of synchronized femtosecond and picosecond laser pulses in a two-beam-pumped Ti:sapphire laser

<正>Two operating modes,independent self-mode-locking and cross-mode-locking,are presented in a two-beampumped double-cavity dual-wavelength femtosecond Ti:sapphire laser.Synchronization of femtosecond and picosecond laser pulses is achieved by properly adjusting the cavity length matching and distributing the pump laser powers in the two laser cavities,and moreover,a timing jitter of 517 fs between femtosecond and picosecond pulses is obtained,with wavelength tuning ranges around 36 and 22 nm in the femtosecond and picosecond cavities,respectively.     

Dynamics of high-power ultrashort laser pulses in resonant media

Work supported by Russian Fund for Basic Research, Project 93-02-14271.     

Generation of multiply charged silicon and germanium ions by excimer laser pulses

Plasma bursts were produced by focusing excimer-laser (XeCl, 308 nm) pulses on Ge and Si targets. At moderate laser fluences (30 MW/cm²) high-intensity Ge³⁺ and Si³⁺ ion pulses were extracted from the laser-produced plasma. A peculiar electrical circuit allows a self-bunching of the beam. By time-of-flight method, the currents produced by the ions of different charge number were measured. Peak currents of 620 mA and 800 mA were recorded for Ge³⁺ and Si³⁺ ions, respectively, with an extraction voltage of only 400 V.     

Fiber delivery of femtosecond pulses from a Ti:sapphire laser

We propose a way to deliver nanojoule-energy, 100-fs pulses at 800 nm through a few meters of standard optical fiber. Pulses from a mode-locked laser are compressed temporally, and then spectrally, to produce the desired pulses at the end of the fiber. Initial experiments agree well with calculations and demonstrate the benefits of this technique: For an energy of ~0.5 nJ , the delivered pulses are ~5 times shorter than those delivered by other techniques. The issues that must be addressed to scale the technique up to delivered pulse energies of 5 nJ are identified, and the apparatus employs only readily available components. Thus we expect it to find use in the many applications that would benefit from fiber delivery of femtosecond pulses.     

Generation of 0.66-TW pulses at 1 kHz by a Ti:sapphire laser

A 1-kHz, 0.66-TW Ti:sapphire laser has been developed. We obtained 21-fs, 14-mJ pulses with an extraction efficiency of 32% in the final amplifier. The dispersion through the system was successfully compensated for by insertion of a pair of prisms in a regenerative amplifier. The pulses were characterized by frequency-resolved optical gating and were in good agreement with dispersion calculated by three-dimensional ray tracing.     

Passive compression of KrCl excimer laser pulses in naphthalene solutions

The width of KrCl laser pulses has been compressed from 5.2 ns to less than 800 ps using naphthalene as the saturable absorber dye. It was found that the width of the compressed laser pulse decreased with both the input laser intensity and the concentration of naphthalene in the solution. The pulse shortening mechanism is attributed to excited state S₂-S_n transitions in naphthalene.     

High-order harmonics in static gas target by 795-nm Ti:sapphire femtosecond laser pulses

The 5th - 23sd high-order harmonics generation in rare gases in static gas target with 120-fs, 85-m J/pulse,10-Hz laser system was investigated. Compared with the traditional gas target, static gas target is simple to be used in experiment, and the experimental parameters can be easily controlled. The effects on highorder harmonics due to laser intensities (energy), polarization, gas densities, confocal parameter, and phase mismatch were studied in this paper.     

Coherent excitation of molecular vibrational modes by high-power ultrashort infrared laser pulses

Coherent dynamics of multiphoton excitation of molecular vibrational modes by subpicosecond IR laser pulses differs greatly from that of picosecond pulse excitation. The resonance response of a molecule is primarily determined by the power broadening rather than the laser carrier frequency. Selective excitation of high vibrational levels is possible with the use of subpicosecond pulses.     

X-ray production by irradiation of solid targets with sub-picosecond excimer laser pulses

A table-top excimer laser system generating sub-ps pulses was used to irradiate solid targets at intensities of up to 4×10¹⁵ W/cm². Soft X-ray spectra of various materials were measured. The X-ray conversion efficiencies were between 1–5%. Streak camera measurements showed instrument-limited X-ray pulse duration of a few ps.Partially based on the plenary talk X-Ray Generation by Sub-Picosecond UV Laser by F. P. Schäfer, G. Kühnle, S. Szatmári, and M. Steyer, presented at the XVI Int. Quant. Electron. Conf., Tokio, July 18–21, 1988, Technical Digest (The Japan Society of Applied Physics) p. 2     

Studies of collisionless shockwaves using high-power laser pulses in laboratories

The remarkable experimental progress in the studies of collisionless shockwave(CS)in laboratories employing highpower lasers is briefly reviewed.The results show that CS can be generated in laser-produced plasmas due to the microturbulence associated with instabilities.CS is one of the most important astronomical phenomena.It has been found in supernova remnants(SNRs),Sun–Earth space,etc.This paper focuses on CS in ways relevant to SNRs.Laboratory astrophysics(LA),a new interdisciplinary frontier of astrophysics,plasma and laser physics,has developed rapidly in recent years.As an accessory to the astronomical observation,LA experimenters can closely study some astronomical events scaled-down to controllable phenomena.     

Numerical modeling of thermal effects in a high-power injection-locked cw Ti:sapphire laser

With the FEA and matrix methods, the thermal lenses induced by the thermooptic effect, thermally induced mechanical strain and end face bulging in a Ti:sapphire crystal are analyzed. The results show that there is an unignorable strain-induced lens in a high pump power region. With the thermal lens effect, an injection-locked cw Ti:sapphire laser is numerically simulated. We find that the poor mode matching between the lasing and pump beams due to thermal lens will cause the slope efficiency decreasing. The calculated results agree with the reported experimental data, and we also predict that the thermal lens is obviously active at a certain pump power level.