Amplification of 193-nm femtosecond seed pulses generated by third-order, nonresonant, difference-frequency mixing in xenon

The X-Ray Emission Effectiveness of Plasma Mirrors: Reexamining Power-Law Scaling for Relativistic High-Order Harmonic Generation

Ultrashort pulsed lasers provide uniquely detailed access to the ultrafast dynamics of physical, chemical, and biological systems, but only a handful of wavelengths are directly produced by solid-state lasers, necessitating efficient high-power frequency conversion. Relativistic plasma mirrors generate broadband power-law spectra, that may span the gap between petawatt-class infrared laser facilities and x-ray free-electron lasers; despite substantial theoretical work the ultimate efficiency of this relativistic high-order-harmonic generation remains unclear. We show that the coherent radiation emitted by plasma mirrors follows a power-law distribution of energy over frequency with an exponent that, even in the ultrarelativistic limit, strongly depends on the ratio of laser intensity to plasma density and exceeds the frequently quoted value of  -8/3 over a wide range of parameters. The coherent synchrotron emission model, when adequately corrected for the finite width of emitting electron bunches, is not just valid for p-polarized light and thin foil targets, but generally describes relativistic harmonic generation, including at normal incidence and with finite-gradient plasmas. Our numerical results support the ω-4/3 scaling of the synchrotron emission model as a limiting efficiency of the process under most conditions. The highest frequencies that can be generated with this scaling are usually restricted by the width of the emitting electron bunch rather than the Lorentz factor of the fastest electrons. The theoretical scaling relations developed here suggest, for example, that with a 20-PW 800-nm driving laser, 1 TW/harmonic can be produced for 1-keV photons.

Direct autocorrelation measurements of mid-infrared picosecond pulses by quantum-well devices

We report the direct autocorrelation of ultrashort mid-infrared laser pulses, using an unbiased GaAsy/GaAlAs quantum-well device as a nonlinear photovoltaic medium. Using this method, we autocorrelate ultrashort (3-ps) low-energy (~500-nJ) pulses of 10.6-microm light. This approach should permit the autocorrelation of subpicosecond infrared pulses.

Generation of high-power subpicosecond pulses at 155 nm

Subpicosecond vacuum-ultraviolet radiation at 155 nm with pulse energies above 0.2 mJ has been obtained by near-resonant four-wave difference-frequency mixing in a Xe gas jet. Laser fields for the mixing process have been generated by a short-pulse KrF dye excimer laser system and a Raman converter. The process permits tuning in a broad vacuum-ultraviolet range and can be scaled up to higher output energies.

High-repetition-rate high-power femtosecond ArF laser source

170-fs, 0.8-microJ optical pulses at 193 nm generated by frequency quadrupling of high-power Ti:sapphire laser pulses are amplified in an ArF gain module. Double-pass amplification at a 400-Hz repetition rate resulted in 290-mW average power with pulse durations of ~ 300 fs.

Generation of tunable femtosecond pulses to as low as 172.7 nm by sum-frequency mixing in lithium triborate

A tunable 1-kHz repetition-rate regenerative Ti:sapphire amplifier system is used to produce 200-fs vacuum-ultraviolet pulses in the range of 172.7-187 nm by phase-matched sum-frequency mixing in lithium triborate of the Ti:sapphire's fourth harmonic and a parametrically generated infrared pulse.

Short-pulse amplification and gain dynamics of an ArF excimer amplifier

Subpicosecond pulses at 193 nm, generated by a nonresonant difference-frequency mixing process in xenon, have been amplified in an ArF excimer gain module to output energies of as much as 10 mJ. Investigations on the gain characteristics of the ArF excimer amplifier yield a saturation energy density of 1.9 mJ/cm(2) and a maximum small-signal gain coefficient of 0.15 cm(-1). Gain recovery measurements have been performed. A dominant gain recovery time of ~3 ns with indications of a small fast contribution in the picosecond range have been observed.

Femtosecond gain characteristics of the discharge-pumped ArF excimer amplifier

The gain characteristics of a discharge-pumped ArF excimer amplifier are measured with ~700-fs-long pulses. The small-signal gain and saturation energy are found to be 0.17 cm(-1) and 3.65 +/- 0.15 mJ/cm(2), respectively. The maximum output energy density extracted from the deeply saturated amplifier is as much as 10 mJ/cm(2). The demonstrated femtosecond gain characteristics of ArF indicate that, by utilizing sufficiently high seed pulse energies, the ArF excimer laser is expected to show a performance similar to a femtosecond high-brightness KrF excimer laser system.

Efficient generation of subpicosecond seed pulses at 193 nm for amplification in ArF gain modules by frequency mixing in nonlinear optical crystals

Phase-matched sequential frequency mixing in three ,beta-barium borate crystals was used for efficient generation of subpicosecond UV pulses tunable at approximately 193 nm. Double-pass amplification of these seed pulses in a conventional ArF excimer gain module resulted in 800-fs, 1.5-mJ optical pulses.

Spectrally compensated sum-frequency mixing scheme for generation of broadband radiation at 193 nm

A dispersively compensated scheme for sum-frequency mixing of broadband ultrashort laser pulses is reported. An increase of the bandwidth of the sum-frequency mixing process by 12 times compared with the noncompensated bandwidth of the given crystal has been demonstrated. Mixing radiation at 266 and 707 nm in a 1-mm-thick beta-barium metaborate crystal by using the compensated scheme results in an output bandwidth of 0.6 nm at 193 nm, which corresponds to a minimum output pulse duration of 90 fs.