Over the last decade there have been spectacular developments in ultrafast laser technology, due to the introduction of solid state active materials and of new mode-locking and amplification techniques. These advances, together with the discovery of new nonlinear optical crystals, have fostered the introduction of ultrafast optical parametric amplifiers as a practical source of femtosecond pulses tunable across the visible and infrared spectral ranges. This article summarizes the recent progress in the development of ultrafast optical parametric amplifiers, giving the basic design principles for different frequency ranges and in addition presenting some advanced designs for the generation of ultrabroadband, few-optical-cycle pulses. Finally, we also briefly discuss the possibility of applying parametric amplification schemes to large-scale, petawatt-level systems.

Ultrafast optical parametric amplifiers

Ultrafast vibrational dynamics of hydrogen bonds in the condensed phase.

Frequency down-conversion of solid-state laser sources to the mid-infrared spectral range using non-oxide nonlinear crystals

We report on an intense mid-infrared light source that provides femtosecond pulses on a microjoule energy level, broadly tunable in the 3–20-µm wavelength range with pulse durations as short as 50 fs at 5 µm. The pulses are generated by phase-matched difference-frequency mixing in GaSe of near-infrared signal and idler pulses of a parametric device based on a 1-kHz Ti:sapphire amplifier system. Pulse durations are characterized with different techniques including autocorrelation measurements in AgGaS2, two-photon absorption in InSb, and cross-correlation measurements with near-infrared pulses in a thin GaSe crystal. A subsequent zero-dispersion stretcher of high transmission allows for optimum pulse compression, a more detailed amplitude and phase characterization and, ultimately, amplitude shaping of the mid-infrared pulses.

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Generation, shaping, and characterization of intense femtosecond pulses tunable from 3 to 20 µm

We present a novel procedure for vibrationally resolved sum-frequency generation (SFG) in which a broad-bandwidth IR pulse is mixed with a narrow-bandwidth visible pulse. The resultant SFG spectrum is dispersed with a spectrograph and detected in parallel with a scientific-grade CCD detector, permitting rapid and high signal-to-noise ratio data acquisition over a 400?cm-1 spectral region without scanning the IR frequency. Application to the study of a self-assembled monolayer of octadecanethiol is discussed.

Vibrationally resolved sum-frequency generation with broad-bandwidth infrared pulses.

A tunable regenerative Ti:sapphire amplifier system working at a 1-kH(z) repetition rate pumps an optical parametric generator providing near-infrared pulses tunable in the wavelength range from 1 to 2.5 microm. The signal and idler pulses with a duration below 100 fs are mixed in a AgGaS(2) crystal to generate pulses at the difference frequency. The midinfrared output is continuously tunable between 3.3 and 10 microm, with pulse energies of as high as 50 nJ and durations of 160 fs, as directly determined from cross-correlation measurements.

V. Petrov

Papers

Solid-state laser system for the generation of midinfrared femtosecond pulses tunable from 3.3 to 10 microm.