Recent advances in the generation and amplification of ultrashort laser pulses are remarkable due to broad applications in many areas such as ultrafast spectroscopy, imaging and material processing. Recently, optical parametric chirped pulse amplification (OPCPA) turned out to be an efficient method to amplify ultrashort pulses. Using this technique, energies of intensive ns or sub-nanosecond (sub-ns) pump pulses can be efficiently transferred to the spatially and temporally synchronized stretched low-energy seed pulses in a suitable nonlinear crystal. OPCPA is a promising alternative to widely used regenerative and multi-pass amplifiers. It offers some advantages such as extremely broad gain bandwidth, high contrast ratio, low thermal effect, low nonlinear wavefront distortion and compact experimental performance without electro-optic modulators.
Looking at the recent progress in OPCPA, it was divided in two directions. The first trend was concentrated on the development of exceptionally high peak power (TW-level) laser systems at low repetition rates between single short to 10 Hz. Such high-energy OPCPA’s were seeded by pulses from Ti:sapphire laser at the degenerate point near 1 m. The second tendency was related to the development of more compact and stable fs OPCPA systems operating in kHz repetition rates with intermediate powers as alternative of regenerative and multi-pass amplifiers.
In this work, we report on experimental design and characteristics of a Cr:forsterite based OPCPA, what we believe to be the first demonstration in kHz repetition rates. Recently, a complex multi-cascade broadband Cr:forsterite OPCPA was demonstrated with slightly different pump and seed wavelengths to generate J-energies, but at a low repetition rate of 2 Hz. In this work, a kHz diode-pumped frequency-doubled Nd:YVO4 laser was used as pump laser delivering the shortest ns pulses (≤10 ns), up to now. Suitable gain medium was carefully selected by performing theoretical analysis of phase matching properties of different nonlinear crystals such as DKDP, KDP and BBO. Both collinear and noncollinear phase matching geometries were considered and characterized for broadband parametric process. The bandwidth broadening is a prior condition for generation of ultrashort pulses. It turned out that DKDP seems to be the best candidate for Cr:forsterite based OPCPA. Subsequently, first experiment results of the non-degenerate single-pass OPCPA delivering pulses near 935 nm and 1235 nm, respectively, were presented and discussed.