Sub-Picosecond Tm:YAP Regenerative Amplifier Operating out of the Window of Water Vapour Absorption

Abstract

High energy ultrashort laser pulses in the vicinity of 2-μm are in demand for numerous applications in spectroscopy, remote sensing, material processing, medicine and for driving secondary radiation sources, such as optical parametric amplifiers (OPAs) and THz as well as HHG frequency converters. Thulium (Tm) and Holmium (Ho) doped laser crystals are commonly employed for the generation of mJ-level laser pulses with the center wavelength around 2 μm. However, Ho-based laser media have a rather narrow gain bandwidth which limits their applications. In contrast, Tm-doped laser crystals have substantially broader gain spectrum and are suitable for the generation of femtosecond 2-μm pulses. The Tm³⁺ doped YAlO3 (Tm:YAP) laser crystal has a relatively high thermal conductivity and is birefringent, which is beneficial for overcoming thermally induced depolarization at high output power levels. Recently, Tm:YAP was employed for the amplification of mJ level femtosecond pulses [1-3], however the reported amplifiers operate in the vicinity of 1940 nm, which is strongly attenuated by atmospheric air due to strong water vapour absorption. Consequently, these systems can only operate in sealed enclosures purged with dry gasses.