Generation of intense near and mid-infrared femtosecond radiation (1.2–2.4 $\mu$m) with the use of the broadband parametric down-conversion in a type-II BBO crystal pumped by a Ti:sapphire laser and its application for the generation of terahertz radiation in organic crystals

A two-stage optical parametric amplifier is fabricated on the basis of type-II BBO crystals pumped by the intense radiation of a Ti:sapphire laser. Femtosecond radiation tunable from the near to mid-infrared range at wavelengths of 1.1–1.6 $\mu$m (signal wave) and 1.6–2.6 $\mu$m (idler wave) is generated with a total energy conversion efficiency of 8%. The output energy of generated infrared pulses at wavelengths of 1.3 and 2 $\mu$m is 840 and 280 $\mu$J, respectively. It is experimentally demonstrated that terahertz radiation can be subsequently generated in a DAST organic crystal using the optical rectification process under the pumping by generated mid-infrared radiation. The developed model of the generation of terahertz radiation shows that the optical–terahertz conversion efficiency to 3.6% can be increased by chirping femtosecond mid-infrared radiation ($\sim$2 $\mu$m) to 200 fs.