Generation of Intense Near and Mid-Infrared Femtosecond Radiation (1.2–2.4 μm) 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 μm (signal wave) and 1.6–2.6 μm (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 μm is 840 and 280 μJ, 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 (~2 μm) to 200 fs.