Advanced nonlinear materials - LiGaS 2 (LGS), $\mathrm{HgGa}_{2} \mathrm{~S}_{4}$ (HGS) and BaGa 2 GeS 6 (BGGS) - were studied for parametric down conversion of Cr:Forsterite laser pulses into 1.5 $-8 \mu \mathrm{m}$ spectral region. Total conversion efficiency as high as $18 \%$ was achieved in HGS based OPA resulting in 0.4 - 2.4-gigawatt 80 fs pulses. Using LGS, broadband mid-IR pulses with energy up to $20 \mu \mathrm{J}$ were obtained. After bulk compression in a Ge plate, a pulse duration as low as 60 fs was measured, corresponding to three optical cycles of $5.9 \mu \mathrm{m}$ carrier wavelength. New non-oxide BGGS crystal was compared with HGS, showing great potential for efficient parametric amplification in mid-IR. The developed source provides numerous opportunities for time-resolved pump-probe experiments and opens access to attosecond physics and material sciences.

We report on the development of a tunable (1.5-6.5 mu m) femtosecond optical parametric amplifier (OPA) based on a novel, to the best of our knowledge, BaGa2GeS6 2 GeS 6 (BGGS) crystal with a Cr:Forsterite pumping laser. Total conversion efficiency as high as 28% is achieved in a robust two-stage setup resulting in the generation of a 340-mu J 1.67-mu m signal and 100-mu J 4.65-mu m idler pulses. A 5-optical-cycles 94-fs 6-mu m idler pulses are demonstrated with a propriate dispersion compensation by Ge and GaAs plates. An experimental estimate is given for the effective nonlinearity of a BGGS material, which for our nonlinear process reaches 19.5 pm/V for Type!! phase matching. The crystal is additionally tested as a final amplifier in a high-energy OPA, where total output reaches 1.2 mJ with more than 40% conversion efficiency. The demonstrated high nonlinearity, high damage threshold, and chemical stability of the polished surface make BGGS crystal an ideal candidate for the development of high-energy OPAs with multi-millijoule pumping lasers. (c) 2024 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.

The generation of terahertz radiation in a BNA crystal pumped by 1.24-µm femtosecond laser radiation from a Cr:forsterite laser system with a pulse duration of 100 and 35 fs and a pump density of 10 mJ/cm 2 has been realized. The achieved generation efficiency is 0.1%. It is found that a decrease in the pump pulse duration from 100 to 35 fs leads to the generation of high-frequency components in the ranges of 2.5–6.5 THz and 9‒10.5 THz in the generated radiation spectrum. Simulation of the terahertz radiation generation based on the solution of Maxwell’s equations by the finite-difference time-domain method has made it possible to adequately describe the measured spectra. The generation of broadband high-frequency terahertz radiation in the BNA crystal pumped by the Cr:forsterite laser system allows one to consider this schematic as an alternative to sources based on the BNA crystal pumped by a Ti:sapphire laser system.

We demonstrate an experimental and theoretical comparison of non-oxide LiGaS2, HgGa2S4, and AgGaS2 crystals performance for wavelength conversion into the near and mid-IR range 1.5–8 μm in optical parametric amplifier pumped by Cr:Forsterite laser, delivering 100 fs pulses at 1.24 μm. It is shown that exceptionally high total energy conversion efficiency into the idler (4–5 μm) and signal (1.65–1.8 μm) waves up to 18% can be achieved using the HGS crystal, providing high nonlinearity, while the LGS crystal is more preferable for generating few-cycle mid-IR pulses due its unique dispersive properties. Our source features high peak power in gigawatt regime (0.4–2.4 GW) with pulse duration below 80 fs and optical synchronization with high harmonic generation (HHG) and THz beamlines, which is ideal for pump-probe experiments of nonlinear and strong-field physics.

It has been shown that the spectrum of intense few-cycle terahertz radiation generated in a DAST organic crystal can be controlled by chirping 1.24-μm pump femtosecond laser radiation of a chromium forsterite laser system. It has been found that an increase in the linear chirp of generating radiation results in the narrowing of the spectrum of terahertz radiation and its redshift. The simulation of the generation of terahertz radiation within the model of three-wave mixing has shown that this effect is due to a change in the phase matching width of the degenerate generation of the difference frequency of terahertz range. In addition, the comparative analysis of terahertz radiation spectra generated in DAST, DSTMS, OH1, and BNA organic crystals indicates that the spectral–temporal properties of terahertz radiation can be more roughly controlled by choosing an appropriate crystal. The proposed approach to control the terahertz radiation spectrum by chirping the pump pulse provides the foundation for spectroscopic studies using intense terahertz radiation with controlled spectral–temporal properties.

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.

Different schemes of parametric amplification (PA), aimed at designing a source of femtosecond near-IR (1.3 – 2.2 μm) radiation, are compared by solving a system of truncated equations describing three-wave mixing. A terawatt Ti : sapphire laser with an energy of 60 mJ and a pulse duration of 50 fs is used as a pump source for PA schemes. The dependences of the output energies, pulse durations, and spectral widths of signal and idler waves on the BBO crystal length for two types of phase matching and on the group-delay dispersions for the pump and signal waves is investigated. It is shown that in the case of direct PA, using a type-II phase-matching BBO crystal of optimal length, one can obtain signal (1.333 μm) and idler (2 μm) waves with pulse durations of 34 and 32 fs, respectively, with a total energy conversion efficiency up to 40 %. The application of double chirping scheme increases the total conversion efficiency to 60 %; however, the spectral width of generated pulses decreases. The spectral width can only be increased by reducing the conversion efficiency. In this case, a more simple and compact solution is the scheme of direct PA with a transform-limited pump pulse.