This review highlights the development of ultrafast sources in the near- and middle-IR range, developed in the laboratory of Nonlinear Optics and Superstrong Laser Fields at Lomonosov Moscow State University. The design of laser systems is based on a powerful ultrafast Cr:Forsterite system as a front-end and the subsequent nonlinear conversion of radiation into the mid-IR, THz, and UV spectral range. Various schemes of optical parametric amplifiers based on oxide and non-oxide crystals pumped with Cr:Forsterite laser can receive pulses in the range of 4–6 µm with gigawatt peak power. Alternative sources of mid-IR ultrashort laser pulses at a relatively high (MHz) repetition rate are also proposed as difference frequency generators and as a femtosecond mode-locked oscillator based on an Fe:ZnSe crystal. Iron ion-doped chalcogenides (Fe:ZnSe and Fe:CdSe) are shown to be effective gain media for broadband high-peak power mid-IR pulses in this spectral range. The developed sources pave the way for advanced research in strong-field science.

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.

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.

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