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.

We have developed a robust optical parametric amplifier (OPA) based on three-${\mathrm{AgGaS}}_2$-crystal pumping by a Cr:Forsterite GW femtosecond laser system, generating 150 fs pulses in dual bands of 1.6–2.0 μm (signal wave) and 3.5–5.5 μm (idler wave). By introducing a negative prechirp to the pump, a combined efficiency in two waves of greater than 10% was achieved, with signal energy up to 110 μJ and idler energy up to 43 μJ. Operation parameters of the system (intensity up to $90\mathrm{TW}/{\mathrm{cm}}^2$) make OPA a promising tool for driving nonlinear optical phenomena, including generation of optical harmonics and laser-induced extreme states of matter in solids and liquids. As a proof of principle, we generated harmonics up to the sixth order and sum frequencies in 5 mm thick polycrystalline ZnSe.

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.

Pulses with a spectral width of 450 nm at a wavelength of 2.2 μm are generated in a parametric amplifier based on a type-I BBO crystal pumped by the second harmonic (620 nm) of a Cr:forsterite laser. Such a broadband radiation is obtained in a specific regime of the group velocity matching near the vertical region of the tuning curve. The generated pulses can be compressed to a duration of about 2.5 optical cycles (34 fs) in a medium with positive group-velocity dispersion.