An ultrashort-pulse mid-infrared laser system tunable within a wavelength range of similar to 5-11 mu m is experimentally demonstrated. The system is based on difference frequency generation in a nonlinear crystal, where a Ti:Sapphire pump beam is mixed with a signal pulse formed through self-phase modulation of the Ti:Sapphire laser pulse under its filamentation in a CO2 gas cell. Three nonlinear crystals were examined in this setup: ZnGeP2, AgGaS2, and LiGaS2. Central wavelength tuning from similar to 5.5 mu m to similar to 10 mu m was carried out with AgGaS2 and LiGaS2 crystals. The LiGaS2 crystal provided the highest mid- infrared pulse energy of 2.7 mu J at 6 mu m wavelength and broadband pulse spectrum within 7.5-11.5 mu m wavelengths. The ZnGeP2 crystal provided the highest efficiency of 0.16 % for frequency conversion into similar to 10 mu m wavelength region, but that took place at low pump pulse energy/intensity (0.3 mJ/similar to 30 GW/cm(2)), which, being higher, resulted in lower efficiency due to nonlinear absorption.

The efficiency of AgGaS2, BaGa4Se7, and HgGa2S4 crystals has been investigated in a mid-IR frequency difference generator based on a femtosecond ytterbium fiber laser with a wavelength of 1.03 μm, pulse duration of 0.25 ps, pulse repetition rate of 10 kHz, and average radiation power of 5 W. It is shown that under the given experimental conditions the highest efficiency of difference-frequency generation (up to 7.5

The sum-frequency generation of broadband CO laser radiation (λ ≈ 5–6 μm) in a new nonlinear BaGa2GeS6 crystal at type I and II phase matching at the variation of polar and azimuth angles of this crystal has been experimentally investigated. A small mismatch ( 3°) between the values of measured and calculated phase matching angles was found. Also, based on experimental data and their comparison with calculations, a set of coefficients was determined of the nonlinear susceptibility tensor of BaGa2GeS6, which best describes the experimental results.

Broadband sum-frequency conversion of multiline ( 60 spectral lines within 5–6 μm wavelength interval) Q-switched CO laser emission in an AR-coated ZnGeP2 crystal was experimentally studied by application of both single-pass and double-pass optical schemes. The maximum conversion efficiency in the double-pass scheme reached 10

Generation of ultrashort mid-IR pulses spanning from 8.5 to 10.5 μm with high energy (up to 4.5 μJ) was experimentally demonstrated through difference frequency generation in BaGa 2 GeSe 6 crystal pumped by 100-fs 0.95-μm Ti:sapphire laser pulses. Optical damage threshold and two-photon absorption coefficient were determined for this pump pulses. Frequency conversion efficiency reached 0.24% at 1.85 mJ pump pulse energy and was decreased at higher one. Estimations indicate that application of 15 mm in diameter wide-aperture BaGa 2 GeSe 6 sample will allow one to increase pump pulse energy up to ~10 mJ, and to increase the mid-IR pulse energy up to 24 μJ at the same efficiency.

In order to increase the energy of a signal wave for a difference frequency generator, a spectral broadening of 100-fs pulses from a Ti:sapphire laser (center wavelength of 950 nm) is experimentally studied during their filamentation in five different gases: N2, NH3, He, CO2, and CO. The greatest broadening and the highest energy in the Stokes region of the spectrum are observed for CO2. Variation in the CO2 pressure in the gas cell shows that for a Ti:sapphire laser with a pulse energy of several mJ, the highest radiation energy in the Stokes wing with a shift of ∼1000 cm–1 is achieved at a pressure of 1 bar. Also, for each of the studied gases, the nonlinear refractive index is estimated at a pressure of 1 bar.

Frequency conversion of CO and CO 2 lasers emission in nonlinear crystals resulted in significant expansion of their output spectral range up to $\sim 2-20 \mu \mathrm{m}$ and the increase of the number of spectral lines generated by these hybrid systems.

We experimentally demonstrate laser system generating 100 -fs mid-IR pulses tunable within of 5.5-9.5 $\mu$m wavelength range. This system is based on difference frequency generation of femtosecond Ti:sapphire laser pulses in a nonlinear AgGaS 2 crystal.

The effect of focusing, taking into account self-focusing, on the interference of SRS (stimulated Raman scattering) and self-phase modulation in a 8-mm BaWO4 crystal pumped by laser pulses with a duration of 0.3 ps and a wavelength of 515 nm is experimentally studied. The maximum efficiency of SRS conversion (~23%) to the Stokes component of the ν1 = 925 cm–1 strongest mode is obtained with a lens with a focal length of 40 mm at the linear focus shift towards the rear facet of the crystal. The increase in efficiency, when the linear focus is shifted to the rear facet, is associated with an increase in the distance between the linear and nonlinear foci, which results in an increase in the effective length of the nonlinear interaction.

We report an experimental study of broadband sum-frequency generation of a nonselective Q-switched CO laser (pulse duration, 0.3 μs; repetition rate, 90 Hz) in ZnGeP2 crystals with and without an antireflective interference coating. The uncoated crystal surface is found to be optically damaged at a laser radiation intensity of 0.033 GW/cm2. Under the same conditions, no damage to the antireflection-coated surface of the crystal is observed. The maximum efficiency of broadband sum-frequency generation of the CO laser in the antireflection-coated sample is 4.8

Terahertz (THz) NH3 lasing with optical pumping by electron-beam-sustained discharge "long" (-100 vs) CO2 laser pulses was obtained. The NH3 laser emission pulses and the "long" pulses of the CO2 pump laser were simultaneously measured with nanosecond response time. The NH3 lasing duration and its delay with respect to the pump pulse were measured for various CO2 laser pulse energies. For the CO2 laser pump line 9R(30), three wavelengths of 67.2, 83.8, and 88.9 vm were recorded. For the CO2 laser pump line 9R(16), only a single NH3 laser line with a wavelength of 90.4 vm was detected.

The research studies of e-beam sustained discharge gas lasers initiated by Nikolai Basov in early 1970s made it possible to develop lasers based on the fundamental transitions of carbon monoxide molecule with high laser power and efficiency. Soon, under his scientific supervision, lasing on first-overtone transitions of CO molecule was obtained. Following these results, about ten years ago a compact slab CO laser excited by a repetitively pulsed capacitive RF discharge and cryogenic cooling of its electrodes, operating without forced pumping of its active medium was for the first time developed at the N.G. Basov Quantum Radiophysics Division of the P.N. Lebedev Physical Institute. At present, the average power of such lasers with active medium volume of ~ 35 cm 3 reaches 40 W on CO molecule fundamental transitions (in the wavelength range of 5.06–5.92 μm) and 6 W on first-overtone transitions (λ = 2.60–3.05 μm). Under Q-switching, those repetitively pulsed lasers allow one to obtain laser emission with a peak power up to 5 kW which made it possible to apply them in experiments on laser radiation frequency conversion in nonlinear crystals into the spectral range of ~ 2–20 μm.

A terahertz NH3 laser optically pumped by “long” (~100 μs) pulses of an electron-beam-sustained-discharge CO2 laser is demonstrated for the first time. The NH3 laser pulses and the “long” pulses of the CO2 laser are simultaneously measured with nanosecond resolution. The duration and the delay of the NH3 laser pulse relative to the pump pulse are measured depending on the pulse energy of the pump CO2 laser. The following emission wavelengths of the terahertz NH3 laser were observed upon pumping by the 9R(30) line of the CO2 laser: 67.2, 83.8, and 88.9 μm.