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.

A compact IR spectrograph based on a line array of pyroelectric sensors and operating in the vicinity of 10-μm-wavelength has been developed. The development was motivated by various tasks requiring prompt measurement of the spectral characteristics of multifrequency radiation in this spectral range. The spectrometer’s performance was tested using a wavelength-tunable CO2-laser. With a fixed position of the diffraction grating, the spectrometer covers a wavelength range of approximately 0.6 µm (wavenumber range of approximately 50 cm–1) with a spectral resolution of approximately 0.02 µm (which is approximately 0.2 cm–1), which allows one to reliably separate two adjacent CO2-laser lines.

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.

An ultrashort-pulse mid-infrared laser system tunable within a wavelength range of ∼ 5–11 μm 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 ∼ 5.5 μm to ∼ 10 μm was carried out with AgGaS2 and LiGaS2 crystals. The LiGaS2 crystal provided the highest mid- infrared pulse energy of 2.7 μJ at 6 μm wavelength and broadband pulse spectrum within 7.5–11.5 μm wavelengths. The ZnGeP2 crystal provided the highest efficiency of 0.16 % for frequency conversion into ∼ 10 μm wavelength region, but that took place at low pump pulse energy/intensity (0.3 mJ/∼30 GW/cm2), which, being higher, resulted in lower efficiency due to nonlinear absorption.

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

The interaction of femtosecond laser pulses with the surface of silica glass has been studied. As a result of interference between the incident radiation and surface plasmon polaritons, the formation of self-organizing subwavelength periodic structures with a period of 250 nm was observed. The minimum pulse energy at which recording occurs without surface ablation has been revealed.

The interaction of femtosecond laser radiation with a wavelength of 1030 nm with chalcogenide glasses of various compositions has been studied. The dependence of the optical transmission of chalcogenide glasses on the pulse energy and frequency has been experimentally established. The compositions of glasses for their use as an optical medium for laser micromachining in the infrared range have been established. It is shown that Ge7Se93 glass is the most suitable optical medium for spectral studies of diamond in the near and mid-IR range. Keywords: direct laser recording, femtosecond laser pulses, chalcogenide glasses, IR optical materials.

We measured and simulated the spectrally resolved angular distributions of 0.3–1-THz emission from the two-color filament with its plasma length (∼40 mm) exceeding the dephasing length (∼25 mm) between the fundamental (740 nm) and the second harmonic (370 nm) pulses in air. We show that only the forwardly propagating on-axis terahertz (THz) radiation is sensitive to the variation of the phase offset φ between fundamental and second harmonics, while the ring-like THz beam carrying ≳80% of the overall THz yield is independent of φ. Utilization of the THz ring allows one to omit the tedious adjustment of the frequency-doubling crystal position in the experiment.

The simple mid-IR laser source based on femtosecond Ti:Sapphire laser and successive frequency conversion of its stretched up to 50 ps pulses in SrMoO4 Raman-active crystal and LiGaS2 second order nonlinear crystal is demonstrated. Energy of the mid-IR pulse at 11.4 mu m wavelength was up to 250 nJ that was four times higher than the previous results for the similar setup. The influence of pump pulse intensity on spectral and energetic parameters of laser pulses after SrMoO4 and LiGaS2 crystals were studied in details.

The luminescence dynamics of vibrationally excited CO molecules upon excitation of a gas mixture containing carbon monoxide in a pulsed electroionization discharge has been experimentally measured. A numerical model of vibrational level kinetics was used to analyze the experimentally measured luminescence signals of vibrationally excited molecules and to determine the relaxation rate constant of the first vibrational level of CO molecules during their collisions with water molecules at Т = 300 K.

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.

At the selected frequencies from 0.3 to 10 THz we measured the two-dimensional (2D) distributions of fluence and polarization of terahertz (THz) emission from a single-color femtosecond filament. At the majority of frequencies studied, the THz beam has a donut-like shape with azimuthal modulations and radial polarization. At the maximal modulation, THz beam takes the form of the two lobes and polarization of the THz field degenerates into orthogonal to the laser pulse polarization direction. Violation of the radially polarized donut beam shape is due to destructive interference of THz waves driven by light pressure directed along the laser beam propagation axis and ponderomotive force parallel to the laser polarization.

Experimental results on drilling of PMMA by mid-IR lasers are presented and discussed. Proper choice of a CO laser beam focusing conditions made it possible to produce high aspect ratio (similar to 100) holes. During the laser drilling a waveguide-like structure of the hole was formed in PMMA with almost a constant sub-millimeter diameter along its whole length. Characteristics of the holes drilled by CO laser (wavelength 5.0-5.5 mu m) and CO2 laser (10.6 mu m) beams are compared.

The beam self-cleaning phenomenon is theoretically predicted by the two-dimensional nonlinear Schrödinger equation, which describes self-focusing, and is observed in the case of femtosecond laser filamentation in the collimated regime of propagation. However, the impact of external focusing on the self-cleaning has not been investigated so far. In this paper we systematically study this impact in a wide range of focusing conditions. We show that the energy range, in which self-cleaning can be observed, shrinks monotonically with the numerical aperture growth at some point vanishing at all.

The terahertz (THz) radiation emitted by an air-based femtosecond filament biased by a static electric field is known to have on-axis shape and relatively low frequency spectrum in contrast to the unbiased single-color and two-color schemes. Here, we measure the THz emission of a 15-kV/cm-biased filament in air produced by a 740-nm, 1.8-mJ, 90-fs pulse and demonstrate that a flat-top on-axis THz angular distribution of the emission at 0.5-1 THz transforms into a contrast ring-shaped one at 10 THz.

Dependences of a cryogenic slab radio-frequency discharge CO laser output power on a distance between mirrors of a hybrid negative-branch waveguide-unstable resonator were experimentally studied. The maximum output power was observed at the resonator length longer than the one calculated by taking into account the mirrors radii of curvature. Optimization of the resonator length made it possible to get the output power increase up to 20%–25%. The results obtained can be used for designing not only slab laser systems with hybrid waveguide-unstable resonators, but also for high-power lasers with full-sized negative-branch unstable ones.

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.

In the present study, copper and silver nanoparticles with a concentration of 20 µg/cm2 were synthesized using the method of laser-induced forward transfer (LIFT). The antibacterial activity of the nanoparticles was tested against bacterial biofilms that are common in nature, formed by several types of microorganisms (mixed-species bacteria biofilms): Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. The Cu nanoparticles showed complete inhibition of the bacteria biofilms used. In the course of the work, a high level of antibacterial activity was demonstrated by nanoparticles. This activity manifested in the complete suppression of the daily biofilm, with the number of bacteria decreasing by 5–8 orders of magnitude from the initial concentration. To confirm antibacterial activity, and determine reductions in cell viability, the Live/Dead Bacterial Viability Kit was used. FTIR spectroscopy revealed that after Cu NP treatment, there was in a slight shift in the region, which corresponded to fatty acids, indicating a decrease in the relative motional freedom of molecules.

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.