Influence of CO2-laser radiation on the quasiline fluorescence spectra of anthracene vapor

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 53, No. 5, pp. 722–726, November, 1990.     

Self-diffraction of CO2-laser radiation in SF6

Self-diffraction of CO₂-laser radiation (=10.51 m) has been observed in gaseous SF₆. Different orders of self-diffraction have been studied, up to the third. The amplification due to degenerate resonant multiphoton parametric processes has been measured to be as large as eight. The experimental estimates have been derived for the effective nonlinear susceptibilities (coefficients of nonlinear interaction) of the third, fifth, and seventh orders. The self-diffraction may essentially affect nonlinear processes including optical phase conjugation.     

Structural transformations of polysaccharides exposed to CO2-laser radiation

We have used IR spectroscopy to study conformational transformations of polysaccharide macromolecules (dextran, pullulan, amylose, and microcrystalline cellulose) and changes in their structural ordering when exposed to cw emission of a CO₂ laser. We have established that the structures of conformationally labile polysaccharides are the most sensitive to laser radiation. The effect of laser treatment is greatest for lower molecular weight polymers. We have observed for the first time changes in the conformational states of dextran macromolecules in the direction of an increase in the structural ordering when exposed to emission from a CO₂ laser. This quite different from purely thermal treatment, where disordering of the polysaccharides structure occurs. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 2, pp. 164–169, March–April, 2006.     

Effective upconversion of CO2-laser radiation in sodium vapors

The effective upconversion of CO₂-laser radiation to the uv spectral range has been obtained in sodium vapors, the photon efficiency being 65%, the corresponding power efficiency being 2640%.     

Phase conjugation of CO2-laser radiation by a three-beam interaction

The distortion correction of a CO₂-laser radiation wavefront is studied by using forward resonant parametric scattering in gaseous SF₆ and retrace after retroreflection from a mirror.     

Gas breakdown near solid targets by pulsed CO2-laser radiation

Conclusions In conclusion, let us note some important problems whose solution, in our opinion, will make for a better undertanding of the physical mechanisms of processes occuring in a low-threshold breakdown of gases near solid targets. First is the systematization of data on threshold-breakdown intensities (dependence of S_br on the area of the irradiation spot and laser-pulse duration over wide ranges of these quantities, on the pressure and kind of gas surrounding the target, and on the radiation wavelength). Analysis of such data would make it possible to construct a more orderly theory of the process. Also of great interest is the transfer of heat to a solid target from the plasma of the low-threshold breakdown of a gas and from the shock waves propagating in the plasma. It is advisable to carry out numerical calculations on the gasdynamic processes occurring near a solid target under irradiation by a pulsed CO₂ laser, with account for the counterpressure of the ambient gas and for various regimes breakdown-plasma propagation with subsequent comparison of these data with experimental results.Translated from Izvestiya Vysshykh Uchebnykh Zavedenii, Fizika, No. 11, pp. 34–60, November, 1977.     

Time-dependent thermal lensing and Kerr nonlinearity in CS2 with CO2-laser radiation

We report on optical limiting and z-scan in CS₂ as a function of the pulse duration of 10 µm TEA CO₂-laser radiation. We present a comprehensive and simple model for the shape of a laser pulse transmitted through this limiting device. For the first time, we propose the use of an optical limiting device for beam shaping.     

Effect of diffusion on absorption and saturation of infrared radiation in molecular gases

Effect of diffusion on absorption of infrared radiation and saturation of absorption in molecular gases is considered. Incorporating the diffusion term, a theory is developed from multi-level rate equations, both for homogeneous and inhomogeneous broadening cases. It is shown that the effect of diffusion is characterized by a diffusion functionK'(k ₂ a), which varies inversely with the radius of the laser beam at low pressures and small beam sizes. Experimental results with seven molecular gases pumped by the CO₂ laser beam around 10.6 μm are reported.     

The frequency,fluence and pressure dependence of the absorption of pulsed CO2-laser radiation by CF2HCl

Absorption measurements in the CF₂HCl fundamental vibrational band v₃, and combination band v₅ + v₉, for laser energy fluence between 0.1–1.2 cm⁻² and 1–100 Torr gas pressure, are reported. Three distinct regions are experimentally observed for the fluence dependence of the absorption cross section σ and the average number of absorbed photons <n>. Adding Ar buffer gas to CF₂HCl enhances the absorption efficiency only in the v₃ band.     

Single mode CO2-laser pulses of high power

Single longitudinal mode CO₂-laser pulses of 200 MW power have been produced by seeding an unstable resonator cavity with single mode radiation from a hybrid low pressure — high pressure CO₂ laser system. The results indicate that a ratio of dominant over residual mode intensities of better than 10⁵ were achieved.     

CW CO2-laser annealing of arsenic implanted silicon

CW CO₂-laser annealing of arsenic implanted silicon was investigated in comparison with thermal annealing. Ion channeling, ellipsometry, and Hall effect measurements were performed to characterize the annealed layers and a correlation among the different methods was made. The laser annealing was done with power densities of 100 to 640 W cm⁻² for 1 to 20 s. It was found that the lattice disorder produced during implantation can be completely annealed out by laser annealing with a power density of 500 W cm⁻² and the arsenic atoms are brought on lattice sites up to 96±2%. The maximum sheet carrier concentration of 6×10¹⁵ cm⁻² was obtained for 1×10¹⁶ cm⁻² implantation after laser annealing, which was up to 33% higher than that after thermal annealing at 600 to 900°C for 30 min.     

Influence of the modal composition of the radiation on the oscillation dynamics of a CO2-laser with a saturable absorber

The influence of the modal composition (transverse modes of a single longitudinal mode) of the laser radiation on the oscillation dynamics of a CO₂-laser with a saturable absorber in the cavity is investigated. Passive Q-switching in initiation of the fundamental mode TEM₀₀ and the modes of the first family TEM₀₁ and TEM₁₀ is considered. It is established that in the case of multimode oscillations sequences of single pulses with an irregular change in their amplitude can be observed. The multimode oscillations obtained are compared with similar single-mode oscillations, and their special features and differences are discussed. Reported at the Second International Scientific and Technical Conference on Quantum Electronics, Minsk, November 23–25, 1998. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 5, pp. 681–687, September–October, 1999.     

Shape and delay of CO2-laser pulses in fog

The problem of propagation of 10.6 m-CO₂ laser pulses in fog has been formulated and solved numerically, making use of Duhammel's principle. Fog droplets are considered Mie scatterers in the Rayleigh limit. Evaporation, power loss and time delay of pulse peak have been studied. Possible extensions of the technique have been discussed.