Measuring photoionization cross-sections of excited atomic states

A new method of photoionization cross-section measurement based on the observation of saturation in the ion yield as a function of radiation intensity has been proposed. The photoionization cross-sections for the 6²P_1/2 and 6²P_3/2 levels of Rb atoms of the fundamental and second harmonics of ruby laser radiation are measured, with a tunable pulsed dye laser used for excitation. The following values of cross-sections are obtained: (1.7±0.4)·10⁻¹⁷ cm² and (1.5±0.4)·10⁻¹⁷ cm² for the levels 6²P_3/2 and 6²P_1/2, respectively, ionized by radiation of v₂=14403 cm⁻¹, and (1.9±0.5)·10⁻¹⁷ cm² for the 6²P_3/2 level ionized by v₂=28806 cm⁻¹ radiation.     

Laser ablation parameters of atherosclerotic arteries

Summary The threshold of atherosclerotic plaque ablation in water by the XeCl laser radiation was measured to be of (1.5±0.2) J/cm². Within the simple thermal model this value corresponds to the mean temperature of about 373 K in the irradiated volume as for other angioplasty lasers. Time-of-flight probing of ablation in air by the XeCl and CO₂ lasers revealed microsecond lifetimes of ablated volumes that confirm the mechanism of explosive boiling of superheated tissue water. So the local temperature must be about 582 K which can be due to inhomogeneous light distribution and absorption. The short lifetime leads to the absence of heat diffusion and, hence, to the ablative character of tissue destruction.     

Isotopically selective dissociation of CCl4 molecules by NH3 laser radiation

The voltage-current characteristics of a UV preionised CO₂ laser operating at pressures ?13 atmospheres have been investigated and the quasi-steady glow and breakdown fields measured. The discharge resistivity has been found to be a function of the applied excitation field and a simple model has been developed to explain the results obtained.     

Selective dissociation of SF6 molecules in a two-frequency infrared laser field

The dissociation of SF₆ in the field of two infrared frequencies is studied. It is shown that the selectivity of dissociation is increased compared to the single frequency dissociation case. The dispersion characteristics of the vibrational quasicontinuum have been obtained. A theoretical model of the processes is discussed.     

Voltage-current characteristics of superatmospheric pressure CO2 laser discharges

The IR NH₃ laser radiation was applied for selective dissociation of CCl₄ molecules. The dissociation yield, its pressure dependence and isotopic selectivity were measured. Two-frequency dissociation of CCl₄ by the NH₃ laser and the CO₂ pump laser radiations was carried out. It was shown that the NH₃ laser is very effective for CCl₄ dissociation.     

Monomer counterrotations and tunneling splitting in CO dimer by data of millimeter wave spectroscopy

Analysis of the rotational spectrum of the molecular dimer (CO)₂ measured in the millimeter wave range has been performed and four new rotational states are revealed. Three of these states are characterized by almost free rotations of both monomers in the dimer. These states have approximately the same first term σ in the expansion of the rotational energy in powers of the rotational angular momentum J for various values of the momentum projections on the dimer axis (K=0, 1, 2) and various rotational constants B. The intrinsic rotational angular momenta of CO dimers, j₁=j₂=1, are determined from the σ value. In addition, a state with K=2 is found which corresponds to one of the known shape isomers of (CO)₂. The values of the tunneling splitting for each of the new states are determined. The results indicate that previous data on the suppressed tunneling are determined by the asymmetry of internal rotations in the CO monomers rather than by the _K value.