Nikolai V. Karlov

Lase action on resonant molecular flows through capillaries

New experimental results are reported pointing to the possibility of a laser control of the resonant gases transit through capillaries in the Knudsen and intermediate regimes.

Pulsed CO 2 laser with double modulation

For the pulse pumped CO 2 laser we used Q-switching to investigate inversion kinetics. The pump was synchronized with the Q-switching mirror. It was possible to obtain the Q-switch pulses at any phase of the pump pulse. The repetition rate was 50 Hz and the pump pulse duration was 4 or 10 ms. It was found that there is an optimum delay in switching the cavity Q-factor after the discharge started. The giant pulse intensity increased several times after the discharge was switched from CW to pulses. The inversion rise time was 1-2 ms and its lifetime was strongly dependent on the discharge current, due to plasma heating during the current pulse. Increasing the helium percentage in the discharge prolonged the inversion lifetime because of high thermal conductivity of helium gas. Gaseous BCl 3 was chosen to obtain the CO 2 laser giant pulses with bleachable filter. The vibronic frequency V 3 of the B11Cl 3 molecules coincides with the P lines of the CO 2 laser. Rarer B10Cl 3 corresponds to less active R lines. Pure BCl 3 did not give the giant pulses. Adding helium to the BCl 3 cell gave the pulses. The best results came from adding very small amounts of ammonia NH 3 because of the effective vibrational energy transfer between colliding BCl 3 and NH 3 molecules.

Multiphoton spectroscopy of the gasdynamically cooled SF6: third harmonic generation and dissociation spectrum

Abstract The third harmonic generation spectrum originating in the system of the low laying SF 6 vibrational levels has been investigated for the gasdynamically cooled gas (T rot ≅ 30 K) using a continuously tuned CO 2 -laser. A HF*-luminescence technique has been applied to obtain the SF 6 dissociation spectrum. The spectral features revealed did allow to make an adequate choice of the anharmonicity constants.

MECHANISM OF COLLISIONLESS DISSOCIATION OF POLYATOMIC MOLECULES

A detailed investigation of the effect of collisionless dissociation of polyatomic molecules was carried out in a cycle of experiments [4], in which collisionless dissociation of polyatomic molecules was revealed to have a distinguishing feature of exceeding importance for laser photochemistry and laser isotope separation, viz., isotopic selectivity of the dissociation process. The experimentally observed features of collisionless dissociation were theoretically explained in [5-6]. The explanation was based on the subdivision of the energy spectrum of the vibrational states into two qualitatively different regions. The first part of the spectrum includes the lower vibrational levels down to the energies of 4-5 laser photons. As shown in [5-6], the remaining vibrational levels, located in regions of higher energies and contained in the second part of the spectrum, are so closely spaced that they form a quasicontinuum of vibrational states. This division of the spectrum into two parts is generally speaking arbitrary, since the quasicontinuum does not have an abrupt boundary on the lowenergy side; nevertheless, this division reflects correctly the specifics of the spectrum of polyatomic molecules. As a result, in contrast to the one-dimensional nonlinear oscillator model, satisfactory qualitative agreement was obtained between the theoretical and the experimental results. The process of excitation of polyatomic molecules was correspondingly subdivided in [5-6], in accord with the subdivision of the spectrum, into two stages. The first stage is resonant excitation of several low-lying levels of a mode active in the IR region, up to states lying in the quasicontinuum. Use was made in this case of the system of vibrational levels of a one-dimensional nonlinear oscillator. This made it possible to explain the resonant character of the energy acquisition during the first stage, and consequently the isotopic selectivity of the collisionless dissociation of polyatomic molecules~ During the second stage, the molecules landing in the quasicontinuum region were resonantly excited, in view of the high level density, in the region of the quasicontinuum, up to dissociation states or even ionization states [7]. It is precisely the second stage which strongly distinguishes the process of excitation of polyatomic molecules from the excitation of diatomic molecules, and permits a qualitatively correct identification of the distinguishing features of collisionless dissociation of polyatomic molecules.

Sources of atomic vapor for laser isotope separation

ConclusionsThus, our experimental investigations of the methods of obtaining a vapor of neutral atoms of the refractory and chemically active rare element (Gd) have shown that both investigated methods — electron-beam evaporation and cathode sputtering — are promising. The fact that the levela9D5 is equally singled out in the electron-beam evaporation and in the cathode sputtering is evidence of the decisive importance of the processes of establishment of the distribution of the populations over the sublevels of the ground state of the evaporated atoms. It is obvious here that the determination of the properties of this distribution for other elements calls for investigations similar to those described above.The question of the choice of source of neutral atoms should be solved separately for each chosen laser isotope separation scheme.

Heterogeneous Selective Processes under the Action of the Laser Radiation

Selective heterogeneous processes as compared to the selective processes in the homophase conditions are characterized by their small typical energies. From a variety of heterogeneous processes, we have approached the processes of physical sorption and adsorbed molecules diffusion over the surface of substance phase separation. The action of radiation on a heterophase system changes the state of the latter. In the case of a multicomponent substance system, the heterogeneous molecular-kinetic processes of the resonance components can be distinguished from those of nonresonance components, and their selective control can be carried out.

Isotope separation of the lanthanoid group elements by the method of two-step selective photoionization

ConclusionsThe experiments on the laser separation of the isotopes of the elements of the lanthanoid group have shown that obtaining isotopically pure materials by the method of selective photoionization is feasible.The data obtained are necessary for the planning of experiments on LIS of rare-earth elements of significant weight.In conclusion, the authors express their gratitude to V. V. Arinin, M. N. Glasko, V. N. Markov for help with the experiments and to A. M. Prokhorov for constant interest and support.

Laser induced atomic-molecular reaction of the rare-earth ytterbium and europium metals with HCl molecules

In the crossed atomic and molecular beams the chemical reactions of ytterbium and europium atoms with HCl molecules were observed at the laser excitation of atoms. At the excitation of ytterbium metastable states3P 0 and3P 2 an indicated amount of the reaction product was increased by a factor of three as compared to the case of3P 1 state excitation.

Separation of samarium isotopes by the two-step photoionization method

Separation of samarium isotopes was performed by the two-step photoionization method. The characteristics of the apparatus employed are described and a 154Sm photoionization current of J = 1.4×10–14 A is reported.

Selectivity of two-stage photoionization of atoms

A fairly general kinetic scheme is used in an analysis of two-stage pulse laser photoionization of a mixture of two isotopes. Expressions for the total number of selected ions, quantum efficiency, and separation coefficient are derived allowing for the resonant transfer of the excitation, charge exchange, and deterioration of the excitation selectivity due to absorption in the laser line wings. Various schemes for the separation of the required atoms are considered from the point of view of yield and efficiency of the method.