Enrichment of CH3F nuclear spin isomers by resonant microwave radiation

Theoretical model of the coherent control of nuclear spin isomers by microwave radiation has been developed. Model accounts the M-degeneracy of molecular states and molecular center-of-mass motion. The model has been applied to the 13CH3F molecules. Microwave radiation excites the para state (J=11,K=1) which is mixed by the nuclear spin-spin interaction with the ortho state (9,3). Dependencies of the isomer enrichment and conversion rates on the radiation frequency have been calculated. Both spectra consist of two resonances situated at the centers of allowed and forbidden (by nuclear spin) transitions in the molecule. Larger enrichment, up to 7%, can be produced by strong radiation resonant to the forbidden transition. The spin conversion rate can be increased by 2 orders of magnitude at this resonance.Comment: REVTEX, 14 pages + 6 eps figure

Coherent population trapping: its physics and historical roots

There presented basic information on coherent population trapping (CPT) and related phenomenon of electromagnetically induced transparence, ‘dark’ and ‘bright’ (anomalous absorption) states is presented. Spectrum transformation is considered in probe field spectroscopy for Λ-scheme in various settings. The close relation is revealed between the effect of CPT in the manifold of magnetic sublevels and the phenomenon of optical pumping (optical orientation and optical alignment). CPT is shown to be generalized to the case of several transitions with a common upper level and with the corresponding number of light fields each being in quasiresonance with its ‘own’ transition

Explosive evaporation of Rb or K fractal clusters by low power CW radiation in the presence of excited atoms

In this paper we describe a new, spectacular, unpredictable effect of the explosive evaporation of metallic Rb or K fractal clusters, only in the presence of excited atoms stimulated by resonant CW laser radiation in a heat-pipe glass cell. Evaporation occurs at low laser-power density, in the presence of a buffer gas. The effect consists of the generation of optically thick, sharply localized alkaline metals vapour clouds propagating in the cell against the laser beam. These clouds are charged and exhibit a strong luminescence of Rb or K spectral lines. We believe that the explosive evaporation of metallic fractal clusters observed is explained by the laser excitation of alkali atoms. The excited atom collides into the surface of the clusters and transfers its internal energy to the surface locally. This energy greatly raises the temperature of this local part of the clusters surface, melts it and decreases the fractal surface area. Because, in general, any fractal cluster systems have a high surface energy, some of processes which leads to decreasing their surface area can liberate the surface energy. This energy increases the total temperature of the clusters and eventually leads to the thermal explosion of the cluster

Explosive evaporation of Rb or K fractal clusters by low power CW radiation in the presence of excited atoms

In this paper we describe a new, spectacular, unpredictable effect of the explosive evaporation of metallic Rb or K fractal clusters, only in the presence of excited atoms stimulated by resonant CW laser radiation in a heat-pipe glass cell. Evaporation occurs at low laser-power density, in the presence of a buffer gas. The effect consists of the generation of optically thick, sharply localized alkaline metals vapour clouds propagating in the cell against the laser beam. These clouds are charged and exhibit a strong luminescence of Rb or K spectral lines. We believe that the explosive evaporation of metallic fractal clusters observed is explained by the laser excitation of alkali atoms. The excited atom collides into the surface of the clusters and transfers its internal energy to the surface locally. This energy greatly raises the temperature of this local part of the clusters surface, melts it and decreases the fractal surface area. Because, in general, any fractal cluster systems have a high surface energy, some of processes which leads to decreasing their surface area can liberate the surface energy. This energy increases the total temperature of the clusters and eventually leads to the thermal explosion of the cluster

Frequency stabilization of a broad-band dye laser by light-induced drift

none7A new method for frequency locking of a broad-band laser based on light-induced drift is presented. The main advantages of the technique are: good stabilisation provided by sensitivity and good signal-to-noise ratio of the error signal; unnecessary dithering of the laser frequency; use of an atomic transition with low frequency drift. The method is well suited to broad-band applications because the light-induced drift effect can naturally integrate over a broad-band of frequencies (of the order of the Doppler width) to find the average. Tests carried out on Na immersed in a buffer gas of Ar, have allowed long-term frequency stabilisation of the central frequency of a 2.5 GHz-bandwidth dye laser.noneS. N. ATUTOV; R. CALABRESE; V. GUIDI; P. LENISA; S. PETRUIO; E. MARIOTTI; L. MOI AND A.M. SHALAGINS. N., Atutov; Calabrese, Roberto; Guidi, Vincenzo; Lenisa, Paolo; S., Petruio; E., Mariotti; L. MOI AND A. M., Shalagi

Frequency stabilisation of a broad-band dye laser by light-induced drift

A new method for frequency locking of a broad-band laser based on light-induced drift is presented. The main advantages of the technique are: good stabilisation provided by sensitivity and good signal-to-noise ratio of the error signal; unnecessary dithering of the laser frequency; use of an atomic transition with low frequency drift. The method is well suited to broad-band applications because the light-induced drift effect can naturally integrate over a broad-band of frequencies (of the order of the Doppler width) to find the average. Tests carried out on Na immersed in a buffer gas of Ar, have allowed long-term frequency stabilisation of the central frequency of a 2.5 GHz-bandwidth dye laser

Observation of sodium molecular formation induced by resonant laser atomic excitation and three body collisions.

none10A huge chemical shift in the sodium atom-dimer reaction is observed in a gas buffered cell upon resonant laser excitation. Atomic fluorescence quenching and molecular fluorescence enhancement are simultaneously detected during a few ms resonant laser pulse. The chemical shift is due to the formation of an excited sodium molecule in a three-body collision between two sodium atoms (at least one of them excited) and a buffer gas atom, followed by molecule stabilisation through radiative decay to the bound ground state. The dependence of the chemical shift on the buffer gas pressure, on the sodium density and on the laser intensity has been measured and agreement with our model has been foundnoneS. N. ATUTOV; V. BIANCALANA; S. BRANDT; R. CALABRESE; P. LENISA; E. MARIOTTI; L. MOI; K. NASYROV; A. M. SHALAGIN; R. WEYNANDSS. N., Atutov; V., Biancalana; S., Brandt; Calabrese, Roberto; Lenisa, Paolo; E., Mariotti; L., Moi; K., Nasyrov; A. M., Shalagin; R., Weynand