Summary form only given, as follows. We investigated the hidden alignment of Ne plasma in a magnetic field observing the optical characteristics of the medium-absorption and refraction. A tunable single frequency laser beam was used as a probe beam. Depending on the direction of the applied magnetic field and the geometry of observation, the dependence of the plasma birefringence or dichroism on the magnetic field was registered. The dye laser was tuned to /spl lambda/=607.4 nm (2p/sub 3/-1s/sub 4/ Ne transition). The dependence on the external magnetic field of the laser beam intensity passed through the Ne discharge cell was registered, for various laser frequencies in the limits of the absorption line. At the edge of the absorption line, the signal of the dichroism consists of two Lorentzian components while at the center of the absorption line the wide component is absent. The wide component width depends on neon pressure as: H(P)=(1.64/spl plusmn/0.03) gauss + P(torr) (0.33/spl plusmn/0.08) gauss/torr. This value is in a good agreement with other results concerning the lifetime of the 1s/sub 4/ state. The mechanism of alignment formation in this state is not clear. This state could not be aligned by light absorption following a quantitative calculation. The irradiation of atoms is isotropic within the limits of all the absorption line because of the high magnitude of absorption for the 1s/sub 4/-1s/sub 0/ transition. We consider the optical pumping as the most probable mechanism for alignment of this state. The magnitude of absorption on the s-p neon transitions are not high. The intensity of the spontaneous emission beam along the tube is greater than in the perpendicular direction. If the quantization axis coincides with the tube axis, this beam empties the magnetic sublevels with M=/spl plusmn/1, thus creating longitudinal alignment. The absence of a signal at the center of the absorption line can be explained by the high selfabsorption on the s-p transitions. The width of the narrow component of the signal is approximately 0.7 gauss. Its pressure dependence is small. We have established experimentally the absence of signals of such width in the spontaneous emission from 2p levels. Hence, all optical mechanisms of alignment transmission from higher or from lower states to the 1s/sub 4/ state are excluded. Apparently this signal arises from alignment of metastable state 1s/sub 5/. In our opinion the collisions are the most probable mechanism of alignment transmission.
Summary form only given, as follows. We investigated the hidden alignment of Ne plasma in a magnetic field observing the optical characteristics of the medium-absorption and refraction. A tunable single frequency laser beam was used as a probe beam. Depending on the direction of the applied magnetic field and the geometry of observation, the dependence of the plasma birefringence or dichroism on the magnetic field was registered. The dye laser was tuned to /spl lambda/=607.4 nm (2p/sub 3/-1s/sub 4/ Ne transition). The dependence on the external magnetic field of the laser beam intensity passed through the Ne discharge cell was registered, for various laser frequencies in the limits of the absorption line. At the edge of the absorption line, the signal of the dichroism consists of two Lorentzian components while at the center of the absorption line the wide component is absent. The wide component width depends on neon pressure as: H(P)=(1.64/spl plusmn/0.03) gauss + P(torr) (0.33/spl plusmn/0.08) gauss/torr. This value is in a good agreement with other results concerning the lifetime of the 1s/sub 4/ state. The mechanism of alignment formation in this state is not clear. This state could not be aligned by light absorption following a quantitative calculation. The irradiation of atoms is isotropic within the limits of all the absorption line because of the high magnitude of absorption for the 1s/sub 4/-1s/sub 0/ transition. We consider the optical pumping as the most probable mechanism for alignment of this state. The magnitude of absorption on the s-p neon transitions are not high. The intensity of the spontaneous emission beam along the tube is greater than in the perpendicular direction. If the quantization axis coincides with the tube axis, this beam empties the magnetic sublevels with M=/spl plusmn/1, thus creating longitudinal alignment. The absence of a signal at the center of the absorption line can be explained by the high selfabsorption on the s-p transitions. The width of the narrow component of the signal is approximately 0.7 gauss. Its pressure dependence is small. We have established experimentally the absence of signals of such width in the spontaneous emission from 2p levels. Hence, all optical mechanisms of alignment transmission from higher or from lower states to the 1s/sub 4/ state are excluded. Apparently this signal arises from alignment of metastable state 1s/sub 5/. In our opinion the collisions are the most probable mechanism of alignment transmission.
The dichroism of a neon gas discharge plasma in a weak magnetic field is investigated by scanning the 3 s 2 -2 p 4 transition by monochromatic laser radiation. Magneto-optical resonances of the intrinsic macroscopic alignment and hidden alignment of the 2 p 4 level are separated. Against the background of these resonances, resonances attributed to coherence transfer from the 1 s 2, 4, 5 levels and the birefringence of the wings of the nearest absorption lines from the 1 s 4, 5 levels are observed. A new type of alignment is revealed—integral hidden alignment, whose lifetime, in contrast to the case with macroscopic alignment, increases without bound with increasing radiation trapping.
Summary form only given. The resonance laser interaction with an atomic system with degenerate levels creates coherent properties in the medium. Depending on the laser polarization and the experimental geometry it could be alignment, orientation or optical pumping. This coherence could be destroyed by application of a magnetic field, which removes the level degeneracy. This process has an effect on the optical characteristics of the medium, such as absorption and fluorescence from the levels involved. They show the resonance dependence on the applied magnetic field with widths, depending on /spl gamma//sub a/, /spl gamma//sub b/, and /spl gamma//sub ab/, where /spl gamma//sub I/ is the width of the upper or lower state of the transition, resonant to the laser beam, /spl gamma//sub ab/ is the width of the optical transition a/spl rarr/b. Using different experimental geometry, /spl gamma//sub a/, /spl gamma//sub b/, and /spl gamma//sub ab/ could be measured, as well as some rate constants of these levels. We investigated the coherent properties of the 2/sup 3/ P/spl rarr/3/sup 3/ D transition of He I under resonant laser radiation. Due to the peculiarities of the coherent signals, registered in the lateral and forward direction the cross-section for velocity selective collisions for the 3/sup 3/ D He I level were obtained. The influence of the strong laser field on the widths and shapes of the signals was determined. The cross-section, for depolarizing collisions of the 3/sup 3/ D level was measured, too.
The authors have investigated the zero-field level crossing lineshape in resonance absorption. A single-mode HeNe laser beam at 633 nm is applied to an external neon-gas absorption cell in a longitudinal magnetic field. They compare the measured lineshapes with theoretical predictions. Two superposed nonlinear Lorentzian-shaped resonances, known as the population effect of the 2p 4 -3s 2 transition and the Zeeman coherence effect of the lower 2p 4 level, appear on the background caused by the inhomogeneous broadening. Taking into account the background and the power broadening the authors obtain the linewidths at zero pressure gamma (2p 4 ,3s 2 )=(7.7+or-2.1) MHz and gamma (2p 4 )=(8.4+or-1.2) MHz. For the neon pressure broadening the authors get for pressures below 200 Pa (1.5 Torr) d gamma (2p 4 ,3s 2 )/dp=0.20+or-0.02 MHz Pa -1 and d(2p 4 )/dp=0.040+or-0.007 MHz Pa -1 . Their values are in acceptable agreement with the values obtained with other spectroscopic methods.
The interaction of polychromatic radiation of a dye laser with a neon gas-discharge plasma in shielded cylindrical tubes at medium gas pressures (1-30 Torr) near atomic spectral absorption lines of NeI atoms with wavelengths 650.6 and 656.2 nm was experimentally studied. Along the direction of propagation of the laser radiation, a shift in the central frequency of absorption is observed in the presence of inhomogeneities in the plasma column. The character of the optical transmission spectrum near narrow resonances was empirically shown to substantially depend on the density of absorbing atoms in a plasma; if this density exceeds 1012 cm-3, the contour of the transmission spectrum near the absorption resonance acquires a dispersive form. The general laws of the formation of nonstationary plasma transmission spectra depending on the laser power, the density of absorbing atoms, the nature of plasma inhomogeneities along the direction of propagation of laser radiation are examined in detail. The role of nonlinear and coherent effects and phase self-modulation during resonant interaction of short pulses of polychromatic laser radiation with gas-discharge plasma in narrow shielded tubes is discussed.
The fluorescent light from two atomic levels is studied assuming that the atoms are subjected to a gas discharge, to a static magnetic field, and, simultaneously, to a laser beam having the transition frequency between the atomic levels. Calculations are developed in the formalism of irreducible tensor operators. One takes into account the existence of isotropic relaxations and cascade effects due to spontaneous emission between the upper and the lower levels. Following Lamb, the laser beam is described classically by its electric field, and its effects are calculated by perturbation theory. It is predicted that the σ component of fluorescent light exhibits the Hanle effect, which allows one to measure the relaxation rates\Gamma(0)and\Gamma(2)of the population and of the alignment of the emitting level, respectively. Experimental agreement with the theoretical analysis has been found for the3s_{2}, 2s_{2}, and2P_{4}levels of Ne. Among the experimental results obtained by this method are the natural widths and the collision cross sections for population (quenching collision) and for alignment. Several transition probabilities are also derived. Furthermore, the theory of coherent imprisonment of the fluorescent line has been found valid even if laser pumping light is used.
The forward-scattered light observed when a single-mode dye laser interacts with the three neon transitions 1 s 5 ( J = 2)-2 p s ( J = 2), 1s 3 ( J = 0)-2 p 5 ( J = 1), and 1 s 4 ( J = 1)-2 p 7 ( J = 1) has been investigated as an applied longitudinal magnetic field is varied. The 1 s 5 and the 1 s 3 states are metastable. This condition allows a comparison of the spectra for the cases 1 s 5 ( J = 2)-2 p 8 ( J = 2) and 1 s 3 ( J = 0)-2 p 5 ( J = 1) in order to discuss whether the complex line shapes obtained for the J = 2 to J = 2 atomic system are due to higher-order coherences or whether they originate from coherences between m = ±1 states. Experimental and calculated line shapes are presented. The calculations have been performed with the use of a semiclassical model for the light/matter interaction. A J = 0 to J = 1 (or a J = 1 to J = 1) model reproduces the overall shapes of the recorded spectra for all three transitions. The results show that, even when laser beam spatial effects and the sample isotopic effects are taken into account, interpretations of forward-scattering spectra in order to determine atomic parameters can reliably be done for simple J = 0 to J = 1 systems only.