ABSTRACT
Theoretical studies of the characteristics of the spatial relaxation of the average energy of electrons in inert gases (He, Ne, Ar, Kr, Xe) in a uniform electric field had been carried out. Conditions were considered when spatial relaxation has the character of damped oscillations. The calculations were performed using the Monte Carlo technique both without and taking into account the secondary electrons that appeared due to the ionization of atoms by electron impact. It was shown that the inclusion of secondary electrons leads to a noticeable decrease in the spatial relaxation length even in the case when the contribution of the ionization process to the electron energy balance is relatively small. For these gases, the upper boundary of the the electric field strength was determined, where the spatial relaxation of the average energy has the character of damped oscillations.
ABSTRACT
The effect of the laser frequency tuning rate on a weak optical absorption line profile ~(10-5-10-7) cm-1 under conditions when the molecules were in a high-quality optical resonator was studied. The authors used a diode laser and an analytical cavity with two pairs of mirrors with reflectivity of 99% and 99.98% in the ~1.4 µm region. Water vapor at reduced pressure (0.03-1) Torr served as an absorbing medium. A high spectral resolution was obtained by directing laser radiation into the cavity with a small offset relative to its axis (off-axis ICOS). The frequency tuning rate was varied within (102-103) cm-1 s-1. With the increase of the rate, a shift and asymmetry of the Doppler absorption profile were observed. When the tuning direction was changed and the rate was kept the same, the effect preserved in time and mirrored symmetrically on the frequency scale. The measurements were consistent with calculations that took into account the finite lifetime of photons in the cavity and the real ratio of the effective optical path to the coherence length of the laser radiation. Limitations on the frequency tuning rate were discussed using quantitative absorption spectroscopy methods for measuring molecule concentrations.
ABSTRACT
Light-induced director orientation of polymeric liquid-crystalline systems was investigated. The materials under study were composed of a nematic liquid-crystalline polymer (NLCP) and a small amount (0.05-0.5 wt.%) of conformationally active (azobenzene) or stable (anthraquinone) dye impurity. Light action on the homogeneously aligned polymer films above glass transition temperature leads to the director reorientation and, consequently, to a change in the extraordinary refractive index. The effect is associated with the dye molecule excitation and related change of intermolecular forces. In the case of NLCP with conformationally active dye dopant, an extremely high orientational optical response was detected (nonlinear coefficient is n_{2}â¼0.1cm^{2}/W). In contrast, the efficiency of orientational light action on NLCP with conformationally stable dye dopant is of the same order of magnitude as that of dye-doped low-molar-mass liquid crystals. At the normal light incidence on the NLCP doped with azo-dye, the threshold director orientation is observed which is similar to the Fréedericksz transition under the action of magnetic and electric fields. The obtained high-orientational optical response of NLCP caused by azo-dye dopant in combination with the possibility of the recording of deformed structure in the glassy state, typical for polymer compounds, reveals new opportunities in photonics applications.
ABSTRACT
Cavity ring-down spectroscopy with an off-axis multipass cell and space separated detectors is proposed to record absorption spectra without modulation of the diode laser intensity. The spectral resolution is approximately 0.0003 cm-1. The whole spectrum is obtained for one continuous tuning of the laser frequency for approximately 20 ms. When comparing this method to conventional CRDS the required rise time is 1000 times slower. The recording of the whole spectrum for one measurement gives additional possibilities of signal extraction at relatively high noise. The technique is applied to absorption measurement of NO2 in atmosphere.
Subject(s)
Spectrum Analysis/methods , Lasers , Light , Nitrogen Dioxide/analysis , Time FactorsABSTRACT
Carbon dioxide decomposition in a non-self-sustained discharge was studied by the methods of diode laser spectroscopy and mass-spectrometry. It was shown that the effective control of the mechanism of a plasmachemical reaction is possible by varying the parameter E/N. This allowed us to reduce the energy cost of dissociation CO(2) by more than on an order of magnitude as compared to the dissociation process in a self-sustained glow discharge.
