Effect Of Laser Polarization Research Articles

Generation of high-order rotational lines in hydrogen by four-wave Raman mixing in the femtosecond regime

More than 40 rotational Raman lines are generated using an 800-fs Ti:sapphire laser. The spectral region extends from the near-infrared to the far-ultraviolet with a considerably flat intensity distribution. The effects of laser polarization, pulsewidth, hydrogen pressure, and focusing conditions on the efficiencies of stimulated Raman scattering, four-wave Raman mixing, self-phase modulation, self-focusing, and harmonic generation are investigated. A white light continuum, generated by self-phase modulation, acts as a seed beam for the generation of high-order rotational lines through four-wave Raman mixing. Strong self-phase modulation, however, suppresses the generation of the Raman emission, due to a line broadening of the pump beam. Thus, optimization of experimental conditions is necessary for the efficient generation of high-order rotational lines.

Formation of CN Radical by DC Discharge of CH<sub>3</sub>CN and LIF Measurement

Jet cooled cn radical beam was formed by cold cathode dc: discharge of ch3cn under molecular beam conditions. the cylindrical cold cathode was placed between the skimmer and the nozzle to prevent the nozzle from being clogged by carbon particles. the pulsed photon counting lif measurement was seriously jeopardized by the high intensive scattering laser light due to cn(b(2)sigma)'s short lifetime (70 ns) and weak fluorescence. by using an attenuator to reduce laser intensity or a polaroid to reduce the scattering laser intensity, we obtained lip spectra with good s/n ratio. with the theoretical simulaed spectra, the effects of laser polarization on lif were discussed and the relative populations of cn rotational and vibrational states were obtained.

Axis-switching transitions and the stimulated emission pumping spectrum of HCN

Six of the 14 unidentified bands in the stimulated emission pumping (SEP) spectrum of HCN are shown to be forbidden transitions to l″=1 e parity levels of the ground state. The band origins agree with predictions within the error of the anharmonic expansion; the rotational constants, when corrected for rotational-l doubling, agree within experimental error. Rotational-l resonance between l″=0 and l″=2 is found in highly excited bending levels, confirming the extrapolation of the rotational-l resonance and doubling constant q2 from microwave and infrared measurements to 17 000 cm−1. The rotational intensity of the l″=1 bands due to the axis-switching mechanism of Hougen and Watson [Can. J. Phys. 43, 298 (1965)] is shown to be greater than some of the observed allowed rotational transitions to l″=2 when laser polarization effects are taken into account. A qualitative Franck–Condon analysis of the SEP spectrum provides unusually strong evidence for the axis-switching mechanism. The eight remaining unassigned bands are evidently perturbed and are assigned based on agreement between sums of observed rotational constants and sums of zero-order (unperturbed) rotational constants predicted by the anharmonic expansion, the magnitude of the rotational-l resonance, and the expected Franck–Condon factors.

Polarization dependence in the laser-assisted ionizing collision He*(2 1,3S)+He(1 1S)+ħω→He +(1 2S)+He(1 1S)+e −

The effect of laser polarization on the laser-assisted He + ion signal is investigated experimentally in order to check existing theoretical calculations. Two important features are deduced from the data: First, the laser-assisted cross section is essentially the same for laser polarization parallel or perpendicular to the relative velocity of the collision system. Secondly, the laser-assisted ion signal exhibits, for both polarizations, the expected shift with respect to the initial kinetic energy of the reactants, which is a characteristic effect of the laser-assisted process under study.

The 2 + 1 REMPI spectra of cyclic ketones in a cold molecular beam. 2. The n .fwdarw. 3s Rydberg transition of methyl-substituted cyclohexanones and cyclopentanones

The two-photon excitation of the n ..-->.. 3s Rydberg transition in monomethyl and dimethyl isomers of cyclohexanone and cyclopentanone has been studied by resonance enhanced multiphoton ionization (2 + 1 REMPI). This transition has been found to be highly sensitive to both the orientation and position of methyl substituents on the cyclic ketone ring. Cis and trans configurations of dimethyl isomers show characteristic 3s transition energy shifts which are additive in nature and can be used to predict the transition energy of other structures. The spectroscopic energies of configurational isomers appear to reflect relative ground-state stabilities. This correlation has been supported by thermodynamic data and molecular mechanics calculations of ground-state energies. Laser polarization effects are found to be useful in determining the degree of chromophore asymmetry in chiral molecules.

Forbidden Transitions of LiI in Laser-Induced Fluorescence Spectroscopy for the Measurement of Low-Frequency Electric Fields in Plasmas

Three forbidden transition (42P-22P, 42D-32D and 22P-42F) due to the Stark effect in the LiI energy system were theoretically investigated for the measurement of low-frequency electric fields in plasmas. Numerical results concerning the intensities of the forbidden transitions and the polarization characteristics are presented in which the effect of the electron spin is taken into account. The excitation of the levels of n=4 is supposed to be possible using tunable lasers and thus, the effect of laser polarization is also considered. The first two transitions (42P-22P and 42D-32D) are suitable for measuring a rather strong electric field (1 kV/cm) and can also be used to give the direction of the electric field in plasmas. The third transition is applicable to a weak-field measurement down to about 0.1 kV/cm.

Formation and dissociation of , , and ions by ruby laser radiation

Multiphoton ionization of K2, Rb2, and Cs2 in beam conditions by pulsed ruby laser radiation (λ = 6946.0 Å, pulse duration ~10 ns) and subsequent dissociation of the dimer ions by one or more additional photons have been observed. Ground-state dissociation energies of these ionic species have been determined directly from the time of flight of the dissociation fragment pairs, and from the use of retarding potentials, to be [Formula: see text], [Formula: see text], and [Formula: see text]. These observed values have been compared with the theoretical and experimental work of other authors. Our results for the [Formula: see text] and [Formula: see text] ions are the first direct measurements of their ground-state dissociation energies. The effect of laser polarization on the dissociation mechanism has also been experimentally investigated.

Formation and dissociation of by ruby laser radiation

The formation and dissociation of [Formula: see text] in an atomic beam by ruby laser radiation have been observed. Values of the dissociation energy of [Formula: see text] have been determined by the time of flight of the resulting Na+ ions and the potential needed to stop them. These results, with a mean of 1.02 ± 0.09 eV, have been compared with the calculated and observed values of others. The effects of laser polarization vs. dimer axis orientation have been clearly demonstrated.

The effect of laser polarization on the two-laser excitation of a diatomic molecule

A theoretical calculation demonstrates that a larger fraction of an ensemble of diatomic molecules (hydrogen fluoride) can absorb energy from two lasers of different frequencies when the electric field vectors are parallel than when they are perpendicular to one another.

Directional effects in double-beam photoemission of (10 [formula omitted]0) and (0001) Te

Strong laser beam direction vs crystal orientation dependence of double-beam photoemission spectra is reported in trigonal tellurium. This is demonstrated to be due to the large anisotropy of the electron escape probability function in such low symmetry materials, rather than specific laser polarization effects which were absent in the present experimental data.