The angular distribution of spin-oriented Rb photofragments produced by photodissociation of RbI molecules using circularly polarized UV light at 266 nm has been investigated for the first time applying the method of Doppler-resolved paramagnetic Faraday rotation. The observed signals could successfully be explained as the sum of two contributions being due to incoherent and coherent excitation of the RbI molecules. For the ratio of the two corresponding anisotropy parameters we obtain a value of −0.33 as a preliminary result.
A study has been made on the oriented ground state 5 2 S 1/2 Rb atoms produced in molecular photodissociation. Low-pressure RbI vapours have been photolysed by a beam of circularly polarized impulse laser radiation at 266 nm. The resulting Rb atoms were probed by a resonance atomic line at 794.8 nm from a discharge Rb lamp in two different experimental geometries. A free precession of the oriented atomic spins in an external magnetic field was detected by a dichroism of the atomic vapours. The initial degree of spin orientation was found to be P c = (20 +or- 2)%.
The optical magnetic birefringence (Faraday) technique that can be used to study the anisotropy distributions of the angular momenta of photofragments produced in molecular photodissociation is compared theoretically and experimentally with the magnetic dichroism technique. The frame independent tensor form of the general expression describing the difference between an initial and a final polarization matrix of a probe light beam passing through the photofragment vapor is presented and analyzed. The procedure of detection of the photofragment electron orientation and alignment angular distributions by Doppler spectroscopy using each of the techniques is studied theoretically. The angular independent anisotropy orientation and alignment parameters describing photodissociation dynamics that can be determined from these studies are presented. It is shown that in principle each of the techniques can give the same information about the photodissociation dynamics; however, the birefringence technique has an undeniable advantage since it leads to an increase in accuracy of the experimental data. Both magnetic birefringence and magnetic dichroism techniques were used experimentally to study the spin orientation of ground state Rb atoms produced in photodissociation of RbI at 266 nm by circularly polarized laser light. The experiment was not of the Doppler spectroscopy type, but use of different 85 Rb and 87 Rb isotopes in the dissociation cell and in the probe light source allows detection of the oriented atomic photofragments separately by each of the techniques. Obtained experimental results are in agreement with the theoretical predictions. Contribution of the orientation of the Rb hyperfine structure energy states to the observed signals were also studied and treated theoretically. The initial degree of the electron spin orientation of the Rb atoms produced in the reaction was found to be P e = 0.11 ± 0.02.
We report the selective population of Rb or Cs
np 2P23 (
n=5, 6;
F=4, 5) hyperfine states by the photodissociation of a transient, alkali-rare gas diatomic molecule. Circularly polarized (${\ensuremath{\sigma}}^{\ensuremath{-}}$), amplified spontaneous emission (ASE) on the
D2 line of Rb or Cs (780.0 and 852.1 nm, respectively) is generated when Rb-Xe or Cs-Xe ground state collision pairs are photoexcited by a ${\ensuremath{\sigma}}^{+}$-polarized optical field having a wavelength within the
D2 blue satellite continuum, associated with the $B{^{2}\mathrm{\ensuremath{\Sigma}}}_{\frac{1}{2}}^{+}\ensuremath{\leftarrow}X{^{2}\mathrm{\ensuremath{\Sigma}}}_{\frac{1}{2}}^{+}$ ($\text{free}\ensuremath{\leftarrow}\text{free}$) transition of the diatomic molecule. The degree of spin polarization of Cs (
6p 2P23), specifically, is found to be dependent on the interatomic distance (
R) at which the excited complex is born, a result attributed to the structure of the $B{^{2}\mathrm{\ensuremath{\Sigma}}}_{\frac{1}{2}}^{+}$ state. For Cs-Xe atomic pairs, tuning the wavelength of the optical field from 843 to 848 nm varies the degree of circular polarization of the ASE from 63% to almost unity because of the perturbation, in the $5\ensuremath{\le}R\ensuremath{\le}6\text{ }\text{ }\AA{}$ interval, of the ${^{2}\mathrm{\ensuremath{\Sigma}}}_{\frac{1}{2}}^{+}$ potential by a $d\ensuremath{\sigma}$ molecular orbital associated with a higher $^{2}\mathrm{\ensuremath{\Lambda}}$ electronic state. Monitoring only the Cs
6p 2P23 spin polarization reveals a previously unobserved interaction of CsXe ($B{^{2}\mathrm{\ensuremath{\Sigma}}}_{\frac{1}{2}}^{+}$) with the lowest vibrational levels of a $^{2}\mathrm{\ensuremath{\Lambda}}$ state derived from Cs
(5d)+Xe. By inserting a molecular intermediate into the alkali atom excitation mechanism, these experiments realize electronic spin polarization through populating no more than two
np 2P23 hyperfine states, and demonstrate a sensitive spectroscopic probe of
R-dependent state-state interactions and their impact on interatomic potentials.
In photodissociation of a homonuclear diatomic molecule, conservation of linear and angular momenta requires that each atomic fragment follow identical but oppositely directed trajectories with respect to the molecular center of mass. For certain values of the incident photon energy, one of the atoms will be electronically excited while the other will be in its ground state. When a detector records the undispersed fluorescence from the decay of the excited atom it cannot distinguish which trajectory the excited atom followed and hence whether the photon possesses a blue or red Doppler shift corresponding to recoil towards or away from the detector. According to the principle of superposition in quantum mechanics, the wave function of the photon must be a sum over two paths corresponding to emission from an excited atom in either of the two recoil directions. Detection of such photons gives rise to an interference between the probability amplitudes for the two paths that is manifested in the output from the photodetector as a beat frequency. Since photodissociation of an ensemble of molecules gives rise to a distribution of recoil directions relative to the electric vector of the incident radiation, a range of beat frequencies must be present in the detected signal. This paper gives a calculation of expected output voltage waveforms from a photodetector viewing atomic fluorescence excited by molecular photodissociation. Expressions are given for partial Fourier transforms of the photodetector signals. The results show that the shape of the voltage waveforms depends strongly on the asymmetry parameter for recoil of the photofragments and on whether or not the magnetic sublevels of the excited atomic state are created in a coherent superposition.