M.V. Suryanarayana

Isotope shift and hyperfine structure measurements of 4s 2S1/2 → 6s 2S1/2 two-photon transition of potassium isotopes

Hyperfine splittings for the 39K and 41K isotopes and the isotope shift for the 4s 2S1/2 → 6s 2S1/2 two-photon transition have been measured using sub-Doppler fluorescence spectroscopy. We have accurately measured the transition isotope shift, and a discrepancy has been found in the earlier reported transition isotope shift value, which has been corrected. The resulting hyperfine splitting values of 418.2 (5) and 230.4 (1.3) MHz for the 39K and 41K isotopes respectively are in agreement with previous measurements. The precision of the absolute frequency values for the two-photon transition has been improved by about two orders. Our measured magnetic dipole constants for the upper 6 2S1/2 state for the 39K and the 41K isotopes are consistent with the earlier measured values.

Investigations on the 1 S 0 λ 1 → 1 P 0 1 λ 2 → 1 S 0 nonresonant——→ M+ photoionization pathway for selective ionization of rare calcium and strontium isotopes

Optical selectivities have been calculated by use of the density matrix approach for ns2 1S0−nsnp 1P10− nsms (or np2) 1S0 double-resonance photoionization pathways to establish the possibility of selective ionization of rare calcium and strontium isotopes for continuous-wave laser excitation. Numerical integration of the density matrix equations for double-resonance ionization has been carried out by incorporation of the effects of Doppler broadening, velocity-dependent interaction times, time-varying Rabi frequencies, and laser bandwidths. The conditions for obtaining optimum selectivities have been evaluated. This study results in five new photoionization pathways (two for calcium and three for strontium) whose optical selectivities were found to be a few orders higher than the previously studied photoionization schemes. The effect of laser linewidth of the excitation lasers and Doppler width have also been investigated.

Absolute frequency determination of the 5P3/2-->7S1/2 transition in 87Rb.

We report the absolute frequency of the important 5S(1/2)-->7S(1/2) two-photon transition in (87)Rb. We access the upper state using two dipole-allowed transitions via the intermediate 5P(3/2) state. This allows us to use much lower laser intensities compared to directly driving the two-photon transition, thereby avoiding potential errors due to the AC Stark shift. Collisional shifts are also minimized because the atomic density required is several orders of magnitude smaller. Our values are consistent with earlier frequency-comb measurements.

Calculation of 91 Zr optical selectivities in two-color resonant three-photon ionization schemes

Optical selectivity calculations have been carried out for the 91Zr isotope for two-color resonant three-photon photoionization schemes. The density-matrix equations of motion were solved numerically for collinear, counterpropagating, linearly polarized laser beams having Gaussian temporal profile. Calculations were carried out incorporating the effects of Doppler broadening, magnetic sublevel degeneracy, and laser bandwidths. The selectivities and ion yields were determined for various Rabi frequencies and ionization rates. Thereby, the optimal Rabi frequencies for the first and second excitation steps and ionizaton rate for the ionizaton step were determined. The ionization efficiency as a function of detuning of the excitation lasers was also investigated. Two of the photoionization schemes investigated yielded a selectivity of ∼10, with an ion yield of ∼23%.

Study of line shapes in the selective ionization of ^176Yb isotope in a two-step resonance, three-step ionization scheme

Ytterbium enriched in 176Yb is used for the production of the 177Lu radioisotope, which has applications in cancer treatment. We have theoretically studied the two-step resonant, three-step photoionization of the 176Yb isotope using the density-matrix approach. To simulate experimentally realistic conditions, the Doppler averaging, magnetic sublevel degeneracy, time-varying Rabi frequencies, ionization rate, angular divergence, and laser bandwidth have all been incorporated into the theoretical model. Calculations have been carried out to identify the optimized Rabi frequencies for evaluating the separation factor. The effect of the laser line shape on the excitation profile has also been thoroughly studied. We could obtain large separation factors of ~5000 for the 176Yb isotope, and the excitation conditions identified in this work may be utilized in the separation of the desired isotope.

Isotope selective near-resonant two-photon ionization of calcium isotopes

A near resonant two-photonionization scheme , has been investigated for the isotope selective excitation of 41Ca isotope for its applications as a tracer in bio-medical studies. The ionization efficiency and optical selectivity have been calculated for various powers of the excitation and ionization laser. Under the optimized excitation/ionization laser powers the ionization efficiency and the optical selectivity for the studied scheme are found to be 1.3 × 10−4 and ~1.0 × 104, respectively. The ionization efficiency is two orders of magnitude higher than the step-wise excitation process. In combination with a mass spectrometer, an overall selectivity of ~1010 can be obtained which is adequate for bio-medical applications.

Isotope-selective excitation of 41Ca isotope in Doppler-free two-photon continuous-wave excitation: a case study

Seven schemes are studied theoretically for Doppler-free two-photon excitation of rare (41)Ca isotope using single-mode continuous-wave lasers. The ionization efficiencies and optical selectivities for all the schemes are calculated for various powers of the excitation and ionization lasers and for various focusing conditions of the two lasers. To maximize the ionization efficiencies and the optical selectivities, wavelength-dependent Stark compensation is used. Certain laser wavelengths of the ionization step termed as magic wavelengths are identified for compensating the Stark shift induced by the excitation laser. The effects of the Stark-shift-induced asymmetry and its reversal by selecting the appropriate magic wavelength for the ionization step for various excitation and ionization laser intensities are investigated. The ionization efficiency and optical selectivity for the best scheme after Stark compensation are found to be 8.4 x 10(-4) and approximately 9 x 10(3), respectively.