Stress measurements in glass by use of double thermal gratings.

We developed a nondestructive and noncontact method for measuring stress at the midplane of tempered glass plates that uses Bragg scattering from a pair of thermal gratings. These gratings are formed by 1064-nm beams from a seeded Nd:YAG laser, and we measure the polarization state of light from a 532-nm beam that scatters from both thermal gratings. The change in polarization of the doubly scattered light with separation between the two gratings allows measurement of the in-plane stress. A model of the Bragg scattering efficiency, experimental investigations of the scattered beams, and stress measurements are reported.

Trace detection of krypton using laser-induced fluorescence.

Highly sensitive detection of neutral Kr atoms was accomplished by the use of laser-induced fluorescence. In one experiment, Kr at 40 parts per 10(12) in He was detected at a signal-to-noise ratio of 500 by time-resolved fluorescence measurements. The Kr metastable 1s(5) level was populated by cascade after two-photon excitation to the 2p(6) level by the frequency-tripled output of a pulsed single-longitudinalmode dye laser. After a delay, when scattered laser light and cascade resonance fluorescence became negligible, trace quantities of Kr were detected by the use of a pulsed-laser pumping scheme. In a related experiment, (78)Kr/(86)Kr isotope ratios ranging from 1 to 0.1 were measured with a resonant isotopic depletion technique first proposed by Makarov [Sov. J. Quantum Electron. 13, 722 (1983)]. The (86)Kr metastable population was selectively depleted by optical pumping to a higher-lying state that relaxed to the ground state by means of radiative cascade. After the (78)Kr/(86)Kr ratio of metastables had been enriched by a factor of 10, the (78)Kr population was probed by pulsed excitation. Premixed (78)Kr/(86)Kr ratios were measured to within an accuracy of 10%, even for unresolved, Doppler-broadened transitions.

Resonant isotopic depletion spectroscopy.

We have devised a simple new scheme to increase the isotopic selectivity in optical rare-isotope detection experiments. We can effectively remove interfering isotopes from an atomic beam by optically pumping them into a state that is invisible to the optical detection system. The selectivity of this resonant depletion scales exponentially with the isotope shift and yields almost unlimited selectivity in principle. We have demonstrated a selectivity of 2.3 x 10(5) with a single laser excitation in a beam of metastable krypton atoms. With better laser stability we may be able to improve the selectivity much further.

Laser-enhanced electron-impact ionization spectroscopy.

Sequential photon-excitation, electron-impact ionization with subsequent mass analysis has been applied to a barium atomic beam. High-resolution, Doppler-free laser excitation produces the 6s6p(1)P(1) excited state, which is then ionized by electron bombardment. The excited state is selectively ionized when bombardment energies are between the excited- and ground-state ionization thresholds. Mass discrimination has permitted the recording of individual optical spectra for all the stable isotopes, including the 0.1% abundant (130)Ba and (132)Ba, in a sample with natural isotopic abundances.