E. C. Benck

A linear combined trap for on-line spectroscopy

The linear combined trap is a superposition of the conventional Paul and Penning traps in one device. Using a four-rod structure, a linear configuration can be constructed. Such a linear combined trap is particularly well suited for catching ions produced externally, since both the effective potential due to the driving RF-field and the DC-magnetic field contribute to the ion confinement. The use of this novel trap for on-line laser and mass-spectroscopy of rare short-lived isotopes is proposed.

Cavity-enhanced photothermal spectroscopy : dynamics, sensitivity, and spatial resolution

The spectrally resolved low-level absorption of thin films and of solid and liquid surfaces was measured by cavity-enhanced photothermal spectroscopy. The technique is ultrasensitive and can determine surfacespecific absorbances alpha(omega) ~ 10(-6) at a power density of 10(4)W/cm(2). Both cases of continuous wave and modulated laser light absorption were studied experimentally and are interpreted theoretically. It is shown that it is possible to achieve a spatial resolution of absorbance variations in the few-micrometer range. The thermal diffusivity can also be simultaneously measured by observing the time evolution of the surface temperature during laser irradiation.

Nuclear moments of the neutron-deficient thallium isotopes

The nuclear moments of the neutron-deficient187,188Tl isotopes were determined by measuring the hyperfine structure splittings of the λ=535 nm line in neutral thallium. An optical efficiency of 2×10−4 photons per radioactive ion was achieved using collinear fast beam laser spectroscopy with a large solid angle fiber optical array detector. Most of the moments can be interpreted fairly well in the single particle model.

Nuclear spectroscopy using lasers at Oak Ridge National Laboratory: experiments with stable (past) and radioactive (future) tandem beams

Abstract Fast beam collinear laser spectroscopy has yielded information on nuclear structure on the long chain of neutron deficient Tl isotopes (186 ≤ A ≤ 205) using heavy ion fusion evaporation reactions to produce Tl-ion beams which for the most neutron deficient isotope were only about 104/s. The new radioactive heavy ion beam facility projected to be completed in 1995 requires even higher sensitivities at the few 10 nuclei/s level. Two examples to realize such ultra-sensitive measurements employing laser techniques are described. They are: field-ionization spectroscopy in a fast beam and stored ion spectroscopy in a novel linear combined trap.

Isotope shift measurements on the neutron-deficient thallium isotopes

Isotope shifts of the neutron-deficient thallium isotopes were measured on-line at the UNISOR mass separator. Spectroscopy was carried out using collinear fast beam laser spectroscopy in neutral thallium. The changes of the mean square charge radii were derived from the measurements. The changes in charge radii of the I=7 isotopes, including the newly measured188Tl, are compared to the results in mercury and lead.

Ultra‐sensitive detection of krypton atoms utilizing stepwise‐laser excitation and field ionization

Two photon stepwise‐laser excitation followed by field ionization is being applied to the ultra‐sensitive detection of krypton atoms. Using a collinear laser‐fast beam geometry with laser‐induced fluorescence detection, we have previously made measurements with krypton beam intensities on the order of 104 atoms/sec. By utilizing the higher collection and detection efficiencies inherent with charged particle detection, we hope to be able to make measurements with beam intensities on the order of 10 atoms/sec.

Cavity‐enhanced detection of surface photovaporization

Cavity‐enhanced detection is used to monitor minute vapor plumes produced by focusing a pulsed laser beam onto a surface placed inside a resonant optical cavity. The photovaporization signals from a variety of different materials are examined, with emphasis being placed on their amplitude and temporal structure.

Line shapes in cavity enhanced spectroscopy

The radiative absorption and emission of atoms inside an optical cavity are being studied using a Na atomic beam and a resonant confocal cavity driven by a single‐mode dye laser. As the sodium density is increased, the line shape and intensity of the transmitted and emitted light changes due to the coupling between the Na atoms and the intense cavity fields.

On-line hyperfine structure and isotope shift measurements with diffuse light collection and photon burst detection

An experiment is presently being set up which combines collinear-fast-beam laser spectroscopy with photon burst spectroscopy. Selectivity is provided by the large kinetic isotope shifts together with the practically Doppler free linewidth of the fluorescence from the fast atom beam. The photon burst detection, based on photon correlations in the resonance fluorescence, increases the sensitivity, so that on-line optical isotope shift and hyperfine structure measurements on low intensity radioactive beams become feasible. In order to improve photon burst detection the solid angle of detection and the observation time have to be optimized. To this end a diffuse reflecting cavity has been designed and built, which collects fluorescence over a 45 cm length of the beam and covers the full solid angle. The light collection efficiency of the cavity is calculated to be about 45%. The cavity is being tested with a 11 keV beam of krypton atoms, probing the near infrared transitions in our apparatus at Texas A&M Univ...

Measurement of glitter-point velocities on the sea surface using circular scanning with a collimated narrow laser beam

Alaser device (lidar) for remotely measuring the parameters of the glitter-point motion on the sea surface has been developed. The system employs a He-Ne laser to provide the probe beam. Circular scanning was performed by means of a piezoelectrically controlled mirror that had a frequency of rotation of 2 kHz. The positions of glitter-point echo pulses were compared with the reference signal of the mirror controller to trace the time evolution of the glitter-point coordinates on the circumference of the circular laser beam track. The measurements yielded the velocity distribution of the glitter points. The results were obtained under natural conditions and indicate an anisotropy of the glitter-point motion that is related to the sea conditions and the wind direction.