Erling Riis

Optical molasses and multilevel atoms: experiment

The cooling mechanisms for laser cooling of atoms in optical molasses have been investigated experimentally. A significant simplification over the usual three-dimensional geometry has been obtained by studying the optical molasses in one or two dimensions only. By proper choice of polarizations the behavior of a pure two-level system as well as the more complicated effects of polarization gradients on laser cooling of a multilevel atom were observed.

Calibration of the electrical response of piezoelectric elements at low voltage using laser interferometry

A laser interferometric method is described by which the length‐to‐voltage sensitivity of piezoelectric elements, as used e.g., in scanning tunneling microscopes, can be calibrated. The method is based on measuring the optical frequency of a laser locked to a piezoelectrically tuned interferometer, relative to a stable reference. The high sensitivity of this technique allows the calibration to be carried out in the low‐voltage regime.

Laser cooling of a fast ion beam

A theoretical analysis of light-pressure cooling of a fast ion beam is given. The light-induced velocity changes are compensated by accelerating the ions by an external electric field. By analyzing the Fokker–Planck equation, cooling times and the ultimate temperature of the ions are given. It is argued that the transverse heating and the diffusion to velocities that are not cooled should pose no serious problems in realistic experimental cases. The particular physical conditions in a heavy-ion storage ring are finally discussed.

Applications of laser cooling and trapping

Recent work done at Stanford in the manipulation of atoms and particles is summarized. Techniques to further increase our control of neutral particles such as atomic fountains, funnels, and trampolines have been demonstrated. These techniques are now being combined with a new type of velocity selection in order to study atom/surface interactions and to improve the limit on the charge neutrality of atoms. Trapping techniques have also allowed us to manipulate single molecules of DNA in aqueous solution while observing the molecules in fluorescence.

Improving Laser Coherence

The convenient approximation of a real laser field by a Coherent State is again a relevant topic of interest, as laser spectroscopy scenarios are being developed in which remarkably long atomic lifetimes and extended interaction times (~100 s) can be enjoyed. Years ago, appropriate locking techniques were shown to allow precise locking of a laser field to a cavity, even in the milliHz domain, but lab vibrations modulated the cavity length and so the obtained optical frequency. Methods such as mechanical isolation (on a heroic scale) or active anti-vibration approaches are sufficiently productive such that, by now several groups have developed visible optical sources with ~Hz linewidths. Still, linewidths in the 100 milliHz domain have seemed very challenging — all the margins have been used up. We discuss mounting systems for an optical reference cavity, particularly an improved one based on implementing vertical symmetry, which provides dramatic reduction in the vibration sensitivity and can yield sub-Hz linewidths on an ordinary optical table in an ordinary lab. Interesting and commanding new issues — such as temporally-dependent spatial structure of the EO-modulated probe beam, and thermallygenerated mechanical position noise — are found to dominate the laser phase errors in the sub-Hz linewidth domain. The theoretical scaling — and the spectral character — of this thermal noise motion of the cavity mirror surfaces have been studied and confirmed experimentally, showing an ~1 x10 m/Sqrt(Hz) thermal noise amplitude at 1 Hz, with a 1/Sqrt(f) amplitude spectral density, with f being the Fourier frequency of this noise process. For effective temperature stabilization, multi-point thermal control and dual thermal shells provide stable operation near the ULE thermally-stationary point. Spectral filtering in the optical and vacuum paths is critically important to prevent ambient thermal radiation from entering the inner shell. The observed frequency drift-rate of ~0.05 Hz/s is not yet ideally stable, but it appears possible to compensate drift accurately enough to allow 1 radian coherence times to approach ~100 s ― if other problems such as the thermal noise can be adequately suppressed. Recent JILA spectra of lattice-trapped cold Sr atoms show an excellent prospect for ultrahigh resolution spectroscopy and highly stable optical atomic clocks and make us anxious to perfect improved phase-stable laser sources for the S0 – P0 doubly-forbidden transition at 698 nm. These laser developments are aided by optical comb techniques, allowing useful phase comparison of several prototype stable laser sources, despite their various different wavelengths.

Hyperfine structure in 167Er I+II+III: multiconfiguration Dirac-Fock interpretation of measurements

The authors report the first high-resolution measurement of hyperfine structure (HFS) in the 4f12 configuration of 167Er III. Together with recent measurements of HFS in the 4f126s2 configuration of 167Er I and in the 4f126s configuration of 167Er II, these data constitute the first detailed description of HFS along several ionisation stages in a rare-earth element. Based on ab initio, multiconfiguration Dirac-Fock calculations of the magnetic dipole and electric quadrupole coupling constants for experimentally observed levels, several conclusions are drawn in a discussion of the present status of understanding of HFS in typical rare-earth system.

Fundamental Tests of Special Relativity and the Isotropy of Space

When one considers tests of special relativity and the isotropy of space, the experiment of MICHELSON and MORLEY [1] immediately comes to mind. These scientists might not have anticipated that one hundred years after their landmark experiment, there is an ever increasing interest in the subject. The discovery of the anisotropy in the 3K cosmic blackbody radiation and its subsequent interpretation as due to the earth’s motion through the 3K radiation rest frame [2] makes it interesting to reconsider experiments that can test for the one way speed of light. Indeed, high resolution laser spectroscopy appears to have the most to offer in terms of improved techniques and increased precisian for these tests.

Precision measurements using laser cooled atoms

A number of experimental applications of laser cooling of neutral atoms are described. In an experiment on atomic fountains, laser-cooled atoms pushed up on a vertical trajectory by radiation pressure were observed to turn around due to gravity. A compact cesium fountain that would give three to four orders of magnitude increase in the counting rate over the first experiment can be designed, and the trapping and cooling can be done with diode lasers, suggesting a practical clock. In order to increase the time-averaged flux of such a fountain and also create a continuous fountain, an atomic funnel that can produce an atomic beam of very low velocity ( approximately 270 cm/s) at densities of 10/sup 8/ atoms/cm/sup 2/ has been devised.<<ETX>>

Optical Molasses with a New Twist

Publisher Summary This chapter outlines the essential features of optical molasses for multilevel atoms in the present scenario. When the three-dimensional cooling and confinement of atoms was first demonstrated, the so-called optical molasses was consistent with the predictions of a two-level theory. As more experiments were conducted, it became clear that many of the features of molasses worked better than predicted. The most startling discovery was that atoms could be cooled to temperatures well below the Doppler limit predicted for a two-level system and that the lowest temperatures were found at detunings larger than the optimum detuning for a two-level system. Recently, enhanced cooling of multilevel atoms has been observed, which provides a new insight into the behavior of optical molasses. The new cooling mechanism depends on the presence of Zeeman sublevels of an atom and the interaction of these levels in a light field with polarization gradients.

Towards laser cooling of fast beams: Acceleration by laser radiation pressure

Abstract We report on the acceleration of 100 keV Ne atoms by the light pressure force of a resonant laser beam. An acceleration of 0.12 V/μs or 6 × 10 5 ms −2 has been observed. This experiment verifies the potential application of laser cooling in heavy ion rings.