David H. McIntyre

Laser Cooling

 

My research interests are based upon high resolution laser spectroscopy and precision atomic physics. The techniques of laser cooling and trapping, diode laser frequency stabilization, and nanostructure fabrication are currently being used to perform experiments in atom optics and atom interferometry. Our research laboratory contains nine optically stabilized diode lasers, a Michelson wavemeter, optical spectrum analyzers, a radio frequency spectrum analyzer, a rubidium atomic beam in a differentially pumped vacuum chamber, and several vibration isolated optical tables.

A three-grating atom interferometer is under construction. The matter-wave source is a laser cooled atomic rubidium beam and the amplitude transmission gratings are fabricated in thin, free-standing silicon nitride films. Atoms in a thermal beam are slowed using Zeeman-tuned laser cooling and are loaded into a two-dimensional magneto-optic trap or funnel which compresses the atoms and directs them into an intense, slow beam [1]. Atoms are ejected from the funnel with controllable velocities in the range of 3-10 m/s, with temperatures of order 0.5 mK. CCD images show atoms in the trap and downstream in a probe region. Picture One (24 Kb jpeg file) shows atoms expanding as they travel due to the finite temperature. Picture Two (46 Kb jpeg file) shows an orthogonal view of atoms seemingly at zero temperature, but the downstream probe acts also as a trap in one dimension to again compress the atoms. In this experiment, the rubidium cooling transition at 780 nm is excited with commercial diode lasers which are frequency stabilized using optical feedback from diffraction gratings [2]. We fabricated the 250-nm spacing gratings using high-resolution electron-beam lithography at the National Nanofabrication Facility.

The atom interferometer will be used to perform precision physical measurements and to test basic ideas in quantum measurement theory. The long interaction times of the slow atoms give the interferometer high sensitivity. Applications will be pursued in inertial sensing, in gravitational measurements, and in measurements of radiative level shifts of atomic ground states. The interferometer will also be used to perform "which-path" type experiments that illustrate the principle of complementarity.

In collaboration with C. E. Fairchild (OSU) and J. Cooper (JILA), I have studied diode laser noise and its effects on spectroscopic measurements. An atomic resonance converts laser frequency noise into intensity noise. We have carefully measured this resultant intensity noise and have compared it to a theoretical model of the laser as a phase- diffusing field. We find good agreement between theory and experiment [3].

We continue to develop new techniques for laser diode frequency control. We have developed a simple, digital frequency-offset locking system and are now pursuing phase locking of diode lasers. We have implemented and studied a novel means of optical feedback stabilization of a diode laser using saturated absorption in an optically thick atomic vapor [4]. 

References:

  1. Rubidium Atomic Funnel (T. B. Swanson, N. J. Silva, S. K. Mayer, J. J. Maki, and D. H. McIntyre), J. Opt. Soc. Am. B 13, 1833 (1996).
  2. Stabilized Diode-Laser System with Grating Feedback and Frequency-Offset Locking (J. J. Maki, N. S. Campbell, C. M. Grande, R. P. Knorpp, and D. H. McIntyre), Opt. Commun. 102, 251 (1993).
  3. Diode Laser Noise Spectroscopy of Rubidium (D. H. McIntyre, C. E. Fairchild, J. Cooper, and R. Walser), Opt. Lett. 18, 1816 (1993).
  4. Optically Stabilized Diode Laser using High-Contrast Saturated Absorption (C. J. Cuneo, J. J. Maki, and D. H. McIntyre), Appl. Phys. Lett. 64, 2625 (1994).