Harold Metcalf

Spectrally narrow pulsed dye laser without beam expander

We have developed a simplified version of the side-pumped pulsed dye laser which has a spectral halfwidth of 1.25 GHz and a peak power of 10 kW at 600 nm. The basic laser consists of only four components (output mirror, dye cell, diffraction grating, and tuning mirror) and is exceptionally easy to align. Since the beam expander has been eliminated, the laser cavity can be made quite compact. Under the condition of reduced gain, the laser has been operated in a single mode.

Synchronous cavity mode and feedback wavelength scanning in dye laser oscillators with gratings

A simple result of scalar diffraction theory is used to derive the round trip phase accrual of a plane wave in dye laser oscillators containing gratings. This is used to determine configurations where the standing wave condition is satisfied at the feedback wavelength throughout an angle scan. We find that at least one such exactly synchronous configuration always exists regardless of oscillator type.

Cooling and trapping of neutral atoms

Abstract As early as 1917, Einstein had predicted that momentum is transferred in the absorption and emission of light, but it was not until the 1980s that such optical momentum transfer was used to cool and trap neutral atoms. By properly tuning laser light close to atomic transitions, atomic samples can be cooled to extremely low temperatures, the brightness of atomic beams can be enhanced to unprecedented values, and atoms can be manipulated with extraordinary precision. In this review several of the techniques for laser cooling and trapping of neutral atoms are described.

Laser cooling and electromagnetic trapping of neutral atoms

Atoms in a thermal beam can be cooled, decelerated, and stopped using the radiation pressure from a nearly resonant laser beam. Several groups have already used this laser-cooling process on an atomic sodium beam. The techniques and results of the various experimental groups are reviewed, and applications of laser-cooled atoms, in particular the possibility of confining them in electromagnetic traps, are discussed.

Atomic nanofabrication: atomic deposition and lithography by laser and magnetic forces

Atomic deposition on a surface can be controlled at the nanometre scale by means of optical and magnetic forces. Impingement of atoms on the surface can lead to growth of a structured array (direct deposition) or to chemical modifications of the surface (neutral atom lithography). In this report we survey requirements, present the current results, and explore the potential applications of this method of nanofabrication.

Low Cost Nitrogen Laser Design for Dye Laser Pumping

A pulsed cross-field molecular nitrogen laser (3371 A) has been simply constructed from two plate glass strips 5 cm by 1.2 m. During operation twenty 500-pF capacitors evenly spaced along the channel arecharged from a 0.012-microF storage capacitor by a thyratron at up to 30 Hz. This distributed charge is available for discharge when the gas breakdown starts. The flowing gas laser produces a 160-kW, 10-nsec (full-width half-maximum) light pulse when operated at 15 kV and at a pressure of 20 Torr. The laser has successfully pumped a tunable dye laser.

Quantized motion of atoms in a quadrupole magnetostatic trap

We consider quantized motion of neutral atoms cooled below the recoil limit in a quadrupole magnetostatic trap. Because of Majorana transitions to untrapped levels near the point of zero field at the trap center, all quantum levels have a nonzero decay rate. The Schrodinger equation associated with the potential gμB · S (S is the total atomic spin) takes the form of coupled equations in r when the spinor components are expanded in spherical harmonics. We integrate the multichannel problem numerically to obtain asymptotic phase shifts, resonance energies, and widths. For S = 1/2, the lowest levels have widths somewhat less than their spacing. Thus the trap quantum-level structure might possibly be observable if the atoms are sufficiently cold, namely, in the 0.1-μK regime for most atoms and attainable trap field gradients. The width decreases rapidly with increasing MJ, the angular momentum about the symmetry axis. Spectroscopic linewidths of a few hertz are possible if there is enough population in the lowest levels with a few MJ quanta. The decay rate of the lowest levels, however, is probably too rapid for studying Bose–Einstein condensation in such a trap.

Diode-laser deceleration and collimation of a rubidium beam

We report the use of frequency-chirped diode lasers to decelerate a thermal atomic beam of Rb and, in a separate experiment, the use of frequency-stabilized diode lasers to collimate the beam with optical molasses. For this we used a 100-mW cw laser-diode array injection locked to light from a low-power, frequency-narrowed, single-stripe diode laser. Also, a novel scheme for imaging the neutral-atom beam profile has been developed for monitoring the collimation experiments in two dimensions. We have increased both beam brightness and intensity by a factor of more than 20.

Magneto-optical trapping and its application to helium metastables

A quantitative discussion of several interesting and attractive properties of magneto-optical traps is presented. Calculations are given for the trap depth, sample size, and intrinsic cooling capability of this especially simple example of a radiative force trap. The discussion is directed toward the cooling and confinement of metastable 23S neutral helium, and a new loading procedure suitable for this atom is proposed. It is planned to operate the trap and to cool atoms in it with 1.08-μm light from solid-state, single-mode lasers pumped by efficient diode lasers. Because of the dissipative nature of the radiative force, a trapped sample of atoms may be magnetically compressed without increasing its millikelvin optical temperature, so that a subsequent adiabatic expansion can cool it to the nanokelvin temperature range.

Narrowband, high power light from diode lasers.

We have used a 100-mW cw laser diode array to amplify the light from a low power, single stripe diode laser (both lasers commercially available). The input light was spectrally narrowed and frequency stabilized to <300 kHz using optical feedback from a Fabry-Perot cavity, and the amplified beam had the same spectral characteristics. Also, the ~90-mW amplified beam had a single diffraction-limited spatial mode corresponding to the full 100-microm width of the array, indicating that all its stripes were coherent. When viewing the output of the free-running laser array, we observe that the input light causes its output spectrum and spatial distribution to be dramatically narrowed. We have tested a simple quantitative model of this process.