D.M. Warrington

Optical bistability in a gaussian cavity mode

Abstract The mean field treatment of dispersive and absorptive bistability for two-level atoms in an optical cavity is extended to account for the gaussian envelope of the cavity mode. The principal modification to the plane wave cavity case is the raising of the critical threshold for absorptive bistability as compared to thresholds for dispersive bistability.

Narrow-linewidth master-oscillator power amplifier based on a semiconductor tapered amplifier

The output of a grating-stabilized external-cavity diode laser was injected into a semiconductor tapered amplifier in a master-oscillator power amplifier configuration, producing as much as 500 mW of power with narrow linewidth. The additional linewidth that is due to the tapered amplifier is much smaller than the typical linewidth of grating-stabilized laser diodes. To demonstrate the usefulness of the narrow linewidth and high output power, we used the system to perform Doppler-free two-photon spectroscopy with rubidium.

Efficient, low-threshold collinear and noncollinear beta-barium borate optical parametric oscillators.

The performance of collinear and noncollinear pulsed barium borate optical parametric oscillators with third-harmonic Nd:YAG pumping is analyzed. The effects of tangential phase matching and pump Poynting vector walk-off compensation are shown to enhance noncollinear operation. However, we show that these effects are mutually exclusive for a typeI beta-barium borate optical parametric oscillator and furthermore that tangential phase matching is dominant. The selection of a collinear or a noncollinear configuration is determined by pump divergence and spot size as well as by crystal aperture. With a pump divergence of 4mrad, noncollinear operation is optimal. The highest slope efficiency, 37%, and the lowest threshold, 5mJ, are obtained with nearly perfect tangential phase matching. For a pump divergence of less than 2mrad and a similar spot size, collinear operation gives the lowest threshold, 3.2mJ, and the highest slope efficiency, 33%.

Observation of polarization switching: D1 line of sodium in a Fabry-Perot

Abstract We report observation of the complete polarization switching sequence for a gas of atoms with a J = 1 2 to J = 1 2 transition, exposed to resonant or near resonant, linearly polarized laser excitation in an optical cavity. The sequence is from linearly polarized cavity output at low input power to predominantly circularly polarized output at intermediate power and back to linearly polarized output at high input power. The switching is abrupt, exhibits hysteresis and, when hyperfine optical pumping effects are minimized, is phenomenologically in accord with predictions from theory.

Observation of separated, polarised ring structures induced by nonlinear beam reshaping

Abstract A 400 mW elliptically polarised cw gaussian laser beam tightly focused in high density sodium vapour buffered by argon gas, and detuned by 10–30 GHz on the blue side of the sodium D 1 transition, is found to produce multiple rings of alternate circular polarisation at the cell exit window. A model which treats the coherent propagation of a polarised radiation field in a medium of homogeneously broadened J= 1 2 →J= 1 2 atoms is found to reproduce the essential features of the experiment, and suggests a simple physical explanation of the phenomenon.

Output coupling of a Bose-Einstein condensate formed in a TOP trap

Two distinct mechanisms are investigated for transferring a pure 87Rb Bose-Einstein condensate in the |F = 2, mF = 2 state into a mixture of condensates in all the mF states within the F = 2 manifold. Some of these condensates remain trapped whilst others are output coupled in the form of an elementary pulsed atom laser. Here we present details of the condensate preparation and results of the two condensate output coupling schemes. The first scheme is a radio-frequency technique which allows controllable transfer into available mF states, and the second makes use of Majorana spin-flips to populate all the manifold sub-states equally.

Tunable high-repetition-rate visible solid-state lasers based on intracavity frequency doubling of Cr:forsterite

High-repetition-rate solid-state lasers broadly tunable in the red-orange and infrared spectral regions are reported. Wavelengths between 590 and 670 nm and between 1170 and 1360 nm have been generated by gain-switched Cr:forsterite lasers incorporating intracavity frequency doubling in KTP. Broadband, tuned, and narrow-band systems operating at repetition rates between 1 and 20 kHz have been developed. Maximum visible output power of 40 mW was achieved by frequency doubling of a narrow-band infrared laser, corresponding to a fundamental to second-harmonic conversion efficiency of more than 30%.

LOW-THRESHOLD, SINGLE-FREQUENCY, COUPLED CAVITY TI:SAPPHIRE LASER

A novel coupled resonator was developed for narrow-bandwidth, tunable, solid-state lasers. Stable, single-longitudinal-mode, gain-switched titanium:sapphire pulses were obtained across a 130-nm operating range limited by the cavity optics. The low threshold fluence of 0.7 Jcm(-2) makes the cavity attractive for other tunable laser media, particularly when gain is low or parasitic loss is high. A model has been developed that can be used to predict the mode structure of the coupled cavity and for optimization at specific wavelength regions.

Observation of cw stimulated Raman emission in the neon 2p→1s manifold

Abstract We report previously unobserved cw laser emission from a commercial HeNe laser. This lasing is based on near-resonant stimulated electronic Raman scattering (SERS) involving NeI 1s5→2p→1s4, and 1s5→2p→1s2, electronic states when the laser cavity is pumped externally by cw dye laser radiation. Two of the emitted lines [2p2→1s4 (603.0 nm) and 2p2→1s2 (659.9 nm); both pumped at 588.2 nm (1s5→2p2)] are explored in some detail. Output power of the Raman laser has been measured as a function of the laser-atom detuning, the Ne discharge current and the pumping laser power. These Raman lines can be several times stronger than the 633 nm HeNe laser output itself. The observations are qualitatively consistent with calculations of Raman gain showing the possibility of all 14 dipole-allowed 2p→1s Stokes-Raman laser lines being observable with commercial HeNe lasers, given mirror coatings of sufficient spectral width.

Laser and absorption saturation measurements of Cr4+ crystals, pumped by broadband pulsed 940 nm radiation

Abstract The characteristics of a 940 nm pumped Cr 4+ :forsterite laser have been investigated using a pulsed colour centre laser as the excitation source. Laser threshold, slope efficiency and temporal behaviour have been determined for high and low Cr 4+ doped material. 940 nm pumping is found to be more efficient than 532 and 730–770 nm excitation. Discrepancies with 1064 nm pumping are attributed to excited state absorption. Absorption saturation measurements have been used to assess the potential applications of Cr 4+ :forsterite, Cr 4+ :YAG and Cr 4+ : Lu 3 A1 5 O 12 (LuAG) as passive Q-switches for Nd lasers in the 940 nm region.