We describe CW atomic Rb vapor lasers, operating at 795 nm pumped by line-narrowed laser diode arrays using volume transmission gratings. Various laser architectures have been explored with output power up to 800 mW.
The use of high-power ${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$AlxAs diode laser arrays for optical pumping of Rb vapor has been examined both theoretically and experimentally. Our studies show that large atomic polarizations can be obtained using the broad spectral output of a diode laser array if the Rb resonance line is collisionally broadened by several atmospheres of a buffer gas. The objective was to study the effectiveness of diode laser arrays as light sources for optically pumped spin-exchange polarized 3He targets. The average Rb polarization was deduced at three different Rb vapor pressures using the polarization induced in the 3He buffer gas. The largest 3He polarization observed was 53% using a 20-W diode array with 1.9-nm full width at half maximum spectral width in 10.5 amagat of 3He. This result compares favorably with other light sources for this target. The measured average Rb polarizations are compared to theoretical calculations.
We report a quasicontinuous wave (CW) linearly polarized rubidium vapor laser. The pumping source consists of five laser diode bars and its linewidth is reduced from the raw 1.8 to 0.2 nm by a bulk volume Bragg grating. Instead of adopting the “quasi-waveguide structure” gain cell, the pumping light of the rubidium vapor laser propagates freely in the vapor cell. The pumping light with polarization perpendicular to one of the rubidium laser is coupled into the resonator cavity by the polarized beam splitter. This laser configuration is suitable for a convection-cooling diode-pumped alkali vapor laser.
We demonstrate direct microwave modulation of diode lasers operated with optical feedback from a diffraction grating. We obtain substantial fractions of the laser power (2–30%) in a single sideband at frequencies as high 6.8 GHz with 20 mW of microwave power and simple inefficient microwave coupling. Using a single diode as modulated at 6.6 GHz, we trapped 87Rb atoms in a vapor cell. With only 10 mW of microwave power we laser trapped 85% as many atoms as were obtained by using two lasers in the conventional manner.
We have studied laser optical pumping of Rb at densities up to 4\ifmmode\times\else\texttimes\fi{}1014 atoms/cm3 and produced polarized 3He by spin exchange with Rb. Numerical calculations show that for a high-density Rb vapor GaAlAs diode laser arrays can provide results similar to those obtained with a broadband Kr+-ion--dye-laser system. We have confirmed these calculations with measurements using a 40-GHz full width at half maximum bandwidth dye laser and 100- and 500-mW GaAlAs diode laser arrays (Spectra Diode Labs Array Nos. SDL-2410C and SDL-2450C). We have optically pumped Rb of density [Rb]=4\ifmmode\times\else\texttimes\fi{}1014 atoms/cm3, and we have measured up to 70% 3He polarization in a 4-cm3 volume with 600 mW from the dye laser. With the diode laser arrays, we have pumped with 30 and 300 mW with results comparable to those obtained with the dye laser. With a 1-W diode laser array, we anticipate 70--80 % 3He polarization in a 4-cm3 volume.
We have demonstrated microwave modulation of a diode laser which is operated with optical feedback from a diffraction grating. By directly modulating the diode laser current at frequencies up to 6.8 GHz, we observed 2-30% of the laser power in a single sideband for 20mW of microwave power. Using such a diode laser modulated at 6.6GHz, we have trapped {sup 87}Rb in a vapor cell. With 10mW of microwave power, the number of trapped atoms was only 15% smaller than the number obtained using two lasers in the conventional manner. A microwave modulated diode laser should also be useful for driving stimulated Raman transitions between the hyperfine levels of Rb or Cs.