Using frequency-narrowed, tunable laser diode arrays with integrated volume holographic gratings for spin-exchange optical pumping at high resonant fluxes and xenon densities

Next-generation laser diode arrays with integrated ‘on-chip’ volume holographic gratings can provide high power with spectrally narrowed output that can be tuned about the rubidium D1 line—without causing significant changes to the laser’s flux or spectral profile. These properties were exploited to independently evaluate the effects of varying the laser centroid wavelength and power on batch-mode Rb/129Xe spin-exchange optical pumping (SEOP) as functions of xenon partial pressure and cell temperature. Locally optimized SEOP was often achieved with the laser tuned to either the red or blue side of the Rb D1 line; global optimization of SEOP was observed at lower cell temperatures and followed the D1 absorption profile, which was asymmetrically broadened and red-shifted from the nominal wavelength. The complex dependence of the optimal wavelength for laser excitation on the cell temperature and Xe density appears to result from an interplay between cell illumination and the Rb/129Xe spin-exchange rate, as well as [Xe]cell-dependent changes to the Rb absorption lineshape that are in qualitative agreement with expectations based on previous work [Romalis et al., Phys. Rev. A, 56:4569–4578, (1997)], but significantly greater in magnitude. These next-generation lasers provide a ∼2–3-fold improvement in 129Xe polarization compared to conventional broadband lasers.