Dual-channel amplification in a single-mode diode laser for multi-isotope laser cooling
The output from two grating-stabilized external-cavity diode lasers were injected into a single-mode diode laser. Operating at a wavelength of 780 nm, this laser produced 50 mW of power with two main frequency components of the same spectral characteristics of the seed lasers. The power ratio of the amplified components was freely adjustable due to gain saturation, and amplification was observed for frequency differences of the two seed lasers in the range from 73 MHz to 6.6 GHz. This system was used to realize a dual isotope magneto-optic trap (MOT) for rubidium (85Rb and 87Rb). The resulting position and cloud size of the dual isotope MOT was the same as that of the single species MOTs to within "±10 and "±20 $μ$m, respectively. We also characterized the additional spectral components produced by four wave mixing (FWM) in the diode laser amplifier and utilized a particular FWM sideband to realize hyperfine pumping and subsequent laser trapping of 85Rb in the absence of a "repump" laser dedicated to hyperfine pumping.