Universal scheme for optically-detected T$_{1}$ measurements

A two laser pump-probe scheme for measuring spin flip (T$_{1})$ lifetimes in GaAs-related materials has been developed. The pump and probe beams are switched on and off electronically, with pulse widths and delays controlled by a two-channel pulse generator. The effect of the pump beam on the probe beam is seen by monitoring the Kerr rotation of the reflected probe beam. The technique has broad applicability, and should work for any material in which Kerr rotation spin measurement can be employed. The authors have applied this technique to a lightly-doped GaAs layer (n=3E14 cm$^{-3})$, to compare it with two other samples (at slightly higher\footnote{Colton et al., Phys. Rev. B \textbf{75}, 205201 (2007).} and slightly lower\footnote{Fu, et al., Phys. Rev. B \textbf{74}, 121304(R) (2006).} doping levels) whose T$_{1}$ dependence on field had substantial qualitative and quantitative differences from each other. Results for this sample will be presented.