Abstract

We propose a transient technique for measuring velocity distributions in gaseous samples cooled to the mK and μK ranges. A pair of short laser "pump" pulses with wavevectors k₁ and k₂ prepares ground-state, sub-level population gratings of periodicity 2-π/ |k₁ — k₂|, which relax from thermal motion and collisional effects. A third "probe" pulse can be strongly reflected from the grating provided the probe delay is in the range of the grating relaxation time T_r. When relaxation is by thermal motion, T_r ≈ (|k₁ — k₂| v₀)⁻¹ where the characteristic velocity v₀ is in the range from 1 to 10 cm s⁻¹ for typical laser-cooled samples (e.g.);¹ T_r is then in the ms or μs range depending on the choice of |k₁ − k₂|.

© 1994 IEEE