Broadband optical delay with a large dynamic range using atomic dispersion

We report on a tunable all-optical delay line for pulses with optical frequency within the Rb D2 absorption line. Using frequency tuning between absorption components from different isotopes, pulses of 10 ns duration are delayed in a 10 cm hot vapour cell by up to 40 ns while the transmission remains above 10%. The use of two isotopes allows the delay to be increased or decreased by optical pumping with a second laser, producing rapid tuning over a range of more than 40% of the initial delay at 110°C. We investigate the frequency and intensity ranges in which this delay line can be realized. Our observations are in good agreement with a numerical model of the system.