Frequency evaluation of collimated blue light generated by wave mixing in Rb vapour

An evaluation of the absolute frequency and tunability of collimated blue light (CBL) generated in warm Rb vapour excited by low-power cw laser radiation at 780 nm and 776 nm has been performed using a Fabry–Perot interferometer and a blue diode laser. For the conditions of our experiments, the CBL tuning range is more than 250 MHz around the resonant frequency of the 85Rb 5S1/2 (F = 3)→6P3/2 (F' = 4) transition. A simple technique for stabilizing the power and frequency of the CBL to within a few per cent and 10 MHz, respectively, is suggested and demonstrated.