HE-4 OPTICAL-PUMPING WITH FREQUENCY-MODULATED LIGHT

Recently a distributed Bragg reflection (DBR) laser diode was commerci alised by SDL (USA) for helium optical pumping experiments. An interes ting feature of the new device is the possibility of frequency modulat ion of the diode output by modulating the current intensity, leading t o a new pumping scheme called optical pumping with frequency modulated light. We develop this method to induce spin precession and obtain ne w resonances in He-4 atomic gas, simply by modulating the frequency of the pumping light at the Larmor frequency of atomic states in a stati c magnetic field. These resonances are analysed with a simple model ta king into account velocity changing collisions.