Optical high-order subharmonic excitation of free cyclotron electrons

Homogeneous laser radiation in the visible or infrared range can excite high-order subharmonics at the cyclotron frequency of free electrons in the millimeter or microwave range. This may provide coherent links between lasers and rf or microwave frequency standards. In order to divide the frequency of a CO(2) laser (lambda approximately 10 microm) by a factor of 100 down to lambda approximately 1 mm in one step, a cw laser power as low as 10(-6) W is sufficient.