High-harmonic generation by a bichromatic bicircular laser field

The generation of circularly polarized high-order harmonics is considered b y a bichromatic laser field whose two components with frequencies omega and 2 omega are circularly polarized in the same plane, but rotate in opposite directions. Both exact and approximate (obtained by using the saddle-point method) results for the harmonic spectra are presented. The effect of the ratio of the intensities of the two components on the harmonic spectrum is investigated. For the case where the high-frequency field has twice the int ensity of the low-frequency field, the possibility of generating a train of attosecond pulses is pointed out that consists of circularly polarized har monics all having the same helicity.