We theoretically investigate the strong-field ionization of in circularly polarized laser fields by calculating the photoelectron energy spectra and the logarithm of the differential ionization rate. In circular polarization laser fields, if the emission directions of a photoelectron are averaged, the photoelectron energy spectra usually have a bell shape and a single broad peak at the middle-energy region (Ren et al. [Phys. Rev. A 78, 043411 (2008)]). In this paper, our theoretical results show that when the emission directions of a photoelectron are not averaged, the photoelectron energy spectrum has a complex double-peak or a multipeak structure with interference valleys. The locations of the interference valleys are independent of the laser intensity, but dependent on the emission direction and final kinetic energy of the photoelectron. In order to completely understand the interference effect, we also carry out the calculations for the logarithm of the differential ionization rate. We find that the interference light and dark stripes alternate with the emission directions and kinetic energies of the photoelectron: if (), the interference stripes are light; if (), the interference stripes are dark. No matter what the kinetic energies of the photoelectron are, for the emission direction of the stripes are always light.
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