Femtosecond laser pulses with new properties have been required for the great progress of femtosecond laser spectroscopy experiments. For example, simultaneous multiple ultrashort femtosecond laser pulses with different frequencies are needed in multicolor pump-probe experiments. Here, we have designed a much more simple and compact system for multicolor femtosecond pulse generation by using cascaded four-wave mixing in a 0.5 mm thick CaF2 plate. Multicolor femtosecond pulses with a sub-10 fs Fourier transform limit pulse width have been obtained by using two oppositely chirped incident pulses. These ultrashort multicolor femtosecond pulses will be used as a new laser source in femtosecond laser spectroscopy.

multicolor femtosecond laser; cascading four-wave mixing; Fourier transform limit pulse width

Chinese Academy of Science; 强场激光物理国家重点实验室; Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences; Tongji university