Due to the absence of suitable laser media, broadband long wavelength sources rely on optical parametric amplification (OPA), methods to down-convert the frequency of short wavelengths Ti:Sapphire lasers.  Collinear OPA schemes provides passively CEP stable idler pulses which do not suffer from angular dispersion but with the drawback of narrower bandwidth for each amplification stage at non-degenerate wavelengths. Experiments in photochemistry and photobiology often additionally require tunability of the central wavelength therefore OPA systems which are capable of providing enough tunability for these applications are favorable

We have proposed an dual-crystal OPA (DOPA) scheme in which using a broadband pump laser, the group delay will be compensated using a simple optical crystal, this will result in important improvement on the gain and the bandwidth of the collinear schemes and create the possibility of using multi-stage OPA schemes without loss on the bandwidth. A sub-four-cycle IR driver source which applying optimized conditions theoretically is capable of providing an output powers of order of 10 W for the 1300 nm center wavelength will be realized. This scheme is capable of preserving the bandwidth as high as a SOPA, meaning that shorter pulse durations for an OPA system can be achieved using simple group delay compensation technique. The designated operable wavelengths of the system provides adequate tunability as a feature for different applications. The proposed scheme can be used as the driver field for high harmonic generation directly or can be a strong pump field for generating few-cycle and attosecond pulses used in a hollow core fiber system. As many trials previously had shown, using OPA systems in combination with a gas filled hollow fiber, using a pump field of 1200-1500 nm wavelength with initially broader bandwidth and shorter pulse durations is a promising method to achieve single-cycle pulse durations, our group delay compensated system is a perfect candidate for such applications and provides a broadband IR field and is able to provide a valuable source for attosecond pulse generation.

This work “Tunable broadband intense IR pulse generation at non-degenerate wavelengths using group delay compensation in a dual-crystal OPA scheme” was supported by the National Natural Science Foundation of China under Grants No. 11204095, No. 11574101, and No. 11234004.