Research On The Generation Of Ultrafast Mid-infrared Pulsed Laser Via The Oppositely Dual-chirped Optical Parametric Amplification

Ultrashort pulse lasers that can be directly generated by laser mode-locking technology are still mainly concentrated in the near infrared band.Due to the lack of a suitable gain medium,high peak power mid-infrared ultrashort pulse lasers can generally only be obtained indirectly using nonlinear frequency conversion techniques based on optical second-order nonlinear effects.Optical parametric amplification imposed reversed temporal chirps intrinsically is beneficial for bands that are difficult to reach for ordinary level lasers,such as,the mid-infrared band of 3-5μm,and the generated idler wave may even suffer a spectrum broadening compared with the driving pulsed lasers.What’ s more,it can reduce the influence of group velocity mismatch on temporal walk-off for the stretched pulses.However,wide bandwidth phase-matching(PM)is still a decisive factor in subsequent energy boosting.Based on the characteristics of optical parametric amplification imposed reversed temporal dual chirps,we obtain the working conditions required for ideal broadband phase matching by elemental equation derived from phase-matching condition.It shows that the group velocity of the idler is between the group velocity of the signal and pump,which is the premise for achieving ideal broadband phase matching.On this basis,the gain spectrum of OPA can be tailed by adjusting the correspondence between different frequency components of the signal-pump,and that broadest one can be obtained at an optimum chirp-ratio.For different nonlinear processes,we systematically analyz the group velocity relation and gain spectrum characteristics of different nonlinear crystals with different matching types in different wavelengths,To explore appropriate nonlinear media for various potential applications.Among them,PPLNoeo crystal is satisfied with Type-II QPM and exhibits stable group velocity relation in the extremely wide spectral range(980nm-1600nm@790nm &1300nm-2000 nm @1030nm),conforming to the expected near-ideal broadband phase matching characteristics.On this basis,a potential technical approach that is suitable for constructing a tunable imposed reversed temporal chirps OPA laser system is proposed and numerically verified.