Designable cascaded nonlinear optical frequency conversion integrating multiple nonlinear interactions in two KTiOAsO_4 crystals

We demonstrated a novel cascaded nonlinear frequency conversion that integrated OPO, SFG and SRS in two KTA crystals, realizing an efficient wavelength conversion from 1064 nm to multi-wavelength around 630 nm. The OPO and SRS were both performed in an x-cut KTA crystal to realize a noncritically phase-matched OPO and X(ZZ)X Raman conversion. The SFG was achieved in a (θ = 90^◦, φ = 24.3^◦)-cut KTA crystal with a type-II phase-matching configuration. Benefitting from the strong pulse-narrowing induced by the combined effect of OPO and SRS, a minimum pulse width of 13.5 ns was obtained, corresponding to a pulse energy of 0.3 mJ and a pulse peak power of 22.2 kW. The multiple operation parameters of wavelength, average output power, pulse duration and repetition rate can be coordinated to explore new treatment plan in photodynamic therapy. Furthermore, the designability of cascaded nonlinear optical frequency conversion could make the nonlinear optical technology accessible to a much wider range of potential users.