Fig. 1. Class II phase matching conditions of KTP crystals and relationship between effective nonlinear coefficients and cutting angles.(a) Angle tuning curves under 532 nm laser pumping; (b) curve of effective nonlinear coefficient varying with θ

Fig. 2. Device diagram of 972 nm seed injection optical parametric oscillator frequency doubling output 486 nm blue light

Fig. 3. Working time sequence of RHF locking method

Fig. 4. Variation of OPO signal light energy with pump energy before and after seed injection

Fig. 5. Pulse waveform of signal light before and after seed injection. (a) Before seed injection; (b) after seed injection

Fig. 6. Profile of signal pulse with seed injection and without seed injection

Fig. 7. Analysis of signal light spectrum and beam quality after seed injection. (a) Signal light spectrum after seed injection; (b) beam quality analysis of 972 nm signal laser

Fig. 8. Variation of 486 nm blue light pulse energy and conversion efficiency with signal light pulse energy

Fig. 9. Pulse waveform and beam quality analysis of 486 nm blue light. (a) Pulse waveform; (b) beam quality analysis

Fig. 10. Power stability of 972 nm signal light and 486 nm blue light. (a) 972 nm signal light; (b) 486 nm blue light