Spatial walk-off can severely increase the threshold of critical phase-matched optical parametric oscillations (OPOs) and distort the output beam quality. With 16-layer KTP stacks for walk-off compensation, noncritical phase-match-like (NCPM-like) and quasi-phase-match-like OPOs with enhanced angular acceptance have been demonstrated based on two different KTP bonding orientations. In the NCPM-like composite, output pulse energy of 49 (mu)J has been achieved at pump energy of 523 (mu)J with pulse duration of 15 ns and repetition rate of 1 KHz. The OPO threshold as low as 254 (mu)J (44.6 MW/cm~(2)) has been achieved.
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