Noncritical Phase Matching in LBO Crystal

What is non-critical phase matching (NCPM)?

In a birefringent nonlinear crystal, phase matching is usually reached by cutting and angle-tuning the crystal so the ordinary and extraordinary waves stay in step. Non-critical phase matching (NCPM) instead reaches phase match with the propagation along a principal axis, and tunes the mismatch to zero with temperature. The big pay-off is that the beams walk off in the same direction with no spatial walk-off, and the angular acceptance becomes very wide — so the crystal tolerates a tightly focused, high-quality beam and is forgiving to align.

Why LBO is the NCPM crystal of choice

LBO (LiB₃O₅) supports practical NCPM conditions for important conversions — most notably type-I NCPM SHG of 1064 nm to 532 nm near ~148°C, and of 1.3 µm lines — while keeping its very high damage threshold and broad UV-visible transparency. The combination of zero walk-off, wide angular acceptance and high damage threshold makes temperature-tuned LBO the preferred choice for high-average-power, high-beam-quality green and UV generation.

Applications

NCPM LBO is used in high-power green and UV generation, CW and high-average-power second-harmonic systems, and any design where beam quality and tight focusing matter. See our BBO vs LBO vs KTP comparison for how LBO's NCPM compares with angle-tuned BBO and KTP, and the LBO product page.

Frequently asked questions

Why is NCPM "non-critical"? Because no angle tuning is needed — the beam propagates along an axis and temperature provides the match, so angular alignment is non-critical.

Does NCPM need an oven? Yes — LBO NCPM typically runs above room temperature (e.g. ~148°C for 1064→532 nm), so a stable heated mount is required.

NCPM vs angle-tuned SHG? NCPM gives zero walk-off and wide angular acceptance at the cost of temperature control; angle tuning is simpler but has walk-off and tighter angular tolerance.