Abstract

Lithium triborate (LBO) crystal has been recently studied for frequency doubling, tripling, and optical parametric oscillation (OPO) at room temperature.¹,² We have reported high-temperature noncritical phase matching (NCPM) frequency doubling and mixing in LBO crystal, in which the advantages of NCPM include no-walk-off, large acceptance angle, and high efficiency.³ In this paper we demonstrate what is, to our knowledge, the first experimental investigation of OPO in LBO crystal in which a tuning range of 915-1300 nm was achieved in LBO crystal by temperature tuning of 137-149°C. An OPO efficiency of 10% at the degenerate point was achieved by using an uncoated, noncritical-cut (i.e., θ = 90°, ϕ = 0°) LBO crystal with dimensions of 2 mm × 2 mm × 18.7 mm. A Quantel Nd:YAG laser, TEM₀₀ mode, 10-ns pulse width at 1064 nm was doubled to 532 nm by a CD*A (type I) crystal. The emitted green light was down-collimated to a spot size of 1 mm and pumped an OPO resonator with the appropriate coated mirrors. The measured OPO threshold power of the pump (532 nm) was about 2 mJ at the degenerate point. We will discuss the key parameters of cavity length, temperature tuning ranges, and angular tuning curves at various temperatures (22-150°C). Results of NCPM will also be compared with those of the angle-tuned critical case (at room temperature).

© 1990 Optical Society of America