The development of nonlinear optical (NLO) borate crystals for generation of visible and UV light is reviewed. We first discussed on the basic principles of laser frequency conversion. Then, we examine the trends in research on NLO crystals. The background and present status of NLO borate crystals are summarized. The main considerations are focused on the discussion of crystals like CsLiB6O10 (CLBO), GdxY1−xCa4O(BO3)3 (GdYCOB) and K2Al2B2O7 (KAB). Properties of related materials like β-BaB2O2 (BBO), LiB3O5 (LBO), KBe2BO3F2 (KBBF), Sr2Be2BO7 (SBBO), CsB3O5 (CBO), GdCa4O(BO3)3 (GdCOB) and YCa4O(BO3)3 (YCOB) are included for comparison. We aim to provide a complete view of developing a new NLO borate material for actual laser applications. This review covers various aspects including the search for new materials, the growth of bulk crystals, the characterization of crystal properties as well as the development of new techniques to overcome obstacles in actual laser application, namely, thermal dephasing and laser-induced damage. Finally, perspectives on NLO borate crystals and all-solid-state UV lasers are evaluated.

Recent development of nonlinear optical borate crystals: key materials for generation of visible and UV light

A broadly tunable femtosecond optical parametric generator includes a cavity having a pumping section in which is located a nonlinear crystal selected from the group CTA and RTA, cut for noncritical phasematching. The plane of the optical x axis and or the optical y axis of the crystal is aligned with the axis of the pumping section. A Ti:S laser pumping beam is directed into the pumping section either collinearly or noncollinearly with the pumping section axis and impinges on the crystal to produce signal and idler beams. The laser is tunable to produce OPO output beams between about 1 and 4 μm.

Tunable optical parametric oscillator

Recent developments in beta -barium borate (BBO), lithium triborate (LBO), and potassium titanyl phosphate (KTP) optical parametric oscillators are reviewed It is noted that, with suitable nonlinear optical crystals and pump sources, virtually any wavelength ranging from the UV to the mid IR can now be reached with optical parametric oscillators The technology is better developed at the present time for the near-UV to 45 mu m range, however, largely due to the availability of large, high-quality BBO, LBO, MgO:LiNbO/sub 3/, and KTP crystals For the 1-10 mu m range, AgGaS/sub 2/ and AgGaSe/sub 2/ show great promise >

Optical parametric oscillators

A visible BaB2O4 optical parametric oscillator (OPO) pumped by a single-axial-mode 355-nm source has been demonstrated. An average output power of 140 mW with a signal wave conversion efficiency of 13 percent and an idler conversion efficiency of 11 percent for a total conversion efficiency of 24 percent has been achieved. The oscillator has continuously tuned from 412 nm to 2.55 microns limited by the infrared transmission range of the crystal. Through injection seeding, single-axial-mode OPO operation with a corresponding OPO linewidth of less than 3 GHz was obtained.

Visible BaB2O4 optical parametric oscillator pumped at 355 nm by a single‐axial‐mode pulsed source

We report a novel, two‐crystal, walkoff‐compensated optical parametric oscillator design using β‐BaB2O4, which significantly improves the performance of the device. The oscillator is pumped at 354.7 nm and is tunable throughout 0.42–2.3 μm with overall conversion efficiencies as high as 32%. We also report on demonstration of linewidth narrowing in the same β‐BaB2O4 oscillator, obtaining linewidths as narrow as 0.3 A.

L.K. Cheng

Papers

Growth and characterization of low temperature phase barium metaborate crystals