Nonlinear Optical Crystals: A Complete Survey

Deep ultraviolet (absorption edge 6.2 eV) nonlinear optical (NLO) materials are of current interest owing to their technological applications and materials design challenges. Technologically, the materials are used in laser systems, atto-second pulse generation, semiconductor manufacturing, and photolithography. Designing and synthesizing a deep UV NLO material requires crystallographic non-centrosymmetry, a wide UV transparency range, a large second-harmonic generating coefficient (dij > 0.39 pm/V), moderate birefringence (Δn ∼ 0.07), chemical stability and resistance to laser damage, and ease in the growth of large high-quality single crystals. This review examines the known deep UV NLO materials with respect to their crystal structure, band gap, SHG efficiency, laser damage threshold, and birefringence. Finally, future directions with respect to new deep UV NLO materials are discussed.

Deep Ultraviolet Nonlinear Optical Materials

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

The primary goal of this review is to present a clear chemical perspective of borates in order to stimulate and facilitate the discovery of new borate-based optical materials. These materials, whic...

Borates: A Rich Source for Optical Materials.

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

We report the first successful operation of a β‐BaB2O4 optical parametric oscillator (OPO) tunable in the visible and the near infrared. The OPO was pumped at 354.7 nm and was tunable throughout 0.45–1.68 μm. A maximum total energy conversion efficiency of 9.4% was measured from the OPO containing a 10.5 × 10.5 mm2 × 11.5 mm long, 30° cut β‐BaB2O4 crystal grown in our laboratory. Using the optical parametric luminescence technique, we have measured the 354.7 nm and 266 nm pumped OPO tuning curves (type I and type II) in β‐BaB2O4 throughout the ∼0.3–3.3 μm range. The implication of these results on the validity of the published Sellmeier equations is discussed.

Broadly tunable optical parametric oscillation in β‐BaB2O4

We report the operation of a β‐BaB2O4 singly resonant optical parametric oscillator broadly tunable in the ultraviolet, visible, and infrared regions of the spectrum This optical parametric oscillator was pumped at 266 nm and was continously tunable throughout 033–137 μm A novel cavity design was implemented which has applicability to other parametric oscillators The oscillation threshold of this device was measured and compared to the calculated result

Ultraviolet optical parametric oscillation in β‐BaB2O4

Growth and characterization of low temperature phase barium metaborate crystals

Intracavity doubling in β‐BaB2 O4 (BBO) of femtosecond pulses into the ultraviolet with high efficiency is reported. Pulse widths down to 43 fs at a 108 Hz repetition rate and outputs as high as 20 mW per arm of the femtosecond laser on a continuous‐wave basis can be achieved. The ultraviolet pulse widths were determined through detailed cross‐correlation measurements based on sum‐frequency mixing to 210 nm in ultrathin BBO crystals.

Femtosecond ultraviolet pulse generation in β‐BaB2O4

Almost all current results on ultrafast processes are derived from femtosecond lasers in the visible or near infrared. There is a clear need to extend the wavelength range of high repetition rate femtosecond pulses into the ultraviolet (uv). Frequency doubling (SHG), both extra1- and intracavity2, represents one technique for generating such pulses. However, the results achieved so far have been far short of what have been achieved in the visible. In this talk, we report an intracavity doubling experiment using the new nonlinear optical crystal β-BaB2O4 (BBO) that results in nearly complete recovery of the normal visible fundamental output power in the form of femtosecond uv pulses at the second harmonic. Recent success in our laboratory in growing and fabricating high quality BBO crystals3 has enabled us to generate the shortest uv pulses reported so far, less than 45 fs at 315 nm.

W. R. Bosenberg

Papers

Broadly tunable optical parametric oscillation in β‐BaB2O4

Ultraviolet optical parametric oscillation in β‐BaB2O4

Growth and characterization of low temperature phase barium metaborate crystals

Femtosecond ultraviolet pulse generation in β‐BaB2O4

Femtosecond Ultraviolet Pulse Generation in β-BaB 2 O 4