An experimental technique using powders is described which permits the rapid classification of materials according to(a) magnitude of nonlinear optical coefficients relative to a crystalline quartz standard and(b) existence or absence of phase matching direction(s) for second‐harmonic generation.Results are presented for a large number of inorganic and organic substances including single‐crystal data on phase‐matched second‐harmonic generation in HIO3, KNbO3, PbTiO3, LiClO4·3H2O, and CO(NH2)2. Iodic acid (HIO3) has a nonlinear coefficient d14∼1.5×d31 LiNbO3. Since it is readily grown from water solution and does not exhibit optical damage effects, this material should be useful for nonlinear device applications.

A Powder Technique for the Evaluation of Nonlinear Optical Materials

A theoretical study is presented on the optimization of second harmonic generation (SHG) and parametric generation (PG) by a laser beam in a uniaxial nonlinear crystal. Numerically computed curves show the dependence of the SHG power, and the reciprocal of the PG threshold power, on the parameter l/b, where l is the optical path length in the crystal and b is the confocal parameter (determined by the focal length of the focusing lens and the minimum radius of the laser beam, assumed to be in the TEM00 mode of an optical resonator). The calculations take full account of diffraction and double refraction. In the absence of double refraction, the optimum focusing condition is found to be l/b=2.84. For PG the optimization of the crystal length l is also discussed, and curves are given showing the dependence of the threshold on l for the case in which signal and idler have the same losses. It is shown that the computed functions are also relevant to the mixing of two Gaussian beams and to parametric amplificat...

Parametric Interaction of Focused Gaussian Light Beams

Ferroelectric lithium niobate (LiNbO3) is widely used in integrated and guided-wave optics because of its favorable optical, piezoelectric, electro-optic, elastic, photoelastic, and photorefractive properties. However, detailed summaries of its pertinent physical properties and crystal structure are not readily available. In this tutorial paper, the important tensor physical properties and their mathematical descriptions are compiled and presented. The essential features of the structure of lithium niobate, including its hexagonal and rhombohedral unit cells, are illustrated and the principal (Cartesian) axes used in the description of the anisotropic properties are specified relative to the crystal structure. Errors in property coefficient values and structure information that have been propagated in the literature are corrected.

Lithium niobate: Summary of physical properties and crystal structure

We review progress in quasi-phase-matched optical parametric oscillators in bulk periodically poled LiNbO3. Using the electric-field poling process, we can reliably fabricate 0.5-mm-thick crystals with uniform domain structures over a 15-mm length. Periodically poled material retains the low-loss and bulk power handling properties of single-domain LiNbO3, and quasi phase matching permits noncritical phase matching with d33, the highest-valued nonlinear coefficient. Optical parametric oscillators pumped by 1.064-μm pulsed Nd:YAG lasers have been operated over the wavelength range 1.4–4 μm with tuning by temperature or by quasi-phase-matched period. We have shown an oscillation threshold as low as 0.012 mJ with a Q-switched pump laser and pumping at greater than ten times threshold without damage. We have also demonstrated a cw doubly resonant oscillator near 1.96 μm pumped directly with a commercial cw diode laser at 978 nm.

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Quasi-phase-matched optical parametric oscillators in bulk periodically poled LiNbO 3

CONTENTS 1. Introduction 609 2. Geometrical Optics of a Nonlinear Medium (Equations, Focal Points, Nonlinear Aberrations, Nonstationary Processes) 617 3. Wave Optics of a Nonlinear Medium (Diffraction Corrections to the Self-focusing Length, Formation of Proper Optical Waveguide, Nonstationary Processes) 624 4. Nonlinear Optical Effects in the Field of Self-focusing Beams (Stimulated Scattering in Liquids, Experimental Data, Self-focusing and Parametric Amplification) 629 5. Conclusion (Unsolved Problems, Diffraction in Nonlinear Interactions) 632 Cited Literature 634

https://iopscience.iop.org/article/10.1070/PU1968v010n05ABEH005849/pdf

Self-focusing and diffraction of light in a nonlinear medium

OPTICALLY‐INDUCED REFRACTIVE INDEX INHOMOGENEITIES IN LiNbO3 AND LiTaO3

The Curie temperature, birefringence, and phase‐matching temperature of LiNbO3 are shown to vary with the stoichiometry of the melt from which the crystals are pulled. The range of melt stoichiometry, indexed by the Li/Nb mole ratio, was varied from 1.20 to 0.80. This Li/Nb variation changes the Curie temperature, refractive index for the extraordinary ray, and the phase‐matching temperature by 120°C,.03, and 320°C respectively. The relevance of these changes are discussed in terms of the susceptibility of LiNbO3 to index inhomogeneities.

CURIE TEMPERATURE, BIREFRINGENCE, AND PHASE‐MATCHING TEMPERATURE VARIATIONS IN LiNbO3 AS A FUNCTION OF MELT STOICHIOMETRY

Several important characteristics of optical parametric oscillators can be substantially improved by nonresonantly reflecting the pump wave back upon itself after it has passed through the nonlinear medium. Benefits are reduced thresholds, decreased buildup times, and improved efficiencies. Steady-state analyses of doubly and singly resonant oscillators are presented.

R. G. Smith

Papers

OPTICALLY‐INDUCED REFRACTIVE INDEX INHOMOGENEITIES IN LiNbO3 AND LiTaO3

CURIE TEMPERATURE, BIREFRINGENCE, AND PHASE‐MATCHING TEMPERATURE VARIATIONS IN LiNbO3 AS A FUNCTION OF MELT STOICHIOMETRY

Improvement of optical parametric oscillators by nonresonant pump reflection

Optically-Induced Refractive Index Inhomogeneities in LiNbO 3 , and LiTaO 3