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

Recent advances in the field of nonlinear optical phenomena are reviewed with particular empphasis placed on such topics as parametric oscillation self-focusing and trapping of laser beams, and stimulated Raman, Rayleigh, and Brillouin scattering. The optical frequency radiation is treated classically in terms of the amplitudes and phases of the electromagnetic fields. The interactions of light waves in a mterial are then formulated in terms of Maxwell's equations and the electric dipole approximation. In this method, non-linear susceptibility tensors are introdueed which relate the induced dipole moment to a power series expansion in field strengths. The tensor nature and the frequency dependence of the nonlinearity coefficients are considered. The various experimental, observations are described and interpreted in terms of this formalism.

https://ieeexplore.ieee.org/iel5/5/31089/01447053.pdf

Nonlinear optics

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.

/pdf/quasi-phase-matched-optical-parametric-oscillators-in-bulk-3gnsflghce.pdf

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

OPTICALLY‐INDUCED REFRACTIVE INDEX INHOMOGENEITIES IN LiNbO3 AND LiTaO3

LiNbO3: AN EFFICIENT PHASE MATCHABLE NONLINEAR OPTICAL MATERIAL

Spectral diffusion in the inhomogeneous paramagnetic resonance lines of ${\mathrm{Ce}}^{3+}$ and ${\mathrm{Er}}^{3+}$ in CaW${\mathrm{O}}_{4}$ at concentration \ensuremath{\sim}${10}^{18}$ spins/cc has been studied by electron spin echo techniques. Measurements show that the spreading of excitation through the line can be approximately described by a diffusion kernel in the form of a Lorentzian function whose width is linear in time. Local field fluctuations due to spin-spin flips and spin-lattice flips appear to be the primary cause of diffusion. In (Ca,Ce)W${\mathrm{O}}_{4}$ below 4.2\ifmmode^\circ\else\textdegree\fi{}K the lattice time is long, and spin-spin flips predominate, leading to a diffusion rate which is independent of temperature. In (Ca,Er)W${\mathrm{O}}_{4}$ lattice relaxation is more rapid, and the diffusion parameter varies as the lattice time. Nuclei of ${\mathrm{W}}^{183}$ in the host crystal have been observed to give a modulation in the envelope of spin echoes, but the corresponding local fields are smaller than those arising from electron spins at the concentrations studied.

Spectral Diffusion in Electron Resonance Lines

Experiments demonstrating continuous operation of a solid-state optical maser are described. A continuous coherent wave at 1.065 \ensuremath{\mu} is obtained from trivalent neodymium in CaW${\mathrm{O}}_{4}$, operating at about 85\ifmmode^\circ\else\textdegree\fi{}K. At room temperature a continuous wave at 1.058 \ensuremath{\mu} is obtained. Room temperature operation is possible due to the large splitting between the terminal state of the maser transition and the ground state (\ensuremath{\sim}2000 ${\mathrm{cm}}^{\ensuremath{-}1}$). Near threshold power output \ensuremath{\sim}10 mw is observed, using silver coatings only.

Continuous Operation of a Solid-State Optical Maser

We report the first observation of donor-acceptor pair lines in CdS. The spectrum correlates with a distant pair peak at 5176 \AA{}, an ${I}_{1}$ line at 4888.52 \AA{}, and an ${I}_{2}$ line at 4869.30 \AA{}. Several other pair-line spectra were observed in the vapor-grown undoped platelets used in these experiments. One of these correlated with the same ${I}_{1}$ line and distant pair peak, but with an ${I}_{2}$ line at 4869.17 \AA{}. Zeeman experiments confirmed that these lines were donor-acceptor pair lines. The Zeeman pattern of the pair lines could be predicted, using a crystal field and a $j\ensuremath{-}j$ coupling constant. These constants were determined by the splittings of the pair lines in zero field. For $\mathbf{H}\ensuremath{\parallel}c$, the hole $g$ value was the same as for an isolated acceptor. A theoretical wurtzite spectrum was calculated on the basis of Coulomb interactions. The spectrum was much more complicated than a theoretical zinc-blende spectrum and was sensitive to both the dielectric-constant ratio $\frac{{\ensuremath{\epsilon}}_{\ensuremath{\perp}}}{{\ensuremath{\epsilon}}_{\mathrm{II}}}$ and the $\frac{c}{a}$ ratio of the CdS lattice. The experimental lines could not be assigned, but the line densities were in agreement with what was expected for a pair-line spectrum involving a simple donor and acceptor.

K. Nassau

Papers

OPTICALLY‐INDUCED REFRACTIVE INDEX INHOMOGENEITIES IN LiNbO3 AND LiTaO3

LiNbO3: AN EFFICIENT PHASE MATCHABLE NONLINEAR OPTICAL MATERIAL

Spectral Diffusion in Electron Resonance Lines

Continuous Operation of a Solid-State Optical Maser

Donor-Acceptor Pair Lines in Cadmium Sulfide