A. A. Ballman

Coherent Emission from Rare Earth Ions in Electro‐optic Crystals

We report the observation of coherent emission from three rare‐earth ions in electro‐optic crystals. Oscillation is observed from Nd3+ ions in Bi4Ge3O12, LiNbO3, and Ba0.75Ca0.25Nb26O at room temperature, and from Tm3+ and Ho3+ ions in LiNbO3 at 77°K. Second‐harmonic radiation is obtained from LiNbO3:Tm3+ and electric‐field modulation of threshold is observed for certain crystals of LiNbO3:Nd3+. The latter effect is believed to arise from crystal strain. The propagation angle for phase‐matched second‐harmonic generation is calculated to lie at 43° to the c axis for both LiNbO3:Tm3+ and LiNbO3:Ho3+ at 77°K. Phasematched second‐harmonic generation from LiNbO3:Nd3+ is not possible, since the maser line is an extraordinary wave. However, the polarization of the maser line in LiNbO3:Nd3+ is appropriate for phasematched parametric frequency conversion in the near infrared. Attempts to observe such radiation were not successful due to the limited power available in the fundamental.

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

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.

Calcium Niobate Ca(NbO3)2—A New Laser Host Crystal

Large single crystals of calcium niobate Ca(NbO3)2, grown by the zochralski technique, are transparent and can be doped with rare earth or transition metal ions. Laser action has been observed in calcium niobate doped with trivalent neodymium, holmium, praseodymium, erbium, and thulium.

Lithium Tantalate Light Modulators

Light intensity modulators have been developed using single‐domain lithium tantalate as the electro‐optic material. A broadband transistor amplifier which can develop 0.2‐W output power drives the modulator sample which presents a capacitive load of 5 pF. Approximately 80% modulation is achieved from dc to 220 Mc/sec, when the light is made to traverse the sample twice. The modulation bandwidth is limited by the transistor amplifier. Very little acoustic ringing is observed when the modulator is used as a fast light switch.

Elasto‐Optic Properties of Bi12GeO20, Bi12SiO20, and SrxBa1−xNb2O6

The elasto‐optic matrix elements for longitudinal waves in four new single crystals have been measured. Piezoelectric bismuth silicon oxide and bismuth germanium oxide, cubic point group 23, show an elasto‐optic strength of 6.0 and 6.6, respectively, relative to fused silica based on an equal acoustic power criterion discussed below. Ferroelectric crystals from the strontium barium niobate system, tetragonal point group 4mm, were also studied. One with a Sr to Ba ratio of 3:1 showed an elasto‐optic strength of 26; another with a ratio of 1:1 had a strength of 5.8.

Pyroelectric copying process

An electrostatic copying process based on the pyroelectric effect is described. The effect is demonstrated with single crystals of LiTaO3, ceramic plates of lanthanum‐modified lead zirconate‐titanate (PLZT), and polymer films of polyvinylidene fluoride (PVF2). By employing thin films (0.8 mil) of PVF2 to minimize thermal diffusion, we have obtained sufficient resolution to allow charge distributions (images) to be visually observed by dusting the films with conventional electrostatically charged inks. Since the pyroelectric effect is not wavelength dependent, certain advantages over photoconductive techniques, with their inherent wavelength dependence, are possible.

Light beam scanning and deflection in epitaxial LiNbO3 electro‐optic waveguides

We report a method of scanning and deflecting a light beam in an electro‐optic waveguide of epitaxial LiNbO3 film. The method involves the use of the electro‐optic effect for excitation of a proper distribution of the refractive index which causes the light beam to deflect. The angle of deflection is found to vary continuously with the intensity of the applied field. We are able to scan a light beam in the plane of the film up to 4°. We also present a theory for the light beam deflection and show that our method does optimize the deflection efficiency.

Reduction of the Susceptibility to Optically Induced Index Inhomogeneities in LiTaO3 and LiNbO3

It has been established that LiTaO3 can be made resistant to laser‐induced inhomogeneities in the index of refraction at power levels as high as 500 W/cm2. This is accomplished by annealing LiTaO3 in an electric field of 250 V/cm at a temperature of 700°C for ½ h and then cooling the crystal to room temperature with the field on at a rate of 100°C/h. The susceptibility to laser‐induced index changes in LiNbO3 is reduced by this treatment but not to the same extent as in LiTaO3. A mechanism is proposed to explain the observed reduction in susceptibility to damage.

Growth of Beryl Single Crystals for Microwave Applications

Beryl crystals containing transition metal ions can he grown from a number of mineralizing fluxes. Of these V2O5 appears to be particularly advantageous for growing beryl by transfer methods. The Cr3+ containing crystals grown by this method are particularly suitable for microwave device applications as indicated by a resonance linewidth of 100 Mc at the X band.