| Diamond is one kind of wide-gap semiconductors whose bandgap is about 5.5 eV. It is the material with the largest hardness, and is often used as an abrasive. Diamonds possess many excellent properties, for example, low specific heat, good mechanical strength and high corrosion resistance. These perfect properties ensure diamonds are used widely in the industry. In addition, diamonds have been regarded as a kind of optical materials. It has a good transparency over very wide range of the electromagnetic spectrum (from 225nm to the far infrared). Diamonds are also regarded as an attractive material for optoelectronic devices.Only a few reports on the third-order nonlinear optical effects of diamond crystals have been published by now. E. Anastassaki et al. observed the second-order electro-optic effect (Kerr effect) in natural type IIa diamond. They used a well-known method based on the elliptical properties of the light that emerges from a birefringent crystal placed between two crossed polarizers, and measured the total phase difference to estimate the Kerr coefficient. K. Arya et al. calculated the third-order nonlinear optical susceptibility tensor of groupâ…£crystals by the tight-binding orbital model in 1979. M. D. Levenson et al. investigated the details of the dispersive behavior of the third-order nonlinear optical susceptibility tensor in natural and synthetic diamonds by frequency mixing experiments in 1974. In this thesis, a nonzero element of the third-order nonlinear optical susceptibility tensor ? x(y3x)y of synthetic type Ib diamonds is investigated at the wavelength of 650 nm by using the transverse electro-optical modulation system and the theory of Kerr effect.The samples used in our experiments are provided by Zhengzhou ZhongNan Jete Superabrasives Co., Ltd., they are irregular cuboctahedrons, which includes eight hexagonal planes and six quadrilateral planes. All the hexagonal faces are {111} planes, and the quadrilateral faces are {100} ones. The distance of the opposite {111} planes is about 2mm. The samples belong to type Ib diamonds. We design the configuration which is used to bind the sample according to the shape of the sample. The modulating electric field is applied along to the direction of [111] axis. The [1 11] axis is chosen as the propagation direction of the probing beam. The propagation direction of the probing beam is not perpendicular to the direction of the applied electric field in our experiment. We modify the classic transverse electro-optic modulation system to meet the best sensitivity and linearity. The intensity of the output beam is calculated on these conditions. A 650nm CW laser diode is used as the light source, and the probing beam is received by the Si photodetector connected with the lock-in amplifier. We calculated the nonzero element of the third-order nonlinear optical susceptibility tensor of synthetic type Ib diamonds ? x(y3x)y ? 2.17 ? 10 ?23 m 2 /V2on the basis of the relationship between the modulating voltage and photoelectric signal. And then the applied electric field is applied along to the [100] axis, the propagation direction of the probing beam is [001] axis, ? x(x3x)x ? ?x(x3y)y is obtained, which is about 3.18 ? 10?22 m 2 V 2. According to the experimental data of M. D. Levenson and N. Bloembergen, ? x(x3x)x ? 5.32 ? 10?22 m 2 V2and ? x(x3y)y ? 2.03 ? 10?22 m 2 V2 are calculated,thus all the nonzero elements of the Kerr coefficient for diamond at 650nm are obtained, they are S1 1 ? 4.73 ? 10?23 m 2 V2, S1 2 ? 1.80 ? 10?23 m 2 V2,S 44 ? 1.93 ? 10?m V.Finally we calculate the condition that the modulating electric field is applied along to the direction of [110].A simple and feasible method for measuring the third-order nonlinear optical susceptibility of diamond crystal is obtained by our experiment. This method only requires very cheap experimental equipments and very simple experimental operations, and can provide high measurement precision. According to our experiment, diamond has potential applications in high voltage sensors based on Kerr effect. |
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