Zhang Shaojun

Electrooptic properties and electrooptic Q switch of La3Ga5SiO14 single crystal

The electrooptic coefficients of La3Ga5SiO14 (langasite, LGS) single crystal have been determined. The results obtained are γ11=2.2 pm/V and γ41=1.8 pm/V. With the propagating light along the optical axis and the applied electric field parallel to the x or y axis, LGS single crystal has been configured as a Pockels cell placed in the laser cavity. The Pockels cell successfully acted as an on-off Q switch, and the output power of the YAG laser was 2 J at modulated frequencies of 1, 10 and 20 times/s.

La3Ga5SiQ14 single-crystal Q switch used as an electro-optic device.

A new kind of electro-optic Q switch is designed by use of a La3Ga5SiQ14 (LGS) crystal. Because the LGS crystal is optically active, the Q switch is based on the consideration that the total rotation angle of the polarization plane is zero, whereas the polarized wave propagates through the Pockels cell back and forth, with the polarization plane gyration and electro-optic effect existing simultaneously. The LGS Q switch is a practical electro-optic device that can be used in medium output energy lasers to partially take the place of deuterated potassium dihydrogen phosphate and lithium niobate Q switches.

Mutual action of the optical activity and the electro-optic effect and its influence on the La3Ga5SiO14 crystal electro-optic Q switch

We have studied the mutual action of the optical activity and the electro-optic effect and its influence on the electro-optic Q switch. The birefringence (g33/n_o)(Delta/n_o)^2 resulting from the mutual action is calculated. In the polarization-light interferometric experiment setup, the outgoing light intensity expression is given by I = A_0^2 cos^2 {[(pi/lambda)(g33/n_o)l - β] + (pi/lambda)[(−2Delta) + (g33/n_o)(Delta/n_o)^2]l} for the optically active crystal on which the voltage is applied. The influence on the electro-optic Q switch caused by the mutual action is discussed. Based on these discussion, we have designed a type of electro-optic Q switch by using the optically active crystal La3Ga5SiO14. This Q switch can behave as normally as those that are not optically active.

Growth and Second-Harmonic Generation Properties of Tm3+, Yb3+, Bi3+ and Li+ Doped GdCa4O(BO3)3 Crystals

The rare-earth ions (Yb3+, Tm3+) and Li+, Bi3+ ions doped GdCa4O(BO3)3 crystals were grown using the Czochralski pulling method. The second-harmonic generation conversion efficiencies of the GdCOB:Yb and GdCOB:Tm crystals are 31.3% and 33.3%, respectively, while the undoped GdCOB crystal is 27.9%. The conversion efficiencies of Yb3+, Tm3+ doped GdCOB are improved by 12% and 19%, respectively, compared to that of the undoped one. The conversion efficiencies of Li+, Bi3+ doped GdCOB crystals are 33% and 38.3%, which are improved by 15% and 37% as compared to that of the undoped crystal. The results are discussed using the anion group theory.

Low Threshold and High Efficiency Nd:S-VAP Laser

The absorption spectrum of a new sort of crystal Nd:S-VAP was measured, which showed that Nd:S-VAP can be appropriately pumped at 583.0 and 809.0 nm. By using tunable dye-laser (570.0-600.0 nm) as pumping light, the performance of low threshold and high efficiency Nd:S-VAP laser has been realized. The characteristics of the output laser, such as 1.5 nm linewidth, 5 ns pulse width, almost total polarity, up to 50% conversion efficiency, down to 2 mJ threshold energy and so on, were presented. Meanwhile, the prospect of Nd:S-VAP crystal for low threshold, high efficiency miniature laser was discussed.

Nonlinear Optical Properties of Perfectly Polarized KIO3 Single Crystal

The nonlinear optical properties of a perfectly polarized KIO3 single crystal were investigated. The principal refractive indices and nonlinear optical coefficients have been measured. The results are as follows: n1 = 1.6967, n2 = 1.8329, n3 = 1.8358 for 0.5893 μm; d31 = 1.2|d31 (LiIO3)|, d32 = 1.8|d31 (LiIO3)|. The intensity of the frequency-doubled light of the KIO3 single crystal with 2.96 mm thickness is 1.2 times as large as that of the KTP single crystal with the same thickness.

Theory of intracavity-frequency-doubled quasi-three-level cw lasers

The rate equations for the intracavity-frequency-doubled quasi-three-level lasers are developed. By normalizing the related parameters, it is shown that the general solution to the rate equations is dependent upon four dimensionless parameters: the normalized reabsorption loss, the pump to laser-mode size ratio, the normalized pump level, and a parameter written as ηshg, which is related to the ability of the nonlinear crystal to convert the fundamental to the second harmonic. By numerically solving these rate equations, a group of general curves are obtained to express the relations between the solution and the four dimensionless parameters.

Investigation of the nonsymmetry of effective nonlinear optical coefficient expressions for low-symmetry crystals

For low-symmetry crystals that belong to 2 and m point groups, two kinds of nonlinear optical coefficients matrix were derived after the positive directions of the optical coordinate axes were defined with the aid of the piezoelectric coordinate axes. These two kinds of nonlinear optical coefficient matrix are the cause of the nonsymmetry of the effective nonlinear optical coefficients about the x, y, and z optical coordinate planes. For the corresponding wave vector k(theta,phi) in the Nth quadrant, the effective nonlinear optical coefficient expressions are d_eff^I=a_i^e2[d_ijk(omega3,omega2,omega1)]N+2^a_j^e1a_k^e1 (Type I) and d_eff^II=a_i^e2[d_ijk(omega3,omega2,omega1)]N+1^a_j^e1a_k^e2 (Type II), where N is the number of the quadrant. Only one kind of nonlinear optical coefficient matrix is the maximum effective nonlinear optical coefficient. It is necessary to find out which quadrant, in which the wave vector k(theta,phi) is located, corresponds to the maximum effective nonlinear optical coefficient.