Measurement of the refractive index and thermal refractive index coefficients of Nd:YAP crystal

Sulfur-doped graphitic carbon nitride for Tm:YAIO3 laser operation at 2.3 µm

We report on the first, to the best of our knowledge, passive Q-switching operation at 2.3 µm passively based on Tm:YAIO₃ (Tm:YAP) ³H₄→³H₅ transition with sulfur-doped graphitic carbon nitride (g-gC₃N₄) as the saturable absorber. Sulfur-doping engineering in g-C₃N₄ was manifested to enhance its mid-infrared nonlinear saturable absorption characteristics, which was confirmed by the conventional open-aperture Z-scan experiment with the excitation at 2.3 µm. The large effective nonlinear absorption coefficient of S-gC₃N₄ was determined to be -0.68cm/GW, indicating the remarkable MIR optical response. Initiated by S-gC₃N₄, a passively Q-switched laser operating at 2274.6 nm was configured with a-cut 3.0 at.% Tm:YAP as the gain medium. Stable Q-switching pulses were generated with the shortest pulse width of 140 ns, corresponding to the maximum peak power of 21.8 W. The experimental results reveal the effectiveness of sulfur doping to improve the performance of g-C₃N₄ in the MIR pulse generation.

Anisotropic thermal analyses of a high efficiency Tm:YAP slab laser and its intra-cavity pumping for Ho lasers

We evaluate the thermal effects of a c-cut Tm:YAP slab laser by considering the anisotropic properties of the biaxial YAP crystal. Significant improvements in thermal stress were demonstrated by selecting the crystallographic a-axis, which possesses higher thermal conductivity and thermal expansion, as the direction of the slab thickness. A maximum laser power of 30 W (E//a) at 2 µm was obtained under an incident LD power of 55 W with an optical conversion efficiency of 55.4% and slope efficiency of 61.8% using the a-slab. The slab laser was then used for realizing compact Ho lasers via intra-cavity pumping, resulting in a 0.8 W Ho:YAG laser and a 5.5 W Ho:YAP laser (E//b) at 2.12 µm and 2.13 µm, respectively.

Continuous-wave Tm:YAlO3 laser at ∼2.3 μm

The orthorhombic Tm³⁺:YAlO₃ crystal is promising for laser operation at the H₄3→F₄3 (1.5 μm) and H₄3→H₅3 (2.3 μm) transitions. Stimulated-emission cross-sections for these transitions are determined with polarized light. Peak values of 0.59×10^-20  cm² and 0.80×10^-20  cm² are found at 1438 nm and 2275 nm, respectively, both for E∥b. The cross-relaxation defining the upper-laser level lifetime is quantified. Continuous-wave lasing at the H₄3→H₅3 transition is achieved with an a-cut 1.5 at.% Tm:YAlO₃ crystal. The laser generated 254 mW at 2273 nm with a slope efficiency of 17.8% and linear polarization (E∥b).

Analysis on preferential free running laser wavelength and performance modeling of Tm³⁺-doped YAP and YLF

The preferential free running laser wavelength at room temperature for different axes cuts of Tm³⁺-doped YAP and YLF is comparatively analyzed in this paper. The polarized gain spectrum of Tm:YAP and Tm:YLF with different product values of Tm³⁺-doped concentration and crystal length is theoretically calculated under various cavity output mirror transmissions. From the gain spectrum, it straightforwardly determines the preferential free running laser wavelength for a given light polarization. In addition, a rate equation model is further used to model and compare the laser output performance for both the free running and some common artificially selected oscillating wavelengths, including 1.99 and 1.94 μm of Tm:YAP, and 1.89, 1.91, and 1.94 μm of Tm:YLF, respectively. To achieve an expected laser oscillating wavelength with acceptable output performance, our analysis presented here is very beneficial for one to choose the most suitable axis cut of crystal.

Sellmeier's equation and the expression of the thermal refractive-index coefficient for a Nd0.007Gd0.993VO4 crystal

The principal refractive indices of a Nd0.007Gd0.993VO4 crystal for wavelengths of 0.488, 0.6328, 1.064, 1.0795, and 1.3414 microm under the temperature range of 20-170 degrees C are measured by the autocollimation method, and the Sellmeier's equation and the expression of the thermal refractive-index coefficient are then obtained. The reliability of these results is checked by comparing the calculated values with the measured values for the measured wavelengths and the temperature region, as well as with the published values by Studenikin et al. [Quantum Electron. 25, 1162-1165 (1995)] for wavelengths of 0.491, 0.546, 0.578, 0.632, 0.808, and 1.062 microm at 20 degrees C. In addition, the birefringence and the thermal coefficient of the birefringence were obtained by measured results. The results show that the birefringence is larger than that of a YVO4 crystal and that the thermal coefficient of birefringence is less than that of a YVO4 crystal. Therefore it can be expected that the GdVO4 crystal is not only an excellent laser crystal but also an excellent birefringent crystal used in a modern optical transmission system as a passive fiber-optic component.

Measurement of refractive indices and thermal refractive-index coefficients of 7.5-mol.% Nb:KTiOPO4 crystal

The principal refractive indices and the thermal refractive-index coefficients of 7.5-mol.% Nb:KTiOPO(4) crystal were measured by autocollimation for wavelengths of 0.53975, 0.6328, 1.0795, and 1.3414 microm from room temperature to 143 degrees C. The Sellmeier equations at room temperature were obtained and used to calculate the optimal phase-matched angles for 1.0642 and 1.0795 microm. The calculated and experimental values are in good agreement.

Simple autocollimation laser refractometer with highly sensitive, fiber-optic output

A simple autocollimation scheme for a laser refractometer with a highly sensitive, single-mode, fiber-optic output is described. It allows for the determination of the refractive index and dispersion of optical materials with an accuracy exceeding 10(-5), which is confirmed by both experimental and analytical investigations.

Measurement of refractive indices and thermal refractive-index coefficients of LiNbO(3) crystal doped with 5 mol. % MgO

The principal refractive indices and the thermal coefficients for a LiNbO(3) crystal doped with 5 mol. % MgO have been measured by a minimum-deviation method for the wavelengths of 0.53975, 0.6328, 1.0795, and 1.3414, microm in the temperature range 20-154.5 degrees C. The constants of modified Sellmeier equations are all given in the described temperature range. The measured results were used to calculate the type I critical phase-matching angles for 1.0795- and 1.3414-microm second-harmonic generation at room temperature and the noncritical phase-matching temperature for 1.0795-microm second-harmonic generation for LiNbO(3) crystal doped with 5 mol. % MgO. The values obtained agree well with the experimental results.