CsB₃O₅ (CBO) crystal possesses a relatively large effective nonlinear optical coefficients, a high laser damage threshold (26 GW/cm² for 1.0 ns pulses at 1053 nm), and a wide optical transparency range (167-3400 nm). CBO crystal can be expected to generate more efficient and high power ultraviolet light by frequency conversion of Nd:YAG laser radiation than LiB₃O₅ (LBO) crystals. This work presents the progress of CBO crystal on growth, properties, as well as output of ultraviolet laser.

A free of scattering centers CBO crystal, up to 47×45×41 mm³ in size and 221 g in weight, has been grown by the top-seeded solution growth (TSSG) method from Cs₂O-B₂O₃-MoO₃ system. The suitable region for CBO crystal growth was investigated by the growth experiments, viscosity and volatility measurements, which confirmed that the optimal molar ratio of Cs₂O: B₂O₃: MoO₃ was 2:3:2.5. The grown CBO crystals possess high optical quality. The full-width at half-maximum (FWHM) of the rocking curve is 0.0057 º, and the optical homogeneity is at the level of 10-6 cm^-1. The optical absorption at the critical wavelengths of 1064 and 532 nm was measured to be 200 and 60 ppm cm^-1, respectively. The laser-induced damage threshold (LIDT) at λ=1.064 nm and τ=5.0 ns is about 4.50 GW cm^-2.

Thermophysical properties including the specific heat, thermal diffusion, thermal conductivity, and thermal expansion were systemically investigated for the first time. The specific heat was measured to be 0.512-0.796 J·g^-1·K^-1 in the temperature range from 25 to 300°C. According to the measured thermal diffusion coefficients, the thermal conductivities along the a-, b-, and c-axis at 30°C were calculated to be κ_a =1.43 W·m^-1·K^-1, κ_b =2.50 W·m^-1·K^-1, and κ_c =1.51W·m^-1·K^-1, respectively. CBO exhibits strongly anisotropic thermal expansion behavior, and the mean thermal expansion coefficients in the temperature range from 25 to 500 °C are α_a=46.77×10⁻⁶/°C, α_b=18.39×10⁻⁶/°C, and α_c= -3.80×10⁻⁶/°C.

Principal refractive indices of crystal CsB₃O₅ (CBO) at the wavelengths of 0.266, 0.355, 0.532, 0.473, 0.633, 1.064, and 1.338μm were accurately measured by using auto-collimation method within the temperature range from 40 to 190ºC. Equations of thermal refractive index coefficients as a function of wavelength were derived and reported for the first time, which could be used to calculate the principal thermal refractive indices at different wavelengths. Sellmeier equations at different temperatures were derived and used to calculate the phase-matching (PM) angles for the third-harmonic generation (THG) and the fourth-harmonic generation (FHG) of CBO crystal at different temperatures.

In addition, a high-power 278 nm ultraviolet (UV) laser through fourth harmonic generation (FOHG) of a diode-pumped 1112 nm Nd:YAG laser has been demonstrated in CBO crystal for the first time. The maximum average output power of the 278 nm laser is up to 1.5 W. The results demonstrated that CBO crystal is a promising NLO material for UV high-power lasers below 300 nm.

Key words: CsB₃O₅; nonlinear optical crystal; thermophysical property; thermal refractive index coefficient

References

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[2] Y. C. Wu, P. Z. Fu, J. X. Wang, Z. Y. Xu, L. Zhang, Y. F. Kong and C. T. Chen, Opt. Lett., 22 (24) ( 1997) 1840-1842.

[3] N. A. Pylneva, L. L. Pylneva, A. B. Meshalkin, V. I. Kosyakov and A. B. Kaplun, The 16th international conference on crystal growth (ICCG16), Beijing, China, August 8-13, 2010.

[4] H. Y. Shen, D. Y. Zhang, W. Liu, W. Z. Chen, G. F. Zhang, G. Zhang, and W. X. Lin, Applied Optics, 38 (1999) 987-990.

1. PRESENTATION: Research Advancement of Nonlinear Optical Crystal CsB3O5, Zip archive data, at least v2.0 to extract, 0MB

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