Optical Scattering Centers in Polycrystalline Nd:YAG Laser

Abstract

For the present study, 1.1‐at.%‐Nd‐doped YAG ceramics with controlled amounts of grain‐boundary phase were fabricated by a solid‐state reaction method using high‐purity powders. The optical scattering loss of the Nd:YAG ceramics, obtained from Fresnels equation, increased simply with increased amounts of grain‐boundary phase. The continuouswave laser output power of the Nd:YAG ceramics clearly was related to the scattering loss coefficients of the specimens that, in turn, were affected by the amount of grain‐boundary phase. Although the scattering loss coefficients of Nd:YAG ceramics with grain‐boundary‐free structure and a lower pore volume (}150 vol ppm) were almost equivalent to those of a 0.9‐at.%‐Nd‐doped YAG single crystal grown by the Czochralski method, the laser output power of the Nd:YAG ceramics exceeded that of the Nd:YAG single crystal with increased exciting power under excitation with an 808 nm diode laser because of the large amount of neodymium additives. Lasing performance was not affected by the existence of grain boundaries in the polycrystalline specimen.

Fabrication of Nd:YAG transparent ceramics with both TEOS and MgO additives

“…Because of low sintering activity of commercial powders, some additives are necessary in the sintering process. It is well known that the use of TEOS as sintering aid is required to reach fully dense and transparent Nd:YAG ceramics by removing the microstructural heterogeneities such as pores and secondary phases [12][13][14]. However, in our practical work, it is hard to prepare high quality Nd:YAG transparent ceramics only using TEOS as sintering aid if commercial oxide powders were used as the staring materials.…”

Effects of sintering additives on preparation of CaF2 transparent ceramics

“…Grain size of sample A is bigger than that of sample B, so there are more grain boundaries in sample B comparing with sample A. Though the existence of grain boundaries in ceramics has little relationship to optical scattering [25] , in this study, most of the pores locate at the grain boundaries, pores volume of sample B is bigger than sample A, which results in the worse transmittance ability of sample B. This also can be explained by the contrast of relative density.…”

Influence of pH values on (Nd+Y):Al molar ratio of Nd:YAG nanopowders and preparation of transparent ceramics

“…Both specimens B and C have over 80% transmission at the wavelength of 1064 nm. However, at the wavelength of 400 nm, the transmission of specimens B and C are both lower than 80%, the reason is that the scattering intensity increases with the decrease of wavelength according to the Rayleigh's equation [21]. Maybe small amount of scattering centers still exist in the specimens only cannot be detected by instruments.…”

“…During the sintering process, residual Al 2 O 3 is prone to diffuse along the YAG grain boundaries, and obstructs normal growth act as grain growth inhibitor, which leads to production of many pores in the specimen A. This is because the decrease of pores depends on grain growth [21]. When the (Nd + Y):Al molar ratio is 0.598 (specimen B) and 0.603 (specimen C), which is very close to 0.6, no secondary phases are observed along the grain boundaries, and pores have been removed completely.…”