Femtosecond Pulse Laser Modification and Terahertz Time Domain Spectroscopy of Yttrium Aluminum Garnet Transparent Ceramics
Date
2016-02
Authors
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Publisher
New York State College of Ceramics at Alfred University. Inamori School of Engineering.
Abstract
A femtosecond pulse laser was used to investigate the effects of ultra-short pulses of broadband infrared radiation on single crystals and polycrystalline ceramics of yttrium aluminum garnet (YAG), both pure and doped with neodymium. Transparent YAG responded by generating colored light in the visible spectrum, while opaque ceramics exhibited localized densification and ablation. in addition to the physical modification of the microstructure, the femtosecond pulse laser was used to preferentially segregate yttrium atoms within the optical interaction volume of the YAG material. This demonstrates that fs-pulse lasers can be used to preferentially modify the microstructural and chemical properties of dense ceramic materials.
Terahertz time-domain spectroscopy (THz-TDS) was also employed to characterize the dielectric properties of YAG compositions synthesized with precisely controlled and varying stoichiometric atomic rations. A correlation between the x-ray diffraction (XRD) and THz-TDS data indicated that chemical variation in the YAG solid solution had an effect on the dielectric properties; in yttrium rich compositions, phases of YAlO3 formed while compositions rich in aluminum, phases of Al2O3 formed. The precipitation of these phases rendered the material inhomogeneous resulting in a significant change in the optical and dielectric properties due to the composite nature of the material.
YAG ceramics were synthesized with a range of bulk densities, grain sizes, and pore volumes to investigate the effect of microstructure on the THz properties. Bulk density was the dominant factor, exhibiting a linear relationship between density absorption coefficient, real dielectric constant, and refractive index. THz-TDS measurements were also performed at a range of temperatures between 293K and 493K which showed that above 350K there is linear relationship between THz absorption and temperature.
Description
Thesis completed in partial fulfillment of the requirements for the degree of Master of Science in Materials Science and Engineering at the Inamori School of Engineering, New York State College of Ceramics at Alfred University
Type
Thesis
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Keywords
YAG, Optical materials