Polycrystalline Nd:YAG ceramics lasers
Introduction
Since Nd-doped YAG laser material was first discovered by Guesic et al. [1] in 1964, progress in the fabrication technique (the Czochralski (Cz) method) has rapidly improved its optical quality. In recent years, Nd:YAG (Nd:Y3Al5O12) lasers have been applied with remarkable success to various industrial fields such as medical operation [2], [3], metal processing [4], and others only single crystals created by the Cz technique [5], [6], however, have been used as laser materials. It is extremely difficult to dope more than 1 at.% of Nd homogeneously as a luminescence element in a YAG single crystal, because the effective segregation coefficient of elemental Nd for the host material (the YAG single crystal) is ∼0.2.
Attempts to synthesize solid-state laser material from polycrystalline YAG ceramics have been reported by de With et al. [7] and Sekita et al. [8]. Because a solid-state laser demands severe optical requirements, however, synthesizing Nd:YAG laser material of polycrystalline ceramics is technically very difficult. The present work produced polycrystalline, transparent Nd:YAG with optical characteristics nearly equal to those of a single crystal. A simple, solid-state reaction among high-purity Al2O3, Y2O3, and Nd2O3 powders was used in this fabrication method. The Nd:YAG produced by that method oscillated successfully by diode laser excitation.
Section snippets
Experimental
The present work used the same powders of Al2O3, Y2O3 and Nd2O3 as starting materials as used in the previous work [9], [10]. To fabricate the specimens, those starting powders were weighed so that the Nd content in the resultant YAG ceramics would be from 1.1 to 4.8 at.%. After the Al2O3, Y2O3, and Nd2O3 powders had been mixed with 0.5 mass% of tetraethyl orthosilicate (TEOS) as a sintering aid, the mixture was milled for 12 h with high-purity Al2O3 balls. The milled slurry was dried using a
Results
Fig. 1 shows reflection microscope photographs of 1.1 at.% Nd:YAG ceramics after thermal etching. The specimens consisted of grains measuring several tens of micrometers, and perfect pore-free structure.
Fig. 2 shows the relationships between transmittance of 3 mm thick specimens sintered at 1750 °C for 1∼50 h in vacuum and sintering time. The optical transmittance of these specimens was saturated at 2 h, as shown in this figure.
Fig. 3 shows the relationship between the logarithm of optical
Discussion
As mentioned earlier, high-quality, transparent Nd:YAG ceramics were fabricated successfully in the present work by a solid-state reaction using highly reactive Al2O3, Y2O3, and Nd2O3 powders as starting materials. Optical characteristics such as transmittance, fluorescence lifetime, and fluorescence spectra were similar to those of an Nd:YAG single crystal. For a solid-state laser, the beam must be amplified at the inside of the materials, and hence a high-quality fabricating technique is
Acknowledgements
This research was supported by associate Professor T. Taira (Institute for Molecular Science), and Professor K. Yosida (Osaka Institute of Technology).
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