The Preparation Of High-performance Nd:YAG Laser Transparent Ceramics And Laser Experiments

With advantages of single crystal and glass and avoiding their disadvantages, neodymium doped yttrium aluminum Garnet?Nd:YAG? is widely used as laser gain medium and transparent window material for its good optical property, mechanical strength, stable physical and chemical property.Commercial high purity yttrium oxide, aluminum oxide and neodymium oxide were chosen as raw material in this paper. With tetraethyl orthosilicate and magnesium oxide as sintering aid, 1at% Nd:YAG laser transparent ceramic was prepared at 1780? by vacuum sintering technique through a solid action routine. In experiments, effect of different raw material Y₂O₃ heat treatment temperature and the mechanism were deeply researched and discussed in detail; Y₂O₃ powder with small particle and uniform size was fabricated by high energy ball milling and elements were made by this powder for related analysis; the sample biscuits were prepared by cold isostatic pressing technique which have shown its advantage comparing with custom manual pressing; optimum heating rate and heat preservation time were confirmed by researching the heating stage and heat preservation stage separately in vacuum sintering process, relatively analyzing the phenomenon and discussing the mechanism; internal cause of effect of annealing treatment on sample transmittance was explored; finally the experiment scheme was improved and high quality samples were obtained. Then a optical system was built for the laser output experiment. Finally we have conclusions as following:1) Based on observation of scanning electrical microscope?SEM? images, raw material Y₂O₃ particles have a block structure with some faults and many interspaces exist in the faults. In some degree, these interspaces can form porosity in samples which could affect the transmittance. By 2h heat treatment at 1100?, the interspaces could be effectively eliminated to reduce the porosity forming and the sample transmittance was raised.2) By high energy ball milling, Y₂O₃ powder with small particle and uniform size was fabricated. Theoretically, with large specific surface area and strong activity, small particles can promote the sintering process and enhance the densification degree of samples.3) Using cold isostatic pressing, the sample biscuits owned good density and homogeneity. In one hand, this can reduce the porosity before sintering in the maximum degree. In another hand, good homogeneity is helpful to obtain uniform grain size and reduce the loss of laser in sample to improve the transmittance.4) The 1?/1.5min heating rate could provide enough time for porosity eliminating and has prevented the appearance of big grain which would reduce the grain boundary amount for eliminating the porosity. Sample transmittance is high with this heating rate.5) Prolonging the heat preservation time in sintering process was useful to eliminate the porosity effectively and increase the sample density for a high transmittance. In relative experiments we have found that the increase of transmittance was minimal when heat preservation time exceeded 30 h. Considering experiment cost and target comprehensively, 30 h has been confirmed as the optimum heat preservation time.6) Annealing treatment could eliminate the oxygen vacancy and stress in simples and enhance the transmittance in visible light range.7) Analysis of the non-ideal result of laser output experiments can be summarized as two aspects. Firstly, the ceramic sample threshold value may have a problem. The seco nd phase consisting of tiny porosities and impurities formed scattering and absorption centers and reduce the sample absorption to 808 nm wavelength incident light. Secondly, the samples' too small actual thickness might be less than the absorption length of the 808 nm incident light whose intensity became 1/e of its original value when it entered the samples. Thus there was no enough energy to emit laser with wavelength of 1064 nm stably.