Sapphire is an important optical material, which has been widely used in many fields such as science and technology, national defense and civil industry. Due to the unique mechanical processing characteristics of sapphire crystal, the precision grinding and polishing technology of IC wafer processing can obtain ultra-precise nano-sized substrate wafers, which have been widely used in science and technology, national defense and civil industry, electronic technology and many other fields. As the largest application field of sapphire substrate wafers, LED chips have been widely used in the LED lighting industry, which has an important impact on the development of the sapphire industry.
Using the stress viewer developed and manufactured by Suzhou PTC Optical Instrument Co., Ltd. to detect the sapphire ingot, the conoscopic pattern can be observed. The conoscopic pattern is composed of black crosses and concentric interference color circles. The interference color circle is centered on the intersection of the black cross (the dew point of the optical axis) and forms a concentric ring. The number of interference color circles depends on the size and thickness of the birefringence of the crystal. When the local regular structure of the crystal is destroyed, the generated stress changes the direction of the optical axis at this position. And when the beam passes through this position, the black cross in the obtained conoscopic pattern is deformed. Therefore, the stress of the crystal can be detected by observing the conoscopic pattern at each position of the crystal.
