| 摘要 |
<p>PURPOSE:To decrease a residual strain quantity by maintaining the temp. of a glass body until the double refraction quantity of the glass body attains a prescribed value after heating up the glass body to a set temp., then slowly cooling the glass body while controlling the temp. in such a manner that the double refraction quantity is kept within the range of the set value. CONSTITUTION:The light L0 generated from a laser generator 1 is branched to light L1 and light L2. The light L1 is passed through a linear polarizer 3 and is detected by a photodetector 4 which transmits a beat signal B1 for reference. On the other hand, the light L2 is passed through a half-wave plate 5 to the glass body 6 held within the glass body housing chamber of a heat treatment device 7; further, this light is passed through a linear polarizer 8 and is detected by a photodetector 9 which transmits a beat signal B2 for measurement. The phase difference between this signal B1 and the signal B2 is detected and is sent to an MPU 12. The signal is sent therefrom to the heat treatment device 7 to control the temp. and to heat the glass body 6 up to the set temp. within a viscous flow temp. region, by which the strain is relieved. The glass body is then slowly cooled to the temp. off the viscous flow temp. region while the low cooling rate is so controlled that the double refraction quantity is kept within the range of the set temp. The strain relieving of the glass body 6 is thus controlled in the shorter time than heretofore.</p> |
