| 摘要 |
PROBLEM TO BE SOLVED: To obtain a method and an apparatus in which the thickness of a transparent material can be monitored precisely by a measurement which is performed before the material enters a cooling kiln for annealing by a method wherein a beam of light at a modulated optical frequency is focused so as to be shone at the transparent material, two beams of light reflected by respective surfaces are made to interfere and the number of vibrations per modulation cycle of an interference signal is decided. SOLUTION: The image of the output A of a laser diode 1 which comprises a dispersion-type Bragg reflector(DBR) is formed in a point B by a lens 16. A beam of output light from the point B is reflected by two surfaces of a transparent material 2 to be tested, Beams of reflected light are regarded as coming from an apparent point B1 and an apparent point B2. The distance between the point B1 and the point B2 is proportional to the thickness (e) of the transparent material 2 which is measured substantially. Then, two means of reflected light received by an optical fiber 5 via a lens 6 are made to interfere, and the number of vibrations per modulation cycle or an interference signal is decided by a detector. Thereby, the difference in a passage between the two beams of light and the thickness (e) of the transparent material 2 are estimated, and a change in the phase of the interference signal is decided.
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