| 摘要 |
PURPOSE:To measure film thickness, etc., of large objects to be measured and improve the detection sensitivity and measurement accuracy of acoustic wave by providing a microphone on one end and a transparent window on the other end of open end of pipe side wall which is prepared near the surface of the object to be measured and in which light for generating acoustic wave to the object passes through. CONSTITUTION:After laser light outputted from an Ar ion laser 1 is modulated at a frequency f and gathered by a lens 3, it enters the surface 6 to be measured through a quartz window 5 for incident laser light. Since the laser chopping frequency f coicides with natural oscillation f0 of columnar vibration of a metallic pipe 4, the sound generated on the surface 6 resonated, so that it can be detected highly sensitively. This signal is amplified by a preamplifier 8, measured by a lock-in amplifier 9, and processed by a computer 10. Because the acoustic wave generated from a sample is detected while the other end of the pipe 4 is not being brought into contact with the sample, the film thickness of large sample can be measured. Also, the detection sensitivity and measurement accuracy of the acoustic wave can be improved thanks to the resonant effect of the pipe 4. |
