| 摘要 |
PROBLEM TO BE SOLVED: To make it possible to precisely control an oscillation wavelength of a laser beam source by forming a hole or a gap on the side of a diaphragm and forming the side opposing to the diaphragm side of the inner space airtight. SOLUTION: In the case of a microphone 15, a gap between respective parts is sealed so that perfect airtightness is preserved and, on the other hand, a pin hall 151c is provided in the center of a diaphragm 151 as a gas flow passage, a detection gas inside a cell 14 comes in and out of an inner space 152 of the microphone 15 by way of the pin hall 151c and the inner space 152 is made to preserve its pressure P1 to the same as a pressure P1 inside the cell 14. Thus, whatever pressure the pressure inside the cell 14 may be, the inner space 152 makes its pressure P1 the same as the inner pressure P1 of the cell 14 by leaving it for a while with the microphone 15 installed in the cell 14, the diaphragm 151 becomes expanded flatly and a sound pressureΔP inside the cell 14 can be measured.
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