| 摘要 |
PURPOSE:To minimize variation of temperature in the optical path length, by causing changes in volume of an internal space filled with a fluid of a fluid sealing means and in the pressure associated with changes in the temperature of an optical path length adjusting member occupying a part thereof to vary refractive index of the fluid with changes in the pressure and temperature. CONSTITUTION:A fluid sealing means 2 contains two mirrors 1 which transmit light at a specified rate and are so arranged to be parallel and face other separated at a specified distance and seals a fluid therebetween. Light travels in the direction of the arrow along an optical axis 4, reflected repeatedly between two mirror 1 and, then, a part of the light coinciding with a resonance frequency transmits the mirrors. Here, the light occupies the volume of an optical path length adjusting member 3 with the thermal expansion modulus differing from the means 2 therewithin 2 without blocking reflected light. Then, the volume of the space filled with the fluid is changed by variations in the volume of the member with changes in the temperature to shift the pressure of the fluid. Changes in the optical path length associated with changes in the temperature caused with respect to refractive index of the fluid act to cancel changes in the temperature at a distance between the mirrors 1. |
