Development of a Fiber-Optic Probe Hydrophone for a Cryogenic Liquid
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We report the progress of developing a fiber-optic probe hydrophone (FOPH) system applicable to the measurement of local density/pressure fluctuations in a cryogenic liquid. The measurement principle is based on a law of classical optics known as “Fresnel’s reflection loss.” We use this principle at the end-face of a single-mode optical fiber that is immersed in liquid helium. Since the refraction index of liquid 4He is a function of density, and the refraction index of the core of the optical fiber is constant, the pressure can be obtained by measuring the reflectivity. We have succeeded in measuring the temperature dependence of the static density, and we go on to discuss the possibility of application to acoustic pressure measurements.
KeywordsCryogenic sensor Hydrophone Local pressure probe Acoustics
We thank K. Tojo of Chuo University and R. Nomura of Tokyo Institute of Technology for fruitful discussions. We acknowledge support from a Grant-in-Aid for Young Scientists (B) (Grant No. 22740201 and 24740206) from The Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan.
- 7.M. Minnaert, Philos. Mag. A 16, 235 (1933) Google Scholar