Toward an accurate frequency standard at 1.5 μm based on the acetylene overtone band transition

• Published in: IEEE transactions on instrumentation and measurement 1999-04, Vol.48 (2), p.563-566
• Main Authors: Onae, A., Okumura, K., Yoda, J., Nakagawa, K., Yamaguchi, A., Kourogi, M., Imai, K., Widiyatomoko, B.
• Format: Article
• Language: English
• Subjects: Acetylene; Frequency standards; Holes; Instrumentation; Lasers; Spacers; Spectral lines; Windows (intervals)
• ISSN: 0018-9456
• DOI: 10.1109/19.769658

We have made a frequency standard operating at the 1.5 mu m region using the saturated absorption of the v sub(1)+v sub(3) band of super(13)C sub(2)H sub(2 ). To enhance the moderate power from a laser diode and to saturate a very weak molecular overtone transition, we used a Fabry-Perot (FP) cavity and inside of it we put an acetylene cell. In order to obtain a longer life time for the cell, we designed a new scheme consisting of a cavity with a ULE (ultralow expansion) glass spacer and a baked and sealed-off cell with Brewster windows. We observed the saturated spectrum having a 1 MHz spectral linewidth. The signal obtained using the same cell ten months later had the same signal-to-noise ratio (SNR) and spectral linewidth. We made two versions of the frequency standard and observed a beat note between these two lasers from which we derived the frequency stability, in terms of the square root of the Allan variance sigma ( tau )=2.410 super(-13) at an integration time tau =1000 s