3 May 2001 Sub-Doppler resolution molecular spectroscopy in the 1.66-μm region
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We constructed a widely tunable spectrometer with sub-Doppler resolution and high sensitivity in the 1.66-micrometer region using a Fabry-Perot cavity as an absorption cell and a low- power extended-cavity laser diode as a light source. The light electric field is enhanced at the antinodes of the standing wave in the cavity cell, which enabled observation of saturated absorption spectra of the molecular overtone bands even though their transition dipole moments are small. The spectrometer sensitivity was drastically enhanced using a frequency modulation technique. The attained sensitivity allowed us to reduce sample gas pressure, optical power, and modulation amplitude, which resulted in a resolution of 320 kHz. We applied the spectrometer to precise frequency measurements of the 2(nu) 3-band transitions of methane, and determined 66 frequency differences between them and two absolute frequencies with an accuracy of 40 and 600 kHz, respectively. We also recorded hyperfine-resolved spectrum of the 2(nu) 4 band of methyl iodide, which gave unambiguous assignments.
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Chikako Ishibashi, Chikako Ishibashi, Kotaro Suzumura, Kotaro Suzumura, Hiroyuki Sasada, Hiroyuki Sasada, "Sub-Doppler resolution molecular spectroscopy in the 1.66-μm region", Proc. SPIE 4269, Laser Frequency Stabilization, Standards, Measurement, and Applications, (3 May 2001); doi: 10.1117/12.424484; https://doi.org/10.1117/12.424484

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