High-sensitivity CW Fabry-Perot enhanced spectroscopy of CO2 and C2H2 using a 1064-nm Nd:YAG laser

We have investigated the weak absorption lines of CO2 (20(0)3 <-- 00(0)0) R(6), C2H2 (2100(0)1(1) <-- 0000(0)0(0)) R(12), and C2H2 (1200(0)3(1) <-- 0000(0)0(0)) P(6) near 1064 nm using CW cavity ring-down spectroscopy and CW cavity transmission. An effective interaction length of more than 30 km was achieved (cavity finesse approximate to 86000) and the sensitivity was approximate to 10(-8) cm(-1). Higher sensitivity of 3.3 x 10(-11) cm(-1)/root Hz was obtained by cavity-enhanced wavelength modulation spectroscopy. The absorption coefficients, pressure broadening coefficients, lineshapes, line strengths, and absolute wavelengths of those lines were determined, some of them for the first time. The measurements were carried out over a wide range of pressures from the strongly inhomogeneous to the strongly homogeneous region.