Some new FIR laser lines of optically pumped12CH316OH,12CH316OD, and12CH3I,12CH3Br,12CD2Cl2absorption spectroscopy of water and acetonitrile

The wavelength, polarization, and output power of several lines of the optically pumped CW FIR
¹²
CH
3
¹⁶
OH (methanol) and
¹²
CH
3
¹⁶
OD (1-D deuterated methanol), methyl iodide, methyl bromide, and deuterated methylene chloride lasers have been determined. In addition to lines already reported in the literature, seven strong lines have been observed. Optimum performance of the laser system is achieved by means of an improved coupling of the CO
2
pump power into the resonator and extraction of the FIR power from the resonator. Measurements on the power absorption coefficient of water using the laser indicate that
\alpha(\bar{\nu})
rises to almost 1100 Np ċ cm
^-1
at 170 cm
^-1
, and then shows a gradual fall with an increase in frequency. A strong temperature dependence of the 200 cm
^-1
peak in
\alpha(\bar{\nu})
is predicted, with a decrease in the frequency of maximum power absorption coefficient with an increase in temperature. The range of measurements for acetonitrile is extended to lower frequencies so as to overlap with those determined from other millimeter wave techniques. For highly power-absorbing liquids,
\alpha(\bar{\nu})
is estimated to be within ± 5 percent.