Saturation Spectroscopy with the NH3 Laser
The NH3 laser, optically pumped by CO2 laser radiation at 9.2 μm, operates at 12.08 μm wavelength and has been demonstrated to be capable of a short term frequency stability of a few hundred Hertz . Since the laser radiation is strongly absorbed in NH3 one could gain additional long term stability by locking the laser to a saturated absorption dip in NH3. The precision of the lock would be considerably improved if the 3 hyperfine structure components of the 12 μm sP(7,0) transition could be resolved. However, using the present published value for the upper state quadrupole coupling constant (eqQ)v 2 = 1,a  the calculated separation of these components was uncertain by ≥ 100 kHz.