Absolute frequency measurement of a CO2/OsO4 stabilized laser at 28.8 THz

. A cw carbon dioxide laser operating on the 10 μm R(0) I transition (28.832 THz) was frequency stabilized by a servo lock to the saturated absorption dip of the Q(15) transition of 188 OsO 4 . The laser frequency was measured with a cesium-clock-based frequency chain. In addition, the absorption line frequencies Q(14) of 188 OsO 4 and sQ(4,3) of 15 NH 3 , were measured relative to the frequency of Q(15).