Extension of absolute frequency measurements to 148 THz: Frequencies of the 2.0- and 3.5-μm Xe laser

Absolute infrared frequency measurement has been extended to 148 THz (the highest frequency ever directly measured) with measurement of the two strong cw laser lines of Xe. The frequencies were synthesized with stabilized CO2 and 3.39-μm He-Ne lasers and mixed on a W-Ni point-contact diode. The measured frequencies are νXe(2.0μm)=147.915 850(15) THz and νXe(3.5μm)=85.459 997(3) THz.