Precision Heterodyne Calibration
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The frequencies of 12C18O2, 13C16O2 and 13C18O2 isotope lasers have been measured to better than 3 MHz (0.0001 cm−1) by comparison with a 12C16O2 reference laser. Heterodyne techniques were used to generate 139 difference frequencies in a liquid-nitrogen cooled HgCdTe photodiode. Microwave frequency counter measurements of the difference frequencies were then used to calculate new values for the band centers and rotational constants of the rare isotopes. It is shown that an additional thousandfold improvement in accuracy and a greatly extended spectral range can be readily achieved.
KeywordsDifference Frequency Rotational Constant Band Center Noise Bandwidth Saturation Resonance
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