Remote Sensing by Infrared Heterodyne Spectroscopy
Infrared heterodyne spectroscopy is a convenient technique for measuring atomic and molecular spectral lines with high sensitivity and specificity. The instrumental spectral resolving power can be made arbitrarily high although signal-to-noise considerations limit the maximum useful resolving powers (λ/∆λ) to ∽107 for passive sensing. Nevertheless, this provides the capability to resolve completely individual spectral lines, even when the line shapes are doppler-limited at temperature/molecular mass ratios as low as ∽2K/amu. Since the heterodyne process beats the source radiation against a laser local oscillator whose frequency is precisely known (typically to better than 1/107), the methodology provides very precise internal frequency calibration enabling great specificity in line identification and measurement of source motion.
KeywordsRemote Measurement Laboratory Source Remote Observation Laser Heterodyne Individual Spectral Line
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