Detecting species in a dilute medium

摘要

Method and apparatus for detecting a species in a dilute medium, the species having a spectral feature, the apparatus comprising: a beam source arranged to generate a first laser beam and a second laser beam coherent with each other, and having a matching chirp pattern. Beam guide arranged to pass at least the first laser beam through the dilute medium; a beam mixer arranged to mix the first and the second laser beams to form a mixed beam. Detector arranged to detect, during the chirp pattern, the mixed beam and to measure changes in the mixed beam caused by refractive index variations in the dilute medium across a spectral feature. Output providing a signal that changes in response to the measured changes.

主权项

1. A method of detecting a species in a dilute medium comprising:
providing a first laser beam and a second laser beam coherent with each other, and having a matching chirp pattern; passing at least the first laser beam through the dilute medium, whilst the chirp pattern of the first laser beam crosses at least a part of a spectral feature of the species; mixing the first and the second laser beams to form a mixed beam; detecting the mixed beam to form an output signal during the chirp pattern; processing the output signal to measure changes in the mixed beam caused by refractive index variations in the dilute medium across the spectral feature; determining a measure of the species from the changes in the measured properties; and the method further comprising applying an optical frequency shift to the first or second laser beam before mixing the first and the second laser beams.