Patent ID: 9244006
Filing Date: 2016-01-26
CPC Classification: G01N

Claim Text:
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.