Abstract: A method of gas detection comprises emitting radiation of different wavelengths across the absorption spectrum of a gas towards a target area; and analysing the spectrum of returned laser light from the target area to identify the gas in the target area using the time correlation of the emitted radiation and the returning radiation. The radiation is modulated using respective orthogonal modulation codes for the different wavelengths and the modulation codes are modified by the insertion of a gap between each bit of the modulation code, the gap having a duration of at least n-1 bits where n is the number of different wavelengths.

Abstract: A method of operating an optical device, the method comprising tuning a first emission wavelength of a first output radiation of a laser device continuously within a first wavelength spectrum by modulating a drive current thereof with a first drive current modulation having a frequency of at least 100 kHz. The first wavelength spectrum comprises a first spectral feature associated with at least part of a gas absorption spectrum of at least one gas. The method comprises the steps of modulating the first output radiation of the laser device with a first output modulation, the first output modulation comprising a first plurality of binary pulses, scanning the first wavelength spectrum at a rate of at least 1 ?m per second, projecting the first output radiation towards a first target area, receiving scattered radiation from the first target area, and processing the scattered radiation.