Tdlas architecture for widely spaced wavelength

A method for measuring a concentration of at least one target species comprising:

• generating (i) a first laser beam having a first wavelength and (ii) a second laser beam having a second wavelength, the first wavelength and the second wavelength corresponding to respective absorption lines of the at least one target species;
• coupling (i) at a first proximal end of a first optical waveguide, the first laser beam into a first fundamental mode of the first optical waveguide, and (ii) at a second proximal end of a second optical waveguide, the second laser beam into a second fundamental mode of the second optical waveguide, wherein at a first distal end of the first optical waveguide and a second distal end of the second optical waveguide, a first optical axis of the first optical waveguide is parallel to a second optical axis of the second optical waveguide;
• transmitting, through a measurement zone that includes the at least one target species, a probe signal that includes (i) the first laser beam emitted from the first distal end and (ii) the second laser beam emitted from the second distal end;
• determining a first signal strength of the probe signal at the first wavelength and a second signal strength of the probe signal at the second wavelength;
• and
• determining, from the first signal strength and the second signal strength, a concentration of the at least one target species.