TDLAS architecture for widely spaced wavelengths

A pitch head for widely spaced wavelength tunable diode laser absorption spectroscopy comprising:

• a housing configured to optically couple with a fiber bundle, the fiber bundle comprising distal ends of at least a first and second input fibers, wherein the first input fiber is a single mode fiber that carries laser light at a first wavelength and the second input fiber is a single-mode fiber that carries laser light at a second wavelength, wherein laser light of the first and second wavelengths cannot co-propagate in a single transverse mode with simultaneously high efficiency on a single-mode fiber;
• wherein the distal ends of at least the first and second input fibers are stripped of their respective coatings, and wherein a first fiber optic core of the first input fiber, and a second fiber optic core of the second input fiber are arranged with their claddings adjacent to each other forming a bundled configuration;
• and
• a transmitting optic configured to project respective beams of laser light from each of the at least first and second fiber optic cores, through a measurement zone;
• wherein the housing is oriented such that the respective beams reach a catch head located across the measurement zone a select distance from the housing.

A method for widely spaced wavelength tunable laser diode laser spectroscopy comprising:

• generating a first laser beam of a first wavelength;
• generating a second laser beam of a second wavelength;
• carrying the first laser beam on a first single-mode optical fiber and the second laser beam on a second single-mode optical fiber, wherein laser light of the first and second wavelengths cannot co-propagate in a single transverse mode with simultaneously high efficiency on a single-mode fiber;
• stripping distal ends of the first and second single-mode optical fiber of their respective coatings;
• arranging a first fiber optic core of the first single-mode optical fiber with its cladding adjacent to the cladding of a second fiber optic core of the second single-mode optical fiber forming a bundled configuration;
• forming a fiber bundle from the bundled configuration of the first and second fiber optic cores;
• transmitting, with a pitch head, respective beams of laser light, from each of the first and second fiber optic cores of the fiber bundle, through a measurement zone;
• receiving each respective beam at a catch head located across the measurement zone a select distance from the pitch head;
• detecting, at the catch head, an optical power of light in each of the first and second wavelengths;
• and
• determining a concentration of targeted species having an absorption line at the first and second wavelengths.