Systems and methods for measuring trace contaminants in gas matrix using integrated cavity output spectroscopy

A laser absorption spectrometry system for gas measurement, comprising:

• an off-axis integrated cavity output spectroscopy (ICOS) assembly comprising:
• a gas cell comprising:
• a cell body defining an optical cavity;
• and
• an input mirror and an output mirror positioned in the optical cavity;
• a tunable diode laser configured to emit laser light coupled off-axis into the optical cavity;
• a collimator positioned in an optical path between the tunable diode laser and the gas cell, and optically coupled to the tunable diode laser through an optic fiber, wherein the collimator includes a reflective collimation mirror that reflects the laser light into parallel light, and wherein surfaces of the reflective collimation mirror and end surface of the optic fiber are positioned such that reflections from the input mirror are further reflected by the reflective collimation mirror away from the gas cell;
• and
• a detector arranged to measure laser light exiting the optical cavity;
• and
• an ICOS calibration computing device comprising at least one processor in communication with at least one memory device, and the at least one processor programmed to:
• determine a parameter of the ICOS assembly based on at least one of data collected by the detector or simulation data to reduce etalons caused by the laser light being reflected back and forth between surfaces in the off-axis ICOS assembly.

A laser absorption spectrometry system for gas measurement, comprising:

• an off-axis integrated cavity output spectroscopy (ICOS) assembly comprising:
• a gas cell comprising:
• a cell body defining an optical cavity;
• and
• an input mirror and an output mirror positioned in the optical cavity;
• a tunable diode laser configured to emit laser light coupled off-axis into the optical cavity;
• and
• a collimator positioned in an optical path between the tunable diode laser and the gas cell, and optically coupled to the tunable diode laser through an optic fiber, wherein the collimator includes a reflective collimation mirror that reflects the laser light into parallel light, and wherein surfaces of the reflective collimation mirror and end surface of the optic fiber are positioned such that reflections from the input mirror are further reflected by the reflective collimation mirror away from the gas cell;
• wherein one or more parameters of the off-axis ICOS assembly are optimized to reduce noise from etalons, wherein when light travels back and forth between parallel surfaces and/or quasi-parallel surfaces in the optical path, the light and its reflections interfere with one another and cause the etalons, the etalons introducing the noise in absorption spectra of the light by gasses in the gas cell.