Optical cavity-enhanced frequency comb spectroscopy

A method for determining a characteristic of a target gas in a fluid sample, the method comprising:

• causing a frequency comb illumination source to emit pulsed light comprising a plurality of frequency comb wavelengths,
• wherein the pulsed light is directed at an optical cavity comprising a plurality of cavity resonance modes, and
• wherein the fluid sample is disposed within the optical cavity;
• adjusting at least one of a physical characteristic of the optical cavity and a physical characteristic of the pulsed light to align a frequency comb wavelength of the plurality of frequency comb wavelengths with a cavity resonance mode of the plurality of cavity resonance modes,
• receiving, from a photodetector positioned to receive a transmitted light, an electrical signal proportional to an amplitude of the transmitted light,
• wherein the transmitted light passes through the fluid sample within the optical cavity;
• and
• determining a characteristic of the fluid sample based on the electrical signal.

A system for determining a concentration of a target gas within a fluid sample, the system comprising:

• a fluid sample intake, configured to receive the fluid sample into a fluid sample chamber;
• an optical cavity comprising a plurality of cavity resonance modes,
• wherein a portion of the fluid sample chamber is within the optical cavity;
• a frequency comb illumination source configured to emit pulsed light comprising a plurality of frequency comb wavelengths;
• a photodetector positioned to receive transmitted light passing through the portion of the fluid sample chamber within the optical cavity,
• wherein the photodetector is configured to generate an electrical signal proportional to an amplitude of the transmitted light;
• and
• a controller electrically connected to the photodetector,
• wherein a frequency comb wavelength of the plurality of frequency comb wavelengths is configured to align with a cavity resonance mode of the plurality of cavity resonance modes, and
• wherein the controller is configured to determine the concentration of the target gas within the fluid sample based on the electrical signal received from the photodetector.