Spectroscopic devices, systems, and methods for optical sensing of molecular species

A spectroscopic device for detecting one or more gas species of interest in a gas sample, the device comprising:

• a sensing unit that comprises:
• a light source module,
• a detector module, and
• a sample cell between the light source module and the detector module;
• wherein the light source module comprises a light source module housing and a light source that is configured to transmit an interrogation light beam along an optical path directed toward the detector module;
• wherein the detector module comprises a detector module housing, a detector, and a reference gas;
• said detector is in the detector module housing;
• wherein the detector is positioned in the optical path such that the optical path extends from the light source through the sample cell and the reference gas toward the detector.

A spectroscopic method for detecting one or more gas species of interest in a gas sample, the method comprising:

• transmitting an interrogation light beam from a coherent light source through a sample cell containing one or more gas species of interest to be detected, and a reference gas at below atmospheric pressure, said reference gas comprising at least one of the one or more gas species of interest to be detected in the sample cell;
• detecting the intensity of the light beam after passing through the reference cell and the sample cell;
• generating a direct absorption spectroscopy (DAS) signal based on the detected light intensity;
• generating a wavelength modulated spectroscopy (WMS) signal based on the detected light intensity;
• and
• generating calibration information by setting the direct absorption spectroscopy (DAS) signal as the constant reference signal for the wavelength modulated spectroscopy (WMS) signal.