1. Field of Endeavor
The present application relates to gas spectroscopy and more particularly to a fiber optic coupled multipass gas minicell.
2. State of Technology
This section provides background information related to the present disclosure which is not necessarily prior art.
U.S. Pat. No. 8,309,929 for tunable photonic cavities for in-situ spectroscopic trace gas detection includes the following information: “Gas analysis is conventionally performed using laboratory analytical techniques, e.g., gas chromatography or mass spectrometry (GC-MS), which do not satisfy current device and material constraints for unattended, flexible ground sensors, or for lightweight, highly sensitive systems for avionic operations. Absorption spectroscopy is a powerful alternative approach for gas in-field detection and identification, and several interesting techniques have been developed including tunable diode laser absorption spectroscopy (TDLAS). Typically, this occurs in the infrared (IR) region of the spectrum. Recently, micromechanically tunable vertical-cavity surface-emitting lasers (VCSELs) have been implemented in such fashion for near infrared (NIR) spectroscopy. Unfortunately, many existing TDLAS systems exhibit drawbacks that limit their deployment, including the need for cryogenic cooling, a requirement for a bulky multipass cell, or a long hollow or porous fiber with a relatively slow time response.”
Tunable Absorption Spectroscopy is a common technique for gas detection and simply provides the chemical fingerprint of components by the absorption of the light at the wavelengths which resonate with the molecules inducing vibrations and rotations. By simply shining light through a volumetric gas sample on a detector, when the wavelengths is right, quench will occur and a dip in the power will be recorded at the detector.
In order to improve sensitivity various approaches are taken, from increasing the number of passes of light through the volume (thus increasing the absorption in discrete defined spaces) to implementing modulation techniques to remove background and noise.
Applicants have developed an extremely small and robust cell in which a very small volumes of gas is sampled while maintaining high sensitivity and specificity by combining it with highly tunable VCSELs (to provide various absorption lines of one specie and capture varies elements at once) and wavelength modulation spectroscopy (to extract high harmonics which are not affected by the 1/f noise).