Herriott Cell - Herriott Cell - Trace Gas Monitor Product Description:

The Herriott cell Herriott cell trace gas monitor is a compact, pre aligned, and easy-to-use product from Mesa Photonics that can be set up in just a few minutes. Including the fiber collimator and detector, its structure is only 30 centimeters long, weighs only 400 grams, and has an optical path length of 6 meters. Simply connect the fiber optic of the laser to the collimator and the coaxial cable to the detector, and it will be ready to operate. No additional optical components or calibration are required. This unit is an ideal choice for outdoor open path measurement, including deployment on airborne drones. Mesa Photonics' Herriott cells have been successfully installed on battery powered drones as part of a NASA funded research project (contract NNX15CA09C).

A key advantage of Herriott cells is that due to the easy availability of high reflectivity mirrors, most of the raw laser power can reach the detector. The reflectivity of the gold-plated mirror in Mesa Photonics' Herriott cells is sufficiently high, with a reflection loss between 60% and 40% at wavelengths ranging from 1500 nm to 20 μ m. For most available lasers, especially ready-made near-infrared lasers, the noise far exceeds the limit of shot noise.

Herriott cells were initially developed by Herriott and Schulte at Bell Labs in the mid-1960s for use as optical delay lines [Applied Optics 4 883 (1965)].

The compact design and reentrant optical trajectory of Herriott cells are highly suitable for tunable diode laser absorption spectroscopy (TDLAS). The beam is refocused on each reflection to minimize divergence and allow for significant light transmission within small structures. In the design of Mesa Photonics, the laser beam passes through 34 times between two mirrors. Compared to White cells, Herriott cells are cheaper, easier to align, and most importantly, less likely to produce unwanted optical interference fringes.

TDLAS typically scans an independent gas absorption line using a single narrowband laser frequency. In order to achieve the highest selectivity, analysis is generally carried out under low pressure, at which point the absorption line will not widen due to pressure. This measurement method was proposed by Hinkley and Reid and has developed into a highly sensitive and commonly used monitoring technique for trace gases in the atmosphere.

Mesa Photonics' Herriott cells are designed for near-infrared wavelengths (~750 to 2600nm). Longer wavelength options are available. The shell of Herriott cells is made of 3D printed nylon and coated with epoxy resin to improve moisture resistance. The mirror is fixed in a commercial cage component secured by carbon fiber rods to maintain structural rigidity and lightweight.

Product features:

• Near infrared wavelength (~750 to 2600nm)
• Longer wavelengths are available for selection
• Stable structure and small volume
• Easy to operate and align
• High cost-effectiveness