Gas cells for tunable diode laser absorption spectroscopy employing optical diffusers. Part 1: single and dual pass cells |
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Authors: | J Hodgkinson D Masiyano R P Tatam |
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Institution: | 1. Engineering Photonics Group, School of Engineering, Cranfield University, Bedfordshire, MK43 0AL, UK 2. Two Trees Photonics, Garamonde Drive, Wymbush, Milton Keynes, MK8 8LW, UK
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Abstract: | New designs for gas cells are presented that incorporate transmissive or reflective optical diffusers. These components offer
simple alignment and can disrupt the formation of optical etalons. We analyse the performance–limiting effects in these cells
of random laser speckle (both objective and subjective speckle), interferometric speckle and self-mixing interference, and
show how designs can be optimised. A simple, single pass transmissive gas cell has been studied using wavelength modulation
spectroscopy to measure methane at 1651 nm. We have demonstrated a short-term noise equivalent absorbance (NEA, 1σ) of 2×10−5, but longer term drift of up to 3×10−4 over 22 hours. |
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