Gas cells for tunable diode laser absorption spectroscopy employing optical diffusers. Part 1: single and dual pass cells
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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.
KeywordsInterference Fringe Speckle Noise Laser Speckle Tunable Diode Laser Absorption Spectroscopy Wavelength Modulation Spectroscopy
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- 1.H.I. Schiff, G.I. Mackay, J. Bechara, in Air Monitoring by Spectroscopic Techniques, ed. by M.W. Sigrist (Wiley, New York, 1994), Chap. 5 Google Scholar
- 9.F. Capellani, G. Mellandrone, G. Restelli, in Monitoring of Gaseous Pollutants by Tunable Diode Lasers, ed. by R. Grisar, H. Preier, G. Schmidtke, G. Restelli (Kluwer Academic Publishers, London, 1987), pp. 51–60 Google Scholar
- 12.J. Hodgkinson, R.D. Pride, C. Tandy, D.G. Moodie, G. Stewart, in Applications of Optical Fiber Sensors, ed. by A.J. Rogers. Proc. SPIE, vol. 4074 (SPIE Press, Bellingham, 2000), pp. 90–98 Google Scholar
- 13.J. Chen, A. Hangauer, R. Strzoda, M.-C. Amann, Laser spectroscopic oxygen sensor using diffuse reflector based optical cell and advanced signal processing, accepted for publication. Appl. Phys. B (2010). doi: 10.107/s00340-010-3956-3 (this issue)
- 22.J.W. Goodman, in Laser Speckle and Related Phenomena, ed. by J.C. Dainty (Springer, Berlin, 1975), Chap. 2 Google Scholar
- 23.A.E. Ennos, in Laser Speckle and Related Phenomena, ed. by J.C. Dainty (Springer, Berlin, 1975), Chap. 6 Google Scholar