Mars laser hygrometer

Christopher R. Webster; Gregory J. Flesch; Kamjou Mansour; Robert Haberle; Jill Bauman

doi:10.1364/AO.43.004436

Applied Optics
Vol. 43,
Issue 22,
pp. 4436-4445
(2004)
•https://doi.org/10.1364/AO.43.004436

Mars laser hygrometer

Christopher R. Webster, Gregory J. Flesch, Kamjou Mansour, Robert Haberle, and Jill Bauman

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Christopher R. Webster, Gregory J. Flesch, Kamjou Mansour, Robert Haberle, and Jill Bauman, "Mars laser hygrometer," Appl. Opt. 43, 4436-4445 (2004)

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Abstract

We have designed and built a miniature near-IR tunable diode laser (TDL) spectrometer for measuring in situ the water vapor mixing ratio either in the Martian atmosphere or thermally evolved from Martian soil or ice samples. The laser hygrometer uses a thermoelectrically cooled single-mode distributed-feedback TDL at 1.87 μm to scan over a selected vibration-rotation line of both H₂O and CO₂ near 5327.3 cm^-1. A working prototype that weighs only 230 g has been built and used to generate spectra whose analysis demonstrates precision sensitivities as fine as 1 part in 10⁶ by volume in 1 s or 0.1 part in 10⁶ in 10 s at Martian pressures and temperatures. Absolute uncertainties of ∼5% are calculated.

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Mirror spacing	55.28 mm
Radius of curvature	80.1624 mm
Focal length	40.0812 mm
Mirror diameter	25.400 mm
Mirror hole diameter	3.00 mm
Mirror edge thickness	3.81 mm
Mirror material	Zerodur
Surface coating	Gold on chrome, Al₂O₃ overcoat
Total path length	55.27 cm
Optical configuration	10-pass
Symmetry	C-3
Rotation angle (theta)	72 deg counterclockwise as viewed from laser
Spot pattern diameter, nominal	1.905 cm
Injection hole location: R-L centered	3.0 mm above mirror center
Vertical injection angle	(-)6.7898 deg (down)
Horizontal injection angle	(-)9.3067 deg (left)
Laser and detector spacing from injection hole, measured normal to back of mirror	3.1 cm
Laser to detector horizontal spacing	1.0155 cm
Laser detector vertical distance above injection hole	0.3691 cm

Entire Spectral Scan		Processed Spectral Scan
Component	Bytes	Component	Bytes
512 points (direct spectrum)	1024	5 points in the direct spectrum	10
512 points (2 f spectrum)	1024	5 points in the 2 f spectrum	10
		Indices of these 5 points	10
Pressure and temperature values	8	Pressure and temperature values	8
5-V sense line voltage	2	5-V sense line voltage	2
Total number of bytes	2058		40

Wavelength Region (μm)	Minimum-Detectable Volume Mixing Ratio Achieved (ppmv)
Wavelength Region (μm)	0.26-s Single Scan	10-s Average (38 scans)
1.37	1.6	1
1.87	0.5	0.1

Mirror spacing	55.28 mm
Radius of curvature	80.1624 mm
Focal length	40.0812 mm
Mirror diameter	25.400 mm
Mirror hole diameter	3.00 mm
Mirror edge thickness	3.81 mm
Mirror material	Zerodur
Surface coating	Gold on chrome, Al₂O₃ overcoat
Total path length	55.27 cm
Optical configuration	10-pass
Symmetry	C-3
Rotation angle (theta)	72 deg counterclockwise as viewed from laser
Spot pattern diameter, nominal	1.905 cm
Injection hole location: R-L centered	3.0 mm above mirror center
Vertical injection angle	(-)6.7898 deg (down)
Horizontal injection angle	(-)9.3067 deg (left)
Laser and detector spacing from injection hole, measured normal to back of mirror	3.1 cm
Laser to detector horizontal spacing	1.0155 cm
Laser detector vertical distance above injection hole	0.3691 cm

Entire Spectral Scan		Processed Spectral Scan
Component	Bytes	Component	Bytes
512 points (direct spectrum)	1024	5 points in the direct spectrum	10
512 points (2 f spectrum)	1024	5 points in the 2 f spectrum	10
		Indices of these 5 points	10
Pressure and temperature values	8	Pressure and temperature values	8
5-V sense line voltage	2	5-V sense line voltage	2
Total number of bytes	2058		40

Abstract

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Tables (3)

Applied Optics