IrSens 2 RTD 2013 - Nano-Tera · Design consideration III: ... IrSens 2 RTD 2013 Our new design for...
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1 Empa, Laboratory for Air Pollution & Environmental Technology, Swiss Federal Laboratories for Materials Science and Technology, Switzerland 2 IRsweep GmbH, Switzerland 3 FHNW, Institute for Aerosol and Sensor Technology,University of Applied Sciences, Switzerland Cylindrical multipass reflection cells for optical trace gas sensing 1,2 1 3 1 Markus Mangold , Béla Tuzson , Herbert Looser , and Lukas Emmenegger Concept - single piece multipass reflection cell with cylindrical cell body Design consideration I: (p/q)-star polygon Design consideration III: respective mirror arrangement Design consideration II: Off-plane surface shape A star polygon is fully described by its number of spikes p and its density q. All (p/q) pairs with no common divisor describe a star that can be drawn in a single line. The optical path length through a gas sample is a decisive parameter in laser spectroscopy to achieve high instrumental sensitivity and analytical precision. Small absorption signals are usually compensated for by the use of multipass cells, the most widely known being those based on the design of White [1] or Herriott [2]. For more compact configurations, variations of a pair of cylindrical or astigmatic mirrors have been proposed [3,4]. Nevertheless, the footprint of such multipass cells generally ranges from about 0.2–1 m with volumes up to 5 L, which makes the optical cell often becoming the size-limiting element in laser spectroscopic trace gas analyzers. Concentric mirror arrangement: - d/r = 2. - beam focalized to center at every reflection. - non-ideal beam diverges. - sensitive to misalignment: Acknowledgements The authors would like to acknowledge the SNSF and NanoTera (www.nano-tera.ch) for financial support. IrSens 2 RTD 2013 Our new design for a compact multipass reflection cell for MIR laser spectroscopy combines the optical mirror with the cell body [5]. It consists of a single-piece, diamond turned cylinder. The cylinder has a single window serving as entrance and exit aperture. A light beam entering the cylinder propagates on a star-shaped pattern determined by the entrance angle. With proper design of the surface shape, the light beam is refocalized after each reflection. This leads to minimal aberration and reproducible propagation of the laser beam. The patented [6] absorption mask reduces interference fringes and enables highest accuracy trace gas analysis. φ p = 11 q = 5 p = 11 q = 4 p = 11 q = 3 Entrance angle φ = 90° · (1 - 2q/p) Spherical Surface with radius r r Cylindrical Surface: flat Parabolic Surface: 2 y = a·x y x y x While the circular surface shape in the in- plane direction is given by the cylindrical shape of the cell, the shape of the off- plane surface can be freely chosen. Spherical and parabolic surfaces are superior to a simple flat surface because they refocalize the beam after every reflection. d = 2r = 4f r f d = r = 2f r f Confocal mirror arrangement: - d/r = 1. - beam is in turns focalized and collimated. - non-ideal beam propagates stably. - tolerant towards misalignment: Design consideration IV: in-axis vs. off-axis illumination In a confocal, parabolic mirror arrangement, we can exploit the perfect focussing of a parabolic mirror under non-centric illumination to create off-axis illumination beam patterns. By this, we increase the distance between adjacent reflections and reduce the likelyhood of spill-over leading to interference fringes. transmission 0 1 beam deflection (deg) 0 0.2 -0.2 transmission 0 1 beam deflection (deg) 0 0.2 -0.2 Final design parameters: - r = 72 mm - p = 89 - q = 36 - φ = 17.19 deg - optical path = 1224 cm - parabolic mirror shape - confocal arrangement - off-axis illumination 1603.95 1604 1604.05 1604.1 1604.15 1604.2 0.996 0.997 0.998 0.999 1 1.001 transmission -1 wavenumber (cm ) 1.5 ppm HDO absorption 12 ppb NO 2 absorption Application: NO concentration measurements with parabolic, confocal cell 2 averaging time (s) Allan deviation (ppb) time (s) 0 200 400 600 800 1000 1200 1400 10 16 1 0.1 0.01 [NO ] (ppb) 2 1 10 100 1000 With the new cell design, we have peak-to-peak interference fringes of < 1‰. Using a low pass filter, they are reduced to below 0.2‰. In terms of NO measurements 2 this corresponds to a detection limit of < 200 ppt. [1] J. U. White, J. Opt. Soc. Am. 32, 285 (1942). [2] D. Herriott, H. Kogelnik, and R. Kompfner, Appl. Opt. 3, 523 (1964). [3] J. B. McManus, P. L. Kebabian, and M. S. Zahniser, Appl. Opt. 34, 3336 (1995). [4] J. A. Silver, Appl. Opt. 44, 6545 (2005). [5] B. Tuzson, M. Mangold, H. Looser, A. Manninen and L. Emmenegger, Opt. Lett. 38, 257 (2013). [6] M. Mangold, B. Tuzson and L. Emmenegger, Switzerland Patent 01884/12, (2012). References Original data Filtered data
Transcript of IrSens 2 RTD 2013 - Nano-Tera · Design consideration III: ... IrSens 2 RTD 2013 Our new design for...
1 Empa, Laboratory for Air Pollution & Environmental Technology, Swiss Federal Laboratories for Materials Science and Technology, Switzerland
2 IRsweep GmbH, Switzerland3 FHNW, Institute for Aerosol and Sensor Technology, University of Applied Sciences, Switzerland
Cylindrical multipass reflection cells for optical trace gas sensing1,2 1 3 1Markus Mangold , Béla Tuzson , Herbert Looser , and Lukas Emmenegger
Concept - single piece multipass reflection cell with cylindrical cell body
Design consideration I: (p/q)-star polygon
Design consideration III: respective mirror arrangement
Design consideration II: Off-plane surface shape
A star polygon is fully described by its number of spikes p and its density q. All (p/q) pairs with no common divisor describe a star that can be drawn in a single line.
The optical path length through a gas sample is a decisive parameter in laser spectroscopy to achieve high instrumental sensitivity and analytical precision. Small absorption signals are usually compensated for by the use of multipass cells, the most widely known being those based on the design of White [1] or Herriott [2]. For more compact configurations, variations of a pair of cylindrical or astigmatic mirrors have been proposed [3,4]. Nevertheless, the footprint of such multipass cells generally ranges from about 0.2–1 m with volumes up to 5 L, which makes the optical cell often becoming the size-limiting element in laser spectroscopic trace gas analyzers.
Concentric mirror arrangement:
- d/r = 2.- beam focalized to center at every reflection.- non-ideal beam diverges.- sensitive to misalignment:
Acknowledgements
The authors would like to acknowledge the SNSF and NanoTera (www.nano-tera.ch) for financial support.
IrSens 2 RTD 2013
Our new design for a compact multipass reflection cell for MIR laser spectroscopy combines the optical mirror with the cell body [5]. It consists of a single-piece, diamond turned cylinder. The cylinder has a single window serving as entrance and exit aperture. A light beam entering the cylinder propagates on a star-shaped pattern determined by the entrance angle. With proper design of the surface shape, the light beam is refocalized after each reflection. This leads to minimal aberration and reproducible propagation of the laser beam. The patented [6] absorption mask reduces interference fringes and enables highest accuracy trace gas analysis.
φ
p = 11q = 5
p = 11q = 4
p = 11q = 3
Entrance angle φ = 90° · (1 - 2q/p)
Spherical Surfacewith radius r
r
Cylindrical Surface:flat
Parabolic Surface:2
y = a·x
y
x
y
x
While the circular surface shape in the in-plane direction is given by the cylindrical shape of the cell, the shape of the off-plane surface can be freely chosen.
Spherical and parabolic surfaces are superior to a simple flat surface because they refocalize the beam after every reflection.
d = 2r = 4f
r
f
d = r = 2f
r
f
Confocal mirror arrangement:
- d/r = 1.- beam is in turns focalized and collimated.- non-ideal beam propagates stably.- tolerant towards misalignment:
Design consideration IV: in-axis vs. off-axis illumination
I n a con foca l , pa rabo l i c m i r ro r arrangement, we can exploit the perfect focussing of a parabolic mirror under non-centric illumination to create off-axis
illumination beam patterns. By this, we increase the distance between adjacent reflections and reduce the likelyhood of spill-over leading to interference fringes.
tra
nsm
issi
on
0
1
beam deflection (deg)0 0.2-0.2
tra
nsm
issi
on
0
1
beam deflection (deg)0 0.2-0.2
Final design parameters:- r = 72 mm- p = 89 - q = 36- φ = 17.19 deg- optical path = 1224 cm
- parabolic mirror shape- confocal arrangement- off-axis illumination
1603.95 1604 1604.05 1604.1 1604.15 1604.20.996
0.997
0.998
0.999
1
1.001
transm
issi
on
-1wavenumber (cm )
1.5 ppm HDO absorption
12 ppb NO 2
absorption
Application: NO concentration measurements with parabolic, confocal cell2
averaging time (s)
Alla
n d
evi
atio
n (
ppb)
time (s)0 200 400 600 800 1000 1200 1400
10
16
1
0.1
0.01
[NO
] (p
pb
)2
1 10 100 1000
With the new cell design, we have peak-to-peak interference fringes of < 1‰. Using a low pass filter, they are reduced to below 0.2‰. In terms of NO measurements 2
this corresponds to a detection limit of < 200 ppt.
[1] J. U. White, J. Opt. Soc. Am. 32, 285 (1942).[2] D. Herriott, H. Kogelnik, and R. Kompfner, Appl. Opt. 3, 523 (1964).[3] J. B. McManus, P. L. Kebabian, and M. S. Zahniser, Appl. Opt. 34, 3336 (1995).
[4] J. A. Silver, Appl. Opt. 44, 6545 (2005).[5] B. Tuzson, M. Mangold, H. Looser, A. Manninen and L. Emmenegger, Opt. Lett. 38, 257 (2013).[6] M. Mangold, B. Tuzson and L. Emmenegger, Switzerland Patent 01884/12, (2012).
References
Original dataFiltered data
