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Avancerede optiske metoder til måling af luftforurening i indeklima og udeluft “Upconversion detection for IR-spectroscopy of TCE and PCE detection”
Christian Pedersen Gruppeleder, DTU Fotonik
11. 05. 2015 2
• To map out the indoor climate at locations in the Copenhagen area.
• Investigate the potential of a new technology giving fast response and clarify potential sources and pathways of toxic gasses into building
• Todays technology relays on: “ATD-tubes” or “Orsa-tubes” – giving average concentrations over a 2 week period
• No simple approach exists for measurements of short time variationser
• No simple approach exists for leak detection
Motivation & background
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Expectations and perspective
• Real-time measurements of PCE and TCE
• Monitoring of changes in concentration (e.g. measurement per minute)
• Localization of leaks
• Measurements of many other gasses can be relavent in the future (e.g. PCB)
• Develop a fast reliable optical system for detection of PCE/TCE (in the range of 1 mg/m3
Target
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Mid-IR Wavelength
region: 2-15 µm
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Mid-IR: 2-15 µm is called the “fingerprint region”:
-Fundamental absorption bands of nearly all gasses
(NOX,CO2, CH4…., explosives)
-Chemical vibration bands of large molecules
- heat
Mid-IR Applications
Trichloroethylene
FOSS 29. 01. 2014 6 DTU Fotonik, Danmarks Tekniske Universitet
Origin of Mid-IR detector noise
Light emission from
room temperature “objects”
Planck radiation
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Upconversion
Upconversion detector
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A candle observed at 3 µm
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Detector benchmark A collaboration with Lund University
Cooled Indium-Antimonide detector
(Judson Technologies J10D)
First generation
upconversion detector
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x500
0.5 1 2 3 4 5 10 20 30
101
102
103
104
105
Acetylene concentration [ppm]
Dete
cte
d p
ho
tons (
VIS
)
Line integrated IR DFWM signal intensities
Fit to ax2
Acetylene measument at 3 µm using
Degenerate Four Wave Mixing
(collaboration with Lund University)
- 500 times improvement sensitivity compared to the cooled InSb detector deployed in the test
- Probe volume is appr. 10 mm^3 (!)
- Sensitivity= 0.5 ppm
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Concept and setup for TCE and PCE detection
Light source Multi-pass gas cell
Mixing laser Up-converter unit NIR camera
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Light souce
Multi-pass gas cell
Mixing laser
NIR camera
Up-converter unit
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Absorption spectra
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TCE spectrum measured at high concentrations
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TCE Measurements filled/empty cell at 944.3 cm-1
Measured absorbance in 36 m cell:
0.008 at 944.3 cm-1
Equivalent to a TCE concentration of:
0.31 ppm
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PCE measurement – 915 cm-1 (1400 µg/m3)
Average 1293 Concentration
1265
1297 0.196 ppm
Ratio 1.0238 1329 µg/m3
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PCE detection at 915.3 cm-1 - “dynamics”
Measured absorbance in 36 m cell:
0.557 at 915.3 cm-1
Equivalent to a PCE concentration of:
10.3 ppm
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Absorption on 1 % water vapor (example of “cross contamination”)
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Status & outlook • The absorption spectra of PCE
and TCE are well separated in
this spectral range.
• High concentrations of both PCE
and TCE can be measured with
short acquisition time.
• Addition work on noise/drift
reduction to facilitate averaging
-> improved signal to noise
• Cross contamination from e.g.
water or CO2 needs to be
removed for ppb measurements
using mathematical models.
• Make a compact robust system
for field test