Tunable laser gas monitoring uses tunable lasers to detect gases based on their unique absorption spectra. It provides very high sensitivity down to ppt levels without interference from other gases. Measurements are absolute without drift or calibration needed. Real-time monitoring at 10 Hz or faster is possible with very low maintenance as the system does not wear out. Reducing the sample pressure allows more specific measurements of target gases even in mixtures and enhances stability without requiring gas drying.

1. © TDL Sensors Ltd 2012
Tunable Laser Gas Monitoring

2. © TDL Sensors Ltd 2012
 Very high sensitivity - ppt, ppb, ppm concentrations
 Measure the gas you want without interference from other gases
 Large dynamic range - 5 orders of magnitude
 Absolute measurements
– no drift, no calibration, inherently linear
 Real-time (10 Hz or faster response)
 Very low maintenance
 Does not wear out
Advantages of laser based gas analysers:
Tunable Laser Gas Monitoring

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Based upon high-resolution
laser spectroscopy
Tunable Laser Gas Monitoring

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Tunable Laser Gas Monitoring
Mid IRNear IRUV-Vis Visible

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0.7-2.7 µm
Laser diodes, VCSELs
3-5 µm 4.2->12 µm
DFGs
QCLs
Tunable Laser Gas Monitoring
We use the IR spectral
region for gas
measurements
Tunable lasers available
within this region

6. © TDL Sensors Ltd 2012
Tunable Laser Gas Monitoring
NIR Mid-IR
Each gas
absorbs light in
a characteristic
way.
Hydrogen Fluoride (HF)
Carbon Dioxide (CO2)Nitric Oxide (NO)Ammonia (NH3)Carbon Monoxide (CO)Methane (CH4)Water (H2O)
This means that each gas has a unique spectrum or “fingerprint”.

7. © TDL Sensors Ltd 2012
Tunable Laser Gas Monitoring
Tunable
laser
Photodetector
I0
Beer - Lambert Law:
 L
I
I
T )(exp)(
0
 






Absorption
coefficient
PathlengthTransmission

I
I0
Laser frequency tuned
I
Transmission
Signal out
Gas
Gas in Gas out
Measurement cell
L

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Laser wavelength is tuned rapidly – no photodetector filters
Spectra are recorded 1000s of times per second
Not affected by particulate attenuation or changes in mirror
reflectivity
Full spectrum analysis performed
Powerful pattern recognition signal processing methods used
Absolute concentration measured – no drifting like other
techniques
Tunable Laser Gas Monitoring

9. © TDL Sensors Ltd 2012
Full spectrum analysis performed
Powerful pattern recognition signal processing methods used
Absolute concentration measured – no drifting like other
techniques
Tunable Laser Gas Monitoring

10. © TDL Sensors Ltd 2012
Tunable Laser Gas Monitoring
Extractive gas analyser multipass optical cell

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Very long pathlengths can be
achieved using a laser
- 7.6 m standard
- 70 m enhanced

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Sample gas stream is often measured at
atmospheric pressure
However, TDL can also measure at
reduced sample pressure

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Advantage of measuring at reduced
sample pressure

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Reduced sample pressure advantages
• Very specific measurement(s)
• Multi-gas measurements with one laser
• Enhanced stability
• No liquid phase water
• No gas sample stream drying required

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Example:
HCl 1 ppm
H2O 30 % Vol
emissions from a stack
Reduced sample pressure advantages

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1010 mbarA
Pathlength = 760 cm, Temperature = 360 K
Reduced sample pressure advantages
-20 -10 0 +10

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Peak widths narrow
Reduced sample pressure advantages
-20 -10 0 +10
100 mbarA
Pathlength = 760 cm, Temperature = 360 K

18. © TDL Sensors Ltd 2012
Reduced sample pressure advantages
-20 -10 0 +10
1010 mbarA
Pathlength = 760 cm, Temperature = 360 K

19. © TDL Sensors Ltd 2012
Reduced sample pressure advantages
-20 -10 0 +10
100 mbarA
Pathlength = 760 cm, Temperature = 360 K

20. © TDL Sensors Ltd 2012
Reduced sample pressure advantages
-2 -1 0 +1 +2
1010 mbarA
Pathlength = 760 cm, Temperature = 360 K

21. © TDL Sensors Ltd 2012
Isolated HCl peak
- even in the
presence of high
humidity
-2 -1 0 +1 +2
100 mbarA
Reduced sample pressure advantages
Pathlength = 760 cm, Temperature = 360 K

22. © TDL Sensors Ltd 2012
Isolated HCl peak
Can also access H2O peaks to
report dry gas conc
Reduced sample pressure advantages
-2 -1 0 +1 +2
100 mbarA
Pathlength = 760 cm, Temperature = 360 K

23. © TDL Sensors Ltd 2012

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Technology
Contact
TDL Sensors Ltd
48 Grafton Street
Manchester M13 9XX
United Kingdom
Tel: +44 (0)161 606 7289
info@tdlsensors.co.uk
www.tdlsensors.co.uk