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Tunable Diode Laser Absorption Spectroscopy


Tunable Diode Laser Absorption Spectroscopy

What is TDLAS?

TDLAS exploits the rotational vibrational absorption features of gases for laser-based trace gas detection. Sometimes, it is referred to as TDLS, TLS, TLAS or (with a reference) even as TDLARS.

Basics of Tunable Diode Laser Absorption Spectroscopy

Key Features & Technology

Key Features

TDLAS is a very strong tool for highly selective and sensitive measurements. It enables:

  • sensitive detection of ppm to ppb (or even ppt!) level concentrations
  • in situ measurements
  • contactless techniques
  • operation at or above room temperature
  • measurement of sticky gases
  • portable gas detectors

TDLAS Technology

TDLAS is one of the most sensitive, selective and robust technologies for trace gas monitoring. It is based on the Lambert-Beer law which states a logarithmic relation between the

  • transmission of light through a gas
  • product of the attenuation coefficient of the gas
  • distance the light travels through the gas

When a gas has an absorption feature at a specific wavelength, the transmitted intensity declines exponentially with:

I(ν,t) = I0(ν) e-S(T) g(ν,ν0) n L

With n being the number density of the molecular absorbers, I0(ν) the initial laser intensity and I(ν,t) the intensity detected after the probe with an absorption length L.

The absorption line profile is characterized by the temperature-dependent, spectrally integrated line strength S(T), and the normalized (area=1) shape function g(ν,ν0), which is centered at the wavelength ν0.

(Source: #47 High-speed tunable diode laser absorption spectroscopy for sampling-free in-cylinder water vapor concentration measurements in an optical IC engine;
O. Witzel, A. Klein, S. Wagner, C. Meffert, C. Schulz, V. Ebert, Appl. Phys. B, 109, 3, Nov. 2012, pp. 521-532.)

Compared to other highly sensitive technologies, such as gas chromatography TDLAS instruments show

  • high selectivity
  • low cost of ownership
  • fail-safe operation

Types of TDLAS

TDLAS is carried out in form of e. g.:

  • direct absorption spectroscopy
  • 2f spectroscopy
  • cavity enhanced spectroscopy (CRDS)
  • light detection and ranging techniques (LIDAR)
  • photo acoustic spectroscopy (PAS)
Standard TDLAS setup

A standard TDLAS setup consists of:

  • a wavelength tuning DFB laser; emitting monochromatic light at the absorption line of the trace gas
  • an optical lens to collimate the laser light
  • a gas sample cell; in this case filled with H2O
  • a photo detector on which the laser light is focused; measuring the transmission
Find the perfect wavelength

Your setup

Select your target wavelength

Selecting a suitable absorption line for the TDLAS application is the principal challenge before designing the measurement setup. The outcome of the measurements is highly influenced by the strength of the absorption line as well as by interferences from other gases and the setup itself.

In our Applications by Gas section, we present the most commonly used target wavelengths for major industrial gases.


Applications & Papers

Papers & Links
H2O & O2
Monitoring of gas in the lungs and intestines of newborn infants: H2O and O2

Child mortality is high among preterm newborn infants. They are often affected by free gas in lungs and intestines, which may lead to the breakdown of vital organs. The current diagnosis is based on X-ray radiography. According to a study a bed-side, rapid, non-intrusive, and gas-specific technique for in vivo gas sensing would improve diagnosis and enhance the babies' chance of survival. The detection method is based on laser spectroscopy

[ 51 ]
Monitoring of breath gas: NH3

Ammonium is used as a biomarker for helicobacter pylori infections. These infections are responsible for stomach ulcers. Breath analysis diagnoses the disease in a non-invasive way sparing patients a disagreeable gastroscopy.

[ 63 ]
Early fire detection: CO

Early fire detection technologies rely on highly sensitive detection of carbon monoxide. Coal-fired power plants, steel mills or biomass deposits use these smoke detectors to increase process and workers safety.

Emission control: NOx

NH3 is added in combustion processes to reduce emissions of the flue gas NOx. The two compounds will react to uncritical N2 and H2O. To avoid any corrosive or environmental effects from overuse, the gas volume needs to be continuously monitored.

[ 178 , 117 , 116 , 72 , 3 ]
Emission control of greenhouse gases: CO2

Environmental policies have been implemented worldwide to reduce greenhouse gas emissions. According to the United States Environmental Protection Agency, human activities account for more than three quarters of CO2 emissions. They are mainly due to the combustion of fossil fuels for energy generation, transportation and industry. Remote sensing technologies have been introduced to quantify CO2 and CO emissions in atmosphere.

[ 178 , 115 , 105 , 93 ]
Control of hazardous gases: H2S

H2S occurs as a corrosive, toxic and explosive side product in the petrochemical industry. Continuous monitoring of this hazardous compound is critical to avoid corrosion of natural gas pipelines and ensure workers safety. Real-time analysis is essential to guarantee that burning fuels are H2S clean in order to prevent acid rains.

[ 76 , 69 , 3 ]
Quality control in natural gas pipelines: CO2

CO2 is a natural diluent in oil and gas deposits. When it reacts with H2S and H2O steel pipelines corrode. Real-time monitoring of CO2 at natural gas custody transfer points is necessary to avoid contaminated gas from flowing downstream. Immediate measures may be taken to purify the natural gas.

[ 115 ]
Quality control in natural gas pipelines: H2O

Water vapour measurement is critical for gas companies to meet quality specifications and to protect pipelines from corrosion. False positives are very costly. Often the gas cannot be delivered if it is "wet".

Combustion control in high temperature processes: H2O

Water vapour is often examined in combustion and propulsion processes as it is a primary product of hydrogen and hydrocarbon fuels.

[ 154 , 153 , 121 , 120 , 70 , 65 , 28 , 17 , 16 , 15 ]
CO2 & CH4
Combustion control in high temperature processes: CO2 and CH4

Continuous monitoring of contents like CO2 or CH4 concentrations is essential for the efficiency of high-temperature processes in e. g. incinerators, furnaces or petrochemical refineries. Managing the CO2 content in combustion processes simultaneously reduces greenhouse gas emissions. This is also relevant for energy generating industries like coal burning power plants.

[ 154 , 124 , 121 , 115 , 112 , 111 , 96 , 94 , 62 , 45 , 40 , 35 , 12 ]
Process Control: C2H2

Acetylene is a by-product in the cracking process of ethylene production. The petrochemical industry minimizes the compound via hydrogenation. This process enhances the purity and quality of the manufactured ethylene.

[ 7 , 2 ]
Papers & Links
# 3 Gas monitoring in the process industry using diode laser spectroscopy
I. Linnerud, P. Kaspersen, T. Jaeger, Appl. Phys. B, 67, 1998, pp. 297-305,
# 10 Continuous wave, distributed feedback diode laser based sensor for trace-gas detection of ethane
K. Krzempek, R. Lewicki, L. Naehle, M. Fischer, J. Koeth, S. Belahsene, Y. Rouillard, L. Worschech, F.K. Tittel , Appl. Phys. B , 106, 2, 2012, pp 251-255.,
# 15 Scanned-wavelength-modulation spectroscopy near 2.5 µm for H2O and temperature in a hydrocarbon-fueled scramjet combustor
C. S. Goldenstein, I. A. Schultz, R. M. Spearrin, J. B. Jeffries, R.K. Hanson, Appl. Phys. B,, 116, 3, September 2014, pp 717-727.,
# 16 Diode laser measurements of linestrength and temperature-dependent lineshape parameters of H2O-, CO2-, and N2-perturbed H2O transitions near 2474 and 2482 nm
C.S. Goldenstein, J.B. Jeffries, R.K. Hanson, Journal of Quantitative Spectr. & Radiative Transfer, 130, 2013, pp. 100–111.,
# 17 Wavelength-modulation spectroscopy near 2.5 µm for H2O and temperature in high-pressure and -temperature gases
C.S. Goldenstein, R.M. Spearrin, J.B. Jeffries, R.K. Hanson, Appl. Phys. B, 116, 3, September 2014, pp 705-716.,
# 28 In situ combustion measurements of H2O and temperature near 2.5 µm using tunable diode laser absorption
A. Farooq, J.B Jeffries, R.K Hanson, Meas. Sci. Technol., 19, 2008, 075604, pp. 11.,
# 32 Single-frequency Sb-based distributed-feedback lasers emitting at 2.3 µm above room temperature for application in tunable diode laser absorption spectroscopy
A. Salhi, D. Barat, D. Romanini, Y. Rouillard, A. Ouvrard, R. Werner, J. Seufert, J. Koeth, A. Vicet, A. Garnache, Appl. Opt., 45, 20, pp. 4957-4965,
# 35 TDLAS-based sensors for in situ measurement of syngas composition in a pressurized, oxygen-blown, entrained flow coal gasifier
R. Sur, K. Sun, J.B. Jeffries, R.K. Hanson, R.J. Pummill, T. Waind, D.R. Wagner, K.J. Whitty, 2014, Appl. Phys. B, 116, 1, 2014, pp. 33-42,
# 43 Chemical analysis of surgical smoke by infrared laser spectroscopy
Michele Gianella, Markus W. Sigrist , Appl. Phys. B, 109, 3, November 2012, pp. 485-496.,
# 46 TDLAS-based open-path laser hygrometer using simple reflective foils as scattering targets;
A. Seidel, S. Wagner, V. Ebert, Appl. Phys. B, 109, 3, November 2012, pp. 497-504.,
# 47 High-speed tunable diode laser absorption spectroscopy for sampling-free in-cylinder water vapor concentration measurements in an optical IC engine;
O. Witzel, A. Klein, S. Wagner, C. Meffert, C. Schulz, V. Ebert, Appl. Phys. B, 109, 3, November 2012, pp. 521-532.,
# 48 Absolute, spatially resolved, in situ CO profiles in atmospheric laminar counter-flow diffusion flames using 2.3 µm TDLAS
S. Wagner, M. Klein, T. Kathrotia, U. Riedel, T. Kissel, A. Dreizler, V. Ebert , Appl. Phys. B, 109, 3, November 2012, pp. 533-540.,
# 52 Antireflection-coated blue GaN laser diodes in an external cavity and Doppler-free indium absorption spectroscopy
L. Hildebrandt, R. Knispel, S. Stry, J.R. Sacher, F. Schael , Appl. Opt., 42, No. 12, 2003, pp. 2110-2118.,
# 56 Widely tunable quantum cascade lasers with coupled cavities for gas detection
P. Fuchs, J. Seufert, J. Koeth, J. Semmel, S. Hoefling, L. Worschech, A. Forchel, App. Phys. Lett., 97, 2010, 181111,
# 62 High-sensitivity interference-free diagnostic for measurement of methane in shock tubes
R. Sur, S. Wang, K. Sun, D. F. Davidson, J. B. Jeffries, R. K. Hanson, Journal of Quantitative Spectroscopy and Radiative Transfer, Vol. 156, May 2015, pp. 80-87,
# 65 H2O temperature sensor for low-pressure flames using tunable Diode laser Absorption near 2.9 µm
S. Li, A. Farooq, R.K. Hanson, Meas. Sci. Technol., 22, 2011, pp. 125301-125311.,
# 67 New Opportunities in Mid-Infrared Emission Control
P. Geiser, Sensors, 2015, pp. 22724-22736.,
# 68 Field laser applications in industry and research
F. D'Amato, A. Fried, App. Phys. B, 119, 2015, pp. 1-2.,
# 69 A quartz-enhanced photoacoustic sensor for H2S trace-gas detection at 2.6µm
S. Viciani, M. Siciliani de Cumis, S. Borri, P. Patimisco, A. Sampaolo, G. Scamarcio, P. De Natale, F. D'Amato, V. Spagnolo, App. Phys. B, 119, 2015, pp. 21-27,
# 70 In situ H2O and temperature detection close to burning biomass pellets using calibration-free wavelength modulation spectroscopy
Z. Qu, F.M. Schmidt, App. Phys. B, 119, 2015, pp. 45-53.,
# 71 Novel utilisation of a circular multi-reflection cell applied to materials ageing experiments
D.A. Knox, A.K. King, E.D. McNaghten, S.J. Brooks, P.A. Martin, S.M. Pimblott , App. Phys. B, 119, 2015, pp. 55-64.,
# 72 TDLAS-based NH3 mole fraction measurement for exhaust diagnostics during selective catalytic reduction using a fiber-coupled 2.2-µm DFB Diode laser
F. Stritzke, O. Diemel, S. Wagner , App. Phys. B, 119, 2015, pp. 143-152.,
# 73 Time-multiplexed open-path TDLAS spectrometer for dynamic, sampling-free, Interstitial H218O and H216O vapor detection in ice clouds
B. Kuehnreich, S. Wagner, J.C. Habig, O. Moehler, H. Saathoff, V. Ebert , App. Phys. B, 119, 2015, pp. 177-187.,
# 78 Ppb-level formaldehyde detection using a CW room-temperature interband cascade laser and a miniature dense pattern multipass gas cell
L. Dong,Y. Yu,.C. Li, S. So, F. Tittel, Optics Express, Vol. 23, Issue 15, 2015, pp. 19821-19830.,
# 84 Optical gas sensing: a review
J. Hodgkinson, R. P. Tatam, Measurement Science and Technology, Vol.24, No.1, 2013,
# 85 Frequency modulation characteristics for interband cascade lasers emitting at 3 µm
J. Li, Z. Du, Y. An, Appl. Phys. B, 2015, 121:7–17.,
# 87 Optical‑feedback cavity‑enhanced absorption spectroscopy with an interband cascade laser: application to SO2 trace analysis
L. Richard, I. Ventrillard, G. Chau, K. Jaulin, E. Kerstel, D. Romanini , Appl. Phys. B, 2016, 122:247.,
# 90 Optical feedback cavity-enhanced absorption spectroscopy with a 3.24 µm interband cascade laser
K. M. Manfred, G. A. D. Ritchie, N. Lang, J. Roepcke, J. H. van Helden , Appl. Phys. Lett. 106, 2015, 221106.,
# 93 Interband cascade laser-based optical transfer standard for atmospheric carbon monoxide measurements
J. A. Nwaboh, Z. Qu, O. Werhahn and V. Ebert , App. Optics, Vol. 56, No.11, 10. April 2017, pp. E84-E93.,
# 94 Compact optical probe for flame temperature and carbon dioxide using interband cascade laser absorption near 4.2 μm
J. J. Girard, R. M. Spearrin, C. S. Goldenstein, R. K. Hanson, Elsevier , Combustion and Flame, Vol.178, April 2017, pp. 158 – 167.,
# 96 Fiber-coupled 2.7 μm laser absorption sensor for CO2 in harsh combustion environments
R. M. Spearrin, C. S. Goldenstein, J. B. Jeffries and R. K. Hanson, Meas. , Sci. Technol., 24.April.2013, 055107.,
# 100 Multiheterodyne spectroscopy using interband cascade lasers
L. A. Sterczewski, J. Westberg, C. L. Patrick, C. S. Kim, M. Kim, C. L. Canedy, W. W. Bewley, C. D. Merritt, I. Vurgaftman, J. R. Meyer and G. Wysocki, Opt. Eng., 57(1), Januar 2018, 011014,
# 105 Design and performance of a dual-laser instrument for multiple isotopologues of carbon dioxide and water
J. B. McManus, D. D. Nelson and M. S. Zahniser , Optics Express, Vol.23, Issue 5, 2015, pp. 6569-6586.,
# 106 Recent progress in laser‑based trace gas instruments: performance and noise analysis
J. B. McManus, M. S. Zahniser, D. D. Nelson et. al., Appl. Phys. B, 2015, 119: 203.,
# 117 The driver design for N2O gas detection system based on tunable interband cascade laser
L. Liao, J. Zhang, D. Dong, E3S Web Conf., Vol.78, 2019, 03002.,
# 119 Interband cascade laser based quartz-enhanced photoacoustic sensor for multiple hydrocarbons detection
A. Sampaolo, S. Csutak, P. Patimisco, M. Giglio, G. Menduni, V. Passaro, F. K. Tittel, M. Deffenbaugh, V. Spagnolo, Proc. SPIE 10540, Quantum Sensing and Nano Electronics and Photonics XV , 26th January 2018, 105400C,
# 127 Narrow linewidth characteristics of interband cascade lasers
Y. Deng , B.-B. Zhao, X.-G. Wang, C. Wang, Appl. Phys. Lett., Vol.116, 2020, 201101,
# 128 Quartz-enhanced photoacoustic spectroscopy for hydrocarbon trace gas detection and petroleum exploration
A. Sampaoloa, G. Mendunib,P. Patimiscoa, M. Giglioa, V. M.N. Passaroc, L. Donga, H. Wua, F. K. Tittel, V. Spagnoloa, , Fuel, Vol.277, 2020,
# 129 Sub-ppb-level CH4 detection by exploiting a low-noise differential photoacoustic resonator with a room-temperature interband cascade laser
H. Zhen, Y. Liu, H. Lin, R. Kan, P. Patimisco, A. Sampaolo, M. Giglio, W. Zhu, J. Yu, F. K. Tittel, V. Spagnolo, Z. Chen, Opt. Expr., Vol. 28, Iss. 13, 2020, p. 19446.,
# 131 Unveiling quantum-limited operation of interband cascade lasers
S. Borri , M. Siciliani de Cumis , S. Viciani , F. D’Amato, P. De Natale, APL Phot., Vol.5, Iss.3, 2020, 036101,
# 140 Interband cascade laser arrays for simultaneous and selective analysis of C1–C5 hydrocarbons in petrochemical industry
J. Scheuermann, P. Kluczynski, K. Siembab, M. Straszewski, J. Kaczmarek, R. Weih, M. Fischer, J. Koeth, A. Schade, S. Höfling, Appl. Spectrosc, January 2021, 2021,
# 147 Hydrogen sensor based on tunable diode laser absorption spectroscopy
V. Avetisov, O. Bjoroey, J. Wang, P. Geiser, K. G. Paulsen, Sensors, Vol.19, Iss.23, 2019, 5313.,
# 151 The interband cascade laser
J. R. Meyer, W. Bewley, C. L. Canedy, C. S. Kim, M. Kim, C. D. Merritt, I. Vurgaftman, Photonics, Vol. 7, No. 3 (75), 2020,
# 157 MHz laser absorption spectroscopy via diplexed RF modulation for pressure, temperature, and species in rotating detonation rocket flows
A. Nair, D. Lee, D. I. Pineda, J. Kriesel, W. A. Hargus Jr., J. W. Bennewitz, S. A. Danczyk, R. M. Spearrin, Appl. Phys. B, Lasers and Optics, 126, 2020,
# 163 Towards a dTDLAS‑Based Spectrometer for Absolute HCl Measurements in Combustion Flue Gases and a Better Evaluation of Thermal Boundary Layer Effects
Z. Qu, J. Nwaboh, O. Werhahn, V. Ebert, Flow, Turbulence and Combustion, 106, 2021, 533 - 546,
# 166 Mid-infrared hyperchaos of interband cascade lasers
Y. Deng, ZF. Fan, BB. Zhao et al. , Light Sci. Appl., 11, 2022,
# 173 Quantification of Elevated Hydrogen Cyanide (HCN) Concentration Typical in a Residential Fire Environment Using Mid-IR Tunable Diode Laser
S. Ghanekar, G. P. Horn, R. M. Kesler, R. Rajasegar, J. Yoo and T. Lee, Appl. Spectrosc., 77(4), 2023, 382-392,
# 175 Proof-of-Concept Tabletop Tunable Diode Laser Absorption Spectrometer Instrument (TDLAS) for the Detection of H2O(v) in Lunar Regolith for the Canadian Multipurpose Autonomous Penetrator for Lunar Exploration (MAPLE) Project
A. Gmereka, Dr. A. Elleryb, Dr. E. Cloutisc, B. Thibodeaud, IAC, 73rd, 2022, Paris, France,
# 178 Quartz-Enhanced Photoacoustic Sensors for Detection of Eight Air Pollutants
R. De Palo, A. Elefante, G. Biagi, F. Paciolla, R. Weih, V. Villada, A. Zifarelli, M. Giglio, A. Sampaolo, V. Spagnolo, P. Patimisco, Adv. Phot. Res., Vo. 4, Iss. 6, 2023,
# 181 High-speed laser absorption measurements of carbon oxides in linear detonation channels
K. L. Fetter, B. R. Steavenson, B. M. Ng, A. Andrade, C. S. Combs, D. I. Pineda, AIAA Aviation 2023 Forum, 2023, 4384,
# 186 Measurement of CO2 isotopologue ratios using a hollow waveguide-based mid-infrared dispersion spectrometer
H. Zhang, T. Wu, Q. Wu, W. Chen, C. Ye, M. Wang, X. He, Anal. Chem., 95 (50), 2023, 18479-18486,
# 191 Wavelength Tuning in Resonant Cavity Interband Cascade Light Emitting Diodes (RCICLEDs) via Post Growth Cavity Length Adjustment
N. Schäfer, R. Weih, J. Scheuermann, F. Rothmayr, J. Koeth, S. Höfling, Sensors, 24, 2024, 3843,
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The high-resolution transmission molecular absorption database from the Harvard-Smithsonian Center for Astrophysics provides an excellent compilation of spectroscopic parameters.

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