tdls

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• Principle FTIR/Grating Spectroscopy:• Broad-band radiation source (Globar)• Frequency analysis by grating or interferometer

• Principle Tunable Diode Laser Spectroscopy:• Narrow-band laser diode

• Measurement of spectrum by tuning laser diode

Gas

Tunable Diode Laser Spectroscopy (TDLS)

R. Engelbrecht, J. Euring, F. Kuntz, L.-P. Schmidt. A Fibre-Optic Diode Laser Spectrometer for Sensitive Simultaneous Measurement of CO2and CO Gas Concentrations. 10. Int. Fair and Conf. SENSOR 2001, Germany.

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Experimental Set-Up for TDLS

P.W. Werle et al. / Spectrochimica Acta Part A 60 (2004) 1685–1705

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Principle: Laser Diode

Matti Kaivola:http://omm.hut.fi/optics/l_o/2005/luennot/kalvot.shtml

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Spectral Coverage

P.W. Werle et al. / Spectrochimica Acta Part A 60 (2004) 1685–1705.

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Materials

Compound Wavelength/nm Applications (Examples)

GaN/AlGaN blue/green Disc data storage

ZnSSe 447-480 Disc data storage

ZnCdSe 490-525 Disc data storage

AlGaInP/GaAs 620-680 Replacements for HeNe lasers, eg bar code

scanners

Ga0.5In0.5P/GaAs 670-686

GaAlAs/GaAs 750-870

GaAs/GaAs (pure) 904

In0.2Ga0.5As/GaAs 980-1050

InGaAsP/InP 1100-1650 Chemical sensors

In0.73Ga0.27As0.58 P0.42 1330 Optical communication, metrology

In0.58Ga0.42As0.9 P0.1 1550 Optical communication, metrology

AlGaAsSb/InGaAsSb 2000-3000 Chemical sensors

GaAs/AlGaAs 6000-12000 Quantum cascade laser chemical sensors

PbEuSeTe 3300-5800 Cryogenic, high resolution spectroscopy

PbSSe 4200-8000 Cryogenic, high resolution spectroscopy

PbSnTe 6300-29000 Cryogenic, high resolution spectroscopy

http://www.chemsoc.org

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Tuning of a Lead-Salt Diode Laser

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Tunable Laser Diode Spectrometer

PolychromatorSAE Technical Paper No. 840470, Staab, Klingenberg & Riedel; 1984

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Tunable Diode Laser Spectrometer

R. Engelbrecht, J. Euring, F. Kuntz, L.-P. Schmidt. A Fibre-Optic Diode Laser Spectrometer for Sensitive Simultaneous Measurement of CO2and CO Gas Concentrations. 10. Int. Fair and Conf. SENSOR 2001, Germany.

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9Exhaust Measurement: DEGAS System for

Measurement of Car Exhausts

• Based on Lead-Salt Laser Diodes• Temporal resolution: 5 ms• Number of gases: 3

• Determined by selection of diodes• One diode per gas

Gas Range (ppm) Limit ofDetection (ppm)

CO 2000 10

NO 4000 20

CO2 4000 20

CH4 2000 5

NO2 2000 10

NH3 (at 1600 cm-1

) 10000 50NH3 (at 1050 cm

-1) 2000 10

www.ipm.fraunhofer.de

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10Exhaust Measurement: DEGAS System for

Measurement of Car Exhausts

Time (s)

beforeCat.-Conv.

afterCat.-Conv.

beforeCat.-Conv.

afterCat.-Conv.


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New Laser Source: Quantum Cascade Laser (QCL)

• Series of Quantum Wells (QW)• QW: thin layer which can confine particles in the dimension

perpendicular to the layer surface

• Produced by layers of different materials• Example: GaAs quantum well embedded in AlGaAs

• Energy states in quantum wells are quantized• Transitions between states: Absorption or Emission of

Photon possible• Typical layer thickness: Å - nm

Principle (simplified):

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Quantum Cascade Laser

• Interband transition• photon energy limited bybandgap Eg of material

• Telecom, CD, DVD,…

• Intersubband transition• photon energy depends on layerthickness and can be tailored⇒Wavelength selection

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QCL Laser

• Cascade

• each electron emits N photons

• Available wavelengths (room temperature!): 3.4 – 17 µm

Bonetti, Blaser: “Developments in the Field of QuantumCascade Lasers”, 34. IR-Kolloquium, 2004

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New Lasers for Tunable Diode Laser Spectrometry

Wavelength (µm)

Laser Sources

Absorption Signatures ofGases

Quantum CascadeLaser

(Overtone)


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