Near Infrared (NIR) Spectroscopy Instrumentation Paul Geladi

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Near Infrared (NIR) Spectroscopy
InstrumentationPaul Geladi
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Paul Geladi
Head of Research NIRCE Chairperson NIR Nord Unit
of Biomass Technology and Chemistry Swedish
University of Agricultural Sciences Umeå Technobot
hnia Vasa paul.geladi _at_ btk.slu.se paul.geladi
_at_ uwasa.fi
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(No Transcript)
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Content

• Spectroscopy?
• Instrumentation
• Modes of measurement

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Content

• Spectroscopy?
• Instrumentation
• Modes of measurement

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Content

• Spectroscopy?
• Energy levels in atoms, molecules, crystals
• Example IR-NIR calculations
• Related techniques

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Content

• Spectroscopy?
• Energy levels in atoms,molecules, crystals
• Example IR-NIR calculations
• Related techniques

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Spectroscopy

• Interaction of radiation and matter
• Electromagnetic radiation
• Gases, liquids, solids, mixtures
• Heterogeneous materials

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Electromagnetic radiation
Cosmic Gamma Xray UV VIS NIR IR Micro Radio
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Electromagnetic radiation

• Cosmic gt 2500 KeV
• Gamma 10-2500 KeV
• Xray 0.1-100 KeV
• Ultraviolet 10-400 nm
• Visible 400-780 nm
• Near Infrared 780-2500 nm
• Infrared 2500-15000 nm
• Microwave GHz
• Radio MHz-KHz

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Why interaction?

• Photon energy matches some energy level
• E hn
• E hc/l
• Plancks constant ????6.63 10-34

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Some useful constants

• qe 1.60217646210-19 As
• me 9.1093818810-31 Kg
• c 2.99792458108 m/s
• h 6.6260687610-34 Js
• 1 Joule to Electronvolt 6.2415063630940281018

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Units

• Joule (energy)
• Electron volt (KeV)
• Wavelength (nm, mm, mm)
• Inverse cm (cm-1)
• Frequency (GHz,MHz,KHz)

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Content

• Spectroscopy?
• Energy levels in atoms,molecules, crystals
• Example IR-NIR calculations
• Related techniques

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HCl molecule (no true sizes)
electron
Xray
UV,VIS
H
Cl
NIR,IR
UV,VIS
Gamma ray
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Photon-matter interaction

• Atomic nucleus gamma ray
• Inner electron Xray
• Outer electron, chemical single bond UV
• Chemical double, triple bond UV,VIS
• Molecular vibration overtone NIR
• Molecular vibration IR
• Molecular rotation Micro

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E
Quantized energy levels
First excited level
hn
Ground level
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What can be measured?

• Emission
• Absorption
• Fluorescence

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E
Emission
First excited level
Thermal
hn????
Ground level
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E
Absorption
First excited level
Thermal
hn???
Ground level
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E
Fluorescence
First excited level
hn???
hn out
Ground level
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Techniques?

• Gamma spectrometry
• Instrumental neutron activation analysis
• Xray spectrometry
• UV-VIS spectrometry (AES,AAS,ICP...)
• NIR spectrometry
• IR spectrometry
• Raman spectrometry
• Microwave spectrometry

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What can be used?
Intensity
Position
Intensity, integral
Width
Energy
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Special topics

• Polarization
• Time resolved spectroscopy

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Content

• Spectroscopy?
• Energy levels in atoms,molecules, crystals
• Example IR-NIR calculations
• Related techniques

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Vibrational spectroscopy
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Morse curves

• The Morse curve describes the potential energy V
  of a diatomic molecule as a function of
  interatomic distance x.
• V De 1-exp(-bx)2

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De 5 b 0.5
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• If the atoms go far apart the bond breaks.
• It is impossible to press the atoms close
  together. Enormous amounts of energy are needed.

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De 10 b 0.4
Zero equilibrium distance
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F Fundamental O1 First overtone O2 Second overtone
Quantum levels discrete
O2
O1
F
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This was diatomic molecules

• Polyatomic molecules
• M3N-6 quantized vibration modes
• M3N-5 linear molecules (N1)
• N3 , M3 H2O, H2S, SO2
• N4 , M6 etc

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Triatomic molecules

• G(a,b,c)v1(a1/2) v2(b1/2) v3(c1/2)
• Energy levels
• abc0 (0,0,0)
• a1 bc0 (1,0,0)
• a2 bc0 (2,0,0)
• a0 b1 c0 etc (0,1,0)

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Hot band
Overtone
Combination band
(0,0,2)
Fundamental
(0,2,0)
(0,0,1)
(2,0,0)
(0,1,0)
(1,0,0)
(0,0,0)
Ground level
a
c
b
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Intensity

• Some transitions are more probable
• Gives more intense bands
• Fundamentals in Gas phase
• Overtones in liquid,solid
• Combination bands in liquid, solid

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Hot bands

• Only exist because of thermal excitation
• Boltzmann
• Ne No exp(-DE/kT)
• Ne number excited, No number ground
• k Boltzmann constant 1.380650310-23 J/K
• DE energy difference

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Why cm-1?

• Additive

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S02

• wavenumber band
• 519 v2
• 606 v1-v2
• 1151 v1
• 1361 v3
• 1871 v2v3
• 2296 2v1
• 2499 v1v3

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Thermal radiation

• Plancks law
• W(l) c1l-5exp(c2l-1 T-1)-1
• T K
• c1 1.9110-12
• c2 1.438104
• ?l mm

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Radiance
4000 K (Tungsten melts)
3500 K
3000 K
2500 K
2000 K
mm
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Planck curves

• More total energy for high temperature
• More UV for high temperature
• More flat curve for low temperature

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Content

• Spectroscopy?
• Energy levels in atoms,molecules, crystals
• Example IR-NIR calculations
• Related techniques

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Energy supply

• Photon
• Thermal
• Electron -
• Proton
• Ion -

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Optics

• Electron optics
• Ion optics

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Techniques

• Electron microscopy
• Electron spectroscopy
• Mass spectrometry
• Ion microscopy

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Transmission
Mono- chromator
Detector
Readout electronics
Radiation source
Sample cell
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Transmission
Mono- chromator
I0
It
Detector
Readout electronics
Radiation source
Sample cell
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Lambert-Beer-Bouguer lawTransmissionAbsorbance
T It / I0 A log10 ( I0 / It) -log10 (It /
I0)
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Lambert-Beer-Bouguer law
A klC l path length k constant C
concentration
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Reflection
Mono- chromator
Detector(s)
Readout electronics
Radiation source
Sample cell
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Reflection
Mono- chromator
Detector(s)
I0
Ir
Readout electronics
Radiation source
Sample cell
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Lambert-Beer-Bouguer lawReflectionPseudoabsorba
nce
R Ir / I0 A -log10 (Ir / I0)
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Content

• Spectroscopy?
• Instrumentation
• Modes of measurement

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What can be changed?

• Radiation source
• Monochromator
• Sample cell
• Detector

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Radiation source

• Tungsten-halogen lamp (Car type)
• Coated tungsten SiC
• Laser(s)
• LEDs
• LED arrays

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ln(Energy flux)
3000K
1000K
0.2
1
ln(Wavelength), mm
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1300
Energy flux
LEDs
1000
1150
1520
Wavelength, ?m
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What can be changed?

• Radiation source
• Monochromator
• Sample cell
• Detector

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Monochromator

• Glass filter
• Interference filters
• Prism
• Grating
• Interferometer
• Electrooptical

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Monochromator

• Glass filter not selective
• Interference filters
• Prism too primitive, never used
• Grating
• Interferometer
• Electrooptical

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Interference filter
Low RI coating
Glass
Multiple reflections
High RI coating
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Tilting interference filter
Low RI coating
Glass
Different pathlengths
High RI coating
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There are also gradual interference filters

• Disk with increasing thickness
• Rotate for new wavelength bands

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Filter wheel
Filter wheel
Detector(s)
Readout electronics
Radiation source
Sample cell
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Grating
Pathlength difference
Mirror staircase
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Grating
Exit slit
Entrance slit
Monochromatic
Polychromatic
Rotate
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Interferometer
Fixed mirror
Semitransparant mirror (50)
Moving mirror
Sample
Detector
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Interferometer
Fixed mirror
a
Semitransparant mirror (50)
Moving mirror
b
Wavelengths for which b-a whole cycle
reach detector
Detector (interferogram)
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Interferometer
Interferogram Fourier transform Spectrum
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What can be changed?

• Radiation source
• Monochromator
• Sample cell
• Detector

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Content

• Spectroscopy?
• Instrumentation
• Modes of measurement

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Modes of measurement

• This is a real strong point of NIR spectroscopy.
  There are many modes of measurement
• Transmission
• Diffuse reflection
• Fiber optic based
• -Transflection
• -Interaction

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Det
Det
Integrating sphere
Det
Mirror
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Transflectance probe
Fiber bundle
Sapphire mirror
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Mixed solutions

• Use tunable laser instead of monochromator (more
  lasers?)
• Use LEDs in different wavelengths instead of
  monochromator
• Use array of detectors instead of scanning
  monochromator
• DIODE ARRAY

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Grating
Entrance slit
Diode array
Polychromatic
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Filter wheel instrument with interference filters
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Interferometric instrument
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Process NIR spectrometer based on moving grating
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Transmision instrument
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Sample changer for seeds (transmission)
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Diffuse reflectance instrument (rotating cup)