Far Infrared Spectroscopy
on Biological Material
Investigation of the potentially dangerous effects that THz radiation might
induce in living organisms
Adriana Matei
1. Physikalisches Institut, Universität Stuttgart, Deutschland
Universität Stuttgart
Martin Dressel
Boris Gorshunov
Support
EU-Project: THz-Bridge
Motivation
170-175 GHz Satellite communication
100 GHz Mobile phones
28.3THz
CO2-Laser (Surgery, Industry)
10.7 THz H2O Laser
Process vs. frequency
Region
Microwave
Far Infrared
Infrared
VIS and UV
Frequency
1 – 100 GHz
0.1 – 30 THz
30 – 435 THz
435 THz –
10 PHz
Wavelength
300 – 3 mm
3 mm – 10 m
10 m – 690 nm
690 nm – 30 nm
3.3 – 1000 cm-1
1000 – 14500 cm-1
14500333564 cm-1
Energy
4.09x10-3 0.409 meV
0.409 – 124 meV
124 meV- 1.8 eV
1.8 eV – 41.3 eV
Molecular
process
Rotation of
polyatomic
molecules
Rotation of
small molecules
Vibrations of
flexible bonds
Electronic
transitions
Wavenumber 0.033 - 3.3 cm-1
THz radiation induced effects
• Heating due to high frequency radiation
(ex: microwave oven)
• If the resonant frequency is met  distinct lines 
 what is happening if samples are exposed for longer time
at resonant frequency
Experimental techniques
Fourier Transform Spectrometer
Bruker IFS 113 v
Spectral range 10 cm-1 – 10 000 cm-1 300 GHz – 300 THz
Resolution
0.03 cm-1
3 Sources
Temperatures 2 – 300 K
6 Detectors
Sample chamber
1.2 K
Bolometer
4.2 K
Bolometer
Reflection unit
Michelson
interferometer
Coherent Source Spectrometer
Spectral range 1 – 40 cm-1 30 GHz – 1.2 THz
Resolution
Temperatures
Sources:
Lenses:
backward wave oscillator
monochromatic, coherent
tunable, powerful
10-4 – 10-5 cm-1
2 – 300 K
Mach-Zehnder Interferometer
polyethylene
Beamsplitter, polarizer:
free standing wire grids
Mirror 1
Grid
Analyzer
Detector: Golay cell,
He-cooled bolometer
Detector
Source
Polarizer
N
S
Mirror 2
Grid
(beam-splitter)
Sample
Blood components
Blood – liquid tissue of red colour consisting of plasma and 7
types of cells
Plasma – watery medium (92% water, 6-8% proteins),
straw-coloured, suspension of cells and cell fragments
albumin
Main plasma proteins
alpha
globulins beta
gamma
Serum – blood plasma without fibrinogen and other clotting
factors; (H4522 Sigma Aldrich)
Optical Properties of Water
at room temperature
water
T()
d
10
5
10
4
10
3
10
2
10
1
10
0
10
0
1 m
10
Transmission
-1
 (cm )
Absorption coefficient
-1
10
0
10
1
2
10
10
-1
Frequency (cm )
after: Palik, Handbook of Optical
Constants of Solids
3
10
4
10
-1
10
-2
10
-3
10
10 m
100 m
1
2
10
3
10
-1
Frequency (cm )
Reflection not considered
4
10
How to overcome “water problem“
• Reflectivity measurements
• Sample container: cuvette
with Si windows
• Measurements in vacuum
Reflectivity setup
Sample
Cuvette
Sample thickness: few mm
Window: Si
FIR Beam
Gold mirror
Vacuum shroud
Reflectivity measurement
(R)
• Fabry-Perot resonator:
Δν=1/2nd
Si
0.7
0.6
d = 2 mm; n = 3.4
water
water
d
Si
Reflectivity
0.5
0.4
0.3
0.2
0.1
0.0
200.0
water fit
200.5
201.0
201.5
202.0
-1
Frequency (cm )
202.5
Dielectric constant
(e`, e``)
6
eps1
eps2
water
Transmission,
Phase
e´, e``
4
2
Sample
Spacer
0.350 mm
Quartz windows
d=2mm, n=1.87
0
0
100
200
300
400
500
-1
Frequency (cm )
600
700
Dielectric properties for selected materials
Chemical composition
ε’ (10 cm-1)
ε ’’ (10 cm-1)
Nr.
Sample
1
Water
H2O
4.6
4.4
2
Propanol
(CH3)2 CHOH
2.5
0.39
3
Fructose pellet (sugar)
3.9
0.04
4
Sucrose pellet (sugar)
3.2
0.04
5
Chocolate
3.2
0.08
6
Sunflower oil
2.4
0.06
5
0.79
7
Honey
C6H12O6
C6H12O6
Water
– 17.1 %
Carbohydrates – 82.1 %
Minerals
– 0.5%
Complex refractive index
(n, k)
2.5
2.0
water
n
n,k
1.5
1.0
k
0.5
0.0
0
100
200
300
400
500
600
700
-1
Frequency (cm )
N* = n + ik = (ε` + iε ``)1/2
Absorption coefficient α
6000
Absorption coefficient
5000
water
4000
3000
2000
1000
0
0
100
200
300
500
400
-1
Frequency (cm )
600
700
Serum and water reflectivity
0.6
0.5
Reflectivity
0.4
0.3
0.2
0.1
H4522
water
0.0
200
201
202
-1
Frequency (cm )
Sensitivity improvement
Sample
Cuvette
Gold mirror
Thin sample (10 - 20m)
 higher sensitivity
FIR Beam
Gold mirror
Vacuum shroud
Conclusions
Development/testing of a new technique for FIR measurements of liquids
Measured optical properties of water in FIR/SubMM
No differences observed between serum and water
 sensitivity of the technique
 improvements of the method