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Terahertz Imaging Application to art conservation. Ayesha Younus. J.C. Delagnes, E. Abraham, P. Mounaix Centre de Physique Moléculaire Optique et Hertzienne, UMR 5798. UNIVERSITE BORDEAUX I. 1. Contents. I- Introduction II- Experimental setup Emission and Detection of THz radiation - PowerPoint PPT Presentation
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1
UNIVERSITE BORDEAUX I
Ayesha Younus
J.C. Delagnes, E. Abraham, P. Mounaix
Centre de Physique Moléculaire Optique et Hertzienne, UMR 5798
I- IntroductionII- Experimental setup
Emission and Detection of THz radiationTransmission imaging, Time-dependent THz signal and SpectrumReflection imagingLongitudinal & Transversal Resolutions
III- Results Image galleryArt conservation (graphite, painting pigments)
IV- Conclusions & Perspectives
Contents
Introduction
Freq 0.1-10 THz Wavelength 0.03-3 mm
Energy 0.4-40 meV Non destructive and contactless Imaging
Transparent to amorphous materials, clothing, plastic, tissues, papers, wood, semiconductors...Strong interaction with polar molecules
Negligible heating or ionizing effects
THz Imaging in Bordeaux : pulsed THz imaging with a femtosecond laserApplication to art conservation (Centre de Recherches et de Restauration des Musées de France)
THz Generation
LT-GaAs : Low Temp GaAs
THz Detection
Varying the time delayMap the THz field in time domain
0 5 10 15 20-1000
-500
0
500
1000
1500
2000
inte
nsité
(pA
)retard (ps)
delay
LIA: lock in Amp
Broadband Spectroscopic THz imaging
Raster scanning
Spectral responseTemporal response
0.0 0.5 1.0 1.5 2.0 2.5 3.0
1
10
100
Frequency (Hz)
Ampli
tude
0 5 10 15 20-1000
-500
0
500
1000
1500
2000
inte
nsité
(pA
)
retard (ps)
ProbePump
Laser
Sample
THz
sample
D ES
Imaging THz : Reflection Setup
Beam splitter
Sample
PC Emitter
PC Detector
ProbePump
5 10 15 20 25
-2,00E-010
0,00E+000
2,00E-010
4,00E-010
miroir + feuille devant
miroirarrière LS
feuillearrière LS
miroir
feuille
inte
nsi
ty (
A)
time delay (ps)
MirrorPaper
THz
Transversal Resolution
200µm
Images at 2 THz
0 200 400 600 800 1000 1200 1400 1600 1800 2000 22000
20
40
60
80
100
C=65%
C=75%
inte
nsity
(a.
u.)
distance (µm)
280µm V
C=50%
500µm
410µm
0 100 200 300 400 500 600 700 800 900 1000 1100 1200 13000
20
40
60
80
100
inte
nsity
(a.
u.)
distance (µm)
270µm
ABmin = 0.66λ/NA
ABmin = 0.66*150/0.44
ABmin =225µm
Results
• Image Gallery- THz Imaging of various objects- Extraction of spectroscopic information
• Investigation of graphite properties (pencil leads)- THz spectroscopy of graphite- THz imaging of documents written with pencil leads
• Investigation of painting pigments (Centre de Recherches et de Restauration des Musées de France) - THz spectroscopy of pigments- THz imaging of paint layers on canvas, imaging of hidden graphite sketch
Image gallery
0 5 10 15 20 25
-3
-2
-1
0
z
HH
thic
knes
s (m
m)
distance (mm)
T
Graphite on paper
Differentiation between 2 pages
12 14 16 18 20 22
-1
0
1
2
3
TH
z tr
ansm
issi
on (
%)
retard (ps)
158 fs
THz transmission spectra
0.0 0.5 1.0 1.5 2.00.0
0.2
0.4
0.6
0.8
1.0
2B 4B 6B 6B
Tra
nsm
issi
on
TerahertzTransmission as a function of page
numbers, detection limit
0 20 40 60 80 100 120 140 160 180 200 220 2400,1
1
10
100
tra
nsm
issi
on
(%
)
nombre de pages
limite de detection du signal : 0,15%soit environ 200 pages
Graphite on paper: Grades from HB to 8B
Image at 2 THz
Phase
0 5 10 15 20-1000
-500
0
500
1000
1500
2000
inte
nsité
(pA
)
retard (ps)
“Broadband terahertz imaging of documents written with lead pencils”, accepted to Optics Communications (2009)
Image at 2 THz
THz imaging and art conservation : Painting pigments
Samples: Talens, « Van Gogh acrylic colours »1: titanium white PW62: oxide black PBk113: ultramarin PB294: brilliant blue PB15/PG7/PW65: carmin PR236: naphtol red light PR112/PO347: burnt sienna PR1018: azo yellow light PY3/PY749: azo yellow deep PY74/PO4310: permanent green deep PG7/PY128
Echantillon Indice moyen
1 2.13
2 2.74
3 1.93
4 1.91
5 1.78
6 1.73
7 1.65
8 1.58
9 1.68
10 1.64
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
8×10-10
6×10-10
4×10-10
2×10-10
0×10-10
FTT 002_ref_diaf
FT of 03_#1
FT 04_#2
FT 005_#3
FT of 06_#4
FT 007_#5
FT 008_#6
FT o009_#7
FT of0010_#8
FT of 011_#9
10-10
10-12
10-14
Frequency (THz)
THz transmission spectra
Graphite on canva and 4 colors (same thickness)
Imax-Imin Phase
Titaniumwhite
Azo yellowlight
ultramarin
Brilliantblue
Transmission imaging
Graphite on canva & ultramarin (3 diff thicknesses)
Image at 1 THz Phase
1st layer: 30-40 µm
2nd layer: 290-350 µm
3rd layer: 510-550 µm
30 µm
270 µm
515 µm
Transmission imaging
Transmission Reflection
0 2 4 6 8 10 12
0,0
0,5
1,0
0 2 4 6 8 10 12
-0,5
0,0
0,5
1,0
0 2 4 6 8 10 12
-0,5
0,0
0,5
1,0
inte
nsity
(a.
u.)
time delay (ps)
e=340 µm
e=600 µm
Reflection Imaging
canva
1st layer: 30-40 µm
2nd layer: 290-350 µm
3rd layer: 510-550 µm
Graphite on canva and multiple colors
Transmission imaging
Imax-Imin PhaseImage at 1 THz Image at 2 THz
Conclusions and perspectives
THz radiation posses unique properties which distinct it from existing technologies (optics, ultrasounds, x-rays)
Interest of femtosecond technology for the generation and detection of pulsed THz radiations, importance of broadband spectroscopic measurements
Perspectives: painting pigments: investigation of old pigments (C2RMF) Inspection of various kinds of wood: determination of wood properties (aging, origin, arche) from the analysis of ring sections of stem
Projects:Art-Tera : CPMOH, C2RMF et LOATera-Scan : 3D Tomographic THz Imaging, CPMOH, LaBRINew detectors / new sources (GES Montpellier) *
* Wave field effect transistor as a resonant detector for 1 Terahertz imaging applications, accepted to Optics Communications (2009)
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