terahertz imaging application to art conservation
DESCRIPTION
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 PresentationTRANSCRIPT
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)