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)