imaging and spectral information with time-domain...

OCT4ART – July 2008 Gaël Latour

Imaging and spectral information withtime-domain OCT

Application to works of art

Gaël LatourInstitut des Nanosciences de Paris (INSP)

[email protected]

OCT4ART – Torun, Poland – 3-5 July 2008

Latour et al., Applied Optics, in submission


Optical techniques to study works of art

Purpose: obtaining information from the studied work of art

Pigment

Dye

Varnish

Surface state

Number of layers

Thickness of a layer…

Interest of the optical techniques:non destructive and without any contact analysis


Overview

Setup

Acquisition and processing

Imaging: painting

Imaging: music instruments

Spectral information

Time-domain OCT: imaging and spectral information


Michelson interferometerSetup

Detector

Light source

IBeamsplitter

I1I2

Mirror

Mirror

Equal optical paths

Interference pattern


PC

Piezoelctrictransducer

Mirauobjective

Halogenlamp

CCD

Lens

beam splitter

mirror

Mirau objective

interferometric objective

Sensitive in the visible range

Stability of the device

Setup at the INSPSetup


Overview

Setup


Imaging: painting





For each position of the objective, one image is recorded

300 µm

200 µm

Lateral resolution~ 2 µm

xy

z

Δz ~ 30 nm

AcquisitionAcquisition and processing


x

y

z

Interferogram

0,4

0,6

0,8

1

-3 -2 -1 0 1 2 3Différence de chemin optique (µm)

Inte

nsité

(u.a

.)

0

0,2

0,4

0,6

0,8

1


Inte

nsité

(u.a

.)

Envelop

I(z)

Axial resolution ~ 1,5 µm

Imaging

x

z

Image x-z Stratigraphy of the sample



Overview

Setup


Imaging: painting





30 µm

300 µm200 µm

Air

Painting

Microscope slab

Pigments30 µm

300 µm

False colors images

From axial slices, reconstruction of 3D imaging

Interface air/paint

Pigments

Interface paint/glass

Ultramarine blueon glass

Imaging: one pictorial layerImaging: painting


Viridian green

Chrome yellow

20 µm

300 µm3D Image

Chrome yellow

Viridian green20 µm

20 µm

Imaging of stratified layers

Viridian green on chrome yellow

Imaging: stratified layers

Latour et al., Proceeding SPIE Congress, Münich, vol. 6618-5 (2007)

Imaging: painting


300 µm

Imaging: varnished paint layer

Interface air/varnish

Varnish

PaintingInterface varnish/paint30 µm

Viridian greenVarnish

3D Images

Imaging: painting


Overview

Setup


Imaging: painting





Imaging: music intruments

x

z Interface air / varnish

Pigments? Wood?

Stratified layers?

Presence of pigments?

Interface varnish / wood?

Precious and delicate objects

Wood instruments: violin, cello…


OCT: device for the study of music intruments?Imaging: Music instruments

Music Museum LaboratoryJean-Philippe EchardStéphane Vaiedelich

(Cité de la Musique, Paris)

Conservator and violin makerBalthazar Soulier

(Staatliche Akademie der BildendenKünste, Stuttgart)

Interest of OCT?

School samples

wood wood + under layer

varnish pigments

Instruments

Collaborations


Wood

Among the wood species: choice of maple

Back, headpiece and rib

Landolfi, Milan, XVIIIth (private collection)

Imaging: Music instruments


Wood: maple

80 µm

300 µm

200 µm

80 µm

300 µm

200 µm

x

yz

xy

300 µm

200 µm

yz

200 µm

80 µm

xz

300 µm

80 µm

1 cm



Wood + under layer + varnish

varnish

under layer

wood

interface between varnish and under layer

wood

under layersandarac varnish



OCT: imaging

Painting

Number of layers

Thicknesses

Surface state

Presence of fillers

Informations about the wood

Music instruments

and …


Overview

Setup


Imaging: painting



I(λ)Time-domain OCT: imaging and spectral information


0,4

0,6

0,8

1


Inte

nsité

(u.a

.)

Interferogram Fourier Transform

I(λ)

Central wavelength ~ 620 nm

Spectral width ~ 150 nm

Spectral resolution: 2 to 5 nm

Glass


Spectral transfer function of the device

Spectral information from OCT

0

0,5

1

450 550 650 750Wavelength (nm)

Inte

nsity

(u.a

.)

I(λ)


Air

Red dye

Glass200 µm

30 µm

x

z

Raw data

Spectra

OCT spectrum = transmittance spectrum

Red dye on glass

Spectral information: dye

Absorbing and non difffusing medium

0

0,5

1

450 550 650 750Longueur d'onde (nm)

Inte

nsité

Interface colorant-verre

Interface air-verre

Spectral information from OCTI(λ)

Reproducible spectra


Chrome yellowpainting

0

0,5

1

450 550 650 750Longueur d'onde (nm)

Inte

nsité

rela

tive

spectre1spectre2spectre3spectre4spectre5spectre6

Spectra of several pigments

Spectra from several pigments are different

Spectral information: pictorial layer

Diffusing medium

Spectra obtained after FT

Outlook: Obtaining reproducible spectra

Identification of pigments by comparison with a database of spectra

Spectral information from OCTI(λ)


OCT applied to works of art

? Thicknesses of layers

Time-domain OCT

3D Imaging

?Thickness of a varnish

Presence of fillers

Spectral informationValidation on dyes

OutlookSpectral information on pigments

Axial resolution: 1,5 µm

Sensitive in the visible range

…


Thank you for your attention …Gaël Latour - [email protected]

Aknowledgements:Isabelle Emond (INSP), Jean-Philippe Echard and Stéphane Vaiedelich (Cité de la Musique, Paris) Balthazar Soulier (SABK, Stuttgart)

imaging and spectral information with time-domain...

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