Marc GEORGES , Philippe C. LEMAIRE , Centre Spatial de Liège, Angleur (B)

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Centre Spatial de LiègeUniversité de Liège

© Centre Spatial de Liège, LAVINYA, London

2004

Pulsed holographic interferometry with Pulsed holographic interferometry with photorefractive crystals. Recent advances of the photorefractive crystals. Recent advances of the

european “PHIFE” projecteuropean “PHIFE” project

Marc GEORGESMarc GEORGES, Philippe C. LEMAIRE, Philippe C. LEMAIRE, , Centre Spatial de Liège, Angleur (B)Centre Spatial de Liège, Angleur (B)

Gilles PAULIAT, Gérald ROOSENGilles PAULIAT, Gérald ROOSEN

Laboratoire Charles Fabry de l ’Institut d ’Optique, Orsay (F)Laboratoire Charles Fabry de l ’Institut d ’Optique, Orsay (F)

Igor ALEXENKO, Giancarlo PEDRINIIgor ALEXENKO, Giancarlo PEDRINI, , Institut für Technische Optik, Stuttgart Institut für Technische Optik, Stuttgart (D)(D)

Sébastien RYHONSébastien RYHON, , OPTRION S.A., Liège (B)OPTRION S.A., Liège (B)

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Photorefractive effectPhotorefractive effect– DefinitionDefinition

– Application to holographic interferometryApplication to holographic interferometry

cw Photorefractive holographic cameracw Photorefractive holographic camera– applied to vibrationapplied to vibration

Pulsed system Pulsed system – applied to vibrationapplied to vibration

– discussion : drawback lead to PHIFE projectdiscussion : drawback lead to PHIFE project

PHIFE projectPHIFE project– goalsgoals

– partnershippartnership

– laboratory studieslaboratory studies

– present/future workpresent/future work

SummarySummary

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Photorefractive EffectPhotorefractive Effect

1. Fringe pattern created by 1. Fringe pattern created by interference between 2 wavesinterference between 2 waves

2. Charges generated by photo-excitation in 2. Charges generated by photo-excitation in

illuminated area, migrate and are trapped in dark areailluminated area, migrate and are trapped in dark area

3. Local space charge field3. Local space charge field

Pockels effectPockels effect4. Modulation of refractive index 4. Modulation of refractive index nn

THICK PHASE HOLOGRAMTHICK PHASE HOLOGRAM

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n = n = nnsatsat (1-exp(-t/ (1-exp(-t/))))

PR effect is dynamic and reversiblePR effect is dynamic and reversible


– Recording energy at saturation : ERecording energy at saturation : Ess = = .I.I

– Diffraction efficiency : Diffraction efficiency : = I= Idiffdiff/I/Irefref ~ ( ~ (n)n)22

Application to holographic interferometryApplication to holographic interferometryinterference between diffracted beam (reference object state)interference between diffracted beam (reference object state)

cw laserscw lasers

pulsed laserspulsed lasers

Object state 0 Object state 1Object state

2

transmitted beam (deformed object state)transmitted beam (deformed object state)

Interferogram 1Interferogram 1

Interferogram 2Interferogram 2incident

diffracted

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Application to pulse holographic interferometryApplication to pulse holographic interferometry


t

record

readout

CCD emptied

– First pulse :First pulse :• Hologram recordingHologram recording

• object state 0object state 0

– Second pulse :Second pulse :• Hologram readoutHologram readout

• object state 1object state 1

• Interferogram showing (state 1 - state 0)Interferogram showing (state 1 - state 0)

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Photorefractive crystalsPhotorefractive crystals

Visible(blue-green)

Sillenite Bi12SiO20 (BSO)

FerroelectricsLiNbO3, BaTiO3

High sensitivity : ES ~ 1-10 mJ/cm2

Poorest efficiency : ~ 0.1 %

Poor sensitivity : ES ~ 1 J/cm2

Highest efficiency : ~ 100 %

NIR(=1 µm)

SemiconductorsCdTe, GaAs

Highest sensitivity : ES ~ 0.1-1 mJ/cm2

Poor efficiency : ~ 1 %

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Particular properties : depend on crystal cutParticular properties : depend on crystal cut

Photorefractive effectPhotorefractive effect

l 4 n l

1

a

P2

P1

Pdiff

Pt

Anisotropic diffraction Isotropic diffraction

Interferogram contrast depends on the analyser orientation Interferogram contrast depends on the product :-coupling constant-crystal thickness

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Developed by CSL : 1993-1998Developed by CSL : 1993-1998

– Optical head : L=25 cm, 1 kgOptical head : L=25 cm, 1 kg

– Laser : DPSS, VERDI 5WLaser : DPSS, VERDI 5W

– Laser light brought by optical fiberLaser light brought by optical fiber

– Specialty fiber developedSpecialty fiber developed

(5 m, Transmission 80%, 5W injected)(5 m, Transmission 80%, 5W injected)

Cw Holographic CameraCw Holographic Camera

Now commercialized by spin-off OPTRIONNow commercialized by spin-off OPTRION

– Quantification of displacements :Quantification of displacements :• Phase-shiftingPhase-shifting• Carrier fringes with FFTCarrier fringes with FFT

– Response time : Response time : • 5-10 seconds 5-10 seconds • can be tuned by reference beam intensitycan be tuned by reference beam intensity

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Applications : Stroboscopic Real-TimeApplications : Stroboscopic Real-Time

a

t0-T +T

holographicrecording

stroboscopicreadout

Cw Holographic CameraCw Holographic Camera

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Pulsed experimentsPulsed experiments

Developments since 1998 (CSL and LCFIO)Developments since 1998 (CSL and LCFIO)– Use Q-switch YAG laser (COHERENT Infinity)Use Q-switch YAG laser (COHERENT Infinity)

frequency doubled : 532 nm (adapted to sillenite frequency doubled : 532 nm (adapted to sillenite crystals)crystals)

pulses : 3 nspulses : 3 ns

energies : 0 to 400 mJ/pulseenergies : 0 to 400 mJ/pulse

repetition rate : 0,1 to 30 Hzrepetition rate : 0,1 to 30 Hz

– Photorefractive crystal under isotropic diffraction processPhotorefractive crystal under isotropic diffraction process

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a

Pockels 1

a

Pockels 3

aa

delayline

M4

M5

M1

M2M3

PRcrystal O1O2PBC3O3

O3’

Cam 1

Cam 2

PBC2HWP1

DL

CL

DL

M6

object

a

CSP2

Pockels 2

a

lighttrap


– Pulse 1 : all energy used for the recording Pulse 1 : all energy used for the recording

– Pulse 2 : readoutPulse 2 : readout• decrease Edecrease Eobjobj to avoid CCD blooming to avoid CCD blooming

• decrease Edecrease Erefref to not erase the hologram to not erase the hologram

– Phase Phase measurement : measurement :• Cam 1 : I = ICam 1 : I = I0101 (1+m sin (1+m sin ))

• Cam 2 : I = ICam 2 : I = I0202 (1+m cos (1+m cos ))

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Application to vibrations : 4 pulse techniqueApplication to vibrations : 4 pulse technique

a

0 t

A f=

D12 + D2

2

2 1 – cos

a

W1

t0

a

R1

a

W2

T/4

a

R2

0

1

2

3

4

5

0 50 100 150 200 250 300 350 400

Am

plit

ude

(m

)

fréquence (Hz)

0

0,05

0,1

0,15

0,2

0,25

0,3

0,35

0,4

0 50 100 150 200 250 300 350 400

Am

plit

ude

(

m)

fréquence (Hz)

Amplitude of the frequency response in 2 pointsAmplitude of the frequency response in 2 points


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Drawbacks :Drawbacks :– Use of single-pulse laser (tricky synchronization)Use of single-pulse laser (tricky synchronization)

– Energy balance between pulsesEnergy balance between pulses

– Change of polarization state of reference beam at readout (Pockels Change of polarization state of reference beam at readout (Pockels cell)cell)

Improvements :Improvements :– Use of double-pulse lasersUse of double-pulse lasers

– Different pulse energiesDifferent pulse energies

– Passive change of polarization statePassive change of polarization state

PHIFE project started end 2001PHIFE project started end 2001

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PHIFEPHIFE

Pulsed Holographic Interferometer for the analysis of Fast Pulsed Holographic Interferometer for the analysis of Fast EventsEvents

Goal : Develop a holographic cameraGoal : Develop a holographic camera– giving high resolution results typical of PRCsgiving high resolution results typical of PRCs

– working with working with double-pulse YAG Q-switch laserdouble-pulse YAG Q-switch laser• 25 Hz repetition rate25 Hz repetition rate

• energies 800 mJ (1064 nm) and 350 mJ (532 nm)energies 800 mJ (1064 nm) and 350 mJ (532 nm)

• variable delays (down to 10 microseconds)variable delays (down to 10 microseconds)

– provides provides phase quantified dataphase quantified data

– integrated to the laser head (single box)integrated to the laser head (single box)

– adapted or adaptable to adapted or adaptable to different applicationsdifferent applications : :• solid objects (vibrations, shocks, …)solid objects (vibrations, shocks, …)

• transparent objects (aerodynamic studies in windtunels)transparent objects (aerodynamic studies in windtunels)

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Development of holographic headsDevelopment of holographic heads– ““Real-time” systems based on double-pulse lasersReal-time” systems based on double-pulse lasers

• 1064 nm : CdTe/AsGa1064 nm : CdTe/AsGa

• 532 nm : Bi532 nm : Bi1212SiOSiO2020

PHIFEPHIFE

t

record

readout

CCD emptied

– Phase quantification techniquesPhase quantification techniques• obtain a processable interferogram on a single pulseobtain a processable interferogram on a single pulse

• Techniques possible :Techniques possible :– Phase-shifting (multi-camera)Phase-shifting (multi-camera)

– FFT + carrier fringe (single-frame analysis)FFT + carrier fringe (single-frame analysis)

– othersothers

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PHIFEPHIFE Partners :Partners :

– Dantec Ettemeyer (co-ordinator, D)Dantec Ettemeyer (co-ordinator, D) : : Final integratorFinal integrator

– Centre Spatial de Liège (B)Centre Spatial de Liège (B) : : Laboratory developments (532 nm)Laboratory developments (532 nm)

– Laboratoire Charles Fabry de l ’Institut d ’Optique, Orsay (F)Laboratoire Charles Fabry de l ’Institut d ’Optique, Orsay (F) : : Laboratory developments (1064 nm)Laboratory developments (1064 nm)

– Institut für Technische Optik, Stuttgart (D)Institut für Technische Optik, Stuttgart (D)• CCD triggering system and fast frame grabberCCD triggering system and fast frame grabber

• Phase processing algorithmsPhase processing algorithms

– Innolas, (UK, D)Innolas, (UK, D) : : Double-pulse single-cavity laser developmentDouble-pulse single-cavity laser development

– Optrion, Liège (B)Optrion, Liège (B) : : Industrial Holographic head developmentIndustrial Holographic head development

– Amitronics, Seefeld (D)Amitronics, Seefeld (D) : : Industrial end-user (vibrations)Industrial end-user (vibrations)

– European Transonic Windtunel, Köln (D, UK, F, NL)European Transonic Windtunel, Köln (D, UK, F, NL) : : Industrial end-Industrial end-user (aerodynamics)user (aerodynamics)

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PHIFEPHIFE Laboratory experiments (cw YAG lasers)Laboratory experiments (cw YAG lasers) Different wavelengthsDifferent wavelengths

– 532 nm : Bi532 nm : Bi1212SiOSiO2020

– 1064 nm : AsGa - CdTe1064 nm : AsGa - CdTe

Different crystal configurations (anisotropic vs. isotropic)Different crystal configurations (anisotropic vs. isotropic)– Same object - same field - same illumination powerSame object - same field - same illumination power

– Anisotropic diffraction : better contrast - lower light levelAnisotropic diffraction : better contrast - lower light level

ANISOTROPICANISOTROPIC ISOTROPICISOTROPIC

Choice : anisotropicChoice : anisotropic- better quality- better quality- phase quantification easier- phase quantification easier

– Isotropic diffraction : no output polarizer - more light - larger objectsIsotropic diffraction : no output polarizer - more light - larger objects

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PHIFEPHIFE

Different recording geometriesDifferent recording geometries– Classical “co-propagating” geometryClassical “co-propagating” geometry

CCD camera

frontal objective lensrelay

objective lens

crystal

reference beam

CCD camera


objective lens

crystal

reference beam

– Novel “90°-geometry”Novel “90°-geometry”

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PHIFEPHIFE 90° geometry90° geometry

– BSO crystal at 532 nm : Optical ActivityBSO crystal at 532 nm : Optical Activity

– AsGa crystal at 1064 nm : No Optical activityAsGa crystal at 1064 nm : No Optical activity

CCD camera


objective lens

crystal

reference beam

polarizer

polarizer

CCD camera

reference beam

polarizer

polarizer

QWP

QWPQWP

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Phase-shifting with multi-camera systemPhase-shifting with multi-camera system

PHIFEPHIFE

CCD camera

non-polarizingbeamsplitter

QWP

polarizerpolarizer

• Cam 1 : I = ICam 1 : I = I0101 (1+m sin (1+m sin ))

• Cam 2 : I = ICam 2 : I = I0202 (1+m cos (1+m cos ))

non-polarizingbeamsplitter

/2QWP

Polarizer

Polarizer

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PHIFEPHIFE

FFT single frame processing with carrier fringesFFT single frame processing with carrier fringes– carrier obtained by active techniques : carrier obtained by active techniques :

• moving optical elements between pulsesmoving optical elements between pulses

• Not possible or very difficult due to short delaysNot possible or very difficult due to short delays

– carrier obtained with new patented technique (LCFIO) :carrier obtained with new patented technique (LCFIO) :• 2 orthogonal polarisations (anisotropic diffraction)2 orthogonal polarisations (anisotropic diffraction)

• Birefringent plate after the crystalBirefringent plate after the crystal

• Phase shift between two orthogonal polarisationsPhase shift between two orthogonal polarisations

• Phase shift proportional to beam transverse coordinatesPhase shift proportional to beam transverse coordinates

• Result : rectilinear fringesResult : rectilinear fringes

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PHIFEPHIFE FFT single frame processing with carrier fringesFFT single frame processing with carrier fringes

– Demonstration in cw regime, response time typ. 500 msDemonstration in cw regime, response time typ. 500 ms

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PHIFEPHIFE FFT single frame processing with carrier fringesFFT single frame processing with carrier fringes

– Larger objectLarger object

CARRIERCARRIER

CARRIER + OBJECT DISPLACEMENTCARRIER + OBJECT DISPLACEMENT PHASE AFTER FFT PROCESSINGPHASE AFTER FFT PROCESSING

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PHIFEPHIFE

Prototype building : choice of best configurations/geometriesPrototype building : choice of best configurations/geometries– Modular designModular design

– 2 crystals considered2 crystals considered• BiBi1212SiOSiO2020 (anisotropy - co-propagating) (anisotropy - co-propagating)

• AsGa (anisotropy - 90°)AsGa (anisotropy - 90°)

– 2 phase quantification techniques2 phase quantification techniques• 2-camera system (with both AsGa - Bi2-camera system (with both AsGa - Bi1212SiOSiO2020))

• FFT with carrier fringes (only with AsGa)FFT with carrier fringes (only with AsGa)

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PHIFEPHIFE

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PHIFEPHIFE

CAD views by OptrionCAD views by Optrion

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PHIFEPHIFE

Present-future work :Present-future work :– Integration of industrial holographic headIntegration of industrial holographic head

– Integration of holographic head with laserIntegration of holographic head with laser

– Integration of softwareIntegration of software

– Validation on known cases (with counter-measurements)Validation on known cases (with counter-measurements)

– Industrial testsIndustrial tests• Vibrations,…Vibrations,…

• AerodynamicsAerodynamics

Documents

Marc GEORGES , Philippe C. LEMAIRE , Centre Spatial de Liège, Angleur (B)