Centre Spatial de Lige Universit de Lige Pulsed

Centre Spatial de Liège Université de Liège Pulsed holographic interferometry with photorefractive crystals. Recent advances of the european “PHIFE” project Marc GEORGES, Philippe C. LEMAIRE, Centre Spatial de Liège, Angleur (B) Gilles PAULIAT, Gérald ROOSEN Laboratoire Charles Fabry de l ’Institut d ’Optique, Orsay (F) Igor ALEXENKO, Giancarlo PEDRINI, Institut für Technische Optik, Stuttgart (D) Sébastien RYHON, OPTRION S. A. , Liège (B) © Centre Spatial de Liège, LAVINYA, London 2004 1

Centre Spatial de Liège Université de Liège ¨ Summary Photorefractive effect – Definition – Application to holographic interferometry ¨ cw Photorefractive holographic camera – applied to vibration ¨ Pulsed system – applied to vibration – discussion : drawback lead to PHIFE project ¨ PHIFE project – – © goals partnership laboratory studies present/future work Centre Spatial de Liège, LAVINYA, London 2004 2

Centre Spatial de Liège Université de Liège Photorefractive Effect 1. Fringe pattern created by interference between 2 waves 2. Charges generated by photo-excitation in illuminated area, migrate and are trapped in dark area 3. Local space charge field Pockels effect 4. Modulation of refractive index Dn THICK PHASE HOLOGRAM © Centre Spatial de Liège, LAVINYA, London 2004 3

Centre Spatial de Liège Université de Liège ¨ Photorefractive Effect PR effect is dynamic and reversible incident Object state 0 Object state 1 Object state 2 Interferogram 1 Interferogram 2 diffracted – Recording energy at saturation : Es = t. I – Diffraction efficiency : h = Idiff/Iref ~ (Dn)2 cw lasers pulsed lasers Dn = Dnsat (1 -exp(-t/t)) ¨ Application to holographic interferometry interference between diffracted beam (reference object state) transmitted beam (deformed object state) © Centre Spatial de Liège, LAVINYA, London 2004 4

Centre Spatial de Liège Université de Liège ¨ Photorefractive Effect Application to pulse holographic interferometry – First pulse : • Hologram recording • object state 0 record readout – Second pulse : • • • © Hologram readout object state 1 Interferogram showing (state 1 - state 0) Centre Spatial de Liège, LAVINYA, London 2004 CCD emptied 5

Centre Spatial de Liège Université de Liège Visible (blue-green) NIR (l=1 µm) © Photorefractive crystals Sillenite Bi 12 Si. O 20 (BSO) High sensitivity : ES ~ 1 -10 m. J/cm 2 Poorest efficiency : h~ 0. 1 % Ferroelectrics Li. Nb. O 3, Ba. Ti. O 3 Poor sensitivity : ES ~ 1 J/cm 2 Highest efficiency : h~ 100 % Semiconductors Cd. Te, Ga. As Highest sensitivity : ES ~ 0. 1 -1 m. J/cm 2 Poor efficiency : h~ 1 % Centre Spatial de Liège, LAVINYA, London 2004 6

Centre Spatial de Liège Université de Liège ¨ Photorefractive effect Particular properties : depend on crystal cut Anisotropic diffraction Interferogram contrast depends on the analyser orientation © Centre Spatial de Liège, LAVINYA, London 2004 Isotropic diffraction Interferogram contrast depends on the product : -coupling constant -crystal thickness 7

Centre Spatial de Liège Université de Liège ¨ Cw Holographic Camera Developed by CSL : 1993 -1998 – – Optical head : L=25 cm, 1 kg Laser : DPSS, VERDI 5 W Laser light brought by optical fiber Specialty fiber developed (5 m, Transmission 80%, 5 W injected) – Quantification of displacements : • Phase-shifting • Carrier fringes with FFT – Response time : • 5 -10 seconds • can be tuned by reference beam intensity ¨ © Now commercialized by spin-off OPTRION Centre Spatial de Liège, LAVINYA, London 2004 8

Centre Spatial de Liège Université de Liège ¨ © Cw Holographic Camera Applications : Stroboscopic Real-Time Centre Spatial de Liège, LAVINYA, London 2004 9

Centre Spatial de Liège Université de Liège ¨ Pulsed experiments Developments since 1998 (CSL and LCFIO) – Use Q-switch YAG laser (COHERENT Infinity) frequency doubled : 532 nm (adapted to sillenite crystals) pulses : 3 ns energies : 0 to 400 m. J/pulse repetition rate : 0, 1 to 30 Hz – Photorefractive crystal under isotropic diffraction process © Centre Spatial de Liège, LAVINYA, London 2004 10

Centre Spatial de Liège Université de Liège Pulsed experiments – Pulse 1 : all energy used for the recording – Pulse 2 : readout • decrease Eobj to avoid CCD blooming • decrease Eref to not erase the hologram © Centre Spatial de Liège, LAVINYA, London 2004 – Phase f measurement : • Cam 1 : I = I 01 (1+m sin f) • Cam 2 : I = I 02 (1+m cos f) 11

Centre Spatial de Liège Université de Liège ¨ Pulsed experiments Application to vibrations : 4 pulse technique Amplitude of the frequency response in 2 points © Centre Spatial de Liège, LAVINYA, London 2004 12

Centre Spatial de Liège Université de Liège ¨ Pulsed experiments Drawbacks : – Use of single-pulse laser (tricky synchronization) – Energy balance between pulses – Change of polarization state of reference beam at readout (Pockels cell) ¨ Improvements : – Use of double-pulse lasers – Different pulse energies – Passive change of polarization state ¨ © PHIFE project started end 2001 Centre Spatial de Liège, LAVINYA, London 2004 13

Centre Spatial de Liège Université de Liège ¨ ¨ PHIFE Pulsed Holographic Interferometer for the analysis of Fast Events Goal : Develop a holographic camera – giving high resolution results typical of PRCs – working with double-pulse YAG Q-switch laser • 25 Hz repetition rate • energies 800 m. J (1064 nm) and 350 m. J (532 nm) • variable delays (down to 10 microseconds) – provides phase quantified data – integrated to the laser head (single box) – adapted or adaptable to different applications : • solid objects (vibrations, shocks, …) • transparent objects (aerodynamic studies in windtunels) © Centre Spatial de Liège, LAVINYA, London 2004 14

PHIFE Centre Spatial de Liège Université de Liège ¨ Development of holographic heads – “Real-time” systems based on double-pulse lasers • 1064 nm : Cd. Te/As. Ga • 532 nm : Bi 12 Si. O 20 record readout CCD emptied – Phase quantification techniques • obtain a processable interferogram on a single pulse • Techniques possible : – – – © Phase-shifting (multi-camera) FFT + carrier fringe (single-frame analysis) others Centre Spatial de Liège, LAVINYA, London 2004 15

Centre Spatial de Liège Université de Liège ¨ PHIFE Partners : – – – Dantec Ettemeyer (co-ordinator, D) : Final integrator Centre Spatial de Liège (B) : Laboratory developments (532 nm) Laboratoire Charles Fabry de l ’Institut d ’Optique, Orsay (F) : Laboratory developments (1064 nm) – Institut für Technische Optik, Stuttgart (D) • CCD triggering system and fast frame grabber • Phase processing algorithms – Innolas, (UK, D) : Double-pulse single-cavity laser development – Optrion, Liège (B) : Industrial Holographic head development – Amitronics, Seefeld (D) : Industrial end-user (vibrations) – European Transonic Windtunel, Köln (D, UK, F, NL) : Industrial enduser (aerodynamics) © Centre Spatial de Liège, LAVINYA, London 2004 16

Centre Spatial de Liège Université de Liège ¨ ¨ PHIFE Laboratory experiments (cw YAG lasers) Different wavelengths – 532 nm : Bi 12 Si. O 20 – 1064 nm : As. Ga - Cd. Te ¨ Different crystal configurations (anisotropic vs. isotropic) – Same object - same field - same illumination power – Anisotropic diffraction : better contrast - lower light level – Isotropic diffraction : no output polarizer - more light - larger objects Choice : anisotropic - better quality - phase quantification easier ANISOTROPIC © Centre Spatial de Liège, LAVINYA, London 2004 ISOTROPIC 17

Centre Spatial de Liège Université de Liège ¨ PHIFE Different recording geometries – Classical “co-propagating” geometry – Novel “ 90°-geometry” © Centre Spatial de Liège, LAVINYA, London 2004 18

Centre Spatial de Liège Université de Liège ¨ PHIFE 90° geometry – BSO crystal at 532 nm : Optical Activity – As. Ga crystal at 1064 nm : No Optical activity © Centre Spatial de Liège, LAVINYA, London 2004 19

Centre Spatial de Liège Université de Liège ¨ PHIFE Phase-shifting with multi-camera system • Cam 1 : I = I 01 (1+m sin f) • Cam 2 : I = I 02 (1+m cos f) © Centre Spatial de Liège, LAVINYA, London 2004 20

Centre Spatial de Liège Université de Liège ¨ PHIFE FFT single frame processing with carrier fringes – carrier obtained by active techniques : • moving optical elements between pulses • Not possible or very difficult due to short delays – carrier obtained with new patented technique (LCFIO) : • • • © 2 orthogonal polarisations (anisotropic diffraction) Birefringent plate after the crystal Phase shift between two orthogonal polarisations Phase shift proportional to beam transverse coordinates Result : rectilinear fringes Centre Spatial de Liège, LAVINYA, London 2004 21

Centre Spatial de Liège Université de Liège ¨ PHIFE FFT single frame processing with carrier fringes – Demonstration in cw regime, response time typ. 500 ms © Centre Spatial de Liège, LAVINYA, London 2004 22

Centre Spatial de Liège Université de Liège ¨ PHIFE FFT single frame processing with carrier fringes – Larger object CARRIER + OBJECT DISPLACEMENT PHASE AFTER FFT PROCESSING CARRIER © Centre Spatial de Liège, LAVINYA, London 2004 23

Centre Spatial de Liège Université de Liège ¨ PHIFE Prototype building : choice of best configurations/geometries – Modular design – 2 crystals considered • Bi 12 Si. O 20 (anisotropy - co-propagating) • As. Ga (anisotropy - 90°) – 2 phase quantification techniques • 2 -camera system (with both As. Ga - Bi 12 Si. O 20) • FFT with carrier fringes (only with As. Ga) © Centre Spatial de Liège, LAVINYA, London 2004 24

Centre Spatial de Liège Université de Liège © Centre Spatial de Liège, LAVINYA, London 2004 PHIFE 25

Centre Spatial de Liège Université de Liège ¨ © PHIFE CAD views by Optrion Centre Spatial de Liège, LAVINYA, London 2004 26

Centre Spatial de Liège Université de Liège ¨ PHIFE Present-future work : – – – Integration of industrial holographic head Integration of holographic head with laser Integration of software Validation on known cases (with counter-measurements) Industrial tests • Vibrations, … • Aerodynamics © Centre Spatial de Liège, LAVINYA, London 2004 27