现代光学测试技术 教学课件 ppt 作者 王文生 Chapter6 Holographic interferometry.pdf

Wang wensheng §§§§ 6.1 General Principle ★★ Principle Compare two or many coherent wavefronts which are produced at different time, different condition, and at least, one wave is holographicdifferent time, different condition, and at least, one wave is holographic reconstructed wavefront, these waves interfere, occurs interference pattern. Fi ttii tft?From interpreting interferogram, get Deformation Displacementstress vibration … …Displacement stress vibration … … ?Example: Object amplitude After deformation Interfere: §§ 6 1 Gl P ii l ?Intensity is modulated by §§ 6.1 General Principle Intensity is modulated by Bright Peak Dark Valley ★★Features of holographic interferometry Conventional Holographic Formed at same timeAt different timeFormed at same time At different time Pass different path Along the same path R is bounded by form R is original O wave O: Smooth plane sphericalO: irregular formO: Smooth plane, spherical, O: irregular form, aspherical rough surface, large size ★★ Classification Real-time interferometry Double exposure interferometry §§ 6 1 Gl P ii l iif( ii) §§ 6.1 General Principle Time-average interferometry(Vibration) Two-wavelength holographic interferometry Double-source holographic interferometry (Surface relief) ★★ Disadvantage 1. High requirement on the light source Si lhlhSpacial coherence, temporal coherence Brightness 2. Low sensitivity of high-resolution2. Low sensitivity of high resolution Holographic photo layers §§ 6 2 Rl tith d il h l§§ 6.2 Real-time method-single hologram Interference pattern of two waves one is reconstructed by hologramInterference pattern of two waves, one is reconstructed by hologram and is initial state of the object as R, other is scattered by the object during observation. ★★ St★★ Step: 1. O(x, y) and R(x, y) interfere, occurs interferogram on H 2. H home position at accuracy 3. Deformed object wave interfere with reconstructed wave produce fringes 4 Obthhf f id i tt4. Observe the change of fringes and interpret Original reconstructed wave: Scattered wave : If of object is no changed §§ 6.2 Real-time method-single hologram N i tf §§ 6.2 Real time method single hologram No interferogram If object is deformed ★★ Condition of high contrast Diffraction efficiency D Adt Advantage: Investigation dynamic process with λ accuracy Disadvantage: Resolve: ①① BSO crystal Home position Resolve: ①① BSO crystal ②② TPF thermoplasticphotoconductor film §§ 6 2 Real-time method-single hologram ★★Requirement 1 Cttditi §§ 6.2 Real-time method-single hologram 1. Contrast condition In R or O path placed Attenuator ※※ Filter must be high quality otherwise phase distortion is induced. 2. Coherence condition Equal O P 3. Polarization condition polarizer Scattering object eliminates polarization about 50% 4. Stability condition Triple mirror Corner cube 5. Resolution condition §§ 6 2 Real-time method-single hologram§§ 6.2 Real-time method-single hologram Deformation of a metal plate with real-time HDeformation of a metal plate with real time H §§ 6 3 Dblth d§§ 6.3 Double-exposure method ★★ P ii l★★ Principle: •Exposure two holograms of a single object in different state on the same light sensitive layer •Read out by R, reconstructed wave A01 A02, A01A02 interfere, produce interferogram. ★★ Characters: •No home position problem •Read out beam may differ from reference beamRead out beam may differ from reference beam, The scale distortion and displacement of image will be identical for both wave, image will be identical for both wave, interference fringes remains unchangedinterference fringes remains unchanged •Both exposure time and condition of illumination should be identical, both amplitude of reconstructed wave then be same. §§ 6 3 Double exposure method ◆◆ Recording H §§ 6.3 Double-exposure method Amplitude transmittance ◆◆ Reconstruction Reconstructed object waves Let §§ 6 4 Tith d§§ 6.4 Time-average method -Many holograms (for vibration measurementyg( ★★ Principle ◆◆ If an object vibrates during an exposure The duration of the exposure exceeds the period of vibrations, then H will record the waves scattered by object, in all states, reconstructed waves form an interferogram, which indicates the nature of vibration. ◆◆ Extreme (amplitude) position (A, B) come to a full stop, exposure time are greater, and contribution to total exposure arepg,p maximum. Therefore we can approximately consider: the hologram obtained corresponding to the two Amplitude position of Object O as a hologram produced by the double exposure methodof Object O as a hologram produced by the double exposure method. Amplitude of O : O Vibration : A1(x, y, 0) §§ 6 4 Time average method ?According to Fresnel diffraction, at H §§ 6.4 Time-average method Series expansion Let §§ 6 4 Time average method ★ H recording §§ 6.4 Time-average method If harmonic vibration J: Besel function •Read out with, reconstructed A(x, y) i。