Joint International Physics Summer School Optics (Olomouc, August 28 September 01, 2017) Speckle phenomenon and its potential for metrology Pavel Horváth* & Petr Šmíd** *Palacký University, Faculty of Science, Regional Centre of Advanced Technologies and Materials, Joint Laboratory of Optics of Palacky University and Institute of Physics AS CR, 17. listopadu 1192/12, 771 46 Olomouc, Czech Republic **Institute of Physics of the Czech Academy of Sciences, Joint Laboratory of Optics of Palacky University and Institute of Physics AS CR, 17. listopadu 50a, 772 07 Olomouc, Czech Republic
Contents 1. Speckle and its origin. I - 2. Speckle basic properties. 3. Some applications of speckle. 4. Speckle s potential for metrology PA RT Speckle correlation method. Electronic speckle pattern interferometry. 5. Conclusion. PA RT II Pa - ve l Pe tr H or vá t Šm íd h
1. Speckle and its origin Speckle field: arises if an object with a rough surface is illuminated by a coherent optical beam. a result of the interference of multiple coherent spherical waves generated by point sources forming the object s surface. Speckle pattern: a chaotic (random) pattern consisting of dark and bright speckles. Illustration of a speckle field origin in case of reflection of coherent light from an object s rough surface.
1. Speckle and its origin Condition of speckle field origin: roughness of object s surface ( random changes of height profile Δ ) is on the scale of an optical wavelength λ of incident light: (Δ λ = 500 nm). the rough object introduces path differences greater than one wavelength of used light. The surfaces of most materials comply the condition of roughness: metals, paper, wood, rubber, plant leafs, human tissue... visibility and properties of speckle pattern then depend only on the coherence and polarization of the incident light. Physical origin of speckle (diffuse reflection of light wave from an object s rough surface).
2. Speckle basic properties Objective and subjective speckle: FREE SPACE O B SP JE EC C T KL IVE E SU SP BJ E C EC KL T I V E E IMAGE FIELD A) Objective and B) subjective laser speckle pattern recorded by a CMOS camera.
2. Speckle basic properties 2-D speckle size in the speckle pattern: The average size d of the objective speckle formed on a screen at a distance L, by reflecting (or scattering) of coherent light from a circular region of a diameter D is given by: L d 1.22 D, where λ is the wavelength of the laser light. Formation of objective speckle.
2. Speckle basic properties 2-D speckle size in the speckle pattern: L d 1.22 D Influence of the distance L between the object plane and observation plane on the speckle size d! L1 < L2 d1 < d 2 Formation of objective speckle.
2. Speckle basic properties 2-D speckle size in the speckle pattern: L d 1.22 D Influence of the distance L between the object plane and observation plane on the speckle size d! L1 < L2 d1 < d 2 Formation of objective speckle.
2. Speckle basic properties 2-D speckle size in the speckle pattern: L d 1.22 D Influence of diameter D of circular illuminated region of the object s surface on the speckle size d! D1 > D2 d1 < d 2 Formation of objective speckle.
2. Speckle basic properties 2-D speckle size in the speckle pattern: L d 1.22 D Influence of diameter D of circular illuminated region of the object s surface on the speckle size d! D1 > D2 d1 < d 2 Formation of objective speckle.
2. Speckle basic properties 2-D speckle size in the speckle pattern: L d 1.22 D Influence of wavelength λ of incident laser light on the speckle size d! λ1 < λ2 d1 < d2 Formation of objective speckle.
2. Speckle basic properties 2-D speckle size in the speckle pattern: L d 1.22 D Influence of wavelength λ of incident laser light on the speckle size d! λ1 < λ2 d1 < d2 Formation of objective speckle.
2. Speckle basic properties 3-D speckle visualization in speckle field: [Source of the pictures: POSPĚCH, M. Shape Analysis of a Speckle in Speckle Pattern. Olomouc, 2010. 70 s. Diploma thesis. Palacký University in Olomouc.]
3. Some applications of speckle Two-faced of speckle phenomenon: GOOD Dr. Jekyll EVIL Mr. Hyde [Source of the picture: http://www.runtimedna.com/jekyll-and-hyde.html/] Musical Jekyll & Hyde by composer Frank Wildhorn
3. Some applications of speckle Two-faced of speckle phenomenon: GOOD EVIL Unwanted noise during reconstruction of holograms or interferograms: Wide variety of practical applications: optics (measurement of refraction index of liquids), holography, holographic interferometry. mechanics (measurement of object s roughness and deformation), astronomy (detection of binary stars, 0 measurement of diameter of astronomical objects), biology (measurement of biological activity), ecology (detection of air pollution). Images of interferometry fringes. A) corrupted by speckle noise, and B) after speckle reduction.
3. Some applications of speckle BIOLOGY / ECOLOGY Monitoring of biological activity of plant using difference image of biospeckle. Optical set-up. Syngonium. Biospeckle difference images of Singonium plant (a) before, (b) two days, and (c) three weeks after giving the artificial acid rain. [Source of the pictures: KADONO, H., TAKAHASHI, G., TOYOOKA, S. Monitoring of biological activity of plant using difference image of biospeckle. In 19th Congress of the ICO, Consortini, A., Righini, G. C., eds., Proc. SPIE, 2002, 4829, pp. 955-956.]
3. Some applications of speckle ASTRONOMY Detection of binary stars by a stellar speckle interferometry. Inventor of the technique: A. Labeyrie (1970). Interferometer = telescope (light is reflected from all parts of telescope mirror into its centre of curvature and then the speckle is arised due to interference). Laboratory simulations showing the principles of stellar speckle interferometry. (A: astronomical objects; B: short exposure photographs; C: diffraction patterns of row B; D: sum of 20 diffraction patterns.) Short exposure photographs of star α Orionis is taken on a 4 m class telescope (exposure time 10 ms; filter bandwith 10 nm). [Source of the pictures: DAINTY, J.C.,Ed., Laser Speckle and Related Phenomena. Springer-Verlag, Berlin, 1984.]
3. Some applications of speckle Rayleigh criterion: ASTRONOMY 1,22 D Δa angular resolution of a telescope, D diameter of a telescope mirror, λ operating wavelength. (for D = 4 m, λ = 400 nm Δa = 0.025 ) Project of hypertelescope Carlina 1 (2004) Balloon altitude: 120 m, Balloon lift: 70 kg, Gondola mass: 12 kg, Mirror segments: zerodur, 250 mm diameter, spherical surface, 70 m curvature radius, Focal length: 35 m. Principle of hypertelescope. Many small mirrors are distibuted on spherical surface (green). Helium balloon carries a gondola that contains focal optics (blue). The red arrows show the light rays. Optical set-up of hypertelescope. [Source of the pictures: http://www.obs-hp.fr/~dejonghe/index.html]