Laser Speckle interferometry: theory and applications
Maria L. Calvo Department of Optics, Complutense University of Madrid 17th February 2017, 11:00 Leonardo Building ‐ Budinich Lecture Hall
Winter College on Optics 2017: Advanced Optical Techniques for Bio‐imaging. 13‐24 February 2017 1 Outline
• To introduce, study and discuss the concept and fundamentals of laser speckle.
• To interpret the speckle formation: first order statistics.
• Some classical techniques: stationary and dynamic laser speckle imaging.
• Dynamic speckle in an image forming system.
• Applications in biomedicine: biospeckle
Maria L. Calvo Lecture Notes. Winter College “Advanced Optical Techniques for Bioimaging”, ICTP, Trieste, 13‐24 February, 2017 2 Contents
• Introduction: speckle phenomenon. • Speckle formalism: first order statistics. Random interference phenomenon. • Speckle formation in an image forming system. • Dynamic speckle in image forming systems: basic principles. • Contrast function in dynamic laser speckle. • Speckle equivalent phenomena in non‐linear optics • Applications in Biomedicine: examples of biospeckle. • Experimental laboratory. • Conclusions • Main references.
Maria L. Calvo Lecture Notes. Winter College “Advanced Optical Techniques for Bioimaging”, ICTP, Trieste, 13‐24 February, 2017 3 Introduction: Speckle phenomenon • Observed in early 60’s as the use of laser sources started to be introduced in the laboratories. • Pioneering work of J. W. Goodman and J. C. Dainty. • Speckle effect is readily observed with highly coherent illumination. • There is a granular structure of the coherent pattern.
Formation and observation of speckle requires high spatio‐temporal coherence.
Maria L. Calvo Lecture Notes. Winter College “Advanced Optical Techniques for Bioimaging”, ICTP, Trieste, 13‐24 February, 2017 4 Speckle pattern
• Speckle pattern consists of a multitude of bright spots where the random interference has been highly constructive. • Dark spots where the random interference has been highly destructive. • Irradiance levels in between these extremes. Randomly varying intensity pattern
We observe a continuum of values of irradiance which has the appearance of a chaotic jumble of "speckles". It is a coherent light scattering phenomenon becoming visible to the naked eye, with visible laser sources. (i.e., He‐Ne laser).
Reference: M. L Calvo, “Coherencia óptica”, Investigación y Ciencia (Spanish version of Scientific Maria L. Calvo Lecture Notes. Winter College “Advanced Optical American), p.p. 66‐73 (May 1995). Techniques for Bioimaging”, ICTP, Trieste, 13‐24 February, 20175 First‐order statistics of a polarized speckle pattern
• Random walk model Im ak N • Single scattering of coherent (laser) light by a collection of particles (roughness or scatterers) E dispersed through a volume. • Scatterers dimension is much greater than the Re wavelength of the illuminating radiation. • Single polarized component of the scattered Constructive addition complex field amplitude E