Wave interference

In physics, interference is a phenomenon in which two coherent waves are combined by adding their intensities or displacements with due consideration for their phase difference. The resultant wave may have greater intensity (constructive interference) or lower amplitude (destructive interference) if the two waves are in phase or out of phase, respectively. Interference effects can be observed with all types of waves, for example, light, radio, acoustic, surface water waves, gravity waves, or matter waves as well as in loudspeakers as electrical waves. Etymology The word interference is derived from the Latin words inter which means "between" and fere which means "hit or strike", and was coined by Thomas Young in 1801. Mechanisms The principle of superposition of waves states that when two or more propagating waves of the same type are incident on the same point, the resultant amplitude at that point is equal to the vector sum of the amplitudes of the individu

Broadband Digital Holographic Camera for Microscopy

Zahra Monemhaghdoust

In this thesis, we explore a combination of analog and digital holographic techniques to demonstrate high speed quantitative phase imaging (QPI) using low coherence (broad bandwidth) light sources. Off-axis digital holographic microscopy is inherently a coherent method of phase quantification and thus suffers from coherent noise. However, only one measurement is required to retrieve field information which gives an advantage in term of image acquisition speed. While incoherent methods of phase quantification remove the problem of coherent noise, they require acquiring several measurements which is sometimes not acceptable in the study of dynamical systems. Therefore, this thesis is an attempt to extend off-axis digital holographic microscopy from the coherent to the incoherent regime to maintain the benefit of high speed measurement capability of off-axis holography while reducing the coherent noise. First, we demonstrate that by using a suitable combination of holographic gratings, off-axis digital holographic microscopy can work with spectrally broadband illumination sources. Holographic gratings introduce a tilt in the coherence plane of one of the reference or object arms of an off-axis digital holographic microscope to expand the interference area to the whole field of view of the camera. Although QPI provides useful information in addition to state-of-the-art intensity-based microscopic imaging, its use has not permeated yet far beyond research laboratories. One potential reason is the need for a stand-alone dedicated microscope system, which is expensive and not back-compatible to the existing wide-field microscopes. In this Regard, the second part of this thesis explores an add-on camera module which can be attached to the camera port of any standard intensity microscope. The techniques developed to extend the off-axis DHM in the first part of the thesis will be used to demonstrate a proof-of-concept camera module which operates with broadband light sources. Overall, through the combination of analog and digital holography, the goal of this work is to extend full-field off-axis holography to incoherent regime to benefit from real-time speckle-free measurements, optical sectioning and realization of a digital holographic camera which can be placed in the image plane of a standard optical microscope.

EPFL2015

Spatial fringe analysis techniques for multiple phase and phase derivative estimation

Rishikesh Dilip Kulkarni

Analysis of fringe patterns for the accurate estimation of phase and phase derivatives is of crucial importance in optical interferometry as these quantities provide important information on the physical parameters under study. A wide range of applications including the measurement of object surface displacement, strain, changes in the refractive index and object shape are made possible by accurate fringe analysis. The essential characteristics of any fringe analysis technique include noise robustness, high accuracy, computational efficiency and single frame demodulation capability. The thesis proposes a wide range of fringe analysis techniques to address the problem of accurate estimation of phase and phase derivatives. It also offers solution to the problem of simultaneous estimation of multiple phase and phase derivatives from a single frame of the interference field. For the purpose of our study, we have considered single/multicomponent real/complex sinusoidal fringe patterns recorded in single/multi-wave digital holographic/speckle interferometry setups. A piecewise polynomial phase approximation allows for the simultaneous estimation of multiple phases. Signal processing techniques are exploited for the accurate estimation of the polynomial coefficients. The autoregressive model of the fringe pattern provides a generalized and powerful approach for the direct estimation of phase derivatives from single/multi-component real/complex sinusoidal fringe patterns. The technique based on matrix enhancement and matrix pencil is proposed for the simultaneous estimation of multiple phase derivatives. The matrix enhancement approach provides a unique way for the reliable filtering of highly noisy fringe patterns. In a different approach more adopted to the multicomponent signal analysis, techniques based on windowed Fourier transform and noise subspace inflation are proposed for the robust and reliable separation of the multiple signal components. Independent analysis of these signal components further provides the multiple phase or/and phase derivatives estimates. In the case of complex sinusoidal fringe pattern, we have also proposed for the first time a method for the simultaneous estimation of unwrapped phase and phase derivatives of arbitrary order. The thesis ends by providing a solution to the difficult yet important problem of closed fringe pattern demodulation. The proposed methods are evaluated with number of simulation examples under different variable parameters such as signal to noise ratio, amplitude ratio of signal components, window size, basis dimension, etc. The error analyses performed with respect to these variables demonstrate the noise robustness offered by the proposed methods. The proposed methods are also found capable of handling complex fringe patterns in a computationally efficient manner. Experimental validations of the proposed methods are performed with fringe patterns recorded in single/multi wave digital holographic interferometry and digital speckle pattern interferometry setups. The single frame fringe analysis capability of the proposed methods makes them highly suitable for dynamic measurement applications.

EPFL2016

Broadband Digital Holographic Camera for Microscopy

Zahra Monemhaghdoust

EPFL2015

Spatial fringe analysis techniques for multiple phase and phase derivative estimation

Rishikesh Dilip Kulkarni

EPFL2016

Wavelet analysis of interference patterns and signals

Broadband Digital Holographic Camera for Microscopy

Spatial fringe analysis techniques for multiple phase and phase derivative estimation

Wavelet analysis of interference patterns and signals

Broadband Digital Holographic Camera for Microscopy

Spatial fringe analysis techniques for multiple phase and phase derivative estimation