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ABSTRACT: Several existing strategies for estimating the axial intensity derivative in the transport-of-intensity equation (TIE) from multiple intensity measurements have been unified by the Savitzky-Golay differentiation filter - an equivalent convolution solution for differentiation estimation by least-squares polynomial fitting. The different viewpoint from the digital filter in signal processing not only provides great insight into the behaviors, the shortcomings, and the performance of these existing intensity derivative estimation algorithms, but more important, it also suggests a new way of improving solution strategies by extending the applications of Savitzky-Golay differentiation filter in TIE. Two novel methods for phase retrieval based on TIE are presented - the first by introducing adaptive-degree strategy in spatial domain and the second by selecting optimal spatial frequencies in Fourier domain. Numerical simulations and experiments verify that the second method outperforms the existing methods significantly, showing reliable retrieved phase with both overall contrast and fine phase variations well preserved.
Optics Express 03/2013; 21(5):5346-5362. · 3.59 Impact Factor
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ABSTRACT: The application of a single cube beam splitter (SCBS) microscope to micro-optics characterization is presented. The SCBS in the optical path, with a small angle between the optical axis and its central semireflecting layer, not only gives off-axis digital holograms but also provides dual-channel imaging. It is a unique and easy way to perform uniformity inspection across the entire microlens array. Experimental results on physical spherical phase compensation, single lens characterization, dual-channel imaging, and uniformity inspection are provided to demonstrate the unique properties of SCBS microscopy.
Applied Optics 02/2011; 50(6):886-90. · 1.41 Impact Factor
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ABSTRACT: A new optical configuration for digital holographic microscopy is presented. Digital off-axis holograms are recorded by use of a single cube beam splitter in a nonconventional configuration to both split and combine a diverging spherical wavefront as it emerges from a single point source. Both the amplitude and the phase can then be reconstructed, yielding intensity and phase images with improved resolution. The novelty of the proposed configuration is its simplicity, minimal number of optical elements, insensitivity to vibration, and its inherent capability to compensate for the phase curvature that results from the illuminating wavefront in the case of microscopic samples.
Applied Optics 06/2009; 48(15):2778-83. · 1.41 Impact Factor
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ABSTRACT: Digital micro-holography technique, a combination of digital holography with microscopy, can be used to measure and analyse the micro-structure and status information of samples when the digital hologram registered is reconstructed numerically by some numerical methods based on the principle of scalar diffraction or coherent image. By summarizing the development of digital micro-holography, Fresnel approximation reconstruction algorithm and two-wavelength technique are introduced to study the three dimensional phase reconstruction of phase grating. Experimental results show good agreement with true parameters of phase grating. It also analyses the aberration of the image reconstructed by Fresnel approximation approach and two-wavelength technique.
Journal of Physics Conference Series 07/2007; 48(1):1418.
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ABSTRACT: A digital phase-shifting in-line holographic system based on the single coherence beam is developed. A series of phase-shifting fringes are generated by computer and outputted by a digital micro-mirror device (DMD). These fringes modulate the coherence beam because of the intensity modulation ability of DMD. In this work, the reconstructed conjugate image would not appear because of applying the phase-shifting algorithm. And calibration for the value of the optical phase shift is not necessary. An experiment based on a lens-less digital in-line micro-holographic setup with a phase grating specimen is conducted to demonstrate the validity of the present method.
Optics and Lasers in Engineering.
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ABSTRACT: This paper discusses methods to eliminate and/or suppress aberrations in digital micro-holography (DMH) with specific examples for post-magnification DMH and lens-less DMH along with a phase subtraction approach. In post-magnification DMH, the reference wave interferes with the object wave to form a hologram, which is then magnified by a microscope objective (MO) and recorded by CCD. This compensates for the quadratic phase error usually present in the pre-magnification DMH and also it is easier to isolate the useful information in pre-processing. In this paper differences between post-magnification and pre-magnification DMH are compared and analyzed with the specimen of a phase grating with period 30 lines/mm and height 0.3 μm. A lens-less DMH is also described that can eliminate the quadratic error and most of wave-front errors of the projecting light. Finally, a phase subtraction method is demonstrated which can eliminate most of the system aberrations.
Optics and Lasers in Engineering.
