Showing papers by "Pietro Ferraro published in 2011"

Automatic focusing in digital holography and its application to stretched holograms

Abstract: The searching and recovering of the correct reconstruction distance in digital holography (DH) can be a cumbersome and subjective procedure. Here we report on an algorithm for automatically estimating the in-focus image and recovering the correct reconstruction distance for speckle holograms. We have tested the approach in determining the reconstruction distances of stretched digital holograms. Stretching a hologram with a variable elongation parameter makes it possible to change the in-focus distance of the reconstructed image. In this way, the proposed algorithm can be verified at different distances by dispensing the recording of different holograms. Experimental results are shown with the aim of demonstrating the usefulness of the proposed method, and a comparative analysis has been performed with respect to other existing algorithms developed for DH.

3D lithography by rapid curing of the liquid instabilities at nanoscale

Abstract: In liquids realm, surface tension and capillarity are the key forces driving the formation of the shapes pervading the nature. The steady dew drops appearing on plant leaves and spider webs result from the minimization of the overall surface energy [Zheng Y, et al. (2010) Nature 463:640–643]. Thanks to the surface tension, the interfaces of such spontaneous structures exhibit extremely good spherical shape and consequently worthy optical quality. Also nanofluidic instabilities generate a variety of fascinating liquid silhouettes, but they are however intrinsically short-lived. Here we show that such unsteady liquid structures, shaped in polymeric liquids by an electrohydrodynamic pressure, can be rapidly cured by appropriate thermal treatments. The fabrication of many solid microstructures exploitable in photonics is demonstrated, thus leading to a new concept in 3D lithography. The applicability of specific structures as optical tweezers and as novel remotely excitable quantum dots–embedded microresonators is presented.

Digital holographic microscopy with pure-optical spherical phase compensation

Abstract: Telecentric architecture is proposed for circumventing, by the pure-optical method, the residual parabolic phase distortion inherent to standard configuration of digital holographic microscopy. This optical circumvention produces several important advantages. One is that there is no need for computer compensation of the parabolic phase during the phase map recovering procedure. The other is that in off-axis configuration, the spatial frequency useful domain is enlarged. The validity of the method is demonstrated by performing quantitative measurement of depth differences with high axial resolution.

Dynamic DIC by digital holography microscopy for enhancing phase-contrast visualization

Abstract: Differential image contrast (DIC), through the numerical managing and manipulation of complex wavefronts obtained by digital holography (DH), is investigated. We name the approach Dynamical Differential Holographic Image Contrast (DDHIC). DDHIC dispenses from special optics and/or complex setup configurations with moveable components, as usually occurs in classical DIC, that is not well-suited for investigating objects experiencing dynamic evolution during the measurement. In fact, the technique presented here, is useful for floating samples since it allows, from a single recording, to set a posteriori the best conditions for DIC imaging in conjunction with the numerical focusing feature of DH. By DDHIC, the movies can be easily built-up to offering dynamic representation of phase-contrast along all directions, thus improving the visualization. Furthermore, the dynamic representation is useful for making the proper choice of other key parameters of DIC such as the amount of shear and the bias, with the aim to optimize the visualized phase-contrast imaging as favorite representation for bio-scientists. Investigation is performed on various biological samples.

Identification of bovine sperm head for morphometry analysis in quantitative phase-contrast holographic microscopy

Abstract: An investigation is reported of the identification and measurement of region of interest (ROI) in quantitative phase-contrast maps of biological cells by digital holographic microscopy. In particular, two different methods have been developed for in vitro bull sperm head morphometry analysis. We show that semen analysis can be accomplished by means of the proposed techniques . Extraction and measurement of various parameters are performed. It is demonstrated that both proposed methods are efficient to skim the data set in a preselective analysis for discarding anomalous data.

Twin-beams digital holography for 3D tracking and quantitative phase-contrast microscopy in microfluidics.

Abstract: We report on a compact twin-beam interferometer that can be adopted as a flexible diagnostic tool in microfluidic platforms with twofold functionality. The novel configuration allows 3D tracking of micro-particles and, at same time, can simultaneously furnish Quantitative Phase-contrast maps of tracked micro-objects by interference microscopy, without changing the configuration. Experimental demonstration is given on for in vitro cells in a microfluidic environment.

Driving and analysis of micro-objects by digital holographic microscope in microfluidics

Abstract: We propose an optical configuration in which floating particles in a microfluidic chamber can be characterized by an interference microscopy configuration to obtain quantitative phase-contrast maps. The configuration is simply made by two laser beams from the same laser source. One beam provides the optical forces for driving the particle along appropriate paths, but at same time works as the object illumination beam in the holographic microscope. The second beam plays the role of the reference beam, allowing recording of an interference fringe pattern (i.e., the digital hologram) in an out-of-focus image plane. The system and method are illustrated and experimental results are offered for polymeric particles as well as for in vitro cells with the aim to demonstrate the approach.

Self-assembling of multi-jets by pyro-electrohydrodynamic effect for high throughput liquid nanodrops transfer

Abstract: Destabilization of liquid film by electro-hydro-dynamics (EHD) pressure is achieved through the pyroelectric effect on a polar dielectric crystal. We show that by destabilizing the liquid film, periodical self-assembled multi-jets are obtained. The multi-jets operate simultaneously and could be exploited to dispense liquids with nanolitre drops. Such multiple self-assembled liquid jets have significant potential applicability for high-throughput liquid transfer by this novel pyro-EHD ink-jet approach. Since the method avoids the use of nozzles and electrodes, it is especially suitable for highly viscous liquids. Here we present and discuss the new multi-jet process and the results obtained with a liquid polymer (PDMS).

Coherent light microscopy : imaging and quantitative phase analysis

Abstract: Quantitative Phase Microscopy with Digital Holography Approach with High-Coherence Light Sources.- Quantitative Phase Microscopy with Digital Holography Approach with Low-Coherence Light Sources.- Digital Holographic Microscopy with Femtosecond Laser Sources for Characterization of Fast Dynamic Events and Process.- Quantitative Microscopy with a Photorefractive-Based Principle.- Application of Interference Microscopy in Microfluidics and Optofludics Systems.- Optofluidic-Based Microscope.- Characterization of Optical Microsystems Devices (Microlenses, Liquid Lenses, Integrated Optics Interferometrers, Waveguides, MEMs, MOEMs).- Super-Resolution in Interference Microscopy.- Microscopy with UV Light Sources.- Microscopy with IR Sources.- 3D Imaging for Analysis and Tracking of Particles in Fluidodynamic Physics.- Visualization of Trapping Systems to Study Paths of Particles.- Optical Coherent Method for Evaluation and Recognition of Bio-Agents.- Special Methods with Fabrication and Characterization of Self-Assembled Structures. Phase Shifting Techniques in Microscopy.

Pyroelectric Adaptive Nanodispenser (PYRANA) microrobot for liquid delivery on a target.

Abstract: Manipulation of micro-sized objects in lab-on-a-chip and microfluidic environments is essential for different experiments and procedures ranging from chemical to biological applications and for experimental biotechnologies. For example polymeric particles, useful as targets for encapsulating or for being covered by drug vaccines, can be manipulated and controlled with the aim of releasing them to specific sites. Here we show a novel ElectroHydroDynamic tool able to control and manipulate dielectric micro-targets by a touch-less approach. This approach allows one to manipulate liquids and nano-particles simultaneously for specific delivery applications (i.e. decoration and coating). Thus a sort of EHD micro-robot is proposed. This flexible tool provides a new and powerful way to operate various tasks as demonstrated by the experiments reported here.

Exploring the capabilities of Digital Holography as tool for testing optical microstructures

Abstract: A demonstration of the capabilities of Digital Holography (DH) in microscope configuration is presented for inspecting and qualifying optical microstructures. Different structures with dimensions ranging from hundreds to few tens of microns are investigated, analyzed and characterized by DH showing that the technique is suitable either for liquid as well as polymeric microlenses. Thanks to the numerical reconstruction of the complex wavefields, we show that DH is able to retrieve not only the morphology of each single structure element but also to furnish accurate information on all the changes (spontaneous or induced) occurring during the inspection time, such as the curvature variation of liquid microlenses or the wavefront distortion.

Simultaneous Multiplane Imaging in Digital Holographic Microscopy

Abstract: Reduced depth of field is a severe limitation in microscopy since, at high magnification, only a portion of the imaged volume along the optical axis is in good focus at once. We demonstrate that, adopting a numerical quadratic deformed diffraction grating into the reconstruction process of digital holograms, it is possible to image three planes at different depths simultaneously, gaining flexibility dispensing with a physical grating. Moreover, multiplexed holograms recorded with two different wavelengths can be obtained in focus simultaneously by a single reconstruction. Description of the method and applications for macroscopic and microscopic biological samples are reported.

Infrared digital holography for large objects investigation

Abstract: In this work we show several acquisition setups and techniques which make it possible to obtain holographic recording and reconstruction of large objects by means of Infrared Digital Holography (IDH). In previous works it was demonstrated that, using the long wavelength coherent radiation produced by a CO 2 laser instead of visible radiation, it is possible to obtain advantages in terms of larger field of view and lower seismic noise sensitivity. The only drawback using this wavelength is represented by the low resolution of current recording devices in this spectral region. The reported methods may have industrial applications where investigation of large dimension samples is needed.

Detection and visualization improvement of Spermatozoa cells by Digital Holography

Abstract: Numerical analysis is implemented to investigate biological sample starting from Digital Holographic (DH) recording. The aim is to improve visualization and detection of cow spermatozoa. Digital holograms are recorded in the off-axis geometry where optical setup is a Mach-Zehnder interferometer. Then holograms are numerically manipulated to retrieve, besides the usual Quantitative Phase Map (QPM), Differential Interference Contrast (DIC) visualization. Furthermore, a new approach , named digital self-referencing holography, is described it’s able to accomplish quantitative phase analysis especially useful for specimen flowing in microfluidic channels.

Infrared digital holography applications for virtual museums and diagnostics of cultural heritage

Abstract: Infrared digital holograms of different statuettes are acquired. For each object, a sequence of holograms is recorded rotating the statuette with an angular step of few degrees. The holograms of the moving objects are used to compose dynamic 3D scenes that, then, are optically reconstructed by means of spatial light modulators (SLMs) using an illumination wavelength of 532 nm. This kind of reconstruction allows to obtain a 3D imaging of the statuettes that could be exploited for virtual museums.

Simultaneous multiplane imaging in digital holographic microscopy

Abstract: We describe a numerical method applied to the reconstruction of a digital hologram, that allows to obtain the image of an object at three planes at different depths simultaneously. In order to do this, we introduce a numerical quadratic deformed diffraction grating into the algorithm.

Optical-frequency-comb based interrogation of fiber resonators

Abstract: Strain sensing at the 10 -13 level, from the mHz to the kHz frequency range, is performed using a fiber Bragg-grating resonator interrogated by an optical-frequency-comb stabilized laser. The optical-comb synthesizer is a fs-pulsed fiber laser phase-locked to a quartz oscillator, which provides for a very high laser-frequency stability. The comb teeth span over the 1510-1580 nm spectral interval. Therefore, the OFS is also used as a coherent radiation source for fiber-loop cavity ring-down evanescent-wave spectroscopy of analytes diluted in liquid samples. Keywords: strain sensors, fiber Bragg grating, laser frequency locking, optical fiber resonator, optical frequency comb, evanescent wave spectrosc opy, cavity ring-down. 1. INTRODUCTION In the last decade, the invention of optical frequency-comb synthesizers (OFCS) has allowed unprecedented accuracy and precision in spectroscopy experiments as well as measurements of fundamental physical constants 1,2 . Originally devised for metrological applications, OFCSs have recently been proposed as infrared light sources for broadband, high-sensitivity molecular spectroscopy

Infrared Digital Holography for large object investigation

Abstract: Digital Holography in the infrared range presents some advantages compared with the visible range. A much higher stability, a wider view angle and shorter acquisition distances are achievable, allowing easier acquisition of large object holograms.

Quantitative Phase Microscopy for Accurate Characterization of Microlens Arrays

Abstract: Microlens arrays are of fundamental importance in a wide variety of applications in optics and photonics. This chapter deals with an accurate digital holography-based characterization of both liquid and polymeric microlenses fabricated by an innovative pyro-electrowetting process. The actuation of liquid and polymeric films is obtained through the use of pyroelectric charges generated into polar dielectric lithium niobate crystals.

New high compression method for digital hologram recorded in microscope configuration

Abstract: We propose a new method to compress digital holograms (DHs) using a sparse matrix representation. Using digital holography to numerically manage complex wavefields, we are able to apply an adaptive mask, based on a threshold filter, to the object wavefield. From there, we store the result of this filtering by sparse representation. We demonstrate that the proposed sparse representation gives us the possibility to obtain high compression factor with minimal loss in the quality of the reconstructed image. This technique is efficient for storage and transmission of DHs and we propose a multiplexing structure for storage the compressed data.

Holographic microscope for quantitative phase-contrast imaging of particles driven by optical forces in microfluidics

Abstract: We demonstrate that particles floating in the microfluidic environment can be driven by optical forces along preferential directions. Meanwhile the particles can be imaged by a digital holographic microscope with the aim to get their quantitative phase-contrast signature.

Quantitative Phase Contrast in Holographic Microscopy Through the Numerical Manipulation of the Retrieved Wavefronts

Abstract: In this chapter we show how digital holography (DH) can be efficiently used as a free and noninvasive investigation tool capable of performing quantitative and qualitative mapping of biological samples. A detailed description of the recent methods based on the possibility offered by DH to numerically manage the reconstructed wavefronts is reported. Depending on the sample and on the investigation to be performed it is possible, by a single acquired image, to recover information on the optical path length changes and, choosing the more suitable numerical method, to obtain quantitative phase map distributions. The progress achieved in the reconstruction methods will certainly find useful applications in the field of the biological analysis.

Comprar Coherent Light Microscopy | Zalevsky, Zeev | 9783642158124 | Springer

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An algorithm for the estimation of the in-focus distance for speckle holograms

Abstract: Searching and recovering the correct reconstruction distance in digital holography can be a cumbersome and subjective procedure. Here we show an algorithm for the automatically estimating the in-focus image and recovering the correct reconstruction distance for speckle holograms. We have tested the approach in determining the reconstruction distances of stretched digital holograms. Stretching a hologram with a variable elongation parameter gives us the possibility to change the in-focus distance of the reconstructed image. In this way, the proposed algorithm can be verified at different distances by dispensing the recording of different holograms. Experimental results are shown with the aim to demonstrate the usefulness of the proposed method and a comparative analysis has been performed with respect to other existing algorithms developed for digital holography.

Dynamic differential image contrast by digital holography for imaging and quantitative phase microscopy

Abstract: Numerical managing and manipulation of complex wavefronts is performed to retrieve Differential Image Contrast (DIC) visualization starting from Digital Holographic (DH) recording. Dynamical Differential Holographic Image Contrast (DDHIC) is the name of the proposed technique. It dispenses from special optics and/or complex setup configurations with moveable components, as usually occurs in classical DIC. DDHIC presents as an appropriate method for investigating objects experiencing dynamic evolution during the measurement. In fact, it will be proved that it’s useful for floating samples since it allows, from a single recording, to set a-posteriori the best conditions for DIC imaging. Dynamic representation of phase-contrast along all directions will be presented improving the specimen visualization. Furthermore, it is useful for making the proper choice of DIC key parameters as the amount of shear and the bias, with the aim to optimize the visualized phase-contrast imaging. Investigation is carried out on different biological samples.

Infrared digital holography for 3D display

Abstract: We report on Infrared Digital Holography (IRDH) and discuss the advantages offered by this technique. Efficient recording-reconstructions of IR holograms of various objects, which differ in composition and dimensions, are shown. We demonstrate optical holographic display by means of a liquid crystal based Spatial Light Modulator (SLM), which gives the chance to get direct 3D imaging and display of the IR holograms. Finally, 3D dynamical scenes can be numerically synthesized and displayed in the visible region, using holograms of different objects.

Dispensing and manipulation of nano-drops by pyro-EHD (electro-hydro-dynamic) effect

Abstract: Nano- and pico-droplets have been extracted and dispensed from sessile drop or liquid film reservoirs through pyroelectric effect activated by a hot tip or an IR laser source on polar dielectric substrates. The manipulation of liquids in 2D and 3D was demonstrated without the need of high-voltage power supplies and/or circuits.

Improving Numerical Aperture in DH Microscopy by 2D Diffraction Grating

Abstract: In this chapter an approach using a 2D phase grating to enhance the resolution in digital holographic microscopy exploiting the electro-optic effect is proposed. We show that, by means of a tunable lithium niobate phase grating, it is possible to increase the numerical aperture of the imaging system, thus improving the spatial resolution of the images in two dimensions. The enhancement of the numerical aperture of the optical system is obtained by recording spatially multiplexed digital holograms. Furthermore, thanks to the flexibility of the numerical reconstruction process, it is possible to selectively use the diffraction orders carrying useful information for optimizing the diffraction efficiency and to increase the final spatial resolution.

Trapping and manipulating micro-objects by bessel beams obtained through polymeric microaxicons

Abstract: Optical trapping is accomplished by means of polymeric micro-axicons, a sort of conical lenses with great depth of focus. A survey of several applications will be given.