Andrea Finizio - Academia.edu (original) (raw)

Papers by Andrea Finizio

Optics Letters, 2006

Combining the concept of lateral shear interferometry (LSI) within a digital holography microscop... more Combining the concept of lateral shear interferometry (LSI) within a digital holography microscope, we demonstrate that it is possible to obtain quantitative optical phase measurement in microscopy by a new single-image-processing procedure. Numerical lateral shear of the reconstructed wavefront in the image plane makes it possible to retrieve the derivative of the wavefront and remove the defocus aberration term introduced by the microscope objective. The method is tested to investigate a silicon structure and a mouse cell line.

Optics Letters, 2004

A method for controlling the size of amplitude and phase images reconstructed from digital hologr... more A method for controlling the size of amplitude and phase images reconstructed from digital holograms by the Fresnel-transform method is proposed and demonstrated. The method can provide a constant reconstruction pixel width in the reconstructed image plane, independent of the recording and reconstruction distance. The proposed method makes it possible to maintain the size of an object for a sequence of digital holograms recorded at different distances and, therefore, to subtract phase maps for an object recorded at different distances. Furthermore, the method solves the problem of superimposition in multiwavelength digital holography for color display and holographic interferometry applications.

Digital holography is proposed as a non-contact method for the inspection and characterization of... more Digital holography is proposed as a non-contact method for the inspection and characterization of MEMS. The method can be useful for assessing the fabrication process and the functionality as well as the reliability of micromachined structures.

Optics Letters, 2005

We demonstrate experimentally that correct phase imaging without 2 ambiguity is obtainable in dig... more We demonstrate experimentally that correct phase imaging without 2 ambiguity is obtainable in digital holography by using a multiwavelength approach in the microscope configuration. We describe a general approach for removing chromatic aberrations and for controlling the pixel size of the reconstructed phase image in multiwavelength digital holography when the Fourier transform method is adopted for the numerical reconstruction of digital holograms. The retrieved phase is affected by the unavoidable, unwanted chromatic aberration. The correct phase can be obtained by evaluating the phase from the reference holograms reconstructed at different wavelengths to compensate for the chromatic aberration.

Applied Optics, 2003

An approach is proposed for removing the wave front curvature introduced by the microscope imagin... more An approach is proposed for removing the wave front curvature introduced by the microscope imaging objective in digital holography, which otherwise hinders the phase contrast imaging at reconstruction planes. The unwanted curvature is compensated by evaluating a correcting wave front at the hologram plane with no need for knowledge of the optical parameters, focal length of the imaging lens, or distances in the setup. Most importantly it is shown that a correction effect can be obtained at all reconstruction planes. Three different methods have been applied to evaluate the correction wave front and the methods are discussed in detail. The proposed approach is demonstrated by applying digital holography as a method of coherent microscopy for imaging amplitude and phase contrast of microstructures.

Optics and Lasers in Engineering, 2002

Off-axis holograms recorded with a CCD camera are numerically reconstructed in amplitude by calcu... more Off-axis holograms recorded with a CCD camera are numerically reconstructed in amplitude by calculating through the Fresnel–Kirchhoff integral. A phase-shifting Mach–Zehnder interferometer is used for recording four-quadrature phase-shifted off-axis holograms. The basic principle of this technique and its experimental verification are described. We show that the application of this algorithm allows for the suppression of the zero order of diffraction

Optics Communications, 2000

Measurement of the refractive index of liquids is of great importance in applications such as the... more Measurement of the refractive index of liquids is of great importance in applications such as the control of adulteration of liquids and pollution monitoring. We present and discuss a fringe projection technique for measuring the index of refraction of transparent liquid materials. In the proposed technique a fringe pattern produced by a reflective grating interferometer is imaged by a lens before passing through a cell containing the liquid sample under test. The interference pattern consists of a family of parallel straight fringes that are digitized by a CCD array. The focal shift, which is induced by the liquid sample, produces changes in the spatial frequency of the projected pattern. Spatial frequency of the fringe pattern is analysed by means of a one-dimensional Fourier transform and phase demodulation procedure. The principle of the proposed fringe projection refractometer relies on a comparative measurements of the refractive index of the sample under test with respect to a reference liquid. The method is simple and can be easily interpreted geometrically. q

Optics Letters, 2009

We show here that through an adaptive deformation of digital holograms it is possible to manage t... more We show here that through an adaptive deformation of digital holograms it is possible to manage the depth of focus in 3D imaging reconstruction. Deformation is applied to the original hologram with the aim to put simultaneously in focus, and in one reconstructed image plane, different objects lying at different distances from the hologram plane (i.e., CCD sensor). In the same way, by adapting the deformation it is possible to extend the depth of field having a tilted object entirely in focus. We demonstrate the method in both lensless as well as in microscope configuration.

Optics Express, 2007

In this paper, we address 3D object visualization and recognition with multi-wavelength digital h... more In this paper, we address 3D object visualization and recognition with multi-wavelength digital holography. Color features of 3D objects are obtained by the multiple-wavelengths. Perfect superimposition technique generates reconstructed images of the same size. Statistical pattern recognition techniques: principal component analysis and mixture discriminant analysis analyze multi-spectral information in the reconstructed images. Class-conditional probability density functions are estimated during the training process. Maximum likelihood decision rule categorizes unlabeled images into one of trained-classes. It is shown that a small number of training images is sufficient for the color object classification.

Optics Express, 2003

We demonstrate fabrication of periodically poled lithium niobate samples by electric field poling... more We demonstrate fabrication of periodically poled lithium niobate samples by electric field poling, after patterning by interference lithography. Furthermore we investigate the poling process at an overpoling regime which caused the appearance of submicron dot domains very similar to those induced by backswitch but different in nature. We show the possibility for realizing submicron-scaled three-dimensional domain patterns that could be applied to the construction of photonic crystals and in nonlinear optics. We show that high etch-rate applied to such structures allows to obtain pyramidal-like submicron relief structures which in principle could find application for waveguide construction in photonic bandgap devices. . 5. E.J. Lim, M.M. Fejer and R.L. Byer, "Second-harmonic generation of green light in periodically poled planar Lithium Niobate waveguide," Electron. Lett. 25, 174-175 (1989). 6. M. Yamada and K. Kishima, "Fabrication of periodically reversed domain structure for SHG in LiNbO 3 by direct electron beam lithography at room temperature," Electron. Lett. 27, 828-829 (1991). 7. M. Yamada, N. Nada, M. Saitoh, and K. Watanabe, "First-order quasi-phase matched LiNbO 3 waveguide periodically poled by applying an external field for efficient blue second-harmonic generation," Appl. Phys. Lett. 62, 435-436 (1993). 8. J. Webjörn, V. Pruneri, P.St.J. Russell, J.R.M. Barr and D.C. Hanna, "Quasi-phase-matched blue light generation in bulk lithium niobate, electrically poled via periodic liquid electrodes," Electron. Lett. 30, 894-895 (1994). , "Intracavity second harmonic generation of 0.532µm in bulk periodically poled lithium niobate," Opt. Comm. 116, 159-162 (1995).

Optics Letters, 2001

It is demonstrated for the first time to the authors' knowledge that digital holographic image re... more It is demonstrated for the first time to the authors' knowledge that digital holographic image reconstruction can be applied to correction of image reconstruction in the presence of severe anamorphism and aberrations. It is shown that anamorphism and aberrations can be taken into account and compensated for separately to yield a correct-image reconstruction. Anamorphism and aberrations are introduced by a holographic recording system based on a ref lective grating interferometer (RGI). The strong anamorphic behavior of the RGI prevents reconstruction of a correct image unless that behavior is compensated for in the process of numerical holographic reconstruction.

Optics Express, 2004

In-situ monitoring of domain reversal in congruent lithium niobate by a digital holographic techn... more In-situ monitoring of domain reversal in congruent lithium niobate by a digital holographic technique is described. While the ferroelectric polarization is reversed by electric field poling, the twodimensional distribution of the phase shift, due mainly to the linear electrooptic and piezoelectric effects, is measured and visualized. Digital holography is used to reconstruct both amplitude and phase of the wavefield transmitted by the sample to reveal the phase shift induced by adjacent reversed domains during the poling. The resulting movies of both amplitude and phase maps, for in-situ visualization of domain pattern formation, are shown. The possibility of using the technique as tool for monitoring in real-time the periodic poling of patterned samples is discussed.

Optics Express, 2005

We present a new method for numerically reconstructing digital holograms on tilted planes. The me... more We present a new method for numerically reconstructing digital holograms on tilted planes. The method is based on the angular spectrum of plane waves. Fast Fourier transform algorithm is used twice and coordinate rotation in the Fourier domain enables to reconstruct the object field on the tilted planes. Correction of the anamorphism resulting from the coordinate transformation is performed by suitable interpolation of the spectral data. Experimental results are presented to demonstrate the method for a singleaxis rotation. The algorithm is especially useful for tomographic image reconstruction.

Measurement Science & Technology, 2004

Digital holographic microscopy (DHM) can be described as a non-invasive metrological tool for ins... more Digital holographic microscopy (DHM) can be described as a non-invasive metrological tool for inspection and characterization of microelectromechanical structures (MEMS). DHM is a quick, non-contact and non-invasive technique that can offer a high resolution in both lateral and vertical directions. It has been employed for the characterization of the undesired out-of-plane deformations due to the residual stresses introduced by technological processes. The characterization of these deformations is helpful in studying and understanding the effect of residual stress on the deformation of a single microstructure. To that end, MEMS with different geometries and shapes, such as cantilever beams, bridges and membranes, have been characterized. Moreover, DHM has been applied efficiently to evaluate variations of the structure profile due to some external effects. As an example, the characterization of a cantilever subjected to a thermal process has been described. The results reported show that DHM is a useful non-invasive method for characterizing and developing reliable MEMS.

Optics Express, 2008

Lens effect was obtained in an open microfluidic system by using a thin layer of liquid on a pola... more Lens effect was obtained in an open microfluidic system by using a thin layer of liquid on a polar electric crystal like LiNbO 3 . An array of liquid micro-lenses was generated by electrowetting effect in pyroelectric periodically poled crystals. Compared to conventional electrowetting devices, the pyroelectric effect allowed to have an electrode-less and circuitless configuration. An interferometric technique was used to characterize the curvature of the micro-lenses and the corresponding results are presented and discussed. The preliminary results concerning the imaging capability of the micro-lens array are also reported.

Optics Communications, 1999

The possibility that an interferometric method, previously developed for measuring long focal len... more The possibility that an interferometric method, previously developed for measuring long focal length systems, can be equally well applied to measuring very short focal length optics and a 1 mm aperture radius diffractive lens is demonstrated. The measurement can be easily performed despite some limiting factors such as small aperture, which drop the available light intensity, and very short focal length, which magnified impurities on the optical elements, both resulting in high noise in the fringe pattern. It is easy to predict that other approaches would fail in the presence of such limiting factors. The method is based on a reflective grating interferometer and measurement of the effective focal length is performed within the limit of paraxial approximation. Focal length is obtained by the knowledge of the spatial frequency of two interferometric fringe patterns imaged by the lens under test. The spatial frequencies are evaluated by using an FFT algorithm.

Optics Express, 2008

An approach that uses an electro-optically tunable two dimensional phase grating to enhance the r... more An approach that uses an electro-optically tunable two dimensional phase grating to enhance the resolution in digital holographic microscopy is proposed. We show that, by means of a flexible hexagonal 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 augment of the numerical aperture of the optical system is obtained by recording spatially multiplexed digital holograms. The grating tuneability allows one to adjust the intensity among the spatially multiplexed holograms maximizing the grating diffraction efficiency. Furthermore we demonstrate that the flexibility of the numerical reconstruction allows one to use selectively the diffraction orders carrying useful information for increasing the spatial resolution. The proposed approach can improve the capabilities of digital holography in threedimensional imaging and microscopy.

Optics Letters, 2003

We propose a new method for focus tracking during the recording of a sequence of digital hologram... more We propose a new method for focus tracking during the recording of a sequence of digital holograms while the sample experiences axial displacement. Corrected reconstruction distances can be automatically calculated, and well-focused amplitude and phase-contrast images can be obtained for each digitized hologram. The method is demonstrated for inspection of microelectromechanical systems subjected to thermal load. The method can be applied as a quasi-real-time procedure.

Optics Communications, 1995

A new design of interferometer which makes use of a reflective-type diffraction grating is develo... more A new design of interferometer which makes use of a reflective-type diffraction grating is developed. The layout is easy to align and compact and it is suitable for measuring the refractive indices of transparent materiats. 0030-4018/95/$09.50

Applied Optics, 1999

We present a new, folded reversal interferometer. It is based on the reflective grating interfero... more We present a new, folded reversal interferometer. It is based on the reflective grating interferometer and can be applied for optical isolation and testing of coma aberration. The interferometer has several advantages in respect to other existing optical reversal configurations. A carrier can be easily added for phase retrieval in interferometric fringe patterns for mapping coma aberration. Furthermore, in an asymmetric optical configuration a lateral shear can also be added, transforming it in a reversal shearing interferometer. The principle of operation of the interferometer is described, and the application for measuring the coma aberration of a parabolic mirror used off axis is demonstrated.

Optics Letters, 2006

Combining the concept of lateral shear interferometry (LSI) within a digital holography microscop... more Combining the concept of lateral shear interferometry (LSI) within a digital holography microscope, we demonstrate that it is possible to obtain quantitative optical phase measurement in microscopy by a new single-image-processing procedure. Numerical lateral shear of the reconstructed wavefront in the image plane makes it possible to retrieve the derivative of the wavefront and remove the defocus aberration term introduced by the microscope objective. The method is tested to investigate a silicon structure and a mouse cell line.

Optics Letters, 2004

A method for controlling the size of amplitude and phase images reconstructed from digital hologr... more A method for controlling the size of amplitude and phase images reconstructed from digital holograms by the Fresnel-transform method is proposed and demonstrated. The method can provide a constant reconstruction pixel width in the reconstructed image plane, independent of the recording and reconstruction distance. The proposed method makes it possible to maintain the size of an object for a sequence of digital holograms recorded at different distances and, therefore, to subtract phase maps for an object recorded at different distances. Furthermore, the method solves the problem of superimposition in multiwavelength digital holography for color display and holographic interferometry applications.

Digital holography is proposed as a non-contact method for the inspection and characterization of... more Digital holography is proposed as a non-contact method for the inspection and characterization of MEMS. The method can be useful for assessing the fabrication process and the functionality as well as the reliability of micromachined structures.

Optics Letters, 2005

We demonstrate experimentally that correct phase imaging without 2 ambiguity is obtainable in dig... more We demonstrate experimentally that correct phase imaging without 2 ambiguity is obtainable in digital holography by using a multiwavelength approach in the microscope configuration. We describe a general approach for removing chromatic aberrations and for controlling the pixel size of the reconstructed phase image in multiwavelength digital holography when the Fourier transform method is adopted for the numerical reconstruction of digital holograms. The retrieved phase is affected by the unavoidable, unwanted chromatic aberration. The correct phase can be obtained by evaluating the phase from the reference holograms reconstructed at different wavelengths to compensate for the chromatic aberration.

Applied Optics, 2003

An approach is proposed for removing the wave front curvature introduced by the microscope imagin... more An approach is proposed for removing the wave front curvature introduced by the microscope imaging objective in digital holography, which otherwise hinders the phase contrast imaging at reconstruction planes. The unwanted curvature is compensated by evaluating a correcting wave front at the hologram plane with no need for knowledge of the optical parameters, focal length of the imaging lens, or distances in the setup. Most importantly it is shown that a correction effect can be obtained at all reconstruction planes. Three different methods have been applied to evaluate the correction wave front and the methods are discussed in detail. The proposed approach is demonstrated by applying digital holography as a method of coherent microscopy for imaging amplitude and phase contrast of microstructures.

Optics and Lasers in Engineering, 2002

Off-axis holograms recorded with a CCD camera are numerically reconstructed in amplitude by calcu... more Off-axis holograms recorded with a CCD camera are numerically reconstructed in amplitude by calculating through the Fresnel–Kirchhoff integral. A phase-shifting Mach–Zehnder interferometer is used for recording four-quadrature phase-shifted off-axis holograms. The basic principle of this technique and its experimental verification are described. We show that the application of this algorithm allows for the suppression of the zero order of diffraction

Optics Communications, 2000

Measurement of the refractive index of liquids is of great importance in applications such as the... more Measurement of the refractive index of liquids is of great importance in applications such as the control of adulteration of liquids and pollution monitoring. We present and discuss a fringe projection technique for measuring the index of refraction of transparent liquid materials. In the proposed technique a fringe pattern produced by a reflective grating interferometer is imaged by a lens before passing through a cell containing the liquid sample under test. The interference pattern consists of a family of parallel straight fringes that are digitized by a CCD array. The focal shift, which is induced by the liquid sample, produces changes in the spatial frequency of the projected pattern. Spatial frequency of the fringe pattern is analysed by means of a one-dimensional Fourier transform and phase demodulation procedure. The principle of the proposed fringe projection refractometer relies on a comparative measurements of the refractive index of the sample under test with respect to a reference liquid. The method is simple and can be easily interpreted geometrically. q

Optics Letters, 2009

We show here that through an adaptive deformation of digital holograms it is possible to manage t... more We show here that through an adaptive deformation of digital holograms it is possible to manage the depth of focus in 3D imaging reconstruction. Deformation is applied to the original hologram with the aim to put simultaneously in focus, and in one reconstructed image plane, different objects lying at different distances from the hologram plane (i.e., CCD sensor). In the same way, by adapting the deformation it is possible to extend the depth of field having a tilted object entirely in focus. We demonstrate the method in both lensless as well as in microscope configuration.

Optics Express, 2007

In this paper, we address 3D object visualization and recognition with multi-wavelength digital h... more In this paper, we address 3D object visualization and recognition with multi-wavelength digital holography. Color features of 3D objects are obtained by the multiple-wavelengths. Perfect superimposition technique generates reconstructed images of the same size. Statistical pattern recognition techniques: principal component analysis and mixture discriminant analysis analyze multi-spectral information in the reconstructed images. Class-conditional probability density functions are estimated during the training process. Maximum likelihood decision rule categorizes unlabeled images into one of trained-classes. It is shown that a small number of training images is sufficient for the color object classification.

Optics Express, 2003

We demonstrate fabrication of periodically poled lithium niobate samples by electric field poling... more We demonstrate fabrication of periodically poled lithium niobate samples by electric field poling, after patterning by interference lithography. Furthermore we investigate the poling process at an overpoling regime which caused the appearance of submicron dot domains very similar to those induced by backswitch but different in nature. We show the possibility for realizing submicron-scaled three-dimensional domain patterns that could be applied to the construction of photonic crystals and in nonlinear optics. We show that high etch-rate applied to such structures allows to obtain pyramidal-like submicron relief structures which in principle could find application for waveguide construction in photonic bandgap devices. . 5. E.J. Lim, M.M. Fejer and R.L. Byer, "Second-harmonic generation of green light in periodically poled planar Lithium Niobate waveguide," Electron. Lett. 25, 174-175 (1989). 6. M. Yamada and K. Kishima, "Fabrication of periodically reversed domain structure for SHG in LiNbO 3 by direct electron beam lithography at room temperature," Electron. Lett. 27, 828-829 (1991). 7. M. Yamada, N. Nada, M. Saitoh, and K. Watanabe, "First-order quasi-phase matched LiNbO 3 waveguide periodically poled by applying an external field for efficient blue second-harmonic generation," Appl. Phys. Lett. 62, 435-436 (1993). 8. J. Webjörn, V. Pruneri, P.St.J. Russell, J.R.M. Barr and D.C. Hanna, "Quasi-phase-matched blue light generation in bulk lithium niobate, electrically poled via periodic liquid electrodes," Electron. Lett. 30, 894-895 (1994). , "Intracavity second harmonic generation of 0.532µm in bulk periodically poled lithium niobate," Opt. Comm. 116, 159-162 (1995).

Optics Letters, 2001

It is demonstrated for the first time to the authors' knowledge that digital holographic image re... more It is demonstrated for the first time to the authors' knowledge that digital holographic image reconstruction can be applied to correction of image reconstruction in the presence of severe anamorphism and aberrations. It is shown that anamorphism and aberrations can be taken into account and compensated for separately to yield a correct-image reconstruction. Anamorphism and aberrations are introduced by a holographic recording system based on a ref lective grating interferometer (RGI). The strong anamorphic behavior of the RGI prevents reconstruction of a correct image unless that behavior is compensated for in the process of numerical holographic reconstruction.

Optics Express, 2004

In-situ monitoring of domain reversal in congruent lithium niobate by a digital holographic techn... more In-situ monitoring of domain reversal in congruent lithium niobate by a digital holographic technique is described. While the ferroelectric polarization is reversed by electric field poling, the twodimensional distribution of the phase shift, due mainly to the linear electrooptic and piezoelectric effects, is measured and visualized. Digital holography is used to reconstruct both amplitude and phase of the wavefield transmitted by the sample to reveal the phase shift induced by adjacent reversed domains during the poling. The resulting movies of both amplitude and phase maps, for in-situ visualization of domain pattern formation, are shown. The possibility of using the technique as tool for monitoring in real-time the periodic poling of patterned samples is discussed.

Optics Express, 2005

We present a new method for numerically reconstructing digital holograms on tilted planes. The me... more We present a new method for numerically reconstructing digital holograms on tilted planes. The method is based on the angular spectrum of plane waves. Fast Fourier transform algorithm is used twice and coordinate rotation in the Fourier domain enables to reconstruct the object field on the tilted planes. Correction of the anamorphism resulting from the coordinate transformation is performed by suitable interpolation of the spectral data. Experimental results are presented to demonstrate the method for a singleaxis rotation. The algorithm is especially useful for tomographic image reconstruction.

Measurement Science & Technology, 2004

Digital holographic microscopy (DHM) can be described as a non-invasive metrological tool for ins... more Digital holographic microscopy (DHM) can be described as a non-invasive metrological tool for inspection and characterization of microelectromechanical structures (MEMS). DHM is a quick, non-contact and non-invasive technique that can offer a high resolution in both lateral and vertical directions. It has been employed for the characterization of the undesired out-of-plane deformations due to the residual stresses introduced by technological processes. The characterization of these deformations is helpful in studying and understanding the effect of residual stress on the deformation of a single microstructure. To that end, MEMS with different geometries and shapes, such as cantilever beams, bridges and membranes, have been characterized. Moreover, DHM has been applied efficiently to evaluate variations of the structure profile due to some external effects. As an example, the characterization of a cantilever subjected to a thermal process has been described. The results reported show that DHM is a useful non-invasive method for characterizing and developing reliable MEMS.

Optics Express, 2008

Lens effect was obtained in an open microfluidic system by using a thin layer of liquid on a pola... more Lens effect was obtained in an open microfluidic system by using a thin layer of liquid on a polar electric crystal like LiNbO 3 . An array of liquid micro-lenses was generated by electrowetting effect in pyroelectric periodically poled crystals. Compared to conventional electrowetting devices, the pyroelectric effect allowed to have an electrode-less and circuitless configuration. An interferometric technique was used to characterize the curvature of the micro-lenses and the corresponding results are presented and discussed. The preliminary results concerning the imaging capability of the micro-lens array are also reported.

Optics Communications, 1999

The possibility that an interferometric method, previously developed for measuring long focal len... more The possibility that an interferometric method, previously developed for measuring long focal length systems, can be equally well applied to measuring very short focal length optics and a 1 mm aperture radius diffractive lens is demonstrated. The measurement can be easily performed despite some limiting factors such as small aperture, which drop the available light intensity, and very short focal length, which magnified impurities on the optical elements, both resulting in high noise in the fringe pattern. It is easy to predict that other approaches would fail in the presence of such limiting factors. The method is based on a reflective grating interferometer and measurement of the effective focal length is performed within the limit of paraxial approximation. Focal length is obtained by the knowledge of the spatial frequency of two interferometric fringe patterns imaged by the lens under test. The spatial frequencies are evaluated by using an FFT algorithm.

Optics Express, 2008

An approach that uses an electro-optically tunable two dimensional phase grating to enhance the r... more An approach that uses an electro-optically tunable two dimensional phase grating to enhance the resolution in digital holographic microscopy is proposed. We show that, by means of a flexible hexagonal 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 augment of the numerical aperture of the optical system is obtained by recording spatially multiplexed digital holograms. The grating tuneability allows one to adjust the intensity among the spatially multiplexed holograms maximizing the grating diffraction efficiency. Furthermore we demonstrate that the flexibility of the numerical reconstruction allows one to use selectively the diffraction orders carrying useful information for increasing the spatial resolution. The proposed approach can improve the capabilities of digital holography in threedimensional imaging and microscopy.

Optics Letters, 2003

We propose a new method for focus tracking during the recording of a sequence of digital hologram... more We propose a new method for focus tracking during the recording of a sequence of digital holograms while the sample experiences axial displacement. Corrected reconstruction distances can be automatically calculated, and well-focused amplitude and phase-contrast images can be obtained for each digitized hologram. The method is demonstrated for inspection of microelectromechanical systems subjected to thermal load. The method can be applied as a quasi-real-time procedure.

Optics Communications, 1995

A new design of interferometer which makes use of a reflective-type diffraction grating is develo... more A new design of interferometer which makes use of a reflective-type diffraction grating is developed. The layout is easy to align and compact and it is suitable for measuring the refractive indices of transparent materiats. 0030-4018/95/$09.50

Applied Optics, 1999

We present a new, folded reversal interferometer. It is based on the reflective grating interfero... more We present a new, folded reversal interferometer. It is based on the reflective grating interferometer and can be applied for optical isolation and testing of coma aberration. The interferometer has several advantages in respect to other existing optical reversal configurations. A carrier can be easily added for phase retrieval in interferometric fringe patterns for mapping coma aberration. Furthermore, in an asymmetric optical configuration a lateral shear can also be added, transforming it in a reversal shearing interferometer. The principle of operation of the interferometer is described, and the application for measuring the coma aberration of a parabolic mirror used off axis is demonstrated.