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This paper is focused on the design, implementation and testing of an active reflector, to be used to support deformation monitoring studies based on Synthetic Aperture Radar interferometry. The device is designed to work in C-band with Sentinel-1 data, operating at 5.405 GHz ± 50 MHz. A brief description of the active reflector is provided. It consists of two antennas and an amplifying section. The active reflector has been tested in different experiments. In this paper, we describe the experiment carried out in the Parc Mediterrani de la Tecnologia (Castelldefels, Barcelona). The result shows a strong correlation with temperature. A calibration test was carried out to experimentally derive a calibration curve to correct the effect of temperature on phase stability, This work is part of a project that has received funding from the European GNSS Agency under the European Union's Horizon 2020 research and innovation programme, with grant agreement No 776335, project GIMS, "Geodetic Integrated Monitoring System". This work has been partially funded by AGAUR, Generalitat de Catalunya, through the Consolidated Research Group RSE, "Remote Sensing" (Ref: 2017-SGR-00729).

[EN] Sentinel-1 interferometric time-series allow for the accurate retrieval of the target’s temporal decorrelation and, therefore, the inversion of land cover information and its temporal monitoring. This paper describes the development of an observation scenario for monitoring monthly deforestation over the Amazon rainforest, which relies on the use of radar for overcoming the physical limitations of optical sensors caused by the presence of cloud coverage. Specifically, we implement a classification scheme that exploits multi-temporal SAR features, such as backscatter, spatial textures, and interferometric parameters, to map forested areas. Distinct forest maps are generated for consecutive months and further processed to detect deforestation phenomena and map clear-cuts evolution. The obtained results are validated by selecting cloud-free Sentinel-2 multispectral data on the selected area and acquired during the same observation time., [ES] Las series temporales interferométricas Sentinel-1 permiten la estimación precisa de la decorrelación temporal de la muestra y, por tanto, la recuperación de información acerca de la cobertura terrestre y su seguimiento temporal. Este artículo describe el desarrollo de un escenario de observación para el seguimiento de la deforestación mensual sobre la selva amazónica, basándose en el uso de datos radar para superar las limitaciones físicas propias de los sensores ópticos debido a la presencia de cobertura nubosa. En particular, se ha implementado un esquema de clasificación que explota las características multitemporales SAR, como la retrodispersión, texturas espaciales y parámetros interferométricos, para identificar áreas de bosque. Distintos mapas de bosque para meses consecutivos fueron generados y procesados para detectar fenómenos de deforestación y su evolución. Los resultados obtenidos fueron validados a partir de imágenes Sentinel-2 libres de nubes adquiridas sobre la misma zona y hora de observación., The performed work has been partially financed through the HI-FIVE project, granted by the ESA Living Planet Fellowship 2018. The authors gratefully acknowledge the Sentinel-1 mission management, in the person of Luca Martino and Pierre Potin, for providing an additional acquisition scheduling over the state of Rondonia.

The worldwide incidence of skin cancer has risen rapidly in the last decades, becoming one in three cancers nowadays. Currently, a person has a 4% chance of developing melanoma, the most aggressive form of skin cancer, which causes the greatest number of deaths. In the context of increasing incidence and mortality, skin cancer bears a heavy health and economic burden. Nevertheless, the 5-year survival rate for people with skin cancer significantly improves if the disease is detected and treated early. Accordingly, large research efforts have been devoted to achieve early detection and better understanding of the disease, with the aim of reversing the progressive trend of rising incidence and mortality, especially regarding melanoma. This paper reviews a variety of the optical modalities that have been used in the last years in order to improve non-invasive diagnosis of skin cancer, including confocal microscopy, multispectral imaging, threedimensional topography, optical coherence tomography, polarimetry, self-mixing interferometry, and machine learning algorithms. The basics of each of these technologies together with the most relevant achievements obtained are described, as well as some of the obstacles still to be resolved and milestones to be met. This research was supported by the Ministerio de Economía, Industria y Competitividad (MINECO), the Agencia Estatal de Investigación (AEI) and the European Regional Development Fund (FEDER) under the grants DPI2017-89414-R and FIS2017-89850-R. L.R-B. thanks the Spanish Government for the predoctoral FPI grant she received, grant number DPI2017-89414-R. S. P-G. thanks AGAUR for the FI grant she received, grant number 2020FI_B2 00068. C.Y. thanks CONACYT Mexico for the grant he received, grant number 472102

The back-reflection of emitted laser beam (optical feedback, also know as selfmixing) from various external interfaces are sufficient to cause instability, and prohibiting its use in various fields such as communication, spectroscopy, imaging to name a few. So it is desirable to study the laser dynamics and the conditions causing it to be stable in spite of strong optical feedback. With the aid of mathematical formulation, simulation and backed by experimental evidences, it is demonstrated that the frequency deviation of the laser emission due to current (intensity) modulation alters the dynamic state and boundary conditions of the system such that even under large optical feedback strength, the laser may attain stability and retain single modal state. The frequency deviation resulting from former is shown to modify the phase of the system in opposite direction to that induced by the later, showing that there exists an optimal modulation current which compensates the effect of optical feedback and may be used to retain the laser in single modal stationary state. The method thus provides a methodology to avoid optical feedback-induced instability in semiconductor lasers by using the proper amplitude of current (intensity) modulation.

A modification to the extended CLEAN deconvolution method for passive microwave interferometric radiometers is presented to account for the interferometer beam patterns that vary depending on the source position within the interferometer field of view. This method is developed for the newly proposed multisatellite rotating microwave interferometric radiometer concept for geostationary atmospheric sounding, which is found to have a spatially varying beam pattern. The proposed method is implemented by the piecewise application of Fast Fourier Transform (FFT)-based convolution, i.e., the image is divided into discrete segments, where the beam pattern is assumed to be constant within each segment. This approach allows the proposed method to exploit the speed advantage of the FFT. Applying this method to the proposed multisatellite interferometer shows a twofold improvement in the radiometric accuracy of the restored brightness temperature map, as compared with the constant beam pattern CLEAN.

Purpose: To compare the postoperative refractive predictability of IOLMaster 500 and Pentacam HR on the basis of keratometry and anterior chamber depth values in eyes with an indication for multifocal intraocular lens (IOL) implantation. Methods: This was a retrospective study conducted on 118 eyes treated with phacoemulsification and multifocal intraocular lens implantation. Only the eyes that achieved emmetropia in the dynamic refraction performed on postoperative day 30 were included. Haigis’ formula was used in each case to calculate the intraocular lens power, and the intraocular lens with the target refraction closest to emmetropia was implanted. Four lens calculation scenarios were tested by combining keratometry and anterior chamber depth measurements obtained using the two devices. Results: IOLMaster 500 and Pentacam HR differed with regard to mean keratometry (D 0.07 ± 0.03 D; p=0.0065) and anterior chamber depth (D 0.08 ± 0.01 mm; p

We present experimental results of a low-emission self-mixing interferometer that uses a coupled interferometric effect to improve the signal produced by a vibrating target. This method is intended to be useful in applications where the target is prone to be damaged by high-intensity laser sources. The beam of a Fabry-Perot laser diode is split and ~21% of the original emission is used to measure the harmonic micro-displacements of the target using the self-mixing effect. A portion of the residual beam, which also carries the interferometric information related to the target displacement, is reinjected back into the laser cavity by means of a fixed reflector, causing a second interferometric phenomenon that improves the signal-to-noise ratio of the measurement by up to ~13 dB. A theoretical description of the phenomena is also proposed. Further, we apply this technique to the two most common self-mixing sensing schemes: internal photodiode and junction voltage. The reported results show good agreement with theory and prove the capability of the method to enhance the SNR in SMI schemes. Consejo Nacional de Ciencia y Tecnología (472102); Ministerio de Economía y Competitividad (FIS2017-89850R).

Over the past two decades, integrated photonic sensors have been of major interest to the optical biosensor community due to their capability to detect low concentrations of molecules with label-free operation. Among these, interferometric sensors can be read-out with simple, fixed-wavelength laser sources and offer excellent detection limits but can suffer from sensitivity fading when not tuned to their quadrature point. Recently, coherently detected sensors were demonstrated as an attractive alternative to overcome this limitation. Here we show, for the first time, to the best of our knowledge, that this coherent scheme provides sub-nanogram per milliliter limits of detection in C-reactive protein immunoassays and that quasi-balanced optical arm lengths enable operation with inexpensive Fabry–Perot-type lasers sources at telecom wavelengths., Horizon 2020 Framework Programme (EuroNanoMed 3-H2020 DrNanoDAII); Ministerio de Economía y Competitividad (2019/PCI 2019-2, CTQ2017-86994-R, SEV-2017-0706); Junta de Andalucía, Proyectos Excelencia-Retos (P18-RT-1453, P18-RT-793); Fondos Europeos de Desarrollo Regional (CTQ2016-75870-P, PID2019-104293GB-I00, RD16/0006/0012, TEC2016-80718-R, UMA18-FEDERJA-007, UMA18-FEDERJA-219); H2020 Marie Skłodowska-Curie Actions (713721).

We demonstrate a novel method that makes an efficient use of laser nonlinear dynamics when subject to optical self-injection for subwavelength displacement sensing purposes. The proposed methodology combines two different phenomena taking place inside the laser cavity: optical self-injection, which results in optical feedback interference, and laser continuous wave frequency modulation, giving rise to a wavelength sweeping effect in the laser’s emission. We present a combination of these phenomena to measure vibration amplitudes below $\lambda /2$ with the resolutions of a few nanometers, bandwidth dependent upon the distance of external target, amplitude, and frequency of current modulation. The basic theoretical details and a mathematical model are presented for the developed measurement principle. Experimental results with the system working as a vibrometer to measure a target vibration of amplitude ${\lambda }/{5}$ (137.5 nm) with a mean peak-to-peak error of 2.4 nm just by pointing the laser diode onto the target and applying some signal processing are also demonstrated.

Two common-path interferometers based on C O 2 and N d : Y 3 A l 5 O 12 (Nd:YAG) lasers are benchmarked with a two-arm microwave interferometer on a hydrogen plasma produced by an RF discharge and injected into a large magnetic-confinement vessel. The ∼ 10 19 m − 2 line-integrated electron density is clearly measured in agreement by the interferometers. The frequency spectrum of the measured data is analyzed on the 20 kHz range for all interferometers and up to 600 kHz for the Nd:YAG laser-based interferometer. Mechanical vibration measurements performed on the components of the two common-path interferometers result in a peak-to-peak displacement up to about one and twenty wavelengths for the C O 2 and Nd:YAG laser-based interferometers, respectively. Such results set for the first time, to the best of our knowledge, a quantitative limit for the displacement that the two second-harmonic dispersion interferometers can sustain while still providing a high sensitivity for accurate plasma density measurements.

The on-demand tailoring of the properties of light, such as phase, polarization or spatial shape, has completely changed the landscape of photonic-based applications. In this way, complex light fields have become an ubiquitous tool in areas of research such as classical and quantum communications, optical tweezers and super-resolution microscopy, among many others. Here we will present some novel applications to optical metrology. First we will show how appropriate tailoring of the properties of light interacting with chiral molecules can enhance their chiral response by two orders of magnitude compared to circularly polarized light. As a second application, we will present a highly sensitive digital technique capable to measure layer thickness in the nanometer regime. This technique is interferometric in nature and contrary to others based on the same principle does not require the highly engineered construction of holders. Finally, we will describe a novel laser remote sensing technique that enables the direct measurement of the transverse component of velocity, a measure that up to now has relied in complicated techniques based on measurements of the longitudinal component of the velocity. This technique offers the possibility to also measure in a direct way the vorticity in fluids, a measure that is commonly measured through the curl of the fluid velocity.

Prior to the application of any persistent scatterer interferometry (PSI) technique for the monitoring of terrain displacement phenomena, an adequate pixel selection must be carried out in order to prevent the inclusion of noisy pixels in the processing. The rationale is to detect the so-called persistent scatterers, which are characterized by preserving their phase quality along the multi-temporal set of synthetic aperture radar (SAR) images available. Two criteria are mainly available for the estimation of pixels' phase quality, i.e., the coherence stability and the amplitude dispersion or permanent scatterers (PS) approach. The coherence stability method allows an accurate estimation of the phase statistics, even when a reduced number of SAR acquisitions is available. Unfortunately, it requires the multi-looking of data during the coherence estimation, leading to a spatial resolution loss in the final results. In contrast, the PS approach works at full-resolution, but it demands a larger number of SAR images to be reliable, typically more than 20. There is hence a clear limitation when a full-resolution PSI processing is to be carried out and the number of acquisitions available is small. In this context, a novel pixel selection method based on exploiting the spectral properties of point-like scatterers, referred to as temporal sublook coherence (TSC), has been recently proposed. This paper seeks to demonstrate the advantages of employing PSI techniques by means of TSC on both orbital and ground-based SAR (GB-SAR) data when the number of images available is small (10 images in the work presented). The displacement maps retrieved through the proposed technique are compared, in terms of pixel density and phase quality, with traditional criteria. Two X-band datasets composed of 10 sliding spotlight TerraSAR-X images and 10 GB-SAR images, respectively, over the landslide of El Forn de Canillo (Andorran Pyrenees), are employed for this study. For both datasets, the TSC technique has showed an excellent performance compared with traditional techniques, achieving up to a four-fold increase in the number of persistent scatters detected, compared with the coherence stability approach, and a similar density compared with the PS approach, but free of outliers.

Introduction Measuring the chemokine CXCL9 in urine by enzyme-linked immunosorbent assay (ELISA) can diagnose acute cellular rejection (ACR) noninvasively after kidney transplantation, but the required 12- to 24-hour turnaround time is not ideal for rapid, clinical decision-making. Methods We developed a biolayer interferometry (BLI)−based assay to rapidly measure urinary CXCL9 in 200 pg/ml in subjects with ACR and ≤100 pg/ml in subjects with stable kidney function without cellular infiltrates. In samples obtained after treatment for ACR, BLI CXCL9 measurements detected biopsy-proven intragraft infiltrates despite treatment-induced reduction in serum creatinine. Discussion Together, our proof-of-principle results demonstrate that BLI-based urinary CXCL9 detection has potential as a point-of-care noninvasive biomarker to diagnose and guide therapy for ACR in kidney transplantation recipients.

In this paper we present a technique based on self-mixing interferometry as a method for the acquisition and reconstruction of the arterial pulse wave. A modification of the classic fringe counting reconstruction algorithm is proposed to deal with some of the problems caused by biological tissue surface roughness, therefore allowing a reconstruction of the arterial displacement with a resolution of 400 nm. The traits of the arterial pulse wave have been retrieved with high detail, allowing their interpretation by a skilled practitioner. The heart beat measurements show a good agreement when compared to the readings of a commercial pulse-meter, therefore proving the versatility and the viability of the technique for the measurement of other cardiovascular signals.

Photonic biosensors offer label-free detection of biomolecules for applications ranging from clinical diagnosis to food quality monitoring. Both sensors based on Mach-Zehnder interferometers and ring resonators are widely used, but are usually read-out using different schemes, making a direct comparison of their fundamental limit of detection challenging. A coherent detection scheme, adapted from optical communication systems, has been recently shown to achieve excellent detection limits, using a simple fixed-wavelength source. Here we present, for the first time, a theoretical model to determine the fundamental limit of detection of such a coherent read-out system, for both interferometric and resonant sensors. Based on this analysis, we provide guidelines for sensor optimization in the presence of optical losses and show that interferometric sensors are preferable over resonant structures when the sensor size is not limited by the available sample volume. Yes

We propose differential optical feedback interferometry, a technique able to measure nanometer-size amplitude displacements by comparing the optical power of two lasers subject to optical feedback. In this letter, the principles of the technique are explained in detail, and its limits are explored by simulation. Theoretical results are presented showing that the technique can measure nanometer scale displacements with resolution within the angstrom scale. An experimental setup for validation has been built, and a series of experimental tests were performed using a capacitive sensor as a reference. Results show good agreement between theory and experiment with a reasonable reduction in performance due to mechanical coupling and signal noise. The proposed technique, thus, provides measurements of a very high resolution using an extremely simple and robust experimental setup.

The use of Global Navigation Satellite System (GNSS) signals for mesoscale altimetry was first proposed in [1]. Since then, many experiments and a couple of space missions have been carried out to validate the concept in multiple fields including not only ocean scenarios, but also land and ice [2]. The ensemble of these techniques is referred to as GNSS Reflectometry (GNSS-R). The most complete observable of these techniques is the so-called Delay Doppler Map (DDM), which is the 2D cross-correlation between the reflected signal and a reference one at different Doppler frequencies. In the conventional method (cGNSS-R), the reference signal is a clean replica of the transmitted one, whereas in the interferometric technique (iGNSS-R), the reference signal is the direct onesignal itself.

This paper proposes the use of the wavelet transform as a technique that is suited for fringe detection and analysis of optical feedback interferometry (OFI) signals, thus allowing the retrieval of extremely small physical motion phenomena. A novel algorithm based on wavelet transform is used to process the OFI signal simultaneously in the time and frequency domains, enabling precise detection of signal fringes and, thus, the extraction of amplitude features of the vibrating target with error in the order of 0.1 lambda. Furthermore, using a complex Morlet wavelet as an analyzing wavelet enables us to extract important information from the time envelope of the OFI signal. Such an envelope can be useful in detecting fringes even in the presence of speckle reducing the error in a displacement reconstruction. Examples of OFI applications, including nanometric displacement sensing without direction ambiguity as well as the measurement of the frequency and velocity of vibrating targets and the detection in time of no periodic events, are also presented using this wavelet approach. (C) 2015 Optical Society of America

The use of a simplified version of the liquid mirror approach to validate absolute planarity reference flats is described in detail. It is shown that the approach can serve the purpose, providing a measurement of the peak-to-valley departure from planarity that in experiments is within 7 nm uncertainty (2σ) over a diameter of 90 mm.

OBJETIVO: Comparar a precisão e reprodutibilidade de dois biômetros ultra-sônicos convencionais e um biômetro óptico para o cálculo da lente intra-ocular (LIO) acomodativa. MÉTODOS: Pacientes com catarata foram submetidos aos exames em 3 biômetros distintos (IOLMaster®, Axis II® e Humphrey Mod. 820®), antes da cirurgia para implantação da lente intra-ocular acomodativa de silicone (C&C Vision AT-45). No biômetro Humphrey Mod. 820 utilizou-se a técnica de contato e o Axis II foi usado para as técnicas de contato e imersão. O método de interferometria óptica foi realizado pelo IOLMaster. O comprimento axial (AL), profundidade da câmara anterior (ACD) e a ceratometria corneana (K) foram os parâmetros oculares analisados. RESULTADOS: Foram submetidos aos exames 34 pacientes com média de idade de 70,6 anos e idade variando entre 53 e 90 anos. A menor média do comprimento axial (23,12 mm), foi obtida no Axis II (contato) e maior (23,21 mm) no Humphrey Mod. 820 (contato). A maior média da profundidade da câmara anterior (3,10 mm) no IOLMaster e a menor (2,97 mm) no Humphrey Mod. 820 (contato). A reprodutibilidade para os dados de comprimento axial foi significativamente grande para todos os biômetros [3,02%, 3,07 % e 3,19% respectivamente para Humphrey Mod. 820 e Axis II (imersão), Axis II (contato) e IOLMaster]. Os biômetros foram extremamente concordantes nas medidas dos parâmetros analisados (99,01% e 94,77% respectivamente para o comprimento axial e ceratometria corneana). Os coeficientes de Pearson (r) demonstraram alta correlação entre os aparelhos nas medidas do comprimento axial e profundidade da câmara anterior. CONCLUSÃO: Os métodos do estudo para o cálculo da lente intra-ocular acomodativa, demonstraram que houve precisão e reprodutibilidade dos resultados, podendo evitar insatisfação visual do paciente no pós-operatório da cirurgia de catarata decorrente de erros no cálculo da lente intra-ocular. PURPOSE: To compare reproducibility, level of agreement and correlation of two ultrasonic biometers and one optical biometer for the calculation of accommodative intraocular lens. METHODS: Cataract patients were submitted to the examination with 3 different biometers (IOLMaster, Axis II and Humphrey Mod. 820) before the implant of the C&C Vision AT-45 accommodative silicone intraocular lens. The Axis II biometer was used for both contact and immersion biometry. Axial length, anterior chamber depth and keratometry were the analyzed biometric parameters. RESULTS: Thirty-four patients from 53 to 90 years old (mean 70.6 y) were submitted to the examination with the three different biometers. The lowest mean axial length (23.12 mm) was obtained with the Axis II/contact and the highest (23.21 mm) with the Humphrey biometer. The lowest mean anterior chamber depth (2.97mm) was obtained with the Humphrey and the highest (3.10mm) with the IOLMaster. Reproducibility for axial length was high for all the biometers tested (coefficient of variation: 3.02% for Humphrey and Axis II / immersion; 3.07 % for Axis II/contact and 3.19% for IOLMaster). All biometers presented nearly equal results of the analyzed parameters (99.01% for axial length and 94.77% for anterior chamber depth). Pearson's coefficient showed a high correlation between the biometers, regarding the axial length and anterior chamber depth measurements. CONCLUSION: The devices used in this study showed excellent reproducibility and high level of agreement and of the axial length, anterior chamber depth and keratometry measurements, making it possible to reduce errors of intraocular lens calculation and visual insatisfaction after cataract surgery. Universidade Federal de São Paulo (UNIFESP) Departamento de Oftalmologia Setor de Pesquisa Clínica Universidade Federal de São Paulo (UNIFESP) Departamento de Oftalmologia UNIFESP, Depto. de Oftalmologia Setor de Pesquisa Clínica UNIFESP, Depto. de Oftalmologia SciELO

This paper describes a method for calculating the phase profile of digitized interferograms obtained from a phase shifting interferometer. A phase-retrieval algorithm is presented which uses total least-squares fitting of the ellipses obtained when one of the intensity profiles is plotted against the others. A propagation-of-error analysis and experimental results are also given.

In Fourier transform spectroscopy (FTS), nonlinearity amplitude distortions in the interferograms are mainly due to detector. In the case of photoconductive detectors, as for instance, the semiconductor Mercury-Cadmium-Telluride detector (MCT), that is the detector most frequently employed for high-performance infrared measurements, the nonlinearities have been often discussed in the literature. For other infrared detectors, such as bolometers, the effect is not studied with equal attention; nevertheless, also with these detectors some nonlinearity is expected to be present. Amplitude distortions in the interferogram induce, through Fourier transform, radiometric errors in the acquired spectra. In order to eliminate radiometric errors, the interferograms must be corrected before Fourier transformation, by using either a measurement or a model of the real response of the acquisition system. An assessment of nonlinearity errors in FTS can also be made after Fourier transformation using the harmonic features that are introduced in the measured spectra by the nonlinear response. Usually nonlinearity was detected by looking for a nonzero signal in the low-frequency region of the spectrum, where the spectral response should be equal to zero. This procedure may be difficult in presence of 1/f noise, that prevents an accurate identification of the low frequency feature. In this paper, a method for the detection and characterisation of small nonlinearity effects by way of an analysis of the amplitude of the second harmonic feature in the acquired spectral distribution is presented and discussed. The method is applied to real measurements obtained with a far IR interferometer with an 3He-cooled bolometric detector.

In this paper, we explore the possibility of joining two measurement techniques that share a similar time frame and that are interested in describing the properties of materials through the study of the micro and nanometric scale. Atomic force microscopy (AFM) is a well established method capable of measuring different material properties by examining the deflection of a micro-cantilever caused by the sample surface force interactions. The cantilever deflection is typically estimated using the optical lever technique which requires a careful alignment of the laser beam and the cantilever. To reduce such problem, we propose the use of differential self-mixing interferometry (DSMI). A test to prove the feasibility of applying the DSMI on an AFM cantilever will be discussed as well as the problems found during the measurement. Preliminary results show that DSMI is capable of following up cantilever sinusoidal displacements with amplitudes in the range of 200 and 100nm which can usually be found in AFM non-contact and taping modes.

In this paper, the performance of a nearly zero inclination and low eccentricity geosynchronous synthetic aperture radar (GEOSAR) mission for midlatitude (30 $^{\circ}$ –60 $^{\circ}$ ) Earth observation is analyzed. The slow motion of such satellites with respect to the Earth's surface makes it necessary to consider long coherent combination of pulses during hours to reach the desired along-track resolution. A system based on moderate transmitted powers and antenna sizes is considered. The necessary sensitivity in such GEOSAR system is obtained from the accumulated energy of the raw data using a pulse repetition frequency above the Doppler bandwidth and a long integration time. Several issues as a result of the long acquisition, such as target and atmospheric phase screen decorrelation, speckle noise impact on the received signal, and satellite station-keeping requirements, are analyzed. The feasibility of such systems to be placed on a broadcasting communication satellite makes nearly zero inclination GEOSAR a low-cost alternative of current SAR missions.

The reliability of any final differential synthetic aperture radar (SAR) interferometry (DInSAR) product is directly related to the phase quality of the interferograms involved in the processing. Performing an appropriate selection of high-quality pixels is hence mandatory in order to avoid the inclusion of noisy data in the processing and thus obtain reliable deformation information within the area of study. In this framework, a new full-resolution pixel selection method based on exploiting the spectral properties of pointlike scatterers is presented. The method is developed from the concept of the so-called coherent scatterers, which are characterized by having a correlated spectrum in a single acquisition, but now involving the temporal axis in the detection. Using the spectral properties of scatterers to perform the DInSAR pixel selection step presents some advantages with respect to the well-known permanent scatterer (PS) approach. On the one hand, the radiometric calibration of data is not required since the detection is now not dependent on the amplitude behavior of scatterers. On the other hand, a reliable pixel selection can be performed even with a reduced number of images due to the nature of the estimator. In contrast, its main limitation relies on the loss of range resolution involved in the sublook generation process. The method is more suited for urban scenarios where the density of temporally stable pointlike scatterers is generally higher. In this context, the final deformation maps obtained using the new method presented are compared, in terms of density and phase quality, with the ones obtained with the well-known traditional PS approach, showing a similar performance. Finally, since both methods characterize pointlike scatterers from different points of view, the combination of both techniques is proposed leading to a significant increase in the pixels' density and giving place to a meaningful improvement in the final DInSAR results.

This paper describes the Microwave Interferometric Reflectometer (MIR) instrument back-end for GNSS reflectometry (GNSS-R) applications. MIR uses the interferometric (iGNSS-R) and conventional (cGNSS-R) techniques for altimetry and scatterometric observations. MIR is intended for low altitude aircrafts, and can track up to 4 pairs of satellite/reflection points simultaneously. The back-end computes real-time 2D cross-correlations in the delay/Doppler plane and performs incoherent averaging after proper delay and Doppler tracking. Initial results from ground measurements are shown.

Purpose: To compare the ocular anterior chamber depth, white-to-white distance, anterior chamber angle, and pupil diameter, as measured with two different Scheimpflug imaging devices. Methods: This transversal study included 80 right eyes from 80 subjects aged from 20 to 40 years. Their spherical equivalents ranged from -4.25 to +1.00 diopters (D). Each eye's anterior chamber depth, white-to-white distance, anterior chamber angle, and pupil diameter, were measured for far vision using both the Galilei G4 (double Scheimpflug camera) and the Pentacam HR (single Scheimpflug camera) systems. Results: Mean anterior chamber depths were calculated as 3.12 ± 0.23 mm and 3.19 ± 0.24 mm when measured with the Galilei G4 and the Pentacam HR, respectively. The mean white-to-white distance measured was 11.84 ± 0.31 mm and 11.90 ± 0.43 mm when measured with the Galilei G4 and the Pentacam HR, respectively. Mean pupil diameters were measured as 3.22 ± 0.58 mm and 3.22 ± 0.52 mm when measured with the Galilei G4 and the Pentacam HR, respectively. Finally, the mean anterior chamber angle was 34.30 ± 2.86 degrees when it was measured with the Galilei G4, and 39.26 ± 2.85 degrees when measured with the Pentacam HR. A comparative analysis revealed that the Galilei G4 yielded a significantly lower (P0.05) for both devices were obtained for the white-to-white distance measurements. Conclusion: The Galilei G4 and Pentacam HR Scheimpflug systems cannot be used interchangeably because they produce significant measurement differences.

This paper provides a wrap-up of some of the activities undertaken by SMOS L1 team to fine tune the instrument calibration and modeling that eventually has resulted into a SMOS full-polarimetric measurement and image reconstruction enhanced performance

In this paper, a self-mixing interferometry sensor has been used as a proximity probe to measure possible runout in permanent magnet synchronous motors, for fault diagnosis. A general procedure for the measurement of the 2-D trajectory of the motor shaft is described in detail, including procedures for the characterization of the uncertainty due to the shape of the shaft, and the management of speckle noise. The performance of the proposed sensor has been compared to that of a commercial Polytec laser vibrometer, for validation purposes. Results show inaccuracies in the order of ±6 μm, which agree well with the measured uncertainty introduced by shaft surface imperfections.

We demonstrate an optical scheme for measuring the thickness of thin nanolayers with the use of light beam ’ s spa- tial modes. The novelty in our scheme is the projection of the beam reflected by the sample onto a properly tailored spatial mode. In the experiment described below, we are able to measure a step height smaller than 10 nm, i.e., one- eightieth ( 1 ∕ 80 ) of the wavelength with a standard error in the picometer scale. Since our scheme enhances the signal-to-noise ratio, which effectively increases the sensitivity of detection, the extension of this technique to the detection of subnanometric layer thicknesses is feasible

Nowadays, several global navigation satellite system (GNSS) services coexist at L-band and some more will be available in the near future. These new signals were originally conceived to enhance the location accuracy, but they also offer a promising opportunity for improved GNSS-reflectometry (GNSS-R) retrievals. This work gives closed form expressions for GNSS-R waveform simulation using the composite GPSL1 and L5 and Galileo E1, E5, and E6 signals as function of the receiver bandwidth. The impact of the observation geometry and sea state on the waveform shape is studied in airborne and spaceborne conditions. Finally, the altimetric height bias using the derivative method is analyzed as function of the receiver bandwidth.

An adaptive autofocus technique for the control of speckle effect in optical feedback interferometry (OFI) is discussed. The beam spot size effect over the OFI signal is presented, justifying the proposed approach. An automated setup for the control of speckle effect using a liquid lens with electro-optical focusing is demonstrated. The spot size is modified according to the signal to noise ratio (SNR) bounds selected for the captured OFI signal, therefore avoiding signal fading caused by speckle effect and possible chaotic behavior because of strong feedback. The quality and shape of the acquired OFI signal when the spot size change takes place shows a transient oscillation without any additional effects over the OFI SNR and the OFI shape. Experimental examples are provided proving the effectiveness of the approach for speckle control in displacement and velocity measurements within a movement range of 20 mm. (C) 2014 Elsevier B.V. All rights reserved.

Global navigation satellite systems (GNSS) signals offer a promising opportunity to perform mesoscale altimetry with worldwide coverage using small satellites. However, unlike the signals used in classical altimeters, the GNSS signals have smaller bandwidth and lower transmitted power. This paper analyzes the achievable height precision of the Global Navigation Satellite System Reflectometry (GNSS-R) altimeters based on the Cramer-Rao bound for time-delay estimation. Precision bounds for the composite signals GPS L1 and L5 and Galileo E1, E5, and E6 in a spaceborne mission scenario are assessed, and the optimum receiver bandwidths which minimize them are obtained.

Received Signal Strength (RSS) localization is widely used due to its simplicity and availability in most mobile devices. The RSS channel model is defined by the propagation losses and the shadow fading. These parameters might vary over time because of changes in the environment. In this paper, the problem of tracking a mobile node by RSS measurements is addressed, while simultaneously estimating a two-slope RSS model. The methodology considers a Kalman filter with Interacting Multiple Model architecture, coupled to an on-line estimation of the observation’s variance. The performance of the method is shown through numerical simulations in realistic scenarios.

This paper develops an analysis of the SAR impulse response function from the interferometric point of view, with the intention of studying its phase behavior in the presence of high squint angle values. It will be pointed out that in this case, a phase ramp is present in the range direction, which, in combination with a certain degree of misregistration between the two images induces an offset in the generated interferometric phase. This behavior, if not compensated, imposes strong limits on the performance of the interferometric techniques in a squinted case, especially for airborne SAR systems. The article proposes two new techniques, which are appropriate to correct the phase bias coming from this source. The first one is based on a modification of the azimuth compression filter, which cancels the phase ramp of the range impulse response function for one specific squint value. In case the SAR processing is performed with variable squint over range, the authors propose a second method oriented to estimating the expected misregistration and thus, the phase bias by means of an iterative approach. Simulated data as well as real corner reflector responses are used to show that the correct topography can be recovered precisely even in the presence of phase bias coming from the squinted geometry.

Synthetic aperture radar (SAR) systems are inherently band limited in both range and azimuth, and hence, the point spread function (PSF) has the shape of a bidimensional sinc function. In addition, all SAR images are slightly oversampled, and as a consequence, the contribution of a single target extends to more than a single cell. The main lobe and the side lobes of strong scatterers are sometimes clearly visible in the images. This characteristic of the SAR images must be considered when applying differential interferometric synthetic aperture radar (DInSAR) pixel selection algorithms. For persistent scatterers, the properties, for instance, the amplitude stability, are preserved in both redundant information around the main lobe and side lobes. For this reason, a cluster of pixels rather than just the pixel position corresponding to the exact location of the target will be detected. Spatially variant apodization (SVA) is a nonlinear filter based on cosine-on-pedestal weighting functions able to achieve a total side-lobe cancelation without degrading the original image resolution. When working with complex data under complex scattering scenarios, the PSF moves away from the ideal bidimensional sinc, and the SVA performance worsens. The amplitude and phase of the original images could be distorted by the SVA filtering compromising the pixel selection and the quality of the final DInSAR results. In this letter, SVA is used to method locate in the image the side lobes of high-power scatterers and generate a mask while preserving the amplitude and phase of the original images.

In the last years, the GPS signals have been validated as opportunity signals in a wide range of reflectometry-based remote sensing applications for sea, land or ice scenarios. Recently, the first Galileo satellites have started transmitting the new signal E1, which shares the band with the GPS L1 signal. This work compares the performance of both signals in space and airborne scenarios for sea state and altimetry determination.

When applying seismic interferometry to image sub-vertical salt flanks or structures with large dips from vertical or deviated wells, we are often confronted with poor target illumination. Strong directionalillumination footprints caused by non-ideal placement of sources at the surface degrade the interferometric image quality and may prevent the retrieval of particular dips in the image. The effect of the well's orientation on the interferometric image is investigated. Moreover, a method is presented to estimate the imageable dips in an interferometric image, which can be used to design a more favorable shooting geometry and to gain additional knowledge about the target structures.

We present a method for recording on-axis color digital holograms in a single shot. Our system performs parallel phase-shifting interferometry by using the fractional Talbot effect for every chromatic channel simultaneously. A two-dimensional binary amplitude grating is used to generate Talbot periodic phase distributions in the reference beam. The interference patterns corresponding to the three chromatic channels are captured at once at different axial distances. In this scheme, one-shot recording and digital reconstruction allow for real-time measurement. Computer simulations and experimental results confirm the validity of our method.

We introduce a new measurement system called Nanopolar interferometer devoted to monitor and characterize single nanoparticles which is based on the interferometric phase modulated ellipsometry technique. The system collects the backscattered light by the particles in the solid angle subtended by a microscope objective and then analyses its frequency components. The results for the detection of 2 μm and 50 nm particles are explained in terms of a cross polarization effect of the polarization vectors when the beam converts from divergent to parallel in the microscope objective. This explanation is supported with the results of the optical modelling using the exact Mie theory for the light scattered by the particles.

A self-mixing laser interferometer has been combined with a compact and robust optical system including an adaptive optical element in the form of a voltage controllable liquid lens. The use of the liquid lens enables the self-mixing interferometer to adjust the optical focus position and the beam spot diameter on the target surface, and subsequently the feedback level within the laser cavity. The optical system has been designed to focus the beam at distances from a few centimetres from the front facet of the laser diode to infinity. With such a simple arrangement, it is possible to modify and control the intensity of the back reflected light from the target surface into the laser cavity, by simply changing the voltage applied to the lens to modify the focus condition on the target surface. The final effect obtained is full active control of the feedback level of the self-mixing effect taking place. This has allowed keeping the feedback level of the interferometer in the desired regime for measurements along very long distances and for different measurement situations, so extending the capabilities of a classical self-mixing interferometer. The advantage of the proposed adaptive optical head is thus its combination of precise metrology capabilities plus a great potential in automated feedback control and operator-free industrial applications. Signal reconstruction of the target vibration amplitude presents a maximum error of λ/16 as compared with a commercial capacitive sensor in the whole focusable range for displacement measurements. An improved working range of 6.5 cm to 280 cm staying in the same feedback regime has been experimentally demonstrated.

An analysis of speckle effects in self-mixing interferometry signals has been performed. We will characterize the effect of surface roughness and laser spot size on the speckle modulation of the signal, and we will propose two simple experimental approaches to overcome the amplitude fading induced by speckle effect. Differently to the techniques proposed up to the moment, our first approach uses an adaptive optical element in the form of a voltage programmable liquid lens, which adaptively changes its focal length to modify the speckle pattern. Our second approach combines two laser signals which present different performance parameters. By using any of these simple methods, the introduction of inaccuracies in the measurement process due to speckle is avoided.

We propose a fourth-order interference scheme for optical coherence tomography operating with broadband incoherent (or quasi-incoherent) light. It is shown that using this proposal, an axial resolution improvement by a factor of 2 and a better sensitivity for weakly reflecting samples are obtained than with the standard second-order correlation scheme. From a practical perspective, we suggest the use of broadband Q-switched pulses and performing ultrafast intensity correlation with a nonlinear crystal. The global performance of our proposal is illustrated by means of numerical simulations

Proceedings of: 17th Topical Conference on High-Temperature Plasma Diagnostics, Albuquerque, New Mexico, 11-15 May 2008 A high spatial resolution two-color (CO2, lambda=10.6 mum, He-Ne, lambda=633 nm) interferometer for density profile measurements in the TJ-II stellarator is under development and installation, based in the currently operational single channel two-color heterodyne interferometer. To achieve the objectives of 32 channels, with 4-5 mm lateral separation between plasma chords, careful design and calibration of the interferometric waveforms for both the measurement and vibration compensation wavelengths are undertaken. The first step has been to set up in our laboratories an expanded-beam heterodyne/homodyne interferometer to evaluate the quality of both interferometric wavefronts, a reported source of poor vibration compensation and thus low resolution in the density profile measurements. This novel interferometric setup has allowed us to calibrate the spatial resolution in the profile measurements resulting in ~2 mm lateral resolution in the reconstruction of the interferometric wavefront.

We present an adaptive and dynamic hexagonal electro-optic phase array. The proposed device consists of a 2-dimensional hexagonal array of periodically inverted ferroelectric domains, along the z-axis, in lithium niobate crystals. The phase step is achieved via the application of an external electric field, along the z-axis, through transparent electrodes. Thanks to the electro-optic effect the phase step can changed with continuity over all the 0 to 2π by applying a variable voltage. In this way different patterns can be generated. In fact, one important property of this new proposed configuration of array illuminator is the intrinsic flexibility. Such flexible array could be potentially used in a variety of applications such as optical interconnects, tunable lithographic masks, 2D optical trapping and assembling of particles or wavefront phase modulators. As example, photolitography experiments are performed by means of this optical phase mask with electrooptically tunable phase step. In fact, the collimated beam of an argon laser passes through the phase mask and the near field intensity patterns, at different planes of the Talbot length and for different values of the applied voltage, are used for photolitographic experiments.

Quantitative Phase Microscopy (QPM) by means of Lateral Shear Interferometry (LSI) is presented as a metrological tool to investigate dynamical behaviour of living cells. QPM achieved by a Digital Holographic Microscope (DHM), in transmission geometry, allows to reconstruct object shape from the numerical reconstruction of the complex field transmitted by the object. This geometry is useful in special case of biological material because they present an amplitude contrast too small for quantitative amplitude microscopy. DHM realized with a Mach-Zehnder interferometer provides the object phase map which is simply related to the object height. This technique gives a detailed map of the internal structure of the cell. The main trouble in QPM is the removal of the aberration due to the optical setup. Usually, in DHM the aberrations are eliminated by subtraction of a reference phase map (acquired without sample cell) from the object phase map. We propose a method, based on LSI, for the aberration removal that avoids this double exposure and makes use of the single object hologram. The reconstructed wavefront and its shifted replica are subtracted to obtain a shearogram from which the phase map of the object can be completely retrieved. Both shifted replica and subtraction are processed numerically. This method allows to remove optical aberrations more efficiently and faster than other conventional techniques and provides real time monitoring of cell samples.

In this paper is reported a method for measuring the thickness of a silicone nitride layers employed for fabricating silicon MEMS bi-morph structures. The method allows the precise evaluation of layer thickness by adopting Digital Holographic Microscope. The measurement is based on the fact that the silicon nitride layer is transparent to the visible light. The optical phase difference (OPD) between the light beam traveling through the layer and portion of the beam in air is measured exploiting an interferometric technique. The approach is very simple and can be utilized even for inspection of non-planar or stressed structures. Experimental values have been compared with ellipsometric measurements.

We demonstrate a dual interferometric technique for simultaneous and independent measurements of the temperature dependence of the thermo-optic and thermal expansion coefficients in ferroelectric crystals. The crystal temperature can be changed from room temperature up to about 200°C by an actively stabilized heater (stability < 0.1°C). The thermal expansion coefficient is determined using a moire interferometer and monitoring the period of a grating written on the z-face of the crystal sample as a function of the temperature of the crystal. The thermo-optic coefficients of both ordinary and extraordinary axes are estimated by measuring the optical path variation measured by a Mach-Zehnder interferometer with one arm passing through the crystal perpendicularly to the crystal z-axis. This method can be applied to a wide variety of optical materials, when an accurate knowledge of the temperature dependence of the refractive index and thermal expansion is needed.

Digital Holographic Microscopy (DHM) is an optical interferometric technique for not destructive testing of micro-electro-mechanical systems (MEMS). A characterization process based on a no-contact technique allows us to analyze deformations, warping, residual stress, cracks and more other defects of MEMS, without destroy them. The flexibility of this technique allows us to improve novel numerical reconstruction algorithm for the recovery of more information. The post processing of the acquired holograms allows to reduce noise, optical aberrations, defocusing. In particular, the hologram reconstruction process has been modified to obtain Extended Focus Images (EFI). In Digital holographic microscopy, the use of microscopy objectives with high magnifications, reduces the focus depth. This means that for extended object a single reconstructed image with all the details in focus is not possible to obtain. Using a multiple reconstruction process and opportune resizing algorithms a full focused reconstructed images of extended object has been obtained without any mechanical movement. In particular, the advantages of the EFI technique are unique for dynamical characterization by DHM of extended objects, where the techniques based on multiple acquisitions fail. The EFI technique has been applied to obtain a best focused reconstructed image and profile of some micromechanical systems. It is demonstrated that this new approach allows to improve the accuracy in the EFI image when compared to the previous experimental results. Focusing of zones at different quote has been obtained evidencing, shape, crack and deformation impossible to observe otherwise at the same time. Moreover, these technique of reconstruction and analysis can be advantageous in many other fields of application.

A novel and simple phase-shifting point-diffraction interferometer using a z-cut lithium niobate wafer is proposed. The pinhole is realized by an optical lithography process, aluminum deposition, and subsequent lift-off on the surface of the wafer. The phase shifting is obtained by inducing the electro-optic effect along the z crystal axis. We demonstrate experimentally the possibility of retrieving an aberrated wavefront.