Implementation of differential self-mixing interferometry systems for the detection of nanometric vibrations

In this Thesis, we explore Self-mixing interferometry (SMI ), a method capable of producing high resolution optical path related measurements in a simple, compact and cost-effective way. Even with a notably less complex setup than traditional interferometric methods, SMI can produce measurements with a resolution well below the micrometric scale (N'2) which is sufficient for most industrial applications. The SMI effect is produced when a small part of the laser power impacting a target is back-scattered and re-injected into the laser cavity. As a result, the phase and amplitude of the laser wave is modified generating a signature beat, which can be "easily" related to different optical path-related dynamics. The main advantage of this method in relation to other interferometric methods is the simple setup consisting mainly of a single mode laser diode (LO) equipped with a simple electronic system readout a simple optical system may be used to collimate/focus the beam allowing measurements at larger distances. Because of the small amount of reflected optical power required to allow the effect, the technique can produce high resolution measurements even with diffusive targets. While the SMI method has been largely studied in the last three decades, there are still several topics worth the development of further research. One of those topics, how to increase the resolution on displacement measurements, is one of the main topics covered in this work. Classical SMI methods allow the reconstruction of displacement measurement with a resolution of N'2. The use of special processing algorithms can push further this limit reaching values in the order of e.g. N32. In this work, we propose a method to increase even further this limit reach values better than N100.The idea discussed, differential self-mixing interferometry (OSMI) proposes the use of a reference modulation (mechanical or electrical) to be used as a reference for the measurement. Simulated results have shown that under ideal conditions, it may be possible to reach resolutions in the order of N1000. In practice, however, this limit is much smaller (N100) because of LO dynamics, and different practical limitations present in the amplification and readout electronics. Experiments and measurements are presented along the second chapter of this work to present proof of the proposed method. After exploring the basics of OSMI, possible applications for classic SMI and DSMI were pursued. The obtained results are presented in the following sections. First, a review on potential biomedical measurements using SMI is discussed. The obtained results suggest that it is possible to obtain some key values related to biomedical constants (e.g. P.PW) using a displacement SMI measurement. The method, however, may not be reliable enough especially on long time measurements. Moreover, the use of certain wavelengths must be avoided during long exposures as they may prove harmful to the soft tissue due to the requirements of a small laser spot. lt is observed that SNR may lead to difficulties during the signal processing stage which may impact the results of the reconstructed signal. Next, the DSMI method was tested in an AFM-like cantilever system. The results suggest that is possible to follow the motion of a micrometric size cantilever oscillating at low frequencies with a high resolution. Higher frequencies may be achieved by using an electronic reference modulation configuration. The proposed system was able to detect some artefacts on the motion which maybe attributed to possible deflections on the cantilever surface. Possible enhancements to the method are suggested for any researcher who wants to expand the topic.En esta Tesis, se explora la interferometría auto-mezclante, mejor conocida por su nombre en inglés Self-m ixing interferometry (SMI), un método capaz de producir mediciones relativas al cambio del camino óptico en un haz laser. La técnica está caracterizada por su tamaño compacto, bajo coste y alta resolución. Pese a su simplicidad, la resolución alcanzada por sistemas basados en SMI se encuentra por debajo de la escala micrométrica (N2), lo cual es suficiente para la mayoría de las aplicaciones industriales. El efecto SMI se genera cuando una pequeña parte de la potencia óptica del láser es retro reflectada por un blanco y reinyectada en la cavidad láser. Como resultado, se genera una modulación de la amplitud y fase del láser, la cual puede ser "fácilmente" relacionada con diferentes efectos relativos al camino óptico del láser. La principal ventaja del método SMI es la simplicidad del sistema de medición el cual está compuesto de un diodo láser (LO) equipado con una tarjeta de procesamiento electrónico. una lente de enfoque o colimación puede ser utilizada con el fin de regular la reinyección de potencia y la distancia al blanco. Debido a que el SMI se genera con una pequeña cantidad de potencia es posible realizar mediciones incluso en blancos con reflexión difusa. . Si bien el método SMI ha sido estudiado ampliamente durante las 3 últimas décadas, aún existen diversos puntos de interés en su estudio. Uno de estos puntos corresponde a la mejora de resolución en la medida de desplazamiento, el cuál es uno de los temas abordados en el presente trabajo. Los métodos clásicos SMI para la medición de desplazamiento permiten alcanzar una resolución en el orden de A/2. El uso de algoritmos de procesamiento especializados puede permitir mejorar el límite de la técnica alcanzando resoluciones (por ejemplo) en el orden de N32. En este trabajo proponemos un método que teóricamente permitiría alcanzar resoluciones mejores que N1OO. La discusión en este punto se sitúa sobre la técnica differential self-mixing interferometry (DSMI), la cual hace uso de una modulación de referencia (mecánica o electrónica) para realizar la medición. Los resultados de diversas simulaciones sugieren que, en condiciones ideales, la técnica es capaz de producir una resolución superior a N1000. En la práctica, el límite encontrado es menor (N100), lo cual puede ser atribuido a condiciones de ruido y efectos de no linealidad en el láser. Para apoyar la idea propuesta diversas medidas simuladas y experimentales son presentadas a lo largo de esta Tesis. Después de explorar las ideas básicas de DSMI, un grupo de posibles aplicaciones para SMI y DSMI fueron exploradas en este trabajo. Una revisión de posibles aplicaciones biomédicas utilizando SMI fue explorada. Los resultados obtenidos sugieren que es posible obtener valores relacionados con constantes biomédicas de interés (p.e. APW) utilizando medidas de desplazamiento basadas en SMI. El método, sin embargo, no es lo suficientemente fiable como para producir medidas estables en un uso prolongado. El SNR de la señal puede introducir complicaciones durante el procesado SMI que puede derivar en errores de reconstrucción de la señal original. . El método DSMI fue probado en un prototipo de sistema AFM equipado con un cantiléver. Los resultados obtenidos sugieren que la técnica es capaz de medir movimientos producidos por un cantiléver de dimensiones micrométricas con alta resolución en bajas frecuencias. La medición de oscilaciones de mayor frecuencia podría ser alcanzada utilizando una configuración basada en modulación electrónica. El sistema propuesto fue capaz de detectar artefactos en el movimiento que podrían ser atribuidos a deflexiones en el cantiléver. Algunas posibles mejoras a esta implementación son sugeridas como puntos para futuras investigaciones alrededor de este tema.Postprint (published version

Frequency-Modulated Optical Feedback Interferometry for Nanometric Scale Vibrometry

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.Postprint (author's final draft

Extraction of vibration parameters from optical feedback interferometry signals using wavelets

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 AmericaPreprin

Interferometría autorrealimentada para la medición de deformación en materiales estructurales sometidos a cargas dinámicas

Postprint (author's final draft

Treatment with tocilizumab or corticosteroids for COVID-19 patients with hyperinflammatory state: a multicentre cohort study (SAM-COVID-19)

Objectives: The objective of this study was to estimate the association between tocilizumab or corticosteroids and the risk of intubation or death in patients with coronavirus disease 19 (COVID-19) with a hyperinflammatory state according to clinical and laboratory parameters. Methods: A cohort study was performed in 60 Spanish hospitals including 778 patients with COVID-19 and clinical and laboratory data indicative of a hyperinflammatory state. Treatment was mainly with tocilizumab, an intermediate-high dose of corticosteroids (IHDC), a pulse dose of corticosteroids (PDC), combination therapy, or no treatment. Primary outcome was intubation or death; follow-up was 21 days. Propensity score-adjusted estimations using Cox regression (logistic regression if needed) were calculated. Propensity scores were used as confounders, matching variables and for the inverse probability of treatment weights (IPTWs). Results: In all, 88, 117, 78 and 151 patients treated with tocilizumab, IHDC, PDC, and combination therapy, respectively, were compared with 344 untreated patients. The primary endpoint occurred in 10 (11.4%), 27 (23.1%), 12 (15.4%), 40 (25.6%) and 69 (21.1%), respectively. The IPTW-based hazard ratios (odds ratio for combination therapy) for the primary endpoint were 0.32 (95%CI 0.22-0.47; p < 0.001) for tocilizumab, 0.82 (0.71-1.30; p 0.82) for IHDC, 0.61 (0.43-0.86; p 0.006) for PDC, and 1.17 (0.86-1.58; p 0.30) for combination therapy. Other applications of the propensity score provided similar results, but were not significant for PDC. Tocilizumab was also associated with lower hazard of death alone in IPTW analysis (0.07; 0.02-0.17; p < 0.001). Conclusions: Tocilizumab might be useful in COVID-19 patients with a hyperinflammatory state and should be prioritized for randomized trials in this situatio

Safety at the interface A story of crane operations offshore

Published in Cranes Today April 1983 pp23-24LD:6861.70(EASAMS-PP--131) / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

Cost-effective laser feedback sensor for nanometric scale acoustic perturbations

Postprint (published version

Adaptive autofocus technique for speckle control in optical feedback interferometry

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.Postprint (published version

Ultracompact vibrometry measurement with nanometric accuracy using optical feedback

The nonlinear dynamics of a semiconductor laser with optical feedback (OF) combined with direct current modulation of the laser is demonstrated to suffice for the measurement of subwavelength changes in the position of a vibrating object. So far, classical Optical Feedback Interferometry (OFI) has been used to measure the vibration of an object given its amplitude is greater than half the wavelength of emission, and the resolution of the measurement limited to some tenths of the wavelength after processing. We present here a methodology which takes advantage of the combination of two different phenomena: continuous wave frequency modulation (CWFM), induced by direct modulation of the laser, and non-linear dynamics inside of the laser cavity subject to optical self-injection (OSI). The methodology we propose shows how to detect vibration amplitudes smaller than half the emission wavelength with resolutions way beyond ¿/2, extending the typical performance of OFI setups to very small amplitudes. A detailed mathematical model and simulation results are presented to support the proposed methodology, showing its ability to perform such displacement measurements of frequencies in the MHz range, depending upon the modulation frequency. Such approach makes the technique a suitable candidate, among other applications, to economic laser-based ultrasound measurements, with applications in nondestructive testing of materials (thickness, flaws, density, stresses), among others. The results of simulations of the proposed approach confirm the merit of the figures as detection of amplitudes of vibration below ¿/2) with resolutions in the nanometer range.This work is partially supported by European Union and Spanish Ministry of Science and Innovation through project DPI2011-25525.Peer ReviewedPostprint (published version

Dealing with speckle effects in self-mixing interferometry measurements

Postprint (published version