A laser beam characterization method is reported, which is applicable to arbitrary and ideal laser beam intensity profiles. This method, called the scattered light imaging method (SLIM), is based on scattered light imaging of a laser beam and provides a complete visualization of it in the region of interest. The method was applied to characterize an arbitrary pedestal-shaped beam and compared with a conventional method (camera scanning). The results we presented show that, for arbitrary beams, it seems much more meaningful to know the intensity profile evolution than to determine an $M^2$ value. Therefore the SLIM is a powerful tool for a new and more complete type of laser beam characterization.

In this paper, we report on the development of an intensity-modulated fiber-optic sensor for angular displacement measurement. This sensor was designed to present high sensitivity, linear response, and wide bandwidth and, furthermore, to be simple and low cost. The sensor comprises two optical fibers, a positive lens, a reflective surface, an optical source, and a photodetector. A mathematical model was developed to determine and simulate the static characteristic curve of the sensor and to compare different sensor configurations regarding the core radii of the optical fibers. The simulation results showed that the sensor configurations tested are highly sensitive to small angle variation (in the range of microradians) with nonlinearity less than or equal to 1%. The normalized sensitivity ranges from $(0.25\times V_{\max })$ to $(2.40\times V_{\max })\mathrm{mV}/\mathrm{\mu rad}$ (where $V_{\max }$ is the peak voltage of the static characteristic curve), and the linear range is from 194 to 1840 μrad. The unnormalized sensitivity for a reflective surface with reflectivity of 100% was measured as $7.7\mathrm{mV}/\mathrm{\mu rad}$. The simulations were compared with experimental results to validate the mathematical model and to define the most suitable configuration for ultrasonic detection. The sensor was tested on the characterization of a piezoelectric transducer and as part of a laser ultrasonics setup. The velocities of the longitudinal, shear, and surface waves were measured on aluminum samples as 6.43, 3.17, and $2.96\mathrm{mm}/\mathrm{\mu s}$, respectively, with an error smaller than 1.3%. The sensor, an alternative to piezoelectric or interferometric detectors, proved to be suitable for detection of ultrasonic waves and to perform time-of-flight measurements and nondestructive inspection.

The replacement of copper wires by optical fibers for control and monitoring of aircraft systems are gaining more and more acceptance due to weight reductions and their intrinsic reliability. The present investigation proposes a new method for producing fiber optical guidelines in carbon fiber reinforced polymer (CFRP) composites using laser texturing and machining. Laser texturing was used to improve the adhesion bonding between the CFRP parts and laser machining is used to create a channel where the optical fiber will be placed and protected. The results show that using only 20W of a Nd:YAG pulsed laser it is possible to enhance the joint resistance of CFRP composites and also protecting the optical fiber embedded in between two CFRP pieces. Using the proposed technology, the maximum load of a lap joint increased by 85% and the optical fiber remained integral even under severe bending conditions

This work presents a novel nonlinear control system designed for interferometry based on variable structure control and sliding modes. This approach can fully compensate the nonlinear behavior of the interferometer and lead to high accuracy control for large disturbances, featuring low cost, ease of implementation and high robustness, without a reset circuit (when compared with a linear control system). A deep stability analysis was accomplished and the global asymptotic stability of the system was proved. The results showed that the nonlinear control is able to keep the interferometer in the quadrature point and suppress signal fading for arbitrary signals, sinusoidal signals, or zero input signal, even under strong external disturbances. The system showed itself suitable to characterize a multi-axis piezoelectric flextentional actuator, which displacements that are much smaller than half wavelength. The high robustness allows the system to be embedded and to operate in harsh environments as factories, bringing the interferometry outside the laboratory.

The present work concerns with the modeling, development and application of a novel control strategy based on sliding mode control, for two beam quadrature interferometers, with the high-gain approach. In this case, by reading the control signal the demodulation process does not require phase unwrapping algorithms, i.e., the output signal presents a straight-line relationship with the interferometer total phase shift. This system was implemented in a digital platform to control a bulk Michelson interferometer whose performance was experimentally determined, showing its capability on achieving real-time measurement and presenting wider dynamic range and bandwidth (52.5 rad in low frequencies and 5.8 rad up to 500 Hz) when compared with the literature. Moreover, this performance can be improved even further by simply increasing the feedback gain.

In this work, we present an analysis of the influence of geometrical parameters on the sensitivity and linear range of a fiber optic angular displacement sensor, through computational simulations and experiments. The geometrical parameters analyzed are the lens focal length, the gap between fibers, the fiber cladding radii, the emitting fiber critical angle (or, equivalently, the emitting fiber numerical aperture), and the standoff distance (distance between the lens and the reflective surface). Besides, we analyze the sensor sensitivity regarding any spurious linear displacement. The simulation and experimental results show that the parameters that play the most important roles are the emitting fiber core radius, the lens focal length, and the light coupling efficiency, whereas the remaining parameters have little influence on the sensor characteristics.