There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

To improve the performance of particle image velocimetry in measuring instantaneous velocity fields, direct cross-correlation of image fields can be used in place of auto-correlation methods of interrogation of double- or multiple-exposure recordings. With improved speed of photographic recording and increased resolution of video array detectors, cross-correlation methods of interrogation of successive single-exposure frames can be used to measure the separation of pairs of particle images between successive frames. By knowing the extent of image shifting used in a multiple-exposure and by a priori knowledge of the mean flow-field, the cross-correlation of different sized interrogation spots with known separation can be optimized in terms of spatial resolution, detection rate, accuracy and reliability.

Theory of cross-correlation analysis of PIV images : Image analysis as measuring technique in flows

This review describes induction coil sensors, which are also known as search coils, pickup coils or magnetic loop sensors. The design methods for coils with air and ferromagnetic cores are compared and summarized. The frequency properties of coil sensors are analysed and various methods for output signal processing are presented. Special kinds of induction sensors, such as Rogowski coil, gradiometer sensors, vibrating coil sensors, tangential field sensors and needle probes are described. The applications of coil sensors as magnetic antennae are also presented.

/pdf/induction-coil-sensors-a-review-19wdku49yx.pdf

Induction coil sensors—a review

After a brief examination of known insulating laser crystals and the stimulated emission channels of their generating activator ions, this article reviews recent advances in the development of novel lasing crystals and ceramics, as well as inorganic and organic nonlinear-laser crystals for χ(3) and cascaded χ(3) ↔ χ(2) frequency converters Several new modern attractive technologies in the physics and techniques of crystalline lasers are also discussed

https://onlinelibrary.wiley.com/doi/pdf/10.1002/lpor.200710008

Laser crystals and ceramics: recent advances

This tutorial presents a guided tour of laser feedback interferometry, from its origin and early development through its implementation to a slew of sensing applications, including displacement, distance, velocity, flow, refractive index, and laser linewidth measurement Along the way, we provide a step-by-step derivation of the basic rate equations for a laser experiencing optical feedback starting from the standard Lang and Kobayashi model and detail their subsequent reduction in steady state to the excess-phase equation We construct a simple framework for interferometric sensing applications built around the laser under optical feedback and illustrate how this results in a series of straightforward models for many signals arising in laser feedback interferometry Finally, we indicate promising directions for future work that harnesses the self-mixing effect for sensing applications

Laser feedback interferometry: a tutorial on the self-mixing effect for coherent sensing

A comprehensive review of the work done by our group, during the last few years, on diode-pumped cw operating bulk Er : Yb phosphate glass is presented. The high performance of this laser in terms of output power, laser slope efficiency, single longitudinal and transverse mode operation, laser tunability and frequency stability, amplitude noise, and active mode-locking operation, are considered. The combination of this high performance and potential low cost makes these laser devices attractive for a variety of applications including spectroscopy, metrology, optical radars, optical communications, and all optical switching.

Diode-pumped bulk erbium-ytterbium lasers

A tunable, single‐frequency, diode‐pumped miniature Er:Yb:glass laser of high power is described. The laser exhibits two intervals of continuous tuning, from 1549 to 1563 nm (Δλ=14 nm) and from 1531 to 1540 nm (Δλ=9 nm), respectively. For an input pump power of 140 mW, a single frequency output power of 20 mW at 1563 nm has been obtained. The tuning characteristics are found to be strictly related to the gain–loss balance of the laser cavity.

Widely tunable single-frequency erbium-ytterbium phosphate glass laser

Several studies demonstrated that the human chest wall is made of at least two but perhaps more independent mechanical components, and that their relative contribution to the total chest wall mechanics is significantly affected by several respiratory disorders, supporting the possible clinical usefulness of this information. Unfortunately, the determination of local chest wall mechanics requires the accurate assessment of local chest wall displacement, which, up to now, can only be obtained by complex, expensive, and bulky equipment. In this paper, we present a new approach based on a custom-made low-cost self-mixing laser interferometer able to directly measure vibrations on human skin with very high accuracy and temporal resolution. A novel signal processing algorithm has also been developed to estimate the motion of the subject's skin also in the presence of signal fading. The system has been validated both in vitro and in vivo on seven healthy volunteers. The results showed good accuracy and very low signal noise compared with available techniques. We conclude that this approach, considering its advantages, might allow the development of new diagnostic tools for the clinical evaluation of respiratory diseases.

Measurement of Local Chest Wall Displacement by a Custom Self-Mixing Laser Interferometer

A new method for accurate reconstruction of the displacement information from an interferometric signal is described. The method also allows calculation of the correct target movement at extremely low signal-to-noise ratios (SNRs) and in the presence of disturbances. The proposed method is experimentally validated in the case of a self-mixing laser vibrometer developed for the characterization of an ultrasound solder.

Novel Measurement Method for Signal Recovery in Optical Vibrometer

This paper addresses the analysis and design of an optical sensor for the real-time measurement of the tilt angle in hypersport motorcycles. The aim of this paper is to design a compact, reliable, and low-cost optical triangulator that is capable of accurate in-field measurements in the harsh environment of sport motorcycles. An analytical computation of the required system sensitivity and achievable accuracy is carried out. The detrimental effects of solar interference are also described and discussed. The proposed instrumentation, which is realized with ad hoc laser emitters, is shown to have superior performance with respect to a previous solution based on light-emitting diode (LED) emitters. Such novel triangulators are shown to provide good and reliable performances for the proposed application to maintain low costs and small sizes, overcoming the problem of solar interference. The performance of the proposed sensor is assessed by experiments on an instrumented motorbike in a racetrack.

Cesare Svelto

Papers

Diode-pumped bulk erbium-ytterbium lasers

Widely tunable single-frequency erbium-ytterbium phosphate glass laser

Measurement of Local Chest Wall Displacement by a Custom Self-Mixing Laser Interferometer

Novel Measurement Method for Signal Recovery in Optical Vibrometer

Optical Sensors for Real-Time Measurement of Motorcycle Tilt Angle