Self-Mixing Laser Distance-Sensor Enhanced by Multiple Modulation Waveforms

Optical rangefinders based on Self-Mixing Interferometry are widely described in literature, but not yet on the market as commercial instruments. The main reason is that it is relatively easy to propose new elaboration techniques and get results in controlled conditions, while it is very difficult to develop a reliable instrument. In this paper, we propose a laser distance sensor with improved reliability, realized through a wavelength modulation at a different frequency, able to decorrelate single measurement errors and obtain improvement by averages. A dedicated software is implemented to automatically calculate the modulation pre-emphasis, needed to linearize the wavelength modulation. Finally, data selection algorithms allow to overcome signal fading problems due to the speckle effect. A prototype demonstrates the approach with about 0.1 mm accuracy up to 2 m of distance at 200 measurements per second

Proximity Sensor using Self-mixing Effect

This paper is about the utilisation of the well-known self-mixing effect as base for the development of a novel proximity detector. The common used setup for this kind of a sensor is based on two elements: a laser as an emitter and a position-sensitive sensor as a detector. The sensor developed detects the optical power reflected by the object within the laser cavity itself, with no need of any additional detectors. One of the main feature is the ability to measure diffusive target accessible only from one side. A continuous range of measurement starting from 10 mm up to 80 mm is obtained by means of two different physical phenomena: from 0 up to 5mm the detection is only dependent by the level of the optical power returned into the laser cavity, whereas from 5 mm up to 80 mm reading the frequency of the modulation of the interferometric signal. The main advantage of the novel sensor is the elimination of the external detector. In addition, multiple devices configurations can be utilized and there is no need of any optical filters, cause the laser cavity itself works as an optical filter. Background rejection is intrinsically obtained because self-mixing effect shows a sharp cut-off after the focus

Noise Decrease in a Balanced Self-Mixing Interferometer: Theory and Experiments

In a self-mixing interferometer built around a laser diode, the signals at the outputs of the two mirrors are in phase opposition, whereas noise fluctuations are partially correlated. Thus, on making the difference between the two outputs, the useful signal is doubled in amplitude and the signal-to-noise ratio is even more enhanced. Through a second-quantization model, the improvement is theoretically predicted to be dependent on laser facets reflectivity. The results are then validated by experimental measurements with different laser types that show very good agreement with theoretical results. The new technique is applicable to a number of already existent self-mixing sensors, potentially improving significantly their measurement performances

Electrostatic diagnostics of nanosecond pulsed electron beams in a Malmberg\u2013Penning trap

A fast electrostatic diagnostic and analysis scheme on nanosecond pulsed beams in the keV energy range has been developed in the Malmberg\u2013Penning trap ELTRAP. Low-noise electronics has been used for the detection of small induced current signals on the trap electrodes. A discrete wavelet-based procedure has been implemented for data postprocessing. The development of an effective electrostatic diagnostics together with proper data analysis techniques is of general interest in view of deducing the beam properties through comparison of the postprocessed data with the theoretically computed signal shape, which contains beam radius, length, and average density as fit parameters

Er:Yb phosphate glass laser with nonlinear absorber for phase-sensitive optical time domain reflectometry

A novel laser for phase-sensitive optical time-domain reflectometry (Φ-OTDR) is presented. The advantages of a compact solid-state laser are listed, current problems are shown. Experiments with a microchip single-optical-element laser, from setup construction to usage in Φ-OTDR system, are presented. New laser scheme with two-photon intracavity absorber is suggested and its advantages are described

Roadmap on signal processing for next generation measurement systems

Signal processing is a fundamental component of almost any sensor-enabled system, with a wide range of applications across different scientific disciplines. Time series data, images, and video sequences comprise representative forms of signals that can be enhanced and analysed for information extraction and quantification. The recent advances in artificial intelligence and machine learning are shifting the research attention towards intelligent, data-driven, signal processing. This roadmap presents a critical overview of the state-of-the-art methods and applications aiming to highlight future challenges and research opportunities towards next generation measurement systems. It covers a broad spectrum of topics ranging from basic to industrial research, organized in concise thematic sections that reflect the trends and the impacts of current and future developments per research field. Furthermore, it offers guidance to researchers and funding agencies in identifying new prospects.AerodynamicsMicrowave Sensing, Signals & System