Laser Beam Deflection Research Articles

MEMS-Scanner Testbench for High Field of View LiDAR Applications

LiDAR sensors are a key technology for enabling safe autonomous cars. For highway applications, such systems must have a long range, and the covered field of view (FoV) of >45° must be scanned with resolutions higher than 0.1°. These specifications can be met by modern MEMS scanners, which are chosen for their robustness and scalability. For the automotive market, these sensors, and especially the scanners within, must be tested to the highest standards. We propose a novel measurement setup for characterizing and validating these kinds of scanners based on a position-sensitive detector (PSD) by imaging a deflected laser beam from a diffuser screen onto the PSD. A so-called ray trace shifting technique (RTST) was used to minimize manual calibration effort, to reduce external mounting errors, and to enable dynamical one-shot measurements of the scanner’s steering angle over large FoVs. This paper describes the overall setup and the calibration method according to a standard camera calibration. We further show the setup’s capabilities by validating it with a statically set rotating stage and a dynamically oscillating MEMS scanner. The setup was found to be capable of measuring LiDAR MEMS scanners with a maximum FoV of 47° dynamically, with an uncertainty of less than 1%.

A liquid crystal stackable phased array to achieve fast and precise nonmechanical laser beam deflection

In this study, a novel liquid crystal (LC) stackable optical phased array (SOPA) for fine tracking with fast and precise beam steering is proposed. The SOPA was composed of multiple layers of sliced phase shifters (SPSs). Each SPS had two parts for loading different voltages to form programmable phase steps. All LC materials were compatible with this architecture, including blue-phase, polymer network, and ferroelectric LCs. To verify and evaluate the properties of this SOPA scheme, a three-layered SOPA prototype was designed and fabricated according to the standard processing of LC devices. A couple of steering experiments, with steering angles ranging from −100 to 100 μrad in a step of 10 μrad, were performed. The steering efficiency recorded in all the experiments exceeded 90%. All the measured switching time of angle-to-angle were less than 10 ms. Herein, the fastest switching time reported was only 1.52 ms.

Determination of gradient index based on laser beam deflection by stochastic particle swarm optimization

Determination of gradient index based on laser beam deflection by stochastic particle swarm optimization

Interferometric, absolute sensor of angular micro-displacement

A design of a new, absolute sensor for measurement of an angular micro-displacement is presented. In this sensor deflections of incident laser beam generate changes of the constant of the interference fringes that are created by the double arm special interferometer. Fringe constant is determined using a CCD camera and proposed analysis algorithms. Sensor's operating principle and metrological properties are presented. Sensor was tested using reference interferometer. Obtained measurement uncertainty is equal to ±10 μrad in the multi-milliradian range. The concept of a two-sensor system for increasing twice the measuring range is presented.

Study on Satellite-to-ground Laser Communications with Existence of Atmosphere<sup>*</sup>

The laser beam used to establish a communication channel between satellite and ground segments has a small divergence angle and a tiny spot on the Earths surface, which may lead to the fail of the system. So its important to study the deflection of laser beam by the Earths atmosphere and find a way to calibrate this error. Both theoretical analysis and real data processing method are used to obtain the mathematical model for divergence angle of laser communication beam and its correction function. Then the model has been applied to the data, which was used to describe the atmosphere state by traditional ground segments to obtain the critical elevation angle. According to the results of calculation, our conclusion will be that the correction should be done when the critical elevation happens.

Tomographic reconstruction of refractive index fields based on laser beam deflection measurement

Refractive index as one of the most important optical properties of materials is the key to utilize refractive index elements. However, it is very difficult to measure or estimate refractive index of media, especially for multi-dimensional inhomogeneous refractive index distribution. Therefore, an inverse scheme is presented for reconstructing refractive index field in rectangular gradient index medium based on ray deflection measurement in this work. A collection of rays from given positions along given directions transit the semitransparent medium and all exit boundary positions are recorded to construct the objective function of inverse problem. Runge–Kutta ray tracing technique is employed to simulate the curved ray path determined by Fermat principle in gradient-index medium. Conjugate gradient method as an inverse algorithm is used to reconstruct refractive index field. A series of simulation experiments are done to show the performance of the inverse strategy we developed. The results indicate that this inverse strategy for reconstructing refractive index field is accurate and effective.

Improving SLM additive manufacturing operation precision with H-infinity controller structure

SLM (Selective Laser Melting) is the most widespread additive manufacturing technique of metal part. The desired part is elaborated through local melting of a raw metal powder bed by means of laser. In industrial machines, galvanometer motors achieve the laser beam deflection and focus control tasks. This paper proposes a H-infinity controller synthesis which improves the system accuracy and robustness towards physical features. Compared to a conventional control scheme, results obtained with the H-infinity controller implemented in an open architecture test bench consisting of a 2-axis laser deflection system showed improved accuracy performance while operation rapidity is optimized.

Wavefront distortion due to the shock wave and boundary layer in the supersonic flow over a compression ramp

Optical devices equipped in supersonic flight vehicles are subjected to distortions of optical paths due to aero-optical effects, potentially resulting in the degradation of sensing and imaging performance. In this study, the aero-optical effects of the supersonic flow over a two-dimensional compression ramp are investigated through experimental and numerical methods. The experiment is conducted by measuring the wavefront of the laser beam propagated through the test section of a supersonic wind tunnel using a two-dimensional Shack-Hartmann sensor. The individual contribution of the shock wave and boundary layer to the wavefront distortion is identified by conducting a ray-tracing computation through the density of the flow field obtained from a two-dimensional numerical simulation that solves the Reynolds-averaged Navier-Stokes equations. The numerically-obtained wavefront is compared with the time-averaged wavefront measured using the Shack-Hartmann sensor. The deflection angle of the ray at the center of the laser beam is analyzed to assess the aero-optical effects caused by the shock wave and boundary layer. The individual contribution of the shock wave and boundary layer to the wavefront distortion was analyzed for various incidence angles of the laser beam. For the present experimental setup, as boundary layers at the top and bottom walls have the opposite direction of the density gradient, the resultant laser beam deflections are mostly governed by the density gradient across the shock wave.

Study on Satellite-to-ground Laser Communications with Existence of Atmosphere

The laser beam used to establish a communication channel between satellite and ground segments has a small divergence angle and a tiny spot on the Earth’s surface, which may lead to the fail of the system. So it’s important to study the deflection of laser beam by the Earth’s atmosphere and find a way to calibrate this error. Both theoretical analysis and real data processing method are used to obtain the mathematical model for divergence angle of laser communication beam and its correction function. Then the model has been applied to the data, which was used to describe the atmosphere state by traditional ground segments to obtain the critical elevation angle. According to the results of calculation, our conclusion will be that the correction should be done when the critical elevation happens.

Closed-loop laser illumination algorithm using return photon counts.

Boresight and jitter are two fundamental pointing errors of laser illumination systems. A triangular-scanning algorithm is proposed to estimate the direction of the boresight via a three-step maximum boresight estimation and laser beam deflection procedure. On this basis, the closed-loop laser illumination (CLLI) for non-cooperative targets is realized, and the Cramer-Rao lower bounds (CRLB) performance in the lower limit of the pointing error is analyzed. Additionally, a Monte Carlo simulation system is built, and the performance of the CLLI algorithm is analyzed. The simulation results demonstrate that the triangular-scanning algorithm has good performance and can accurately estimate the direction of the boresight to achieve CLLI. Further study shows that the simulation results agree well with theoretical estimations and approximate the CRLB at the lower limit.

Collapse Dynamics of Hemispherical Cavitation Bubble in Contact with a Solid Boundary

The dynamics of electrochemically produced hemispherical bubble at solid-liquid interface is investigated experimentally. Time-resolved photography is applied to measure the position of bubble wall as a function of time. By means of stroboscope schlieren photography with 1 μs exposure time it is shown that the development of instabilities of the bubble shape are general feature of the bubble dynamics in contact with the solid boundaries. The acoustic transients emitted after cavitation bubble collapse were registered with the laser beam deflection technique. Duration of the transient of 50–60 ns enables to estimate maximum pressure as 2.5 kbar, when the maximum bubble radius is 1 mm.

Issues of constructing scanning hybrid 3D measuring heads for high-precision contact and non-contact coordinate measurements of product dimension

The article presents a model of mechanical contact of a spherical tip and a product with small forces according to elastic deformations (further – deformations) taking into account the appearance of material deformations in the gap between them along the perimeter of the contact zone in the form of so-called piles-up. Dependences are obtained that link the gap with the deformation and the piles-up size. A graph is constructed for these parameters, the general form of which is close to the function of a single jump ∼1(l-Rpile), where Rpile is the radius of the pile-up.The developed design and operating principle of the scanning hybrid fiber-optical measuring head (FOMH) based on the use of a small-sized spatial light modulator in the form of a fiber-optic piezoscanner with the formation of scanning movements of the laser beam and the measurement of gaps between the tip and the product are described. The possibilities of providing high-precision measurements of laser beam deflection angles during scanning movements by using acousto-optic heterodyne interference measurement systems are considered.

Acousto-optical deflector for non-mechanical manipulating using optical tweezers

Optical tweezers are widely used in various fields of science and technology, such as biophysics, cytology and solid-state physics. Most of the existing optical tweezers use mirror or mirror-lens systems to manipulate the position of the trap. Such systems require precise alignment and do not allow the trap to be moved quickly from one arbitrary point to another due to the inertia of the mirror and lenses. We discuss acousto-optic scanning characterized by high precision and repetition rate for manipulating micro-objects using optical tweezers. Bragg diffraction of light via ultrasonic waves allows creating robust solid-state devices for precise and fast laser beam deflection. We describe a scheme of the optical tweezers with PC-driven two-dimensional scanning implemented by two sequential acousto-optical cells.

Laser micromachining of titanium alloy in water and ice at different temperatures

A clean cut surface with less thermal damage is typically desired in laser micromachining process. Many kinds of cooling substances can be employed to assist the laser ablation for limiting the thermal damage in workpiece and also gaining a higher material removal rate. This paper presents and compares the water- and ice-assisted laser ablation of titanium alloy, in which the effects of water/ice temperature, laser traverse speed and number of laser passes on morphology and dimensions of laser-ablated surface were experimentally investigated. A parametric model for the laser beam refraction at air-water/ice and water-gas bubble interfaces was also developed to determine the refracted distance at the workpiece surface under the different incident angles and water/ice layer thicknesses. The results revealed that the laser ablation in water can produce a clean groove on the metal surface, while only recast and spatters of titanium oxides were found on the laser-scanned track when processing in ice. A remarkable groove can be obtained by using high water temperature together with slow laser traverse speed and more numbers of laser passes. However, the laser beam scattering in water was more apparent than in ice due to water wave, the high refractive index of water and the formation of gas bubbles during the ablation. The findings presented in this study could provide a better understanding of the water- and ice-assisted laser ablation as well as their capability for damage-free fabrication of micro-/submicro-devices.

Laser and electron deflection from transverse asymmetries in laser-plasma accelerators.

We report on the deflection of laser pulses and accelerated electrons in a laser-plasma accelerator (LPA) by the effects of laser pulse front tilt and transverse density gradients. Asymmetry in the plasma index of refraction leads to laser steering, which can be due to a density gradient or spatiotemporal coupling of the laser pulse. The transverse forces from the skewed plasma wave can also lead to electron deflection relative to the laser. Quantitative models are proposed for both the laser and electron steering, which are confirmed by particle-in-cell simulations. Experiments with the BELLA Petawatt Laser are presented which show controllable 0.1-1 mrad laser and electron beam deflection from laser pulse front tilt. This has potential applications for electron beam pointing control, which is of paramount importance for LPA applications.

Micro-cantilever Sensors for Efficient Gas Sensing

Abstract Micro-cantilever has been progressively used for the development of miniaturized sensors for gas sensing, biochemical analysis, medical applications and quality and process control. Micro-cantilevers are fabricated with rectangular silicon slabs having thickness below 1 µm. For gas sensing applications, Si cantilever surface is modified with appropriate sensing materials for selective adsorption of gas/vapor or biomolecules. The bending of the cantilever due to different surface conditions is measured with laser beam deflection to get the sensitivity of the sensor. The current article discusses the background, principle of operation and bending characteristics of micro-cantilever gas sensors. Various applications and applicability of the micro/nano cantilever gas sensors have also been covered in the present report. Finally, the article has been concluded with future prospects of microcantilever gas sensors for multiple potential applications. Keywords: Microcantilever, gas sensing, fast response, selectivity, biosensor Cite this Article Deepika Saxena, Arnab Hazra and Sukumar Basu . Micro-cantilever Sensors for Efficient Gas Sensing. Journal of Semiconductor Devices and Circuits . 2019; 6(3): 16–24p.

Analysis of a biaxial fiber Bragg grating accelerometer intended for seismic applications

This paper describes a fiber Bragg grating based biaxial accelerometer prototype intended for seismic applications. The work includes the accelerometer structural scheme, optical scheme, sensibility, frequency response and the laser beam deflection method used for calibration. Results of this work show that the device is suitable for seismic measurements because its measurement range goes from 0.5 Hz to more than 20 Hz in frequency and from 0 g to 1.2 g in acceleration amplitude.

Effect of Coherent Structures on Aero-Optic Distortion in a Turbulent Boundary Layer

The deflection of a small-aperture laser beam was studied as it passed through an incompressible turbulent boundary layer that was heated at the wall. The heating at the wall was sufficiently mild that the temperature and density fields acted as passive scalars with a Prandtl number of 0.71. Simultaneous particle image velocimetry and Malley probe laser deflection measurements were performed in overlapping regions of the boundary layer to identify correlations between coherent velocity structures, passive scalar transport, and optical beam deflection. Streamwise gradients in the streamwise and wall-normal velocity fields were observed to be correlated to the deflection of the optical beam and to streamwise density gradients. The passage of a large-scale motion through the beam path was shown to affect the statistics of the optical beam deflection as well as the local distribution of small-scale velocity features. The wall-normal small-scale velocity features were consistently correlated to the beam deflection, throughout different phases of the large-scale motion convection. The observations motivated a hypothesis that views the large scales as heat carriers, whereas the small scales modify the local sense of a velocity and density gradient toward a streamwise gradient that directly affects the optical beam deflection.

Analysis of Scattering Light from In-flight Particles in Suspension Plasma Spray for Size Measurement

Suspension plasma spray (SPS) is an emerging coating process for making surfaces with superior properties. In this process, in-flight spray particle characteristics such as size, velocity, and temperature have a direct influence on the properties of the deposited coatings. Accordingly, online diagnostic tools to characterize the in-flight particles in the SPS are sought by research laboratories and industrial centers for process optimization and control. However, small particle size, high temperature, and radiation of the plasma make it challenging to carry out these measurements. In this study, we used a light diffraction (LD) approach to measure online the size of in-flight particles sprayed from a well-predefined size distribution. Laser beam refraction by the hot plasma/gas jet is one of the main sources of noise for such size measurement. Successful measurements were achieved by shielding the measurement section and filtering the plasma radiation to reduce the influence of the laser refraction and plasma radiation. Results showed that the LD method has the potential to be used to monitor online the size distribution of in-flight particles in the SPS process.

Experimental study of a fiber Bragg grating accelerometer for seismic measurement

This paper presents a fiber Bragg grating accelerometer prototype for seismic applications, including accelerometer scheme, calibration method and accelerometer resonance frequencies. The acceleration calibration and measurements were obtained from the laser beam deflection method. A series of experiments were carried out and results shows an accelerometer sensitivity of 8.07 mV/g (where 1g= 9.81 m/s2) at 0.5 Hz and 2.63 mV/g at 50 Hz, the measured range scale goes from 0 to 35 m s-2.