Galvanometer Mirror Research Articles

Line-scan phase-resolved synthetic wavelength LiDAR using an off-axis holographic approach.

We demonstrate a novel, to our knowledge, approach for phase-resolved coherent 3D surface imaging that utilizes synthetic wavelength phase-based ranging and line-scan off-axis holography. Our proof-of-concept system employs an akinetic tunable laser to perform fast wavelength switching and a galvanometer mirror for slow-axis mechanical scanning. Quantitative depth measurements of an anodized aluminum plate and 3D-printed depth calibration targets and a printed circuit board are demonstrated. Analyses of both shot-noise limited system performance and speckle noise are also presented. The proof-of-concept system achieves micron-scale depth precision with a FOV of 12.8 mm × 34 mm and a 50 ms image acquisition time.

Thermomagnetic recording of highly Bi-substituted iron garnet film using scanning laser for spatial light modulation

Spatial light modulations (SLM) utilizing the magneto-optical (MO) effect of magnetic materials are expected to offer fast switching and small pixel sizes as small as the wavelength of the light. However, the small MO effect is a major issue. In this paper, we report a thermomagnetic recording of highly bismuth-substituted garnet film, known for large Faraday effects. Y0.5Bi2.5Fe4GaO12 (Bi,Ga:YIG) film with a Faraday rotation of −4.66 degrees was used as an MO medium. A laser scanning thermomagnetic recording system using a Galvanometer mirror was developed and the size and quality of recorded magnetic domains were investigated. The smallest recorded magnetic domain diameter was 0.62 μm with a small standard deviation of 0.09 μm. Line patterns with a width of 1 μm can be recorded in this film. We found that Bi,Ga:YIG films have potential as a material for SLMs with fast switching, submicron pixel size, and large MO effect.

Compressive sensing-based multi-focus line-scanning two-photon microscopy for fast 3D imaging

Fast 3D volume imaging methods have been playing increasingly important roles in biological studies. In this article, we present the design and characterization of a multi-focus line-scanning two-photon microscope. Specifically, a digital micromirror device (DMD) is employed to generate a randomly distributed focus array on a plane (i.e., x-z) via binary holography. Next, a galvanometric mirror scans the focus array in a direction normal to the plane (i.e., y-axis) over the imaging volume. For sparse samples, e.g., neural networks in a brain, 1-3 foci are used together with compressive sensing algorithm to achieve a volume imaging rate of 15.5 volumes/sec over 77 × 120 × 40 µm3. High-resolution optical cross-sectional images on selected planes and regions can be generated by sequentially scanning the laser focus generated on the x-z plane with good imaging speeds (e.g., 107 frames/sec over 80 × 120 × 40 µm3). In the experiments, microbeads, pollens, and mouse brain slices have been imaged to characterize the point spread function and volume image rate and quality at different sampling ratios. The results show that the multi-focus line-scanning microscope presents a fast and versatile 3D imaging platform for deep tissue imaging and dynamic live animal studies.

A laser field synchronous scanning imaging system for underwater long-range detection

A novel underwater optical imaging system is proposed to improve underwater image degradation, which is severely deteriorated due to absorption and scattering under artificial illumination. The light source employs a line laser with 520 nm wavelength and a mirror galvanometer that controls the one-dimension scanning of the laser beam to form a planar illumination light field. The camera adopts an sCMOS image sensor with an electronic rolling shutter exposure pattern, compressing the camera’s instantaneous field of view(IFOV) into a narrow strip by reducing the exposure time. Meanwhile, the system controls the light source to irradiate the IFOV of the camera only synchronously, which significantly compressed the overlapping volume of the light path between the camera and the light source so that the backscattered light captured by the camera was dramatically reduced. Experimental results at different turbidity and distances in pool environments show that the laser field synchronous scanning imaging system obtains excellent performance in contrast ratio (CR) and contrast signal-to-noise ratio (CSNR). In the turbidity experiment, the peak CR of the target image improved by a factor of 3.88, and the peak CSNR improved by a factor of 2.33 in 19.6 FTU. In the distance experiment, the peak CR of the target image improved by a factor of 5.57, and the peak CSNR improved by a factor of 1.67 at a distance of 13 m, achieving a clear imaging range of 15 m. This system substantially diminishes the impact of light backscattering on imaging quality, which effectively facilitates further development of the underwater task and renders the system highly applicable in underwater imaging.

High-Throughput Two-Photon 3D Printing Enabled by Holographic Multi-Foci High-Speed Scanning.

The emerging two-photon polymerization (TPP) technique enables high-resolution printing of complex 3D structures, revolutionizing micro/nano additive manufacturing. Various fast scanning and parallel processing strategies have been proposed to promote its efficiency. However, obtaining large numbers of uniform focal spots for parallel high-speed scanning remains challenging, which hampers the realization of higher throughput. We report a TPP printing platform that combines galvanometric mirrors and liquid crystal on silicon spatial light modulator (LCoS-SLM). By setting the target light field at LCoS-SLM's diffraction center, sufficient energy is acquired to support simultaneous polymerization of over 400 foci. With fast scanning, the maximum printing speed achieves 1.49 × 108 voxels s-1, surpassing the existing scanning-based TPP methods while maintaining high printing resolution and flexibility. To demonstrate the processing capability, functional 3D microstructure arrays are rapidly fabricated and applied in micro-optics and micro-object manipulation. Our method may expand the prospects of TPP in large-scale micro/nanomanufacturing.

Towards Ultraviolet Microbeam Scanning and Lens-Less UV Microbeam Microscopy with Mirror Galvanometric Scanners: From the History of Research Instrumentation to Engineering of Modern Mechatronic Optical Systems

This article aims to ensure continuity between classical methods of ul-traviolet microscopy or/and micromanipulation using ultraviolet mi-crobeam and lens-less ultraviolet microscopy and microbeam exposure of cells and tissues. Considering the history of the development of the method and the possibility of working with different methods of mechanical scanning, the authors propose to use mirror galvanometers and an electromechanical scanning system in the mechanical engineering of lensless microbeam installations. These installations make it possible to provide both scanning with an ultraviolet microbeam to obtain a line scan image, and precision micromanipulation at the level of individual cells or individual organelles (in the case of large cells). We propose to extrapolate mathematical models previously developed for galvanic mirrors of light-beam oscilloscopes for microbeam scanning systems, position-sensitive micromanipulation, and real-time microphotometric cell analysis.

An all-pass based internal model principle controller for galvanometer mirror steering

Galvanometer is a critical component for beam steering in additive manufacturing, profilometry, and medical imaging. In these applications, the quality of the process relies on the precision motion control of the galvanometer to either track or reject narrow-band signals. From the internal model principle, this can be accomplished by incorporating the dynamic model of the reference or disturbance signal in the feedback loop. This paper proposes an innovative internal model principle controller based on numerically robust all-pass filters. The main concept revolves around converting the controller design into a phase response design problem with all-pass filters. For the proposed approach, the targeted frequencies of the internal model can be arbitrarily placed without sacrificing the performance. Further, it produces lower-order controller and is robust against quantization effect. When combining with frequency estimation algorithm and adaptive filter, it can be readily applied to unknown and time-varying disturbance rejection. The advantages of the proposed method are demonstrated by comparing with conventional approaches through analysis, simulation, and experimentation.

Engineering-Physical Method for Determining the Thermal Conductivity of Objects with Micrometric Thickness and a Complex Structure

Introduction. The application of functional coatings on products, the performance properties of which are localized in the surface layer is a trend in modern mechanical engineering and materials science. The issues considered in this regard are relevant, in particular, for thermal-barrier coatings of turbine blades of steam and gas turbine engines. It is worth mentioning the materials that experience significant thermal loads during operation. In this case, the lack of reliable methods for predicting the thermophysical properties of the coating seems to be a problem. The work objective is to create a computational and analytical methodology for determining the thermal conductivity of coatings. This approach is based on experimental data and takes into account structural parameters of the material.Materials and Methods. The experiments were carried out with the blades of a high-speed gas turbine of a locomotive engine made of heat-resistant chromium-nickel alloy Inconel 713LC. An experimental multiphase coating of the Nb-Ti-Al intermetallic system with a thickness of about 80 microns was applied using vacuum ion-plasma technology. The two-beam scanning electron microscope Zeiss CrossBeam 340 was used in the work. The thermal conductivity of the coatings was determined by an experimental technique based on the measurement of the contact potential difference (CPD). Numerical values of this difference were obtained using a mirror galvanometer with high voltage sensitivity. A special signal amplifier and a USB oscilloscope were used to record the readings.Results. The calculation apparatus of the thermal conductivity determination technique is based on the experimental values of ∆φ CPD:– for the base metal (Inconel 713LC) +846 mkV;– for the coating Nb-Ti-Al – 90 mkV.The solution to the problem of the distribution of particles in a force field with a potential difference ∆φ is described by the Boltzmann distribution. Starting from the obtained result, we get:– CPD at the boundary of the contacting metals;– energy and thermal conductivity of the Fermi level;– electron relaxation time.The multidirectional influence that the dimensional differences of the particles of the second phase have on the effective thermal conductivity is considered. For this case, a dimensionless value of the effective thermal conductivity in the direction of each axis and the effective thermal conductivity of the composite are found. Porosity is taken into account according to the Maxwell – Aiken dependence and introduced into the general calculation system. The thermal conductivity of Nb-Ti-Al is established: λNbTiAl = 4,76 W/m.K. Thus, the thermal barrier coating Nb-Ti-Al fully meets its functional purpose.Discussion and Conclusion. The method of determining thermal conductivity described in the article is applicable only to conductive consolidated materials or composites with a continuous conductive matrix. The presented work completes the initial stage of creating a computational and analytical model for predicting the thermal conductivity of materials and coatings. The results of testing the model for materials with a complex structure showed its satisfactory accuracy. This indicates the expediency of using the two considered elements of the model. The first one is the instrumental measurement of the CPD. The second one is taking into account the features of the structural and phase state of the material. With the development of the model, it is expected to overcome its weaknesses:– the impossibility of using non-conductive objects to determine the thermal conductivity;– a significant decrease in the accuracy of determining thermal conductivity for materials and coatings with a gradient structure.

Line Scan Hyperspectral Imaging Framework for Open Source Low-Cost Platforms

With advancements in computer processing power and deep learning techniques, hyperspectral imaging is continually being explored for improved sensing applications in various fields. However, the high cost associated with such imaging platforms impedes their widespread use in spite of the availability of the needed processing power. In this paper, we develop a novel theoretical framework required for an open source ultra-low-cost hyperspectral imaging platform based on the line scan method suitable for remote sensing applications. Then, we demonstrate the design and fabrication of an open source platform using consumer-grade commercial off-the-shelf components that are both affordable and easily accessible to researchers and users. At the heart of the optical system is a consumer-grade spectroscope along with a basic galvanometer mirror that is widely used in laser scanning devices. The utilized pushbroom scanning method provides a very high spectral resolution of 2.8 nm, as tested against commercial spectral sensors. Since the resolution is limited by the slit width of the spectroscope, we also provide a deconvolution method for the line scan in order to improve the monochromatic spatial resolution. Finally, we provide a cost-effective testing method for the hyperspectral imaging platform where the results validate both the spectral and spatial performances of the platform.

Scanning mirror based higher order Bessel-gaussian beams integrated in time (HOBBIT) with applications toward the photoacoustic effect.

We demonstrate a new method for the generation of beams with rapidly tunable orbital angular momentum (OAM). This method is based on using a single-axis scanning galvanometer mirror to add a phase tilt on an elliptical Gaussian beam that is then wrapped to a ring using optics that perform a log-polar transformation. This system can switch between modes in the kHz range and use relatively high power with high efficiency. This scanning mirror HOBBIT system was applied to a light/matter interaction application using the photoacoustic effect, with a 10 dB enhancement of the generated acoustics at a glass/water interface.

Enabling High Precision Gradient Index Control in Subsurface Multiphoton Lithography.

Multiphoton lithography inside a mesoporous host can create optical components with continuously tunable refractive indices in three-dimensional (3D) space. However, the process is very sensitive at exposure doses near the photoresist threshold, leading previous work to reliably achieve only a fraction of the available refractive index range for a given material system. Here, we present a method for greatly enhancing the uniformity of the subsurface micro-optics, increasing the reliable index range from 0.12 (in prior work) to 0.37 and decreasing the standard deviation (SD) at threshold from 0.13 to 0.0021. Three modifications to the previous method enable higher uniformity in all three spatial dimensions: (1) calibrating the planar write field of mirror galvanometers using a spatially varying optical transmission function which corrects for large-scale optical aberrations; (2) periodically relocating the piezoelectrically driven stage, termed piezo-galvo dithering, to reduce small-scale errors in writing; and (3) enforcing a constant time between each lateral cross section to reduce variation across all writing depths. With this new method, accurate fabrication of optics of any index between n = 1.20 and 1.57 (SD < 0.012 across the full range) was achieved inside a volume of porous silica. We demonstrate the importance of this increased accuracy and precision by fabricating and characterizing calibrated two-dimensional (2D) line gratings and flat gradient index lenses with significantly better performance than the corresponding control devices. As a visual representation, the University of Illinois logo made with 2D line gratings shows significant improvement in its color uniformity across its width.

Compact, high-speed multi-directional selective plane illumination microscopy.

We present an elegant scheme for providing multi-directional illumination in selective plane illumination microscopy (SPIM). Light sheets can be delivered from one of two opposed directions at a time and pivoted about their center for efficient stripe artifact suppression using only a single galvanometric scanning mirror to perform both functions. The scheme results in a much smaller instrument footprint and allows multi-directional illumination with reduced expense compared with comparable schemes. Switching between the illumination paths is near instantaneous and the whole-plane illumination scheme of SPIM maintains the lowest rates of photodamage, which is often sacrificed by other recently reported destriping strategies. The ease of synchronization allows this scheme to be used at higher speeds than resonant mirrors typically used in this regard. We provide validation of this approach in the dynamic environment of the zebrafish beating heart, where imaging at up to 800 frames per second is demonstrated alongside efficient suppression of artifacts.

Electrochemical contributions: Hans Wenking (1923–2007)

Electrochemical contributions: Hans Wenking (1923–2007)

Machine learning assisted interferometric structured illumination microscopy for dynamic biological imaging

Structured Illumination Microscopy, SIM, is one of the most powerful optical imaging methods available to visualize biological environments at subcellular resolution. Its limitations stem from a difficulty of imaging in multiple color channels at once, which reduces imaging speed. Furthermore, there is substantial experimental complexity in setting up SIM systems, preventing a widespread adoption. Here, we present Machine-learning Assisted, Interferometric Structured Illumination Microscopy, MAI-SIM, as an easy-to-implement method for live cell super-resolution imaging at high speed and in multiple colors. The instrument is based on an interferometer design in which illumination patterns are generated, rotated, and stepped in phase through movement of a single galvanometric mirror element. The design is robust, flexible, and works for all wavelengths. We complement the unique properties of the microscope with an open source machine-learning toolbox that permits real-time reconstructions to be performed, providing instant visualization of super-resolved images from live biological samples.

Single Plane Illumination Microscopy for Microfluidic Device Imaging

Three-dimensional imaging of live processes at a cellular level is a challenging task. It requires high-speed acquisition capabilities, low phototoxicity, and low mechanical disturbances. Three-dimensional imaging in microfluidic devices poses additional challenges as a deep penetration of the light source is required, along with a stationary setting, so the flows are not perturbed. Different types of fluorescence microscopy techniques have been used to address these limitations; particularly, confocal microscopy and light sheet fluorescence microscopy (LSFM). This manuscript proposes a novel architecture of a type of LSFM, single-plane illumination microscopy (SPIM). This custom-made microscope includes two mirror galvanometers to scan the sample vertically and reduce shadowing artifacts while avoiding unnecessary movement. In addition, two electro-tunable lenses fine-tune the focus position and reduce the scattering caused by the microfluidic devices. The microscope has been fully set up and characterized, achieving a resolution of 1.50 μm in the x-y plane and 7.93 μm in the z-direction. The proposed architecture has risen to the challenges posed when imaging microfluidic devices and live processes, as it can successfully acquire 3D volumetric images together with time-lapse recordings, and it is thus a suitable microscopic technique for live tracking miniaturized tissue and disease models.

Spectroscopy of individual Brownian nanoparticles in real-time using holographic localization.

Individual nanoparticle spectroscopic characterization is fundamental, but challenging in liquids. While confocal selectivity is necessary to isolate a particle in a crowd, Brownian motion constantly offsets the particle from the light collection volume. Here, we present a system able to acquire holograms and reconstruct them to precisely determine the 3D position of a particle in real time. These coordinates drive an adaptive system comprising two galvanometric mirrors (x,y, transverse directions) and a tunable lens (z, longitudinal) which redirect light scattered from the corresponding region of space towards the confocal entrance of a spectrometer, thus allowing long spectral investigations on individual, freely-moving particles. A study of the movements and spectra of individual 100 nm Au nanoparticles undergoing two types of aggregations illustrates the possibilities of the method.

Angle of View Switching Method at High-Speed Using Motion Blur Compensation for Infrastructure Inspection

Efficient imaging is achieved under conditions of high relative velocity between the camera and the subject by using the following imaging system; two galvanometer mirrors are placed vertically in front of the camera, one for motion blur compensation and the other for switching the angle of view. The proposed system can overcome the shortcomings of conventional imaging systems with motion blur compensation, such as a small angle of view, and efficiently acquire high-resolution images. If the angle is changed for each capture while the mirrors are stationary for the exposure time, the natural frequency of the mirrors produces noise, leading to a poor resolution. However, this issue can be managed by generating and using an input that does not contain a natural frequency component. A target moving in one dimension can be captured and it is confirmed that the angle of view was extended from the obtained image. It is expected that the camera will be used for inspections under conditions where the relative speed between the camera and target is high, such as in highway tunnel inspections.

Mapping the effect of substrate temperature inhomogeneity during microwave plasma-enhanced chemical vapour deposition nanocrystalline diamond growth

It is important to account for variance in substrate temperature during microwave plasma-enhanced chemical vapour deposition (MPECVD) nanocrystalline diamond growth, as this has a significant impact on the uniformity of the grown film. In this work, an in-situ method of mapping the substrate temperature under MPECVD growth conditions is demonstrated, employing a mirror galvanometer to scan the field of view of a dual-wavelength pyrometer across the substrate. Temperature maps generated were compared to plasma electron densities simulated using a finite element model. An increase in temperature and simulated plasma density were seen towards the centre of the holder. The properties of nanocrystalline diamond films were mapped using ex-situ Raman spectroscopy and spectroscopic ellipsometry (SE). A greater SE-measured bulk thickness and bulk sp3 fraction, as well as a greater first-order diamond Raman intensity and lower full width at half maximum were seen in the higher-temperature central region, demonstrating the impact of substrate temperature inhomogeneity during growth. The temperature mapping technique demonstrated allows easy evaluation of the impact of substrate holder design, microwave power and chamber pressure on substrate temperature homogeneity, and therefore optimisation of growth conditions for uniform diamond film growth.

Direct laser interference patterning via scanning optics using the Michelson-Morley configuration

Direct Laser Interference Patterning (DLIP) is a promising method to realize patterns on surfaces, based on two or more beams, interference. Compared with the traditional direct laser writing approach, DLIP allows control of the features’ shape and size below the size of the laser beam. The standard configuration of a DLIP system is based on fixed optical elements and the movement of the sample via a motorized axis. This work proposes a new optical setup for two-beam DLIP. A Michelson-Morley interferometer was used, realizing the interference of a split beam. A nanosecond pulsed green laser was used to realize the interference phenomenon. The innovative concept combines the interferometer with an industrial scanner head for beam steering. The work explores possibility to use the galvanometric mirrors in DLIP to expand the process capabilities towards larger areas without moving the workpiece. Moreover, the concept is adaptable for different laser wavelengths and optical solutions permitting a degree of flexibility in the pattern period. An optical model is proposed for the first time to describe the design requirements and the pattern period for scanning optics. The developed prototype was used to pattern a biodegradable magnesium alloy with known difficulties for nanosecond pulse ablation. Two strategies namely point by point and continuous scanning were investigated. Periodic linear patterns were produced with periodicity equal to 23 µm and with a productivity up to 6.5 cm2/min.

Underwater Multispectral Laser Serial Imager for Spectral Differentiation of Macroalgal and Coral Substrates

The advancement of innovative underwater remote sensing detection and imaging methods, such as continuous wave laser line scan or pulsed laser (i.e., LiDAR—Light Detection and Ranging) imaging approaches can provide novel solutions for studying biological substrates and manmade objects/surfaces often encountered in underwater coastal environments. Such instruments can be used shipboard or coupled with proven and available deployment platforms as AUVs (Autonomous Underwater Vehicles). With the right planning, large areas can be surveyed, and more extreme and difficult-to-reach environments can be studied. A prime example, and representing a certain navigational challenge, is the under ice in the Arctic/Antarctic or winter/polar environments or deep underwater survey. Among many marine biological substrates, numerous species of macroalgae can be found worldwide in shallow down to 70+ m (clear water) coastal habitats and are essential ecosystem service providers through the habitat they provide for other species, the potential food resource value, and carbon sink they represent. Similarly, corals also provide important ecosystem services through their structure and diversity, are found to harbor increased local diversity, and are equally valid targets as “keystone” species. Hence, we expand current underwater remote sensing methods to combine macroalgal and coral surveys via the development of a multispectral laser serial imager designed for classification via spectral response. By using multiple continuous wave laser wavelength sources to scan and illuminate recreated benthic environments composed of macroalgae and coral, we show how elastic (i.e., reflectance) and inelastic (i.e., fluorescence) spectral responses can potentially be used to differentiate algal color groups and certain coral genus. Experimentally, three laser diodes (450 nm, 490 nm, 520 nm) are sequentially used in conjunction with up to 5 emission filters (450 nm, 490 nm, 520 nm, 580 nm, 685 nm) to acquire images generated by laser line scan pattern via high-speed galvanometric mirrors. Placed directly adjacent to a large saltwater imaging tank fitted with optical viewports, the optical system records target substrate spectral response using a photomultiplier preceded by a filter and is synchronously digitized to the scan rate by a high sample rate Analog-to-Digital Converter (ADC). Acquired images are normalized to correct for imager optical effects allowing for fluorescence intensity-based pixel segmentation via intensity thresholding. Overall, the multispectral laser serial imaging technique shows that the resulting high resolution data can be used for detection and classification of benthic substrates by their spectral response. These methods highlight a path towards eventual pixel-wise spectral response analysis for spectral differentiation.