Scanning Principle Research Articles

Single-pixel positron beam diagnosis via compressive sampling.

The morphology is a crucial indicator for diagnosing a low-energy, low-brightness particle beam. However, conventional positron beam diagnosis, based on the pixel scanning principle, is limited by physical constraints, such as the resolution of detector pixels. Here, we have presented a novel slow positron diagnosis method using compressive sampling. With a 100 × 100 pixel-sized mask, for example, the positron beam morphology can be significantly reconstructed with a peak signal-to-noise ratio of ∼40 dB, even at half the sampling rate compared to pixel scanning. It explores a promising approach for positron beam diagnosis with an ultra-high resolution and fast sampling rates.

Drone Multiline Light Detection and Ranging Data Filtering in Coastal Salt Marshes Using Extreme Gradient Boosting Model

Quantitatively characterizing coastal salt-marsh terrains and the corresponding spatiotemporal changes are crucial for formulating comprehensive management plans and clarifying the dynamic carbon evolution. Multiline light detection and ranging (LiDAR) exhibits great capability for terrain measuring for salt marshes with strong penetration performance and a new scanning mode. The prerequisite to obtaining the high-precision terrain requires accurate filtering of the salt-marsh vegetation points from the ground/mudflat ones in the multiline LiDAR data. In this study, a new alternative salt-marsh vegetation point-cloud filtering method is proposed for drone multiline LiDAR based on the extreme gradient boosting (i.e., XGBoost) model. According to the basic principle that vegetation and the ground exhibit different geometric and radiometric characteristics, the XGBoost is constructed to model the relationships of point categories with a series of selected basic geometric and radiometric metrics (i.e., distance, scan angle, elevation, normal vectors, and intensity), where absent instantaneous scan geometry (i.e., distance and scan angle) for each point is accurately estimated according to the scanning principles and point-cloud spatial distribution characteristics of drone multiline LiDAR. Based on the constructed model, the combination of the selected features can accurately and intelligently predict the category of each point. The proposed method is tested in a coastal salt marsh in Shanghai, China by a drone 16-line LiDAR system. The results demonstrate that the averaged AUC and G-mean values of the proposed method are 0.9111 and 0.9063, respectively. The proposed method exhibits enhanced applicability and versatility and outperforms the traditional and other machine-learning methods in different areas with varying topography and vegetation-growth status, which shows promising potential for point-cloud filtering and classification, particularly in extreme environments where the terrains, land covers, and point-cloud distributions are highly complicated.

Comparison of patient setup accuracy for optical surface-guided andX-ray-guided imaging with respect to the impact on intracranial stereotactic radiotherapy.

The objective of this work is to estimate the patient positioning accuracy of asurface-guided radiation therapy (SGRT) system using an optical surface scanner compared to an X‑ray-based imaging system (IGRT) with respect to their impact on intracranial stereotactic radiotherapy (SRT) and intracranial stereotactic radiosurgery (SRS). Patient positioning data, both acquired with SGRT and IGRT systems at the same linacs, serve as abasis for determination of positioning accuracy. Atotal of 35patients with two different open face masks (578 datasets) were positioned using X‑ray stereoscopic imaging and the patient position inside the open face mask was recorded using SGRT. The measurement accuracy of the SGRT system (in a"standard" and an SRS mode with higher resolution) was evaluated using both IGRT and SGRT patient positioning datasets taking into account the measurement errors of the X‑ray system. Based on these clinically measured datasets, the positioning accuracy was estimated using Monte Carlo (MC) simulations. The relevant evaluation criterion, as standard of practice in cranial SRT, was the 95th percentile. The interfractional measurement displacement vector of the SGRT system, σSGRT, in high resolution mode was estimated at 2.5 mm (68th percentile) and 5 mm (95th percentile). If the standard resolution was used, σSGRT increased by about 20%. The standard deviation of the axis-related σSGRT of the SGRT system ranged between 1.5 and 1.8 mm interfractionally and 0.5 and 1.0 mm intrafractionally. The magnitude of σSGRT is mainly due to the principle of patient surface scanning and not due to technical limitations or vendor-specific issues in software or hardware. Based on the resulting σSGRT, MC simulations served as ameasure for the positioning accuracy for non-coplanar couch rotations. If an SGRT system is used as the only patient positioning device in non-coplanar fields, interfractional positioning errors of up to 6 mm and intrafractional errors of up to 5mm cannot be ruled out. In contrast, MC simulations resulted in apositioning error of 1.6 mm (95th percentile) using the IGRT system. The cause of positioning errors in the SGRT system is mainly achange in the facial surface relative to adefined point in the brain. In order to achieve the necessary geometric accuracy in cranial stereotactic radiotherapy, use of an X‑ray-based IGRT system, especially when treating with non-coplanar couch angles, is highly recommended.

Design and Implementation of a Non-Common-View Axis Alignment System for Airborne Laser Communication

This paper proposes a non-common-view axis alignment method for the alignment requirements of airborne laser communication systems. The system consists of a ground transmitting end and an airborne relay terminal. The ground transmitting end uses a camera and a pan-tilt for image tracking, while the airborne relay end uses a two-dimensional mirror to control the beam to achieve non-common-view axis alignment between the transmitting and receiving sides. The working principle and process of both the transmitter and receiver of the non-common-view axis alignment system for airborne laser communication were compared with traditional wireless optical alignment methods. The design process of the two-dimensional mirror used in this paper is introduced, the scanning trajectory of the two-dimensional mirror is simulated and analyzed according to the beam scanning principle, and the field experiment link is set up to carry out the airborne laser communication experiment. The experimental results show that when the link distance is 10 m, the tracking errors of the system in the azimuth and pitch directions are 19.02 µrad and 22.35 µrad respectively, and the amplitude of the electrical signal output by the signal detector is 84.0 mV; When the link distance is 20 m, the tracking errors of the system in the azimuth and pitch directions are 39.66 µrad and 33.94 µrad respectively, and the amplitude of the electrical signal output by the signal detector is 23.0 mV. Using this method, the alignment can be completed without data return, and the establishment of the reverse link can also be realized while the transmission link is quickly established, and there is no need for an air stability platform. The feasibility of the application of the non-common-view axis alignment method to the airborne laser communication system is verified.

Uncertainty evaluation of an on-machine chromatic confocal measurement system

On-machine optical measurement receives growing attention as a viable quality assurance technique to satisfy the increasingly critical requirements for dimensional accuracy and surface finish upon precision components. It preserves the temporal and spatial consistency between manufacturing and measurement activities, allowing for a substantial productivity improvement and a great opportunity for on-line quality control. However, additional uncertainty can be introduced under the harsh on-machine measuring environment degrading the measurement quality. The explicit research on the on-machine measurement uncertainty is therefore essential but rarely carried out to date. To fill this gap, this paper presents the uncertainty investigation of an on-machine areal measuring instrument based on the chromatic confocal scanning principle. The vibration transmitted from neighboring machine tools is found to strengthen the drive vibration and to cause an overestimation of the roughness in the static noise test. The motion-induced disturbance and subdivisional error are recognized as artefacts in the flatness map influencing the evaluation of the flatness deviation, though they can be attenuated by the notch filter. Based on further evaluation on the roughness parameters, the uncertainty contributions from the noise and the corrected flatness deviation are found to be 18nm and 50nm respectively in Sz for the rough surface (pulse energy=250μJ). An uncertainty budget concerning all these influencing factors enables a systematic uncertainty quantification for the on-machine measurement.

Research of Non-mechanical Beam Scanning Technology

Laser beam scanning technology has been widely used in various fields such as LIDAR, photoelectric detection and space optical communication, etc. Mechanical scanning has problems such as inflexibility and low scanning rate. This paper introduces the basic principles of acoustic-optical scanning, electro-optical scanning, optical phased array and MEMS scanning, and analyses the advantages and disadvantages of several scanning methods and the main application scenarios, and finds that the current optical scanning technology is developing towards large scanning angle, high accuracy, fast response and miniaturization, among which the liquid crystal optical phased array and MEMS scanning technology are relatively mature. The scanning angle of the LCD optical phased array can reach ±10°, and the scanning angle of the MEMS can reach 6.6°*4.4°, which has a broad development prospect.

Precision Measurement of Complex Optics Using a Scanning-Point Multiwavelength Interferometer Operating in the Visible Domain

The growing demands of optical systems have led to increasingly complex aspheres and freeforms. In this paper, an established measurement system in asphere production, which is also a promising approach in high-precision freeform metrology, is presented. It is based on a scanning-point multiwavelength interferometer approach. The scanning principle enables great flexibility, reduces setup time and costs, and has almost no limitations in spherical departure. Due to the absolute measurement capability, the utilized multiwavelength approach is beneficial for segmented, annular, and discrete surfaces, which are common designs of modern applications’ optical elements. The metrology system enables measurements on a nanometer scale on a great variety of apertures—from 1 to 1000 mm. Recently, a new short-coherence multiwavelength interferometer operating in the visible domain has been developed. It enables the high-precision measurement on silicon-coated surfaces, which can be found in space applications and are also commonly used for extreme-ultraviolet (EUV) lithographic setups, which will be used as an example throughout this work. Owing to the large absolute measurement capability, applied grating structures for suppressing infrared light in the EUV process can easily be measured. This paper summarizes the basic working principles of the proposed metrology system, explains the special requirements for different fields of application, highlights the capabilities of the visible multiwavelength approach, and shows the measurement results.

Двухканальная гиперспектральная система

The article discusses the construction of television hyperspectral imaging systems. Examples of practical use of multi-scale images are given. A combined hyperspectral system with two channels is considered: the first one performed on the basis of the Fabry-Perot interferometer is for small-scale observation, and the second one performed on the basis of a prism is for large-scale observation. The principles of constructing channels of a combined hyperspectral system based on scanning by spatial and spectral coordinates are considered. A variant of constructing a multi-angle (multi-slit) hyperspectral system for the prism variant based on the principle of scanning by spatial coordinate is proposed. The possibility of implementing a multi-angle channel using a megapixel photodetector with increased sensitivity is analyzed. The initial and calculated data are given. Structural electrical and optical circuits are considered, and resulting technical characteristics are analyzed.

Rigorous Density Correction Model for Single-Scan TLS Point Clouds

Terrestrial laser scanning (TLS) can acquire high-precision and high-resolution 3D point clouds of the scanned targets, and the common technical challenge is how to accurately and efficiently process the massive unorganized point clouds. Density is one of the most fundamental and significant quantities that can be derived for each point by counting the number of neighbors in a given 3D space. It contains key information of the target geometric features and thus plays an important role in TLS data processing (e.g., classification and feature extraction). However, density usually varies remarkably for different scenes with varied scan geometry (e.g., distance and incidence angle), scan resolution (e.g., horizontal and vertical angular resolutions), and object geometry (e.g., slope, size, and spatial attitude), thereby greatly hindering its full capability in reflecting the geometric discrepancies of different targets. The density must be corrected before reliably used as a proxy for target geometric features. In this study, a generalized rigorous model is proposed to correct the density of single-scan TLS point clouds based on the mathematically deduced relation between density and related influencing factors. The superiority of the proposed model over existing models is that it is rigorously developed based on the instrumental scanning principles and target spatial geometry and can be used for different instruments, scanning scenes, targets, and scanning parameters. The proposed model is verified by a series of indoor quantitative control experiments and three natural scenes with totally different instruments and scanning conditions. The results show that the proposed model can accurately simulate the density variation at different scanning geometries with an average correlation coefficient of 0.9957 between the calculated and actual densities. The effects of all influencing factors on density are significantly removed in complex natural scenes by the proposed model where the coefficient of variation of the density from a homogeneous surface after correction is reduced by 72.31%, on the average. The proposed model exhibits good performance in terms of the feasibility, effectiveness, and generality and can derive a corrected density value that is a proxy of target geometric size. Additionally, the proposed model can be conducted on each scan individually before the co-registration in the actual TLS campaign with a number of single scans, which has tremendous application value in facilitating TLS data interpretation.

АНАЛІЗ СУЧАСНИХ МЕТОДІВ МЕДІАВИМІРЮВАННЯ

<div><p><strong><em>Purpose. </em></strong><em>Generalization and structuring of data regarding the methodology of media measurements, analysis of the results of actual media measurements conducted in Ukraine, identification of dynamics and modern trends of media consumption.</em></p><p><strong><em>Research methodology. </em></strong><em>In the course of the study, the method of system analysis was used to generalize the methods of sociological research of the mass media; the method of statistical analysis is applied to reproduce certain characteristics of the audience on an imaginary model that reflects its various aspects; the method of structural-functional analysis was used to determine the structure of the audience and studies of the function of the media in relation to the integration of society</em>.</p></div><p><strong><em>Results.</em></strong><em> The audience of mass communication media is considered as a stable group of people who have common informational needs. A review of media audience research was carried out in the main areas: audience measurement, studying the relationship of the media audience to the products produced by them and the dynamics of audience preferences, studying the impact of the media on the audience. The main quantitative methods of mediametry were analyzed: diary panels; survey panels, such as personal interviews, telephone, self-administered, online surveys; panels built according to the principle of electronic scanning – peoplemeters, radiometers, radio control. Considered a classification of the types of audience measurement, namely: technical means of recording, diaries or self-reports, telephone surveys, questionnaires or personal interviews. Such stages of media research as processing of received information and determination of mediametric indicators are analyzed. The main stages of the development of television audience measurements in Ukraine are considered. The main indicators characterizing the radio audience are highlighted: frequency of listening for the last week, average rating for 15 minutes of broadcast in thousands of people (AQH) or percentage (AQH%), average weekly or average monthly coverage of stations. The indicators of the measurement of the audience of print media – coverage and socio-demographic profile of readers are considered. The results of audience research conducted by the Kantar Ukraine research company, the Kyiv International Institute of Sociology, and the Nielsen Media Ukraine company were analyzed. The methodological features of Internet audience research are indicated. The results of Internet media measurement were analyzed by the operators of research markets AC Nielsen, ComScore, Mediametrie, TNS, Factum Group, which includes the companies InMind and Gemius.</em></p><p><strong><em>Novelty. </em></strong><em>The article summarizes and structures the data on the methodology of media measurements, reveals the dynamics and modern trends of media consumption.</em></p><p><strong><em>Practical meaning.</em></strong><strong><em> </em></strong><em>The results of the study can be used to improve the methods of measuring media consumption, comparative analysis of the results of media studies conducted in Ukraine and countries around the world.</em></p><p><strong><em>Key words: </em></strong><em>audience measurement, mediametric studies, media measurement methodologies, structuring of current data, diary panels.</em></p>

Double-DQN-Based Path-Tracking Control Algorithm for Orchard Traction Spraying Robot

The precise path-tracking control of tractors and trailers is the key to realizing agricultural automation. In order to improve the path-tracking control accuracy and driving stability of orchard traction spraying robots, this study proposed a navigation path-tracking control algorithm based on Double Deep Q-Network (Double DQN). Drawing on the driver’s driving experience and referring to the principle of radar scanning and the principle of image recognition, a virtual radar model was constructed to generate a virtual radar map. The virtual radar map was used to describe the position relationship between the traction spraying robot and the planned path. Combined with the deep reinforcement learning method, all possible robot driving actions under the current virtual radar map were scored, and the best driving action was selected as the output of the network. In this study, a path-tracking algorithm was self-developed with a deep Q-network trained by driving the traction spraying robot in a simulated virtual environment. The algorithm was tested in both simulations and in a field to follow a typical ‘U’-shaped path. The simulation results showed that the proposed algorithm was able to achieve accurate path-tracking control of the spraying trailer. The field tests showed that when the vehicle speed was 0.36 m/s and 0.75 m/s, the maximum lateral deviation of the algorithm was 0.233 m and 0.266 m, the average lateral deviation was 0.071 m and 0.076 m, and the standard deviation was 0.051 m and 0.057 m, respectively. Compared with the algorithm based on the virtual radar model, the maximum lateral deviation was reduced by 56.37% and 51.54%, the average lateral deviation was reduced by 7.8% and 5.0%, and the standard deviation was reduced by 20.31% and 8.1%, respectively. The results showed that the Double-DQN-based navigation path-tracking control algorithm for the traction spraying robot in the orchard had higher path-tracking accuracy and driving stability, which could meet the actual operational requirements of traditional orchards.

Ultrasound scanning techniques

BackgroundUltrasound is an essential tool for the hepatobiliary and pancreatic surgeon. MethodsThis review focuses on transabdominal, open intraoperative, and laparoscopic ultrasonography of the liver, biliary tract, and pancreas. The goal is to obtain optimal ultrasound images through an understanding of the equipment setup, transducer (probe) selection, terminology, and general scanning principles. Outlined is a structured, standardized approach necessary to obtain complete information when doing intraoperative ultrasound. When done by the surgeon, the goal of the examination typically is to answer a question or questions through a focused rather than a comprehensive diagnostic examination. Finally, presented are the details of techniques specific to scanning each of the major organs. ResultsA structured, standardized ultrasound scanning approach provides for optimal image acquisition. It allows one to develop standardized views of common structures resulting in "pattern recognition," making learning and interpreting images easier. A standardized approach ensures a complete ultrasound examination, and it minimizes the chance of missed findings. SummaryThe general principles for transabdominal, open intraoperative, and laparoscopic ultrasonography scanning are similar. One can gather considerable information using these modalities during a clinical examination, procedure, or operation. For success, it is critical to develop a standardized approach to scanning and use it every time. This facilitates familiarity when viewing images, making it easier for the novice to learn and gain experience. Using a systematic approach ensures that the experienced ultrasonographer obtains all the essential information needed at the time of surgery.

Development of an on-machine measurement system with chromatic confocal probe for measuring the profile error of off-axis biconical free-form optics in ultra-precision grinding

Ultra-precision grinding of large-scale free-form optics made of hard brittle material is faced with several thorny problems, such as the grinding process is complex, hard to estimate the wear of the grinding wheel and the on-machine measurement technique of profile error is immature, which seriously affects the rapid convergence of profile accuracy. The on-machine measurement of profile error can effectively avoid the re-installation error introduced into the compensation period, and then the effectiveness and machining efficiency of compensation grinding are enhanced. Therefore, we developed an on-machine measurement system with a chromatic confocal probe for measuring the profile error of off-axis biconical free-form optics in ultra-precision grinding. First, the on-machine measurement system was developed on a 4-axis ultra-precision machine tool, and the scanning principles and position calibration were studied. Then, the scanning strategy was systematically researched, which included the centering approach, scanning path planning, scanning parameter calculation, and the evaluation principle of profile error. Finally, the on-machine measurement experiments were carried out on the off-axis biconical free-form optics with a width of 220 mm and height of 100 mm. The sub-micron variation range of measurement results is achieved by measuring the full-aperture profile error under different sampling parameters. The developed on-machine measurement system and scanning strategy can significantly improve the profile accuracy and machining efficiency of the large-scale free-form optics made of hard brittle material, and reduce the production cost.

Automatic Landing of Unmanned Aerial Vehicles via Wireless Positioning System with Pseudo-Conical Scanning.

In this work, a wireless UAV unmanned landing system is considered, using the principles of pseudo conical scanning with a phased antenna array (PAA). The basic requirements for the characteristics and parameters of the system as a whole and of its components are defined. Special attention is paid to the primary sensor of the system—PAA with electronic scanning. A variant with a minimum number of four states on the radiation pattern of a low-budget patch PAA was studied. A linear regression of the difference characteristics of the measured radiation beams is proposed, which allows the practical application of the recommended landing algorithm with low computational complexity. Systematic and random positioning errors, both by measurement and by Monte Carlo simulation, were studied. Obtained statistical results prove the algorithm convergence and acceptable accuracy for the system implementation. They are applied if necessary to adjust the Kalman filter parameters. The proposed wireless system can be used for unmanned landing, tracking, and navigating the UAV in flight, or wireless navigation of other mobile objects.

A high-efficiency and high-precision automatic 3D scanning system for industrial parts based on a scanning path planning algorithm

To achieve high-precision and high-efficiency 3D scanning of industrial parts, this research proposes an automated 3D scanning system based on path planning algorithms, in which the 3D scanning sensor is realized based on the principle of raster projection. The proposed automated scanning system is composed of a robotic arm, a 3D scanner, and a turntable to achieve a complete 3D scanning of the object to be measured. More precisely, this paper proposes a virtual 3D scanning principle, which can accurately determine whether a certain point on the CAD model can be scanned by a viewpoint. Further, this paper proposes a path planning algorithm based on the virtual 3D scanning principle, which can calculate the optimal scanning path required to scan the object according to the CAD model of the scanned object. Furthermore, to ensure the accuracy of the system, a high-precision system calibration method is proposed to establish the accurate positional relationship between various parts of the system. Firstly, this research proposes a camera calibration algorithm based on close-range photogrammetry, which can calculate the high-precision interior and exterior orientation parameters of the camera, and apply the method of calculating camera external parameters to the hand-eye calibration, making the accuracy of hand-eye calibration is also improved accordingly. In addition, this research proposes a photogrammetry-based projector calibration algorithm to determine the positional relationship between the projector and the camera in the 3D scanner, and a turntable calibration method to determine the positional relationship between the rotation center of the turntable and the camera. Eventually, according to different usage requirements, two 3D scanning data splicing methods are proposed. One is a high-efficient automatic splicing method based on the results of system calibration without pasting mark points, and the other is a high-precision data splicing method based on photogrammetry. Experimental results demonstrate that this system has higher accuracy and better performance in system calibration, scanning path calculation, and multi-view scanning data splicing.

Research status of sensor demodulation technology of fiber grating ultrasonic signal

Compared with ordinary gratings, phase-shifted fiber gratings have better ultrasonic response sensitivity and higher upper response frequency. The application of phase-shifted fiber gratings in ultrasonic signal detection has gradually become a research hotspot. This paper mainly introduces the demodulation principle of tunable laser power scanning and wavelength feedback control techniques such as wavelength stabilization, frequency stabilization and laser tracking. Most of the existing demodulation techniques are only suitable for single optical channel, and the demodulation frequency is low. The development direction of fiber Bragg grating demodulation technology is multi-channel synchronous stable high frequency demodulation.

Piezoelectric MEMS Mirror with Lissajous Scanning for Automobile Adaptive Laser Headlights.

The emergence of smart headlights with reconfigurable light distributions that provide optimal illumination, highlight road objects, and project symbols to communicate with traffic participants further enhances road safety. Integrating all these functions in a single headlight usually suffers from issues of bulky multi-functional add-on modules with high cost or the use of conventional spatial light modulators with low optical efficiency and complex thermal design requirements. This paper presents a novel laser headlight prototype based on biaxially resonant microelectromechanical systems (MEMS) mirror light modulator for mapping blue laser patterns on phosphor plate to create structured white illumination and tunable road projection. The proposed headlight prototype system enables reconfigurable light distribution by leveraging laser beam scanning with fewer back-end lens and simple thermal design requirements. Built with thin-film lead zirconate titanate oxide (PbZrTiO3) actuators, the MEMS mirror achieved high-frequency biaxial resonance of 17.328 kHz, 4.81 kHz, and optical scan angle of 12.9°. The large mirror design of 2.0 mm facilitates more refined resolvable projection pixels, delivers more optical power, and provides moderate optical aperture to possibly serve as the common spatial light modulator of headlight and the light detection and ranging (LiDAR) towards all-in-one integration. The carefully designed bi-axial resonant frequency improves the device’s robustness by offsetting the lowest eigenmode away from the vehicle vibration. By establishing the laser headlight prototype systems of both 1D and 2D scanning modes, a mathematical model of laser modulation and MEMS electrical control principles of Lissajous scanning are proposed to tune the projection pattern density and shapes. It laid the foundation for developing a laser scanning control system with more complex project functions and prompting the application of MEMS for compact headlight system that addresses night driving visibility, eliminates glare effect, and renders interactive projection capabilities.

Study of 3D scanning technologies and scanners in orthodontics

Digital dental scanners are devices which are used to capture optical impression of intra and extra oral structures of the patient’s mouth. The basic principle of digital scanning is based upon optical phenomena like optical triangulation, coherence tomography, parallel confocal imaging and three-dimensional motion videos capturing technique. In orthodontic practice, digital scanners can be successfully used in efficient treatment planning, custom appliance fabrication, clear aligner technology and orthognathic surgical simulation. From digital record keeping, digital cast models, occlusogram, extra oral and intra oral scanners to software for cephalometric analysis, etc. have taken the orthodontic practice to newer heights. Intraoral digital scanner that utilizes the parallel-confocal imaging technology and point and stitch reconstruction to generate digital impressions which are accurate and powder free. Digitization has revolutionized the conventional orthodontics completely. In modern day orthodontic dental practice digital extra-oral and intra-oral scans are used to fabricate working and study cast models that facilitates construction of fixed orthodontic appliances, retainers and custom trays for lingual orthodontic procedures. Digital scanners are the new face of impression making and digital cast fabrication in dentistry. This review aims to identify advantages of utilising digitally scanned impressions over the conventional impression making techniques and application of digital scanning technology pertaining to the speciality of orthodontics in dental practice.

Compressive nano-FTIR chemical mapping

Nano-Fourier-transform infrared spectroscopy (nano-FTIR) combines infrared spectroscopy with scanning probe microscopy (SPM) techniques and enables spectroscopic imaging of molecular and electronic properties of matter at nanometer spatial resolution. The spectroscopic imaging can be used to derive chemical mappings, i.e. the spatial distribution of concentrations of the species contained in a given sample. However, due to the sequential scanning principle underlying SPM, recording the complete spectrum over a large spatial area leads to long measurement times. Furthermore, the acquired spectrum often contains additional signals from species and lineshape effects that are not explicitly accounted for. A compressive chemical mapping approach is proposed for undersampled nano-FTIR data that utilizes sparsity of these additional signals in the spectral domain. The approach combines a projection technique with standard compressed sensing, followed by a spatially regularized regression. Using real nano-FTIR measurements superimposed by simulated interferograms representing the chemical mapping of the contained species, it is demonstrated that the proposed procedure performs well even in cases in which the simulated interferograms and the sparse additional signals exhibit a strong spectral overlap.

Off-axis optical scanning holography [Invited

Optical scanning holography (OSH) involves the principles of optical scanning and heterodyning. The use of heterodyning leads to phase-preserving, which is the basic idea of holography. While heterodyning has numerous advantages, it requires complicated and expensive electronic processing. We investigate an off-axis approach to OSH, thereby eliminating the use of heterodyning for phase retrieval. We develop optical scanning theory for holographic imaging and show that by properly designing the scanning beam, we can perform coherent and incoherent holographic recording. Simulation results are provided to verify the proposed idea.