High-precision Laser Research Articles

An AI-Based Deep Learning with K-Mean Approach for Enhancing Altitude Estimation Accuracy in Unmanned Aerial Vehicles

In the rapidly evolving domain of Unmanned Aerial Vehicles (UAVs), precise altitude estimation remains a significant challenge, particularly for lightweight UAVs. This research presents an innovative approach to enhance altitude estimation accuracy for UAVs weighing under 2 kg without cameras, utilizing advanced AI Deep Learning algorithms. The primary novelty of this study lies in its unique integration of unsupervised and supervised learning techniques. By synergistically combining K-Means Clustering with a multiple-input deep learning regression-based model (DL-KMA), we have achieved substantial improvements in altitude estimation accuracy. This methodology represents a significant advancement over conventional approaches in UAV technology. Our experimental design involved comprehensive field data collection across two distinct altitude environments, employing a high-precision Digital Laser Distance Meter as the reference standard (Class II). This rigorous approach facilitated a thorough evaluation of our model’s performance across varied terrains, ensuring robust and reliable results. The outcomes of our study are particularly noteworthy, with the model demonstrating remarkably low Mean Squared Error (MSE) values across all data clusters, ranging from 0.011 to 0.072. These results not only indicate significant improvements over traditional methods, but also establish a new benchmark in UAVs altitude estimation accuracy. A key innovation in our approach is the elimination of costly additional hardware such as Light Detection and Ranging (LiDAR), offering a cost-effective, software-based solution. This advancement has broad implications, enhancing the accessibility of advanced UAVs technology and expanding its potential applications across diverse sectors including precision agriculture, urban planning, and emergency response. This research represents a significant contribution to the integration of AI and UAVs technology, potentially unlocking new possibilities in UAVs applications. By enhancing the capabilities of lightweight UAVs, we are not merely improving a technical aspect, but revolutionizing the potential applications of UAVs across industries. Our work sets the stage for safer, more reliable, and precise UAVs operations, marking a pivotal moment in the evolution of aerial technology in an increasingly UAV-dependent world.

Demonstration of an ultra-wideband wavelength self-adaptive and high-precision single-frequency laser linewidth measurement system.

An ultra-wideband wavelength self-adaptive and high-precision single-frequency laser linewidth measurement system (SFLLMS) is constructed. The SFLLMS enables parameter measurement of the laser in the wavelength range of 1-2.05 µm with a 9 Hz linewidth measurement resolution and ±45 Hz linewidth measurement accuracy. The wavelength measurement accuracy of the constructed system is ±0.008 nm, and it consumes less than 4.9 s for a single measurement. The wavelengths and linewidths of lasers in the 1 µm band with a center wavelength of 1064.5222 nm, the 1.5 µm band with a center wavelength of 1550.1973nm, the 1.94 µm band with a center wavelength of 1940.8327 nm, and the 2.05 µm band with a center wavelength of 2049.0460 nm were measured using the constructed SFLLMS. The wavelength measurement accuracy and linewidth measurement accuracy were calculated. The times for single linewidth measurement at different powers of the four lasers were also recorded.

Constraints on Covariant Horava-Lifshitz Gravity from precision measurement of planetary gravitomagnetic field

Abstract As a generalization of Einstein’s theory, Horava-Lifshitz has attracted significant interests due to its healthy ultraviolet behavior. In this paper, we analyze the impact of the Horava-Lifshitz corrections on the gravitomagnetic field. We propose a new planetary gravitomagnetic field measurement method with the help of the space-based laser interferometry, which is further used to constrain the Horava-Lifshitz parameters. Our analysis shows that the high-precision laser gradiometers can indeed limit the parameters in Horava-Lifshitz gravity and improve the results by one or two orders when compared with the existing theories. Our novel method provides insights into constraining the parameters in the modified gravitational theory, which facilitates a deeper understanding of this complex framework and paving the way for potential technological advancements in the field.

Review of high-precision femtosecond laser materials processing for fabricating microstructures: Effects of laser parameters on processing quality, ablation efficiency, and microhole shape

Femtosecond lasers are promising tools for achieving high-precision processing of thin materials without causing any thermal surface damage and bulk distortion. However, thermal damage can occur even with ultrashort laser pulses. This is because of high electron penetration depth and heat accumulation at high fluence and high repetition rate. Nanoparticle redeposition can be dramatically altered with variation in repetition rate. The symmetry of microholes and ablation efficiency vary with laser polarization. The laser wavelength affects the ablation efficiency and surface roughness. Therefore, understanding these laser–matter interactions that depend on the laser parameters is essential for high-precision laser processing. This article reviews laser–matter interactions in the 64FeNi alloy, as well as analytical models for designing the desired hole size and taper angles. This can help establish strategies for creating various high-precision microstructures using femtosecond lasers.

Research on 3D laser SLAM algorithm based on graph optimization

Abstract Aiming at the problems that the positioning accuracy of laser Simultaneous Localization and Mapping (SLAM) is affected by the misclassification of close feature points and incorrect feature matching in the environment with redundant features, a 3D laser SLAM algorithm based on graph optimization was proposed. Firstly, to reduce the feature extraction error problem, the distance threshold is used to filter the close point cloud and improve the accuracy of feature classification, enhanced reliability of optoelectronic measurement data. Secondly, to improve the consistency of feature matching, based on the rough matching based on k-dimensional tree (KD-Tree), a two-stage fine matching based on geometric consistency is introduced to improved laser point alignment accuracy. The proposed method is compared with the mainstream localization algorithms based on KITTI dataset. Compared with Lidar-IMU Odometry with Sparse Adaptive Mapping and Fast LiDAR-Inertial Odometry, the positioning error of the proposed method is reduced by 21.88%and 24.43%on average, which showsthe superiority of the present algorithm in the application of optoelectronics and optical technology, and provides new ideas and methods for the development of high-precision laser navigation technology.

Iterative correction of robotic grinding using spatial feedback for precision applications

Since the advent of robots, many tasks that were originally performed by humans have now been tasked to industrial robots. From a manufacturing standpoint, robots have primarily been used in pick-and-place or other non-machining operations that require high repeatability. However, with the increasing availability of CAD/CAM software and the development of high-precision metrology, comes the opportunity to integrate robots into a wider variety of manufacturing processes through the use of feedback control. One such machining operation that is being explored is precision grinding of metal parts. Most other work in this area has focused on force regulation to improve grind quality; however, this paper takes a different approach. In this work, an Iterative Learning Control (ILC) algorithm is implemented to correct the geometric error directly by altering the toolpath trajectory. Specifically, in this framework, a conservative initial cutting trajectory is implemented using a 6-DoF robotic grinding system, and the resulting part geometry is measured via a high-precision laser scanner. Based on the resultant geometric error, the toolpath is corrected and then rerun on the part. This process is then repeated iteratively until sufficient accuracy is achieved. Due to the inability to replace material in overground regions, the controller is designed with an emphasis on reducing overshoot which cannot be corrected. The controller is experimentally validated by grinding an elliptical pocket which meets FAA specifications for corrosion removal in aircraft. The results showed that within seven iterations the entire error surface could be brought to a tolerance of ±0.150 mm for the given geometry.

High-precision laser monitoring system with enhanced non-uniform scanning for railway safety

High-precision laser monitoring system with enhanced non-uniform scanning for railway safety

Development and Validation of a New Type of Displacement-Based Miniatured Laser Vibrometers.

Developing a miniatured laser vibrometer becomes important for many engineering areas, such as experimental and operational modal analyses, model validation, and structural health monitoring. Due to its compact size and light weight, a miniatured laser vibrometer can be attached to various mobilized platforms, such as an unmanned aerial vehicle and a robotic arm whose payloads can usually not be large, to achieve a flexible vibration measurement capability. However, integrating optics into a miniaturized laser vibrometer presents several challenges. These include signal interference from ghost reflectance signals generated by the sub-components of integrated photonics, polarization effects caused by waveguide structures, wavelength drifting due to the semiconductor laser, and the poorer noise characteristics of an integrated laser chip compared to a non-integrated circuit. This work proposes a novel chip-based high-precision laser vibrometer by incorporating two or more sets of quadrature demodulation networks into its design. An additional set of quadrature demodulation networks with a distinct reference arm delay line length can be used to conduct real-time compensation to mitigate linear interference caused by temperature and environmental variations. A series of vibration measurements with frequencies ranging from 0.1 Hz to 1 MHz were conducted using the proposed laser vibrometer to show its repeatability and accuracy in vibration and ultrasonic vibration measurements, and its robustness to test surface conditions. The proposed laser vibrometer has the advantage of directly measuring the displacement response of a vibrating structure rather than integrating its velocity response to yield the measured displacement with a conventional laser Doppler vibrometer.

High-precision DSM-based laser ranging method integrated with free space optical communication.

Free space optical communication (FSOC) technology has been developed rapidly and practically applied in many scenarios such as satellite-related ones, in unmanned aerial vehicles, for underwater use, etc. In certain applications, it is very important to obtain the high-precision position and distance information. The laser ranging technology is one of the main ways to realize it. Moreover, it would be more interesting to accomplish the laser ranging integrated with the FSOC, which can effectively control the size, weight, and power of the FSOC terminals. However, in existing integrated laser communication and ranging solutions, the ranging accuracy is in the millimeter-level. To further improve the accuracy of laser ranging and communication rate in the integrated architecture, we propose a harmonic phase ranging method combined with delta-sigma modulation (DSM) based on a 10 Gb/s coherent FSOC. Through the DSM technology, a harmonic is converted into a digital signal which can be simply combined with the communication data and transmitted together in the FSO link. The laser ranging can thus be effectively combined with FSOC to realize an integrated architecture. Finally, the root means square error of the laser ranging are improved to ∼0.303 mm. Compared with the existing solutions, our proposed scheme shows both advantages of higher-precision ranging and higher communication rate.

Hierarchical triply periodic minimal surface shell lattices with superior isotropic elasticity: Design guidelines, fabrication, and validation

Hierarchical triply periodic minimal surface (TPMS) shell lattices exhibit a wide range of tailorable properties that can be fine-tuned by lattice design. Recent advances in additive manufacturing towards high resolution enable the precise fabrication of hierarchical TPMS lattices. However, the isotropic behavior of hierarchical TPMS lattices has received little attention. In this study, we focus on the design of hierarchical TPMS lattices to explore their superior isotropic elasticity. By considering three unique geometric parameters of hierarchical TPMS: cell length ratio, relative density, and order number, multiple representative isotropic hierarchical TPMS lattices can be achieved at the same given relative density, which significantly expands its design space. The resultant lattices retain a minimal mid-surface and exhibit a large range of tailorable stiffness. To validate their isotropic elasticity, high-precision laser powder bed fusion was adopted to fabricate representative isotropic lattices and their anisotropic counterparts. Morphology observation and micro-CT scan show that the fabricated samples are dense, and their geometries are highly consistent with the designed models. Quasi-static compression tests further confirm the isotropic elasticity in the new designs. Moreover, a prediction rule was proposed to assess whether an isotropic hierarchical TPMS lattice can be obtained from two selected single-level lattices, which significantly enhances the design efficiency. As a result, the design method and principles can be summarized in this study to provide effective design guidelines to swiftly create hierarchical shell lattices with superior isotropic elasticity.

Multidimensional ultrashort optical pulse manipulation using spatial light modulation.

Ultrashort optical pulse manipulation is one of the key techniques for applications such as high-speed imaging and high-precision laser processing. In this study, we demonstrate the multidimensional manipulation of ultrashort optical pulses by integrating spatial dispersion and spatial light modulation. Specifically, by modulating the phase of each wavelength, we achieve arbitrary adjustments in multiple dimensions, including number of sub pulses, time interval, intensity, and pulse width simultaneously and independently with a simple setup and few calculations. The performance of the optical pulse manipulation method is verified through both numerical simulations and experiments.

The Suppression Effect of an Imaging System on the Geometric Tilt-to-Length Coupling in a Test Mass Interferometer

Tilt-to-length (TTL) coupling noise arises from angular misalignments of interfering beams in optical path length (OPL) measurements and significantly impacts the accuracy of interferometry measurement systems. This paper focuses on geometric TTL coupling in a test mass (TM) interferometer and examines how an imaging system influences TTL noise suppression. First, the analytical expression of the geometric TTL coupling in a TM interferometer with alignment errors is derived and confirmed through numerical simulation. Subsequently, an imaging system is incorporated into the geometric model and the corresponding analytical expressions are obtained under two common conjugate relationships. Nevertheless, the TTL coupling remains beyond the requirement of TM interferometer, as the residual TTL coupled with alignment errors persists even with the imaging system. Therefore, an optimal position of the imaging system capable of eliminating the second-order term of the TTL coupling is determined. Meanwhile, the first-order term can be mitigated through in-orbit calibrations. These findings offer valuable guidance for the design and adjustment of imaging systems in space-borne gravitational wave detection missions, which require high-precision laser interferometry.

Macro-micro synchronization strategy based on fuzzy time-delay compensation for high-precision laser on-the-fly processing

Real-time control systems of macro-micro manipulators commonly confront time-delay challenges to achieve high precision and synchronization performance, because macro and micro subsystems always have significant difference mainly in mechanical inertia. In this paper, a self-designed PC-based real-time controller utilized in laser on-the-fly processing is introduced as a study case of macro-micro systems. A dynamic time-delay compensation method for this case is proposed based on efficient fuzzy-model prediction and special data compression/extension algorithm. This method takes account of the practical time-delay fluctuation and has capability of adjusting the compensator adaptively rather than fixing the compensator as a constant, compared with the conventional static compensation. Experimental results show that, after applying the dynamic compensation, the process error caused by time-delay is eliminated from 1.059 mm to 0.001 mm, while the quality of synchronization appears even better than the static compensation with the error of 0.014 mm. Besides, the proposed method is computationally optimized, and the extra load of real-time kernel merely fluctuates within 3 % of the total computation performance capacity.

Measurement of 3D joint surface morphology and estimation for shear mechanical behavior: A theoretical model and experimental investigation

The majority of rock engineering instabilities are primarily due to shear slips and failures on the joint surfaces, and the measurement of joint surface morphology is crucial for shear strength evaluation. In this study, the high-precision 3D laser scanner was first used to characterize and digitally reconstruct the surface morphology of various joints. The evaluation method of joint surface roughness was modified according to the 2D profile data and shear direction. Then, the effects of normal stress and initial joint roughness coefficient on the shear mechanical behavior were investigated by experimental method. The damage evolution characteristics and failure mechanism of the joint surface are analyzed by acoustic emission monitoring and image binarization calculations. The research results indicate that as the normal stress and initial joint roughness coefficient increase, the peak shear stress and shear displacement, residual strength, and cumulative AE counts of rock joints display an increasing trend. Based on the evolution of mechanical parameters, a new mechanical model of rock joints to predict shear strength and deformation was developed, which was validated by comparing the theoretical prediction curves with test results. A good concordance was achieved between the shear test and theoretical results, indicating that the developed model can effectively predict the shear strength and deformation of joint surfaces under different normal stress and roughness. This research results are expected to provide a valuable guidance for early warning and evaluation of geological disasters.

On the accuracy of the gradient method for determining the mean integral refractive index of air for large-scale dimensional measurements

The results of the analysis of the accuracy capabilities of the gradient method for determining the mean integral value of the group refractive index of air along the path of the laser radiation propagating on the surface atmospheric layer are presented. The mean integral refractive index of air is used in precision laser ranging as a correction to the results of large-scale dimensional measurements, taking into account the difference between the speed of the laser radiation propagation in the atmosphere and the speed of light in vacuum. The performed analysis includes a critical review of publications underpinning this method, and the prospects for its use in high-precision laser measurements of horizontal baselines of up to 5 km long with an expanded uncertainty of less than or equal to 1 mm are considered. This method has been studied in the framework of the Project 18 SIB01 GeoMetre “Large-Scale Dimensional Measurements for Geodesy” executed in accordance with the European Metrology Programme for Innovation and Research (EMPIR).

Integrated Strategy in Road Assesment for Tameroddo-Majene City Boundary Road Section Preservation

Tameroddo – Majene City boundary road section is a national road in West Sulawesi, a road connecting South Sulawesi and Central Sulawesi provinces. Its existence is essential for increasing accessability and mobility between regions, for it does not only support economic growth in the West Sulawesi Province, but it also has some positive impacts on socioeconomic development for surrounding areas. Traffic volume, overload, and rainfall are factors that accelerate intensity of road surface irregularities. An analysis of road pavement conditions is, therefore, required to provide existing data for road preservation, to ensure its optimum function in accordance with planned durability. This research is aimed at providing assessment results of the road section conditions, and to compare the results between IRI and PCI measures, as well as to provide an overview or description of the road section conditions. This can, thereafter, be used as an important database for a better planning and implementation. Road assessment had been conducted using an integrated method, by IRI measure performed by using ‘The Hawkeye’ vehicle equipped with high precision laser profilers and accelerometers, DMI, and high-speed cameras along with GPS, incorporating Dinamic Time Warping (DTW) technique, to automatically detect and classifies road irregularities on paved roads. This method, however, followed by manual inspection (or subjective measures). Survey result shows that based on IRI method, ‘fair’ condition reaches 67%, and lightly damaged reaches 33%. While based on PCI method, ‘good’ (equivalent with ‘fair’) condition reaches 66%, and ‘bad’ condition (or equivalent with ‘lightly damaged’) condition reaches 34%. This means that the study found some differences, even though it was only a little. Based on analysis result, amongst total lenght of the road lane had been under assesment (81,8 km), 74,4 km is of ‘fair’ condition, thus it requires a routine maintenance, while the rest 8,4 km is of ‘lightly damaged’ and it requires a regular maintenance.

Time distribution of stimulated transition probabilities

In recent years, an increasing number of experimental results have been published for a wide variety of systems in which high-precision, ultra-fast, and ultra-short laser pulses techniques have been used to study time-resolved dynamical processes. In the absence of a theoretical prediction of the time distribution of the transition probabilities, the lifetimes τ are generally extracted by fitting the decay time with an exponential, bi-exponential or three-exponential function. In fitting the data, the short-time behavior is generally neglected. The purpose of this study is to show that an explicit formula for the time distribution of the transition probability can be determined rigorously using time-dependent perturbation theory. A formula that perfectly fits an important subset of the experimental results from t = 0 to t=∞ . We show that by following a route different from the usual procedure for deriving transition amplitudes and Einstein coefficients in time-dependent perturbation theory, one ends up with a time-dependent factor, that is, a temporal distribution function of the transition probabilities, and for the Einstein coefficients. The time distribution reported here looks in the time domain similar to the Planck distribution in the frequency domain. In fact, the behavior of the time distribution, with a maximum at 2τln⁡2 , and with τ playing the role of temperature, resembles the behavior of the Planck frequency distribution. We present several examples to demonstrate that the theoretical formula allows for easier fitting of the experimental results reported in the literature. We also show that the time distribution explains the difference in resonance heights between the experimental and theoretical blue laser spectra.

High-precision hyperspectral laser scanning for improved radiometric correction of backscatter intensity

High-precision hyperspectral laser scanning for improved radiometric correction of backscatter intensity

Optical penetration models for practical prediction of femtosecond laser ablation of dental hard tissue.

To develop and practically test high-precision femtosecond laser ablation models for dental hard tissue that are useful for detailed planning of automated laser dental restorative treatment. Analytical models are proposed, derived, and demonstrated for practical calculation of ablation rates, ablation efficiency and ablated morphology of human dental enamel and dentin using femtosecond lasers. The models assume an effective optical attenuation coefficient for the irradiated material. To achieve ablation, it is necessary for the local energy density of the attenuated pulse in the hard tissue to surpass a predefined threshold that signifies the minimum energy density required for material ionization. A 1029 nm, 40 W carbide 275 fs laser was used to ablate sliced adult human teeth and generate the data necessary for testing the models. The volume of material removed, and the shape of the ablated channel were measured using optical profilometry. The models fit with the measured ablation efficiency curve against laser fluence for both enamel and dentin, correctly capturing the fluence for optimum ablation and the volume of ablated material per pulse. The detailed shapes of a 400-micrometer wide channel and a single-pulse width channel are accurately predicted using the superposition of the analytical result for a single pulse. The findings have value for planning automated dental restorative treatment using femtosecond lasers. The measurements and analysis give estimates of the optical properties of enamel and dentin irradiated with an infrared femtosecond laser at above-threshold fluence and the proposed models give insight into the physics of femtosecond laser processing of dental hard tissue.

O252: Studying the neuronal regenerative response to in-vitro laser axotomy

Abstract Aims Outcomes of peripheral nerve injury (PNI) remain suboptimal, and the intrinsic mechanisms directing regeneration of injured peripheral neurons are not completely understood. To study the cellular response to injury, it is critical to deploy a model that facilitates a precise and controlled transection. We aim to recreate clinical outcomes at a micrometer level and analyse the impact of injury parameters, such as the proximity of injury to the cell body, on neuronal survival and regeneration. Methods We cultured adult rat dorsal root ganglion (DRG) neurons and transected individual neurites with a high-precision laser at 25um and 125um from the cell body. We monitored for 24 hours using time-lapse microscopy and analysed cell survival and neurite regeneration, comparing between two distance groups. Results Following laser transection at 25um from the cell body, 56% (n=25) of neurons survived for 24 hours and 33.3% (n=12) regenerated. When laser-transected at 125um, 75% (n=40) of neurons survived and 73.1% (n=26) regenerated. The mean regenerative distance was 19.9um (n=4) when injured at 25um and 173.9um (n=19) at 125um. Discussion Our laser axotomy method facilitated efficient and precise transection of individual neurites. Distal injuries generated significantly higher survival rates and regenerative length and rates compared to proximal injuries. These findings mimic clinical outcomes where distal injuries have greater recovery than proximal injuries, thereby demonstrating the efficacy of this model for investigating cellular mechanisms directing peripheral neuron regeneration. We envisage that this model will facilitate future studies aiming to accelerate peripheral neuron regeneration in a clinical context.