Search Results (40)

Wide-beam laser direct energy deposition (LDED) has been widely used due to its superior deposition efficiency. To achieve optimal laser-powder coupling, this technique typically employs rectangular powder nozzles. This study establishes a simulation model to systematically investigate the powder flow field characteristics of rectangular symmetric nozzles. Through parametric analysis of powder feeding rate, carrier gas flow rate, and shielding gas flow rate, the effects on powder stream convergence behavior are quantitatively evaluated to maximize powder utilization efficiency. Key findings reveal that, while the powder focal plane position is predominantly determined by nozzle geometry, powder feeding parameters exhibit negligible influence on flow field intersections. The resulting powder spot demonstrates a rectangular profile slightly exceeding the laser spot dimensions, and the powder concentration exhibits a distinctive flat-top distribution along the laser’s slow axis, contrasting with a Gaussian distribution along the scanning direction. Experimental validation through powder collection tests confirms strong agreement with the simulation results. Furthermore, a mathematical model was developed to accurately describe the powder concentration distribution at the focal plane. These findings provide fundamental theoretical guidance for optimizing powder feeding systems in wide-beam LDED applications. Full article

We report on the formation of homogeneous nanostructures using a two-step ablation process with square flattop beams of femtosecond (fs) laser pulses. The Gaussian beam output from a ytterbium fs laser system was converted to a square flattop beam by a refractive beam shaper and a square mask. This beam was split into two with a diffraction optical element, and then the downsized beams were spatially and temporally superimposed on a titanium surface. In the first step, the interference fringes of these two beams formed grooves with a period of 1.9 µm through ablation. Next, the surface was irradiated at normal incidence by a single beam to form a homogeneous line-like nanostructure with a period of 490 nm in a 53 μm square area. This nanostructure had a constant period and was formed over 95% of the laser-processed area, indicating that the ratio between the nanostructure and modification area was over six times larger than that for a Gaussian beam. Full article

We present a 520 μJ microsecond burst-mode pulse fiber amplifier with a GHz-tunable intra-burst repetition rate and a nearly flat-top pulse envelope. The amplifier architecture comprises a microsecond pulse seed, a high-bandwidth electro-optic modulator (EOM), two pre-amplifier stages, a waveform-compensated acoustic-optic modulator (AOM), and two main amplifier stages. To address amplified spontaneous emission (ASE) and nonlinear effects, a multistage synchronous pumping scheme that achieved a maximum energy output of 520 μJ and has a peak power of 160 W was used. To produce a flat-topped burst pulse envelope, the AOM generates an editable waveform with a leading edge and a high trailing edge to compensate for waveform distortion, resulting in a 5 μs nearly flat-top pulse envelope at maximum energy. The laser provides an adjustable intra-burst pulse repetition rate range of 1–5 GHz through the high-bandwidth EOM modulation. The intra-burst pulse jitter time of the laser remains below 4.31 ps at different frequencies. Moreover, the beam quality of the amplifier is M²x = 1.04 and M²y = 1.1. This amplifier exhibits promising potential and can be further amplified as an optical drive source for high-power, large-bandwidth microwave photon (MWP) radar applications. Meanwhile, it is also potentially applicable as a pulse source for high-speed optical communications, the high-precision processing of special materials, and LIDAR ranging. Full article

Propagation properties represent a critical aspect of laser beams utilized in free space optical (FSO) communications. We examined the evolution characteristics of the electric field associated with partially coherent flat-topped beam rectangular arrays propagating bidirectionally through the turbulent atmosphere and plasma links. Utilizing the optical transmission matrix, alongside the second moment theory and Wigner distribution functions, we derived analytical expressions for both the intensity distribution and propagation factors of the partially coherent flat-topped beam rectangular arrays affected by the atmospheric turbulence and plasma disturbances. The numerical results indicate that appropriately selecting parameters such as beam order, transverse spatial coherence width, and beam width can effectively mitigate the adverse effects on propagation properties caused by the turbulent atmosphere and plasma. Our results have significant implications for FSO communications within specific environmental contexts. Full article

Sub-array-level digital arrays effectively diminish the computational complexity and sample demand of space-time adaptive processing (STAP), thus finding extensive applications in many airborne platforms. Nonetheless, airborne sub-array-level digital array radar still encounters pronounced performance deterioration in highly heterogeneous clutter environments due to inadequate training samples. To address this issue, a clutter-sensing-driven STAP approach for airborne sub-array-level digital arrays is proposed in this paper. Firstly, we derive a signal model of sub-array-level clutter sensing in detail and then further analyze the influence of the sidelobe characteristics of the conventional sub-array joint beam on clutter sensing. Secondly, a sub-array joint beam optimization model is proposed, which optimizes the sub-array joint beam into a wide beam with flat-top characteristics to improve the clutter-sensing performance in the beam sidelobe region. Finally, we decompose the complex optimization problem into two subproblems and then relax them into the low sidelobe-shaped beam pattern synthesisproblem and second-order cone programming problem, which can be effectively solved. The effectiveness of the proposed approach is validated in a real clutter environment through numerical experiments. Full article

We demonstrate a compact, partially end-pumping Innoslab laser based on a micro-cylindrical lens array homogenizer. A dimension of 12 × 0.4 mm² flat-top pumping line with a Gaussian intensity distribution across the line was simulated by the ray tracing technique. The rate equations considering the asymmetric transverse spatial distributions are theoretically developed. The simulation results are in good agreement with the experimental results. Preliminary data shows that for a pump power of 260 W, a maximum pulse energy of 15.7 mJ was obtained with a pulse width of 8.5 ns at a repetition frequency of 1 kHz. The beam quality M² factors in the unstable and stable directions were 1.732 and 1.485, respectively. The technology has been successfully applied to temperature and humidity profiling lidar and ozone lidar and has been productized, yielding direct economic value. Full article

Laser cladding provides advanced surface treatment capabilities for enhancing the properties of components. However, its effectiveness is often challenged by the formation of hot cracks during the cladding process. This study focuses on the formation mechanism and inhibition of hot cracks in a novel cobalt-based alloy (K688) coating applied to 304LN stainless steel via laser cladding. The results indicate that hot crack formation is influenced by liquid film stability, the stress concentration, and precipitation phases. Most hot cracks were found at 25°–45° high-angle grain boundaries (HAGBs) due to the high energy of these grain boundaries, which stabilize the liquid film. A flat-top beam, compared to a Gaussian beam, creates a melt pool with a lower temperature gradient and more mitigatory fluid flow, reducing thermal stresses within the coating and the fraction of crack-sensitive, high-angle grain boundaries (S-HAGBs). Finally, crack formation was significantly inhibited by utilizing a flat-top laser beam to optimize the process parameters. These findings provide a technical foundation for achieving high-quality laser cladding of dissimilar materials, offering insights into optimizing process parameters to prevent hot crack formation. Full article

Background/Objectives: Recurrent aphthous stomatitis (RAS) is one of the most common oral mucosal lesions and a very debilitating lesion, especially in paediatric and adolescent patients. The current pharmacotherapy offers a pain relief but not without side effects, and therefore photobiomodulation (PBM) can be an alternative therapy. To the authors’ best knowledge, no published study has explored the efficacy of λ 980 nm laser PBM in the management of all RAS subtypes in paediatric and adolescent patients, and therefore, this prospective observational clinical study was conducted to bridge this gap by evaluating λ 980 nm laser PBM efficacy in symptomatic RAS management in paediatric and adolescent patients. The objectives were to evaluate (1) pain intensity alleviation; (2) wound healing rate; (3) wound size closure; (4) a complete resolution; (5) evidence of recurrence; and (6) patients’ treatment satisfaction. Methods: The study’s variables were assessed at the following timepoints: T0: pre-treatment; T1: immediately after first PBM session; T2: 5 hours (h) post first PBM session (via telephone call); T3: immediately after second PBM session (three days post first PBM session); T4: three-day follow-up (after complete PBM treatments); T5: two-week follow-up; and T6: three-month follow-up. The following PBM dosimetry and treatment protocols were employed: λ 980 nm; 300 mW; 60 s; 18 J; CW; flattop beam profile of 1 cm² spot size; 18 J/cm²; and twice-a-week irradiation (72 h interval). Results: At T1, significant immediate pain intensity relief was reported. 33.33% recorded “4” and 66.67% reported “5” on the quantitative numeric pain intensity scale (NPIS), and this continued to improve significantly (83.33%) at T2. All the subjects reported “0” on the NPIS at T3, T4, T5 and T6. There was a significant reduction in the lesion surface area (>50% complete healing) at T3 compared to T0. Complete healing (100%) with no evidence of scarring and lesion recurrence observed at T4, T5 and T6. Very good patients’ satisfaction was reported at all timepoints. Conclusions: This is the first report demonstrating λ980 nm efficacy in all RAS subtype management in paediatric and adolescent patients with a 3-month follow-up, whereby its PBM dosimetry and treatment protocols were effective from scientific and practical standpoints, and hence multicentre RCTs with large data are warranted to validate its reproducibility and to enrich the knowledge of PBM application in all RAS subtypes. Full article

Photoacoustic imaging (PAI) is a rapidly developing biomedical imaging technology. Linear array-based photoacoustic tomography (LA-PAT) is one of the most popular configurations of cross-sectional PAI due to its simplicity and clinical translatability. However, when using an optical fiber for LA-PAT, the optical beam shape is deformed due to rapid divergence and, therefore, a larger area on the tissue is illuminated (and the illumination across the linear array is non-uniform), leading to the acquisition of PA signals outside the desired cross-section, which generates artifacts and degrades image resolution. A Powell lens is an optical element that converts a circular beam profile to a nearly linear flat-top profile. In this paper, a Powell lens is used to generate a uniform line illumination scheme that is evaluated with Zemax OpticStudio 2023 R1.02. The system is then characterized experimentally, and the performance is compared with a conventional illumination scheme in LA-PAT. Full article

In recent years, laser technology has made significant advancements, yet there are specific requirements for the energy concentration and uniformity of lasers in various fields, such as optical communication, laser processing, 3D printing, etc. Beam shaping technology enables the transformation of ordinary Gaussian-distributed laser beams into square or circular flat-top uniform beams. Currently, LCOS-based beam shaping algorithms do not adequately meet these requirements, and most of these algorithms do not simultaneously consider the impact of phase quantization and zero-padding, leading to a decrease in the practicality of phase holograms. To address these issues, this paper proposes a novel segmented beam shaping algorithm that combines iterative and simulated annealing approaches. This paper validated the reliability of the proposed algorithm through numerical simulations. Compared to other algorithms, the proposed algorithm can effectively reduce the root mean square error by an average of nearly 37% and decrease the uniformity error by almost 39% without a significant decrease in diffraction efficiency. Full article

A prospective observational case series included six patients who presented with discoloured upper and lower teeth extending from the right second premolar to the left second premolar. The photoactivation dosimetry and treatment protocol were as follows: λ 450 nm, 1 W, CW; flattop beam profile; 1 cm²; 15 J/spot; 10 irradiated spots; an irradiation time of 15 s/spot; three whitening cycles in a single session. Blanc One ULTRA⁺ was the bleaching agent. A visual analogue scale (VAS) was utilised to evaluate the pain intensity and dental hypersensitivity during treatment immediately after complete treatment (T1), 24 h (T2), and 8 h (T3) postoperatively, and at an 8-month follow-up timepoint (T4), whereas the dental colour shade change was assessed using the VITA colour shade guide pre-treatment (T0), T1, and T4. The Gingival index and modified Wong Baker faces scale were utilised to evaluate gingival inflammation and patients’ treatment satisfaction, respectively. Our findings revealed a reduction in the dental colour shade of the six cases between 2 and 10- fold (average of 3.5-fold) at T1 and maintained at T4, indicating significant improvement in the colour shade change with optimal outcomes. The percentage of this improvement for all the patients was ranged between 16.6% and 33.3%. At all timepoints, a “0” score was provided for pain intensity, dental hypersensitivity, and gingival inflammation. Our study demonstrates the feasibility and safety of a λ 450 nm laser delivered with a flattop handpiece to achieve optimal whitening outcomes without adverse effects. This offers a useful guide for dental clinicians for vital in-office tooth whitening. Extensive clinical studies with large data are warranted to validate our study protocol. Full article

A key issue of X-ray free-electron lasers is the quality of the photoelectron beams generated from a photocathode by laser pulses in the high-gradient RF gun. Controlling the shape of these laser pulses can strongly reduce the transverse emittance of the generated electron bunch. For this purpose, a laser pulseshaper at 515 nm is presented that can be used directly with alkali antimonide photocathodes for photoemission. The first results regarding generation and measurement of flattop and parabolic pulses as well as introduction of modulations for THz generation are presented and show the potential for emittance optimization with 3D ellipsoidal pulses with the proposed pulseshaper. The experiments are carried out for Cs${}_2$Te photocathodes, which require second harmonic generation of the shaped pulses and thus allow investigation of pulseshape preservation in nonlinear frequency conversion processes. Full article

Electronic toll collection (ETC), known as a non-stop toll collection system which can automatically realize payment by setting the identification antenna at the entrance, is always suffering from information exchange interruption caused by beam switching. A circularly polarized sector beam antenna array operating at 5.8 GHz with flat-top coverage is proposed, based on the weighted constrained method of the maximum power transmission efficiency (WCMMPTE). By setting the test receiving antennas at the specific angles of the ETC antenna array to be designed, constraints on the received power are introduced to control the radiation pattern and obtain the optimized distribution of excitations for antenna elements. A 1-to-16 feeding network, based on the microstrip transmission line theory is designed to feed a 4 × 4 antenna array. Simulation results show that the half-power beamwidth covers an angular range of −30° to 30° while the axial ratio is below 3dB, which meets the ETC requirements. Furthermore, the gain fluctuation among the needed range of −30° to 30° is lower than 0.7 dB, which is suitable for the ETC system to achieve a stable signal strength and uninterrupted communication. Full article

Peripheral facial paralysis (PFP) is a common condition where oxidative stress (OS) is involved in the pathophysiology of facial paralysis, inhibiting peripheral nerve regeneration, which can be featured in Bell’s palsy, Ramsay Hunt syndrome and Lyme disease. The current standard care treatments lack consensus and clear guidelines. Hence, the utilization of the antioxidant immunomodulator photobiomodulation (PBM) can optimize clinical outcomes in patients who are unresponsive to standard care treatments. Our study describes three unique cases of chronic PFP of various origins that were unresponsive to standard care treatments, but achieved a significant and complete recovery of facial paralysis following PBM therapy. Case presentations: Case #1: a 30-year-old male who presented with a history of 12 years of left-side facial paralysis and tingling as a result of Bell’s palsy, where all the standard care treatments failed to restore the facial muscles’ paralysis. Eleven trigger and affected points were irradiated with 1064 nm with an irradiance of ~0.5 W/cm² delivered with a collimated prototype flat-top (6 cm²) in a pulsed mode, with a 100 µs pulse duration at a frequency of 10 Hz for 60 s (s) per point. Each point received a fluence of 30 J/cm² according to the following treatment protocol: three times a week for the first three months, then twice a week for another three weeks, and finally once a week for the following three months. The results showed an improvement in facial muscles’ functionality (FMF) by week two, whereas significant improvement was observed after 11 weeks of PBM, after which the House–Brackmann grading scale (HBGS) of facial nerve palsy dropped to 8 from 13 prior to the treatment. Six months after PBM commencement, electromyography (EMG) showed sustainability of the FMF. Case #2: A five-year-old female who presented with a 6-month history of severe facial paralysis due to Lyme disease. The same PBM parameters were utilized, but the treatment protocol was as follows: three times a week for one month (12 consecutive treatment sessions), then the patient received seven more sessions twice a week. During the same time period, the physiotherapy of the face muscles was also delivered intensively twice a week (10 consecutive treatments in five weeks). Significant improvements in FMF and sustainability over a 6-month follow-up were observed. Case #3: A 52-year-old male who presented with severe facial palsy (Grade 6 on HBGS) and was diagnosed with Ramsay Hunt syndrome. The same laser parameters were employed, but the treatment protocol was as follows: three times a week for three weeks, then reduced to twice a week for another three weeks, then weekly for the next three months. By week 12, the patient showed a significant FMF improvement, and by week 20, complete FMF had been restored. Our results, for the first time, showed pulsed 1064 nm PBM delivered with a flat-top handpiece protocol is a valid and its treatment protocol modified, depending on the origin and severity of the condition, which is fundamental in optimizing facial paralysis recovery and alleviating neurological symptoms. Further extensive studies with large data are warranted to validate our PBM dosimetry and treatment protocols. Full article

Light detection and ranging (LiDAR) technology, a cutting-edge advancement in mobile applications, presents a myriad of compelling use cases, including enhancing low-light photography, capturing and sharing 3D images of fascinating objects, and elevating the overall augmented reality (AR) experience. However, its widespread adoption has been hindered by the prohibitive costs and substantial power consumption associated with its implementation in mobile devices. To surmount these obstacles, this paper proposes a low-power, low-cost, single-photon avalanche detector (SPAD)-based system-on-chip (SoC) which packages the microlens arrays (MLAs) and a lightweight RGB-guided sparse depth imaging completion neural network for 3D LiDAR imaging. The proposed SoC integrates an 8 × 8 SPAD macropixel array with time-to-digital converters (TDCs) and a charge pump, fabricated using a 180 nm bipolar-CMOS-DMOS (BCD) process. Initially, the primary function of this SoC was limited to serving as a ranging sensor. A random MLA-based homogenizing diffuser efficiently transforms Gaussian beams into flat-topped beams with a 45° field of view (FOV), enabling flash projection at the transmitter. To further enhance resolution and broaden application possibilities, a lightweight neural network employing RGB-guided sparse depth complementation is proposed, enabling a substantial expansion of image resolution from 8 × 8 to quarter video graphics array level (QVGA; 256 × 256). Experimental results demonstrate the effectiveness and stability of the hardware encompassing the SoC and optical system, as well as the lightweight features and accuracy of the algorithmic neural network. The state-of-the-art SoC-neural network solution offers a promising and inspiring foundation for developing consumer-level 3D imaging applications on mobile devices. Full article