Blue Beam Research Articles

Tandem neural network-assisted inverse design of highly efficient diffractive slanted waveguide grating.

Virtual reality devices featuring diffractive grating components have emerged as hotspots in the field of near-to-eye displays. The core aim of our work is to streamline the intricacies involved in devising the highly efficient slanted waveguide grating using the deep-learning-driven inverse design technique. We propose and establish a tandem neural network (TNN) comprising a generative flow-based invertible neural network and a fully connected neural network. The proposed TNN can automatically optimize the coupling efficiencies of the proposed grating at multi-wavelengths, including red, green, and blue beams at incident angles in the range of 0°-15°. The efficiency indicators manifest in the peak transmittance, average transmittance, and illuminance uniformity, reaching approximately 100%, 92%, and 98%, respectively. Additionally, the structural parameters of the grating can be deduced inversely based on the indicators within a short duration of hundreds of milliseconds to seconds using the TNN. The implementation of the inverse-engineered grating is anticipated to serve as a paradigm for simplifying and expediting the development of diverse types of waveguide gratings.

In Situ Synchrotron Investigations of Beam Diameter Influence on Vapor Capillary Formation during Laser Beam Welding of Copper Alloy with a Blue Laser Beam Source

Laser beam welding as a reliable tool for high-precision joining of batteries or microelectronics is more and more the choice for achieving reproducible results in production processes. In addition to a high automation capability, the precise control of the energy deposition into the material plays an important role, especially when highly reflective materials, such as copper or aluminum, must be welded together. Alongside the use of highly brilliant fiber lasers in the near-infrared range with a focal diameter of a few tens of micrometers, diode lasers in the wavelength range of 445 nm are increasingly being used. Here, beam diameters of a few hundred micrometers can be achieved. With a wavelength of 445 nm, the absorptivity in copper can be increased by more than a factor of 10 compared to a near-infrared laser beam sources in solid state at room temperature. This paper presents the in situ X-ray observation of laser welding processes on CuSn6 with a laser beam source with a wavelength of 445 nm using synchrotron radiation at DESY Petra III Beamline P07 EH4 in Hamburg, Germany. For the experiments, the laser radiation was focused via two separate optics to focal diameters of 362 µm and 609 µm. To characterize the dynamics of the vapor capillaries depending on the different focal diameters dF, the parameters were varied with respect to laser power PL and feed rate v. For the investigations, a synchrotron beam of 2 × 2 mm2 in size with a photon energy of 89 keV was used, and the material samples were analyzed by means of phase-contrast videography to show the boundaries between solid, liquid, and gaseous material phases. The results of this paper show the welding depths achieved and how the geometry of the vapor capillary behaves by changing the focal diameter, laser power and feed rate.

Process comparison of laser deep penetration welding in pure nickel using blue and infrared wavelengths

AbstractLaser sources with wavelengths in the visible blue spectrum are suitable for heat conduction mode welding of materials like copper and nickel due to the significantly increased Fresnel absorption compared to infrared laser radiation. Recently, blue laser sources with 445 nm wavelength have become available with sufficient power and beam parameters to exceed the intensity threshold for laser deep penetration welding. In laser beam deep penetration welding, the total absorption is significantly increased due to the multiple reflections in the keyhole compared to heat conduction mode welding. However, since the absorbed energy per reflection inside the keyhole is wavelength-dependent, it can be hypothesized that the choice of laser wavelength causes changes in the local energy distribution inside the keyhole, changing the keyhole dynamics. To investigate this, laser beam deep penetration welding experiments were carried out on 2.4068 pure nickel using an infrared laser source and a blue laser source with comparable beam properties. The experiments were monitored and compared by a multi-sensor setup and metallographic analyses. This setup included measurements of airborne acoustic emissions and two high-speed video cameras for spatter tracking and tracking of the keyhole area. The use of a blue laser beam led to a lower spatter quantity, an increase of porosity and a significant change of acoustic emissions, proving the hypothesis for pure nickel.

Interaction of Culture Medium and Artificial Light Type on Pigmentation of Micro-Propagated Opuntia Plants

Opuntia is recognized economically as a significant crop for its nutritional, functional, and therapeutic properties and its potential in the pharmaceutical, cosmetic, and bioenergy industries. Opuntia is conventionally propagated by seed or vegetative propagation via rooted scions or grafting. However, multiplication procedures are insufficient for extensive spreading. One of the alternative techniques is in vitro. For this reason, the objective was to evaluate the growth of different components combined with light conditions to induce callus, embryogenesis, and the possible synthesis of a component in the genus Opuntia. The existence of genes involved in pigment synthesis in genotypes of different fruit colors was complementarily analyzed. In this study, we used different combinations of fructose (2 g/L) with prickly pear juice (2 mL/L), mannitol (4 g/L), silver nitrate (AgNO3: 1 mg/L), 2,4-dichlorophenoxyacetic acid (2,4-D: 2 mg/L), and indole-3-acetic acid (IAA: 1 g/L), with white, blue, and red LEDs (light-emitting diodes) and laser beams. These explants yielded sufficient contents of simple phenols, gallic acid equivalents (GAE: 2283.30 ± 6.29 mg/100 g), and coumaric (2155.0 ± 35.0 mg/100 g) and ferulic (2176 ± 27.9 mg/100 g) acids for the genotype Tapón aguanoso, and chlorogenic acid (CGA: 380.22 ± 22.05 mg/100 g) for the Copena V1 genotype. Upon analyzing the genotypes of different fruit pigmentations, we also observed the following: enzyme 4,5 estradiol dioxygenases can be present in all genotypes (regardless of pigmentation); enzyme 5,3 glucosyltransferases (GTs) could be induced in pigment synthesis in the genotypes of orange to purple fruits. Sequencing primer-amplified fragments for GT showed high similarity to uridine diphospho (UDP)-glucose from other species. This allows us to infer that it is possible to obtain products of high therapeutic value in the near future under controlled conditions.

Hands-on visualization of the effect of fictitious forces with a laser pointer

Inertial motion looks like accelerated motion when observed from the point of view of a non-inertial reference frame. A non-inertial observer can then describe the trajectories by introducing fictitious forces, like the centrifugal and Coriolis forces, that arise from the coordinate change between reference frames. This well-known fact is part of the typical Physics syllabus for undergraduate scientists and engineers, and a number of interesting classroom demonstrations have been discussed in the literature. We present a complementary possibility for the visualization of the effect of fictitious forces by shining a blue laser beam on a rotating platform covered with a phosphorescent vinyl sheet. The laser can be moved in order to simulate inertial motion in the laboratory frame for the trajectory of the laser spot. This gets immediately imprinted in the rotating phosphorescent material resulting in non-inertial trajectories that can be readily observed and compared to the dynamics governed by fictitious forces. Since friction is not considered, this hands-on activity can be considered as a direct demonstration of the effect of pure fictitious forces in and out of the classroom. The approach is simple, inexpensive, fast and non-destructive, and can therefore be very convenient for active lecture demonstrations or individual activities of students. We also describe some educational possibilities of how to use the procedure in the classroom or in the laboratory.

Super-resolution multicolor fluorescence microscopy enabled by an apochromatic super-oscillatory lens with extended depth-of-focus

Planar super-oscillatory lens (SOL), a far-field subwavelength-focusing diffractive device, holds great potential for achieving sub-diffraction-limit imaging at multiple wavelengths. However, conventional SOL devices suffer from a numerical-aperture-related intrinsic tradeoff among the depth of focus (DoF), chromatic dispersion and focusing spot size. Here, we apply a multi-objective genetic algorithm (GA) optimization approach to design an apochromatic binary-phase SOL having a prolonged DoF, customized working distance (WD), minimized main-lobe size, and suppressed side-lobe intensity. Experimental implementation demonstrates simultaneous focusing of blue, green and red light beams into an optical needle of ~0.5λ in diameter and DOF > 10λ at WD = 428 μm. By integrating this SOL device with a commercial fluorescence microscope, we perform, for the first time, three-dimensional super-resolution multicolor fluorescence imaging of the “unseen” fine structures of neurons. The present study provides not only a practical route to far-field multicolor super-resolution imaging but also a viable approach for constructing imaging systems avoiding complex sample positioning and unfavorable photobleaching.

Mode analysis and measurement of single-emitter blue diode lasers.

Recent developments in blue diode lasers have been hindered by the challenge of balancing high power with beam quality. Typically, high-power blue diode lasers exhibit low beam quality due to the output of multiple longitudinal and lateral modes. A promising solution to this problem is to control and shape the blue beam mode output from a single emitter. To achieve this, it is key to have full knowledge of the properties of the output mode under various conditions. In this paper, we explore the mode characteristics of an InGaN single-emitter laser diode that has a typical wavelength of 447nm (wavelength range: 440-455nm). We measure and analyze the near-field mode using the box model, finding that the near-field mode excited by the blue diode laser overlapped near the threshold current of 0.32A. The p=2 order lateral mode of longitudinal mode groups 3 and 4 overlapped with the p=4 order mode of adjacent longitudinal mode groups. Through a Fourier transform of the near-field mode, we obtain the far-field mode and reveal a spatial law of mode distribution that is similar to the near-field mode. As the current is gradually increased and approaches the rated current of the laser diode, the near-field mode continuously has new longitudinal mode groups added to the long-wavelength side of the starting group. We observe an increase in the number of longitudinal mode groups and high-order lateral modes, leading to more mode overlaps. Additionally, we observe a gradual shift in the peak energy of the modes to the long-wavelength side. This study reveals the mode characteristics of broad-area blue diode lasers, providing crucial information to achieve high-quality laser beams in such systems.

A Study on the Development of a White Light Source Module for a Large-Capacity Searchlight Using a Blue Laser Diode

In this paper, a large-capacity white light source module using a high-power blue laser diode and a reflective spaced phosphor was designed. The reflective spacing phosphor ensured thermal stability. The proposed white light module is a reflective phosphor structure with a bi-directional optical system based on a rhombus prism lens. The rhombus prism optical system can greatly narrow the blue laser beam width and a long-wavelength band-pass filter of 500 nm or more is applied to change the movement path of the laser beam and transmit white light excited by the phosphor. A dichroic filter was applied to the fold mirror part and a planar convex lens was designed to focus the blue laser beam so that the phosphor was irradiated. Finally, a high-power white light source is obtained from the pre-optics unit to which the dichroic filter is applied. In order to use the proposed white light source as a searchlight, a divergence angle of 4° or less is required. For this implementation, a large-area collimating lens combining an aspheric condensing lens and an achromatic lens was applied. It was confirmed that the divergence angle of 4 degrees or less was satisfied at the focal length (FL) of 38.5 to 42.5 mm of the optical lens of the laser white light module emitter and the collimating optical system.

Non-Mechanical Multiplexed Beam-Steering Elements Based on Double-Sided Liquid Crystal Metasurfaces

We propose, optimize, fabricate and test beam-steering elements based on double-sided liquid-crystal (LC) metasurfaces allowing for diffractive and spectral multiplexing, and thus covering three different beam deflection directions each. While straightforward parallel design requires one diffractive beam-steering element per a direction determined by Bragg’s law, double-sided LC-metasurfaces are remarkably flexible and allow optimization for three operation modes at different applied voltages: zero-voltage mode with dominant +1 order red light and +2 order blue light diffraction; intermediate mode at 1.4–1.6 V voltage with dominant +1 order blue light diffraction; and transparent mode at 5 V voltage. We comprehensively study three such elements with 6, 8 and 10 micrometer periods and verify their capability of deflecting blue and red light beams with 40–70% efficiencies in nine target directions with 10 ms characteristic switching times.

Demonstrating Mechanical Beats on Phosphorescent Foil in Real Time

The interference pattern between two harmonic oscillations with slightly different frequencies are called beats. The beats, as a combined motion, have two different periods, one approximately equal to the period of the original oscillations, and another that is significantly longer and is related to the variable amplitude of the motion. The main objective of this presented work is to engage students’ attention and demonstrate in a simple way the concept of mechanical beats as a resultant motion of combined oscillations, but also to experience it through a visual projection. The proposed experimental setup is constructed in a way that satisfies both objectives and it consists of two parts that allow us to demonstrate in real time the combination of two harmonic motions. In the first part, the resultant motion is generated by the oscillations of two parallel rulers equipped with mirrors, and in the second part the visual demonstration of the beat occurs on a phosphorescent rotating foil by using a blue violet laser beam.

Effective electromagnetic interference shielding properties of micro-truss structured CNT/Epoxy composites fabricated based on visible light processing

In this work, a novel self-writing visible light processing method is employed to fabricate self-propagating polymer waveguide based porous epoxy matrix, which subsequently turns into micro-truss structured carbon nanotube (CNT)/epoxy conductive composites through CNT dip-coating. It is discovered that, by illuminating a photosensitive epoxy pre-polymer with intersecting blue LED beams simultaneously for only 15 min, 3D micro-truss structured epoxy matrix with thickness of ∼1.8 mm is obtained. When incorporating CNTs with a low content of 1.20 vol%, the micro-truss structured CNT/epoxy composites exhibit high electrical conductivity of 62.93 S/m. These composites show absorption-dominated shielding mechanism, and high electromagnetic interference (EMI) shielding efficiency (SE) of 34.5 dB is obtained in the X band with 1.20 vol% of CNT. The specific shielding efficiency (SSE) of the CNT/epoxy composites is up to 100 dB cm3 g−1, and the corresponding SSE/t eliminating the effect of thickness is up to 535 dB cm2 g−1, which is much higher than that reported in other studies with the same CNT contents. This work provides a quick and scalable technique to prepare polymer matrix with ordered porous structures, and would also inspire and guide the fabrication of well-ordered porous conductive polymer composites with superior EMI shielding performances.

Laser-assisted 3D printing of carbon fibre reinforced plastic parts

Laser-assisted 3D printing process of fabricating carbon fibre reinforced plastic parts by sandwiching fibres between plastic layers was developed to improve the bond strength of the fibres to the plastic layers. Here, bundled carbon fibres are placed on the 3D-printed lower plastic layer, and the upper plastic layer is deposited on the fibres. Next, the two layers sandwiching the fibres are laser-heated using a blue diode laser beam. The plastic colour changed the heating temperature at the interface between the fibres and the plastic layer due to the transmittance and absorption phenomena; the translucent layer having high transmittance was most appropriate. The strength and rigidity of the 3D-printed carbon fibre reinforced plastic parts were improved by laser heating. Carbon fibre reinforced plastic parts having closed cross-sections are manufactured and strengthened by optimising the sandwiched fibre orientation. Besides, a tailored part locally reinforced by the carbon fibres is easily 3D-printed, and the deformation behaviours are observed.

Trans-spectral vector beam nonlinear conversion via parametric four-wave mixing in alkali vapor.

Coherent frequency conversion of vector beams (VBs) without distorting their intensity profile or spatial polarization distribution is important for novel applications in quantum and classical regimes. Here, we experimentally and theoretically investigate VB transfer from near-infrared to blue light using a Sagnac interferometer, combining the parametric four-wave mixing process in atomic vapor. The vector probe beam is converted into a completely different wavelength, and the vector mode of the generated blue beam is highly similar to the incident probe beam. These results may provide a feasible solution for communication interfaces in classical and quantum science fields based on atomic ensembles.

High power continuous laser at 461 nm based on a compact and high-efficiency frequency-doubling linear cavity.

A Watt-level continuous and single frequency blue laser at 461 nm is obtained by frequency-doubling an amplified diode laser operating at 922 nm via a LBO crystal in a resonant Fabry-Pérot cavity. We achieved a best optical conversion efficiency equal to 87% with more than 1 W output power in the blue, and limited by the available input power. The frequency-converted beam is characterized in terms of long term power stability, residual intensity noise, and geometrical shape. The blue beam has a linewidth of the order of 1 MHz, and we used it to magneto-optically trap 88Sr atoms on the 5s2 1S0 - 5s5p 1P1 transition. The low-finesse, linear-cavity doubling system is very robust, maintains the lock for several days, and is compatible with a tenfold increase of the power levels which could be obtained with fully-fibered amplifiers and large mode area fibers.

Modeling mixing dynamics in uncovered baffled and unbaffled stirred tanks

AbstractThis paper presents results of measurements performed in uncovered baffled and unbaffled stirred tanks. The Laser Doppler Anemometry (LDA) set consists of a 300 mW argon‐ion laser generating two pairs of blue and green beams. Additionally, three turbulence models are verified to simulate mixing dynamics in uncovered baffled and unbaffled stirred tanks. Simulations are performed using both the steady‐ and the transient‐state approach. The unbaffled tank was modeled using both the single‐ and the multiphase approaches. The cited correlations of the central vortex depth are used to verify the multiphase calculations. In order to reduce the computational time, a simplified numerical model is proposed. It assumes a single‐phase simulation without the central vortex. The flow fields below the central vortex level are compared between the single‐ and the multiphase approach. The simplified model can be used both to design and optimize the mixing process.

Exit Pupil Expansion Based on Polarization Volume Grating

In this paper, we demonstrate a waveguide display structure which can realize a large field of view on a two-dimensional plane and a larger exit pupil size at the same time. This waveguide structure has three polarization volume gratings as its coupling elements. We use Zemax to simulate the effect of monochromatic and full-color two-dimensional exit pupil expansion and actually prepared a monochromatic waveguide with a two-dimensional exit pupil expansion structure. For the red, green, and blue light beams, it can achieve a large diffraction angle and can achieve diffraction efficiency of more than 70%. The waveguide structure shown can have an angle of view of 35° in the horizontal direction and 20° in the vertical direction, and an exit pupil of 18 mm long and 17 mm wide was achieved at the same time. As measured, the overall optical efficiency was measured as high as 118.3 cd/m2 per lumen with a transparency of 72% for ambient light.

16.9 MW, efficient 486.1 nm blue optical parametric oscillator using single BBO crystal

A single-resonant beta barium borate crystal optical parametric oscillator with high pulse energy output at the H-β Fraunhofer line of 486.1 nm was demonstrated. Pumped by a single-frequency 355 nm ultraviolet pulsed laser at 10 Hz repetition rate with maximum pulse energy of 411 mJ, maximum output energy of 162 mJ blue laser pulse at 486.1 nm was successfully obtained from a plano-concave cavity with a 40% output coupler, the corresponding optical-to-optical conversion efficiency was up to 39.4%, and the pulse width was around 9.6 ns. The blue laser beam size was 4.4 mm × 5.1 mm with the beam divergence angles of θx = 2.2 mrad and θy = 2.5 mrad. The peak power of output blue laser was 16.9 MW, and the signal linewidth was around 0.34 nm.

Nonlinear optical and photoacoustic properties of aqueous crystalline hemoglobin. Towards facile detection of hemoglobin concentration in blood

In this work, nonlinear optical properties of hemoglobin are studied under the irradiation of a blue LED laser beam. The z-scan setup is applied in order to determine nonlinear optical responses. Photoacoustic waves are created in a hearable sound region. Sounds are recorded by a microphone and analyzed by using Fourier transform to evaluate the sonic frequencies. The suspensions of hemoglobin in water are prepared in the range of 120–160 mg/mL that is in the range of hemoglobin concentration in blood. It is found that the amplitude of photoacoustic (PA) signals and nonlinear absorption coefficients depend directly to the hemoglobin concentration. On the other hand, blood of rabbit is studied using this method and results are compared with the crystalline hemoglobin findings. It is concluded that the frequency domain of photoacoustic waves created by hemoglobin is similar to that observed for the blood sample. It means that the main portion of photoacoustic response in blood is due to its hemoglobin content and amplitude of the sonic signals is directly related to the concentration of hemoglobin. FT-IR studies confirmed that the vibrational levels of hemoglobin had no a significant effect on the recorded PA signals and the main PA effect has been originated from explosion of the micro- and nano-bubbles. Moreover, from the UV–Vis spectrum of hemoglobin, it can be conferred that absorption of the blue photons by the porphyrin ring leads to the evaporation of water molecules and generation of the mentioned bubbles responsible for the created sonic waves after explosion. This study would be considered as a fast and simple method to determine hemoglobin concentration in the real blood samples using nonlinear optical and photoacoustic characterizations.

3D structuring of dense alumina ceramics using fiber-based stereolithography with interparticle photo-cross-linkable slurry

In this paper, we demonstrated optical fiber-based stereolithography of alumina ceramics using concentrated slurry with low monomer content for enabling rapid firing of the printed green objects. Photo-cross-linkable alumina slurries were designed using a partial complex of polyethyleneimine and oleic acid (PEI-OA) as reactive polymer dispersants and multifunctional acrylates (MA) as monomers. The effects of the processing parameters, such as oleic acid contents, MA contents, particle contents, and particle sizes, on photocuring properties were systematically investigated. We found that the reactive amine sites of PEI-OA attached to particles and MA volume concentrations in the liquid phase were the most dominant factors to improve the photocuring properties. Therefore, a slurry composed of larger alumina particles with higher solid contents and PEI-OA with lower OA contents was more favorable for achieving photocuring under reduced MA content. The designed photocurable slurry was then applied to ceramic stereolithography using optical fiber. 3D alumina green parts were drawn by passing blue laser beam through an optical fiber in a droplet of photocuring slurry and dense sintered alumina were successfully fabricated by rapid drying (<10 min) and debinding (<1 h) without any structural collapse.

Employing a Laser Headlight Electrical System to Measure and Calculate Electro-Optic Conversion Efficiencies of Blue-Beam Laser Diodes

In this study, a laser headlight electrical system was developed and implemented to measure and compare the electro-optic characteristics of the blue-beam laser diodes (BBLDs). To observe different temperatures (from negative to positive temperatures) that cause optical output power (OOP) and electrical power variations of the BBLDs, BBLDs were placed in an ambient temperature testing chamber, and the electro-optic characteristics of the BBLDs were measured to estimate the electro-optic conversion efficiencies. The different OOPs and electro-optic conversion efficiencies at different temperatures can be obtained when OOP adjustment was performed by average current and low-frequency pulse-duty cycle modulation technologies. Moreover, this study developed a human–machine interface using the LabVIEW software; therefore, the laser headlight electrical system can be controlled and monitored by a computer with the controller area network (CAN) bus communication. Finally, the prototype of the laser headlight electrical system was achieved, and three BBLDs were driven; furthermore, the white light of the headlight can be produced by mixing blue laser beams with a yellow fluorescence ceramic wafer.