Laser Illumination Research Articles

Novel strategy: Fabrication of phosphor-in-glass via modulation of glass composition for dynamic laser illumination

Novel strategy: Fabrication of phosphor-in-glass via modulation of glass composition for dynamic laser illumination

Photophysical Investigation of Dyes and Dye-PMMA Systems: Insights into Absorption, Emission, and Charge Transfer Mechanisms.

The photophysical properties of five dyes, i.e., perylene, anthracene, aminoanthracene, 1,6-diphenylhexatriene, and 7-diethylamino-4-methylcoumarin, in solvent and attached to the poly(methyl methacrylate) (PMMA) polymer, were studied via DFT and TD-DFT calculations. Their absorption and emission spectra were calculated, while for the PMMA-dye systems, their absorption spectra were measured experimentally, in good agreement with the calculated ones. In the PMMA-dye systems, charge transfer from the dye to PMMA was observed, and in the case of perylene, electron transfer from its ground state was also observed. It was found that the PMMA-dye systems can interact photochemically via laser illumination, and provided that the charge transfer will be enhanced by using the appropriate laser parameters, the systems may be candidates for the design of materials for specific nanopatterning needs.

Synthesis of 2‐Inch Hexanary Medium‐Entropy Alloy Monolayer Via Chemical Vapor Deposition with Superior Photoelectric Properties

AbstractMixing entropy engineering is a promising strategy to tune the physical and chemical properties of materials. Although high‐entropy in van der Waals bulk solids have been reported, entropy engineering in 2D monolayers remains unconquered. In this work, the epitaxial growth of a 2‐inch 1T″ hexanary medium‐entropy alloy monolayer (ReaWbMocIndSxSey) is reported via the chemical vapor deposition method. The atomic structure and chemical composition are confirmed by X‐ray photoelectron spectroscopy, scanning transmission electron microscopy, energy dispersive X‐ray spectroscopy and electron energy loss spectroscopy, illustrating the uniform distribution of the six elements. The hexanary medium‐entropy alloy photodetectors show an ultrawide photo‐response from visible to near‐infrared wavelengths with a responsivity of 100.2 A W−1 under 520 nm laser illumination. Meanwhile, the hexanary medium‐entropy alloy monolayer exhibits excellent electrocatalytic hydrogen production with an overpotential of 176.6 mV in dark. Importantly, an overpotential of 43.7 mV at 10 mA cm−2 with a lowered Tafel slope of 51.9 mV dec−1 under 520 nm laser irradiation is obtained due to the excellent conductivity. The work opens a new way to design mixing = entropy alloys and enables the application of transition metal dichalcogenides in photo‐enhanced electrocatalytic hydrogen production.

Speckle-illumination spatial frequency domain imaging with a stereo laparoscope for profile-corrected optical property mapping.

Laparoscopic surgery presents challenges in localizing oncological margins due to poor contrast between healthy and malignant tissues. Optical properties can uniquely identify various tissue types and disease states with high sensitivity and specificity, making it a promising tool for surgical guidance. Although spatial frequency domain imaging (SFDI) effectively measures quantitative optical properties, its deployment in laparoscopy is challenging due to the constrained imaging environment. Thus, there is a need for compact structured illumination techniques to enable accurate, quantitative endogenous contrast in minimally invasive surgery. We introduce a compact, two-camera laparoscope that incorporates both active stereo depth estimation and speckle-illumination SFDI (si-SFDI) to map profile-corrected, pixel-level absorption ( ), and reduced scattering ( ) optical properties in images of tissues with complex geometries. We used a multimode fiber-coupled 639-nm laser illumination to generate high-contrast speckle patterns on the object. These patterns were imaged through a modified commercial stereo laparoscope for optical property estimation via si-SFDI. Compared with the original si-SFDI work, which required images of randomized speckle patterns for accurate optical property estimations, our approach approximates the DC response using a laser speckle reducer (LSR) and consequently requires only two images. In addition, we demonstrate 3D profilometry using active stereo from low-coherence RGB laser flood illumination. Sample topography was then used to correct for measured intensity variations caused by object height and surface angle differences with respect to a calibration phantom. The low-contrast RGB speckle pattern was blurred using an LSR to approximate incoherent white light illumination. We validated profile-corrected si-SFDI against conventional SFDI in phantoms with simple and complex geometries, as well as in a human finger in vivo time-series constriction study. Laparoscopic si-SFDI optical property measurements agreed with conventional SFDI measurements when measuring flat tissue phantoms, exhibiting an error of 6.4% for absorption and 5.8% for reduced scattering. Profile-correction improved the accuracy for measurements of phantoms with complex geometries, particularly for absorption, where it reduced the error by 23.7%. An in vivo finger constriction study further validated laparoscopic si-SFDI, demonstrating an error of 8.2% for absorption and 5.8% for reduced scattering compared with conventional SFDI. Moreover, the observed trends in optical properties due to physiological changes were consistent with previous studies. Our stereo-laparoscopic implementation of si-SFDI provides a simple method to obtain accurate optical property maps through a laparoscope for flat and complex geometries. This has the potential to provide quantitative endogenous contrast for minimally invasive surgical guidance.

Energy-Efficient Deployment of Laser Illumination for Rotating Vertical Farms

As the global population grows, vertical farming offers a promising solution by using vertically stacked shelves in controlled environments to grow crops efficiently within urban areas. However, the shading effects of farm structures make artificial lighting a significant cost, accounting for approximately 67% of total operational expenses. This study presents a novel approach to optimizing the deployment of laser illumination in rotating vertical farms by incorporating structural design, light modeling, and photosynthesis. By theoretically analyzing the beam pattern of laser diodes and the dynamics in the coverage area of rotating farm layers, we accurately characterize the light conditions on each vertical layer. Based on these insights, we introduce a new criterion, cumulative coverage, which accounts for both light intensity and coverage area. Then, an optimization framework is formulated, and a swarm intelligence algorithm, Differential Evolution (DE) is used to solve the optimization while considering the structural and operational constraints. It is found that tilting lights and placing them slightly off-center are more effective than traditional vertically aligned and center-aligned deployment. Our results show that the proposed strategy improves light coverage by 4% compared to the intensity-only optimization approach, and by 10% compared to empirical methods. This study establishes the first theoretical framework for designing energy-efficient artificial lighting deployment strategies, providing insights into enhancing the efficiency of vertical farming systems.

High-resolution compressive 3D imaging through phase ranging with a single-pixel photodetector

Single-pixel three-dimensional (3D) imaging is of great potential to the light detection and ranging (Lidar) system. Combining high-precision ranging with compressed sensing (CS) imaging enables the acquisition of high-resolution and accurate depth maps under non-scanning conditions. In this study, we present that a phase ranging system can be combined perfectly with the CS algorithm perfectly for real 3D imaging through only two reconstructions, along with high accuracy and fast depth measurement. A structured detection architecture based on amplitude-modulated continuous-wave laser illumination and single-pixel detector with high-precision 3D image reconstruction at 128 × 128 resolution using only a 5% sampling rate were used. The minimum identifiable target width of this system is 0.2 cm, corresponding to a resolving angle of 0.33 mrad. This system paves the reality of high-precision and fast 3D imaging for continuous-wave Lidar detections.

Engineering Floquet Moiré Patterns for Scalable Photocurrents.

While intense laser irradiation and moiré engineering have independently proven powerful for tuning material properties on demand in condensed matter physics, their combination remains unexplored. Here we exploit tilted laser illumination to create spatially modulated light-matter interactions, leading to two striking phenomena in graphene. First, using two lasers tilted along the same axis, we create a quasi-1D supercell hosting a network of Floquet topological states that generate controllable and scalable photocurrents spanning the entire irradiated region. Second, by tilting lasers along orthogonal axes, we establish a 2D polarization moiré pattern giving rise to closed orbital propagation of Floquet states, reminiscent of bulk Landau states. These features, imprinted in the bulk of the irradiated region and controlled through laser wavelength and tilt angles, establish a new way for engineering quantum states through spatially modulated light-matter coupling.

Enhanced performance and long-term stability of 2D photodetectors through hexagonal boron nitride encapsulation

Two-dimensional (2D) semiconductor materials, such as molybdenum disulfide (MoS2), demonstrate considerable potential for optoelectronic applications, largely due to their atomic thickness, tunable bandgap, and capacity for heterostructure integration. Nevertheless, the development of 2D photodetectors that can achieve high responsivity, a fast response time, and long-term stability remains a significant challenge. The present study is a systematic investigation of the effects of top and bottom encapsulation with hexagonal boron nitride (h-BN) on the performance and stability of 2D photodetectors. By employing a dry transfer process to fabricate a high-quality h-BN/MoS2/h-BN structure, we provide effective protection against environmental degradation. The encapsulated devices exhibited a responsivity increase of one to two orders of magnitude under 532 nm laser illumination, in comparison to those without encapsulation. Additionally, the rise and decay times were markedly reduced, by approximately two orders of magnitude, from 0.538 and 3.43 ms to 23.1 and 99.6 μs, respectively. Moreover, the devices demonstrated sustained performance over a 60-day storage period, with response times remaining faster than pre-encapsulation levels. This study highlights the potential of h-BN encapsulation for enhancing both the performance and stability of 2D photodetectors, advancing the development of more reliable optoelectronic devices.

Angular dependence of random laser emission by using ZnO-CuO heterostructure as scatterer and its applications in biocompatible imaging.

The angular dependence of random laser (RL) generation in a commercially available rhodamine 6G (Rh6G) dye has been demonstrated using ZnO-CuO heterostructure as passive scatterers. The grass-like superstructure formed at a 1M:1M molar ratio of ZnO-CuO significantly enhances scattering, resulting in RL spikes with a full width at half maximum (FWHM) of just a few nanometer and a noticeable reduction in the RL threshold. RL emission spectra were collected over an angular spread of 0-180 degrees, revealing a remarkable shift in RL emission from 566nm to 580nm. Additionally, we explored RL using a biological extract from Caesalpinia sappan L (Biancaeasappan L) and demonstrated speckle-free imaging with an affordable handheld microscope called the Foldscope. The biocompatibility of the wood extract shows significant potential for applications in speckle-free imaging. We had assessed the Pearson correlation coefficient between images captured under LED, RL, and conventional laser illumination. It is observed that the value of the coefficient becomes the lowest under RL illumination which confirms the formation of high-resolution and artifact-free images.

Photoreconfigurable Metasurface for Independent Full-Space Control of Terahertz Waves.

We present a novel photoreconfigurable metasurface designed for independent and efficient control of electromagnetic waves with identical incident polarization and frequency across the entire spatial domain. The proposed metasurface features a three-layer architecture: a top layer incorporating a gold circular split ring resonator (CSRR) filled with perovskite material and dual C-shaped perovskite resonators; a middle layer of polyimide dielectric; and a bottom layer comprising a perovskite substrate with an oppositely oriented circular split ring resonator filled with gold. By modulating the intensity of a laser beam, we achieve autonomous manipulation of incident circularly polarized terahertz waves in both transmission and reflection modes. Simulation results demonstrate that the metasurface achieves a cross-polarized transmission coefficient of 0.82 without laser illumination and a co-polarization reflection coefficient of 0.8 under laser illumination. Leveraging the geometric phase principle, adjustments to the rotational orientation of the reverse split ring and dual C-shaped perovskite structures enable independent control of transmission and reflection phases. Furthermore, the proposed metasurface induces a +1 order orbital angular momentum in transmission and +2 order in reflection, facilitating beam deflection through metasurface convolution principles. Imaging using metasurface digital imaging technology showcases patterns "NUIST" in reflection and "LOONG" in transmission, illustrating the metasurface design principles via the proposed metasurface. The proposed metasurface's capability for full-space control and reconfigurability presents promising applications in advanced imaging systems, dynamic beam steering, and tunable terahertz devices, highlighting its potential for future technological advancements.

Dual-function switchable terahertz surface plasmon device driven by a GST metasurface

Surface plasmons (SPs) are one of the most effective information carriers for on-chip systems due to their two-dimensional propagation properties. Benefitting from the highly flexible designability, metasurfaces have emerged as a promising route in realizing SP devices. However, related studies are mainly focused on passive devices. Here, by introducing nonvolatile phase-change material Ge2Sb2Te5 (GST) into the metasurface design, we experimentally demonstrate a dual-function switchable SP device in the terahertz regime. Specifically, the device works as a spin-dependent directional plane-wave SP coupler when GST is in the amorphous state, while it works as a spin-dependent directional SP Fresnel zone plate (FZP) when GST is in the crystalline state. The states of GST are switched back and forth using thermal excitation and nanosecond laser illumination, respectively. Our method is simple and robust, and can find broad applications in on-chip photonic devices.

Nanobubble nucleation by pulsed laser illumination of colloidal gold nanoparticles.

This study expands upon a technique our team previously developed for generating nanobubbles on demand with a collimated pulsed laser beam. This work highlights how the controlled addition of gold nanoparticles enhances nanobubble generation efficiency in water, even at laser intensities well below the threshold for multiphoton ionization. Specifically, we investigated the influence of nanoparticles of three distinct sizes on the laser fluence threshold for bubble nucleation and the lifetime of the resultant nanobubbles. Our findings confirm that nanoparticles with a diameter of 60nm exhibit the greatest nucleation efficiency, achieving nearly 45% at a fluence threshold of around [Formula: see text]. Interestingly, nanoparticle size did not impact the nanobubble lifetime.

Study on Influence of AC Poling on Bulk Photovoltaic Effect in Pb(Mg1/3Nb2/3)O3‐PbTiO3 Single Crystals

AbstractThe bulk photovoltaic effect (BPVE) provides a theory of surpassing the Schockley–Queisser limit. However, improving the BPVE efficiency to a level comparable to that of the semiconductor‐based efficiencies is challenging in practice due to conflicting material design requirements. Previous works have shown that a stacked domain structure in a rhombohedral BiFeO3 ferroelectric epitaxial thin film is able to satisfy the criteria of both a small mean free path for an optimized photocurrent and a large distance between electrodes for an optimized photovoltage. Nevertheless, this hypothesis has remained difficult to verify with other materials due to the complication of domain wall manipulation. This work takes advantage of the recent advances in controlling the domain structure in rhombohedral Pb(Mg1/3Nb2/3)O3‐PbTiO3 (PMN‐PT) single crystals via AC poling. By comparing the photovoltage and photocurrent values after domain manipulations in four types of commercial PMN‐PT samples, this work validates the hypothesis of the stacked domain structure enhancing the BPVE by witnessing a simultaneous increase of over 35% for both the open‐circuit voltage and short‐circuit current from DC to the AC‐poled states under a 405 nm laser illumination. This result paves the way for further improving the BPVE efficiency in ferroelectrics.

Backlight Imaging Based on Laser-Gated Technology

Backlight imaging refers to the process of capturing images when the light source directly enters the lens of imaging devices or against a high-brightness background, which usually suffers from degraded imaging quality caused by direct or reflected strong light. Traditional backlight imaging methods involve reducing light flux, expanding dynamic range, and utilizing avoidance angles. However, these methods only partially address the issue of backlighting, and are unable to effectively extract information from the areas overwhelmed by the backlight. To overcome these limitations, this paper reported a backlight imaging technique based on active illumination laser gated imaging technology (AILGIT), originally applied in underwater scattering imaging. Given that backlight imaging is essentially a form of scattering imaging, this technique is likely applicable to backlight scenarios. The AILGIT employs nanosecond-gated imaging components synchronized with nanosecond pulse laser illumination to spatially slice the target. This method allows the camera to capture target signals within specific slices only, which effectively suppresses ambient light and scattering interference from the medium and achieves high-contrast imaging with strong backlight suppression. Experiments obtained dynamic backlight imaging results for a vehicle with headlight on at night from a distance of 500 m, with 60 frames per second and a 4.2 by 2.8 meters’ field of view, where wheel contours and the license plate can be clearly distinguished. The result not only demonstrates the potential of AILGIT in suppressing strong backlight, but also lays the foundation for further research on laser 3D imaging and subsequent processing techniques for backlight targets.

Extension of the Side Distance Measurement Aspect Ratio in the Measurement of a Slot or Bore Using a Commercial Laser Triangulation Sensor.

We propose a new commercial laser triangulation sensor modification to enable the measurement of slots or bores side distance. The study showed the possibility of extending the sensor depth range for a slot or bore side distance measurement using a bypass of the illumination laser beam compared to a simple single mirror attachment to the sensor probe. We derived relations allowing for evaluation of the modified sensor side measurement range in desired depth based on the sensor parameters and the reflective mirror size and position. We demonstrated the functionality of the proposed measurement arrangement with an attachment to the commercial laser triangulation sensor and assessed the side-wall distance measurement. The results show the correct measurement depth and range prediction and the ability to perform side surface distance measurements at depths of more than 3.5 times the slot size.

Manipulating π-π Interactions between Single Molecules by Using Antenna Electrodes as Optical Tweezers.

Via conductance measurements of thousands of single-molecule junctions, we report that the π-π coupling between neighboring aromatic molecules can be manipulated by laser illumination. We reveal that this optical manipulation originates from the optical plasmonic gradient force generated inside the nanogaps, in which the gapped antenna electrodes act as optical tweezers pushing the neighboring molecules closer together. These findings offer a nondestructive approach to regulate the interaction of the molecules, deepening the understanding of the mechanism of π-π interaction, and open an avenue to manipulate the relative position of extremely small objects down to the scale of single molecules.

Researches on projectile muzzle velocity measurement system based on high-speed camera binocular intersection measurement and laser illumination

Abstract In order to reduce the impact of muzzle flame and smoke blurring on the flight trajectory imaging quality of projectile when measuring muzzle velocity in current weapon testing systems, a projectile velocity measurement system based on sequential pulsed laser illumination was studied. The wavelength of the pulsed laser is 532nm and the narrow-band filters with the same center wavelength were put in front of the camera lens which was used to suppress the influence of the flame. The pulsed laser and the filter helped the system to capture the images of the muzzle projectile wrapped in flames. The spatial movement distance of the projectile was calculated based on the principle of binocular intersection. The flying time of the projectile was determined by the high-speed camera shooting rate and the image frames intervals. The system was used to test the muzzle velocity of the projectile fired from a 12.7mm ballistic gun. The experiment results show that laser illumination effectively suppressed the influence of muzzle flames on projectile imaging. According to the calibration and binocular vision imaging algorithms, the muzzle velocity of the projectile was calculated with an accuracy of better than 0.3%. The method can measure the initial velocity of the projectile with the help of sequential pulsed laser illumination and short exposure time (as short as 1.1μs), which has great application value for range testing.

“Ideal Laser Illumination: Light Engines for MERFISH, STORM, PALM, and PAINT”

“Ideal Laser Illumination: Light Engines for MERFISH, STORM, PALM, and PAINT”

High-thermal-conductivity YAGG:Ce color converters on AlN substrate enabling high power and superior luminance in static and dynamic reflective laser illumination

High-thermal-conductivity YAGG:Ce color converters on AlN substrate enabling high power and superior luminance in static and dynamic reflective laser illumination

(Invited) Group IV Mid-Infrared Optoelectronics Leveraging Nanoscale Growth Substrates

Mid-infrared (MIR) optoelectronic devices are of utmost importance to a plethora of applications such as night vision, thermal sensing, autonomous vehicles, free-space communication, and spectroscopy. To this end, leveraging the ubiquitous silicon-based processing has emerged as a powerful strategy that can be accomplished through the use of group IV germanium-tin (GeSn) alloys. Indeed, due to their compatibility with silicon and their tunable bandgap energy covering the entire MWIR range, GeSn semiconductors are frontrunner platforms for compact and scalable MIR technologies. However, the GeSn large lattice parameter has been a major hurdle limiting the quality of GeSn epitaxy on silicon wafers. These limitations are further exacerbated as Ge1−xSnx layers and heterostructures with Sn contents at least one order of magnitude higher than the solubility are needed for device structures relevant to MWIR applications. In this regime, the as-grown layers are typically under a significant compressive strain, which impacts the bandgap directness and increases its energy at the Γ point, thus hindering the device performance and limiting the covered range of the MIR spectrum. This compressive strain build-up not only affects the band structure but also limits the incorporation of Sn atoms in the growing layer, making the control of Sn content a daunting task.In this presentation, we will show and discuss how sub-20 nm Ge nanowires provide effective compliant substrates to grow Ge1−xSnx alloys with a composition uniformity over several micrometers with a very limited build-up of the compressive strain. Ge/Ge1−xSnx structures with Sn content spanning the 6 to 18 at.% range are achieved. We will also demonstrate the integration of the obtained materials in optoelectronic device processing leading to tunable detectors and emitters [1,2]. For instance, photodetectors based on these materials were found to exhibit a high signal-to-noise ratio at room temperature and provide a tunable cutoff wavelength covering the 2.0 µm to 3.9 µm range. Additionally, the processed detectors were also integrated in uncooled imagers enabling the acquisition of high-quality images under both broadband and laser illuminations without the use of the lock-in amplifier technique. Finally, progress towards achieving nanoscale GeSn lasers will also be discussed [2].