In photonic crystal slab (PCS) structures, the bound states in the continuum (BICs) and circularly polarised states (dubbed C-points) are critical topological polarisation singularities in momentum space that have garnered significant attention owing to their novel topological and optical properties. In this study, we engineered a novel PCS imager featuring two C-points with opposite chirality through symmetry breaking, resulting in maximal asymmetric transmission responses characterised by near-unity circular dichroism (CD) values. By harnessing the chiral selectivity of the C-points, a high-CD PCS imager can provide two sets of optical transfer functions (OTFs) to facilitate both edge detection and bright-field imaging. Notably, one set of OTFs was finely tuned to a Lorentzian line shape to achieve perfect edge detection. We developed a multifunctional imaging system by integrating a PCS imager into a traditional optical system. Both theoretical and experimental demonstrations confirmed that this system provides bright-field and edge-enhanced images with micrometer-scale resolution. Furthermore, these two independent functions can be easily switched by altering the circular polarisation state of the light source.
In this study, a ray tracing model based on the law of reflection in vector form was developed to obtain the design parameters of multipass cells (MPC) with dense spot patterns. Four MPCs with distinct patterns were obtained using an established mathematical model. An MPC with a four-concentric-circle pattern exhibited the longest optical path length (OPL) of approximately 38 m and an optimal ratio of optical path length to volume (RLV) of 13.8 cm-2. A light-induced thermoelastic spectroscopy (LITES)-based methane (CH4) sensor was constructed for the first time using the developed optimal MPC and Raman fiber amplifier (RFA). A novel trapezoidal-tip quartz tuning fork (QTF) was used as the detector to further improve the sensing performance. The CH4-LITES sensor exhibited an excellent linear response to optical power and CH4 concentration. The minimum detection limit (MDL) of the CH4-LITES sensor reached 322 ppb when the output optical power of the RFA was 350 mW. The Allan deviation of the system indicated that the MDL decreased to 59.5 ppb when the average time was increased to 100 s.
One of the challenges in the field of multi-photon 3D laser printing lies in further increasing the print speed in terms of voxels/s. Here, we present a setup based on a 7 × 7 focus array (rather than 3 × 3 in our previous work) and using a focus velocity of about 1 m/s (rather than 0.5 m/s in our previous work) at the diffraction limit (40×/NA1.4 microscope objective lens). Combined, this advance leads to a ten times increased print speed of about 108 voxels/s. We demonstrate polymer printing of a chiral metamaterial containing more than 1.7 × 1012 voxels as well as millions of printed microparticles for potential pharmaceutical applications. The critical high-quality micro-optical components of the setup, namely a diffractive optical element generating the 7 × 7 beamlets and a 7 × 7 lens array, are manufactured by using a commercial two-photon grayscale 3D laser printer.
Meta-devices, known for their capability to manipulate light fields at a subwavelength scale, have gained significant traction in the realm of quantum photonics in recent years. They are being utilized in miniaturized applications such as the preparation of quantum light sources and the control and detection of quantum states. In this review, we provide a systematic explanation of the working principles and notable applications of meta-devices in quantum optical information processing, while also outlining potential directions for the future development of quantum meta-devices.
Although terahertz (THz) spectroscopy and imaging offer a variety of applications in medical diagnosis of malignant and benign neoplasms, their translation into clinical practice is hampered by the absence of endoscopic systems capable of sensing the THz optical properties of the hard-to-access tissues. In this review, we focus on recent attempts to address this challenge. To better highlight the need for THz endoscopes, we start with a brief overview of THz medical applications, with an emphasis on neoplasms diagnosis. We then consider the two existing principles of THz endoscopy. The first uses the fiber-coupled THz photoconductive antennas (PCAs) for the THz generation and detection in close proximity to a hard-to-access object, where optical fibers are applied to flexibly deliver the laser pump and probe beams to the THz emitter and detector. The key technology of the second approach is the THz optical fibers capable of delivering the THz waves to an analyte and then detecting the reflected and back-propagated THz signal. Despite this approach still lacking the efficient commercially available THz fiber optics, most recent developments pave the way to solve these problems. In this review, several notable examples of THz endoscopic systems based on different guiding mechanisms, material platform, and manufacturing strategies are discussed.
In recent years, metasurfaces on planar substrates have been extensively investigated and methods for their fabrication have been implemented. However, fabricating metasurfaces on highly curved surfaces remains challenging because of the difficulty in achieving precise mechanical positioning on curved geometries using current lithographic techniques. This limits applications that require finer and more accurate structures. This paper introduces a novel lithographic approach for patterning structures on curved surfaces. By leveraging the natural aberration of a convex lens to focus the beams, this approach enables the creation of adjustable ring and split-ring configurations. Ring-shaped patterns with an average structural width of 1.79 µm were exposed, exceeding the resolution of previously reported annular lithography techniques by a factor of 10. Moreover, this approach offers a defocus tolerance that is 10 times greater than that of conventional direct laser writing lithography, thus reducing the influence of positional errors caused by substrate geometry. Consequently, patterns on a photoresist-coated dome were successfully exposed, marking a pioneering achievement. This study paves the way for creating ring-shaped metasurfaces and other structures on highly curved surfaces.
Assembling metal nanoparticles into a well-defined array and constructing strongly coupled hybrid systems enable high-quality resonances with narrow linewidths, which offer new opportunities to circumvent the hurdle of plasmonic losses. Herein, we propose a light-driven approach for generating plasmonic arrays by leveraging the self-organized patterns of tightly confined surface plasmon polaritons in single metal nanowires, which exhibit optimized unit structures, tunable interparticle spacings with supra-wavelength or sub-wavelength periods beyond the diffraction limit, and flexible alignment directions. We theoretically and experimentally show the mechanism of generating field patterns via the interplay of a standing wave and optical beating, followed by the formation of periodic geometries under a spatially modulated temperature distribution. We also fabricate plasmonic arrays on microfibres with diameters down to ~1.4 μm and thereby construct a series of hybrid plasmonic–photonic resonators with narrow-band resonances (~3.9 nm linewidth) as well as a barcode system with high multiplexing capacity. Our results show the potential of simple, low-cost, and high-efficiency fabrication of plasmonic arrays and hybrids that may find applications in plasmonic array lasers, information encryption, and high-resolution distributed sensing.
High-power laser coatings play a critical role in enabling optical manipulation in various laser applications, including beam alignment and control in high-power laser systems. These coatings rely on multilayers and microstructures, such as antireflective (AR) and highly reflective (HR) coatings, filters, and beam splitters, to enhance their performance. This review focuses on laser coatings used for manipulating optical fields, their principal limitations, and laser-induced damage in high-power applications. The concepts, principles, and progress made in exploring the optical performance and distinctive functions of the optical coatings and optimising the laser resistance through structural optimisation, material engineering, and defect elimination are highlighted. Finally, future directions for improving the design flexibility, fabrication feasibility, advanced detection techniques for high-resolution defect characterisation, and further consideration of minimising the optical loss are discussed to meet the evolving demands of modern high-power laser systems.
Holographic patterns that integrate printings and holograms into a single device have received extensive attention in optical security owing to their attractive aesthetics and concealment. However, the sophisticated structures of metasurface-based optical devices require a time-consuming fabrication process, hindering the practical application of holographic patterns in optical security. In this study, a novel double-layer holographic pattern that employs simple microholes and microvoids as optical modulation units is designed and experimentally demonstrated. The two layers of the structure arrays are synchronously processed in a transparent material through a single serial-stitching of dynamic 3D spatially modulated femtosecond pulses that are proposed for the rapid fabrication of large-area multi-layered patterns. The fabricated holographic pattern appears as a dynamic grayscale image under white light incident at different angles and projects encoded holographic images under laser illumination. By transforming microholes into microcraters by ultrasonic treatment, the reconfiguration of the holographic pattern can be realized based on refractive index modulation using liquid immersion. The proposed reconfigurable holographic patterns with simple structures and visible sizes enable the recoding of multiple pieces of information, making them practical optical security elements with a wide range of applications in anti-counterfeiting and information encryption.
X-ray scintillation detectors play an irreplaceable role in medical imaging, security inspections, and nondestructive detection. Recently, all-inorganic lead-free metal halide scintillators have attracted attention for addressing the drawbacks of lead-halide perovskites, such as severe self-absorption and toxicity. Nevertheless, high-resolution, flexible, and cost-effective lead-free scintillators are desirable for X-ray imaging applications. In this study, we designed a zero-dimensional hybrid cuprous halide, (MTP)2Cu4I6 (MTP+ represents [C19H18P]+), and synthesized single crystals. (MTP)2Cu4I6 shows intense yellow emission (618 nm) and a large Stokes shift of 185 nm, almost eliminating the effect of self-absorption. As a result, (MTP)2Cu4I6 exhibited a near-unity photoluminescence quantum yield (99.9%) with a light yield of 43800 photons per megaelectron volt. Moreover, (MTP)2Cu4I6 demonstrates an impressive detection performance with a fast response time of 2.18 μs, a good linear response ranging from 0.038 μGyair s-1 to 53.4 μGyair s-1, and a low detection limit of 37.6 nGyair s-1. In a conceptual experiment, large-area flexible (MTP)2Cu4I6/polydimethylsiloxane (PDMS) scintillation films were fabricated to investigate their X-ray imaging performance. The (MTP)2Cu4I6/PDMS film exhibits a high-spatial resolution of 10.2 lp mm-1 when the modulation transfer function is 0.2 and superior flexible detection performance. The short lifetime, high-light yield, low toxicity, and low cost of (MTP)2Cu4I6 facilitate the development of next-generation X-ray scintillators.
Ultra-high-precision, computer-controlled sub-aperture polishing technology is crucial for achieving full-band, high-precision optical components. However, this convolution material-removal method introduces a significant number of mid-spatial frequency (MSF) errors, which adversely impact the performance of optical systems. To address this problem, we propose a novel controllable spiral magnetorheological finishing (CSMRF) method that disrupts the mechanism of conventional constant tool influence function (TIF) convolution material removal. In this paper, we leverage the advantages of a time-varying spacing strategy and theoretically analyze how time-varying spacing, combined with the spiral swing process of the TIF, mitigates MSF ripple errors. The time-varying spacing method highlights the importance of controlling the characteristic frequency, whereas the CSMRF method has a smoothing effect on the errors within the MSF band. Our findings confirm that time-varying spacing and spiral swinging have complementary effects in managing MSF errors. Furthermore, by constraining the MSF and specific frequency errors, we identify the optimal combination of adaptive spacing and spiral angle using a genetic algorithm. We apply a non-negative gradient constraint dwell-time solution algorithm based on the Lagrange regularization method to deterministically evaluate the specific MSF error. Using the application of an inertial confinement fusion optical element as an example, we observe a 99.938% decrease in the amplitude of the PSD curve of the mid-frequency ripple error with a spatial period of 1 mm, whereas the mid-frequency PSD curve remains within the standard line. Therefore, the proposed method can effectively control the specific MSF error distribution. This variable convolution kernel (TIF) sub-aperture polishing method provides a new concept for full-band cooperative error control.
In the area of computer-aided optical design most software packages rely on a surface list based data structure. For classical on-axis lenses – such as camera lenses - the list-based data structure is a suitable way for managing lens data. However, for modern high-end optical systems such as off-axis free-form designs, multi-path systems or for accurate tolerance analysis of complex opto-mechanical systems, the list-based approach often reaches its limits. In this paper we present a new tree-like data structure that is able to solve many of the problems that emerge from surface list based data structures.
Thermal protection and comfort are essential for instruments and humans, especially in high-temperature scenarios such as fires and steelworks. Existing thermal protective windows absorb external radiation and heat when exposed to thermal sources, thereby failing to provide thermal comfort to users. Herein, we present a nanophotonic-engineered thermal protective window (NETPW) strategy that incorporates a visible-light transparent broadband directional thermal emitter and a low-emissivity coating into commercial polycarbonate (PC) windows. In comparison to a PC window exposed to a 700 K thermal source at a half-view angle of 50°, the proposed NETPW exhibits remarkable temperature reduction (~77.7 ℃) by reflecting external radiation and enhancing directional radiative cooling. Simultaneously, the NETPW effectively inhibits heat emissions toward users, resulting in a significant improvement in thermal comfort, with a user’s sensible temperature reduction of 57 ℃. Moreover, the NETPW exhibits high visible transparency, high-temperature resistance, scratch resistance, and impact resistance. The seamless integration with existing windows provides a novel approach for controlling thermal emission and optimizing energy exchange.
Endoscopes are indispensable for minimally invasive optical applications in medicine and production engineering. The smallest lensless endoscopes often use digital optics to compensate the intrinsic distortions of light propagation of multimode or multicore fibers. However, due to the wavelength dependency of the distortion, the approach is restricted to a narrow spectral range, which prevents multispectral imaging modalities. We employ a spatial light modulator with a high stroke above 2
, to generate a hologram which minimizes overall phase distortion for multiple spectral bands. This enables lensless multicore fiber single-shot RGB endoscopy, for the first time in the world. Many applications in advanced manufacturing and biomedicine such as in vivo tissue classification are enabled.
Quartz tuning forks have been recently employed as infrared photodetectors in tunable laser diode spectroscopy because of their high responsivities and fast response time. As for all sensitive elements employed for photodetection, the main drawback is the limited bandwidth of their absorption spectrum. For quartz crystals, the high absorptance for wavelengths above 5 µm guarantees excellent performance in the mid-infrared range, that cannot be easily extended in the visible/near-infrared range because of its transparency from 0.2 to 5 µm. In this work, we report on the development of a laser surface functionalization process to enhance the optical absorption of quartz crystals, named hereafter Black Quartz, in the 1-5 µm spectral range. Black Quartz consists of surface modification of quartz crystal by ultra-fast-pulsed-laser-processing to create localized matrices-like patterns of craters on top. The surface modification decreases the transmittance of quartz in the 1-5 µm range from > 95% down to < 10%, while the transmittance above 5 µm remains unchanged. The Black Quartz process was applied on two quartz-tuning-forks mounted in a tunable laser diode spectroscopy sensor for detecting two water vapor absorption features, one in the near infrared and the other one in the mid-infrared. A comparable responsivity was estimated in detecting both absorption features, confirming the extension of the operation in the near-infrared range. This works represents an important and promising step towards the realization of quartz-based photodetector with high and flat responsivity in the whole infrared spectral range.
ISSN 2689-9620 EISSN 2831-4093
Indexed by:
- ESCI (IF 10.6)
- DOAJ
- Scopus
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- CNKI
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2021, 2(3): 350-369. doi: 10.37188/lam.2021.024
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2023, 4(2): 143-167. doi: 10.37188/lam.2023.011
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2023, 4(4): 519-542. doi: 10.37188/lam.2023.031
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2021, 2(3): 313-332. doi: 10.37188/lam.2021.020
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2021, 2(1): 59-83. doi: 10.37188/lam.2021.005
