Ultra-intense ultrashort laser pulses are pivotal for frontier sciences, yet their development is hindered by the inherent difficulty in fabricating mirrors that simultaneously achieve broad bandwidth, high reflectance, and a high laser-induced damage threshold (LIDT). The pursuit of high optical performance with multilayer structures inevitably introduces defects and discontinuous interfaces, which promote electric field enhancement and thus deteriorate femtosecond laser resistance. Here, we address this challenge by applying post-deposition thermal annealing in air to Ta2O5/SiO2 multilayer reflective films fabricated by ion beam assisted electron beam evaporation. This process effectively enhances the femtosecond LIDT without sacrificing spectral performance, with its efficacy governed by a critical temperature. Mechanistically, the oxidation behavior during air annealing reduces oxygen vacancies within the films, thereby suppressing light absorption pathways induced by defects. Simultaneously, thermal diffusion promotes atomic migration, leading to film densification and passivation of the originally discontinuous Ta2O5-SiO2 interfaces, which enhances the resistance to strong electric fields. The high-reflection film exhibits reinforced structure and performance, along with an approximately 47% increase in the LIDT. This work establishes air annealing as a convenient and effective strategy for manufacturing robust optical components critical for high-power laser systems.

In addressing the key technical challenges of achieving ultra-broadband and high film-thickness uniformity for meter-class large-aperture space telescopes, this study utilized a self-developed 4 m-class large-aperture thin-film deposition system. By employing plasma-assisted electron-beam evaporation technology and a co-evaporation method with inner and outer dual-ring multi-evaporation sources, precise control of film-thickness uniformity within a 2 m range was achieved. A composite film structure combining a metal reflective layer and an ultraviolet-enhanced dielectric layer was adopted to realize high reflectivity across an ultra-broad spectrum from ultraviolet to long-wave infrared. Experimental results show that the average reflectance of the composite film reaches 91.52% in the 0.25 similar to 0.38 mu m spectral band and 99.40% in the 0.38 similar to 12 mu m spectral band. The thickness uniformity of ZrO2 and MgF2 films within the 2 m aperture area was controlled at 1.37% and 3.12%, respectively, meeting the requirements for high uniformity in large-aperture space applications. Radiation testing confirmed that the change in film reflectance is less than 1% under a total irradiation dose of 3.66 x 10(8) rad(Si), satisfying the demands for operation in harsh space environments. This research provides an innovative solution for thin-film technology in large-aperture, ultra-broad-spectrum space optical systems and holds significant value for engineering applications.

Buried defects in extreme ultraviolet (EUV) mask blanks introduce phase perturbations in the reflected wavefront and degrade lithographic imaging performance, making accurate characterization of multilayer phase defects essential for mask inspection. Through-focus scanning optical microscopy (TSOM) provides rich optical signatures of nanoscale structures, but quantitative inversion of defect geometry from TSOM images remains challenging due to the complex nonlinear relationship between optical response and structural parameters. A physics-informed deep learning model is developed for the inversion of EUV multilayer defect parameters from TSOM images. The axial position of the maximum intensity in the TSOM image, determined by defect-induced phase modulation, enables reliable identification of defect polarity and distinguishes bump and pit defects, thereby simplifying the defect parameter inversion process. TSOM images are further decomposed into differential and symmetric components to form a dual-channel representation. The differential component highlights phase-related asymmetry, while the symmetric component captures global structural information. These physically meaningful components are used as input to a convolutional neural network (CNN) to learn the nonlinear mapping between TSOM features and defect parameters. Using only 401 simulated samples for each defect type, the model achieves mean relative inversion errors of 2.55% for bump defects and 3.28% for pit defects. The model also exhibits robustness against noise and training stability, with an average inference time of 0.823 ms per sample. The results demonstrate that the proposed physics-informed TSOM-based deep learning model enables accurate, robust, and data-efficient inversion of EUV multilayer defect parameters, providing a promising approach for EUV mask blank inspection and optical metrology applications.

HfO2 thin films were prepared using radio frequency (RF) ion source-assisted deposition, and the effects of auxiliary ion energy on the microstructure, optical properties, and residual stress of the films were systematically studied. The experimental results showed that when the auxiliary ion energy increased, the extinction coefficient, compressive stress, and optical band gap were gradually increased. These changes were attributed to increased grain boundary defects, crystal structure disorder, and grain size decrease due to high-energy ion bombardment. The HfO2 films deposited at a lower ion energy (600 V) exhibited higher surface quality (RMS = 0.78 nm), better optical properties (k = 10⁻5), and lower residual stress (1.26 GPa).

The development of hybrid optics/microwave communication systems puts forward a new requirement for beam splitters to efficiently transmit microwave signals and simultaneously reflect optical signals.Owing to mechanical constraints,the physical thickness of beam splitters is of the order of tens of millimeters.The corresponding electrical thickness has the same order of magnitude as microwave wavelengths,and the resulting multi-beam interference effect significantly reduces the microwave transmittance,impacting the beam splitting quality.This study presents a new optics/microwave beam splitter based on the ability of the frequency selective surface[FSS]to shape the resonant curve.A beam splitter sample,whose physical thickness and substrate material are 20 mm and quartz glass,respectively,is designed,simulated,fab-ricated,and characterized to validate the feasibility of this strategy.The measured results show that the minimum micro-wave transmittance between 35 and 36.5 GHz with an incidence angle of 45° under TE polarization is 86.43％,and the mean value of the reflectance spectra from 450 to 900 nm and that from 7.7 to 10.5 μm both exceed 96％.This FSS-based optics/microwave beam splitter is expected to play a key role in hybrid optics/microwave communication systems.

In this paper, we propose a cavity-coupled perfect absorber (CCPA) consisting of a bottom gold layer, a SiO 2 layer, and multilayer MIM (metal–insulator-metal) nanowires. By coupling the Fabry-Pérot (F-P) cavity mode with the magnetic plasmons (MPs) resonance mode in multilayer MIM structure, the MPs resonance in the multilayer MIM structure is enhanced and leads to increased absorption of the structure. By designing and optimizing the parameters, near-perfect absorption in the mid-infrared wavelengths can be achieved. The positions of the two absorption peaks can be adjusted by changing the width of the nanowires and the thickness of the SiO 2 layer, resulting in the formant excitation at any position in the mid-infrared. The full-width at half-maximum (FWHM) of the short-wave peak is only 0.076 µm, and the FWHM of the long-wave peak is only 0.46 µm. The long-wave absorption peak maintains high efficiency and stability even at large incident angles, exhibiting “omnidirectional” characteristics. The tunable mid-infrared emission peak can be matched to the characteristic spectra of gases, making it suitable for infrared radiation sources in gas detection.

We present a dual-layer hafnium dioxide (HfO2) grating capable of full-color modulation in the visible spectrum by leveraging the magnetic dipole resonance induced by the lower-layer HfO2 grating, while the upper-layer HfO2 grating serves as a refractive index matching layer to effectively suppress high-order Mie resonances at shorter wavelengths. The HfO2/HfO2 grating exhibits a significantly larger distribution area in the CIE 1931 chromaticity diagram compared to the HfO2 grating. Furthermore, the structural color saturation closely approximates that of monochromatic light. Under varying background refractive index environments, this structure consistently exhibits high-quality structural color. However, the hue of the structural color undergoes alterations. When the polarization angle is below 20°, the saturation of the acquired structural color remains remarkably consistent. However, exceeding 20° results in a significant degradation in the quality of the structural color. This study demonstrates the promising potential for diverse applications, encompassing fields such as imaging and displays.

In this paper, we proposed a triple layer structure consisting of the bottom silver layer, thin silicon oxide space layer, and ultrathin semiconductor silicon film with nano hole array achieving three absorption peaks with narrow band. The absorption spectrum can be easily controlled by adjusting the structural parameters including the radius and period of the nano hole array, and the maximal absorption can reach 99.0% and the narrowest full width of half maximum can reach about 6.5 nm in theory. We also clarified the physical mechanism of the proposed structure in details by finite-difference time-domain simulation, in which the three narrow band perfect adsorption peaks can be attributed to electric dipole resonance, magnetic dipole resonance and plasmonic resonance respectively. At the same time, we used a low-cost nanosphere lithography method to fabricate the proposed nano hole array in large area. In experiment, the absorption peak of the proposed triple layer structure can reach up to 98.3% and the narrowest full width of half maximum can reach up to about 10.1 nm. The highest quality factor Q can reach up to 98.4. This work can open a new avenue for high-quality factor narrow band perfect absorption using ultrathin semiconductor film and benefit for many fields such as infrared sensors, plasmonic filters, and hyperspectral imaging.

Abstract In this paper, we propose a cavity-coupled perfect absorber (CCPA) consisting of a bottom gold layer, a SiO2 layer, and multilayer MIM (Metal-Insulator-Metal) nanowires. By coupling the Fabry-Pérot (F-P) cavity mode with the magnetic plasmons (MPs) resonance mode in multilayer MIM structure, the MPs resonance in the multilayer MIM structure is enhanced, and leading to increased absorption of the structure. By designing and optimizing the parameters, near-perfect absorption in the mid-infrared wavelengths can be achieved. The positions of the two absorption peaks can be adjusted by changing the width of the nanowires and the thickness of the SiO2 layer, resulting in the formant excitation at any position in the mid-infrared. The full-width at half-maximum (FWHM) of the short-wave peak is only 0.076 µm, and the FWHM of the long-wave peak is only 0.46 µm. The long-wave absorption peak maintains high efficiency and stability even at large incident angles, exhibiting "omnidirectional" characteristics. The tunable mid-infrared emission peak can be matched to the characteristic spectra of gases, making it suitable for infrared radiation sources in gas detection.

Conventional infrared polarization imaging and detection systems are normally complex, bulky, and expensive, since rare existing absorber components possess polarization selectivity, especially in the long-wavelength infrared (LWIR) range. In this study, we propose a novel high-performance metamaterial absorber with ultra-broadband high absorption and polarization selectivity in the entire LWIR atmospheric window. The absorber can realize an absorptance higher than 90% with a 4750 nm bandwidth due to different surface plasmons coupled with optical phonons. It exhibits precise polarization-selective absorption at the target wavelength; specifically, it can selectively trap TM-polarized light while restricting the absorption of TE-polarized light. In addition, the designed metamaterial exhibits remarkable spectral stability when the geometric parameters of the microstructure change, which is of great benefit in its manufacturing process. The proposed ultra-thin absorber provides a promising approach to simplify LWIR imaging and detection systems and further improve their performance.

In this paper, we proposed a double-layer all-dielectric grating. Under the premise of ensuring the strength of the resonance peak, the upper SiO2 grating layer suppresses the tendency of high-order dipole resonance excitation and improves the transmittance at the non-resonant position (T > 99%). The distribution of chromaticity coordinates on the CIE 1931 chromaticity diagram also proves that suppressing side peaks can effectively increase the saturation of structural colors, which is essential for a high precision imaging system. The cyclic displacement current excites the magnetic dipole resonance, which causes the magnetic field to be confined in the high refractive index material HfO2 grating layer. By adjusting the duty cycle of the grating structure, a reflection spectrum with low full width half maximum (FWHM) (∼2 nm) and high-quality factor Q (∼424.5 nm) can be obtained. And the spectral intensity is more sensitive to the polarization angle. This work is of great significance to the development of sensors, display imaging and other fields. At the same time, the material of the grating filter meets the requirements of high damage threshold of the high-power laser system, and its high-power laser application potential is inestimable.

The traditional minus filter is composed of many layers of thin films, which makes it difficult and complicated to manufacture. It is sensitive to incident light angle and polarization. Here, we propose a near-infrared narrow-band minus filter with a full width at half maximum around 5 nm made of all-dielectric Si-SiO2 structures without any ohmic loss. The stop band transmittance of the proposed filter is close to 0, while its broad pass band transmittance is as high as 90% in the work wavelength range. Theoretical analysis shows that the transmission dip originated from magnetic dipole resonance: Its position can be tuned from 1.3 µm to 1.8 µm by changing the thickness of Si structure, and the proposed structure is insensitive to changes in incident light angle and polarization angle. We further studied its potential applications as a refractive index sensor. The sensitivity of dip1 and dip2 are as high as 953.53 nm/RIU and 691.09 nm/RIU, while their figure of merit is almost unchanged: 59.59 and 115.18, respectively.

In this paper, we propose an all-dielectric metamaterials structure which contains four asymmetric square holes in the unit cell to design a high-sensitivity refractive index sensor in the long-wave infrared region. Theoretical analysis of the electromagnetic field distributions shows that the four transmission dips originate from magnetic dipole, electric quadrupole and Toroidal dipole. And its position can be tuned by adjusting different geometric parameters, which can optimize the structure to obtain a narrower linewidth to improve the performance of the sensor. Finally, we evaluate the performance of the structure as refractive index sensor by changing the refractive index of the tested substrate. The results show the refractive index sensor has high sensitivity in the long-wave infrared region: the highest sensitivity is 2803 nm/RIU and the figure of merit will reach up to 350.

Although metasurfaces have received enormous attention and are widely applied in various fields, the realization of multiple functions using a single metasurface is still rarely reported to date. In this work, we propose a novel dual-functional metasurface that can be applied as a mid-infrared narrowband thermal light source in optical gas sensing and a long-wave infrared broadband absorber in photodetection. By actively tailoring the structure and constituent materials of the metasurface, the device yields an absorptivity of over 90% from 8 µm to 14 µm, while it exhibits an emissivity of 97.4% at the center wavelength of 3.56 μm with a full width at half-maximum of 0.41 µm. Notably, the metasurface is insensitive to the incident angle under both TM- and TE-polarized light. The proposed dual-functional metasurface possesses many advantages, including a simple structure, thin thickness, angle and polarization insensitivity, and compatibility with optical devices, which are expected to simplify the existing imaging systems and improve the performance of photodetection equipment.

We report a theoretical study of a perfect absorber based on the metal-insulator-metal (MIM) structure, which achieves perfect absorption of single and double peaks in the visible range. The top Ag and middle SiO 2 are arranged in a periodic nanopillar array. Adjusting the structural parameters of the nanopillars to indirectly control the absorption spectrum, theoretically the maximum single-peak absorption can reach more than 99.0% and the maximum double-peak absorption can reach more than 90.0%. We investigate its absorption mechanism through simulations and calculations, and explain the results well with the SPP scattering mode and F-P cavity theory. We find that through the double-peak absorption process, the mode split phenomenon appears as the thickness of SiO 2 increases. Therefore, the selective appearance of absorption peaks can be achieved, which provides the possibility of application in absorbers.

We propose a novel cavity-coupled MIM nano-hole array structure that exhibits a tunable dual passband in the near-infrared regime. When compared with the traditional single metal film, the designed structure provides a coupling effect between Gspp and SPP to significantly reduce the linewidths of the two transmission peaks. We also reveal the physical origin of the positive and negative influence of the cavity effect on the transmission of high-frequency and low-frequency peaks. This work supplies a new modulation theory for plasmonic devices based on the EOT phenomenon and has a wide application prospect in the fields of infrared sensor, plasmonic filter, and hyperspectral imaging.

In this study, we propose and fabricate a perfect absorber on a planar substrate using alternate silicon dioxide and ultrathin metallic lossy chromium (Cr) films. Furthermore, we transfer the absorber to a curved substrate via an optimization design of symmetric structures. The absorber exhibits a highly efficient absorption and large incident-angular tolerance characteristics in the whole visible region. We investigate each layer contribution to the absorption theoretically, and find that ultrathin (~5 nm) lossy Cr films play a dominant absorptive role. Using the effective interface method, we calculate the phase difference on the lossy Cr front surface. It is close to the destructive interference condition, from which we clarify why the proposed structures can produce a highly efficient absorption.

In common plasmonic configurations, energy loss and field enhancement are mutually restricted. In a vast majority of cases, high confinement goes together with high loss, which is a serious limitation for some applications. In an attempt of breaking this rule, which holds true for surface plasmon polariton (SPP) resonators, a multilayer trench grating microstructure with an asymmetric waveguide is considered. It supports both Fabry-Perot (FP) and cavity modes, whose hybridization exhibits unusual properties. The electric field enhancement was modulated by regulating the corresponding absorption and radiation quality factors. At the same time, energy loss was reduced, which is fundamentally ascribed to the mutual recycling of radiation energy between FP and cavity resonators. The maximum total quality factor and strongest field enhancement were both observed at the vicinity of quasi-static limit, thereby signifying that the structure exhibited simultaneous optimizations of field enhancement and loss inhibition, which is crucial to the design of high-quality SPP-based devices.

We studied the infrared absorption of a top sulfur hyperdoping layer covering an fs-laser irradiated microstructured Si substrate. To clarify the hyperdoping concentration distributions, and to find out how the top hyperdoping layer affects infrared absorption from 1200 to 2000 nm, a continuous etching treatment was utilized. Then we interpreted the thermal stabilization of both infrared absorption and sulfur hyperdoping concentration. The fundamental cause for infrared-absorption degradation under thermal annealing was explained. Furthermore, we discussed in detail how the interaction between the top hyperdoping layer and surface microstructure contributed to the high infrared absorption by a series of theoretical simulations using a finite-difference time-domain method. A strong localization of an incident electromagnetic wave was observed around the top sulfur hyperdoping layer covering microstructured Si, which played a critical role in improving infrared absorption. The results in this paper are especially beneficial to the subsequent fabrication of photoelectric devices and infrared response improvement.

In this paper, a metal-dielectric-metal structure based on a Fabry–Perot cavity was proposed, which can provide near 100% perfect narrow-band absorption. The lossy ultrathin silver film was used as the top layer spaced by a lossless silicon oxide layer from the bottom silver mirror. We demonstrated a narrow bandwidth of 20 nm with 99.37% maximum absorption and the absorption peaks can be tuned by altering the thickness of the middle SiO2 layer. In addition, we established a deep understanding of the physics mechanism, which provides a new perspective in designing such a narrow-band perfect absorber. The proposed absorber can be easily fabricated by the mature thin film technology independent of any nano structure, which make it an appropriate candidate for photodetectors, sensing, and spectroscopy.