PURPOSE:FLASH radiation therapy using high-energy x rays combines ultrahigh dose rate irradiation with the physical characteristics of high-energy x-ray beams, achieving a significant reduction in normal tissue biological damage while maintaining sufficient tissue penetration, thereby presenting great potential for clinical translation. However, the absence of a traceable absolute dosimetry method for FLASH x-ray beams remains a substantial limitation to its clinical implementation. This study aims to establish a quasi-adiabatic water-controlled probe-type graphite calorimeter for the absolute measurement of absorbed dose to water in the 10 MV FLASH x-ray beam, to address the current lack of a traceable dosimetry standard for x-ray FLASH radiation therapy. METHODS AND MATERIALS:A probe-type graphite calorimeter was developed, employing thermally stabilized water as the thermal control medium to precisely regulate the thermal equilibrium of the graphite core. This quasi-adiabatic system is designed to facilitate accurate absolute dose measurements under ultrahigh dose rate conditions. RESULTS:The results indicate that for a single irradiation with a total dose exceeding 2 Gy, the mean type A relative uncertainty, determined from 5 repeated measurements using the sample standard deviation, is less than 0.2%. By deriving the necessary correction factors for determining the absolute dose (ie, in Gy) of FLASH photon radiation therapy, the uncertainty in water absorbed dose measurement is determined to be 1.0% (k = 1). CONCLUSIONS:This study develops a probe-type graphite calorimeter for the absolute measurement of absorbed dose to water in 10 MV FLASH x-ray beams. The system is designed to address the current lack of a traceable dosimetric standard for x-ray FLASH radiation therapy, thereby supporting its clinical translation and application.

Purpose FLASH radiotherapy using high-energy X-rays combines ultra-high dose-rate irradiation with the physical characteristics of high-energy X-ray beams, achieving a significant reduction in normal tissue biological damage while maintaining sufficient tissue penetration, thereby presenting great potential for clinical translation. However, the absence of a traceable absolute dosimetry method for FLASH X-ray beams remains a substantial limitation to its clinical implementation. This study aims to establish a quasi-adiabatic water-controlled probe-type graphite calorimeter for the absolute measurement of absorbed dose to water in the 10 MV FLASH X-ray beam, to address the current lack of a traceable dosimetry standard for X-ray FLASH radiotherapy. Methods and Materials A probe-type graphite calorimeter was developed, employing thermally stabilised water as the thermal control medium to precisely regulate the thermal equilibrium of the graphite core. This quasi-adiabatic system is designed to facilitate accurate absolute dose measurements under ultra-high dose rate conditions. Results The results indicate that for a single irradiation with a total dose exceeding 2 Gy, the mean Type A relative uncertainty, determined from five repeated measurements using the sample standard deviation, is less than 0.2%. By deriving the necessary correction factors for determining the absolute dose (i.e., in Gy) of FLASH photon radiotherapy, the uncertainty in water-absorbed dose measurement is determined to be 1.0% (1σ). Conclusions This study develops a probe-type graphite calorimeter for the absolute measurement of absorbed dose to water in 10 MV FLASH X-ray beams. The system is designed to address the current lack of a traceable dosimetric standard for X-ray FLASH radiotherapy, thereby supporting its clinical translation and application.

Perovskite-quantum dot (PQD) photoresists exhibit excellent optoelectronic properties and have become key modules for the construction of next-generation optoelectronic devices, including micro-LEDs, lasers, and optical anti-counterfeiting. However, traditional preparation of PQD photoresist requires a lot of solvent, harsh conditions, and a time-consuming process, which hinders the development of PQDs. Herein, we demonstrate in situ synthesis of CsPbX3 (X = Br, Cl) PQDs photoresist based on polymerizable monomer tricyclic decane dimethanol diacrylate (TCDDA) for 3D printing. TCDDA not only acts as an eco-friendly solvent and efficient ligand to synthesize and stabilize the PQDs, but also serves as a functional monomer for photopolymerization to encapsulate the PQDs. The PQD photoresist is suitable for photolithography on different substrates, including metals, inorganic materials, polymers, and even paper. Furthermore, we performed 3D printing of arbitrary 3D objects with the smallest feature size of 17 mu m by using the PQD photoresist. As a proof-of-concept, we depict the potential application of the PQDs photoresist for optical encryption through the construction of quick response (QR) codes and binary codes. This study provides a versatile method for the synthesis of PQD photoresist, and will pave the way for potential applications in flexible optoelectronic devices and anti-counterfeiting.

Ionization chambers used for air kerma measurements in photon beams typically utilize a wall and cavity design primarily either of cylindrical or spherical shape. The corrections and conversions of such chambers have been widely studied using Monte Carlo (MC) codes. In this work, we look at two ionization chambers with a shape that is a combination of spherical and cylindrical, which we will refer to as a compound geometry. The chambers share similar structures but possess varied volumes. They were separately investigated under specific 60Co gamma radiation fields, where the corrections and conversions for air kerma reproductions including the wall effect were studied via comprehensive MC simulations using EGSnrc. The reproduced air kerma values were disseminated to three thimble chambers, the calibration factors of which demonstrated consistency between experiments and simulations. A similar to 0.1% discrepancy was observed from both of the different types of thimble chambers. Aside from providing specific results for these chambers, the investigation of the differences aims to highlight the importance of MC simulations in the calculation of chamber correction factors, especially for those cannot be readily deduced by experiment.

Ultrafast laser irradiation triggers structural transformations in diamond with broad potential across many fields. Understanding how laser energy modifies the diamond lattice is essential for achieving the intended properties. However, the coupled thermal and mechanical responses make it hard to clarify the transformation pathways. Herein, pump-probe imaging is used to capture surface reflectivity, while a molecular dynamics-coupled two-temperature model (MD-TTM) follows atomistic transformation, revealing thermomechanical behavior and phase transition mechanisms. At fluences below 2.28 J/cm2, the sp3 lattice damage is mainly attributed to Coulomb explosion and remains confined to only a few atomic layers. At elevated fluences, the interaction includes both Coulomb explosion and phase explosion, which not only ablate surface material but also promote notable transformation from sp3 to sp2 bonding. The surface removal initiates shock waves that propagate inward, disrupting the typical compression-to-tension evolution of the stress wave. This leads to residual stress accumulation, relaxation, and renewed buildup with increasing fluence. When the laser fluence increases from 5.05 J/cm2 to above 9.18 J/cm2, the dynamic stress rises from roughly 30 GPa to beyond 100 GPa, resulting in stacking faults and extensive lattice damage within the diamond. Because the material is removed through single-atom ejection instead of cluster flow, the surface roughness remains below 2 nm, along with a low specific contact resistivity of 3×10−6 Ω cm2 and a sheet resistance of 280 Ω. The results outline a processing window that allows efficient surface removal without bulk lattice damage and demonstrate a fast, controllable single-pulse laser strategy for high-quality diamond surface engineering in microelectronic and optoelectronic applications.

This paper proposes a method for precise in-situ monitoring of laser-induced diamond graphitization using terahertz technology, achieved through the construction of a terahertz sensor based on metasurface array structures. The method enables high-sensitivity, non-contact terahertz sensing of the electrical conductivity of the graphite layer on the diamond surface. Leveraging the tunable nature of graphite conductivity with laser energy density, combined with CST electromagnetic simulations and localized field enhancement effects, the study establishes the quantitative correlation of structural parameters with terahertz responses. This demonstrates a highly sensitive mechanism in which spectral variations of the resonance frequency exhibit pronounced dependence on the physical properties of graphite. Furthermore, the technology provides a precise and non-destructive solution for monitoring material degradation in nuclear reactors, with significant potential for practical applications.

大部分用于辐射剂量学研究的辐照器都安装比活度较高的放射源，这类放射源只能采用合规的容器运输以完成现场装源。为了使国产辐照器能够更好地符合国内外放射源的运输及安装要求，研制了一种新型三重屏蔽辐照器，用于进行现场装源及开展后续工作。首先基于对辐照器的精确构建，开展了系统的模拟计算，分析了辐照器对射束的控制特性。然后结合模拟计算和分析，研究了开展辐射剂量学相关研究所关心的辐射场性能。本工作研制的新型三重屏蔽辐照器适用于现场装源，散射腔能够将射束中的散射成分减少25%。辐照器的三重屏蔽结构能够将常规工作区域的射线强度衰减约7个数量级，据此为辐照器的关键部件安装方案的优化提出了建议。准直器组对辐射野平面内能谱的影响约为0.2%。利用辐照器构建的辐射场计算了三种典型电离室的 60 Co γ空气比释动能绝对测量相关的壁修正因子，与早期发表的结果偏差小于0.2%。在现行要求下，该辐照器可作为支撑辐射剂量学相关工作的一个备选方案，其紧凑的结构可以扩展剂量率的动态范围，从而在相对较长周期提供服务。

Micro–nano fabrication technology is critical to high-end fabrication, bridging the gap between microscopic and macroscopic scales. Femtosecond laser fabrication, owing to its ultrafast nonlinear effects and three-dimensional direct writing capabilities, has demonstrated unique advantages in the fabrication of functional micro–nano structures. Phase holographically modulated femtosecond laser technology, as a representative of spatial optical field modulation, modulates the phase of the incident laser field to flexibly transform a single focal point into various spatial optical fields, including multifocal arrays, patterned optical fields, and three-dimensional optical fields, according to specific fabrication requirements. This technology not only improves fabrication precision and efficiency but also provides greater flexibility in femtosecond laser fabrication. This review systematically summarizes recent technological advances, focusing on four aspects: algorithms for generating phase holograms, exceeding the diffraction limit to improve fabrication resolution, optimizing fabrication quality, and improving fabrication efficiency. It aims to provide theoretical foundations and technical references to support the practical application of modulated femtosecond laser technology in the fabrication of functional micro–nano structures.

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.

Objective.To experimentally determine beam quality correction factors (kQ) for six cylindrical and four parallel-plate ionization chambers (ICs) in both spread-out Bragg peak (SOBP) and single-layer proton beam configurations.Approach.Water calorimetry was implemented to establish absorbed dose to water (Dw) at 10 g cm-2depth for SOBP and single-layer proton beams. IC measurements were performed under identical geometrical conditions as calorimetric measurements, with the exception of water temperature control in the phantom. Systematic evaluation of ion recombination and polarity effects was achieved through sequential measurements at operational voltages of -400 V, -300 V, -200 V, -150 V, and +400 V in scanned proton beams. All chambers were calibrated against the60CoDwstandard at the National Institute of Metrology to obtainDwcalibration coefficients (ND,w). ThekQvalues were determined through integrated water calorimetry and IC measurements.Main results.The relative standard uncertainties inDwdetermination were quantified as 0.43% for SOBP beams and 0.51% for single-layer beams. The experimentally determinedkQvalues demonstrated agreement with both TRS-398 reference data and published literature within declared measurement uncertainties.Significance.This work presents the first comprehensive determination ofkQfactors for SOBP and single-layer proton beams using water calorimetry. The obtainedkQvalues with reduced uncertainties (0.56%-0.63%) establish metrological traceability for ten clinical IC models, directly enhancing the accuracy of scanned proton beam dosimetry in radiotherapy practice.

Micro-structured silicon surface plays a significant role in the electronics industry. Crystalline and amorphous phases of silicon, which have significantly different physical properties, can be transformed into each other using femtosecond laser, and assisted chemical etching enables the easy fabrication of various micro-structures. However, efficient and controllable fabrication of micro-cylinders, micro-rings, and micro-ring grooves on silicon surfaces still remains a challenge. Here, we propose a temporally modulated single-shot femtosecond pulse lithography technology, combining laser-induced silicon modification and chemical etching. In this technology, the occurrence of recrystallization allows for the flexible manipulation of the shape of the modified area, transitioning from circular to annular shapes by adjusting the laser fluence. This corresponds to the formation of micro-cylinders and micro-rings after etching. In the case of temporally shaped pulses, with an increasing pulse delay, the micro-rings formed after etching gradually transform into micro-ring grooves, as the recrystallization area created by the first sub-pulse is reacted by the second sub-pulse. Due to the characteristics of the single shot, the technology, when combined with the flying punch method, can be used for the high-efficiency fabrication of large-area silicon surface micro-structure arrays.

BACKGROUND:The clinical use of flattening filter free (FFF) radiotherapy has significantly increased in recent years due to its effective enhancement of dose rates and reduction of scatter dose. A proposal has been made to adjust the incident electron angle of the accelerator to expand the application of FFF beams in areas such as large planning target volumes (PTVs). However, the inherent softening characteristics and non-uniformity of lateral dose distribution in FFF beams inevitably lead to increased dosimetry errors, especially for ionization chambers widely used in clinical practice, which may result in serious accidents during FFF radiotherapy. PURPOSE:This study constructs a comprehensive Monte Carlo model that encompasses not only conventional FFF beams but also incorporates FFF beams with varying incident electron angles, to investigate dosimetry errors and correction methods in FFF radiotherapy. METHODS:We have innovatively introduced a FFF output correction factor ( k Q F F F , Q W F F ${k}_{{Q}_{FFF},{Q}_{WFF}}$ ) to address dosimetry errors in various ionization chambers under different incident electron angle conditions in FFF beams. The primary variations in k Q F F F , Q W F F ${k}_{{Q}_{FFF},{Q}_{WFF}}$ were analytically determined to result from changes in s w , a i r ${s}_{w,air}$ and the perturbation correction terms of the ionization chamber. RESULTS:Ionization chambers with smaller sensitive volumes typically exhibit reduced dosimetry errors. Our findings indicate that for ionization chambers with sensitive volumes ranging from 0.016  to 0.125 cm3, the dosimetry error under various FFF beam conditions consistently remains below 1.15%. This study provides crucial guidance for selecting appropriate ionization chambers in FFF radiotherapy. CONCLUSION:A correlation was established between the absorbed dose to water in beams with a flattening filter (WFF) and those without (FFF), defined by the FFF output factor ( O F Q F F F , Q W F F $O{F}_{{Q}_{FFF},{Q}_{WFF}}$ ). Using the proposed Monte Carlo model, the O F Q F F F , Q W F F $O{F}_{{Q}_{FFF},{Q}_{WFF}}$ can be derived and applied to theoretically calculate the absorbed dose to water in FFF beams at varying incident electron angles, with a relative standard uncertainty of 0.2. This study provides a valuable reference for clinical dose measurements and crucial support for establishing dose calibration standards in FFF radiotherapy.

为测量小野输出因子,采用国际原子能机构(IAEA)出版的TRS483报告方法,测量了 Elekta Synergy直线加速器标称6 MV、10 MV辐射场的组织模体比(TPR20,10(10)),6 MV、10 MV能量TPR20,10(10)分别为0.683和0.735.通过计算电离室适用的最小半高宽验证了多种电离室可测射野范围,选用的电离室可测最小半高宽在3～4 cm之间.对探测器灵敏体积、测量剂量和剂量率线性、漏电流、重复性和稳定性进行比较,选择了 18种不同型号共21支探测器,在加速器TPR20,10(10)为0.683和0.735的辐射场,源皮距(SSD)分别为90 cm和100 cm的条件下计算1 cm×1 cm,2 cm×2cm,3 cm×3cm,4cm×4cm,5 cm×5cm 和8cm×8cm方野与 10cm×10cm 方野的探测器电荷比值得到未修正的射野输出因子,乘以TRS-483报告的修正系数后得到修正射野输出因子,修正后的射野输出因子与平均值最大差异小于2.5％.结果表明:使用TRS-483报告的修正因子可提高不同探测器测量小野剂量的一致性.

Objective:To study the influence of intensive magnet fields on radiation dose measurement, and to demonstrate the feasibility of measuring magnet field correction factor by a combination of medical linac with variable magnet fields in view of needing for accurate measurement of the doses from reference beam arising in MR image-guided radiotherapy.Methods:A photon radiation field and a variable field with 6 MV nominal high voltage were produced by using conventional medical electron linear accelerator equipped with a pair of electromagnets with magnetic field strength up to 1.5 T. Both PTW30013 and PTW31010 ionization chambers were used to test the responses of ionization chambers under different magnetic field strengths at four orientations in which the angles between ionization chamber axis and magnetic field direction were 0°, 180°, 90° and 270°, respectively. The magnetic factors, kB, M was calculated and compared with the reported values in literature. Results:The response of ionization chamber was proportional to the magnetic field strength before it reached to a peak around 1 T, and then fell down as the magnetic field continued to rise. When the magnetic field was 0.35 T, the magnetic factors of PTW31010 were 0.988 2±0.000 3 and 0.997 4±0.000 4 corresponding to 90° and 0° directions, the discrepancy between 0° scenario and literature was 0.05% ± 0.04%. When the magnetic field reached 1.5 T, the magnetic factor of PTW30013 was 0.958 9±0.000 5 at the situation of 90°, which was 0.60% ± 0.05% different from the literature value.Conclusions:Conventional 6 MV medical accelerator equipped with electromagnet can be used to measure the magnetic field factor of reference dosimetry for MRIgRT.

Structural colors provide a highly stable and ecofriendly dyeing mechanism. The ability to adjust structural colors by a single pixel enhances their flexibility and application range. However, achieving single-pixel control and dynamic adjustment of structural colors remain a challenge yet. In this study, we propose a coloring method involving microcurve surfaces fabricated using a spatially modulated femtosecond laser hybrid technology, which combines spatially modulated femtosecond laser-assisted wet etching and molding. The fabricated microcurve surface exhibits bright colors under white light irradiation, and the color of each pixel can be adjusted independently by changing the morphology of the modified region inside fused silica using a femtosecond laser. With the high flexibility of femtosecond laser fabrication, color lightness can be accurately controlled through the quantitative adjustment of the arrangement of microcurve surfaces in an array, and various color patterns can be fabricated through the programmable arrangement of different microcurve surfaces. Additionally, the color exhibits strong dynamic characteristics, that is, different colors correspond to different external forces.

Several new glass vessels, thermistor probes, and water phantoms have been designed and built at the National Institute of Metrology (China) to upgrade and develop the existing water calorimeter. The increased plane-parallel vessels have shorter thermal stability times and shallower positioning depths (∼1.3 cm) than the previous cylindrical vessels, which makes them suitable for electron beams. The sensitivity of the new probes is 10% greater than the previous ones. In this study, detailed experimental and theoretical investigations of various factors affecting the new water calorimeter are performed. The system uncertainty of the water calorimeter is reduced and the robustness of the determination of the absorbed-dose-to-water D w is improved using a variety of geometric detector vessels and two kinds of high-purity water systems saturated with high-purity gases. This new calorimeter is employed as a primary standard for determining the D w , has achieved a combined standard uncertainty of 0.24% for a 60 Co beam, 0.27% for 6 MV and 10 MV photon beams and 0.30% for a 25 MV photon beam. The beam quality conversion factors k Q of ten cylindrical and three plane-parallel ionization chambers are measured using the new calorimeter to improve the reference dosimetry accuracy of high-energy clinical photon beams.

We report a femtosecond laser print-assisted dry etching technology for high-efficiency, high-quality, and tailored fabricating of a micro-convex surface (MCS) on hard and brittle materials. Liquid ultraviolet curing adhesive (UVCA) was transferred from a donor substrate to a receiving substrate by femtosecond laser-induced forward transfer, and the transferred microdroplet spontaneously has a smooth surface under the action of surface tension. And then an MCS with a high-quality surface was formed on hard and brittle materials by UV curing and dry etching. The effects of laser parameters and receiving substrate surface free energy on MCS morphology were investigated. According to the variation of the numerical aperture, the two methods to change the morphology of the MCS were divided into independent/joint regulation of diameter and height. We showed that a hexagonal array containing a variety of MCS morphologies can be fabricated on a fused silica by setting the appropriate parameters. And the fabrication time of an MCS in a large-area array was only 1.1 s.

Antireflective microstructures fabricated using femtosecond laser possess wide-ranging applicability and high stability across different spectral bands. However, due to the limited aspect ratio of the focused light field, traditional femtosecond laser manufacturing faces challenges in efficiently fabricating antireflective microstructures with high aspect ratio and small period, which are essential for antireflection, on curved surfaces. In this study, we present a robust and efficient method for fabricating high-aspect-ratio and basal surface insensitive antireflective microstructures using a spatially shaped Bessel-like beam. Based on theoretical simulation, a redesigned telescopic system is proposed to flexibly equalize the intensity of the Bessel beam along its propagation direction, facilitating the fabrication of antireflective subwavelength structures on the entire convex lens. The fabricated microstructures, featuring a width of less than 2 µm and a depth of 1 µm, enhance transmittance from 75% to 85% on Diamond-ZnS composite material (D-ZnS) surfaces. Our approach enables the creation of high aspect ratio subwavelength structures with a z-position difference exceeding 600 µm. This practical, efficient, and cost-effective method is facilitated for producing antireflective surfaces on aero-optical components utilized in aviation.

In this study, the influence of femtosecond double-pulses in inducing bulge structures on thin gold films were experimentally examined. The experimental results indicate that the morphology of bulge structures evolved alternately with an increase in the time delay between two subpulses under the condition that the total pulse energy remained the same. This phenomenon is different from that observed in previous studies in which femtosecond double-pulses were used for processing metal materials. Through the combination of the two temperature model and the generalized thermoelastic theory, the stress distribution inside the gold film was calculated under different time delays. Moreover, the aforementioned experimental phenomenon was explained using the superposition principle of the stress waves generated by two subpulses. The infrared reflection spectra of gold bulge arrays processed under different time delays were also investigated. This research presents a strategy for obtaining detailed understanding regarding the physical mechanism of the interaction between femtosecond double-pulses and thin metal films. It also presents a strategy for optimizing the parameters of pulse trains to adjust the stress distribution to achieve the shape evolution of the formed structures.

Laser-induced periodic surface structures (LIPSSs) are a universal phenomenon that can be observed on a variety of materials, including metals, semiconductors, and dielectrics, upon irradiation with ultrafast laser pulses. It has found various potential applications in the fields of optics, biologics, and mechatronics due to its efficient and flexible fabrication process and subwavelength quasi-periodic property. However, LIPSSs face the challenge of uniformity control because the formation of micro-/nanostructures induced by ultrafast laser is a complex process involving multiple interacting factors, including laser energy deposition, phase change, light scattering, and instantaneous local changes of material properties and their feedback mechanisms. Recently, there has been some significant progress regarding the control of LIPSS uniformity. In this work, we review recent experimental and methodological advances on this topic from three aspects: 1) laser-induced modified-LIPSS, 2) feedback mechanism of LIPSS formation, and 3) ultrafast laser pulse shaping. This review can stimulate further investigations into the uniformity control of LIPSSs to support and accelerate the industrial applications of uniform LIPSSs.