BACKGROUND AND PURPOSE:Although X-ray FLASH radiotherapy (FLASH-RT) has shown promise in reducing normal tissue toxicity, its effects on the testis and the underlying mechanisms remain poorly understood. This study aimed to investigate the characteristics and mechanisms of X-ray FLASH-RT-induced testicular injury in C57BL/6J mice. METHODS:Testicular injury was evaluated following FLASH-RT at different doses (0, 2, 6, 8, 12, and 20 Gy) and time points (days 1, 7, 21, and 70), with conventional radiotherapy (CONV-RT) as a comparator. Histological and functional damage was assessed by hematoxylin and eosin staining, Ki-67 immunostaining, TUNEL staining, and epididymal sperm counts. Testicular tissues collected on day 7 after irradiation were subjected to RNA sequencing and proteomic analysis. The role of GSTM3 in response to FLASH-RT and CONV-RT was validated in mouse testes and in the GC-1 mouse spermatogonia cell line. Ferroptosis was evaluated by detecting ferroptosis-related proteins and ultrastructural changes using transmission electron microscopy. In addition, a FLASH-RT-resistant GC-1 cell line (GC-1R) was established and analyzed by single-cell RNA sequencing (scRNA-seq). RESULTS:FLASH-RT-induced testicular injury exhibited dose- and time-dependent features. On day 7 after 6 Gy irradiation, FLASH-RT caused less histological damage than CONV-RT. Integrated transcriptomic and proteomic analyses implicated ferroptosis in this process and identified GSTM3 as a FLASH-RT-responsive molecule. Functional experiments showed that GSTM3 downregulation aggravated FLASH-RT-induced testicular injury, whereas GSTM3 overexpression conferred protection. These effects were accompanied by significant alterations in ferroptosis-related markers, including GPX4, FTH1, ACSL4, and 4-HNE. Moreover, the ferroptosis inhibitor liproxstatin-1 (Lip-1) reversed the aggravated injury caused by GSTM3 downregulation. By contrast, modulation of GSTM3 expression did not significantly affect CONV-RT-induced injury in either mouse testes or GC-1 cells. ScRNA-seq analysis of GC-1R cells further suggested that radiation resistance may be associated with suppression of ferroptosis. CONCLUSION:GSTM3 alleviates FLASH-RT-induced testicular injury by modulating ferroptosis. These findings improve our understanding of FLASH-RT-induced testicular injury and suggest potential strategies to protect against this damage.

FLASH radiotherapy (FLASH-RT), as a burgeoning and promising cancer treatment approach, spares normal tissues from radiation damage by delivering ultra-high doses to tumors within an extremely short duration, without compromising anti-tumor efficacy. Specifically, electron-based FLASH-RT can be used to treat superficial skin cancers, offering unique advantages in clinical radiotherapy. To enhance understanding of the physical characteristics of acoustic waves induced by ultra-high-dose-rate pulsed electron-beam irradiation, this study developed an integrated simulation workflow based on Monte Carlo and k-space pseudospectral methods. This computational framework enables full end-to-end simulation of single-pulse dose delivery to a target in electron-based FLASH-RT, followed by the spatial propagation and attenuation of the resulting acoustic waves. To capture acoustic waves generated by single-pulse irradiation from a linear accelerator, a dedicated data acquisition (DAQ) system was also designed and implemented based on analysis of simulated acoustic signal characteristics. The differences between simulated and experimental signals across multiple domains were compared under various conditions. The developed simulation workflow and DAQ system facilitate a comprehensive study of the physical properties of acoustic waves induced by ultra-high-dose-rate pulsed electron-beam irradiation and the development of an electron-based FLASH-RT dosimetry system.

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.

FLASH radiotherapy (FLASH-RT) is an emerging radiation therapy technique that delivers ultra-high radiation doses within an extremely short time frame, ensuring effective tumor control while significantly reducing damage to normal tissues. During X-ray FLASH-RT, quantitative reconstruction of the delivered dose distribution in irradiated regions is crucial for dosimetric evaluation and radiotherapy efficacy prediction. X-ray-induced acoustic imaging (XAI), which detects acoustic waves generated by X-ray absorption, has been preliminarily verified in our previous study as an online and noninvasive dosimetry tool during FLASH-RT due to its high sensitivity to radiation deposition. However, conventional reconstruction methods used in XAI (e.g., time reversal) provide a fast solution while dose artifacts remain. To address this challenge, this study proposes a novel physics-informed deep learning framework, termed X-TRUNet, for non-invasive dose reconstruction based on Encoder–Decoder architecture to effectively suppress dose artifacts and improve reconstruction accuracy in X-ray FLASH-RT. Simulation results on standard medical phantoms indicate that the proposed method achieves an RMSE as low as 0.00017, a PSNR exceeding 40 dB, and an SSIM above 0.99 in reconstructed dose images; even under extreme noise conditions (SNR = 0 dB) typical of X-ray FLASH-RT environments, this method still maintains clinically acceptable performance metrics, significantly outperforming conventional reconstruction methods. These studies show the promising potential of the proposed method for achieving high-precision quantitative dosimetry in XAI using an array transducer, potentially enabling in vivo dose verification for X-ray FLASH-RT.

This study aimed to evaluate whether the clinical prototype of intraoperative electron FLASH radiotherapy (CPIO-EFLASH), with a source-surface distance (SSD) of 50 cm, could achieve ultra-high dose rates, effectively control tumors, and trigger the FLASH tissue-sparing effect in preclinical models. Subcutaneous tumor-bearing mice (4T1 breast cancer, U87-MG glioma, PAN02 pancreatic cancer) and healthy C57BL/6 female mice (whole-brain, thorax, abdomen and single-leg irradiation) were subjected with ultra-high dose rate radiotherapy (UHDR-RT, ≥ 40 Gy/s), conventional doserate radiotherapy (CONV-RT,0.07 Gy/s), or sham radiotherapy (Control). We evaluated survival status, tumor growth suppression, apoptosis, proliferation, and DNA damage in tumor tissues, along with radiation-induced injuries to the brain, lung, intestine, and skin tissues. The actual dose rates of UHDR-RT ranged from 192 to 473 Gy/s. No significant difference in tumor growth suppression was observed between the UHDR-RT and CONV-RT. Two months post whole-brain irradiation, UHDR-RT demonstrated better spatial learning and memory abilities compared to CONV-RT. At 120 days post whole-thorax irradiation and 90 days post whole-abdomen irradiation, the survival rates of UHDR-RT were also significantly higher. Histological analyses revealed more severe injury to lung and intestinal tissues in the CONV-RT group. Additionally, UHDR-RT exhibited milder radiation-induced skin injury from 2 to 8 weeks post-irradiation. The CPIO-EFLASH can achieve ultra-high dose rates (≥ 40 Gy/s at an SSD of 50 cm) and trigger significant normal tissue-sparing effects. Integrating electronic FLASH technology into intraoperative radiotherapy may bring potential clinical benefits by effectively treating tumors, while minimizing radiation-induced injury to normal tissues. Our findings highlight the necessity for further clinical trials of CPIO-EFLASH in intraoperative radiotherapy.

Background: To compare neural damage induced by ultra-high dose rate FLASH radiotherapy (FLASH-RT) with that induced by conventional dose rate radiotherapy (CONV-RT) in healthy mice. Methods: Eighty adult male C57BL/6J mice were divided into five groups: Sham, CONV-RT10Gy, CONVRT20Gy, FLASH-RT10Gy, and FLASH-RT20Gy. Three days post-irradiation, morphological changes in neurons within the dentate gyrus (DG), CA1, and CA3 were observed using hematoxylin and eosin and Nissl staining. The malondialdehyde (MDA), reduced glutathione (GSH), glutathione peroxidase (GSHPX), superoxide dismutase (SOD), catalase (CAT), and hydroxyl radical (OH-) levels were measured using assay kits. Quantitative reverse transcription PCR was used to assess interleukin (IL)-1b, IL-6, inducible nitric oxide synthase (iNOS), and tumor necrosis factor (TNF)-a mRNA expression levels in hippocampus. Immunofluorescence was employed to observe microglial activation in the DG. Results: Compared with Sham, CONV-RT10Gy and CONV-RT20Gy exhibited disorganized neuronal arrangements and blurred nucleoli in the DG; the number of Nissl body was reduced, but FLASH-RT10Gy and FLASH-RT20Gy alleviated these abnormalities. Moreover, FLASH-RT20Gy mitigated the upregulation of MDA and downregulation of GSH, GSH-PX, SOD, CAT, and OH- levels in the hippocampus of mice subjected to CONV-RT20Gy. Additionally, FLASH-RT20Gy attenuated the upregulation of IL-1b, IL-6, iNOS, and TNF-a mRNA levels in hippocampus of mice subjected to CONV-RT20Gy and diminished microglial activation in the DG. Conclusion: FLASH-RT mitigate the structural and functional disruptions in hippocampal neurons induced by CONV-RT and alleviate oxidative stress and inflammation in hippocampal tissue by reducing microglial activation. (c) 2025 Published by Elsevier Ltd on behalf of Tsinghua University Press. This is an open access article

Free-electron laser (FEL) operating in the terahertz (THz) spectral regime has found significant applications in diverse research fields. Nevertheless, fiber-based THz modulators based on FEL systems remain relatively underexplored. This study proposes a THz modulator based on side-polished fiber integrated with GaAs/Au nanoparticles (Nps) that demonstrates effective compatibility with the China Academy of Engineering Physics' THz FEL system. The modulator operates under high-power THz pulses (3 W) and achieves effective amplitude modulation across a broad frequency range from 1.6 to 3.0 THz. Owing to structural mode resonance, the modulator reaches the maximum modulation depth at 2.7 THz. The modulation depth was further enhanced by simultaneously applying optical and electrical modulation, i.e., optoelectronic synergistic optimization. Under a pump laser power of 235 mW, the peak modulation depth increases from 58.56% (at 0 V) to 67.11% (under 2.0 V). This investigation provides a solid foundation for the future application of fiber-based THz modulators in materials science, atomic physics, and biomedical studies, demonstrating their potential to advance the development of THz technology.

The Chinese Academy of Engineering Physics Terahertz Free Electron Laser Facility (CAEP THz FEL, CTFEL) has been operated as a user facility for over five years. To further meet the growing demands of modern science, an upgrade project for an infrared-terahertz free electron laser facility based on CTFEL has been proposed to broaden the frequency range from 0.1–4.2 to 0.1–125 THz. Recently we upgraded the CTFEL photoinjector in order to fulfill the beam injection requirements of the infrared-terahertz free electron laser facility. In this paper, we measured the beam parameters of the upgraded CTFEL photoinjector. A Michelson interferometer was constructed to measure the auto-correlation of the coherent transition radiation emitted by the electron bunch. Both the Kramers–Kronig reconstruction method and the time-domain fitting approach have been employed to estimate the bunch length, resulting in a root-mean-square bunch length of 0.30 ps. A normalized transverse emittance of 5.62 π mm mrad was determined by a quadrupole scan. The measured mean energy of the electron bunch is adjustable between 6 and 8 MeV with an energy spread of less than 0.5%. These measurements prove that the upgraded CTFEL photoinjector fulfills the injection requirements of the facility to be built.

Dual-plane lensless coherent imaging is investigated with China Academy of Engineering Physics terahertz free electron laser (CAEP THz FEL, CTFEL). It is the first demonstration of THz imaging on the CTFEL. Different from real-time acquisition with a continuous-wave laser, a scheme of multiframe acquisition and averaging is proposed to obtain a full-field image with the pulsed CTFEL. A normalization operator based on the image itself is introduced to integrate the positive absorption constraint into the reconstruction routine. To break through the limited aperture of the THz detector array, the aperture synthesis technique is employed to enhance both the field of view and spatial resolution. In the reconstruction, the multiplane phase retrieval is formulated as an optimized inverse problem regularized by the total variation and absorption constraint. We experimentally demonstrate the success of the proposed method with biological and polymer samples and achieve a subwavelength lateral resolution of 85 mu m (0.85 lambda). Considering the advantages of CTFEL and lensless coherent imaging, this work is expected to pave the way for the research and applications of CTFEL-based THz imaging.

PURPOSE:This study investigated whether the Flash effect could be triggered using a compact single high-energy x-ray source (CHEXs) FLASH radiation therapy with or without two 30-second pauses during irradiation in mice. METHODS AND MATERIALS:The integral dose and beam time structure of the CHEXs were measured using an EBT-XD radiochromic film and a beam current transformer. Healthy C57BL/6J female mice and subcutaneous tumor models were irradiated under different conditions: sham, FLASH radiation therapy (FLASH1: delivering the total dose in 1 delivery; FLASH3: the total dose was split into 3 identical deliveries with two 30-second pauses, simulating gantry rotation time requirements in 3-field conformal radiation therapy), and conventional dose rate radiation therapy. Various total doses were administered to the corresponding normal tissues (whole body, whole thorax, whole abdomen, and skin) and tumors (CT26 and Lewis lung carcinoma). Survival status, normal tissue damage, and tumor growth suppression were recorded. RESULTS:The average dose rate of the CHEXs ranged from 244 to 388 Gy/s. For whole-body, whole-thorax, and skin irradiation, both FLASH1 and FLASH3 demonstrated protective effects. For whole-abdomen irradiation, FLASH1 exhibited a superior protective effect. No significant differences in tumor growth responses were observed between the FLASH1, FLASH3, and conventional dose rate radiation therapy groups (P > .05). CONCLUSIONS:Both CHEXs with or without two 30-second pauses during irradiation can trigger the Flash effect. This suggests that CHEXs may be beneficial for 3-dimensional conformal radiation therapy.

Purpose Preclinical studies have demonstrated that FLASH radiation therapy (RT) delivered at ultrahigh-dose rates exerts a preferential normal tissue-sparing effect. This study aimed to delineate the disparities in delayed cognitive function and biological outcomes of whole-brain irradiation in healthy mice, comparing FLASH-RT with conventional RT (CONV-RT). Methods and Materials Eighty adult male C57BL/6J mice were divided into 5 groups: Sham, CONV-RT10Gy, CONV-RT20Gy, FLASH-RT10Gy, and FLASH-RT20Gy. Whole-brain irradiation was conducted on mice using a miniaturized x-ray FLASH platform at field-average dose rates of 2 Gy/min for CONV-RT and 213 Gy/s for FLASH-RT. Two months after irradiation, we assessed the mice’s cognitive function and the number of astrocytes and neurons in the hippocampus, then conducted proteomic analyses of their hippocampus. Results Following the administration of a 20 Gy FLASH-RT dose, the incidence of radiodermatitis was markedly lower than that observed with CONV-RT, accompanied by an improvement in survival rates. Compared with the Sham and FLASH-RT groups, the CONV-RT group exhibited reduced exploration of the open arms in the elevated plus maze, diminished preference for the novel arm in the Y-maze, a lower discrimination index in the novel object recognition test, and prolonged latency to reach the platform in the water maze test. Compared with the FLASH-RT group, the CONV-RT group exhibited an increase in astrocytes and a decrease in neurons in the hippocampus. Proteomic analysis revealed that FLASH-RT may improve the oxidative stress damage caused by CONV-RT. Conclusions This study demonstrated that FLASH-RT conferred significant advantages over CONV-RT in preserving delayed cognitive function and reducing radiation-induced toxicity in healthy mice. Compared with CONV-RT, FLASH-RT mitigated behavioral deficits across multiple cognitive domains and attenuated hippocampal oxidative stress, highlighting its neuroprotective potential. These findings provided compelling preclinical evidence supporting the therapeutic promise of FLASH-RT as a safer alternative to conventional RT for protecting normal brain function.

Quasi-bound states in the continuum (QBIC), with exceptionally high-Q factors and the local field enhancement effect, have found potential applications in matter sensing. Introducing the QBIC mechanism into terahertz (THz) metasurfaces can significantly enhance the interaction between incident THz waves and matter, providing a feasible platform for the detection of biochemical substances. Currently, most experimental studies on terahertz QBIC metasurfaces utilize metallic structures. By contrast, research on terahertz all-dielectric QBIC metasurfaces generally remains at the simulation stage due to the high fabrication process requirements, and transitioning to the experimental stage still poses many challenges. In this paper, a hollow-structured all-silicon metasurface supporting THz QBIC is proposed. The resonance of THz QBIC is excited via a simple hollow structure and observed in experiment. Simulations and experimental results demonstrated that the designed THz QBIC metasurface can achieve sensing of Auramine O. Notably, it is the first study, to our knowledge, to employ a metasurface to sense Auramine O. Additionally, the sensing performance maintains good stability under different humidity and temperature conditions. This study provides new references and insights for the design and implementation of THz QBIC, and also opens a new pathway for the detection of Auramine O.

Purpose Recent studies indicated that ultrahigh dose rate (FLASH) radiation can reduce damage to normal tissue while maintaining anti-tumour activity compared to conventional dose rate (CONV) radiation. This paper provides a comprehensive description of the current status of the Platform for Advanced Radiotherapy Research (PARTER), which serves as the first experimental FLASH platform utilizing megavoltage X-rays and has facilitated numerous experiments. Methods and Materials PARTER was established in 2019 based on a superconducting linac to support experimental FLASH studies using megavoltage X-rays. Continuous upgrades have been made to the accelerator, collimators, flattening filters, monitors, other auxiliary devices, and irradiation process in order to achieve optimal results. Passive and active dosimeters are employed for measuring dose distribution and to ensure traceability of radiation doses. Results The dose monitors and dosimeters demonstrate reliable performance with acceptable stability. At PARTER, the maximum mean dose rate is approximately 400 Gy/s at a surface-source distance of 20 cm (over 1000 Gy/s at smaller distances), with an instantaneous dose rate of approximately 8E5 Gy/s. Both passive and active dosimeters exhibit good linearity and agreement during FLASH X-ray irradiation. The monitors show good linearity to dose rate, with short-term fluctuations within 1.5 % for the diamond monitor. The discrepancy between measured absorbed dose and dose protocol is typically less than 4 %. The X-ray energy spectra on PARTER are comparable to those for megavoltage CONV linacs operating in flattening filter-free mode. The maximum field size of the FLASH beam is 4.5 cm × 4.5 cm. The FLASH dose profile demonstrates satisfactory flatness (1.04) and similar penumbra compared to clinical CONV linac, while the percentage depth dose curve of FLASH X-rays is steeper than that of the clinical megavoltage CONV X-ray. Conclusions PARTER represents a pioneering platform for conducting megavolts FLASH X-ray irradiation in biological experiments. It effectively fulfills the requirements of preclinical research on megavoltage X-ray FLASH and undergoes continuous upgrades to meet increasingly demanding performance criteria.

Ultra-high dose rate radiotherapy (FLASH radiation) can naturally render normal tissues around the tumor tissue resistant to radiotherapy. In contrast, the tumor tissue remains sensitive to radiation under the same conditions. However, the effects of different fractions and dose rates on FLASH radiation remain unclear. This study aimed to determine the optimal dose rate and fraction of FLASH radiation for thoracic radiotherapy. Female Balb/c mice aged 6-8 weeks were irradiated with different dose rates (100 Gy/s or 250 Gy/s) and fractions (1, 2, or 4). Survival was observed in mice receiving 30Gy, with lung tissue examined for acute radiation damage 48 h post-radiation. Late radiation pneumonia and survival rates were monitored in mice irradiated with 20 Gy. The median overall survival (OS) was not reached on the 95th day for mice irradiated with 250 Gy/s FLASH radiation, while it was 89.5 days for those irradiated with 100 Gy/s (P = 0.0436). Mice irradiated with 30 Gy/2 Fr and 250 Gy/s FLASH had shorter median OS than those with 30 Gy/1F (P = 0.0132). However, there was no significant difference in OS between mice irradiated with 30 Gy/2 F and 30 Gy/4 F. Survival curves for mice receiving 20 Gy showed no significant difference in toxicity between different dose rates and fractions. FLASH radiation at 250 Gy/s reduced the incidence of acute radiation pneumonitis in mice compared to 100 Gy/s. Different fractions of irradiation influenced survival in mice, but they were only observed in acute radiation reactions and not chronic radiation reactions. Among the tested fraction methods, fraction 2 had the worst impact on the survival of mice, while fractions 1 and 4 showed similar effects and improved survival compared to fraction 2.

Low-emittance photoinjector-enabled cutting-edge scientific instruments, such as free-electron lasers, inverse Compton scattering light sources, and ultrafast electron diffraction, will greatly benefit from the improved repetition rate. In this paper, we proposed a specifically designed S-band radio frequency (RF) photoinjector to obtain low emittance and kilohertz (kHz) high-repetition rates simultaneously. By lowering the gradient, much lower RF power is needed to feed the electron gun, and then the heat problem is much easier to handle. Meanwhile, by optimizing the length of the gun’s first cell from the normal case of 0.6-cell to 0.4-cell, the launch phase and the extraction field are significantly improved, thus ensuring the generation of low-emittance electron beams. In our design, the proposed 1.4-cell RF gun can work effectively under different field gradients ranging from 30 MV/m to 100 MV/m. For a standard case of 60 MV/m, 2.5 MW peak RF power with μs level pulse width is sufficient, thus offering the feasibility of improving the repetition rate to kHz level with a standard 5 MW irradiation klystron. In addition, simulated electron beams with a low emittance of 0.29 mm.mrad@200 pC can be generated by this proposed photoinjector, showing that this high-repetition rate injector holds the potential to deliver high-quality beams comparable to those of state-of-the-art S-band photoinjectors. Combining the merits of low emittance and high-repetition rate, this proposed photoinjector will provide a new possibility for future free-electron laser facilities operating at repetition rates ranging from kHz to tens of kHz.

Significance Extreme ultraviolet (EUV) lithography technology is critical for realizing highend chip manufacturing at the 7 nm node and below. Currently, EUV lithography machines mainly use laser plasma (LPP) light sources. The maximum EUV power achieved by an LPP light source is approximately 500 W. For nodes smaller than 3 nm, satisfying the power requirements of LPP light sources is difficult. The development of EUV lithography in the future will require more powerful light sources. A free - electron laser based on energy recovery linacs (ERL - FEL) can achieve a laser output with high repetition frequency, high average power, and high energy efficiency. With the development of FEL and ERL technologies, an ERL - FEL light source can achieve an output power of more than 10 kilowatts at a wavelength of 13.5 nm and is thus a promising highpower EUV lithography light source. Progress A free - electron laser is a type of radiation laser based on free electrons in vacuum. Compared with those of traditional lasers, the radiation wavelength does not depend on the excited medium but is related only to the electron beam energy and undulator magnetic field. An energy recovery linac accelerates the electron beams in the acceleration phase. After application, the accelerated electron beams return to the main accelerator during the deceleration phase and the power of the highenergy electron beam is converted into the microwave acceleration field power to accelerate the subsequent injected electron beams, which can achieve highefficiency energy recovery and utilization. The FEL light source based on ERL technology provides a new technical route for the development of highpower EUV lithography. Since Madey first proposed the concept of free - electron lasers in 1971, at least 50 FEL facilities have been built worldwide, and at least 20 FEL facilities are currently under construction or planned. In 1965, Tigner first proposed the concept of energy - recovery linacs. In recent decades, ERL technology has been regularly applied in different fields, and countries worldwide have conducted research and construction work on ERL facilities. One of the most important applications of ERL is in the generation of highpower FELs. Global ERL - FEL light sources that have been constructed mainly include the JLAb FEL in the United States, Novosibirsk FEL in Russia, ALICE in the United Kingdom, and JAEA FEL and cERL in Japan. In addition, Peking University, the Institute of High Energy Physics of the Chinese Academy of Sciences, the Shanghai Institute of Applied Physics of the Chinese Academy of Sciences, and China Academy of Engineering Physics have conducted physical design and theoretical research studies on ERL - FELs. However, no ERL - FEL facilities have been fully constructed in China. In 2015, KEK proposed an ERL - FEL plan for EUV lithography light sources based on a cERL, which can generate an EUV laser power greater than 10 kW. Russia, Germany, and Israel have proposed a compact EUV - FEL light source with an output power of approximately 5 kW. The Shanghai Advanced Research Institute of the Chinese Academy of Sciences has also proposed a fully coherent EUV light source plan based on the ERL. Although ERL - FEL light sources for EUV lithography have significant development potential, many key technical problems must still be solved. To obtain a kilowatt - level EUV - FEL output, the facility must operate in a state of high average current and high beam power for a long period, which places higher requirements on photocathode injectors, superconducting accelerators, and energy recovery technology. Conclusions and Prospects Traditional LPP technology encounters bottlenecks below the 3 nm node. In the future, the development of EUV lithography will require kilowatt - level highpower light sources. An ERL - FEL light source can achieve an output power above the kilowatt level and is considered to be a highly promising next - generation lithography light source. This study introduces the working principles, development status, and key technical challenges of highpower ERL - FEL light sources.

Ultra-narrow pulses serve as critical components in numerous applications. These pulses have ultra-fast leading edges that typically function as precision trigger signals to synchronize various instruments. Ultra-narrow pulses inherently exhibit an ultra-wide bandwidth, gaining significant attention in diverse electronic systems encompassing communications, radar imaging, electronic warfare, and others. Although several techniques have been explored for generating ultra-narrow pulses, field programmable gate arrays (FPGAs) offer a promising alternative in terms of flexibility and integration. This study introduces a scalable delay pulse synchronizer method with a resolution of 23 ps. A programmable, successive, narrow pulse sequence operating at a 1-GHz repetition frequency is implemented within a monolithic FPGA. The performance of the proposed method is evaluated using an existing board with a general commercial FPGA in the laboratory. This new method presents a convenient and efficient approach of achieving ultra-narrow pulse synchronization, being applicable across various fields.

As terahertz (THz) technology advances, the interaction between THz radiation and the living body, particularly its effects on the immune system, has attracted extensive attention but remains poorly understood. This study firstly elucidated that exposure to 3 THz-FEL radiation markedly suppressed contact hypersensitivity reactions in mice induced by DNFB, as evidenced by a reduction in ear thickness and a discernible recovery in the Th1/Th2 cell balance. 3 THz irradiation led to cellular stress in the irradiated skin locale, increasing the levels of IL-4 and IL-10 and modulating the activity and migration of dendritic cells and mast cells. Furthermore, THz irradiation precipitated a rapid alteration in the skin lipidome, altering several categories of bioactive lipids. These findings offer new insights into the immunomodulatory effects of THz radiation on living organisms and the potential underlying mechanisms, with implications for the development of therapeutic approaches in managing skin allergic diseases.

Absorbers are devices that internally consume electromagnetic waves to partially or completely attenuate them. The basic idea is to absorb electromagnetic radiation by resonating the intended surface with the incident electromagnetic waves. This article focuses on the development of the absorber (from single-band to multi-band, narrow to broadband, non-tunable to tunable, and so on). The basic absorption principle of the current popular and excellent metamaterial graphene absorber is provided, as is the theoretical explanation of impedance matching and how to attain critical performance metrics like tunability, as well as prospects for terahertz (THz) absorber applications. Finally, numerous innovative absorbers are shown as examples, providing new ideas for future researchers.