According to the requirements for high-power laser coating components in the construction of high-power laser facilities in China and， based on the understanding of the damage mechanism of laser coatings， our team at Tongji University has proposed the concept of quantitatively controlling defects in the whole process to prepare laser coatings. Quantitative artificial defects have also been fabricated by using artificial SiO2 spheres with controllable structure and properties. Over the past few decades， we have systematically and quantitatively studied the effects of substrate processing， ultrasonic cleaning， electric field simulation and adjustment， choices of coating material and process parameters， post-treatment after coating， laser conditioning， transferring and preservation of the laser damage characteristics， and damage rules of laser coating components. The validity of the theoretical model of nodule defect electric field enhancement was verified in this study on the basis of the damage morphologies and damage rules， thereby promoting the understanding of the nodule defect damage mechanism. We created new materials and proposed a series of new approaches to improve the damage properties of thin films， realizing the preparation of multi-functional high-intensity laser films that can account for environmental stability， spectral characteristics， and damage characteristics. Our findings will potentially aid the construction of high-power laser facilities and further improvement of laser technology in China.

Nanometrology is a precision measurement technology on the nanometer scale， and it is the basis for advanced nanomanufacturing technology. Traceability is the basic problem of nanometer measurement， and the development of nanometer measurement reference materials is the key link to realizing its metrological traceability and ensuring its uniformity and accuracy. To meet the new requirements of the traceability of nanometer measurement flattening value transmission， we developed three types of self-traceable gratings， including 1D212.8， 2D212.8， and 1D106.4 nm， based on the transition frequency of chromium， by atom lithography and soft X-ray interference technology. On the basis of the silicon line width structure based on multilayer film deposition technology， we explored a self-traceable measurement method of silicon line width based on the lattice constant of silicon. In terms of application， we calibrated scanning probe microscopes， scanning electron microscopes， and other high-precision measuring instruments based on the self-traceable gratings. The research results show that the self-traceable reference material and measurement method can shorten the nanometer metrological traceability chain in various precision instruments and processing technologies and that both offer robust support for advanced nanomanufacturing and a new generation of information technology.

Extreme ultraviolet （EUV） and vacuum ultraviolet （VUV） high-performance， thin-film optical elements considerably improve the capability of conducting high-precision observations and contribute to the development of materials as well as advancements in astronomy， physics， and other disciplines. According to the different application requirements and physical and chemical properties of materials， the Institute of Precision Optical Engineering （IPOE） at Tongji University successfully developed high-performance thin film mirrors， which could meet the application requirements of entire EUV and VUV wavelength ranges （10-200 nm）. This study presents the research progress obtained at the IPOE on the development of EUV and VUV thin-film optical elements. In this paper， the features of thin-film mirrors， monochromators， and polarizers for EUV vacuum band operation are presented. By investigating and characterizing the film’s internal microstructure and its physical and chemical mechanism， a system of film representation， optimization， preparation is established. Additionally， the thickness uniformity， reflectance， response bandwidth， stability， and polarization are improved. The developed mirrors have already been applied to domestic， large-scale scientific instruments （from ground to space）.

Ultralow-loss laser coatings have important applications in precision measurement fields such as gravitational wave detection， optical atomic clocks， and optical cavity ring-down spectroscopy. The cavity length stability and total optical loss of the laser resonator determine the sensitivity and signal-to-noise ratio of the measurement system. With the development of thin-film materials， fabrication processes and detection techniques， significant progress has been achieved in thin-film optical loss and thermal noise research. As regards optical loss， the absorption of the thin film can be controlled at the sub-ppm level， and the scattering of the thin film has become the main contributing factor of optical loss. This paper focuses on defect-induced scattering and interface scattering and presents the research ideas and achievements of thin-film scattering control. The interface scattering of thin films is reduced through optical factor design and interface power spectral density control. The theoretical analysis model of nodule defect-induced scattering is established， and the physical mechanism and the control technology of the defect-induced scattering are proposed. With regard to thermal noise research， this paper primarily introduces the physical mechanism of thin-film mechanical loss， presents the mechanical loss reduction of reflective coating through thin-film material optimization， and the corresponding improvement in the characterization method of mechanical loss.

Extreme ultraviolet （EUV） normal-incidence optical systems are widely used in biological structure microscopic imaging， plasma diagnosis， solar physical observation， and EUV lithography. Therefore， these systems warrant further study. In this paper， the latest developments of the EUV normal-incidence optical system at the Institute of Precision Optical Engineering （IPOE） of Tongji University are presented. Several normal-incidence optical systems used in different applications， such as hot electrons diagnostics， micro-nano imaging， EUV radiation induced damage， and Z-pinch plasma diagnostics are listed. These systems have achieved excellent performance in their respective applications， achieving spatial resolutions of several microns at a millimeter scale field-of-view （FOV） and realizing ultrahigh spatial resolutions on the order of sub-microns for FOVs at tens of microns scale. The systems have also realized ultrahigh-energy-density EUV radiation through a focusing system with large a numerical aperture and helped perform spatiotemporal diagnostics with multi-energy and multi-channels. The research progress of the EUV normal-incidence optical system has provided strong support for the independent and controllable research of plasma diagnostic equipment and technological reserve of advanced manufacturing equipment in China.

High-precision extreme ultraviolet and X-ray observations for space exploration require the development of advanced micro materials for the numerous high-precision optical reflection elements used in such observations. Because short wavelengths are more prone to scattering on optical surfaces， the precision requirements and the fabrication techniques of short-wavelength optical components differ significantly from those of long-wavelength optical components. The Institute of Precision Optical Engineering （IPOE） at Tongji University has 20 years of research experience in this field. We have built a high-accuracy fabrication and measurement platform based on short-wavelength mirrors， developed an ion beam configuration of an ultra-smooth aspheric surface， proposed an absolute measurement method using random off-axis rotation based on Zernike polynomials， and formed a complete technology chain to develop aspheric reflector substrates. These optical components and systems have been successfully applied at several short-wavelength science facilities both in China and abroad. This study will briefly introduce the recent research progress on these optical aspheric reflectors at the IPOE.

Owing to an increased application of novel light sources such as ultra-short and ultra-intense free electron lasers （FEL）， damage resistance of extreme ultraviolet （EUV） and X-ray thin-film mirrors has attracted wide attention. This paper introduces a nanosecond EUV damage instrument manufactured by the Institute of Precision Optical Engineering （IPOE）. EUV damage tests were conducted on boron carbide （B4C） reflective mirrors， gold （Au） and ruthenium （Ru） metal monolayer mirrors， B4C/Ru bilayer mirrors commonly used in EUV and X-ray free electron lasers， and molybdenum-silicon （Mo/Si） multilayer mirrors used in EUV lithography. Damage resistances for thin-film mirrors with different optical materials and structures were determined. Combined with theoretical simulations， damage mechanisms such as thermal melting， thermal stress， and interlayer diffusion-reaction were detected.

The reduced dimensionality of two-dimensional materials gives rise to many novel optical phenomena. In particular， finite size effects and heterogeneities at the micro- to nano-scale significantly modify and even control their linear and nonlinear optical properties. Therefore， optical imaging and spectroscopy of the physical properties at their characteristic length scales are needed to understand and optimize the properties of the two-dimensional materials. In this regime， optical microscopy is one of the most widely applied and effective research techniques. In particular. nonlinear optical microscopy with a high signal-to-noise ratio and resolution under broadband response can effectively characterize the fundamental physical properties of two-dimensional materials， which plays a key role in the elementary research and applications of two-dimensional materials. In this paper， we review the progress of nonlinear optical microscopy in sensitively resolving layer number， crystal axes， grain boundaries， stacking orders， external coupling， etc.， in graphene， transition metal dichalcogenides， and their heterostructures. We discuss the technical challenges of nonlinear optical microscopy and provide a perspective on the future of the field.

To meet the requirements of laser detection， Tongji University established a full link R & D platform for a precision opto-mechanical system encompassing optical design， structural design， component manufacturing， assembly and adjustment integration， performance evaluation and application after more than ten years of construction. For the development of complex optical and mechanical systems， an efficient coupling comprehensive design method of optical， structural， and thermomechanical design has been developed， a precision assembly integration method based on optical and mechanical error decomposition has been established， a high-precision integrated assembly process and technology for the centering and adjustment of transmission optical systems and reflection optical systems have been formed， and optical system wavefront and imaging performance testing instruments have been equipped， which supports the development of precision optical and mechanical systems with various complex functions. This study comprehensively reviews research on the development of precision opto-mechanical systems and instruments for laser detection. To meet the detection requirement of China's XG-III strong laser facility， the first active and passive composite diagnostic device combining VISAR and SOP and a radiation high temperature optical measurement system are developed， which together provide technical support and diagnostic testing for XG-III to conduct the experiment of ultra-high pressure equation of state. To meet the requirements of measuring the laser scattering characteristics of targets and environments in a sea environment， diffused light and dual function parallel light LRCS laser measuring devices， which can accurately measure the laser scattering characteristics of standard scatterers and sea environment in sea environment simulations and provide mathematical models and experimental data for the development of ultra-low altitude lidar， have been developed.

Neutron scattering and diffraction spectrometers are powerful tools used in modern scientific measurements. Neutron film elements and optics have become the key parts of guiders， collimators， benders， polarizers， and flippers， because they can transport， focus， collimate， and polarize neutrons. Currently， owing to the increase in the number of neutron facilities in China， the demand for neutron film elements and optics has also been increasing. In this paper， the development and applications of supermirrors， flippers， guiders， and focusing optics are presented based on the supermirrors at the Institute of Precision Optical Engineering （IPOE） at Tongji University.

The development of precision X-ray diagnostics is important for examining the physical processes in inertial confinement fusion （ICF）. The latest advances in high-performance multilayer grazing X-ray optics at the Institute of Precision Optical Engineering of Tongji University are comprehensively introduced herein. To serve the diagnostic needs of ICF with high spatial， temporal， and spectral resolutions and high efficiency， the current research progress is systematically introduced in terms of multichannel grazing X-ray imaging technology and multilayer grazing X-ray imaging technology with their application effects. Multichannel grazing X-ray imaging is mainly introduced in terms of the multichannel KB imaging microscope and its high-precision online alignment technology. To achieve high spatial resolution （<5 μm） and sixteen imaging channels， high-reset-precision integrated "object-diagnostic microscope-image" indication technology was developed； this effectively guarantees the applicability of the multichannel KB microscope. Multilayer grazing X-ray imaging provides spectral regulation by use of X-ray multilayers， as well as precision aiming technology for online alignment. Several sets of multispectral X-ray diagnostic equipment based on an array of multilayer mirrors have been widely used in domestic laser facilities with spatial resolutions of 3-5 μm and four energy points. The key technical performance indicators are significantly better than those of similar technology from abroad； this affords strong support for domestic ICF diagnostics.

X-ray multilayers are key optical elements in synchrotron radiation and free electron laser facilities， astronomical observations， plasma diagnostics， and lab-based analytical instruments. They can realize highly efficient reflection， monochromatization， and polarization of X-rays. Our group has been conducting systematic studies on the design， fabrication， and characterization of X-ray multilayers during the past 20 years. We have developed a series of high-performance multilayers with world-class level reflectivity at different wavelengths and have built the deposition platform for large size X-ray multilayers based on the magnetron sputtering technique. The largest deposition mirror could achieve a length of 1.2 m. The fabricated， hard X-ray multilayer mirrors have been successfully applied in synchrotron radiation facilities both in China and abroad. Through the combination of multilayer and reflective gratings， innovative， ultrahigh efficiency， tender， X-ray multilayer grating optics have been developed. Compared with conventional single-layer gratings， a maximum efficiency improvement of 40 times could be achieved. This study will introduce the results and progress that were achieved by our group in X-ray multilayer elements.

According to China's construction and engineering mission requirements for high-power laser devices， Tongji University has established a nanosecond- and femtosecond-pulse-laser automated laser-induced damage threshold test system. The system can perform automatic detection， location reinspection， transient diagnosis， and in situ measurement of micrometer and submicrometer damage via a testing process based on the ISO standard and raster scan method. In addition， through extensive academic exchanges and international damage threshold evaluation， an international standard calibration of the measurement results was performed. Utilizing this test system for over a decade， we systematically studied the effects of the following factors on the laser-induced damage threshold： substrate lapping and polishing， ultrasonic cleaning and surface residue， thin film design and large-angle suppression， three-dimensional electric field simulation and the lens-focusing effect， coating material selection and oxidation， geometric shaping control and planarization of nodules， environment retention and transfer control， coating optimization and auxiliary processes， annealing and post-processing， storage environment and anthropogenic pollution， and others. According to the laser damage characteristics of different objects under different parameters and working conditions， the inducement， evolution， and mechanism of laser damage are studied. In addition， the laser damage dynamic characteristics of transmission elements are studied based on pump-probe imaging. Laser-induced damage threshold characterization and damage precursor tracing are the key technologies used by our research group in the development of ultra-high-threshold and large-size laser thin-film devices. Notably， our system provides high-confidence laser-induced damage threshold testing services for several domestic and foreign scientific research institutions， universities， and enterprises.

Computational imaging is an emerging research field that combines optical systems and image processing to achieve specific imaging features. For a long time， this kind of combination in computational imaging has adopted a sequential design mode， that is， the optical system and image processing are designed separately， making it difficult to exploit the synergistic advantages of both entirely. With the rapid development of deep learning， the end-to-end co-design method of optics and image processing algorithms based on deep learning architecture has opened the door to solving this problem. On the one hand， end-to-end co-design can realise the automatic optimal collaboration of optics and image processing by comprehensively exploring the entire solution space. On the other hand， end-to-end design makes it possible to develop specific optical imaging systems. In this paper， we review recent advances in end-to-end co-design of optics and image processing， including full-colour imaging of flat lenses， large field of view imaging， extended depth of field imaging， and super-resolution imaging， and snapshot spectral imaging.