2024

• Record 349 of
  
  Title:Optimization of signal-to-noise ratio of laser heterodyne radiometer
  
  Author(s):Sun, Chunyan(1,2,3); He, Xinyu(1); Xu, Ruoyu(1); Lu, Sifan(1); Pan, Xueping(1); Bai, Jin(1)
  Source: Microwave and Optical Technology Letters  Volume: 66  Issue: 1  DOI: 10.1002/mop.33857  Published: January 2024  
  Abstract:The ground-based laser heterodyne radiometer (LHR), which exhibits the advantages of small size, high spectral resolution, and easy integration, has been used for the remote sensing detection of several gases to meet a wide range of needs. This study aims to optimize the laser heterodyne system for detecting CO2 gas by focusing on existing research. Firstly, using the all-fiber laser heterodyne detection system built by our research group, the power spectrum associated with the radio frequency signals of the detection system is discussed under different conditions: under no irradiation, under sunlight only, under sunlight and laser irradiation at the absorption peak, and under a filter in the spectrum range of 185–270 MHz. Signal-to-noise ratios (SNRs) of the high-resolution spectrum have been obtained using different filter bands of 185–270, 225–270, and 225–400 MHz. Finally, the filter in the 225–270 MHz band, which has the highest SNR, is selected. Consequently, the resolution is improved and the system is further optimized. Furthermore, an optical fiber attenuator is used to change the power of the local oscillator light entering the system, and hyperspectral spectra with varying percentages of input energy and total energy are obtained. When the laser attenuation reaches 40%, the optimal SNR of the system is 486 and can be further improved to meet the expected requirements. This study will provide insights for improving the applicability of laser heterodyne technology in atmospheric sounding. © 2023 Wiley Periodicals LLC.
  Accession Number: 20233714728857
• Record 350 of
  
  Title:Generation of arbitrarily structured optical vortex arrays based on the epicycle model
  
  Author(s):Yuping, T.A.I.(1,2); Haihao, F.A.N.(1); Xin, M.A.(1); Wenjun, W.E.I.(1); Zhang, Hao(1); Tang, Miaomiao(1); Xinzhong, L.I.(1,2,3)
  Source: Optics Express  Volume: 32  Issue: 6  DOI: 10.1364/OE.521250  Published: March 11, 2024  
  Abstract:Optical vortex arrays (OVAs) are complex light fields with versatile structures that have been widely studied in large-capacity optical communications, optical tweezers, and optical measurements. However, generating OVAs with arbitrary structures without explicit analytical expressions remains a challenge. To address this issue, we propose an alternative scheme for customizing OVAs with arbitrary structures using an epicycle model and vortex localization techniques. This method can accurately generate an OVA with an arbitrary structure by predesigning the positions of each vortex. The influence of the number and coordinates of the locating points on customized OVAs is discussed. Finally, the structures of the OVA and each vortex are individually shaped into specifically formed fractal shapes by combining cross-phase techniques. This unique OVA will open up novel potential applications, such as the complex manipulation of multiparticle systems and optical communication based on optical angular momentum. © 2024 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement.
  Accession Number: 20241215766416
• Record 351 of
  
  Title:Depth-Resolved Imaging Through Dynamic Scattering Media Via Speckle Cross-Correlation Under Near-Infrared Illumination
  
  Author(s):Wang, Ping(1,2); Zhou, Meiling(2); Zhang, Yang(2,3); Li, Runze(2); Peng, Tong(2); Zhou, Yuan(2,3); Min, Junwei(2); Yao, Cuiping(1); Yao, Baoli(2,3)
  Source: SSRN  Volume:   Issue:   DOI: 10.2139/ssrn.4690404  Published: January 10, 2024  
  Abstract:Speckle cross-correlation imaging (SCCI) method has the depth-resolved capability, benefiting from the introduction of a reference point. However, the quality of the reconstructed image is severely degraded due to the background noise, which becomes more prominent when imaging through dynamic scattering media. Here, we propose a composite-differential filter-assisted speckle cross-correlation imaging (CDF-SCCI) method, allowing for effectively reducing the background noise of the reconstructed image. The CDF-SCCI method can increase the reconstructed image contrast by a factor of 5. A speckle cross-correlation based imaging system under near-infrared (NIR) illumination is built to enhance the imaging quality further. Quantitative comparison of the reconstructed results through dynamic media with different optical depths reveals the superiority of the NIR illumination over the visible light illumination, extending the maximum optical depth from 7.7 to 10.4. The depth-resolved imaging through various dynamic media, including the SiO2 suspension, milk and anticoagulated pig blood, further demonstrates the potential application of the proposed CDF-SCCI method under NIR illumination in biomedical imaging. © 2024, The Authors. All rights reserved.
  Accession Number: 20240035370
• Record 352 of
  
  Title:Attention Network with Outdoor Illumination Variation Prior for Spectral Reconstruction from RGB Images
  
  Author(s):Song, Liyao(1); Li, Haiwei(2); Liu, Song(3); Chen, Junyu(2); Fan, Jiancun(4); Wang, Quan(2); Chanussot, Jocelyn(5)
  Source: Remote Sensing  Volume: 16  Issue: 1  DOI: 10.3390/rs16010180  Published: January 2024  
  Abstract:Hyperspectral images (HSIs) are widely used to identify and characterize objects in scenes of interest, but they are associated with high acquisition costs and low spatial resolutions. With the development of deep learning, HSI reconstruction from low-cost and high-spatial-resolution RGB images has attracted widespread attention. It is an inexpensive way to obtain HSIs via the spectral reconstruction (SR) of RGB data. However, due to a lack of consideration of outdoor solar illumination variation in existing reconstruction methods, the accuracy of outdoor SR remains limited. In this paper, we present an attention neural network based on an adaptive weighted attention network (AWAN), which considers outdoor solar illumination variation by prior illumination information being introduced into the network through a basic 2D block. To verify our network, we conduct experiments on our Variational Illumination Hyperspectral (VIHS) dataset, which is composed of natural HSIs and corresponding RGB and illumination data. The raw HSIs are taken on a portable HS camera, and RGB images are resampled directly from the corresponding HSIs, which are not affected by illumination under CIE-1964 Standard Illuminant. Illumination data are acquired with an outdoor illumination measuring device (IMD). Compared to other methods and the reconstructed results not considering solar illumination variation, our reconstruction results have higher accuracy and perform well in similarity evaluations and classifications using supervised and unsupervised methods. © 2023 by the authors.
  Accession Number: 20240315384638
• Record 353 of
  
  Title:Repetition rate tuning and locking of solitons in a microrod resonator
  
  Author(s):Niu, Rui(1,2); Wan, Shuai(1,2); Sun, Shu-Man(1,2); Ma, Tai-Gao(1,2); Chen, Hao-Jing(1,2); Wang, Wei-Qiang(3,4); Lu, Zhizhou(3,4); Zhang, Wen-Fu(3,4); Guo, Guang-Can(1,2); Zou, Chang-Ling(1,2); Dong, Chun-Hua(1,2)
  Source: Optics Letters  Volume: 49  Issue: 3  DOI: 10.1364/OL.511339  Published: February 2024  
  Abstract:Recently, there has been significant interest in the generation of coherent temporal solitons in optical microresonators. In this Letter, we present a demonstration of dissipative Kerr soliton generation in a microrod resonator using an auxiliary-laser-assisted thermal response control method. In addition, we are able to control the repetition rate of the soliton over a range of 200 kHz while maintaining the pump laser frequency, by applying external stress tuning. Through the precise control of the PZT voltage, we achieve a stability level of 3.9 × 10−10 for residual fluctuation of the repetition rate when averaged 1 s. Our platform offers precise tuning and locking capabilities for the repetition frequency of coherent mode-locked combs in microresonators. This advancement holds great potential for applications in spectroscopy and precision measurements. © 2024 Optica Publishing Group.
  Accession Number: 20240615521839
• Record 354 of
  
  Title:All-optical neural network nonlinear activation function based on the optical bistability within a micro-ring resonator
  
  Author(s):Zhang, Hui(1); Wen, Jin(1,2); Wu, Zhengwei(1); Wang, Qian(1); Yu, Huimin(1); Zhang, Ying(1); Pan, Yu(1); Yin, Lan(1); Wang, Chenglong(1); Qu, Shuangchao(1)
  Source: Optics Communications  Volume: 558  Issue:   DOI: 10.1016/j.optcom.2024.130374  Published: May 1, 2024  
  Abstract:Training all-optical neural networks in itself remains an unresolved problem, and the challenges compound when the problem is turned into the hardware implementations. In this paper, we propose a nonlinear activation function based on optical bistability within a micro-ring resonator (MRR), achieving threshold control without external modulation. Furthermore, a convolutional neural network similar to the Le-Net-5 architecture is designed, in which all nonlinear activation functions are composed of optical bistable hysteresis loop. The numerical simulation results demonstrate that the recognition rate on the Fashion-MNIST dataset can achieve 91.3%, which means that the optical neuromorphic computation can be implemented by utilizing the nonlinear optical effects themselves in the all-optical hardware. Such a scheme promises access to the all-optical neural network training in the optical hardware environment compared to numerical activation functions. © 2024 Elsevier B.V.
  Accession Number: 20240815608927
• Record 355 of
  
  Title:Enhanced Up-Conversion Emission of NaGdF4: Yb3+ /Eu3+ Crystal via Li+ Doping for Anti-Counterfeiting Application
  
  Author(s):Wang, Chong(1); Ren, Zhong-Xuan(1,2); Li, Dong-Dong(1); She, Jiang-Bo(2)
  Source: Guang Pu Xue Yu Guang Pu Fen Xi/Spectroscopy and Spectral Analysis  Volume: 44  Issue: 2  DOI: 10.3964/j.issn.1000-0593(2024)02-0497-07  Published: February 1, 2024  
  Abstract:Rare earth luminescent materials have gradually become a research hotspot in fluorescence anti-counterfeiting because of their high purity of luminous color, long fluorescent life, stable physical-chemical properties, and low toxicity. A series of NaGdF4: Yb3 + / E u 3 + microcrystals co-doped with various Li+ concentrations were synthesized by the hydrothermal method in this paper. The samples' morphology, size, and up-conversion luminescence properties were analyzed by X-ray diffraction (X R D), scanning electron microscopy (SEM), up-conversion emission spectroscopy, and fluorescence lifetime tests. The crystal with strong luminous intensity was further applied to anti-counterfeiting identification. It shows that all the diffraction peaks of NaGdF4: Yb3 + / E u 3 + / L i + microcrystals are consistent with the standard-NaGdF4 card. No impurity peak was found in the XRD pattern. The hexagonal NaGdF4: Yb3 + / E u 3 + / L i + with high purity and crystallinity was synthesized. The SEM image of the crystal shows that the generated sample is a pure hexagonal phase, with uniform distribution, and no reunion. Co-doped Y b 3 + / E u 3 + / L i + has little effect on crystal structure, morphology and size. It can be seen from the up-conversion emission spectrum that the green luminescence intensity of 15 mol% Li+ doped NaGdF4: Y b 3 + / E u 3 + crystal is 6 times higher than that of the undoped Li+ sample. Adjust the power range of the laser to 0. 8 ~ 2 . 2 W and observe the change in UCL intensity of the samples doped with 0 mol% Li+ and 15 mol% L i + . It can be observed that with the increase of pump power, the up-conversion intensity gradually increases. The number of photons required to generate the up-conversion luminescence n is close to 2, indicating that the emission process of the sample is a two-photon process. The fluorescence lifetime of the ° Di level in the sample is about 1. 4 times that of the undoped one. Finally, the NaGdF4: 0. 2Yb/0. 02Eu/0. 15Li crystal with uniform morphology and strong luminous intensity was further applied as fluorescent ink. Screen printing technology printed The fluorescent anti-counterfeiting patterns on paper, glass and plastic. The pattern emitted bright green light under the pumping of a 980 nm laser. In the natural environment, the anti-counterfeiting pattern on the paper has good concealment. The word "safe" lenght is 5. 5 mm, and the spacing between letters is 0. 5 mm. The boundaries between letters are clear and easy to distinguish under 980 nm excitation. The plastic printed with the anti-counterfeiting pattern was exposed to the outdoor natural environment for a month, and the pattern did not change significantly. It shows that the anti-counterfeiting pattern made of NaGdF4: 0. 2Yb/0. 02Eu/0. 15Li has a high resolution, is easy to identify, and is less affected by the environment, and has excellent application prospects in anti-counterfeiting identification. © 2024 Science Press. All rights reserved.
  Accession Number: 20240815615655
• Record 356 of
  
  Title:The deactivation effects of Nd3+ ion for 2.85 μm laser in Ho3+/Nd3+ co-doped fluorotellurite glass
  
  Author(s):Feng, Shaohua(1,2); Zhu, Jun(1,2); Liu, Chengzhen(1,2); Xiao, Yang(1,2); Cai, Liyang(1,2); Xu, Yantao(1,2); Xiao, Xusheng(1,2); Guo, Haitao(1,2,3)
  Source: Journal of Luminescence  Volume: 266  Issue:   DOI: 10.1016/j.jlumin.2023.120308  Published: February 2024  
  Abstract:The 2.85 μm band has garnered significant attention for its wide range of applications in the mid-infrared region, and Ho3+ doped fluorotellurite fiber shows great promise as a gain medium for the 2.85 μm fiber laser. To achieve efficient population inversion for Ho3+ ions at 2.85 μm, Ho3+/Nd3+ co-doped fluorotellurite glasses with low hydroxyl were synthesized. The deactivation effect of Nd3+ ions to Ho3+: 5I7 levels was investigated through emission spectra and lifetime decay curves under 890 nm excitation. The results show that Nd3+ ions can effectively quench the Ho3+: 2.05 μm emission and help the Ho3+: 5I6 → 5I7 transition to overcome the bottleneck of particle population inversion. Ultimately, the particle population inversion corresponding to 2.85 μm luminescence was realized in the Ho3+/Nd3+ co-doped fluorotellurite glass, and indicates that a maximum of 1.64 W laser at 2.85 μm with a slope efficiency of 8.72 % can be realized under 890 nm pump by numerical simulations. © 2023 Elsevier B.V.
  Accession Number: 20240215352216
• Record 357 of
  
  Title:Hybrid Fiber-Single Crystal Fiber Chirped-Pulse Amplification System Emitting More Than 1.5 GW Peak Power With Beam Quality Better Than 1.3
  
  Author(s):Li, Feng(1); Zhao, Wei(1); Li, Qianglong(1); Zhao, Hualong(1); Wang, Yishan(1); Yang, Yang(1); Wen, Wenlong(1); Cao, Xue(1)
  Source: Journal of Lightwave Technology  Volume: 42  Issue: 1  DOI: 10.1109/JLT.2023.3312399  Published: January 1, 2024  
  Abstract:A hybrid chirped pulse amplification system composed by the monolithic fiber pre-amplifier and a two-stage single-pass single crystal fiber amplifier was demonstrated. A maximum power of 68 W at the repetition rate of 100 kHz was obtained. The laser pulses were amplified and then compressed using a 1600 line/mm grating pair compressor. A short pulse duration of 358 fs and a power of 54 W were obtained at 100 kHz, corresponding to a peak power of 1.508 GW, to the best of our knowledge, this is the highest peak power ever obtained from single crystal fiber at repetition rate above 100 kHz due to the consideration of the third order dispersion which was engraved in the stretcher and the tuning capacity of higher-order dispersion compensation of chirped fiber Bragg grating. Additionally, the beam quality better than 1.3 was obtained. This high peak power CPA system with excellent comprehensive parameters will find various applications in scientific research and industrial applications. © 1983-2012 IEEE.
  Accession Number: 20233814763278
• Record 358 of
  
  Title:Enhanced optical nonlinearity of epsilon-near-zero metasurface by quasi-bound state in the continuum
  
  Author(s):Shi, Wenjuan(1,2); Wang, Zhaolu(1,2); Zhang, Changchang(1,2); Zhang, Congfu(1,2); Li, Wei(1,2); Liu, Hongjun(1,3)
  Source: Materials Today Nano  Volume: 26  Issue:   DOI: 10.1016/j.mtnano.2024.100474  Published: June 2024  
  Abstract:Bound states in the continuum (BICs) provide a powerful way to enhance the nonlinear properties of materials, epsilon-near-zero (ENZ) materials are considered as promising candidates with strong nonlinearities. However, the realization of BIC based on ENZ materials in the near-infrared (NIR) is very challenging due to the large loss in the NIR. Here, a high-quality quasi-BIC based on the ENZ metasurface is proposed for the first time, which is composed of patterned ENZ films embedded in a dielectric-metal hybrid structure, and realizes destructive interference between the Berreman mode and photonic mode to form the Friedrich-Wintergen BIC (FW-BIC). The electric field is strongly confined in the ENZ film, resulting in considerable field enhancement, and the nonlinear refractive index coefficient is 1.63 × 10−12 m2/W, which is three orders of magnitude larger than that of the ITO film. The instantaneous response time is 600 fs and extremely high modulation speed up to the THz level. Benefiting from the perfect absorption and narrow linewidth of quasi-BIC and the change in refractive index of the metasurface induced by Kerr nonlinearity, the absolute modulation is from near-zero to 92% with an extinction ratio of 23.2 dB. It provides a promising platform for the development of integrated ultrafast high-speed photonics. © 2024 Elsevier Ltd
  Accession Number: 20241315815743
• Record 359 of
  
  Title:Simulation of Polarimetric Photoelectric Process in X-Ray Polarization Detector
  
  Author(s):Zheng, Renzhou(1); Qiang, Pengfei(1); Sheng, Lizhi(1); Yan, Yongqing(1)
  Source: Guangxue Xuebao/Acta Optica Sinica  Volume: 44  Issue: 3  DOI: 10.3788/AOS231631  Published: 2024  
  Abstract:Objective X-ray polarization detection is an important means to study the astrophysical properties of intense X-ray sources such as black holes, pulsars, and related gamma-ray bursts. The development of X-ray polarization detectors with excellent performance is the technical basis for related research. Early X-ray polarization detectors were mainly Thomson scattering polarimeters and Bragg polarimeters. However, due to the low modulation factor and narrow detection energy range, the ideal polarization measurement results were not obtained. In 2001, Costa et al. proposed a new way of X-ray polarization detection using the photoelectric effect, in which the X-ray polarization information was obtained by imaging the photoelectron track produced by X-ray photons through a gas detector. The polarimetric photoelectric process is the key physical process for the detector to realize polarization detection. It is of great significance to clarify the photon-gas interaction process and the distribution law of emitted photoelectrons for further understanding the working mechanism of the detector. The polarimetric photoelectric process is an important research content in the development of this type of X-ray polarization detector. Different types of gases have various properties, which will affect the particle transport in the polarimetric photoelectric process and further leads to different detection efficiencies. Therefore, it is necessary to simulate the polarimetric photoelectric process under different conditions. This can provide a theoretical basis and data support for the structure design of X-ray polarization detectors. Methods We simulate the polarimetric photoelectric process of 2-10 keV linearly polarized X-ray photons in several commonly used working gases by the Monte Carlo code Geant4. The selected working gas combinations include He+ C3H8, Ne+CF4, Ne+DME, Ar+CH4, Ar+CO2, Xe+CO2, CF4+C4H10, and DME+CO2. The response relationship of the emission position and azimuthal angle distribution of photoelectron with the polarization direction and energy of the incident photon is discussed. Moreover, the effects of gas thickness, gas component, gas ratio, and photon energy on the detection efficiency are analyzed. Results and Discussions First, the response relationship of the emission position and azimuthal angle distribution of the photoelectron with the polarization direction and energy of the incident photon is clarified. The emission direction distribution probability of the photoelectron is the largest in the polarization direction of the incident photon, and the azimuthal angle distribution can be approximated as a cosine squared function. With the increase in photon energy, the counts of photoelectrons at each angle decrease in different degrees, but all of them show a statistical law that the maximum values occur when the azimuthal angle is 0 or π (- π) (Fig. 6). Moreover, the effects of gas thickness, gas component, gas ratio, and photon energy on the detection efficiency are revealed and quantified. For 2 keV photons entering into 90%Ne+10%DME gas mixture, when the gas thickness is small, the detection efficiency increases rapidly with the increase in gas thickness, from less than 0. 1 at 0. 1 cm to 0. 64 at 1 cm (Fig. 7). When the gas thickness increases to 3 cm, the detection efficiency is greater than 0. 9. Then, with the increase in gas thickness, the detection efficiency gradually approaches 1. For the CF4+C4H10, Ne+CF4, Ne+DME, DME+CO2, and He+C3H8, the detection efficiency decreases with the increase in photon energy, and the large average atomic number of gas can lead to a high detection efficiency (Fig. 8). While for the Xe+CO2, Ar+CO2, and Ar+CH4, when the photon energy is greater than the binding energy of certain shell electrons of Xe or Ar atoms, the detection efficiency will be improved to a certain extent because the corresponding shell electrons begin to be ejected. In addition to the Ar+CO2 which is affected by the electron emission in K- shell, the detection efficiency in each energy range can be effectively improved by increasing the proportion of gas with high atomic number (Fig. 9). Conclusions We simulate the polarimetric photoelectric process of 2-10 keV linearly polarized X- ray photons in several commonly used working gases by the Monte Carlo code Geant4. The response relationship of the emission position and azimuthal angle distribution of the photoelectron with the polarization direction and energy of the incident photon is clarified. The emission direction distribution probability of the photoelectron is the largest on the polarization direction of the incident photon, and the azimuthal angle distribution can be approximated as a cosine squared function. With the increase in photon energy, the counts of photoelectrons at each angle decrease in different degrees, but all of them show a statistical law that the maximum values occur when the azimuthal angle is 0 or π (- π). Moreover, the effects of gas thickness, gas component, gas ratio, and photon energy on the detection efficiency are revealed and quantified. The larger gas thickness and larger average atomic number can lead to higher detection efficiency. In addition, the increase in photon energy can result in a decrease in detection efficiency. However, for the working gases composed of Xe or Ar, when the photon energy is greater than the binding energy of a certain shell electron, the detection efficiency will be improved to a certain extent because the corresponding shell electrons begin to be ejected. The results in this paper can provide some theoretical basis and data support for the structure design of X- ray polarization detectors. In the actual selection of working gases, the drift properties of electrons in gases, the effect of photoelectron drift and diffusion on track thickness and length, and the reconstruction efficiency of the track reconstruction algorithm should also be considered. © 2024 Chinese Optical Society. All rights reserved.
  Accession Number: 20241115728993
• Record 360 of
  
  Title:Research on High-Precision Quantitative Phase Microscopy Imaging Methods
  
  Author(s):Min, Junwei(1); Gao, Peng(2); Dan, Dan(1); Zheng, Juanjuan(2); Yu, Xianghua(1); Yao, Baoli(1)
  Source: Guangxue Xuebao/Acta Optica Sinica  Volume: 44  Issue: 2  DOI: 10.3788/AOS231191  Published: January 2024  
  Abstract:Significance Phase is one of the important attributes of light waves, and its distribution directly affects the spatial resolution of optical imaging and is related to the three-dimensional topography of objects or the refractive index distribution of transparent objects. However, the phase distribution of light waves cannot be directly detected. How to accurately obtain the phase distribution of light waves has become a hotspot in the field of optics. The invention of phase-contrast microscopy has opened the curtain of phase imaging, which has epoch-making significance. It successfully converts the phase distribution of light waves into intensity changes, solving the problem of difficult direct microscopic observation of transparent samples such as cells. Nevertheless, the conversion between phase distribution and intensity change is not a linear relationship in phase contrast microscopy, resulting in phase information that cannot be observed quantitatively. By measuring the phase of light waves, the three-dimensional topography or refractive index distribution of transparent objects can be quantitatively obtained. The refractive index is one of the essential characteristic physical quantities that reflect the internal structure and state of the sample. Therefore, conducting quantitative phase microscopy methods has scientific significance. Quantitative phase imaging has important application value in industrial detection, biomedicine, special beam generation, adaptive optics imaging, and synthetic aperture telescopes. The current quantitative phase microscopy imaging technology mainly obtains the quantitative distribution of phase through interference. Therefore, factors such as the stability of interference devices, limitations on optical diffraction, phase wrapping, coherent noise generated by laser illumination, and sample refocusing during dynamic observation affect the imaging resolution and accuracy of quantitative phase microscopy. Thus, systematic and in-depth research on improving measurement accuracy and stability, spatial resolution, expanding the longitudinal measurement range, suppressing coherent noise, and autofocusing of quantitative phase microscopy imaging has been carried out. A theoretical and technical system centered on high-precision quantitative phase microscopy imaging has been formed. Progress A simultaneous phase shift digital holographic microscopy (DHM) with a common-path configuration has been proposed, which allows the object light and reference light to share the same optical path and components, solving the impact of environmental disturbances on phase imaging fundamentally (Fig. 3), simultaneously recording multiple phase-shift interferograms within one exposure and achieving real-time high-precision quantitative phase imaging. The optical path fluctuation of the system is only 3 nm within 35 min, and the real-time phase microscopy imaging accuracy reaches 4. 2 nm, which is 2. 2 times the accuracy of conventional off-axis interference quantitative phase microscopy imaging (Fig. 5). A super-resolution quantitative phase imaging method based on structural illumination has been proposed. Using the structured light illumination, the spatial resolution of quantitative phase microscopy can be doubled when the spatial frequency of the structural illumination stripe is the same as the highest spatial frequency of the microscopic objective, and super-resolution phase imaging is realized (Fig. 7). A slightly off-axis interference dual-wavelength illuminated digital holographic microscopy has been proposed to expand the longitudinal unwrapped phase measurement range from the wavelength to the micrometer level (Fig. 8), meeting the high-precision phase imaging requirements of thicker samples. Using a low-coherence LED as an illumination light source, the coherent noise in the common laser-illuminated DHM can be reduced by 68% (Fig. 10), and the signal-to-noise ratio (SNR) of images can be improved. The phase measurement accuracy is 2. 9 nm, providing a high-precision solution for the measurement of micro/nano structures and micro electro mechanical system (MEMS) surfaces. Two autofocusing methods based on dual-wavelength illumination and dual beam off-axis illumination have been proposed to meet the autofocusing requirements of high-resolution quantitative phase microscopy imaging for long-term tracking and observation of samples under different conditions (Fig. 11). The former does not rely on the characteristics of the tested sample or other prior knowledge, making it suitable for both amplitude and phase objects. The latter has a simple criterion and can easily determine the optimal imaging surface by reproducing the differences and changes between images, without the need for tedious iterative calculation and with relatively fast processing speed. Conclusions and Prospects Digital holographic microscopy is one of the representative achievements with significant influence and widespread application in the field of quantitative phase imaging, playing an increasingly important role in biomedical, material science, industrial testing, flow field display research, and other fields. We focused on the theoretical and technical issues of high-precision quantitative phase imaging and conducted systematic research on improving measurement accuracy and stability, improving lateral spatial resolution, expanding longitudinal unwrapped measurement range, suppressing coherent noise, and achieving automatic image focusing. With the promotion and application of quantitative phase microscopy imaging technology in other fields such as biological research, high-precision quantitative phase topography microscopy imaging methods will be our future research direction. It is expected that quantitative phase microscopy imaging technology can play a greater role in industrial testing, materials science, and biomedical fields, becoming an indispensable tool for studying the micro world. © 2024 Chinese Optical Society. All rights reserved.
  Accession Number: 20240415420637