2024

• Record 97 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 98 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 99 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 100 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 101 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 102 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
• Record 103 of
  
  Title:Dual-parameter femtosecond mode-locking pulse generation in partially shared all-polarization-maintaining fiber Y-shaped oscillator with a single saturable absorber
  
  Author(s):Bai, Chen(1); Feng, Ye(2); Zhang, Weiguang(1); Zhang, Junying(1); Zhang, Tong(2); Mei, Chao(3); Liu, Pandi(4); Fan, Zhaojin(1); Qian, Jiangxiao(1); Yu, Jia(1)
  Source: Optics and Laser Technology  Volume: 169  Issue:   DOI: 10.1016/j.optlastec.2023.110021  Published: February 2024  
  Abstract:We present a design of a mode-locked fiber laser based on a polarization-maintaining (PM) Y-shaped fiber structure, which employs a single semiconductor saturable absorber mirror (SESAM) and a common polarization beam combiner (PBC) to achieve dual- parameter mode-locking femtosecond pulse in two orthogonal polarization states. The two output pulses have different characteristics, such as repetition frequency (87.3 MHz and 91.3 MHz), average output powers (2.1 mW and 1.9 mW), pulse durations (299 fs and 377 fs) and spectral profiles (centered at 1565.6 nm and 1563.6 nm with spectral width of 9.96 nm and 9.93 nm). The properties of the two pulses are experimentally characterized and their potential applications in areas such as bistable frequency lasers and dual femtosecond optical frequency comb is discussed. © 2023 Elsevier Ltd
  Accession Number: 20233614695327
• Record 104 of
  
  Title:A compact 51.6-W, 26-μJ, Yb-doped all-fiber integrated CPA system through quasi-rectangular pulse pre-shaping
  
  Author(s):Li, Qianglong(1,2,3); Li, Feng(1); Liu, Hongjun(1); Zhao, Wei(1); Zhao, Hualong(1); Wang, Yishan(1); Wen, Wenlong(1); Cao, Xue(1,2,3); Si, Jinhai(2)
  Source: Optics and Laser Technology  Volume: 170  Issue:   DOI: 10.1016/j.optlastec.2023.110300  Published: March 2024  
  Abstract:A compact 51.6-W, 26-μJ all-fiber integrated Yb-doped femtosecond laser source with pulse durations of 692 fs despite ∼18π nonlinear phase shift accumulation in the main amplifier is demonstrated by using fiber quasi-rectangular pulse pre-shaping. The numerical results are in good agreement with the experiment. Due to the advantages of an all-fiber spliced structure and a minimal pulse stretching ratio (from 26.3 ps to ∼70 ps), just a small size of gratings and a short separation distance between the two gratings in the compressor is required. Therefore, the laser source is exceedingly compact, robust, cost-effective, and easy to assemble. This technique is anticipated to accelerate the use of fiber femtosecond lasers in industrial applications. © 2023 Elsevier Ltd
  Accession Number: 20234515013310
• Record 105 of
  
  Title:A different view on the deactivation process of 3-hydroxy-salicylidene-methylamine system
  
  Author(s):Han, Guoxia(1); Wei, Hongyan(2); Yu, Xianghua(3); Zhang, Jialing(1); Ma, Yanbin(1); Liu, Peng(1)
  Source: Chemical Physics Letters  Volume: 835  Issue:   DOI: 10.1016/j.cplett.2023.141004  Published: January 16, 2024  
  Abstract:Schiff bases stand out as a highly significant class of photochromic materials with widespread applications. The exploration of their photochromic mechanisms has garnered substantial interest over the past decades. In this work, we investigated the photochromic mechanism of 3-hydroxy-salicylidene methylamine (3-OH-SMA) by high-level electronic structure calculations and on-the-fly excited state dynamics simulations. Our investigation revealed the identification of three minimum energy conical intersections between S1 and S0 states, while only the one characterized by the central C = N bond twisting motion was involved in the deactivation process. This finding contrasts with previous reports, suggesting that the excited state intramolecular proton transfer (ESIPT) process was the main reaction channel in 3-OH-SMA. The proposed new decay mechanism provides valuable theoretical insights, paving the way for the further enhancement or rational design of photochromic materials. © 2023 Elsevier B.V.
  Accession Number: 20235015192341
• Record 106 of
  
  Title:Experimental Analysis of Coherent Velocity Measurement Based on Near-infrared Single-element SPAD Detector
  
  Author(s):Li, Bin(1); Wang, Xiaofang(2,3); Kang, Yan(2); Yue, Yazhou(1); Li, Weiwei(2,3); Zhang, Yixin(1); Lei, Hongjie(1); Zhang, Tongyi(2,3)
  Source: Guangzi Xuebao/Acta Photonica Sinica  Volume: 53  Issue: 1  DOI: 10.3788/gzxb20245301.0104001  Published: January 2024  
  Abstract:Coherent lidar has advantages of suppressing background noise such as sunlight and detecting sensitivity close to shot noise limit. It is widely used in civil and defense fields such as wind detection，velocity measurement and military target detection. Coherent detection can be divided into heterodyne detection to extract frequency information and homodyne detection to extract phase information. For velocity measurement，heterodyne detection is usually used to extract the Doppler frequency shift of the echo laser from a moving target，and then the velocity of target is retrieved. Conventional heterodyne lidar adopt normal optical detectors，such as PIN detectors，which have limited detection sensitivity for a small number of echo photons. And generally，strong local oscillator laser power is required to suppress thermal and circuit noise，but excessive local oscillator is likely to generate excess shot noise. With the development of Single Photon Avalanche Diode（SPAD）detector with low circuit noise，it not only provides a way for the detection of a small number of echo photons，but also makes it possible to realize heterodyne detection with a weak local oscillator. Researchers have successively adopted InGaAs SPAD array detectors and superconducting nanowire single-photon detectors for near-infrared spectrum， single-element Si SPAD detectors and MPPC detectors for visible spectrum，but there have been few experimental research on heterodyne detection with single-element InGaAs SPAD detector. The heterodyne lidar based on near-infrared SPAD can be integrated in all-fiber structure with an operating wavelength of 1.5 μm，which makes it more suitable for practical working platforms such as airborne. Although the count rate dynamic range of the single-element SPAD is not as good as that of the SPAD array，the current disadvantages of SPAD array，such as low pixel fill-factor，poor uniformity of pixel performance（e.g.，hot pixel），and slow speed of data readout，limit its performance to a certain extent. Besides，compared with superconducting nanowire single-photon detectors，single-element near-infrared SPAD do not require extremely complex and bulky cooling system. Therefore，we established a heterodyne velocimetry experimental system based on a 1.5 μm fiber laser and a single-element InGaAs SPAD detector to analyze the influence of SPAD's dead time，dark count rate and photon count rate for the extracting of beat frequency. The output laser was shifted by 40 MHz using an Acousto-optic Frequency Shifter（AOFS）to simulate the Doppler frequency shift of the echo laser from a moving target. Then，under the experimental set up of 1 μs dead time and 1 ms data acquisition time，we analyzed the influence of different photon count rates on the SNR of the beat frequency spectrum under SPAD's dark count rates of 1.8 kHz，54.4 kHz and 194.4 kHz. The experimental results show that，the SNR increases gradually and then tends to be stable with the increase of the photon count rate. When the photon count rate is close to saturation，harmonic frequency components appear in the low-frequency area of the frequency spectrum as well as the two side regions centered on the beat frequency. The harmonic frequency spacing is basically equal to the photon count rate. The optimal photon count rate which is slightly affected by harmonics is about 90% of saturation count rate of SPAD detector. In addition，as the dark count rate increases，the photon count rate required to extract the beat frequency signal is higher. The experimental results can provide a reference for the development and practical application of all-fiber single-photon Doppler velocity measurement lidar technology. © 2024 Chinese Optical Society. All rights reserved.
  Accession Number: 20240815582095
• Record 107 of
  
  Title:Three-dimensional Bose–Einstein gap solitons in optical lattices with fractional diffraction
  
  Author(s):Chen, Zhiming(1,2); Liu, Xiuye(2); Xie, Hongqiang(1); Zeng, Jianhua(2,3,4)
  Source: Chaos, Solitons and Fractals  Volume: 180  Issue:   DOI: 10.1016/j.chaos.2024.114558  Published: March 2024  
  Abstract:Compared with low-dimensional solitons that are widely studied in various realizable nonlinear physical systems, the properties and dynamics of three-dimensional solitons and vortices have not been well disclosed yet. Using numerical simulations and theoretical analysis, we here address the existence, structural property, and dynamics of three-dimensional gap solitons and vortices (with topological charge s=1) of Bose–Einstein condensates moving by Lévy flights (characterized by fractional diffraction operators, Lévy index 1 © 2024 Elsevier Ltd
  Accession Number: 20240615519018
• Record 108 of
  
  Title:Optical diffraction tomography based on quadriwave lateral shearing interferometry
  
  Author(s):Yuan, Xun(1,2); Min, Junwei(1); Zhou, Yuan(1,2); Xue, Yuge(1,2); Bai, Chen(1); Li, Manman(1); Xu, Xiaohao(1); Yao, Baoli(1,2)
  Source: Optics and Laser Technology  Volume: 177  Issue:   DOI: 10.1016/j.optlastec.2024.111124  Published: October 2024  
  Abstract:Optical diffraction tomography (ODT) is an emerging microscopy that enables quantitatively three-dimensional (3D) refractive index (RI) mapping of subcellular structure inside biological cells without staining. Due to the noninvasive, label-free, and quantitative imaging capability, ODT has become an important technique in the fields of cell biology, biophysics, hematology, and so on. It is customary to acquire a set of two-dimensional (2D) phase images of a transparent sample from different illumination angles by using the classical Mach-Zehnder interferometry (MZI), and then numerically reconstruct the 3D RI distribution of the sample via appropriate tomographic algorithms. However, due to the limited stability of MZI, the cumulative measured phase errors reduce the accuracy of the reconstructed RI. Here, we propose a common-path ODT based on quadriwave lateral shearing interferometry (QLSI), referred as Q-ODT. In QLSI, the object beam carrying the phase information of sample is divided into four copies by a specially designed 2D diffraction optical element, then the diffracted waves interfere with each other to form the interferogram at the image plane. The complex amplitude map of the object is quantitatively retrieved from the single-shot interferogram by using a Fourier analysis algorithm and a 2D phase gradient integration. A spatial light modulator is employed to ensure high-precision illumination angle scanning without mechanical motion by addressing a series of different periods and orientations blazed gratings. The average fluctuation of the measured phases of a test polystyrene bead by acquiring 300 interferograms in 12 s presents 7.6 mrad, surpassing the conventional MZI-based ODT. The 3D RI distribution of the bead reconstructed from 145 complex amplitude maps via multi-illumination angles with a maximum angle of 70° matches the manufacturer's specification well, demonstrating the high accuracy of the 3D RI imaging capability of the Q-ODT. The lateral and axial resolutions of the 3D RI reconstruction were measured to be 306 ± 21 nm and 825 ± 34 nm, respectively. The proposed Q-ODT method successfully reconstructed the intracellular structure of the biological specimens of Eudorina elegans and mouse bone mesenchymal stem cells (BMSC). The Q-ODT offers a new route towards 3D RI imaging for label-free transparent samples in biomedical research. © 2024 Elsevier Ltd
  Accession Number: 20241916034871