Zhang Meng   Chu Yuxi   Zhao Jun   Yan Dongyu   Li Yongzhi   Bi Genyu   Liu Bowen   Hu Minglie  

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On the basis of a home-made femtosecond Yb-doped fiber laser, we designed a compact and efficient third harmonic generation scheme by a simple compensation plate of β-BaB2O4 (BBO) crystal. The compensation plate is optimized through its thickness and cutting angle to reverse both spatial and temporal walk-off. By optimizing the parameters of the compensation plate and incident light intensity, a maximum output of 2.23 W with a repetition rate of 1 MHz at 345 nm is obtained, which implies a conversion efficiency of 23% from infrared to ultraviolet (UV).

       PDF全文 (下载：4)        Chinese Optics Letters ，2021年第19卷第3期 pp.03      

Yang Zixin   Han Lili   Yang Qi   Ren Xianghe   Zaheer Ud Din Syed   Zhang Xiaoyan   Leng Jiancai   Zhang Jiabao   zhang baitao   Yang Kejian   He Jingliang   Li Chunlong   Wang Jun  

      摘要 + 此论文可免费阅读 (可能需要登录)

Two-dimensional (2D) Te nanosheets were successfully fabricated through the liquid-phase exfoliation (LPE) method. The nonlinear optical properties of 2D Te nanosheets were studied by the open-aperture Z-scan technique. Furthermore, the continuous wave mode-locked (CWML) Nd:YVO4 laser was successfully realized by using 2D Te as saturable absorber (SA) for the first time. The ultrashort pulses as short as 5.8 ps were obtained at 1064.3 nm with an output power of 851 mW. This primary investigation indicates that 2D Te SA is a promising photonic device in the fields of ultrafast solid-state lasers.

       PDF全文 (下载：5)        Chinese Optics Letters ，2021年第19卷第3期 pp.03      

Zhang Zongjie   Li Wei   Ma Nan   Huang Xiaoyong  

      摘要 + 此论文可免费阅读 (可能需要登录)

Bright Eu3+-activated double-perovskite Sr2LaTaO6 red-emitting phosphors were successfully synthesized by high-temperature solid-state method. Under near-ultraviolet excitation at 394 nm, the optimal Sr2LaTaO6:0.2Eu3+ phosphors emitted high-brightness red light around 613 nm with the CIE chromaticity coordinates (0.650, 0.349). Notably, the color purity can reach 92%. Impressively, the favorable thermal stability of the Sr2LaTaO6:0.2Eu3+ phosphors were characterized by temperature-dependent emission spectra at different temperatures from 303 to 463 K and the emission intensity at 423 K remained 73% of its value at 303 K. All the results suggested that the as-prepared Sr2LaTaO6:0.2Eu3+ phosphors can be used in near-ultraviolet-excitable white light-emitting diodes as red-emitting color converter.

       PDF全文 (下载：2)        Chinese Optics Letters ，2021年第19卷第3期 pp.03      

Shaomin Li   Liqun Sun  

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Natural Logarithm Wavelength Modulation Spectroscopy (ln-WMS) is demonstrated in this letter. Unlike the conventional WMS-2f technique, it is a linear method even for large absorbance, which is the core advantage of ln-WMS. The treating method used in ln-WMS is to take the natural logarithm of the transmitted intensity. In order to determine the proper demodulation phase, the η-seeking algorithm is introduced, which minimizes the absolute value of the first harmonic within the non-absorbing region. Subsequently the second harmonic of the absorption signal is extracted by setting the demodulating phase as 2η. To illustrate the validity of ln-WMS, it was applied to water vapor experimentally. The result shows that even if the absorbance (base-e) is between 1.60 and 6.26, the linearity between ln-WMS-2f and volume fraction is still established. For comparison, measurement with conventional WMS-2f was also done, whose response no longer kept linearity. The η values retrieved in continuous measurements and the residuals were shown so as to evaluate the performance of the η-seeking algorithm. Time consumed by this algorithm was roughly 0.28s per measurement. As an alternative WMS strategy, ln-WMS has a wide range of potential applications, especially where the absorbance is large or varies over a wide area.

       PDF全文 (下载：6)        Chinese Optics Letters ，2021年第19卷第3期 pp.03      

Dai Jie   Huang Lihua   Zhu Xinran   Guo Kai   ling liqing   Huang Huijie  

      摘要 + 此论文可免费阅读 (可能需要登录)

This paper reports a detection method of two-dimensional (2D) enhancement and three-dimensional (3D) reconstruction for subtle traces with reflectance transformation imaging, which can effectively locate the trace area of interest and extract the normal data of this area directly. In millimeter- and micron-scale traces, during 3D construction, we presented a method of data screening, conversion, and amplification, which can successfully suppress noise, improve surface and edge quality, and enhance 3D effect and contrast. The method not only captures 2D and 3D morphologies of traces clearly but also obtains the sizes of these traces.

       PDF全文 (下载：6)        Chinese Optics Letters ，2021年第19卷第3期 pp.03      

Guo Bo   Guo Xin-Yu   Tang Li-Ge   Yang Wen-Lei   Chen Qiu-Mei   Ren Zhong-Yao  

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We propose and demonstrate the cascaded multi-wavelength mode-locked erbium-doped fiber laser (EDFL) based on ultra-long-period grating (ULPG) for the first time, to the best of our knowledge. Study found that, the ULPG can be used as both a mode-locker for pulse-shaping and a comb filter for multiwavelength generation simultaneously. Using the dual-function of ULPG, three-, four-, five-, six- and seven-wavelength mode-locked pulses are obtained in EDFL, seven of which are the largest number of wavelengths up to now. For the four-wavelength mode-locked pulses, its pulsewidth is about 7.8 ps. In experiment, the maximum average output power and slope efficiency of these pulses are 8.4 mW and 2.03%, respectively. Besides the conventional pulses, hybrid soliton pulses composed of four-wavelength pulse and single soliton are also observed. Finally, the effect of cavity dispersion on the multiwavelength mode-locked pulses is also discussed. Our findings indicate that apart from common sensing and filtering, the ULPG may also possess attractive nonlinear pulse-shaping property for ultrafast photonics application. © 2020 SIOM

       PDF全文 (下载：11)        Chinese Optics Letters ，2021年第19卷第7期 pp.07      

Dang Zhiya   Luo Yuqing   Wang Xue-Sen   Imran Muhammad   Gao Pingqi  

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The instability of lead halide perovskites in various application-related conditions is a key challenge to be resolved. We investigated the formation of metal nanoparticles during transmission electron microscopy (TEM) imaging of perovskite-related metal halide compounds. The metal nanoparticle formation on these materials originates from stimulated desorption of halogen under electron beam, and a subsequent aggregation of metal atoms. Based on shared mechanism, the TEM-based degradation test can help to evaluate the material stability against light irradiation.

       PDF全文 (下载：4)        Chinese Optics Letters ，2021年第19卷第3期 pp.03      

ma xiang   Zheng Shuang   Liu Jia   Chen Quanan   lu qiaoyin   Guo Weihua  

      摘要 + 此论文可免费阅读 (可能需要登录)

We propose a design of single-mode orbital angular momentum (OAM) beam laser with high direct-modulation bandwidth. It’s a microcylinder/microring cavity interacted with two types of second-order gratings: the complex top grating containing the real part and the imaginary part modulation and the side grating. The side grating etched on the periphery of the microcylinder/microring cavity can select a whispering gallery mode with a specific azimuthal mode number. While the complex top gratings can scatter the lasing mode with travelling-wave pattern vertically. With the cooperation of the gratings, the laser works with a single mode and emits radially polarized OAM beams. With an asymmetrical pad metal on the top of the cavity, the OAM on-chip laser can firstly be directly modulated with electrical pumping. Due to the small active volume, the laser with low threshold current is predicted to have a high direct modulation bandwidth about 29 GHz with the bias current of ten times the threshold from the simulation. The semiconductor OAM laser can be rather easily realized at different wavelengths such as the O band, C band and L band.

       PDF全文 (下载：5)        Chinese Optics Letters ，2021年第19卷第8期 pp.08      

Deng Aihua   Zeng Zixuan   Deng Jianliao  

      摘要 + 此论文可免费阅读 (可能需要登录)

We demonstrate a two-component detection of a coherent population trapping (CPT) resonance based on virtually-imaged phased array (VIPA). After passing through a VIPA, the two coupling lights with different frequencies in the CPT experiment are separated in space and detected individually. The asymmetric lineshape is observed experimentally in the CPT signal for each component and the comparison with the conventional detection is presented. The shift of the CPT resonant frequency is studied with both the two-component and one-component detections. Our scheme provides a convenient way to further study the CPT phenomenon for each frequency component.

       PDF全文 (下载：2)        Chinese Optics Letters ，2021年第19卷第8期 pp.08      

Li Ruonan   Sun Lifei   Cai Yangjian   Ren Yingying   Liu Hongliang   Mackenzie Mark D   Kar AK  

      摘要 + 此论文可免费阅读 (可能需要登录)

Optical channel waveguides with depressed cladding configurations have been produced in Nd,Gd:CaF2 laser crystals by using ultrafast laser inscription. Waveguide properties are investigated in terms of guiding behaviors and localized laser-induced lattice damages. Under optical pump of 808 nm light, continuous-wave waveguide lasing at 1.06 μm is achieved, with a single-mode operation and a minimum lasing threshold of 98.8 mW. Furthermore, the visible emissions of Nd3+ with short wavelengths ranging from 415 nm to 550 nm and long wavelengths from 550 nm to 625 nm are observed upon 808 nm laser excitation via the up-converted process. The intensity ratios of two wavelength ranges are proved to be tunable through changing the pumping polarizations.

       PDF全文 (下载：10)        Chinese Optics Letters ，2021年第19卷第8期 pp.08      

Guo Ya   Cai Qiang   Jia Zhiwei   Xu Bingjie   Gao Zhensen   zhang qianwu   Zhang Ruonan   Adonis Bogris   Alan Shore K   Wang Yuncai   Li Pu  

      摘要 + 此论文可免费阅读 (可能需要登录)

All-optical analog-to-digital conversion is a paramount issue in modern science. How to implement real-time and ultrafast quantization to optical pulses with different intensities in an all optical domain is a central problem. Here, we report a real-time demonstration of all-optical quantization scheme based on slicing the supercontinuum in a nonlinear fiber. In comparison with previous schemes through off-line analysis of the power of different optical spectral components in the supercontinuum, this, as far as we are aware, is the first demonstration of such functionality online in the time domain. Moreover, the extinction ratio among the quantized outputs can exceed 10 dB, which further confirms the feasibility of the proposed quantization scheme. The current 3-bit resolution in the proof-of-principle experiment is limited by the current experimental condition, but can be expected to be greatly enhanced through improving both the spectral width of the generated supercontinuum and the number of filtering channels used.

       PDF全文 (下载：7)        Chinese Optics Letters ，2021年第19卷第8期 pp.08      

Zha Songqing   Chen Yujin   Li Bingxuan   Lin Yanfu   Liao Wenbin   Zou Yuqi   Huang Chenhui   Lin Zhanglang   Zhang Ge  

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End-pumped by a 976 nm diode laser, a high-repetition-rate Er:Yb:YAl3(BO3)4 microchip laser passively Q-switched by a Co2+:MgAl2O4 crystal is reported. At a quasi-continuous-wave pump power of 20 W, a 1553 nm passively Q-switched laser with repetition rate of 544 kHz, pulse duration of 8.3 ns and pulse energy of 3.9 µJ was obtained. To our knowledge, the 544 kHz is the highest reported value for the 1.5 µm passively Q-switched pulse laser. In the continuous-wave pumping experiment, the maximum repetition rate of 144 kHz with pulse duration of 8.0 ns and pulse energy of 1.7 µJ was obtained at the incident pump power of 6.3 W.

       PDF全文 (下载：4)        Chinese Optics Letters ，2021年第19卷第7期 pp.07      

Liu Hui   Xie Boyang   Cheng Hua   Tian Jianguo   Chen Shuqi  

      摘要 + 此论文可免费阅读 (可能需要登录)

Topological photonics provide a new opportunity for the examination of novel topological properties of matter in which energy band theory and ideas in topology are utilized to manipulate the propagation of photons. Since the discovery of topological insulators in condensed matter, researchers have studied similar topological effects in photonics. Topological photonics can lead to materials that support the robust unidirectional propagation of light without back reflections. This ideal transport property is unprecedented in traditional optics, and may lead to radical changes in integrated optical devices. In this review, we present the exciting developments of topological photonics and focus on several prominent milestones of topological phases in photonics, such as topological insulators, topological semimetals, and higher-order topological phases. We conclude with the prospect of novel topological effects and their applications in topological photonics.

       PDF全文 (下载：2)        Chinese Optics Letters ，2021年第19卷第5期 pp.05      

Han Tianwen   Chen Hao   Li Wenwan   Wang Bing   Lu Peixiang  

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We investigate the Airy-Talbot effect of an Airy pulse train in time-dependent linear potentials. The parabolic trajectory of self-imaging depends on both the dispersion sign and the linear potential gradient. By imposing linear phase modulations on the pulse train, the Airy-Talbot effects accompanied with positive and negative refractions are realized. For an input composed of stationary Airy pulses, the self-imaging follows straight lines and the Airy-Talbot distance can be engineered by varying the linear potential gradient. The effect is also achieved in symmetric linear potentials. The study provides opportunities to control the self-imaging of aperiodic optical field in time dimension.

       PDF全文 (下载：1)        Chinese Optics Letters ，2021年第19卷第8期 pp.08      

Wang Yurong   Wang Linli   Wu Chenyi   Li Zhaohui   Yang Lei   Wu Guang  

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We report a method to reduce the detection delay temperature drift for a single-photon detector based on the avalanche photodiode (SPAD). Both the SPAD and the comparator were temperature stabilized, resulting in an ultra-low temperature drift as 0.01 ps/℃. A stable time deviation as 0.15 ps @1000 s was realized, while the ambient temperature fluctuated rapidly from 24℃ to 44℃. To our knowledge, this is the first report on the ultra-stable delay SPAD detector in case of rapid increase or decrease of ambient temperature. It is helpful to improve the stability of onboard detectors for the optical laser time transfer between ground and space.

       PDF全文 (下载：1)        Chinese Optics Letters ，2021年第19卷第8期 pp.08      

Xu Shaofu   Zou Weiwen  

      摘要 + 此论文可免费阅读 (可能需要登录)

We propose an optical tensor core (OTC) architecture for neural network training. The key computational components of the OTC are the arrayed optical dot-product units (DPUs). The homodyne-detection-based DPUs can conduct the essential computational work of neural network training, i.e. matrix-matrix multiplication. The dual-layer waveguide topology is adopted to feed data into these dot-product units with ultra-low insertion loss and cross talk. Therefore, the OTC architecture allows a large-scale dot-product array and can be integrated into a photonic chip. The feasibility of the OTC and its effectiveness on neural network training is verified with numerical simulations.

       PDF全文 (下载：4)        Chinese Optics Letters ，2021年第19卷第8期 pp.08      

Lu Yudong   Hu Dejiao   Zhang Mingsi   Li Xiangping   Cao Yaoyu   Li Jiafang   Yang Lechen  

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Plasmonic structural colors have plenty of advantages over traditional colors based on colorants. Pulsed laser provides an important method generating plasmonic structural colors with high efficiency and low cost. Here we present plasmonic color printing Al nanodisc structures through curvature-driven shape transition. We systematically study the mechanism of morphologic evolution of Al nanodisc below the thermal melting threshold. Multi-pulse induced accumulated photothermal effect and subsequent curvature-driven surface atom diffusion model is adopted to explain the controllable shape transition. The shape transition and corresponding plasmonic resonances of nanodisc can be independently and precisely modulated by controlled irradiations. This method opens new ways towards high-fidelity color prints in a highly-efficient and facile laser writing fashion.

       PDF全文 (下载：0)        Chinese Optics Letters ，2021年第19卷第5期 pp.05      

Li Junyan   Qian Na   Hua Shiyu   Zou Weiwen  

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A microwave-chip-based coherent multi-frequency RF driver is developed for a channel-interleaved photonic analog-to-digital converter (PADC) system, which comprises a multi-class optical demultiplexer and supports a sampling speed of 40 GSa/s. The generated signals from the RF driver are adjustable in both amplitude and phase. We analyze the relationship between the characteristics of generated RF driver signals and the demultiplexing performance in theory based on the OSDR. It is the most effective parameter to evaluate the performance of the demultiplexer in a PADC system without an EADC. By precisely adjusting the amplitude and phase of signals, the OSDR is optimized. The results verify the compatibility between the RF driver and the PADC system.

       PDF全文 (下载：5)        Chinese Optics Letters ，2021年第19卷第8期 pp.08      

Wen Qin   Cui Wenwen   Geng Yong   Zhou Heng   Qiu Kun  

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We demonstrate a novel method to control the free spectral range (FSR) of silica micro-rod resonator precisely. This method is accomplished by iteratively applying laser annealing on the already-fabricated microrod resonators. Fine and repeatable increasing of resonator FSR is demonstrated and the best resolution is smaller than 5 MHz, while the resonator Q-factor is only slightly affected by the iterative annealing procedure. Using the fabricated micro-rod resonators, single dissipative Kerr soliton microcombs are generated, and soliton repetition frequencies are tuned precisely by iterative annealing process. The demonstrated method can be used for dual-comb spectroscopy and coherent optical communications.

       PDF全文 (下载：3)        Chinese Optics Letters ，2021年第19卷第7期 pp.07      

MAO Jie   chao wang   xiang Hong   Yu Yong Ji  

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We demonstrate a three-nanosecond equidistant sub-pulse multi-step Q-switched Nd: YAG laser. In the time interval of 100ns-1000ns, three pulses with the same nanosecond interval and the same peak power are obtained at the pulse width of 24ns, 28ns and 36.6ns, respectively. The energy is 32.5mJ and the optical efficiency is 10.8%.The multi-step Q-switched method does not require to insert other optical elements into the traditional Q-switched laser, it is very suitable to obtain pulse group output with several nanosecond pulse intervals.

       PDF全文 (下载：3)        Chinese Optics Letters ，2021年第19卷第7期 pp.07      

Peng Lingzhi   Hong Lihong   Chen Baoqin   He Peng   Li Zhiyuan  

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We use the nonlinear coupled-mode theory to theoretically investigate Second-harmonic generation (SHG) in subwavelength x-cut and z-cut lithium niobate (LN) thin-film waveguide and derive the analytical formula to calculate SHG efficiency in x-cut and z-cut LN thin-film waveguide explicitly. Under the scheme of optimal modal phase matching (MPM), two types of LN thin-film can achieve highly efficient frequency doubling of 1064nm laser with a comparable conversion efficiency due to very consistent modal field distribution of the fundamental wave and second harmonic wave and efficient overlap between them. Such a robust MPM for high-efficiency SHG in both subwavelength x-cut and z-cut LN thin-film waveguides are further confirmed in a broad wavelength range, which might facilitate design and application of micro-nano nonlinear optical devices based on subwavelength LN thin-film

       PDF全文 (下载：6)        Chinese Optics Letters ，2021年第19卷第7期 pp.07      

Yin Cheng   Kan xue fen   Guo Kun   Wang Tao   Xu Jiangmin   Han Qingbang   Wu Jian   Cao Zhuangqi  

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In modern optics, particular interest is devoted to the phase singularities which yield complicated and twisted phase structures by photons carrying optical angular momentum (OAM). In this paper, the traditional M-line method is applied to vortex beam (VB) by a symmetric metal cladding waveguide (SMCW) chip, which can host numerous oscillating guided modes via free space coupling. These ultrahigh order modes (UOMs) result in high angular resolution due to the high finesse of the resonant chip. Experiments show that the reflected pattern of a VB can be divided into a series of inner and outer rings, whilst both of them are highly distorted by the M-lines due to the UOMs’ leakage. Taking the distribution of the energy flux into account, a simple ray optics based model is proposed to simulate the reflected pattern by calculating the local incident angle over the cross-section of the beam. The theoretical simulations fit well with the experimental results and the proposed scheme may enable new applications in imaging and sensing complicated phase structures.

       PDF全文 (下载：2)        Chinese Optics Letters ，2021年第19卷第7期 pp.07      

Sun Lin-Shan   Zhao Bo   Yuan Jia-Qi   Zhang Yan-Rong   Kang Ming   Chen Jing  

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We show that inhomogeneous waveguides of slowly varied parity-time (PT) symmetry support localized optical resonances. The resonance is closely related to the formation of exceptional points separating exact and broken PT phases. Salient features of this kind of non-Hermitian resonance, including the formation of half-vortex flux and the discrete nature, are discussed. This investigation highlights the unprecedented uniqueness of field dynamics in non-Hermitian systems with many potential adaptive applications.

       PDF全文 (下载：4)        Chinese Optics Letters ，2021年第19卷第7期 pp.07      

Shi Yujiao   zhang zhenhui  

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We proposed a nonlinear photoacoustic (PA) technique as a new imaging contrast mechanism for tissue thermal-nonlinearity characterization. When a sine-modulated Gaussian temperature field is introduced by a laser beam, in view of the temperature dependence of the thermal diffusivity, nonlinear PA effect occurs which leads to the production of second-harmonic (SHPA) signals. By extracting the fundamental frequency photoacoustic (FFPA) and SHPA signal amplitudes of samples through lock-in technique, a parameter that only reflects nonlinear thermal diffusivity characteristics of the sample then can be obtained. The feasibility of the technique for thermal-nonlinearity characterization has been studied on phantom samples. In vitro biological tissues have been studied by this method to demonstrate its medical imaging capability, prefiguring great potential of this new method in medical imaging applications.

       PDF全文 (下载：2)        Chinese Optics Letters ，2021年第19卷第7期 pp.07      

Long Jun   Cai Ping   Liu Chiyue   Qu Wei   Yan Hao  

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Aperture synthesis is an important approach to improve the lateral resolution of digital holography (DH) technique. The limitation of the accuracy of registration positions between sub-holograms affects the quality of the synthesized image and even causes the failure of aperture synthesis. It is a major issue in aperture synthesis of DH. Currently intensity images are utilized to find the registration positions of sub-holograms in aperture synthesis. To improve the accuracy of registration positions, we proposed a method based on similarity calculation of the phase images between the sub-hologram, instead of intensity images. Furthermore, a quantitative indicator, degree of image distortion (DID), was applied to evaluate the synthetic results. Experiments are performed and the results verify that the proposed phase-image based method is better than the state-of-the-art intensity-image based techniques in the estimation of registration positions and provides a better synthesized final 3D shape image.

       PDF全文 (下载：1)        Chinese Optics Letters ，2021年第19卷第7期 pp.07      

Deng Lijun   Chen Qi   Bai Yang   Liu Guodong   Zeng Lvming   Ji Xuanrong  

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Photoacoustic microscopy (PAM) has quickly developed into a noninvasive biomedical imaging technique to achieve the detection, diagnosis, and monitoring. Compared with Q-switched Nd: YAG or OPO lasers, using a low cost and small size laser diode (LD) as an alternative light source, is conducive to achieve the miniaturization and integration for preclinical transformation. However, LD’s low peak output power needs the high numerical aperture objective to attain tight focus, which limits the working distance (WD) of the system in only 2-3 millimeters, resulting in not achieving the backward coaxial confocal mode. Here, we present a compact visible LD-based PAM system with a reflective objective to achieve a 22 mm long WD and a 10 µm lateral resolution. Different depth subcutaneous microvascular networks in label-free mouse ears have been successfully reappeared in vivo with a SNR up to 14 dB by a confocal alignment. It will be a promising tool to develop into a handy tool for subcutaneous blood vessel imaging.

       PDF全文 (下载：7)        Chinese Optics Letters ，2021年第19卷第7期 pp.07      

Zhao Yi   Huang Qiuping   Cai Honglei   Lin Xiaoxia   He Hongchuan   Cheng Hao   Ma Tian   Lu Yalin  

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In this paper, we experimentally demonstrate ultrafast optical control of slow light in the THz range, by combing the electromagnetically induced transparency (EIT) metasurfaces with the cut wire made of P⁺-implanted silicon with short carrier lifetime. Employing the optical-pump terahertz-probe spectroscopy, we observed that the device transitioned from a state with a slow light effect to a state without a slow light effect in an ultra-fast time of 5 ps and recovered within 200 ps. A coupled oscillator model is utilized to explain the origin of controllability. The experimental results agree very well with the simulated and theoretical results. This EIT metasurfaces have the potential to be used as an ultrafast THz optical delay device.

       PDF全文 (下载：3)        Chinese Optics Letters ，2021年第19卷第7期 pp.07      

Yan Ming   Wang Yinqi   Wang Xiaoyue   Peng Junsong   Huang Kun   Zeng Heping  

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In this paper, we demonstrated a series of short-living mode-locking (ML) states (each lasting a few to a hundred of s) that happened before a fiber laser reaching a steady ML state. With time-stretched dispersion Fourier transform spectroscopy, a rich diversity of transient multi-pulse dynamics were revealed spectrally and temporally. As a result, we found that the formation of the short-living ML states was related to abundant pump power and their decaying evolution dynamics were possibly governed by gain depletion and recovery. Our results revealed unexpected transient lasing behaviors of a soliton laser and thus might be useful to understand the complex dynamics of mode-locked lasers.

       PDF全文 (下载：18)        Chinese Optics Letters ，2021年第19卷第7期 pp.07      

Li Ke   Gao Yantao   Zhang Haipeng   Du Guohao   Huang Hefei   Xu Hongjie   Xiao Tiqiao  

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Carbon fiber (CF)/pyrolytic graphite (PG) composites are promising structural materials for molten salt reactors because of their superior performance. Due to the minor density difference between CF and PG, existing methods are impractical for efficient three-dimensional characterization of CF/PG composites. Therefore, in this study, a method based on in-line phase-contrast X-ray microtomography was developed to solve the aforementioned problem. Experimental results demonstrate that the method is suitable for comprehensive characterization of CF/PG composites. The relationship between the microporous defects and fiber orientations of such composites was also elucidated. The findings can be useful for improving the manufacturing process of CF/PG composites.

       PDF全文 (下载：12)        Chinese Optics Letters ，2021年第19卷第7期 pp.07      

Chen Jian   Chen Guoliang   Zhan Qiwen  

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A fiber-based source that can be exploited in stimulated emission depletion (STED) inspired nanolithography setup is presented. Such a source maintains the excitation beam pulse, generates ring-shaped depletion beam and automatically realizes dual-beam co-axial alignment that is critical for two beam nanolithography. The mode conversion of depletion beam is realized by using customized vortex fiber, which converts the Gaussian beam into donut-shaped azimuthally polarized beam. The pulse width and repetition frequency of the excitation beam remain unchanged and its polarization states can be controlled. According to the simulated point spread functions of each beam in the focal region, the full-width at half-maximum of the effective spot size in STED nanofabrication could decrease to less than 28.6 nm.

       PDF全文 (下载：4)        Chinese Optics Letters ，2021年第19卷第7期 pp.07