- 标题
- 摘要
- 关键词
- 实验方案
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Laser-Based Phase Contrast for Transmission Electron Microscopy
摘要： Laser control of free electrons has been used to advance the exploration of matter on the atomic scale. For example, temporal modulation of electron waves with light has enabled the study of transient processes with attosecond resolution. By contrast, laser-based spatial shaping of the electron wave function has not yet been realized, even though it could be harnessed to probe radiation-sensitive systems, such as biological macromolecules, at the standard quantum limit and beyond. We demonstrate increased image contrast by laser control of the spatial phase profile of the electron wave function in transmission electron microscopy (TEM). We first realize an electron interferometer, using continuous-wave laser-induced retardation to coherently split the electron beam, and capture TEM images of the light wave. We then demonstrate Zernike phase contrast by using the laser beam to shift the phase of the electron wave scattered by a specimen relative to the unscattered wave. Electrons interact with light via the repulsive ponderomotive potential arising from stimulated Compton scattering. Due to the short electron-light interaction time in a micron-scale laser focus, retardation of the relativistic electrons used in TEM requires an intensity of tens of GW/cm2. Such intensities have so far only been attained with pulsed lasers, but a cw laser is needed in order to work state-of-the-art, continuously operating TEM. The requisite laser intensity is generated by 4000-fold resonant power enhancement in a near-concentric Fabry-Perot optical cavity with a mode waist of w0 = 13 μm. A laser system consisting of a fiber amplifier seeded by a low-power master laser supplies an input laser beam at a wavelength of λ = 1064 nm. The experiments are carried out with 80 keV electrons, in a custom-modified TEM (FEI Titan) equipped with additional electron optics that magnify the diffraction pattern to an effective focal length of f = 20 mm. The cavity is suspended in the TEM column, with its axis orthogonal to the electron beam propagation direction and with the mode waist positioned close to the center of the magnified electron diffraction plane, as shown in Fig. 1. Zernike phase contrast is evident in a typical close-to-focus image (Fig. 1), showing the structure of the carbon film. A high-intensity CW laser field generates Zernike phase contrast in a TEM and significantly increases the image contrast at low spatial frequencies. Such a phase plate will enable dose-efficient data collection in single-particle analysis of biological macromolecules, electron tomography of vitrified cells, and imaging of sensitive materials science specimens. The controllable phase shift in this device can also be used for holographic reconstruction of the post-specimen wave function. Work in the immediate future will include working with 300-keV electrons, which requires constructing a new cavity with lower-loss optical coatings to reach higher laser intensity. We will also study and optimize the imaging properties of the phase-contrast TEM, and apply it to structural biology.
关键词： Zernike phase contrast,Laser control,Fabry-Perot optical cavity,Transmission Electron Microscopy,electron wave function
更新于2025-09-19 17:13:59
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Orthogonal Phase Demodulation of Optical Fiber Fabry-Perot Interferometer Based on Birefringent Crystals and Polarization Technology
摘要： In this paper, we propose and demonstrate the optical fiber Fabry-Perot (F-P) interferometer based on birefringent crystals and polarization technology. For recovering the variation signals, the orthogonal signals are obtained based on the birefringent crystal characteristics and the proposal thickness difference between the two crystals. The differential cross multiplication (DCM) algorithm is utilized to demodulate the orthogonal signals to obtain the phase variation of the optical fiber F-P sensor. The proposed interferometer has a minimum detection phase of 0.014 rad/Hz at the frequency of 25 kHz. In the experiment, two kinds of vibration signals with frequencies of 25 kHz and 15 kHz are used and the proposed interferometer SNR is 70 dB and 75 dB under the corresponding reference environment respectively. The experiment results show that the proposed interferometer can realize the measurement of large dynamic signals and has high stability. The proposed interferometer has the advantages of fast demodulation and good environmental adaptability.
关键词： phase variation,orthogonal signals,birefringent crystals,Optical fiber Fabry-Perot interferometer
更新于2025-09-19 17:13:59
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Microstructured optical fiber based Fabrya??P??rot interferometer as a humidity sensor utilizing chitosan polymeric matrix for breath monitoring
摘要： This study reports a method for humidity sensing based on a specialty microstructured optical fiber (MOF). A suspended tri-core MOF was fabricated using the stack and draw technique. A low finesse sensing head was prepared by depositing a chitosan polymer matrix within the holes of the MOF, forming a Fabry-Pérot interferometer as a sensing platform while the chitosan film acts as the sensing material. The use of the probe for real-time breath monitoring was also successfully demonstrated. The probe possessed a maximum sensitivity of 81.05 pm/(%RH) for 90–95%RH range while the linear region of the sensor ranged from 70–95%RH. The temperature cross correlation was also experimented, and a lower influence of external temperature was observed. The probe shows an ultrafast response during human breath monitoring with a rising time and recovery time of 80 ms and 70 ms, respectively.
关键词： humidity sensing,chitosan polymeric matrix,breath monitoring,microstructured optical fiber,Fabry–Pérot interferometer
更新于2025-09-19 17:13:59
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[IEEE 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Huangshan, China (2019.8.5-2019.8.8)] 2019 18th International Conference on Optical Communications and Networks (ICOCN) - New mechanism Vernier Effect to amplify the sensitivity based on separated Fabry-perot interferometers
摘要： A new method to amplify the sensitivity based on separated Fabry-perot interferometers (FPI) causing Vernier effect is presented and discussed. The spectrum of typical cascaded cavity based on Vernier effect is analyzed and simulated. We also propose a novel structure to realize Vernier effect to amplify sensitivity, using two separated FPI. The simulation shows that the disturbance term in the spectrum is eliminated, and sensitivity is the same as cascaded cavities’.
关键词： Fabry-perot interferometer,Vernier effect
更新于2025-09-16 10:30:52
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[IEEE 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Huangshan, China (2019.8.5-2019.8.8)] 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Highly sensitive refractive index sensor with fiber in-line Fabry-Perot interferometers based on vernier effect
摘要： A highly sensitive refractive index (RI) sensor with fiber in-line Fabry-Perot interferometers based on vernier effect is proposed and experimentally demonstrated. The sensor is fabricated by splicing a short segment of capillary to a commercial single mode fiber (SMF) and then splicing a tiny large mode area fiber to the capillary. There are two micro-channels in the lateral wall of the tube. The sensor exhibits a compact size of less than 1 mm in total length and has the highest RI sensitivity of ~10189.2 nm/RIU within the range of 1.32846 to 1.33327.
关键词： Fabry-Perot interferometer,Optical fiber refractive index sensor,vernier effect
更新于2025-09-16 10:30:52
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[IEEE 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Huangshan, China (2019.8.5-2019.8.8)] 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Highly Sensitive Fiber Optic Pressure Sensor Based on Silica Diaphragm Fabricated by MEMS
摘要： This paper presents the fabrication procedure of a 1.2-μm thick silica diaphragm with high uniformity using microelectromechanical systems (MEMS) technique. The diaphragm fabrication started from a commercially available double-polished 300-μm silicon wafer with a silica layer on its bottom. The silica diaphragm was released from the wafer by photolithography, wet etching and inductively coupled plasma (ICP) etching. A fiber optic Fabry-Perot (FP) pressure sensor was made by thermally bonding the diaphragm to the end face of an etched fiber with an outside diameter of 125 μm. The obtained sensor has a static pressure sensitivity of 12.4 nm/kPa (85.3 nm/psi). It has a great potential to work in medical applications where miniature size and high sensitivity are essential.
关键词： Fabry-Perot (FP) interferometers,MEMS,Fiber optic pressure sensors
更新于2025-09-16 10:30:52
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[IEEE 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Huangshan, China (2019.8.5-2019.8.8)] 2019 18th International Conference on Optical Communications and Networks (ICOCN) - An in-fiber Acceleration Sensor based on Fabry–Perot Cavity
摘要： A compact fiber-optic acceleration sensor based on Fabry–Perot interferometer is proposed and fabricated. The experimental results show that the minimum detectable acceleration of the accelerometer is 0.928 mg and the available bandwidth is 10-90 Hz.
关键词： Acelerometer,Amplitude – frequency characteristics,Sensitivity,Fabry-Perot Interferometer
更新于2025-09-16 10:30:52
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An electro-tunable Fabry–Perot interferometer based on dual mirror-on-mirror nanoplasmonic metamaterials
摘要： Mirror-on-mirror nanoplasmonic metamaterials, formed on the basis of voltage-controlled reversible self-assembly of sub-wavelength-sized metallic nanoparticles (NPs) on thin metallic film electrodes, are promising candidates for novel electro-tunable optical devices. Here, we present a new design of electro-tunable Fabry–Perot interferometers (FPIs) in which two parallel mirrors – each composed of a monolayer of NPs self-assembled on a thin metallic electrode – form an optical cavity, which is filled with an aqueous solution. The reflectivity of the cavity mirrors can be electrically adjusted, simultaneously or separately, via a small variation of the electrode potentials, which would alter the inter-NP separation in the monolayers. To investigate optical transmittance from the proposed FPI device, we develop a nine-layer-stack theoretical model, based on our effective medium theory and multi-layer Fresnel reflection scheme, which produces excellent match when verified against full-wave simulations. We show that strong plasmonic coupling among silver NPs forming a monolayer on a thin silver-film substrate makes reflectivity of each cavity mirror highly sensitive to the inter-NP separation. Such a design allows the continuous tuning of the multiple narrow and intense transmission peaks emerging from an FPI cavity via electro-tuning the inter-NP separation in situ – reaping the benefits from both inexpensive bottom-up fabrication and energy-efficient tuning.
关键词： electro-tunable optical devices,voltage-controlled reversible self-assembly,self-assembled plasmonic nanoparticles,Fabry–Perot interferometers
更新于2025-09-16 10:30:52
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[IEEE 2019 20th International Conference on Solid-State Sensors, Actuators and Microsystems & Eurosensors XXXIII (TRANSDUCERS & EUROSENSORS XXXIII) - Berlin, Germany (2019.6.23-2019.6.27)] 2019 20th International Conference on Solid-State Sensors, Actuators and Microsystems & Eurosensors XXXIII (TRANSDUCERS & EUROSENSORS XXXIII) - Fabrication of Cavity-Sealed Optical Interferometric Surface Stress Biosensor by thin Film Transfer Technique
摘要： We developed a surface stress sensor based on a MEMS Fabry-Perot interferometer with cavity-sealed structure by technique of nanometer-thick parylene sheet for highly sensitive label-free biosensing. The proposed MEMS interferometer can measure the membrane deflection caused by target molecule adsorption as the spectral shift. The proposed cavity-sealed optical interferometer can prevent physical adsorption to the backside of membrane and refractive index drift in the cavity, leading to improvement of sensitivity. We successfully obtained the spectral shift of 77 nm in 10 minutes with the color change associated with the antigen-antibody reaction with a concentration of 1 ng/ml, which improved by 16.7-fold compared with the conventional sensor.
关键词： MEMS biosensor,Surface stress sensor,label-free biosensing,film transfer technique,Fabry-Perot interferometer
更新于2025-09-16 10:30:52
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Microelectromechanical system-based, high-finesse, optical fiber Fabry–Perot interferometric pressure sensors
摘要： A high-finesse, optical fiber, extrinsic Fabry–Perot interferometric (EFPI) pressure sensor based on a microelectromechanical system (MEMS) technique is proposed and experimentally demonstrated. The essential element in the pressure sensor is the high-finesse EFPI cavity that consists of a Pyrex glass wafer, a micromachined silicon wafer, and highly reflective dielectric films. Another Pyrex glass is used for fixing an optical fiber collimator, which allows the realization of the alignment of the incident light. Experimental results show that the proposed sensor exhibits a pressure sensitivity of 1.598 μm/MPa and a high-pressure sensing resolution of 0.002% of the full scale. This sensor is expected to benefit many applications that require high-accuracy pressure measurements, and especially atmospheric pressure applications.
关键词： optical fiber sensor,pressure measurement,microelectromechanical system,extrinsic Fabry–Perot interferometer
更新于2025-09-16 10:30:52