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We propose a scheme for constructing a phase plate for use in an ultrafast Zernike-type phase contrast electron microscope, based on the interaction of the electron beam with a strongly focused, high-power femtosecond laser pulse and a pulsed electron beam. Analytical expressions for the phase shift using the time-averaged ponderomotive potential and a paraxial approximation for the focused laser beam are presented, as well as more rigorous quasiclassical simulations based on the quantum phase integral along classical, relativistic electron trajectories in an accurate, non-paraxial description of the laser beam. The results are shown to agree well unless the laser beam is focused to a waist size below a wavelength. For realistic (off-the-shelf) laser parameters the optimum phase shift of -π/2 is shown to be achievable. When combined with RF-cavity based electron chopping and compression techniques to produce electron pulses, a femtosecond regime pulsed phase contrast microscope can be constructed. The feasibility and robustness of the scheme are further investigated using the simulations, leading to motivated choices for design parameters such as wavelength, focus size and polarization.

Recently, there has been increased interest in the shaping of light fields with an inverse energy flux to guide optically trapped nano- and microparticles towards a radiation source. To generate inverse energy flux, non-uniformly polarized laser beams, especially higher-order cylindrical vector beams, are widely used. Here, we demonstrate the use of conventional and so-called generalized spiral phase plates for the formation of light fields with an inverse energy flux when they are illuminated with linearly polarized radiation. We present an analytical and numerical study of the longitudinal and transverse components of the Poynting vector. The conditions for maximizing the negative value of the real part of the longitudinal component of the Poynting vector are obtained.

Continuous phase plate (CPP) with complex surface structures is used to smooth the focal spot of laser beam. Great demand for CPP in laser fusion system requires mass production technology with low cost. Therefore, the rapid fabrication method for CPP using atmospheric pressure plasma processing (APPP) is presented in this paper. Firstly, the fundamental characteristics of APPP were studied to obtain the optimal processing parameters. Considering the influence on etching rate from surface temperature, trench machining experiments were conducted to establish the exponential model of influence function. Based on this model, the iterative calculation method for dwell time was developed to minimize the thermal effect on machining error, and the sinusoidal surface experiments prove its effectiveness. At last, a 320 mm × 320 mm × 2 mm CPP of BOROFLOAT33 (B33) with 2.78 μm PV was fabricated within 16 h using APPP, and the RMS of form error is 96 nm. The far field focal spot of the machined CPP was calculated. The result shows that the machined CPP has an acceptable beam-shaping function, which demonstrates the potential for fabricating CPP using APPP.

We report on two key discoveries resulting from the combination of the Hilbert phase plate (HPP) and the Wiener filter: firstly, the resolution of the HPP’s mixed image problem through a one-step experiment, and secondly, the unification of the Zernike phase plate (ZPP) and the HPP. When the phase of the HPP is reduced to less than π, it produces a mixed image comprising both the normal and the differential images. The HPPU (left–right unified HPP), proposed to address this issue, required a two-step experimental process. However, during our efforts to resolve the mixed image problem using either the left or right HPP, we discovered that the Wiener filtering process not only addresses this issue but also facilitates the unification of the ZPP and HPP. We will discuss the theoretical development behind these discoveries and their verification through simulations of three phase contrast methods: the Scherzer, ZPP, and HPP methods.

ABCB1/P-glycoprotein is an ATP binding cassette transporter that is involved in the clearance of xenobiotics, and it affects the disposition of many drugs in the body. Conformational flexibility of the protein within the membrane is an intrinsic part of its mechanism of action, but this has made structural studies challenging. Here, we have studied different conformations of P-glycoprotein simultaneously in the presence of ivacaftor, a known competitive inhibitor. In order to conduct this, we used high contrast cryo-electron microscopy imaging with a Volta phase plate. We associate the presence of ivacaftor with the appearance of an additional density in one of the conformational states detected. The additional density is in the central aqueous cavity and is associated with a wider separation of the two halves of the transporter in the inward-facing state. Conformational changes to the nucleotide-binding domains are also observed and may help to explain the stimulation of ATPase activity that occurs when transported substrate is bound in many ATP binding cassette transporters.

Hole-free phase plates (HFPPs), also known as Volta phase plates, were already demonstrated to be well suited for in-focus transmission electron microscopy imaging of organic objects. However, the underlying physical processes have not been fully understood yet. To further elucidate the imaging properties of HFPPs, phase shift measurements were carried out under different experimental conditions. Both positive and negative phase shifts occur depending on the diameter of the zero-order electron beam and the HFPP film temperature. The analysis of Thon ring patterns of an amorphous carbon test sample reveals that the phase-shifting patch can be significantly larger than the size of the zero-order beam on the HFPP film. An HFPP was used for in-focus phase contrast imaging of carbon nanotube (CNT) bundles under positive and negative phase-shifting conditions. The comparison of experimental and simulated images of CNT bundles gives detailed information on the phase shift profile, which depends on the spatial frequency in the vicinity of the zero-order beam. The shape of the phase shift profile also explains halo-like image artifacts that surround the imaged objects.

Spiral phase plate (SPP) is the widely used method in the generation of vortex beam (VB) with fixed topological charges (TCs) for specific wavelength. Although VB with large TCs can be directly generated by using the SPP with high vortex order. The fabrication of high-quality SPPs with high vortex orders usually requires complex manufacturing process and high machining accuracy. An alternative method to generate VBs with large TCs is cascaded multiple SPPs with low order. In this study, we numerically calculate the transmitted light field of cascaded multiple SPPs according to the Huygens–Fresnel diffraction integral, and perform the experimental verifications. Based on cascading 6 SPPs (3 SPPs with TCs of 2, and 3 SPPs with TCs 4, respectively), an VB with TCs as high as 18 is generated. Furthermore, The TCs of the generated VB are detected by coaxial and off-axis interfering with fundamental Gaussian beam or its conjugate beam, respectively. The generated fork and spiral patterns allow us to distinguish the value and sign of TCs carried by the VB. The experimental results coincide well with the theoretical simulations. The fork pattern shows better resolution than the spiral one, and the petal pattern with small spiral allows us to distinguish large TCs with a higher resolution.

The direct femtosecond laser writing of phase optical elements in glasses represents a promising technique for controlling light beams and developing new functional devices that operate on the birefringence effect. In this study, phase plates were written in the volume of silica and nanoporous glasses using a laser beam. For the first time, the chromatic dispersion curves of birefringence were measured for such plates using multiple methods. This allows the retardance of birefringent elements fabricated by direct laser writing to be estimated, even when using commercial birefringence analysis systems operating at a specific wavelength.