An x-ray framing camera based on pulse-dilation technology is reported. This camera first dilates the electron signal generated from a pulsed photo-cathode (PC), and then detects the dilated electron pulse by using a gated microchannel plate (MCP). While the PC is only applied with a direct current (DC) voltage, the camera's temporal resolution without pulse-dilation is about 81 ps. It is the gated MCP's temporal resolution. While an excitation pulse is applied on the PC, the electron pulse's temporal width is dilated, and the resolution is improved to 14 ps. Furthermore, the camera's temporal resolution uniformity is measured and simulated. The results show a 3.5 × drop in temporal resolution along the pulse propagation direction, due to the 5 × decrease of the PC excitation pulse gradient.

Dilation x-ray framing camera and its temporal resolution uniformity.

Periodic noise corrupts digital images during acquisition and transmission stages by adding repetitive patterns. This study introduces a new adaptive Gaussian notch filter (AGNF) in Fourier transform domain for effectively restoring images contaminated with periodic, quasi-periodic and Moire pattern noises. Since periodic noises are sinusoidal functions added to the uncorrupted images, Fourier transform of images make these noisy functions to concentrate as easily distinguishable conjugate peaks in frequency domain. The proposed AGNF effectively identifies the noisy peak positions and adaptively quantifies the associated noisy areas by analysing the ratio of averages of frequencies from adaptively varying neighbourhoods. These identified noisy peaks are then diffused by Gaussian notch filter of adaptively varying sizes. The proposed filter ensures maximum diffusion of identified noisy peak areas by maintaining the minimum frequency values from the outputs of overlapping notch filters. Visual and quantitative experimental analysis of the proposed algorithm with mean absolute error, peak signal-to-noise ratio, mean structural similarity index measure and computation time reveals that AGNF is better in restoring images contaminated with periodic noises when compared to other methods.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-ipr.2018.5707

Adaptive Gaussian notch filter for removing periodic noise from digital images

An x-ray detector using a pulse-dilation technology to achieve high temporal resolution is reported. The electron pulse generated from the photo-cathode (PC) is first dilated by a pulse-dilation device and then imaged onto the microchannel plate (MCP) by a magnetic lens imaging system. Finally, the dilated electron pulse is detected by a gated MCP. A resolution of 14 ps is achieved. In addition, the synchronous gating is studied in the dilation x-ray detector without a 1:1 image ratio. The results show that while the time of flight (TOF) of the electrons is identical, the MCP gating pulse can be timed relative to the PC excitation pulse to gate the dilated electron signal in a single area, and they are unsynchronized in the other area. To avoid the single area synchronization effect, the magnetic lens imaging system used in the detector should allow photoelectrons with a large energy spread to be imaged onto the MCP. This effect can also be reduced by using an MCP gating pulse with a width larger than 500 ps. Moreover, a 1:1 image ratio can avoid this effect. Furthermore, a decreasing electron TOF can eliminate the single area synchronization effect.

Synchronous gating in dilation x-ray detector without 1:1 image ratio

A pulse-dilation framing camera (PFC) and its working principle are introduced. The influence of the dilation pulse on the exposure time is discussed. The measurement of the dilation pulse using the PFC are theoretically analyzed and experimentally verified. The waveform and the entire time history of the potential of the dilation pulse are simulated by the known dilation factors of the PFC in theory, with the potential deviation at the end of the dilation time of pulse being approximately 3.2%. In the experiment, the exposure time and dilation factors of the PFC are measured by using an array of fiber bundles and in taking many measurements, the waveform and the entire time history of the potential of dilation pulse are achieved by the dilation factors, with the potential deviation at the end of the dilation time of pulse being approximately 6.3%. The research results show that the experimental measurement is consistent with theoretical analysis, although there are some deviations, and it is feasible to measure the waveform and the entire time history of the potential of dilation pulse using the PFC. Moreover, the research may provide an idea for new applications of the framing camera.

Measurement of dilation pulses using a pulse-dilation framing camera

Large-format pulse-dilation framing tube with 5 lp/mm spatial resolution

A framing camera with high temporal and spatial resolution is demonstrated using pulse-dilation technology and a magnetic lens. The magnetic field of the magnetic lens is simulated using LORENTZ-3EM software, and the magnetic field distribution on-axis is similar to a Gaussian function. The temporal and spatial resolutions of the instrument are measured using light at the wavelength of 266 nm from a frequency tripled femtosecond laser. The measured exposure time of this camera is ∼11 ps, and the spatial resolution is better

Demonstration of 11-ps exposure time of a framing camera using pulse-dilation technology and a magnetic lens

A framing camera using pulse-dilation technology is reported in this article. The camera uses pulse dilation of an electron signal from a pulsed photo-cathode (PC) to achieve high temporal resolution. While the PC is not pulsed, the measured temporal resolution of the camera without pulse-dilation is about 71 ps. While the excitation pulse is applied on the PC, the measured temporal resolution is improved to 4 ps by using the pulse-dilation technology. The spatial resolution of the dilation framing camera is also measured, which is better than 100 μm. The relationship between the temporal resolution and the PC bias voltage is obtained. The variation of the temporal resolution with the gradient of the PC excitation pulse is also provided.

/pdf/dilation-framing-camera-with-4-ps-resolution-3hf2pbrbm7.pdf

Dilation framing camera with 4 ps resolution

A framing camera based on the pulse-dilation technology is simulated by using the Monte Carlo method. The camera uses pulse dilation of an electron signal from a pulsed photocathode (PC) to achieve high temporal resolution. When the PC is not pulsed, the theoretical temporal resolution of the camera without pulse dilation is about 90 ps. When the excitation pulse is applied on the PC, the theoretical temporal resolution is improved to 1.9 ps using the pulse-dilation technology. The relationship between the temporal resolution and the PC bias voltage is obtained. The variation of the temporal resolution with the gradient of the PC excitation pulse is also provided. Furthermore, the connection between the temporal resolution and the drift length is acquired.

Simulation of a dilation x-ray framing camera

Observation of electron beam moiré fringes in an image conversion tube.

Simulated and measured spatial resolution of framing converter using short magnetic focusing

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