A two-dimensional ultrafast X-ray imager (UXI) composed of a time-dilation device, an electron-beam imaging unit, a gated microchannel plate (MCP) framing tube, and a pulser was developed. The time-dilation device extends the time spread of the electron signal generated by the pulsed photocathode (PC), and the electron-beam imaging unit images the electron pulse from PC to MCP. Finally, the gated MCP framing tube samples the dilated electron pulse. The time resolution and image size of the UXI were measured with an X-ray generated by a terawatt laser targeting device. When a driving pulse with a 2 V/ps slope is applied to the PC, the measured time resolution is 21 ps, and the image size is 12 mm × 3.9 mm. Furthermore, the image size varies with the time resolution. The results show that as the time resolution improves, the image size decreases. The use of two opposite-transmission PC driving pulses could improve the image size. Moreover, the measured UXI spatial resolution is 5 lp/mm, and the spatial resolution will be worse with the increasing off-axis distance.

The temporal resolution uniformity of a time-dilation framing camera is studied, and the ideal photocathode (PC) pulse curve is determined, while the temporal magnification factor is kept constant. To obtain the ideal curve, a series of linear pulses with the same slope are superposed. The variance in the temporal resolution and the number of linear pulses required are compared, while the superposition results with different slopes are used as the PC voltage. As the slope of the linear pulses decreases, the variance decreases, which means that the uniformity of the temporal resolution is improved, but the number of linear pulses required increases. In this study, linear pulses with a slope of 1 V/ps are superposed. Nine linear pulses with a front edge time of 200 ps, amplitude of 200 V, and flat top time of 1 ns are superimposed to approximate the ideal PC pulse curve with a constant temporal magnification factor of 10; the trigger times of the pulses are 0, 0, 0, 185, 200, 350, 450, 605, and 790 ps. When the superposition result is applied as the PC voltage and the measured signal is synchronized to the PC pulse at 128 ps–1 ns, the temporal resolution error is within 5%.

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