Fig. 1. (a) Schematic of the entire system. The focal lengths of lenses , , and are 40, 80, 60 and 80 cm, respectively. (b) Optical arrangement schematic for various diagnostics modes. A rectangular aperture (RA) is used to limit the FOV of the relay image on the GOI, preventing crosstalk between the images. The distance δx between beam splitters plays a crucial role in the multi-frame shadowgraph mode, as it determines the framing time interval. In the interferometer mode, this distance is set to be sufficiently small. In the AFR mode, a streak filter is positioned at the Fourier plane, and the beam splitters merely serve to attenuate the probe and shield against stray light.

Fig. 2. Image of a USAF test target, with an optical system magnification of approximately 2.4 and a contrast value of around 10% for G5E1 (32 lp/mm).

Fig. 3. Schematic demonstrating how the beam splitters produce separation and interference. The FOV of the interference is determined by the separation angle of the beam splitters, while the spacing of the fringes is determined by both the separation angle and distance to the Fourier plane.

Fig. 4. (a) Interferogram without plasma; fringe spacing: 360 μm. (b) Interferogram without plasma; fringe spacing: 640 μm. Frames 1 and 2 in (a) and (b) share the same diagnostic FOV, and they are formed by the interference of the (N–1)th and Nth beams and Nth and (N+1)th beams, respectively.

Fig. 5. (a) Interferogram with plasma. (b) Interferogram without plasma. (c) Reconstructed electron density. The data in the shaded region in (a) indicate that the fringes are densely packed together due to the large plasma gradient, resulting in being unresolvable. The coordinates of the top of the cone are set as the origin of the coordinates.

Fig. 6. (a) The AFR result with the straight lines parallel to the x-axis, and (b) the corresponding preliminary binarization results. (c) The AFR result with the straight lines parallel to the y-axis, and (d) the corresponding preliminary binarization results.

Fig. 7. Image of the streak filter.

Fig. 8. (a) The electron density results at x = 0 of Figure 6(a). (b) The electron density results at x = 0 of Figure 6(c).

Fig. 9. (a) The reference shadowgrams, acquired using one pair of beam splitters, are annotated with the acquisition time for each frame, with frame 1 serving as the temporal baseline. The distance between beam splitters is set to 18 cm, resulting in a time delay of 1.2 ns along the horizontal direction. The obstruction caused by the target holder makes the cone tip invisible, and the estimated position of the cone is indicated in frame 1. (b) The reference shadowgrams, acquired using two pairs of beam splitters, are annotated with the acquisition time for each frame, with frame 1 serving as the temporal baseline. The tip of the cone is denoted in frame 8, with its lateral dimensions measuring approximately 150 μm. The distances between the two pairs of beam splitters are set to 6 and 18 cm, resulting in a time delay of 1.2 ns along the horizontal direction and 0.4 ns along the vertical direction, as illustrated. The gating time of reference shadowgrams is set to 5 ns to observe the field of view of each frame. (c) The plasma shadowgrams corresponding to the reference shadowgrams (b). The gating time of plasma shadowgrams is set to 200 ps to achieve high time resolution of each frame.

Fig. 10. The longitudinal scale of the plasma ejected from the cone tip in Figure 9(c).