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Most resonant inelastic x-ray scattering (RIXS) studies of dynamic charge order correlations in the cuprates have focused on the high-symmetry directions of the copper oxide plane. However, scattering along other in-plane directions should not be ignored as it may help understand, for example, the origin of charge order correlations or the isotropic scattering resulting in strange metal behavior. Our RIXS experiments reveal dynamic charge correlations over theq_x-q_yscattering plane in underdoped Bi₂Sr₂CaCu₂O_8+δ. Tracking the softening of the RIXS-measured bond-stretching phonon, we show that these dynamic correlations exist at energies below approximately 70 meV and are centered around a quasi-circular manifold in theq_x-q_yscattering plane with radius equal to the magnitude of the charge order wave vector,q_CO. This phonon-tracking procedure also allows us to rule out fluctuations of short-range directional charge order (i.e., centered around [q_x= ±q_CO,q_y= 0] and [q_x= 0,q_y= ±q_CO]) as the origin of the observed correlations. 

Abstract Compressed ultrafast photography (CUP) is an emerging potent technique that allows imaging a nonrepeatable or difficult‐to‐produce transient event in a single shot. Despite many recent advances, existing CUP techniques operate only at visible and near‐infrared wavelengths. In addition, spatial encoding via a digital micromirror device (DMD) in CUP systems often limits its field of view and imaging speeds. Finally, conventional reconstruction algorithms have limited control of the reconstruction process to further improve the image quality in the recovered datacubes of the scene. To overcome these limitations, this article reports a single‐shot UV‐CUP that exhibits a sequence depth of up to 1500 frames with a size of 1750 × 500 pixels at an imaging speed of 0.5 trillion frames per second. A patterned photocathode is integrated into a streak camera, which overcomes the previous restrictions in DMD‐based spatial encoding and improves the system's compactness. Meanwhile, the plug‐and‐play alternating direction method of multipliers algorithm is implemented to CUP's image reconstruction to enhance reconstructed image quality. UV‐CUP's single‐shot ultrafast imaging ability is demonstrated by recording UV pulses transmitting through various spatial patterns. UV‐CUP is expected to find many applications in both fundamental and applied science.