Non-Line-of-Sight Imaging with Picosecond Temporal Resolution

Non-line-of-sight (NLOS) imaging enables monitoring around corners and is promising for diverse applications. The resolution of transient NLOS imaging is limited to a centimeter scale, mainly by the temporal resolution of the detectors. Here, we construct an up-conversion single-photon detector with a high temporal resolution of $\sim 1.4\mathrm{ps}$ and a low noise count rate of 5 counts per second (cps). Notably, the detector operates at room temperature, near-infrared wavelength. Using this detector, we demonstrate high-resolution and low-noise NLOS imaging. Our system can provide a $180\mu \mathrm{m}$ axial resolution and a 2 mm lateral resolution, which is more than 1 order of magnitude better than that in previous experiments. These results open avenues for high-resolution NLOS imaging techniques in relevant applications.

Figure 1

Experimental setup and testing of performance. (a) Experimental setup for NLOS imaging with a picosecond temporal resolution UCSPD. (b) The SFG photon counts while scanning the delay line with different pump power. (c) Detection efficiency and dark count rate of the SPD after time gating on the TDC. The detection efficiency is calculated by dividing the maximum SFG count by the input signal photon count.

Figure 2

Determination of axial spatial resolution. (a) Experimental setup for axial resolution test. (b) One of the reconstructed images. The black box contains 300 pixels used in statistical analysis. (c) The reconstructed albedo along the axial direction of the selected pixel in Fig. 2(b). (d) Reconstructed distance distribution of the selected 300 pixels in Fig. 2(b).

Figure 3

Lateral spatial resolution. (a) The hidden resolution chart used for the lateral resolution test. The intervals between strips in the four groups are 4, 3, 2, and 1 mm, respectively. (b) The reconstructed front view of the resolution chart with $64\times 64$ sampling points on the visible wall.

Figure 4

Reconstruction of letters. (a) Hidden USTC letters. (b) Front view of the reconstructed image of USTC with $64\times 64$ sampling points on the visible wall and 0.5 ps scanning time bin on the delay line. (c) Front view of the reconstructed image of USTC with 5 ps temporal resolution. (d) Hidden word of SCIENCE. (e) Front view of the reconstructed image of SCIENCE with $128\times 128$ sampling points on the visible wall and 0.5 ps scanning time bin on the delay line. (f) Front view of the reconstructed image of SCIENCE with 5 ps temporal resolution.