Improving the ranging performance of chaos LiDAR.

Chaos lidar has gained significant attention due to its high spatial resolution, natural anti-interference capability, and confidentiality. However, constrained by the power of the chaos laser, the sensitivity of the linear detector, and the hardware bandwidth, chaos lidar is greatly restricted in the application of long-distance target detection and imaging. To overcome these constraints, we propose a novel, to the best of our knowledge, chaos lidar based on Geiger mode avalanched photodetectors (GM-APDs) in a previous study called chaos single-photon (CSP) lidar. In this paper, we compare the CSP lidar with the linear mode chaos lidars by combining with lidar equation. Regarding the ranging principle, the CSP lidar is fully digital and breaks through the constraints of a detector's bandwidth and ADC's sampling rate. The simulation results indicate that the detection range of the CSP lidar is approximately 35 times and 8 times greater than that of a continuous-wave chaos lidar and pulsed chaos lidar, respectively. Although the detection accuracy of the CSP lidar is only at the centimeter level and is lower than the linear mode chaos lidars, its consumption of storage resources and power is greatly reduced due to 1-bit quantization in the GM-APD. Additionally, we investigate the impact of GM-APD parameters on the signal-to-noise ratio (SNR) of the CSP lidar system and demonstrate that the dead time difference between GM-APDs has a negligible effect. In conclusion, we present and demonstrate a new chaos lidar system with a large detection range, high SNR, low storage resources and power consumption, and on-chip capability.

Chaos single photon LIDAR and the ranging performance analysis based on Monte Carlo simulation.

With the advent of serial production lidars, single photon lidar faces an increasingly severe threat of crosstalk. In this paper, we first propose the concept of Chaos Single Photon (CSP) lidar and establish the theoretical model. In CSP lidar system, chaos laser replaces pulsed laser, and the physical random sequence generated by a Geiger mode avalanche photodiode (GM-APD) responding to chaos laser substitutes the traditional pseudo-random sequence. The mean density of '1' code of the CSP lidar system can exceed 10 million counts per second (Mcps) with a dead time immunity. The theoretical models of detection probability and false alarm rate are derived and demonstrated based on Poisson distribution. The bit error rate (BER) is introduced into the CSP lidar system for evaluating the range walk error intuitively. Additionally, the simulation results indicate that the CSP lidar system has a robust anti-crosstalk capability. Compared with the traditional pseudo-random single photon (PRSP) lidar system, the CSP lidar system not only overcomes range ambiguity but also has a signal to noise rate (SNR) of 60 times, reaching 10000 when the mean echo photoelectron number is 10 per nanosecond. Benefited from large-scale arrays and extremely high sensitivity properties of GM-APDs, we are looking forward to the applications of the CSP lidar in weak signal detection, remote mapping, autonomous driving, etc.

Highly Thermal Conductive Graphite Films Derived from the Graphitization of Chemically Imidized Polyimide Films.

With the large-scale application and high-speed operation of electronic equipment, the thermal diffusion problem presents an increasing requirement for effective heat dissipation materials. Herein, high thermal conductive graphite films were fabricated via the graphitization of polyimide (PI) films with different amounts of chemical catalytic reagent. The results showed that chemically imidized PI (CIPI) films exhibit a higher tensile strength, thermal stability, and imidization degree than that of purely thermally imidized PI (TIPI) films. The graphite films derived from CIPI films present a more complete crystal orientation and ordered arrangement. With only 0.72% chemical catalytic reagent, the graphitized CIPI film achieved a high thermal conductivity of 1767 W·m-1·K-1, which is much higher than that of graphited TIPI film (1331 W·m-1·K-1), with an increase of 32.8%. The high thermal conductivity is attributed to the large in-plane crystallite size and high crystal integrity. It is believed that the chemical imidization method prioritizes the preparation of high-quality PI films and helps graphite films achieve an excellent performance.