A Coherent Detection Method With 106 Higher Intensity Response Sensitivity Than Normal Heterodyne Interferometry

Based on the Nd: YVO4 microchip laser frequency-shifted feedback system, we carry out the detection of ultra-weak light signals, and verify that the response limit of the proposed system can reach 0.5 photon per second (corresponding to 2.1 x 10(-7) photon's energy per frequency modulation cycle of 0.42 mu s), with approximately linear response to weak light. Then, the system is compared with the traditional Mach-Zehnder heterodyne interference system, the comparison results confirm the higher intensity response sensitivity of the laser feedback technology (about six orders of magnitude) when detecting both cooperative and non-cooperative targets. On this basis, a verification experiment is carried out on long-distance weak light imaging, and the THU pattern made of unpolished aluminum blocks is successfully reconstruct at 60 m distance (with an additional 10(-7) attenuation provided by the neutral density filter added to the optical path). During the imaging process, the response energy as low as 2 x 10(-5) photon is achieved in each frequency modulation cycle of 0.42 mu s. The successful implementation of the laser frequency-shifted feedback detection enables an anti-disturbance and sensitive coherent method in weak light signals detection.

Automated summary

Based on the Nd:YVO4 microchip laser frequency-shifted feedback system, ultra-weak light signals are detected with a response limit of 0.5 photon per second. The laser feedback technology shows higher response sensitivity compared to the traditional Mach-Zehnder heterodyne interference system in detecting cooperative and non-cooperative targets. In a long-distance weak light imaging experiment, a THU pattern made of unpolished aluminum blocks is successfully reconstructed at a distance of 60 m, achieving a response energy as low as 2 x 10^(-5) photon per frequency modulation cycle of 0.42 μs.