Development of a high-speed optical system for lightning flash observation

To study the lightning attachment process of cloud-to-ground lightning flash, we develop a high-speed optical system of photodiodes array named Lightning Leader Progression Feature Photic Observation System (LiPOS) for lightning flash observation. It consists of power supply, signal capture, noise suppression, signal conditioning and collection, and electromagnetic shielding modules. The designed observation circuit mounted at the camera's film plane of a 50 mm lens contains eight light receiving channels of photodiodes which are arranged in a vertical array. The system can use time difference of arrival of light signals in different receiving channels to determine the velocity. Besides, the specially designed T-type feedback network of the conditioning module can improve the stability of the amplifying circuit, while the noise suppression and electromagnetic shielding modules can provide the anti-interference ability for the LiPOS. In particular, we design and make a laser source with fast rise time to test the temporal resolution. It shows that the waveforms with rise time over 39.6 ns can be measured by the designed LiPOS. Moreover, the observation of the spark gap experiment is carried out to validate the LiPOS. The experimental results show that the observed 1-D velocities are 1.53 × 107 and 4.32 × 106 m/s, respectively.