High-speed photon Doppler velocimetry for laser-driven flyer acceleration studies

Photon Doppler velocimetry (PDV), a high-speed velocimetry technique, was implemented for measuring the rear-surface velocity of a laser-driven flyer. This system is compact and rugged compared to the VISAR and Fabry–Perot interferometer-based diagnostics that are often employed in laser-driven flyer experiments to measure the velocity of fast-moving surfaces. The main components of this system are an ultra-low bandwidth 2W CW laser operating at 1550 nm, an optical circulator, a fibre-optic probe, a fast photodiode (<35 ps rise time and >10 GHz bandwidth) and a high-bandwidth (8 GHz) digitizer with 20 GSa/s sampling rate. The maximum flyer velocity that can be measured by our implementation of this diagnostic is 5 km/s which is limited by the bandwidth of electronic components used in the system. Here, we also studied the optimization of the diagnostic using different types of speakers with different in-house developed software depending on the applications. Finally, the system was used to measure the rear-surface velocity of a laser-driven flyer in the air. The maximum flyer velocity measured is ∼1.49 km/s. One-dimensional (1D) radiation-hydrodynamics simulations using the HYADES code were performed and were found to be in excellent agreement with the measured velocities.