Pulse Picking PIV: A Single-Cavity Fiber Laser System For Highly Flexible Repetition Rates And Pulsing Schemes
C. Geschwindner, K. Westrup, A. Dreizler, B. Böhm
Technical University of Darmstadt, Department of Mechanical Engineering, Reactive Flows and Diagnostics, Germany
A novel single-cavity laser system with flexible pulsing schemes suitable for particle image velocimetry (PIV) measurements is presented. The system is based on the concept of picking selected pulse pairs from an ultra-high repetition rate fiber laser which enables time-resolved and conventional dual-pulse PIV at highly flexible recording frame rates. Pulse picking PIV laser systems allow for the use of high-quality low speed dual-frame PIV cameras as well as highspeed cameras in both dual-frame and continuous recording modes, enabling the investigation of highly-transient phenomena at limited fields of view using time-resolved PIV as well as statistical PIV measurements with larger fields of view and higher spatial resolutions. The single-cavity output additionally avoids the alignment of laser beams of laser pulses, which is otherwise necessary in conventional dual-cavity PIV laser systems. Two pulse picking systems were set up and tested: An acousto-optic deflector selecting pulses using the diffraction across an acoustic wave and an electro-optic modulator rotating the polarization state of selected pulses in a Pockels cell. The performance of both systems was evaluated in terms of achievable inter-pulse durations, beam profile alterations, and pulse energy losses caused by the introduction of additional optical elements in the beam path.