Optical fiber array for the delivery of high peak-power laser pulses for fluid flow measurements

Fiber delivery of 64.7 mJ laser pulses (approximately 6 ns duration) from a Q-switched Nd:YAG laser operating at 532 nm is demonstrated. A custom diffractive optical element was used to shape the laser beam and facilitate coupling into a linear fiber array. This launch arrangement achieves an improvement in launch efficiency compared with a circular fiber bundle evaluated in previous work and the delivery of higher pulse energies is demonstrated. The bundle is capable of delivering light of sufficient pulse energy and, importantly, with suitable focusability, to generate a thin light sheet for the fluid flow measurement technique of particle image velocimetry (PIV). Fiber delivery offers an advantage, in terms of optical access, for the application of PIV to enclosed measurement volumes, such as the cylinder of a combustion engine.