Fiber-optic delivery of high-peak-power Q-switched laser pulses for in-cylinder flow measurement.
A bundle of optical fibers was constructed to deliver Q-switched frequency-doubled Nd:YAG laser pulses for the purpose of particle image velocimetry. Data loss that is due to fiber speckle was reduced by ensuring that each fiber was different in length by more than the coherence length of the laser being delivered. Hence, their speckle patterns will overlap but not interfere, producing more even illumination that is shown to reduce data loss. A custom-made diffractive optical element and careful endface preparation help to reduce damage to the fibers by the required high peak powers. With this method, pulse energies in excess of 25 mJ were delivered for a series of experimental trials within the cylinder head of an optically accessed internal combustion engine. Results from these trials are presented along with a comparison of measurements generated by conventionally delivered beams.
Stephens
Timothy J
TJ
School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, UK. T.J.Stephens@hw.ac.uk
Haste
Martin J
MJ
Towers
David P
DP
Thomson
Martin J
MJ
Taghizadeh
Mohammed R
MR
Jones
Julian D C
JD
Hand
Duncan P
DP