Thursday, 14. April 2016
PIV is known as a very precise measurement technique for fluid dynamics. The underlying fundamentals rely on a proper timing of the laser pulses used to illuminate two consecutive camera frames.
Typical PIV lasers show a deviation of the desired behavior, especially when they are operated over a longer period of time. The natural wearing processes of the optical laser pump mechanism can lead to a variation in time for the light pulses generated after a pair of electrical trigger pulses, the Q-switch signals. Normally, it is assumed that the two laser pulses have a displacement dt in time which is the same as the electrical triggers.
Automatic Correction of PIV Laser Timing
Detailed investigations of LaVision have shown, that the assumption of a proper dt is not true under all operation conditions. Typical timing error of Nd:YAG lasers are up to 50 ns. For diode pumped Nd:YLF/Nd:YAG based high-speed laser systems this error goes up to 1000 ns, leading to significant systematical error in PIV results.
These errors are eliminated by the usage of the Laser Timing Stabilizer. This device is looped into the electric trigger lines and measures the corresponding optical delay. The electronics inside the Laser Timing Stabilizer compares the timing of the incoming Q-Switch triggers, measures the light pulse and automatically corrects for any systematical mismatch within nanoseconds precision.
The Laser Timing Stabilizer is a simple stand-alone add-on device to mitigate the systematic timing errors of PIV lasers. It ensures a precise dt (i.e. the time separation between the two laser pulses of a PIV laser) with any laser type at any working condition, without affecting the laser beam.
Laser Timing Stabilizer with ultra-fast photo-diode and fiber coupling.
A fiber coupling connects the Laser Timing Stabilizer directly at the laser exit. Any other place of the experiment where the intensity level of the laser light is high enough works as a pick-up as well. The rugged optical fiber leads the collected scattered light into the Laser Timing Stabilizer electronics where an ultra-fast photodiode measures the inherent time.
The Laser Timing Stabilizer is simply inserted into the trigger lines between the external trigger source (e.g. LaVision’s Programmable Timing Unit PTU) and the laser trigger input. No software control is required as the intelligent electronics automatically detects timing errors and corrects the laser operation on-line during the operation of the laser system.
Increase PIV accuracy, reduce uncertainty
The Laser Timing Stabilizer leads to accurately triggered laser pulses and therefore minimized timing errors in the PIV measurements. The result is a decreased PIV uncertainty where - beside the particle displacement - the accurate timing is one of the two crucial parts of the PIV technique.
Together with our sophisticated Stereo-PIV and tomographic PIV algorithms, the Laser Timing Stabilizer is another milestone for LaVision’s confidence to deliver one of the world’s most accurate fluid dynamics measurement systems.