The significance of coherent flow structures for the turbulent mixing ...

4 Multiplane Stereo Particle Image Velocimetry
necessary to minimise the probability of laser induced damage. Due to the thermal sensitivity
of the laser material and the unstable resonator, the previously mentioned adjustments should
be performed under thermal equilibrium conditions.
4.2.2 Generation and controlling of the timing sequence
In order to trigger all necessary components quickly and easily a 16 channel sequencer-board
with an output frequency between 0.01 Hz and 1 MHz has been used. The width of each pulse
is freely adjustable according to the specifications of the used equipment. The delay of all
output trigger pulses with respect to the input trigger can be selected in the range from 50 ns
up to 140 s with a resolution of 50 ns (12.5 ns jitter). Figure 4.4 shows the user-interface for
the generation and operation of the appropriate timing-sequence.
FIGURE 4.4: Window-interface to select and control the laser- and camera-timing
The first two sliders located at the top of the window control the pulse separation for
both laser pairs separately whereas the third one determines the time-interval between the
first pulses of each laser pair. Thus, all pulse combinations described in section 4.3 and 4.4
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