PicoQuant GmbH HydraHarp 400 Software V. 3.0.0.1
the next section for instructions). If there are counts coming in, you can try to set an upper limit of the count
axis so that the histogram is scaled for best viewing. Start with logarithmic display so that weak signals can be
seen.
If so far you used uncorrelated light, you may now want to move to time–correlated measurements. With a
detector signal e.g. laser induced, or a ‘fake’ electrically derived from the laser SYNC, you can try to obtain a
histogram that should be a narrow peak, as opposed to the flat distribution of uncorrelated light. This requires
an experimental setup that delivers the signals at the two input channels with a more or less constant relative
delay. For the HydraHarp in histogramming mode, this delay must be such that the Channel 1..8 (detector)
signal comes later than the SYNC signal (forward start–stop mode). In addition, the delay must be chosen so
that it fits in the measurement range of the histogrammer (max. 67 µs). To obtain such a timing it may be
necessary to adjust the input offsets.
If you have an appropriate setup installed and a measurement running, you can slightly vary all levels
(including SYNC) for best timing response. If there is no clear optimum for any level, return to the center of its
stable working range. For optimization purposes you also may want to switch to a higher resolution. If the
rough setup is complete and a time–correlated signal peak is present in the histogram, the Full Width Half
Maximum (FWHM) of the signal peak is displayed on–line as a figure of merit. You can adjust the input offsets
to place the signal properly within the boundaries of the SYNC frame. You can also adjust your axis limits to
optimize the display. Note that you can double–click all the rate meters to enlarge them as separate windows.
This is useful for optical alignment work, if the PC screen is in some distance from your optical table.
Input Troubleshooting
Whenever there is a problem, first check your cabling, detector power supply and SYNC source. To be
absolutely sure, check the signals with a fast oscilloscope (50 Ω input). Disconnect the scope when you are
done. Never try to deliver the signals to multiple 50 Ω loads in parallel, using simple T–pads. If you have
multiple detectors, try to test your setup with one detector first to keep things simple.
If you cannot get a stable SYNC rate reading of expected figures, there may be several reasons:
● there is no proper SYNC signal (voltage, polarity, pulse width, frequency)
● the SYNC CFD level setting is inappropriate
● the SYNC divider setting is inappropriate
● Note that at small rates the meter display may fluctuate between two discrete values.
Reasons for zero input channel counts are:
● wrong input selection for the rate meters
● no or inappropriate signal (voltage, polarity, pulse width, frequency)
● inappropriate CFD levels
● preamplifier or detector failure
Note that all rate meters are updated at the display refresh rate you have selected in the general settings
dialog. In oscilloscope mode the update frequency is equal to the acquisition time. If nothing seems to happen
at all, you may be in oscilloscope mode with a very long acquisition time set.
Once count rates > 0 are being displayed you should then also see counts appearing in the histogramming rate
meter, if your measurement range is large enough. Make sure the offset is set to 0. If there are histogramming
counts but no histogram is building up on the screen, check the time and count axis bounds. It is best to start
with a wide display range and then narrow it down. Similarly, a logarithmic count axis setting is the safest way
to see even small histograms. If your measurements stop earlier than expected, make sure the Stop at level is
not set to less than 4,294,967,295 unless you have experimental reason to limit the count height.
In the process of set-up you should observe the warning icon that may appear at the bottom right of
the main window. When the HydraHarp software is running with functional hardware it continuously
collects information about the input signals and the current acquisition settings. If these settings
together with the input rates indicate possible errors, the software will activate the warning icon.
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