Calibration Run with N2 Laser
We used the in situ N2 laser near the OM on string 5, OM35.  Several attenuators were used  with neutral density rating of
ND 0.0, 1.0, 2.0, 3.0.  So the dimmest run is 0.001 as bright as the brighest runs.  A receiver OM542 is separated from the N2 laser by a distance of about 100m.
If we selected an OM that was closer, then the OM received too much light over too short a time span.  Any more distant, and the OM did not recieve enough light to test the integrated dynamic range properly.

run_5333_wavehisto.root   (N2 laser run: Root file with charge histograms and summed waveforms for all channels, nd3.0 = dimmest)
run_5334_wavehisto.root  (N2 laser run: Root file with charge histograms and summed waveforms for all channels, nd2.0 )
run_5335_wavehisto.root  (N2 laser run: Root file with charge histograms and summed waveforms for all channels, nd1.0 )
run_5337_wavehisto.root   (N2 laser run: Root file with charge histograms and summed waveforms for all channels, nd0.0 = brightest)
ch542_nd00_qhist.gif             charge histogram for OM542, brightest  N2 run
ch542_nd10_qhist.gif 
ch542_nd20_qhist.gif
ch542_nd30_qhist.gif            charge histogram for OM542, dimmest  N2 run
wavesum_om542_nd00.gif         sum of waveforms to form a composite from brightest run    (OM542)
wavesum_om542_nd10.gif
wavesum_om542_nd20.gif     sum of waveforms to form a composite waveform for next to dimmest run (OM542)
 

Individual Waveforms
This study was done using OM542 as the receiver at a distance of 100m.  Its depth is approximately the same as the N2 laser module.   OM542 (LED-aom) represented a compromise between too few photons for more distant OMs (although the photons are spread over a a greater amount of time) and too close, where too many photons arrive within a short time span.  For more waveforms from OM542 and others, see sample waveforms.
 
Npe = 180
OM 542, ND00
Run 5337

x-axis = 10ns/bin
y-axis=1.2mV/bin

Notice wide TOT for first LE 
 

Npe = 18
OM 542, ND01
Run 5335

x-axis = 10ns/bin
y-axis=1.2mV/bin

Notice that you can count the individual PE hits.

Npe = 1.8
OM 542, ND20
Run 5334

x-axis = 10ns/bin
y-axis=1.2mV/bin

Not typical, most waveforms have only 1 or 2 pulses i n them. 


 
 

Integrated Dynamic Range (IDR)
We investigated two approaches to estimate the integrate dynamic range of the TWR system: visual inspection of the composite waveforms and plotting the histogram of the sum of the negative voltage over the complete waveform (ie, we summed only those bins in the waveform with a voltage less than the baseline value). These estimates provide a lower limit to the true capabilities.  First, we had limited control over the gain of the prompt output from the ORBs since they were also being used by the muon DAQ.  Also, the TO crew has already calibrated the time delay for the muon DAQ so we felt it was not prudent to lower the gain of the prompt channel.  Second: the maximum output from the prompt ORB channels is only 1.2V, which is much smaller than typical for the delayed output.  Typically, our instanteneous dynamic range was less than 10 pe and often only a few pe.

This study was done using OM542 as the receiver at a distance of 100m.  Its depth is approximately the same as the N2 laser module.   OM542 (LED-aom) represented a compromise between too few photons for more distant OMs (although the photons are spread over a a greater amount of time) and too close, where too many photons arrive within a short time span.

IDR (Method 1): estimate from composite waveforms
composite waveform, dim light Npe= 1.8/pulse

Run 5334:  ND2.0, Composite of 138 waveforms.
Units of x-axis is 10ns/channel
Units of y-axis is 1.2mV/channel
Estimated charge is 430, using FWHM*(V_peak/N_wave)

The jitter is due to the relatively few waveforms in the compositie.  The overshoot is clearly visible.

Composite waveform, OM542, ND10 Npe= 18/pulse

Run 5335:  ND1.0, Composite of 1228 waveforms.
Units of x-axis is 10ns/channel
Units of y-axis is 1.2mV/channel
Estimated charge is 3030, using FWHM*(V_peak/N_wave)

Notice the strong overshoot on the right side of the pulse. Clearly some of the signal is shifted to positive values, but the simple estimate of charge ignores this contribution.

compossite waveform, OM542, ND00, brightest Npe= 180/pulse

Run 5335:  ND0.0, Composite of 531 waveforms.
Units of x-axis is 10ns/channel
Units of y-axis is 1.2mV/channel
Estimated charge is 23,400, using FWHM*(V_peak/N_wave)

Notice that pulse shape is slightly rounded near bottom, suggesting that saturation of the instanteneous signal is beginning.

Table 1:  Summary of results from composite waveform
Npe (laser) Q_est Ratio  Expect. Ratio
1.8 (ND02)
18   (ND01)
180 (ND00)
430
3030
23400

7.0
7.7

10
10

So this estimate shows that the  charge measured is almost linearly proportional to the known brightness variation by the laser.  Clearly, we need to find a better estimator of the charge contained in the pulse.

We also computed the "charge histogram" of the individual waveforms for OM542.

IDR (method 2):  Charge integration
 
Charge Histo, ND3.0
Npe = 0.18
Charge distribution, ND20
Npe = 1.8
Charge Histo, ND1.0
Npe=18
Charge histo, ND0.0
Npe=180

Digital Filtering
T. Feser implemented the FFTW subroutine to remove baseline shifts and slow overshoots of the waveform.  It works well for waveforms with individual pulses, but does not work so well for complex waveforms.  For example, we show a waveform from OM 542 for the brightest N2 laser run.

ch542_fft_before_and_after_filtering.gif   (OM 542 waveform before  (top black line) and after FFT filtering (red line))

The filtered wavefom is highly distorted.  Clearly, the FFT filtering scheme does not work well with a pulse width close to 0.5us wide.