Performed from 15 Dec 98 to 23 Dec 98
N2 and YAG laser setup
YAG Laser : Continuum Surelite Laser III-10
N2 Laser : Laser Science, Inc., VSL-337ND (same as one in the TOF lab)
1 TOF scintillation counter with 2 PMT's (Hamamatsu R3478S)
2 BBC counters
1) YAG laser results.
Top left: time difference between BBC1 and BBC2 [channel], Top right: time difference between TOF1 and TOF2 [channel], Bottom left: time of flight = (TOF1+TOF2)/2-(BBC1+BBC2)/2 [channel], where 1 channel = 25 psec.
2) N2 laser results. Same definitions for each panel as above.
3) Slewing curve using YAG laser in one of PMT's (scatter plot)
3) Slewing curve using YAG laser in one of PMT's (fitting curve)
Summary:
1) With the YAG laser, timing resolution in tof is 10ch / sqrt(2) = 180 ps.
2) With the N2 laser, timing resolution in tof is 7ch / sqrt(2) = 120 ps.
Using the YAG laser, TOF has poor timing resolution of 180 psec compared to its intrinsic time resolution of ~ 80 psec. It will be due to its slow duration time (~4.5 nsec in rise time, while it is 2.1 nsec in the N2 laser) and fine structures seen in the oscilloscope.
However, by taking many events (of the order of 10k), it is possible to extract the centroid of the timing distribution as the time offset with good resolution (~ a few psec shown as error in the Gaussian fit), because the shape of the distribution is good. Also, practically, to use another laser in the laser hut separately from EMCAL is not easy, considering a data acquisition scheme.
Therefore, for Day-1, we should use EMCAL's YAG laser, and it is important to consider an upgrade option to improve timing performance of the YAG laser.