Status of the T2K TPC Laser Calibration

1
Status of the T2K TPC Laser Calibration

• April 4, 2006, TPC Canada Meeting, UVic Triumf

2
Spreading Light

• Central Cathode shined by a red laser
• Lens and Fiber Holder

3

• New lens
• Accident with old lens (f6mm,d6mm)
• Changed to new lens (f12mm,d6mm)
• Same fiber-lens efficiency (13 )
• Arranged fiber so aperture now 20 half opening
  angle
• Lens and Fiber Holder put in the prototype

4

Fiber

• Damage threshold
• 600 µm 2.7mJ - 5ns pulses
• 800 µm 4.8mJ - 5ns pulses
• 800 µm (after flattening the ends)
• stable and homogeneous pattern
• aperture 20 half opening angle
• only 13 fiber and lens efficiency
• need at least 1.5 mJ to extract e-
• Tom at continuumlaser.com says he will guide us
  (via telephone) to get wanted energy from laser
  (max for minilite 8 mJ 5 ns pulses)

5
Distribution

• Tried to measure light distribution with UV LED
  detector and an amplifier
• Accuracy of setup too poor for any conclusions
• Result might indicate that the intensity ratio
  between the edge and center of the pattern disk
  is decreasing and is therefore small at cathode
• Might increase energy needed to give enough light
  to the cathode corners

6

T2K

• Suggested for the T2K TPC
• 3 laser disks on each cathode side
• aperture 27 half opening angle
• need 1.0 mJ for each disk
• 323 18 mJ
• Fiber bundles?
• Many lasers?

7

Alternatives

• UV LED Emitters
• Power out 1 W (Strongest I could find, but with
  375 nm...)
• Aperture 10
• Assume they can be pulsed in 100 ns
• One LED will then shine cathode with 0.9 nJ/cm2
• Needed 13 nJ/cm2
• Flash lamps
• rapp-opto.com has lamps and fiber packages
• Gert Rapp writes In general I assume that we
  (and I believe nobody in the world) can generate
  300 iJ of UV light at 270 nm in a 500ns pulse to
  be coupled into a light guide.
• We have decided I will call him

8
Conclusions and Future Work

• For prototype use 5 m of UVM 800 µm fiber
• Low efficiency
• Gain homogeneous and stable pattern

• A Minilite laser (model 2, 266 nm) will arrive
  April 17

• A second holder have to be constructed
• to focus laser light into fiber (will use own
  lens)
• to prevent spreading of UV light
• construction will start once we have the laser

• More info here

http//particle.phys.uvic.ca/hansen/T2K/LASERCAL/
log.html http//particle.phys.uvic.ca/hansen/T2K/
LASERCAL/prototype.html http//particle.phys.uvic.
ca/hansen/T2K/LASERCAL/t2k.html