Light Guide Information

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Light Guide Collection

References to Simulation

  1. Path to repository for GEANT3 routines (Elton):
    • The code I have used to compute light guide collection acceptances for the Bcal (See GlueX-doc-1077 and GlueX-doc-959) are stored under svn at svn ls The original code came from Blake (UofR) and modified to suit my application. If anyone wants to use it they should contact me for more details. My own suggestion to begin light guide simulations would be to find out more about IU's GEANT4 stand-alone simulations. There are some updates on reflectivities that are more realistic than the ones in GEANT3 (Matt?).
  2. GEANT4 routines (Beni):
    • Code: get it from GUIDEIT
    • Fiber simulation on portal; this is a comprehensive report for light propagation down our fibers, and explains the use of all the GUIDEIT switches/flags.

Prototypes from Plastic Craft

  • Twelve light guides arrived from Plastic Craft on Friday April 1, 2011. They correspond to the light guides that form the inner twelve locations on a single wedge.
Single guide with quarter for scale
Twelve guide arrangement
Guide#12 with chip

Dimensions / comments

  • Dimensions of Light Guides .
  • Histogram of dimensions relative to nominal
  • Measured the distance along the wide base of four guides (10, 11, 11, 12) is 85.52 mm.
  • The measurements show that most dimensions are within our tolerances, measured within 0.2 mm but likely better than that. Note that dimensions of the widths have some additional uncertainty since they are being measured on an angled surface.
  • Both light guides #11 seem to have a discoloration (tan/brown) compared to the other ones (can be noted in the enlarged picture of the arrangement above). In visual checks with a hand-held laser, no differences we visible between a #20 guide and a #11. So the discoloration could be a surface effect.
  • One of the light guides #12 has a small chip near the base

Quick transmission measurement

  • We took a quick look at the transmission through the light guide using the procedure shown in the Test Setup Figure with the help of Sasha and Vitaly Baturin. Used a #20 light guide. Dimensions are approximate as the setup was jury-rigged for the occasion.
  • Pinhole test: Check bulk attenuation. Used two 1mm2 pinholes separated by the height of the light guide (8 cm). Measured currents were 3.2 nW/cm2 (no light guide) and 3.4 nW/cm2 (with light guide), indicating that there was no visible bulk attenuation through the light guide over the 8 cm. Note that the small aperture reduced the light to extremely low levels; background levels were on the order of about 0.3 nW/cm2.
  • Transmission test: Limited entrance angles to the light guide to less than 17 degrees(side) and 23 deg (corner) using a 1x1mm2 and 12x12m2 square apertures separated by 2 cm. This corresponds to a maximum angle in the light guide of 15 degrees (maximum angle inside the fibers is 27 degrees). The light exiting the collimation system was determined by placing the light sensor directly over the 12x12 cm aperture (18.5 nW/cm2). The light through the light guide was determined by placing the light guide base over the 12x12 aperture and taking a reading of light at the top exit (10 nW/cm2), giving a transmission of about 54%. Within the accuracies of the measurements, we confirm the expectation for transmission.
  • A more robust and reproducible setup is under design/fabrication.

Transmission vs wavelength

  • Plastic Craft has provided the information from MatWeb regarding the material used in their light guide. As far as transmittance, they indicate 90-92% for visible wavelengths.
  • Matt Shepherd from Indiana University was kind enough to measure the light transmission through one light guide #20 and one light guide #11 and compare with the transmission of the light guides for the forward calorimeter (Fcal) and also their lead glass. In the Figure are shown four measurements of each light guide in comparison with the transmission of the UVT light guides for the Fcal. The transmission was measured with air as the reference. Positioning these light guides in the spectrophotometer was a challenge because of the shape and small aperture on one end. He repositioned the light guide four different times for each guide to get an idea of the systematic error. All four positions directed the light beam along the long axis of the guide, two in each direction. The plots show that the Plastic Craft material has a higher threshold at about 400 nm, as expected for regular acrylic. However, at 400 nm the transmission is about 80% and it also does not seem to reach full transmission (about 90% on the plot) till about 650 nm. The Fcal light guide has a lower threshold (about 360 nm) and reaches full transmission at about 400 nm.

First-Article Light Guides from USM

Photos upon inspection of one light guide of each type when light guides first arrived from USM.

  1. Set of 10 guides on the gluing wand
  2. Set of 10 guides. View through the base of the guides showing the O-ring for the seal on the top face.
  3. Set of 10 guides on the gluing wand. Holes on the light guides for LEDs are visible. Packing boxes are shown in the background.

Wrapping Tests

  1. Test of tedlar, acid-free paper and Al mylar

Installation of Monitoring Boards

Forty Bcal monitoring boards arrived from Athens yesterday, March 6, 2012. We installed a string of 10 this afternoon. A blob of UV-curing glue was placed on the PCB board behind the LED. The LED was then positioned on the edge of the hole away from the module. The glue was cured shining the light through the end of the light guide.

  1. First string of Bcal monitoring boards
  2. Close-up of first string of Bcal monitoring boards

Gluing Light Guides and Photos

  1. Procedures for gluing light guides
  2. Photos

Rework of Glued Light Guides

  1. Light Guide Rework Plan