Measured the transmission and reflection coefficients of dichroic filters over the incidence angles of 10-75 degrees in 5 degree increments. This characterization is done using LED sources and well understood PMTs.
Materials
- R7600-U200 PMTs (1x1 in)
- 50/50 beam splitter (1x1x1 cm)
- dichroic filters (dimensions?)
- Knight
- 500 nm longpass - square
- Edmund
- 500 nm shortpass - square (best results)
- 500 nm longpass - circular
- Knight
- LEDs
- 405 nm
- 450 nm
- 505 nm
- collimator
- rotating platform
- cardboard PMT covers
- felt sheilding
Specs
- PMTs operated at -800 V
- LEDs operated at 2 V
- oscilloscope
- channels (all 3 same settings)
- DC50
- 450 mV/div
- 270 mV offset
- timebase
- 20 ns/div
- 2.5 GS/s
- trigger
- Auto 10 mV
- Positive edge
- channels (all 3 same settings)
- source
- frequency: 1 kHz
- amplitude: 3.5 Vpp
- offset: 2.1 Vdc
- pulse width: 40 ns
- rise edge: 10 ns
Setup
- Collimated LED sent at a 50/50 beam splitter
- half goes to normalization PMT
- half goes to dichroic filter
- transmitted and reflected light detected by PMTs
Notes
- Transmission and reflection PMTs are always angled up at 20 degrees (including when normalized) to avoid reflections off of the glass PMT face returning into the setup.