1. Testing the LED system used in the single station test with a PMT.. Progress so far Edward Overton

2. Setup… Single Station Sheffield Test LED1 LED2 LED3 Added Termination to reduce reflections. Increased resistors on LEDs to help even out current in LEDs and reduce impedance mismatch. Switched LED direction (my borrowed pulse generator can’t do –ve pulses).

3. First Attempt at measuring brightness (very brute force): Connect LED->PMT, wrap in tape. Set LED to same settings as single station test Turn up PMT gain until seeing light… (needed very little gain) Gives a good idea of brightness at each LED as a function of time. This produced lots of light in the PMT and allowed the brightness of the LED to be measured in a single shot.. LEDPMT

4. First Attempt at measuring brightness (very brute force): LED1

5. First Attempt at measuring brightness (very brute force): LED2

6. First Attempt at measuring brightness (very brute force): LED3 30mV/div

7. First Attempt at measuring brightness (very brute force): LED3 No Termination 60mV/div PMT in saturation? Much more light

8. Second Attempt at measuring brightness (more realsitic): Cover PMT end, except for small hole (<1mm) Place LED ~10cm from PMT in dark box. Turn up PMT gain to maximum and look for single hits Turn up LED until PMT sees on average 2 electrons Used persistence on scope to get an idea of how dense the light was. Probably more realistic Diffused LEDPMT

9. LED1 Afterglow… Apparent in ~50/5000 triggers (about 1%) Was apparent in all LEDs LED1

11. LED2

12. LED1 LED3

13. Conclusion Lack of termination makes the final LED in the chain much brighter. Added termination resistor reduces the un-evenness. The increased resistor on each LED also seems to improve uniformity LED seems to have a small amount of afterglow (seen in single photons).