Balloon – EUSO Xenon / UV LED Flasher Calibration

1. Balloon – EUSO Xenon / UV LED Flasher Calibration Evgeny Kuznetsov for UAH / MSFC GLS team University of Alabama in Huntsville JEM-EUSO Workshop - Toulouse

2. Flasher Calibration Technique • GLS flasher contains Xenon Lamp with 355nm optical filter and 365nm UV LED with 1W optical output. • Receiving sensor is based on calibrated PMT (R8900-03) with attached BG3 filter. Integrated PMT response ( pulse area) for single photoelectrons was measured at different supply voltages from 700V to 900V. Entrance aperture was reduced by a mask with round a window - 1cm in diameter. • For flasher calibration PMT sensor was installed in a dark room at 5.00m distance from flasher. Light source ( Xenon Lamp or UV LED ) was triggered from external pulse generator and PMT responses were recorded by LeCroy scope, which measured pulse area for 8 consecutive time frames – each 2.5ms wide, representing integration over 8 EUSO GTU time frames. • To attenuate output of light sources - Xenon flasher was equipped with an extra 0.1% neutral density filter. For calibration of UV LED a neutral density filter of 1% was installed in front of the PMT sensor. • Number of photoelectrons integrated by LeCroy scope in each GTU was calculated as a ratio of measured pulse area over a single photoelectron level of the PMT sensor, with a correction for attenuating ND filters. • PMT sensor with attached BG3 filter represents PDM pixel with equivalent filter transparency and PMT quantum efficiency, that eliminates needs in photon to p.e.conversion. Calibration data is documented in photoelectrons. JEM-EUSO Workshop - Toulouse

3. Functional Diagrams for Calibration Setups Dark Room 0.1% neutral density filter 355nm optical filter 1p.e. = 18pV*s 1 cm diameter aperture HV Power Supply U = 500; 600V; 800V; 1000V HV Power Supply U = -800V PMT R8900-03 Cooling jacket Xenon lamp BG3 filter 5.00m LeCroy Oscilloscope Pulse generator Pulse area measurements over 2.5ms Xenon lamp trigger Setup for the Xenon flasher calibration 1 cm diameter aperture 365nm UV LED Dark Room 1% neutral density filter 1p.e. = 18pV*s Cooling jacket HV Power Supply U = -800V PMT R8900-03 LED Driver BG3 filter 5.00m Arbitrary waveform generator LeCroy Oscilloscope Pulse generator Pulse area measurements over 2.5ms Multi-step waveform UV LED trigger Setup for the UV LED flasher calibration JEM-EUSO Workshop - Toulouse

4. Images of the Xenon / UV LED Flasher and Calibrated PMT Sensor UV LED Balloon-EUSO GLS lasher consists of High Voltage power supply box and Xenon lamp box Xenon Lamp Holder with mounted filters Xenon lamp box, holding 365nm UV LED and cooling jacket with Xenon lamp and mounted optical and neutral density filters Calibrated PMT sensor with 1cm diam. aperture JEM-EUSO Workshop - Toulouse

5. Calibration Data Representation • Xenon flasher was calibrated at 4 different Xenon lamp voltages ( 500V; 600V; 800V; 1000V) , that allows to adjust light intensity by factor ~ 3.5 • UV LED has large dynamic range. It was calibrated at 12 control voltage levels, stepping up with 2.5ms time intervals which allow to achieve projected levels at focal PDM pixel from 1.7 to 51 photoelectrons for distance between GLS and Balloon-EUSO : 115,000 feet • Xenon and UV LED flasher calibration data is provided for each of control settings in two forms: - number of photoelectrons, integrated by PMT sensor with 1cm diameter aperture for 8 consecutive GTU time frames (2.5ms each); - projected number of photoelectrons at the Balloon-EUSO focal PDM pixel for the distance between GLS and balloon = 115,000 feet • Scaling factor: PDM_f_pixel = Pulse_area/18pVs*(R1/R2)2*D2/D1*F*Natm/NDF Single P.E. = 18pVs; B-EUSO throughput = 30% ( lens_system) * 0.1855 (Ratio: light at central pixel – to 1 cm2) JEM-EUSO Workshop - Toulouse

6. UV LED Control Strobe Control voltage applied to UV LED driver from arbitrary pulse generator 2.7V; 2.75V; 2.8V; 2.9V; 3.0V; 3.2V; 3.4V; 3.6V; 3.8V; 4.0V; 4.2V; 4.3V. These levels were programmed in order to achieve projected number of photoelectrons at focal PDM pixel from 1.7 to 51 photoelectrons JEM-EUSO Workshop - Toulouse

7. UV LED Calibration Characteristics Projected number of photoelectrons at focal pixel versus control voltage. Calibration curve was measured before and after flight in Canada JEM-EUSO Workshop - Toulouse

8. Calibration of the Xenon Flasher Projected number of photoelectrons at focal PDM pixel at 4 high voltage settings. Integrated number of photoelectrons over 8 consecutive GTU time frames. Calibration was conducted after the flight in Canada. JEM-EUSO Workshop - Toulouse

9. Correction of the Xenon_Flasher Calibration Data for Optical Filter Degradation • Both Xenon flasher and UV LED flasher were tested an NSSTC after flight in Canada at the same as pre-flight measurement conditions • UV LED flasher characteristics are unchanged within 5% precision • Xenon flasher showed ~ 30% lower light output in comparison with pre-flight calibration. This was caused by degradation of the optical filter transparency. • As the Xenon flasher was not operated after flight in Canada - it was calibrated again at NSSTC and this calibration data is documented ( as 100% light output) • In order to correct data for Xenon flasher output during flight – 355nm optical filter was characterized and further exposed to flashes of Xenon lamp to build degradation curve versus Xenon lamp exposure. • Correction of the in-flight Xenon flasher light output data must be done using in-flight Xenon flasher execution schedule ( Number of flashes at 1000V; duration) and extrapolated slope of the optical filter degradation curve ( to be extrapolated into negative number of flashes – that corresponds to in-flight operations) • Xenon flasher operation table during flight ( to be checked / corrected) was created, using comments from Johannes Eser and temperature log data (temperature/humidity loggers recorded environment data in both HV Power Supply and in Xenon Lamp boxes during the whole campaign. JEM-EUSO Workshop - Toulouse

10. Xenon Flasher Execution Schedule During Flight Flight local time US Central Day time Temperature log data recorded in the Xenon lamp box JEM-EUSO Workshop - Toulouse

11. After Flight Optical Filter Test Non-exposed area Exposed filter area 355nm optical filter, used with Xenon flasher was exposed to light flashes only in central region (22mm in diameter) – outer region was covered by lamp holder. After flight transparency test showed degradation of transparency of exposed area by 32% in comparison with transparency of non-exposed filter area. JEM-EUSO Workshop - Toulouse

12. 355nm Optical Filter Degradation Test JEM-EUSO Workshop - Toulouse

13. UV LED and Xenon Flasher Calibration data (for Xenon Flasher: End-of-Flight conditions) )* - Calibrated PMT: R8900-03 (QE = ~ 24% at 355nm) with 1cm diameter entrance aperture with BG-3 filter, attached via optical grease. For PDM focal pixel scaling factor: see page 5. - Number of photoelectrons at calibrated PMT sensor is calculated as a ratio of PMT response pulse integral (over 2.5ms) to single photoelectron weight with correction for neutral density filters ( For a case when ND filter is not installed) JEM-EUSO Workshop - Toulouse

14. Miscellaneous Hamamatsu PMT R8900-03 spectral characteristics. BG 3 Optical filter transparency vs wavelength. Data from SHOTT Germany JEM-EUSO Workshop - Toulouse

15. LED angular characteristics Since the balloon is at an altitude between 30.5 and 36.6 km. the transmission to the balloon is the same as it will be to JEM-EUSO. When the helicopter is at 10,000 ft (3.05 km), the transmission will be ~58% according to the chart above which comes from the 2010 purple book. Xenon lamp L6604 spectrum JEM-EUSO Workshop - Toulouse