eusoballoon optics test Baptiste Mot, Gilles Roudil, Camille Catalano, Peter von Ballmoos Test configuration Calibration of the light beam Exploration of the focal plan with the NIST PSF with the CCD camera

1 - Configuration of the optics tests Typical light source : 390nm LED 1m collimator to create a parallel light beam Typical Incident angle of 3.5° CCD camera + NIST calibrated photodiode used at the focal plan The optics system is composed from only two fresnel lenses

The optics efficiency 3 - Focal Spot size 4 - Trigger efficiency 5 – Laser / Flasher tests Quercy 5 – Laser / Flasher tests Quercy 2 - Global optical efficiency  opt 2 - Global optical efficiency  opt 1 - Global Electronic Noise   FSnoise 1 - Global Electronic Noise   FSnoise

2 – Calibration of the collimated beam Grid pattern placed on the aperture of the instrument ~160 measurements with the NIST -> scan of the entire beam, calibrated in light power

2 – Calibration of the collimated beam Visualisation of the beam with azurins in white paper on the aperture of the instrument -> the photo of the white screen is comparable with the NIST measurements from the NIST mapping of the beam from the photo of the white paper on the aperture

2 – Calibration of the collimated beam Beam characteristics from NIST mapping measurement : Sum of all measurements : 1444 nW (lower bound) – 1469 (upper bound) Number of measurements : 132 (lower bound) – 146 (upper bound) => Average power in the beam : 10.5±0.5 nW/cm 2 Area of effective light beam from the camera photo : 7665 ±200 cm 2 => Total flux in beam incident on L1 : 80494±4370 nW (~5% error)

3 – Exploration of the focal plan Method : Measurement of the light flux with the NIST along an axis perpendicular with the optical axis Approximation of the encircle energy with the calculation at each position of the integrated flux on a ring of 1cm of thickness (size of the nist = 1cm^2). The integrated flux is then summed with those from the inner rings. Method to approximate the encircle energy collimatorCollimated light beam Optical system NIST measurements along perpendicular axis

3 – Exploration of the focal plan Scan of the focal plan with the NIST, in linear scale. Blue = direct measurement of the NIST Red = encircle flux Results :

3 – Exploration of the focal plan Scan of the focal plan with the NIST, in logarithmic scale. Blue = direct measurement of the NIST Red = encircle flux Results :

3 – Exploration of the focal plan Conclusion : Full Width at Half Maximum = ~8mm Flux in the collimated beam : 80494±4370 nW Flux in the centered cm^2 : 24.55±0.1 mW Efficiency of the system : (defined as the fraction of the flux collected in the cm 2 centered on the focal spot) e opt = 30.5±3 %

3 – Exploration of the focal plan Digression about the 3 lenses system : The same study has been made for the 3 lenses system. - > 89446±3100 nW (~3.5% error) Calibration of the beam :

3 – Exploration of the focal plan Encircle energy with the NIST : e opt = 12.4±0.6 %

3 – Exploration of the focal plan Comparison between 2lenses and 3lenses systems : Efficiency much better with the 2lenses configuration Focal spot more peaked according to NIST measurements -> much less diffuse light

The focal spot 3 - Focal Spot size 4 - Trigger efficiency 5 – Laser / Flasher tests Quercy 5 – Laser / Flasher tests Quercy 2 - Global optical efficiency  opt 2 - Global optical efficiency  opt 1 - Global Electronic Noise   FSnoise 1 - Global Electronic Noise   FSnoise

4 – study of the focal spot Knowing that the position of the PDM directly tuned with the whole instrument, this part will focus on : -> measurement of the PSF at different angles with 3lenses system -> limits on the depth of focus -> comparison with 2lenses system Same test setup than for the efficiency, moving the CCD along the optical axis for different incidence angles

4 – study of the focal spot The shape of the spot from the CCD camera : CCD size =8x8mm -> only central part of the PSF -> Important to understand the behaviour of the spot around the focal point -> used necessary in complementarity with NIST measurement Incidence angle : 0° 390nm LED High peak in the center BUT important “tails” around Due to inherent design of the fresnel lenses

4 – study of the focal spot Gaussian fit on each spot image to have Full Width at Half Maximum typical CCD image of the focal spot for the 3 lenses system : pixels ADU unit

4 – study of the focal spot Typical results for 2° of incidence angle, 390nm LED, the CCD moving along the optical axis of the 3 lenses system : Best PSF size = 1.5mm Best position = 392mm from rear lens (optimal theorical value = 385mm) Depth of focus at 10 % : 2mm

4 – study of the focal spot Incidence angle (in degrees) Best PSF size (in mm) Best position from rear lens (in mm) Depth of focus at 10% (in mm) Same study at different incidence angles for 390nm for the 3 lenses system : Typical : Best PSF size = 1.5mm Depth of focus = 1.5mm

4 – study of the focal spot 2 lenses system : Incidence angle 3°, 390nm Best PSF = 3mm (~2mm with same source size) Best position = 425mm (~same for other wavelengths) Depth of focus at 10% = 5.7mm

In a conclusion The PSF of the system has a narrow peak in the center (typically 2mm size) in a focusing range of ~5mm -> this will not be seen by the PDM (pixel size of 3mm) -> But FWHM of 8mm from NIST measurement yes. The NIST study showed that there is much less diffuse light in the 2 lenses system than in the 3 lenses system (encircle energy more steep at center and less after) -> better focusing power of the 2lenses system Much better efficiency for the 2lenses system : e opt = 30.5±3 %