simulations, tests and production

Transcription

1 LIGHT FUNNELS: simulations, tests and production J.A. Aguilar, A. Basili, V. Boccone, A. Christov, M. della Volpe, T. Montaruli, M. Rameez University of Geneva, Switzerland 17/07/2013 1

2 Open Cone Design Values are constrained by the telescope design: TOP PSF angular pixel size top physical size f/d and Camera diameter Cutoff angle 26.8 mm 13.4 mm mm Dimensions: Angular pixel size: 0.25 Cutoff angle: 24 Length: 36.7 mm 10.9 mm 5.5 mm 9.4 mm BOTTOM Comp. Factor: ~6 2

3 Simulations All simulations done with Zemax, an optical and illumination design software Efficiency is calculated as the ratio between the light recorded on the top/bottom detectors for different incident angles of light. Source spectrum uses the Cherenkov spectrum convoluted to the SiPM response. SiPM window (n = 1.41) or air (n=1) 3

4 Shape Optimization Bèzier curves (1) Image from: A. Okumura (2012) arxiv: P3 line optimized Bèzier object created in C and imported as DLL to ZEMAX Merit function (in red) 4

5 Shape Optimization Bèzier curves (2) Bèzier shape reduces the amount of light transmitted beyond cut-off ~40% more than parabolic. 5

6 Coating Simulation Reflectivity Al+dichroic filter (by Thin Film Physics AG) Simulated transmission curve with several types of reflectors and cone shapes. A comparison with full PMMA cone is also shown. Refractive index s angular dependency is a key factor to take into account for best performances. 6

7 Angular dependency Not all material under study has data with angular dependency. Tests with ellipsometer are foreseen. Distribution of rays on the sensor Distribution of rays on the cone All incident rays within cutoff angle (0-24 ) reflect on the cone at angles > 40 Coating must be optimized for angles accordingly. The curved shape of the cone makes the coating process extremely challenging and a rather complex verification sample must be used to optimize the coating parameters 7

8 Test Setup (1) LED Splitter Diffuser PhotoDiode Diaphragm Focusing lens Aperture 0.5 mm Focusing lens Motorized Rotating Support Collimation of the beam has been verified measuring it s size at several distances. Uniformity of the beam is reasonably good if distance of the target is within cm. Image from: L. Platos (2012) 8

9 Test Setup (2) The goal of the optical setup is to measured the collection efficiency. Two steps measurement: 1. measure light collected by a large area pin diode placed at the entrance window of the concentrator 2. measure light at the end of the light concentrator The ratio between the two measurements, as a function of the angle, give us the collection efficiency: 9

10 Measurements (1) First measurements on a coated sample: 1. Non optimal surface roughness 2. Parabolic shape Systematic errors from instrumentation not included. X-axis bars represent bin size. changing plane of rotation shows some differences 10

11 Measurements (2) Measurements done at smaller wavelengths: 1. Verify coating behaviour 2. Allow optimization of dichroic layers A close interaction with industrial partners may lead to fine tuning of the coating process. Systematic errors from instrumentation not included. X-axis bars represent bin size. 11

12 Quality of the cone Measurements on uncoated cone: 1. to monitor anomalies between faces 2. to estimate the quality of the surface roughness Nearly 20% of transmitted light reaches the sensor without any reflection. Tests on better polished samples are currently on going 12

13 Alignment issue ~0.5 deg ~0.03 deg Current (A) Current (A) Before zeroing After zeroing CR1-Z7E (from Thorlabs) presents a backlash < 1 arcmin, but does not have a zero. Alignment is carried out with a pin-hole ( mm) in front of the sensor and fitting with a gaussian. Mounting and unmounting the mechanical support may lead to misalignment between the two steps. 13

14 Upgraded mechanical support In order to study coating uniformity a new supporting structure has been designed and is currently under production in our mechanical workshop 14

15 Production fast prototyping In order to do a first check of the cone design we chose a fast prototyping technique: 1. Steel master with 3D printing 2. Silicone mold from master to reproduce max. 20 halves. 3. Polyurethane material manually injected. To get a mirror like surface, ready for coating, the master has been manually polished. This technique, if properly applied, would easily guarantee a surface roughness of less than 50 nm. 15

16 Production photogrammetry 16

17 Production coating and plastic Coating: currently in contact with: 1. Thin Film Physics AG (CH) 2. BTE (DE) 3. Savimex (FR) Set of requirements needed: Plastic: currently in contact with: 1. Initial (FR) 2. ViaOptics (DE) 3. Savimex (FR) 4. Gaggione (1) (FR) (1) no black policarbonate available Silicon is a pollutant in the coating process which should be avoided at all costs! An injection molding process is required. 17