Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Optical calibration from ten to hundreds of meters for the Neutrino Burst Experiment (a poor man’s Km3 underwater neutrino telescope) NESTOR/NOA Spyridon Koutsoukos A light beacon can be used to give a short light pulse that will be used to calibrate in time and synchronise optical elements in different parts of the telescope. This light beacon should have: •Sufficient light intensity to be seen from optical elements tens or hundreds of meters away •Light pulse duration in the order of few nanoseconds. S. Koutsoukos VLVnT '08 conference, Toulon 2 The optical properties of water will affect our choice of source, the number of beacons needed, and their positioning. •Attenuation, will affect the light intensity needed, light wavelength and maximum distance between beacons and optical elements. •Scattering will affect the pulse width over long distances. A photon can be scattered a number of times before it is detected. •Dispersion will also affect the pulse width over long distances. If possible light sources with narrow linewidth should be used. S. Koutsoukos VLVnT '08 conference, Toulon 3 How much light do we need? For a point source: AI 0 R / L I e 2 4R where I is the light intensity at distance R, I o is the total emitted light intensity, A is the target area and L the transmission length. For λ=460nm the transmission length L is about 55m (NIM A 349 1994 242-246) An 1,2nJ light pulse at 460nm produces ~2,78 * 109 photons. If these are distributed uniformly on a spherical surface, only ~2650 photons will be emitted in the solid angle defined by the area of a 13’’ PMT at 300m, and about 10 photons will reach the PMT’s surface. S. Koutsoukos VLVnT '08 conference, Toulon 4 Potential light sources, advantages and disadvantages •LEDs •Solid state lasers •Semiconductor lasers •Gas and dye lasers S. Koutsoukos VLVnT '08 conference, Toulon 5 Energy per pulse LED Laser Diode SS laser S. Koutsoukos 50 – 100 pJ <500 pJ >1mJ Pulse duration Operational lifetime ~ 10 ns up to 100.000 hours <1ns >10.000 hours Few fs >10.000 hours Price Other ~ €0,5 Small size and weight, good shock resistance, low power/heat ~ €1000 Small size and weight, good shock resistance, low power/heat ~ €5000 €50000 SHG needed, can be very big, shock sensitive, narrow linewidth Can be very big, shock sensitive, high power cooling needed Gas laser 100s μJ <1ns 1.000s of hours >€10000 Dye laser 100s μJ <1ns Few hours >€10000 VLVnT '08 conference, Toulon 6 Engineering aspects • Power requirements • Heat dissipation • Shock resistance • Operational lifetime • Geometrical aspects S. Koutsoukos VLVnT '08 conference, Toulon 7 NuBE (Neutrino Burst Experiment) Beacons S. Koutsoukos VLVnT '08 conference, Toulon 8 NuBE description 4-floor NESTOR tower (floor diameter = 32m) Floor to floor distance = 30m Tower to string distance = 300m Node to node distance in string = 300m Each node has two clusters with 8 OMs each Beacon is situated 60m over topmost floor. S. Koutsoukos Indicative numbers Photons per OM (0,2nJ) Photons per OM (2nJ) Floor 1 (top) 2900 29000 Floor 2 800 8000 Floor 3 260 2600 Floor 4 (bottom) 97 970 Strings 0,9 9 VLVnT '08 conference, Toulon 9 Electronics aspects •Pulse width for LED sources •Timing and synchronisation of multiple sources within the beacon S. Koutsoukos VLVnT '08 conference, Toulon 10 Conclusions One can construct a beacon to illuminate and synchronise optical elements up to hundreds of meters away. Careful selection of the position of the beacon is important. Different light intensities for different areas of the telescope may be necessary. A semiconductor laser beacon can provide adequate power, pulse duration of ~1ns, low price and good electrical and mechanical properties. S. Koutsoukos VLVnT '08 conference, Toulon 11