The N2 laser setup is devised to test the properties of a GridPix in an analytical way. With the setup we can generate in the focal point of the laser beam a confined charge at certain position in the gas on a well known moment. Subsequently, we may observe where and on which moment the charge arrives at the GridPix. By means of 3 remotely controlled stages the focal point, and thus the charge cloud, can be accuately positioned everywhere in the 20 mm high drift space. By scanning across the chip at different drift distances one may:

• reconstruct the trajectories of the drift paths
• deduce the drift velocity
• measure the diffusion, time walk etc.

The pulsed N2 laser emits at 337 nm, i.e. the near UV, the pulse width is 1 ns, repetition frequency may be tuned to 5 Hz maximum. The energy of a single pulse is aound 80 uJ. The Nikhef laser operates according to the MOPA (Master Oscillator Power Amplifier) principle. The system constsist infact of two synchronized lasers. The first one, the Oscillator, starts to emit a laser beam having high divergence because of the absence of the double mirror system (the short duration of the laser pulse (1 ns) does not permit reflections between two mirrors. Subsequently the beam is 20 x expanded, reducing the beam divergence very substantially, but at the cost of a great loss of beam power. The weak, but very parallel beam is now directed into the Amplifier, the second stage of the laser, where it is enhanced to a powerful beam that is almost diffraction limited. The Nikhef N2 laser has been developed in the 80's. It has been used frequenly in the past for the calibration and characterisation of gaseous detectors and detector systems. As such N2 lasers have been implemented in two big LEP experiments (L3 and Delphi). For detailed information see the thesis at the university of Amsterdam: Fred Hartjes, A diffraction limited nitrogen laser for detector calibration in high energy physics, 6 November 1990.

Some documentation

• Few slides on Fred's Nitrogen laser setup
• NI 6024 multi purpose DAQ
• CAN interface for miniHV
• Laser beam attenuator disk and disk support
• Instruction for using XYZ stages
• Schematics of chip/detector boards: Next_1
• Schematics of CERN breakout board

last update: -- MartinVanBeuzekom - 2013-03-08