1. Mini-workshop on Laser pulse – shaping Zeuthen (30.11.-1.12.2006) Online observation of pulse energy

2. Mini-workshop on Laser pulse – shaping Zeuthen (30.11.-1.12.2006) Why do we need this? 1.At the moment no absolute information on laser pulse energy hitting the cathode 2.Experiments on Quantum efficiency (QE) of cathode materials are foreseen

3. Mini-workshop on Laser pulse – shaping Zeuthen (30.11.-1.12.2006) Current energy measurements: - “online” with PMT @ virtual cathode - “offline” with Powermeter Problems: - no absolute long-term calibration of PMT (e.g. degradation effects) - possible drift of PMT-signal within one pulse-train => Use of calibrated Photodiode

4. Mini-workshop on Laser pulse – shaping Zeuthen (30.11.-1.12.2006) Disadvantages of Photodiodes: 1.Limited range of measurable energies (typically 100nJ – 1mJ) 2.Effected by x-rays 3.PD as energy sensors are limited to rep. rate of max. 10kHz Solutions: 1.Special Silicon-diodes exist for desired range of 1-100nJ 2.Shielding is no problem 3.Next slide…

5. Mini-workshop on Laser pulse – shaping Zeuthen (30.11.-1.12.2006) Idea: Pick one pulse out of every train and measure the energy (-> rep. rate only 10Hz) Trigger => Calibration of PMT possible for every pulse train

6. Mini-workshop on Laser pulse – shaping Zeuthen (30.11.-1.12.2006) Problem with Pockels cell driver : custom made!!!