Accurate High Voltage measurements based on laser spectroscopy

The ALIVE experiment at the TU Darmstadt is a collinear laser spectroscopy setup that has been developed for the measurement of high voltages in the range of 10 to 100 kV with highest precision and accuracy. Here, ions with a well-known mass and transition frequency are accelerated with the voltage that has to be measured and their Doppler shift is examined precisely with laser spectroscopic methods. An accuracy of at least 1 ppm is targeted which is of interest for metrology as well as applications like, e.g. the KATRIN experiment. We present the results we achieved with ⁴⁰Ca⁺ ions where the well-known 4S_1/2 → 4P_3/2 and the 3D_3/2→ 4P_3/2 transitions were used to identify the ion velocities before and after the acceleration which are already in the 5 ppm level. To improve this uncertainty, indium ions from a liquid metal ion source and an alternative pump and probe approach will be used in the next stage.