Stabilization of an Ultrathin Liquid Sheet Target System for Ion Acceleration at 1 kHz Repetition Rate

In laser ion acceleration, the accelerated ions leave the target in a direction close to normal to its surface [1]. One of the major challenges in laser particle acceleration is to renew the target so that the new ones shall be at the same position shot after shot [2]. A possible embodiment of a high repetition rate target is a thin sheet of liquid created by two microjets [3]–[5]. The flow dynamics of the liquid sheet is as stable as the stability of all the conditions that influence it. The relative position of the nozzles or the pressure of the liquid may change stochastically. Mechanical vibrations or the interaction with laser pulses may cause periodical changes in the flow dynamics. As a result, the pointing of the normal to the surface of the liquid sheet is changing continuously, making the resulting ion beam unstable [4], [5]. In this paper we introduce the development of an active stabilisation system which has been proven to work with laser pulses at 1kHz repetition rate.