Development of an ultrathin liquid sheet target for laser ion acceleration at high repetition rates in the kilohertz range

A colliding microjet liquid sheet target system was developed and tested for pairs of round nozzles of 10, 11 and 18 mu m in diameter. The sheet's position stability was found to be better than a few micrometers. Upon interaction with 50 mJ laser pulses, the 18 mu m jet has a resonance amplitude of 16 mu m at a repetition rate of 33 Hz, while towards 100 Hz it converges to 10 mu m for all nozzles. A white-light interferometric system was developed to measure the liquid sheet thickness in the target chamber both in air and in vacuum, with a measurement range of 182 nm-1 mu m and an accuracy of +/- 3%. The overall shape and 3D shape of the sheet follow the Hasson-Peck model in air. In vacuum versus air, the sheet gradually loses 10% of its thickness, so the thinnest sheet achieved was below 200 nm at a vacuum level of 10-4 mbar, and remained stable for several hours of operation.