Targ3 is the third meeting focused on the last targetry advances for laser-driven particle acceleration and laser radiation sources. The prior workshops, Targ1 and Targ2, were held in October 2013 in Garching (Germany), and April 2015 in Paris (France) at the Université Pierre et Marie Curie respectively. The TargN workshop series brings together experts and key players involved in the last trends on intense laser-plasma research, requiring design of specific targets aimed at particular requirements to exploit unique opportunities ushered by such extreme peak laser powers.
With the advent of the PW era there are now many lasers with peak power capability beyond 100 TW and up to the PW level with multi PW lasers on the horizon. Some of this ultrahigh power lasers operate in single shot mode due to their low repetition rate, meanwhile other systems are able to work at one shot per second with single pulse PW power levels. In addition, 10 PW 10Hz laser systems are foreseen. This useful combination of high single pulse power with high repetition rate can bring new PW era science and technology by enabling research and technological development that utilizes both solid and fluid target design. Although liquid and gas targetry is naturally predisposed toward high repetition rate operation, it nonetheless features densities that are much lower than those afforded by solid targets, for which alignment can be more critical. Meanwhile, liquid targets are becoming more accessible for high power lasers due to the rapid improvement in manufacturing and vacuum compatibility. However, different target configurations share common issues associated with alignment procedures. Indeed extreme laser intensities can require extremely small focal diameters (of the order of the diffraction limit) and commensurately short focal lengths that reduce confocal distances. On the other hand, because of the requirements in predictability and efficiency of the laser-matter interaction experiments and the use of ultrathin film targets, laser contrast levels must be increased considerably. Targetry techniques continue to be a rapidly advancing component of laser-driven high energetic particle and photon source technology with an increasing variety of options and more demanding constrains. As a result, target development, motion for replenishment and micro-positioning are major limiting issues that have also motivated these TargN series of workshops.
By bringing together experts and key players, the third of this series, Targ3 features a focus on novel target designs, advancements and highlights important aspects of target performance (notably in terms of particle and photon yield), typically involving experiments that include relativistic laser intensities, (i.e. >1018 W/cm2 or beyond) and the strict experimental conditions imposed by PW class lasers. This workshop engagement therefore affords a pragmatic assessment of targetry with regard to the broad range of capabilities, experimental options and future prospects. Targ3 also presents an excellent opportunity for young researchers to present recent results and novel ideas, as well as to train PhD students on the specialized use and critical need for innovative targetry techniques in the PW era.