Recent development for a plasma diagnostic with optically trapped microparticles

Summary form only given. The idea to use microparticles for plasma diagnostic purposes was implemented during the last years by several experiments as electrostatic or thermal probes
^1-5
. In contrast to the commonly used diagnostic methods, microparticles rarely influence the surrounding plasma. However, the particle position and, thus, the measurement is mostly restricted to the plasma sheath region by the force balance. A change in the position, often possible only into one direction, is then associated with a considerable effort or just by changing the discharge and, thus, by changing the plasma parameters itself. Based on the principle of laser tweezing6, we present a noninvasive method for trapping and arbitrary manipulation of the microparticles position in the plasma7. We demonstrate how an externally applied force on the particle is determined by a position determination in the trap. Furthermore, we present the current stage of development as well as some possible plasma diagnostic applications.