Four-beam laser interferometry for three-dimensional microscopic coordinate measurement.
We propose a new method for calibrating the three-dimensional (3-D) behavior of a scanning stage. Four laser interferometers are used to determine the position of the corner point of a corner mirror attached to the stage. We calculated the 3-D coordinate of the corner point by using only the length information given by the four laser interferometers; thus a method is realized that is traceable from the practical definition of length and that facilitates the optical alignment that is necessary for the interferometers. We calibrated a commercial 3-D stage by the proposed method with a coordinate accuracy of 20-30 nm.
Laser interferometric calibration of microscan mechanisms by using three laser beams
Abstract A method for calibrating the three-dimensional behavior of general microscanning mechanisms is proposed. In the propsed method, a three-dimensional scale determined by three laser interferometers and a nonlinear least-squares method is used for estimating the point-by-point errors in the measurment volume. A commercial microscanning table is calibrated in a 17.4 μm × 17.4 μm × 8.7 μm volume by the proposed method. Steps to achieve subnanometer accuracy and application to the coordinate measuring system over the small volume are discussed.
Ionization by drift and ambipolar electric fields in electronegative capacitive radio frequency plasmas.
Unlike α- and γ-mode operation, electrons accelerated by strong drift and ambipolar electric fields in the plasma bulk and at the sheath edges are found to dominate the ionization in strongly electronegative discharges. These fields are caused by a low bulk conductivity and local maxima of the electron density at the sheath edges, respectively. This drift-ambipolar mode is investigated by kinetic particle simulations, experimental phase-resolved optical emission spectroscopy, and an analytical model in CF(4). Mode transitions induced by voltage and pressure variations are studied.