Improved measurement performance of the Physikalisch-Technische Bundesanstalt nanometer comparator by integration of a new Zerodur sample carriage

Abstract

The paper describes recent improvements of Physikalisch-Technische Bundesanstalt's (PTB) reference measuring instrument for length graduations, the so-called nanometer comparator, intended to achieve a measurement uncertainty in the domain of 1 nm for a length up to 300 mm. The improvements are based on the design and realization of a new sample carriage, integrated into the existing structure and the optimization of coupling this new device to the vacuum interferometer, by which the length measuring range of approximately 540 mm with sub-nm resolution is given. First, measuring results of the enhanced nanometer comparator are presented and discussed, which show the improvements of the measuring capabilities and verify the step toward the sub-nm accuracy level.

Multi-dimensional grating interferometer based on fibre-fed measurement heads arranged in Littrow configuration

“…During preliminary experiments, the fibre-fed interferometric system was qualified by a comparison measurement with the vacuum X-interferometer of the NMC by using a plain mirror attached to its bridge [15]. As a result, the standard uncertainty caused by periodic nonlinearities was determined to be below 1 nm.…”

Investigation into the limitations of straightness interferometers using a multisensor-based error separation method

“…The mechanical setup of the Nanometer Comparator is schematically illustrated in figure 2. The system under test was mounted on a slide inside a sample carriage [28]. The slide was supported, with almost no friction, on air bearing pads.…”

“…For the purpose of straightness measurements, the NMC was equipped with a sample carriage providing a mirror parallel to its general moving direction with a length of over 600 mm [28] and three heterodyne y-interferometers [7] probing the position of this mirror. The three y-interferometers were arranged nonequidistantly to increase the lateral resolution of the reconstruction [33], which is defined by the nonequidistant interspaces and the uncertainties of the three y-interferometers.…”

“…It is used for the calibration of line scales [25], encoder systems [26] and photomasks [27] to disseminate the unit of length to industry. A deeper insight into the setup is presented in [25][26][27][28][29][30]. In this contribution, only the components essential for the straightness measurements are addressed.…”

“…Figure 2. Schematic drawing of the Nanometer Comparator: 1: vacuum chamber for the x-, yaw-and pitch-interferometers; 2:x-interferometer beam splitter[29]; 3: vacuum bellow connecting the moving slide and the vacuum chamber guiding the measurement beams; 4: pipes for the reference beams of the interferometers; 5: bridge with all reference mirrors; 6: sample carriage with long-range y-mirror and moving mirrors of the vacuum interferometers[28]; 7: moving slide; 8 + 9: voice coil and linear motor for the positioning of the slide; 10: granite base (size: 3.15 × 0.8 × 0.7 m 3 ); 11: active vibration isolation; 12: piezo elements connecting the air bearings and the slide; 13: straightness reflector mounted on the bridge; 14: straightness interferometer (interferometer head and splitting element) mounted on the sample carriage.…”