Title : Nanoscale tilt measurement with improvised optical interferometric configurations
Abstract:
The applications of the measurement of small tilt angle range from leveling devices to planetary measurement, X Ray interferometers, coordinate measurement methods etc. Non Interferometric methods such as collimators, laser triangulation cannot measure tilts below a fraction of radians. But, Interferometric methods can measurement of smaller tilts up to a few milliradians. The Michelson interferometer is most commonly used to measure tilt angle where any one of the mirrors or both mirrors are rotated to obtain the fringe pattern. However, the lower limit of measurable tilt is limited by the beam size and associated optics. As the fringe width increases with decrease of tilt angle, one would reach a limit where the width of the bright fringe equals the beam size. Below this tilt, we cannot distinguish between a bright fringe of width greater than the beam size and a fringe free field. We present some improved interferometric configurations where the sensitivity of measurement is highly enhanced and thereby the lower limit of tilt measurement is pushed down. The modified configurations of Michelson interferometer and Cyclic interferometer presented here would provide double or manifold sensitivity. These improvised interferometric configurations use a Double sided mirror and / or multiple reflections to enhance the sensitivity. Tilts as low as 500 nano radian have been measured accurately. The incorporation of polarization in these interferometers would further enhance the sensitivity and tilts at nanoscale could be measured which could not be achieved by existing interferometric methods. The various existing methods of tilt measurement along with the proposed novel methods shall be presented.
