Showing papers by "Charles Joenathan published in 2016"

Dual-arm multiple-reflection Michelson interferometer for large multiple reflections and increased sensitivity

Abstract: Michelson interferometer is one of the most popular optical interferometric systems used in optical metrology. Typically, Michelson interferometers are used to measure object displacement with wavefront shapes to one half of the laser wavelength. As testing components and device sizes reduce to micro and nano size, a sensitivity of half the wavelength of light cannot be used to measure several hundred picometer displacement. Multiple-reflection interferometers have been proposed and are used to increase the sensitivity in a Michelson interferometer; however, when altering the number of reflections, the system alignment becomes cumbersome. We describe some of the problems associated with the current multiple-reflection interferometer and introduce a setup for matching path lengths to increase the resolution and allow for the reduction of the stringent requirement on the coherence length of the lasers used. Theoretically, we show that more than 1000 reflections can be achieved. Experimental results of up to 100 reflections are presented in this paper.

Increasing the sensitivity for tilt measurement using a cyclic interferometer with multiple reflections

Abstract: Measurement of tilt plays an important role in metrological applications and consequently, several methods have been proposed in the recent past. Classical interferometric methods can measure angles with high accuracy but are easily susceptible to external turbulences. We propose to use a cyclic interferometer to measure tilt in which the sensitivity to tilt measurement is double when compared with that of the classical Michelson interferometer. Since the counter propagating beams travel identical paths, the interferometer is insensitive to external vibrations and turbulence and thus can be used under harsh environmental conditions. The novelty in the technique lies in creating multiple reflections in the tilt mirror to enhance the measurement accuracy by the way of increasing the sensitivity. This paper presents the basics of the interferometer and experimental results to quantify the increase in sensitivity. By increasing the number of reflections, it is shown that sensitivity can be further improved to measure tilt angles below 5 μ rad .

Effect of beam quality on tilt measurement using cyclic interferometer

Abstract: Accurate measurement of angles is extremely important in various metrological applications. Interferometry has always been an excellent technique for accurate measurements. Several methods have been proposed for accurate tilt measurement using interferometric techniques. Almost all of them use the Michelson configuration which is extremely sensitive to environmental vibrations and turbulences. We know that a cyclic interferometer is extremely stable. Even though it is not sensitive to displacement changes, it is twice sensitive to tilt compared to that of a Michelson interferometer. We have enhanced the sensitivity to measure tilt using multiple reflections in a cyclic interferometer. Since the input beam is collimated, we have studied the effect of aberration of the input beam on the accuracy of tilt measurement. Experimental results on this study are presented in this paper.