Some experiments based on interferometry, such as studying refractive index changes, need a long time to be completed, and any movement or oscillation in the order of wavelength during that time may wash out the interference fringes or at least reduce the quality of the interferogram. In this work, a new technique is presented to enhance the interferometric data during such experiments. The main idea behind this technique is the use of a reference beam to monitor all surrounding changes during the experiment. Laser light was divided into two parallel beams and then entered into a Mach-Zehnder interferometer. One of the beams was used as a reference signal to measure interferometer drift and the other one was passed through the sample to measure the refractive index changes simultaneously in a single interferometer. Noise was extracted from the data with a written computer code to achieve a noise-free output.

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Irreversible changes in the refractive index of a dye-doped polymer film by photo induced bleaching were measured with a Mach-Zehnder interferometer. The decrease in the refractive index of the film for various laser powers and various radiation times has been investigated. A beam-processing machine with two simultaneous outputs has been designed to make use of this change in the refractive index to fabricate a channel waveguide. This method is simple and one step, and does not involve any solvent or mask; and also due to photobleaching, the pattern is not reversible.

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