Fabrication of uniform diffraction gratings using laser interference lithography for simultaneous measurement of refractive index

Abstract

sThe refractive index is one of the important optical properties. Many researchers have studied various methods of measuring refractive index. In this paper, we can easily measure the refractive index of liquids by using diffraction gratings fabricated by flat-top laser interference lithography. Using the diffraction grating for the measurement of the refractive index has the advantage of a wide measurement range. To fabricate the diffraction gratings, we suggest a special laser manufacturing method named flat-top laser interference lithography. The reason which we have chosen Flat-top laser interference lithography is that it can fabricate uniformly and large area micro/nanostructures on the substrate, using a 360 nm continuous-wave(C.W) laser. This optical system is an experiment in which micro/nanopatterning is performed by converting the Gaussian beam shape into a Flat-top shape and causing laser interference. We fabricated transmission diffraction grating on a glass wafer by flat-top laser interference lithography. The transmission diffraction grating is set to measure the refractive index of several liquids. When the laser is normally incident to the transmission diffraction grating, diffraction occurs then we set the beam-profiler, which can sense several optical properties, at 1st diffraction order. Depending on the type of liquid, 1st diffraction order may be displaced. We can easily measure this displacement and calculate the refractive index of liquids including water, benzene, and ethyl alcogol each value of 1.310, 1.501, and 1.3677. The calculated refractive index corresponds to the true values.