Fabrication of phase diffractive optical elements by direct laser writing process in aluminum thin films

Abstract

We present a novel method of forming the phase diffractive optical elements (DOEs) by direct laser writing in thin films of aluminum with the help of the circular laser writing system CLWS-200S. The quality of the aluminum films were investigated depending on the parameters of magnetron sputtering process. Circular phase diffraction gratings of Al 2 O 3 on the quartz substrate with a period of 4 μm and 50% duty cycle were fabricated for the desired wavelength of 532 nm. In the visible wavelength spectrum, Al 2 O 3 has a refractive index of 1.8 which is higher than the refractive index of quartz 1.5 that provides a significant refractive index contrast. As a result, this fact reduces the requirement of high aspect ratio of the diffractive element structures in the Al 2 O 3 film as compared to the structures in quartz by 20%. This method of phase diffraction optical elements forming substantially reduces the time, fabrication steps, costs of production and significantly improves the quality of the elements in comparison with traditional process.