Diffractive optical elements (DOE) with an arbitrary topology are widely used in various fields of modern science and technology. Our paper is dedicated to diffractive optics, which is produced by circular laser writing on CLWS-300. In the process of fabrication of diffractive element, a pre-calculated pattern is written on the optical substrate. During this process, writing errors occur that can introduce distortions into the wavefront generated by diffractive optical element. The error of the angular coordinate can make the most significant contribution to the total error. In addition, this type of error is the most difficult to control and correct.
In this paper, we propose a method for measuring the angular coordinate error of the circular laser writing systems based on laser interferometry. The method includes writing special test samples and their subsequent control using a conventional Fizeau interferometer. The angular coordinate error is calculated from the phase map. This method allows detecting errors of the angular coordinates up to 1-2 ang. sec. The test pattern can also be written on the same substrate within a single fabrication process with main pattern. This allows certification and quality control of the fabricated diffractive optical element. In addition, laser writing system can be periodically tested to verify that angular coordinate error is within acceptable limits. The method described in article can be extended to any writing system operating in the polar coordinate system.
One of the promising methods for manufacturing high-aperture and sub-wavelength diffractive optical elements (DOE) is direct laser writing on thin metal films in regime of through oxidation. The amplitude diffractive metal/oxide structure is formed directly by localized laser heating without post-processing using liquid or dry etching. Optical diffractometry based on an analysis of the diffraction pattern obtained from a locally illuminated region of the grating is quite suitable indirect method for inspecting the metal/oxide gratings with a submicron period. Measurement of the angular distribution of diffraction orders allows determining local period of the DOE structure, and measuring the intensity distribution over all diffraction orders allows determining the duty cycle of the grating. In this paper, the configurations of instrumentation schemes of metal/oxide gratings monitoring and algorithms for processing of diffraction patterns formed at illuminating the metal/oxide gratings by probe laser beam are considered.
The important effects, techniques, and factors are considered that aim to increase the spatial resolution of a scanning direct laser writing of diffractive structures on thin films of transition metals from titanium group (Ti, Zr, and Hf). The writing process is based on metal oxidation under the thermal action of a tightly focused laser beam. Scanning speed of the laser beam and film thickness were varied to get a regime of through oxidation (TO) of the metal film under laser heating. It results in strong increase of the film transmission in exposed area. TO ensures a strong threshold due to feedback connected with decreasing of laser power absorption near center of focused gaussian laser spot. To the best of our knowledge, the direct laser writing of amplitude diffractive structures on Zr and Hf films were performed for the first time. The new regime of direct laser writing on thin Zr films was revealed. It allows forming tracks with width of 100 nm and less at laser spot diameter of 700 nm and laser wavelength of 532 nm. In this work, the spectral dependence of the refractive index and extinction coefficient of hafnium films was first experimentally determined in the wavelength range of 250–1100 nm.
The development of specialized non-destructive methods for monitoring of microstructured optical elements is necessary for introduction of diffractive, micro-optical and conformal optical elements into production. However, a wide variety of such elements, as well as their production technologies, set many tasks in the implementation of process control both at the final and at the intermediate stages of the formation of a multilevel and binary phase element. All this requires the use of various expensive equipment, each of which individually does not allow solving the whole range of tasks. Multichannel scanning measuring system that implementing spectroscopic and diffraction testing methods was developed at IAE SB RAS. The device includes four measuring channels allowing to measure the following parameters and characteristics: transmission function of half-tone masks in zeroth order or as sum of all diffraction orders; thickness of transparent films covered on substrate (by the spectroscopic method in reflection); measurement of the zero-order intensity of diffraction structures, both in transmission and in reflection in range of wavelengths from 200 nm to 1100 nm; measurement of the diffraction efficiency of the first and zero orders of diffraction in reflected light (including for structures made in optically transparent materials) for monitoring the parameters of the formed relief of multilevel elements.