Voldemar Petrovich Koronkevich

Polar coordinate laser pattern generator for fabrication of diffractive optical elements with arbitrary structure

A precision laser pattern generator for writing arbitrary diffractive elements was developed as an alternative to Cartesian coordinate laser/electron-beam writers. This system allows for the fabrication of concentric continuous-relief and arbitrary binary patterns with minimum feature sizes of less than 0.6 microm and position accuracy of 0.1 microm over 300-mm substrates. Two resistless technologies of writing on chromium and on amorphous silicon films were developed and implemented. We investigated limit characteristics by writing special test structures. A 58-mm f/1.1 zone plate written directly is demonstrated at a lambda/50 rms wave-front error corresponding to a 0.06-microm pattern accuracy. Several examples of fabricated diffractive elements are presented.

Processing parameter optimization for thermochemical writing of DOEs on chromium films

Computer-generated holograms are limited by conventional lithographic fabrication capabilities which rely on accurate deposition, exposure, and developing of photosensitive chemicals. We present an alternate fabrication technology that uses a focused laser beam to write patterns by inducing a thermochemical change in a bare metal film. The patterns are developed using a single etching step that dissolves the non- exposed metal. The thermochemical writing method allows holograms to be directly written onto large-diameter, thick, and non-flat substrates, requiring no intermediate steps that compromise the ultimate accuracy. Circular patterns for optical testing were written using a polar-coordinate laser writer. The laser power and control requirements are shown to be modest and the etching is shown to be tolerant of temperature and concentration variations. The technology is demonstrated with the fabrication of CGHs up to 136 mm in diameter used for optical testing.

Accuracy potential of circular laser writing of DOEs

The circular laser writing system for writing of arbitrary patterns of diffractive elements in chromium films and photoresists has been developed as an alternative method for laser or e-beam writing in x-y system of coordinates. This system is able to generate binary amplitude and continuous- tone patterns with features of less than 1 micrometers and accuracy of 0.1 micrometers on substrates up to 300 mm diameter. Construction of the circular laser writing system (CLWS) designed at the IA&E and writing strategies such as laser beam addressing in polar coordinate system are described. This article presents the overview and analysis of writing errors. The characteristics of zone plates and linear gratings fabrication and methods of errors measurement are given. The measurements of wavefront errors of binary f/1.1 zone plates and linear polar system gratings with period of less than 5 micrometers fabricated by CLWS demonstrate the high quality of writing strategy.

Fabrication of diffractive optical elements by direct laser-writing with circular scanning

A new circular laser writing system for fabrication of computer generated holograms is described. The results of diffractive element synthesis without photoresists usage are presented.

Diffractive-refractive intraocular lenses

Optical characteristics and properties of AcrySof ReSTOR® bifocal intraocular lenses (Alcon, USA) and elastic polymer MIOL-Akkord lenses (Russia) are compared. The lenses differ by the form of refractive component, the type of diffractive microstructure, and their fabrication technology. Investigations showed that the lenses have similar optical characteristics in resolution, but the bifocal properties of the MIOL-Akkord are much less dependent on the pupil diameter.

New fabrication method for diffractive optical elements with deep phase relief

The application of continuous-tone photomasks for fabrication of diffractive optical elements with a deep phase relief is explored. Results of computer simulation for technological process are reported and compared with experiment. The experimental testing of offered technique was carried out on thick AZ4562 photoresist layers. The possibility of deep phase relief fabrication has been proven. The application of the new technique to fabrication of multiorder diffractive elements is discussed.

New application for x-ray lithography: fabrication of blazed diffractive optical elements with a deep-phase profile

The use of the X-ray lithography to produce blazed diffractive optical elements (DOEs) is described. The proposed method allows one to make highly efficient blazed DOE with a deep phase profile (ten wavelengths and more) using a single X-ray mask with a binary transmission pattern. Unlike the well-known multilevel DOEs, blazed ones do not involve fabrication and aligning of a set of masks. DOEs with a profile depth of 10 micrometers and more and zone sizes of down to 1 micrometers can be obtained due to the short wavelength and high penetrability of X- rays. The first experimental samples of blazed DOEs with a 10 micrometers -height profile (lenses and gratings) were fabricated by X-ray lithography with synchrotron radiation using the X-ray masks, prepared in accordance with the pulse-width modulation algorithm. Diffraction efficiency for lenses was measured for white light. It is higher than 80 percent for the central part of the lenses (inside a 10 mm diameter) and about 60 percent for an area of 20 mm diameter.

Kinoforms with increased depth of focus

Techniques for calculation of two types of kinoform optical elements with increased causticdepth are presented: first, the elements that produce an image of the axial point as a straight line without projective transformation (axicons); second, the elements that extend caustic without changes in projecting properties of the optical system (generalized zone plates - GZP). The transmission function of kinoform axicons is determined from the second-order differential equation derived from the integral Kirchhoff-Fresnel approximation with the stationary phase technique for the given intensity distribution along the focal line. It is shown that with the given procedures one can calculate axicons that provide arbitrary desired intensity distribution along the focal line for the given amplitude distribution of the field of the illuminating lightwave. Low concentration of radiation is an important feature of axicon focusing that limits its application. Therefore, modification of lens caustic by introducing controlled aberrations is of particular interest. It is suggested to determine GZP zone topology with the tautochronizm principle and the requirement of concentration of power of the radiant energy flow from a ring zone of small width to a focal line of small length. The produced samples of kinoform axicons and GZPs have ben experimentally studied.

Laser technologies in diffractive optics

Computer-generated holograms are limited by conventional lithographic fabrication capabilities, which rely on accurate deposition, exposure, and developing of photosensitive chemicals. We present alternate fabrication technologies, which use a focused laser beam to write submicron patterns by inducing changes in a metal or silicon film and LDW glass. Circular laser writing systems built at IA&E are described. This paper has reviewed some techniques and equipment for the fabrication of binary, multilevel and continuous-relief DOEs developed at IA&E.

Rectangular focus spots with uniform intensity profile formed by computer-generated holograms

An optical beam shaping system based on a single Computer Generated Hologram has been realized. It focuses a laser beam with Gaussian profile to a square area with uniform intensity. In order to achieve a rectangular focal spot which is as close as possible to the size of the diffraction spot, we investigated two different hologram calculation methods. The first is based on a ray tracing approach, while the second one uses an iterative Fourier transform algorithm. Computer simulations and experimental results are shown.