We fabricated and experimentally studied diffractive optical elements intended to focus near IR light into a ring and a twin-spot. Fabrication technology and the performances of the fabricated optical elements are discussed.

Holographic optical lens elements (HOES) are volume gratings in thick material such as dichromated gelatine (DCG) which suffer from the wavelength mismatch between the recording process and the practical application e.g., at laser diode wavelengths. Wavelength mismatch between recording and reconstruction is caused by the fact that the best recording materials are sensitive only in the blue region of the spectrum. The advantage of volume gratings (thickness 13pin) is the large angle of deflection of the first diffraction order with a high diffraction efficiency. An optimized recording geometry using only spherical wave fronts allows on the one hand for the elimination of one of the third order aberrations (predominantly: astigmatism) or on the other hand for the fulfillment of the Bragg condition. To optimize the properties of holographic optical lens elements with one aspheric recording wave a kind of iterative procedure for the manufacturing is proposed /1,2/. Each iteration consists of three different steps (fig. 1):

Using numerical and analytical approaches, we have computed the optical elements (focusators) required for focusing laser light into a narrow ring, a wide ring and a set of rings. A numerical comparison of the various computational techniques is reported. Finally the operation of a fabricated rotor axicon to focus light into a ring is reported.

The method has been proposed for computing Fresnel-type multi-focal lenses on the basis of special-type phase nonlinearity. Multi-focal lens is represented as a mathematical superposition of a thin lens and nonlinearity distorted Fresnel lens. Selection of the nonlinearity-type is reduced to the problem of the groove form determination for the phase diffraction grating with pre-set energy distribution between orders. In particular, bifocal lens and multi-focal lens have been investigated.

We report creation by photolithography techniques of the phase rotor filter, an optical element whose complex transmittance depends in a linear fashion on the azimuth angle. Relationships are given that describe the scalar diffraction of coherent light by the rotor filter. The results of the numerical simulation and experiments are discussed.

We report the creation of novel computer-generated holographic optical elements. The method of computing diffraction gratings producing a continuous focal pattern in the form of a line and also gratings that have N orders in a row of equal energy is described. The method has also been developed for coding the filter-complex transmittance functions in order to form and analyze the transverse modes. All the above elements are realized as glass-substrate binary-phase refractive holograms by projection photolithography by using photoreduction. The minimum line width is 2.5 mkm. These elements may also be fabricated as reflective holograms.Photo-masks and the results of an investigation of the intensity distribution produced by the elements are presented. The investigation results confirm the synthesized elements' high quality.

A new method is investigated for synthesis of computer-generated optical elements: focusators that are able to focus the radial-symmetrical laser beam into complex focal contours, in particular into alphanumeric symbols. The method is based on decomposition of the focal contour into segments of straight lines and semi-circles, following corresponding spacing out of the focusator on elementary segments (concentric rings or sectors) and solution of the inverse task of focusing from focusator segments into corresponding elements of the focal contour. The results of numerical computing of the field from synthesized focusators into the letters are presented. The theoretical efficiency of the focusators discussed is no less than 85%. The amplitude masks and the results of operational studies of synthesized focusators are presented.