Ruslan K. Nasyrov

Zone-boundary optimization for direct laser writing of continuous-relief diffractive optical elements

Enhancing the diffraction efficiency of continuous-relief diffractive optical elements fabricated by direct laser writing is discussed. A new method of zone-boundary optimization is proposed to correct exposure data only in narrow areas along the boundaries of diffractive zones. The optimization decreases the loss of diffraction efficiency related to convolution of a desired phase profile with a writing-beam intensity distribution. A simplified stepped transition function that describes optimized exposure data near zone boundaries can be made universal for a wide range of zone periods. The approach permits a similar increase in the diffraction efficiency as an individual-pixel optimization but with fewer computation efforts. Computer simulations demonstrated that the zone-boundary optimization for a 6 microm period grating increases the efficiency by 7% and 14.5% for 0.6 microm and 1.65 microm writing-spot diameters, respectively. The diffraction efficiency of as much as 65%-90% for 4-10 microm zone periods was obtained experimentally with this method.

Combined computer-generated hologram for testing steep aspheric surfaces

A novel type of a combined (or multiplex) computer-generated hologram (CGH) and a method for interferometric testing of steep axially symmetric aspheres is presented. The method is based on a hybrid CGH containing two different diffractive structures. The presented new type of Diffractive Fizeau Null Lens (DFNL) design eliminates the transmitted wavefront distortion (TWD) of the CGH substrate and increases the accuracy of the surface test. The method was approved by testing a spherical reference mirror with an f-number of f/0.65.

Aspherical wavefront shaping with combined computer generated holograms

Abstract. The problem of metrological standards development for aspherical wavefronts is discussed. A method for aspherical wavefront shaping by means of combined (or twin, multiplexed) computer generated hologram (CCGH) is presented. The CCGH reconstructs two wavefronts: the first one is used for calibration of the second one by means of a Fizeau interferometer and a highly reflective flat reference surface. Different CCGH encoding methods are discussed. The design of a CCGH with subaperture division in the shape of angular sectors is presented. The absence of cross-talk errors in both wavefronts was demonstrated experimentally.

Method for increasing the accuracy of wavefront reconstruction from a set of interferograms

A new approach to the wavefront (phase) reconstruction from interferograms is proposed based on the classical method of fringe tracing using a sample of interferograms with different numbers and orientations of interference fringes. Wavefronts reconstructed from individual interferograms are averaged, and the test surface quality is judged by the data obtained. Averaging the phase by several interferograms makes it possible to reduce the variance of the phase reconstruction error caused by random noise and inhomogeneities in aperture illumination and interference fringe distribution, as well as to reduce the effect of instability of external conditions.

Freeform corrector for laser with large aperture YAG:ND3+ active element

Abstract. The results of transmitted wavefront distortion correction are presented for a YAG:Nd3+ active element with a diameter 45 mm. Halftone mask and proximity printing were used for fabrication of the freeform corrector. Experimental results show a three-fold decrease of the wavefront distortion. Because the corrector presented a high damage threshold, it can be used with high power laser systems.

Diffractive variable attenuator for femtosecond laser radiation control

We present a diffractive phase variable attenuator for femtosecond laser radiation control. It allows the control of beam power up to 0.75.10(13) W/cm(2) without introducing serious distortions in spectra and beam shape while it operates in zero order diffraction. The attenuator can operate with wavelengths from DUV to IR.

Micro-holographic methods for sub-micrometer grating fabrication in fused silica with UV femtosecond laser

The optical layouts incorporating binary phase diffractive grating and a standard micro-objective were used for femtosecond microfabrication of periodical structures in fused silica. Two beams, generated in Talbot type interferometer, interfered on a surface and in the bulk of the sample. The method suggested allows better control over the transverse size of the grating pitch, and thus control the reflection strength of the waveguide or fibre grating. We present the examples of direct inscription of the sub-micrometer periodical structures using a 267 nm femtosecond laser radiation.

Features of the 85Rb Spectrum in a Cell with an Antirelaxation Coating

Distortion of the spectrum of the D1-line of 85Rb in optical cells with an antirelaxation coating on the inner walls of the cell is studied. The spectrum shape is found to be significantly dependent on the velocity and direction of changes in the laser frequency. A physical explanation is provided for these features, which are confirmed by numerical simulations. The effect of the magnetic field on the spectrum shape is discussed.

Diffractive optics for precision alignment of Euclid space telescope optics (Conference Presentation)

We present a method for precise alignment of lens elements using specific Computer Generated Hologram (CGH) with an integrated Fizeau reference flat surface and a Fizeau interferometer. The method is used for aligning the so called Camera Lens Assembly for ESAs Euclid telescope. Each lens has a corresponding annular area on the diffractive optics, which is used to control the position of each lens. The lenses are subsequently positioned using individual annular rings of the CGH. The overall alignment accuracy is below 1 µm, the alignment sensitivity is in the range of 0.1 µm. The achieved alignment accuracy of the lenses relative to each other is mainly depending on the stability in time of the alignment tower. Error budgets when using computer generated holograms and physical limitations are explained. Calibration measurements of the alignment system and the typically reached alignment accuracies will be shown and discussed.

Diffractive focusing fan-out element for the parallel DNA sequencer

Various issues of creation of diffractive optical elements transforming one laser beam with small divergence to a matrix of converging beams with a diffraction size of focused spots in the plane of object illumination and their application for problems of DNA sequencing and microscopy are considered. The parameters of diffractive elements are calculated and optimized in the approximation of the Fresnel–Kirchhoff diffraction theory. Diffractive elements are fabricated by the method of direct laser writing on a photoresist by using a circular laser writing system. Experimental characteristics of a diffractive element creating a matrix consisting of 33 × 33 beams, which are focused in one plane at a distance of 210 mm, are presented. The degree of nonuniformity of beam intensities determined by the ratio of beam intensities in the central region to intensities of peripheral beams is 1/2.5, which is potentially sufficient to be used in DNA sequencing problems. The maximum distortions of spot positions in the entire focusing field is <0.15%.