Design and optimization of a dispersive unit based on cascaded volume phase holographic gratings

We describe a dispersive unit consisting of cascaded volume-phase holographic gratings for spectroscopic applications. Each of the gratings provides high diffractive efficiency in a relatively narrow wavelength range and transmits the rest of the radiation to the 0th order of diffraction. The spectral lines formed by different gratings are centered in the longitudal direction and separated in the transverse direction due to tilt of the gratings around two axes. We consider a technique of design and optimization of such a scheme. It allows to define modulation of index of refraction and thickness of the holographic layer for each of the gratings as well as their fringes frequencies and inclination angles. At the first stage the gratings parameters are found approximately using analytical expressions of Kogelnik's coupled wave theory. Then each of the grating starting from the longwave sub-range is optimized separately by using of numerical optimization procedure and rigorous coupled wave analysis to achieve a high diffraction efficiency profile with a steep shortwave edge. In parallel such targets as ray aiming and linear dispersion maintenance are controlled by means of ray tracing. We demonstrate this technique on example of a small-sized spectrograph for astronomical applications. It works in the range of 500-650 nm and uses three gratings covering 50 nm each. It has spectral resolution of 6130 - 12548. Obtaining of the asymmetrical efficiency curve is shown with use of dichromated gelatin and a photopolymer. Change of the curve shape allows to increase filling coefficient for the target sub-range up to 2.3 times.Comment: 10 pages, 7 figures. Proc. SPIE 10233. Conference "Holography: Advances and Modern Trends V" (Prague, Czech Republic

Optical scheme of small-size curved detector spectrofluorometer

We present two versions of a compact spectrograph optical scheme based on aberration-corrected concave holographic grating. It is shown that performance of a widely-known flat-field spectrograph scheme can be significantly improved by means of use of a curved detector and introduction of an additional condition of coma correction.The spectrograph provides spectral resolution up to 0.23 nm over an extended working range of 250-900 nm and can be used for fluorescence analysis of waste water

Digital Holographic Positioning Sensor for a Small Deployable Space Telescope

We propose a system and a technique to measure misalignments of individual optical elements in a deployable telescope for a small satellite, and we demonstrate its application for a 2230 mm F10.3 Ritchey–Chretien type telescope. The system uses laser point sources at the edge of each of the deploying segments to form an interference pattern at the telescope image sensor. By processing the interferograms in the Fourier domain and comparing them to the computed ones, it becomes possible to measure the position of the primary mirror segments with a precision of 0.8μm and the axial displacement of the secondary mirror with the precision of 0.1 nm. Such a system would allow to build a deployable telescope fitting in a 1U CubeSat and align it in space with a sufficient accuracy, thus providing a gain in collecting power, reaching a factor of 2.49 with respect to a single mirror telescope fitting on a 1U CubeSat

A Tribute to Sergey Odinokov

“My main goal was to point out new phenomena and spread the ideas, which will become the starting points for new research” [...

A Tribute to Sergey Odinokov

“My main goal was to point out new phenomena and spread the ideas, which will become the starting points for new research” [...