Dr. Sanjay Kumar Keshri Profile

Dr. Sanjay Kumar Keshri

Optical Engineer at Technological Univ Dublin

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Publications (3)

Proceedings Article | 13 April 2020 Presentation + Paper

Optimisation of the performance of holographic beam-shaping diffractive diffusers through refinement of the recording process

Cara Jones, Suzanne Martin, Sanjay Keshri, Dervil Cody, Kevin Murphy

Proceedings Volume 11367, 1136706 (2020) https://doi.org/10.1117/12.2555774

KEYWORDS: Diffusers, Holography, Speckle, Speckle pattern, Modeling, Volume holography, Diffraction, Beam shaping, Photopolymers, Diffraction gratings, Holographic optical elements

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Proceedings Article | 1 April 2020 Presentation

Multilayer photopolymer for broad spectral range holographic optical elements (Conference Presentation)

Sanjay Keshri, Izabela Naydenova, Kevin Murphy, Suzanne Martin

Proceedings Volume 11367, 113670Q (2020) https://doi.org/10.1117/12.2556006

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Diffractive Optical Elements (DOEs) utilize diffraction at sub-micron features to re-direct and control light. Volume phase holographic materials, such as photopolymer, are advantageous for use in fabricating optical elements because the diffraction efficiency can approach 100%, the whole element can be recorded in one exposure and high diffraction and slant angles are possible. Self-developing photopolymers also facilitate mass manufacture. Holographic gratings have been developed for numerous applications including spectroscopy, solar concentration, and monochrome LEDs, however, the inherent angular and wavelength selectivity of the volume phase hologram generally restricts applications to laser systems and sources with narrow spectral ranges. Multiplexing more than one grating into a single photopolymer layer can extend the range, however, unwanted additional gratings are frequently recorded. In this paper, we discuss laminating multiple photopolymer HOEs together as a method for increasing the wavelength and angular working range of devices. This involves combining HOEs designed to produce the desired output beam for different angular and/or spectral input beams. Stacking of photopolymer layers has previously been demonstrated to increase the angular range of gratings and recently the authors produced a compound HOE with significantly broadened wavelength and angular selectivity curves by laminating two HOEs recorded sequentially at a single wavelength. However, such solutions are not easily translated to more complex elements such as lenses where the spatial frequency and grating slant angles are varying. This paper discusses laminating together two photopolymer layers sensitized for different recording wavelengths for the purpose of holographically recording a compound-element volume-HOE lens for use with a broadband LED. The angular and wavelength selectivity are characterized and the challenges and advantages of the different approaches are discussed and compared.

Proceedings Article | 15 May 2017 Presentation + Paper

Comparison of two methods for equalising the diffraction efficiency of different spatial frequency components of holographic optical elements

S. Keshri, K. Murphy, V. Toal, I. Naydenova, S. Martin

Proceedings Volume 10233, 102330X (2017) https://doi.org/10.1117/12.2265598

KEYWORDS: Refractive index, Volume holography, Modulation, Photopolymers, Collimation, Diffraction, Holographic optical elements, Spatial frequencies, Holography, Light emitting diodes, Diffraction gratings, Diffractive optical elements, Holograms, Spectroscopy, Ultrafast lasers

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