Available under a Creative Commons Attribution Non-Commercial Share Alike 4.0 International Licence
1.3 PHYSICAL SCIENCES, Optics
A holographic optical element (HOE) was developed to collimate a monochromatic light-emitting diode (LED). The fabrication was achieved by the interference of collimated and diverging beams from a 532 nm laser to produce the required photonic structure in a self-developing photopolymer material. The experimental values of diffraction efficiency and spatial period across the HOE were compared with their expected theoretical values. Good agreement was found for the spatial period; however, the diffraction efficiency varied significantly across the lens. In this paper, two approaches have been taken to address this variation: (1) modification of recording geometry and (2) optimization of recording intensity and exposure time at constant energy. The performance of an optimized HOE (cylindrical holographic lens) was then demonstrated using a 532 nm laser beam. The optimized conditions for the cylindrical holographic lens were used to fabricate a spherical holographic lens of the same numerical aperture for LED applications. This type of lens has the potential to be used in combination with LED sources.
S. Keshri, K. Murphy, V. Toal, I. Naydenova, and S. Martin, "Development of a photopolymer holographic lens for collimation of light from a green light-emitting diode," Appl. Opt. 57, E163-E172 (2018).