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

A volume cylindrical holographic lens is fabricated in a photopolymer material to obtain a simple, lightweight and inexpensive lens which can collimate a diverging light beam. For a collimated beam, it is necessary to have uniform intensity across the beam diameter and to achieve equal diffraction efficiency for different regions of the cylindrical holographic lens, two methods are discussed. In the first method, the diffraction efficiency is improved by modifying the recording geometry in order to operate at a range of spatial frequencies for which the photopolymer provides higher diffraction efficiency. In the second method, the recording has been carried out with varying laser power and exposure time while keeping the exposure energy constant, in order to improve the material's performance at the lower spatial frequencies. The second approach increases the uniformity of diffraction efficiency across the Holographic optical elements (HOEs) even when low spatial frequency components are present. The results obtained provide cylindrical holographic lenses with overall higher and uniform diffraction efficiency. This type of lens has the potential to be used in combination with LED sources and different lighting applications.