Transmission volume holograms for LED illumination
The application of transmission holograms in automotive headlamp systems is a possible new field of application for holographic elements. However, it requires the adaptation of holograms to light-emitting diodes (LEDs) as reconstruction light sources. This includes the consideration of the reconstruction wavefront shape. Therefore, computer-generated holograms (CGHs) are designed for different LED wavefront approximations and recorded in a photopolymer. Within experiments, the performance of the optimization is analyzed. For reconstruction, an automotive-certified LED is used and the reconstructed image is recorded. The correlation of the ideal and the real reconstructed image is used as indicator for a successful adaptation within the design process. It is shown that there are clear differences regarding the improvement of the correlation between the considered wavefront approximations. The best results are achieved with a wavefront, determined from an interferometric measurement, and with a wavefront with Lambertian characteristic.