Guiding light inside an optically transparent medium by total internal reflection (TIR) is common and useful in thin planar optical devices. vHOEs offer unique ways to create selective in- and out-coupling of TIR light. As such vHOEs typically have to be recorded in an edge-lit configuration as the necessary high diffraction angles could not be generated by two free-space beams outside the medium. To record such an edge-lit vHOE, bulky recording blocks or liquid baths are used in complex and hard to align recording setups.
We present in this paper our findings to use instant-developing photopolymer film (Bayfol® HX) to generate 2nd harmonics in the index profile of phase gratings while using free-space recording setups. Those 2nd harmonic components enable the vHOE to diffract at such large angles that they replay in an edge-lit configuration. We will discuss in this paper selected materials and beneficial recording parameters to tune the diffraction efficiency towards 2nd harmonic replay. By this - in reported specific cases - the cumbersome and complex edge-lit recording can be substituted by easy-to-use free-space setups. This process significantly simplifies master recordings for vHOEs with edge-lit functionalities which later can be used in contact copy schemes for mass replication.