Abstract

Several plastics have been used to record IR interference patterns when a CO₂ laser was used as a light source. Recording materials were in the form of PMMA thin films (20-60-μm thickness) and Lexan and acrylate blocks (4-5-mm thickness). Thin films presented different transmittance, depending on their thickness, blocks absorbing completely IR radiation. To characterize the media, interference gratings with different spatial frequencies were recorded. Modulation of the recording material during exposure time was monitored by measuring diffraction efficiency when a He-Ne laser beam was sent to the recording area. Permanent gratings were recorded with the three materials, maximum diffraction efficiencies of ~20% for red light were obtained. One characteristic of Lexan was the possibility of recording transient gratings which showed diffraction efficiencies of the order of 1.5% when exposure times of ~80 ms and power densities of ~28 W/cm² were present. This method is a means to detect information carried by IR wavelengths by using visible light. Finally, the response of these IR recorded diffractive elements when IR light is used in the reconstruction step has been studied.

© 1988 Optical Society of America