Shared aperture for two beams of different wavelength using reflective phase gratings and the Talbot effect

A shared aperture system for two laser beams with different wavelengths and composed entirely of reflective phase gratings is described. Beams that share an aperture are collinear, and they have the same transverse phase profile across the aperture as their respective sources. Using the Talbot effect that is observed in Fresnel diffraction from periodic objects, we preserve the phase of the beams, and we maximize the efficiency of the system. An experimental Talbot shared aperture system using He-Ne and He-Cd beams has an efficiency of 88.1% for the He-Ne beam and 70.3% for the He-Cd beam. These measured efficiencies agree well with theoretical predictions and computer simulations.