Adaptive optics correction using coherently illuminated diffractive objects

Adaptive Optics (AO) is an established technique for improving image quality and compensating for aberrations induced by focusing through samples with varying thickness and refractive index. Future optical data storage schemes with multiple data layers may require the correction capabilities of AO systems. However, the diffractive phase introduced by light reflected from optical storage media might be problematic for high-performance systems. A laser beam focused onto grooved media has a reflection with a baseball-shaped variation in the pupil, caused by the overlap in diffracted orders with the zero-order reflection. This pupil variation is significant in intensity, and simulations and experiments show that there is an associated small variation in phase. If the diffractive phase is sufficiently small, measurement of the total phase with aberrations by a wavefront sensor could enable application of AO correction with diffractive media samples. Simulations and experiments are presented to examine the capability of an adaptive optics microscope system to compensate for diffractive effects with a coherently illuminated sample. AO systems are commonly implemented with incoherent objects, but this could be extended to other applications by characterizing the performance of an AO system with a coherent reflection from a diffractive surface. Data storage media are used as targets for investigating these intensity and phase variations caused by coherence effects, with well-defined grating parameters creating diffraction patterns that are modeled and verified experimentally. There are potential applications outside of data storage, such as coherent freespace optical communication.