Effect of spherical aberration on real-image fidelity from replayed in-line holograms of underwater objects

Abstract

The real image of a line object, located in water of refractive index n _w and recorded on an in-line Fraunhofer hologram, is calculated by use of the Huygens–Fresnel principle. The presence of the water–glass and glass–air interfaces or the change in effective wavelength between recording and replay introduce wave-front aberrations. Spherical aberration dominates for a perfectly aligned finite-aperture hologram, and its effect on the replayed image of a finite-width line object is evaluated. Numerical results are compared with experimental data of a 10-μm wire located in water 50.0 mm from a 10-mm-thick glass window, and good agreement is demonstrated. It is shown that the error on the linewidth is less than 1.5%, and the shift in focal plane from the Gaussian plane is less than 16 μm, for a replay-to-recording wavelength ratio μ in the range 0.98 < μn _w < 1.02.

© 1998 Optical Society of America