EFFECT OF SPHERICAL-ABERRATION ON REAL-IMAGE FIDELITY FROM REPLAYED IN-LINE HOLOGRAMS OF UNDERWATER OBJECTS

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 wavefront aberrations. Spherical aberr ation dominates for a perfectly aligned finite-aperture hologram, and its effect on the replayed image of a finite-width line object is eval uated. Numerical results are compared with experimental data of a 10-m u m 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 lin ewidth is less than 1.5%, and the shift in focal plane from the Gaussi an plane is less than 16 mu m, for a replay-to-recording wavelength ra tio mu in the range 0.98 < mu n(w) < 1.02. (C) 1998 Optical Society of America.