Fresnel Diffraction: Single Slit

The more accurate Fresnel treatment of the single slit may give a pattern which is similar in appearance to that of the Fraunhofer single slit except that the minima are not exactly zero. In these circumstances the Fraunhofer diffraction from the slit is a satisfactory approximation of the optical phenomenon. But for circumstances where the distance to the screen is not sufficiently large compared to the width of the diffracting slit, the Fresnel diffraction pattern may be dramatically different.

Comparison: Fraunhofer & Fresnel Slit

The more accurate Fresnel treatment of the single slit may give a pattern which is similar in appearance to that of the Fraunhofer single slit except that the minima are not exactly zero. In these circumstances the Fraunhofer diffraction from the slit is a satisfactory approximation of the optical phenomenon. But for circumstances where the distance to the screen is not sufficiently large compared to the width of the diffracting slit, the Fresnel diffraction pattern may be dramatically different.