For infinitely long extension of the slit, one obtains on exten- sion in the slit direction in the spectrum. This changes for a finite length of the slit.
The zero points of the Sinc function are located at ...– 2/a, –1/a,1/a,2/a,...(see Fig.6).
(c) Grid:
A grid is a composite diffracting structure. It consists of a peri- odic sequence (to be represented by a so-called comb func- tion comb) of individual identical slit functions sinc.
Fig. 6: Infinitely long slit with the width a and its Fourier spec- trum.
The grid consists of M slits having a width a and a slit sepa- ration d (>a) in the x direction. As a result, the field strength distribution can be in the front focal plane can be represented as follows:
M