THEORETICAL-STUDY OF TALBOT-LIKE BANDS OBSERVED USING A LASER-DIODE BELOW THRESHOLD

We report on a theoretical study of an interferometric system in which half of a collimated beam from a broadband optical source is intercep ted by a glass slide, the whole beam subsequently being incident on a diffraction grating and the resulting spectrum being viewed using a li near CCD array. Using Fourier theory, we derive the expression of the intensity distribution across the CCD array. This expression is then e xamined for non-cavity and cavity sources for different cases determin ed by the direction from which the slide is inserted into the beam and the source bandwidth. The theoretical model shows that the narrower t he source linewidth, the higher the deviation of the Talbot bands' vis ibility (as it is dependent on the path imbalance) from the previously known triangular shape. When the source isa laser diode below thresho ld, the structure of the CCD signal spectrum is very complex. The numb er of components present simultaneously increases with the number of g rating lines and decreases with the laser cavity length. The model als o predicts the appearance of bands in situations not usually associate d with Talbot bands.