Spectral shifts and spectral switches of a pulsed Gaussian beam from a rectangular aperture in the far field

Abstract

The far-field anomalous spectral behaviours of a space-time-dependent Gaussian pulsed beam passing through a rectangular aperture are studied. By expanding a hard aperture function into a finite sum of complex Gaussian functions and starting from the Fresnel diffraction integral, the approximate analytical expression for the spectral intensity of a space-time-dependent Gaussian pulsed beam passing through a rectangular aperture is derived. Meanwhile, the corresponding closed-forms for the slit and the unapertured cases are also given as special cases of the general results. The red and blue shifts and the spectral intensity distribution are studied and illustrated with numerical calculations. Specifically, it is shown that the spectral switch takes place when the truncation parameter is equal to particular values or the observation position is at the critical diffraction angle. The possibility of tunable spectral switching in the far field with an apertured pulsed beam by varying the size of the rectangular aperture is highlighted.

Spectral Switches of Gaussian Pulse from Adjustable Tilted Mirror in Far Field

“…In a previous work, the spectral switches and peak shift in the diffracted spectrum were utilized in information encoding and transmission in free space, and the rms bandwidth or spatial coherence of the incident field was used to modulate the incident light, which is not easy to do. 8) Although some previous research has studied the relationship between the aperture function and the diffracted angle 10) or used the aperture width to control the spectral switches, 23) the diffracted angles for the occurrence of a spectral switch always exist in some specific directions [as in eq. (2) of ref .…”