Observation of fine interference structures at total internal reflection of focused light beams

We report the experimental observation of fine interference patterns in a reflection profile of a focused laser beam when it undergoes total internal reflection from a dielectric interface near its critical angle. In addition, we show that similar interference structures routinely appear in the reflection profile when long-range optical surface waves are excited at the plane interface by the focused laser beam. In both cases these interference patterns do not appear at all if the incident beam may be reckoned as a plane wave, that is, when the waist of the focused beam is much larger than the Goos-Hänchen shift or the surface wave propagation length correspondingly. A modified formula for the Goos-Hänchen shift is presented, and it is shown that a maximum value of the shift may reach several tens of microns for wide beams.

Figure 1

A sketch of the experimental setup.

Figure 2

Reflection profiles near the critical angle: experimental data (dotted lines in the left column) and theoretical calculations (solid curves in the right column). Data of TIR from the bare prism for $p$- and $s$-polarization are shown in (a) (measurements) and (b) (simulations), while TIR data from the multilayer coated prism for the $p$-polarized beam are shown in (c) (measurements) and (d) (simulations).

Figure 3

The reflection profile of $s$-polarized focused laser beam from the multilayer coated prism, supporting the $s$-polarized surface mode. Experimental data (a) and theoretical calculations (b).

Figure 4

The Goos-Hänchen shift near the critical angle at the glass-water interface according to Eq. (2) for 1- and 10-mm-wide laser beams.

Figure 5

The axes of coordinates and the explanatory scheme for calculations.