Retention of Radiation on a Reflective Glass Surface

On a silica glass surface, we superimpose two Gaussian 532 nm cw-TEMoo laser beams of different brightnesses and a long coherence time.  We use diode lasers due to their better thermal stability. The interaction between the laser beams is assisted by a capacitor voltage set across the glass surface, for a fine adjustment of the vibrational frequencies of surface dipoles to an isotropic energy environment. We use low voltages (< 5.3V) for having a linear optical response for silica glasses to the incident radiation from a weak probe laser and preserving their transparency window. This background energy shifts the dipoles’ vibrational frequency by a few eV/h.  The bright coupler is oriented at normal incidence on the glass surface and modifies the interaction of the probe alone with the same dipoles. The surface dipoles align along the resultant electric field of the two linearly polarized laser beams. Although the two laser beams are reflected by the surface in different directions, they superimpose on the surface and create an array of aligned dipoles that act as a diffraction grating.  An interference pattern with a sinusoidal dependance is observed in a range of 5° near Brewster angle. A change in the angular resolution is observed as the voltage changes. Thus, as the voltage increases, the interference fringes shrink with a decrease of the angular separation from 0.78° at no voltage, to 0.50° at 1.3V, and 0.23° at 5.3V, while the Brewster angle shifts to larger angles from 56.68° at no voltage, to 57.06° at 1.3V, to 58.07° at 3.3V and 59.90° at 5.3V.  The shrink of the interference pattern allows to identify pairs of voltages where a maximum of interference in one angular position changes into a minimum for the same angular position, but different voltage. This change in the optical reflectivity of a surface can be used as an optoelectronic switch with STOP and GO phases by keeping lasers in a fixed position and changing only the voltage across the surface.