Variable-spacing diffraction grating employing elastomeric surface waves

Variable-spacing diffraction gratings may be useful for controlling the deflection of a light beam. We introduce a method for making such a variable grating through the use of variable-frequency surface waves in elastomeric substrates. Elastomers have an extremely low Young's modulus compared with that of conventional solids, which allows surface waves to be created with low power and to travel much more slowly than waves in conventional surface-wave devices. To date, the best results have been obtained with a thin silicone elastomer membrane supported upon the surface of water. It has been found that the propagation speed of such waves is consistent with that in a previously developed analytical model, which predicts the dispersion relationship in terms of the membrane's thickness, tension, and modulus. Such a system has been used to cause a variable deflection of a light beam, in agreement with numerical predictions.