Abstract: An extremely non-degenerate two photon absorption (END-2PA) method and apparatus provide for irradiating a semiconductor material substrate simultaneously with two photons each of different energy less than a bandgap energy of the semiconductor material substrate but in an aggregate greater than the bandgap energy of the semiconductor material substrate. A ratio of a higher energy photon energy to a lower energy photon energy is at least about 3.0. Alternatively, or as an adjunct, the higher energy photon has an energy at least about 75% of the bandgap energy and the lower energy photon has an energy no greater than about 25% of the bandgap energy.

Abstract: A useful optical device to provide continuously variable rotation of polarization of linearly polarized light in a wavelength-independent manner. This device features a cell of twisted nematic liquid crystal sandwiched between an input window and a rotatable output window, both with surfaces prepared so as to orient the nematic liquid crystal molecules. This optical device has different applications such as: variable-angle polarization rotator; using broad band polarizers as an energy attenuator; working in both cases as a wavelength independent and temporal pulse width independent device. The low cost, the very wide field of view, the wavelength and pulse width independence, the high efficiency, and its mechanical simplicity make of this new optical device a very useful and novel invention.