Extremely Non-Degenerate Two-Photon Absorption (2PA): High Coefficients with Larger-Gap Semiconductors

Abstract

Researchers at the University of Central Florida have developed a method for improving multi-photon optical sensing. The new method enables non-degenerate two-photon absorption (ND-2PA), allowing much larger 2PA coefficients than degenerate two-photon absorption (D-2PA). Thus, applications of larger-gap semiconductors can now benefit from extremely large 2PA coefficients. This improvement can be one to three orders of magnitude higher when comparing extremely non-degenerate two-photon absorption (END-2PA) to degenerate counterparts, as demonstrated by theoretical calculations. The advancement is based on a method to achieve END-2PA using photons in a ratio of energy difference causing the energies of individual photons to approach intermediate-state resonances, enabling higher 2PA. Realizing the benefits of high 2PA beyond narrow-gap semiconductors, to larger gap semiconductors with direct bandgaps including CdTe, GaAs, ZnSe, ZnO, and ZnS, can be useful for optical switching, infrared (IR) detection, imaging, and applications of lasers and amplifiers based on two-photon gain.

Technical Details

The UCF method calls for simultaneously irradiating, continuously or pulsed, a semiconductor material substrate with two photons of different energy, wherein each photon's energy is less than the bandgap energy and the aggregate energy of the photons is greater than the bandgap energy. This irradiation reversibly changes a material property, such as optical transmittance or electrical conductivity, of the semiconductor material substrate to achieve higher 2PA when the ratio of photon energies for a higher energy photon (with at least about 75 percent of the bandgap energy) to a lower energy photon (with no greater than about 25 percent of the bandgap energy) is at least about 3.0.

Benefit

Market Application