Non-degenerate Two-Photon Absorption in Semiconductors
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Solution Overview
Problem
Existing two-photon absorption processes in semiconductor materials are limited in the near infrared/visible range, as scaling rules indicate that large two-photon absorption coefficients are not accessible in these regions, restricting their practical applications.
Innovation Solution
The implementation of a non-degenerate two-photon absorption (ND-2PA) method using semiconductor materials with simultaneous irradiation of two photons, where the higher energy photon is at least 75% and the lower energy photon is no greater than 25% of the bandgap energy, allowing their aggregate energy to exceed the bandgap, thereby enhancing two-photon absorption coefficients by one to three orders of magnitude.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If degenerate two-photon absorption is used in narrow-gap semiconductors, then large two-photon absorption coefficients are achieved, but the method is not applicable in near infrared/visible range
Solution Approach 1:
The patent changes the fundamental parameters of the two-photon absorption process by using non-degenerate photons with different energies instead of degenerate photons with identical energies. This allows the process to occur in wide-gap semiconductors at visible and near-infrared wavelengths, expanding the applicability range while maintaining large absorption coefficients through resonance enhancement with intermediate states
Solution Approach 2:
The patent introduces intermediate quantum states as mediators in the two-photon absorption process. By tuning the photon energies to resonate with these intermediate states, the absorption coefficient is dramatically enhanced, enabling the process to work in wide-gap semiconductors where degenerate 2PA would be negligible
2Measurement precision
If non-degenerate two-photon absorption with intermediate state resonances is used, then two-photon absorption coefficients are enhanced by one to three orders of magnitude, but the device complexity increases
Solution Approach 1:
The patent exploits parameter changes in photon energy to achieve resonance with intermediate states. By carefully selecting the energies of the two photons to match intermediate state transitions, large enhancement is achieved without requiring complex device structures, relying instead on spectral parameter optimization
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables significant enhancements in two-photon absorption coefficients, enabling applications such as enhanced sensitivity detection, imaging, and optical switching, and provides a means for observing subgap radiation, even at room temperature, with potential implications for lasers and amplifiers based on two-photon gain.
Implementation Method 1
non-degenerate two-photon absorption (ND-2PA) method using semiconductor materials with simultaneous irradiation of two photons, where the higher energy photon is at least 75% and the lower energy photon is no greater than 25% of the bandgap energy, allowing their aggregate energy to exceed the bandgap
Data Source
AI summary
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.