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Extremely nondegenerate two-photon absorption in direct-gap semiconductors [Invited]
Claudiu M Cirloganu1, Lazaro A Padilha, Dmitry A Fishman
1CREOL: The College of Optics and Photonics, University of Central Florida, 4000 Central Florida Blvd, Orlando, FL 32816, USA.
Optics Express
|November 24, 2011
Summary
Researchers achieved significant enhancement in two-photon absorption (2PA) in semiconductors like ZnSe by using widely different photon energies. This breakthrough allows access to strong 2PA previously limited to narrow-gap materials.
Area of Science:
- Materials Science
- Optics
- Solid-State Physics
Background:
- Two-photon absorption (2PA) is a nonlinear optical process crucial for applications like optical limiting and 3D microfabrication.
- Traditionally, significant 2PA is observed in narrow-gap semiconductors, limiting material choices.
- Exploring 2PA with non-degenerate photons offers a new pathway to enhance this effect in wider-gap materials.
Purpose of the Study:
- To investigate the enhancement of two-photon absorption (2PA) in direct-gap semiconductors using extremely non-degenerate photon pairs.
- To measure 2PA coefficients and nonlinear refraction enhancements under these conditions.
- To explore the potential of using widely different wavelengths to achieve strong 2PA in common semiconductors.
Main Methods:
- Measurement of 2PA spectra in GaAs, CdTe, ZnO, ZnS, and ZnSe using picosecond or femtosecond laser pulses.
- Employing pairs of extremely non-degenerate photons with energy ratios up to ~12.
- Calculation of nonlinear refraction, including two-photon, AC-Stark, and Raman contributions.
Main Results:
- A 270-fold enhancement in 2PA was observed in ZnSe when using photons with an energy ratio of ~12, compared to degenerate 2PA.
- Achieved 2PA coefficients as high as 1 cm/MW in ZnSe, a value comparable to narrow-gap semiconductors.
- Observed a smaller, but highly dispersive, enhancement in nonlinear refraction within the 2PA regime.
Conclusions:
- Using widely different photon energies significantly enhances 2PA in direct-gap semiconductors, broadening material accessibility for nonlinear optical applications.
- This method provides a route to achieve strong 2PA effects in materials like ZnSe, previously unattainable.
- The study highlights the potential for tailored nonlinear optical responses by controlling photon energies in non-degenerate 2PA processes.
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