Three-photon absorption in semiconductor quantum dots: experiment.

Area of Science:

• Quantum dots
• Semiconductor physics
• Nonlinear optics

Background:

• Semiconductor quantum dots (QDs) exhibit unique optical properties due to quantum confinement.
• Three-photon absorption (3PA) is a nonlinear optical process with potential applications in optoelectronics and photonics.

Purpose of the Study:

• To compare the theoretical predictions of the four-band model with experimental measurements of 3PA in CdSe and ZnS quantum dots.
• To investigate the influence of quantum dot size on 3PA cross-sections.

Main Methods:

• Theoretical calculations using the effective-mass approximation and a four-band model.
• Experimental measurements of frequency-degenerate 3PA in CdSe and ZnS quantum dots of varying sizes.

Main Results:

• The four-band model qualitatively predicts the magnitude of 3PA cross-sections (10^-79 to 10^-77 cm^6s^2photon^-2).
• The model correctly predicts an increasing trend of 3PA cross-sections with increasing quantum dot size.
• Discrepancies observed for smaller QDs suggest the need to account for valence band mixing in the theoretical model.

Conclusions:

• The four-band model provides a good theoretical framework for understanding 3PA in semiconductor quantum dots.
• Quantum dot size is a critical factor influencing 3PA cross-sections.
• Further theoretical refinement, including valence band mixing, is necessary for improved accuracy in smaller quantum dots.