Direct determination of multiphoton absorption cross-sections by transient absorption spectroscopy

Area of Science:

• Materials Science
• Optics
• Photochemistry

Background:

• Single- and multi-photon absorption cross-sections are key for light-matter interactions in spectroscopy, photochemistry, and advanced imaging.
• Conventional measurement methods face limitations due to sample properties, concentration, and high excitation intensities, impacting reliability and sample integrity.

Purpose of the Study:

• To present a direct, robust, and versatile method for quantifying absorption cross-sections across single- to multi-photon regimes.
• To report novel three-photon and four-photon absorption cross-sections for CsPbI3 perovskite nanocrystals and CdSe/ZnS quantum dots.
• To establish a generalizable tool for discovering and optimizing photon-harvesting materials.

Main Methods:

• Developed a method based on the saturation behavior of transient absorption signals.
• Applied the method to measure three- and four-photon absorption cross-sections using 1700 nm and 2100 nm excitation.
• Validated the method's applicability to weakly or non-emissive materials.

Main Results:

• Reported the first measurements of three- and four-photon absorption cross-sections for CsPbI3 perovskite nanocrystals and CdSe/ZnS quantum dots.
• Demonstrated that these materials exhibit absorption cross-sections at least an order of magnitude higher than incumbent materials for mouse deep-brain imaging.
• Showcased the method's independence from photoluminescence signals.

Conclusions:

• The developed method offers a reliable and versatile approach to quantify absorption cross-sections.
• CsPbI3 perovskite nanocrystals and CdSe/ZnS quantum dots show significant potential for advanced imaging and photon-harvesting applications.
• This work provides a valuable tool for accelerating the development of next-generation optical materials.