Interpretations of High-Order Transient Absorption Spectroscopies

Area of Science:

• Physical Chemistry
• Spectroscopy
• Photophysics

Background:

• Transient absorption (TA) spectroscopy is crucial for studying excited-state energetics and dynamics.
• High pump intensities in TA spectroscopy introduce higher-order responses beyond the desired third-order.
• Previous studies showed pump-intensity dependence can separate response orders, but higher-order information was undescribed.

Purpose of the Study:

• To provide a general framework for understanding high-order transient absorption spectra.
• To extend fundamental TA processes (GSB, SE, ESA) to higher orders.
• To elucidate the novel spectral and dynamical information contained within each higher order of response.

Main Methods:

• Development of a theoretical framework for analyzing high-order TA spectra.
• Extension of standard TA processes (ground-state bleach, stimulated emission, excited-state absorption) to higher orders.
• Utilizing pump-intensity-dependent measurements to isolate and interpret different orders of optical response.

Main Results:

• Each higher order introduces two new processes: stimulated emission and excited-state absorption from previously inaccessible states, and negations of lower-order processes.
• New spectral features and dynamical information are accessible at each successive order of response.
• The relative signs of signals across different orders can identify dominant contributing processes.

Conclusions:

• High-order TA spectroscopy offers a richer understanding of excited-state phenomena.
• The framework presented allows for the interpretation of complex spectral responses.
• This method provides a powerful tool for detailed photophysical characterization.