Detection of excited state absorption cross-section of porphyrin through cw and femto-second laser pump-probe technique

TL;DR

This paper presents a method to directly measure excited state absorption cross-sections of porphyrin derivatives using a dual wavelength pump-probe technique with cw and femtosecond lasers, providing new quantitative data.

Contribution

It introduces a novel dual wavelength pump-probe approach to measure excited state absorption cross-sections of porphyrin molecules in solid films.

Findings

Measured excited state absorption cross-sections for H2TPP and H2TPP(OH)4.

Demonstrated the use of cw and femtosecond lasers in pump-probe spectroscopy.

Analyzed the effect of absorption on pulse shape as a function of fluence.

Abstract

We report on direct detection of excited states absorption cross-section using dual wavelength pump-probe technique. Also, we experimentally demonstrate using porphyrin composite molecules (porphyrin derivatives such as 5,10,15,20-meso-tetrakis phenyl porphyrin (H2TPP), 5,10,15,20 - meso-tetrakis(4-hydroxyphenyl) porphyrin (H2TPP(OH)4)). The cw laser at 761 nm wavelength is used as a pump to maintain excited state population. Changes in the population of excited states lead to the change in transmission are monitored using femto-second probe pulses of 130 fs width and repeated at a 1kHz rate with central wavelength around 800 nm. Transmittance changes due to excited state population are modeled using rate equation approach. The effect of the absorption on the transmitted pulse shape has been discussed as a function of fluence. Obtained excited state absorption cross-sections of H2TPP and H2TPP(OH)4 doped boric acid glass (BAG) films are 4.9X10-18 cm2 and 1.2X10-17 cm2 respectively.