Defocus-induced phase contrast enhancement in pattern illumination time-resolved phase microscopy

Kenji Katayama,Tatsuya Chugenji,Kei Kawaguchi

doi:10.1063/5.0072245

Abstract

Photo-excited charge carrier dynamics in photocatalytic materials with rough surfaces have been studied via measurements using pattern-illumination time-resolved phase microscopy. Optimal defocusing is necessary for the phase-contrast detection of the refractive index change due to the photo-excited charge carriers. The signal enhancement of the phase-change was explained theoretically and experimentally. The optical phase variation due to the transmission of a rough surface is coupled with the quadratic phase term in Fresnel diffraction, and a slight defocusing can convert the phase image to the corresponding amplitude image. The phase-contrast image due to the photo-excited charge carriers is also enhanced by the defocusing. The explanation was supported by wave optics calculation, and the enhancement was demonstrated for two types of TiO2 substrates with different roughnesses.

Highlights

Time-resolved spectroscopy provides various information on electrical, thermal, and chemical properties via charge carrier dynamics, thermal dynamics, and chemical reaction dynamics, where a pulsed pump light impinges a perturbation to a sample, and the following dynamics are monitored via fluorescence, absorption, deformation, refractive index, etc
This spectroscopy has been used to study the basic properties of “crystals,” and it has been extended for the study of the charge carrier dynamics in photo-devices such as solar cells and photocatalysts
Rough surfaces made of semiconductor particles calcined on a surface are mainly used

Summary

Introduction

Time-resolved spectroscopy provides various information on electrical, thermal, and chemical properties via charge carrier dynamics, thermal dynamics, and chemical reaction dynamics, where a pulsed pump light impinges a perturbation to a sample, and the following dynamics are monitored via fluorescence, absorption, deformation, refractive index, etc. A patterned pump light illumination is used to apply the image recovery calculation in informatics theory to the observed images, and the phase-contrast imaging is used instead of the absorption change measurement [patternillumination time-resolved phase microscopy (PI-PM)].

Results

Conclusion