Nonlinear Absorption Measurements of Aza-Borondipyrromethene Dyes by the Z-Scan Method

We studied the effects of bromine substitution on the nonlinear absorption properties of aza-dipyrromethene dyes. Nonlinear absorption is measured at wavelengths of 1200, 1500, and 1700nm At 1200nm, excited-state absorption due to two-photon excitation appears, and it is more pronounced in the brominated polymethine cyanine.

I. Introduction

Organic molecules have been widely studied for nonlinear optical applications such as optical limiting and all-optical switching. An ideal optical limiter should have high transmission for low irradiance light and low transmission for high irradiance. This effect can be implemented utilizing mechanisms such as nonlinear absorption (NLA), including two-photon absorption (2PA), reverse saturable absorption, nonlinear refraction, and nonlinear scattering [1]. Azadipyrromethenes dyes’ (Aza-BODIPY) potential for optical power limiting (OPL) in the near infrared region has been reported [2], and their excellent chemical and physical stability enabled the use of this class of dyes for the first solid-state devices for OPL in this spectral range [3]. The OPL mechanism of Aza-BODIPY is triggered by 2PA but its efficiency strongly relies on the spectral overlap between 2PA and excited-state absorption (ESA). We designed two new molecules and their halogenated counterparts to explore the 2PA/ESA overlap.