How to assess good candidate molecules for self-activated optical power limiting

Abstract

Abstract. Reverse saturable absorbers have shown great potential to attenuate laser radiation. Good candidate molecules and various particles have successfully been incorporated into different glass matrices, enabling the creation of self-activated filters against damaging laser radiation. Although the performance of such filters has been impressive, work is still ongoing to improve the performance in a wider range of wavelengths and pulse widths. The purpose of this tutorial is, from an optical engineering perspective, to give an understanding of the strengths and weaknesses of this class of smart materials, how relevant photophysical parameters are measured and influence system performance and comment on the pitfalls in experimental evaluation of materials. A numerical population model in combination with simple physical formulas is used to demonstrate system behavior from a performance standpoint. Geometrical reasoning shows the advantage of reverse saturable absorption over nonlinear scattering due to a fraction of scattered light being recollected by imaging system optics. The numerical population model illustrates the importance of the optical power limiting performance during the leading edge of a nanosecond pulse, which is most strongly influenced by changes in the two-photon absorption cross section and the triplet linear absorption cross section for a modeled Pt-acetylide. This tutorial not only targets optical engineers evaluating reverse saturable absorbing materials but also aims to assist researchers with a chemistry background working on optical power limiting materials. We also present photophysical data for a series of coumarins that can be useful for the determination of quantum yields and two-photon cross sections and show examples of characterization of molecules with excited triplet states.

Nonlinear materials for optical power limiting : characterization and modelling

“…This thesis is in large parts based on my licentiate thesis [1], in particular chapter 1 and 4. Chapter 2 & 3 are a summary of article 4 [16], while also reusing parts of the licentiate thesis. Chapter 4 is more than a summary of the first three articles since it also ties them together into a larger picture [17][18][19].…”

“…where σ is the fraction of light scattered and η a factor (possibly more than 1) representing deviations from spherical scattering [16]. The difficulty of removing scattered light from the beam-path has been known in the research field [34].…”

“…In this chapter numerical population models are described in a more verbose manner than was possible in the tutorial article [16]. Population modelling is widely used to model the photophysical dynamics of chromophores [10,11,13,31,40,84].…”

“…Initially, it was used to qualitatively test the hypothesis of 2PA field enhancement being the cause of OPL enhancement at 600 nm for PE2-CH 2 OH [18,19]. In the tutorial article it was further developed to investigate the impact on OPL performance of varying different photophysical parameters [16]. It is also possible to use a point model to check the validity of 2PA measurements by the Z-scan method [10].…”

“…Bulk glasses are preferable for practical optical power limiting devices [2,16,22]. Thin films are susceptible to surface damage [23] and misalignment of the beam waist [24]; suspensions to agglomeration or precipitation [24] and solutions to breakdown products fouling the cuvette surfaces [25].…”