Nonlinear absorption and nonlinear refraction: maximizing the merit factors

Abstract

Both nonlinear absorption and nonlinear refraction are effects that are potentially useful for a plethora of applications in photonics, nanophotonics and biophotonics. Despite substantial attention given to these phenomena by researchers studying the merits of disparate systems such as organic materials, hybrid materials, metal-containing molecules and nanostructures, it is virtually impossible to compare the results obtained on different materials when varying parameters of the light beams and different techniques are employed. We have attempted to address the problem by studying the properties of various systems in a systematic way, within a wide range of wavelengths, and including the regions of onephoton, two-photon and three-photon absorption.The objects of our studies have been typical nonlinear chromophores, such as π-conjugated molecules, oligomers and polymers, organometallics and coordination complexes containing transition metals, organometallic dendrimers, small metal-containing clusters, and nanoparticles of various kinds, including semiconductor quantum dots, plasmonic particles and rare-earth doped nanocrystals. We discuss herein procedures to quantify the nonlinear response of all of these systems, by defining and comparing the merit factors relevant for various applications.

Third-Order Nonlinear Optical Properties of Infrared Emitting PbS and PbSe Quantum Dots

“…The measurements of NLO absorption, with the use of the Z-scan technique, should be performed using low repetition rate, short laser pulses excitation (most preferable are kilohertz, femtosecond excitation sources) in order to minimize the unwanted contribution from thermal effects or excited state absorption. 44 While performing the measurements in the wavelength region of non-negligible linear absorption, the effect of saturable absorption should also be taken into account. On the other hand, the calculation of n 2 values should account for the contributions from solvent and cuvette cells to obtain the values characterizing the pure material.…”

“…It should be emphasized that the values of NLO parameters, for any types of materials, are highly wavelength-dependent. The measurements of NLO absorption, with the use of the Z -scan technique, should be performed using low repetition rate, short laser pulses excitation (most preferable are kilohertz, femtosecond excitation sources) in order to minimize the unwanted contribution from thermal effects or excited state absorption . While performing the measurements in the wavelength region of non-negligible linear absorption, the effect of saturable absorption should also be taken into account.…”

One‐Photon and Two‐Photon Photophysical Properties of Tetrafunctionalized 5,10,15,20‐tetrakis(m‐hydroxyphenyl)chlorin (Temoporfin) Derivatives as Potential Two‐Photon‐Induced Photodynamic Therapy Agents

“…where I is the integrated emission intensity, C is the molar concentration, φ is the OPE fluorescence quantum yield, and n is the refractive index of solvent ( sam refers to sample and ref to reference) [62,63,64] . The normalized σ 2 values were estimated, following Equation (5), where M denotes the molecular weight of the compounds. …”

Nonlinear Optical Pigments. Two-Photon Absorption in Crosslinked Conjugated Polymers and Prospects for Remote Nonlinear Optical Thermometry

“…In a similar manner as we did in the analysis of TPEF results of Mod1 and Mod2 (Section 2.1), we have performed a normalization procedure of the 2PA cross sections of investigated polymers and model compounds by calculating molar mass-normalized 'σ 2 /M' merit factors (Table 1) [59,61]. A comparison of these values reveals that Pol1 and Pol2 feature σ 2 /M values of 1.42 and 1.67, whereas for model compounds Mod1 and Mod2 those parameters take values of 0.56 and 1.10, respectively.…”