Two-Photon Excitation and Optical Spatial-Profile Reshaping via a Nonlinear Absorbing Medium

Abstract

Two-photon processes have recently received considerable attention, as they offer opportunities for both fundamental research and technological applications. In this paper, we illustrate both of these opportunities by reporting on a study of two-photon properties and discussing one specific application of a new chromophore, tris[4-(7-benzothiazol-2-yl-9,9-diethylfluoren-2-yl)phenyl]amine . This new compound exhibits a large two-photon absorptive cross section and, more importantly from the application point of view, a high photochemical/photothermal stability. The nonlinear optical properties of an AF-350 solution were studied with ∼800-nm laser pulses in both nanosecond and femtosecond regimes. The two-photon excited fluorescence spectrum and temporal behavior were compared with the corresponding results obtained for one-photon excitation. There is an ∼11-ps delay between an ultrashort pump pulse and the first peak of the two-photon induced fluorescence signal, whereas no delay was measured between the pump pulse and the first peak of the one-photon induced fluorescence. The measured effective two-photon absorption (TPA) cross section is σ 2 ) (151 ( 23) × 10 -20 cm 4 /GW for 7-ns, 810-nm laser pulses and σ 2 ) (0.61 ( 0.02) × 10 -20 cm 4 /GW for 135-fs, 796-nm laser pulses. One specific application reported here is the spatial-profile reshaping and smoothing of a focused laser field.

Enhanced Two‐Photon Absorption of Organic Chromophores: Theoretical and Experimental Assessments

“…[33,36,57] In turn, exploitation of intermolecular interactions through branching strategies and the supramolecular approaches offers even more possibilities to tune or enhance TPA properties. This has already been demonstrated for branched chromophores built from the gathering of either dipolar [108][109][110][111][112][113][114][115][116][117][118][119][120][121][122][123] or quadrupolar [97,102,[124][125][126] sub-chromophores via common conjugated core moieties and multichromophore structures in which subchromophores interact only via electrostatic interactions. [127] Alternative routes such as those based on porphyrins, [128][129][130][131][132][133][134][135][136] oligomers and polymers [103,[137][138][139] have been explored as well.…”

Synthesis, Spectroscopic and Nonlinear Optical Properties of Multiple [60]Fullerene–Oligo(p‐phenylene ethynylene) Hybrids

“…[107] On the other hand, other groups have synthesized octupolar molecules with an amide core that has been shown to allow some degree of conjugation through the center. [107,118,119] Moreover, the superiority of the g values of 12 over 14 further suggests that the degree of p delocalization plays a more crucial role than the (multi)polar symmetry in controlling the NLO behavior of the molecules synthesized here.…”

Starburst Triarylamine Donor–Acceptor–Donor Quadrupolar Derivatives Based on Cyano‐Substituted Diphenylaminestyrylbenzene: Tunable Aggregation‐Induced Emission Colors and Large Two‐Photon Absorption Cross Sections

“…[11,12] Many dyes with large 2PA were designed and synthesized. However, most of 2PA dyes are hydrophobic, and their fluorescence is often quenched on aggregation, although they may show high fluorescence efficiency in solutions, which greatly limits their applications, and especially their biophotonic applications.…”