Ultrafast response of resonant third-order optical nonlinearity of organic J-aggregates

虽然单光子共振增强了三阶光学非线性，但由于激发态的产生，它们的响应可能非常慢。此外，光学材料容易损坏。在本研究中，含有有机染料的薄膜，菁染料、方菁染料、克罗康染料、萘菁染料以及它们的类J聚集体同时表现出高的三阶光学非线性和非常快的响应。利用飞秒简并四波混频技术测量了染料分子的非线性光学性质，首先测量了染料分子的共振超极化率，得到了10^<-30>- 2 × 10^<-28>esu的数值。这些值只包含自发电子响应，不包括较慢的响应，如人口光栅。然后，我们测量了聚合物膜、溶胶-凝胶二氧化硅膜和包含这些染料和聚集体的纯膜的三阶光学非线性极化率的电子值。给出J类聚集体的薄膜、电子χ^&lt;（3）&gt;和激光波长如下：菁染料NK-2612 / PVA膜（20重量%）1.1 × 10^<-7>esu（850 nm），花青染料DTDC / PMMA膜（20wt%）2.1 × 10 <-8>^esu（850 nm），花青染料NK-3261 /纯膜1.1 × 10 ^<-7>esu（850 nm），菁染料NK-1969 /溶胶-凝胶二氧化硅膜（30wt%）2 × 10 ~ 6 <-8>esu（850 nm），硅2，3-萘二酰双（三己基硅氧）纯膜4 × 10 ~ 6 <-7>esu（800 nm）。我们研究的所有J-聚集体在共振条件下表现出非常快的光学非线性响应。

Although one-photon resonance enhances the third-order optical nonlinearity, their response could be very slow due to production of excited states. In addition, optical materials could be easily damaged.In the present study, thin films containing organic dyes, e.g., cyanine dyes, squarilium dyes, croconium dyes, naphthalocyanine dyes, and their J-like aggregates, showed high third-order optical nonlinearity and very fast response at the same time. The optical nonlinearity was measured using femtosecond degenerate four-wave mixing technique.First, we measured resonant molecular hyperpolarizabilities of dye monomers, and obtained values of 10^<-30> - 2 × 10^<-28> esu. These values contain only spontaneous electronic response and do not include slower responses such as population gratings. Then, we measured electronic values of third-order optical nonlinear susceptibility of polymer films, sol-gel silica films, and neat films including these dyes and aggregates.The thin films which gave J-like aggregates, electronic χ^<(3)>, and laser wavelength were as follows : Cyanine dye NK-2612 / PVA film (20 wt%) 1.1 × 10^<-7> esu (850 nm), cyanine dye DTDC / PMMA film (20wt%) 2.1 × 10^<-8> esu (850 nm), cyanine dye NK-3261 / neat film 1.1 × 10^<-7> esu (850 nm), cyanine dye NK-1969 / sol-gel silica film (30 wt%) 2 × 10^<-8> esu (850 nm), Silicon 2, 3-naphthalocyanine bis(trihexylsilyloxide) neat films 4 × 10^<-7> esu (800 nm). All J-aggregates we studied show very fast optical nonlinear response under resonant conditions.