Enhanced third harmonic generation by organic materials on high-Q plasmonic photonic crystals

The enhanced optical nonlinearity enabled by localized plasmonic fields has been well studied for all-optical switching processing (AOSP) devices for future optical communication systems. In this work, plasmonic photonic crystals with a nonlinear polycarbonate/polymethine blend cladding layer are designed to enhance the third harmonic generation (THG) at the telecom wavelengths (~1550 nm). Due to the presence of he two-dimensional (2-D) gold nano-patch arrays with improved Q-factor and high local fields, more than 20 × of enhanced THG signals in the hybrid organic-plasmonic nanostructure are experimentally observed. The enhanced THG in the hybrid organic-plasmonic materials suggested that such extraordinary nonlinear effects can be used for AOSP devices and wavelength conversion.This is the publisher’s final pdf. The published article is copyrighted by the Optical Society of America and can be found at: http://www.opticsinfobase.org/oe/home.cfm

Quasi-three-level Model Applied to Measured Spectra of Nonlinear Absorption and Refraction in Organic Molecules

Materials with a large nonlinear refractive index (2) and relatively small linear and nonlinear absorption losses, namely, two-photon absorption (2PA, of coefficient 2), have long been sought after for applications such as all-optical switching (AOS). Here we experimentally determine the linear and 2PA properties of several organic molecules, which we approximate as centrosymmetric, and use a simplified essential-state model (quasi-three-level model) to predict the dispersion of 2. We then compare these predictions with experimental measurements of 2 and find good agreement. Here “quasi”-three-level means using a single one-photon allowed intermediate state and multiple (here two) two-photon allowed states. This also allows predictions of the figure-of-merit (FOM), defined as the ratio of nonlinear refractive phase shift to the 2PA fractional loss, that determines the viability for such molecules to be used in device applications. The model predicts that the optimized wavelength range for a large FOM lies near the short wavelength linear absorption edge for cyanine-like dyes where the magnitude of 2 is quite large. However, 2PA bands lying close to the linear absorption edge in certain classes of molecules can greatly reduce this FOM. We identify two molecules having a large FOM for AOS. We note that the FOM is often defined as the ratio of real to imaginary parts of the third-order susceptibility ((3)) with multiple processes leading to both components. As explained later in this paper, such definitions require care to only include the 2PA contribution to the imaginary part of (3) in regions of transparency.Abstract © 2016 Optical Society of Americ

Nonlinear Spectra/Dispersion Of Quinolinium Dyes Using Dual-Arm Z-Scan

We report two-photon absorption spectra and nonlinear refraction dispersion of a new series of quinolinium heptamethine cyanine dyes measured using our dual-arm Z-scan and fit of spectra and dispersion with an essential-state model. © 2013 The Optical Society

Nonlinear Spectra/Dispersion Of Quinolinium Dyes Using Dual-Arm Z-Scan

We report two-photon absorption spectra and nonlinear refraction dispersion of a new series of quinolinium heptamethine cyanine dyes measured using our dual-arm Z-scan and fit of spectra and dispersion with an essential-state model. © 2013 Optical Society of America

Thermochromic Polymer Film Sensors for Detection of Incipient Thermal Damage in Carbon Fiber–Epoxy Composites

Carbon fiber–epoxy composites have become prevalent in the aerospace industry where mechanical properties and light weight are at a premium. The significant non-destructive evaluation challenges of composites require new solutions, especially in detecting early-stage, or incipient, thermal damage. The initial stages of thermal damage are chemical rather than physical, and can cause significant reduction in mechanical properties well before physical damage becomes detectable in ultrasonic testing. Thermochromic fluorescent probe molecules have the potential to sense incipient thermal damage more accurately than traditional inspection methods. We have designed a molecule which transitions from a colorless, non-fluorescent state to a colorful, highly fluorescent state when exposed to temperature–time combinations that can cause damage in composites. Moreover, this molecule can be dispersed in a polymer film and attached to composite parts as a removable sensor. This work presents an evaluation of the sensor performance of this thermochromic film in comparison to ultrasonic C-scan as a method to detect incipient thermal damage in one of the most widely used carbon fiber–epoxy composite systems. Composite samples exposed to varying thermal exposures were used to evaluate the fluorescent thermal sensor films, and the results are compared to the results of ultrasonic imaging and short-beam shear tests for interlaminar shear strength

Nonlinear Spectra/Dispersion Of Quinolinium Dyes Using Dual-Arm Z-Scan

We report two-photon absorption spectra and nonlinear refraction dispersion of a new series of quinolinium heptamethine cyanine dyes measured using our dual-arm Z-scan and fit of spectra and dispersion with an essential-state model. © 2013 Optical Society of America

Nonlinear Spectra/Dispersion Of Quinolinium Dyes Using Dual-Arm Z-Scan

We report two-photon absorption spectra and nonlinear refraction dispersion of a new series of quinolinium heptamethine cyanine dyes measured using our dual-arm Z-scan and fit of spectra and dispersion with an essential-state model. © 2013 Optical Society of America