Enhancement Of Nonlinear Absorption Research Articles

Nano-Dispersed Organic Liquid and Liquid Crystals for All-Time-Scales Optical Switching and Tunable Negative-and Zero- Index Materials

We present an overview of recent results obtained in nano-dispersed nonlinear neat organic liquids and liquid crystals. Experimental observations confirm the enhancement of nonlinear absorption in gold nano-spheres doped neat nonlinear liquids and extension of the bandwidth of efficient all-optical switching operation for visible-near infrared lasers in time scales ranging from sub-picoseconds through nanoseconds and microseconds and longer. Similar nano-particulate doped liquid crystal films also exhibit efficient all-optical switching capabilities for microseconds – cw lasers. Meta-materials fabricated with core-shell nano-spheres dispersed nematic liquid crystals show effective refractive indices that are tunable from negative through zero to positive values.

Nonlinear Absorption and Nonlinear Refraction of Self-Assembled Porphyrins

Nonlinear refraction and nonlinear absorption of self-assembled porphyrins in the nanosecond and picosecond regimes were studied at 532 nm by the Z-scan technique. First, a marked difference in nonlinear refraction was observed between self-assembled zinc porphyrins and free base porphyrins; however, the effects of self-assembly and metallization on nonlinear absorption are small. Second, an enhancement of nonlinear absorption was observed for the monomeric components of self-assembled structures by adding pyridine, while their nonlinear refractions remained almost unchanged as pyridine was added. It is expected that the metallization and addition of ligand can provide more convenient routes to alter the optical nonlinearities of porphyrins than the modifications of molecular structures of traditional covalent-bond organic materials.

Measurement of third order susceptibility by nonresonant nondegenerate four wave mixing in polymer embedded cadmium sulfide quantum dot systems

Abstract We report clear evidence of third order nonlinearity χ(3) in polymer embedded cadmium sulfide quantum dot system as a result of nonresonant nondegenerate four frequency mixing. We notice thickness dependent enhancement of nonlinear absorption with increase in incident intensity of light. Two pump beams (λ = 1064 nm) were oppositely directed into the sample and to receive phase conjugated signal, a probe beam was focused at the point of intersection on the sample. In the conditions satisfying self diffraction phenomena, we have measured change in refractive index as a function of incident power. We have observed very high value of third order susceptibility (χ(3) ∼ 10−7 e.s.u.) and predict figure of merit as high as ∼1.9 for the thinnest quantum dot sample (0.54 μm). Nonlinear susceptibility drops by nearly 10 times for the thickest sample (1.211 μm) due to considerable suppression in nonlinear absorption.

Observation of huge nonlinear absorption enhancement near exciton resonance in GaN

Huge excitonic enhancement of two-photon absorption near the exciton-transition energy was observed in the GaN system. The peak value of the nonlinear absorption coefficient is at least 1500 cm/GW, corresponding to an enhancement factor of >100. The room temperature exciton dephasing time is also obtained based on a spectral analysis to be ∼150 fs in bulk GaN, which is close to the exciton ionization time.

Third-order nonlinearity and optical limiting studies in phosphorus (V) porphyrins with charge transfer states

Enhancement in the third-order nonlinearity v ð3Þ , nonlinear absorption and optical limiting threshold with the introduction of charge transfer (CT) states are observed in a new class of azoarene phosphorus (V) porphyrins. Introduction of axial azoarene groups into the phosphorus porphyrin structure led to a rise in the measured hci values. Faster intersystem crossing from CT states to triplet and excited state absorption from the triplet states contribute to the enhancement of nonlinear absorption thereby reducing the optical limiting threshold by a factor of 2. 2002 Elsevier Science B.V. All rights reserved.

Nonlinear refraction and absorption in hetero- thiometallic planar clusters

The nonlinear absorption and refraction of the clusters [MoS4Cu4Br2(py)6] and [Et4N]2[MoS4Cu4(SCN)4(2-pic)4] have been investigated using the z-scan technique with a ns laser at 532 nm wavelength. They have the same planar ‘open’ structures and the same skeleton metal atoms; the only difference is that the former has halogen ligands while the latter possesses pseudo-halogen groups – SCN – as ligands. Alteration of nonlinear refractive index and enhancement of nonlinear absorption were found in these two clusters. A steady state model of excited state nonlinear refraction was proposed to explain this phenomenon.