G. R. Möhlmann

Two photon absorption of di‐alkyl‐amino‐nitro‐stilbene side chain polymer

The two photon absorption spectrum has been measured in the 780–1600 nm range for a di‐alkyl‐amino‐nitro‐stilbene side‐chain polymer. A single two photon peak centered at 920 nm is observed with a peak two photon coefficient of 5.5 cm/GW. Bleaching via two photon absorption at this wavelength is investigated by measuring a refractive index change after an intensive exposure.

Comparison of quasi‐phase‐matching geometries for second‐harmonic generation in poled polymer channel waveguides at 1.5 μm

We have investigated three different quasi‐phase‐matching approaches to second‐harmonic generation (SHG) in DANS (4‐dimethylamino‐4′‐nitrostilbene) poled polymer channel waveguides at 1.5 μm. Periodic photobleaching and periodically poled electrodes deposited directly on the film produced unacceptably high propagation losses. However, periodic electrodes on the substrate gave low losses and useful SHG.

Modal dispersion phase matching over 7 mm length in overdamped polymeric channel waveguides

Phase‐matched second harmonic generation over 7 mm is demonstrated using the modal dispersion of a composite 4‐dimethylamino‐4′‐nitrostilbene/polyetherimde channel waveguide. For a 1‐mm‐long sample a record figure of merit for polymers of η=P2ω/(PωL2)=14%/W cm2 was measured at 1550 nm. This is comparable to the value reported for LiNbO3 at that wavelength. The efficiency in longer samples is limited by fundamental and harmonic waveguide losses.

Large, nonresonant, intensity dependent refractive index of 4‐dialkylamino‐4’‐nitro‐diphenyl‐polyene side chain polymers in waveguides

We report the experimental evaluation of the intensity‐dependent index of refraction of a new class of third order nonlinear materials, side chain polymers containing 4‐dialkylamino‐4’‐nitro‐stilbene and 4‐dialkylamino‐4’‐nitro‐diphenylbutadiene as side groups. The measurements, based on nonlinear grating coupling into planar waveguides with 30 ps pulses at 1.064 μm, showed large electronic nonresonant n2 Kerr coefficients.

The cubic susceptibility dispersion of Alkoxy-nitro-stilbene (MONS) and Di-alkyl-amino-nitro-stilbene (DANS) side chain substituted polymers : comparison with the two-level model

The complex cubic susceptibility dispersion of side chain polymers containing 4‐dialkylamino‐4’‐nitro‐stilbene, 4‐alkoxy‐4’‐nitro‐stilbene as their side groups has been measured in the range of 0.953 μm to 1.904 μm with third harmonic generation. A two level model is compared to the experimental data in the three‐photon‐resonance spectral region. Microscopic local field cascading was found to give an important contribution to the third order susceptibility. Nonlinear susceptibilities comparable to those of fully conjugated backbone polymers are obtained.

Third order nonlinearity of 4‐dialkylamino‐4’nitro‐stilbene waveguides at 1319 nm

The intensity dependent optical properties of 4‐dialkylamino‐4’nitro‐stilbene polymer channel waveguides were measured at 1319 nm with a pulse modulated Mach–Zehnder interferometer to be n2=0.8×10−13 cm2/W and β2<0.08 cm/GW. This material is promising for all‐optical switching at 1319 nm because it satisfies both the W and T figures of merit.

Measurement of third-order nonlinearities of side-chain-substituted polymers

Abstract Optical third harmonic generation at 1.904, 1.579 and 1.064 μm experiments have been performed on thin films fabricated from side chain polymers containing effectively 4-dialkylamino-nitro-benzene, 4-dialkylamino-4′-nitro-stilbene, 4-dialkylamino-4′-nitro-diphenylbutadiene, 4-dialkylamino-4′-nitro-diphenylhexatriene as the side groups. We have measured values of χ (3) (−3ω; ω, ω, ω) in the range of 0.54 × 10 −12 to 7.42 × 10 −12 esu, at 1.904 μm incident radiation, which are comparable to the nonresonant values found in fully conjugated back-bone polymers [1]. The values of χ (3) at both 1.904 and 1.579 μm change by a factor of 15 as the conjugation length is increased.

Quasi‐phase matched surface emitting second harmonic generation in poled polymer waveguides

Quasi‐phase matched (QPM) surface emitting second harmonic generation was demonstrated with nonlinear/linear multilayer waveguides in poled polymer based devices. The nonlinear/linear multilayer film was fabricated with a 4‐dimethylamino‐4′‐nitrostilbene (DANS) side chain polymer and a cross‐linkable clear polymer. Large efficiency improvement was observed with a combination of QPM and strong field parallel poling.

Third-Order Nonlinearities in Organic Polymers and the Role of Microscopic Cascading of Second-Order Hyperpolarizabilities

Abstract We investigate the third-order nonlinearity of DANS and DAN2 side-chain polymers by tunable third-harmonic generation and nonlinear distributed coupling. The large third-order susceptibility can be interpreted in terms of microscopic cascading of second-order hyperpolarizabilities.

Stimulated Raman scattering from H2+ ions

Abstract The observation of optical signals due to light scattering from H2+ molecular ions is reported and discussed. By focusing Q-switched 1064 nm Nd : YAG laser light in H2 at 20 bar, optical frequencies have been generated. They are assigned partly to stimulated Raman scattering from H2+ and partly from H2 molecules. The scattered radiation (Stokes-shifted 1064 nm beam) was transformed into visible light via higher-order four-wave mixing processes. The frequencies thus obtained could be observed with the naked eye if the scattered light was dispersed and projected on a white screen. The temperature of the gas in the focal region of the laser beam was estimated to be 1030 ± 300 K.