Picosecond Optical Nonlinearity Research Articles

Picosecond optical nonlinearities in symmetrical and unsymmetrical phthalocyanines studied using the Z-scan technique

We present our experimental results on the picosecond nonlinear optical (NLO) studies of symmetrical and unsymmetrical phthalocyanines, examined using the Z-scan technique. Both the open-aperture and closed-aperture Z-scan curves for three samples were recorded and the nonlinear coefficients were extracted from the theoretical fits. The nonlinear absorption/refraction contribution from the solvent was also identified. The observed open aperture behaviour for these molecules is understood in terms of the absorption coefficients of these molecules near 800 nm and the peak intensities used. It is established that these phthalocyanines exhibit large optical nonlinearities and, hence, are suitable for optical limiting applications.

The excited-state absorption and third-order optical nonlinearity from 1-dodecanethiol protected gold nanoparticles: Application for optical limiting

Few studies have been carried out on near-IR picosecond optical nonlinearity and excited-state absorption of stable gold nanoparticles. In this article, the near-IR picosecond optical nonlinearity from 1-dodecanethiol protected gold nanoparticles (Nano-1) was investigated by using Z-scan technique. The incident laser is a Q-switched/mode-locked Nd:YAG pulses laser with a duration of 35 ps at 1064 nm. The experimental results indicate that Nano-1 solution in tetrahydrofuran (THF) shows high excited-state absorption and a negative third-order refraction index. Due to this high excited-state absorption, a highly effective optical limiting behavior was observed for Nano-1 in THF solution in solution with a low optical limiting threshold.

Investigation of picosecond optical nonlinearity in porphyrin metal complexes derivatives

Porphyrin metal complex derivatives were experimentally studied using the Z-scan technique and the optical Kerr gate method with picosecond pulses at 532 nm. The sign and magnitude of the nonlinear refraction and nonlinear absorption were determined for a negatively charged meso-tetrakis( p-sulfonatophenyl)porphyrin (TPPS 4) and a positively charged meso-tetrakis(4- N-methyl-pyridiniumyl)porphyrin (TMPyP) in their free-base forms and their Fe(III) and Mn(III) complexes. The results were phenomenologically understood and the origin of the nonlinearity was inferred.

Time-resolved picosecond optical nonlinearity and all-optical Kerr gate in poly (3-hexadecylthiophene)

A time-resolved anisotropic configuration exploiting the Z-scan technique in a one color pump-and-probe arrangement was implemented to measure the time response and the value of the nondiagonal component of the third-order nonlinear susceptibility of a chloroform solution of poly (3-hexadecylthiophene). In addition, an all-optical Kerr gate with picosecond response using the polymeric solution was implemented.

Ultrafast recombination processes in lead chalcogenide semiconductors studied via picosecond optical nonlinearities

Picosecond recombination processes of photoexcited electron-hole plasma in lead chalcogenides are directly monitored via time-resolved pump-probe experiments at wavelengths from 3 to 10 mu m. Bleaching of the interband absorption due to band filling gives rise to a large change in the refractive index. The time-resolved change of absorption of PbSe at T=70 K reveals a rapid recombination within 100 ps for excitation densities above 7*1017 cm-3. Comparative measurements of mid-infrared luminescence spectra demonstrate that this behaviour is due to recombination by stimulated emission. At T=300 K, Auger recombination on a time scale of 2 ns is observed below the threshold of stimulated emission. The analysis of the time-resolved data gives an Auger coefficient of 1.1+or-0.3*10-28 cm6 s-1 for a carrier density of 3*1018 cm-3.

Picosecond optical nonlinearities in a strained InAs/GaAs hetero n-i-p-i structure

The nonlinear optical properties of a n-i-p-i structure containing strained superlattice quantum wells in the intrinsic regions are studied using picosecond pump and probe pulses of the same photon energy. For pump fluences as low as 1.1 μJ/cm2, a blue shift of the excitonic resonance, caused by the screening of the built-in space-charge field and the accompanying reduction in the quantum-confined Stark effect, is clearly observed. At higher fluences, the onset of bleaching of the excitonic absorption is observed. The nonlinearities associated with the quantum confined Stark effect in the hetero n-i-p-i are directly compared to those arising from excitonic bleaching in identical strained superlattice quantum wells under flatband conditions. The picosecond time resolution allows a more accurate estimation of the carrier density in the hetero n-i-p-i by ignoring the density-dependent recombination and a quantitative comparison between the strength of the nonlinearities in the two structures. Although such comparisons depend on the optical fluence and structure of the hetero n-i-p-i, we find that the magnitudes of the nonlinearities in these two specific structures are comparable on a per carrier basis, although their spectral signatures are quite distinct.

Picosecond optical nonlinearities in lead chalcogenide semiconductors

Optical nonlinearities of PbSe are studied in picosecond pump-probe experiments at wavelengths from 4 to 8 μm. Excitation of an electron-hole plasma leads to a shift of the absorption edge to higher energies and to large changes of the refractive index by up to −0.1 for a carrier density of 4×1017 cm−3. The optical nonlinearities result from band filling by both electrons and holes. The time-dependent absorption change shows a partial recovery within 100 ps, giving evidence of enhanced recombination rates. Theoretical calculations of the absorption change are in agreement with the experimental data.

Picosecond Optical Nonlinearities and Stimulated Emission in Indirect AlxGa1−xAs

AbstractThe nonlinear optical properties of indirect‐gap AlxGa1−xAs in the presence of a dense electron‐hole plasma are studied by picosecond luminescence and transient transmission spectroscopy. The fundamental X‐band gap is found to be renormalized by exchange and correlation effects within the plasma. Higher‐lying band gaps in the same sample are also renormalized but here the electron‐exchange contribution to the narrowing is negligible. Strong plasma‐induced nonlinearities like persistent bleaching of absorption, enhanced absorption, and large changes of the refractive index are observed at the direct absorption edge for lattice temperatures of 15 as well as 293 K. Stimulated emission from the indirect X‐band is made possible by alloy‐disorder induced band mixing.

Semiconductor-doped fibre waveguides exhibiting picosecond optical nonlinearity

Multicomponent-glass-based optical fibre has been fabricated having a core region doped with semiconductor crystallites. The fibre is shown to exhibit optical nonlinearity with picosecond response times.

Time-resolved picosecond optical nonlinearity in semiconductor-doped glass

Time-resolved measurements of the optical nonlinearity in a semiconductor-doped glass reveal an unsaturated 15 Ps FWHM impulse response with a peak-to-background contrast of more than 10.