Guglielmo Lanzani

Transient absorption three-beam pump-push-probe experiments demonstrate that cyclodextrin-encapsulation of conjugated polymer chains prevents interchain effects, such as energy migration and charge hopping. In the unencapsulated polymer, transient population of high-lying singlet states leads to interchain ionization, generating long-lived charge-separated species. Supramolecular encapsulation prevents this process; with high-lying singlets undergoing on-chain ionization, followed by very rapid charge recombination. Threading is an efficient way to control charge recombination and to obtain a material suitable for photonic applications, where the push effect can be implemented for all-optical ultrafast switching.

In this work modulation of laser emission from polymer nano-structured lasers was explored through three different optical techniques. We show all optical control of polymer distributed feedback lasers based on polyfluorenes (PFO and F8BT) by applying a gating pulse, which completely switch-off emission in the sub-ps time scale. The switching mechanism is assigned to photo-injection of charge carriers induced by the gate transition. This is a resonant non-linear process, that might work at high bit-rate, paving the way toward plastic, large-scale integrated, ultrafast optical logic. New opportunities may also be offered by two other techniques: Two-photon two-color pumping allows lasing action only in presence of two different pulses, one in the visible and one in the IR, resonant with the second telecommunication window. This may allow to convert telecommunication signal from a fiber to visible range and thus to Plastic Optical Fibers for organic photonics. Another technique we explored uses a blend of F8BT and a photochromic material, (1,2-bis-(5-phenyl-2-methyl-3-tienyl) perfluocyclopentene))(C4). With a UV pulse we are able to change C4 structure, thus overlapping its absorption spectrum with F8BT emission and modulating yellow ASE emission.

In principle, an artificial retina should mimic as much as possible the spectral sensitivities of the real retina. For technological reasons, building such an artificial device can lead to spectral approximations in comparison with the real sensitivities. To understand if possible discrepancies can determine big differences in the final perception, the whole visual system should be taken into consideration, not only the retinal input signal difference. This paper aims at investigate how retinal sensitivity differences should affect the final perception. However, answering to this question is a very complex problem related to the whole visual system, that we do not want to extensively address in this paper. We only want to investigate the relationship between the spatial aspects of color perception and the spectral differences among cone sensitivities. Moreover, a personal interdifference has been observed in cone spatial distribution between human subjects, without any corresponding significant difference in final color sensation. It is likely that spatial compensation, performed by human observers, strongly decreases this subjectivity in color signal. We aim at address if a similar principle should be considered in artificial vision. In this paper we analyze the interdifference among integrated values obtained using different organic-based artificial sensors with different spectral sensitivities. Experiments show a significant decrease of the effect of spectral sensitivity sensor differences when a spatial color correction is applied.

The authors realize three photodiodes based on organic materials, which have photoresponse curves matched to the colorimetric functions of the standard observer. Such a system of detectors is used for realizing a three-stimuli colorimeter. They report the result of measurements in different spectral areas and suggest possible application of the device in color science and artificial vision.