Intrinsic and effective third-order optical non linearities

Dottorato di ricerca in ingegneria elettronica ed informatica. 11. ciclo. A.a. 1997-98. Relatore G. P. Banfi. Coordinatore V. CantoniConsiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7, Rome; Biblioteca Nazionale Centrale - P.za Cavalleggeri, 1, Florence / CNR - Consiglio Nazionale delle RichercheSIGLEITItal

Molecular Weight Induced Order in Poly-3BCMU Spun Films

We report here on the linear and non linear optical response of some batches of the polydiacetylene poly-3BCMU with molecular weight ranging from some ten thousands to several hundred thousands. Thin films were formed by spin coating from chloroform solutions. The refractive index of the films was evaluated by m-line spectroscopy, the visible absorption spectra were recorded and the two-photon absorption spectrum was measured in the range 800-1400 nm by using femtosecond pulses at 1kHz repetion rate. the two- photon absorption coefficient was two times larger in the case of films made from polymers with higher molecular weight. The refractive index also varied by 5x10-2 at 840 nm, with larger values and increased birefringence pertaining to films made from high molecular weight polymers. The results of our experiment suggest that in poly-3BCMU films with high molecular weight a more ordered planar arrangement of the polymer chains is promoted

Two-photon absorption spectrum of 3-butoxycarbonylmethylurethane polydiacetylene thin films

We report the two-photon absorption (TPA) spectrum of a film of poly[4,6-dacadiyne-1,10-diolbis(3-butoxycarbonyl-methyl-urethane)]—commonly known as poly(3-BCMU)—in the wavelength range lambda = 1.6–0.7 µm. We find that the TPA coefficient of the film, which was prepared by spin coating, increases from [approximate] 2 cm/GW at 1.45 µm to 170 cm/GW at 0.8 µm. The main features of the spectrum can be accounted for by a three-level model with a two-photon state positioned at 2.8 e

Wavelength shifting of optical pulses in a polydiacetylene waveguide

We characterize the process of wavelength shifting (generation of a pulse at the wavelength Lambda – Delta from a signal at Lambda + Delta under the action of a pump at lambdap) in a planar waveguide of poly (3BCMU) for short. With a propagation length of 4.5 mm, pulses of 20 ps time duration, and signal wavelength around 1.3 µm, we observe wavelength conversion with 1% efficiency when the energy of the pump pulse per unit width is about 10–5 J/m

Molecular Weight Induced Order in poly-3BCMU spun films

Poly-3-butoxycarbonylmethylurethane (poly-3BCMU) spun films were formed from polymer batches with different molecular weight (from about 100,000 to 375,000 g/mol). The two-photon absorption (TPA) spectrum of poly-3BCMU films was measured in the near infrared from 800 to 1350 nm by using femtosecond pulses. Although the TPA spectrum features were the same in all investigated films, the TPA coefficient β was two times larger in the films obtained from the higher molecular weight batches. As the number of repeat units in all polymer batches was well above the saturation limit of the hyperpolarisability γ in conjugated chains, the observed behaviour can be explained with the assumption that a more ordered and planar arrangement of the polymer chains is promoted in the polymer films with higher molecular weight. This hypothesis is confirmed by the measurement of the film refractive index and birefringence

Wavelength conversion in lithium niobate by a cascaded second-order process

wavelength conversion, nonlinear optics, optical waveguide