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New organic molecular crystals with large quadratic nonlinearities
Journal of Crystal Growth 79 (1986) 681 North-Holland, Amsterdam
681
N E W ORGANIC M O L E C U L A R CRYSTALS WITH LARGE Q U A D R A T I C N O N L I N E A R I T I E S *
J. ZYSS Laboratoire de Bagneux (LA CNRS 250), Centre National d'Etudes des T~lOcomrnunications, 196 Avenue Henri Ravera, F-92220 Bagneux, France
The search f o r new materials with large quadratic nonlinearities is mainly oriented towards applications in optical telecommunications or optical signal processing involving the generation of new frequencies, signal amplification, emission or oscillation, electro-optic modulation, etc. Organic molecular crystals exhibiting efficiencies at least one order of magnitude higher than those of LiNbO 3, have been developed using well-established molecular engineering principles. Moreover, their transparencies, ranging from the visible to the near-infrared, are well-adapted to the emission wavelengths of semiconductor lasers developed for optical fiber telecommunications systems. Three new molecular crystals possessing highly polarizable electron systems by interaction with electron-donor and -acceptor substituents have quasi-optimal crystalline structures: N-(4nitrophenyl)(L)-profinol (NPP), nitro-4-phenyl-N(methyl-cyanomethyl)-amine ( N P A N ) and 3methyl-4-nitropyrinidine-l-oxide (POM). These crystals being respectively monoclinic (P2l) and orthorhombic (Fdd 2 and P212121) are under investigation both in bulk and waveguide forms. In the case of NPP it is possible to achieve a type-I
non-critical phase-matching at ~ = 1.15 /~m involving the nonlinear coefficient d21 = 200 × 1 0 - 9 e.s.u., the highest value of a phase-matchable coefficient measured so far. This measurement was achieved by using a single crystalline NPP layer. Moreover, amplification and parametric emissions for 100 fs pumping at ~ = 6 2 0 nm have been demonstrated ** Similar experiments have been performed on POM in the picosecond range. By using a modified Bridgman-Stockbarger method, some 2-3 cm long N P A N single crystal cored fibres have been obtained [1]. Femtosecond infrared pulse propagation is being performed so as to help characterize eigenmodes energy distribution and possible phase-matching wavelength. The crystal orientation with respect to the waveguide axis permits the observation of nonlinear waveguiding effects. Some new ways of organizing noncentrosymmetric organic structures exhibiting statistical polar order, such as Langmuir-Blodgett films, are under current investigation.
* This work is partially supported by the ESPRIT Project No. 443 (Molecular Engineering for Optoelectronics).
** In collaboration with the "Laboratoire d'Optique Appliqu6e", ENSTA, Palaiseau, France.
References
[1] P. Vadakovic, to be published.
0022-0248/86/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
681
N E W ORGANIC M O L E C U L A R CRYSTALS WITH LARGE Q U A D R A T I C N O N L I N E A R I T I E S *
J. ZYSS Laboratoire de Bagneux (LA CNRS 250), Centre National d'Etudes des T~lOcomrnunications, 196 Avenue Henri Ravera, F-92220 Bagneux, France
The search f o r new materials with large quadratic nonlinearities is mainly oriented towards applications in optical telecommunications or optical signal processing involving the generation of new frequencies, signal amplification, emission or oscillation, electro-optic modulation, etc. Organic molecular crystals exhibiting efficiencies at least one order of magnitude higher than those of LiNbO 3, have been developed using well-established molecular engineering principles. Moreover, their transparencies, ranging from the visible to the near-infrared, are well-adapted to the emission wavelengths of semiconductor lasers developed for optical fiber telecommunications systems. Three new molecular crystals possessing highly polarizable electron systems by interaction with electron-donor and -acceptor substituents have quasi-optimal crystalline structures: N-(4nitrophenyl)(L)-profinol (NPP), nitro-4-phenyl-N(methyl-cyanomethyl)-amine ( N P A N ) and 3methyl-4-nitropyrinidine-l-oxide (POM). These crystals being respectively monoclinic (P2l) and orthorhombic (Fdd 2 and P212121) are under investigation both in bulk and waveguide forms. In the case of NPP it is possible to achieve a type-I
non-critical phase-matching at ~ = 1.15 /~m involving the nonlinear coefficient d21 = 200 × 1 0 - 9 e.s.u., the highest value of a phase-matchable coefficient measured so far. This measurement was achieved by using a single crystalline NPP layer. Moreover, amplification and parametric emissions for 100 fs pumping at ~ = 6 2 0 nm have been demonstrated ** Similar experiments have been performed on POM in the picosecond range. By using a modified Bridgman-Stockbarger method, some 2-3 cm long N P A N single crystal cored fibres have been obtained [1]. Femtosecond infrared pulse propagation is being performed so as to help characterize eigenmodes energy distribution and possible phase-matching wavelength. The crystal orientation with respect to the waveguide axis permits the observation of nonlinear waveguiding effects. Some new ways of organizing noncentrosymmetric organic structures exhibiting statistical polar order, such as Langmuir-Blodgett films, are under current investigation.
* This work is partially supported by the ESPRIT Project No. 443 (Molecular Engineering for Optoelectronics).
** In collaboration with the "Laboratoire d'Optique Appliqu6e", ENSTA, Palaiseau, France.
References
[1] P. Vadakovic, to be published.
0022-0248/86/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)