Makoto Kaji

Two and three component photoinitiating systems based on coumarin derivatives

This study shows that several coumarin or ketocoumarin/additives combinations (bisimidazole derivative, mercaptobenzoxazole, titanocene, oxime ester) are able to initiate quite efficiently a radical polymerization reaction. The interactions between the excited states of coumarins or a ketocoumarin and various additives have also been studied by laser absorption spectroscopy, time resolved fluorescence and photoconductivity; the redox potentials of these different compounds have been measured and allowed the calculation of free enthalpy variations for a possible electron transfer reaction. The whole results explain the interaction mechanism and show that the coumarins are able to form radicals through an electron transfer reaction with the different additives whereas the ketocoumarin leads to an energy transfer with bisimidazole and to an hydrogen abstraction with the benzoxazole derivative.

Blue light emission from a laser diode pumped ring resonator with an organic second‐harmonic generation crystal of 8‐(4’‐acetylphenyl)‐1,4‐dioxa‐8‐azaspirol[4.5]decane

A laser diode pumped ring resonator was built with a new organic second‐order nonlinear optical crystal, 8‐(4’‐acetylphenyl)‐1,4‐dioxa‐8‐azaspiro[4.5] decane. Ultraprecision diamond polishing was used for the crystal and optically flat surfaces and roughnesses of less than λ/10 were achieved. The surfaces were dip coated with a perfluorinated polymer thin film to suppress surface reflection loss. Under resonant conditions, fundamental power was enhanced and a blue second‐harmonic emission with wavelength of 405.5 nm was observed.

Generation of a violet phase‐matched second‐harmonic wave with a new organic single crystal, 8‐(4’‐acetylphenyl)‐1,4‐dioxa‐8‐azaspiro[4.5] decane

A new organic nonlinear optical material, 8‐(4’‐acetylphenyl)‐1, 4‐dioxa‐8‐azaspiro[4.5]decane (APDA) was synthesized. Under collinear type I phase‐matching conditions, second‐harmonic beams in a 380–450 nm wavelength region were obtained from a Ti‐sapphire laser pumping with the single crystal. Nonlinear optical properties and sample preparation of the single crystal are reported.