ANTIREFLECTION COATING WITH FLUOROPOLYMER FOR A NOVEL ORGANIC NONLINEAR-OPTICAL CRYSTAL - 8-(4'-ACETYLPHENYL)-1,4-DIOXA-8-AZASPIRO [4.5]DECANE (ADPA)

Prior to the frequency doubling of a laser diode through a ring resona tor, reflection loss on the surface of a novel organic second-order no nlinear optical crystal, -(4'-acetylphenyl)-1,4-dioxa-8-azaspiro[4.5]d ecane (APDA), was decreased. An optically flat crystal surface with a flatness of lambda/10 (lambda = 633 nm) and surface roughness of 1.5 n m rms was obtained when an ultraprecision diamond turning lathe was us ed to machine the crystal surface. After this surface was coated antir eflectively with an amorphous fluorinated polymer, Teflon AF-2400, the transmittance at 810 nm was increased to 98%. A laser-diode-pumped ri ng resonator was built with this crystal, and a blue second-harmonic e mission at 405.5 nm was successfully generated.