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.