Two-photon polymerization of gratings by interference of a femtosecond laser pulse

Two-photon polymerization, initiated by 2,7-bis[[4-(dimethylamino)-phenyl] methylene]-cycloheptanone and 1,1′,2,2′-bis(o-chlorophenyl)-4,4′,5,5′-tetraphenyl-bisimidazole, was employed to fabricate refractive index-modulated holographic gratings by the interference of a femtosecond laser pulse at wavelength of 810 nm. The diffraction efficiency of the grating was up to 57% and the refractive index modulation reached 4.3×10−3 after thermal fixation with the film thickness of 40 μm. And dependence of the diffraction efficiency and refractive modulation on laser pulse energy was also investigated.