Multiple Beam Internal Structuring of PMMA

Spatial light modulator addressed with computer generated holograms is used to diffract femtosecond laser pulses into > 15 parallel beams and focused simultaneously inside poly(methyl methacrylate) (PMMA) for high throughput 3D refractive index modification. Uniform modification throughout the structure is demonstrated and used to create a 19 m pitch, 5 5 3.5 mm 3 thick volume grating in < 50 minutes with first order Bragg diffraction efficiency > 65%. Thick volume phase gratings are created by carefully stitching filamentary modifications. PMMA shows a remarkable time dependent n, related to the photochemistry during and after exposure.