Optical characterization of PMMA phase gratings written by a 387 nm femtosecond laser

We report on the fabrication of optical Bragg type phase gratings in polymethyl methacrylate substrates by a femptosecond Ti: Sapphire laser. As for their optical characterization, a spatially resolved microscopy interferometric technique is used to investigate the two-dimensional distribution of the refractive index change produced by the irradiation process. The technique gives a direct and quantitative two-dimensional profile of the index of refraction in irradiated PMMA, providing information on how the fabrication process depends on the laser irradiation.

Research highlights► Phase gratings written in PMMA samples by a femtosecond laser are studied. ► Two dimensional phase maps of the refractive index changes are shown. ► Interferometric techniques are used to measure the refractive index changes. ► Femtosecond laser pulses induce localized optical phase variation in PMMA samples. ► Digital holography is used to reconstruct amplitude and phase of the field.