Ultrafast laser inscription of volume phase gratings with low refractive index modulation and self-images of high visibility.

Abstract

Ultrafast laser inscription of volume phase gratings with low index contrast and self-images with visibility of 0.96 is demonstrated. It is also demonstrated that phase differences of π/2 for visible light are achievable with only one layer of structures induced in bulk borosilicate glass by direct laser writing. The fabrication method avoids the stitching of several layers of structures and significantly reduces the time of process. The increment of visibility with the induced phase difference is proved and results are compared with the expected for planar phase gratings.