Phase Masks are traditionally surface relief gratings etched in fused silica for use in the ultra-violet range (193nm to ~ 400nm). Because of etching limitations during fabrication, the ratio of grating period divided by the illuminating light wavelength is limited to values greater than 1.

For Phase Mask applications that require illuminating light wavelength greater than 400nm and small grating periods, a situation which yields an aspect ratio lower than 1, Ondax volume holographic grating (VHG) Phase Masks provide a solution.

Ondax Phase Masks are based on volume Bragg diffraction as the figure on the left illustrates. With these Phase Masks, there is only one diffraction order and the aspect ratio can be much lower than 1. The angle of diffraction Θ is related to the period Λ of the grating and the illumination wavelength λ by the mathematical relation: 2*Λ*sinΘ=λ

The volume holographic grating is contained throughout the material thickness. The material is a silicate glass optimized to work with low loss and scatter above 400nm.

The VHG Phase Masks essentially serve as a precision beam splitter that divides an incident monochromatic beam into two outgoing beams. The illumination needs to be collimated, narrow band and incident on the VHG at the Bragg angle. By generating two outgoing beams, a Phase Mask creates an interference pattern (see figure left). This pattern is located in the space where the outgoing beams overlap. These Phase Masks are manufactured holographically and thus have no stitching errors.

The period of the VHG Phase Masks range from a few hundred nanometers to several micrometers. The grating areas come in a wide variety of dimensions, ranging from a few millimeters square to 20mm x 20mm. Custom wavelengths and efficiencies available in 4-6 weeks.

Call 626.357.9600 or e-mail requests at sales@ondax.com