53022BK02-239H Milton Roy Plane Holographic Diffraction Grating

The MKS / Richardson Gratings / Milton Roy Gratings Plane Holographic Series Diffraction Gratings have a sinusoidal groove shape, created by recording interference fringe fields in photoresist material. Since the grooves are symmetric, they do not have a preferred blaze direction. The range of useful diffraction efficiency is controlled by varying the modulation (the ratio of groove depth to groove spacing). The lower the modulation, the shorter the wavelength limit to which the grating can be used, but the peak efficiency may be lowered as well. Holographic gratings contain no periodic errors or "ghosts" as they are generated optically.

Holographic diffraction gratings have a sinusoidal surface profile generated optically by recording an interference pattern onto a photoresist-coated substrate. The photoresist is then coated with a vacuum deposited metal layer to produce a master grating, which may be used as a mold to produce replicated gratings. The final product typically consists of a substrate, a resin bonding layer, a patterned metal reflective layer, and a protective over coating. Holographic blazed gratings are generated by bombarding a holographically produced master with an angled beam of ions to etch the sinusoidal surface profile into a symmetric triangular profile. Holographic gratings are ideal for use in spectroscopy systems requiring very high resolution.

Holographic diffraction gratings can have very high diffraction efficiency, even above that of flat aluminum reflectors, at the design wavelengths and orientation. Diffraction efficiency is highly dependent on polarization state. Planar holographic gratings typically feature narrower spectral bandwidth, and have their peak efficiency at a shorter wavelength for P-polarization compared to S-polarization. For laser cavity applications this property may be used to feed back light from a specifically chosen wavelength and polarization state back into the laser gain medium to control the output of the laser. Conversely, applications such as spectrometers designed to operate using unpolarized light may require the use two gratings in conjunction with a polarizing beamsplitter to obtain optimum results.

Like their ruled counterparts, holographic gratings are most efficient when used in the Littrow configuration, or aligned so that the diffraction angle of the dominant diffraction order is coincident with the input beam, effectively behaving as a retroreflector at a specific wavelength. This geometry is especially useful for applications using a diffraction grating inside a laser cavity to select a particular wavelength. Only the exact chosen wavelength will reflect into the laser cavity. Holographic gratings are particularly useful because they have peak efficiency only at a particular polarization, allowing them to be used as a substitute for a Brewster window to control the laser output polarization.