Type IV, Aberration Corrected Gratings

Type IV aberration-corrected gratings are typically recorded using two point sources. As a consequence, the grating grooves are no longer straight and parallel, but instead correspond to confocal hyperboloids or ellipsoids. Optimizing the position, angles and arm lengths of the two sources provides the optical designer with the degrees of freedom necessary to minimize aberrations, typically astigmatism and coma. Auxiliary optics such as gratings provide the optical designer with additional flexibility for recording more specific goove patterns and distributions (see US patent 4842353 "Diffraction apparatus with correcting grating and method of making," A.Thevenon et al., for a description of our methods).

Type IV aberration-corrected gratings have become the dispersive element of choice in many spectroscopic systems, as they require no other optics in the instrument for imaging or focusing. These gratings are used in various configurations, including monochromator, spectrograph and monograph (scanning spectrograph) systems.

Type IV, Aberration Corrected Gratings

Using this technology, HORIBA Jobin Yvon has designed several new grating types for specific applications: Type IV, Aberration Corrected, Flat Field and Imaging Gratings: These concave gratings disperse, collimate and refocus light from the entrance slit onto a plane surface; these gratings are well-suited to take advantage of solid-state detectors with either a linear or 2D array of independent photosensitive elements.

Type IV, Aberration Corrected, Monochromator Gratings: these concave gratings are specifically designed for use with an entrance slit and an exit slit. Wavelength scanning is performed by a simple rotation of the grating.

Variable Line Spacing Gratings (VLS gratings) for Vacuum UV applications: Gratings and mirrors used in the far vacuum UV and soft X-ray regimes must be operated in grazing incidence, to enhance the reflectivity of the coatings. The considerable astigmatism of traditional Type I concave gratings at grazing incidence results in low signal throughput at the instrument exit slit. To correct astigmatism and coma in this difficult case, HORIBA Jobin Yvon has developed specific aberration corrected plano and concave holographic gratings, which present a variation of the groove density according to a specified polynomial law (VLS gratings).

HORIBA Jobin Yvon optical engineers will recommend a standard Type IV aberration-corrected grating or will custom-design a specific aberration-corrected grating to maximize performance for a given application.