Spherical Holographic Gratings Research Articles

High-dispersion spherical holographic gratings in a modified Rowland mounting

For holographic gratings requiring an extreme dispersion, I consider a modified Rowland mounting, in which the recording laser sources are moved away from the grating, to reduce the uncorrected higher-order aberrations. In addition, I choose the geometric parameters such that first-type coma is corrected. Then a plane multimode deformable mirror (MDM) or two auxiliary spherical holographic gratings (R3 device) are used to aberrate the grating's recording sources; correction up to the fourth order is sufficient to obtain high image quality. Applied to the FUSE-Lyman (FUSE is Far Ultraviolet Spectroscopic Explorer) grating, with a groove density as high as 5767 grooves/mm, these recording devices produce a resolution (chromatic resolving power) as great as 611,000 with the MDM and 3,030,000 with the R3 device. These results far exceed the specified performance of 30,000. Since diffraction limits the resolution to 482,000, the images are diffraction limited with both devices.

Recording high-dispersion spherical holographic gratings in a modified Rowland mounting by use of a multimode deformable mirror

To reduce the uncorrected higher-order aberrations for holographic gratings requiring an extreme dispersion, we have modified the Rowland mounting by moving the recording laser sources away from the grating. Then, with a multimode deformable plane mirror to record the grating, the correction of all the aberrations up to the fourth order inclusive is found sufficient to obtain a high-quality image. Applied to the FUSE-LYMAN grating, with a groove density of as much as 5740 grooves/mm, for which a resolution of 30,000 was required, this new recording device produces a resolution from 139,000 to 222,000 over the spectral range.

Theory of spherical holographic gratings recorded by use of a multimode deformable mirror

We present the theory of spherical holographic gratings recorded by use of a deformable plane mirror and consider its application to the optimized Rowland Mounting. We illustrate the efficiency of such a mounting by computing two high-resolution gratings (3800 grooves/mm) with f/24 and f/10 apertures.

Holographic gratings for the Far Ultraviolet Spectroscopic Explorer: development, imaging, and efficiency tests of two prototypes

We report on a study and test of two 6000-groove/mm prototype holographic gratings for NASA's FarUltraviolet Spectroscopic Explorer (FUSE) mission. The first grating was designed and developed onthe basis of the FUSE requirements as specified at the end of the first study in 1992. This design relieson an ellipsoidal grating, recorded with aberrated wave fronts to correct sagittal coma. The secondgrating corresponds to the new design adopted after the complete mission was restructured in1993. With this solution a new family of spherical holographic gratings recorded with stigmaticsources was permitted to increase the aperture size while simplifying the figuring and recording of theblank. The design, fabrication, and testing of each prototype are described, and we show that thechallenging requirement of a 30,000 resolving power at 1000 Å, with a 25% groove efficiency, is reached.

Comparison of grating designs for the Lyman Far-Ultraviolet Spectroscopic Explorer spectrograph

Various grating designs have been proposed by several investigators for possible use with the Lyman/Far-Ultraviolet Spectroscopic Explorer mission. The image quality, the feasibility, and the efficiency of five designs are compared, each using a distinct type of grating: (1) a grating ruled on a deformed ellipsoidal or toroidal blank, (2) an ellipsoidal grating recorded holographically with two auxiliary spherical mirrors, (3) a spherical holographic grating recorded with two auxiliary spherical holographic gratings, (4) a spherical ruled grating with variable spacing and straight grooves, and (5) a spherical ruled grating with a groove pattern that is determined theoretically (hybrid grating). From a purely theoretical viewpoint, grating (5) provides the finest images, followed by gratings, (3), (1), (4), and (2). In view of the current technological limitations, the order of practical importance is gratings (4), (1), (2), (3), and (5).

Practical VUV stigmatic configurations for spherical holographic gratings

Stigmatic configurations for spherical holographic gratings are generally explained by the properties of the harmonic conjugate points; this global approach, however, does not explain how the various aberrations generated by the blank are cancelled by the hologram. In this paper, light path function analysis is used to explain this balancing effect and to derive practical VUV configurations.

Rigorous and approximated stigmatism for gratings ruled on quadrics

Many classical configurations lead to perfect stigmatism with spherical holographic gratings. Stigmatism is also reached by using quadrics. The author presents the properties of a first set of stigmatic quadrics, which work in Wadsworth mounting, and give those of a second set, suitable for Wadsworth and Rowland mountings.

Stigmatic properties of spherical holographic gratings

In a recent paper (ibid., vol.14, p.235, 1983) the author described some new stigmatic properties of spherical holographic gratings. This paper describes some specific diffraction limited configurations, as well as spectrometers for line profile measurements.

New holographic grating devices for hot plasma diagnostics. I. Stigmatic properties of spherical holographic grating

In laser induced confinement fusion or in ion driven fusion the understanding of the physical process taking place in the plasma atmosphere surrounding the target is extremely important. Plasma diagnostics requires line ratios and line broadening measurements to be made at very short wavelengths. The author presents the design of stigmatic normal and grazing incidence devices fitted with spherical holographic gratings.

Stigmatic coma free VUV devices for high resolution line profiles measurements

Optical devices for line profile measurements must have a symmetrical instrumental profile to allow the use of classical deconvolution methods. Such devices must be then coma free and simultaneously the astigmatic curvature must be eliminated. In a first approach we consider a modified version of a Rowland circle set-up, and in a second one, a new type of stigmatic and coma free spectrometer fitted with spherical holographic gratings each of them covering a restricted spectral range.