Aberration-corrected Concave Gratings Research Articles

Laser Induced Breakdown Spectroscope on Chandrayaan-2 Rover:A Miniaturized Mid-UV to Visible Active Spectrometer for Lunar Surface Chemistry Studies

Laser Induced Breakdown Spectroscope (LIBS) instrument flown in Chandrayaan-2 mission to the Moon, is one of the scientific instruments on the Pragyaan rover. It is primarily developed to carry out in situ investigations for the elemental composition study of lunar regolith and pebbles on the Moon surface in a previously unexplored high latitude area in the southern polar region. A pulsed laser source, a set of optical lenses and mirrors, an aberrationcorrected concave holographic grating and a linear detector, are the principal electro-optical accessories of the instrument. The developed LIBS is a lightweighted (~1.1 kg) and low power consuming (≤1.2 W) compact instrument. This paper presents the system engineering and development aspects of the LIBS instrument along with results from environmental tests. Performance evaluation of the instrument during endto- end testing is satisfactory and within desired specifications. Details on ground calibration techniques used to evaluate the instrument capability are also presented.

SPACE-RESOLVING VUV AND SOFT X-RAY SPECTROSCOPY IN THE TANDEM MIRROR GAMMA 10 PLASMA

Vacuum ultraviolet (VUV) and soft X-ray (SX) spectroscopic measurements are important means to diagnose radiation power loss, impurity ion densities and effective charge of confined plasma, Z eff , in magnetically confined plasmas such as fusion plasmas. We have constructed space- and time-resolving flat-field VUV (150–1050Å) and SX (20–350Å) spectrographs by using aberration-corrected concave gratings with varied line spacing. Absolute calibration experiments have been conducted at the Photon Factory in the High Energy Accelerator Research Organization. Absolute sensitivities of the VUV and SX spectrographs have been obtained for the two (S and P) polarization geometries. Thus, absolute intensities of emission spectra from impurity ions can be measured together with their radial distributions in plasmas. The total radiation power was determined to be less than 6 kW within ±20% of error in our normal plasma operation. Density profiles of impurity ions were reduced by using absolute emissivities of impurity lines and a collisional-radiative model. Moreover, the value of Z eff is estimated to be 1.00 in the tandem mirror GAMMA 10 plasma.

Absolute calibration of space-resolving soft X-ray spectrograph for plasma diagnostics

A grazing incidence flat-field soft X-ray (20–350 Å) spectrograph was constructed and applied for impurity diagnostics in the GAMMA 10 fusion plasma. The spectrograph consisted of a limited height entrance slit, an aberration-corrected concave grating, a microchannel-plate intensified detector and an instant camera/a high speed solid state camera. An absolute calibration experiment for the SX spectrograph was performed at the Photon Factory in the High Energy Accelerator Research Organization with monitoring the incident synchrotron beam intensity by using an absolutely calibrated XUV silicon photodiode. From the results of absolute calibration of the spectrograph, the radiation loss from the plasma was obtained.

Design for an aberration-corrected concave grating for a mid-infrared long-slit spectrometer

A new design for an aberration-corrected concave grating for the spectral region near 10 microm is presented. It was designed for use in the ground-based astronomical medium-resolution (lambda/Dlambda approximately 100) Mid-Infrared Camera and Spectrometer (MICS). It provides a flat focal plane for a wide spectral range (7.5-13.5 microm) with small aberrations, permitting efficient long-slit observations in the mid-infrared region. It permits a simple design of the spectrometer without collimator and camera mirrors, which is quite advantageous for cryogenic instruments. The grating has variable spacing grooves to reduce aberrations. In addition, the grating surface figure is designed to be toroidal and in the direction perpendicular to the grooves, aspherical, to suppress the aberrations further over a wide spectral range. The angle of the grooves is also varied to yield better efficiency near the blaze angle. The grating was fabricated by high-quality ultraprecision machining, which made these features possible. Test observations confirmed that the designed spectral resolution was achieved.

Off-axis pivot mounting for aberration-corrected concave gratings at normal incidence

The off-axis pivot-point mounting for toroidal uniform line-space (TULS) gratings and spherical varied line-space (SVLS) is presented: One scans the spectrum by rotating the grating about the pivot point. The best choice for the location of the point is discussed: For a monochromator the location is chosen such that the grating is moved approximately along the bisector of the subtended angle; for a spectrometer, it is chosen such that the grating is moved approximately along the direction of the incident ray. Minimizing the spectral defocusing caused by the rotation of the grating determines the optimum length of the pivot arm. The pivot points for TULS and SVLS gratings are found to be located on opposite sides with respect to the normal to the grating. In a comparison of the optical performance, the spectral focusing is similar, but the spatial aberrations can be fewer for a SVLS grating.

Design of a high-resolution extreme-ultraviolet imaging spectrometer with aberration-corrected concave gratings

A high-resolution extreme-ultraviolet imaging spectrometer is designed for the Japanese solar mission Solar-B. A spherical varied-line-space (SVLS) grating and a toroidal uniform-line-space (TULS) grating are chosen as candidates for use in the spectrometer to yield high spectral and spatial resolution within the spectral range 25-29 nm. The spectral image-focusing properties and the mechanical tolerances for fabrication and alignment are compared for the two types of grating. The SVLS design is found to be superior to the TULS design for off-plane spectral images and in ease of fabrication and optical alignment.

Calibration of space-resolving VUV and soft X-ray spectrographs for plasma diagnostics.

Vacuum ultraviolet (VUV) and soft X-ray measurements are important means of diagnosing impurities in magnetically confined plasmas used in fusion research. Recently, space- and time-resolving flat-field VUV (150-1050 A) and soft X-ray (20-350 A) spectrographs have been constructed by using aberration-corrected concave gratings with varied-spacing grooves which give a wide simultaneous spectral coverage on a microchannel-plate intensified detector. Calibration experiments have been performed at beamlines 11A and 11C at the Photon Factory of the High Energy Accelerator Research Organization. The relative efficiency of the VUV spectrograph has been measured for P-polarization geometry in the spectrograph. In the soft X-ray spectrograph, efficiencies have been obtained for several different points of irradiation on the grating along the groove direction and for two (S and P) polarization geometries.

The design of aberration-corrected concave holographic gratings for the Lyman-far-ultraviolet spectroscopic explorer high-resolution spectrograph

A design procedure for two aberration-corrected spherical concave gratings operating in the spectral range 91–103 nm (extreme-ultraviolet) is presented. The first configuration is a Rowland circle mount whereas the second is based on the conditions of stationarity with respect to wavelength for the second-order aberration coefficients, as well as the condition for stationary meridional coma. The first design has better resolution whilst the latter design has a better overall degree of aberration correction. Holographic gratings recorded with two diverging stigmatic sources are considered for both designs. The theoretical performance of these gratings is very good across the spectral range of interest. The combination of simplicity and comparatively low cost together with very good aberration correction performance makes these grating designs attractive for the Lyman Far-Ultraviolet Spectroscopic Explorer.

The design of aberration-corrected concave holographic gratings for the Lyman-far-ultraviolet spectroscopic explorer high-resolution spectrograph

The design of aberration-corrected concave holographic gratings for the Lyman-far-ultraviolet spectroscopic explorer high-resolution spectrograph

Applications of holographic gratings to two-dimensional spectroscopy

Calculations are presented for a set of aberration-corrected holographic concave gratings for possible use in space mission instruments. It is concluded that, for the visible range 0.26-1.02 μm when detectors with a 15-μm pixel size are used, a total field of view of ∼1° is possible at an aperture of ƒ/7.0. For the infrared regions 0.9-2.5 μm and 2.4-4.2 μm, in which detector arrays have larger pixel sizes of 30-40 μm, a spatial field of view of ∼2° at ƒ/7.0 and ∼1.0° at ƒ/3.5 can be achieved. An exploration of spectrum lengths showed that performance starts to fall off sharply for lengths over 15 mm at a focal length of 150 mm (i.e., a spectral angular extent of∼6°).

Aberration-corrected concave grating for the mid-infrared spectrometer aboard the Infrared Telescope in Space

A mechanically ruled aberration-corrected concave grating was developed for use in the low-resolution mid-infrared spectrometer aboard the cryogenically cooled Infrared Telescope in Space. The design and the performance testing of the grating are reported. The spectrometer requires a wide spectral range (4.5-11.7 µm) and a wide field of view (8 × 8 arcmin) with a low wavelength resolution (Δλ ≤ 0.3 µm). The aberration-corrected concave grating provides a flat focal plane with a small aberration in the spatial direction compared with those caused by the finite size of the entrance slit. It also permits a simple design for the spectrometer, which is advantageous for applications in space cryogenic instruments. The measurements of the wavelength resolution and the spatial resolution are shown to be in good agreement with the predicted performance. The diffraction efficiency of the grating is more than 80% at the blaze wavelength (6 µm) and fairly high (>30%) over the entire wavelength range in question. The grating produces polarization of less than 10% for λ < 6.4 µm and of 10-20% for 6.7 µm <λ 9.7 µm. These results indicate the potential applicability of this type of grating to the wide-field IR spectroscopic observations.

Holographic diffraction gratings generated by aberrated wave fronts: application to a high-resolution far-ultraviolet spectrograph

We investigated the ability of aberration-corrected concave holographic gratings used in the Rowland mount at normal diffraction to provide high spectral resolution in the far-ultraviolet region. By assuming that astigmatism and spherical aberration are geometrically corrected by an ellipsoid, we show that holography can be used to correct the remaining prominent second-type coma. Stigmatic sources require a laser wavelength that is too far in the ultraviolet for current recording technology. However, at 3336 A a simple compact symmetric mount, which involves two spherical mirrors, can generate aberrated wave fronts that can be used to record a coma-corrected holographic grating. When compared with the equivalent equally spaced straight-groove grating, which requires a modified ellipsoid substrate, holography cancels the additional asymmetrical term of deformation that permits the use of a simpler surface for the substrate. Some areas of potential difficulty in the holographic mounting are briefly analyzed.

Design of an in-water spectrograph for irradiance measurements in the ocean

A low focal ratio ( f /l.8) visible range (350 nm to 750 nm) spectrograph containing an aberration-corrected concave holographic grating and a 512-channel linear array image sensor has been designed for use in an in-water spectroradiometer. A ray-trace analysis using different input wavelengths has been made, so as to optimize and assess the optics. The design analysis also includes calculations on the expected resolution, system etendue, and the simulated response of the complete system to a known in-water spectrum. The modular design concept of the spectrograph can be exploited by using it as a basic building block for other spectral measurements in the ocean.

A Blazed Holographic Concave Grating for Monochromators

Abstract The theory of blazed holographic gratings given in a previous paper is applied to the design of a blazed holographic aberration-corrected spherical concave grating. Two solution types are found which cover different ranges of blaze wavelength and aberration. The use of the refractive indices of the substrate, and the medium in front of the photoresist, as optimising parameters is demonstrated. Four ray-traced solution examples are given which include the distributions of blaze angle and wavelength across the grating surface.

Normal incidence monochromator with an aberration-corrected concave grating for synchrotron radiation

Normal incidence monochromator with an aberration-corrected concave grating for synchrotron radiation

Use of aberration-corrected concave gratings in optical demultiplexers

A method of designing aberration-corrected concave gratings and their mounting for optical demultiplexers is described. An aberration-corrected concave grating for a demultiplexer has been designed and fabricated for use in a six-channel multiplex system in the 800-nm wavelength region. A coupling efficiency of 55% and signal cross talk of less than ~3 × 10−4 have been achieved experimentally.

Mechanically ruled aberration-corrected concave gratings for a flat-field grazing-incidence spectrograph

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text Toshiaki Kita, Tatsuo Harada, N. Nakano, and H. Kuroda, "Mechanically ruled aberration-corrected concave gratings for a flat-field grazing-incidence spectrograph," Appl. Opt. 22, 512-513 (1983) Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

Mechanically ruled aberration-corrected concave gratings

Aberration-corrected concave gratings with curved and variable spacing grooves are ruled with a numerically controlled ruling engine. In the design of aberration-corrected concave gratings, mechanical methods allow more freedom to choose the amount of space variation than do holographic methods. A highly efficient visible-UV monochromator and a coma-type aberration-reduced Seya-Namioka monochromator have been designed and fabricated using mechanically ruled aberration-corrected concave gratings. The gratings can be used with VUV monochromators and spectrographs with improved image focusing properties.

Mechanically ruled aberration-corrected concave grating for high resolution Seya-Namioka monochromator.

An aberration-corrected concave grating especially for reducing coma-type aberration has been developed to improve the resolution of Seya-Namioka monochromators by utilizing the technology of varied groove spacings. The optimum amount of space variation is calculated by using the light path function, and the concave grating is ruled with a numerically controlled ruling engine. A concave grating with 1/600 mm average spacing and 500 mm radius of curvature was designed and ruled for a Seya-Namioka monochromator which covers the spectral wavelength range of 200-800 nm. The quality of spectral images obtained with the new concave grating was examined both theoretically and experimentally and the results show the effectiveness of aberration correction in the resolution and luminosity of the monochromator.

Design of holographic concave gratings for Seya-Namioka monochromators

The theory of the holographic grating is applied to the design of aberration-corrected holographic concave gratings for use with Seya–Namioka monochromators. A method of determining the proper recording parameters is described. The performance of gratings that would be produced by use of the proper recording parameters is evaluated in terms of the magnitude of the aberration terms and the degree of spread in spot diagrams. The results indicate that properly designed holographic concave gratings show much improved performance over mechanically ruled concave gratings.