A post-polishing experiment was conducted to see if the wavefront performance of a volume-phase holographic grating with thin substrates could be improved. The ability to postpolish the grating assembly after production of the grating could lead to much improved imaging performance. The ability to use lower quality substrates can reduce the upfront cost and risk involved with using high performance substrate units.

Large area volume phase holographic (VPH) gratings have been made for use in spectrographs attached to large telescopes and for scanning LIDAR systems. Examples of the transmitted wavefronts, the spectral efficiency measurements and other parameters such as uniformity, scatter, absorption and Q have been gathered and presented. Two exposure layouts have been used and are described along with some discussion of modulation and bulk index of processed DCG. A discussion of thickness regimes is given. A special case (Dickson) design is presented with examples of performance and some intrinsic properties.

The need of new generation dispersing elements with higher throughput and with higher dispersion capabilities has now met a widely shared answer in the technology of Volume Phase Holographic Gratings (VPHG). Our group is increasingly involved in the design and realization of VPHGs both for edge basic research, testing different manufacturers, sizes and resolutions, and for existing instruments upgrades, letting observing astronomers to take advantage of new possibilities with higher performances in their common use instrumentations. In Asiago Observatory, we refurbished the AFOSC camera and spectrograph, whose twins are spread all over the world, from Chilean based ESO-Danish telescope, to Bologna (Italy) South Africa and China. In our laboratory we reproduced the cooled environment of infrared cameras, obtaining the first proofs of the good behavior of VPHG in future IR spectrograph designs.

The recent interest of the astronomer community for volume phase holographic gratings is directly related to the enhancement of spectrograph throughput since this kind of grating can rise higher diffraction efficiency. Indeed, dichromated gelatine technology has demonstrated capability for 70-90% efficiency. From the heritage of several diffractive and holographic projects and applications, the Centre Spatial de Liege has recently decided to invest in the large-scale DCG grating technology. This paper will present the new facility which is now fully operational, its capability and first results obtained.

Highly efficient Volume phase holographic (VPH) gratings do not lend themselves to use in existing spectrographs except for grism spectrographs where VPH grisms can be designed that disperse but do not deviate the light. We discuss our program to outfit existing spectrographs [the Imaging grism instrument (IGI) on the McDonald Observatory Smith Reflector, and the Hobby-Eberly Telescope Marcario Low Resolution Spectrograph (LRS)] with efficient VPH grisms. We present test data on sample gratings from Ralcon Development Lab, and compare them to theoretical predictions. We have created a simple test bench for efficiency measurements of VPH gratings, which we describe. Finally we present first results from the use of VPH grisms in IGI and the LRS, the latter being the largest grism ever deployed in an astronomical spectrograph. We also look forward to using VPH grisms in the LRS infrared extension, which covers the wavelength range from 0.9 to 1.3 microns.

The VISIR instrument for the European Southern Observatory (ESO) Very Large Telescope (VLT) is a thermal-infrared imager and spectrometer currently being developed by the French Service d'Astrophysique of CEA Saclay, and Dutch NFRA ASTRON Dwingeloo consortium. This cryogenic instrument will employ precision infrared bandpass filters in the N-(λ=7.5-14μm)and Q-(λ=16-28μm) band mid-IR atmospheric windows to study interstellar and circumstellar environments crucial for star and planetary formation theories. As the filters in these mid-IR wavelength ranges are of interest to many astronomical cryogenic instruments, a worldwide astronomical filter consortium was set up with participation from 12 differing institutes, each requiring instrument specific filter operating environments and optical metrology. This paper describes the design and fabrication methods used to manufacture these astronomical consortium filters, including the rationale for the selection of multilayer coating designs, temperature-dependant optical properties of the filter materials and FTIR spectral measurements showing the changes in passband and blocking performance on cooling to <50K. We also describe the development of a 7-14μm broadband antireflection coating deposited on Ge lenses and KRS-5 grisms for cryogenic operation at 40K.

Silicon grisms are suitable optical devices that allow for a spectroscopic mode able to effectively complement the natural imaging mode of IR cameras, providing high spectral resolution (R>5000) in the near infrared. We present a review of the fabrication process aimed to produce IR grisms with high refractive index. Such devices are intended to implement a high resolution mode in the Near IR Camera-Spectrograph, NICS, the user instrument at the focal plane of the Italian national telescope Galileo. Litho masking and anisotropic etching techniques have been employed to get, firstly, silicon gratings of suitable size for astronomical use, then warm bonding techniques have been used to obtain the final grisms in echelle configuration. The results and the problems encountered in the bonding procedure are presented along with a future implementation of silicon grisms in space instrumentation.

EMIR is a multiobject intermediate resolution (R ≈ 4000) near infrared spectrograph with image capabilities to be mounted on the Gran Telescopio Canarias (GTC). EMIR shall provide image and spectra of a wide FOV (6x6 arcmin in imaging mode and 6x4 arcmin in multiobject spectroscopic mode), and will use grisms as dispersive elements. The use of grisms has great advantages in the design and manufacture of infrared spectrographs but there are not many suitable materials for the EMIR requirements. The grisms material must have good transmission in the working spectral range (1.0 - 2.5 μm) and given the required resolution, a high refractive index is necessary. Also the required homogeneity of the grism material makes it difficult to find a good candidate due to the large size of the EMIR grisms. Furthermore the technical difficulties related to the grooving process on large surfaces is an important issue to be addressed. Taking into account all those constraints and the EMIR requirements, several sets of materials, rulings and dimensions have been identified. These alternative solutions for EMIR grisms are proposed and analysed in terms of their physical characteristics, expected resolution, spectral coverage on detector and diffraction efficiency. Current status of the procurement of the devices will be given.

The mid-infrared high dispersion spectrograph (IRHS; tentative name) with a resolving power of 200,000 at 10 μm is a candidate of the second-generation instrument for the 8.2m Subaru Telescope. A germanium immersion grating will be employed as a dispersing element for this instrument. Germanium immersion gratings for the prototype IRHS were successfully fabricated by using a nano precision 3D profile grinding/turning machine and ELID grinding method on diamond machining. As a result, the fabricated gratings observed to have grooves with ideal saw-tooth shape, smooth surface and acceptable wave front error of a diffraction beam at 10μm. In the present paper, we characterized the performance of the developed immersion gratings.

A set of 48 ultraviolet-visible filters in the Wide Field Camera 3 will be deployed on the Hubble Space Telescope in 2004. We summarize the specifications for the filters, derived through interaction with the Science Oversight Committee. A detailed characterization of the 48 filters is presented.

Faint Object Camera and Spectrograph (FOCAS) is a versatile open use optical instrument of the 8.2m Subaru Telescope for the enabling imaging and spectroscopic observations. A suite of nine grisms optimized for different resolving powers and appropriate wavelength ranges have been planned for this instrument. Five grisms among the nine were fabricated by a replication method and four additional grisms with the resolving power of 5,000 are under fabrication using the volume phase holographic (VPH) gratings. A very high dispersion Echelle grism with the resolving power over 10,000 is also developing with a VPH grating sandwiched between two high index prisms. The high dispersion VPH grisms are 110 by 106 mm in aperture size and 110 mm in maximum thickness. We employed a photosensitive resin as the recording material for a thick VPH grating. In the present paper, we report the result of evaluation of the diffraction efficiency of the replica grisms and the VPH gratings by means of the rigorous coupled-wave analysis (RCWA) method to derive the optimum design parameters. An optimized VPH grating with a size of 50 by 50 mm was experimentally fabricated by means of a two-wave interference exposure at 532nm. The measured diffraction efficiency of this VPH grating is 88% at 400nm. We performed spectroscopic observations of Leonid meteors by using an image intensified CCD video camera and an experimentally fabricated VPH grism as an objective dispersion element at Nobeyama, National Astronomical Observatory of Japan in November, 2001. Consequently, we successfully obtained numerous high-quality spectroscopic data of meteors.

Schott has delivered blanks for large lenses and prisms since many decades. Glass and glass ceramics objects with dimensions above 300 mm diameter or edge lengths will remain challenges for a glass manufacturer. This holds especially when the quality specifications exceed the standard level significantly. Optical glass blocks of more than half a ton have been produced with outstanding internal quality. Although the manufacturing process is well controlled there are restrictions on the availability of such objects (glass types, long process times e.g.). Implications of the glass production process are presented as a guideline for designers in order to avoid unnecessary time losses. The similarity of the production process of the glass ceramic ZERODUR to that of optical glasses results in high homogeneity with regard to the coefficient of thermal expansion as well as to the optical properties. This qualifies ZERODUR for even higher demanding applications especially when reproducibility in series production is required.

SAGEM, through its REOSC product line, is offering a high skill of optics design fabrication and assembly to the astronomical community. Beside large projects like ESO VLT, SOFIA or the Spain GTC, SAGEM is continuously active with smaller projects. In this paper, we will present our recent work in the field of thin films with mirror broadband and durable coating and large area filters for multimegapixel camera. Latest results of Sofia primary mirror integration will be presented. Work on large prime focus correctors like the one of CFHT MegaPrime and the SALT Spherical Aberration Corrector. For space astronomy it is our new activity of mold smoothing for large telecom antenna or submillimeter reflectors that will be presented.

We summarize the reasons why aspheric surfaces, including non-rotationally-symmetric surfaces, are increasingly important to ground and space-based astronomical instruments, yet challenging to produce. We mainly consider the generic problem of producing aspheres, and then lightweight segments for the primary mirror of an Extremely Large Telescope. We remark on the tension between manufacturability of spherical segments, and performance with aspheric segments. This provides the context for our presentation of the novel Precessions process for rapid polishing and form-correction of aspheric surfaces. We outline why this is a significant step beyond previous methods to automate aspheric production, and how it has resulted in a generalized, scaleable technology that does not require high capital-value tooling customized to particular types of optical form. We summarize implementation in the first two automated CNC machines of 200mm capacity, followed by the first 600mm machine, and the current status of the process-development program. We review quantitative results of polishing trials, including materials relevant to large and instrumentation optics. Finally, we comment on the potential of the technology for space optics and for removing quilting in honeycomb substrates.

Ultra lightweight mirrors of silicon carbide (SiC) are used for a large number of space telescopes, and SiC is also candidate as hopeful material for segmented mirrors of the next generation ground based telescopes from 20 to 100 m in diameter. However, an SiC mirror is difficult to shape because the material is very hard and brittle. We are developing an SiC mirror by means of an ultra-precision rotary grinding machine (800 mm in diameter) and the ELID (ELectrolytic In-process Dressing) grinding method. The method is suitable for fabrications of very hard materials, such as crystalline silicon and sapphire, ceramics, glasses, hard metals and so on. In this study, we present results of test fabrication for the SiC mirrors by means of ELID grinding method and evaluations of the profile deformation of the lightweight mirrors by using FEM simulation method.

The application of organic photochromic materials in astronomy is opening new possibilities which we are investigating in order to design innovative devices for future instrumentation. The photochromic property of transparent/opaque transition (although in a limited wavelength range) and the changes in intrinsic refractive index have led our studies to application in astronomic spectrographs, both as focal plane mask (for MOS application) and as dispersive elements (volume phase holographic gratings, VPHG), respectively. In both cases the possibility to write and erase devices with suitable irradiation has revealed a new perspective for non-disposable and fully customizable items for spectroscopy. Pursuing this goal we have synthesized a series of novel photochromic materials belonging to the diarylethenes. They fulfill the requirements of thermal stability and fatigue resistance necessary to build functional devices. Prototypes of high contrast focal plane mask working in the H-alpha spectral region have been manufactured and characterized both in laboratory and with the AFOSC camera at Asiago telescope (1.8 m). A custom writing robot (ARATRO) which, taking imaging frames and with the aid of interactive mask design software and ad hoc control electronics, is able to write MOS masks, has been constructed. The design of the MOS masks allow the fitting in the AFOSC slit wheel. The overall set-up is ready for the sky tests.

Sputter deposition at long-throw distances (15-30 in.) and low pressures (<1 mTorr) were developed mainly for the semiconductor industry to deposit metals and dielectrics into trenches or vias on silicon and gallium arsenide wafers. Scientists found that sputter depositions performed at pressures below 1 mTorr (0.13 Pa) results in a virtually collision-free trajectory of the sputtered atoms from the target to the substrate. If the throw distance (source to substrate) is increased at these low pressures, the activated (ionized) gas and target atoms maintain their energy. We used this methodology along with dc-pulsed sputtering to deliver additional energy at the substrate. This allowed us to coat large optics (>21-in. diameter) in a standard box coater using smaller-diameter sputter cathodes. This paper will discuss the process used to successfully coat a 22-in.-diameter optic for the Keck Telescope in Hawaii with a new Wide-Band Durable Silver Mirror. The process uses smaller-diameter sputter cathodes in a 4-ft.-x-4-ft.-x-5-ft. box coater. We will also discuss how the process can be scaled to 36-in. or larger optics for use on terrestrial or space-based platforms.

We describe a multi-element refractive corrector for the prime focus of the proposed Lowell four-meter telescope. The design provides sub-half arcsecond images over a two-degree field of view, with a flat image surface and images that are confocal across a broad wavelength band covering the U to I spectral range. Initial studies cover the feasibility of fabrication and explore the possibility of a simple atmospheric dispersion corrector.

This paper describes the optical design of VISTA (Visible and Infrared Survey Telescope for Astronomy) in the infrared and visible configurations. The design is based on a fast quasi Ritchey-Chretien Telescope with an f/1 primary and an f/3 secondary. The large field of views available: 1.65 degrees in the IR and 2.1 degrees in the visible, makes use of the latest technology in optical materials, active optics and large arrays of detectors. The residual third order spherical aberration for on-axis images introduced in the two-mirror design is used to compensate the residual spherical aberration in the field corrector lenses. The infrared camera is included in the telescope optimization, letting the radii of curvature and conic constants of the two mirrors in the telescope vary in order to get the best performance across the entire IR detector array. It also contains an innovative cold baffle with a special black coating. The visible camera contains an ADC incorporated in the field corrector lenses. The acquisition, guiding and wavefront sensing of this telescope is integrated in the instruments.

A new interactive approach in the field of optical calculations has now resulted in a new fast telescope design using exclusively spherical surfaces, and which offers small central obstruction and wide diffraction-limited field. It is a new concept of relay telescope, based on a new relay lens design that allows sequential optimization of the essential requirement, i.e. image quality. It is possible to adjust successively the monochromatic axial spot, the monochromatic off-axis spot, the polychromatic axial spot and the polychromatic off-axis spot. Each adjustment is obtained interactively by ray-trace software, each being almost completely independent, except for the last one which requires repeated resetting of the previous adjustments. We will explain the main principles of operation and present the results obtained for a 500 mm diameter telescope and comarative performance with well-known Newton and Richey-Chretien equivalent designs.

VISTA is the Visible and Infrared Survey Telescope for Astronomy that has been designed by the UK ATC. The design incorporates two cameras covering the visible and near-IR wavelengths. An important concern in designing the telescope and cameras is the level of stray, scattered and background light. In the IR camera, K-band (approx. 2.0-2.3 microns) thermal emission from the telescope structure contributes ~50% of the sky background. Therefore a cold baffle is necessary. Due to the large field-of-view, and size of the required optics, a cold stop is precluded. Therefore baffling is provided by a long cryostat and a system of cold baffles with a coating that must absorb in-band light but reflect thermal radiation from the cryostat window, thus reducing the thermal load on the cryostat. In addition, the temporally and spatially variable OH airglow from the atmosphere is obscured by a warm (and hence non-absorbing) annular baffle around the secondary mirror. We report here on the modelling of the scattered and background light for VISTA. The model includes accurate models for the geometry of baffles and optical surface properties of all surfaces in the system. The optical specification is taken from a ZEMAX model and imported into TracePro to generate a fully three-dimensional telescope model, with a simple dome. For both cameras the analysis has been done for the case of scattered light from a full moon at various incident angles from 0 degrees (on axis) to 65 degrees. It is shown that a reflective baffle around the secondary mirror does not significantly impair the performance of the visible camera. Ghosting from bright stars in the field has also been calculated for both cameras. Results indicate that the level of scattered and ghosts is below the limits specified for VISTA.

A stray light analysis of the Apache Point Observatory 3.5 meter telescope system was done to understand the performance for a variety of imaging modes. The telescope system consists of the 3.5-m telescope, its enclosure, and its associated imaging cameras. The purpose of the study was to assess the stray light performance of this system, identify where modification(s) would improve the system off-axis rejection characteristics, and assess the effectiveness of those modifications. A detailed telescope system geometry model was created, and scatter models were created for telescope and enclosure components. The computer model we created duplicated the pinhole stray light images taken with the telescope, thereby verifying the model. The Point Source Transmittance (PST), a commonly used metric for assessing stray light was used to evaluate the stray light performance of the system for a number of off-axis angles and to suggest modifications to enhance the system. The baseline PST of the existing system shows virtually no falloff with off-axis angle in the plane of the observatory slit. This is the result of (1) the focal plane having a large, unobstructed view of the Nasmyth mirror and cell, primary mirror cell, and baffles mounted on the Nasmyth cell, (2) relatively unobstructed illumination of telescope over a large range of angles in the plane of the slit, and (3) secondary and Nasmyth baffles that are not enclosed. These attributes create a series of first-level scatter paths that directly illuminate the focal plane. Our approach to stray light reduction was to address the light paths revealed by the various PST calculations. Our calculations have shown that significant gains can be realized with simple modifications to the telescope system.

We have acquired spatial-spectral datacubes of astronomical objects using the Livermore visible-band imaging Fourier transform spectrometer at Apache Point Observatory. Each raw datacube contains hundreds of thousands of spectral interferograms. We present in-progress demonstrations of these observations.

Direct-imaging surveys require telescope designs which maximize the product of the primary mirror diameter times the field of view. While a 4.0-m telescope would not be considered "large" by modern standards, the provision of a 2.0-degree field corrector would make it comparable in imaging information-gathering capacity to an 8.0-m telescope with a 1.0-degree field corrector which is at or near the present state-of-the-art. We have explored plausible optical design options for such a 4.0-m telescope within the confines of a set of specifications which emphasize practical issues. These include realistic image quality requirements, mechanical simplicity, ease of construction, minimum cost and freedom from restrictive constraints on the primary mirror shape and the telescope structure, such that it could potentially be used in other optical configurations. We present a mechanically robust optical solution which uses a 4.0-m f/2.08 parabolic primary mirror and a refracting field corrector containing 4 powered lens elements with 2 mild aspherics located on softly curved surfaces, ample room for filter(s) and a shutter, with a flat vacuum dewar window and a flat 2.0-degree diameter field of view. We discuss or specifications and we provide a fully-quantitative system prescription as well as our analysis of the system's expected direct-imaging performance in the traditional Umod, B, V, R, (V+R) and I passbands. While we recongize that other optical designs may prove to be superior to ours by some standard(s) of measure, we believe that our solution provides a useful and realistic baseline design which is competitive for the intended purposes.

We describe a new system (WIZARD: Wide-field Imager of Zodiacal light with ARray Detector) for the zodiacal light observation developed by a Korean and Japanese zodiacal light observation group. Since the zodiacal light is faint and wide-spread all over the sky, it consists of a very sensitive CCD camera of a quantum efficiency of 90% at 460(nm) and a wide angle lens with the field-of-view of 49x98 (degree). WIZARD is designed to measure the absolute brightness of diffuse sky in visible wavelengths. The zodiacal component will be separated from the integrated starlight, the airglow continuum and the scattered light in the atmosphere in the data reduction procedure. We got a first image by WIZARD in 2001 at Mauna Kea (4200m, Hawaii) under the collaboration with SUBARU Telescope. We observed the zodiacal light and the gegenschein in 2002 again, and got the excellent images. In this paper, we describe the design of WIZARD and report the performance examined by the laboratory measurements and the observations at Mauna Kea in 2002.

UVES is the UV-Visual high-resolution Echelle Spectrograph mounted at the 8-m Kueyen (UT2) telescope of the ESO VLT. In order to allow use of UVES at its highest resolution of up to 110 000, also during non-optimal seeing conditions, the instrument is equipped with Bowen-Walraven type image slicers. These devices have exit slits of 0.3, 0.44 and 0.68 arcseconds and possibility to view the sky next to the slicer for sky subtraction. This paper addresses the relevant UVES optical design aspects, image slicer design and manufacturing, observing procedures and usage statistics. In the last part of the paper we give examples of high-S/N observations made with the 0.3 arcsecond image slicer.

We present here details of the manufacture of a deployable image slicing IFU for UIST (a new imager spectrometer for UKIRT). We also present the alignment methods developed and used to achieve optimal transmission and give results for laboratory testing of the IFU at cryogenic temperatures in its operational configuration in UIST. These tests covered transmission, scattered light, alignment of exit pupils and the spatial and spectral PSFs. The calibration and automatic data reduction methods which produce spectra (in the form of an x, y, λ data-cube) aligned in wavelength and the two spatial dimensions for all the observed pixels will be described.

A research and development activity on an Image Slicer System for Integral Field Spectroscopy is conducted with possible applications on future instrumentation for major ground-based (VLT second-generation instruments) and space (NGST, SNAP) observatories. These instruments need high-photometric accuracy, compactness and will possibly work under cryogenic environment, while multi-integral field units may require mass production. Several prototypes have been manufactured since March 2000. This paper provides an overview of the difficulties and limits of the design for different applications, and will describe technology developments and performance evaluation. In particular, the assembly of Zerodur micro-optical elements required an original method of assembly using high precision molecular adhesion, in order to comply with optical tolerances. Following the exact characteristics of the optical elements, diffraction and straylight analyses have been performed in the NIR range. It was found that diffraction effects due to the image slicer induce energy losses less than a few percents and do not induce any crosstalk between pseudo-slits. With a good baffling, scatter can be controlled to minimize the background increase to less than 10^-4 times the incident flux.

We describe a new concept for an integral field unit that allows the collection of a very large number of spectra. We also describe a complementary low cost spectrograph. Both are necessary for the design of integral field spectrographs with huge numbers of spatial elements. These concepts were developed for the Million Element Integral Field Unit and Spectrograph (MEIFUS) that we are proposing for an 8-m and a larger version for an Extremely Large Telescope (ELT, a 30-m telescope). The 8-m version of this spectrograph would give 2.2 million spectra, each 200 pixels long, covering a field of view of 5.2' x 5.2'. The ELT version would give 1.5 million spectra, each 600 pixels long, with a field of 2.7’ x 3’. The new concept of microslices for integral field units allows us to pack a large number of short spectra tightly on the detector without oversizing the spectrograph. It uses a series of independent cylindrical microlens arrays, as opposed to spherical or "simulated spherical using cylindrical" microlenses. We used the specific characteristics of our instrument, especially the short spectra, to develop a concept of a low cost spectrograph. We show that MEIFUS fills a technological gap between other integral field systems and Fabry-Perot instruments. We believe that integral field spectrographs with such a large number of spatial elements would be too expensive if they were to use fibers, typical slicer systems or typical spectrograph designs.

PMAS, the Potsdam Multi-Aperture Spectrophotometer, has a modular layout which was intended to provide for flexible operation as a travelling instrument and to accomodate different telescopes. The Telescope Module is the part of the instrument which serves the purpose of mechanical and optical interfacing to the telescope. It contains optical systems to re-image the telescope focal plane onto the lens array, to illuminate the lens array from an internal calibration light source, and to observe an area around the 3D spectroscopy field-of-view with a cryogenic CCD system for acquisition, guiding, and for the simultaneous determination of point-spread-function templates for 3D deconvolution. We discuss the opto-mechanical design and manufacture of these subsystems.

PMAS, the Potsdam Multi-Aperture Spectrophotometer, is a new integral field (IF or 3D) instrument. It features a lenslet/optical fiber type integral field module and a dedicated fiber spectrograph. As the instrumental emphasis is on photometric stability and high efficiency, good flat field characteristic across the integral field is needed. The PMAS fiber module is unique in the sense that the design allows the replacement of individual fibers. This property, together with the fact that the fibers are index-matched at both ends, makes it possible to achieve and maintain a high efficiency. We present the opto-mechanical design for this fiber-module and, using various data sets from previous observing runs, demonstrate the increase of performance as a result of the optimization of the fiber-components.

Electrostatically actuated micro-mirrors represent one of the most promising technologies for future adaptive optics systems. Due to their relatively high prototyping cost and long fabrication cycle, simulation is one of the key points of their design and optimization. Finite element analysis, behavioral modeling and electronic CAD packages are generally used to study each part of the mirror. This paper shows how the emerging VHDL-AMS language can be used to combine all these simulation tools, and obtain a dynamical simulation of the complete micro-mirror device. This model can then be used as a tool to optimize the characteristics of the mirror and its control electronics to match the specifications of various adaptive optics systems.

In recent years the interest for integral field spectroscopy has increased consistently among the astronomical community. Larger detectors, efficient fibers, etc. made possible to record simultaneously spatial and spectral information of extended area of sky. The typical spectrograph that processes the Integral field data has a focal reducer configuration, i.e. a refractive collimator re-imaging the pupil on a dispersing element and a camera to re-image the focal plane with suitable pixel sampling. The focal reducer configuration is very common in the panorama of astronomical instrumentation. Nevertheless few of them offer an integral field mode. Via the example of d.o.lo.res, the Low Resolution Spectrograph of the Galileo National Telescope (TNG), we analyze the possibility to retrofit some of them with an Integral field unit designed and manufactured a posteriori.

SPIFFI is the near-infrared integral field spectrograph of the SINFONI VLT instrument. SPIFFI uses an image slicer with plane mirrors as its integral field unit. The integral field unit consists of two stacks of mirrors, each with 32 mirrors, rearranging a two-dimensional field-of-view of 32 x 32 pixels into a one-dimensional pseudo slit, which is fed into a long-slit spectrograph. The image slicer is constructed solely from Zerodur and is operated at a cryogenic temperature of 77 Kelvin. Only optical contacting is used for the assembly of the individual slicer mirrors and the image slicer on its base-plate. The special slicer mount holds the image slicer stress-free and compensates for the different thermal coefficients of expansion of the Zerodur image slicer and the Aluminium mount. Tests at room and cryogenic temperatures show the performance of the image slicer, the durability of the optical contacting technique, and the accuracy of the slicer mount.

Integral Field Spectroscopy (IFS) is a powerful tool for astronomy, of particular importance to large aperture telescopes. We have designed and constructed a prototype integral field unit (IFU) for multiple-IFS which may be deployed to any desired position in a 30' diameter field of view and will deliver a good image quality simultaneously at visible (0.45 - 1.0 μm) and near infrared (1.0 - 1.8 μm) wavelength ranges. The design and construction of the multiple-IFU for the prime focus of an 8-meter telescope is discussed in this paper. The IFU uses optical fibers whose flexibility is an important advantage for a multiple-IFU. Simple and compact optics is essential for the design of the IFU. Key design issues, such as the fore-optics, microlens array and fiber bundle, are described in detail. Finally the achievable performance of the IFU is estimated.

We present an overview of the past and current development of the Imaging Fourier Transform Spectrometer (IFTS) concept for ground telescopes produced in collaboration between ABB Bomem and Université Laval. This instrument intends to produce spectra of variable resolutions up to R = λ/Δλ = 10 000 from the near UV to the near IR (350 nm to 900 nm). It is designed to fit the f/8 focus of the Mont Mégantic 1.6m optical telescope in Québec. The large number of spatial elements (> 1 million pixels) is the novel aspect of this FTS design along with innovative metrology system. Heritage from Next Generation Space Telescope (NGST) IFTS concept, Lawrence Livermore National Laboratory (LLNL)- ABB Bomem instrument and commercial ABB Bomem DA series FTS are reviewed. Techniques for accurately servoing the moving mirror alignment to a value smaller than 0.1 arc second and position to sub nanometer value are discussed. Also presented are results from the assembled interferometer sub-system.

VISTA is the Visible and Infrared Survey Telescope for Astronomy that has been designed by the UK ATC. The design incorporates two cameras covering the visible and near-IR wavelengths. The 4-m primary mirror has an active support system with 84 axial actuators that is used, in conjunction with the 5-axis support system for the 1.2-m secondary mirror, to maintain the image quality at seeing-limited conditions (~0.6 arcsec at Cerro Paranal, Chile). A system of curvature sensing is proposed to measure the low-order aberrations of the telescope and camera, which uses a pair of CCD arrays located at the edge of the camera focal-plane array. The analysis presented here uses simulated extra-focal images of point sources generated using the optical design program ZEMAX and demonstrates that this off-axis curvature-sensing technique will provide adequate measurements of low-order aberrations under the expected SNR, seeing conditions and field crowding. Even with the VISTA f-ratio of 3.26, an extra-focal distance of only 1 mm is shown to be sufficient to obtain rms wavefront errors accurate to a few tens of nanometres (under ideal and fully time-averaged seeing conditions). The demonstrated insensitivity to crowding means a field of 35 arcmins², such as obtained with VISTA on a standard CCD, is sufficient to guarantee finding a suitably bright guide star.

We report on a technique to measure the surface figure of mirrors under extreme vibrational conditions. Measurements are presented of the surface figure changes of Zerodur primary mirrors with both spherical and parabolic shapes, manufactured for the NASA Deep Impact program. Conditions ranged from room temperature to 130K. The interferometer was located outside the cryogenic vacuum chamber and did not require any active or passive vibration isolation. We show measurement repeatability of better than 1/500 waves RMS at 633nm.

While telescopes with segmented optics (currently Keck and HET and in the future GTC, CELT, GSMT, NGST, etc) present extra challenges in terms of optical alignment, they also present the opportunity for using an alignment technique not available to telescopes with monolithic optics. We present a technique for aligning telescope secondary mirrors utilizing the segmented nature of the primary. The data required is gathered in direct image mode and can be collected from science instrument detectors (as compared to a wavefront sensor). From this data aberrations (focus and coma) are calculated from which secondary piston and tip/tilt (or decenter) corrections are determined. In addition, tip/tilt corrections for each of the primary mirror segments can also be calculated. Furthermore, other aberrations are available to determine other alignment or support issues including differentiating secondary tip/tilt from decenter, focal surface tilt, and instrument aberrations. This technique has been used nightly on the Keck I and II telescopes over the last 8 years and has made a significant improvement in image quality.

The next generation of cryogenic, infrared (IR), space optical instrumentation (for NGST and other missions) will require a knowledge of refractive indices for constituent optical materials to a level of accuracy which is not currently attainable. The rationale for and design of a broadband, absolute, prism refractometer for measuring refractive index at cryogenic temperatures to very high absolute accuracy is discussed. The refractometer design also permits similar measurements through the far ultraviolet where accurate refractive index data are scarce for most UV optical materials. The technical challenges in achieving high accuracy in these wavelength regions and at extremely cold temperatures are presented, along with novel solutions under development to meet those challenges.

The Ritchey-Common test is a well-known method for large flat measurements. This paper describes a straightforward implementation of the formulas, to allow accurate surface height calculation using relatively few separate measurements. Both Ritchey-Common test and direct measurement results are presented. In comparison of the two methods, the Ritchey-Common test is in good agreement with the direct measurement.

For dioptic instruments working in the near-infrared (NIR), the choice of materials for lenses is mostly limited to special glasses or crystals. Most commonly used are CaF₂, BaF₂, infrared fused silica, ZnS and ZnSe. Those materials can in general not provide good chromatic correction for fast systems. Moreover, the high index materials, as well as infrared glass like Schott IRG, are quite limited with regard to availability in larger sizes and thicknesses and/or optical quality. An investigation was made for optical glasses from the Schott and Ohara catalogues with high transmission up to a wavelength of 2.4 μm. For the most promising materials, the transmission from λ0.35μm to λ3.0μm, was measured in the lab with high spectral resolution. A systematic analysis of combinations of those optical glasses with the infrared materials was performed and the combinations with extremely good chromatic correction in the NIR are presented. There were several combinations found which are well corrected even from λ0.55μm to λ2.5μm, as needed for some designs of adaptive optics systems.