The InfraRed Imaging Spectrograph (IRIS) is one of three first light science instruments for the Thirty Meter Telescope (TMT). It will provide dedicated function of imaging and integral field spectroscopic observations in parallel with the assistance of a Narrow Field InfraRed Adaptive Optics System (NFIRAOS). The IRIS imager delivers celestial light to a dual-channel Integral Field Spectrograph (IFS) through a pair of pick-off mirrors in the central field. The IFS creates multi-functional ability to explore the universe in IR (0.84 – 2.4um) with moderate spectral resolution of R=4,000/8,000 and four spaxel scales of 4, 9, 25, 50 milli-arc-seconds (mas). An image slicer serves one of the two spectral channels as its Integral Field Unit (IFU) in two coarse spaxel scales of 25 and 50mas over the continuous science fields of 2.2x1.125 arc-seconds (arcsec) and 4.4x2.25 arcsec respectively. It splits the field to 88 unit systems, and then re-images at two parallel slits in order to take full advantage of the detector (4Kx4K @ 15um). This paper describes a novel all-reflective design of image slicer, which uses a new ‘brick stage’ layout to stagger the adjacent mirrors and deliver image quality close to diffraction limit. The quasi-telecentric optical design gives more friendly interfaces with pre-optics and spectrograph than the conceptual design. Here, more technical issues are discussed to guide the further study on optical performance and fabrication feasibility.
The Maunakea Spectroscopic Explorer (MSE) project will transform the CFHT 3.6m optical telescope to a 10m class dedicated multi-object spectroscopic facility, with an ability to measure thousands of objects with three spectral resolution modes respectively low resolution of R≈3,000, moderate resolution of R≈6,000 and high resolution of R≈ 40,000. Two identical multi-object high resolution spectrographs are expected to simultaneously produce 1084 spectra with high resolution of 40,000 at Blue (401-416nm) and Green (472-489nm) channels, and 20,000 at Red (626-674nm) channel. At the Conceptual Design Phase (CoDP), different optical schemes were proposed to meet the challenging requirements, especially a unique design with a novel transmission image slicer array, and another conventional design with oversize Volume Phase Holographic (VPH) gratings. It became clear during the CoDP that both designs presented problems of complexity or feasibility of manufacture, especially high line density disperser (general name for all kinds of grating, grism, prism). At the present, a new design scheme is proposed for investigating the optimal way to reduce technical risk and get more reliable estimation of cost and timescale. It contains new dispersers, F/2 fast collimator and so on. Therein, the disperser takes advantage of a special grism and a prism to reduce line density on grating surface, keep wide opening angle of optical path, and get the similar spectrum layout in all three spectral channels. For the fast collimator, it carefully compares on-axis and off-axis designs in throughput, interface to fiber assembly and technical risks. The current progress is more competitive and credible than the previous design, but it also indicates more challenging work will be done to improve its accessibility in engineering.
The design and performance of a three-channel image and long-slit spectrograph for the new 4-m telescope in China are described. The direct imaging covers a 3 arcmin by 3 arcmin field of view and a large wavelength range 370-1,600 nm, it has two optical channels and one near infrared channel with different filters. The spectrograph with a long slit is to provide two observing modes including the following spectral resolutions: R1000 and R5000. For dispersing optical elements it use volume-phased holographic grisms (VPHG) at each of the spectroscopic modes to simplify the camera system. The low resolution mode (R1000) is provided by consecutive observations with the spectral ranges: 360-860 nm, however it adopts only one VPHG for the first light. The spectral range of medium resolution mode (R5000) is 460- 750nm, it is constrained with the use of a 4k × 4k CCD detector of 15 μm pixel size. Peak efficient in the spectrograph are achieved to be higher than 50% in different resolution mode.
The Next Generation Palomar Spectrograph (NGPS) is designed for Cassergrain focus of the Hale 200-inch telescope to replace the old Palomar Double Spectrograph (DBSP). NGPS have higher throughput, efficiency and realities spectrograph. NGPS is designed as three channels to cover the wavelength from 365nm to 1050nm with no spectral gap and delivers a resolving power with a 1.5” slit exceeding R=1800 overall the observable range. The peak efficiency of the whole throughput (from sky to detector) at the wavelength is 35.3% which is consistent with throughput achieved by some of the world’s most efficient spectrographs.
The LAMOST completed its first five years of operation in June 2017, and 9 million low resolution spectra are obtained. The spectrographs have been upgraded in 2017, and the resolution can reach up to 7500(with 2/3 slit). In the midresolution mode, the wavelength can cover 495nm-535nm(blue band) and 630nm-680nm(red band). The LAMOST will carry out the middle resolution spectroscopic survey in September 2018, and 3 million middle resolution spectra will be obtained. This paper describes the requirements, optical design and mechanical design of the LAMOST-MRS (the LAMOST middle resolution spectrograph)
Except for the spectroscopic survey telescope LAMOST, there are only two 2m class general purpose telescopes for precision observation in China (2.16m in Xinglong and 2.4m in Lijiang). Chinese astronomical community unanimously agrees that a 10m class large diameter general purpose optical/infrared telescope is urgently needed in China for a wide range of scientific research. The configuration for LOT with primary aperture 12m has been selected by Chinese government for the Thirteen-five-years plan in July, 2016. The concept design introduced here has been approved by Chinese astronomical community and Chinese Academy of Sciences in Dec. 2017, and submitted into the formal funding procedure of Chinese government. For quite a long time, China will very likely have only one 10m class telescope, therefore LOT should be a general-purpose telescope including multi-foci. The Nasmyth focus, prime focus, Cassegrain focus and coudé focus have been considered or reserved. Also, LOT will closely combine with the development of new technologies, such as AO, GLAO, fiber and instrument related new technologies, to make it has powerful capability for the frontier sciences. The four-mirror Nasmyth system, optimized according to the GLAO requirements, has a f-ratio about 14 and field of view 14 arecmin with excellent image quality. Some off-axis four-mirror Nasmyth optical systems are also presented in this paper. The primary focus system has a f-ratio 2 and 1.5degree field of view with 80% light energy encircled in 0.5 arecsec, which will let LOT complementary with the coming 30m-class telescopes. A double–layer Nasmyth platforms are proposed to accommodate more instruments, such as the wide field imaging spectrograph, broad band medium resolution spectrograph, high resolution spectrograph and multi-object fiber spectrographs and so on. Not all optical systems will be constructed in the same time, which will be in stages depending on the science and funding situation.
The Maunakea Spectroscopic Explorer (MSE) project will transform the CFHT 3.6m optical telescope into a 10m class dedicated multi-object spectroscopic facility, with an ability to simultaneously measure thousands of objects with a spectral resolution range spanning 2,000 to 40,000. MSE will develop two spectrographic facilities to meet the science requirements. These are respectively, the Low/Medium Resolution spectrographs (LMRS) and High Resolution spectrographs (HRS). Multi-object high resolution spectrographs with total of 1,156 fibers is a big challenge, one that has never been attempted for a 10m class telescope. To date, most spectral survey facilities work in single order low/medium resolution mode, and only a few Wide Field Spectrographs (WFS) provide a cross-dispersion high resolution mode with a limited number of orders. Nanjing Institute of Astronomical Optics and Technology (NIAOT) propose a conceptual design with the use of novel image slicer arrays and single order immersed Volume Phase Holographic (VPH) grating for the MSE multi-object high resolution spectrographs. The conceptual scheme contains six identical fiber-link spectrographs, each of which simultaneously covers three restricted bands (λ/30, λ/30, λ/15) in the optical regime, with spectral resolution of 40,000 in Blue/Visible bands (400nm / 490nm) and 20,000 in Red band (650nm). The details of the design is presented in this paper.
Design a best light-weighting collimator to conform to the requirements of opto-mechanical design. Good surface accuracy is our aim, based on a less mass. The ratio of diameter to thickness, the type, size and thickness of pocket, the thickness of the mirror, the support size and position, the thickness of the wall and so on is concerned. Besides, comparing two kinds material is also discussed. In addition, we consider the situation that the orientation vary in support plane. Use the orthogonal table to analyze these elements, and find the better methods. According to the analysis in ANSYS, the collimator mass can reduce to 103 kg, below 159 kg; the ratio of light-weight can reach 70%; the peak-valley value is below 100 nm, that meets the request of below 200 nm.
The pre-slit system of Chinese SONG spectrograph is a multi-function unit. The main function is to direct the incoming light from the coudé path to the entrance slit of the spectrograph. The specific functions includes maintaining exit pupil stable, fast guiding and telescope focus corrections. The original optics of this pre-slit system were designed by Aarhus University in Denmark. We built the system and designed the software for it. This system holds a guide/slit-viewing camera, a pupil-viewing camera, two tip-tilt mirrors and its tip-tilt controllers. So it includes two sets of the fast-steering mirror systems applied to image tracking and correction. When this image tracking and correction systems is running, the real-time software algorithm will be presented and simulated simultaneously. From the images taken with camera, a closed loop signals are generated for the tip-tilt mirror to correct image motion. When the camera exposure time is 25ms,the correcting frequency of slit imge tip-tilt motion is about 30Hz. The correcting frequency of pupil imge tip-tilt motion is about 1Hz. In addition, a temperature control system surrounding the spectrograph is necessary to keep spectrograph at a constant temperature. The test results shows that the error is about ±0.005°C in 69.4 hours. The results prove that the pre-slit system of Chinese SONG spectrograph is effective and feasible.
Exoplanet detection, a highlight in the current astronomy, will be part of puzzle in astronomical and astrophysical future,
which contains dark energy, dark matter, early universe, black hole, galactic evolution and so on. At present, most of the
detected Exoplanets are confirmed through methods of radial velocity and transit. Guo shoujing Telescope well known
as LAMOST is an advanced multi-object spectral survey telescope equipped with 4000 fibers and 16 low resolution fiber
spectrographs. To explore its potential in different astronomical activities, a new radial velocity method named
Externally Dispersed Interferometry (EDI) is applied to serve Exoplanet detection through combining a fixed-delay
interferometer with the existing spectrograph in medium spectral resolution mode (R=5,000-10,000). This new
technology has an impressive feature to enhance radial velocity measuring accuracy of the existing spectrograph through
installing a fixed-delay interferometer in front of spectrograph. This way produces an interference spectrum with higher
sensitivity to Doppler Effect by interference phase and fixed delay. This relative system named Multi-object Exoplanet
Search Spectral Interferometer (MESSI) is composed of a few parts, including a pair of multi-fiber coupling sockets, a
remote control iodine subsystem, a multi-object fixed delay interferometer and the existing spectrograph. It covers from
500 to 550 nm and simultaneously observes up to 21 stars. Even if it’s an experimental instrument at present, it’s still
well demonstrated in paper that how MESSI does explore an effective way to build its own system under the existing
condition of LAMOST and get its expected performance for multi-object Exoplanet detection, especially instrument
stability and its special data reduction. As a result of test at lab, inside temperature of its instrumental chamber is stable
in a range of ±0.5degree Celsius within 12 hours, and the direct instrumental stability without further observation
correction is equivalent to be ±50m/s every 20mins.
The design, construction, and preliminary test of an advanced image slicer(AIS) Integral Field Unit(IFU) experiment
system is introduced in the paper.The ultimate optimized IFU will be installed for further test on 1m Telescope in Wei
Hai. This IFU employs an all-mirror design associated with a classical spectrograph. It operates in the visible wavelength
range (380nm -770nm) and divides the telescopic field of view into the nine sub-fields. This paper also describes the
components test results and overall IFU system performance. At last, we discuss some possible science applications by
using the IFU on Chinese small telescopes.
One of the Large Sky Area Multi-Object Spectroscopic Telescope (LAMOST) scientific requirements require the ability
of the low resolution spectrograph(LRS) to measure velocities to a accuracy of 4km/s over the entire 5 degree field in 2
hours objects observation. This requirement results in the specification of image movement less than 0.6μm/hours
(0.05pixl/hours corresponding to the science detector).There are 16 spectrographs for LAMOST telescope, so we expect
the design aspects of the instrument directed towards achieving the stability goal. In this paper we present the last design
aspects of the instrument which enable meeting the 4km/s requirement, and the recent test results of the LRS’s Stability
Performance. The test results show that the stability performance of LAMOST-LRS can meet the the stability goal, the
image shift along the direction of dispersion is not influenced by the external factors, and the image shift along vertical
dispersion direction meet the technical requirements when the environmental temperature of the spectrograph room is in
It's a very important point that fully open up power of Gou Shoujing telescope (LAMOST) in exoplanet detection field
by developing a multi-exoplanet survey system. But it's an indisputable truth in the present astronomy that a traditional
type of multi-object high resolution spectrograph is almost impossible to be developed. External Dispersed
Interferometry is an effective way to improve the radial velocity measuring accuracy of medium resolution spectrograph.
With the using of this technique, Multi-object Exoplanet Search Spectral Interferometer (MESSI) is an exploratory
system with medium measuring accuracy based on LAMOST low resolution spectrograph works in medium-resolution
mode (R=5,000 - 10,000). And it's believed that will bring some feasible way in the future development of multi-object
medium/high resolution spectrograph. After prototype experiment in 2010, a complete configuration is under the
development, including a multi-object fixed-delay Michelson interferometer, an iodine cell with multi-fiber optical
coupling system and a multi-terminal switching system in an efficient fiber physical coupling way. By some effective
improvement, the interferometer has smaller cross section and more stable interference component. Moreover, based on
physical and optical fiber coupling technique, it's possible for the iodine cell and the switching system to simultaneously
and identically coupling 25 pairs of fibers. In paper, all of the progress is given in detail.
The China-made telescope, LAMOST, consists of 16 Spectrographs to detect stellar spectra via 4000 optical fibers. In
each spectroscope, many movable parts work in phase. Those parts are real-time controlled and managed by field
controllers based on FPGA. The master control board of controllers currently being used is constructed by Altera's
Cyclone II Development Kit. However, now Altera no longer produce such Kits. As the needs for maintenance and
improvement, a backup control board is developed, so that once any field controller is broken, another can changed in
time to ensure the control system not being interrupted. Using the newer Altera FPGA chip 3C40 as master control chip
can minimize the change in the original design frame of the control structure so as to reduce the workload of software
and hardware migration.
This paper describes the design process of the Spectrographs backup field controller based on Cyclone 3C40 and gives
the problems and solutions encountered during migration for controller hardware and software. The improved field
controller not only retains the original controller functions, but also can serve for more motors and sensors due to the
increase of input and output pins. Besides, no commodity supply limits, which saves expenses. The FPGA-field
controller can also be used in other telescopes, astronomical instruments and industrial control systems as well.
Optical fibres play more and more important roles in astronomy, for example, to transfer light from the focus point of
telescopes to spectrometers. In this paper, a novel designed, a fibre-brush-shape converter was designed to transfer circle
input of a fibre to a line-shape output. The brush-shape converter consists of several bare fibres at one end, one fibre at
the other end and a taper between them. The light propagating from the bare fibres to the single fibre will be coupled.
According to the theoretical and calculated results, the power of the light could be confined in the core of the fibre if the
parameters of the taper are appropriate.
In order to detect the weak light of the protostars in astronomy, we design a new type of photonic crystal fibers with high
numerical aperture. Through controlling the number and the diameter of the air holes around the central fiber core, the
numerical aperture can also be adjusted to apt different applications. With the help of the big air holes, the loss can be
reduced to less than 0.1dB/km. So this kind of high numerical aperture fibers has the strong ability to collect light and the
loss is very low.
Nigel is a fiber-fed UV/visible grating spectrograph with a thermoelectrically-cooled 256×1024 pixel CCD camera,
designed to measure the twilight and night sky brightness from 300nm to 850 nm. Nigel has three pairs of fibers,
each with a field-of-view with an angular diameter of 25 degrees, pointing in three fixed positions towards the
sky. The bare fibers are exposed to the sky with no additional optics. The instrument was deployed at Dome A,
Antarctica in January 2009 as part of the PLATO (PLATeau Observatory) robotic observatory. During the 2009
winter, Nigel made approximately six months of continuous observations of the sky, with typically 104 deadtime
between exposures. The resulting spectra provide quantitative information on the sky brightness, the auroral
contribution, and the water vapour content of the atmosphere. We present details of the design, construction
and calibration of the Nigel spectrometer, as well some sample spectra from a preliminary analysis.
The China-made telescope, LAMOST, consists of 16 spectroscopes to detect stellar spectra via 4000 optical fibers. In
each spectroscope, many movable parts work in phase. Those parts are real-time controlled and managed by field
controllers based on FPGA. This paper mainly introduces how to use DSP Builder module library in MATLAB /
Simulink to construct the IP control core on FPGA chip. This method can also be used to design the control core of PID
arithmetic, to carry out arithmetic simulation and generate VHDL language file, as well as to integrate it into SOPC
developing environment so as to repeatedly use. In this way, the design period of the control system may be shortened
and design process simplified. Finally due to the reversibility and programmability of the IP control core ,a system on a
chip for field controllers of spectroscope is realized, which meets astronomical control requirements, providing an
effective scheme for embedded system in astronomical instrument applications.
The 16 low resolution spectrographs (LRS) have been successfully commissioned for the LAMOST. The LRS design
employs a dual-beamed and bench-mounted, with large-beamed, fast Schmidt cameras and Volume Phase Holographic
(VPH) transmission gratings. The design wavelength range is 370-900nm, at resolutions of R=1000and R=10000. Each
spectrograph is fed by 250 fibers with 320 micron in diameter (corresponding 3.3 arcsec), composed of one F/4 Schmidt
collimator, a dichroic beam-splitter, four VPH gratings, articulating Schmidt cameras that are optimized at blue band
(370-590 nm) and red band (570-900 nm), and field lens near the focal plane service as the vacuum window of CCD
detector cryogenic head. In this paper, we present the testing result of the LRS on the image quality, spectra resolution,
efficiency and observing spectra.
A large Schmitt reflector telescope, Large Sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST), is being
built in China, which has effective aperture of 4 meters and can observe the spectra of as many as 4000 objects
simultaneously. To fit such a large amount of observational objects, the dispersion part is composed of a set of 16
multipurpose fiber-fed double-beam Schmidt spectrographs, of which each has about ten of moveable components realtimely
accommodated and manipulated by a controller. An industrial Ethernet network connects those 16 spectrograph
controllers. The light from stars is fed to the entrance slits of the spectrographs with optical fibers.
In this paper, we mainly introduce the design and realization of our real-time controller for the spectrograph, our design
using the technique of System On Programmable Chip (SOPC) based on Field Programmable Gate Array (FPGA) and
then realizing the control of the spectrographs through NIOSII Soft Core Embedded Processor. We seal the stepper
motor controller as intellectual property (IP) cores and reuse it, greatly simplifying the design process and then
shortening the development time. Under the embedded operating system μC/OS-II, a multi-tasks control program
has been well written to realize the real-time control of the moveable parts of the spectrographs. At present, a number of
such controllers have been applied in the spectrograph of LAMOST.
The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) project is one of the National Major
Scientific Projects undertaken by the Chinese Academy of Science. There are 16 low resolution multipurpose fiber-fed
spectrographs in total, enabling it to obtain the spectrum of celestial objects as faint as down to 20.5. Building auto-focusing
systems for the spectrographs is important due to the popularity of instruments. The system enables the optical
system to automatically compensate changes in accordance to external variables, such as temperature, timidity, to ensure
the spectrum collected more reliably. Image-based algorithm is utilized to calculate the departure of CCD plane from
optical focal plane. The calculation also aids to regulation of the system. The defocus value is transformed to the
controlling computer of each spectrograph. A driving step-motor performs refocusing function by moving the fiber slit
unit to its right position.
A multipurpose fiber-fed double-beam Schmidt spectrograph using VPHG (volume phase holographic gratings) is under construction for LAMOST (The Large Sky Area Multi-Object Fiber Spectroscopic Telescope). There are 16 such spectrographs (hereafter referred to as LRSs) for the project. The spectrographs are designed with wavelength coverage from 370 to 900 nm, with spectral resolutions of 1000-10000, and with multi-object capability over a 5 degrees field of view. Each spectrograph will be accommodating 250 fibers of 320 microns diameter (corresponding 3.3 arcsecs). The 200 mm diameter collimated beam is split into two separate channels. The blue channel is optimized for 370nm-590nm, and the red channel for 570nm-900nm. The LRS can work in several varied resolution modes. The optical design and performance is described. The spectrograph is of simple design with moderate image quality and good throughput. Progress on the construction of LRS is reported as well.