The Multiplexed Survey Telescope (MUST) is 6.5m class optical telescope to be located in China, at Saishiteng Mountain, Lenghu Town, Qinghai Province. The elevation is approximately 4.350m above sea level. The telescope consists of an Alt-Azimuth telescope housed in an enclosure, called “Dome” constituted by a base and a rotating part. The MUST Rotating Enclosure will provide environmental protection and control to the Telescope during operation and standby conditions as well as providing the infrastructure required for the operation of the Telescope. The Auxiliary Building will house plant, maintenance and storage facilities. The Auxiliary Building will also include the necessary housing for the installation of the coating facility for the primary and secondary mirrors. The Dome must operate continuously without rotational travel limits to accommodate the Telescope cadence and travel, so this prevents the use of a utility cable wrap. Moreover, in order to minimize the power transferred to the rotating part, the azimuth drives are located in the fixed lower enclosure. A non-corotating dome architecture is chosen in order to improve flexibility during telescope maintenance and material handling. The rotating enclosure dome includes a moving wind screen, ventilation doors and a rear access door for main mirror handling. An air duct system aligns when the Dome is in its parked position and provides air cooling for temperature conditioning of the Dome during the daytime. A bridge crane and a series of ladders, stairs and platforms provide for the inspection, maintenance and repair of all of the Dome mechanical systems. The contract to design and build the rotating dome and design the lower enclosure and auxiliary building was awarded to EIE GROUP in Mestre- Venezia, Italy in 22/12/22. In this paper, we present the preliminary design of the dome and auxiliary building facility and their sub-systems.
MUltiplexed Survey Telescope (MUST) proposed by Tsinghua University is a 6.5-meter widefield telescope for the ground-based spectroscopic survey. To realize the design target of large field of view of 7 square degrees, the effective aperture of the secondary mirror is preliminarily designed to be 2.4 meters, and the mass of the secondary mirror assembly is supposed to be about 3 tons. Under different zenith angles, the attitude variation of the secondary mirror assembly will affect the stability of the optical axis and result in the spot drift of the focus image on the focal plane. In this paper, a simulation model of the top end assembly is established. Finite element analysis is carried out to investigate the effects of different parameters of the top end assembly on the performance of the optical system, including the vane horizontal offset angle, the vane altitude offset angle, and different forms of ring assembly. Based on the simulation results, an optimized top end assembly is preliminarily obtained and the magnitude of spot drift on the focal plane could be effectively limited at different zenith angles and field of view (FOV).
The MUltiplexed Survey Telescope (MUST) is a 6.5-meter aperture wide field spectroscopic survey telescope built by Tsinghua University. In the optical system of MUST, the second mirror is designed as a hyperbolic flat-convex reflector with an effective aperture of 2.4 meters. In order to achieve high imaging quality under different zenith angles, lightweighted mirror structure is adopted to effectively reduce the weight of the secondary mirror and depress the deformation of the surface figure. In this paper, a preliminary finite element model of the second mirror with multi-point passive support is established and numerical simulation is utilized to investigate the effects of different light-weighted schemes. In the simulation, parameters of the mirror structure are taken into consideration, including the distribution and the structural forms of the light-weighted holes, the back plate and the rib, and the distribution of the passive supports. According to the optimization results, a light-weighted secondary mirror with 36-point axial support is finally achieved to significantly reduce the weight by more than 70% and effectively improve the surface accuracy to 20nm RMS value. To our best knowledge, this is one of the largest aperture light-weighted secondary mirror with passive supports and the presented light-weighted design could provide a reference for the future development of 2-meter class secondary mirror.
KEYWORDS: Telescopes, Mirrors, Active optics, Distortion, Design and modelling, Multiplexing, Wavefronts, Mirror surfaces, Image quality, Chemical elements
MUltiplexed Survey Telescope (MUST) proposed by Tsinghua University aims to build a 6.5-meter widefield telescope for the ground-based spectroscopic survey. MUST adopts the Ritchey-Chretien system with the Cassegrain focus, consisting of an active support primary mirror, a passive support secondary mirror and a multiple-element widefield corrector. In order to fulfill the needs of the widefield spectroscopic survey, the primary mirror is supported in a specific approach rather than traditional methods, which results in optical distortions in the center region of the beam. In this paper, we presented a self-compensation method using the corrector itself to compensate the optical distortion caused by the primary mirror. Based on the optical system of MUST, an optical model of the self-compensation is established, and numerical simulation is conducted to implement the optimization of the corrector and investigate the self-compensation ability. Simulation results indicate that the surface shapes of the elements inside the corrector could be evolved to realize the self-compensation through the optimization of the widefield corrector, including the materials, surface shapes and load conditions. By using the presented self-compensation method, the optical distortions are well compensated and the image quality at the focal plane could be effectively improved.
The Shack-Hartmann wavefront sensor (SHWFS) is widely used in an adaptive optics (AO) system to measure the wavefront. The measurement accuracy of the SHWFS is limited by the micro-lens array, which is a core component of it. A deflectometry system (DS) is constructed to offer a high resolution measurement for the AO system, which could be used to test the surface shape of the deformable mirror (DM). The configuration and principle of the DS are presented. The surface shape testing and close-loop performance are analyzed in simulation and experiment. Results show that the DS has good ability in surface shape testing and close-loop correction.
We investigate the distortion caused by the differences between the working environment and the mounting temperature in the surface shape of the deformable mirror (DM) used in the National Ignition Facility. The characteristics of the surface distortion appeared on the DM under different temperature fields, such as the uniform and gradient working environment temperature, are studied in theory and experiments. Under the uniform working environment temperature, the distorted surface shape reveals the high-frequency and actuator-corresponding characteristics. The distorted surface shapes and their dependence on the actuators’ distribution and structural parameters of the DM are analyzed by using the finite element method. The analysis on the distorted surface shape under the gradient working environment temperature indicates that the changes of the peak and valley (PV) or root-mean-square (RMS) value rely on the temperature gradient as well as the difference between the mirror and the environment with a certain rule. To compensate the temperature induced surface shape distortion (TID), its essential mechanism is analyzed systematically based on the thermal stress characteristics, which shows that the actuators’ tilt caused by the thermal expansion coefficient difference between the mirror and the steel base is the essential reason. An efficient method based on an auxiliary temperature compensation module (TCM) and a hybrid closed-loop control algorithm (HCLA) are presented accordingly. In the simulation and the experiment, the DM’s TID could be effectively depressed and a well-compensated DM surface shape is finally achieved.
Dark field illumination (DFI) is an elegant inspection technique sometimes used to detect particles on a specular surface. However, traditional DFI struggles with repeatability, limiting its applications in automated inspection. We present an improvement to DFI by introducing a modulated dark field illumination (MDFI) that utilizes the phase rather than the intensity in the detection of defects. For modulated dark field illumination (MDFI), the phase-based information is independent from the reflectance of the surface, but has a higher sensitivity to the light scattered from a defect than DFI. As a result, we obtain a robust computational image process method that is insensitive to the environment and provides clearly defined defect information. In order to extend the application to industry, the instantaneous MDFI systems were developed and validated.
A low-cost, compact intracavity deformable mirror (DM) consisting of a mirror unit, a heater unit, a cooler unit and a base unit is proposed to compensate the thermal distortion of a linear resonator passively Q-switched (PQS) laser in this paper. The thermal distortion of the PQS laser is measured using the active deflectometry method. Simulation results indicate that the surface shape of the DM (DMSS) matches well with the measured thermal distortion at the given pumping current. Experiment results verify that the PQS laser with the designed DM could achieve high output power and good beam quality at high pumping currents, as the DM prominently compensates the thermal distortion in the laser.
Dynamic metrology holds the key to overcoming several challenging limitations of conventional optical metrology, especially with regards to precision freeform optical elements. We present two dynamic metrology systems: 1) adaptive interferometric null testing; and 2) instantaneous phase shifting deflectometry, along with an overview of a gradient data processing and surface reconstruction technique. The adaptive null testing method, utilizing a deformable mirror, adopts a stochastic parallel gradient descent search algorithm in order to dynamically create a null testing condition for unknown freeform optics. The single-shot deflectometry system implemented on an iPhone uses a multiplexed display pattern to enable dynamic measurements of time-varying optical components or optics in vibration. Experimental data, measurement accuracy / precision, and data processing algorithms are discussed.
The aberration in the center position of wavefront can be corrected well when the deformable mirrors (DM) used in high-resolution adaptive optics system of telescope. However, for the defocus and spherical aberration of telescope, the four corners of the wavefront cannot be corrected well. A novel correction method with different levels and regions of deformable mirror is proposed to solve this problem. The control elements of wavefront in four corners are divided. And every four or five DM units in one corner is in a group. Compared with conventional correction method, the location-grouping method showed significant advantages in correction of different order aberrations.
Deformable mirror is a widely used wavefront corrector in adaptive optics system, especially in astronomical, image and laser optics. A new structure of DM--3D DM is proposed, which has removable actuators and can correct different aberrations with different actuator arrangements. A 3D DM consists of several reflection mirrors. Every mirror has a single actuator and is independent of each other. Two kinds of actuator arrangement algorithm are compared: random disturbance algorithm (RDA) and global arrangement algorithm (GAA). Correction effects of these two algorithms and comparison are analyzed through numerical simulation. The simulation results show that 3D DM with removable actuators can obviously improve the correction effects.
KEYWORDS: Bragg cells, Wavefront sensors, Wavefronts, Signal to noise ratio, Sensors, Charge-coupled devices, Acousto-optics, Photovoltaics, Heterodyning, High power lasers
A versatile wavefront sensor is described, using a two-dimensional acousto-optic modulator (AOM) driven with double radio frequencies in both the orthogonal directions. Inserted in the spectral plane in a 4-f system, the AOM acts like a moving double-frequency crossed grating. The proposed wavefront sensor inherits the advantages of a double-frequency grating lateral shearing interferometer in the aspects of high-resolution slope estimations and structure compactness. The sensor naturally performs as a heterodyne detection system, thanks to the inherent property of traveling waves in acousto-optic modulators. Variable shear can be acquired conveniently by electronically adjusting the driving frequencies, with the optimal performance achieved under different circumstances involving parameters such as accuracy, dynamic range, and signal-to-noise ratio. Beyond the proposed concept, theory analysis is presented in detail, and simulations are carried out to demonstrate the principle and validation of the proposed wavefront sensor.
Optical array technology is an attractive method of achieving high power output using diode bars, which is different from using traditional diode stacks. Reflectors are the main optical elements in optical array diode lasers, and their influences of alignment errors on the output beam are analyzed using the matrix method. Analytical expressions of the beam size and deviation influenced by the misalignment of the reflectors are deduced, and the misalignment tolerances are also given. Based on the results, it is helpful to adjust the reflectors to achieve an output beam of good beam quality from the optical array diode lasers.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.