Large telescopes are developing, and promoted by new technological developments. In order to study the method of mirror seeing detection for large aperture optical system, the relationship between mirror seeing and slope information is derived first. In order to evaluate the results more comprehensively, the normalized point source sensitivity was introduced to evaluate the results. Finally, according to the previous analysis, the experiment was carried out. The change normalized point source sensitivity under different conditions is calculated. By comparing with RMS of wavefront, the better statistical characteristic of sensitivity of normalized point source was verified.
Warping Harness is a mechanism which can periodically correct the low order surface errors of mirror. The main correction objects are the residual error of the mirror machining, the stress distortion caused by the coating, the surface error caused by the temperature load, even with the errors caused by the gravity change, and so on. In principle, the zero moment point of the Whiffletree structure can be adjusted by changing the deflection of the warping harness blade. Due to the closed force system, once the moment induced by the warping harness changes, the load distribution on the whiffletree structure varies too. In practice, the structure of Warping Harness is installed on each group of Whiffletree joints and works with the structure of Whiffletree. The servo stepping motor is employed to control the bending of the spring blade to change the distribution of the support force, and then the correction of the main mirror surface figure is completed. This paper mainly introduces the correction principle of Warping harness and its principle, and demonstrates the preliminary design of the system.
Tertiary mirror of thirty meter telescope (TMT) has the tracking and pointing capabilities, and its structure is similar to an alt-az telescope. The cradle serves a similar function to the center block of the track frame, its structure directly affects the performance of the system. M3 prototype as an example, in order to improve stiffness to weight ratio of the cradle, the mathematical model of topology optimization design of the cradle was established and the optimization was performed. Then a spliced truss structure for cradle was designed based on the result of the topology optimization. By using finite element method, the static and dynamic analysis of cradle under different conditions was done according to the working characteristics. The results showed that under the conditions of the gravity vertical along the x, y, z, the maximum deformation of cradle was 0.064mm, 0.015mm, 0.025mm respectively, and the first modal frequency is 74.4Hz. Results showed the structure designed meets the requirement.
The Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) team is developing Giant Steerable Science Mirror (GSSM) for Thirty Meter Telescope (TMT). This paper will combine PSSn to analyze the error characteristics of GSSM. To evaluate the performance of the large telescope under different kinds of error source, the normalized point source sensitivity is introduced, which is firstly studied by the group of thirty meter telescope team to balance all the deviation of the telescope and also budget the error. First and foremost, the character of the normalized point source sensitivity is studied in the very first part and the advantage in the evaluation in all the frequency domain. Then the PSSn is compared with the traditional metric, such as RMS and the multiplication property is discussed. The experienced formula is used to show the relationship between the PSSn and the error sources, static and dynamic. Lastly, the method is applied to a large aperture telescope.
The Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) team is developing Giant Steerable Science Mirror (GSSM) for Thirty Meter Telescope (TMT) which has got into the preliminary design phase in 2017. To develop the passive support structure system for the largest elliptic-plane flat mirror and a smoothest tracking mechanism for the gravity-variant condition, CIOMP had developed a 1/4 scale, functionally accurate version of the GSSM prototype as the pre-construction of GSSM. The prototype incorporates the same optical-mechanical system and servo control system as GSSM. The size of the prototype mirror is 898.5mm×634mm×12.5 mm with elliptic-plane figure and is supported by 18 points whiffletree on axial and 12 points whiffletree on lateral. The main objective of the preconstruction includes validate the conceptual design of GSSM and increase more confidence when meet the challenge during the development of GSSM. The assembling, integration and verification of the prototype have been completed based on the test results. CIOMP has got the sufficient test results during the pre-construction phase and got into the preliminary design for GSSM.
The Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) team is developing the Giant Steerable Science Mirror (GSSM) for Thirty Meter Telescope (TMT) which will enter the preliminary design phase in 2016. The GSSM is the tertiary mirror of TMT and consists of the world’s largest flat telescope mirror (approximately 3.4m X 2.4 m X 100mm thick) having an elliptical perimeter positioned with an extremely smooth tracking and pointing mechanism in a gravity-varying environment. In order to prepare for developing this unique mirror system, CIOMP has been developing a 1/4 scale, functionally accurate version of the GSSM prototype during the pre-construction phase of GSSM. The prototype will incorporate the same optomechanical system and servo control system as the GSSM. The size of the prototype mirror is 898.5mm×634mm×12.5mm with an elliptical perimeter. The mirror will be supported axially by an 18 point whiffletree and laterally with a 12 point whiffletree. The main objective of the preconstruction phase includes requirement validation and risk reduction for GSSM and to increase confidence that the challenge of developing the GSSM can be met. The precision mechanism system and the optical mirror polishing and testing have made good progress. CIOMP has completed polishing the mirror, the prototype mechanism is nearly assembled, some testing has been performed, and additional testing is being planned and prepared. A dummy mirror is being integrated into the cell assembly prototype to verify the design, analysis and interface and will be used when testing the prototype positioner tilt and rotation motions. The prototype positioner tilt and rotator structures have been assembled and tested to measure each subsystem’s jitter and dynamic motion. The mirror prototype has been polished and tested to verify the polishing specification requirement and the mirror manufacturing process. The complete assembly, integration and verification of the prototype will be soon finished. Final testing will verify the prototype requirements including mounted mirror surface figure accuracy in 5 different orientations; rotation and tilt motion calibration and pointing precision; motion jitter; and internally generated vibrations. CIOMP has scheduled to complete the prototype by the end of July 2016. CIOMP will get the sufficient test results during the pre-construction phase to prepare to enter the preliminary design for GSSM.
The Changchun Institute of Optics, Fine Mechanics and Physics (CIOMP) team is developing the Giant Steerable Science Mirror (GSSM) for Thirty Meter Telescope (TMT) which will get into the preliminary design phase in 2016. To develop the passive support structure system for the largest elliptic-plan flat mirror and smoothest tracking mechanism for the gravity-invariant condition, CIOMP is designing and building a 1/4 scale, functionally accurate version of the GSSM prototype. The prototype will incorporate the same optical-mechanical system and electric control system as the GSSM. The size of the prototype mirror is 898.5mm×634mm×12.5mm with elliptic-plan figure and will be supported by 18 points whiffletree on axial and 12 points whiffletree on lateral. The mirror surface figure will be evaluated by SlopeRMS which is the final evaluation method used in the actual GSSM. The prototype allows the mirror point to and be tested in five specified gravity orientations and meet the requirements of SlopeRMS. The prototype testing platform will have the interfaces with direct drive systems. The jitter testing will be implemented on the prototype system to verify the bearing, the encoder, the servo control algorithm in the low speed up to 5 arcsecond per second. The total prototype system configured mirror surface figure will be better than 1 micro radian SlopeRMS in each tested orientation. The positioner jitter will be less than 0.1 arcsecond RMS for tilt and rotator axis respectively and will be analyzed with frequency domain to meet the requirements of the TMT adaptive optics system. The pre-construction will be completed at the beginning of 2016 and provide the technical support to the preliminary design of GSSM.
As lithography still pushing toward to lower k imaging, traditional illumination source shapes may perform marginally in resolving complex layouts, freeform source shapes are expected to achieve better image quality. Illumination optimization as one of inverse lithography techniques attempts to synthesize the input source which leads to the desired output wafer pattern by inverting the forward model from mask to wafer. This paper proposes a method to optimize illumination by using simulated annealing algorithms (SA). A synthesis of the NILS values at multi-critical mask locations over a focus range is chose as the merit function. The advantage of the SA algorithm is that it can identify optimum source solutions without any additional apriori knowledge about lithographic processes. The results show that our method can provide great improvements in both image quality and DOF.
As lithography still pushing toward to lower K1 imaging, traditional illumination source shapes may perform marginally in resolving complex layouts, freeform source shapes are expected to achieve better image quality. Illumination optimization as one of inverse lithography techniques attempts to synthesize the input source which leads to the desired output wafer pattern by inverting the forward model from mask to wafer. Usually, inverse lithography problem could be solved by standard numerical methods. Recently, a set of gradient-based numerical methods have been developed to solve the mask optimization problem based on Hopkins' approach. In this study, the same method is also applied to resolve the illumination optimization but based on Abbe imaging formulation for partially coherent illumination. Firstly we state a pixel-based source representation, and analyze the constraint condition for source intensity. Secondly, we propose an objective function which includes three aspects: image fidelity, source smoothness and discretization penalty. Image fidelity is to ensure that the image is as close to the given mask as possible. Source smoothness and discretization penalty are to decrease the source complexity. All of the three items could be described mathematically. Thirdly, we describe the detailed optimization flow, and present the advantages of using Abbe imaging formulation as calculation mode of light intensity. Finally, some simulations were done with initial conventional illumination for 90nm isolated, dense and elbow features separately. As a result, we get irregular dipole source shapes for isolated and dense pattern, and irregular quadrupole for elbow pattern. The results also show that our method could provide great improvements in both image fidelity and source complexity.