At present, the Institute of Mechanics of the Chinese Academy of Sciences has undertaken the methodological screening of the laser interference ranging system and the development of the ground simulation system, and has made progress in the near future. Scientific researchers have successfully broken through the international technology blockade and key device embargoes, and successfully designed a multi-functional laser interferometer optical path that eliminates noise and precision ranging.
The two scientific plans of space gravitational wave detection and earth gravity field spatial measurement have great scientific significance and wide application value. Space gravitational wave detection can not only test Einstein's general theory of relativity, but also open a new window for observing the early universe; and advanced gravity field measurement will study the spatial and temporal distribution of the Earth's massive water, glacial change, ocean circulation and atmospheric circulation. , change and migration phenomena provide an effective basis for analysis.
The core technology of these two scientific programs is the laser interference ranging system, which is used to obtain the variation of the star spacing caused by the disturbance of the space gravitational wave or the gravity field. The space gravitational wave detection requires the displacement measurement accuracy of the picometer level between the satellites of the order of one million kilometers. For the space measurement of the earth's gravity field, the nanometer range measurement accuracy is also obtained between the satellites of the order of 100 kilometers. .
The beam emitted by the single-frequency laser interferometer from the laser is split and collimated and split into two paths by the beam splitter, and reflected from the fixed mirror and the movable mirror respectively to merge with the beam splitter to generate interference fringes. When the movable mirror moves, the change of the intensity of the interference fringe is converted into an electrical pulse signal by the photoelectric conversion element and the electronic circuit in the receiver, and the total number of pulses is calculated by inputting the reversible counter after being shaped and amplified, and then by the computer. According to the formula [356-11], λ is the laser wavelength (N is the total number of electric pulses), and the displacement amount L of the movable mirror is calculated. When using a single-frequency laser interferometer, the surrounding atmosphere is required to be in a stable state, and various air turbulences will cause a change in the DC level and affect the measurement result.
The dual-frequency laser interferometer adds an axial magnetic field of about 0.03 Tesla to the HeNe laser. Due to the Zeeman splitting effect and the frequency pulling effect, the laser produces two different frequencies of left and right circularly polarized light of 1 and 2. After 1/4 wave plate, it becomes two mutually perpendicular linearly polarized lights, and then split into two paths through the beam splitter. After passing through the polarizing plate 1, it becomes a reference beam having a frequency of f1 - f2. The other way is divided into two paths by the polarizing beam splitter: one path becomes a beam containing only f1, and the other path becomes a beam containing only f2. When the movable mirror moves, the beam containing f2 is reflected by the movable mirror to become a beam containing f2±Δf, and Δf is an additional frequency generated by the Doppler effect when the movable mirror moves, and the sign indicates movement. Direction (Doppler effect is proposed by Austrian CJ Doppler, that is, the frequency of the wave changes when the wave source or receiver moves). This light beam and the light beam reflected from the fixed mirror and containing only the light of f1 pass through the polarizing plate 2 and are combined into a measuring beam of f1 - (f2 ± Δf).
The measuring beam and the reference beam are subtracted from the respective photoelectric conversion elements, amplifiers, and shapers into a subtractor, and the output is an electrical pulse signal containing only ±Δf. After being counted by the reversible counter, the amount of displacement of the movable mirror can be obtained by equivalent conversion (by 1/2 laser wavelength) by an electronic computer. The dual-frequency laser interferometer uses the frequency change to measure the displacement. This displacement information is carried on the frequency difference between f1 and f2, and is insensitive to the change of the DC level caused by the change of the light intensity, so the anti-interference ability is strong. It is often used to verify the coordinate accuracy of length measuring machine, coordinate measuring machine, lithography machine and machining center, and also can be used as measuring system for length measuring machine and high precision coordinate measuring machine. High-precision straightness measurement, flatness measurement and small angle measurement are also possible with the corresponding accessories.
The two scientific plans of space gravitational wave detection and earth gravity field spatial measurement have great scientific significance and wide application value. Space gravitational wave detection can not only test Einstein's general theory of relativity, but also open a new window for observing the early universe; and advanced gravity field measurement will study the spatial and temporal distribution of the Earth's massive water, glacial change, ocean circulation and atmospheric circulation. , change and migration phenomena provide an effective basis for analysis. The core technology of these two scientific programs is the laser interference ranging system, which is used to obtain the variation of the star spacing caused by the disturbance of the space gravitational wave or the gravity field. The space gravitational wave detection requires the displacement measurement accuracy of the picometer level between the satellites of the order of one million kilometers. For the space measurement of the earth's gravity field, the nanometer range measurement accuracy is also obtained between the satellites of the order of 100 kilometers. . This is undoubtedly a major challenge in current measurement.
In 2008, led by the National Microgravity Laboratory of the Institute of Mechanics of the Chinese Academy of Sciences, the Institute of Theoretical Physics of the Chinese Academy of Sciences, the Institute of Physics of the Chinese Academy of Sciences, the Wuhan Institute of Physics and Mathematics of the Chinese Academy of Sciences, Huazhong University of Science and Technology, China Eastern Red Satellite Co., Ltd., etc. The Chinese Academy of Sciences space gravitational wave research and demonstration group; in 2009, the Chinese Academy of Sciences included space gravitational wave detection in the 2050 medium and long-term development plan of the Chinese Academy of Sciences; in 2011, the US NASA exited the "LISA" program, ESA sought 20% cooperation from China, of which Pimi precision The laser interferometer is listed as one of the possible loads of China's contribution; in 2012, in response to the cooperation initiatives of international counterparts, the Institute of Mechanics and the University of Chinese Academy of Sciences led the establishment of the Space Gravity Wave Detection Working Group of the Chinese Academy of Sciences.
In order to cooperate with and promote the implementation of scientific programs such as space gravitational wave detection, Mechanics has undertaken the development of laser interference ranging system methodology (ChinesePhysics Letters, 2012, 29 (7) 079501-3) and ground simulation systems. Under the support of the Strategic Center of the Chinese Academy of Sciences Space Center and the research equipment development project of the Chinese Academy of Sciences, the researchers broke through the international technology blockade and key device embargoes, and successfully designed a multi-functional laser interferometer optical path that eliminates noise and precision ranging. A multi-noise suppression scheme was developed to develop a laser interferometer with a range accuracy better than 100 pm/Hz 1/2. Phase detection accuracy was developed using hardware platforms such as digital phase-locked loop technology (DPLL) and field programmable gate array (FPGA). High-precision phase meter better than 2π×10-5rad/Hz1/2 (Rev.Sci.Instrum.2014, 85,024503); using differential wavefront detection technology and phase sensitive pointing sensor, the development of pointing control accuracy is up to 10nrand/Hz1/2 laser pointing control simulation system (Rev.Sci.Instrum. 2014, 85, 074501); using electro-optical phase modulator, phase-locked control module, etc. to establish phase-locking accuracy better than 2π×10-4rad/Hz1 /2 laser phase lock control simulation system; at the same time, applied for a number of technical invention patents; successfully built a space laser interference ranging ground simulation device. This marks a solid step in the field of space precision ranging technology, and has accumulated valuable knowledge and experience, laying the technical foundation.
At present, the Institute of Mechanics of the Chinese Academy of Sciences has undertaken the methodological screening of the laser interference ranging system and the development of the ground simulation system, and has made progress in the near future. Scientific research personnel broke through the international technology blockade and key device embargo, successfully designed a multi-functional laser interferometer optical path that eliminates noise and precision ranging, and a multi-mode noise suppression scheme to develop a laser interferometer with excellent ranging accuracy; Digital phase-locked loop technology and field programmable gate array and other hardware platforms have developed high-precision phase meters with excellent phase detection accuracy. Using differential wavefront detection technology and phase-sensitive pointing sensor, laser pointing with high pointing control precision has been developed. Control simulation system; using electro-optic phase modulator, phase-locked control module, etc. to establish a laser phase-locked control simulation system with excellent phase-locking accuracy. At the same time, the researchers also successfully built a space laser interference ranging ground simulation device.
The above achievements indicate that China has further developed in the field of space precision ranging technology and laid the technical foundation for subsequent research. The project has recently passed the acceptance of an expert group organized by the Chinese Academy of Sciences. (
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