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Research On Frequency Stabilization Technology Of Nd:YAG Laser Based On The There Harmonic Demodulation Of Iodine Absorption Spectrum

Posted on:2017-04-17Degree:MasterType:Thesis
Country:ChinaCandidate:J C WuFull Text:PDF
GTID:2308330503987134Subject:Instrument Science and Technology
Abstract/Summary:PDF Full Text Request
In recent years, in the promotion of various types of electronic products, the processing performance and efficiency of semiconductor manufacturing equipment, such as microelectronic lithography and other semiconductor manufacturing equipment has been rapidly improved. Existing high-end microelectronic lithography machine widely used the fast ultra precision laser interferometer as the high speed, dynamic, real-time position and attitude measurement method and its relative measurement accuracy of 10-8; the new generation and the next generation microelectronic lithography machine may use advanced ultra precision laser interferometer or in the interferometer based on fusion plane grating technology to form a multi-dimensional grating interferometer, to meet the 10-9 relative precision demand. With the development of the next generation of fast ultra precision laser interferometer and grating interferometer, the demand for frequency accuracy and power of the laser source, will greatly exceed the capabilities of gas laser respectively used in laser interferometer system. In order to meet the needs of coherent light source, taking the Nd: YAG laser with the output power to hundreds of milliwatts or even a few watts as research object, this paper focuses on the methods and critical technologies of laser frequency stabilization based on external modulation of iodine absorption spectrum. The research contents are as followed:(1) Taking the typical laser heterodyne interferometry system and grating interferometer system in lithography machine as example, this paper analyses principles of laser heterodyne interferometry and grating interferometry, and establishes the model of displacement measurement error relevant to laser frequency and power consumption and power demand of laser. Based on this, the requirement of output power and frequency accuracy of laser is presented.(2) Under the condition of normal running, the random range of Nd:YAG laser’s initial frequency is greatly out of the scanning range of resonant cavity PZT, which leads to the problem that it can not be fully covered by the predetermined absorption spectrum and can not be ordered to output the characteristic signal of ultra fine component. To solve the problems, A method for two parameters of laser crystal temperature and resonant cavity PZT voltage is proposed that it scans the frequency by the laser crystal temperature briefly and resonant cavity PZT scans finely to realize the full scan coverage of the super fine absorption component of the iodine molecule is realized by the laser frequency.(3) There are dozens of ultra-precision absorption peaks in iodine molecules and such absorption peaks own light intensity modulation slope noises, making specific absorption peaks difficult to recognize effectively and lock precisely. In order to solve these problems, methods based on threshold value trigger, first peak identification and sequence count of absorption spectrum ultra-precision absorption peak are designed to feature absorption peaks. Besides, light intensity modulation slope noises existing in absorption peaks are estimated by employing sliding window digital. integration average method, and precise lock of laser frequency to iodine molecule specific ultra-precision components are achieved.(4) To develop the device based on iodine absorption spectrum external modulation and third harmonic demodulation. Laser frequency modulation light path, iodine absorption and difference detection light path, third harmonic a cquisition and digital demodulation circuit, absorption peak distinguish count and lock control unit, frequency stabilization device integration mechanical structure and so on are designed as well as a Nd:YAG laser frequency stabilization device is integra ted.The integrated Nd:YAG laser frequency stabilization device has been tested and experiment results showed that the proposed device can achieve the complete coverage of iodine absorption, effective recognize and precise lock of specific absorption peaks. Once the frequency is stabilized, the output power of laser is greater than 27 m W and relative frequency stabilization is 1.2×10-9(1h). It is indicated in the further uncertainty analysis that the output frequency accuracy of frequency stabilization device is 1.2×10-9(1h).
Keywords/Search Tags:frequency-stabilization, Iodine absorption spectrum, external modulation, three harmonic
PDF Full Text Request
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