Haijun Gao

Chinese Academy of Sciences, Peping, Beijing, China

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Publications (7)5.19 Total impact

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    ABSTRACT: A dual-frequency laser interferometer has been developed based on a low-performance commercial interferometer. An optical resolution of 1.24 nm and a nanometer-scale accuracy have been achieved by using unique techniques to obtain an optical subdivision factor of 1/8. A method for reducing static positioning errors was also shown. The measurement of a free-falling body was performed to test the maximum achievable target velocity of the device. The experimental setup for measuring the static positioning errors was also given. The new interferometer could be widely used in nanometer-scale fabrications and measurements.
    Applied Optics 05/2006; 45(10):2246-50. DOI:10.1364/AO.45.002246
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    ABSTRACT: A new dual-frequency laser displacement measurement interferometer with nanometer precision has been developed. An eight-pass optical subdivision technology is proposed to improve resolution based on commercial interferometers. A static positioning error measuring method has been used to examine the precision and repeatability of the laser interferometer. An optical resolution of 1.24 nm and an accuracy of nanometer scale have been achieved.
    Chinese Optics Letters 09/2005; 3(9):513-515.
  • Haijun Gao, Zhaogu Cheng, Guoliang Xu
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    ABSTRACT: A novel high-average-power pulsed CO2 laser with a unique electrode structure is presented. The operation of a 5-kW transverse-flow CO2 laser with the preionized pulse-train switched technique results in pulsation of the laser power, and the average laser power is about 5 kW. The characteristic of this technique is switching the preionized pulses into pulse trains so as to use the small preionized power (hundreds of watts) to control the large main-discharge power (tens of kilowatts). By this means, the cost and the complexity of the power supply are greatly reduced. The welding of LF2, LF21, LD2, and LY12 aluminum alloy plates has been successfully achieved using this laser.
    Optical Engineering 06/2005; 44(6). DOI:10.1117/1.1921187
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    ABSTRACT: The ABCD law of parameter q for fundamental-mode Gaussian beam is deduced in this paper. The result shows that the changes of focal length and focal depth are not related to the orders of the Gaussian beam modes when focus lens moves along optical axis in a large range, indicating that the ABCD law of parameter q can be used for any order modes. A laser focusing setup is designed, and the response characteristics of oil pressure system therein are also studied.
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    ABSTRACT: A measurement interferometer available for wafer stage metrology of lithography has been investigated by means of resolution-extending of optical subdivision based on commercial interferometers. Factors that determine the accuracy, linearity and repeatability of nanometer-scale measurements of displacements exceeding hundreds of millimeters and of target velocities exceeding hundreds of millimeters per second are also discussed.
    Proceedings of SPIE - The International Society for Optical Engineering 01/2004; DOI:10.1117/12.596381
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    ABSTRACT: Research on change of Rayleigh range ZR of output beams and effect of focusing characteristics caused by the dynamic process of resonator deformation especially for the HR coupler in high power CO2 Laser is given in this paper. An adaptive optics system which can compensates the change of Rayleigh range ZR was used. The real-time control of focus position was achieved.
    Proceedings of SPIE - The International Society for Optical Engineering 03/2003; DOI:10.1117/12.497938
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    ABSTRACT: The focusing characteristics of higher-order mode Gaussian beams in flying optics were investigated in detail. On the basis, a novel adaptive laser processing system for flying optics was developed. In the system, a lens with long focal length and two adaptive deformable mirrors controlled by hydraulic were employed. The lens was near the laser source for some distance and the two adaptive mirrors were integrated together with parabolic focusing mirror. The system has the advantages of compact structure and easy control. The system can keep the focus position and the focus radius constant for long distance laser processing.
    Proceedings of SPIE - The International Society for Optical Engineering 03/2003; DOI:10.1117/12.497930