Thickness measurement by means of continuous wave terahertz based on photomixing

LIU Ziye; LIU Jianjun; HONG Zhi

doi:10.7510/jgjs.issn.1001-3806.2016.04.009

In order to measure thickness of a specimen with a continuous wave terahertz imaging system based on photomixing, its 2-D thickness was measured by means of the phase information obtained from the imaging system. A continuous wave terahertz imaging system based on photomixing was established by using two external cavity laser diodes. The specimen was placed on the X-Y motorized precision translation stage and point-to-point scanning images were generated. Both the amplitude and phase information can be obtained simultaneously through the system. The signal-to-noise ratio of the system was 68dB at the frequency of 0.47THz. The deviation between the calculated result and the actual measurement was less than 0.02mm. The influences of the interference of plane specimen and transmission intensity on thickness measurement accuracy were analyzed. The results show that, the higher refractive index of the plane specimen is, the greater interference influence on thickness measurement becomes. The accuracy increases with the increase of terahertz transmission. The accuracy of thickness is better than 2.0% when the transmission coefficient is higher than 0.5.

Thickness measurement by means of continuous wave terahertz based on photomixing

Corresponding author: HONG Zhi, hongzhi@cjlu.edu.cn

1. Centre for THz Research, China Jiliang University, Hangzhou 310018, China

Received Date: 2015-05-22

Accepted Date: 2015-06-08

Available Online: 2016-07-25

Abstract: In order to measure thickness of a specimen with a continuous wave terahertz imaging system based on photomixing, its 2-D thickness was measured by means of the phase information obtained from the imaging system. A continuous wave terahertz imaging system based on photomixing was established by using two external cavity laser diodes. The specimen was placed on the X-Y motorized precision translation stage and point-to-point scanning images were generated. Both the amplitude and phase information can be obtained simultaneously through the system. The signal-to-noise ratio of the system was 68dB at the frequency of 0.47THz. The deviation between the calculated result and the actual measurement was less than 0.02mm. The influences of the interference of plane specimen and transmission intensity on thickness measurement accuracy were analyzed. The results show that, the higher refractive index of the plane specimen is, the greater interference influence on thickness measurement becomes. The accuracy increases with the increase of terahertz transmission. The accuracy of thickness is better than 2.0% when the transmission coefficient is higher than 0.5.

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Reference (17)

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Thickness measurement by means of continuous wave terahertz based on photomixing

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