基于光子混频连续太赫兹波的厚度检测

为了将光子混频的连续太赫兹波透射成像系统应用于样品厚度检测中,采用该系统获得的相位信息对样品进行了2维厚度测量。利用两个外腔半导体结构的激光器搭建了基于光子混频的连续太赫兹波透射成像系统,并利用X-Y 2维电动平移台放置样品进行点点扫描成像。该系统可同时获得样品的幅度信息和相位信息,在太赫兹波辐射频率0.47THz时,系统信噪比可达68dB。计算得出的厚度值与实际样品的厚度值最大相差0.02mm;另外还分析了平行平面样品干涉效应和样品不同透射强度对厚度测量的影响。结果表明,样品折射率越高,平行平面干涉效应对厚度测量影响越大;样品透射系数越大,测量精度也越高。当样品太赫兹波透射系数大于0.5时,厚度测量精度优于2.0%。

Thickness measurement by means of continuous wave terahertz based on photomixing

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.