一种测量表面粗糙度的激光外差干涉仪

An Instrument Used For Measuring Surface Roughness

本文讨论激光外差干涉技术测量表面粗糙度仪器的工作原理。作者利用两个声光调制器产生差频光,解调拍频信号并进行鉴相处理,精确测量表面粗糙度。文中还讨论了设计研制的表面粗糙度外差干涉仪的具体技术问题,对不同样品及加工表面进行实测,并与传统触针测试方法、干涉显微镜所得到的结果进行了比对,理论分析与实验结果一致:仪器灵敏度为10(?),测量精度10nm。

In this paper the principle of a non-contact optical instrume-nt for measuring surface roughness with heterodyne interferometer is mentio-ned.A frequency difference of2.25MHz between reference arm and measuringarm is obtained by utilizing two acousto-optic modulators in the interferomet-er.The beam is focused into a spot on the tested surface by a objective lensand the surface is moved by a stepper motor along a precision guide.Thebeams from the surface under test and the reference mirror are recombined andthe phase of the interference pattern signal of optical beat is proportional tothe surface undulation,thus the microtopography can be measured by comparingthe phase.The phase demodulation technique is employed to improve the resolution upto 0.36 degrees,corresponding to one thousandth wavelength.Height variationof 10 nm can be resolved,while the theoretical height resolution is 10 angst-roms.With AGC,frequency demultiplication and pulse counting techniques,the measuring range is extended to 30 microns.After calibration,many typesof samples are measured,the results are compared with ones by stylus instru-ment and interference microscope,they coincide each other.The simplest layout and the less optics are used in the interferometer wit-hout any polarizer and lens designed specially as other interferometers.