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A test unit is described which includes an automatic focusing device and a displacementsensor for lens movement. The resolution of the unit is 20 nm in the range of 4 0 jim. In addition , a technique for ensuring the focal spot using the character of the laser diode is presented. This measuremet principle can be widely used in the areas of precision manufacture , optical industry and soft materials testing. 1 Introduction There are many cases in research , development and manufacture where one has to survey and monitorthe surface profiles of polished and machined parts. It is so important that a lot of testing methods have been put forward'. Of all the techniques used , the instruments using a mechanical stylus are the most direct2 and utilized widely. In some instances , however , the samples may be damaged by the stylus. Andthe horizontal resolution limited by the stylus diameter can not be tolerated in other conditions. Thus , a non-contact measurement with high horizontal resolution is strongly required.Several non-contact testing processes have been proposed and partially realized in recent years. Theybased on optical measuring principles3 and got some suceesses4'5. Here we report a testing system whichmake use of the techniques of optical disc and high sensitivity inductor displacement sensor. It has not onlyhigh resolution but also large measuring range. After being applied in testing some gratings and focusboards, it has been proved valuable. |
