Studies On Digital Knife-edge Testing Technology

Knife-edge testing technology has many advantages, for example simple equipments, low cost, with little damnification by noncontact testing, fast and high precision. For a long time, there has been no breakthrough on knife-edge testing technology because of its shortcoming in qualitative testing. With the development of computer technology and image processing technic, digital knife-edge testing technology has been put forward. The computer can be used to disposal the images recorded by the CCD detector and the quantificational results will be obtained soon. Therefore, the applied field of knife-edge testing technology has been broadened.This paper expatiates the status quo of surface characterization test of optical components domestic and overseas, and introduces the common means used to test surface characterization of optical components, sequentially puts forward the practical significance and applied value of this studies. After introducing the key steps of digital knife-edge testing technology in detail, we validate the testing on both large aperture optical component and micro-mirror array. The main results obtained from the experiments have been summarized as follows:1. According to the principle of knife-edge testing, we compare the perfect focus with actual focus to find the image difference between them when the knife-edge is moving, and put forward the concept of the darkening threshold of each pixel with corresponding mathematic expression.2. After analyse the curve of illumination response of one pixel while the knife-edge is moving through the image, we fit the measured illumination data withBoltzman model, and then present the numeric calculating method. The Boltzman model is chosen not only because the physical meaning of each parameter inside is definite but also the model can simplify the calculating process.3. Aiming at the characteristics of large aperture optical component, combining with the experimental thoughts of the digital knife-edge testing technology and tightly holding the relative slope of each surface unit, we establish the geometry model of large aperture optical component for the digital knife-edge testing for the first time, which model has the simple form and can be applied extensively.4. The great difficulty is to identify the shadow image in micro-mirror array testing. We experiment again and again with deep consideration and put forward the dynamic identifying method in the course of micro-mirror array testing.5. Based on the geometry model which had been established, we make sure the choice of the experiment project and complete the experimental equipment design of the digital knife-edge testing. We validate the reconstruction of the full surface in three dimensionalities and calculate the relevant parameters of the tested surface characterization, and then make a breakthrough in knife-edge testing for realize the quantitative, high speed and precise testing.6. The software used to process experimental data has been programmed, which includes several kinds of functions, such as P-V and RMS value calculation and reconstruction of the actual three-dimension surface. What's most important is the software can be applied to both large aperture optical component and micro-mirror array.