A set of lateral shear optical tests with a liquid crystal display

Abstract

In the literature it is possible to find the implementation of interferometric lateral shear tests with a liquid crystal display (LCD). We collected them and implemented others not previously reported. We show the versatility that the LCD offers to test of optical surfaces, so that graduate students can experience the following tests: the Foucault test, the Wire test, the Hartmann test, the Ronchi test and the null Ronchi test. Although these tests have been studied and developed since many years ago, they require different screens for each test. One advantage of using a LCD is that it can display many different screens, and therefore all mentioned tests can be developed. Another advantage is that, by digitizing the patterns observed with a CCD camera, it is possible to analyze them to obtain quantitative results instead of qualitative results; hence we use the Ronchi test as lateral shear interferometer to develop the phase shifting interferometry (PSI). In order to validate our method with the PC we implement the PSI using the Hariharan algorithm on the LCD. We used a LED as illuminating source avoiding the use of expensive sources of light. A Ronchi grating with a big period was required when testing optical surfaces with large ƒ /#, vice versa. This was done easily from the PC on the LCD, with a software that we developed with Visual C++ 6.0, a program to control the different parameters of the screens displayed on the LCD.