Phase shifting methods in Ronchi interferometer.

• Main Authors: Yuan-Chen Chung, 鍾元振
• Other Authors: Jenn-An Lin
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/26354362446912374686

碩士 === 淡江大學 === 物理學系 === 91 === The thesis first derives the intensity distribution of the interferogram on the observation plane of the Ronchi interferometer . Then we discuss th- eoretically what happens when synchronous phase detection method is used in Ronchi test for any form of one- dimensional grating. As the Ronchi gra- ting is used, it seems that the reconstructed phase could be erroneous due to the interference involved higher order diffracted beams other than zero and first orders. To get rid of the unwanted interference terms, we should choo- se phase-step N and lateral shear s so as to satisfy the condition Ns>2. A simulation is given to see the effect. If a Sine grating is used instead, no requirement on Ns is needed. Therefore, Sine grating should be a better choice than Ronchi grating in Ronchi test. Experiments are done to record interferograms with 2 4 different phase steps for both Ronchi grating and Sine grating. The thesis first derives the intensity distribution of the interferogram on the observation plane of the Ronchi interferometer . Then we discuss theoretically what happens when synchronous phase detection method is used in Ronchi test for any form of one- dimensional grating. As the Ron- chi grating is used, it seems that the reconstructed phase could be errone- ous due to the interference involved higher order diffracted beams other than zero and first orders. To get rid of the unwanted interference terms, we should choose phase-step N and lateral shear s so as to satisfy the co- ndition Ns>2. A simulation is given to see the effect. If a Sine grating is used instead, no requirement on Ns is needed. Therefore, Sine grating should be a better choice than Ronchi grating in Ronchi test. Experiments are done to record interferograms with 2 4 different phase steps for both Ronchi grating and Sine grating. In the case of Ronchi test, the reco- nstructed phase for N=24 is much better than N=4. It is because N=24 satisfies Ns>2, and N=4 is not. As far as synchronous phase detection is concerned, the result from the Sine grating should be perfect. However, the reconstructed phase curve for Sine grating with N=4 appeared a little wiggling. Most likely, it comes from the phase shifting error, quantized effect, nonlinear effect of detector and vibrations. For Sine grating with N=24, the reconstructed curve is very smooth and should be more ac- curate because it average out all the errors which are not synchronous. The reconstructed phase can be fitted or integrated to obtain the wave front aberration function of the lens under test. In addition, we also apply Hariharan Algorithm to five interferograms with /2 phase shifting among them, it could efficiently decrease some errors than N = 4 in synchronous phase detection.