USING SPATIAL LIGHT MODULATOR FORCOMMON-PATH PHASE SHIFTINGINTERFEROMETRIC MICROSCOPE

• Main Authors: NG KIN KIAN, 吳景根
• Other Authors: 陳政雄
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/53395867573472309638

碩士 === 國立中興大學 === 電機工程學系所 === 102 === Common Path Interference Microscope can minimize external interference, such as vibration, temperature change, the variation of refractive index are the mainly influencing factors of the stability of the system. Common path interference microscope is a kind of instrument more suitable for frontline scene measurement. In addition to the advantages of anti-interference, and the architecture that is able to change objective with different ratios is put forward, namely the ratio of the general objective can be achieve interference. Compared with traditional interference objective, the proposed common optical path interference microscope is of lightweight, low cost and high stability. Fourier transform is made by using imaging surface and split light is made on Fourier plane; phase shifting is made on the light field with split light to reach interference. Therefore, a set of 4f-phase shifting box is designed, which can easily combine with general optical microscope. The optical components in 4f-phase shifting box include Fourier lens, Polarizer, Analyzer and Spatial Light Modulator. The light with polarization modes are formed by light source through polarizer and light source is made through spatial light modulator; a spatial light modulator is used to spectroscopic field in the Fourier plane spectroscopic field and carries out phase shifting against the diffracted light; finally interference is made in the plane of charge coupled device (CCD). The sample of transmission and reflection model are respectively used to verify the structure of common optical path interference microscope; according to different characteristics of the sizes of the sample or sample requirements, lighting ways and objectives with different ratios are respectively altered; the sample reconstructed after phase shifting through spatial light modulator is used to prove that under different lighting ways or altering objectives with different ratios can get the features of the trend of the sample; in order to verify the accuracy of the trend and actual samples, the reflection type of standard sample is used as the object under test; the reconstruction results of Mirau interferometer and three-step phase shifting method are used as reference value and compared with common path interference microscope system. The reconstruction result of Mirau interferometer and three-step phase shifting method is 1Rad and the reconstruction result of the architecture of common optical path interference microscope is 0.04 Rad. The relative error percentage of the sample information rebuilt with two methods reaches 95%. System error is mainly because the used light source lacks of spatial coherence and the joined the SLM reduces the contrast ratio of the system, which seriously affect the accuracy of the system. If He- Ne laser is used as light source, it is possible to achieve good demand of spatial coherence, but its time coherence of light source also is very good, causing the system to produce unnecessary multiple reflection, microstructure out of spatial light modulator, and severely decreasing the imaging quality of the whole system. Due to bad quality of imaging, through it is rebuilt with three-step phase shifting method in the laboratory, and after reconstruction, the very great noise causes the non-convergence of iterative phase, so the laser light source is not joined into system considerations. The common path interference microscope proposed can reach Phase Contrast Microscope through the method of phase shifting to observe samples with low visibility and successfully reconstruct the feature trend diagram of samples in the vibration frequency, but the obtained actual value of the phase is not correct. Thus, currently, the technology of spatial light modulator is not suitable for our optical path system;moreover, it lacks space coherence on the system. So, all the Phase information of samples cannot be obtained.