| Summary: | 碩士 === 國立東華大學 === 電機工程學系 === 96 === Surface plasmon resonance (SPR) is a developing technique which can be used to measure dielectric constant variation in many application areas. In the other hand, Mach-Zehnder interferometer is also an optical measurement system, but has limited resolution due to its character of easily disturbed by environment. However, it is necessary to consider and enhance the resolution when combines these two sub-systems together to setup a measurement tool. First of all, noise suppression and clear phase counting are the critical issues in this topic.
We present a modified Mach-Zehnder interference configuration to replace original one to enhance resolution. In the configuration, a 632.8nm wavelength laser beam is split into a reference and a signal beam by a beam splitter. This reference beam is then traveling through an attenuator and a phase retarding plate which are used to tune beam’s intensity and phase, respectively. Nevertheless, the other signal beam is traveling through a Krestchmann coupler and a quarter waveplate to excite surface plasmon wave and to change the reflecting beam’s polarization state, respectively. These outlet beams will be combined and interfering each other by the other beam splitter, and collected by a CCD. From these CCD captured patterns, the phase information caused from Plasmon resonance can be analyzed by a computer filter program using in Matlab.
We measured and compared the data coming from the modified and conventional Mach-Zehnder configurations by using the same samples with concentration range of 0%~6% ( 0 to 6×10-4 ppm) alcohol. The result shows that the modified Mach-Zehnder interferometer has higher resolution of 2.142×10-5 than the conventional one’s 1.28×10-5. It has 67% improvement, therefore we have successfully demonstrated that the modified Mach-Zehnder configuration can efficiently reduce the noise caused by the environment.
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