서강대학교

초록/요약

The balanced-path scheme proposed by Yoon et al., has been applied to the homodyne I/Q-interferometer. It will be shown that the new scheme can provide a 30dB rejection of vibration noise in the scanning interferometer application in which 11dB better common vibration rejection over the heterodyne scheme. Therefore, it allows high sensitivity and high stability phase and amplitude measurements for high speed scanning interferometer applications. It will be shown that the new scanning interferometer scheme is very useful for diagnosing a sample that requires complex analysis. As one example, the balanced-path homodyne I/Q-interferometer has been applied for obtaining phase and amplitude images of the protein biochip samples prepared by using the sandwich ELISA. The amplitude images are used for diagnosing homogeneity of the sample, while the phase images are used for measuring the phase difference between samples treated with different concentrations of IL-5. It will be shown that new interferometer scheme can easily identify the biochip treated with 1pg/ml or 40fM concentration of IL-5. The average RMS phase noise in the typical measurement interval, 5 minutes, is 2.85 ?10-5 rad at which the corresponding concentration for S/N=1 is ? 1.2fg/ml or 48aM. As another example, application of this interferometer scheme to high scan speed coherent microscopy will also be discussed. It will be shown that the scanning speed of the new balanced-path scheme can be increased significantly over the previous scanning interferometer arrangement because vibration noise can be rejected in balanced-path arrangement. The maximum scanning speed is 1mm/s which is limited by the scanning stage. The complexity in the optical arrangement which may be responsible for performance degradation caused by misalignments between optical components and/or susceptibility to environmental perturbations in previous balanced-path homodyne interferometer scheme has been simplified by using a specially designed polarizing beam displacer. The balanced-path homodyne I/Q interferometer can be constructed by using the polarizing beam displacer and ?/4-plate. It will be shown that this new scheme not only has simple optical arrangement but also provides significant improvement in both short and long term stabilities over the previous arrangement. The application biochips prepared for the same sandwich ELISA but 5x5?m2 pattern size are used as the samples. The scanning speed is 1mm/s which is the maximum speed of the step motor stage. It will be shown that this new interferometer can still easily identify the biochip treated with 1pg/ml or 40fM concentration of IL-5. The short-term phase noise, 10?5rad, for which the equivalent concentration at signal-to-noise ratio 1 is ~0.1 fg/ml or 4 aM, tells us that our new scheme can provide extremely high sensitivity in biochip readout sensing. The application for optical microscope is also discussed. We will show that the measurement results on both amplitude and phase are well explained by using the Fresnel reflection of the incident probe beam at the film with complex reflectance. The new interferometer scheme has also been applied for measuring the displacement of load cell which can be used for a precision weight measurement. This preliminary study shows that our new interferometer scheme can be used for precision weight measurement.