디지털 홀로그래피 현미경 정밀도 향상을 위한 간섭무늬 안정화 시스템 구축에 관한 연구

Abstract

Holography is an optical technique in which the wave nature of light is used to produce three-dimensional images of an object of interest. In addition to the at 2D representation of a photograph, the holograph also records the depth of eld by recording the phase of an incoming wave eld. The principles of holography can also be used to examine the optical properties of transparent media. The refractive index of a transparent material is dened to be the fraction by which light slows down as it propagates through the medium. A digital holographic microscope (DHM) has been constructed to measure the refractive index of living biological cells as this information has been shown to be an indicator of cell health and is also central to cellular biomechanics measurements made with optical force instruments. In order to nd the index, the DHM records interferograms which quantitatively measures laser light's change in phase as it traverses the cells. These interferograms are then processed to reveal the cell's refractive index and height. The theory and design for the DHM will be presented along with a full discussion of the interferogram processing algorithms. The experimental procedure will be outlined in detail, and verication for the integrity of the index measurements will be discussed. Finally, a summary of refractive index measurements made of red cells at several wavelengths will be presented. A digital holographic microscope that can be used to measure the refractive index of biological cells at different wavelengths that extend to the near‐infrared spectrum was built. The interference pattern produced by the reference and object beams was recorded by a CCD camera. The recording process followed a special procedure called decoupling procedure. Three digital holograms with different interference patterns were recorded by varying the refractive index of the cell medium. holographic experiments based on LabVIEW are demonstrated in this work in order to offer a teaching modal by making full use of LabVIEW as an educational tool. Digital incoherent holography enables holograms to be recorded from incoherent light with just a digital camera and spatial light modulator ，and three-dimensional properties of the specimen are revealed after the hologram is reconstructed in the computer． The experiment of phase shifting incoherent digital holography is designed and implemented based on the principle of Fresnel incoherent correlation holography． An automatic control application is developed based on LabVIEW， which combines the functions of major experimental hardware control and digital reconstruction of the holograms． The basic functions of the system are completed and a user-friendly interface is provided for easy operation． The students are encouraged and stimulated to learn and practice the basic principle of incoherent digital holography and other related optics-based technologies during the programming of the application and implementation of the system. Due to the characteristics of the optical metrology technique, a process to remove some noise due to the complexity of an optical system is essential. for constructing an noise-reduced interference system, has less noise factors than the conventional transmissive type of the digital holography system. Also, in order to stabilize the digital holography system, the corresponding error signal to the movement of the interference fringes generated by the external environment, when the external air flow, th vibration and so on are applied to the interferometer, is controlled. An interference fringes stabilization system can be constructed by using a method that the low electric voltage is applied to a piezo-electric element. The measured results are compared with those obtained from the conventional transmissive type of the digital holography system. It is confirmed that the digital holography system with an interference fringes stabilization system can obtain more stable results than the conventional method.