3-dimensional measurements by infrared phase-shifting digital holography

本研究的目的是开发一种新的技术，能够在成像元件性能不如可见光区的红外区形成良好的三维图像，并实现利用相位重构的干涉测量和显微术。我们首先演示了彩色图像的重建，通过使用3波长激光（He-Cd激光，636 nm，537 nm和441 nm）。相移量在中心波长处是正确的，但在其他波长处包含误差。我们进行了计算机模拟评估的影响，证明是不严重的。比较了两种重建算法，阐明了选择的条件。在红外波段，采用波长为830 nm，输出功率为30 mW的激光，对点、漫反射物体和位相物体进行了重建。通过相位重构可以定量分析镜面形和液面形状。对于漫反射表面，我们采取了物体照明或物体变形倾斜前后的重建相位差，以测量表面形状和位移，分辨率分别为10微米和10 nm。总之，在红外波段，我们可以用相移数字全息术重建出令人满意的三维图像，并能对可见光区不透明的硅晶体和生物物体进行三维测量。

The purpose of this research is to develop a new technique that enables to form good 3-dimensional image in the infrared region where performances of imaging components are not so good as in the visible region and to realize interferometry and microscopy that make use of phase reconstruction. We first demonstrated reconstruction of colored images by using a 3-wavelength laser (He-Cd laser, 636 nm,537 nm, and 441 nm). The amount of phase shift was correct at the central wavelength but contains errors at the other wavelengths. We conducted computer simulation for evaluating the effect that proved not to be serious. We also compared two algorithms of reconstruction and clarified the conditions for choice. The phase shifting error could be removed by an achromatic phase shifter to provide better images.In infrared region we employed a laser of wavelength 830 nm and output power of 30 mW to reconstruct a point, diffusely reflecting objects, and phase objects. By means of phase reconstruction we could analyze surface shape of mirrors and liquid surfaces quantitatively. For diffusely reflecting surfaces, we took the difference of the reconstructed phases before and after tilt of the object illumination or object deformation to measure surface shape and displacement with resolutions of 10 micrometers and 10 nm, respectively. We also could extend the object size by employing an imaging setup.In conclusion, we can reconstruct satisfactory 3-dimensional images by using the phase-shifting digital holography in the infrared region and will be able to attain 3-dimensional measurements on Silicon crystals and biological objects which are opaque in the visible region.