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域形成良好的三维图像，并实现利用相位重建的干涉测量和显微术。我们首先演示了使用三波长激光（He-Cd激光，636 nm，537 nm和441 nm）重建彩色图像。在中心波长处相移量是正确的，但在其他波长处存在误差。我们进行了计算机模拟评估，结果证明效果并不严重。对两种重构算法进行了比较，明确了选择的条件。相移误差可以通过消色差移相器去除，以提供更好的图像。在红外区域，我们使用波长为830 nm，输出功率为30 mW的激光器来重建点、漫反射物体和相位物体。通过相位重建，可以定量地分析镜面和液体表面的形状。对于漫反射表面，我们利用物体光照倾斜前后或物体变形前后的重建相位之差，分别以10微米和10纳米的分辨率测量表面形状和位移。我们还可以通过使用成像设置来扩展对象的大小。综上所述，利用相移数字全息技术可以在红外区域重建出令人满意的三维图像，并且可以对可见光区域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.