Studies On Laser Interferometric Imaging

The essence of imaging is obtaining the intensity reflectivity of the illuminated objects. The basic steps of the laser interferometric imaging is as follows: firstly, forming laser interference fringes in a certain space; secondly, the scattered light is yielded from an object which travels across the interference field, then a detector is employed to detect the scattered light; finally the image is reconstructed through certain processes to the scattering light. In this thesis, it was proved that the intensity of the return signal is the convolution of the intensity reflectivity of the object and the fringes intensity, as the fringes intensity is known, the information of the intensity reflectivity of the object could be sampled from the return signal. From the point of view of frequency domain, the process of scanning an object with the interference fringes could be regarded as windowing the spectrum of the object, and the form of the window is decided by the form of the fringes. For reconstructing the image of an object with certain resolution, two-dimension(2D) spectrum with a certain bandwidth of the object must be collected. Another noticeable point is that the formed fringes should have the spectrum which is concentrated on zero and low area in which the objects' spectrum be concentrated. Some progress has been made both in theoretical and experimental areas in this thesis. The theoretic aspects are: 1) The principle of laser interferometric imaging is clarified with the theory of frequency analysis. 2) The resolution limit of imaging with circular interference fringes is given out.3) The basis of selecting the departure in eccentric circular fringes imaging is brought out;4) The influence of the self-clutter induced by object's motion and the way is explored that the self-clutter may be reduced.5) The concept of imaging with gradually varying space frequency linear(GVSFL) fringes isproposed, including both 2D imaging with multi-direction scanning and 2D imaging with one time relative linear motion. In experimental aspect: 1) A 2D image of an object situated at 0.52 meters is reconstructed with circular interference fringes in the laboratory.2) An experimental is completed to demonstrate 2D imaging with GVSFL fringes, adapting multi-direction relative motion.3) An experiment is completed to demonstrate 2D imaging with GVSFL fringes, the object traveling through the fringes for only one time.4) Clear circular fringes are formed at the distance of about 60 meters and it's parameters are well consistent with computed parameters.5) GVSFL fringes are formed which parameters are well consistent with computed values.The above progress shows that the laser interferometric imaging has good prospect.