微分干渉コントラスト

differential interference contrast

[目次：理論(電子の散乱／回折／結像)]

光学密度すなわち屈折率のみが異なる物体は透過顕微鏡ではコントラストを示さないが、屈折率の違いによって与えられる明暗のこと。光学顕微鏡の場合には、ポラライザで光を偏向が異なる2本の光線に分け、試料の異なる場所を通し、試料を透過するさい二つの場所で異なる位相差を生じた光を、ポラライザで偏向を区別しない1本の光線に戻して、干渉させてコントラストをつける手法。二つの光線の間にさらにバイアス位相差を与えると物体の輪郭に影をつけた像が得られる。電子顕微鏡の場合、物体を通過した電子線の半分にバイアス位相を与えて鮮明なコントラストを得る試みがなされている。

Contrast formed by the difference of optical density or refractive index. It is noted that a substance with different refractive indices does not show any contrast in the transmission microscope. In the case of an optical microscope, "differential interference contrast" is obtained by the following way. Light is split into two rays with different polarizations by a polarizer and these two rays are passed through different specimen areas. At this event, a phase difference arises between the two rays depending on the difference of the optical density of the areas. Then, the two rays with the different phases are put back unpolarized by the polarizer to make interference between the two. As a result, the differential interference contrast is produced. When an additional bias phase is given between the two rays, an image with a shadow on the object edge is formed. In the case of TEM, an attempt has been made to obtain a sharp contrast image by giving an additional bias phase to a half of the electron beam that passes through an object specimen.