Development of Phase Contrast X-ray Microscopy

我们建议开发两种新的X射线显微镜操作模式，这两种模式将利用相位对比度来成像60 nm或更高分辨率的厚的、水合的生物样品。与使用吸收对比度的现有X射线显微镜相比，相衬显微镜在某些波长提供了更高的本征对比度，从而减少了辐射剂量，并有可能改善厚样品的穿透性和景深。我们将研制一台全息相衬X射线显微镜，它将利用光刻胶探测器以高空间分辨率记录参照波与经过样品的幅度和相位变化的波之间的干涉图样，并通过数值全息再现来恢复复杂的样品波。将开发一种差分相位对比度X射线显微镜，它将使用菲涅耳波带板形成聚焦X射线斑点，通过该斑点扫描样品，并将使用光学杠杆探测器来测量样品中的折射率梯度和X射线吸收。这些显微镜的操作将通过成像测试对象进行验证，然后将使用各种水合和未切片的生物标本来演示它们的操作。

We propose to develop two new operational modes of x-ray microscopes which will make use of phase contrast for imaging thick, hydrated biological specimens with 60 nm or better resolution. Compared to current to current x-ray microscopes which use absorption contrast, phase contrast microscopes offer the promise of higher intrinsic contrast at certain wavelengths and thus reduced radiation dose, plus the possibility of improved penetration and depth of field for thick specimens. A Holographic Phase Contrast X-ray Microscope will be developed which will use a photoresist detector to record with high spatial resolution the interference pattern between a reference wave and a wave which has undergone amplitude and phase changes by passage through the specimen; the complex specimen wave will be recovered by numerical hologram reconstruction. A Differential Phase Contrast X-ray Microscope will be developed which will use a Fresnel zone plate to form a focusses x-ray spot through which a sample is scanned, and which will use an optical lever detector to measure refractive index gradients as well as x-ray absorption in the sample. Operation of these microscopes will be verified by imaging test objects, and then their operation will be demonstrated using a variety of hydrated and unsectioned biological specimens.