Development of Phase Contrast X-ray Microscopy

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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.