Phase contrast microscope for short wavelength radiation and imaging method

#Short wavelength microscopes are devices that produce a magnified image of an object utilizing electromagnetic radiation in the extreme ultraviolet (EUV) and x-ray regime. The wavelengths range from 20 nanometers (nm) to 0.02 nm. These microscopes typically develop image contrast by relying on photoelectric absorption in the test object. Different elements, or structures formed of elements, attenuate the x-rays to varying degrees.

#In a typical short wavelength microscope configuration, a focusing element, such as a condenser, is used to concentrate the radiation on the test object. An objective, such as a zone plate, collects the radiation after transmission through the object and forms an image on a detector, such as a charge-coupled device or film. Intervening scintillators are sometimes required, depending on the specific wavelength and detector used.

#Absorption-based x-ray microscopy, however, tends to impose certain limitations on the types of structures that can be imaged. Generally, absorption contrast decreases in proportion to the third power of the photon energy of the radiation. This tends to motivate for the use of lower energies, but lower energies may not provide sufficient penetration through the object.

#In the accompanying drawings, reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale; emphasis has instead been placed upon illustrating the principles of the invention. Of the drawings:

#FIGS. 1A and 1B are schematic views of optical trains of a phase contrast microscope illustrating why the phase plate 116 (not shown in figure) is placed at the back focal plane 130 of the objective 118 in prior art implementations and the validity conditions for the implementation of phase contrast imaging according to the present invention;

#FIG. 2A is a schematic view of an optical train of a phase contrast x-ray microscope according to the present invention;

#FIGS. 1A and 1B schematically illustrate why phase plates are placed at the back focal planes of objectives in the typical phase contrast microscope configuration and the validity conditions for the phase contrast imaging configuration according to the present invention.

#Four important parameters characterize the illumination beam 112: 1) the brightness B, 2) the field of view (FOV), 3) the mean numerical aperture NAc,=sin θ, and 4) the angular spread Δθ.

#The photon flux incident on the test object 10 within the field of view (FOV) is proportional to B*2π*(1−cos θ), which approximately equals to (B*2π*sin θ*Δθ) for small θ. The exposure time is inversely proportional to this photon flux.