In this work we present the application of a 2D single grating wavefront sensor to align and characterize the 100 nm focus at the Coherent X-ray Imaging (CXI) endstation at the Linac Coherent Light Source (LCLS). The results agree well with a model of the system, indicating that the mirrors perform as designed when alignment is optimized. In addition, a comparison with the imprint technique confirms the validity of the results, which showed that wavefront-based alignment resulted in negligible astigmatism. Analysis of the retrieved focus profile indicates that intensities <1021 W=cm2 are achievable with currently available LCLS beam parameters and optimal mirror alignment.
We present a method for the optimization of the illumination in soft x-ray (SXR) full-field microscopes. The method
consists of imaging a single periodic grating with a period large compared to the wavelength of the illumination and
obtaining its Fourier spectrum in two orthogonal directions. The analysis of the cut-off frequency along the two
perpendicular directions allows the identification of angled illumination, which can be corrected in-situ by using the
Fourier analysis iteratively. The ability to characterize the illumination conditions and aberrations in the EUV/SXR
microscopes with a fast and simple analysis is critical to achieve the best quality images with the highest spatial
We demonstrate lensless diffractive microscopy using a tabletop source of extreme ultraviolet (EUV) light from high harmonic generation at 29 nm and 13.5 nm. High harmonic generation has been shown to produce fully spatially coherent EUV light when the conversion process is well phase-matched in a hollow-core waveguide. We use this spatial coherence for two related diffractive imaging techniques which circumvent the need for lossy imaging optics in the EUV region of the spectrum. Holography with a reference beam gives sub-100 nm resolution in short exposure times with fast image retrieval. Application of the Guided Hybrid Input-Output phase retrieval algorithm refines the image resolution to 53 nm with 29 nm light. Initial images using the technologically important 13.5 nm wavelength give 92-nm resolution in a 10-minute exposure. Straightforward extensions of this work should also allow near-wavelength resolution with the 13.5 nm source. Diffractive imaging techniques provide eased alignment and focusing requirements
as compared with zone plate or multilayer mirror imaging systems. The short-pulsed nature of the extreme ultraviolet source will allow pump-probe imaging of materials dynamics with time resolutions down to the pulse duration of the EUV.
Phase sensitive x-ray microscopy techniques are important in the study of samples that exhibit phase contrast. One way
to detect these phase effects is to optically implement the radial Hilbert transform by using spiral zone plates (SZPs),
resulting in the imaging of the amplitude and phase gradient in a sample. This is similar to differential interference
contrast imaging in light microscopy. Soft x-ray microscopy using a SZP as a single element objective lens was
demonstrated through the imaging of a 1 μm circular aperture at a wavelength of 2.73 nm. A regular zone plate, a
charge 1 SZP, and a charge 2 SZP were fabricated on a silicon nitride membrane using electron beam lithography. The
negative e-beam resist hydrogen silsesquioxane (HSQ) was used for patterning, and the zone plates were electroplated
with nickel. These zone plates were then used as the imaging optic in a soft x-ray microscopy setup.
Researchers long have relied on research involving small animals to unravel scientific mysteries in the biological sciences, and to develop new diagnostic and therapeutic techniques in the medical and health sciences. Within the past 2 decades, new techniques have been developed to manipulate the genome of the mouse, allowing the development of transgenic and knockout models of mammalian and human disease, development, and physiology. Traditionally, much biological research involving small animals has relied on the use of invasive methods such as organ harvesting, tissue sampling, and autoradiography during which the animal was sacrificed to perform a single measurement. More recently, imaging techniques have been developed that assess anatomy and physiology in the intact animal, in a way that allows the investigator to follow the progression of disease, or to monitor the response to therapeutic interventions. Imaging techniques that use penetrating radiation at millimeter or submillimeter levels to image small animals include x-ray computed tomography (microCT), single-photon emission computed tomography (microSPECT), and imaging positron emission computed tomography (microPET). MicroCT generates cross-sectional slices which reveal the structure of the object with spatial resolution in the range of 50 to 100 microns. MicroSPECT and microPET are radionuclide imaging techniques in which a radiopharmaceutical is injected into the animal that is accumulated to metabolism, blood flow, bone remodeling, tumor growth, or other biological processes. Both microSPECT and microPET offer spatial resolutions in the range of 1-2 millimeters. However, microPET records annihilation photons produced by a positron-emitting radiopharmaceutical using electronic coincidence, and has a sensitivity approximately two orders of magnitude better than microSPECT, while microSPECT is compatible with gamma-ray emitting radiopharmaceuticals that are less expensive and more readily available than those used with microPET. High-resolution dual-modality imaging systems now are being developed that combine microPET or microSPECT with microCT in a way that facilitates more direct correlation of anatomy and physiology in the same animal. Small animal imaging allows researchers to perform experiments that are not possible with conventional invasive techniques, and thereby are becoming increasingly important tools for discovery of fundamental biological information, and development of new diagnostic and therapeutic techniques in the biomedical sciences.
Dual-modality imaging is a technique where computed tomography or magnetic resonance imaging is combined with positron emission tomography or single-photon computed tomography to acquire structural and functional images with an integrated system. The data are acquired during a single procedure with the patient on a table viewed by both detectors to facilitate correlation between the structural and function images. The resulting data can be useful for localization for more specific diagnosis of disease. In addition, the anatomical information can be used to compensate the correlated radionuclide data for physical perturbations such as photon attenuation, scatter radiation, and partial volume errors. Thus, dual-modality imaging provides a priori information that can be used to improve both the visual quality and the quantitative accuracy of the radionuclide images. Dual-modality imaging systems also are being developed for biological research that involves small animals. The small-animal dual-modality systems offer advantages for measurements that currently are performed invasively using autoradiography and tissue sampling. By acquiring the required data noninvasively, dual-modality imaging has the potential to allow serial studies in a single animal, to perform measurements with fewer animals, and to improve the statistical quality of the data.