Showing papers by "Stefano Marchesini published in 2009"

Soft X-ray diffraction microscopy of a frozen hydrated yeast cell.

Abstract: We report the first image of an intact, frozen hydrated eukaryotic cell using x-ray diffraction microscopy, or coherent x-ray diffraction imaging. By plunge freezing the specimen in liquid ethane and maintaining it below −170 °C, artifacts due to dehydration, ice crystallization, and radiation damage are greatly reduced. In this example, coherent diffraction data using 520 eV x rays were recorded and reconstructed to reveal a budding yeast cell at a resolution better than 25 nm. This demonstration represents an important step towards high resolution imaging of cells in their natural, hydrated state, without limitations imposed by x-ray optics.

Direct observation of the transfer of orbital angular momentum to metal particles from a focused circularly polarized Gaussian beam.

Abstract: It is well known that a circularly polarized Gaussian beam carries spin angular momentum, but not orbital angular momentum. This paper demonstrates that focusing a beam carrying spin angular momentum can induce an orbital angular momentum which we used to drive the orbital motion of a micron-sized metal particle that is trapped off the beam axis. The direction of the orbital motion is controlled by the handedness of the circular polarization. The orbiting dynamics of the trapped particle, which acted as an optical micro-detector, were quantitatively measured and found to be in excellent agreement with the theoretical predictions.

Ab Initio Undersampled Phase Retrieval

Abstract: Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009

Short-pulse laser induced transient structure formation and ablation studied with time-resolved coherent XUV-scattering

Abstract: The structural dynamics of short-pulse laser irradiated surfaces and nano-structures has been studied with nm spatial and ultrafast temporal resolution by means of single-shot coherent XUV-scattering techniques. The experiments allowed us to time-resolve the formation of laser-induced periodic surface structures, and to follow the expansion and disintegration of nano-objects during laser ablation.

Coherent Imaging at FLASH

Abstract: We have carried out high-resolution single-pulse coherent diffractive imaging at the FLASH free-electron laser. The intense focused FEL pulse gives a high-resolution low-noise coherent diffraction pattern of an object before that object turns into a plasma and explodes. In particular we are developing imaging of biological specimens beyond conventional radiation damage resolution limits, developing imaging of ultrafast processes, and testing methods to characterize and perform single-particle imaging.

Binary pseudo-random gratings and arrays for calibration of the modulation transfer function of surface profilometers: recent developments

Abstract: The major problem of measurement of a power spectral density (PSD) distribution of the surface heights with surface profilometers arises due to the unknown Modulation Transfer Function (MTF) of the instruments. The MTF tends to distort the PSD at higher spatial frequencies. It has been suggested [Proc. SPIE 7077-7, (2007), Opt. Eng. 47 (7), 073602-1-5 (2008)] that the instrumental MTF of a surface profiler can be precisely measured using standard test surfaces based on binary pseudo-random (BPR) patterns. In the cited work, a one dimensional (1D) realization of the suggested method based on use of BPR gratings has been demonstrated. Here, we present recent achievements made in fabricating and using two-dimensional (2D) BPR arrays that allow for a direct 2D calibration of the instrumental MTF. The 2D BPRAs were used as standard test surfaces for 2D MTF calibration of the MicromapTM-570 interferometric microscope with all available objectives. The effects of fabrication imperfections on the efficiency of calibration are also discussed.

Cryo diffraction microscopy: Ice conditions and finite supports

Abstract: Cryo specimen conditions greatly alleviate radiation damage in x-ray microscopy. In diffraction microscopy with plane-wave illumination, a finite support constraint is required in order to obtain a reconstructed image, but this demands that there be an area outside the specimen which is free of optical response. We report here observations based on our early attempts in cryo diffraction microscopy, where ice scatter from outside the cell and ice deposition during data taking have been problems. We outline solutions that are being implemented for future experiments.

Ultrafast coherent X-ray diffractive imaging with the FLASH Free-Electron Laser

Abstract: High-resolution ultrafast coherent diffractive imaging has been carried out at the FLASH FEL. Reconstructed images show no effect of sample destruction. Time resolved imaging was achieved by time-delay holography and with a synchronized optical laser.