This study explores the capabilities of the Coherent X-ray Imaging Instrument at the Linac Coherent Light Source to image small biological samples. The weak signal from small samples puts a significant demand on the experiment. Aerosolized Omono River virus particles of $40 nm in diameter were injected into the submicrometre X-ray focus at a reduced pressure. Diffraction patterns were recorded on two area detectors. The statistical nature of the measurements from many individual particles provided information about the intensity profile of the X-ray beam, phase variations in the wavefront and the size distribution of the injected particles. The results point to a wider than expected size distribution (from $35 to $300 nm in diameter). This is likely to be owing to nonvolatile contaminants from larger droplets during aerosolization and droplet evaporation. The results suggest that the concentration of nonvolatile contaminants and the ratio between the volumes of the initial droplet and the sample particles is critical in such studies. The maximum beam intensity in the focus was found to be 1.9 Â 10 12 photons per mm 2 per pulse. The full-width of the focus at halfmaximum was estimated to be 500 nm (assuming 20% beamline transmission), and this width is larger than expected. Under these conditions, the diffraction signal from a sample-sized particle remained above the average background to a resolution of 4.25 nm. The results suggest that reducing the size of the initial droplets during aerosolization is necessary to bring small particles into the scope of detailed structural studies with X-ray lasers.

No abstract

We use a Mach-Zehnder type autocorrelator to split and delay XUV pulses from the FLASH soft X-ray laser for triggering and subsequently probing the explosion of aerosolised sugar balls. FLASH was running at 182 eV photon energy with pulses of 70 fs duration. The delay between the pump-probe pulses was varied between zero and 5 ps, and the pulses were focused to reach peak intensities above 10¹⁶W/cm² with an off-axis parabola. The direct pulse triggered the explosion of single aerosolised sucrose nano-particles, while the delayed pulse probed the exploding structure. The ejected ions were measured by ion time of flight spectrometry, and the particle sizes were measured by coherent diffractive imaging. The results show that sucrose particles of 560-1000 nm diameter retain their size for about 500 fs following the first exposure. Significant sample expansion happens between 500 fs and 1 ps. We present simulations to support these observations.

spectra are overlapping. An alternative isotope separation method based on polarization selection rules using broadband lasers has been previously applied for separation of odd and even isotopes of Zr, Gd, and Yb where the isotope shifts are small and the hyperfine spectra are complex [1][2][3][4][5][6][7][8]. Isotope separation of many of these elements is of great importance to nuclear industry [1][2][3][4][5][6]. In this method, odd isotopes with nonzero nuclear spin are selectively excited, while even isotopes with zero nuclear spin are prohibited from excitation by judiciously choosing a proper excitation sequence of angular momenta of the levels and the laser polarizations. However, this method is applicable to elements having states with low total angular momentum (J values).Atomic samarium (Sm I) has seven naturally abundant isotopes 144 Sm (3.1 %), 147 Sm (15 %), 148 Sm (11.3 %), 149 Sm (13.8 %), 150 Sm (7.4 %), 152 Sm (26.6 %), and 154 Sm (22.6 %). Among these, 149 Sm, with high thermal neutron absorption cross section (40,140 barns), is a promising candidate as burnable poison in nuclear reactors [9]. The use of natural samarium as a burnable poison was discarded previously because of the large residual negative reactivity worth of samarium isotopes and their daughter products at the end of life of the fuel. Recently, Renier et al. [10] have investigated the potential benefits of using enriched samaria (Sm 2 O 3 ) as a burnable poison in the fuel pellets of PWRs and shown that the use of Sm enriched in 149 Sm has greatly reduced this residual absorber problem.In this paper, we report isotope-selective photoionization of atomic samarium (Sm I) using two-color resonance ionization polarization spectroscopy with broadband lasers. We have identified a two-color excitation scheme 0 cm −1 (J = 0) → 15650.5 cm −1 (J = 1) → 33116.8 cm −1 (J = 1) → Sm + for selective excitation of the odd isotopes of Sm I [11,12]. Using this scheme, selective excitation of Abstract An isotope separation method based on polarization selection rules is applied to atomic samarium by using two-color resonance ionization spectroscopy with broadband lasers. In this method, odd isotopes with nonzero nuclear spin are selectively excited, while even isotopes with zero nuclear spin are prohibited from excitation using two parallel linearly polarized lasers. We have identified a two-color excitation scheme 0 cm −1 (J = 0) → 15650.5 cm −1 (J = 1) → 33116.8 cm −1 (J = 1) → Sm + for selective excitation of the odd isotopes of Sm I. Using this scheme, selective excitation of odd isotopes of Sm I ( 147 Sm and 149 Sm) with an isotopic selectivity better than 40 has been demonstrated. In addition, the effect of different polarization states of the excitation lasers and relative polarization angle between them on the selectivity of odd isotopes has also been studied. The dependence of the even mass isotope signal on the relative polarization angle followed sin 2 θ, which is in excellent agreement with theoretical predictions.