Enhancement of harmonic generation using a two section undulator

Enhancement of the 2nd and 3rd harmonic of the wavelength of a Free-Electron Laser (FEL) has been measured when a single electron beam is crossing a two-section undulator. To produce the harmonic radiation enhancement, the undulator is arranged so that the resonance wavelength of the 2nd undulator (downstream) matches a harmonic of the 1st undulator (upstream). Both the fundamental and the harmonic optical fields evolve in the same optical cavity and are coupled out with different extraction efficiency, through a hole in one of the cavity mirrors. We present measurements that show that the optical power at the 2nd and 3rd harmonic can be enhanced, by about one order of magnitude, in two configurations: when the resonance wavelength of the 2nd undulator matches the harmonic of 1st one (harmonic configuation), or when the gap of the 2nd undulator is slightly larger than first one (step-tapered configuration). We examine the dependence of the harmonic power on the gap of the 2nd undulator. This fundamental/harmonic mode of operation of the FEL may have useful applications in the production of coherent X-ray and VUV radiation, a spectral range where high reflectivity optical cavity mirrors are difficult or impossible to manufacture

Derivation of distal airway epithelium from human embryonic stem cells

The pluripotency of embryonic stem cells (ESC) is offering new opportunities in tissue engineering and cell therapy. We have shown previously that alveolar epithelial cells, specifically type II pneumocytes, can be derived from murine ESC and hypothesized that a similar protocol could be used successfully on human ESC. Undifferentiated human ESC were induced to form embryoid bodies that were transferred into adherent culture conditions and grown in a medium designed for the maintenance of mature small airway epithelium. On inverted microscopy, the generated cells showed the cobblestone-like morphology of epithelium. The presence of surfactant protein C, a specific marker of type II pneumocytes, and its corresponding RNA were demonstrated by immunostaining and reverse transcription polymerase chain reaction, respectively. Electron microscopy revealed frequent cells with the typical ultrastructure of type II pneumocytes. This study provides evidence for in vitro induction of the differentiation from human ESC of alveolar type II cells, which have the potential for therapeutic use or construction of an in vitro model of human lung. © Mary Ann Liebert, Inc

Contrasting effects of mitogenic growth factors on oligodendrocyte precursor cell migration

We have examined the effects of the mitogenic growth factors platelet derived growth factor (PDGF), basic fibroblast growth factor (bFGF) and glial growth factor-2 (GGF-2) on oligodendrocyte precursor migration. In an agarose drop migration assay PDGF and bFGF stimulated migration while GGF-2 had no effect. The migration-enhancing effect of bFGF cannot be blocked by neutralising antibodies against PDGF, confirming that this effect is direct and not mediated via upregulation of PDGF receptors. Based on our results, we propose a model in which the differing effects of PDGF and GGF-2 ensure appropriate numbers of oligodendrocyte precursor cells in the vicinity of axons to be myelinated during development