Status of the King's College laboratory x-ray microscopes

ABSTRACT Two laboratory scale x-ray microscopes using laser generated plasma sources are being developed at King's College. One systemuses dark field imaging while the other is a scanning x-ray microscope and progress with both is described. In particular,preliminary results from an extensive characterisation of the laser plasma source at the Lasers for Science Facility, CLRCRutherford Appleton Laboratory, are discussed. This characterisation has shown that the source is eminently suitable for x-ray microscopy. Keywords: x-ray microscopy, laser generated plasma sources 1. INTRODUCTION In a laser generated plasma (LGP) source a high power pulsed laser beam is focused to a small spot on an appropriate target suchas Mylar or a metal. Such sources provide an attractive alternative to synchrotrons for various applications of soft x-rays, inparticular x-ray microscopy.' Both ofthe microscopes described here will use such a source, namely that at the Lasers for ScienceFacility at the CLRC Rutherford Appleton Laboratory (RAL), UK. In section 2, the design and current status ofa dark field x-raymicroscope (DFXM) are discussed, while in section 3 a scanning transmission x-ray microscope (SSXM) based on a scannedsource is described.The main advantages of LGPs, as compared to synchrotrons, are well knwn1 Briefly, these result from the relatively lowcost and small size of the lasers, meaning that such sources can be situated in users' own laboratories. This alleviates thedisadvantages associated with synchrotrons, i.e., remoteness, high cost and competition for beam time. In the past. the maindisadvantages of LGPs for x-ray microscopy have been their relatively low brilliances and their limited tunability. However, aswill be discussed in section 4, the LGP source at RAL can now approach in brilliance (albeit at selected wavelengths) secondgeneration synchrotrons such as the National Synchrotron Light Source at Brookhaven where much pioneering work on x-raymicroscopy has been carried out. Additionally, recent experiments carried out by the authors using metal targets have shown thatthe source can, in principle, offer tunability; these results will be discussed in a subsequent paper.