X-ray microscopy: Undulators today, FELs tomorrow?

Short wavelength FELs would make possible the flash imaging of thick, hydrated biological specimens at high resolution. This could be a significant development in x-ray microscopy both because of the possibility of freezing biological and thermal motion, and because it might allow the image to be recorded before cellular ultrastructure could be altered by radiation damage. While it has recently been shown that the gross structure of initially living cells remains intact for about an hour after a 100 nm resolution image has been made, it has been argued that sub-100 nm resolution ultrastructure may be modified over millisecond time scales in higher resolution imaging. X-ray holography appears to be the optical technique best suited to flash x-ray imaging, provided the experiment and detector be designed to capture the hologram yet not be damaged by the multiple pulses which would be required from at least one short wavelength FEL design