## Linac Coherent Light Source

The Linac Coherent Light Source (LCLS) came on line in September of 2009, capable of producing x-ray laser pulses of wavelengths from 1 to 0.15 nm.  The source will be a laser pulsed photo-cathode in development (led by Howard Padmore) over the next 2 years.  The x-ray free electron laser (XFEL) pulses are $10^{-13}$ sec of $10^{12}$ photons.  This photon pulse is so energetic it destroys the sample viewed, but not before a snapshot is collected.  One technique for imaging proteins is to prepare an aerosol spray and inject a collimated stream into the electron beam.  A large set of diffraction images (up to 10 million) of the molecule in random orientations are generated.  The data is categorized, averaged, and fit together iteratively to form the best 3D diffraction representation.  The 3D electron density map can then be generated from the assembled diffraction volume.