Aerosol Imaging with a Soft X-Ray Free Electron Laser

Abstract

Lasers have long played a critical role in the advancement of aerosol science. A new regime of ultrafast laser technology has recently be realized, the world's first soft x-ray free electron laser. The Free electron LASer in Hamburg, FLASH, user facility produces a steady source of 10 femtosecond pulses of 7–32 nm x-rays with 10¹² photons per pulse. The high brightness, short wavelength, and high repetition rate (> 500 pulses per second) of this laser offers unique capabilities for aerosol characterization. Here we use FLASH to perform the highest resolution imaging of single PM2.5 aerosol particles in flight to date. We resolve to 35 nm the morphology of fibrous and aggregated spherical carbonaceous nanoparticles that existed for less than two milliseconds in vacuum. Our result opens the possibility for high spatial- and time-resolved single particle aerosol dynamics studies, filling a critical technological need in aerosol science.

Special thanks are due to the scientific and technical staff of the FLASH at DESY, Hamburg, in particular to R. Treusch, J. Schneider, S. Dusterer, T. Tschentscher, J. Feldhaus, R. L. Johnson, U. Hahn, T. Nunez, K. Tiedtke, S. Toleikis, E. L. Saldin, E. A. Schneidmiller, and M. V. Yurkov. We are grateful to our collaborators in T. Moller's group at Technische Universitat Berlin for accommodating our experiment in their vacuum chamber. This work was supported by the following agencies: The U.S. Department of Energy by Lawrence Livermore National Laboratory in part under Contract W-7405-Eng-48 and in part under Contract DE-AC52-07NA27344, Lawrence Livermore National Laboratory (the project 05-SI-003 from the Laboratory Directed Research and Development Program of LLNL); the U.S. Department of Energy by the SLAC National Accelerator Laboratory in part under contract number DE-AC02-76SF00515; the Deutsches Elektronen-Synchrotron, a research center of the Helmholtz Association. Additional support comes from the DFG Cluster of Excellence at the Munich Centre for Advanced Photonics (www.munich-photonics.de), from the Virtual Institute Program of the Helmholtz Society, and by the Swedish Research Council.

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