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 10 12 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 Address correspondence to Michael J. Bogan, Stanford PULSE Institute for Ultrafast Energy Science, SLAC National Accelerator Laboratory, 2575 Sand Hill Road MS59, Menlo Park, CA 94025, USA. E-mail: mbogan@slac.stanford.edu 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.

Time-resolved imaging using x-ray free electron lasers

“…Variations on the principle of flash X-ray imaging demonstrated in this experiment have subsequently been used in a wide range of coherent experiments at FLASH and elsewhere [7,9,12,18,19,33,50]. [9] to study the morphology of aerosols in free flight, Figure 5. These studies revealed the shape and structure of micron-sized particulate matter in free space without the need to suspend the particles on a supporting membrane -a significant advance over previous techniques that required samples to be first attached to a membrane for study by electron microscopy.…”

Digital holographic imaging of aerosol particles in flight

“…Traditionally, holograms are Digital holographic imaging has been demonstrated in multiple small-particle systems and across visible and X-ray wavelengths, see e.g. [3][4][5][6][7][8][9][10][11]. Examples of work applying holography to aerosols are scarce, and to the best of our knowledge have not yet been reported for in situ imaging of aerosol particles in the 0:1225 mm size range using visible light.…”

Expansion-maximization-compression algorithm with spherical harmonics for single particle imaging with x-ray lasers

“…To overcome low signal-to-noise, the experiment involves a large number of diffraction measurements (10 4 -10 6 ) and each measurement must be of a new copy of the particle, which is assumed to have an identical structure. Such datasets are achievable because XFELs have high repetition rates (> 100 Hz [3]) and serial injection technology has been developed to continuously deliver fresh sample into the beam path [4,5]. A consequence of this experimental approach is that particle orientation is not measured and must be determined by analyzing the diffraction data [6].…”