Penn State Castleman Group

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Updated January 7, 2014


Strong-field Laser Cluster Studies

A home built femtosecond laser is used to study the interaction of intense light and matter. Our interest are in learning about the laser intensities necessary to remove electrons from a gas phase sample. Clusters exhibit an extreme enhancement in ionization that produces highly charged ions through a mechanism that is not yet fully understood. The ultrafast laser is able to strip multiple electrons before any significant nuclear rearrangement occurs, leaving highly charged ions in close proximity. These ions repel one another giving rise to a Coulomb explosion releasing large amounts of kinetic energy. This was first observed in the Castleman labs, and has remained a topic of interest ever since.

Coulomb Explosion


Recently, we have begun performing intensity resolved experiments which allow us to determine the exact energy requirements for producing these explosions in a variety of samples. We observe the ions and magnitude of the explosion through time-of-flight mass spectrometry. The homebuilt laser is a colliding pulse mode-locked ring dye laser capable of generating laser pulses of around 100 femtoseconds centered at 624 nm with energies of up to 3 mJ per pulse. We can also utilize the laser to perform pump-probe spectroscopy which allows us to determine the time of a reaction.

Colliding Pulse Mode-locked Ring Dye Laser