ImPhys Seminar

20 March 2017 | 12:45 - 13:30
location: Lecture Room E
by webmaster ImPhys

Lecturer: Gerward Weppelman (Charged Particle Optics) and Elizabeth Carroll (Charged Particle Optics)

'Creating ultrafast electron pulses using a microfabricated laser-triggered Beam Blanker'(Gerward Weppelman)

Ultrafast electron pulses enable imaging of transient dynamics with nanometer and femtosecond resolution. Such pulses are typically created by illuminating a flat photocathode or a cold-field emitter with femtosecond laser pulses. Using a cold field emitter, an ultrafast Scanning Electron Microscope (USEM) has been realized but such an USEM has the disadvantage that it cannot be easily switched back to continuous beam operation.
Here, we present a beam blanker for use in regular EMs that allows switching between continuous-beam and ultrafast modes of operation. We use a microfabricated beam blanker that controlled by a photoconductive switch, illuminated with femtosecond laser pulses. We show the laser triggered deflection of the electron beam. Using COMSOL simulations we show that our design can deliver sub 100 fs electron pulses. We will also discuss the energy dispersion in the electron pulse.

'Highly-specific single-cell manipulations in the developing zebrafish brain' (Elizabeth Carroll)

During early development, the brain forms many synapses that will not survive to adulthood.  The factors of nature and nurture that determine which synapses survive, and how this shapes the way our brains are individually wired, are two of the fundamental questions that inspire my research.  Genetically encoded  fluorescent sensors,  optical imaging with single-photon sensitivity, and optogenetics are three modern optical tools that, together, offer a revolutionary approach to use light to measure and manipulate synapse and circuit development in living animals. I will describe how I apply these tools in the zebrafish, focusing on recent work on the development of the retinotectal projection, which carries information from the retina to the visual processing center of the zebrafish brain, the optic tectum.  I will briefly describe how we have used optogenetic glutamate receptors to optically mimic the effect of chronic exposure to an anti-convulsant drug, dizocilpine, which alters synapse formation at a critical period of brain development.  Then I will describe some of the optical challenges in multiphoton optogenetics and my future plans to extend  this work to single-cell and single-synapse manipulations in the ImPhys Department. 









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