Month: May 2014

Pockels cell modulation via look-up tables

The Scanbox card keeps the laser power per pixel constant across the imaging field despite variations in dwell time during the resonant scanning cycle.  It also blanks the laser entirely near the edges of each line.  The shape of the modulation signal is fully programmable, although each change requires a firmware update to the board. We achieve this by having a pixel counter for the line as an input to a look-up table which, in turn, drives a digital-to-analog converter.

We use a Conoptics system which accepts a 2Vp-p maximum modulation signal into a 1kOhm (unipolar) termination leading to 750Vp-p output modulation on the Pockels cell.  The oscilloscope snapshot below show the line synchronization of the resonant mirror controller along with the Pockels cell modulation during bidirectional scanning.

pockels2

 

 

 

 

Scanbox prototype (circa 2013)

Having done its service with honor for more than a year we had so say our goodbyes to one of only two working models of the original Scanbox prototype. Today we transitioned the two-photon microscope to the latest version of the Scanbox card.  Some students and postdocs watched with much concern as cables were being pulled apart. One of them, who could not bear the spectacle, and wondered about the future of his experiments, decided to retreat to his office.  In the end, however, everything worked as expected and everyone is now back in business.

The last working version of the original Scanbox prototype is now in a nice laboratory at Hopkins.  I am sure our colleagues will take good care of it and provide a proper burial when time comes.

Scanbox prototype (circa 2013)

Scanbox prototype (circa 2013)