Delay Generator

This box synchronizes two pulsed lasers.  When the first laser fires some of the light falls on a photo diode.  The signal from the photo diode is ~200mV and ~20nS long.  This input and an adjustable reference level are sent to a high speed comparator.  The comparators output is used to trigger a couple of one-shots.  The first one-shot gates a photomultiplier tube (PMT) immediately while providing a variable delay to the second one-shot.  The second one-shot provides a fixed width output pulse to trigger the second laser.  This allows the first laser to fire (ablating a target) while the PMT is off (no risk of destroying it).  Immediately after the first laser fires the PMT is turned on to monitor the probe beam.  After a few uS the second laser will fire (probing the plasma that the first laser created).  This delay circuit is currently being used in Dr. Kwong's lab.