Laser pulse stretching via active feedback control with slow Q-switching

Holographic methods have been proposed to record bubble tracks of high-energy particles in large bubble chambers like the one at Fermi National Accelerator Lab. It has been shown that the high-power densities of standard Q-switched laser pulses induce parasitic boiling in the chamber liquid which blurs the hologram. Rectangular stretched light pulses of 1-5-μs duration are needed to provide the required beam energy but at significantly reduced power densities. Apparently, reproducible spikefree rectangular laser pulses of >0.5 μs have not been achieved before, although attempts have been made by several groups. A closed-loop Pockels cell controller (pulse stretcher) using MOSFET technology provided a solution. Using the Wagner and Longegel giant-pulse equations and nodal circuit analysis, a set of state equations was generated and then solved numerically. The resulting computed pulse shapes are highly correlated with those measured