Picosecond time-resolved absorption in the mid-infrared by seeded optical parametric generation.

An apparatus to probe picosecond photoinduced absorption in semiconductors between 2 microns and 5 microns with picosecond resolution is described. The infrared source is based on difference frequency mixing an amplified picosecond dye laser pulse with a synchronized white light continuum pulse. The choice of liquid for continuum generation is discussed and applications to transient absorption in Germanium and in trans-polyacetylene are presented.