A broadly tunable autocorrelator for ultra-short, ultra-high power infrared optical pulses

We describe the design of a crossed-beam, optical autocorrelator employing an uncoated, birefringent beamsplitter to split a linearly polarized incident pulse into two orthogonally polarized pulses, and a type II SHG crystal to generate the intensity autocorrelation function. The sapphire beamsplitter accommodates extremely broadband tunability while precluding any temporal distortion of the ultrashort optical pulses at the dielectric interface, while the specific design provides efficient operation between 1 and 4 mu m. Furthermore, the use of Type II SHG completely eliminates any single-beam doubling, so the autocorrelator can be operated at very shallow crossed-beam angles without generating a background pedestal. The autocorrelator has been constructed and installed in the Mark III laboratory at Duke University as a broadband diagnostic for ongoing compression experiments on the chirped-pulse FEL.