Imaging and Autocorrelation of Ultrafast Infrared

Abstract

Te diode arrays, which are harder to use, more expensive, and have less spatial resolution than standard CCD cameras. In this Letter we describe practical applications in which the nonlinear response of Si devices to IR light is used for laser beam profiling and pulse autocorrelation. The Letter is not a quantitative fundamental study of nonlinear multiphoton absorption in Si. Inasmuch as the electronic bandgap in Si is #1.12 eV (l # 1.1 mm, or n # 9034 cm ) at room temperature, it might seem surprising that a Si device would respond to light in the range l # 3 11 mm, e.g., with the energy of 3 -- 9 photons needed to create an electron -- hole pair in bulk Si. Two-photon-induced photoconductivity in a Si CCD camera was used previously 3 to image light at l # 1.41 mm. Likewise, temporal autocorrelation 4--8 and cross correlation 9 of near-IR ultrafast laser pulses by an approach similar to that described here was reported for hn 1 , hn 2 , Ega , #hn 1 1 hn 2 #. For these tw