Low-temperature-grown GaAs coplanar waveguide single-photonÕtwo photon absorption autocorrelator

Previously, we have described a low temperature grown GaAs device that uses single-photon absorption to perform a carrier lifetime limited optical autocorrelation of picosecond optical pulses. In this article, we describe how this same device could be used to perform an autocorrelation of femtosecond optical pulses by utilizing two-photon absorption ~TPA!. Furthermore, we propose how to model and minimize the photocurrent’s dependence on the single-photon absorption ~SPA! response of the midlevel traps. We find that the SPA response produces a distortion on the TPA autocorrelation signal at low intensities. At large peak intensities (Ipeak'3G W cm ), however, we find that the SPA distortion becomes nearly two orders of magnitude smaller than the TPA signal, and decreases further with increasing intensity. In our discussion, we also describe some of the tradeoffs between using a photoconductor with a large two-photon absorption coefficient and midlevel states as a TPA autocorrelator. © 2004 American Institute of Physics. @DOI: 10.1063/1.1644025#