High sensitivity third-order autocorrelation measurement by intensity modulation and third harmonic detection.

We demonstrate a novel (to our knowledge) method for high sensitivity measurement of pulsed light at the telecommunication wavelength of 1558 nm using a GaAsP photomultiplier tube. By modulating the input power and analyzing the harmonic components, high sensitivity third-order autocorrelation is obtained in the wavelength and power regimes where a mixture of two-photon absorption and three-photon absorption in the photomultiplier tube is present.