Figure 1: Pump–probe experimental set-up and nominal AOS results.

(a) Schematic of the pump–probe experimental set-up. A 780-nm pump beam is used for the GaAs and Si targets and a 390-nm pump beam is used for the SiC target. A 1,550-nm probe beam is used for all the targets, and it is re-collimated and focused on the InGaAs detector using two 25-mm-focal length lenses. *A second harmonic generation (SHG) crystal and bandpass filter are placed in the beam path to form the 390-nm pump beam (at a conversion efficiency of 10%). ^**The focusing element takes the form of a microscope objective or dielectric spheres. (b) Experimental differential transmission of the probe beam, ΔT/T, is shown normalized versus time, for pump photoinjection of the bulk Si, SiC and GaAs targets, using a microscope objective as the focusing element, as depicted in the inset.