Optical absorption cross section of quantum dots

We have measured the modal optical absorption spectrum of a three-layer system of InAs quantum dots in a slab waveguide geometry, observing distinct absorption peaks for the ground and excited states. The spectrally integrated absorption cross section for the ground and first excited states are determined to be sigma(0) = (0.43 +/- 0.1) x 10(-15) and (0.92 +/- 0.2) x 10(-15) cm(2) eV, respectively. Assuming that the spectral shapes are determined primarily by the inhomogeneous size distribution of dots the Gaussian linewidths are 16 and 19 meV for the ground and first excited state transitions, respectively. The peak ground state absorption cross section is 1.1 x 10(-14) cm(2). The ground state spectrally integrated cross section estimated by a theory with the envelope function overlap integral taken to be unity is 0.40 x 10(-15) cm(2) eV, in agreement with the measured value. We conclude that on the basis of the spectrally integrated cross section there is no evidence for a substantial reduction in the strength of the fundamental light-matter interaction in dots compared with systems of higher dimensionality.