The authors perform transmission spectroscopy on single quantum dots and examine the effects of a resident carrier's spin, the incident laser spot size, polarization, and power on the experimental contrast. They demonstrate a factor of 5 improvement in the maximum contrast by using a solid immersion lens to decrease the spot area. This increase yields a maximum signal to noise ratio of ~2000 Hz-12, which will allow for megahertz detection frequencies. The authors anticipate that this improvement will allow further investigation of spectral fluctuation and open up the feasibility for an all-optical readout of an electron spin in a quantum dot. © 2007 American Institute of Physics.