For velocity measurements in turbulent wall boundary layers with laser-Doppler anemometry (LDA), a probe volume diameter of 30 μm or less is needed in flow rigs of typical laboratory scale to resolve steep gradients in mean velocity and turbulence quantities. It is also advantageous if signals from very small particles can be detected lo enhance the data rate, This paper describes optical solutions to optimize the LDA sensitivity and to achieve such small measuring volumes. The feasibility of a suitably designed optical system is demonstrated in a two-dimensional boundary layer flow.