Gaseous unburned hydrocarbons (UHC) are investigated in an atmospheric pressure combustor with premixing and prevaporization. The rectangular combustion chamber is equipped with silica quartz windows allowing laser-based investigations in the UV regime. A new double shell concept is employed to atomize the fuel (n-heptane) and to stabilize the flame. For the detection of UHC, a tuneable ArF (λ ≈ 193 nm) or KrF (λ ≈ 248 nm) excimer laser is used. The results show that this imaging technique is feasible in an atmospheric pressure, liquid fuelled combustor. Liquid and gaseous fuel is detected inside the vortices induced by the double shell, where the main combustion processes occur. Furthermore, droplets and UHC can be found along the symmetry line of the double shell. Comparing the two approaches used for the visualization of UHC, it turns out that the application of a KrF laser seems to be more suitable.