Mode-locked semiconductor lasers are a promising source for applications such as ultrafast optical sampling. For such an application, the reduction of timing jitter of the pulse source in a cost-effective manner is a key challenge. While monolithic devices have been the source of much recent interest, external cavity lasers have been less well studied. In this work, the noise of an external cavity laser under passively mode-locked operation is evaluated. A ridge-waveguide super-large optical cavity material system is used.