A mode locked semiconductor disk laser with an output beam having an ultra-short pulse length which provides the incident beam to a non linear microscope. The wavelength of the beam is at or near the action cross section maximum absorption wavelength for creating two photon excited fluorescence of a fluorescent biological marker in a sample. Semiconductor disk lasers combine excellent beam quality and output power, stability while maintaining simplicity and easiness of operation. In addition, these types of lasers are ideally suited for mass production as they are built in wafer-scale technology enabling a high level of integration. Importantly this non expensive, turn-key, compact laser system could be used as a platform to develop portable non-linear bio-imaging devices for clinical studies, facilitating its wide-spread adoption in “real-life” applications.