Scaling high-power ultrafast VECSELs into the femtosecond regime

Abstract

Since the invention of the semiconductor laser diode, just 2 years after the first successful demonstration of a laser, the technology has made such rapid progress that continuous wave (cw) semiconductor lasers can now be found in many everyday objects. Examples are CD/DVD/Bluray players or laser printers. This breakthrough in semiconductor lasers was possible due to the semiconductor technology which enabled a high level of integration and cost-efficient mass production particularly wafer-scale technology.Besides cw operation, where light is emitted continuously over time, a laser can also generate short pulses of light, referred to as ultrafast lasers.But so far, ultrafast lasers have been only used in industry and research, in areas such as biology, medicine or metrology. The reason for this is the great complexity and the high costs of these systems, for example the titanium sapphire laser and the diode-pumped solid-state lasers. New application areas, such as the optical clocking of microprocessors, free-space data communication, multi-photon microscopy or stabilized gigahertz frequency combs generate a demand for low-cost and compact ultrafast laser sources. Semiconductor lasers would be ideally suited to this demand, but conventional semiconductor lasers are edge-emitters, for which the light propagates in the epitaxial layers. This means their power cannot simply be scaled up by increasing the mode size and they have strongly assymetric beam profiles, which makes them unsuitable for many ultrafast applications, which need a high brightness at high power levels.xxi Abstract Optically pumped vertical-external-cavity surface-emitting lasers (VEC-