High Brightness, Low Noise CW and GHz Repetition Rate Mode-Locked Semiconductor Disk Lasers

Abstract

Optically-pumped semiconductor disk (vertical external cavity) lasers offer marked advantages over high power edge emitters. They offer high brightness, high noise suppression, no facet damage, multiple tens of Watt CW TEM00 single frequency, narrow line emission and enormous flexibility in intra-cavity tunable SHG and DFG high efficiency sources. Optically-pumped semiconductor disk lasers (OPSLs), also referred to as vertical external-cavity semiconductor lasers (VECSELs), offer enormous flexibility in their compact cavity design, excellent TEM00 beam quality as single frequency multiple tens of Watts wavelength agile sources and high brightness raw power sources with demonstrated power exceeding 100 Watts from a single emitter. At the latter power levels, there is evidence for strong lateral ASE and lasing when the spot size exceeds 1 millimeter. The compact cavity arrangement facilitates high power intra-cavity SHG generation in the visible and UV and OPSL technology now underlies Coherent's main product line of commercial semiconductor laser sources. The high circulating intra-cavity powers have also enabled the demonstration of record high power room temperature tunable THz emission via intra-cavity DFG. High peak and average power mode-locking has been demonstrated when a saturable semiconductor absorber mirror (SESAM) is inserted in the cavity. The short cavity lengths provide for high repetition rates in the 1–10 GHz range and such sources are currently being investigated as seed sources for frequency comb generation. Current challenges lie in SESAM degradation that becomes evident when pulse durations decrease towards 100 fs and peak power densities reach the multi-kW range. The current short pulse record is 95 fs. Different SESAM growth methodologies are being investigated including ultrafast surface state recombination of a near surface grown QW, low temperature QW growth, graphene and other saturable absorber sources.