Researchers from Marburg, Germany and Tucson, Arizona have claimed a first with a semiconductor disk laser that has an output power of over 100W, with a heat sink temperature of 3°C.
With a power output of 100W and more, semiconductor disk lasers have the potential for wider applications such as materials processing. To achieve this power output the researchers at Philipps Universität, Marburg and the College of Optical Sciences, Tucson, needed to find a way of avoiding thermal rollover, which is caused by two mechanisms in the Vertical External Cavity Surface Emitting (VECSEL) semiconductor, which generates the laser.
‘This [100W] milestone was reached as the result of many careful design and optimisation steps both on the theoretical and on the experimental side,’ said Philipps Universität graduate student, Bernd Heinen.
Thermal rollover is partly caused by the chip’s active resonant periodic gain (RPG) multiple quantum well’s gain peak shifting more rapidly to a longer wavelength than the gain peak of the RPG’s micro-cavity resonance. The way the researchers avoided this thermal rollover was to optimise the design of the VECSEL chip so its multiple quantum well gain peak is at a shorter wavelength than the RPG’s micro-cavity resonance, at room temperature. This means that when the maximum operational temperature is reached the gain peak for the micro-cavity resonance and multiple quantum will coincide.
Previously the Tucson, Marburg team pushed the performance to around 70W but at a heat sink temperature of -15°C. Improved thermal management also helped the team achieve the 100W performance. This thermal management partly involved bonding an upside-down grown VECSEL chip to a heat spreader mounting that was chemically vapour deposited diamond.
The international team see VECSEL lasers as a pathway for developing multi-Watt and kW class high brightness, high power semiconductor lasers. Their wavelength flexibility through epitaxial design is expected to offer good performance at targeted wavelengths. The high intra-cavity powers that can approach kW levels in VECSEL semiconductors are also expected to lead to the efficient generation of high-power, high brightness visible and ultraviolet sources through intra-cavity second and fourth harmonic generation.
The researchers think VECSELs will replace many current commercial bulky laser sources, such as Argon ion lasers. Intra-cavity difference frequency generation has recently led to the demonstration of an efficient room temperature CW terahertz sources. The Tucson, Arizona company Nonlinear Control Strategies also contributed to the VECSEL lasers work.