Thermal Characteristics of GHz Passively Mode-Locked Semiconductor Disk Laser

A 1.3 GHz repetition rate optically pumped passively mode-locked semiconductor disk laser with 5.5 ps pulse duration and 204 mW average output power at 978 nm wavelength was demonstrated. Main factors preventing the mode-locked laser from higher output power, such as the epitaxy structure of wafer and thermal characteristics of gain chip were investigated, and corresponding methods to improve the thermal performance of the laser, e.g., growing the wafer in a reversed sequence, removing substrate entirely and using a diamond as heat spreader, were proposed. The experimental results showed that both the microcavity mode of laser and the emission wavelength of QWs redshifted when the pump power increased, but their redshift rates were different. This suggested us to consider a pre-offset between the emission wavelength of QWs at room temperature and the target wavelength of laser at an intense pump, and the pre-offset values of the wavelength should be designed deliberately to guarantee the resonant periodic gain structure working properly when the temperature in the active region approaches the desired value.