Wavelength tunable picosecond pulse bunch laser around 3 µm through PPMgLN –based DFG with temperature insensitive high power scaling

Abstract

We report a bunch-mode-operated, wavelength-tunable, temperature-insensitive high power, mid-infrared (MIR) laser based on difference frequency generation (DFG) in a periodically poled Magneoisum-oxide doped Lithium Niobate (PPMgLN) chip. Two synchronized fiber lasers each with master oscillator power amplifier (MOPA) structures are utilized as pump and signal sources for the DFG. The pump laser is seeded by a mode-locked Yb fiber laser around 1030 nm with fundamental repetition rate of 16.32 MHz and pulse duration of 8.5 ps. Each pulse of the pump seed is multiplied by a factor of 16, forming the pulse bunch, and then amplified to 27.8 W. A super-luminescent light emitting diode (SLED) around 1580 nm is triggered by the first pulses of the pump bunch and adopted as the signal seed, which is amplified to 4 W afterwards. The pulse duration and spectral bandwidth of the signal are ~ 5 ns and 50 nm, respectively, covering the total duration of the pump bunch in the time domain and signal wavelength tuning range in the spectral domain, respectively, enabling wavelength-tuning DFG with temperature-insensitive power scaling. High power pulse bunch MIR laser can always be realized within the crystal temperature range from 25 to 95 °C with corresponding idler wavelength from 3.03 μm to 2.84 μm. The highest idler power of 4.6 W is achieved at 3.0 μm with pump-to-idler conversion efficiency of ~ 16.5%. It is believed that such a bunch-mode-operated, mid-infrared ps laser source with high output power within the whole temperature-wavelength tuning range are of great value to the evaluation of wavelength dependent laser bio-ablation.