High Quantum Efficiency Gain-Switch Thulium-Doped Fiber Lasers

Since the invention of the first laser in 1960,as a widely used tool,lasers have profoundly changed our lives.Owing to the spectral overlap with the absorption peaks of several major molecules in air(e.g.,H2 O,CO2),~2-μm laser sources are now playing a more and more important role,and have been applied in various areas,such as remote sensing,light detection,industry,military and medical treatment.In addition,they are also excellent pump sources for 2.4 μm solid-state lasers and 3-5 μm optical parametric oscillators.The high repetition rate,ultrashort pulse lasers have important research and application value in the eye-safe-radar and optoelectronic countermeasure field and have become one of the hottest topics.Gain-switched technique is a simple way to produce stable and high power pulsed lasers.It uses pulsed sources to pump the doped fiber and introduce periodic short-temporal high gain regions,and finally stimulate short pulsed laser emission from the gain fiber.In this paper,we propose hybrid-pumped resonant gain-switched thulium fiber lasers to realize high-average-power and high-pulse-energy 2-μm laser emissions.Based on numerical simulation,laser dynamics(pulse peak power,pulse energy,pulse duration,etc.)of this kind of laser system are investigated in detail.By taking advantages of the 793 nm continuous wave pump and the 1900 nm pulsed pump,performance of the laser emission can be significantly improved,with the highest average power of 28 W,peak power of 3.5 kW,pulse energy of 281 μJ,and narrowest pulse duration of 92 ns,all of which can be further optimized through designing the cavity parameters and the pumping circumstance.Compared with the pump pulses,two times improvement in pulse energy and average power has been achieved.This hybrid resonant gain-switched system has an all-fiber configuration,high quantum efficiency and low heat load,and can be steadily extended into the cladding pump scheme,thus paving a new way to realize high power(>100 W average power)and high pulse energy(>1 mJ)2 μm thulium fiber lasers.