High-Efficiency Ho³⁺-Doped Down-Conversion Green Fiber Laser

Since the first ruby laser was manufactured by American scientist Maiman in 1960,laser has attracted much attention as a light source with high monochromatism,high coherence and excellent direction.Today,the band covered by the laser spectrum has been expanded from the deep ultraviolet band(ARF excimer laser)of 193 nm to the mid-infrared band(HCN gas laser)of more than 3um.As an important branch of the visible light band laser,the green light band(495-570 nm)laser has many important applications,including but not limited to the fields of biomedical,color display,laser storage and optical communication.In terms of scientific research,green laser can also be used as an excellent sum-frequency source for ultraviolet and deep ultraviolet lasers.As far as fiber lasers are concerned,there are many ways to produce green light.The two most common ways are to use rare earth ion doped fiber to produce green light by up conversion or down conversion.Theoretically,any gain fiber can produce green light laser as long as the emission spectrum of rare earth ions doped by the gain fiber contains the emission peak of green light.However,up to now,no matter the fiber laser doped with Pr3+,Yb3+,Er3+ or Ho3+ ions,no matter the up-conversion or down-conversion method can be used to obtain high power and high efficiency green light.Therefore,the innovation of this project is to use Blue-ray LD to pump a high-power,high-efficiency(by far the most efficient)green light laser.In this project,we try to use several Ho:ZBLAN doped fibers with different lengths(doping concentration of 5000 ppm,core/cladding diameter of 7.5/125 μm,gain fiber length of 25 cm/19.5 cm/17.5 cm)as the resonator of the laser and make comparison,including the comparison of power and slant efficiency,so as to get the optimal cavity length range.We use down-conversion method to pump,using a 3.4 W blue-ray LD as the pump source.A high quality green laser with a threshold of 360mW,a maximum power of 380 mW,a maximum skew efficiency of 60%,a laser half width of less than 0.5 nm,and a laser wavelength of 544.43 nm is obtained by using the end-pumped method.It is the green fiber laser with the highest skew efficiency so far.After that,we extended the original optical path and tuned the green light with a band-pass filter.Finally,we obtained a green light tuned laser with a tuning range of 538.12-545.21 nm,a tuning width of more than 7 nm,a laser threshold of 456 mW and a maximum output power of 131.1 mW.