| Visible light laser has been well known in the fields of laser display and medical treatment due to the human eye’s sensitivity to it.From the first ruby laser realized by American Maiman to the present,the research of visible light laser has been throughout the development history of laser.Since the acquisition of deep red laser by Maiman,the wavelength range of visible light laser continuously covers the whole visible light field and the laser power is constantly improved.Specially,the yellow laser plays an important role in laser medical treatment,laser imaging,laser sodium guide star and Bose-Einstein condensation and many other civil and scientific research fields.Compared with other visible laser wavelengths,the common rare-earth ion laser gain materials rarely emit light in the yellow waveband.In the early days,the means of obtaining yellow laser were mainly limited to dye laser and laser conversion of nonlinear optical effects,such as sum-frequency 1 μm laser,frequency-doubled 1.1μm laser,four-wave mixing,Raman laser and Dy3+-doped crystal and fiber laser.Although dye lasers have the advantages of wavelength tunability and high power,their biggest problem is that they require long-term and costly maintenance,which is hard to put into some specific applications.Nd-doped crystal is the earliest and most widely studied laser crystal,the sum-frequency yellow-light lasers based on it were developed earlier and more mature.The advantage of frequency-doubled yellow laser is that some Yb3+-doped crystals themselves can play the role of frequency doubling,so the yellow laser can be obtained without additional frequency doubling crystals.Besides,yellow laser can also be generated by pulsed laser pumping Yb3+-doped nonlinear fiber excited four-wave mixing.With the development of Raman laser research,Raman frequency shift of green laser or frequency doubling of 1.14—1.17 μm Raman laser to obtain the yellow laser has also made good progress.Most of these schemes utilize nonlinear effect to indirectly obtain the yellow laser,which inevitably reduces the pump efficiency and increases the complexity of laser system.In recent years,pumping rareearth ion-doped crystals and fibers to produce visible laser have gained popularity.The energy transition of Dy3+,4F9/2→6H13/2,provides a direct access to yellow laser.Specially,the Dy3+-doped fiber lasers are more attractive to researchers because of their compact structure,high efficiency and good beam quality.This thesis focuses on the study of Dy3+-doped fluoride fiber yellow laser.On the basis of the previous studies,we summarized the experience,and carried out in-depth experimental studies,constructed a high-efficiency fiber yellow laser with wavelength tunability.The aim is to develop a miniaturized,tunable and high-performance yellow laser source.To solve the problem that Dy3+:ZBLAN fiber is difficult to realize lowloss fusion,we use coating technology to deposit material on the end-facet of the fiber to make the fiber end-facet mirrors.A miniaturized,low-loss all-fiber yellow laser resonator is realized by docking the fiber end-facet mirrors with fluoride gain fiber.It not only avoids using the traditional bulk input/output couplers to destroy the structure of all-fiber resonator,but also avoids the problem of fusing fluoride fibers and the high technical difficulty of engraving gratings on fluoride fibers.The low-cost and easy-torealize yellow fluoride fiber laser has been successfully obtained.We utilized the existing conditions to compare and optimize the length of the Dy3+:ZBLAN fiber and the reflectance of the yellow-light fiber output mirror.By using the 95 cm Dy3+:ZBLAN fiber and the fiber end-facet mirror with a reflectance of about 48%at 575 nm,up to 300 mW yellow laser output at 575 nm was obtained,with a laser slope efficiency of 3 1.7%.Then we successfully tuned the wavelength of the yellow laser by using a visible light blazed grating.A yellow laser with a slope efficiency of 34.9%was successfully obtained by placing the blazed grating at the input end of the resonator without affecting the pump light coupling path and the yellow laser output from the fiber end.It is,to the best of our knowledge,the highest power and conversion efficiency of a yellow Dy3+-doped fiber laser.The tunable wavelength range of continuous tuning from 568.7 nm to 581.9 nm up to 13.2 nm was realized.In addition,the laser wavelength is strictly limited by the angle of the blazed grating.The spectrum has a 3-dB bandwidth less than 0.05 nm and has very good stability.In this paper,the output characteristics of the tunable yellow fiber laser are demonstrated in detail.The existing problem in the experiment and the improvement direction that can further improve the tuning range of the tuning range are analyzed.The development of the Dy3+-doped fluoride fiber yellow light laser is prospected. |
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