| Pulsed fiber laser has the advantages of high peak power,narrow pulse width,low processing thermal effect and excellent beam quality.It has been widely used in the fields of ultra-precision processing,medical diagnosis and surgery,lidar,ultrafast spectroscopy and so on.At present,it is an effective method to obtain pulsed laser by using optical materials with saturated absorption characteristics as Q-switcher or mode locker in laser cavity.Passive mode locking is a technology that uses saturable absorber to modulate the laser signal in the cavity to obtain ultrafast laser.Semiconductor saturable absorber mirror(SESAM)is currently the most widely used saturable absorber with stable performance,but its development is limited by its narrow working wavelength,high manufacturing cost and low damage threshold.Carbon nanotube(CNT)is a kind of SA material studied in recent years.The operating band of CNT is about 1?2 ?m,but it tends to agglomeration and scatter light,resulting in increased loss in laser cavity,resulting in increased loss in the laser cavity.Therefore,the search for new SA materials with excellent properties has become a research hotspot in recent years.In this thesis,the applications of several two-dimensional transition metal tellurides such as palladium telluride(PdTe2),platinum telluride(PtTe2)and nickel telluride(NiTe2)in modelocked and Q-switched fiber lasers are studied.The specific research contents are as follows:(1)PdTe2 nanosheets are prepared by liquid phase stripping method and high-speed centrifugation technology,and applied to fiber laser modulation to realize wide-band modelocked signal output.The size of the prepared nanosheets is about 400 ?m.The thickness is about 2 nm.In this experiment,PdTe2 is used as a saturable absorber in Yb-doped,Er-doped and Tm-doped fiber lasers for the first time.A stable mode-locked signal can be obtained in Yb-doped fiber lasers,with a central wavelength of 1069 nm,a pulse width of 887.2 ps and a repetition rate of 8.921 MHz;The center wavelength of the mode-locked signal is 1563.5 nm,the frequency is 7.927 MHz and the pulse width is 560.41ps in Er-doped fiber lasers;The mode-locked pulse signal is obtained in Tm-doped fiber laser,the central wavelength is 1952.7 nm and the repetition rate is 15.5 MHz,The pulse width is 1.1 ps by theoretical calculation.At the same time,it obtains mode-locked signals in 1069 nm,1563.5 nm and 1952.7 nm,indicating that PdTe2 has broadband response and is very suitable for fiber laser modulation.(2)PtTe2 nanosheets are prepared by liquid phase stripping and high-speed centrifugation.The size of the nanosheets are about 100?200 nm and the thickness is less than 10 nm.Two different saturable absorption devices are prepared using PtTe2 nanosheets,namely PtTe2/PVA film and PtTe2 tapered fiber saturable absorber.PtTe2/PVA thin film is applied to erbium-doped fiber laser to realize Q-switched pulse output,and the minimum pulse width is 2.63 ?s,the maximum single pulse energy is 36.65 nJ,the modulation depth is 0.9%.In addition,PtTe2 tapered fiber saturable absorber with a modulation of 8.9%is made by directly dropping the dispersion containing PtTe2 nanosheets onto the prepared tapered fiber.The mode-locked pulse output is realized for the first time in Er-doped fiber laser with a central wavelength of 1565.5 nm,a frequency of 9.76 MHz and a pulse width of 882.9 fs.Compared with PtTe2/PVA SA,PtTe2 tapered fiber SA has greater modulation depth and is more conducive to obtaining mode-locked fiber lasers with narrower pulse width.(3)NiTe2 powder is prepared by solid-state reaction method.The mixed dispersion containing NiTe2 nanosheets is obtained by ultrasonic stripping method and the dispersion is dropped on the prepared conical fiber to form NiTe2 conical fiber saturable absorber.The prepared NiTe2 has a good two-dimensional layered structure with a size of about 100 nm and a thickness of 5 nm below,and has good crystallinity.In this experiment,stable Q-switched Er-doped fiber laser with a pulse interval of 19.81?s and a maximum single pulse energy of 21.3 pJ,and an Er-doped mode-locked fiber laser with a central wavelength of 1567.3 nm and a pulse width of 1.07 ps are realized based on NiTe2.In addition,a Tm-doped mode-locked fiber laser is also obtained,showing a central wavelength of 1966.08 nm and a pulse width of 3.38 ps.The experimental results show that NiTe2 is suitable for applications in broadband ultrafast photonics,and it is a valuable work to study its application in the field of fiber laser modulation.All the above experimental results show that diverse fiber lasers can be realized based on the two-dimensional transition metal telluride saturable absorbers. |
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