| The 2?m lasers,which emission wavelengths match well with the typical absorption spectra of many gaseous pollutants and can be strongly absorbed by water molecules and other biological tissues,have significant applications in the fields of medical treatment,air monitoring,laser radar,molecular spectroscopy and scientific research etc..In addition,the 2 ?m lasers also can be used as pump sources of optical parametric oscillatosr and amplifiers(OPOs and OPAs)based on ZnGeP and other nonlinear crystals for achieving mid-and far-infrared lasers.Due to the wide application requirements,the research on the 2?m solid state lasers has become one of the hot scientific topics in recent years.At present,pumping crystals doped with rare earth ions such as Tm3+ Ho3+ and so on by using diode or fiber laser,is still the most effective way to obtain the 2?m laser.There are many research directions of 2?m solid state lasers,including the exploration of new laser crystals and ceramics,development on novel optical devices,techniques for improving laser power and efficiency,generation of pulsed lasers,single frequency lasers,wavelength tunable lasers,and so on.In this paper,the theoretical and experimental investigations of Tm3+ or Ho3+ doped crystals and ceramics based on novelly developed active and passive optical modulation devices have been performed.The contents of this paper are as follows:1.Introduction on the basic principles of the active and passive Q-switching based on two-dimensional acousto-optical(AO)modulator,the LiNbO3(LN)electro-optical(EO)modulator and the saturable absorber(SA)have been presented.In addition,the mechanism and dynamic process of mode-locked pulse generations have been stated.Furthermore,the fundamental principles of wavelength tunable lasers in 2?m regions by using birefringent quartz plate have been analyzed.2.By using Tm:YAP crystal as the laser gain medium,the pulsed laser characteristics based on novel active and passive modulation devices have been investigated.Firstly,the physical structure of multi-layered black phosphorus(BP)nanoplatelets has been studied in details together with their saturable absorption characteristics.The BP SAM was prepared successfully,based on which,the Q-switched pulses with a duration of 181 ns and an average output power of 3.1 W were generated at a pulse repetition rate of 81 kHz.Pulses with a pulse energy of 39.5?J were generated,which,to the best of our knowledge,set a record among those of BP SA-based Q-switched lasers.The results indicate the promising potential of multilayered BP nanoplatelets as SAs for achieving efficient pulsed lasers at around 2?m.By using a SESAM,continuous wave mode-locked laser with pulse duration of 1.7ps was achieved.With a LN EO modulator,a diode-pumped all-solid-state actively Q-switched Tm:YAP laser at 2 ?m was realized.At the repetition rate of 25 Hz,2.52mJ pulses with duration of 78.4 ns were generated.By using the birefringent quartz plate,a wavelength tunable CW laser output from 1887.lnm to 2080.8nm has been realized.3.The laser characteristics of Tm:BaYF have been studied.The fluorescence spectrum of the Tm:BaYF crystal delivered a wavelength tunable CW laser output from 1843.8nm to 1997.1nm.With an AO modulator,an actively Q-switched Tm:BaYF laser was realized.At a repetition rate of 500 Hz,1.3 mJ pulses with duration of 305 ns were generated.In SESAM mode-locking regime,a synchronously tri-wavelength mode-locked Tm:BaYF laser with pulse width of 27.5 ps has been successfully achieved.4.The laser characteristics of Tm:LuGGG disordered crystal were studied.The influence of different ion doping concentrations on the continuous-wave laser characteristics was analyzed.A wavelength tunable CW Tm:LuGGG laser with output wavelengths from 1907.5nm to 2055.9nm was realized.A passively Q-switched Tm:LuGGG laser based on graphene was achieved,corresponding to a pulse duration of 1.29 ?s.By using a SESAM,continuous-wave mode-locked Tm:LuGGG laser was achieved,too.The results show that the disordered structure Tm:LuGGG,not only has good thermal mechanical properties,but also has inhomogeneous broadening spectrum,which is very favorable for generating ultrashort pulses at 2 ?m.5.The laser characteristics of Ho:YAG ceramic under intracavity pumping were studied.A compact Ho:YAG ceramic laser intracavity pumped by a diode-pumped Tm:BaYF crystal laser was realized in 2?m region.The spectral and output power characteristics were investigated.Compared with the Ho3+ ion laser sensitized by Tm3+ ions,the intracavity pumping method can take the advantages of both LD and in-band pumping,which is beneficial to obtain high efficiency laser at room temperature.6.The spectral and laser characteristics of a Ho:YLF crystal fiber grown with the micro-Pulling Down method were investigated.Both the CW and EO Q-switching regimes of Ho:YLF crystal fiber lasers have been realized.The average output power,pulse energy and pulse width of the Q-switched laser under different repetition frequencies were studied.Passively mode-locked Ho:YLF crystal fiber laser with SESAM was also designed and investigated.The study results show that the Ho:YLF crystal fiber laser has a low thermal effect,which is beneficial for obtaining high power and high efficiency lasers at 2?m. |
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