Research On Mid-infrared Laser Based On In-band Pumped Holmium Ions Doped Fluoride Crystals

The 2.1?m holmium laser is located in the absorption peak of water and the "atmospheric window".Holmium laser has important application value in the fields of atmospheric monitoring,remote sensing,military and medical treatment.With the continuous emergence and improvement of new laser materials,directly pumped mid-infrared solid-state laser devices have attracted much attention due to the advantages of compact structure,stability and high efficiency,and have been developing new important applications.It is an important way to generate 2.1 ?m laser based on in band pumped holmium doped fluoride.The holmium gain doped medium 2.1?m mid-infrared laser pumped by thulium-doped 1.9 ?m laser has the characteristics of high conversion efficiency,small size and good beam quality.It is an important technical means to achieve high energy and high power 2.1 ?m laser output.It is one of the research hot points in the field of laser and has an important development prospect."One generation of materials,one generation of devices",the emergence of new laser gain media and new low-dimensional saturated materials provides an opportunity for the development of a new generation of high efficiency holmium doped mid-infrared pulse lasers.In this paper,the dynamic mechanism of passively Q-switched and passively mode-locked operation of 2.1 ?m solid-state laser is studied theoretically and experimentally around holmium doped fluoride gain medium and novel saturable absorption modulation device.The stable operation of 2.1 ?m pulse laser with in band pumped Ho3+ doped fluoride gain medium is realized.Combined with the crystal structure,the spectral properties and energy transfer process of holmium doped fluoride crystal and single crystal fiber are studied theoretically and experimentally.The relevant laser experiment prototype is built,and the high-efficiency laser output is realized.The results provide a technical reference for the development of this kind of miniaturized 2.1 ?m laser,and also provide a certain reference for the optimization of the preparation of related materials.The main research work of this paper is as follows:1.The application and generation of mid infrared 2.1 ?m laser are analyzed.The continuous laser tuning technology,short pulse Q-switching technology and mode locking technology of ultrashort pulse laser are summarized.Combined with laser technology,the research progress of holmium doped laser is reviewed.The excellent properties of holmium doped fluoride materials are analyzed.Finally,the research content and significance of the full text are summarized.2.Based on the study and characterization of the spectral characteristics of the traditional Ho: YLF crystal and the novel Ho: SrF₂ single crystal fiber,the in band pumped continuous wave(CW)laser output of holmium doped fluoride crystal is realized.Based on the study of energy level lifetime and spectrum,combined with Judd-Ofelt theory and Fuchtbauer-Ladenburg formula,the emission cross section and effective gain cross section of Ho: SrF₂ single crystal fiber are calculated.The feasibility of 2.1 ?m band laser generated by Ho: SrF₂ single crystal fiber is verified by experiments.The output power of single crystal fiber laser exceeds watt level,and the slope efficiency is up to 48.2%.The high output power and wide continuous tuning range show that Ho: YLF crystal has the potential to realize ultrafast laser operation.3.Research on passively Q-switched holmium pulse laser based on in band pumping: The Ho: YLF laser and Ho: SrF₂ single crystal fiber laser are built by using mathcad software to design reasonable resonators.High performance of low dimensional saturable absorbers(silver nanorods and graphyne)has been successfully fabricated.We characterized their nonlinear optical chacterization at 2.1 ?m.For the first time,they were used as passive Q-switched devices in in band pumped holmium lasers.The stable output of Ho: YLF crystal and Ho: SrF₂ single crystal fiber pulse laser is achieved,respectively.The repetition rate is tens of k Hz and the pulse width is hundred nanoseconds.4.In band pumped active Q-switched holmium doped pulse laser characteristics: Combined with the acousto-optic modulation switcher,the Ho:YLF crystal and Ho:SrF₂ single crystal fiber were used to conduct active pulsed laser experiments.Using Ho:YLF crystal as the gain medium and setting the repetition frequency to 100 Hz,the pulse width obtained is 47.12 ns,and the corresponding peak power is 22.29 W.For the Ho:SrF₂ laser,the narrowest pulse width obtained at the corresponding repetition frequency is 52.38 ns,and the peak power is 24.43W.5.Based on the study of the pulse laser characteristics of the dual loss modulation technology of the acousto-optical modulators and the gold nanobipyramids material: The in band pumped Ho: YLF pulse laser with effective pulse width compression is realized.Combined with theoretical analysis,the modulation mechanism of two Q-switches in holmium-doped pulsed lasers is studied,which provides an effective solution for the development of high symmetry and narrow pulse width 2.1 ?m waveband miniaturized lasers.6.Characteristics of in-band pumped Ho: YLF ultrashort pulse laser based on SESAM saturable absorber: The 2.1 ?m Q-switched mode-locked laser is realized.Based on the theoretical calculation of ABCD matrix and the simulation of mathcad,a mode-locked resonator is designed.Using semiconductor saturable absorption mirror as mode-locking device,a Qswitched mode-locked pulse laser with 100% modulation depth is realized.The narrowest pulse width obtained in the experiment is 1.22 ns,and the corresponding repetition frequency is 109.8 MHz.7.Based on Tm crystal intracavity pumped Ho crystal,the characteristics of two different wavelengths of pulsed laser are studied.Using Tm:YLF and Tm:YAP crystals to carry out intracavity pumping laser experiments on Ho:YLF crystals,the laser output of 2.1?m was successfully obtained under the laser pumping of two different Tm-doped crystals.The results show that the laser gain medium doped with Ho3+ can give full play to the advantages of LD and in-band pumping,which is conducive to obtain high efficiency laser output at room temperature.