Study On The Output Performance Of A 2 Micrometer Solid State Laser Based On MOFs Materials

The 2μm wavelength laser coincides with the absorption peak of water molecules,and is located in the safe wavelength of human eyes and the atmospheric transmission window.Therefore,this wavelength pulsed lasers have important prospects for applications in laser medicine,aerosol detection,laser frequency conversion,and specialty plastic processing.In recent years,the compact and low-cost 2μm band pulsed solid laser modulator SA prepared by simple and low-cost two-dimensional materials is the main modulator.The traditional inorganic graphene 2D materials are limited in the application of high-performance compact 2μm band pulsed solid-state lasers due to their shortcomings.The nonlinear optical（NLO）response of MOFs can be significantly improved through the larger conjugated system formed byπ-d interaction by combining the advantages of inorganic two-dimensional materials synthesis.In this paper,MOFs materials are used as modulator SA.After the NLO performance of MOFs-based SA is verified,semiconductor laser is used as pump source,and single thulium-doped yttrium aluminate Tm:YAl O₃（Tm:YAP）crystal as laser gain medium.The output performance of 2μm band pulsed lasers operated in passive Q-switching（PQS）and passive mode-locking（PML）modes was deeply investigated.First,the principles of PQS and PML are further research.The rate equations of PQS and PML for a quasi-three-level laser system based on MOFs are established and the analytical expressions are obtained.We discuss in detail the physical parameters that affect the laser output pulse energy,peak power and pulse width,such as crystal temperature,crystal length,crystal doping concentration and the transmittance of the laser output coupling mirror.Meanwhile,nonlinear absorption properties and saturation absorption mechanisms based on MOFs as modulators have been explored in depth.Second,MOFs materials are prepared by solvothermal method,and the saturable absorption devices are prepared by spin-coating.A series of fundamental structures and morphologies of the materials were characterized and the nonlinear absorption properties of the materials were tested to verify the nonlinear absorption properties of the MOFs.A Ni-MOFs SA modulator with a modulation depth of 5.37%,an initial transmittance of88.34%,a saturation absorption intensity of 2.6 MW/cm² and an average thickness of about 23 nm was obtained.A ZIF-8 SA modulator with a modulation depth of 4.6%,an original transmittance of 83.79%,a saturation absorption intensity of 0.38 MW/cm² and an average thickness of 55 nm was obtained.Third,the high efficiency of PQS mode Tm:YAP laser with Ni-MOF and ZIF-8materials as SA,respectively,was achieved.The pump power is 9.46 W and the length of the laser resonator constructed is 30 mm.With 2.5%of the transmittance output mirror,the output power of Tm:YAP is 1.52 W,and the central output wavelength of the laser is1994.3 nm under continuous wave mode operation.Ni-MOFs SA were selected as the modulator for the laser under the same resonator parameters.The average output power of the Tm:YAP laser operated in PQS mode is 1.10 W.The narrowest pulse width was1.97μs with 107.27 k Hz of the repetition rate.The corresponding peak power and per-pulse energy are 4.89 W and 10.90μJ,respectively.The central output wavelength is1987.6 nm.The length of the laser resonator is about 35 mm under the same pump power and output mirror transmittance.The output power of the continuous wave mode is 1.31W.Under these conditions,the central output wavelength of the laser is 1993 nm.The average output power of the Tm:YAP laser is 649 m W when the ZIF-8 SA is inserted as a modulator into the resonator of the laser.The narrowest pulse width was 961 ns with a repetition rate of 44.59 k Hz.The corresponding peak power and per-pulse energy are15.16 W and 14.55μJ,respectively.The central output wavelength of the laser is 1988nm.The above studies confirm that ZIF-8 material can be used as an excellent modulator for PQS lasers.Finally,a PML Tm:YAP laser based on ZIF-8 material was implemented.In combination with optical design software,the optical components in the resonator of the Tm:YAP laser with PML mode were designed and selected to obtain the optimal PML laser structure.When the pump power is 40.6 W and under 2%of the transmittance output mirror,ZIF-8 SA acts as the modulator,the Tm:YAP laser operates in PML mode with four mirror chambers which the length of the resonant cavity is 1525 mm（repetition frequency is 98 MHz）.The average power output of the laser is 912 m W.The narrowest pulse width is 737 ps.The corresponding per-pulse energy and peak power are 9.3 n J and12.6 W,respectively.The central output wavelength of the laser is 1935 nm.It has been shown that ZIF-8 has great potential as a modulator in the PML laser field.Great progress has been made in the study of linear and nonlinear optics of MOFs,but there is little research on the third-order nonlinear optical properties of MOFs materials and in solid-state lasers.In this paper,the nonlinear properties of Ni-MOFs and ZIF-8 materials are studied,and high peak power and energy are obtained in PQS and PML solid-state lasers.The current major research work has laid the foundation for ultrafast photonics based on multifunctional MOFs materials.