| The mid-infrared(MIR)1.5-4μm eye-safe band covers important atmospheric transmission windows and a large number of absorption peaks of molecules and atoms,which is an important molecular fingerprint sepcrtral region High-performance lasers in this spectral range have important application value in the fields of medical treatment,laser communication,laser radar,gas detection,photoelectric countermeasures,and scientific research.With the development of laser diode(LD)pump technology,Er3+,Tm3+,Ho3+rare-earth ions doped crystalline lasers gradually become important coherent light sources in the MIR band due to the simple structure,low cost,stability and reliability etc.However,the mature laser emission wavelengths based on rare-earth ions are currently below 3 μm,and the corresponding MIR laser performances are still far behind the 1 μm band.On the other hand,rare-earth ions doped MIR lasers with wavelengths above 3 pm mainly rely on nonlinear frequency conversion processes such as optical parametric oscillators(OPOs).Among them,1μm band laser is the most common pump source.In principle,the conversion efficiency of OPOs is limited by the ratio between the pump and idler wavelengths.So it can effectively improve the conversion efficiency by using long-wavelength laser pumping,which,however,also depends on the MIR laser performances below 3μm.Therefore,rare-earth ions doped MIR solid-state lasers and its pumping optical parametric frequency conversions have become one of the hot topics in laser fields recently.In this dissertation,based on Er3+,Tm3+,Ho3+doped crystals and periodically polarized PPLN optical superlattice,high-power continuous wave(CW),high-energy short pulse,and ultrashort lasers as well as OPOs in the MIR band have been investigated systematically to achieve high-performance solid-state MIR laser output.The main research work of the dissertation includes:1.Based on Er:YAG crystal,research on 1.6 μm band CW and pulse laser has been carried out.Saturable absorbers(SAs)of two-dimensional(2D)nanomaterials such as tungsten disulfide(WS2)and black phosphorus(BP)were prepared by liquid phase exfoliation method,which nonlinear optical absorption characteristics in the 1.6μm band were characterized,respectively.The passively Q-switched Er:YAG lasers based on the prepared 2D SAs in 1.6 μm were realized.Using the WS2-SA,the maximum Q-switched laser output power of 0.42 W was obtained,and the corresponding pulse width and repetition frequency were 1.8 μs and 25.13 kHz,respectively.Using the BP-SA,the maximum Q-switched laser output power of 0.33 W was obtained,and the corresponding pulse width and repetition frequency were 2.8μs and 34 kHz,respectively2.Based on Tm3+ion-doped crystals,research on high-power CW laser output at 2 μm has been carried out.Using diode-wing-pumping technology,the thermal effect of Tm:LuAG crystal was greatly reduced.At the maximum absorbed pump power of 20.1 W,a maximum CW power of 8.5 W was achieved at 2 μm based a Tm:LuAG crystal with a slope efficiency of 44.5%,which is the highest CW output power from the diode-pumped Tm:LuAG lasers as far as we know.Based on the double-rod tandem technology,by using two Tm:YAP crystals,a maximum CW output power of 20.9 W was realized with an emission wavelength of 1985 nm under a maximum incident pump power of 75 W,and the corresponding slope efficiency reached 33.5%.Compared with the maximum output power of 8.23 W obtained by a Tm:YAP crystal,the CW output power has been greatly improved more than two times3.Based on Tm3+ion-doped crystals,research on high-energy Q-switched short pulse and mode-locked ultrashort lasers at 2 μm has been carried out.Based on a LN EO Q-switch with a pulse-on mode,the high-energy output characteristics of diode-pumped Tm:LuAG lasers were studied.At a repetition rate of 100 Hz,a maximum pulse energy of 10.8 mJ was obtained with a minimum pulse width of 52 ns at 2022.9 nm,which is the maximum Q-switched pulse energy ever obtained from diode-pumped Tm:LuAG crystalline lasers.With the aid of semiconductor saturable absorption mirror(SESAM),diode-pumped Tm:CGA CW mode-locked(CWML)ultrashort laser characteristics were studied.The resonator was designed with a 3.85 m ultra-long Z-shaped folding cavity configuration with a dual-output.In CWML regime,a maximum output power of 164 mW was obtained at 1968 nm with a pulse repetition rate of 38.86 MHz and a spectral FWHM of 4 nm.According to the time-bandwidth product for hyperbolic sech2 pulse type,the Fourier transform limit of the pulse width could be as narrow as 1 ps4.Based on Ho3+ion-doped crystals,investigations on the 2-3 μm MIR solid-state lasers have been carried out.Using a double-rod tandem Tm:YAP laser as the pump source,which delivered a maximum output power of 17.3 W at 1940 nm as obtained in Chapter 2 of this dissertation,the characteristics of inband pumped CW Ho:YAP laser were studied.A maximum average output power of 6.5 W with a slope efficiency of 50.6%was achieved at 2.1 μm.Based on this,a pulse-on mode LGS EO modulator was designed with aλ/4 wave voltage of 2400 V,with which stable EO Q-switched Ho:YAP 2.1 μm laser was achieved.At a repetition rate of 2 kHz,a maximum single pulse energy of 1.5 mJ was obtained with a shortest pulse width of 23 ns,corresponding to a highest peak power was up to 65 kW.Based on 1150 nm LD pumping Ho3+,Pr3+co-doped LuLiF4 crystal,a maximum CW output power of 120 mW was achieved at 3 μm.Furthermore,by using a kind of WS2-SA,a passively Q-switched Ho,Pr:LuLiF4 laser at 2955 nm was realized,which delivered a maximum output power of 82 mW,a pulse width of 654 ns at a repetition rate of 90.4 kHz.The results show that WS2 with wide-band saturable absorption performance is an excellent optical modulator for 3 μm MIRwaveband.5.Using high-power 2 μm laser as the pump source,PPLN-OPOs working at 3.8μm MIR band has been studied.Quasi-phase-matching(QPM)temperature-wavelength tuning curve of the 2 μm laser pumped PPLN-OPOs was theoretically analyzed,and a double-pass dual-resonance OPO resonator configuration was designed.Utilizing the self-built diode-pumped AO Q-switched Tm:YAP laser at 1937 nm as the pump source,a PPLN-OPO working at near-degeneracy point of 3872 nm with FWHM of 20 nm was realized,which delivered a maximum output power of about 1.2 W,corresponding to an optical-to-optical conversion efficiency of 19.4%.It is the first time to improve the output power of 2 μm laser pumped PPLN-OPOs over 1 W,to the best of our knowledge. |
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