The Laser Measurement Of The Novel Nd-doped SrLaAlO₄ Crystal And Its Application In Methane Detection

Since the invention of the world’s first ruby laser,lasers become irreplaceable in the fields of national security,frontier scientific research,medical treatment and precision industrial processing.Due to the small volume and high stability,all-solid-state lasers have become the focus of laser device research in achieving high pulse energy and high peak power.Different laser operation regimes require different laser gain media,for example,the high power CW lasers require gain media with large emission cross sections and high thermal conductivity,the Q-switched lasers require long upper-level lifetime,and the ultrafast lasers require ultra-wide gain bandwidth and so on.Therefore,explorations and investigations on the novel gain media with excellent physical and chemical,mechanical,spectral characteristics have never been stopped,which has become one of the hot topics in the fields of material science and laser technology.In this dissertation,the novel crystal Nd:SrLaAlO4 is taken as the research object,and high-quality crystal is grown by exploring the crystal growth technology.The physicochemical properties of Nd:SrLaAlO4 crystal such as spectral and thermal properties are fully characterized.The continuous-wave(CW),Q-switched,wavelength tunable as well as the femtosecond ultrafast laser characteristics of the Nd:SrLaAlO4 crystal are systematically studied.Based on this,mid-infrared wavelength-tunable laser is achieved by using the Nd:SrLaAlO4 laser pumped PPLN-OPO technology,which is furthermore successfully applied for setting up a kind of gas detection system to realize high precision and fast detection of CH4 gas concentration in the atmosphere.The achieved research results are as follows:(1)The crystal growth technology is explored and high quality Nd:SrLaAlO4 crystal is grown.The thermal properties and polarized absorption and emission spectra are systematically measured.By measurement of the density,specific heat,thermal expansion,thermal diffusion the thermal conductivity is calculated to be 4.67 W/(m·K),which is comparable with that of the commercial Nd:YVO4 crystal.The polarized absorption and emission spectra are measured,and the corresponding polarized absorption and emission cross sections are calculated by using the J-O theory,which shows an excited emission cross section of 5.5×10-20 cm2 at 1.07 μm with a full width at half maximum of about 34 nm.The measurement results indicate that Nd:SrLaAlO4 crystal is an excellent laser gain medium,especially suitable for wavelength-tunable and ultra-fast laser devices.(2)The CW and Q-switching laser characteristics of the Nd:SrLaAlO4 crystal are studied.In the CW regime,a maximum output power of 3.54 W was obtained,giving an optical-optical efficiency of 46.4%.By using a Cr4+:YAG wafer as saturable absorber,Q-switched laser pulses with a pulse repetition rate of 48.5 kHz and pulse width of 12.6 ns are generated.In addition,a novel kind of ReSe2 saturable absorber mirror is prepared by using liquid phase stripping method,which Raman spectrum,AFM microstructure and nonlinear saturable absorption characteristics are measured and analyzed.By using the prepared multi-layered ReSe2 saturable absorber,high repetition rate pulsed Nd:SrLaAlO4 laser is obtained,which delivered a maximum pulse repetition rate as high as 553 kHz and the shortest pulse width of 109 ns,respectively.The results well show that two-dimensional ReSe2 saturable absorber is very suitable for generating ultra-high repetition rate pulsed laser due to its ultrafast electron hole relaxation time.(3)The tuning properties and output power of the Nd:SrLaA104 crystal laser are measured.The wavelength-tunable range and corresponding output power characteristics of the tunable Nd:SrLaAlO4 laser under different output couplings are studied systematically.Under an output coupling of 3%,a wavelength tuning range of 32 nm from 1063 to 1095 nm is obtained with a maximum output power of 1.49 W.The results show that by adjusting the losses of different longitudinal modes with the birefringent filter,the Nd:SrLaAlO4 crystal is preferable in generating stable dual-wavelength and tri-wavelength laser,which has an important application potential in differential frequency generated terahertz wave method.(4)The ultrashort pulse laser characteristics of Nd:SrLaAlO4 crystal is investigated.By reasonably designing the resonant cavity structure and optimizing the intracavity dispersion,a passively mode-locked Nd:SrLaAlO4 femtosecond laser is realized,which delivers ultrashort pulses as short as 458 fs,corresponding to a maximum outpout power of 520 mW and a pulse repetition rate of 78.5 MHz.(5)With the Q-switched Nd:SrLaAlO4 laser as the pump source,a mid-infrared gas detection system is set up.The CH4 concentration in the atmosphere is successfully precisely detected by using the system.The detected concentration of CH4 in the atmosphere is 1.90 ppm and the standard deviation is 0.03 ppm.In addition,the mid-infrared tunable laser source can be furthermore developed to detect other gas such as CO,CO2 and etc.