Mid-IR Optical Parametric Oscillator Based On Optical Superlattice

The mid-infrared(mid-IR)lasers in 2-5 ?m region have high atmospheric transmittance.Moreover,the absorption peaks of numerous atoms and molecules are also located in this range.Therefore,the 2-5 ?m mid-IR laser has significant application in a variety of fields,such as frontier science,military,spectroscopy,remote sensing,medical diagnosis etc.Compared to some ion-doped(Ho3+,Er3+,Tm3+ etc.)lasers,optical parametric oscillator(OPO)pumped by mature laser can generate broadband continuous tunable mid-IR laser.Currently,optical superlattice materials based on the quasi-phase matching technology,especially the periodically polarized lithium niobate and lithium tantalate(PPLN,PPLT),are the ideal choice for high-power mid-IR OPO devices for their high nonlinear coefficient and wide transparent range.In addition,PPLN and PPLT are easily for manufacturing and suitable for 1064 nm pumping.To improve the performance(wavelength tuning range,conversion efficiency,output power,beam quality,stability etc.)of OPO is always the target of research.Using the periodically polarized MgO-doped lithium niobate(PPMgO:LN)and stoichiometric lithium tantalate(PPSLT)crystals as non-linear medium,combining the pump laser designing,beam shaping and OPO resonator design,this thesis obtained widely-tunable narrow-linewidth continuous-wave mid-IR laser,high-energy long-pulse mid-IR laser and multi-wavelength,widely-tunable,high power nanosecond mid-IR laser output.The main content include:1.The significant application of the mid-IR laser and the methods to obtain mid-IR laser were introduced.The research status at home and abroad of OPO using superlattice was dicpicted.2.The description of the principle,methods and wavelength tuning of quasi-phase matching technology.The introduction of the basic knowledgement and designing principles of OPO.3.Widely-tunable,narrow-linewidth,continuous-wave mid-IR OPO was studied.Combined with the non-planar ring oscillator(NPRO)seed laser and Innoslab amplifier,a 1064 nm continuous-wave laser with a maximum output power of 83.4W and a bandwidth of 17.69 kHz was obtained.A tuning range of 1344.6-5103.2 nm was realized in a ring cavity OPO based on PPMgO:LN crystal.4.High-energy,microsecond,long-pulse mid-IR OPO was studied.Employing a high-peak-power pulsed laser diode(LD)as the pump source,a Nd:YVO4 crystal as the laser gain medium and a PPMgO:LN crystal as the nonlinear medium,a high pulse energy,microsecond mid-IR laser was obtained.The pulse energy of 3.336,3.500,3.789 ?m were 3.99,3.31,2.50 mJ,respectively.5.Multi-wavelength and widely tunable nanosecond mid-IR OPOs were studied.Considering the contradiction between the non-polarized fiber laser and the need of polarized pump light in OPO,the two polarized beam after polarization beam splitting were coupled into the different channels of a multi-period PPSLT.Then a simultaneously four-wavelength OPO was achieved in a single cavity.An OPO with a tuning range of 1346.6-5076.8 nm was realized when using PPMgO:LN crystal as non-linear medium.6.Q-switched laser pumped high power mid-IR OPO was studied.A high-energy mid-IR OPO was obtained using a side-pumped Nd:YLF Q-switched laser as pump light.The pulse energy at 3.796 ?m was 1.1 mJ.Using a multi-stage Innoslab amplifier as the pump source,mid-IR laser outputs with 10.2 W at 3.791 ?m and 33.3 W at 2?m were obtained.In addition,three mid-IR laser prototypes were fabricated.The reference and promotion for the application of mid-IR laser by this thesis is sincerely expected.