Study On Irradiation Damage Mechanism Of Yb Doped Quartz Glass

Yb-doped quartz fiber lasers have been widely used in space exploration,accelerators and nuclear facilities due to their advantages of high output power,high light-to-light conversion efficiency,good reliability and high beam quality,as well as small size and light weight.However,the presence of high-energy particles in the application environments can induce defects and then cause irradiation damage to the Yb-doped quartz fiber,resulting in reduce of the optical and laser performance of the Yb-doped fiber,decline of overall performance of the safe operation and lifetime of Yb-doped fiber laser,or even failure of laser output,which severely limits the safe operation and lifetime of high-power fiber laser at low/high orbits.Therefore,the radiation resistance of ytterbium-doped quartz optical fiber must be improved.To reveal the photon darkening effect in Yb-doped quartz fiber under the irradiation of high-energy particles is the primary scientific problem to improve the radiation resistance of laser fiber.In this thesis,modified chemical vapor deposition(MCVD)combined with rare-earth ion vapor doping technique was used to prepare quartz optical fiber preforms with various dopant.The intrinsic defects present in the produced preforms before and after irradiation were determined by absorption spectrum,excitation spectrum and fluorescence spectrum,etc,and the effect of dopant on intrinsic defects was obtained.The effects of dopant on the bond structure were studied by using Raman spectroscopy and EPMA.Subsequently,the irradiation was carried out by Co⁶⁰?-rays for Al/Yb/Ce/F co-doped quartz perform samples at different total doses and dose rates.By analyzing the absorption spectrum,optical band gap and fluorescence spectrum under different wavelength excitation,the effect of irradiation dose and dose rate on irradiation-induced defects was obtained,and dynamic mechanism diagram of defects in the Al/Yb/Ce/F co-doped quartz preform samples with various irradiation total dose was established.The main research contents and results are as follows:The effects of different dopants on the types of intrinsic defects,glass network structure and bond valence in quartz preforms were studied.It was found that in the aluminosilicate preform samples,single doping of Ce³⁺ions or Yb³⁺ions will result in obvious absorption peaks due to Al-OHC and Al-E'defects,while,codoping Ce³⁺/Yb³⁺can effectively inhibit Al-OHC and Al E'.Besides,F^-ions replace the bridging oxygen(BO)in the glass network to cause bond breakage,and induce the generation of Al-E'and a small amount of Al-OHC.The 5d energy level of Ce³⁺ion is split in Al/Yb/Ce/F codoping sample,while the energy difference between ²F_5/2 and ²F_7/2 fluctuates only around 2200 cm^-1 and unaffected by the dopants.When the electron transition process of Ce³⁺ion from the5d excited state to the ²F_2/7 ground state at 4f level exists,the energy transfer process will happen from Ce³⁺to ODC(?).Influenced by dopant the fluorescence lifetime of ODC(?)fluctuates within 0-25?s.Ce³⁺ions and Yb³⁺ions exist in the network gap,destroying the network structure.The effects of?-ray irradiation total dose and dose rate on the color centers concentration in Al/Yb/Ce/F co-doped quartz preform samples and the dynamic process of irradiation-induced color centers formation were revealed.Irradiation-induced defects include Al-OHC,Al-E',NBOHC,STEX and E',etc,in which the content of Al-OHC increases with the increasing of the total irradiation dose,which is the main reason for the additional loss in visible range.The content variation of E'color center,Ce³⁺ion and Yb²⁺ion are consistent that all of them first increased with the increasing total dose,when the total dose exceeds 50 krad(Si),the content of them decreased.Because the generation of radiation-induced E'color center need holes,thus a large number of electrons are left in samples,causing Ce⁴⁺+e?Ce³⁺and Yb³⁺+e?Yb²⁺shift to the right,when the total dose exceeds 50krad(Si),the E'color center structure[?Si?⁺Si?]⁺or[?Si?Al?]capture electrons and generated[?Si-Si?]or[?Si-Al?]^-structures,leaving a large number of holes,thus shifting the two reactions above to the left.The optical bandgap of samples decreased with increasing radiation total dose,which is due to the localized non-bridge oxygen(NBO).The fluorescence spectra indicated that the content of NBOHC did increase with the increasing radiation total dose.In addition,there has energy transfer process between Ce³⁺ion and ODC(?),Yb³⁺and Al-OHC,NBOHC and Yb³⁺ion also Al-OHC and Yb²⁺ion.