Study On Ultraviolet Light Sources For Hg~+ Optical Frequency Standard

The Hg⁺ion optical frequency standard is one of the most accurate frequency stan-dard systems in the world.The narrow linewidth tunable deep ultraviolet light sources containing the 194 nm laser,the 254 nm laser and the 282 nm laser are necessary light sources and main difficulties to realize Hg⁺ion optical frequency standard.The main work of this thesis is to produce high-performance deep ultraviolet laser sources with nonlinear frequency conversion,and apply it to the field of precision spectroscopy.This thesis includes the following aspects:1.According to the optimal beam waist obtained by Boyd-Kleinman's best focusing conditions,we designed a series of different cavities for frequency-doubling and sum-frequency-mixing to generate these three deep-ultraviolet lasers.The frequency-doubling cavities are used to generate the 266 nm laser,the 507 nm laser,the 254 nm laser,the 563nm laser and the 282 nm laser,and a sum-frequency-mixing cavity is used to generate the194 nm laser.2.Using the elliptical Gaussian focused beam of the fundamental to generate the266 nm laser in a BBO crystal,and then mix the 266 nm laser and the 718 nm laser to generate a 2.05 m W 194 nm laser whose tuning range is from 193.8 nm to 195.1 nm,it meets the demand for mercury ion optical frequency standards.In addition,we gener-ated the continuous-wave optical squeezing at 532 nm with degenerate parametric down conversion(DPDC)in the BBO crystal.3.We have designed and produced two miniaturized bow-tie doubling cavities with dimensions of 95 mm×66 mm×53 mm and integrated the fourth hanrmonic gener-ation system within 393 mm×274 mm×100 mm.Infrared-to-ultraviolet wavelength conversion can be achieved with this system and a 25 m W 254 nm deep ultraviolet laser is experimentally produced.4.Using Pound-Drever-Hall frequency stabilization,the two 1126 nm lasers are re-spectively locked on two independent ultra-stabilized ULE cavities on two isolation plat-forms,and then the 1126 nm laser of one platform is guided to another platform with accurate cancellation of phase noise.The frequency stability of optical fiber transmission reachs 1×10^-15at 1s.The linewidth of the 1126 nm laser is measured to be 3 Hz by beat-ing the two 1126 nm lasers,and the stability of beating signal is 3×10^-15at 1s.Finally,a 1.2 m W 282 nm laser was obtained by cascade frequency doubling.5.A preliminary study was carried out on the Hg⁺ion optical frequency standard system using deep ultraviolet lasers.We have detected the spectrum of Hg atoms at 254nm,which corresponds to the transition from the ground state 6s²to the excited state of6s6p.The Hg⁺ion is generated by isotope selective photoionization.After compensating for the micromotion,the EMCCD images of single Hg⁺ion and monoisotopic multi-ion crystal are observed.We measure the resonance frequencies of the²S_1/2-²P_1/2transition of the²⁰²Hg⁺,²⁰⁰Hg⁺,and¹⁹⁸Hg⁺experimentally.The ion temperature is 7(3)m K.The²S_1/2-²D_5/2clock transition spectrum of¹⁹⁸Hg⁺ion was obtained by scanning the 282 nm laser.High-performance deep-ultraviolet laser sources are crucial in Hg⁺ion optical fre-quency standard.The development of deep-ultraviolet laser sources will be of great help for Hg⁺ion optical frequency standard in the processes of ion preparation,laser cooling,clock laser generation and so on.