Experimental Research On Spatial Mode Field Distributions Of Narrow Linewidth Non-planar Ring Oscillators

’Shaped like a harp,listen to the sound of nature’,which is the name source of Tian Qin plan—a scientific research plan led by China to detect gravitational wave.One of critical technologies in Tian Qin plan is the high-precision laser interferometric displacement measurement.Therefore,we need to develop a narrow-linewidth seed laser by ourselves.According to existing reports,diode-laser-pumped monolithic nonplanar ring oscillator（NPRO）shows narrow linewidth and low noise performances,which may satisfy the requirement of Tian Qin.With such a background,we investigate narrow-linewidth lasers using NPRO for Tian Qin.In this thesis,the detailed work is composed of following parts:Researches on single-frequency Gaussian mode NPRO laser are carried out.First,we use Matrix transfer theory discussing the optical mode characteristics of NPRO laser,and analyze loss difference between two-direction resonance modes under the influence of Faraday magneto-optic effect generated by an external magnetic field,which helps to obtain the requirement of unidirectional emission for an NPRO laser.Then we use a comercial non-planar ring cavity to carry out experimental investigation on this type of narrow linewidth laser.Subsequently,we design a preliminary package for the laser module.A Gaussian beam at 808 nm with operation power at 250 m W is used to pump the Nd:YAG cavity for lasing at a 1064 nm wavelength.Unidirectional and single-frequency lasing behaviors are observed,maximum optical power greater than 100m W is achieved with 40 m W coupled into a single mode polarization maintaining fiber.We also measure its linewidth by beating two independent fundamental-mode NPRO lasers and obtain a linewidth narrower than 2 k Hz.At the same time,we succeed to tune the laser wavelength by adjusting the temperature of the cavity and using a piezo actuator to stress the cavity.After preliminarily packing the laser module,we implement four environmental tests including shock,random vibration,sine vibration and high-low temperature circulation to test whether the laser module satisfies the requirement of preparatory environmental project or not.The result shows that the laser module can withstand preliminary environmental test at the aviation level.Besides,we demonstrate the direct generation of a vortex laser in such a monolithic nonplanar ring cavity.A variety of transverse patterns of the emitted vortex light beams can be emitted by changing relative positions of the focused Gaussian pump beam on the cavity.Similarly,such vortex laser beams also feature unidirectional and single-frequency charateristics.Spectral linewidth narrower than 2 k Hz is also achieved.Furthermore,we develop a new method using a single pano-concave lens to obtain the topological charge information of the laser.Compared with other fork-type interference detection methods,the optical path of this method is simpler,more compact,and easier to operate.We also compare our method with another method using a single titled biconvex spherical lens as the single conversion element.Through the beat frequency test,we measure frequency noise spectra of the fundamental mode and vortex mode lasers,and verify the low noise characteristics of non-planar ring cavity lasers with the laser frequency noise performance of 0.1 Hz/Hz^1/2@1MHz.Moreover,we report low-noise dual-frequency vortex lasing in our experiments.For instance,phase noise for dual-frequency lasing with frequency difference at 8.2 GHz as low as-118 dBc/Hz at 10kHz offset is measured.