Development And Performance Optimization Of High Stability And High Efficiency Semi-Nonplanar Ring Oscillators

High stability and high efficiency semi-non-planar ring oscillators play an important role in precision measurements such as optical frequency standards,test of Lorentz invariance,and Laser interference gravitational-wave detection.As the developing,the requirements for laser efficiency and power stability are also constantly improve.In gravitational wave detection,the optical power and power stability of the laser are two important factors that affect the signal-to-noise ratio and hence sensitivity of the detection.In order to obtain lasers with high efficiency,high power,Low intensity noise,we carried out laser de-velopment and performance optimization around the pump technology and power stability of the laser.To lay a solid foundation for the deverpement and optimization of the semi-non-planar Nd:YAG laser,we first analyze the basic structure and the thermal stability of the monolithic laser cavity.The heat generation mechanism in the laser crystal,the thermal lens effect of the monolithic crystal and the heat distribution in the crystal are calculated and analyzed.According to the thermal analysis and the stability analysis of the monolithic cavity,suggestions are provided for the optimization of the structural parameters of the cavity.In order to study the limitations of laser efficiency and power output,this paper first built a 1064nm Nd:YAG monolithic laser system with 808nm traditional pumping,then measured and analyzed the laser output characteristics,and determined the main limitations of laser efficiency and power output.Meaning to further improve the laser output efficiency,laser output power,and reduce the energy consumption of the laser.For the first time,the 885 nm thermal boosted pumping was applied to a Nd:YAG crystal to build a semi-non-planar monolithic laser system.By using the 885nm thermal boosted direct pumping,the efficiency of the monolithic laser is increased from 51.3%to 76.9%,which is close to the theoretical limit of the laser's theoretical efficiency of 79%.As a result,the maximum output power of the laser has been increased from 3.9W to 4.5W When the laser was operated at 3 W,the power output has changed from unable to operate continuously for a long period of time to it can operate stably for more than 100 hours.Furthermore,the laser beam quality M2 is 1.12,closing to an ideal Gaussian spot.In addition,the spectral characteristics of the lasers with 808 nm and 885 nm pumping are measured and compared.Based on the above-mentioned investigations,we have focused on the improvement fo the laser power stability.Firstly,we investigat the theoretical model of the laser intensity noise from which the intensity noise spectrum is derived.Then the measurement was performed and the experiemtal result,and the measured value of the noise was consistent with the spectrum obtained by the theoretical model.Based on the noise model,the contribution of each individual source to the intensity noise is quantitatively analyzed,and the laser relaxation oscillation noise and pumping noise are the main sources of laser intensity noise.In addition,the laser relaxation oscillation noise are analyzed and detailed scheme for suppressing relaxation oscillation is discussed.Experimentally investigate the suppression of laser intensity noise by feedback control of laser output power.Using a high-gain noise and wide-bandwidth circuits are actively controlled at high-frequency noise(100kHz-5MHz)and low-frequency noise(10mHz-100kHz)respectively.Suppression of noise from the laser relaxation oscillation is realized at 100 kHz-5 MHz and the noise peak is reduced from 1E-5(1/Hz 1/2)to 7E-8(1/Hz 1/2)at the relaxation frequency,corresponding to a suppression ratio of 40 dB.Intensity noise suppression is also investigated at low-and intermediate-frequencies at 0.01Hz-10Hz,the relative intensity noise is reduced from 1E-2(1/Hzl/2)to 2E-4(1/Hzl/2),close to the requirements of space gravitational wave detection;at 100Hz-3kHz laser intensity noise from 1E-5(1/Hzl/2)is reduced to 4E-7(1/Hzl/2),which is close to the quantum noise limit of the laser.At 2kHz-100kHz,the intensity noise suppression is reduced from 1E-5(1/Hzl/2)to 1E-6(1/Hzl/2),it is also necessary to further increase the suppression effect.By increasing the lasing efficiency,the high-power stability and realiability of the semi-non-planar monolithic Nd:YAG laser have been improved.The laser intensities are also verified for two pumping schemes.These investigations,together with other parametric optimizations,laid the solid foundation for developing ultra-stable lasers in many precision measurements such as optical frequency standard,laser ranging and navigation,and interfermetric gravitiational wave detection.