| All-solid-state continuous-wave(CW)single-frequency lasers with perfect beam quality,low intensity noise,and narrow linewidth have attract growing attentions on the cutting-edge scientific research fields including quantum information,atomic physics,precision measurement,ultra-fine spectroscopy and laser precision ranging and high precision.Especially,after the gravitational wave(GW)signals were successfully being detected in 2015,the weak-signal laser detection technology based on high-power all-solid-state single-frequency CW lasers have aroused great interest of researchers.Therefore,increasing the output power of all-solid-state CW single-frequency lasers and reducing the intensity noise of the lasers have become one of the hot research topics in laser technology field.In addition,the development of the high-power and low-noise all solid-state CW single-frequency laser can also meet the needs of scientific research and military defense fields,such as the construction of cold atom physics,wide area quantum network,the development of high-power single-frequency mid-infrared and deep-UV laser sources and so on.To this end,we have conducted in-depth research on scaling up the optical power and suppression the intensity noise of all-solid-state single-frequency lasers.The specific research contents include:1.A method for accurately measuring the intracavity linear loss of a single-frequency laser with the assistance of the nonlinear loss was proposed.On this basis,a high-quality CW single-frequency laser with an output power over 50 W was achieved by increasing the incident pump power of the laser together with optimizing the transmission of the laser output coupling mirror.The optical power of the laser were further scaled to 104 and 125 W by means of a single-end-pumped 4-stage MOPA system and an optimal designed double-end-pumped 2-stage MOPA system,respectively.The corresponding beam quality M~2 factor were better than 1.4 and 1.25,respectively.2.A method for realizing a 100 W level CW single-frequency laser within a single laser cavity was developed.By inserting two end-pumped laser crystals into a single ring resonator,the severe thermal effects of the laser crystal can be alleviated and the generated thermal lens effect can be easy to manipulated.By inserting an imaging system(IS)into the ring resonator and manipulating the IS,the laser cavity mode can be self-reproduced at the place of each laser crystal and the stability working region(SWR)of the laser can be adjusted.The unidirectional operation of the laser can be realized by inserting an optical diode with high isolation ratio into the ring resonator to effectively eliminate the laser hole burning effect.Stable single-frequency operation of the laser was achieved by introducing sufficient nonlinear loss into the ring resonator as well as optimizing the transmittance of the output coupling mirror.Based on these laser technologies,a 101 W CW single-frequency 1064nm laser was realized in a single ring cavity,for the first time.3.Based on theoretically investigating the intensity noise spectrum of the dual-wavelength laser at fundamental wave(FW)and second-harmonic wave(SHW),the properties of the intensity noise spectrum of the intracavity frequency-doubled laser were comprehensively characterized.The transfer of intensity noise between the FW and SHW was experimentally realized by manipulating the intracavity nonlinear loss.4.The relationship between the longitudinal mode structures(LMS)and the intensity noise of the laser was investigated by manipulating the intracavity nonlinear linear loss of the laser.On this basis,the dependence between the LMS and the intensity noise spectrum of the laser was investigated.The experimental results showed that by decreasing the nonlinear loss of the laser in the single-frequency operating range,the RRO noise of the laser can be effectively suppressed.When the non-linear loss of the laser was insufficient to suppress the side-modes oscillation,the laser oscillated with multi-modes and mode-hopping.In this case,the intensity noise spectrum of the laser would sharply fluctuate in a wide frequency range.This work showed the advantages of single-frequency laser physically.5.The influence of direct and traditional pumping schemes(DPS and TPS)on the intensity noise spectrum of lasers were investigated for the first time.It was found that the laser with employing the DPS can not only scale up the optical power of the laser but also enhance the intensity noise of the laser.Because a highly doped laser crystal with long doping length employed in DPS laser for improving the pump absorption efficiency can increase the number of atoms in the laser crystal.As a result,the interaction between the atoms and the cavity mode was enhances,which resulted in a larger dipole fluctuation noise of the laser.In addition,the large amount of atoms in the laser crystal can also lead to a large of the population inversion,which can enhance the laser's stimulated emission rate(SER)between the population inversions and the laser cavity mode.Consequently,the RRO frequency and peak amplitude can be increased,which delays the frequency of the laser reaching the shot noise level(SNL).6.After the relationship between the SER and the intensity noise spectrum of the laser is investigated,the intensity noise of the laser was successfully suppressed in the broad frequency range by reducing the SER of the laser.The simulation results show that reducing the SER of the laser can effectively suppress the intensity noise in the broad band frequency range.Experimentally,by stretching the cavity length of the resonant cavity to reduce of the SER of the TPS laser,introducing an optimized IS in the resonant cavity to control the SWR of the laser and introducing large enough nonlinear loss into the resonant cavity to suppress the laser intensity noise around the RRO frequency,the laser intensity noise spectral(1 mW)can be 8.6 dB/Hz higher than the SNL frequency at the RRO frequency and reaches the SNL at the cutoff frequency of 1 MHz. |
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