Study On The Key Techniques Of The 1.5 Um Cavity-stabilized Ultra-stable Laser

Ultra-stable laser is also known as ultra-narrow linewidth laser,which has the best monochromaticity.It is usually used for time and frequency and precision spectroscopy and many other frontier science researches.Ultra-stable laser is a vital component in improving the stability of the optical atomic clocks,and the stability of the ultra-stable microwave source based on ultra-stable laser;and it is used in some fundamental physics measurement due to its high precision.1.5 ?m laser is in the low loss window of optical fiber communication,and at present,the best ultra-stable laser system is around 1.5 ?m,which indicates that the ultra-stable optical reference cavity fabrication process and other technologies are mature at this wavelength.Therefore,this paper mainly focuses on the research of 1.5 ?m ultra-stable laser,which can be transmitted to the far end through the fiber and applied in other relevant experiments.An ultra-stable laser usually use a specific frequency stabilization method to stabilize the commercial continuous laser to a corresponding frequency reference.In the experiment,we use the PDH(Pound-Drever-Hall)frequency stabilization method,to lock the commercial 1.5 ?m fiber laser on the most commonly used and most precise frequency reference——the F-P(Fabry–P?erot)cavity,to obtain the cavity-stabilized 1.5 ?m ultra-stable laser and the stability of the cavity is only limited by the thermal noise of the cavity.The thermal noise of the cavity limits the stability of the ultra-stable laser,and the limitation is generally below 1×10-15 level.In this paper,the thermal noise limit of the cavity-stabilized laser is analysed,and the four factors which influence the thermal noise is derived.At the same time,the design of reference cavity is introduced,and the vibration insensitive vertical reference cavity is simulated by finite element analysis.According to the fluctuation of the laboratory environment,the vacuum chamber,thermal shield,seismic isolation platform and acoustic insulation box are designed.After that,we introduce our new method to reduce the thermal noise of the ultrastable laser system,by using multi-cavity and optical frequency synthesis method.In the past researches,the stability of ultra-stable laser is limited by single cavity,but in our thesis,The thermal noise of the ultra-stable laser can be determined by the combination of multiple cavities,and the final noise level will be inversely proportional to?n,where n is the number of the reference cavities.The length of the ultra-stable cavity could be delivered to the laser by tight frequency locking method.In this thesis,several kinds of commonly used locking method are introduced,in which the PDH technology is analysed specifically,including the error signal acquisition,PDH servo circuit design principle and the function of the acousto-optic modulator feedback.The main technical problem——residual amplitude modulation(RAM)in PDH technology is analyzed.The two main causes of RAM are summarized.And current mostly used active control method is introduced.More concisely,we reduce the RAM-induced frequency instability to 1×10-17@1 s,using a homemade Brewster-angle cut electro-optic modulator.This result is comparable to the best active methods in the world.Finally,two identical ultra-laser laser are built to get the laser beat.The beat result shows one laser frequency instability of 7×10-16@1-10 s,and the linewidth less than 185 m Hz.The result reaches the thermal noise limit of the 10 cm-long cavity made of entire ULE(ultra low expansion).And these data achieves the domestic leading level.