| The high efficiency frequency up-conversion of lasers in the nonlinear crystal has been a popular technique,based on the rapidly improvement of the bulk,waveguide and whispering gallery nonlinear crystals.And frequency up-conversion has been applied to a various kinds of applications such as generation of new wavelength lasers,frequency conversion of quantum states,long distance quantum entanglement distribution and efficient infrared single photon detection.Therefore,high efficiency up-conversion has recently received interest also from the field of laser applications.For classical light field,the frequency conversion of the light in the 1.5 ?m telecom band to the visual wavelength region with high efficiency provides a possibility to detect the infrared photon more efficiently,since the detection efficiency of the silicon single photon detector can be up to 5 times higher than that of a InGaAs detector.For non-classical states with weak intensity,e.g.Fock states,squeezed vacuum states and superposition of coherent states,the high efficiency up-conversion not only can improve the nonlinear process but also preserve the distinct non-classical properties of the input states.The inner conversion process are always strong in the nonlinear waveguide,however,the insert loss are very large in the kind of setups.Moreover,the micro-resonator made of nonlinear crystal is also becoming a popular scheme based on its high efficiency.However,frequency up-conversion in bulk crystals have been scrutinized for a variety of designs and crystal materials,resulting in up-conversion efficiencies of weak near-infrared light can exceed 90% under certain conditions.Many theories and experiments have already verified that the power of the frequency up-converted field is related to the fundamental laser powers.To achieve high frequency-conversion efficiency,external resonant cavity is often introduced to enhance the power of at least one of the incident light fields.Nowadays,the doubly resonant external cavity scheme,i.e.both of the fundamental lasers are resonating in the cavity,has received lots of interests.Because of the passive amplification,this scheme can not only decrease the power consuming of the setup,but also increase the interaction path between the light and the crystal to improve the conversion efficiency of the incident laser.The main research works in this dissertation contains the following aspects:1)The realization of the doubly resonant high efficiency frequency up-conversion was investigated.The error signal for the frequency locking between the signal laser and the cavity was obtained by demodulating the frequency up-converted field in the high efficiency conversion process.In the experiments,the signal to noise ratio of the error signals demodulated from the frequency up-converted light and the cavity transmission of the signal light were contrasted;the frequency locking between the weak signal laser and the cavity was realized;under this condition,the signal field conversion efficiency of 73% was achieved;then based on the PDH scheme optimized by a sample and hold circuit,the frequency stabilization between the pulsed pump laser and the external cavity was realized.2)The research on the high efficiency up-conversion for weak light was performed in detail.Under the undepleted pump approximation based on the doubly resonant scheme the conditions of high efficiency up-conversion are investigated,in which the 1064 nm pump laser and the 1583 nm laser were interacted in a 25 mm long periodic poled lithium niobate crystal and the conversion efficiency of 94.6% was realized in the experiment.In the high efficiency conversion process the impedance matched condition and the coupling efficiency were studied and the Pmax was fitted based on the coupling efficiency.Then the method of correcting the conversion efficiency measured by the power meter by using the cavity reflection of the signal field was investigated.3)For the high efficiency sum frequency generation for high power laser,the solution difference of the coupled wave equations based on the undepleted pump approximation and the elliptic integral equation was calculated and incident power range of the signal laser with conversion efficiency over 90% was analyzed combined with the theory of resonator,which was also measured in the experiment.When the cavity was impedance matched at the signal wave length,the long-term power stability and the short-term intensity noise of the output laser were measured and analyzed.Finally,the output beam quality was measured.The innovations in this dissertation are listed as follows:1)Based on the relationship between the intensity amplitude and the detuned frequency of the signal cavity transmission and the output laser and the fact that the information in the fundamental lasers could transfer to the output field,the error signal for frequency locking between the signal laser and the cavity was acquired by demodulating the output laser at the modulation frequency of the signal laser.The contrast between the error obtained from the signal cavity transmission and the output laser demonstrated that the signal to noise ratio of the latter was better than the former and the long-term frequency locking of the signal laser to the cavity was realized on the high efficiency conversion condition.2)Based on the solution of the coupled-wave equations in the undepleted pump approximation and the theory of the resonator,the condition and parameters of high efficiency frequency up-conversion were achieved.Using the experimental data of the single-pass configuration,the reflection of the signal input coupler and the incident pump power were optimized.In the experiment,by designing low cavity finesse for the signal field,the conversion efficiency of 94.6% was obtained for the signal laser with power lower than 25 mW.3)Based on the elliptic integral equation solving the coupled-wave equations and the theory of resonator,the calculated parameters of the sum frequency generation efficiency for high power signal laser was obtained.By using this theory model,the signal power ranges with conversion efficiency over 90% were analyzed in the simulation.After optimizing the experimental parameters,the conversion efficiency of 93% for incident signal power of 275 mW was realized,i.e.the output 636 nm laser power of 637 mW.When the cavity at signal wavelength was impedance matched,the power fluctuation of the output laser was measured to be 1.8%,and the M2 factors were both around 1.09 at the X and Y directions. |
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