Preparation Of Stable Squeezed Vacuum States At 1.06 ?m

Quant?m optics has developed rapidly in the generation and application of non-classical light fields.Precision measurement based on quant?m level has become an important research direction in physics for 30 years.Among them,the squeezed states is one of the most popular directions in quant?m optics.In order to break through the limitation of quant?m noise in precision measurement,an effective method is to minimize the quant?m noise of light source.Limited by Heisenberg's uncertainty relation,when the quant?m noise of one quadrature component is smaller than the shot noise limit(SNL),the other one is necessarily larger than the SNL.The state whose noise distribution satisfy the characteristic above is called squeezed state.Squeezed states have been widely used in precision measurement based on its characteristic.For better use of the squeezed state,a stable and reliable squeezed state source is needed.For generation of the squeezed states,one of the most effective methods is optical parametric oscillator(OPO)parametric down-conversion process.Our experiment is to prepare 1.06 ?m squeezed vacuum states by p?mping an OPO based on a type-I quasi-phase-matched PPKTP(periodically poled potassi?m titanyl phosphate)crystal.In order to obtain a stable output of squeezed vacuum state,we have carried out a series of work as follows:(1)We use unidirectional traveling-wave cavity technique and the intracavity second harmonic generation(SHG)technique to obtain single-frequency laser with high power 1.06?m and 532 nm dual-wavelength.In the experiment,by introducing and controlling the nonlinear loss caused by the SHG,the laser can be kept in stable single frequency operation without mode hops.The result indicates that the 532 nm and 1.06?m outputs as high as 9.5W and 3.1 W are achieved simultaneously under 50 W p?mping,and there is only one longitudinal mode oscillated.The measured phase noises of the 1.06?m and 532 nm lasers reach SNL at the analysis frequencies above 5 MHz.The measured intensity noise of the 1.06?m and 532 nm lasers reach the SNL at the analysis frequencies above 3.5 MHz.The beam quality factor of the 1.06?m is M_x~2=1.06 and M_y~2=1.05.The beam quality factor of the 532 nm is M_x~2=1.09 and M_y~2=1.12.(2)The frequencies of the laser are locked using a confocal Fabry-Pérot(F-P)cavity,and the measured frequency drift is less than±1.5 MHz during a given 3 hours.Furthermore,a feedback loop based on a Mach-Zehnder interferometer(MZI)is designed and used to reduce the power fluctuation and suppress the intensity noise of the 532 nm laser.The measured power fluctuation is less than±0.2%for a given 5 hours.The intensity noise in audio frequency region is suppressed.The mode cleaner is used to improve the beam quality of the two wavelength lasers.The beam quality factor of 1.06?m laser is M_x~2=1.02 and M_y~2=1.01.The beam quality factor of 532 nm laser is M_x~2=1.04and M_y~2=1.01.The intensity noises of the output lasers from the mode cleaner reach the SNL at the analysis frequencies above 1.8 MHz.(3)An auxiliary beam for locking the OPO cavity length is generated by optical serrodyne sideband modulation(SSM).The OPO cavity length is locked by using the auxiliary beam based on the PDH technique.After injecting the p?mp light below the threshold into the OPO cavity,we measured the noise power of the down-converted field with a balanced homodyne detector(BHD).The squeezing level of 7.1 dB is measured at Fourier frequency of 3 MHz.(4)After the OPO cavity length is locked,a coherent control field with a frequency shift of 25 MHz is employed.The coherent control technique is used for locking the squeezing angle of the squeezed vacuum states.The noise distribution of the bright squeezed light field at 25 MHz is detected by a BHD,and the squeezing angle at other frequencies can be determined.In order to measure the squeezed states produced by OPO for a long time,the relative phase between squeezed states and LO beam is locked by coherent control technique.Finally,7.2±0.1 dB phase squeezed vacuum states at Fourier frequency of 3 MHz are generated stably and measured continuously for a given 3 hours.(5)We discuss the influence of common mode rejection ratio(CMRR)and phase jitter between the squeezed vacuum states and LO beam on the measurement results of the squeezed vacuum states.On the basis of the previous work,a BHD whose CMRR is greater than 60 dB in the audio band was used in the experiment.Finally,a 6.1±0.3 dB squeezed vacuum states at audio frequencies from 5 kHz to 20 kHz are generated.A 3.0±0.3 dB phase squeezed vacuum states is obtained at the frequency of 3.5 kHz.The innovative works of this thesis are as follows:(1)We use unidirectional traveling-wave cavity technique and the intracavity SHG technique to obtain single-frequency laser with high power1.06?m and 532 nm dual-wavelength.By introducing and controlling the nonlinear loss caused by the SHG,the laser can be kept in stable single frequency operation without mode hops.The frequencies of the laser are locked using a confocal Fabry-Pérot cavity,and the measured frequency drift is less than±1.5 MHz during a given 3 hours.A feedback loop based on a MZI is designed and used to reduce the power fluctuation and suppress the intensity noise of the 532 nm laser.The measured power fluctuation is less than±0.2%for a given 5 hours.(2)An auxiliary beam for locking the OPO cavity length is generated by optical SSM.The OPO cavity length is locked by using the auxiliary beam based on the PDH technique.After the OPO cavity length is locked,a coherent control field with a frequency shift of 25 MHz is employed.The coherent control technique is used for locking the squeezing angle of the squeezed vacuum states.The noise distribution of the bright squeezed states at 25 MHz is detected by a BHD,and the squeezing angle at other frequencies can be determined.In order to measure the squeezed states produced by OPO for a long time,the phase of LO beam is locked by coherent control technique.Finally,7.2±0.1 dB phase squeezed vacuum states at Fourier frequency of 3MHz are generated stably and measured continuously for a given 3 hours.(3)We discuss the influence of CMRR and phase jitter between the squeezed vacuum states and LO beam on the measurement results of the squeezed vacuum states.Finally,a 6.1±0.3 dB squeezed vacuum states at audio frequencies from 5 kHz to 20 kHz are generated.A 3.0±0.3 dB phase squeezed vacuum states is obtained at the frequency of 3.5 kHz.