Experimental Generation Of Squeezed Vacuum On Cesium D2 Line At Low Frequency

With the rapid development of modern technology,as the most sensitive detection method,optical measurement has been widely applied in many ultra-sensitive detection fields.After a long time of development,optical measurements now can reach and be close to the quantum noise limits in many situations.Thus it becomes very important to go beyond the quantum noise and improve the precision or sensitivity of measurement further.It is well known that squeezed light has provided great potential in improving the performance of optical measurement.The squeezed light round the alkali metal atomic absorption line can be used in scientific research for the interaction between nonclassical light and atoms,such as quantum optical storage,generation of atomic ensembles entanglement and quantum metrology.For practical application,people focused on the two aspects: the high degree of squeezed light for better performance in quantum metrology and expanding the frequency to very low range for specific physical quantity detection,such as the weak magnetic field and the gravitational wave detection.The preparation of squeezed light at such low frequencies needs to overcome a lot of technical problems and faces to great challenges.In this thesis,we mainly use the second harmonic nonlinear effect of PPKTP nonlinear crystal and carry out theoretical and experimental research on the generation of squeezed vacuum field at low frequency corresponding to cesium D2 line.The thesis focuses on the follows:1.A brief review on the development history of the low frequency squeezed light is given and the related basic theory of the quadrature squeezing is presented.2.We have theoretically studied the optical absorption induced thermal effect in the frequency doubling process,and gave a relatively complete cavity design for the four-mirror ring cavity and the semi-monolithic resonant frequency doubling cavity.We report high-efficiency Ti:sapphire-laser-based frequency doubling at the cesium D2 line 852 nm.Beam focusing that is over twice as loose as optimal focusing is used,and the thermal effects due to both the fundamental wave and second harmonic beam absorption are greatly reduced.For the four mirror ring cavity,blue light of 210 mW at 426 nm is obtained with 310 mW of mode-matched fundamental light,corresponding to conversion efficiency of up to 67%.For the semi-monolithic cavity,117.2mw of the blue light is obtained based on the fundmental wavepower of 305 mW,and the highest optical-optical conversion efficiency in the frequency doubling process is up to 42%.The power fluctuation of blue light with the power of 84.5mW is 0.48% in about an hour.3.Using the generated blue light to pump an optical parametric oscillator(OPO),we obtain-3.5dB of single mode squeezed vacuum.Using a home-made balanced homodyne detector,we observe the squeezed vacuum spectrum that is resonant on the cesium D2 line at frequencies from 2.5 kHz to 200 kHz.The phase of the squeezed light is controlled by using a quantum noise locking technique.4.We have analyzed the noise coupling mechanism of the experimental system that limits the generation of squeezed light at the Hz-order frequency,and discussed the possible low frequency band noise sources in the current system in detail.Here is something new:1)We theoretically investigate the light absorption induced thermal effect in the frequency doubling process,and presente a relatively complete cavity design procedure for the high-efficiency frequency doubler.We use the loose focusing which is over twice the usual reported optimal focusing and build the four mirror ring cavity and the semi-monolithic cavity,and achieved stable 426 nm SHG output with high efficiency.2)The squeezed vacuum of-3.5dB on the cesium D2 line is generated in a symmetrical bow-tie ring subthreshold OPO cavity.3).Adopting a quantum noise locking technique without a carrier,we have realized the control of the phase of the squeezed light and obtained a squeezed vacuum at frequencies from 2.5 kHz to 200 kHz using a homemade balanced homodyne detector.