Ladder-type Electromagnetically Induced Transparency Of Atoms On The Surface Of Nanofiber

Optical fiber is widely used in the fields of science,communication and medicine.In a standard glass fiber,the light is guided inside the core and isolated from the outside environment by the cladding,thus achieving low loss and low interference transmission over long distances.In contrast,the diameter of a nanofiber is smaller than the wavelength of light,the laser mode is strongly constrained in the radial direction,and there is a significant evanescent light field around the fiber.These properties make nanofibers a unique tool that can effectively control the strong coupling of light with atoms near surfaces over long distances.Nanofibers are widely used in optical sensing,optical frequency measurement,pulse compression and all kinds of spectroscopy,etc.,and can be easily connected to existing fiber optic networks with very low loss.This makes it possible to envisage a quantum network based entirely on optical fibers.In addition,the nanofiber changes the traditional high-power nonlinear optical condition,and can realize the strong nonlinear effect in the low-power field.This thesis introduces an experimental study based on a nanofiber system.The core of the system is a nanofiber suspended in cesium vapor.The compression of the evanescent laser mode propagating along the fiber significantly increases the nonlinear interaction between the light field and surrounding atoms.It is possible to observe many nonlinear optical effects under low power condition.In this thesis,a new type of nanofiber-cesium vapor system is used to realize the nonlinear effect at ultra-low power.Based on the characteristics of high power density and long interaction of nanofiber,we use the control laser on the order of microwatts to realize the ladder-type electromagnetically induced transparency(EIT)phenomenon of cesium atoms.At the same time,the blue fluorescence signal during the 7P ? 6S transition is measured using the nanofiber system,which provides a new direction for us to study the four-wave mixing phenomenon at ultra-low power.The main research contents of this thesis are as follows:1.In this paper,we use the flame brush technology to obtain high-quality optical nanofibers with high uniformity and low surface roughness.Optical nanofibers with diameters of 500 nm and 400 nm are fabricated for electromagnetically induced transparency experiment and blue fluorescence measurement experiment respectively.The transmission of fiber can reach about 98% after the successful pulling,which can meet the requirements of the experiment.2.Set up the nanofiber-cesium vapor vacuum device required for the experiment.The pulled optical nanofiber is mounted on a holder with a unique heating structure to prevent the accumulation of cesium atoms on the surface of fiber and reduce the optical transmission.3.Set up the experimental scheme.The third chapter introduces the generation of EIT phenomenon under ultra-low power.The probe laser at 852 nm and the control laser at 794 nm counter-propagating enter the nanofiber,and the control laser is locked on the 6P?8S transition of the cesium atom.The probe laser is scanned between the 6S?6P transition,and EIT with a Doppler background is realized.The blue light fluorescence measurement experiment in chapter four is based on the EIT experimental research.For the convenience of measurement,the probe laser and the control laser enter into the fiber in the same direction.By locking the probe laser,scanning the control laser,the blue light produced during the transition from 7P to 6S can be obtained,and counting the blue photons using a single photon counter.4.Using the density matrix equation,numerical simulation of the ladder-type EIT phenomenon in the nanofiber system is carried out.The effect of control laser intensity on the transparent window of EIT is studied,and the theoretical fitting is performed.The effects of probe laser intensity and control laser intensity on the blue fluorescence signal is also studied.