Measurement Of Photoassociated Cesium Molecules Based On Nanofiber Probe

Nanofiber become a new research hotspot in the field of miniaturized integrated sensors due to its small size,softness,flexibility,low loss,and corrosion-resistance.As a new type of sensor element,nanofiber has been widely used in the fields of energy,chemical industry,pharmacy,metallurgy,etc.In addition,nanofiber has also shown its excellent performance in the field of basic scientific research.It has been successfully applied to many quantum technologies,including optical sensing,optical trapping,and quantum optics,as a medium in the interaction of light and matter.Since the size of the nanofiber waveguide is smaller than the optical wavelength guided light will be attenuated as an evanescent field within a radius of about?outside the nanofiber.In this work,we used nanofiber to complete the measurement of the atomic absorption saturation in a hot cesium vapor,and then realized the detection of the cesium molecular spectroscopy in an ultra-cold atomic system.In these two systems,nanofiber has shown its advantages in detecting atomic fluorescence with strong binding field.The laser mode guided by nanofiber strongly constrained in the radial direction,which will be beneficial to the development of technologies and operations that require high-intensity or gradient fields,such as ultra-low-power non-linear devices or atomic detection.In this thesis,we introduced a method allowing to produce almost any profile and waist diameter of the tapered nanofibers.The minimum waist diameter of the nanofiber stretched by this method can reach 300nm,and the transmission can reach 98%.We put the nanofiber into a high vacuum system,and compared its performance with free-space beam.We have detected the trap-loss spectrum of cold atoms with TOF,which lays the foundation for directly measuring the fluorescence of cesium molecules,and photoassociation of cesium molecules and collecting cesium molecular signals.The main research contents of this thesis are as follows:1.The nanofiber stretched by the"flame brushing technique"with a waist diameter of 500nm.After testing,the difference between the waist diameter of our nanofiber and the target fiber is less than 10nm,which meets the experimental requirements.2.We designed a type of fiber holder which can mount nanofiber in a vacuum,as well as a Teflon feedthrough with two channels for bare fibers via the vacuum device.These designs ensure that nanofiber can work in a high-vacuum experimental environment,in which the pressure can reach10^-7Pa.3.We built the nanofiber vacuum system with hot cesium vapor and its supporting optical system.Based on these systems,we observed the transmission spectroscopy of cesium atoms using a tapered optical fiber.We found that with the increase of the input light power,transmission tends to stabilize caused by saturation of upper level population.By rising temperature,the atomic density increase,inducing increases of the absorption capacity of photons and reduce of the transmission.In addition,we compare the performance of TOF system and free-space vapor system.The power-dependent absorption saturation measurement for the TOF system has been achieved three orders of magnitude smaller than free-space vapor system.4.We built the nanofiber ultra-cold atomic system and its supporting magnetic and optical systems.Cesium molecules were prepared by associating light through space incident beam,and the fluorescence of the atoms was collected through the nanofiber,measured by a single photon detector.We compared with the fluorescence signal of the atomic group detected by the camera,and confirmed that we have obtained an effective cesium molecular spectrum.The photoassociation rate in our work was calculated by measuring the atomic loading curve with locking the photoassociation frequency in the molecular spectrum line.