Study Of X-ray Thin Film Planar Cavities And Fano Line Shape

Quantum optics is a discipline that studies the interaction between light and matter under quantum mechanics framework.After half century of vigorous development,it has become one of the most important subjects of physics.In recent decades,with the development of synchrotron radiations and X-ray free electron lasers,X-ray quantum optics has gradually emerged as a new frontier field.X-ray quantum optics study the interaction between X-ray and M?ssbauer nuclear resonance or atomic inner shell electron transitions.By embedding these two systems into the thin film planar cavities as atomic layer,the interaction between X-ray photons and the systems can be manipulated by the so-called X-ray cavity-QED setup,providing new research tools for precision spectroscopies,precision measurements,and X-ray inner shell spectroscopies.Currently,X-ray cavity quantum optics has become an important branch of X-ray quantum optics.However,this field just sprouts,and there were relatively few experimental studies.The further development requires to exploit the new research systems and control methods.This thesis conducts research on X-ray cavity quantum optics based on thin film planar cavities,selecting the inner shell transitions of W atoms in WSi2 and the nuclear resonance transitions of 181Ta and 57Fe as two-level systems.In particular,by adjusting the thickness of the top layer of the thin film planar cavity,the position of the atomic layer in the cavity,and the thickness of the nuclear layer,we studied Fano interference,inner shell hole states and collective effects induced and controlled by the cavity effects,respectively.This thesis contributes to expand the research scopes of X-ray cavity quantum optics and enriching the control methods.The specific research topics are as follows:(1)By adjusting the thickness of the top layer of Pt in the thin film planar cavity,we successfully manipulated the relative amplitude of the continuum path,and observed the new flat line Fano profile for the first time in experiments.The cavity scattering with a broad spectral width can be used as a continuum path,while the atomic resonant scattering with a narrow spectral width can be used as a discrete path.Based on this,we successfully built a two-path Fano interferometer.The experiment was performed at the first-order mode of the cavity without cavity detuning,where the q is a pure imaginary number.By adjusting the thickness of the top layer of Pt in the thin film cavity,i.e.,changing the relative amplitude of the continuum path,we can significantly control the imaginary part of the q factor.We found that when the top layer thickness is 1 nm,the q factor become a pure imaginary number-i,and the interference cross term cancels the resonant discrete term exactly,thereby erasing the signal of atomic resonant scattering.Therefore,only the continuum path without energy-dependence can be detected,which is the flat line Fano pofile.This work not only provides a different approach for studying atomic "invisibility" but also offers a new approach for identifying weak structures near the intense white line in the X-ray spectrum;(2)By changing the position of the atomic layer in the cavity,the core-hole lifetime controlling is realized,and the distributions of photonic density of states under different cavity geometries are revealed by detecting the cavity enhanced decay rates.Different from the previous works that only select limited cavity modes,this work can continuously control the lifetime of core-hole states over a wide range based on the distribution of photonic density of state inside the cavity.The present experimental results are of great significance to study the intrinsic properties of X-ray cavities;(3)By changing the thickness of the nuclear layer of 181Ta and 57Fe in the X-ray thin film planar cavity,we demonstrate the existence of a critical point in the single-photon superradiance as a function of the number of atoms,where the super-radiation rate is maximum.It is found that the superradiance is proportional to the product of the number of atoms and the field strength factor.The thickness of the nuclear layer increases,the effective number of atoms increases,but the field strength at the nuclear layer position decreases due to the absorption effect.Therefore,there is a critical thickness where the superradiance is strongest,and the atom with larger absorption coefficient will have smaller critical thickness.