Resonant Gain Effect In A Coherent Atomic Medium

The introduction of atomic coherence effect promotes the development of quantum optics.Using atomic coherence effect can form new optical medium and change the absorption and dispersion properties of nonlinear optical,which leading to various interesting phenomena.The process of atom-field interaction is the basis of studying atomic coherence.By changing the atom-field interaction,the properties of the field can be controlled.Gain effect is widely used in optical amplification research fields,and can also be applied to electromagnetically inducted grating.In the atom-field interaction medium,atomic coherence effects can be used to regulate the properties of fields.Electromagnetically inducted grating is an important phenomenon in the research direction of atomic coherence effect.The proposed of electromagnetically induced grating opens a new way to study the properties of the atom-field interaction.The gain phase grating can be realized by combining the gain effect with the electromagnetically inducted grating,which greatly improving the first-order and higher-order diffraction efficiency.The gain effect further promotes the development of electromagnetically induced grating,making atomic grating more practical in optical switching and all-optical logic gate.Based on the above research background,the gain phase grating in four-level structure and the optical gain effect in cyclic structure are studied.The development of atomic coherence and electromagnetically inducted grating is described.This paper introduces the semi-classical theory of the atom-field interaction,deduces the density matrix equation of two-level system,and introduces the basic theory of electromagnetically inducted grating.This paper mainly contains the following contents:1.The N-type and tripod-type structures electromagnetically induced phase grating effects are introduced.The results show that the first-order diffraction efficiency of N-type and Tripod type electromagnetically induced phase gratings is 34% and 33% respectively,which are close to that of ideal sinusoidal phase gratings.2.The gain phase grating effect is studied theoretically in a coherent four-level atomic system.The results show that under the action of coherent pump field,the intensity of signal field is amplified,and the zero-order diffraction intensity of electromagnetically induced grating is increased.With the phase modulation,the zero-order diffraction light is effectively modulated to the first-order and higher-order diffraction directions.In contrast with the electromagnetically induced phase grating,the first-order diffraction efficiency of the gain phase grating is higher,and it may have more advantages in the application of optical switching,all-optical network and so on.3.The influence of the intensity of pump field and regulated field on the signal field gain is analyzed theoretically in a coherent closed-loop four-level atomic system.The results show that in a closed-loop four-level system,the regulated field promotes the transition of population among the four levels,leading to enhance the signal gain.When added a weaker regulated field(the intensity of regulated field is equal to that of the signal field),the signal gain is improved 12 times at resonance frequency.Coherent pump field induces signal field amplification,and by increasing the strength of the pumping field,the signal field is transformed from no population inversion gain to population inversion gain.With the enhancement of the pumping field,the gain at the resonant frequency first increases and then decreases.The closed-loop gain system has potential application value in optical amplification and so on.