The femtosecond pulse shaping technique has been shown to be an effective method to control the multi-photon absorption by the light–matter interaction. Previous studies mainly focused on the quantum coherent control...The femtosecond pulse shaping technique has been shown to be an effective method to control the multi-photon absorption by the light–matter interaction. Previous studies mainly focused on the quantum coherent control of the multi-photon absorption by the phase, amplitude and polarization modulation, but the coherent features of the multi-photon absorption depending on the energy level structure, the laser spectrum bandwidth and laser central frequency still lack in-depth systematic research. In this work, we further explore the coherent features of the resonance-mediated two-photon absorption in a rubidium atom by varying the energy level structure, spectrum bandwidth and central frequency of the femtosecond laser field. The theoretical results show that the change of the intermediate state detuning can effectively influence the enhancement of the near-resonant part, which further affects the transform-limited （TL）-normalized final state population maximum. Moreover, as the laser spectrum bandwidth increases, the TL-normalized final state population maximum can be effectively enhanced due to the increase of the enhancement in the near-resonant part, but the TL-normalized final state population maximum is constant by varying the laser central frequency. These studies can provide a clear physical picture for understanding the coherent features of the resonance-mediated two-photon absorption, and can also provide a theoretical guidance for the future applications.展开更多
Surface plasmon polaritons'(SPPs')frequency blue shift is observed in finite-difference time-domain(FDTD)simulation of parallel electron excitation Au bulk structure.Comparing with cold dispersion of SPPs,an o...Surface plasmon polaritons'(SPPs')frequency blue shift is observed in finite-difference time-domain(FDTD)simulation of parallel electron excitation Au bulk structure.Comparing with cold dispersion of SPPs,an obvious frequency blue shift is obtained in low confinement region excitation simulation results.Then,according to SPPs'transverse attenuation characteristics,the excited frequency mode instead of cold dispersion corresponding frequency mode matches it.Thence,this excited mode is confirmed to be SPPs'mode.As is well known the lower the frequency,the smaller the confinement factor is and the lower the excitation efficiency,the wider the bandwidth of excited SPPs is.And considering the attenuation in whole structure,the excited surface field contains attenuation signal.In a low confinement factor region,the higher the SPPs'frequency,the higher the excitation efficiency is,while broadband frequency information obtained in attenuation signal provides high frequency information in stimulation signal.Thence,in the beam-wave interaction,as the signal oscillation time increases,the frequency of the oscillation field gradually increases.Thus,compared with cold dispersion,the frequency of excited SPP is blueshifted This hypothesis is verified by monitoring the time domain signal of excited field in low and high confinement factor regions and comparing them.Then,this frequency-blue shift is confirmed to have commonality of SPPs,which is independent of SPPs'material and structure.Finally,this frequency-blue shift is confirmed in an attenuated total reflection(ATR)experiment.Owing to frequency dependence of most of SPPs'devices,such as coherent enhancement radiation and enhancement transmission devices,the frequency-blue shift presented here is of great influence in the SPPs applications.展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos 51132004,11474096 and 11604199the Science and Technology Commission of Shanghai Municipality under Grant No 14JC1401500the Higher Education Key Program of He'nan Province under Grant Nos 17A140025 and 16A140030
文摘The femtosecond pulse shaping technique has been shown to be an effective method to control the multi-photon absorption by the light–matter interaction. Previous studies mainly focused on the quantum coherent control of the multi-photon absorption by the phase, amplitude and polarization modulation, but the coherent features of the multi-photon absorption depending on the energy level structure, the laser spectrum bandwidth and laser central frequency still lack in-depth systematic research. In this work, we further explore the coherent features of the resonance-mediated two-photon absorption in a rubidium atom by varying the energy level structure, spectrum bandwidth and central frequency of the femtosecond laser field. The theoretical results show that the change of the intermediate state detuning can effectively influence the enhancement of the near-resonant part, which further affects the transform-limited （TL）-normalized final state population maximum. Moreover, as the laser spectrum bandwidth increases, the TL-normalized final state population maximum can be effectively enhanced due to the increase of the enhancement in the near-resonant part, but the TL-normalized final state population maximum is constant by varying the laser central frequency. These studies can provide a clear physical picture for understanding the coherent features of the resonance-mediated two-photon absorption, and can also provide a theoretical guidance for the future applications.
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2017YFA0701000,2018YFF01013001,and 2020YFA0714001)the National Natural Science Foundation of China(Grant Nos.61988102,61921002,and 62071108).
文摘Surface plasmon polaritons'(SPPs')frequency blue shift is observed in finite-difference time-domain(FDTD)simulation of parallel electron excitation Au bulk structure.Comparing with cold dispersion of SPPs,an obvious frequency blue shift is obtained in low confinement region excitation simulation results.Then,according to SPPs'transverse attenuation characteristics,the excited frequency mode instead of cold dispersion corresponding frequency mode matches it.Thence,this excited mode is confirmed to be SPPs'mode.As is well known the lower the frequency,the smaller the confinement factor is and the lower the excitation efficiency,the wider the bandwidth of excited SPPs is.And considering the attenuation in whole structure,the excited surface field contains attenuation signal.In a low confinement factor region,the higher the SPPs'frequency,the higher the excitation efficiency is,while broadband frequency information obtained in attenuation signal provides high frequency information in stimulation signal.Thence,in the beam-wave interaction,as the signal oscillation time increases,the frequency of the oscillation field gradually increases.Thus,compared with cold dispersion,the frequency of excited SPP is blueshifted This hypothesis is verified by monitoring the time domain signal of excited field in low and high confinement factor regions and comparing them.Then,this frequency-blue shift is confirmed to have commonality of SPPs,which is independent of SPPs'material and structure.Finally,this frequency-blue shift is confirmed in an attenuated total reflection(ATR)experiment.Owing to frequency dependence of most of SPPs'devices,such as coherent enhancement radiation and enhancement transmission devices,the frequency-blue shift presented here is of great influence in the SPPs applications.
