The Modulation Of Rare-earth Ions Up-Conversion Luminescence Under Femtosecond Laser Field

Due to their unique 4f structure electrons,rare earth ions feature excellent luminescence properties,like broad light spectrum,immune to surrounding environment and high energy conversion efficiency,and are thus commonly used in doping luminescent materials and find wide applications in new laser sources,optical fiber communication,color display,medical imaging and bio-labeling.In most previous works,CW lasers were commonly used in exciting the doping rare earth ions.With the development of laser technology,femtosecond lasers,featuring ultrashort pulse duration,ultrahigh peak power density and broad light spectrum,are now serving as an ideal excitation source for the doping rare earth ions.This thesis is mainly dedicated to the study of manipulating the luminescence of doping rare earth ions by modulating the parameters of the femtosecond laser pulses,like polarization and spectral phases.The research contents include:1.We have studied the influence of the laser polarization on the up-conversion luminescence in Sm³⁺doped glass sample under excitation of the 800 nm femtosecond laser field of moderate intensity.Experimental results indicate that the modulation efficiency of the laser polarization on the up-conversion luminescence in Sm³⁺doped glass sample gradually decreases with increasing laser intensity.A theoretical excitation model based on the fourth order perturbation theory is introduced to explain the experimental observations and the destructive interference between the two-photon and four-photon absorption is believed to be responsible for the variation of the polarization modulation efficiency.2.We have studied the valence state conversion from Sm³⁺to Sm²⁺in the Sm³⁺doped sodium aluminoborate glass sample under the?-phase shaped 800 nm femtosecond laser irradiation.Experimental results demonstrate that?-phase step modulation can well tune the photoreduction efficiency from Sm³⁺to Sm²⁺in the glass sample.By selectively choosing the laser wavelength position for?-phase step modulation,the resulted photoreduction efficiency can be comparable to that under transform-limited femtosecond laser pulses,while the peak laser intensity is greatly reduced to only 37%of the unshaped one,which is very helpful for preventing the sample from being laser damaged.A theoretical model of?2+1?resonance-mediated three-photon absorption is also proposed to well explain the experimental observations.3.The energy transfer between Tm³⁺and Yb³⁺co-doped in glass sample under the phase shaped 800 nm femtosecond laser pulse irradiation has been investigated.A new energy transfer pathway from multiphoton excited Tm³⁺sensitizer to ground state Yb³⁺activator has been proposed with the laser power and polarization dependences of the emitted luminescence intensity serving as experimental proof.Predictions from a theoretical model agree well with the experimental results.4.The time evolution of the luminescence spectrum in the Er³⁺doped NaYF₄ glass ceramic under the 400 nm femtosecond laser irradiation has been studied by using the combination of a streak camera and a spectrometer.This combination technique incorporates the advantages of both the streak camera of high time-resolution information and the spectrometer of good wavelength-resolution.A new cross relaxation channel between the doping Er³⁺ions has been found by comparing the lifetime and intensity of the luminescence from samples of different Er³ doping concentration.