| The emission spectrum of rare earth ions spans near-infrared to visible, even to ultraviolet band. The tunable and tense upconversion emission of rare earth ions is very important for these applications in biological labeling, light emitting displays, optical data storage, and solid-state lasers. Quantum coherent control based on the femtosecond pulse shaping is widely used to study the nonlinear processes between the light and the materiel, for example, multiphoton absorption, Raman scattering, higher harmonics, resonance-enhanced multiphoton-ionization photoelectron spectroscopy. In this thesis, the enhancing and tuning of trivalent rare earth ions have been studied theoretically and experimentally by quantum coherent control based on the femtosecond pulse shaping. The main research contents are as follows:(1) The luminescence properties of rare earth ions, the mechanism of upconversion luminescence, and the common method for tuning and enhancing upconversion emission were systematically introduced. The idea of coherent control, pulse shaping technique, and the multiphoton transition theory were simply reviewed.(2) The two-photon absorption (TPA) probability in a Pr3+ion system is enhanced to12.3by the shaped ultrashort laser pulses. The TPA is significantly higher than that achieved by a transform-limit pulse. However, the laser intensity of shaped pulses is reduced to37%of the initial transform-limited pulse. In this method, the TPA probability can also be reduced to58%. Furthermore, the effect of the shift of the intermediate energy level and the bandwidth of final states on TPA probability was discussed.(3) We presented a new scheme for quantum coherent control of two-photon absorption (TPA) and color emission in codoped lanthanide ions of Er3+/Tm3+/Yb3+ by properly phase shaping two infrared ultrashort laser beams at central frequencies of10650cm-1and7650cm-1, respectively. Compared with the results irradiated by transform-limited pulses, the TPA probabilities of the blue, green and red emissions are independently controlled in the ranges0-13.3,0-14.5and0-1.0, respectively. The effects of the energy states of lanthanide ions and the laser spectral bandwidths on the coherent features were also discussed. The TPA probabilities for the blue and green emissions increase with the laser spectral bandwidths and decrease with the energy bandwidths of the final level states. As the intermediate energy level shifts in the range10100-10500cm-1, the TPA probabilities for the blue and green emissions change in the ranges7-15and8-17, respectively.(4) We experimentally and theoretically studied the coherent quantum control of green emission in Er3+-doped glass by π-phase-shaped800nm femtosecond laser pulses. The experimental results show that the green emission intensity is enhanced over the transform-limited pulse by7r-phase-shaped pulses as the laser field increases to several1012W/cm2. Coherent control of multiphoton absorption is studied based on the fourth-order perturbation theory, and the theoretical results accord well with the experimental observations.(5) Femtosecond laser-induced resonance-enhanced multiphoton-ionization photoelectron spectroscopy (REMPI-PS) is faced with two drawbacks of low spectral resolution and poor selective excitation due to the broad spectral bandwidth. We proposed a scheme to obtain a high-resolution selective excitation of (2+1) REMPI-PS by combining π and cosinusoidal phase modulation. Our theoretical results indicate that the (2+1) REMPI-PS signals related to neighboring excited states can be differentiated from their indistinguishable photoelectron spectra by the π phase modulation, and then their selective excitation can be realized by supplementally adding the cosinusoidal phase modulation. |
PDF Full Text Request