Study On Frequency Upconversion Luminescence Properties Of Organic Dyes

With the development of lasers and synthesization of novel nonlinearoptical materials, people begin to study on nonlinear optics, especiallymulti-photon process. Two-photon technic has achieved a great progress inrecent decades. The great developments largely promoted nonlinear optics inthe following directions: template fluorescence and up-converted lasing,optical limiting, two-photon fluorescence microscopy, three-dimensionaloptical data storage and two-photon absorption micro-fabrication. We have studied on the linear and nonlinear properties of some novelorganic materials doped in bulk solid polymer or dissolved in DMF solution.The purpose is to give some data information for upconversion dye lasergain medium. Common dye lasers are frequency down-converted emissions,with high conversion efficiency, powerful fluorescence. Because thedirection of fluorescence is isotropic, the tunable extra cavity is located withrespect to the pump direction vertically. Our experimental aim is to makeamplified spontaneous emission oscillate through the cavity by use ofdichroicmirror.High frequency emission can be obtained pumped by low frequency laser,this process is called frequency upconversion luminescence. Commonly,there are four processes, they are (1) Excited State Absorption; (2) EnergyTransfer; (3) Cooperative energy transfer upconversion; (4) Photonavalancheupconversion.Our experimental samples are some novel multi-photon upconversionmaterials. They are D- -A model, with large TPA absorption cross-section, πpowerful fluorescence and good upconversion capability. The linear - 64 -吉林大学硕士学位论文absorption spectra of sample dissolved in DMF was measured by UV-visiblespectrum-meter. It can be found that there is no absorption in the spectrummore than 600nm. Therefore, the absorption, fluorescence and otherluminescence phenomena induced by long wavelength laser are allmulti-photon phenomena. The nonlinear absorption index and cross section σ2 ( β=σ N0 = hν σ2NA d0×10-3) were measured by open-hole z-scan means. 2The pumped source is nanosecond tunable optical parametric oscillator(OPO). One-photon fluorescence, two-photon fluorescence and three-photonfluorescence of the DMF and solid sample were pumped by 450nm, 930nm,1300nm laser, respectively. The different types of upconversion fluorescencehave similar peak locations. The one-photon, two-photon and three-photonupconversion of solid polymers have sharper peaks and blue-shift than dyesolution. These phenomena can be explained by Twisted Intra-molecularChargeTransfer theory model.Enhancing the concentration of solutions and laser power density, an orangeamplified spontaneous emission can be observed easily, this is an analogouslaser phenomenon, abbreviated as ASE. It is can be validated that ASE hassome characters (1) High upconversion efficiency, the net upconversionefficiency is about 20%; (2) Good direction, the direction of ASE is alongthe pumped laser direction; (3) Good homochromy, the width of half ASEspectrum high is about 10 times narrower than fluorescence; (4) Narrowpulse width, shorter than 1ns. Our experimental results proved that onesample has same upconversion efficiency pumped by different laser - 65 -吉林大学硕士学位论文intensity. We measured upconversion efficiency of different wavelength,found that 1# and 5# samples have the highest upconversion efficiency. 1#, 5#, 32# and 35# samples have same luminescence chromophore,experimental results show that rare earth ions lower the threshold of ASE,enhanced the nonlinear absorption cross section and upconversion efficiency.Because of the luminescence of rare earth ions, the fluorescence and ASE oforganic materials with rare earth ions have wider spectrum, these materialshave promising application in tunable dye laser. The dye solutions' ASE spectra can be a...