Researches On The Two-photon Absorption Properties Of Typical Laser Dyes

Two-photon absorption is a non-linear process that materials under the action ofintense light will absorb two long-wave photons and then jump into upper energy states.The materials with large two-photon absorption cross section have widespreadapplications in up-conversion tunable laser,3D optical storage,optical limiting andtwo-photon fluorescence microscopy (TPM). Many organic materials exhibit excellentmolecular decoration and clipping properties and have many advantages such as largernonlinear optical coefficient,shorter relaxation time of the photoresponse,higherphotoluminescence quantum yields and higher laser damage threshold. Organicmaterials are becoming the preferred two-photon absorption materials. The researcheson organic two photon absorption materials are mainly concentrated in organic moleculewith conjugated double bonds structure. Laser dyes with conjugated double bondsstructure are a class of organic materials which have large two-photon absorption crosssection. This dissertation first deals with the simulation analysis on measurement oftwo-photon absorption cross section using z-scan technique based on virtual instrument.On that basis, this paper also explores the effects of solvent environments ontwo-photon absorption by studying laser dyes in different solution. The study result hassignificances to extend application of laser dyes.In order to select proper parameters in experiment, this dissertation presents asimulation of z-scan system. How system parameter of open-aperture z-scan techniqueaffect the result is obtained by simulation:(1)When thin sample approximation is not satisfied, the expression of normalizedtransmittance transform into a divergence series from a convergence series. It is invalidfor z-scan technique. In addition, the trends of the curve are not same when thepolynomial order m is odd or not. Under the condition that laser intensity is certain, theaperture radius should be large enough so that thin sample approximation is satisfied.(2)In z-scan experiment, if the aperture radius is too small. We will not get a fullscale experiment curve because there is no enough scan length. In conclusion, weshould put all influences of laser parameters and scan length together and make ourchoice.Firstly, we validate the validity and reliability of the experiment system. Then, weanalyzes the two-photon absorption properties of tipycal laser dyes (DCM andRhodamine6G) in PMMA and ethanol combining z-scan technology with thetwo-photon fluorescence spectrum. The results show that:(1)Compared with DCM in ethanol, the two-photon fluorescence spectrum ofDCM in PMMA observed exhibits a significant blue shift. This shows that lowest vibration-rotational energy level of DCM in PMMA is higher than that in ethanol. Fortwo-photon absorption in800nm, the detuning in PMMA is less than that in ethanol.Hence, the two photon absorption cross section of DCM in PMMA is larger than inethanol. The results of z-scan also confirm our conclusion about DCM.(2)The two-photon absorption properties of rhodamine6G are nearly the same asDCM. Compared with rhodamine6G in ethanol, the two-photon fluorescence spectrumof rhodamine6G in PMMA observed also exhibits a significant blue shift. This showsthat the lowest vibration-rotational energy level of rhodamine6G in PMMA is higherthan that in ethanol. For two-photon absorption in800nm, the detuning in PMMA is lessthan in ethanol. Hence, the two photon absorption cross section of rhodamine6G inPMMA is larger than in ethanol. The results of z-scan also confirm our conclusion aboutrhodamine6G.