Developing Z-scan Technique Apparatus for Multiphoton Absorption Cross Section Measurement and Comparative Study on Sampling by Oscilloscope, TCSPC and MCS for Photoluminescence Lifetime Measurement

Abstract

Z-scan technique is a single-beam technique that can measure the multiphoton absorption cross section with simplicity of experimental apparatus and high sensitivity. In a gaussian laser beam focusing geometry, thin sample moves along the Z axis which is direction of laser beam propagation. Transmittance of a nonlinear sample is measured as a function of the sample position (z) while the laser intensity is held fixed. The resultant plot of the transmittance takes smooth valley shape form. By fitting the result data, multiphoton absorption cross section can be derived. In order to improve performance of the Z-scan experimental apparatus, MATLAB simulation was performed. The simulation result provided the optimized laser beam diameter and focal length of the lens for laser beam focusing on sample.

Photoluminescence lifetime is an intrinsic property. It is not affected by external condition like excitation wavelength, multiphoton excitation and concentration of fluorophore. Since photoluminescence lifetime is related with unstable excited energy state, it is sensitive to the structure of the fluorophore, temperature, presence of fluorescence quenchers and the change of microenvironment of the fluorophore. Due to this properties, photoluminescence lifetime is used as a complementary method to photoluminescence intensity. There are three typical methods to measure the lifetime, sampling by oscilloscope, time-correlated single photon counting (TCSPC) and multi-channel scaling (MCS). Using sampling by oscilloscope, fluorescence lifetime of Ti:Sapphire rod could be measured and confirmed that the method gives reasonable result. For porphyrin-peptoid conjugate system, fluorescence lifetime result using TCSPC gave the similar lifetime with porphyrin-peptide conjugate system. And the effect of hydrothermal reaction time and temperature on up-conversion nano particle was studied by photoluminescence lifetime using MCS. In this paper, with those three methods, photoluminescence lifetime measurement experiment would be introduced and compared.