Two photon luminescence from quantum dots using broad and narrowband ultrafast laser pulses

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Title: Two photon luminescence from quantum dots using broad and narrowband ultrafast laser pulses
Author: Balasubramanian, Haribhaskar
Abstract: Nonlinear optical microscopy (NLOM ) offers many advantages when imaging intact biological samples . By using ultrafast lasers in the near infrared and two photon excitation (TPE ) , signal production is limited to the focal volume and provides an excellent means for rendering thin , microscopic images from within the sample . Exogenous fluorophores /lumiphores may be used as efficient contrast agents to tag specific targets and provide enhanced signal . The efficiency of the TPE process in these contrast agents is broadly assumed to vary inversely with the laser pulsewidth , ? . In this work , we investigate the TPE efficiency of transform limited broadband ( ~133nm , ~10fs ) and narrowband ( ~11nm , ~170fs ) pulses in the generation of twophoton luminescence from semiconductor nanocrystals or quantum dots (QD's ) both theoretically and experimentally . Compared to standard organic dyes , QD's possess a relatively broad , uniform spectral response that enables better use of the full bandwidth from the broadband laser . Theoretical calculations including both degenerate and non -degenerate TPE indicate a rolloff from the 1 / ? behavior as the pulses' spectral bandwidth becomes broader than the absorption spectra of the QD's . Experimentally measured enhancement in luminescence intensity while using a broadband pulse is compared with the simulated enhancement in two -photon luminescence . A combination of increased understanding of the excitation processes in NLOM and proper selection of contrast agents will help in advancing the role of broadband ultrafast lasers in NLOM .
URI: http : / /hdl .handle .net /1969 .1 /85787
Date: 2008-10-10

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Two photon luminescence from quantum dots using broad and narrowband ultrafast laser pulses. Available electronically from http : / /hdl .handle .net /1969 .1 /85787 .

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