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, τ.
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/τ 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.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/85787 |
| Date | 10 October 2008 |
| Creators | Balasubramanian, Haribhaskar |
| Contributors | Meissner, Kenith E. |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | electronic, born digital |
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