Biomedical Engineering Reference
In-Depth Information
10.10
Conclusions
In this chapter we have presented theoretical results regarding detection of resonant
energy transfer processes in self-assembled InGaAs QDMs. We have shown that
LACS experiments would be a suitable methodology for FRET detection. In this
regard, FRET optical signatures can be detectable in spite of the strong effects
of charge tunneling. As interdot tunnel mixing is controlled by the application of
an external axial electric field, enhancement of FRET optical signatures can be
achieved in the same way.
Although the effects we discuss have yet to be identified in experiments, the
main message of this work is to point out that under suitable conditions Forster
interaction may give rise to clearly identifiable signatures in PL or differential
transmission spectroscopy. In fact, to date most workers in this field see the
Forster interaction as difficult to detect in self-assembled QDMs, partly because
clear signatures in experiments have not been identified from a theoretical point
of view. We emphasize, especially on Fig.
10.6
, for example, that this interaction
can give rise to clearly defined split-off satellites which become stronger as an
electric field is applied across the molecule (“away” from the region where the
electronic tunneling is dominant). This should be easily testable in experiments.
For example, the QDM can be explored via pump-probe differential transmission
spectroscopy measurements of exciton populations. These could in principle exhibit
signatures as those discussed above. For example, the observation of dressed exciton
states in QDs using this technique has appeared recently [
27
-
29
]. An exciton state
can be pumped into the first QD via pulsed broadband laser excitation, creating
a collection of dressed states in the system. A second weak probe pulse can be
sent into resonance with the excitonic transition in the second QD, which has a
slightly different transition energy with respect to the QD, measuring in this way
the transient differential transmission, which reflects the exciton population in the
second QD.
10.11
Appendix: Simulation Parameters
Table 10.1
Constant
parameters used in
simulations
Name
Symbol
Value
6.2 e A
Interband transition moments
μ
T
(
B
)
Exciton recombination time
τ
X
1ns
Biexciton recombination time
τ
XX
0.5 ns
