We have studied the optical properties of a hybrid system consisting of cyanine dye J-aggregates (both PIC and TDBC)
attached to a spherical microcavity. Instead of the commonly accepted chemical bonding of dye molecules to the surface
of microspheres or deposition of dye-doped sol-gel film, in our experiments microspheres were coated with J-aggregate
shell utilizing the layer-by-layer assembly of the ultrathin films. In this approach we aimed to take advantage of light
confinement in the Whispering Gallery Modes (WGMs) microcavity by placing the emitter (shell of J-aggregates) just at
the rim of the microsphere, where the resonant electromagnetic field reaches its maximum. A periodic structure of
narrow peaks was observed in the photoluminescence spectrum of the J-aggregates, arising from the coupling between
the emission of J-aggregates and the WGMs of the microcavity. The most striking result of our study is the observation
of polarization sensitive mode damping caused by re-absorption of J-aggregate emission. This effect manifests itself in
dominating emission from the transverse magnetic modes in the spectral region of J-aggregates absorption band where
the transverse electric (TE) modes are strongly suppressed. Strong suppression of TE modes reflects preferential
tangential orientation of transition dipole moment of J-aggregates in deposited microcavity shell. Observed polarization
sensitive mode damping observed in the spectral region of high J-aggregate absorption can be used for suppression of
unwanted modes in high Q optical resonators. We also demonstrate that the emission intensity can be further enhanced
by depositing a hybrid layer of J-aggregates and Ag nanoparticles onto the spherical microcavity. Owing to the concerted
action of WGMs and plasmonic hot spots in the Ag aggregates, we observe strongly enhanced Raman signal from the Jaggregates.
Microcavities covered by J-aggregates and plasmonic nanoparticles could be thus useful for a variety of
photonic applications in basic science and technology.
Proc. SPIE. 6733, International Conference on Lasers, Applications, and Technologies 2007: Environmental Monitoring and Ecological Applications; Optical Sensors in Biological, Chemical, and Engineering Technologies; and Femtosecond Laser Pulse Filamentation
KEYWORDS: Photodynamic therapy, Tumors, Tissues, Blood, Luminescence, Molecules, Ions, In vivo imaging, Tissue optics, Absorption
As demonstrated by the performed studies, the molecules of tricarbocyanine dye <i>in vivo</i> are localized in the low-permittivity region of the medium, predominantly in the form of contact ion pairs. Comparison of the experimental data
and numerical simulation results has revealed that deformation of the dye fluorescence spectrum upon
photochemotherapy is due to an increased percentage of methemoglobin (up to 50%) in the total hemoglobin
concentration of a tumor tissue. A change in the photosensitizer fluorescence spectrum is observed in the area of a tumor,
where laser radiation affects necrosis of the tissues. An analysis of the spectral data enables one to predict a depth and
extent of the developed tumor necrosis. With the use of spectral methods, the treatment effectiveness may be optimized
by the proper selection of an optimum dose and power density for photoexposure in the process of chemotherapy, with
due regard for the character of pathology and individual features of a patient.
The paper presents recent experimental results on the peculiarities of fluorescence and transient absorption exhibited by indotricarbocyanine dyes in solutions of different nature. The dynamics of transient absorption spectra of the molecules under study is analyzed within the framework of the concept of intra- and intermolecular vibrational relaxation and ultrafast charge transfer in contact ion pairs.