93 research outputs found
Infrared laser pulse triggers increased singlet oxygen production in tumour cells
Photodynamic therapy (PDT) is a technique developed to treat the ever-increasing global incidence of cancer. This technique utilises singlet oxygen (1O2) generation via a laser excited photosensitiser (PS) to kill cancer cells. However, prolonged sensitivity to intensive light (6–8 weeks for lung cancer), relatively low tissue penetration by activating light (630 nm up to 4 mm), and the cost of PS administration can limit progressive PDT applications. The development of quantum-dot laser diodes emitting in the highest absorption region (1268 nm) of triplet oxygen (3O2) presents the possibility of inducing apoptosis in tumour cells through direct 3O2 → 1O2 transition. Here we demonstrate that a single laser pulse triggers dose-dependent 1O2 generation in both normal keratinocytes and tumour cells and show that tumour cells yield the highest 1O2 far beyond the initial laser pulse exposure. Our modelling and experimental results support the development of direct infrared (IR) laser-induced tumour treatment as a promising approach in tumour PDT
Optical Phonons in Carbon Nanotubes: Kohn Anomalies, Peierls Distortions and Dynamic Effects
We present a detailed study of the vibrational properties of Single Wall
Carbon Nanotubes (SWNTs). The phonon dispersions of SWNTs are strongly shaped
by the effects of electron-phonon coupling. We analyze the separate
contributions of curvature and confinement. Confinement plays a major role in
modifying SWNT phonons and is often more relevant than curvature. Due to their
one-dimensional character, metallic tubes are expected to undergo Peierls
distortions (PD) at T=0K. At finite temperature, PD are no longer present, but
phonons with atomic displacements similar to those of the PD are affected by
strong Kohn anomalies (KA). We investigate by Density Functional Theory (DFT)
KA and PD in metallic SWNTs with diameters up to 3 nm, in the electronic
temperature range from 4K to 3000 K. We then derive a set of simple formulas
accounting for all the DFT results. Finally, we prove that the static approach,
commonly used for the evaluation of phonon frequencies in solids, fails because
of the SWNTs reduced dimensionality. The correct description of KA in metallic
SWNTs can be obtained only by using a dynamical approach, beyond the adiabatic
Born-Oppenheimer approximation, by taking into account non-adiabatic
contributions. Dynamic effects induce significant changes in the occurrence and
shape of Kohn anomalies. We show that the SWNT Raman G peak can only be
interpreted considering the combined dynamic, curvature and confinement
effects. We assign the G+ and G- peaks of metallic SWNTs to TO
(circumferential) and LO (axial) modes, respectively, the opposite of
semiconducting SWNTs.Comment: 24 pages, 21 figures, submitted to Phys. Rev.
Disorder induced collapse of the electron phonon coupling in MgB observed by Raman Spectroscopy
The Raman spectrum of the superconductor MgB has been measured as a
function of the Tc of the film. A striking correlation is observed between the
onset and the frequency of the mode. Analysis of the data with
the McMillan formula provides clear experimental evidence for the collapse of
the electron phonon coupling at the temperature predicted for the convergence
of two superconducting gaps into one observable gap. This gives indirect
evidence of the convergence of the two gaps and direct evidence of a transition
to an isotropic state at 19 K. The value of the electron phonon coupling
constant is found to be 1.22 for films with T 39K and 0.80 for films with
T19K.Comment: 5 pages, 4 figure
Near-infrared, mode-locked waveguide lasers with multi-GHz repetition rates
In this work, we discuss mode-locking results obtained with low-loss, ion-exchanged waveguide lasers. With Yb3+-doped phosphate glass waveguide lasers, a repetition rate of up to 15.2 GHz was achieved at a wavelength of 1047 nm with an average power of 27 mW and pulse duration of 811 fs. The gap between the waveguide and the SESAM introduced negative group velocity dispersion via the Gires Tournois Interferometer (GTI) effect which allowed the soliton mode-locking of the device. A novel quantum dot SESAM was used to mode-lock Er3+, Yb3+-doped phosphate glass waveguide lasers around 1500 nm. Picosecond pulses were achieved at a maximum repetition rate of 6.8 GHz and an average output power of 30 mW. The repetition rate was tuned by more than 1 MHz by varying the pump power
Observation of soliton pulse compression in photonic crystal waveguides
We demonstrate soliton-effect pulse compression in mm-long photonic crystal
waveguides resulting from strong anomalous dispersion and self-phase
modulation. Compression from 3ps to 580fs, at low pulse energies(~10pJ), is
measured via autocorrelation
Manifestation of Structure of Electron Bands in Double-Resonant Raman Spectra of Single-Walled Carbon Nanotubes
Developing 1D nanostructure arrays for future nanophotonics
There is intense and growing interest in one-dimensional (1-D) nanostructures from the perspective of their synthesis and unique properties, especially with respect to their excellent optical response and an ability to form heterostructures. This review discusses alternative approaches to preparation and organization of such structures, and their potential properties. In particular, molecular-scale printing is highlighted as a method for creating organized pre-cursor structure for locating nanowires, as well as vapor–liquid–solid (VLS) templated growth using nano-channel alumina (NCA), and deposition of 1-D structures with glancing angle deposition (GLAD). As regards novel optical properties, we discuss as an example, finite size photonic crystal cavity structures formed from such nanostructure arrays possessing highQand small mode volume, and being ideal for developing future nanolasers
Low temperature phase transition in n-pentane C-60 clathrate: a Raman scattering study
We present results on Raman scattering from a C-60.n-pentane
(C-60.(n-C5H12)(0.88)(C7H8)(0.05)) clathrate crystal in the range
20-300 K. The Raman intensity, in particular of the H-g modes,
increases several times with lowering temperature below 160-200 K
accompanied by significant reduction of the linewidths. The onset of
this peculiar temperature behavior correlates with the reported phase
transition in n-pentane clathrate. We argue that these findings give a
Raman scattering signature for a low-temperature orientational phase
transition in C-60.n-pentane similar to that observed for solid C-60.
(C) 2000 Published by Elsevier Science B.V
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