212 research outputs found
On the role of coupling in mode selective excitation using ultrafast pulse shaping in stimulated Raman spectroscopy
The coherence of two, coupled two-level systems, representing vibrational
modes in a semiclassical model, is calculated in weak and strong fields for
various coupling schemes and for different relative phases between initial
state amplitudes. A relative phase equal to projects the system into a
dark state. The selective excitation of one of the two, two-level systems is
studied as a function of coupling strength and initial phases.Comment: 7 pages, 4 figure
Stimulated Raman Adiabatic Passage (STIRAP) as a Route to Achieving Optical Control in Plasmonics
Optical properties of ensembles of three-level quantum emitters coupled to
plasmonic systems are investigated employing a self-consistent model. It is
shown that stimulated Raman adiabatic passage (STIRAP) technique can be
successfully adopted to control optical properties of hybrid materials with
collective effects present and playing an important role in light-matter
interactions. We consider a core-shell nanowire comprised of a silver core and
a shell of coupled quantum emitters and utilize STIRAP scheme to control
scattering efficiency of such a system in a frequency and spatial dependent
manner. After the STIRAP induced population transfer to the final state takes
place, the core-shell nanowire exhibits two sets of Rabi splittings with Fano
lineshapes indicating strong interactions between two different atomic
transitions driven by plasmon near-fields.Comment: 11 pages, 6 figures, accepted, Physical Review
Chirped Pulse Control of Raman Coherence in Atoms and Molecules
A novel chirped pulse control scheme is presented based on Coherent
Anti-Stokes Raman Spectroscopy (C-CARS) aiming at maximizing the vibrational
coherence in atoms and molecules. The scheme utilizes chirping of the three
incoming pulses, the pump, the Stokes and the probe, in the four-wave mixing
process of C-CARS to fulfill the adiabatic passage conditions. The derivation
of the scheme is based on simplifying the four-level system into a
'super-effective' two level system via rotating wave approximation and
adiabatic elimination of the excited state manifold. The robustness, spectral
selectivity and adiabatic nature of C-CARS method may prove useful for sensing,
imaging, and detection. It is demonstrated that the selectivity in excitation
of vibrational degrees of freedom can be controlled by carefully choosing the
spectral chirp rate of the pulses. The C-CARS control scheme is applied to a
surrogate methanol molecule to generate an optimal anti-Stokes signal
backscattered from a cloud of molecules a kilometer away. The theory is based
on the solution of the coupled Maxwell-Liouville von Neumann equations and
focuses on the quantum effects induced in the target molecules by the control
pulse trains. The propagation effects of pulses through the medium are
evaluated and the buildup of the molecular-specific anti-Stokes signal is
demonstrated numerically. A deep learning technique, using Convolutional Neural
Networks (CNN), is implemented to characterize the control pulses and evaluate
time-dependent phase characteristics from them. The effects of decoherence
induced by spontaneous decay and collisional dephasing are also examined.
Additionally, we present the technique of Fractional Stimulated Raman Adiabatic
Passage (F-STIRAP) and demonstrate that it can be utilized for remote detection
in a multi-level system by creation of a maximally coherent superposition
state
Control with EIT: High energy charged particle detection
The strong non-linear optical response of atomic systems in
electromagnetically induced transparency (EIT) states is considered as a means
to detect the presence of small perturbations to steady states. For the 3-level
system, expressions for the group velocity and group velocity dispersion (GVD)
were derived and a quantum control protocol was established to account for the
change in the chirp spectrum of a probe pulse when the steady state was
perturbed. This was applied to the propagation of slow Cherenkov polaritons in
the medium due to the passage of a train of high-energy charged particles (high
energy particles). The choice of the initial steady state with focus on the
slow light condition and strong narrowly confined dispersion, equated to the
continuous trapping of Cherenkov polaritons in the medium along a narrow group
cone, allowing for non-trivial fields to accumulate. Considering another medium
prepared for the detection of the radiation, sweeping of the control field and
detuning parameters in the field-atom parameter space showed the presence of
optimal regions to maximize the first order perturbation in the coherences
creating changes in the optical responses that modify the chirp spectra of
probe pulses.Comment: 32 pages, 9 figure
Impact of Decoherence on Internal State Cooling using Optical Frequency Combs
We discuss femtosecond Raman type techniques to control molecular vibrations,
which can be implemented for internal state cooling from Feshbach states with
the use of optical frequency combs with and without modulation. The technique
makes use of multiple two-photon resonances induced by optical frequencies
present in the comb. It provides us with a useful tool to study the details of
molecular dynamics at ultracold temperatures. In our theoretical model we take
into account decoherence in the form of spontaneous emission and collisional
dephasing in order to ascertain an accurate model of the population transfer in
the three-level system. We analyze the effects of odd and even chirps of the
optical frequency comb in the form of sine and cosine functions on the
population transfer. We compare the effects of these chirps to the results
attained with the standard optical frequency comb to see if they increase the
population transfer to the final deeply bound state in the presence of
decoherence. We also analyze the inherent phase relation that takes place owing
to collisional dephasing between molecules in each of the states. This ability
to control the rovibrational states of a molecule with an optical frequency
comb enables us to create a deeply bound ultracold polar molecules from the
Feshbach state.Comment: 10 pages, 6 figure
Two-step synthesis of polymer fibre material comprising indium-, bismuth-, or antimony-doped nanosized tin oxides
In this paper, we present a method of formation of polymer fibre materials comprising dispersed oxides of rare and trace elements. The results of X-ray diffraction and spectral analyses show that the optimum synthesis conditions of the antimony-doped tin oxide, indium-doped tin oxide, and bismuth-doped tin oxide particles are provided using the "reverse" hydrolytic co-precipitation of hydroxides from chloride solutions combined with the subsequent thermal treatment at 1000°C. Durable fixation of nanoparticles on the fibre surface is confirmed by the atomic emission spectrometry with inductively coupled plasma and transmission electron microscopy. The results show that spraying of a free stream of the thermoplastic polymer melt with a gas stream containing nanoparticles allows obtaining fibre materials, which possess catalytic, photosensitive, as well as heat and sound insulating properties
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