560 research outputs found
Frequency-comb based double-quantum two-dimensional coherent spectroscopy identifies collective hyperfine resonances in atomic vapor induced by dipole-dipole interactions
Frequency comb based multidimensional coherent spectroscopy is a novel
optical method that enables high resolution measurement in a short acquisition
time. The method's resolution makes multidimensional coherent spectroscopy
relevant for atomic systems that have narrow resonances. We use double-quantum
multidimensional coherent spectroscopy to reveal collective hyperfine
resonances in rubidium vapor at 100 C induced by dipole-dipole interactions. We
observe tilted lineshapes in the double-quantum 2D spectra, which has never
been reported for Doppler-broadened systems. The tilted lineshapes suggest that
the signal is predominately from the interacting atoms that have near zero
relative velocity
Spectroscopic Signatures of Electron-Phonon Coupling in Silicon-Vacancy Centers in Diamond
Vacancy centers in diamond have proven to be a viable solid-state platform
for quantum coherent opto-electronic applications. Among the variety of vacancy
centers, silicon-vacancy (SiV) centers have recently attracted much attention
as an inversion-symmetric system that is less susceptible to electron-phonon
interactions. Nevertheless, phonon-mediated processes still degrade the
coherent properties of SiV centers, however characterizing their
electron-phonon coupling is extremely challenging due to their weak
spectroscopic signatures and remains an open experimental problem. In this
paper we theoretically investigate signatures of electron-phonon coupling in
simulated linear and nonlinear spectra of SiV centers. We demonstrate how even
extremely weak electron-phonon interactions, such as in SiV centers, may be
completely characterized via nonlinear spectroscopic techniques and even
resolved between different fine-structure transitions
Frequency comb based four-wave-mixing spectroscopy
We experimentally demonstrate four-wave-mixing spectroscopy using frequency
combs. The experiment uses a geometry where excitation pulses and
four-wave-mixing signals generated by a sample co-propagate. We separate them
in the radio frequency domain by heterodyne detection with a local oscillator
comb that has a different repetition frequency
Comment on "Nonlinear fluctuations and dissipation in matter revealed by quantum light"
In a recent paper [Phys.~Rev.~A {\bf 91}, 053844 (2015)], Mukamel and Dorfman
compare spectroscopies performed with classical vs.~quantum light, and conclude
that \textit{nonlinear} quantum-spectroscopy signals cannot be obtained from
averaging their classical-spectroscopy counterparts over the Glauber--Sudarshan
quasiprobability distribution of the quantum field. In this Comment, we show
that this interpretation is correct only if one assumes that a classical signal
is given by a classical approximation for the field. While such an assumption
can be useful for comparing theoretical results, it is never realized in laser
spectroscopy experiments that typically use coherent states. Thus, instead of
using classical signals, the connection between coherent states and quantum
states of light must be considered. We rigorously show that quantum
spectroscopy can always be projected from the experimentally realized
coherent-state spectroscopy regardless how nonlinear the system response is.Comment: 4 page
Revealing and Characterizing Dark Excitons Through Coherent Multidimensional Spectroscopy
Dark excitons are of fundamental importance in a broad range of contexts, but
are difficult to study using conventional optical spectroscopy due to their
weak interaction with light. We show how coherent multidimensional spectroscopy
can reveal and characterize dark states. Using this approach, we identify
different types of dark excitons in InGaAs/GaAs quantum wells and determine
details regarding lifetimes, homogeneous and inhomogeneous linewidths,
broadening mechanisms and coupling strengths. The observations of coherent
coupling between bright and dark excitons hint at a role for a multi-step
process by which excitons in the barrier can relax into the quantum wells
Mode-Locked Chip Laser using Waveguide Arrays
We demonstrate theoretically that robust mode-locking can be achieved on a
semiconductor chip with a waveguide array architecture. The waveguide arrays
are used as an ideal saturable absorption mechanism for initial noise start-up
as well as pulse shaping and stabilization. The cavity gain is provided by an
injection current and forward biasing of the semiconductor material. The
technology can be integrated directly with semiconductor architectures and
technologies, thus allowing for the potential of an on-chip, broadband device.Comment: 3 pages, 3 figure
Two-dimensional Fourier-transform Spectroscopy of Potassium Vapor
Optical two-dimensional Fourier-transformed (2DFT) spectroscopy is used to
study the coherent optical response of potassium vapor in a thin transmission
cell. Rephasing and non-rephasing spectra of the D1 and D2 transitions are
obtained and compared to numerical simulations. Calculations using the optical
Bloch equations gives very good agreement with the experimental peak strengths
and line shapes. Non-radiative Raman-like coherences are isolated using a
different 2DFT projection. Density-dependent measurements show distortion of
2DFT spectra due to pulse propagation effects
Two-Dimensional Optical Spectroscopy of Excitons in Semiconductor Quantum Wells: Liouville-space pathway analysis
We demonstrate how dynamic correlations of heavy-hole and light-hole excitons
in semiconductor quantum wells may be investigated by two dimensional
correlation spectroscopy (2DCS). The coherent response to three femtosecond
optical pulses is predicted to yield cross (off-diagonal) peaks that contain
direct signatures of many-body two-exciton correlations. Signals generated at
various phase-matching directions are compared.Comment: 27pages,13 figures, accepted for publication in Physical Review
Multidimensional Coherent Photocurrent Spectroscopy of a Semiconductor Nanostructure
Multidimensional Coherent Optical Photocurrent Spectroscopy (MD-COPS) is
implemented using unstabilized interferometers. Photocurrent from a
semiconductor sample is generated using a sequence of four excitation pulses in
a collinear geometry. Each pulse is tagged with a unique radio frequency
through acousto-optical modulation ; the Four-Wave Mixing (FWM) signal is then
selected in the frequency domain. The interference of an auxiliary continuous
wave laser, which is sent through the same interferometers as the excitation
pulses, is used to synthesize reference frequencies for lock-in detection of
the photocurrent FWM signal. This scheme enables the partial compensation of
mechanical fluctuations in the setup, achieving sufficient phase stability
without the need for active stabilization. The method intrinsically provides
both the real and imaginary parts of the FWM signal as a function of
inter-pulse delays. This signal is subsequently Fourier transformed to create a
multi-dimensional spectrum. Measurements made on the excitonic resonance in a
double InGaAs quantum well embedded in a p-i-n diode demonstrate the technique
Quantum-Well Laser Diodes for Frequency Comb Spectroscopy
We demonstrate simple optical frequency combs based on semiconductor quantum
well laser diodes. The frequency comb spectrum can be tailored by choice of
material properties and quantum-well widths, providing spectral flexibility.
Finally, we demonstrate the mutual coherence of these devices by using two
frequency combs on the same device to generate a radio-frequency dual comb
spectrum
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