56 research outputs found
Polarization dependence of semiconductor exciton and biexciton contributions to phase-resolved optical two-dimensional Fourier-transform spectra
We study the coherent light-matter interactions of GaAs quantum wells
associated with excitons, biexcitons and many-body effects. For most
polarization configurations, excitonic features dominate the phase-resolved
two-dimensional Fourier-transform (2DFT) spectra and have dispersive
lineshapes, indicating the presence of many-body interactions. For cross-linear
excitation, excitonic features become weak and absorptive due to the strong
suppression of many-body effects; a result that can not be directly determined
in transient four-wave mixing experiments. The biexcitonic features do not
weaken for cross-polarized excitation and thus are more important.Comment: 4 page, 3 figures, journal article - rapid communicatio
All-optical retrieval of the global phase for two-dimensional Fourier-transform spectroscopy
A combination of spatial interference patterns and spectral interferometry
are used to find the global phase for non-collinear two-dimensional
Fourier-transform (2DFT) spectra. Results are compared with those using the
spectrally resolved transient absorption (STRA) method to find the global phase
when excitation is with co-linear polarization. Additionally cross-linear
polarized 2DFT spectra are correctly phased using the all-optical technique,
where the SRTA is not applicable.Comment: 6 pages, 7 figures, journal publicatio
Optical Detection of a Single Nuclear Spin
We propose a method to optically detect the spin state of a 31-P nucleus
embedded in a 28-Si matrix. The nuclear-electron hyperfine splitting of the
31-P neutral-donor ground state can be resolved via a direct frequency
discrimination measurement of the 31-P bound exciton photoluminescence using
single photon detectors. The measurement time is expected to be shorter than
the lifetime of the nuclear spin at 4 K and 10 T.Comment: 4 pages, 3 figure
Electron-phonon renormalization of the absorption edge of the cuprous halides
Compared to most tetrahedral semiconductors, the temperature dependence of
the absorption edges of the cuprous halides (CuCl, CuBr, CuI) is very small.
CuCl and CuBr show a small increase of the gap with increasing
temperature, with a change in the slope of vs. at around 150 K: above
this temperature, the variation of with becomes even smaller. This
unusual behavior has been clarified for CuCl by measurements of the low
temperature gap vs. the isotopic masses of both constituents, yielding an
anomalous negative shift with increasing copper mass. Here we report the
isotope effects of Cu and Br on the gap of CuBr, and that of Cu on the gap of
CuI. The measured isotope effects allow us to understand the corresponding
temperature dependences, which we also report, to our knowledge for the first
time, in the case of CuI. These results enable us to develop a more
quantitative understanding of the phenomena mentioned for the three halides,
and to interpret other anomalies reported for the temperature dependence of the
absorption gap in copper and silver chalcogenides; similarities to the behavior
observed for the copper chalcopyrites are also pointed out.Comment: 14 pages, 5 figures, submitted to Phys. Rev.
Probing Interband Coulomb Interactions in Semiconductor Nanocrystals with 2D Double-Quantum Coherence Spectroscopy
Using previously developed exciton scattering model accounting for the
interband, i.e., exciton-biexciton, Coulomb interactions in semiconductor
nanocrystals (NCs), we derive a closed set of equations for 2D double-quantum
coherence signal. The signal depends on the Liouville space pathways which
include both the interband scattering processes and the inter- and intraband
optical transitions. These processes correspond to the formation of different
cross-peaks in the 2D spectra. We further report on our numerical calculations
of the 2D signal using reduced level scheme parameterized for PbSe NCs. Two
different NC excitation regimes considered and unique spectroscopic features
associated with the interband Coulomb interactions are identified.Comment: 11 pages, 5 figure
Two-dimensional Fourier-transform spectroscopy of potassium vapor
Optical two-dimensional Fourier-transform (2DFT) spectroscopy is used to study the coherent optical response of potassium vapor in a thin transmission cell. Rephasing and nonrephasing spectra of the D 1 and D 2 transitions are obtained and compared to numerical simulations. Non-perturbative calculations using the optical Bloch equations give very good agreement with the experimental peak strengths and line shapes. Nonradiative Raman-like coherences are isolated using a different 2DFT projection. Comparison between the optical and Raman linewidths shows that dephasing is due to partially correlated energy fluctuations. Density-dependent measurements show distortion of 2DFT spectra due to pulse propagation effects
Photoluminescence studies of isotopically enriched silicon
We report the first high resolution photoluminescence studies
of isotopically pure silicon. New information is obtained on
isotopic effects on the indirect band gap energy, phonon
energies, and phonon broadenings, which is in good agreement
with previous results obtained in germanium and diamond.
Remarkably, the line widths of the no-phonon boron and
phosphorus bound exciton transitions in the Si-28 sample
(99.896% Si-28) are much sharper than in natural Si, revealing
new fine structure in the boron bound exciton luminescence.
Most surprisingly, the small splittings of the neutral acceptor
ground state in natural Si are absent in the photoluminescence
spectra of acceptor bound excitons in isotopically purified Si-
28, demonstrating conclusively that they result from the
randomness of the Si isotopic composition
- …