17 research outputs found
Coherent Phonons in Antimony: an Undergraduate Physical Chemistry Solid-State Ultrafast Laser Spectroscopy Experiment
Ultrafast laser pump-probe spectroscopy is an important and growing field of
physical chemistry that allows the measurement of chemical dynamics on their
natural timescales, but undergraduate laboratory courses lack examples of such
spectroscopy and the interpretation of the dynamics that occur. Here we develop
and implement an ultrafast pump-probe spectroscopy experiment for the
undergraduate physical chemistry laboratory course at the University of
California Berkeley. The goal of the experiment is to expose students to
concepts in solid-state chemistry and ultrafast spectroscopy via classic
coherent phonon dynamics principles developed by researchers over multiple
decades. The experiment utilizes a modern high-repetition rate 800 nm
femtosecond Ti:Sapphire laser, split pulses with a variable time delay, and
sensitive detection of transient reflectivity signals. The experiment involves
minimal intervention from students and is therefore easy and safe to implement
in the laboratory. Students first perform an intensity autocorrelation
measurement on the femtosecond laser pulses to obtain their temporal duration.
Then, students measure the pump-probe reflectivity of a single-crystal antimony
sample to determine the period of coherent phonon oscillations initiated by an
ultrafast pulse excitation, which is analyzed by fitting to a sine wave. Due to
the disruption of in-person instruction caused by the COVID-19 pandemic, during
those semesters students were provided the data they would have obtained during
the experiment to analyze at home. Evaluation of student written reports
reveals that the learning goals were met, and that students gained an
appreciation for the field of ultrafast laser-induced chemistry
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Coherent Phonons in Antimony: an Undergraduate Physical Chemistry Solid-State Ultrafast Laser Spectroscopy Experiment
Ultrafast laser pump-probe spectroscopy is an important and growing field of
physical chemistry that allows the measurement of chemical dynamics on their
natural timescales, but undergraduate laboratory courses lack examples of such
spectroscopy and the interpretation of the dynamics that occur. Here we develop
and implement an ultrafast pump probe spectroscopy experiment for the
undergraduate physical chemistry laboratory course at the University of
California Berkeley. The goal of the experiment is to expose students to
concepts in solid-state chemistry and ultrafast spectroscopy via classic
coherent phonon dynamics principles developed by researchers over multiple
decades. The experiment utilizes a modern high-repetition-rate 800 nm
femtosecond Ti:Sapphire laser, split pulses with a variable time delay, and
sensitive detection of transient reflectivity signals using the lock-in
technique. The experiment involves minimal intervention from students and is
therefore easy and safe to implement in the laboratory. Students first perform
an intensity autocorrelation measurement on the femtosecond laser pulses to
obtain their temporal duration. Then, students measure the pump-probe
reflectivity of a single-crystal antimony sample to determine the period of
coherent phonon oscillations initiated by an ultrafast pulse excitation, which
is analyzed by fitting to a sine wave. Students who completed the experiment
in-person obtained good experimental results, and students who took the course
remotely due to the COVID-19 pandemic were provided with the data they would
have obtained during the experiment to analyze. Evaluation of student written
and oral reports reveals that the learning goals were met, and that students
gained an appreciation for the field of ultrafast laser-induced chemistry
Recommended from our members
Attosecond kinetics of photoexcited germanium
Attosecond transient reflectivity is developed to observe the photoexcitation dynamics in germanium. Attosecond time-resolved measurements of the dielectric function reveal a fewfemtosecond collective electronic response time, which renormalizes the Coulomb interaction between the excited carriers
Recommended from our members
Attosecond kinetics of photoexcited Germanium
Attosecond transient reflectivity is developed to observe the photoexcitation dynamics in germanium. Attosecond time-resolved measurements of the dielectric function reveal a fewfemtosecond collective electronic response time, which renormalizes the Coulomb interaction between the excited carriers
Solid-state core-exciton dynamics in NaCl observed by tabletop attosecond four-wave mixing spectroscopy
Nonlinear wave-mixing in solids with ultrafast x-rays can provide new insight
into complex electronic dynamics of materials. Here, tabletop-based attosecond
noncollinear four-wave mixing (FWM) spectroscopy using one extreme ultraviolet
(XUV) pulse from high harmonic generation and two separately timed few-cycle
near-infrared (NIR) pulses characterizes the dynamics of the Na+ L2,3 edge
core-excitons in NaCl around 33.5 eV. An inhomogeneous distribution of
core-excitons underlying the well-known doublet absorption of the Na+
\Gamma-point core-exciton spectrum is deconvoluted by the resonance-enhanced
nonlinear wave-mixing spectroscopy. In addition, other dark excitonic states
that are coupled to the XUV-allowed levels by the NIR pulses are characterized
spectrally and temporally. Approximate sub-10 femtosecond coherence lifetimes
of the core-exciton states are observed. The core-excitonic properties are
discussed in the context of strong electron-hole exchange interactions,
electron-electron correlation, and electron-phonon broadening. This
investigation successfully indicates that tabletop attosecond FWM
spectroscopies represent a viable technique for time-resolved solid-state
measurements
Decomposition of contributions from core-levels exhibiting spin-orbit splitting in XUV core-level spectroscopy
Attosecond transient absorption spectroscopy (ATAS) is a versatile technique that allows observing ultrafast charge
dynamics in solid-state samples. In ATAS, the transient absorption of a core-level excitation in the extreme UV (XUV) is
measured following optical excitation of the sample. The lack of spin-selectivity in the XUV pulse results in overlapping
XUV absorption spectra from spin-orbit split core-levels and leads to difficulty in disentangling the spectral signatures.
Here, we demonstrate the successful retrieval of the contribution of a single spin-orbit level on the XUV transient
absorption signal. Under the approxn. that the spin-orbit split levels yield identical absorption spectra which are
energetically shifted and weighted by the degeneracy of the spin-orbit states, the contribution of one single spin-orbit
state can be retrieved by the Fourier transform of the measured signal. In this case the energy shift of the spectra from
the spin-orbit split states becomes a phase shift. By dividing out this phase factor and taking the inverse Fourier
transform, the underlying signal referenced to a single spin-orbit level can be retrieved. We apply this method to an
ATAS measurement at the germanium M_(4,5)-edge (30 eV), where the spin-orbit energy splitting (0.57 eV) is comparable
to the germanium band gap (0.66 eV). The successful decompn. of the transient absorption signals yields clear,
spectrally-resolved signatures of electrons and holes such that carrier dynamics can be simultaneously measured and
characterized. The presented method allows decompg. contributions of spin-orbit split core-levels in a transient
absorption spectrum. This allows clearer assignment of spectroscopic features and reveals weak signal contributions not
visible in the exptl. raw data. In the presented case of germanium M-edge spectroscopy, a clear assignment of features
assocd. with electrons, holes and the bandgap becomes possible only after applying this method
Decomposition of contributions from core-levels exhibiting spin-orbit splitting in XUV core-level spectroscopy
Attosecond transient absorption spectroscopy (ATAS) is a versatile technique that allows observing ultrafast charge
dynamics in solid-state samples. In ATAS, the transient absorption of a core-level excitation in the extreme UV (XUV) is
measured following optical excitation of the sample. The lack of spin-selectivity in the XUV pulse results in overlapping
XUV absorption spectra from spin-orbit split core-levels and leads to difficulty in disentangling the spectral signatures.
Here, we demonstrate the successful retrieval of the contribution of a single spin-orbit level on the XUV transient
absorption signal. Under the approxn. that the spin-orbit split levels yield identical absorption spectra which are
energetically shifted and weighted by the degeneracy of the spin-orbit states, the contribution of one single spin-orbit
state can be retrieved by the Fourier transform of the measured signal. In this case the energy shift of the spectra from
the spin-orbit split states becomes a phase shift. By dividing out this phase factor and taking the inverse Fourier
transform, the underlying signal referenced to a single spin-orbit level can be retrieved. We apply this method to an
ATAS measurement at the germanium M_(4,5)-edge (30 eV), where the spin-orbit energy splitting (0.57 eV) is comparable
to the germanium band gap (0.66 eV). The successful decompn. of the transient absorption signals yields clear,
spectrally-resolved signatures of electrons and holes such that carrier dynamics can be simultaneously measured and
characterized. The presented method allows decompg. contributions of spin-orbit split core-levels in a transient
absorption spectrum. This allows clearer assignment of spectroscopic features and reveals weak signal contributions not
visible in the exptl. raw data. In the presented case of germanium M-edge spectroscopy, a clear assignment of features
assocd. with electrons, holes and the bandgap becomes possible only after applying this method
Recommended from our members
Solid-state core-exciton dynamics in NaCl observed by tabletop attosecond four-wave mixing spectroscopy
Nonlinear wave-mixing in solids with ultrafast x-rays can provide new insight
into complex electronic dynamics of materials. Here, tabletop-based attosecond
noncollinear four-wave mixing (FWM) spectroscopy using one extreme ultraviolet
(XUV) pulse from high harmonic generation and two separately timed few-cycle
near-infrared (NIR) pulses characterizes the dynamics of the Na+ L2,3 edge
core-excitons in NaCl around 33.5 eV. An inhomogeneous distribution of
core-excitons underlying the well-known doublet absorption of the Na+
\Gamma-point core-exciton spectrum is deconvoluted by the resonance-enhanced
nonlinear wave-mixing spectroscopy. In addition, other dark excitonic states
that are coupled to the XUV-allowed levels by the NIR pulses are characterized
spectrally and temporally. Approximate sub-10 femtosecond coherence lifetimes
of the core-exciton states are observed. The core-excitonic properties are
discussed in the context of strong electron-hole exchange interactions,
electron-electron correlation, and electron-phonon broadening. This
investigation successfully indicates that tabletop attosecond FWM
spectroscopies represent a viable technique for time-resolved solid-state
measurements