34 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
A solid-state high harmonic generation spectrometer with cryogenic cooling
Solid-state high harmonic generation spectroscopy (sHHG) is a promising
technique for studying electronic structure, symmetry, and dynamics in
condensed matter systems. Here, we report on the implementation of an advanced
sHHG spectrometer based on a vacuum chamber and closed-cycle helium cryostat.
Using an in situ temperature probe, it is demonstrated that the sample
interaction region retains cryogenic temperature during the application of
high-intensity femtosecond laser pulses that generate high harmonics. The
presented implementation opens the door for temperature-dependent sHHG
measurements down to few Kelvin, which makes sHHG spectroscopy a new tool for
studying phases of matter that emerge at low temperatures, which is
particularly interesting for highly correlated materials
Unveiling the Role of Electron-Phonon Scattering in Dephasing High-Order Harmonics in Solids
High-order harmonic generation (HHG) in solids is profoundly influenced by
the dephasing of the coherent electron-hole motion driven by an external laser
field. The exact physical mechanisms underlying this dephasing, crucial for
accurately understanding and modelling HHG spectra, have remained elusive and
controversial, often regarded more as an empirical observation than a firmly
established principle. In this work, we present comprehensive experimental
findings on the wavelength-dependency of HHG in both single-atomic-layer and
bulk semiconductors. These findings are further corroborated by rigorous
numerical simulations, employing ab initio real-time, real-space time-dependent
density functional theory and semiconductor Bloch equations. Our experimental
observations necessitate the introduction of a novel concept: a
momentum-dependent dephasing time in HHG. Through detailed analysis, we
pinpoint momentum-dependent electron-phonon scattering as the predominant
mechanism driving dephasing. This insight significantly advances the
understanding of dephasing phenomena in solids, addressing a long-standing
debate in the field. Furthermore, our findings pave the way for a novel,
all-optical measurement technique to determine electron-phonon scattering rates
and establish fundamental limits to the efficiency of HHG in condensed matter
{\AA}ngstr\"om-resolved Interfacial Structure in Organic-Inorganic Junctions
Charge transport processes at interfaces which are governed by complex
interfacial electronic structure play a crucial role in catalytic reactions,
energy storage, photovoltaics, and many biological processes. Here, the first
soft X-ray second harmonic generation (SXR-SHG) interfacial spectrum of a
buried interface (boron/Parylene-N) is reported. SXR-SHG shows distinct
spectral features that are not observed in X-ray absorption spectra,
demonstrating its extraordinary interfacial sensitivity. Comparison to
electronic structure calculations indicates a boron-organic separation distance
of 1.9 {\AA}, wherein changes as small as 0.1 {\AA} result in easily detectable
SXR-SHG spectral shifts (ca. 100s of meV). As SXR-SHG is inherently ultrafast
and sensitive to individual atomic layers, it creates the possibility to study
a variety of interfacial processes, e.g. catalysis, with ultrafast time
resolution and bond specificity.Comment: 19 page
Polarization-Resolved Extreme Ultraviolet Second Harmonic Generation from LiNbO
Second harmonic generation (SHG) spectroscopy ubiquitously enables the
investigation of surface chemistry, interfacial chemistry as well as symmetry
properties in solids. Polarization-resolved SHG spectroscopy in the visible to
infrared regime is regularly used to investigate electronic and magnetic orders
through their angular anisotropies within the crystal structure. However, the
increasing complexity of novel materials and emerging phenomena hamper the
interpretation of experiments solely based on the investigation of hybridized
valence states. Here, polarization-resolved SHG in the extreme ultraviolet
(XUV-SHG) is demonstrated for the first time, enabling element-resolved angular
anisotropy investigations. In non-centrosymmetric LiNbO, elemental
contributions by lithium and niobium are clearly distinguished by energy
dependent XUV-SHG measurements. This element-resolved and symmetry-sensitive
experiment suggests that the displacement of Li ions in LiNbO, which is
known to lead to ferroelectricity, is accompanied by distortions to the Nb ion
environment that breaks the inversion symmetry of the NbO octahedron as
well. Our simulations show that the measured second harmonic spectrum is
consistent with Li ion displacements from the centrosymmetric position by
0.5 Angstrom while the Nb-O bonds are elongated/contracted by
displacements of the O atoms by 0.1 Angstrom. In addition, the
polarization-resolved measurement of XUV-SHG shows excellent agreement with
numerical predictions based on dipole-induced SHG commonly used in the optical
wavelengths. This constitutes the first verification of the dipole-based SHG
model in the XUV regime. The findings of this work pave the way for future
angle and time-resolved XUV-SHG studies with elemental specificity in condensed
matter systems
Data from: Table-top extreme ultraviolet second harmonic generation
The lack of available table-top extreme ultraviolet (XUV) sources with high enough fluxes and coherence properties have limited the availability of nonlinear XUV and x-ray spectroscopies to free electron lasers (FEL). Here, we demonstrate second harmonic generation (SHG) on a table-top XUV source for the first time by observing SHG near the Ti M2,3-edge with a high-harmonic seeded soft x-ray laser (HHG-SXRL). Further, this experiment represents the first SHG experiment in the XUV. First-principles electronic structure calculations suggest the surface specificity and separate the observed signal into its resonant and non-resonant contributions. The realization of XUV-SHG on a table-top source opens up opportunities for the study of element-specific dynamics in multi-component systems where surface, interfacial, and bulk-phase asymmetries play a driving role in smaller-scale labs as opposed to FELs.File contains data points for main text figures in tab-separated ASCII format. Subfolders contain raw data from the camera in Andor format.See associated journal article and supplementary information
Data from: Probing lithium mobility at a solid electrolyte surface
Solid-state electrolytes overcome many challenges of present lithium-ion batteries such as safety hazards and dendrite formation. However, detailed understanding of the involved lithium dynamics is missing due to a lack of in operando measurements with chemical and interfacial specificities. Here, we investigate a prototypical solid-state electrolyte using linear and nonlinear absorption spectroscopies. Leveraging the surface sensitivity of extreme-ultraviolet second-harmonic generation spectroscopy (XUV-SHG), we obtained a direct spectral signature of surface lithium ions, showing a distinct blue-shift relative to the bulk absorption spectra. First-principles simulations attributed the shift to transitions from the lithium 1s state into hybridized Li-s/Ti-d orbitals at the surface. Our calculations further suggest a reduction in lithium interfacial mobility due to suppressed low-frequency rattling modes, which is the fundamental origin of the large interfacial resistance in this material. Our findings pave the way for new optimization strategies for these electrochemical devices via interfacial engineering of lithium ions.Funding provided by: U.S. Department of EnergyCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000015Award Number: DE-SC0004993Funding provided by: U.S. Department of EnergyCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000015Award Number: DE-SC-0023355Funding provided by: U.S. Department of EnergyCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000015Award Number: DE-AC02-05CH11231Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: ACI-1548562Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: 1852537Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: DMR-1720139Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: ECCS-2025633Funding provided by: Laboratory Directed Research and Development Program at Berkeley Lab *Crossref Funder Registry ID: Award Number: 107573Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: CBET-309147Funding provided by: U.S. Department of EnergyCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000015Award Number: DE-SC0023503Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: DMR-2011924Funding provided by: Office of the President, University of CaliforniaCrossref Funder Registry ID: http://dx.doi.org/10.13039/100014576Award Number: M21PL3263Funding provided by: Office of the President, University of CaliforniaCrossref Funder Registry ID: http://dx.doi.org/10.13039/100014576Award Number: M23PR5931See associated manuscript
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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