3 research outputs found
Selective Suppression of Stimulated Raman Scattering with Another Competing Stimulated Raman Scattering
A three-beam femtosecond
stimulated Raman scattering (SRS) scheme
is formulated and demonstrated to simultaneously induce two different
SRS processes associated with Raman-active modes in the same molecule.
Two SR gains involving a common pump pulse are coupled and compete:
As one of the Stokes beam intensities increases, the other SRS is
selectively suppressed. We provide theoretical description and experimental
evidence that the selective suppression behavior is due to the limited
number of pump photons used for both of the two SRS processes when
an intense depletion beam induces one SRS process. The maximum suppression
efficiency was ∼60% with our experimental setup, where the
SR gain of the ring breathing mode of benzene is the target SRS signal,
which is allowed to compete with another SRS process, induced by an
intense depletion beam, of the CH stretching mode. We anticipate a
potential of this new switching-off concept in super-resolution label-free
microscopy
Origin of the Reversible Thermochromic Properties of Polydiacetylenes Revealed by Ultrafast Spectroscopy
Polydiacetylenes
(PDAs) with thermochromic properties undergo colorimetric
transitions when the external temperature is varied. This capability
has the potential to enable these materials to be used as temperature
sensors. These thermochromic properties of PDAs stem from their temperature-dependent
optical properties. In this work, we studied the temperature-dependent
optical properties of Bis-PDA-Ph, which exhibits reversible thermochromic
properties, and PCDA–PDA, which exhibits irreversible thermochromic
properties, by UV–visible absorption and femtosecond transient
absorption spectroscopy. Our results indicate that the electronic
relaxation of PDAs occurs via an intermediate state in cases where
the material exhibits reversible thermochromic properties, whereas
the excited PDAs relax directly back to the ground state when irreversible
thermochromic properties are observed. The existence of this intermediate
state in the electronic relaxation of PDAs thus plays an important
role in determining their thermochromic properties. These results
are very important for both understanding and strategically modulating
the thermochromic properties of PDAs
Quantum Beats and Phase Shifts in Two-Dimensional Electronic Spectra of Zinc Naphthalocyanine Monomer and Aggregate
The
origin of quantum coherence in two-dimensional (2D) electronic
spectra of molecular aggregates and light-harvesting complexes still
remains an open question. In particular, it could be challenging to
distinguish between electronic and vibrational coherences for a coupled
system, where both degrees of freedom can be simultaneously excited.
In this Letter, we examine quantum beats in the 2D spectra of zinc
naphthalocyanine (ZnNc) aggregate and monomer, and compare their characteristic
features in terms of the frequency and relative phase of diagonal
and off-diagonal amplitude oscillations. The long-lasting oscillating
components (>1 ps) at 600–700 cm<sup>–1</sup> observed
in both the aggregate and monomer are found to be attributed to the
vibrational coherence. The wide phase variations of the 2D spectral
amplitude oscillations are observed not just in the aggregate but
also in the monomer state. This suggests that the unusual 90°
phase shift may be attributed to neither quantum population-to-coherence
transfer nor vibronic exciton coupling