Conspectus
Ultrafast spectroscopy and imaging
have become
tools utilized by
a broad range of scientists involved in materials, energy, biological,
and chemical sciences. Commercialization of ultrafast spectrometers
including transient absorption spectrometers, vibrational sum frequency
generation spectrometers, and even multidimensional spectrometers
have put these advanced spectroscopy measurements into the hands of
practitioners originally outside the field of ultrafast spectroscopy.
There is now a technology shift occurring in ultrafast spectroscopy,
made possible by new Yb-based lasers, that is opening exciting new
experiments in the chemical and physical sciences. Amplified Yb-based
lasers are not only more compact and efficient than their predecessors
but also, most importantly, operate at many times the repetition rate
with improved noise characteristics in comparison to the previous
generation of Ti:sapphire amplifier technologies. Taken together,
these attributes are enabling new experiments, generating improvements
to long-standing techniques, and affording the transformation of spectroscopies
to microscopies. This Account aims to show that the shift to 100 kHz
lasers is a transformative step in nonlinear spectroscopy and imaging,
much like the dramatic expansion that occurred with the commercialization
of Ti:sapphire laser systems in the 1990s. The impact of this technology
will be felt across a great swath of scientific communities. We first
describe the technology landscape of amplified Yb-based laser systems
used in conjunction with 100 kHz spectrometers operating with shot-to-shot
pulse shaping and detection. We also identify the range of different
parametric conversion and supercontinuum techniques which now provide
a path to making pulses of light optimal for ultrafast spectroscopy.
Second, we describe specific instances from our laboratories of how
the amplified Yb-based light sources and spectrometers are transformative.
For multiple probe time-resolved infrared and transient 2D IR spectroscopy,
the gain in temporal span and signal-to-noise enables dynamical spectroscopy
measurements from femtoseconds to seconds. These gains widen the applicability
of time-resolved infrared techniques across a range of topics in photochemistry,
photocatalysis, and photobiology as well as lower the technical barriers
to implementation in a laboratory. For 2D visible spectroscopy and
microscopy with white light, as well as 2D IR imaging, the high repetition
rates of these new Yb-based light sources allow one to spatially map
2D spectra while maintaining high signal-to-noise in the data. To
illustrate the gains, we provide examples of imaging applications
in the study of photovoltaic materials and spectroelectrochemistry.