Medical Design Briefs - October 2024 - 42

Design Briefs
Tunable Lasers Expand for Time-Resolved
Spectroscopy
By Dr. Mark Little, OPOTEK
n physical chemistry, time-resolved spectroscopy
is the study of dynamic processes
in materials or chemical compounds.
Within this field, various techniques including
transient absorption spectroscopy
are used to study the mechanistic and
kinetic details of chemical processes that
occur within just a few picoseconds to a
femtosecond - the equivalent of one
millionth of one billionth of a second.
To conduct this research, labs require
fast lasers that can create an excited electronic
state of a molecule on this time
scale. Since all molecules do not absorb
the same wavelengths of light, these lasers
must be flexible enough to produce
wavelengths across a broad spectrum. In
the past, it was difficult, if not impossible
to conduct spectroscopic research using
inexpensive, fixed wavelength lasers.
This was extremely inefficient when conducting
fundamental research at the academic
level on a wide variety of metal-based
complexes.
As a result, many research labs are
turning to tunable lasers, or optical parametric
oscillators (OPOs), for nanosecond
time-resolved spectroscopy. OPOs
have long been utilized in sophisticated
test and measurement applications such
as mass spectrometry and photoacoustic
imaging. Now, these tunable pulsed lasers
are being utilized due to the high
resolution and variety of nanosecond
wavelength pulses they can produce
from visible light to deep UV.
" You don't want to have to design your
chemistry such that it is tailored just to
the particular wavelengths you have available
in your instrumentation. You want
the lasers to be flexible enough to adapt
to the chemistry you want to explore, "
says Dr. James McCusker, an MSU Foundation
Professor in the department of
chemistry at Michigan State University
who leads a research group of PhD students
in the study of cutting-edge techniques
in spectroscopy. His group conducts
fundamental research on de signing
and synthesizing molecules to absorb in
the visible part of the spectrum. " We only
want to be limited by our imaginations,
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Modern OPOs are user-friendly, integrated systems easily installed and controlled without extensive expertise.
not by what wavelengths we can get out of
a particular laser, " says McCusker, who
has worked in the field for nearly 30
years.
Ultrafast Spectroscopy of Transition
Metals
McCusker's research team studies a class
of compounds known as transition metal
complexes. These compounds are based
on elements from the so-called transition
block of the periodic table. The focus of the
group's research is to understand how a
molecule's structure, composition and absorptive
properties relate to their ability to
carry out light-induced chemical reactions.
According to McCusker, one of the primary
areas of research relates to solar energy
conversion. Transition metal complexes
are an important class of molecules in this
field of research and can be studied using
time-resolved spectroscopy for designing
molecules whose excited-state properties
will enable their use in a wide range of such
compounds to enable new kinds of organic
transformations of potential interest in the
pharmaceutical industry.
" We are pursuing a systematic examination
of chemical perturbations to excited-state
electronic and geometric
structure, " says McCusker. " As a result,
we will be able to develop a comprehenwww.medicaldesignbriefs.com
OPO
lasers are vital for various scientific applications,
including mass spectrometry and photoacoustic imaging.
sive picture of how transition metal chromosphores
absorb and dissipate energy. "
Getting on the Right Wavelength
To facilitate this type of research, fast,
pulsed lasers are required to selectively
excite a molecule to a specific state to
study the compound's excited-state
properties. In the early days of laser development,
lasers were constructed to
operate at very specific wavelengths. Single
wavelength Nd:YAG lasers, for example,
are inexpensive and simple to use.
However, additional hardware is required
to modify a 1064-nm laser before
it can operate at a different harmonic
frequency for testing such as 213, 266,
355, and 532 nm. This adds to the cost of
the laser.
Medical Design Briefs, October 2024

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Medical Design Briefs - October 2024

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