Topics in Current Chemistry (2018) 376:28
1 3
1 Introduction
Among all kinds of spectroscopy methods, time-resolved laser spectroscopy has
been a major player in the elucidation and discovery of matter properties. A vast
range of physical processes and photochemical reactions from the temporal range
of a few nanoseconds down to a few tens of femtoseconds (10
−15
s) have been
successfully elucidated for very small molecular systems in the gas phase [1] up
to complex photo-activated processes in biology [2] and even single molecules
[3]. Due to its versatility and broad spectral application, time-resolved laser spectroscopy is currently a present and necessary partner in the characterization and
development of new materials for technologically relevant applications like those
found in organic voltaics and solar light harvesting [4–9], as well as in data storage [10, 11] and medicine [12–16]. Very few experimental techniques have such
an ample impact on so many different areas of science and technology.
In its most fundamental form, time-resolved laser spectroscopy is based on the
detection of a signal after the excitation with a pulsed laser [17, 18]. The socalled pump-probe method describes this general approach, where pump-induced
changes in the material properties (such as absorption) are measured by a second
probe pulse, and are followed in dependence of the time delay between the two
pulses. In spite of its generality and widespread applicability and broad information content, time-resolved laser spectroscopy still faces many challenges. In its
classical form, time-resolved laser spectroscopy is often unable to unambiguously
assign the origin of features of the optical signal, requiring complex global fitting and data analysis approaches [19, 20]. Similarly, classic time-resolved laser
spectroscopy is also experimentally unable, in certain cases, to map and disentangle how molecular structures change in time, how different molecules interact, or
how, within a certain molecule [21] or aggregate, electronic [22], vibrational and
rotational states are coupled. This is notoriously aggravated for large, polyatomic
molecules and for even larger (bio-)chemical systems [23], where different electronic states or molecular species can contribute to the signal.
Several experimental approaches based on classical time-resolved laser spectroscopy methods, such as pump-probe spectroscopy, have been developed to
overcome such challenges. One of them is based on the tailoring of the electromagnetic properties of the pump pulse. The electric fields of the coherent laser
light are described by the spectral phase and amplitude, and the vectorial nature
of the field is best conceptually visualized by the field polarization. All these
properties can today be experimentally controlled with highest precision and this
control is exploited to selectively induce or enhance specific signals of specific
molecules and/or suppress undesired ones [24–27]. There is an ever-growing
number of applications with these “control knobs” in this active research field of
laser spectroscopy, which is consequently coined quantum control spectroscopy.
This method has been used as a highly specialized tool to study, address selectively, and enhance specific transient spectroscopy features [28–33].
Being the topic of this collection, the most common way to address some of
the ambiguities of the time-resolved laser spectroscopy is based on the use of the
2
Reprinted from the journal
1 3
1 Introduction
Among all kinds of spectroscopy methods, time-resolved laser spectroscopy has
been a major player in the elucidation and discovery of matter properties. A vast
range of physical processes and photochemical reactions from the temporal range
of a few nanoseconds down to a few tens of femtoseconds (10
−15
s) have been
successfully elucidated for very small molecular systems in the gas phase [1] up
to complex photo-activated processes in biology [2] and even single molecules
[3]. Due to its versatility and broad spectral application, time-resolved laser spectroscopy is currently a present and necessary partner in the characterization and
development of new materials for technologically relevant applications like those
found in organic voltaics and solar light harvesting [4–9], as well as in data storage [10, 11] and medicine [12–16]. Very few experimental techniques have such
an ample impact on so many different areas of science and technology.
In its most fundamental form, time-resolved laser spectroscopy is based on the
detection of a signal after the excitation with a pulsed laser [17, 18]. The socalled pump-probe method describes this general approach, where pump-induced
changes in the material properties (such as absorption) are measured by a second
probe pulse, and are followed in dependence of the time delay between the two
pulses. In spite of its generality and widespread applicability and broad information content, time-resolved laser spectroscopy still faces many challenges. In its
classical form, time-resolved laser spectroscopy is often unable to unambiguously
assign the origin of features of the optical signal, requiring complex global fitting and data analysis approaches [19, 20]. Similarly, classic time-resolved laser
spectroscopy is also experimentally unable, in certain cases, to map and disentangle how molecular structures change in time, how different molecules interact, or
how, within a certain molecule [21] or aggregate, electronic [22], vibrational and
rotational states are coupled. This is notoriously aggravated for large, polyatomic
molecules and for even larger (bio-)chemical systems [23], where different electronic states or molecular species can contribute to the signal.
Several experimental approaches based on classical time-resolved laser spectroscopy methods, such as pump-probe spectroscopy, have been developed to
overcome such challenges. One of them is based on the tailoring of the electromagnetic properties of the pump pulse. The electric fields of the coherent laser
light are described by the spectral phase and amplitude, and the vectorial nature
of the field is best conceptually visualized by the field polarization. All these
properties can today be experimentally controlled with highest precision and this
control is exploited to selectively induce or enhance specific signals of specific
molecules and/or suppress undesired ones [24–27]. There is an ever-growing
number of applications with these “control knobs” in this active research field of
laser spectroscopy, which is consequently coined quantum control spectroscopy.
This method has been used as a highly specialized tool to study, address selectively, and enhance specific transient spectroscopy features [28–33].
Being the topic of this collection, the most common way to address some of
the ambiguities of the time-resolved laser spectroscopy is based on the use of the
2
Reprinted from the journal