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T. Szidarovszky et al.
and in practical applications, as well as to the remarkable advances in the available experimental techniques and light sources. For example, the development of
frequency-comb techniques [2–5] facilitates extremely precise and accurate measurements in the frequency domain, while the development of ultrashort and intense
pulsed laser technologies [6, 7] allows for time-resolved spectroscopy on femtosecond or even attosecond [7, 8] timescales.
An often utilized technique of modern spectroscopic methods is the use of two (or
more) light pulses. Some of these pulses act as so-called pump pulses, which induce
specific changes in the system. Subsequent, so-called probe pulses are used then
to measure, directly or indirectly, the changes induced by the pump pulse(s). If the
duration of both the pump and the probe pulses is short with respect to the processes
investigated, repeating the experiment with varying time delays between the pulses
can lead to time-resolved dynamical information [9, 10] or to multidimensional
and/or high-resolution spectra [11, 12]. If the pump and probe pulses overlap in
time, the signal recorded by the probe pulse does not represent the field-free system,
but rather the so-called field-dressed or light-dressed system [13, 14], where the pump
pulse acts as the dressing field. If both the pump and the probe pulses are long with
respect to the timescales of the processes investigated, one obtains static spectral
properties of the light-dressed system. In this chapter we investigate such static
spectra of light-dressed systems and henceforth call it light-dressed spectroscopy.
For atomic systems the theoretical and experimental methods for investigating optical transitions between light-dressed states is well developed [13]. As to
molecules, the concept of light-dressed electronic states, also called light-dressed
potentials, has been utilized with considerable success to understand nuclear dynamics both in experimental and theoretical studies [15–23]. To some extent light-dressed
rovibrational spectroscopy has been adopted for molecular systems. For example,
inducing Autler–Townes-type splittings [24] of rotational transitions with microwave
radiation has been used to deduce molecular parameters [25, 26] as well as to promote
the spectral assignments of rovibronic levels [27].
In previous theoretical studies the rovibronic spectrum of light-dressed Na 2 was
investigated in the context of how the presence of a light-induced conical intersection
(LICI) [28, 29], generated by the dressing field, can be identified in the spectrum [30,
31]. In these works all rovibronic degrees of freedom are incorporated into the concept
of light-dressed states and the modeling work is carried out for both the dressing field
of laser radiation [30] and the quantized dressing field of a microscopic cavity mode
[31]. In a separate paper, we provided a more general and detailed discussion on the
computation and the properties of light-dressed spectra [32].
In this chapter we review in detail the theory of computing light-dressed spectra
induced by laser fields and investigate certain aspects of light-dressed spectroscopy,
including its unique properties on deriving spectroscopic information. Our discussion
closely follows the one presented in [32].
T. Szidarovszky et al.
and in practical applications, as well as to the remarkable advances in the available experimental techniques and light sources. For example, the development of
frequency-comb techniques [2–5] facilitates extremely precise and accurate measurements in the frequency domain, while the development of ultrashort and intense
pulsed laser technologies [6, 7] allows for time-resolved spectroscopy on femtosecond or even attosecond [7, 8] timescales.
An often utilized technique of modern spectroscopic methods is the use of two (or
more) light pulses. Some of these pulses act as so-called pump pulses, which induce
specific changes in the system. Subsequent, so-called probe pulses are used then
to measure, directly or indirectly, the changes induced by the pump pulse(s). If the
duration of both the pump and the probe pulses is short with respect to the processes
investigated, repeating the experiment with varying time delays between the pulses
can lead to time-resolved dynamical information [9, 10] or to multidimensional
and/or high-resolution spectra [11, 12]. If the pump and probe pulses overlap in
time, the signal recorded by the probe pulse does not represent the field-free system,
but rather the so-called field-dressed or light-dressed system [13, 14], where the pump
pulse acts as the dressing field. If both the pump and the probe pulses are long with
respect to the timescales of the processes investigated, one obtains static spectral
properties of the light-dressed system. In this chapter we investigate such static
spectra of light-dressed systems and henceforth call it light-dressed spectroscopy.
For atomic systems the theoretical and experimental methods for investigating optical transitions between light-dressed states is well developed [13]. As to
molecules, the concept of light-dressed electronic states, also called light-dressed
potentials, has been utilized with considerable success to understand nuclear dynamics both in experimental and theoretical studies [15–23]. To some extent light-dressed
rovibrational spectroscopy has been adopted for molecular systems. For example,
inducing Autler–Townes-type splittings [24] of rotational transitions with microwave
radiation has been used to deduce molecular parameters [25, 26] as well as to promote
the spectral assignments of rovibronic levels [27].
In previous theoretical studies the rovibronic spectrum of light-dressed Na 2 was
investigated in the context of how the presence of a light-induced conical intersection
(LICI) [28, 29], generated by the dressing field, can be identified in the spectrum [30,
31]. In these works all rovibronic degrees of freedom are incorporated into the concept
of light-dressed states and the modeling work is carried out for both the dressing field
of laser radiation [30] and the quantized dressing field of a microscopic cavity mode
[31]. In a separate paper, we provided a more general and detailed discussion on the
computation and the properties of light-dressed spectra [32].
In this chapter we review in detail the theory of computing light-dressed spectra
induced by laser fields and investigate certain aspects of light-dressed spectroscopy,
including its unique properties on deriving spectroscopic information. Our discussion
closely follows the one presented in [32].