5.2 Microscopy and Spectroscopy
151
In contrast to g
(2)
(τ ), which addresses the correlation between intensities, the
first-order correlation function g
(1)
(τ ), which can be for instance obtained through
Michelson interferometry, gives the correlation of light fields.
For a theoretical view on this subject, the interested reader is referred to textbooks such as [52]. In practice, the experimental value G
(2)
(0) obtained from pulsed
light represents a time-averaged g
(2)
(0) for every pulse [53], as used for instance in
polariton condensate research to investigate the degree of temporal coherence and
the intensity noise for different regimes of microcavity emission.
The HBT experiment has become an important tool for the characterisation of
single-photon sources such as quantum dots in optical micropillars [54], or for laser
thresholds characterisation, where a transition from bunching to a coherent state
is expected, as demonstrated on semiconductor microcavity lasers [55] (see also
electrically-driven low-threshold nanolasers [56]). Later, it was introduced in efforts
towards the characterisation of a double-threshold behaviour from polariton systems
[26], whereas it had been generally used for density-dependent photon statistics
measurements for polariton condensation effects [53, 57–62]. In combination with
disturbing transient electric fields, pulsed HBT measurements may give additional
insights into the external manipulation of polariton systems below and above a condensation threshold and the impact on intensity noise.
5.3 Basic Material Response
Typically, novel materials and quantum structures are studied using their absorption,
reflection, transmission, emission, or vibrational behaviour. In the following, a brief
introduction to basic spectroscopy modes is given together with examples, and some
of their strengths and drawbacks are summarised.
5.3.1 Absorbance
While laser excitation enables luminescence studies, white-light illumination in
reflection geometry allows one to probe the absorption-behaviour of samples by
recording reflected signal and comparing it to a reference of the light source. Absorption in the low-intensity regime belongs to the field of linear optics, where the
material polarisation is a linear response to the incident light field. In contrast to
nonlinear optics, the) (macroscopic polarisation P = 0 χ(ω, k)E (with susceptibility χ = r − 1, a complex function with real and imaginary part) can be approximated
by the term linear in electric field strength, neglecting contributions of higher-order
151
In contrast to g
(2)
(τ ), which addresses the correlation between intensities, the
first-order correlation function g
(1)
(τ ), which can be for instance obtained through
Michelson interferometry, gives the correlation of light fields.
For a theoretical view on this subject, the interested reader is referred to textbooks such as [52]. In practice, the experimental value G
(2)
(0) obtained from pulsed
light represents a time-averaged g
(2)
(0) for every pulse [53], as used for instance in
polariton condensate research to investigate the degree of temporal coherence and
the intensity noise for different regimes of microcavity emission.
The HBT experiment has become an important tool for the characterisation of
single-photon sources such as quantum dots in optical micropillars [54], or for laser
thresholds characterisation, where a transition from bunching to a coherent state
is expected, as demonstrated on semiconductor microcavity lasers [55] (see also
electrically-driven low-threshold nanolasers [56]). Later, it was introduced in efforts
towards the characterisation of a double-threshold behaviour from polariton systems
[26], whereas it had been generally used for density-dependent photon statistics
measurements for polariton condensation effects [53, 57–62]. In combination with
disturbing transient electric fields, pulsed HBT measurements may give additional
insights into the external manipulation of polariton systems below and above a condensation threshold and the impact on intensity noise.
5.3 Basic Material Response
Typically, novel materials and quantum structures are studied using their absorption,
reflection, transmission, emission, or vibrational behaviour. In the following, a brief
introduction to basic spectroscopy modes is given together with examples, and some
of their strengths and drawbacks are summarised.
5.3.1 Absorbance
While laser excitation enables luminescence studies, white-light illumination in
reflection geometry allows one to probe the absorption-behaviour of samples by
recording reflected signal and comparing it to a reference of the light source. Absorption in the low-intensity regime belongs to the field of linear optics, where the
material polarisation is a linear response to the incident light field. In contrast to
nonlinear optics, the) (macroscopic polarisation P = 0 χ(ω, k)E (with susceptibility χ = r − 1, a complex function with real and imaginary part) can be approximated
by the term linear in electric field strength, neglecting contributions of higher-order