142
5 Optical Measurement Techniques
Fig. 5.7 Scattering-type SNOM (s-SNOM) measurements on a TMDC-covered and an open inplane microcavity structure in GaP substrate. Practically, near-field measurements with s-SNOM
setups typically yield topography information due to the AFM functionality of the technique. a
Topography of the cavity covered by a monolayer-on-hBN stack. Corresponding false-colour nearfield intensity maps of the covered cavity at 532 nm b and at 850 nm c are displayed in greenish and
reddish colours, respectively. d–f Analogue recordings for an open uncovered cavity structure for a
direct comparison of the s-SNOM signals to the covered case in a–c. Reproduced with permission.
[6] Copyright 2019 American Chemical Society
excitation with a stroboscopic detection scheme can further provide access to the
dynamics of a system, as summarised in the next section.
One major advantage of time-integrated acquisition is the possibility of recording high-enough signal through the expansion of the measurement time, enabling
detection of weak signals and improvement of signal-to-noise ratios. However, this
requires that the measurement conditions remain as stable as possible over the integration time, since thermal and position instabilities can spoil the spectrum for different
reasons. Temperature-dependent wavelength shifts for resonances can lead to broadened signatures in recorded spectra, while position fluctuations can easily translate
to inhomogeneous broadening and signal-strength fluctuations or complete loss of
signal from a particular spot.
Time-integrated measurements also bear the advantage that the system is analysed in its steady-state configuration. Although no information about the dynamics
can be obtained, a homogeneously-broadened line can still provide a good estimate
about the emitter’s lifetime or the linewidth of a laser can indicate the coherence
length of a laser.
5 Optical Measurement Techniques
Fig. 5.7 Scattering-type SNOM (s-SNOM) measurements on a TMDC-covered and an open inplane microcavity structure in GaP substrate. Practically, near-field measurements with s-SNOM
setups typically yield topography information due to the AFM functionality of the technique. a
Topography of the cavity covered by a monolayer-on-hBN stack. Corresponding false-colour nearfield intensity maps of the covered cavity at 532 nm b and at 850 nm c are displayed in greenish and
reddish colours, respectively. d–f Analogue recordings for an open uncovered cavity structure for a
direct comparison of the s-SNOM signals to the covered case in a–c. Reproduced with permission.
[6] Copyright 2019 American Chemical Society
excitation with a stroboscopic detection scheme can further provide access to the
dynamics of a system, as summarised in the next section.
One major advantage of time-integrated acquisition is the possibility of recording high-enough signal through the expansion of the measurement time, enabling
detection of weak signals and improvement of signal-to-noise ratios. However, this
requires that the measurement conditions remain as stable as possible over the integration time, since thermal and position instabilities can spoil the spectrum for different
reasons. Temperature-dependent wavelength shifts for resonances can lead to broadened signatures in recorded spectra, while position fluctuations can easily translate
to inhomogeneous broadening and signal-strength fluctuations or complete loss of
signal from a particular spot.
Time-integrated measurements also bear the advantage that the system is analysed in its steady-state configuration. Although no information about the dynamics
can be obtained, a homogeneously-broadened line can still provide a good estimate
about the emitter’s lifetime or the linewidth of a laser can indicate the coherence
length of a laser.