5.5 Fourier-Space Spectroscopy
169
Fig. 5.17 a Optical micrograph of an hBN-encapsulated WSe 2 monolayer, which provides excitonic signatures with spectrally very narrow optical modes close to the homogeneous linewidth
limit. Arrows indicate the flakes according to the stacking sequence (see inset, and label). The bottom layer is marked by dashed lines, the sandwiched monolayer semiconductor by dotted lines. b
Schematic drawing of a Fourier-space projection which enables in-plane-momentum (k ) resolved
signal acquisition. In a simplified sketch, a parabolic free-particle dispersion for in-plane confined
(centre-of-mass) propagation is set in relation to the detectable angle range (limited by the numerical aperture, i.e the maximum collectable angle in air). Parallel optical rays are indicated in grey
and dark grey for a finite and zero angle θ, respectively. Such setup has given unique insight into
excitonic (exciton–polariton) dispersions within the measurable light cone. c, d Comparison of
the dispersions recorded for the TMDC in a at quasi-resonant (c) and off-resonant (d) excitation,
discussed in [66]. Insets: Angle-integrated spectra (XP: exciton–polariton upper branch; ph.ass:
phonon-assisted emission from dark states; X, X* and XX... various excitonic resonances discussed and labelled in [3, 46]). a–d Adapted with permission. [66] Copyright 2019 Optical Society
of America. e Angle-resolved white-light reflection spectrum (false-colour diagram, from black to
white increasing intensity in arb.u.) from a homemade planar tunable Fabry–Pérot-type open microcavity with photonic dispersion of three cavity modes (exhibiting quality factors of up to 250). The
dashed line indicates the WS 2 exciton resonance for targeted coupling experiments. Insets: sketch
of the cavity (top inset) comprising a dielectric mirror and a silver-coated SU-8-polymer micropost
(top facet shown in the bottom inset) with slight concaveness and indicated 2-µm mirror separation.
In fact, bare dielectric mirrors are very useful test samples in Fourier-space spectroscopy setups.
Data obtained by F. Wall in the author’s team, for experiments towards the achievement of tunable
coupling strength studied in [139]
169
Fig. 5.17 a Optical micrograph of an hBN-encapsulated WSe 2 monolayer, which provides excitonic signatures with spectrally very narrow optical modes close to the homogeneous linewidth
limit. Arrows indicate the flakes according to the stacking sequence (see inset, and label). The bottom layer is marked by dashed lines, the sandwiched monolayer semiconductor by dotted lines. b
Schematic drawing of a Fourier-space projection which enables in-plane-momentum (k ) resolved
signal acquisition. In a simplified sketch, a parabolic free-particle dispersion for in-plane confined
(centre-of-mass) propagation is set in relation to the detectable angle range (limited by the numerical aperture, i.e the maximum collectable angle in air). Parallel optical rays are indicated in grey
and dark grey for a finite and zero angle θ, respectively. Such setup has given unique insight into
excitonic (exciton–polariton) dispersions within the measurable light cone. c, d Comparison of
the dispersions recorded for the TMDC in a at quasi-resonant (c) and off-resonant (d) excitation,
discussed in [66]. Insets: Angle-integrated spectra (XP: exciton–polariton upper branch; ph.ass:
phonon-assisted emission from dark states; X, X* and XX... various excitonic resonances discussed and labelled in [3, 46]). a–d Adapted with permission. [66] Copyright 2019 Optical Society
of America. e Angle-resolved white-light reflection spectrum (false-colour diagram, from black to
white increasing intensity in arb.u.) from a homemade planar tunable Fabry–Pérot-type open microcavity with photonic dispersion of three cavity modes (exhibiting quality factors of up to 250). The
dashed line indicates the WS 2 exciton resonance for targeted coupling experiments. Insets: sketch
of the cavity (top inset) comprising a dielectric mirror and a silver-coated SU-8-polymer micropost
(top facet shown in the bottom inset) with slight concaveness and indicated 2-µm mirror separation.
In fact, bare dielectric mirrors are very useful test samples in Fourier-space spectroscopy setups.
Data obtained by F. Wall in the author’s team, for experiments towards the achievement of tunable
coupling strength studied in [139]