236
8 Conclusion and Outlook
For the successful employment of self-mode-locked SDLs in applications, such as
spectroscopy, multi-photon microscopy, material processing and more, it is essential
to reveal the nature of the nonlinearity which causes pulse formation in the self-modelocked device. Thereby, significant improvements can be achieved with respect to the
pulse duration, spectral versatility and performance. The recently understood role of
the microcavity on the nonlinearities in an SDL chip in combination with a better
understanding of the group-delay dispersion in VECSELs may support the sophisticated design of gain chips for self-mode-locking VECSELs, as well as dispersion
compensation efforts. The author expects even peak powers in the order of several
kilo-Watts and pulse durations as short as 100 fs to come into reach as a consequence
of the optimisation of such saturable-absorber-free mode-locked VECSELs.
8.4 Manipulating and Controlling Cavity–Polaritons with
Terahertz Waves
The rich world of light–matter interactions has enabled numerous technological
advances, some widely known as the products of semiconductor photonics achievements, such as LEDs and lasers, others anticipated to bring the next generation of
quantum technologies to commercially-available products, such as quantum communication and information processing devices. Among the interaction effects between
matter and light states, the strong quantum coupling of excitons and photons in
semiconductors remains fascinating, that results in coherent superpositions of the
two components, or quasi-particles called exciton–polaritons [24–26]. The appearance of such mixed modes is interesting from, both, the point of view of fundamental
and applied research. The demonstration of these hybrid quasi-particles in optical
microcavities [27–30] in the semiclassical ensemble regime based on quantum wells
(QWs) [31] and in the quantum limit for quantum dots (QDs) [32–34] opened up new
possibilities with regards to cavity-QED studies [35, 36] and coherent light generation [37, 38]. Strong inter-particle interactions result from the exciton component,
whereas extremely low effective mass and high mobility are due to the photonic
component.
The field of condensation of exciton–polaritons [39–41] emerged in the previous decade shortly after the demonstration of true Bose–Einstein condensates of
dilute atomic gases [42–44] which opened a new chapter in the field of quantum
optics. This major breakthrough on quasi-particles in solids led to a vast exploration
of condensation-related phenomena and phase transitions [45–48], such as a spontaneous coherence build-up, superfluidity and superconductivity. Even the use of
qubits based on polariton Rabi oscillations [49] and novel light sources emitting in
the visible or THz range, such as polariton lasers [37, 50–54], as well as THz bosonic
lasers and the like [55–61], have been proposed.
Within the last few years, a few independent efforts have been made to combine THz radiation and polariton systems in experiments, with the aim to study the
8 Conclusion and Outlook
For the successful employment of self-mode-locked SDLs in applications, such as
spectroscopy, multi-photon microscopy, material processing and more, it is essential
to reveal the nature of the nonlinearity which causes pulse formation in the self-modelocked device. Thereby, significant improvements can be achieved with respect to the
pulse duration, spectral versatility and performance. The recently understood role of
the microcavity on the nonlinearities in an SDL chip in combination with a better
understanding of the group-delay dispersion in VECSELs may support the sophisticated design of gain chips for self-mode-locking VECSELs, as well as dispersion
compensation efforts. The author expects even peak powers in the order of several
kilo-Watts and pulse durations as short as 100 fs to come into reach as a consequence
of the optimisation of such saturable-absorber-free mode-locked VECSELs.
8.4 Manipulating and Controlling Cavity–Polaritons with
Terahertz Waves
The rich world of light–matter interactions has enabled numerous technological
advances, some widely known as the products of semiconductor photonics achievements, such as LEDs and lasers, others anticipated to bring the next generation of
quantum technologies to commercially-available products, such as quantum communication and information processing devices. Among the interaction effects between
matter and light states, the strong quantum coupling of excitons and photons in
semiconductors remains fascinating, that results in coherent superpositions of the
two components, or quasi-particles called exciton–polaritons [24–26]. The appearance of such mixed modes is interesting from, both, the point of view of fundamental
and applied research. The demonstration of these hybrid quasi-particles in optical
microcavities [27–30] in the semiclassical ensemble regime based on quantum wells
(QWs) [31] and in the quantum limit for quantum dots (QDs) [32–34] opened up new
possibilities with regards to cavity-QED studies [35, 36] and coherent light generation [37, 38]. Strong inter-particle interactions result from the exciton component,
whereas extremely low effective mass and high mobility are due to the photonic
component.
The field of condensation of exciton–polaritons [39–41] emerged in the previous decade shortly after the demonstration of true Bose–Einstein condensates of
dilute atomic gases [42–44] which opened a new chapter in the field of quantum
optics. This major breakthrough on quasi-particles in solids led to a vast exploration
of condensation-related phenomena and phase transitions [45–48], such as a spontaneous coherence build-up, superfluidity and superconductivity. Even the use of
qubits based on polariton Rabi oscillations [49] and novel light sources emitting in
the visible or THz range, such as polariton lasers [37, 50–54], as well as THz bosonic
lasers and the like [55–61], have been proposed.
Within the last few years, a few independent efforts have been made to combine THz radiation and polariton systems in experiments, with the aim to study the