234
8 Conclusion and Outlook
laser systems and physics phenomena evolved throughout this Habilitation period,
fortunately. Indeed, the author’s personal research interests have always guided
him back towards nanophotonics and quantum optics subjects, and in the wider
sense light–matter interactions, although the interlude of semiconductor/functional
(nano-) materials studies with various optical spectroscopy techniques can only be
regarded as an invaluable advantage and enriching experience.
2
In summary, the author’s recent endeavours included, on the one hand, investigations on various semiconductor disk laser systems towards self-mode-locking as well
as nonlinear lensing, and even their employment for the high-frequent excitation of
quantum-dot single-photon sources, the achievement of high-power single-frequency
lasing and of tunable THz generation. On the other hand, they included studies on
nanoparticles, van-der-Waals (vdW) heterostructures, and monolayer quantum materials, such as transition-metal dichalcogenides (TMDCs), with a focus on light–matter
interactions and optical properties, as well as the continuation of polariton-physics
research towards ultrafast control and manipulation of coherent quantum states and
Bose–Einstein-like condensates in optical microcavities. Motivated by a long-term
experience in these fields, several preliminary works have been pursued by the author
with the help of his research team in preparation of major research projects and possible future activities. The privilege, that no lack of fundamental science, engineeringrelated and device-oriented work was given, can be evidenced throughout the previous chapters of this work and in the following overview of ongoing research within
the scope of the author’s projects.
8.3 Exploring the Mechanism Behind Self-Mode-Locking
in VECSELs
For many years, semiconductor disk lasers (SDLs), also often referred to as verticalexternal-cavity surface-emitting lasers (VECSELs) [1–3], have been seen as an ideal
platform for the realisation of compact, robust and cost-efficient fs-pulsed lasers
[4, 5]. Naturally, saturable-absorber mirrors, which are embedded in the externalresonator device, have been widely employed to achieve mode-locking with SDLs
due to their maturity and the well-established understanding of key design parameters for ultrashort pulsing [6, 7]. Nonetheless, in many regards the development of
saturable-absorber-free devices has been envisaged as a desirable engineering goal.
This is because the recently obtained and already much discussed self-mode-locking
effect [2, 5, 8–17] has promised the design of such less complex and more flexible
mode-locked VECSELs, provided that the technology is matured and reliable.
2 Amendment: Simultaneously, a unique opportunity was given the author with respect to independent student teaching and supervision, as evidenced by numerous courses on “Quantum Technology”
(full Master level course introduced in 2014 and since then more than five times lectured), “Laser
Spectroscopy” (2019), “Semiconductor Quantum Structures for Photonic Devices” (2017 and 2018,
Zhejiang University), “Semiconductor Physics and Devices” (2014) and many more delivered in
Marburg, as well as in Hangzhou.
8 Conclusion and Outlook
laser systems and physics phenomena evolved throughout this Habilitation period,
fortunately. Indeed, the author’s personal research interests have always guided
him back towards nanophotonics and quantum optics subjects, and in the wider
sense light–matter interactions, although the interlude of semiconductor/functional
(nano-) materials studies with various optical spectroscopy techniques can only be
regarded as an invaluable advantage and enriching experience.
2
In summary, the author’s recent endeavours included, on the one hand, investigations on various semiconductor disk laser systems towards self-mode-locking as well
as nonlinear lensing, and even their employment for the high-frequent excitation of
quantum-dot single-photon sources, the achievement of high-power single-frequency
lasing and of tunable THz generation. On the other hand, they included studies on
nanoparticles, van-der-Waals (vdW) heterostructures, and monolayer quantum materials, such as transition-metal dichalcogenides (TMDCs), with a focus on light–matter
interactions and optical properties, as well as the continuation of polariton-physics
research towards ultrafast control and manipulation of coherent quantum states and
Bose–Einstein-like condensates in optical microcavities. Motivated by a long-term
experience in these fields, several preliminary works have been pursued by the author
with the help of his research team in preparation of major research projects and possible future activities. The privilege, that no lack of fundamental science, engineeringrelated and device-oriented work was given, can be evidenced throughout the previous chapters of this work and in the following overview of ongoing research within
the scope of the author’s projects.
8.3 Exploring the Mechanism Behind Self-Mode-Locking
in VECSELs
For many years, semiconductor disk lasers (SDLs), also often referred to as verticalexternal-cavity surface-emitting lasers (VECSELs) [1–3], have been seen as an ideal
platform for the realisation of compact, robust and cost-efficient fs-pulsed lasers
[4, 5]. Naturally, saturable-absorber mirrors, which are embedded in the externalresonator device, have been widely employed to achieve mode-locking with SDLs
due to their maturity and the well-established understanding of key design parameters for ultrashort pulsing [6, 7]. Nonetheless, in many regards the development of
saturable-absorber-free devices has been envisaged as a desirable engineering goal.
This is because the recently obtained and already much discussed self-mode-locking
effect [2, 5, 8–17] has promised the design of such less complex and more flexible
mode-locked VECSELs, provided that the technology is matured and reliable.
2 Amendment: Simultaneously, a unique opportunity was given the author with respect to independent student teaching and supervision, as evidenced by numerous courses on “Quantum Technology”
(full Master level course introduced in 2014 and since then more than five times lectured), “Laser
Spectroscopy” (2019), “Semiconductor Quantum Structures for Photonic Devices” (2017 and 2018,
Zhejiang University), “Semiconductor Physics and Devices” (2014) and many more delivered in
Marburg, as well as in Hangzhou.