Lasing action from a micro-toroid
Micro-resonators with ultrahigh quality factors (Q-factor) became an important field of study as they find potential applications in numerous fields such as laser action, nonlinear optics, frequency metrology, telecommunications and cavity quantum electrodynamics. The superior optical confinement properties of such resonators make them excellent research tools. Micro-toroids are remarkable micro-resonators; they can simply be produced by CMOS compatible fabrication techniques, and due to their relatively smaller mode volume they have a high confined electromagnetic energy density.
Inducing laser action from a micro-cavity with an ultrahigh Q-factor is a critical step in developing more efficient lasers -both low threshold and no threshold. In this regard, we generated laser action from a silica micro-toroid covered with an active polymer yielding the lowest threshold obtained until now by free space excitation. The active medium was optically excited in the green via femtosecond (fs) laser pulses which results emission in the red. Micro-toroid was fabricated first in a disk shape using optical lithography. Then by selectively etching the silicon substrate underneath the disk area, the disks were suspended on top of the pillars. Subsequently the disks were exposed infrared CO2 laser (=10.6 micron) which melts the structure redefining its geometrical shape to be a toroid due to surface tension of liquid silica.
For our micro-toroid the threshold energy of free space excitation was observed to be an-order-of-magnitude lower than the best reported values.
A. Tulek, D. Akbulut, M. Bayindir
Ultralow threshold laser action from toroidal polymer microcavity, Accepted for publication in Applied Physics Letters
