Focusing And Amplifying Reflectarray Metasurfaces For Stable Laser Cavities
SUMMARY
UCLA researchers in the Department of Electrical Engineering have developed a novel design of reflectarray metasurface that focuses and amplifies THz laser beams with record high efficiency and stability.
BACKGROUND
Terahertz (THz) lasers are widely applicable in THz imaging of sensitive materials such as explosives, drugs, films and coatings, as well as spectroscopy. Current state-of-the-art THz laser technologies employ flat and compact reflectarray metasurfaces to replace conventional bulky curved optics. However, most of these metasurfaces use homogenous materials, which do not provide any focusing effect on the laser beam. Additionally, the issue of loss of power output in these THz lasers were not addressed in existing reflectarray metasurfaces configurations.
INNOVATION
An active, focusing reflectarray metasurface based upon quantum-cascade gain material has been developed to focus and amplify THz laser beams. Contrary to existing setups, this flat reflectarray metasurface utilizes inhomogeneous surface design that acts similar to a parabolic concave mirror, allowing the THz laser beams to focus. This design is also loaded with quantum-cascade (QC) laser active materials that provides high efficiency amplification of the THz beams when focused, dramatically increasing power output. A QC vertical-external-cavity surface-emitting-laser (VECSEL) with hemispherical cavity is created when this reflectarray metasurface design is used in conjunction with a flat output coupler (OC) reflector. This innovation leads to overall improved THz beam stability, pattern and record high slope efficiency. The concept of combining inhomogeneous metasurface designs with QC materials could lead to many applications in beam and wavefront generation.
APPLICATIONS
THz laser technologies in:
- Biological/medical imaging/spectroscopy
- Non-invasive sensing of films and coating for corrosion control
- THz heterodyne detection in astrophysics and space science
- Concept can be applied to a variety of beam and wavefront generation
ADVANTAGES
- Flat and compact
- Record high slope efficiency
- Focuses the laser beam
- Stable beam output
Tolerant to misalignment of optics