Boosting THz lasers with a new type of Bragg grating
US research team demonstrates laser with record-high output power using hybrid second- and fourth-order Bragg grating
In a recent paper published in the journal Nature Communications, a research group at Lehigh University in the US led by Sushil Kumar in collaboration with Sandia National Laboratories, have reported on a technique to enhance the power output of single-mode lasers that are surface-emitting (as opposed to those using an edge-emitting configuration).
Of the two types, the surface-emitting configuration for semiconductor lasers offers distinctive advantages in how the lasers could be miniaturized, packaged and tested for commercial production.
The published research describes a new technique by which a specific type of periodicity is introduced in the laser's optical cavity, allowing it to fundamentally radiate a good quality beam with increased radiation efficiency, thus making the laser more powerful. The authors call their scheme as having a 'hybrid second- and fourth-order Bragg grating' (as opposed to a second-order Bragg grating for the typical surface-emitting laser, variations of which have been used in a wide variety of lasers for close to three decades).
They claim that their hybrid grating scheme is not limited to terahertz lasers and could potentially improve performance of a broad class of surface-emitting semiconductor lasers that emit at different wavelengths.
The report discusses experimental results for a monolithic single-mode terahertz laser with a power output of 170 milliwatts, which is the most powerful to date for such class of lasers. The research shows conclusively that the so-called hybrid grating is able to make the laser emit at a specific desired wavelength through a simple alteration in the periodicity of imprinted grating in the laser's cavity while maintaining its beam quality.
Kumar maintains that power levels of one watt and above should be achievable with future modifications of their technique - which might just be the threshold needed to be overcome for industry to take notice and step into potential commercialisation of terahertz laser-based instruments.
'High power surface emitting terahertz laser with hybrid second- and fourth-order Bragg gratings' by Yuan Jin et al; Nature Communications volume 9, Article number: 1407 (2018)
