Technique for “phase locking” arrays of tiny lasers could lead to terahertz security scanners.
Terahertz radiation — the band of electromagnetic radiation between microwaves and visible light — has promising applications in security and medical diagnostics, but such devices will require the development of compact, low-power, high-quality terahertz lasers.
In this week’s issue of Nature Photonics, researchers at MIT and Sandia National Laboratories describe a new way to build terahertz lasers that could significantly reduce their power consumption and size, while also enabling them to emit tighter beams, a crucial requirement for most practical applications.
The work also represents a fundamentally new approach to laser design, which could have ramifications for visible-light lasers as well.
The researchers’ device is an array of 37 microfabricated lasers on a single chip. Its power requirements are so low because the radiation emitted by all of the lasers is “phase locked,” meaning that the troughs and crests of its waves are perfectly aligned. The device represents a fundamentally new way to phase-lock arrays of lasers.
Scientists from the Light-Matter Interactions Unit, led by Professor Síle Nic Chormaic at the Okinawa Institute of Science and Technology Graduate University (OIST), have developed a new technique to fabricate glass microlasers and tune them using compressed air.
The new technique, published in Scientific Reports, could pave the way for the simple serial production of glass microlasers and could be used in a wide range of applications, such as optical communications, chemical or biosensing.
Microlasers are tiny optical devices a few tens of micrometres in diameter that are able to create intense light with only one colour or wavelength. OIST researchers found a new method to fabricate a special type of glass microlaser, called whispering gallery microlasers. Whispering gallery microlasers are doughnut-shaped or spherical devices produced from glass doped with rare earth elements, such as erbium or ytterbium (Er or Yb). Inside the microlasers, light is reflected over and over creating a 10-100 metre long optical path within a tiny device that’s the size of a grain of sand.
Taking advantage of the different melting temperatures of silica and Er or Yb doped phosphate glass, OIST scientists have devised a new way to produce microlasers via glass wetting, or glass-on-glass fabrication. In this new technique, a strand of Er or Yb doped phosphate glass is melted and allowed to flow around a hollow capillary of silica. This is possible because of the different melting temperatures of silica and phosphate glass at 1500°C and 500°C, respectively. This technique produces bottle-shaped microlasers, which are 170 micrometres in diameter. The bottle-shape can then be modified to become a thin coating of only a few micrometres in diameter around the capillary.