Tiny New Lasers Fill A Long-Standing Gap In The Rainbow Of Visible-Light Colors

Arthur T Knackerbracket has processed the following story:

It's not easy making green. For years, scientists have fabricated small, high-quality lasers that generate red and blue light. However, the method they typically employ-injecting electric current into semiconductors-hasn't worked as well in building tiny lasers that emit light at yellow and green wavelengths.

Researchers refer to the dearth of stable, miniature lasers in this region of the visible-light spectrum as the "green gap." Filling this gap opens new opportunities in underwater communications, medical treatments and more.

Green laser pointers have existed for 25 years, but they produce light only in a narrow spectrum of green and are not integrated in chips where they could work together with other devices to perform useful tasks.

Now scientists at the National Institute of Standards and Technology (NIST) have closed the green gap by modifying a tiny optical component: a ring-shaped microresonator, small enough to fit on a chip. The research is published in the journal Light: Science & Applications.

A miniature source of green laser light could improve underwater communication because water is nearly transparent to blue-green wavelengths in most aquatic environments. Other potential applications are in full-color laser projection displays and laser treatment of medical conditions, including diabetic retinopathy, a proliferation of blood vessels in the eye.

Compact lasers in this wavelength range are also important for applications in quantum computing and communication, as they could potentially store data in qubits, the fundamental unit of quantum information. Currently, these quantum applications depend on lasers that are larger in size, weight and power, limiting their ability to be deployed outside the laboratory.

For several years, a team led by Kartik Srinivasan of NIST and the Joint Quantum Institute (JQI), a research partnership between NIST and the University of Maryland, has used microresonators composed of silicon nitride to convert infrared laser light into other colors. When infrared light is pumped into the ring-shaped resonator, the light circles thousands of times until it reaches intensities high enough to interact strongly with the silicon nitride. That interaction, known as an optical parametric oscillation (OPO), produces two new wavelengths of light, called the idler and the signal.

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