Tiniest Laser Developed -- Confirming 'Spaser' Concept

In a paper published in 'Nature' [1], a team of scientists reported the creation of the tiniest laser since its invention nearly 50 years ago, paving the way for a host of innovations, including superfast computers that use light instead of electrons to process information, advanced sensors and imaging. The research was conducted by Norfolk State University researchers Mikhail A. Noginov, Guohua Zhu and Akeisha M. Belgrave; Purdue University researchers Reuben M. Bakker, Vlad Shalaev and Evgenii E. Narimanov; and Cornell University researchers Samantha Stout, Erik Herz, Teeraporn Suteewong and Ulrich B. Wiesner.

Because the new device, called a "spaser" (which stands for 'Surface Plasmon Amplification by Stimulated Emission of Radiation') is the first of its kind to emit visible light, it represents a critical component for possible future technologies based on "nanophotonic" circuitry, said Vladimir Shalaev of Purdue University.

[Image courtesy: Birck Nanotechnology Center, Purdue University] The color diagram (a) shows the nanolaser's design: a gold core surrounded by a glasslike shell filled with green dye. When a light was shined on the spheres, plasmons generated by the gold core were amplified by the dye. The plasmons were then converted to photons of visible light, which was emitted as a laser. Scanning electron microscope images (b and c) show that the gold core and the thickness of the silica shell were about 14 nanometers and 15 nanometers, respectively. A simulation of the SPASER (d) shows the device emitting visible light with a wavelength of 525 nanometers.

Nanophotonics may usher in a host of radical advances, including powerful "hyperlenses" resulting in sensors and microscopes 10 times more powerful than today's and able to see objects as small as DNA; computers and consumer electronics that use light instead of electronic signals to process information; and more efficient solar collectors.

Nanophotonic circuits will require a laser-light source, but current lasers can't be made small enough to integrate them into electronic chips. Now researchers have overcome this obstacle, harnessing clouds of electrons called "surface plasmons," instead of the photons that make up light, to create the tiny spasers.

The "spaser-based nanolasers" created in the research were spheres 44 nanometers in diameter - more than 1 million could fit inside a red blood cell. The spheres were fabricated at Cornell, with Norfolk State and Purdue performing the optical characterization needed to determine whether the devices behave as lasers.

Past 2Physics article by Vlad Shalaev and his collaborators:
"Large Broadband Invisibility Cloak for Visible Light"

To act like lasers, Spasers require a "feedback system" that causes the surface plasmons to oscillate back and forth so that they gain power and can be emitted as light. Conventional lasers are limited in how small they can be made because this feedback component for photons, called an optical resonator, must be at least half the size of the wavelength of laser light.

The researchers, however, have overcome this hurdle by using not photons but surface plasmons, which enabled them to create a resonator 44 nanometers in diameter, or less than one-tenth the size of the 530-nanometer wavelength emitted by the spaser.

The findings confirm work by physicists David Bergman (Tel Aviv University) and Mark Stockman (Georgia State University), who first proposed the spaser concept in 2003 [2].

"It's fitting that we have realized a breakthrough in laser technology as we are getting ready to celebrate the 50th anniversary of the invention of the laser," Shalaev said.

The first working laser was demonstrated in 1960.

Reference
[1] "Demonstration of SPASER-based Nanolaser" , M. A. Noginov, G. Zhu, A. M. Belgrave, R. Bakker, V. M. Shalaev, E. E. Narimanov, S. Stout, E. Herz, T. Suteewong, U. Wiesner,
Nature, doi:10.1038/nature08318, (Published online 16th August, 2009), Abstract
[2] "Surface Plasmon Amplification by Stimulated Emission of Radiation: Quantum Generation of Coherent Surface Plasmons in Nanosystems", David J. Bergman and Mark I. Stockman, Phys. Rev. Lett. 90, 027402(2003). Abstract.

[Our presentation of this work is based upon a write-up by Emil Venere of Purdue University]