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A nanolaser is a laser able to produce beams at the nanoscale

Limit of conventional laser
There is a fundamental maximum to the resolution of any optical system which is due to diffraction - diffraction limited. Conventional lasers, based on photonic crystals, metal-clad cavities,and even nano-wire, are restricted to being larger than half the wavelength of the optical field both in optical mode size and physical device dimension

Plasmonic Nanolaser - SPASER
SPASER stands for Surface Plasmon Amplification by Stimulated Emission of Radiation. SPASER was first proposed by Mark Stockman of Georgia State University and David Bergman of Tel Aviv University in Israel in January 2003. The first SPASER has been created by scientists at Norfolk State University, Purdue University and Cornell University.

First SPASER
A gold core surrounded by a glasslike shell filled with green dye. The gold core and the thickness of the silica shell were about 14 nanometers and 15 nanometers, respectively. The device emitting visible light with a wavelength of 525 nanometers. When a light was shined on the spheres, plasmons generated by the gold core were amplified by the dye. It 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

Plasmonic laser – UC Berkeley
The plasmonic laser device can generate light in a space of 5nm size which is 100 times smaller than the area produced by conventional lasers. It has a hydrid device consisting of a cadmium sulphide semiconductor nano-wire separated by a 5nm thick insulating layer from a metallic silver surface. Since it is non-metallic, this structure poses little resistance so that SPPs can survive for longer. Nanowire essentially acts an amplifier for nanoscale light and generates laser with the wavelength of 489nm.

Application
Applications are optical computers that use light instead of electrons to process information, and nanometer-sized photonic circuits. It can be also used in imaging and sensing at a scale that is much smaller than the wavelength of visible light. Plasmonic lasers offer the possibility of exploring extreme interactions between light and matter, opening up new avenues in the fields of quantum information technology.