Shape of things to comeNew technology increase potency of beam weapons

Beam weapons a little closer, starships will have to wait // Source: wikia.com

Laser scientists and engineers have long recognized that direct-diode lasers can offer significant advantages over other laser technologies due to their efficiency, reliability, compactness, and relatively low cost. These advantages have made diode lasers an enabling technology for high volume applications in telecommunications and data storage.

Applications for direct-diode lasers have been limited, however, owing to their low brightness — a combination of lower power and poorer beam quality relative to alternative laser technologies. The penetration of direct-diode lasers into the most demanding industrial applications, including metal cutting, and laser welding, has been poor. Instead, direct-diode lasers have been relegated to niches like brazing, heat treating, and paint stripping.

Using beam combining to increase brightness

There are three generally accepted approaches to increasing the brightness of direct-diode lasers:

• Side-by-side beam combining
• Coherent beam combining (CBC)
• Wavelength beam combining (WBC)

Littleton, Massachusetts-based TeraDiode says that only WBC has the necessary qualities to be adapted for use in a high brightness industrial laser — and in weapons.

• Side-by-side beam combining increases output power in proportion to the number of emitters, but decreases beam quality by the same proportion. As a result, brightness cannot be increased.
• Coherent beam combining demands active phase locking of all emitters such that the optical path length difference between emitters is λ/10 or better. Little progress has been made in scaling CBC beyond several watts, despite substantial investment, so CBC is not considered a practical pathway to a high-brightness industrial laser at this time.

Wavelength beam combining is an incoherent, multi-wavelength process. The company says that when it is implemented in TeraDiode’s TeraDrive technology, output power scales in proportion to the number of emitters, while the beam quality of an individual emitter is preserved. Thus, brightness increases with the number of emitters.

In technical terms: WBC can be thought of as the spatial superposition of many independent diode laser external cavities. The angle-to-wavelength conversion property of a diffraction grating is used to provide feedback to each emitter in an array, via a series of lenses, at different wavelengths. The laser resonator is formed between the HR coated back facet of the emitter and the output coupler.

WBC thus allows for brightness scaling of an emitter array because all of the laser elements are spatially overlapped at the output coupler, maintaining the output beam quality of a single element while scaling the output power by the number of elements in the