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Blue laser

Laser which emits light with blue wavelengths

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Blue lasers can be produced by:

Lasers emitting wavelengths below 445 nm appear violet, but are nonetheless also called blue lasers. Violet light's 405 nm short wavelength, on the visible spectrum, causes fluorescence in some chemicals, like radiation in the ultraviolet ("black light") spectrum (wavelengths less than 400 nm).

History

Prior to the 1960s and until the late 1990s, gas and argon-ion lasers were common and suffered from poor efficiencies (0.01%) and large sizes.

In the 1960s, advancements in sapphire creation allowed researchers to deposit GaN on a sapphire base to create blue lasers, but a lattice mismatch between the structures of gallium nitride and sapphire created many defects or dislocations, leading to short lifespans (<10 hours) and low efficiency (<1%).

Additionally, gallium nitride (GaN) crystal layer construction proved difficult to manufacture as the material requires high nitrogen gas pressures and temperatures, similar to the environment for creating synthetic diamonds.

In 1992, Japanese inventor Shuji Nakamura, while working at Nichia Chemicals, invented the first blue semiconductor LED using an InGaN active region, GaN optical guide and AlGaN cladding, and four years later, the first low-power blue laser; eventually receiving the Millennium Technology Prize awarded in 2006, and a Nobel Prize for Physics along with Professor Isamu Akasaki, and Hiroshi Amano in 2014 for this invention. The gain medium defects still remained too high (106–1010 defects/cm2) resulting in a low-power laser with a short, < 300 hour lifespan using pulsed excitation.

In the late 1990s, Dr. Sylwester Porowski, at the Institute of High Pressure Physics at the Polish Academy of Sciences in Warsaw (Poland), developed technology to create gallium nitride mono-crystals with high structural quality using magnesium doping to create fewer than 100 defects/cm2 — at least 10,000 times better than prior attempts. In 1999, Nakamura used Polish-produced GaN crystals, creating lasers with twice the yield and ten times the lifespan of his original designs; 3,000 hours at 30 mW.

In the 2000s, Japanese manufacturers mastered the production of a blue laser with 60 mW of power and long lifetimes, making them applicable for devices that read a dense (due to blue's short wavelength) high-speed stream of data from Blu-ray, BD-R, and BD-RE. Semiconductor lasers enabled the development of small, convenient and low-priced blue, violet, and ultraviolet (UV) lasers, which were previously not available, opening the door for many applications.

Today, blue semiconductor lasers either use a sapphire substrate (primarily used by Nichia, which uses a contract manufacturer: Sony), or a GaN mono-crystal substrate (primarily used by TopGaN), both covered with layers of gallium nitride. The GaN optical guide layer of the Nichia devices is formed from active region InGaN quantum wells or quantum dots spontaneously via self-assembly.

Polish technology is considered less expensive than the Japanese, but has a smaller share of the market. Another Polish company creates GaN crystals for use in blue diodes – Ammono, but does not produce blue lasers.

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