Understanding Lasers

Chapter 9.11.2: Blue, Violet, and Ultraviolet Diode Lasers (Nitrides)

9.11.2 Blue, Violet, and Ultraviolet Diode Lasers (Nitrides)

One of the top laser breakthroughs of the 1990s was the development of blue diode lasers based on gallium indium nitride (GaInN). As shown on the left side of Figure 9-20, this compound can be used for blue and violet lasers; adding aluminum to the compound extends the band gap well into the ultraviolet, although diode lasers have been demonstrated only to about 340 nm. (LEDs have operated at wavelengths shorter than 280 nm.) The materials are often classed as gallium nitride (GaN) compounds. Some are fabricated on GaN substrates; others are deposited on sapphire (Al2O3) or silicon carbide (SiC) substrates.

So far, the most important applications of GaN materials have been in violet diodes emitting near 405 nm, which are used for high-density optical data storage in Blu-Ray and HD-DVD disks. Longer wavelength visible diode lasers can be made by adding indium and reducing gallium concentration. Blue diodes emitting at 440 nm are standard products and ultraviolet diodes emitting at 375 nm are also available.

Shorter-wavelength ultraviolet lasers become increasingly difficult because it's hard to make good electrical contacts with material containing more aluminum, and efficiency decreases as aluminum content increases. Available powers and device lifetimes drop as wavelength decreases below about 370 nm.

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