Laser diodes whose unit price has now come below $1, are offered in many wavelengths from ultraviolet to long-wave infrared: the wavelength is determined by the device structure and its semiconductor materials. Unlike LEDs, laser diodes produce a coherent beam of monochromatic light (one wavelength), which remains collimated at long distance as observed with common laser pointers. They also have a higher radiance (brighter) and are more energy efficient compared to LEDs. The physical mechanisms underpinning these differences is the generation of laser light via a process known as stimulated emission, and the amplification of light using an optical cavity between two mirror surfaces. In contrast, LEDs generate light via spontaneous emission and contain no optical cavity.
The power output of a single laser diode can range from milliwatt to multi-watt levels. Individual emitters can be used alone or combined to form more complicated lasers with different properties and applications. Multiple laser diodes can form a laser diode bar for the optical pumping (energy input) of solid-state lasers. Laser diodes integrated into modules with beam shaping optics and control electronics are useful for many applications. The figure below illustrates the addressable market for laser diodes.
During the past three decades, the average power of laser diodes has increased exponentially, while their average price has decreased exponentially. These incredible advances in semiconductor laser technology enable the development of direct diode lasers (DDLs), including high-power direct diode lasers (HPDDLs) that produce multi-kilowatt output power. Dramatic improvements in laser beam quality now enable users to focus the light to a small point, and this revealed DDLs as rapidly evolving tools for metal, plastic and composite processing. Consequently, DDLs and HPDDLs are emerging as major global trends in industrial manufacturing, with Panasonic (Japan) acquiring the HPDDL manufacturer TeraDiode (USA) to enhance their position in the laser material processing market.