A laser is a device that emits light (electromagnetic radiation) through a process called stimulated emission. Laser light is usually spatially coherent, which means that the light either is emitted in a narrow, low-divergence beam, or can be converted into one with the help of optical components such as lenses. More generally, coherent light typically means the source produces light waves that are in step. They have the same frequencies and identical phase. The coherence of typical laser emission is a distinctive characteristic of lasers. Most other light sources emit incoherent light, which has a phase that varies randomly with time and position. Typically, lasers are thought of as emitting light with a narrow wavelength spectrum ("monochromatic" light). This is not true of all lasers, however: some emit light with a broad spectrum, while others emit light at multiple distinct wavelengths simultaneously.
Uses
Main article: Laser applications
When lasers were invented in 1960, they were called "a solution looking for a problem". Since then, they have become ubiquitous, finding utility in thousands of highly varied applications in every section of modern society, including consumer electronics, information technology, science, medicine, industry, law enforcement, entertainment, and the military.
The first application of lasers visible in the daily lives of the general population was the supermarket barcode scanner, introduced in 1974. The laserdisc player, introduced in 1978, was the first successful consumer product to include a laser, but the compact disc player was the first laser-equipped device to become truly common in consumers' homes, beginning in 1982, followed shortly by laser printers.
Some of the other applications include:
• Medicine: Bloodless surgery, laser healing, surgical treatment, kidney stone treatment, eye treatment, dentistry
• Industry: Cutting, welding, material heat treatment, marking parts
• Defense: Marking targets, guiding munitions, missile defence, electro-optical countermeasures (EOCM), alternative to radar
• Research: Spectroscopy, laser ablation, Laser annealing, laser scattering, laser interferometry, LIDAR, Laser capture microdissection
• Product development/commercial: laser printers, CDs, barcode scanners, thermometers, laser pointers, holograms, bubblegrams.
• Laser lighting displays: Laser light shows
• Laser skin procedures such as acne treatment, cellulite reduction, and hair removal.
In 2004, excluding diode lasers, approximately 131,000 lasers were sold worldwide, with a value of US$2.19 billion. In the same year, approximately 733 million diode lasers, valued at $3.20 billion, were sold.
Examples by power
Different uses need lasers with different output powers. Lasers that produce a continuous beam or a series of short pulses can be compared on the basis of their average power. Lasers that produce pulses can also be characterized based on the peak power of each pulse. The peak power of a pulsed laser is many orders of magnitude greater than its average power. The average output power is always less than the power consumed.
The continuous or average power required for some uses:
• less than 1 mW – laser pointers
• 5 mW – CD-ROM drive
• 5–10 mW – DVD player or DVD-ROM drive
• 100 mW – High-speed CD-RW burner
• 250 mW – Consumer DVD-R burner
• 1 W – green laser in current Holographic Versatile Disc prototype development
• 1–20 W – output of the majority of commercially available solid-state lasers used for micro machining
• 30–100 W – typical sealed CO2 surgical lasers
• 100–3000 W (peak output 1.5 kW) – typical sealed CO2 lasers used in industrial laser cutting
• 1 kW – Output power expected to be achieved by a prototype 1 cm diode laser bar
Examples of pulsed systems with high peak power:
• 700 TW (700×1012 W) – National Ignition Facility, a 192-beam, 1.8-megajoule laser system adjoining a 10-meter-diameter target chamber.
• 1.3 PW (1.3×1015 W) – world's most powerful laser as of 1998, located at the Lawrence Livermore Laboratory
