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While a single or narrow line wavelength spectrum can come from both, one uses feedback to stimulate emission (The lasers uses some kind of feedback like a op amp uses a feedback resistor for gain this usaually takes the form of a feedback mirror set). One is an output coupler and the other a high reflector. The LED does not use feedback.
A laser (from the acronym Light Amplification by Stimulated Emission of Radiation) is an optical source that emits photons in a coherent beam. The verb to lase means "to produce coherent light" or possibly "to apply laser light to", and is a back-formation of the term laser.
Laser light is typically near-monochromatic, i.e. consisting of a single wavelength or color, and emitted in a narrow beam. This is in contrast to common light sources, such as the incandescent light bulb, which emit incoherent photons in almost all directions, usually over a wide spectrum of wavelengths.
Laser action is explained by the theories of quantum mechanics and thermodynamics. Many materials have been found to have the required characteristics to form the laser gain medium needed to power a laser, and these have led to the invention of many types of lasers with different characteristics suitable for different applications.
The laser was proposed as a variation of the maser principle in the late 1950s, and the first laser was demonstrated in 1960. Since that time, laser manufacturing has become a multi-billion dollar industry, and the laser has found applications in fields including science, industry, medicine, and consumer electronics.
LED ::
light-emitting diode (LED) is a semiconductor device that emits incoherent narrow-spectrum light when electrically biased in the forward direction. This effect is a form of electroluminescence. The color of the emitted light depends on the chemical composition of the semiconducting material used, and can be near-ultraviolet, visible or infrared.[1] Rubin Braunstein (born 1922) of the Radio Corporation of America first reported on infrared emission from GaAs and other semiconductor alloys in 1955.[2] Experimenters at Texas Instruments, Bob Biard and Gary Pittman, found in 1961 that gallium arsenide gave off infrared (invisible) light when electric current was applied. Biard and Pittman were able to establish the priority of their work and received the patent for the infrared light-emitting diode. Nick Holonyak Jr. (born 1928) of the General Electric Company developed the first practical visible-spectrum LED in 1962.[3]
There are some differences, but both devices operate on the same principle of having excess electrons in the conduction band of a semiconductor, and arranging it so that the electrons recombine with holes in a radiative fashion, giving off light in the process. What is different about a laser? In an LED, the electrons recombine in a random and unorganized manner. They give off light by what is known as spontaneous emission, which simply means that the exact time and place where a photon comes out of the device is up to each individual electron, and things happen in a random way.
There is another way in which an excited electron can emit a photon however. If a field of light (or a set of photons) happens to be passing by an electron in a high energy state, that light field can induce the electron to emit an additional photon through a process called stimulated emission. The photon field stimulates the electron to emit its energy as an additional photon, which comes out in phase with the stimulating field. This is the big difference between incoherent light (what comes from an LED or a flashlight) and coherent light which comes from a laser. With coherent light, all of the electric fields associated with each phonon are all exactly in phase. This coherence is what enables us to keep a laser beam in tight focus, and to allow it to travel a large distance without much divergence or spreading out.
The main difference between LASERs and LEDs is the operation of energy emission. In case of LEDs, the generated lights are based on the Spontaneous Emission. But, LASERs rely on the Stimulated Emission. And how they are different as sanjiv said before.
the basic principle of emission is diferent
laser is simulated and LED is spontaneous.
apart from that laser has the qualities like coherence, directionality.
while LEDs are very cheap, and lasers are very powerful.
It comes from Stimulated Emission of photons in a diode(photo).
It (As its name suggests - Light amplification by Stimulated emission of Radiation) has more power .
It is coherent in nature .
it is costly .
LED
It comes from Spontaneous emission of photons in a diode(photo).
It has less power.
It is mainly incoherent or noncoherent.
it is cheaper .
While a single or narrow line wavelength spectrum can come from both, one uses feedback to stimulate emission (The lasers uses some kind of feedback like a op amp uses a feedback resistor for gain this usaually takes the form of a feedback mirror set). One is an output coupler and the other a high reflector. The LED does not use feedback.
Single or narrow line wavelenght on LEDs ? On almost all LEDS there is around 10-20nm around central wavelenght and a few spectral lines.
Remarks for other people which has answered:
Laser have always bigger power than LEDs ? There are hundred of lasers of about 3...5mW while almost all IR LED's (920nm or 960nm) have around 8...10mW.
Nowadays there are common LEDS with about 10..30mW ouitput power.
Output power is not a comparable issue between small power lasers and LEDs. Not the same with the monochromaticity, focus and modulation speed.
laser diode is a laser where the active medium is a semiconductor similar to that found in a light-emitting diode. The most common and practical type of laser diode is formed from a p-n junction and powered by injected electrical current. These devices are sometimes referred to as injection laser diodes to distinguish them from optically pumped laser diodes, which are more easily produced in the laboratory.
A light-emitting diode (LED) is a semiconductor device that emits incoherent narrow-spectrum light when electrically biased in the forward direction of the p-n junction. This effect is a form of electroluminescence. An LED is a small extended source with extra optics added to the chip that makes it emit a complex radiation pattern
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