whats differencce stimulated and spontaneous process emission in LED and LASER?
i search much,is there any description mechanic quantum for these process?
thanks for reply.
in a laser there is a resonator that makes the light be all one frequency. in an led there is no resonant structure, and you just get light of many colors.
there are other technical differences, but that is basically it
There are many things more than that.
1. Stimulated emission causes laser action. That is the single factor responsible for all the photons being in the same phase. In a LED, the light is produced by spontaneous emission.
2. The cavity is used to tune the wavelength. Consider a box of side L: it can support only wavelengths such that L=n*lambda/2 where n is an integer.
3. polarization is also important.
i completed:
Light emitting diodes vs. Laser diodes:
LEDs are based on spontaneous emission, and have
1. A broad output beam that is hard to capture and focus
2. A relatively broad spectral profile
3. Low to moderate overall efficiency
4. Moderate to high speed (≈ 1/tmin)
Laser Diodes are based on stimulated emission, and have the opposite characteristics
1. Narrow, highly directed output
2. Sharp, narrow emission spectrum
3. High differential and overall efficiency
4. High to very high speed
Absorption Rate:
Spontaneous Rate:
stimulated Rate:
for more info in about processes see this link
6.772/SMA5111 - Compound Semiconductors
Lecture 20 - Laser Diodes 1 -Outline
http://ocw.mit.edu/courses/electrica.../lecture20.pdf
thank you for seeing my topic
One important point that is being missed is
1. The life time of the excited state. If the life time of the excited state is small, we shall see more of the spontaneous emissions. If the excited state life time is rather long, we shall see more of the stimulated emissions.
I am not so sure about the efficiency, though. What is differential efficiency?