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Hello everyone. Assalamu Alaikum. Welcome to my presentation about laser.
The laser I have chosen to present is the Quantum Cascade Laser. It was first demonstrated at Bell laboratories in 1994 by Faist and others.
Here is the overview of my entire presentation.
On the left we see the basic electronic devices that exploit waves over 300 micro meter. On the right is the usual diode laser that emits between 0.3 to 3 micro meter. In between there is this quantum cascade laser which is a compact widely tunable light source between 3 to 300 micro meter.
This is the overview of infra-red spectrum. Mid infra-red is between 3 to 25um. And Far IR is between 60 to 300um.
This is the band diagram of a typical diode laser…
Quantum cascade lasers are comprised of dozens of alternating layers of semiconductor material, forming quantum energy wells that conﬁne the electrons to particular energy states. As each electron traverses the lasing medium it transitions from one quantum well to the next, driven by the voltage applied across the device. At precisely engineered locations, called the “active region,” the electron transitions from one valence band energy state to a lower one and in the process emits a photon. The electron continues through the structure and when it encounters the next active region it transitions again and emits another photon. The QCL may have as many as 75 active regions, and each electron generates that many photons as it traverses the structure.
Lets see a short animation on how electron moves in a quantum cascade laser.
Molecular Beam Epitaxy is used for the fabrication of QCL.
This is the whole structure of the QCL. The materials, doping concentration and the layer width is given.
As of 2013, this is the list of companies that are providing QCL. MBE = Molecular Beam Epitaxy MOVPE = Metal-Organic Vapor Phase Epitaxy