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SUMMARY:Novel designs and waveguides in terahertz quantum cascade lasers -
  Mr. Yash Shah\, SP Group\, Cavendish Laboratory\, Cambridge
DTSTART:20141117T141500Z
DTEND:20141117T151500Z
UID:TALK55842@talks.cam.ac.uk
CONTACT:Teri Bartlett
DESCRIPTION:20 years since the invention of the quantum cascade laser(QCL)
  and more than a decade since the first terahertz(THz) QCl was realised\, 
 certain issues still remain on the improvement of performance of these las
 ers. QCL\, being a unipolar device\, finds it's analogy with a four level 
 semiconductor system\, there is an injector and collector on either side o
 f the radiative states (upper and lower lasing states) which form reservoi
 rs. The electrons enter the upper lasing level through the injector and ar
 e recycled by the collector. This forms one period in the QCL. A cascade o
 f these periods causes one electron to emit n(theoretically) photons where
  n is the number of periods at the designed electric field.The Fabry Perot
  cavity is formed by a waveguide ridge with the and the superlattice struc
 ture forming the gain medium. The facets are atomically cleaved planes and
  serve as the mirrors for the resonant cavity.\n\nIn this talk\, I will pr
 ovide an overview of novel active region designs and waveguides researched
  and the continuing effort to provide a better the performance of THz QCL.
  These QCLs were designed to provide a broadband spectrum\, ~ .65 THz with
  a temperature performance of 105 K. Will dwell further into potential des
 igns that could be optimised to provide a better spectrum at a higher temp
 erature. Will end the talk with ideas on improving the beam pattern with a
 n integrated waveguide as will as working intrinsically on the mode confin
 ed in the active region.\n
LOCATION:Mott Seminar Room\, Cavendish Laboratory\, Department of Physics
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