Prabhakar Pradhan 's work on Mirrorless Random Laser
Mirrorless Coherent Random Lasers
(Pradhan and Kumar's proposal for new type of lasers)
There are two important and well known effects based on coherent
scattering of waves in condensed matter:
(1)Coherent Back Scattering (CBS)
is responsible for disorder induced localization (i.e. Anderson
localization) in a disordered
medium; and
(2) Coherent Amplification (CA)
is responsible for
photons/light amplification (stimulated) in an amplifying medium (e.g.
laser, maser).
These two effects have been studied independently in great details.
We have proposed that the combination of the
above two
coherent phenomenas
[(1) CBS , and (2) CA ]
brings an interesting aspect of light amplification using localization and
showed possibility of "Mirrorless Random Laser" in a coherently amplifying
disordered medium. Coherent nature of the amplification does not affect
the coherent back scattering which is responsible for localization.
Now light is more amplified in interplay between localization and
amplification, and the system can show lasing action
(by non resonant feed back by localization)
where localization gives the necessary confinement
of a virtual high Q cavity (whose lenght is order of localization lenght)
for the lasing action. The proposal has been theoretically supported
(by differnt model calculations), verified and extended by
several groups, and most recent experiments by
Hui Cao's group at Northwestern University
strongly support our proposal/prediction.
The paper where we first show the possibility of mirrorless
laser using localization
"Localization of light in coherently amplifying random media",
Prabhakar Pradhan, N. Kumar,
Phys. Rev. B50, 9644(1994)[pdf] .
See for details,
"Enhancement of coherent light amplification using Anderson
localization",
Prabhakar Pradhan,
cond-mat/9807312[pdf].
Recent Highlights/Reviews on Our Work on Mirroless Lasers
A nice popular article on "Mirrorless Lasing Action" which
describes : coherent light amplification with coherent feedback due to
Anderson localization of light