82
3 Applications of Zero-Index Metamaterials
Fig. 3.21 Construction of a basic optical resonator consisting of two mirrors enclosing a slab of
an active medium between them
In modern times of low power devices, it is desirable that th should be as low as
possible. The lower the th , the lesser the power required to achieve it! For example,
a Ruby laser has th of the order of 10
17 cm
−3 , while that of a He-Ne laser is of the
order of 10
8 cm
−3 . Clearly, a He-Ne [180] laser works at a lower power supply than a
Ruby laser [178], and hence is a preferred choice. significantly depends on
t c , and t s p, and hence by using a cavity with a longer cavity lifetime (t c ) and an active
medium with a smaller relaxation time (t sp ) and a narrower absorption bandwidth
( the threshold value can be reduced significantly. Another important parameter
which could not be manipulated earlier but is now controllable by using metamaterial
is the refractive index. Refractive index can play a major role in deciding the value
of threshold, since th is directly proportional to cube of n 0 , which means that by
reducing n 0 by a factor of 10, th can be reduced by a factor of 1000, as was seen in
case of A/B ratio. In fact, if refractive index is diminished down to almost zero, th
will also be pushed to negligibly small value. In other words, an active medium with
effectively zero refractive index will have no threshold value of population inversion
to begin lasing action, which means the advent of thresholdless lasers working on
extremely low powers [181, 182]. Such laser sources can prove revolutionary in
the near future, which is expected to be full of nanotechnology and nanophotonic
devices. The potential of zero-index metamaterials in laser cavities is promising and
if implemented successfully will be revolutionary, and hence is worth investigating.
3 Applications of Zero-Index Metamaterials
Fig. 3.21 Construction of a basic optical resonator consisting of two mirrors enclosing a slab of
an active medium between them
In modern times of low power devices, it is desirable that th should be as low as
possible. The lower the th , the lesser the power required to achieve it! For example,
a Ruby laser has th of the order of 10
17 cm
−3 , while that of a He-Ne laser is of the
order of 10
8 cm
−3 . Clearly, a He-Ne [180] laser works at a lower power supply than a
Ruby laser [178], and hence is a preferred choice. significantly depends on
t c , and t s p, and hence by using a cavity with a longer cavity lifetime (t c ) and an active
medium with a smaller relaxation time (t sp ) and a narrower absorption bandwidth
( the threshold value can be reduced significantly. Another important parameter
which could not be manipulated earlier but is now controllable by using metamaterial
is the refractive index. Refractive index can play a major role in deciding the value
of threshold, since th is directly proportional to cube of n 0 , which means that by
reducing n 0 by a factor of 10, th can be reduced by a factor of 1000, as was seen in
case of A/B ratio. In fact, if refractive index is diminished down to almost zero, th
will also be pushed to negligibly small value. In other words, an active medium with
effectively zero refractive index will have no threshold value of population inversion
to begin lasing action, which means the advent of thresholdless lasers working on
extremely low powers [181, 182]. Such laser sources can prove revolutionary in
the near future, which is expected to be full of nanotechnology and nanophotonic
devices. The potential of zero-index metamaterials in laser cavities is promising and
if implemented successfully will be revolutionary, and hence is worth investigating.