  ALPS II, the Any Light Particle Search, is a second-generation Light Shining
through a Wall experiment that hunts for axion-like particles. It uses two
optical cavities; one on each side of the wall, to first generate light
particles from a very strong intra-cavity optical field and then turn these
particles back into photons in the second cavity called the regeneration
cavity. ALPS II will either detect axion-like particles or provide an upper
limit on their coupling strength to two photons of
$g_{a\gamma\gamma}\leq2\times10^{-11}\text{GeV}^{-1}$. The experiment is
currently transitioning from the design and construction phase to the
commissioning phase with science runs expected to start in 2021. One of the
challenges of ALPS II is that one of the cavities will have to track the length
of the other cavity at the pm level. This paper discusses the possibility of
replacing the regeneration cavity with an active regeneration system which
promises a similar signal to noise ratio. For ALPS II, this is a risk reduction
activity. However, the regeneration cavity in ALPS is fundamentally very
similar to signal recycling in interferometric gravitational wave detectors
(LIGO, VIRGO, GEO, and KAGRA) and the basic idea might very well be applicable
there as well.
