  When the background density in a bounded plasma is modulated in time,
discrete modes become coupled. Interestingly, for appropriately chosen
modulations, the average plasmon energy might be made to grow in a ladder-like
manner, achieving up-conversion or down-conversion of the plasmon energy. This
reversible process is identified as a classical analog of the effect known as
quantum ladder climbing, so that the efficiency and the rate of this process
can be written immediately by analogy to a quantum particle in a box. In the
limit of densely spaced spectrum, ladder climbing transforms into continuous
autoresonance; plasmons may then be manipulated by chirped background
modulations much like electrons are autoresonantly manipulated by chirped
fields. By formulating the wave dynamics within a universal Lagrangian
framework, similar ladder climbing and autoresonance effects are predicted to
be achievable with general linear waves in both plasma and other media.
