  A longitudinal mode-locked state can be converted to a transverse mode-locked
state by exploiting the spectral and spatial filtering of an empty optical
resonator. Carrier and amplitude modulation sidebands were simultaneously
transmitted by the conversion resonator, yielding phase-locked superpositions
of up to five transverse modes. Equivalently, an amplitude-modulated beam was
converted into a beam that periodically moved across the transverse plane.
Precise control over the spatial beam shape during oscillation was gained by
independently altering the set of transverse modes and their respective powers,
which demonstrated an increased level of control in the generation of
transverse mode-locked states.

Optics