A method of establishing the properties of a three-mirror laser, where the
properties are the three mirror reflectivities and the two cavity lengths
(i.e., the separations between the mirrors). Initially, a conventional
two-mirror laser is designed, providing values for a laser cavity length
and for power reflectivities of a high reflectance mirror and an
effective mirror. Then, the effective mirror is replaced by a pair of
mirrors with a separation equal to an external cavity length, and
reflectivities that may be varied in tandem so that when the reflections
from the pair of mirrors are in phase, the combined power reflectivity of
the pair of mirrors is equal to that of the effective mirror. A quantity
.GAMMA. is defined to measure the relative shift in power reflectivity
between the pair of mirrors. .GAMMA. is varied over all its possible
values, and various criteria are evaluated with respect to .GAMMA..