ABSTRACT
A. N. Dharamsi, J. App. 71, 2092, 1992
We discuss a new technique for Q-switching lasers by inducing reflectivity changes in one of the cavity's
multilayer-coated mirrors. This mirror is such that, under normal operation,
the constructive interference condition is not satisfied, and it therefore has
a low reflectivity. Towards the end of the laser gain-pumping pulse, suitably
tuned radiation from a short pulse visible/uv laser is shone upon the mirror,
resulting in changes in layer thicknesses and layer indices of refraction, such
that the interference condition is satisfied. In this manner, the cavity Q may
be switched in a short time interval (picoseconds) from a low to a high value.
The mechanisms by which the induced changes occur are discussed, and
calculations of reflectivity as a function of layer thicknesses and indices of
refraction are presented. A general design criterion for successful
implementation of the technique is given, along with some specific examples.
Estimates of the required characteristics of the external, change-inducing
laser are also provided. In principle, the method can be applied to any laser
cavity, including the recently demonstrated soft X-ray multipass laser
cavities, and would find use in many other situations where currently available
techniques do not work. We find the lower bound on the wavelength of the laser
line which can be Q-switched in this manner to be between 200 to 400 Å.
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