Phase-sensitive optical amplifier

The application of Armstrong's super-regenerative principle to a laser amplifier shows that it is possible to control the phase of even a low-gain He-Ne laser amplifier by injecting as few as four or five photons just after the laser is turned on and while it goes through threshold. Estimation of the uncertainties in determining the level of the injected signal and the phase of the laser output indicates that measurements approaching the limit delta-n-delta phi is approximately 1/2 may be possible.