The disclosure describes aspects of laser cavity optical alignment, and more particularly, in situ alignment of optical devices in an optical system for replacement or upgrade. In one aspect, a method for optical alignment in an optical system is described that includes providing, via a positioning system, an optical beam to measure surface features and position of a first device under test (DUT), removing the first DUT from the optical system, placing a second DUT in the optical system at substantially the same position from which the first DUT was removed, providing, via the positioning system, an optical beam to measure surface features and position of the second DUT, aligning the second DUT based on the measurements made of the first DUT and the second DUT, and verifying operation of the second DUT in the optical system. The DUT can be an optical device such as an output optical coupler.