Abstract

Our objective is to assess contemplated optical isolator (Faraday rotator) designs from the point of view of handling incident power loads without generating unacceptable phase distortions. For this purpose, we assume that thermally induced phase aberrations can be described by means of a fourth-order even polynomial,^* which implies that, after refocussing, the irradiance at the original Gaussian focus amounts to¹ For small aberrations, it follows that the degradation in focal intensity is specified by the relation which suggests that, in effect, the isolator "fails" if the RMS spherical aberration exceeds the 2π/14 limit.² The problem we are addressing thus boils down to determining the power level at which the amplitude-weighted variance of δϕ₄r⁴ exceeds the 0.2 limit. In this context, we will first consider the procedure that may allow us to perform this task in a simple but consistent manner for both edge-and face-cooled design candidates. Subsequently, the procedure will be applied to two cases of current interest in designing state-of-the-art optical isolators for CO₂-laser radars.³

© 1987 Optical Society of America