Laser pointing stability measured by an oblique-incidence optical transmittance difference technique

We describe an oblique-incidence optical transmittance technique for determining the pointing stability of a laser. In this technique, we follow the angular drift of a monochromatic laser beam by measuring the relative changes in transmittance through a parallel fused quartz window for s and p polarized components of the beam in response to the drift. This method is shown in the present experiment to have the sensitivity to detect angular changes in the range of 2 μ radians (1 μ radian=10^-6 radian). To demonstrate this technique, we measured the angular drifts of two commercial intensity-stabilized He-Ne lasers.