Submicrometric absolute positioning of flat reflective surfaces using Michelson interferometry

We present a Target Positioning Interferometer (TPI), a system that uses variations of the wavefront curvature to position solid reflective surfaces with submicrometric precision. The TPI is a Michelson interferometer into which a lens is inserted in the target arm and the mirror of the reference arm is slightly tilted. The TPI configuration presented in this work allows us to position the surface of a reflective target on a beam focus within an uncertainty of 350 nm (2σ) in a subsecond timeframe, using a lens with a numerical aperture of NA = 0.20. We support our experimental findings with numerical simulations of the interference pattern using the ABCD matrices’ method, allowing us to define scaling laws for using the TPI with different optics and environments, as well as suggestions to improve the TPI accuracy and adapt the system to different applications. This system is very well suited for accurate and repeatable target positioning used in laser-driven ion acceleration, where a precise alignment is key to optimize the proton acceleration mechanism.