Focal Volume Characterization of a Laser Scanning System

Abstract

Knife edge testing of a focused laser beam is a well-known method of observation of the position of focus. When this test is paired with pinhole scanning, a representation of the focal volume can be observed. These two methods are discussed and applied to an optical system that mimics laser-induced refractive index change (LIRIC), a femtosecond micromachining system developed at the University of Rochester to write diffractive patterns into ophthalmic hydrogels for vision correction. The focused, 405 nm, single-mode diode laser beam is modeled as Gaussian with a beam waist of 1.5 μm, and the experimentally measured waist was found to be between 8 μm. The beam quality is assessed in terms of Gaussian beam waist and the estimated beam quality factor M2, and the possibility of full characterization of the focal volume is explored. An f-theta lens is used to scan the beam, and the properties of f-theta lenses are discussed and modeled.