Two methods for measuring laser beam diameter

Abstract

Two methods for measuring beam diameter are described with the derivation of the equations that make them valid. These methods are the aperture method and the knife edge technique. These methods have been used for decades; however, many do not have a firm grasp of the basic equations that make the methods valid and therefore cannot use and modify the methods with confidence to produce the desired results. The text derives the equations from basic science and mathematics to clarify the underlying concepts of the methods.

Enhanced S2 Fluorescence from a Free-Base Tetraphenylporphyrin Surface-Mounted Metal Organic Framework

“…Because the laser pulse at 400 nm excites the blue edge of the Soret band, higher vibrational levels of the S 2 state , or levels of the S 3 state are populated . Apart from the spectral changes observed at early times, a long-lived (>2 μs) time component corresponds to triplet state absorption …”

A multi-method approach for beam characterization of microfading testers used in cultural heritage conservation science

“…This method uses a relatively smaller size pinhole relative to the expected diameter of the investigated beam. The pinhole is scanned across the beam with the aim of accurately locating its center [23]. The intensity of the beam is measured over the aperture of the pinhole and a plot of intensity as function of beam radius is obtained by scanning the pinhole through the beam.…”

“…Another commonly used conventional way of determining the beam diameter of a point device is the aperture method. The beam diameter may be determined for a Gaussian beam by positioning an aperture in the center of the beam and measuring the fraction of emitted power passing through the aperture [23].…”

Simple precision measurements of optical beam sizes

“…The knife-edge method is somewhat cumbersome, as the aperture has to be moved across the beam in a highly controlled fashion, requiring translation stages or motorized slits. Theory for the knife edge and aperture method is well presented for Gaussian, elliptical and rectangular beams [7]. For high power laser beams, thermal effects have been utilized where the spot temperature is monitored with time and compared with the equilibrium temperature to estimate the beam diameter [8].…”