![\"Beam](\"\/blog\/wp-content\/uploads\/2017\/01\/2017-2-1-p1-e1485786996966.jpg\")
<\/a><\/p>\nThe image above (from BeamGage<\/a>) is a two-dimensional display of power in space.\u00a0 Color is used to represent intensity.<\/p>\n So, where should the line be drawn?\u00a0 What is the beam size?\u00a0 Is it where the blue ends?\u00a0 The purple?<\/p>\n Gaussian beams have a bell-shaped intensity curve. That means that we can\u2019t just say the beam width is measured between the ends of the beam, since a Gaussian beam never ends<\/em>.\u00a0 In reality, at a certain point the hypothetical laser power is so low as to be drowned out by ambient noise.\u00a0 But that doesn\u2019t help answer the question of where to measure beam width.<\/p>\n There are several ways to define beam width for Gaussian beams<\/a>, but here are a few:<\/p>\n 1\/e2<\/sup><\/strong><\/p>\n This is probably the most commonly used in research circles.\u00a0 By the 1\/e2<\/sup> method, you measure beam width between the two points where the intensity is 1\/e2<\/sup> of the peak value.\u00a0 Clear definition, but only about 86% of the laser power is contained within the 1\/e2<\/sup> width.<\/p>\n (Our new \u201cpower through aperture\u201d calculator<\/a> lets you easily see how much of the laser will pass through a given area.\u00a0 For example, choose a beam width of 8 mm and aperture of 10 mm.\u00a0 Common sense states that 100% should pass through, since 10 > 8.\u00a0 However, don\u2019t forget that only 86% of the beam is contained within the 8 mm beam diameter.\u00a0 So how much of the laser is in 10 mm?\u00a0 Check the calculator<\/a> for the answer.)<\/p>\n FWHM<\/strong><\/p>\n Used most often in industrial contexts, this is the simplest method to understand. \u00a0Full-width, half max.\u00a0 That is to say the diameter measured between the two points at which the intensity is half the peak.\u00a0 (Full width is meant to indicate beam diameter rather than half width, which would be the radius.)<\/p>\n D4\u03c3<\/strong><\/p>\n D4\u03c3 stands for distance between the 4\u03c3 values, i.e., four times the standard deviation.\u00a0 This is the ISO standard method for maximum accuracy.\u00a0 However it can overly weight the wings if not using proper background subtraction, such as UltraCal:<\/p>\n<\/a><\/p>\n