# Focal Spot Size Calculator for Gaussian Laser Beams

Use this calculator to get the size and location of your Gaussian laser beam waist at focus, as well as the Rayleigh range.   Input parameters are explained further by mousing-over the information (i) icon.
For a simpler calculator go to: Focusability calculator

Check our other laser measurement tools:
Sensor Finder  • Laser Peak Power Calculator  • Laser Focal Spot Size Calculator  • Laser Power Through Aperture Calculator  • Laser Focusability Calculator

﻿ Gaussian Thin Lens Calculator

 λ Wavelength This field is required. Please enter your laser wavelength, in nanometers. nm * fl Lens focal length This field is required. Please enter your lens focal length, in millimeters. mm * M² Gaussian beam propagation factor This field is optional. If you leave it blank, an M-Squared value of 1.0 will be assumed (ideal beam). θ Beam divergence (half angle) Enter the laser beam half-angle divergence, in milliradians. If you don't have this value, it can be calculated from d₀. mRad d Beam diameter at aperture (d=2ω) Enter the diameter of the laser beam at exit aperture. If you don't have this value, it can be calculated from d₀, z. mm d₀ Beam waist diameter (d₀=2ω₀) Enter the diameter of the laser beam at its initial waist. (Note this may be a virtual focal point.)If you don't have this value, it can be calculated from θ. If you don't have θ mm s Distance from d₀ to lens Enter the distance from the initial beam waist (d₀) to the lens. If you don't have this value, it can be calculated from p, z. mm z Distance between d₀ and exit aperture Enter the distance from the initial beam waist (d₀) to the exit aperture. If you don't have this value, it can be calculated from d, d₀. If you don't have them either, it can be calculated from p, s. mm p Distance from exit aperture to lens Enter the distance from the laser exit aperture to the lens. If you don't have this value, it can be calculated from z, s. mm

Note: Some of the input parameters are mutually dependent and the software will calculate them automatically when possible. A calculated parameter will be locked for editing. If you wish to unlock it, you must erase the value entered which caused it to be locked. Example: A and B are mutually dependent. You enter a value in A and B is calculated and locked. You wish now to edit B. You must first delete A, upon which B will be erased an unlocked.

This calculator uses Sidney Self's equations for focusing spherical Gaussian beams.

Want to measure the actual beam size? Try a BeamTrack Power/Position/Size sensor.
(Or a full-fledged beam profiler, for a complete picture of your laser beam.)

 Read More About This The Challenge of Focus Shift in High Power Laser Material Processing How to Select Power/Energy Sensors Laser Beam Optics Calculators Measure Laser Spot Size & Power Density BeamGage Tutorial: Spot Size and Divergence Measuring beams coming out of a fiber