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 mousingover the information (i) icon.
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 MSquared value of 1.0 will be assumed (ideal beam).  
θ 
Beam divergence (half angle) 
Enter the laser beam halfangle 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 

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 

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 

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 

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 
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 fullfledged beam profiler, for a complete picture of your laser beam.)
Check our other laser measurement calculators: