Laser Focal Spot Size Calculator
Calculate diffraction-limited focal spot size, depth of focus, and Rayleigh range for laser focusing systems. Critical for laser processing, microscopy, and precision optical applications.
Optical Design Tool
Input Parameters
dimensionless
M² = 1 for perfect Gaussian beam ratio
Beam diameter / lens diameter (typically 0.8-1.2) Calculation Results
Focal Spot Characteristics
Spot Diameter (1/e²) - μm
Spot Radius (1/e²) - μm
Numerical Aperture - NA
Depth of Focus
Rayleigh Range - mm
Depth of Focus (2×ZR) - mm
Working Distance - mm
Power Density
Power Density (1W input) - MW/cm²
Intensity Enhancement - ×
System Performance
Calculate to see performance rating
Formula and Theory
Diffraction Limited Spot Size
w₀ = M² × λ × f / (π × w)
Where w is the input beam radius at lens
Numerical Aperture
NA = w / (2 × f)
For air (n=1), limited by lens diameter
Rayleigh Range
ZR = π × w₀² / (M² × λ)
Distance over which spot area doubles
Power Density
I = 2P / (π × w₀²)
Peak intensity for Gaussian beam
Understanding Focal Spot Size
- Diffraction Limit: Minimum achievable spot size determined by wavelength and numerical aperture
- Beam Quality: M² factor determines how close to diffraction limit the system performs
- Filling Factor: Ratio of beam size to lens aperture affects spot size and quality
- Rayleigh Range: Axial distance where beam remains well-focused
- Numerical Aperture: Measure of light-gathering ability and resolution
Applications
Laser Material Processing
Optimize cutting, welding, and drilling processes by controlling spot size and power density.
Laser Microscopy
Design high-resolution imaging systems with optimal focal spot characteristics.
Optical System Design
Select appropriate lenses and beam expanders for specific focusing requirements.
Laser Ablation
Calculate threshold intensities and optimize pulse energy for material removal.