Laser Brightness
Laser brightness is the most important single number characterising a laser's utility for focusing and long-range applications. Unlike raw power, brightness accounts for beam quality — a 1 kW multimode laser can be far less bright than a 10 W single-mode laser.
Key Formulas
Where P is laser power, w₀ is beam waist radius, θ is half-angle divergence, and the minimum BPP equals λ/π for an ideal Gaussian beam.
How to Use
- Select a calculation mode.
- Enter power and beam parameters.
- Click Calculate for brightness and beam quality metrics.
Examples
HeNe laser (1 W, w₀ = 0.5 mm, θ = 0.4 mrad)
B = 1 / (π² × (5×10⁻⁴)² × (4×10⁻⁴)²) ≈ 2.5 × 10¹⁰ W/(m²·sr)
FAQ
What is laser brightness?›
Laser brightness (more precisely, spectral radiance or just radiance) quantifies how much power a laser emits per unit area per unit solid angle. It's the key figure of merit that determines how tightly a beam can be focused and how far it can propagate.
What is the Beam Parameter Product?›
The BPP = w₀·θ (waist radius × half-angle divergence) is a measure of beam quality. For an ideal Gaussian beam, BPP = λ/π. Lower BPP means better focusability. The BPP is invariant through lossless optics.
How does M² affect brightness?›
M² (beam quality factor) increases the BPP by factor M² compared to ideal. Since brightness scales as 1/BPP², brightness scales as 1/M⁴. A beam with M² = 2 has only 1/16th the brightness of an ideal beam.
Why is brightness conserved?›
Brightness conservation is a fundamental consequence of the second law of thermodynamics (Liouville's theorem in optics). No passive optical system can increase the brightness — it can only be reduced by losses or aberrations.
Sources
Author & technical reviewer
Manish Kumar
PhysicsCalcs tools are reviewed with an educational focus: clear formulas, transparent assumptions, and practical context for students and science learners.
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