Spherical vs Aspheric Lens Selection Guide

Topic: Lens Geometry, Aberration Control, System Cost Trade-off

Overview

Spherical and aspheric lenses are widely used for collimation, focusing and imaging in machine vision, sensing and low-power laser systems. The core difference lies in surface curvature: spherical lenses follow a constant radius, while aspheric lenses use continuously varying curvature to correct optical aberrations.

Spherical Lenses

• Surface profile: constant radius of curvature
• Advantages: lower fabrication cost, fast lead time, easy inspection and qualification
• Limitations: inherent spherical aberration; performance drops at high NA or wide bandwidth
• Common materials: BK7 / K9, fused silica, sapphire, ZnSe
• Typical use: simple collimation, low-precision imaging, general-purpose focusing

Aspheric Lenses

• Surface profile: polynomial aspheric curve
• Advantages: effective correction of spherical aberration; fewer elements to achieve the same optical target; compact optical path
• Limitations: higher polishing & metrology cost, tighter manufacturing tolerance, longer lead time
• Common materials: BK7, fused silica, IR-grade substrates
• Typical use: high-speed machine vision, fiber coupling, high-NA laser focusing, compact imaging modules

Selection Checklist for Engineers

• System NA and required spot size
• Working wavelength range (visible, near IR, CO₂ laser)
• Allowed assembly space and element count
• Budget and production volume
• Environmental conditions: temperature, humidity, abrasion risk

Coating Recommendation

Single-layer or broadband AR coatings are standard for spherical lenses. Aspheric lenses usually require wavelength-matched AR coatings; coating uniformity on complex aspheric surfaces must be confirmed before mass production.

Beam Focusing Lens Design for CO₂ Lasers

Topic: 10.6 μm CO₂ Laser Optics, ZnSe Lens, Laser Damage Threshold, Focus Spot Stability

Overview

CO₂ lasers operate at 10.6 μm infrared wavelength. Focusing lenses for CO₂ laser cutting, marking and welding require infrared transmissive substrates, low-absorption AR coatings and careful thermal management. BK7, fused silica and sapphire are not suitable for 10.6 μm transmission; CVD ZnSe is the dominant material for high-power CO₂ laser focusing lenses.

Key Design Parameters

• Focal length: determines spot size and working distance
• Clear aperture: must be larger than incoming beam diameter with margin for beam wander
• Surface figure and irregularity: directly affect beam quality M²
• Laser Damage Threshold (LDT): specified under 10.6 μm continuous-wave condition
• AR coating: low absorption 10.6 μm anti-reflection coating, single-side or double-side

Material Notes

CVD ZnSe is preferred for most CO₂ laser focusing lenses thanks to high transmittance at 10.6 μm and low thermal absorption. Multi-spectral ZnS can be considered for low-power systems where environmental durability is prioritized, but absorption at 10.6 μm is higher than ZnSe.

Common Risks to Avoid

• Insufficient aperture margin leading to beam clipping
• Coating absorption causing thermal lensing and spot drift
• Poor mounting stress introducing wavefront distortion
• Contamination on optical surface accelerating laser-induced damage

Specification Suggestions for RFQ

When submitting drawings for CO₂ laser focusing lenses, provide laser power, beam diameter, required focal length, operating environment and required coating grade. We will evaluate LDT, surface quality and mounting structure together.