I. Basics: What Are Optical Lenses?
Optical lenses are components that alter the direction of light propagation through refraction or reflection.
Primary functions:
Focusing, collimating, beam expansion, beam reduction, imaging, and protection.
Common basic shapes:
a.Convex Lens:
Thick in the center and thin at the edges, causing light to converge (focusing at a focal point).
b.Concave Lens:
Thin in the center and thick at the edges, causing light to diverge (spreading outward from the center).
II. Common Types of Optical Lenses in the Laser Industry
Protective Windows:
1.Location: Installed at the bottom of the laser head to shield internal lenses from contamination or damage by debris.
2.Features: High transmittance, heat-resistant, and dirt-resistant.
3.Common materials: Quartz, fused silica.
1.Function: Concentrate laser beams into small spots to increase energy density, used for cutting, welding, marking, etc.
2.Common focal lengths: 50mm, 100mm, etc.
3.Material: Typically ZnSe (zinc selenide), ideal for CO₂ lasers at 10.6μm.
1.Function: Convert divergent laser beams into parallel light for subsequent focusing.
2.Applications: Fiber lasers and laser heads.
Function: Increase laser beam diameter while reducing divergence angle, improving processing quality.
III. Comparison of Optical Lens Materials
| Material | Characteristics | Common Applications |
| Quartz | High transmittance, heat-resistant, corrosion-resistant | Protective windows, scanning mirrors |
| Fused Silica | Ultra-low thermal expansion, high purity | High-power lasers, ultrafast lasers |
| K9 Glass | Low cost, easy to process, but poor heat resistance | General imaging lenses, measuring equipment |
| ZnSe (Zinc Selenide) | High transmittance for CO₂ lasers (10.6μm), fragile, toxic | CO2 laser cutting, CO2 laser marking |
| Sapphire | Extreme hardness, scratch-resistant | High-end windows, protective covers |
IV. Types of Optical Lens Coatings
Optical lenses often feature specialized coatings to enhance performance:
1.Anti-Reflective (AR) Coating: Reduces surface reflection, improves light transmission. Available in single or multi-band options.
2.High-Reflective (HR) Coating: Reflects nearly all incident light within a specific wavelength range.
3.Beam Splitter Coating: Splits light into specific ratios (e.g., 50% reflection + 50% transmission).
4.DLC (Diamond-Like Carbon) Coating: Scratch- and corrosion-resistant, used for protective lenses.
V. Application Examples of Optical Lenses
| Application Scenario | Required Lens Types |
|---|---|
| Laser cutting machines | Focusing lenses, protective windows, collimating lenses |
| Handheld laser welders | Focusing lenses, protective windows |
| Laser marking machines | Beam expanders, focusing lenses, field lenses |
| Medical lasers (e.g., dermatology) | Focusing lenses, protective windows |
| Microscopes, telescopes, camera lenses | Convex/concave lenses, spherical lenses |
VI. Optical Lens Selection Guide
1. How to Choose Focal Length?
Focal length determines a lens’s ability to focus laser beams, affecting spot size and processing depth.
| Focal Length | Characteristics | Recommended Applications |
|---|---|---|
| Short (50mm, 75mm) | Fast focusing, small spot size, high energy density | Thin sheet cutting, precision welding |
| Medium (100mm, 125mm) | Balances speed and cutting depth | Medium-thickness materials |
| Long (150mm, 200mm) | Deeper focus, suitable for deep penetration | Thick plate cutting, deep welding |
Simple rule:
Thin materials: Short focal length.
Thick materials: Long focal length.
2. How to Choose Material?
Consider laser wavelength and power density:
| Characteristics | Recommended Applications | ||
|---|---|---|---|
| Quartz | 1064nm (fiber lasers) | Heat-resistant, moderate cost, high damage threshold | Fiber laser cutting/welding |
| ZnSe | 10.6μm (CO₂ lasers) | High IR transmittance, fragile | CO₂ laser focusing lenses |
| Sapphire | 1064nm & visible light | Extreme hardness, scratch-resistant | High-end protective windows |
| Fused Silica | 266nm/355nm (UV), 532nm (green), 1064nm | High purity, UV-resistant | UV laser marking, green laser processing |
3. Power Requirements for Lenses
Higher laser power demands better heat resistance and laser damage thresholds.
| Laser Power Range | Recommended Lens Configuration |
|---|---|
| 0–1500W | Quartz protective window + standard AR-coated focusing lens |
| 1500W–3000W | High-heat-resistant quartz + high-power focusing lens |
| Above 3000W | Premium quartz + HR/anti-contamination coated lens |