Confocal Laser Technology: Sub-Micron Thickness for Transparent and Multilayer Materials

When measuring transparent films, glass, liquids, or multi-layer coatings, traditional laser triangulation fails due to surface penetration and multiple reflections. Confocal chromatic sensors solve this by using wavelength-coded light that focuses at different depths. Each layer reflects a specific wavelength, enabling simultaneous measurement of up to 4 layers with 10nm resolution - ideal for lithium-ion battery separators, optical coatings, and pharmaceutical blister films.

1. How Confocal Chromatic Technology Works

A white light source passes through a chromatic lens that focuses different wavelengths at different distances (blue focuses close, red focuses far). When light reflects off a surface, the reflected wavelength indicates the exact distance. For multiple layers, you get multiple reflected peaks - each representing one layer boundary.

2. Measuring Transparent Materials

For a PET film, the sensor sees the top surface (wavelength A) and the bottom surface (wavelength B). Thickness = (distance to bottom) - (distance to top). Unlike triangulation, confocal works on glass, polycarbonate, acrylic, and even wet paint.

3. Multilayer Coating Analysis

Advanced confocal sensors can resolve up to 4 layers simultaneously. Example applications:
- Lithium-ion battery separator: PP/ceramic coating thickness monitoring
- Automotive clear coat + base coat on metal
- Pharmaceutical blister foil: PVC/PE/PVDC layer control
- Optical lens anti-reflective coating stack

Key Insight: Confocal sensors are immune to ambient light, angular tilt up to ±45°, and surface roughness. They achieve 10nm resolution over a 3mm measurement range - 100x better than standard laser sensors.

4. Integration with Extrusion and Coating Lines

LGE's CFS (Confocal Film Sensor) mounts across web lines to measure caliper and coating weight. Output via analog (4-20mA) or real-time Ethernet to extrusion dies or coating heads for closed-loop control. Typical applications include film casting lines, blown film lines, and slot-die coating.

5. Technical Specifications

  • Measurement range: 0.1mm to 10mm per layer
  • Resolution: 10nm (0.01 microns)
  • Layers: Up to 4 simultaneously
  • Standoff: 10mm to 50mm
  • Spot size: 3 to 25 microns
  • Max tilt angle: ±45 degrees
  • Sampling rate: up to 10 kHz

6. Comparison with Other Technologies

  • vs. Laser triangulation: Confocal works on transparent and glossy surfaces; triangulation fails.
  • vs. Ultrasonic: Confocal is non-contact, no gel coupling, works on thin films < 50 microns.
  • vs. Capacitive: Confocal doesn't need conductive target, works at high temperature.

"We replaced an offline lab gauge with LGE's confocal online system. Now we measure every meter of battery separator film instead of one sample per shift. Coating uniformity improved by 35%." - Production Manager, Battery Materials Manufacturer