Fast 3D form measurement using a tunable lens profiler based on imaging with LED illumination

Area of Science:

• Optics and Photonics
• Metrology
• Micro-manufacturing

Background:

• Accurate 3D shape measurement of micro-parts is crucial for quality control in micro-manufacturing.
• Traditional methods often involve complex setups, mechanical scanning, or limited depth of field.

Purpose of the Study:

• To develop and demonstrate a fast, non-contact 3D shape measurement technique for micro-parts.
• To leverage depth discrimination with LED illumination and a tunable lens for enhanced measurement capabilities.

Main Methods:

• A 4f optical imaging setup incorporating an electrically tunable lens at the Fourier plane.
• Utilizing the limited spatial coherence of LED illumination for depth discrimination.
• Implementing a fast depth scan by adjusting the tunable lens without mechanical movement.

Main Results:

• Successfully measured the 3D form of a tilted optically rough surface and a cold-formed micro-cup.
• Achieved measurement speeds with images captured in under a second.
• Demonstrated a height accuracy of ±1.75 μm (1σ) using a step height standard.
• Observed an extended depth of focus in the millimeter range.

Conclusions:

• The presented technique offers a robust, fast, and eye-safe solution for micro-part 3D shape measurement.
• The system's performance can be further improved by optimizing illumination coherence and numerical aperture.
• This method provides an efficient alternative for metrology in micro-fabrication and related fields.