Beam Angle Interferometer (BAI)

Many modern optical systems – including laser-scanning microscopes, semiconductor inspection systems, lithography equipment and precision metrology instruments – require extremely stable laser beam pointing. Angular beam drifts of only a few microradians or even nanoradians can significantly degrade positioning accuracy, imaging quality and measurement precision.

Existing beam angle sensors typically employ quadrant photodiodes or position-sensitive detectors. Their performance is often affected by laser intensity fluctuations, beam profile variations and detector calibration. Other interferometric methods generally monitor the motion of a single interference feature or require complex optical arrangements.

The patented technology introduces a fundamentally different approach for beam angle measurement. The incoming coherent laser beam is split into two or more coherent partial beams using an interferometer. After recombination, the beams generate a high-contrast interference pattern consisting of many intensity maxima and minima recorded by a camera.
Instead of tracking a single interference fringe, the system determines the average displacement of a large number of interference maxima simultaneously. This statistical evaluation improves angular measurement sensitivity approximately with the square root of the number of detected fringes while maintaining excellent robustness against noise.

A focusing optic positioned before or within the interferometer makes the interference pattern sensitive primarily to angular changes of the incident beam while substantially suppressing sensitivity to lateral beam translations. As a result, the system directly measures beam pointing rather than beam position.

• Exceptional angular sensitivity reaching nanoradian-level beam pointing detection
• Higher accuracy through evaluation of numerous interference periods
• Robust operation against intensity and beam profile variations
• Simple optical implementation using commercially available components
• Flexible system design with several interferometer configurations
• High-speed real-time operation
• Easy integration into existing laser systems
• Scalable architecture for laboratory and industrial environments.

• Laser beam stabilization systems
• Laser-scanning microscopes
• Semiconductor lithography
• Wafer inspection
• Coordinate measuring systems
• Optical metrology
• Industrial laser processing
• Precision alignment systems
• Free-space optical communication
• Scientific laser instrumentation
• Aerospace optical systems
• Precision manufacturing

• DE502019010307D1
• EP3871021B1 (validated in DE, FR and GB)
• US12104902B2