Laser multi-reflection differential confocal long focal-length measurement

Area of Science:

• Optics
• Metrology
• Laser Physics

Background:

• Accurate measurement of long focal lengths is crucial for various optical applications.
• Existing methods may face limitations in precision and applicability for extended focal lengths.

Purpose of the Study:

• To introduce a novel Laser Multi-reflection Differential Confocal Focal-length Measurement (LDCFM) method.
• To achieve high-precision measurement of long focal lengths.
• To validate the method's accuracy and uncertainty.

Main Methods:

• Utilizing an optical flat and reflector for repeated beam reflection behind the test lens.
• Leveraging null points of differential confocal response curves to identify convergence points.
• Employing a distance-measuring instrument to track reflector position variations with reflection times.

Main Results:

• The LDCFM method accurately determines convergence point positions.
• Preliminary experiments show a relative expanded standard uncertainty (k=2) of 0.04% for a 9.76 m focal length lens.
• The method demonstrates high precision in long focal length measurement.

Conclusions:

• The LDCFM method provides a reliable and accurate technique for measuring long focal lengths.
• This novel approach enhances precision in optical metrology.
• The LDCFM method offers a new standard for high-precision focal length determination.