Open AccessLaser differential confocal ultra-long focal length measurement
Author(s) -
Weiqian Zhao,
Ruoduan Sun,
Lirong Qiu,
Dingguo Sha
Publication year - 2009
Publication title -
optics express
Language(s) - Uncategorized
Resource type - Journals
SCImago Journal Rank - 1.394
H-Index - 271
ISSN - 1094-4087
DOI - 10.1364/oe.17.020051
Subject(s) - optics , focal length , cardinal point , focus (optics) , confocal , lens (geology) , physics , interference (communication) , observational error , laser , computer science , mathematics , channel (broadcasting) , telecommunications , statistics
A new laser differential confocal focal-length measurement method is proposed for the measurement of an ultra-long focal-length. The approach proposed uses the property of an axial intensity curve that the absolute zero precisely corresponds to the focus of the objective in a differential confocal focusing system (DCFS) to measure the variation in position of DCFS focus with and without a measured ultra-long focal-length lens (UFL), uses the distance between the two focuses to obtain the UFL focal-length, and thereby achieving the precise measurement of ultra-long focal-length. The method has a high focusing precision, a strong anti-interference capability and a short measurement light-path. The theoretical analyses and preliminary experimental results indicate that the relative measurement error is about 0.01% when the method is used for the measurement of back-focus-distance (BFD).