Measurement of laser and LED beams for prediction of angular subtense

Abstract

A measurement method has been devised to enable prediction of the propagation characteristics of a wide range of beams from both coherent lasers and incoherent broadband sources. Knowledge of the propagation behaviour of a beam allows measurements to be made of a range of its properties that are required for classification purposes by the laser safety standards. These measurements include estimates of the most hazardous spot size on the retina and therefore the angular subtense of the apparent source. They also enable unambiguous determination to be made of the nominal optical hazard distance.The methods of measurement used in this work stem from the evolving ISO Standards for the measurement of beam diameter and divergence. The reproducibility and precision suggest that it is a measurement process that could be used by a number of test laboratories to assess a beam and obtain similar results. The apparent transportability of the procedure has yet to be proven but it has led to the suggestion that it be recommended in the Technical Report that is being drafted as an aid to performing the measurements required for the classification of beam according to IEC 60825-1:2001. The paper describes the measurement procedure using CCD array detectors to determine the truncated second moment width of the beam as it propagates through a waist. The methods are independent of subjective judgements and there is no ambiguity over the location of the waist.A measurement method has been devised to enable prediction of the propagation characteristics of a wide range of beams from both coherent lasers and incoherent broadband sources. Knowledge of the propagation behaviour of a beam allows measurements to be made of a range of its properties that are required for classification purposes by the laser safety standards. These measurements include estimates of the most hazardous spot size on the retina and therefore the angular subtense of the apparent source. They also enable unambiguous determination to be made of the nominal optical hazard distance.The methods of measurement used in this work stem from the evolving ISO Standards for the measurement of beam diameter and divergence. The reproducibility and precision suggest that it is a measurement process that could be used by a number of test laboratories to assess a beam and obtain similar results. The apparent transportability of the procedure has yet to be proven but it has led to the suggestion that it be r...