In this experiment the students are encouraged to convert the essential theoretical contents regarding „Laser Safety“ into practice. The application and use of the basics in calculation defined within the standards is submitted and trained by means of practical examples. The major measurement task is to determine the intensity of a laser beam which is defined as power per cross section typically given in W/m². The power is measured by using a calibrated power meter. The cross section and the divergence is determined by a set of imaging lenses with known focal lengths. In addition to the direct exposition also the danger of scattered light is classified by using a scatter probe mounted on a pivot arm.
The experiment is divided into several segments. Aspects such as the following ones have been considered:
1. Determination of the maximum permissible radiation (MPR) for skin and eyes
2. Minimum safety distance from a radiation source for direct and indirect irradiation of the skin and the eyes, (MSD)
3. Characterisation of a pulsed laser systems
4. Requirements for laser safety googles, transmission of optical filter
The fundamentals of IEC 60825 or ANSI Z136 or corresponding literature of laser safety should be known. The danger of lasers are understood by the characteristic properties of the laser radiation. In comparison with other light sources a high energy and power density can be attained, because of the generally small beam divergence the radiation density can be very high even at large distances from the laser (potential danger of lasers used in metrology). Not only the direct radiation also reflected and scattered radiation can cause damage at a large distance from the radiation source. Laser radiation can be generated within a broad spectral range. It extends from a few nanometre up to some hundred micrometres and is, in many cases, outside of the visible spectrum. The damage of the biological tissue (skin, eye) depends strongly on the wavelength and on the duration of the exposition. This is of great importance under safety aspects when classifying the lasers and fixing radiation limits which is also subject of this experiment. By means of two different laser sources all parameters are measured in order to classify each laser and to determine the limits for which the laser can be considered as save. This includes also the characterisation of laser safety goggles.
To determine the maximum permissible radiation (MPR) the laser safety officer needs to know the wavelength, the beam diameter, laser power and finally the mode of operation, if pulsed or continuous mode. To get the MPR from the tables of the laser safety regulations one needs to know the laser intensity in W/m2. The continuous laser power in watt or milliwatt is measured by a calibrated power meter. Dividing the measured value by the beam cross section we get the intensity. In order to determine the MPR in a defined distance, the officer needs to know in addition the divergence of the laser. Due to the large divergence of the pulsed laser it can be measured straight forward by using the goniometer. For the green laser with a much smaller divergence this method fails. That is why we need to increase the divergence first by using a lense (BCL) with known parameter. By using the ABCD parameter, the divergence of the laser source can be calculated backwards based on the measured divergence behind the lens. Such a measurement example is shown in Fig. 2.45.