Irradiation of a protective screen element made of painted constructional steel (2 mm thick) with Nd:YAG laser radiation (wavelength 1064 nm, output 4 kW, beam diameter on the screen 45 mm). On the left is during, on the right directly after irradiation.Breakthrough took place after approximately 10 seconds.

Gas and particle emissions during laser processing.

Manually guided laser cutting process (left); conventional protective glove after laser irradiation (top right), and wound on finger due to unintentional laser irradiation (bottom right)

Sketch of the laboratory set-up for weed control using a laser. An image processing unit recognizes the weeds and points the laser beam at them.

In the group "Safety Technology" (SHT) in the Materials and Processes Department, scientific and technical aspects concerning dangers connected with laser irradiation are covered. Above all, investigations on hazards to people working with lasers are carried out. However, pollution hazards from process by-products are also investigated.

In working with lasers, both primary and secondary hazard potentials are relevant:

• Primary Hazards: Dangers connected with the interaction of organic tissue with direct, reflected or scattered laser radiation.
• Secondary Hazards: Direct danger due to the construction-based features of a laser system (electrical connections, laser gasses, pump lamps etc.), respectively indirect hazards due to application-specific conditions (hazardous materials emitted from the process zone, secondary irradiation or fire hazards due to ignition of inflammable materials, etc.)

Also see the data base "laser safety" (Datenbank Lasersicherheit).

Main areas of work

The main areas of work for the Safety Technology Group are based on possible hazards from using laser radiation.

• Primary Hazards
  • R&D in the field of personal protective equipment (PPE) for protection from laser radiation, e.g. for hand-guided laser material processing
  • Measurement of the radiation exposure in and around laser processing systems, according to the threshold levels, based on laser classification and DIN EN 60825-1
  • Measurement and calculation of irradiation levels of laser processing systems according to MZB values (DIN EN 60825-1)
  • Consulting services on the implementation of laser irradiation protective measures
  • Preparation of hazard analyses for laser production equipment (DIN EN ISO 14121-1)
  • Irradiation experiments and measurements (VMB/SGB) for materials for workplace safety screening and shielding (DIN EN 12254) respectively for laser protection screens
• Secondary Hazards
  • Emission prognoses for identifying the main components (TRGS 402)
  • Emission characterization (BImSchG / TA Luft)
  • Analysis of the working area (TRGS 402)
  • Consulting, respectively measurement and filtration (TA Luft), waste management (EAK)
  • Consulting concerning cutting and welding fumes, see Laser Safety Databank (Datenbank Lasersicherheit)
  • Qualification of filters and personal respiratory equipment
  • Experiment concerning fire and explosion protection during process emission acquisition (Atex-Guidelines)

Current Research Projects

EU Project: Intelligent personal protective clothing for use with high-power, hand-guided laser processing systems (PROSYS-Laser)

Since December, 2009, a European research project within the 7th Framework Programme is being carried out, on the development of innovative passive and active PPE to protect the skin against laser radiation when using hand-held laser devices. The consortium consists of 12 partners, with 8 small or middle-sized enterprises, and 3  research institutes. The LZH is not only involved in scientific work concerning laser technology, but is also the project coordinator.

The goals of this research project are to minimize skin hazards for users of hand-held laser systems, by developing adequate PPE systems, and to support the use of high-power, high beam quality, hand-held laser systems by making laser PPE available at acceptable costs, to open new market segments for high-performance PPE, and to support the standardization of PPE and the related testing procedures regarding the protective properties.

The target developments are based on passive multi-layer systems made of technical textiles with a high resistance to laser radiation, as well as on suitable active systems with sensors which can detect laser radiation. These systems can be used to switch off the laser radiation if accidental irradiation occurs. Furthermore, test methods and corresponding set-ups should be developed, which can be used to qualify the protective level of the textile multi-layer systems developed, respectively the PPE prototypes,

The project is also presented at the website www.prosyslaser.eu.

German Research Association DFG Project: Investigation of the Effect of Laser Radiation on Juvenile Plants Based on Image Processing for Weed Regulation (Laser weeding)

Apart from the main areas of work in the field of laser safety listed above, the Group SHT is also involved in research projects which deal with the interaction of laser radiation with living plants. In February, 2010, a project for non-chemical weed control using laser radiation started. The project is supported by the German Research Association (DFG).

The goal is to use an interdisciplinary research approach with bio-system technicians and laser engineers, to find answers to fundamental questions concerning the use of lasers for weed control in professional gardening and intensive plant production. A damage model (dosis-effect-model) should be developed, which can be used to describe the effect of laser irradiation, depending on the technical and plant-related parameters (laser output, wavelength, energy, beam form, plant species and growth stage), on monocotyledoneous and dicotyledoneous weed cultures.

A central topic in the project is further developing image analysis algorithms, which both recognize weeds in any given terrain, and also the target points on the plant, both of which are necessary for using lasers for weed control. The target points should be integrated in the laser control system, which also is designed for hit feedback. The algorithms and controls which are developed should be experimentally tested and evaluated.