Testing of laser protective barriers and windows

Abstract

Area protection for laser radiation often requires the use of protective barriers and/or windows to confine the beam within a given NHZ specification. As laser power levels increase, the ability of the protective material to withstand the direct beam becomes a concern. Specification is then required of a Penetration Threshold Limit (PTL) for the protective material.This presentation will review a protocol for testing of laser protective barrier materials. Test data will be presented for a number of commercially available laser barrier materials. Laser parameter dependence will be discussed relative to beam diameter and power level and how these factors can affect the PTL for a specific material. The initial results will show PTL values in the range from 20 to 450 W/cm2 depending upon barrier material and beam size for 100 s exposures.In addition, test data will also be presented for a design of a large size laser protective window for the Nd:YAG laser operating at 1064 μm for power levels up to 100 W/CW. A laminated design was chosen so that a long term exposure would be absorbed incrementally in the window layers without exceeding the Damage Threshold Limit (DTL) for the glass protective window material.A design involving two layers of clear glass allowed reduction of the incident 100 W beam to a level below the DTL of 58.9 W/cm2 of the special IR absorbing glass used to reduce the 1064 μm radiation. Each layer of the IR glass has an OD=1.1; hence four layers reduced the beam to a level of 3.4 mW/cm2 which is less than the ANSI MPE requirement of 5.1 mW/cm2 for this wavelength and exposure time.This study was included as part of the laser protection damage study sponsored by NIST and various laser protective device manufacturers.Area protection for laser radiation often requires the use of protective barriers and/or windows to confine the beam within a given NHZ specification. As laser power levels increase, the ability of the protective material to withstand the direct beam becomes a concern. Specification is then required of a Penetration Threshold Limit (PTL) for the protective material.This presentation will review a protocol for testing of laser protective barrier materials. Test data will be presented for a number of commercially available laser barrier materials. Laser parameter dependence will be discussed relative to beam diameter and power level and how these factors can affect the PTL for a specific material. The initial results will show PTL values in the range from 20 to 450 W/cm2 depending upon barrier material and beam size for 100 s exposures.In addition, test data will also be presented for a design of a large size laser protective window for the Nd:YAG laser operating at 1064 μm for power levels up to 100 W/CW. ...