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.