Near-infrared/mid-infrared laser irradiation effects on polyethylene film

Experimental researches of the near-infrared laser with 1085nm wavelength and the mid-infrared laser with 3.8 microns wavelength irradiate on the transparent polyethylene film with a thickness of about 25 microns are carried out. Results show that the burn through time approximate exponentially decreases from 5.76s to 0.85s, for the average power density of the mid-infrared laser increases from 2.9W/cm2 to 37.2W/cm2, and the damage energy density is about 22.2J/cm2. The polyethylene film can be burned through by near-infrared laser irradiation with an average power density of 338.8W/cm2 for 18.6s, and the corresponding damage energy density is up to 6301.7J/cm2. The failure time exponentially decreases from 18.6s to 0.75s with the incident laser density increases from 338.8W/cm2 to 428.5W/cm2, and the corresponding damage energy density approximate exponentially decreases from 6301.7J/cm2 to 321.4J/cm2. The damage of near-infrared laser has obvious threshold effect. The polyethylene film would not be burned through until the laser power density reaches a certain high value, so the damage threshold of polyethylene film by near-infrared laser is 1 ~ 2 orders of magnitude higher than that by mid-wavelength infrared laser. The results are in good agreement with the absorption ratio of polyethylene film at wavelength of 3800 nm and 1085 nm measured under weak light.