<title>Laser ablation thresholds of polymer materials studies</title>

Abstract

The polymer films are widely used as the reflecting materials in any types of the optical systems. It demands the detail studies ofthe basics and threshold parameters of laser ablation destruction such a materials in the power laser radiation with pulse energy density in range from 1 up to 100 i/cm2. The probability of the target laser ablation destruction versus the incident laser radiation energy density dependencies for any polymers the high pressure polyethylene, epoxy compound, polytetraphluoroethylene and rubber for comparing -have been a subject of the experimental studies. It takes into account all of the energy distribution channels -reflectance, scattering and absorbance for laser ablation ofthese samples and . These results show that about I 1 % of absorbed laser pulse energy was transferred to the target as the shock wave spreading in it when the target thickness is greater than the distance which this shock wave spreads in the time oflaser pulse action.

A lidar equation with allowance for the finite width of the lasing line

“…This is the reason for the interest in remote measure ments of the concentration of molecular iodine in gas eous media. The authors of [12,15] assessed the potential of the method of differential absorption and scattering by iodine molecules in the atmosphere in terms of solving such measurement problems. These studies were based on the assumption that the lasing line is a delta function.…”

“…The collecting aperture area of the telescope 10 is S 0 = 0.125 m 2 . The inten sity of laser radiation at a wavelength of 532 nm that made a round trip through an atmospheric layer with iodine molecules in a set concentration is reduced due to the absorption in iodine [12]. This radiation passes through glass optical filter 2 to pho toreceiver 1.…”

“…(11), we finally obtain the lidar equation for Mie backscattering using a lasing line with finite half width Γ: (12) where B = is the lidar calibration con stant. Let us analyze the solution of Eq.…”

“…(12) in the form (14) We then use the error function integral erf (Γ) [11] to rearrange the last two exponential functions in (14): (15) Assuming that K(z) depends only marginally on frequency ν in the studied range 2Γ, G(z) is in this case equal to 1, and the value of exp[-2K(z)z] in the range of 200 < z < 5000 m is also of the order of 1, we can esti mate the elastic backscattering power for half width Γ values ranging from 1 to 4 GHz. We also assume that the instrument function half width is an order of mag nitude greater than the lasing line half width (which is quite acceptable for industrial lasers and the interfer ence optical filters used as the spectrum analyzer of a lidar [12]). The results obtained by solving Eq.…”

“…(18) in the form (19) Assuming that G(z) is in this case equal to 1 and the value of exp[-2K(z)z] within the range of 200 < z < 5000 m is also on the order of 1, we can estimate the half width Γ values ranging from 1 to 5 GHz by hypothesizing that the instrument function half width is an order of magnitude greater than the lasing line half width (which is quite acceptable for industrial lasers and the interference optical filters used as the spectrum analyzers of a lidar [12]). Our results from solving Eq.…”