Thermal fluence deposition and surface pressure generation produced by a CO2 laser pulse (λ=10.6 μm, during 10 μs, maximum intensity 3 MW/cm2) have been measured as a function of angle of incidence ϑ on sheet aluminum in air. We find that air plasma ignition depends on the laser beam intensity I0 only, not on the surface-normal flux I0 cosϑ. Conversely, the fluence deposition and surface pressure depend only on the product I0 cosϑ, and obey the square-root and two-thirds-power dependences observed with simple I0 variation at normal incidence.
The objective of this work was to develop a phenomenological model of pulsed CO 2 laser interaction with reinforced composite materials. Experimental observation has shown that the multilayer composite material delaminates under pulsed CO 2 laser irradiation. This is a consequence of the energy storage mechanism arising out of a finite absorption depth to the laser radiation. A heat transfer model was developed to describe the observed delamination behavior of the composite materials. Good agreement was obtained between the model predictions ami experimental data. The model has been used to extrapolate to high average power irradiation.
Nomenclaturec -specific heat E R = residual fluence E R() = residual fluence for surface at ambient temperature E v = heat of varporization h = laminate thickness R = pulse repetition frequency t = time T = absolute temperature T 0 = ambient temperature x = distance from target surface a. -thermal diffusivity A = laminate displacement Aw = velocity differential across laminate Ap = differential pressure d = constant in Eq. (5) p = material density X = conduction depth X a = absorption depth for laser radiation 8 = temperature, = T-T 0 r -shear stress in laminate li = glass viscosity i] = heat transfer parameter, = x/ (2^fai) £ = heat transfer parameter, =E RQ R/[pcaQ v ] f = mass removal parameter in Eq. (19) o) = Vctf/X Subscripts D = delamination V = vaporization R = removal
READ INSTRUCTIONS BEFORE COMPLETING FORM 1. REPORT NUMBER 2. GOVT ACCESSION NO. 3. RECIPIENT'S CATALOG NUMBER Beam jitter diagnostics were developed and tested on a repped-flowing CO2 e-beam sustainer laser cavity. The limiting source of jitter was found to be due to gas density gradients in the cavity. Both flow-induced gradients and disturbances from the repped discharge contribute. Reduction of the jitter magnitude can be accomplished through temperature control of the gas flow and acoustic suppression.
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