Study on attenuation performance of water fog to 10.6μm laser emission by laser granularity analyzer and transmitter

Abstract

Superfine water fog was generated by several pressure nozzles with a diameter of 0.5mm in a large half-closed space under different pressure varied from 0.1MPa to 0.9MPa. The granularity of the water fog particles was tested with a spray laser particle size analyzer and the transmittance of the water fog to 10.6μm laser emission was tested with a carbon dioxide laser transmitter. By the experimental result, the average diameter varies from 65μm to 5μm with the pressure changes from 0.1MPa to 0.9MPa. On the other hand, the attenuation effect of water fog particles to 10.6μm laser emission rapidly increases with the increment of its diameter when the particles have a smaller size, but the attenuation effect slowly decreases with the increment of its diameter when the diameter is bigger than 15μm. The scattering, absorption and extinction efficiency factors of water fog particles with different diameters to 10.6μm laser emission were calculated according to Van Der Hulst formula. By the calculation, the attenuation effect of water fog particles to 10.6μm laser emission depends on not absorption but scattering function. According to extinction curves, the extinction efficiency factor of water fog particles to 10.6μm laser emission rapidly increases with the increment of its diameter when the diameter is smaller than 15μm. The extinction efficiency factor will slowly decrease with the increment of the diameter when the diameter is bigger than 15μm. Therefore, water fog has the strongest attenuation effect to 10.6μm laser emission when its average diameter is about 15μm and the theoretic calculation is consistent with the experimental result.