In order to measure the change of laser energy coupling coefficient with temperature in mid-infrared wave band, reflectance integrating sphere experiment system was designed and set up. 915nm CW laser was used to heat samples and the wavelength of probe laser is 3.8μm. Chopper and phase-locked amplifier were adopted in the system. Thermal imager was used to measure and record the temperature of samples during laser irradiation. The reflectance of steel and aluminum plates to 3.8μm was measured during 915nm laser irradiation. EDS analysis was done to investigate the change of elemental composition in the samples respectively. The experimental results show that, the results of reflectance and radiation temperature measured by this system are relatively accurate during laser irradiation. In the process of temperature rising from 300K to 785K, the color of 45# steel plates turns blue and black, while the color of aluminum alloy plates is basically unchanged. When temperature reaches about 700K, reflectance of 45# steel decreases obviously with the increase of temperature, while reflectance of aluminum is almost constant. The reflectance is probably determined by the oxide in the surface of samples which is consistent with the results of EDS analysis. Reflectance decreases with the increase of the content of oxygen in the surface. The reason of why the reflectance of aluminum is almost constant is that aluminum oxide is not generate massively under 750K.
Experimental research on the energy coupling characteristic of 45# steel and 304 stainless steel under mid-infrared CW laser irradiation is carried out. Based on the classical electromagnetic theory, the theoretical formula of the energy coupling coefficient is derived under ideal condition. In order to obtain the energy coupling coefficient, an experimental system for reflectance measurement is set up by an integrating sphere. The curves about energy coupling coefficient and the temperature variation are measured respectively. The mechanism about the variation of energy coupling coefficient of sample under mid-infrared CW laser irradiation is also discussed. The experimental results show that the energy coupling coefficient of sample increased with temperature rising, but the curve in the heating stage is not consistent with the curve in the cooling stage, which means the change of the energy coupling coefficient is not a reversible process. Combined with the experimental phenomena and the energy dispersive spectrometry, the qualitative analysis about the differences between the 45# steel and 304 stainless steel is presented after irradiation. It indicates that the oxidation reaction has a significant effect on the laser interaction with sample. Accordingly, the variation of coupling coefficient of 304 stainless steel is not as obvious as that of 45# steel.
Two kinds of anti-laser coating made of reflective / ablative resin, called reinforcement schemes of A and B, are applied to the glass fiber reinforced resin matrix composite plate. The anti-laser performance of these samples to the laser operated at the wavelength of 976nm is tested, under the case of a 0.3 Mach tangential airflow pass over the surface of the sample. The experimental results show that the laser damage threshold of the coating reinforced samples have increased more than 50% compared to the original sample, the reinforcement scheme B is better than A. The laser power density damage threshold of the coating reinforced samples to the near infrared laser is higher than 100W/cm<sup>2</sup>, under the irradiation time is 60 seconds. For the resin reinforced fiber samples, the removal process of the ablation residues has important effects on the perforation time of samples, when there is a strong airflow pass over the surface. The larger laser spot corresponding to the removal of the ablation residues is easier.