Method of near- and far-field measurement and application for mid-infrared laser

The high-repetition 3-5 m mid-infrared laser has gain a lot of attention for its potential applications in civil and military. However, there are many technical difficulties to generate this band laser and it is invisible. Therefore, there are rarely such reports about methods of near- and far-field measurements for the lasers. In this article, the near-field measuring for the parameters of laser was conducted at first. Then, the absolute and relative energy density distribution were obtained by the point detector sampling. At last, the infrared imaging system was used to record the image of laser spot received in a far-field screen in the distance of 180 m. The relative energy density distribution could also be simulated by theory of Fresnel diffraction integral of circular aperture. The theoretical and experimental results show that the wavelength of this laser is about 3.9 m with the properties of high average power, high repetition and stability about 10%. The far-field theoretical results show that the energy density distribution is quasi-Gaussian distribution and agrees well with the average energy density of 6.367nJ/cm2,which is smaller than the evaluation of empirical formula by the factor of 1.3. This work will definitely be helpful to measure the parameters of pulsed high-repetition mid-infrared laser and judge the disturbing threshold for the detectors in more far distance.