| While laser transmits in atmosphere and other media,it is necessary to measure spatiotemporal distribution of the spot intensity and obtain output characteristic parameters accurately.It is of great significance for analyzing atmospheric transmission effect of laser and evaluating comprehensive performance of laser system.Detector array target is an important device for measuring the spatial and temporal distribution of laser intensity.General measurement process is that the laser beam is sampled and attenuated,then reaches photosensitive surface of photodetector.Detector converts the optical signal into an electrical signal,and then outputs a digital signal through analogto-digital conversion.This measurement method has advantages of direct measurement to laser spot,good real time performance,and wide dynamic range,etc.However,the existing measurement technology has disadvantages of poor resistance to laser damage,narrow wavelength response,sensitive to the laser incident angle,and attenuation magnification cannot be continuously quantitatively designed and other issues.In order to improve measurement range of laser power density and tolerance of incident angle,starting from protection sampling attenuation technology,based on characteristics of total reflection and transmission scattering,a protective sampling attenuation structure composed of gold-plated copper base panel,sampling fiber and diffuse scattering sheet is designed and applied to array detection system.The fiber array target spectrometer is developed.This technology realizes to measure high power density laser parameters with high precision and greatly reduces sensitivity of the sampling attenuation structure to incident light wavelength and incident angle.The main research contents of this thesis are as follows:Firstly,starting from principle of interaction between light beam and medium,from perspective of radiation quantity measurement,reflection,transmission,absorption,scattering and other characteristics existing in optical system are discussed.And calculation of optical energy loss existing in transmission optical system is obtained.The wavelength selectivity of absorption and transmission is expounded,which provides a theoretical basis for material selection in optical systems.The relationship between scattering characteristics of medium and size of constituent particles is discussed.The scattering properties of materials are expressed with bidirectional scattering distribution function.And the related scattering model is introduced.Then,the large angle sampling method of the laser beam is studied.The light transmission loss characteristics of the sampling hole with large hole depth/diameter used for high power density laser parameter measurement are analyzed.It is concluded that reducing number of reflections in the hole and increasing reflectivity of inner wall can improve light transmission efficiency of angle sampling.Numerical simulations of sampling holes with different hole design and inner wall reflection characteristics are carried out.Based on the characteristic of total reflection,a structure composed by sampling hole inserted into large numerical aperture fiber is designed for beam sampling.The results show that it can achieve no sensitive light transmission within the aperture angle range,and has a large angle tolerance.The influencing factors of optical fiber sampling light transmission efficiency and outgoing light spot are analyzed.In practical application,sampling fiber parameters can be designed according to the damage threshold of system components.Next,the homogenization and attenuation characteristics of the beam are studied.Based on bidirectional transmission distribution function and ABg scattering model,the angular response characteristics of scattering material and calculation formula of light intensity attenuation ratio are deduced.The scattering simulation model is established.The experimental method of camera imaging is designed.And the angle characteristics and response consistency of various scattering materials are tested.The results show that diffuse scatterer material is the closest to the diffuse transmission characteristics.While the intensity distribution of the outgoing light does not change with the incident angle,which is the best choice for angle measurement applications.The response intensity of diffuse transmission to the detection surface is analyzed.And it is concluded that response intensity of a certain scattering distance has nothing to do with incident spot shape when total power of the incident light remains unchanged.In practical applications,the light intensity attenuation magnification of detection surface can be designed by adjusting scattering distance.Finally,consideration of the research on large angle sampling,homogenization and attenuation for high power density laser beams,combined with thermodynamic simulation and optical design,the protective sampling attenuation structure composed by gold-plated copper substrate panel,sampling fiber,diffuse scattering plate,extinction channel,and detection unit is designed.And the response characteristics of detection unit are experimentally verified.The designed protective sampling attenuation structure is applied to array detection system.And the optical fiber detector array target is developed,which is applied to actual project.And the experimental spot is tested.The results show that the device has good angular characteristics. |
