Study On Beam Shaping For High Power Laser

With the continuous progress of modern science and technology,the application of radiation pressure is attracting extensive attention in recent years,such as micro radiation pressure in the field of cooling and trapping,manipulation and acceleration of cells by laser light,as well as laser-induced mechanical motion and solar sail spacecraft in aerospace domain.However,the measurement method of light radiation pressure is still very limited at present,so it needs to be more conveniently and accurately measured to make the most of it.This paper introduces the high power laser which are widely used now,and gives the development history and output power of semiconductor laser,fiber laser,solid state laser,diode alkali vapor laser pumped by semiconductor lasers.According to the test requirements,solid state laser is chosen,whose rated output power is 50 W.To avoid excessive heating or even ablation of the irradiated reflector,it is necessary to transform a Gaussian beam of original laser source to a top-hat distribution,and then re-collimate and make them parallel beams.This paper prefers refractive optical elements,which have a simple structure that is symmetrical about the central axis and are easier to manufacture.The functional expression of output flat top beam depends on analysizing the principle of aspheric shaping,transmission characteristic and related characteristic parameters which decide irradiance distribution of flat top beam.According to the law of conservation of energy,equivalent ray path condition and Snell’s law of refraction,two aspheric surfaces are introduced.The sag of each aspheric surface needs to be transformed into the even-power series which can be recognized by ZEMAX.With the help of optimization operand‘REAY’,It is more efficient and convenient to write a ZEMAX Programming Language(ZPL)macro to automatically generate the merit function and optimize the lens.As a result,a compact optical design was derived,which has higher expanding ratio than usual.The aluminum reflectors are fabricated by a high precision machine tool with a surface roughness of 8 nm in Ra,and then coated with high-reflective coatings.The experimental results show that radiation pressure induced deformation has an obvious negative correlation with the reflector thickness.And further analysis indicates that such negative displacement is induced by radiation pressure and the positive displacement is caused by thermal expansion of the PLA base,which proved theexistence of light radiation pressure successfully.