Research On The Dispersion Characteristics Of Reflective Grism-pair

Nowadays,ultrashort pulse laser technology has become the main means of detecting the microscopic world,and also the key technology to promote the development of a series of disciplines such as physics,biology,chemistry,and information.The wide application of ultra-short pulse lasers is inseparable from dispersion control devices with wide degrees of freedom to obtain the shortest pulse width.On the other hand,chirped pulse amplification(CPA)is currently an important way to obtain ultra-short pulse lasers with high peak power.In CPA,the dispersion matching between the stretcher and the compressor and the material directly affects the final compression pulse width and beam quality.Therefore,in order to meet the development needs of ultra-short pulse lasers,an optical element capable of performing wide-range,high-degree-of-freedom dispersion control of pulse lasers,such as grism-pair,is required to adjust the pulse width of ultra-short pulse lasers.The grism's dispersion control characteristics with high degrees of freedom also make the design of its operating parameters particularly important.In this paper,we mainly discuss the optical paths and dispersion expressions of a reflection grism-pair compressor,and give a detailed derivation process.The results show that the internal optical path structure of the grism can be divided into three kinds of incident conditions.The angles of the exits will be slightly different for different incident angles,resulting in the difference of the amount of dispersion.Moreover,depending on the specific parameters of the different way the incident optical paths was not necessarily exist.Based on the obtained dispersion formula and its classification,taking BK7 material as an example,a detailed discussion of different grism parameters,variation of the diffraction optical path of grism path inside,and thus obtained the GDD/TOD ratio changes under various incident angles.And the correctness is verified by comparison with the grating formula.Finally,under the condition of fixed Littrow angle,the second and third order dispersion and GDD/TOD change with the grism parameters are obtained.The results show that by fine-tuning the incident angle,the ratio of grism-pair to GDD and TOD can be changed to a large extent,and even the positive and negative relationship,which can be widely used in various ultrafast laser systems and application requirements.Finally,in order to obtain the optimal diffraction efficiency,under the working conditions of fixed incident at the littrow angle,the article gives the second-order and third-order dispersion of the grism and the ratio GDD / TOD with the grism parameters under different optical path modes.Changes.The results show that,even under the working conditions with a fixed incident angle of littrow,by properly designing the grism parameters,the grism-pair can work in different optical path modes,and the positive or negative second-order / third-order dispersion ratio can also be obtained.The high-degree of freedom dispersion control of the reflective grism-pair can not only enrich the regulation of ultrashort pulse laser pulse width.And to overcome the technical problem of the pulse width cannot be perfectly compressed due to the mismatch of material dispersion and the dispersion of the stretcher and compressor in the CPA system,as well as the CPA amplification of the ultrashort pulse laser with a pulse width of less than 100 femtoseconds.It has important application value.