Study On Femtosecond Pulse On-line Monitoring And Control Technology

Femtosecond lasers have a wide range of applications in multiple fields such as medical aesthetics,military weapons,automotive manufacturing,cell phone manufacturing and laser processing.Especially in the field of laser fine processing,femtosecond laser plays an important role.Pulse width is a very important parameter of femtosecond laser,which affects the quality of femtosecond fine processing.The use of dispersive elements to broaden and compress the laser pulse has become one of the hot spots in femtosecond laser research.Nowadays,the pulse width control products on the market are basically single pulse width stretcher or pulse width compressor,which cannot monitor and control the output pulse width of the laser at the same time.This thesis integrates pulse width spreading and pulse width compression in one system,using positive dispersion chirped mirrors to achieve pulse width spreading,using the movement of the motorized displacement stage to change the spacing of negative dispersion transmission grating pairs for pulse width compression.and using a high precision autocorrelator to monitor the pulse width of the system.With the use of a set of control software developed,the system can realize online monitoring and regulation of laser pulse width.The main research content of this thesis is as follows:1.The system mainly consists of three parts:pulse width spreading module,pulse width compression module and pulse width detection module.Several common pulse stretchers and pulse compressors and existing pulse width monitoring methods are introduced,and the advantages and disadvantages of commonly used dispersion compensation devices are introduced.The scheme of using positive dispersion chirp mirrors for pulse width broadening and the scheme of using transmission grating pair for pulse width compression are determined.Finally,the optical path diagram of the whole system and the selection of the main optical components are determined.2.For the optics used in the system,specifically grating pairs,hollow roof prism mirrors,D-shaped mirrors and beamsplitters,the fixtures used for them are determined.A special fixture was designed for the chirp mirrors to make the optical path more compact,and a displacement stage adapter was designed for the displacement stage to facilitate the change of the displacement stage position.A height-climbing mirror was designed for the mismatch of beam center height to reduce the cost and improve the practicality.The base plate and housing of the whole system were designed,and finally the engineering assembly was carried out.A power control module was designed to control the input power of the autocorrelator within a suitable range allowed by changing the position of a continuously variable neutral density filter through a motorized displacement stage.3.The control idea of the whole system software was analyzed,and the software was written in C#language selected using Visual Studio 2019.The software interface was designed,mainly divided into two areas of pulse width display and pulse width control,which realized the stable monitoring and control of pulse width.4.Introduced the main parameters of the two instruments used in the system,the linear displacement stage and the autocorrelator,built the system optical path according to the optical path diagram,and completed the assembly of the whole system prototype.The system software was run for pulse width control,and the monitored data were analyzed to obtain the pulse width detection accuracy and pulse width control accuracy of the system.The faults that may be encountered in the system and the corresponding solutions are also analyzed.