Generation And Measurement Of Few-cycle 1.8μm Laser

Since laser was invented,it has been developing towards shorter pulse width and higher peak power.The few-cycle femtosecond laser in near-infrared plays an important role in generating attosecond pulses.Therefore,how to obtain and characterize the fewcycle near-infrared femtosecond laser pulses has become a research hotspot.At the same time,because the near-infrared femtosecond laser can be used to detect changes in the structure of matter and dynamic processes occuring in the ultrashort time scale,it is widely used in the fields of physics,chemistry,and biology and etc.This thesis sets out to introduce the generation of few-cycle near-infrared femtosecond laser,the construction of the autocorrelator and the frequency-resolved optical gating,and the detection of the two-dimensional material structures and the ultrafast dynamic process using the near-infrared laser.A near-infrared femtosecond laser with a pulse width of 25 fs is obtained by using the multi-plate continuum method.We theoretically analyze the principle of generating few-cycle pulses from multiple continuum,by using which the laser at 1800 nm with a pulse width of 21-cycle is compressed to 4-cycle pulses.This method has the advantages of high flexibility,easy repeat operation,and is suitable for compression of high-power pulses.An autocorrelator and a Frequency Resolved Optical Gating(FROG),which can measure pulse width and phase at the same time,are designed.The rapid development of laser technology has promoted the further improvement of laser measurement technology.The original autocorrelator instrument in the laboratory can only be used to measure the pulse width of 800 nm pulse,and the complete information of the pulse cannot be obtained.Therefore,after comparing the advantages an disadvantages of different pulse measurement methods,i choose to design an autocorrelator and a FROG,which can be used to characterize the pulse information among visible and mid-infrared pulse.The intensity dependence and orientation dependence of the harmonic signals of graphene and Mo S2 are measured.It is found that the intensity-dependent modulation of the third harmonic of graphene and the seventh harmonic of Mo S2 under strong fields is attributed to the ionization channel-closing effects.This phenomenon indicates that harmonics generated by the interaction of near-infrared laser with solid can be used to detect the ultrafast dynamics of electron movement in two-dimensional materials.The orientation dependence of the third harmonic of graphene and the second harmonic of Mo S2 is further analyzed,and it is found that the orientation dependence of the harmonics is closely related to the spatial structure of the lattice,which provides a potential all-optical method to detect the lattice structure of two-dimensional material.