| Laser exhibits various unique applications in the 2?m band.Firstly,most semiconductors are transparent in the 2?m band,which can be focused the laser on a specific target-layer for precision micromachining.Secondly,2?m laser is more effective for processing the plastic and film materials.Finally,the absorption peak of water molecules is near the 2?m wavelength,and laser will be more favorable to the treatment of the biological tissues in the 2?m band.Therefore,it is of great significance to generate lasers at 2?m band and explore their related characteristics.At the same time,self-similar pulse has attracted extensive attention due to their excellent transmission characteristics.This parabolic self-similar pulse can be adopted for solving the problem of limited pulse strength during transmission effectively.The pulse will not deform the high power transmission.Furthermore,the self-similar pulse can resist the splitting of light waves well,and its strict linear chirp makes it effective to compress and obtain ultra-short with higher peak power.Therefore,we mainly investigate the self-similar pulse generation in the 2?m band,and the amplification and compression of self-similar pulse in this paper.The main research contents and innovations are as follows:?1?According to the relevant theoretical knowledge of dispersion and non-linearity,the nonlinear Schr?dinger equation of the pulse transmission in the optical fiber is solved by the stepwise Fourier algorithm.At the same time,we investigated the generation mechanism of the self-similar pulse and the particularity of self-similar pulse in the 2?m band,which provide theoretical basis for subsequent research.?2?The theoretical model of Tm3+mode-locked fiber laser is established.By adjusting the net dispersion value in the cavity,the laser generated a stable 2?m self-similar pulse in the range of 0.02ps2-0.08ps2.At the same time,based on the control variable method,the influence of the parameters,such as dispersion,gain coefficient,saturable absorber,resonator length,and output coupling ratio on the peak power,to the peak power,full width at half maximum?FWHM?,single pulse energy,and pulse duration of a 2?m self-similar pulse within a certain range are analyzed.The simulation results show that the output pulse characteristics can be changed by adjusting the system parameters.Finally,the experimental structure of thulium-doped self-similar pulse laser is constructed for experimental verification.?3?A theoretical model of Tm3+doped fiber amplifier is established to amplify the2?m self-similar pulse.We simulated and analyzed the effects of parameters such as initial pulse shape,pulse width,and UHNA7 fiber length in the amplifier on the time and frequency domain evolution of 2?m self-similar pulse using MATLAB software.The simulation results show that the initial pulse of any shape can eventually evolve into a self-similar pulse,and it is related to the pulse width and the length of the resonator.?4?The amplified self-similar pulse is injected into the compression system by using three methods,such as non-fiber dispersion compensation,ordinary single-mode fiber and dispersion-reducing fiber.According to the different characteristics of each compression method,the obtained pulse is analyzed,and finally the ultra-short pulse with a power of 35.09k W and the FWHM of 391fs is obtained. |
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