1.2?m Ultra-short Pulsed Raman Fiber Lasers

After frequency multiplication,ultra-short pulse laser at 1.2 ?m can be used in biomedicine,spectroscopy,optical coherence tomography and so on.With the development of fluorescent protein as an important means of biomedical research,red fluorescent protein and deep red fluorescent protein need 1.2 ?m ultra-short pulses to produce two-photon excitation,which makes great significance for the development of 1.2 ?m ultra-short pulses.This paper mainly studies the basic theory and experimental research of 1.2 ?m ultra-short pulses generation.The main research contents of this paper are as follows:1.We analyzed the research background and significance of 1.2 ?m band ultrashort pulse laser.Also the research status and progress of 1.2 ?m band laser pulse at home and abroad are investigated.2.The principle of producing 1.2 ?m band pulsed laser by Raman frequency shift using a nonlinear polarization rotation mode-locked fiber laser as seed source is analyzed.In this paper,three main methods of pulse generation in fiber mode-locked lasers are discussed,and analyzed the advantages and disadvantages.The methods of pulse generation in 1.2 ?m band and the principle of stimulated Raman scattering are introduced,and the methods of obtaining supercontinuum spectrum is given.3.We constructed the seed source for obtaining supercontinuum,and obtained a 1 ?m ultrashort pulse laser.Based on the Yb-doped fiber laser with non-linear polarization rotation mode-locked,we experimentally obtained two kinds of laser output,dissipative soliton pulse and noise-like mode-locked pulse.Optimizing the dissipative soliton mode-locked pulse laser,we gained central wavelength adjustable pulse at 1030-1041 nm,the repetition rate of 24.6 MHz,signal-to-noise ratio of 70 d B and pulse width of 13.91 ps pulse.4.Input the obtained seed light into Yb-doped fiber amplifier,the supercontinuum output at 1.2 ?m band is obtained.The fs pulse at 1.2 ?m is generated by filtering.The effects of seed pulses of different central wavelengths and the length of gain fiber on the output spectrum characteristics of Yb-doped fiber amplifier were studied systematically.The 1.2 ?m band ultrashort pulsed light is compressed by grating pairs,coupled into 500 m single mode fiber and 100 m phosphorus-doped fiber respectively,and the output spectrum is further broadened.After 100 m phosphorus-doped fiber,the output spectrum is 1030-1400 nm wide;after 500 m single mode fiber,the output spectrum is 1030-1700 nm wide.The broadband spectrum filtered by the blade method after 500 m single mode optical fibers is obtained.The narrow pulse with 3 d B bandwidth of about 20 nm is filtered out.The pulse width is 297 fs,the repetition frequency is 24.6 MHz and the output power is about 500 m W.5.We analyzed the problems of fiber fusing and coupling efficiency of amplifier encountered in the experiment are analyzed.The effect of thermal deposition in the fiber on the damage of the fiber is emphatically discussed,and the melting point problem is solved.The low coupling efficiency of space optical-optical fiber is discussed,and the corresponding solutions are put forward to improve the coupling efficiency.