| Ultrashort pulse laser technology is a cutting-edge integrated and practical laser technology,which is based on mode-locking technology,nonlinear control technology,and dispersion management technology.In recent years,the rapid development of ultra-short pulse laser technology has greatly promoted the continuous emergence of new materials,new technologies and new industries,which has effectively promoted the frontier research applications on biomedicine,micro-machining,attosecond science,optical frequency combs,high-energy physics,and plasma,and also has become one of the most powerful tools for people to understand and explore the unknown.Fiber laser as an important branch and research direction in the field of ultra-fast laser,involving the development of new fiber-optic mode-locking technology and material,new integrated all-fiber device,high-performance dispersion compensation and pulse modulation device,high-power and high-energy fiber components,monitoring control hardware and software development and many other cutting-edge technology areas.In particular,with the present of new fiber based optic dispersion compensation devices,such as photonic crystal fibers,chirped optical fiber Bragg gratings,optical fiber high-order mode dispersion compensators,and tapered fiber dispersion compensation devices,including novel mode-locking materials such as carbon nanomaterials,graphene,and chalcogenide materials etc.,all of which have greatly promoted the all-fiber process of fiber lasers.However,as the seed light source of the amplification system,all-fiber oscillators still have many shortcomings,such as narrow spectrum width,instability,low SNR and high nonlinearity.Low-repetition-frequency all-optical femtosecond pulse amplification technology is another research hotspot in the field of optical fiber amplification.The key issues of optical fiber amplifier are nonlinearity and dispersion management,the derived problems include:(1)Non-linear accumulation of optical fibers leads to pulse distortion and Spectral splitting,(2)The precise control of mode-locked and amplified pulse repetition rate,(3)pulse compression and high-order dispersion compensation,(4)laser output control and monitoring.To solve the above problems,it is necessary to study the all-fiberization and fiber amplifiers of the fiber oscillator systematically.In addition,through the targeted design and development of high-precision hardware and software optical assistance and support systems to achieve optical and electrical integration,will help promote the commercialization and practicalization of ultra-short pulse fiber lasers.Therefore,it is of great significance to carry out theoretical and experimental research on mode-locked fiber lasers and ultra-short pulse amplification.The innovative research results in this paper includes:(1)For the first time,using the micro-element method combined with the optical properties of mid-infrared materials,a mid-infrared fiber device capable of achieving a dispersion flattened and dispersion decreasing in the wavelength range of 2-5?m is designed.The fiber is of great improtance in the mid-infrared soliton pulse transmission,pulse duration compression,supercontinuum generation etc.(2)A space-type NPE mode-locked fiber oscillator with a dispersion compensation cavity was built experimentally,and a pulse-width picosecond-scale,self-starting,wide-spectrum,high signal-to-noise ratio mode-locked pulse was obtained.By optimizing the design of the structure,further miniaturization,compactization and engineering of the laser are realized.Based on this,an in-depth experimental study of a dissipative soliton mode-locked all-fiber laser is performed.The all-fiber oscillator constructed can achieve a stable,touch-screen controlled,mode-locked output.(3)All-fiber structure based on tapered fiber dispersion and nonlinear compensation was studied in the all-fiber oscillator with 66MHz repetitionrate,65 fs pulse duration,spectrum width up to 37nm and SNR as high as 70 dB.For the first time,the dispersion and nonlinear management of NPE mode-locked fiber oscillators is achieved using tapered fibers,which provides new ideas for dispersion compensation and nonlinear device development for all-optical oscillators.(4)Fiber amplifier adopts optical fiber CPA amplification technology combined with self-designed fiber-optic CFBG,which can not only stretch pulse duration but also can compensate high-order dispersion in the amplication system,and stretched the picosecond pulses to nanoseconds,achieving large amplitude pulse broadening with low nonlinear accumulation.Subsequently,the pulses are amplified by a ytterbium doped single-mode photonic crystal fiber with a large core area(mode field area:3300?m~2)to obtain a high-power laser output with a single mode,which effectively lower the light Kerr effect in high-power optical fiber amplification.Through the acousto-optic modulator under the control of a high-precision RF drive circuit,precise control of the pulse repetition rate from40MHz to 1MHz is achieved.The pre-pulse energy of the frequency-selective output pulse is low,and the amplified pulse is then introduced into the grating pair compressor to compress the pulse duration.The third-order negative dispersion provided by CFBG perfectly compensates for the third-order positive dispersion introduced by the compressor and the cascade optical fiber amplification link,and performs efficient dispersion management for the entire amplification system,which solves the limitation of third-order dispersion problem of in near 100fs pulses compression.Based on the support of above technical,two sets of optical fiber amplifiers with an average output power of 30W and60W,a repetition rate of 1MHz,and a compressed pulse duration of 153fs and 196fs were developed.The initial try of opto-mechatronics was performed,and the test of 24-hour compressed output power stability RMS is as low as 0.63%.In addition,femtosecond laser capsulorhex surgery of pig eyes,steel plate and glass marking applications have also been carried out,and the lasers are in good condition.(5)High power pulse compression is a key part of the ultrashort pulse amplification technique,but the spectral gain narrowing effect in the fiber amplification link greatly limits the Fourier transform limit pulse duration.For further pulse compression,the broaden of pulse spectrum is needed.Therefore,nonlinear spectral broadening and pulse duration compression experiments in gas filled Kagome fiber were carried out,and preliminary experimental results were obtained. |
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