Theorical And Experimental Research Of Nanosecond All-fiber Dual-cavity Laser Based On Novel Passive Modulation

Nanosecond fiber lasers have lots of attractive properties including simple design,high pulse energy and peak power,and they can be widely used in many fields such as laser processing,range-finding,bio-medical diagnostics and military application.The traditional methods to obtain nanosecond pulsed lasers are by active Q-switch,passive Q-switch or gain-switch technology.In recent years,rare-earth doped fibers can be used as saturable absorber for passive modulation in the all-fiber pulsed laser,and they attract more and more attentions.Different from the common saturable absorbers such as semiconductor saturable absorber mirror,carbon nano tube,graphene or bulk crystal,fiber saturable absorber can achieve the real all-fiber design without free-space components,and it can help to reduce the cavity loss and product cost.Meanwhile,it also allows the laser to be integrated in a compact size with reliable and stable output.But the passive pulse generation method with fiber saturable absorber will lead to the large pulse duration and bad stability in the time and amplitude domain.In this dissertation,the pulse generation mechanisms of fiber saturable absorber with novel dual-cavity design are studied theoretically and experimentally in an all-round way to achieve the efficient high power nanosecond operation directly output from the oscillator.Furthermore,this technology can be applied to develop different operating wavelength lasers and it is of significance to the high power nanosecond fiber lasers.The main innovative achievements of this dissertation are presented as following:1.Numerical simulation and dynamic analysis of the nanosecond all-fiber dualcavity laser.The theoretical model of the nanosecond all-fiber dual-cavity laser is developed based on the rate equation and propagation equation to study the principle and dynamic of the dual-cavity.The dual-cavity model is constructed in a linear cavity configuration,which includes an external-cavity and an internal-cavity consisting of fiber Bragg gratings and double clad gain fiber.The pulse generation mechanism is based on the fiber saturable absorber and the cross-modulation of laser cavities.By means of the theoretical model,the pulse evolutions of population inversion,pump power,the internal-and external-cavity radiation as s function of the time domain and position are further studied,and the dual-cavity model can be used to analyze the relation between the cavity design parameters and the output performances.2.High power nanosecond Yb-doped all-fiber dual-cavity laser oscillator and its theorical analysis.In 1 ?m region,the laser diodes with the central wavelength of 976 nm are used as the pump source,and the Yb-doped double-clad fibers are used as the gain medium and the saturable absorber.Morever,the dual-cavity configuration is construsted by the fiber Bragg grating pairs.The all-fiber dual-cavity laser oscillators with different schematic designs including the linear and ring structure,different operating wavelength combination including the 1033 nm,1040 nm,1050 nm,1060 nm,and 1080 nm,different core-diameter schemes including the core-diameters of 7 ?m?10 ?m?20 ?m are achieved.At last,the dual-cavity lasers can achieve the minimum pulse width of <50 ns,the maximum average power of >20 W,and the maximum pulse energy of 0.48 mJ directly output from the oscillator,respectively.And the stability of the dual-cavity is measured,including the timing jitter,peak-to-peak fluctuation and the signal-to-noise ratio.Moreover,the experimental realization of linearly polarized nanosecond dualcavity fiber laser in all polarization-maintaining design is reported by means of the technology of linear polarized radiation generation,and the stable pulsed laser output is verified at average output power of watt level with the pulse width <200 ns and the polarization extinction ratio of >15 dB.3.1570 nm Er/Yb co-doped all-fiber dual-cavity laser oscillator.In 1.5 ?m region,the efficient and stable nanosecond pulse generation is achieved,which is based on the cladding-pumped linear dual-cavity design with the saturable absorber of the single-mode double-clad Er/Yb co-doped and the cross-modulation of two coupled laser cavities.The 1570 nm laser oscillator can achieve the average power of 2.2 W and the minimum pulse width of 173 ns.The repetition rate varies from 14 kHz to 156 kHz.4.The applied research of the nanosecond all-fiber dual-cavity laser oscillator.The optical-mechanical-electrical integration of the nanosecond all-fiber dualcavity laser oscillator with 20 W average power based on the design of core-diameter of 10 ?m is carried out,and the intergration of the platform fiber laser is finished.And then the driving circuit and control system are designed to achieve this compatible laser system to communicate with the hardware and software.Then the optical-electrical performance tests of the dual-cavity laser combined with the commercial laser marker controller and vibrating lens is achieved.Finally,the experiments of dual-cavity laser marking system are carried out according to different materials and analyze the processing effectiveness at the same time.