Pulse energy improving method of self-starting Figure-9 passive mode-locked fiber laser

Abstract

The invention discloses a pulse energy improving method of a self-starting Figurase-9 passive mode-locked fiber laser. The pulse energy improving method is applied to the Figurase-9 fiber laser composed of an equivalent NALM annular cavity, a linear arm, a rotating motor and a pumping source. The method comprises the following steps: 1, obtaining the linear phase shift amount of a nonreciprocal phase shifter; 2, obtaining the splitting ratio of the equivalent NALM annular cavity; and 3, setting the output power of the pumping source and the parameters of the nonreciprocal phase shifter, and performing circulating until the output pulse energy of the Figure-9 fiber laser (1) is improved. According to the invention, higher nonlinear phase shift tolerance during single-pulse mode-locking operation of the Figure-9 fiber laser with the self-starting function can be realized, so that the output monopulse energy is greatly improved, the self-starting low-noise large-energy femtosecond fiber laser capable of stably operating for a long time is obtained, and the laser has a wider application prospect in the field of femtosecond laser pulses.

Description

Technical field [0001] The invention relates to the fields of laser precision processing, laser precision measurement and the like, in particular to a method for improving the pulse energy of a self-starting Figure-9 fiber laser. Background technique [0002] Femtosecond laser pulses have important applications in fields such as strong field physics, attosecond science, precision measurement, and nonlinear optics. Using Ti:Sapphire solid-state laser technology, pulses with peak power up to PW and pulse width as narrow as 15fs can be generated. The fast-developing mode-locked fiber lasers in recent years have shown a more colorful ultrashort pulse phenomenon. Through nonlinear regulation of dispersion, femtosecond pulses of different formats can be generated, such as solitons, dispersion management solitons, self-similar pulses and dissipative solitons, etc. . With the continuous breakthrough of femtosecond pulse fiber amplification and coherent synthesis technology, the use of ...

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Problems solved by technology

However, this asymmetric cavity structure causes the nonlinear phase shift (NPS) experienced by the forward and reverse optical fields in the cavity to have different trends or slopes with the increase of pump power, and it is easy to break through the SA transmittance curve by increasing the pump power. Allowable Δφ for specified single pulse operation NL , restricting the improvement of the output pulse energy

And this kind of asymmetric cavity structure limited by self-starting requirements also limits the use of intracavity dispersion nonlinear control to increase the pulse energy

However, if the cavity asymmetry is reduced, in theory, Δφ can be allowed under extremely strong pumping NL While not breaking through the single-pulse operation range, the positive and negative light fields in the cavity can accumulate enough NPS to increase the pulse energy. The power of the light is extremely high, and the intracavity gain fiber is in a deep saturation state, but this deep saturation has a "self-healing" effect on the weak power fluctuations of continuous light, which is not conducive to amplifying such weak power fluctuations, resulting in a low asymmetry cavity. -9 Fiber lasers are difficult to achieve self-starting of mode locking

Although the pulse energy of the self-starting mode-locked fiber laser in Figure-9 has been improved to a certain extent by choosing a large-mode-field fiber to reduce the accumulation of NPS in the cavity and introducing the hybrid mode-locking of micro-nano material SA to help self-starting, but it has not In principle, it can solve the limitation of the output pulse energy caused by the introduction of linear phase shift and asymmetric cavity to ensure the self-starting function of this laser

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