| Ultrashort burst-mode laser is widely used in the fields of ultrafast laser diagnosis,material micromachining and biomedicine due to its unique pulse energy distribution characteristics.Compared with solid-state laser,fiber laser has the advantages of high reliability,good beam quality,small volume,low maintenance cost and good flexibility,which provides a flexible tool for expanding the application of ultrafast laser in the field of precision machining.In recent ten years,the combination of burst mode and fiber laser has shown excellent performance in laser ablation.Based on the great potential of burst-mode fiber laser in material processing research,it is particularly important to edit the time domain waveform of femtosecond bursts arbitrarily.It has been reported that using acousto-optic modulator and arbitrary waveform generator to generate bursts,and based on this,the improvement of ablation efficiency is verified.This modulation method is difficult to realize the precise control of the intensity of a single pulse,and the circuit control system of this scheme has the disadvantages of large volume and complex operation.The shape of the burst generated by this method is also limited by the limited waveform types of any waveform generator.In order to solve the above problems,this paper proposes a simple,integrated and programmable time-domain waveform control scheme for burst-mode fiber laser of femtosecond pulses,which can not only control the intensity of every single pulse in the burst,but also edit the time-domain waveform of the burst simply and flexibly.The main contents of this paper are as follows:1,The principle,advantages and disadvantages of several intensity modulation methods are analyzed and compared.The feasibility and technical route of using acousto-optic modulator to modulate ultrashort pulse bursts with arbitrary intensity are studied.The related technology and principle of optical fiber amplification of pulse train are introduced.2,Research on the control module of burst laser.Two pulse-train control modules based on field programmable gate array are designed to realize the precise adjustment of pulse laser time-domain characteristics by using acousto-optic modulator.The first pulse train control module can realize the selection of single pulse in the pulse train.Based on this,it shows the control scheme of generating the pulse bursts,so as to realize the programmable control of the repetition rate and the number of pulses contained in the burst.In the second pulse train control module,the amplitude adjustment function of the electrical modulation signal is added to further control the driving voltage of the acousto-optic modulator,so as to realize the accurate control of the energy distribution of each pulse in the burst,thus having the ability to edit any pulse train shape and repetition rate.Compared with the arbitrary waveform generator,this scheme has better operation flexibility,simplified circuit control system,reduced system cost,especially has the ability to control the intensity of any single pulse in the burst.It provides a new pulse control scheme of light source for the further study of ablation cooling process of different materials.3,Based on the programmable modulation technology of pulse time-domain characteristics,combined with ytterbium doped chirped pulse amplification system,high-energy femtosecond bursts with different time-domain waveforms are realized.Five kinds of pulse bursts and amplification are demonstrated,which are rectangular,stair,sine,concave slope and exponential.The pulse bursts with burst repetition rate of 1MHz,burst energy of 20?J and pulse width of 300 fs is produced. |
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