Precise pulse-time shaping is a key technology for operation control and precise physics experiments in high-power laser facilities. Inertial confinement fusion (ICF) laser drivers require that the front-end system generates arbitrary shaping optical pulses to satisfy the time waveform requirements of target physics experiments. To reduce the number of arbitrary waveform generators (AWGs) in a system, multiple shaping pulses are typically generated in the form of pulse trains. However, in the process of time shaping, the earlier pulses affect later pulses. This effect is amplified during the subsequent transmission of the pulse, and this reduces pulse quality. In the pulse generation systems of ICF laser drivers, this effect is detrimental to the precise pulse time shaping of the injected laser, reducing the energy utilization rate of the laser pulse. This significantly affects aspects such as the energy transmission and focusing of the laser, target ablation, plasma formation, and fusion reaction efficiency. The front-end systems of high-power laser facilities generate multiple pulses by utilizing time division multiplexing technology. Therefore, the objective of this study is to solve the crosstalk problem between multiple pulses and further improve the time shaping characteristics of laser pulses.

Figure 2 shows the front-end system structure of a multi-output high-power laser facilities based on time division multiplexing. First, the continuous-wave laser required by the system was generated and then modulated using an acousto-optic modulator (AOM) into a microsecond pulsed laser. The output is amplified using a fiber amplifier to increase the energy of the pulsed laser. Subsequently, a four-way fiber beam splitter was used to divide the pulsed laser into four outputs, which then entered their respective electro-optical modulators. Simultaneously, a sequence pulse containing four sub-pulses was generated by a high-precision AWG; this pulse can be independently and arbitrarily shaped. Subsequently, after being selected as a single pulse by the radio frequency (RF) switch, it was divided into four channels, enters their respective RF amplifiers, and acts on each electro-optical modulator. Finally, an arbitrary shaping output of the four optical pulses was realized.

The signal-to-noise ratio (SNR) of the output pulse of the proposed system is larger, indicating that the output optical pulse has enhanced anti-interference properties (Table 1). In addition, the rising time and shortest pulse of the optical pulse were within 100 ps; this indicates that the response speed of the RF switch is within a reasonable range, and its high-frequency characteristics barely affect the output pulse quality. An AWG is then used to output a wide pulse trains of 25 ns. The SNR of the output optical pulse in the comparison scheme is 36.86 dB, whereas that of the output optical pulse under the system design scheme is 42.76 dB. Furthermore, an AWG is utilized to output a large contrast shaping pulse, which is selected as a single pulse by the RF switch; the contrast ratio of the output optical pulse is 601∶1.

A multi-output system with independent shaping capability, based on time division multiplexing technology, is proposed to meet the requirements of multi-channel signal generation in the front-end system of high-power laser facilities and address the problem of crosstalk between pulses. Notably, the system entails the use of RF switches. It can select the electrical pulse train directly from the output of the AWG; then, each channel passes through the RF amplifier and electro-optical modulator separately. Thus, the arbitrary shaping output of multiple optical pulses can be realized. Based on the single channel of the AWG, the scheme can realize four optical pulse outputs with an independent arbitrary time shaping ability. It can achieve an output with a rising edge of 55 ps, a continuously adjustable pulse width ranging from 67 ps to 25 ns, and a pulse contrast higher than 500∶1. The system can effectively improve the SNR of the output optical pulse and avoid interference between signals; this is conducive to the improvement of the time shaping ability of the laser pulse. Thus, this study provides a technical scheme for the output of several arbitrary time shaping pulses in high-power laser facilities.