## 2 Materials and Methods
### Design of Drive and Control System
When it exceeds the threshold voltage (V\({}_{\text{th}}\)), the drain current of the MOSFET begins to appear, and simultaneously, the load current (I\({}_{\text{L}}\)) is generated. As V\({}_{\text{G}}\) increases, I\({}_{\text{L}}\) also gradually increases until the current reaches the rated value as required by the reference signal, as detected by the current-sensing resistor. Afterward, the system continuously regulates the current to meet the requirements of the reference signal. This dynamic control mechanism ensures precise and stable pulse current output for optimal performance of the microchip laser in various operational scenarios. Figure 6: Control Circuit Structure Diagram. Figure 7: Schematic Diagram of Control Circuit. The drive for the laser necessitates a sufficiently short rise time of a large current, a challenge that conventional DC-DC converters find difficult to address directly. Therefore, an energy storage system is selected as the implementation scheme to store energy, leveraging the discharge characteristics of a capacitor to supply instantaneous current. This approach not only fulfills the requirements of driving the laser but also alleviates the demands on the transient power of the external power source, meeting power limitations in deep space exploration applications. To maintain a minimal voltage drop across the laser terminals during operation, it is typically required that the voltage drop of the energy storage capacitor does not exceed 10% during discharge. According to  
\[C_{\text{min}}=\frac{I_{\text{max}}t_{on}}{\Delta u} \tag{1}\]  
the required capacitance value can be calculated. Here, \(I_{\text{max}}\) represents the required current, \(t_{on}\) is the pulse duration of the current, and \(\Delta u\) is the permissible voltage drop across the energy storage capacitor. The core of the pulse constant current source system lies in the Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET). Its operation in the linear region is harnessed to control the drain current by manipulating the gate voltage. In this configuration, the current exhibits constant characteristics, and the MOSFET responds rapidly to changes in the gate voltage. Moreover, it demonstrates good linearity in response to gate voltage variations, facilitating precise control of the output current. Since the MOSFET operates in the linear region, it needs to endure a certain voltage drop. It is crucial to ensure that it consistently operates within the Forward Biased Safe Operation Area. Additionally, when operating in the saturation region, devices with lower ON resistance should be chosen to minimize power dissipation on the MOSFET. Due to the short duration of the pulse current during laser operation, a high bandwidth requirement exists for the driving system. Consequently, the pulse constant current source system employs analog loop compensation, offering a larger bandwidth compared to digital loop compensation. To enhance the accuracy and stability of the pulse current, a proportional-integral-derivative (PID) control algorithm is employed to regulate the system. It adjusts the system's response speed through the proportional and integral terms, enabling it to respond more rapidly to changes in the input signal and adapt to the requirements of high-bandwidth short-pulse applications. Additionally, the derivative term suppresses system oscillations, ensuring stability and smooth operation. Following Formula (2) below, \(K_{p}\) represents proportional gain, \(\frac{K_{p}}{T_{r}}\) represents integral time constant, and \(K_{p}\tau\) represents derivative time constant. The compensating network incorporates a system compensating poles and zeros. It provides a high gain in the low-frequency range, enhancing the open-loop gain of the system, while rapidly attenuating the loop gain in the high-frequency range. In practical adjustment, it is advisable to start by adjusting the proportional coefficient from the middle toward both ends.