Laser calibration system for scintillation detector

Sumitted to PubDB: 2026-05-07

Category: Master Thesis

Tags: KLM

Principal Authors Ziyu Liu
Date 2026-05-07
Belle II Number BELLE2-MTHESIS-2026-024
Abstract This design aims at the upgrade of the KLM system for Belle II, proposing a time calibration system tailored for high time resolution scintillation detectors. In the KLM upgrade, it is planned to replace the existing RPCs with high time resolution plastic scintillator, enabling the measurement of the four-momentum of $K_L$ mesons and enhancing the event selection capability. These upgrades necessitate the detector's ability to precisely measure time. However, in a detector system with numerous readout electronics channels, the time differences between each channel significantly influence precise measurement. Therefore, a dedicated calibration system is essential to calibrate each electronics channel. In this design, a laser calibration system is developed, utilizing a laser diode with a working wavelength of 450 nm. After testing, the low-side drive circuit using GaN FETs was ultimately selected, and a prototype was made. GaN FETs are high-efficiency switching devices characterized by high turn-on speed, high switching frequency, lower on-resistance, and reduced switching losses. Driving GaN FETs requires a specialized driver, for which the LMG1020 gate driver was chosen. Through design and debugging, the shortest output pulse width achieved was approximately 3.2 ns, enabling the GaN's turn-on time to be around 4 ns, thus realizing short-pulse-width driving. Subsequent testing of the prototype evaluated the laser's performance and the effectiveness of the calibration system. The results demonstrated a time resolution of 12.4 ps on a single SiPM array, and the resolution of the time difference between any channel and the reference time reached 17.3 ps and 18.6 ps, confirming the system's capability to perform calibration tasks. Chapter 1 and Chapter 2 of this thesis will systematically introduce the background and principles of the work. Chapter 3 will detail the design of the two schemes and the selection of components. Chapter 4 will cover the system testing, including the evaluation of the laser's performance and the prototype's operation. Chapter 5 will summarize the work and propose some considerations for future developments.
Institute Nankai

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