J. Eur. Opt. Society-Rapid Publ. 2026, 22, 7 Ó The Author( s), published by EDP Sciences, 2026 https:// doi. org / 10.1051 / jeos / 2025057 Available online at: https:// jeos. edpsciences. org
Journal of the European Optical Society-Rapid Publications
RESEARCH ARTICLE
Nanosecond green pulse trains generated in a burst-mode by a Cr: YAG Q-switched Nd: YAG laser
Hossein Albaji 1, Mohammad Sabaeian 1, 2, and Hajar Alirezaei 2
1 Physics Department, Faculty of Science, Shahid Chamran University of Ahvaz, Iran 2 Center for Research on Laser and Plasma, Shahid Chamran University of Ahvaz, Iran
Received 3 November 2025 / Accepted 29 December 2025
Abstract. We present the development and characterization of a nanosecond-pulsed Nd: YAG laser operating in burst-mode and passively Q-switched using a Cr: YAG saturable absorber. The system is examined in three configurations: free-running, passively Q-switched, and frequency-doubled using an external KTP crystal. In free-running operation, the laser delivers 618 ls pulse duration with a peak output voltage of 12.47 mV. In the Q-switched regime, four cavity lengths are investigated, showing that shorter cavities significantly reduce the Q-switching threshold while increasing both the repetition rate and the number of pulses within each burst. The optimized 275-mm cavity produces bursts containing up to 22 pulses with 45 ns duration and a 56 mV peak voltage at an intra-burst repetition rate( f rep) of 7.142 kHz repetition rate. Pulse energy is estimated from the linear voltage response of an InGaAs fast photodetector to incident optical power. The temporal spacing between consecutive bursts is 13.12 ms, and each burst lasts approximately 250 ls. By integrating an external KTP crystal, second-harmonic generation at 532 nm is achieved, producing 6 ns green pulses with a 65.2 mV peak voltage at an intra-burst repetition rate( f rep) of 3.846 kHz. Beam instabilities related to SHG, known as the“ green problem,” are also observed. These results provide useful guidelines for optimizing burst-mode Q-switched lasers for efficient nanosecond pulse generation and frequency-doubling applications.
Keywords: Nanosecond pulse train, Burst-mode pulse, Nd: YAG laser, Cr: YAG saturable absorber.
1 Introduction
Solid-state Q-switched lasers, known for their compact design and operational simplicity, have become indispensable tools in a wide range of applications, including material processing, range finding, LIDAR systems, medicine, and optical communication technologies [ 1, 2 ]. Among the Q-switching techniques, passive Q-switching offers a particularly attractive solution due to its low cost, straightforward implementation, and the absence of external triggering components. This method relies on saturable absorbers to modulate intracavity losses and generate short, intense laser pulses [ 3, 4 ].
Early implementations used organic dyes as saturable absorbers, but their application has diminished due to issues like photodegradation and limited operational lifespans. In recent years, more stable alternatives – such as LiF: F 2 crystals and semiconductor saturable absorber mirrors( SESAMs) – have been developed. Nevertheless, Cr: YAG( chromium-doped yttrium aluminum garnet) remains the most widely used saturable absorber in passive
* Corresponding author: sabaeian @ scu. ac. ir
Q-switched Nd: YAG lasers, thanks to its excellent compatibility with the 1064 nm emission wavelength and its favorable nonlinear absorption properties [ 3, 5, 6 ]. The Cr: YAG crystal typically exhibits a damage threshold of > 500 MW / cm 2 and an excited-state lifetime of s = 3.8 ± 0.2 ls [ 7, 8 ]. Q-switched solid-state lasers based on Cr: YAG absorbers can deliver output energies in the millijoule range, peak powers in the megawatt range, and pulse durations in the nanosecond regime [ 9 ].
A notable feature of these lasers is their capability to generate burst-mode pulse trains, consisting of multiple high-repetition pulses within a short timeframe [ 10 ]. As illustrated in Figure 1, each pulse burst may contain several individual pulses separated by nanoseconds to hundreds of picoseconds, with burst repetition rates ranging from kilohertz to megahertz [ 9, 11 – 14 ].
In burst-mode Q-switching, the laser emits a group of closely spaced pulses – known as a pulse burst – within each Q-switched cycle. This behavior arises from the interplay between the dynamics of the saturable absorber and the transient gain evolution in the laser medium. Instead of a single pulse, the stored energy is released as a rapid sequence of pulses, offering distinct advantages such as
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