High-Power Lasers and Light–Matter Interactions

High-power laser systems and the study of light–matter interactions at high intensities are crucial for numerous scientific and technological fields, ranging from industrial materials processing [1,2,3,4] and telecommunications [5,6,7,8] to fundamental physics research [9,10,11,12,13,14,15], biomedical applications [16,17,18,19,20,21,22,23], and advanced sensing [24,25,26,27,28,29,30,31]. Continuous advancements are focused on enhancing laser performance parameters—such as average and peak power [32,33,34,35,36], wavelength tunability [37,38,39,40], spectral purity [41,42,43,44,45], temporal pulse characteristics [46,47,48,49]—leveraging these capabilities to explore and exploit the complex interactions between intense light and various media [50,51,52]. This Special Issue highlights emerging developments in laser source technology, pulse manipulation, theoretical modeling, novel sensing applications, and diagnostic methods within the domain of high-power lasers and light–matter interactions.

The development of robust, high-performance laser sources tailored for specific applications remains a critical research direction. Recent efforts have focused on improving power scaling, wavelength accessibility, tunability, and beam quality. For applications requiring precise wavelength control, such as spectroscopy and coherent sensing, Sun et al. [53] proposed an external-cavity semiconductor laser design providing mode-hop-free (MHF) tuning across an extensive 140 nm range (1480–1620 nm), which covers the C + L telecommunication bands. This model achieves high spectral purity (SMSR > 61.65 dB), stable output power (>11.14 dBm), and rapid tuning (up to 200 nm/s), making it suitable for high-resolution vector spectrum analysis. Liu et al. [54] developed a kilowatt-level nanosecond laser system. Employing a hybrid MOPA architecture (fiber seed, Nd:YVO₄ pre-amplifier, and Nd:YAG slab main amplifier), they achieved an average power of 1.24 kW at a 20 kHz repetition rate, with adjustable pulse parameters (1–20 kHz, 10–300 ns), demonstrating high power extraction efficiency (39.1%). The 2 µm wavelength region is important for gas sensing, medicine, and communications application; therefore, Liu et al. [55] focused on optimizing the output of GaSb-based semiconductor lasers operating at this wavelength. By designing and implementing a slanted, wedge-shaped microlens fiber coupling scheme, they improved the output beam’s symmetry and uniformity, achieving stable output power around 210 mW.

Generating short, high-energy laser pulses is another key development direction. In the field of commercial lasers, slab laser technology is naturally the most conventional technical route for obtaining high-energy lasers. In the field of ultra-short laser pulse generation, the compression technique based on nonlinear optics is a hot topic, and nonlinear optical techniques are commonly employed for pulse compression. Liu et al. [56] developed a kilowatt-level nanosecond laser system, employing a hybrid MOPA architecture (fiber seed, Nd:YVO4 pre-amplifier, and Nd:YAG slab main amplifier), They achieved 1.24 kW average power with a 20 kHz repetition rate and adjustable pulse parameters (1–20 kHz, 10–300 ns). Their system has demonstrated high power extraction efficiency (39.1%) and successfully compressed 7.4 ns input pulses down to 48.3 ps, achieving a pulse energy of 5.27 mJ and an SRS stage energy efficiency of 21.84%, thus offering a practical route for high-energy picosecond pulses. Feng et al. [57] investigated pulse compression using SBS followed by passive laser-induced breakdown (LIB) in CCl₄. They have demonstrated that doping the LIB medium with silicon carbide (SiC) nanowires effectively reduces the LIB threshold and enhances the stability of the compressed output. Their method yielded compressed pulses of 254.4 ps with an energy conversion efficiency of 34.2%.

Accurate modeling and characterization are vital for understanding fundamental processes and optimizing the performance of optical systems. For diffraction-limited imaging systems, understanding the point spread function (PSF) is crucial. Song et al. [58] derived a novel analytical solution for the defocused PSF using series expansions of confluent hypergeometric functions. This model provides insights into imaging performance degradation caused by defocusing, is independent of specific system design details, and shows good agreement (<3% RMS error) with numerical FFT methods in weak to medium defocus regimes. In laser Doppler sensors employing intersecting beams, precisely knowing the interference fringe geometry is critical for accurate measurements. Zhang et al. [59] developed and experimentally validated a high-accuracy 3D model for fringe spacing distributions in line-shaped Gaussian beam intersections. Their model, derived from Gaussian beam phase expressions, accurately predicted fringe geometry (average relative difference of <0.6% compared to the experimental results), enabling error minimization in 3D shape and velocity measurements.

High-power and precisely controlled lasers enable unique sensing modalities and material interaction studies. Wang et al. [60] explored the Goos–Hänchen shift (GHS)—a subtle lateral displacement of a reflected beam—as a potential basis for illicit drug detection. By measuring GHS variations for different substances (serum, methamphetamine, and heroin) and correlating them with complex refractive indices and dielectric constants, they have demonstrated the sensitivity of the GHS to these parameters, emphasizing its potential in the development of novel optical sensors for chemical identification. Enhancing the efficiency of photovoltaic devices is a primary scientific objective. To that end, Wang et al. [60] demonstrated broadband (400–2000 nm) spectral response enhancement in amorphous silicon p-i-n photovoltaic modules by incorporating flower-like silver nanoparticles. The observed tenfold increase in peak responsivity was attributed to the near-field plasmonic effects arising from the complex nanoparticle geometry, improving optical energy utilization. Understanding the dynamics of laser–material interactions, such as shock wave generation, is important for applications like laser peening and material processing. Li et al. [61] employed a convolutional neural network (CNN) to predict the temporal evolution of shock wave velocity, induced by the combination of millisecond–nanosecond laser pulses on silicon. The CNN model achieved high predictive accuracy (R² = 0.9865) with limited experimental data, showcasing the potential of machine learning for modeling complex, dynamic laser interaction phenomena.

Probing extreme environments, such as combustion chambers or supersonic flows, requires sophisticated diagnostic techniques. Song et al. [58] provided a timely review of the advances in femtosecond coherent anti-Stokes Raman scattering (fs-CARS) for thermometry. They highlighted the advantages of fs-CARS, such as the suppression of collisional effects and non-resonant background, thus enabling accurate, time-resolved temperature measurements crucial for understanding transient chemical reaction dynamics in harsh environments.

Overall, this Special Issue highlights several key trends in high-power laser technology and light–matter interactions. There is a continuous drive towards higher-power sources [54] and broader, more agile wavelength tuning [53], often tailored for specific application domains. Simultaneously, precise control over the temporal domain, particularly towards the achievement of ultra-short pulses via novel compression schemes [56,57], remains a key focus for accessing high peak intensities and studying ultrafast dynamics. Theoretical modeling and accurate system characterization [59] are increasingly more sophisticated, providing essential tools for optimizing design and performance. Furthermore, the exploration of subtle optical phenomena, such as the GHS for sensing [60] and harnessing plasmonics for device enhancement [61], demonstrate innovative application pathways. The integration of machine learning techniques represents a promising direction for modeling and predicting complex, nonlinear interaction dynamics where analytical solutions are intractable. Advanced diagnostics like fs-CARS are indispensable for probing the extreme conditions often generated or studied using high-power lasers. These advancements are also highlighted in this Special issue.

Future research is projected to continue following these trends, potentially exploring novel gain materials and laser architectures, pushing pulse compression limits further into the femtosecond and attosecond regimes. Moreover, by developing more sophisticated multi-physics models, which are perhaps further enhanced by machine learning, and discovering new applications based on precisely controlled light–matter interactions, this field holds tremendous potential. Integrating multiple functionalities, such as combined sensing and processing capabilities, may be another future direction. Significant progress continues to be made across the field of high-power lasers and light–matter interactions. The recent developments highlighted in this review include the realization of versatile high-power and widely tunable laser sources, innovative techniques for achieving picosecond pulses through nonlinear optics, refined analytical models for optical system performance, the application of optical phenomena and nanostructures for novel sensing and device enhancement, and the use of machine learning and advanced diagnostics to understand complex interaction dynamics. These advancements collectively underscore the role of laser technology in science and industry and point towards continued innovation in the future.