Journal of Russian Laser Research最新文献

We consider the interaction of Gaussian pulse of electromagnetic radiation with a plasma layer located in a constant magnetic field directed along the layer boundaries. We show that, when exposed to a long pulse, the transmitted pulse amplitude decreases due to a partial reflection from the layer boundaries and the influence of electron collisions. When exposed to a short pulse, in the case where the frequencies of the waves excited in the layer are far from the transparency region boundaries, the transmitted pulse broadens due to the group-velocity dispersion. If the frequencies of the excited waves are close to the transparency boundaries, the envelope oscillations appear in the transmitted pulse tail.

LiDAR is one of the main sensors for 3D object detection in autonomous driving. LiDAR has the advantages of high precision and high resolution, but as the distance increases, the points it acquires become sparse, resulting in uneven sampling points and hindering the feature extraction of discrete objects. Current 3D object detection methods using LiDAR ignore the sparse features of the original LiDAR point cloud, resulting in low classification accuracy over small object detection, hindering the development of autonomous driving technology. To address this problem, we propose point cloud Sparse Detection Network (PCSD), an end-to-end two-stage 3D object detection framework. First, PCSD uses a data augmentation algorithm to preprocess the KITTI dataset, then uses voxel point centroids to locate voxel features, and then uses a point sparsity-aware RoI grid pooling module to aggregate local voxel features. Finally, we improve the confidence of the final bounding box by using voxel features with the original point cloud sparse features. Experimental evaluation on the challenging KITTI object detection benchmark shows significant improvements, especially in pedestrian and cyclist classification accuracy improved by 13.22% and 9.33%, respectively, demonstrating the feasibility and applicability of our work.

Terahertz waves possess distinct characteristics, including such as transience, coherence, low energy, penetration, and fingerprint spectroscopy, which render them well-suited for a diverse range of applications in security inspection, nondestructive testing, and environmental detection. However, the efficiency of terahertz wave generation remains constrained by the terahertz source. To address this limitation and minimize losses in the generation process, the selection of band-gap-free semi-metallic materials, as terahertz radiation sources, is of utmost importance. We successfully fabricate TaSe₂ micro-wafer measuring 1×0.5 μm. By employing optical pumping at a wavelength of 1040 nm and a pulse duration of 150 fs, we achieve a terahertz output of nearly 0.005 μW. This output surpasses the terahertz generation efficiency of GaP crystals by approximately 20% under the same power density. Furthermore, we conduct investigations into the impact of incidence and optical polarization on terahertz wave generation. TaSe₂ exhibits suitability for high-efficiency, micro–nano-scale terahertz wave generation applications, such as on-chip terahertz systems and micro–nano terahertz sources.

In recent years, the application scope of LIDAR has been continuously expanding, especially in object detection. Yet existing LIDAR-based methods focus on detecting vehicles on regular roadways. Scenarios with a higher prevalence of pedestrians and cyclists, such as university campuses and leisure centers, have recently received limited attention. To solve this problem, in this paper we propose a novel detection algorithm named SecondRcnn, which is built upon the SECOND algorithm and introduces a novel two-stage detection method. In the first stage, it utilizes 3D sparse convolution on the voxel LIDAR points to learn feature representations. In the second stage, regression is employed to refine the detection bounding boxes generated by the Region Of Interest pooling network. The algorithm was evaluated on the widely used KITTI data set and demonstrated significant performance improvements in detecting pedestrians (4.61% improvement) and cyclist (6.5% improvement) compared to baseline networks. Our work highlights the potential for accurate object detection in scenarios characterized by a higher presence of pedestrians and cyclists. Advancing the use of LIDAR in the field of 3D detection.

In this paper, we introduce a novel approach to control the random lasing based on multiphoton luminiscence in Zinc oxide (ZnO) nanoparticle water suspension during its guided freezing process. The freezing process leads to the formation of a particle layer on the ice surface, consequently reducing the photon’s scattering mean free path in the medium, as well as increase in the efficiency of the second harmonic generation. This results in a lowered random lasing threshold in the system. The post freezing threshold, under the 355 nm wavelength excitation, decreases by an order of magnitude. These effects may have several applications, including the phase transition sensing, monitoring the evolution of porous structures via the ice-templating technique, controlling the random lasing mode, and enhancing various nonlinear optical processes’ effectiveness for nanoparticles and sub-micron particles in suspensions.

We demonstrate a Nd : YLF-YVO₄ intracavity Raman laser in the 1.5 μm eye-safe region. The fundamental wave at 1314 nm from the end-pumped Nd :YLF is down-converted to 1488 nm, utilizing the 890 cm⁻¹ Raman shift of an YVO₄ laser crystal. We use two etalons in the fundamental cavity and Stokes cavity, respectively, to suppress their spectral line width. Under a diode pump power of 43 W at 806 nm, we obtain an average Stokes output power of 3.75 W at an acousto-optic Q-switched pulse repetition frequency of 20 kHz, corresponding to an optical efficiency of 8.7%. With the etalons used, the spectral line width of the Stokes laser is narrowed from over 0.2 to 0.04 nm. The beam quality factor of the eye-safe Stokes output is measured to be 1.12 and 1.19 in the x and y directions, respectively.

The energy distribution of particles in a gaseous system is well understood through the implementation of a statistical tool, namely, the Maxwell–Boltzmann distribution function in the velocity–space coordinate system. The Maxwell–Boltzmann distribution function is utilized to investigate the velocity distribution of plasma particles like electrons, assuming that their collision frequency does not depend on the velocity. However, there is a swift transition in converting the Maxwell–Boltzmann distribution function to the Druyvesteyn distribution function for the case where a collision frequency is directly proportional to the velocity. Our aim is to incorporate the frequency components to investigate the Maxwell–Boltzmann and Druyvesteyn distribution functions. Employing the equation of motion, we observe that the collisional electron velocity is equal to the equilibrium electron velocity ∼eE/m_eω multiplied by the collisional frequency over the external source frequency β = ν/ω corresponding to the externally applied electric field. We investigate the difference in the Druyvesteyn distribution function between sheath and pre-sheath regions, when a stream of electrons is traversing or effusing through the part of a pre-sheath region corresponding to the dimension of the order of mean free path. Velocity and corresponding energy distribution functions are compared for non-effusion and effusion cases in the collisional and non-collisional regimes. The Maxwell–Boltzmann and Druyvesteyn velocity and energy distributions are competitive when the collisional frequency is twice the frequency of the applied electric field.

To improve the output power of solar-pumped lasers, we propose a new configuration of solar disk laser. A rotating parabolic reflector acts as the primary concentrator with top and bottom radii of 1600 and 600 mm, respectively. The incident sunlight is reflected by the primary concentrator to the inlet of the heteromorphic compound parabolic concentrator (HCPC) and is absorbed by the gain medium after multiple reflection. The diameter, thickness, and doping concentration of the Nd :YAG disk are 20 mm, 1 mm, and 1.0 at.%, respectively. The two surfaces of the disk are cooled by heavy water. Owing to the increased surface area of the disk for receiving sunlight, solar absorption by the gain medium is greatly improved. Ray tracing shows that maximum absorbed solar power by the Nd :YAG disk can reach 446 W through optimizing the HCPC. Solving rate equations, we obtain the laser output power in the TEM₀₀ mode as high as ∼123 W, with a conversion efficiency of ∼27%. In addition, we analyze the temperature distribution of the solar-pumped Nd :YAG disk laser. The design of this solar concentrating system and the over-hundred-watts disk laser provides a new idea for further scaling the output power of solar-pumped solid-state lasers.

In this paper, we present the results of an experimental study of the controlled contrast of optical properties of Germanium Telluride (GeTe) and Germanium Antimony Telluride (Ge₂Sb₂Te₅ or GST) 100 nm thin films, caused by laser-initiated reversible phase transitions from the amorphous-tocrystalline state, and vice versa. We demonstrate a high contrast in the transmissivity and reflectivity spectra in the wide wavelength range from 500 to 20,000 nm. We show that such a contrast of optical properties can be controlled in the set–reset mode, when samples of thin films are exposed to a nanosecond laser pulse at a wavelength of 532 nm, with a spatial distribution close to “top hat.” We confirm the laser-initiated changes in the thin film structures by X-ray diffraction analysis methods.

We focus our study on the quantum correlations of coupled photon pairs produced in an open atomic laser system, where quantum coherence is brought about by the superposition of a coherent atomic state and a coherent classical field. Quantum properties produced by photon–photon correlations are a long sought-after goal in quantum information science and technology, because photons combine at room temperature with high speed and long coherence times. The openness of the system under consideration allows quantum decoherence due to temperature and phase fluctuations to influence the quantum correlations generated. The competition between these quantum coherence and quantum decoherence leads to temporal quantum correlations, which we analyze using the time evolution of the density operator. Strong quantum correlations can be achieved by choosing an appropriate amplitude of the classical fields, treating temperature and phase fluctuations, and increasing the atomic injection rate over time. We also show that quantum entanglement is short-lived, quantum steering slowly decreases, but quantum discord increases with increasing heat bath temperature and atomic phase fluctuations. In this study, we explore the behavior of quantum correlations in an open atomic laser system and investigate the dynamics of entanglement, discord, and steering in this system and examine how they evolve over time.