Journal of Russian Laser Research最新文献

We propose and demonstrate a passively mode-locked all-fiber laser utilizing a multimode interference effect in graded-index multimode fiber (GIMF). The mode-locking is obtained due to the Kerr effect in GIMF, which induces the intensity modulation inside the ring cavity laser. We obtain stable soliton mode-locked pulses at a center wavelength of 1574.1 nm, with a fixed repetition rate of 22 MHz and a pulse duration of 650 fs, when the pump power is changed in the range from 66.2 to 140.0 mW. The maximum average output power and pulse energy are recorded at 9.82 mW and 448 pJ, respectively, at a pump power of 140 mW. This proves that a nonlinear optical response in GIMF can be used as a new modulation mechanism for obtaining ultra-short pulses based on all-fiber ring cavity.

We theoretically study resonant hyper-Raman scattering of light by 2 LO phonons in a CdS crystal with the wurtzite structure. The scattering process involving the two-photon dipole transitions to B and C excitons of the s-type is considered. The different sequences of intermediate states are taken into account. It is shown that the inclusion of the possible dipole transitions to the deeper valence band, at certain conditions, can have a noticeable effect on the frequency dependence of the scattering cross section.

Using InSb/GaSb semiconductor quantum dots, we demonstrate the lateral spatial resolution of scattering apertureless near-field microscope equal to 10 – 15 nm at a wavelength of λ = 10.7 μm provided by a single-mode CO₂ laser. The measurement conditions make it possible to undoubtedly exclude any artifacts caused by the sample topography and other similar factors. We identify the strongly localized in-plane near-field signal with a two-dimensional electron gas clamped on the InSb/GaSb interface of quantum dots.

We study the effect of geometric dimensions on the optical properties of equilateral triangular gold and silver nanoprisms with rounded corners. An analytical expression for calculating the spectral characteristics of the main longitudinal plasmonic resonance of such nanoprisms is obtained. As variables, the expression includes the nanoprism dimensions, its composition, and the permittivity of the surrounding environment. Our results demonstrate that the extinction cross sections can be adequately described by this expression for nanoprisms with edge lengths up to a few hundred nanometers. We show that the scattering of free electrons from the metal/environment interface in metallic nanoprisms can be described with the help of the size-dependent dielectric function. Using a simple relation, we evaluate the necessary effective size parameter, which allows one to achieve a good agreement with experimental data. The results obtained are of interest for solving a number of fundamental problems in nanophotonics and nanoplasmonics, as well as for applications in the development of next-generation optoelectronic devices.

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.