Journal of Russian Laser Research最新文献

Lasers with low-coherent radiation have attracted the attention since the first publications on this topic in the 1960s and up to the present time, thanks to their numerous applications. Compact lowcoherent lasers with a flow of the active medium through the pumped region can be done, using dense mixtures of solid particles and a liquid – slurry lasers. The preparation of slurry compositions based on particles like Nd :YVO₄ or Nd :YAG crystal granules meets certain difficulties associated with the use of liquids having high refractive indices, n ≈ 2. Here, we study the properties of a perspective Nd-doped slurry laser in model experiments, comparing parameters of Nd :YVO₄ and Nd :YAG slab lasers in compact plano-spherical resonators with and without a cuvette-diffuser on an immersion mixture of LiF crystal microparticles and isobutyl alcohol, n ≈ 1.39. At a laser diode pump power of 100 W, these lasers (without a cuvette) emit, in a quasicontinuous multimode regime, 1 ms pulses of low-coherent radiation (⋋ ≈ 1064 nm) with a divergence of 20 – 40 mrad and the 21 – 47 W power at the 10 Hz repetition rate. Under the same pumping conditions, we obtain a low-coherent radiation with the 1 – 6 W power and divergence up to 100 mrad in these lasers with a cuvette-diffuser. The spatial coherence of these lasers under changes in the pump current, pump spot sizes, and the state of immersion in the cuvette is estimated from the contrast C of the speckle patterns produced by the radiation. Also, we register C values in the region 0.02 − 0.04, comparable to the thermal sources contrast. The presented scheme demonstrates low-coherent Nd :YVO₄ and Nd :YAG lasers and show the feasibility of creating compact LD-pumped slurry lasers.

In this work, we investigate the performance of doped quaternary AlInGaN last quantum barrier (LQB) of deep-ultraviolet laser diodes (DUV LDs) without the electron blocking layer (EBL). The results indicate that the stimulated radiation recombination rate of the n–p-doped LQB structure increases. Compared with the undoped LQB structure, the threshold current of the n–p-doped structure of quaternary AlInGaN LQB for DUV LDs without EBL decreases from 43.79 to 36.59 mA, the slope efficiency increases from 1.20 to 1.28 W/A, and the threshold voltage increases from 4.62 to 4.63 V. These results demonstrate that the n–p-doped structure can significantly improve the performance of DUV LDs.

Based on the extended Huygens–Fresnel principle and the second-order moments of the Wigner distribution function (WDF), we derive the analytical formulas for the root-mean-square (rms) spatial width, rms angular width, and M²-factor of a partially coherent twisted elliptical vortex beam (PCTEVB) propagating through the inhomogeneous atmospheric turbulence. The spatial spreading, angular width, and M²-factor of a PCTEVB in turbulence are investigated numerically and comparatively. We find an interesting result that the relative rms angular width and M²-factor of PCTEVB with a small ellipticity propagating through turbulence decreases, meaning that the elliptical vortex beam is less affected by the inhomogeneous atmospheric turbulence in comparison with the traditional vortex beam. We also find that the relative M²-factor and the relative rms angular width of PCTEVB mainly depend on the topological charge, twist factor, initial coherent length, zenith angle, and propagation distance. In addition, the PCTEVB, with a small initial coherent length and ellipticity as well as a large twist factor, has a stronger anti-turbulence ability. Our outcomes may have future extensive possibilities in free-space optical communications.

We construct and characterize a small-size fast-axial-flow RF-excited CO₂ laser. The laser, including a pair of 10 cm long electrodes symmetrically positioned around a quartz tube, is driven by an RF generator with the 1 kW maximum power at a frequency of 13.56 MHz. The output power and efficiency of the laser are experimentally measured under different structural and operational conditions, such as the discharge tube diameter, width and length of electrodes, as well as the input RF power. The width of the electrodes is changed in such a way that the ratio of the total width of electrodes to the perimeter of the discharge tube (the so-called geometric ratio) varies in the 0.3 – 0.6 range. The diameter of the discharge tube is also changed in the 20 – 30 mm range. The results show that, for every given discharge tube diameter, optimum performance of the laser is obtained for 0.4 and 0.5 values of the geometric ratio. Although, a maximum output power of 63.5 W can be obtain applying the 1 kW input power, using the 2.6 cm discharge tube diameter, 0.6 geometric ratio, and CO₂ :N₂ :He=1 : 3 : 5 gas mixture at the 90 mbar total pressure. However, an optimum laser efficiency of 7.2% is reached under this condition for the 57.5 W output power. Further, the highest total output power and output power per unit length of the electrodes are obtained for the 20 and 10 cm electrode lengths, respectively.

This paper was stimulated by the experimental studies of solid-state lasers initiated by N. G. Basov and carried out at the Laboratory of Luminescence of the P. N. Lebedev Physical Institute under the direction of M. D. Galanin and A. M. Leontovich in the 1960-ies. Here, the classical parabolic equation method is extended in order to calculate complex eigenfrequencies of optical oscillations in a dielectric-filled open resonator. Accurate estimates confirm a high quality factor of ruby lasers. The developed approach can be used to find complex eigenfrequencies of other dielectric optical objects in laser systems of current interest.

Based on the extended Huygens–Fresnel principle, we derive the analytical expression of the crossspectral density matrix of a partially coherent Laguerre pulsed vector vortex beam (PCLPVVB) propagating through isotropic and anisotropic atmospheric turbulence. Our outcomes reveal that the atmospheric turbulence affects the evolution of spectral intensity distribution of PCLPVVB, and the beam quickly degenerates on propagation in the strong turbulence. We also can find that PCLPVVB with a larger topological charge has a stronger ability to resist the degeneration caused by atmospheric turbulence in comparison with the non-vortex beam. In addition, increasing the initial coherence length and mode order can increase the anti-turbulence ability of PCLPVVB, and the pulse duration significantly affects the spectral intensity of PCLPVVB in turbulence. Our research results are important for some applications in laser radar detection, remote sensing, and free-space optical communication.

We experimentally demonstrate a tunable and switchable low-threshold multi-wavelength erbiumdoped fiber pulsed laser. It is based on a composite structure of Lyot filter and nonlinear optical loop mirror. At a threshold of 30 mW, single-wavelength and dual-wavelength states can be obtained with a tuning range of 5 nm for the single wavelength and 1 nm for the dual wavelength. By adjusting the pump power and polarization controllers, the laser can achieve at most eightuple-wavelength operation. We use the nonlinear optical loop mirror as a saturable absorber to realize stable pulse output. The pulse sequences begin to appear when the pump power is 100 mW. The pulse repetition rate corresponding to the dual-wavelength is 40.52 kHz, and the pulse width is 144 ns. Due to its abundant range of wavelengths and significant pulse phenomenon, the proposed laser is widely used in fiber sensing and other fields.

Single-photon light detection and ranging (LiDAR) provides the single-photon sensitivity and picosecond time resolution, which is rapidly developing in three-dimensional (3D) imaging applications. Spatial resolution and imaging quality of LiDAR based on the single-photon avalanche-diode (SPAD) array detectors are difficult to improve, because currently available SPAD arrays still have small size array, due to the semiconductor manufacturing process limitation, and the functional circuitry around pixels reduces the fill factor. Herein, we propose a photon-efficient LiDAR method that guarantees the coupling relationship between the photosensitive area of each pixel and the corresponding beam spot illuminated on the target and uses 1/4 field of view (FoV) scanning imaging in the photosensitive area. The proposed method can effectively improve the spatial resolution of LiDAR system based on SPAD array detectors. Resolution test experiments show that the best observed (transversal) resolution is 3.1748 lp/mm at a working distance of 2.3 m, over tenfold larger than that of previous methods. Three-dimensional experiments prove that the system can achieve 3D high-resolution single-photon imaging, which is valuable in the fields of remote sensing and long-range target recognition.

In this study, we demonstrate a high-power continuous-wave (CW) Tm:YAP slab laser that is endpumped by laser diodes in a dual-end-pumped configuration. The laser delivers an output power of up to 341.6Wat 1.99 μm, corresponding to a slope efficiency of 49.4% and an optical-to-optical conversion efficiency of 41.6% with respect to the total incident pump power of 822 W. To our knowledge, this is the highest output power of a Tm:YAP laser. At an output power of 300 W, the beam quality factors M² are measured to be 260 in the x direction and 4 in the y direction, respectively. In addition, the power instability at the highest output power is measured to be 0.73% for 30 min. Also, we theoretically analyze the temperature distribution within the Tm:YAP slab crystal by the simulation software COMSOL 5.0.

We report the feasibility of a Ti₃SiC₂ MAX phase material as absorber for Q-switched pulse generation in the 1550 nm region. The proposed saturable absorber (SA) is fabricated by embedding Ti₃SiC₂ particles into polyvinyl alcohol (PVA) thin film and incorporated into Erbium-doped fiber laser (EDFL) cavity via a sandwich-structured fiber-ferrule platform. The SA thin film exhibits a linear absorption of 3.8 dB and a modulation depth of 51% in the 1550 nm region. Using the Ti₃SiC₂/PVA thin filmbased SA within an EDFL ring cavity, a self-started and stable Q-switched pulse train is achieved at a wavelength of 1561.8 nm. It exhibits a maximum pulse energy of 100.7 nJ, a maximum repetition rate of 43.5 kHz, and a minimum pulse width of 5.6 μs at a pump power of 71.5 mW. This result unveils the potential of Ti₃SiC₂ MAX phase material for use as a low-cost and practical SA for pulse generation in the 1550 nm region.