Applied Physics B最新文献

The manipulation of quantum states via mechanical strain offers a pathway to engineer topological excitons in soft semiconductors. Here, we present a theoretical framework that shows that helical strain transforms lead halide perovskite quantum dots (QDs) into a platform for topological excitonics. Using a first-principles-informed framework combining strain-modulated Lamé eigenstates and non-perturbative Coulomb interactions, we identify a strain-driven topological transition at critical ellipticity (k = 0.59 pm 0.02), (corresponding to ≈ 2% torsional strain) marked by inversion of the exciton Chern number ((C = 0 to 1)) and π-Berry phase accumulation. Quantitative calculations yield an exciton binding-energy enhancement up to 45 meV and photoluminescence (PL) redshifts of ≈ 72 meV, in agreement with experimental data. The computed deformation potential (− 0.8 eV/% strain), group-velocity scaling (v ∝ k^1.7), and Chern-number inversion confirm a strain-driven topological crossover supported by Berry-phase accumulation. Comparison with reported PL and diffusion measurements validates the predictive accuracy of the Lamé-Coulomb formalism, which bridges continuum elasticity with quantum confinement. These findings proposes perovskite QDs as experimentally accessible hosts of strain-tunable topological excitons, enabling reconfigurable quantum-photonic and optoelectronic devices based on mechanically programmable excitonic states.

The laser-induced fluorescence of oxygen in organic solvents was investigated as a potential contactless method for quantifying its concentration. The fluorescence was excited directly by a diode laser radiation in the 1270 nm oxygen absorption band. Neither a sensitizer nor singlet oxygen traps were added to the solvent. An uncooled photodiode was used as a detector. A simple kinetic model was used for assessing the oxygen concentration from the signal magnitude and decay time. An advanced model explaining the observed deviation of fluorescence kinetics from single exponential decay is presented. The method was tested with pure and contaminated Freon-113 samples, chloroform, acetone and n-heptane.

Recently, there has been a growing trend toward exploring and exploiting new/additional degrees of freedom in optical beams. This is particularly relevant in the field of multiplexing optical data transmission channels and in the interaction of laser radiation with matter. In this paper, we explore two aspects of additional degrees of freedom in axisymmetric binary elements. The first is the generalized phase dependence on the radius, which leads to variations in the longitudinal beam distribution. The second degree of freedom is associated with the binarization effect, which generates multiple axial diffraction orders. Control of these orders is proposed by introducing a vortex component in the illuminating beam. More specifically, we consider binary axisymmetric and vortex generalized axicons which are optical elements with different power-law dependence of the phase on the radius. Formation of additional axial diffraction orders associated with binarization leading to complex interference distributions on the optical axis is studied analytically, numerically and experimentally. Selection and compensation of such diffraction orders is much more complicated than off-axis ones (which can be simply isolated with an opaque screen), but their use provides a 3D character of control over the distribution and multiplexing of laser beams. It is shown that the use of vortex illuminating beams allows one to effectively solve the problem. At the same time, the allocation of high diffraction orders provides a proportional decrease in the size of the light spot on the optical axis. The experimental results fully confirm the obtained modeling results. The studies performed in this paper can be useful for variations in the size of the focal region, 3D (de-)multiplexing and coding.

The modulation of laser pulse with high photon energies is an important tool for the observation and control of the dynamic of inner-shell electron in atoms and nucleon in atomic nuclear. We present a theoretical method for the reshaping of extreme ultraviolet (XUV) pulses by the modulation of an infrared (IR) pulse combining with the propagation effects of the XUV pulse in helium. The spectrum is redistributed within a specific frequency range around the coherent frequency of the atomic system, which allows for frequency tuning and spectral compression of the XUV pulse, significantly enhancing its radiative intensity at different frequencies. These findings deepen our understanding of the propagation effect and control mechanisms of XUV pulses in atomic media.

This paper proposes a novel square-core optical fiber with an internally gold-coated structure for RI sensing. This novel design offers a wide area for the analyte channel and a flat surface for gold film deposition. Additionally, the unique structure facilitates enhanced field interaction with the gold film, as the metal film is positioned along the core surface. The proposed sensor demonstrates outstanding performance not only in RI sensing but also in cancer cell and pathogen identification. The recorded sensitivities are 25,000 nm/RIU for RI sensing in the range of 1.33–1.41, 8571.43 nm/RIU for cancer cell detection, and 6382.98 nm/RIU for pathogen identification in water. Other performance parameters such as the figure of merit (FOM), sensor resolution, and detection accuracy (DA) also highlight the potential of this sensor in the respective domain. Another contribution of this work is the incorporation of a machine learning approach, called Gaussian Process Regression (GPR), to predict the resonance wavelength for any intermediate RI value, which could broaden the scope of this sensor’s applications.

This paper offers a novel semiconductor metamaterial structure capable of supporting sluggish, dispersionless plasmonic waves. The suggested arrangement demonstrates the slow light phenomena, which is an important aspect of photonic crystals. Incorporating semiconductor ellipsoidal nanowires into the metamaterial structure adds a degree of freedom in order to engineer the propagation of slow light surface plasmon polaritons. Numerical simulations confirm the excited wave’s plasmonicity.

In this study, the spatial coherence of the 46.9 nm capillary discharge extreme ultraviolet (EUV) laser was analyzed. The fringe visibility of the laser was measured using Young’s double-slit method at different transverse positions of the laser spot and showed the same trend as the laser intensity spatial distribution. Additionally, the fringe visibilities corresponding to different Ar pressures were measured and were found to increase with the laser intensities. The results also showed that the relative intensity and maximum fringe visibility of the laser were linearly reduced with a decrease in capillary length from 35 cm to 25 cm. The highest fringe visibility value reached 0.935 under the conditions of a 35 cm capillary length and an internal Ar pressure of 20 Pa. These findings contribute to the expansion of applications for the 46.9 nm lasers.

In this work, hafnium diselenide (HfSe₂)-based saturable absorbers (SA) were fabricated and applied for the modulation of Tm:YAP lasers. In continuous-wave mode, a 12.9 W laser diode was used to pump the Tm:YAP crystal, resulting in an output power of 2.35 W at 1996.2 nm, corresponding to an optical-to-optical conversion efficiency of 19%. In passively Q-switched mode, the Tm:YAP laser modulated by the HfSe₂ SA achieved an average output power of 1.45 W, with a pulse width of 712.8 ns and a pulse repetition frequency of 103.17 kHz at a central wavelength of 1989.1 nm. The corresponding optical-to-optical conversion efficiency was 11.2%, with a single-pulse energy of 14.1 µJ and a peak power of 19.7 W. The rate equation was used to calculate the modulation depth (10%), saturation flux (1 kJ/cm²), and unsaturated loss (0.0505).

We report on a compact, passively Q-switched waveguide laser fabricated via femtosecond direct laser writing (fs-DLW) in an Yb:LuGG crystal. Prior to Q-switching experiments, continuous-wave operation was systematically characterized under various cavity configurations, achieving a maximum output power of 678 mW and a slope efficiency of 53.6% using a 70% output coupler. Passive Q-switching was implemented by incorporating single-walled carbon nanotubes (SWCNTs) as a saturable absorber, enabling stable laser operation over several hours. The 7.39-mm-long waveguide laser operated near 1030 nm, and its Q-switched performance was investigated using three output couplers with different transmissions. The best performance was obtained with a 50% output coupler, yielding pulses as short as 35 ns, a maximum output power of 478 mW, and a highest repetition rate of 2.51 MHz. These results demonstrate the excellent compatibility between fs-DLW-fabricated Yb:LuGG waveguides and SWCNT-based saturable absorbers, offering a promising route toward robust and highly efficient compact pulsed laser sources.

To achieve high-peak-power and highly-stable pulsed laser output at 1112 nm, a birefringent filter (BF) and a Brewster window (BW) were incorporated into an 808 nm laser-diode (LD) side-pumped Nd: YAG cavity. This configuration provides triple functions of polarization control, frequency selection, and spectral filtering, effectively suppressing competing oscillations at the 1116 nm and 1123 nm lines while reducing the number of longitudinal modes at 1112 nm. Furthermore, a pre-biased transversely pressurized electro-optic Q-switching technology was employed to lower the modulation voltage of the MgO: LN crystal, thereby enhancing its extinction efficiency. At a maximum LD pump current of 100 A, an average output power of 2.386 W, a pulse width of 4.82 ns, and a peak power of 4.950 MW were measured from the 1112 nm pulsed laser with a pulse repetition frequency of 100 Hz. The corresponding pulse-to-pulse fluctuation of single-pulse energy and pulse width were ± 0.30% and ± 0.84%, respectively. At 1.0 kHz, the average power, pulse width, and peak power measured 11.389 W, 6.22 ns, and 1.831 MW, respectively, while the power and temporal fluctuation remained low at ± 0.72% and ± 1.77%. These results demonstrate that the proposed technique, which combines pre-biased pressurized MgO: LN electro-optic Q-switching with BW and BF filtering, offers a viable approach to enhancing both the peak power and stability of 1112 nm pulsed lasers.