Applied Physics B最新文献

Changes in environmental conditions will directly influence the intensity of turbulent motion, and a random variation of the refractive index ensues. In this paper, a phase-based moiré deflection tomography is used to explore the effect of thermal disturbance on the spatial and temporal distributions of the refractive index structure constant, which is achieved after passing parallel beams through the indoor convective air turbulence. Initially, experiments are conducted for 60 min under two conditions: with and without the thermal flow field. In each set, 3600 frames of moiré fringes are successfully captured. And then, the temporal and spatial distributions of the refractive index structure constant are obtained. Subsequently, its regularities of distribution are analyzed in combination with the reconstructed temperature of the thermal flow field. Finally, the finding reveals a strong positive correlation between the refractive index structure constant and temperature fluctuations, in particular, the pronounced influence of thermal disturbance leads to a rapid exponential rise in its values. In a word, the related results could provide valuable insights for studying atmospheric optical communication and laser detection.

In this paper, we perform a cryptanalysis of a previously published symmetric cryptosystem that utilizes the Arnold transform (AT), singular value decomposition (SVD), and the fractional Hartley transform (FrHT) domain. By performing an attack-analysis, it is shown that the symmetric cryptosystem is vulnerable to a Known-Plaintext Attack (KPA). If an attacker knows the cipher-text and the order of the FrHT, attacker can recover the correct combination of SVD and AT parameters used in the image encryption algorithm. To overcome the security weakness of the symmetric cryptosystem, we propose an asymmetric phase image encryption by employing the Arnold transform, Singular value decomposition, and Hessenberg decomposition (HD) in the FrHT domain. The scheme is validated using evaluation metrics; mean-square-error, peak signal-to-noise, entropy, 3D mesh-, correlation-, noise-attack-, occlusion-attack-, and linear-attack analyses. Keys generated by SVD and HD make the cryptosystem asymmetric, making it resistant to Known-Plaintext Attack (KPA) and Chosen-Plaintext Attack (CPA).

We introduce a new utilization of an Aerodynamic Lens Stack (ALS) for concentrating aerosols in the production of high energy (>200 keV) electrons through their interaction with intense((>10^{16}) W/cm(^2)), ultra-short (30 fs) laser pulses. The lens was designed and simulated in COMSOL with various parameters such as inlet dimensions and backing pressures. Subsequently, the particle jet was analyzed using particle streak velocimetry (PSV). Following the characterization process, the jet was exposed to the laser, and the emission of electrons was investigated and described. Our results demonstrate the effectiveness of the lens in producing and focussing aerosols originating from liquid sources, underscoring its potential as a precise microtarget for laser interactions.

Coherent mode locking is based on the formation of (2pi) pulses of self-induced transparency in the absorbing medium and (pi) pulses in the amplifying medium. In this regime it becomes possible to generate ultrashort laser pulses down to one oscillation cycle with a pulse duration being much shorter than the polarization relaxation time (T_2) of the amplifying and absorbing medium. In this article a two-section laser model with a ring resonator based on absorbing and amplifying medium with short relaxation times has been applied. We have demonstrated a self-starting regime of coherent mode locking with picosecond and femtosecond laser pulses using numerical simulations for the given model. In addition, we have shown that there is a significant influence of generation frequency detuning on laser pulse duration and intensity. Moreover, we have compared our numerical results with an analytical model of a coherent mode-locked laser based on the area theorem. We believe that the findings of this work can open a pathway towards the practical application of mode locking in mid-IR and THz quantum cascade lasers.

We study Zeeman Electromagnetically Induced Transparency (EIT) in an effective three-level closed (Lambda) system involving the (D_{2}) transition of (^{87}{Rb}). The impact of coupling intensity and detuning, cell temperature, beam diameters, and transit relaxation rate are explored in a controlled manner on EIT width and peak transmission. Narrow EIT features of FWHM (approx 36) kHz and peak transmission (approx 92%) are noted. The dispersive characteristics of the ({^{87}{Rb}}) atomic medium, affecting the group index and group delay of the probe beam are also examined. The group index of the atomic medium has a nonlinear dependence on the coupling intensity, indicating that an optimization of the latter is required to attain a maximum reduction of the group velocity for slow light. For a probe beam diameter of 1.5 cm, a maximum group delay of 0.228 (upmu)s can be achieved corresponding to a group velocity of (v_{g}) =(frac{c}{914}) m/s. Our study especially highlights the impact of a detuned coupling beam on the probe transmission and its group delay. An interesting aspect of a negative group delay is noted for a sufficiently detuned coupling beam at low intensity which signifies the conversion from slow light to fast light.

The laser plasmas produced from the interaction of the high-power laser with the target surface are suitable sources for soft X-ray laser, which has many applications in industry and medicine. In order to create the maximum efficiency of the output soft X-ray laser, the parameters of the pump laser should be optimize. In a double-pulse pump laser, the intensity and width of the pre-pulse, the intensity and width of the main pulse and the delay time between the two pulses are effective parameters in the output X-ray production. In this research, by using a machine learning based on the multiple regression equation, the dependence of the gain coefficient on the pump pulse parameters are investigated and a statistical model for predicting the gain coefficient of soft x-ray laser based on the feature of the pump pulse is presented without the need to numerical solution of the complex hydrodynamic equations.

In this article, we proposed the use of optically pumped spin vertical-cavity surface-emitting laser (Spin-VCSEL) to create a photonic spiking neuron. We studied the dynamics of excitability and inhibitability under optical injection and analyzed the propagation characteristics of spiking information between unidirectionally-coupled Spin-VCSEL neurons. Our results demonstrated that by properly selecting parameters such as negative disturbance intensity from stimulus, pump ellipticity, and frequency detuning, Spin-VCSEL can achieve repeatable spiking output mode. Additionally, under certain conditions, it is possible to achieve inhibitory spiking output by selecting positive disturbance intensity from stimulus. By adjusting the duration and intensity of the disturbance, we can obtain controllable spiking responses for both excitable and inhibitory neurons. Furthermore, we found that under optimized injection strength, the spiking signal from the transmitter of Spin-VCSEL can be successfully propagated to the cascaded receiver with high quality. This work is meaningful because Spin-VCSEL offers new control dimensions such as pump ellipticity. Therefore, our study provides a valuable new choice for neuron construction of photonic spiking neural networks (PSNN).

In this work, experimental studies on the effect of dephasing on modulation transfer are reported. Here Potassium D1 transition, i.e., ³⁹K 4S_1/2(F) → 4P_1/2(F^/), is used as the medium. The 4 S→4P connection is modified by introducing two independent lasers. The separation between ground hyperfine states 4S_1/2(F = 2,1) is almost half of Doppler width (~ 815 MHz). Hence, the two-level connections satisfied by respective lasers are overlapping in nature. In such cases, the existing optical pumping for particular F = 1, 2→ F^/ channel influences each other. Further, the D1 transition itself is an open transition, i.e., it does not have any cyclic decay route. Hence, decay from each of the F^/=2,1 states can also influence the population in the other F^/state. Our pump-probe spectroscopy results clearly show the presence of Four Wave Mixing due to degenerate two-level and Vee (V) coupling, Electromagnetically Induced Transparency (EIT) signals due to single Lambda (Λ) and Double Λ connections. We have studied these signals as a function of dephasing, which is mainly contributed by transit time broadening for two different regimes of pump laser intensities: (i) below and (ii) above saturation intensity level of 4S_1/2(F) → 4P_1/2(F^/) transition. The pump laser is current modulated, and phase-sensitive detection is performed on the probe transmission to study modulation transfer under different values of coherent dephasing. For this purpose, the beam size of the pump laser is varied systematically. This study provides a scope to explore the modulation transfer as a function of transit time broadening, and it may find applications in photonics technology where potassium vapor is used as a medium.

We report the development of a seeded diode-pumped 1338-nm Nd:YAG amplifier which delivers 400-ps, 6-mJ, single-frequency pulses every half second with a fluctuation of (sim)

0.7%. A highly stable pulsed current controller is constructed to drive an 808-nm diode laser array that ensures the high stability of the laser. Numerical calculations show that 9.2 μm or 10.2-μm picosecond (<10  ps) pulses with 100-μJ energy can be generated by mixing the 1338-nm 6-mJ pulses with 1540-nm chirped pulses in a BGGSe nonlinear crystal and compressing the pulse with a grating compressor.

We investigate the behavior of various measures of quantum coherence and quantum correlation in the spin-1/2 Heisenberg XYZ model with added Dzyaloshinsky-Moriya (DM) and Kaplan–Shekhtman–Entin-Wohlman–Aharony (KSEA) interactions at a thermal regime described by a Gibbs density operator. We aim to understand the restricted hierarchical classification of different quantum resources, where Bell nonlocality (subseteq) quantum steering (subseteq) quantum entanglement (subseteq) quantum discord (subseteq) quantum coherence. This hierarchy highlights the increasingly stringent conditions required as we move from quantum coherence to more specific quantum phenomena. In order to enhance quantum coherence, quantum correlation, and fidelity of teleportation, our analysis encompasses the effects of independently provided sinusoidal magnetic field control as well as DM and KSEA interactions on the considered system. The results reveal that enhancing the entanglement or quantum correlation of the channel does not always guarantee successful teleportation or even an improvement in teleportation fidelity. Thus, the relationship between teleportation fidelity and the channel’s underlying quantum properties is intricate. Our study provides valuable insights into the complex interplay of quantum coherence and correlation hierarchy, offering potential applications for quantum communication and information processing technologies.