Applied Physics B最新文献

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.

Through theoretical calculations and field experiments, the setting of gate width in distance gating technology has been optimized in DIM LiDAR. The mathematical relationship between gate width and detection distance has been derived. The relationship curves between gate width and image signal-to-noise ratio(SNR), as well as gate width and atmospheric refractive index structure constant (C_n^2) were obtained. The results indicate that at a constant detection distance, there is a gradual increase in the SNR of the image with increasing gate width, followed by a saturation point. The higher the SNR, the closer the inverted (C_n^2) is to the ultrasonic anemometer. Meanwhile, if the SNR is similar, the inverted (C_n^2) is similar. Finally, the appropriate gate width for this system is given.

In the centre of mass frame, we have investigated the electroweak process ({e}^{+}{e}^{-}rightarrow mu ^{+}mu ^{-}) in the presence of a plane and monochromatic laser wave of linear polarization. We provide the theoretical calculations of the differential cross-section for this process by using the scattering-matrix approach and Dirac-Volkov formalism. The laser-assisted cross-section is computed, and its dependence on the laser parameters is analyzed. We have found that this cross-section increases significantly inside a linearly polarized laser wave co-propagating with the incident particle’s beam, and it passes its corresponding laser-free cross-section by several orders of magnitude.

This study examines the electronic and optical properties of an asymmetric double delta doped quantum wells structure formed within GaAs. The electronic structure of system is obtained within effective mass and envelope wave function approximations. Optical responses are calculated in the framework of the compact density matrix approach. The roles of distance between wells, varying one well electron concentration, as well as length parameter of position-dependent mass, on the total optical absorption coefficients and the relative refractive index changes are investigated. The findings of this study indicate that prominence of optical coefficients occurs at higher energies for position-dependent mass, compared to constant mass case. Augmented right well electron concentrations lead to blue-shifts on the optical properties not only with constant mass but also with position-dependent mass. However, the increase in the wells’ separation results the absorption peaks to move towards lower energies.