Applied Physics B最新文献

This manuscript presents a quantum-cascade-laser-absorption-spectroscopy (QCLAS) diagnostic for the partial pressure and internal temperatures (rotational and vibrational) of nitric oxide (NO) in hypersonic flows. Two quantum-cascade lasers (QCLs) were used to measure four transitions of NO near 1887 cm(^{-1}) and 1930 cm(^{-1}) at 25 or 100 kHz using scanned-wavelength direct absorption. Tests were performed in the Purdue High-Pressure Shock Tube (HPST) using an NO–Ar mixture to confirm the accuracy of the diagnostic. The diagnostic was then applied to characterize the Hypersonic Shock Tunnel (HST) at Sandia National Laboratories. In the HST, two flow cutters were used to direct the measurement line-of-sight through the quasi-uniform core flow exiting the nozzle, thereby avoiding measurement complications associated with the thick boundary layers at the nozzle exit. In the HST, tests were performed with air velocities of 3, 4, and 5 km/s where the rotational and vibrational temperature of NO varied from 150 to 850 K and the partial pressure of NO was near 20 Pa. Additionally, dry bottled air and humid room air were used as test gases to quantify the impact of water contamination on the vibrational non-equilibrium of NO. Comparisons with two CFD predictions using unique rate constants for vibrational relaxation are also presented. The vibrational non-equilibrium of NO was more pronounced for 3 km/s tests, and water had a negligible impact on the thermal non-equilibrium of NO. Lastly, the measured rotational temperature of NO agreed well with CFD predictions, the measured partial pressure of NO was consistently above CFD predictions, and the vibrational temperature had moderate agreement with CFD predictions for 4 and 5 km/s tests, and poor agreement for 3 km/s tests.

We prepared a double-crystal LiTaO₃ (LT) electro-optic (EO) Q-switch and investigated its overall Q-switching performances. The LT EO Q-switch is fabricated from two x-cut LT crystals to utilize the maximum effective EO coefficient. The static and dynamic quarter-wave voltage were measured to be 1200 V and 950 V respectively, which are both considerably lower than those of other commercial EO Q-switches. Besides, the LT Q-switch can operate at a wide temperature range with high temperature stability. The dynamic-to-static ratios at sub-freezing temperatures were up to 80 percent of that at room temperature. Furthermore, the piezoelectric ringing in the LT Q-switch was found to be comparable to that of RTP Q-switches, and it had been successfully operated at a repetition rate of 1 kHz with stable Q-switched laser output. The only disadvantage is the low extinction ratio which is mainly caused by the optical inhomogeneity and can be improved by improving the optical quality of LT crystals. The double-crystal LT EO Q-switches are particularly attractive for Q-switched lasers because of their excellent comprehensive performances.

External cavity diode laser (ECDL) can continuously alter its output optical frequency by tuning the external cavity. Wide mode-hop-free (MHF) range and linear optical frequency tuning are two critical characteristics of the ECDL. However, using an uncoated laser diode (LD) limits the MHF range due to the influence of internal cavity formed by the LD. To obtain linear optical frequency, a triangular wave voltage is generally used to scan the external cavity. Nevertheless, the inherent hysteresis characteristic of piezoelectric transducer (PZT) in the external cavity introduces nonlinearity in the optical frequency. The limited MHF range and nonlinear optical frequency can greatly affect the performance and accuracy of applications with uncoated ECDL as the light source. Therefore, it is crucial to address these two issues of uncoated ECDL. This study introduces a hybrid method incorporating synchronous tuning with proportional-integral-derivative (PID) feedback control. Synchronous tuning facilitates simultaneous changes in both the internal and external cavities output modes, thereby extending the MHF range. PID feedback control utilizes the displacement signal of prism in the external cavity to establish a closed-loop control system, compensating for the PZT’s hysteresis. Through PID feedback control, the uncoated ECDL’s optical frequency tuning nonlinearity is effectively suppressed while its MHF range is extended. Experimental results validate the efficacy of this hybrid method within the triangular wave scanning frequency of 50 Hz.

We propose and numerically demonstrate all-optical logical operations using frequency-switched spiking encoding based on excited photonic spiking distributed feedback semiconductor lasers (DFBs). The results reveal that, DFBs can exhibit the neuron-like dynamic behaviors under optical injection with different intensity and detuning frequency. Utilizing the spiking responses induced by frequency switching, binary data can be encoded into spikes and stable spiking response sequence with 8 orders of magnitude faster than that from biological neurons can be achieved. Furthermore, the reconfigurable all-optical logical operations including OR, AND, XOR can be implemented in a single photonic spiking neuron, and the effects of injection coefficient, duration time and the time delay between two continuous trigger signals on XOR logical operation are discussed. This proposed frequency-encoding-based spiking DFB neuron can pave a new way for all-optical logical operations and future photonic spiking neural network.

In this work, iron-oxide nanoparticle formation in the spray-flame synthesis (SFS) process of the standardized SpraySyn 2.0 burner was investigated in situ using laser-induced incandescence (LII). For the evaluation of these measurements, prior LII-experiments within iron-oxide aerosols (Fe₃O₄ and α-Fe₂O₃) with known primary particle size distribution and morphological properties were performed to determine the thermal accommodation coefficient (TAC) α, which led to approx. α = 0.08. The applicability of the TAC results within the flame was validated using spectrally and temporally resolved measurements in the flame at 65 mm HAB employing a spectrograph. Data for a bimodal particle size distribution, obtained from Transmission Electron Microscopy (TEM), were used in the LII-evaluation. The validated TAC was then used to evaluate the primary particle size evolution from in situ Time-Resolved (TiRe) LII-measurements using PMTs along the centre axis of the burner, ranging from 10 mm to 50 mm HAB. These measurements reveal a relatively constant effective particle diameter along HAB with d_p,eff ≈ 300 nm. To further investigate particle formation in SFS, 2-dimensional time-resolved LII-measurements in the SFS flame were performed, showing a clear particle formation region up to approx. 30 mm HAB, from where on a constant particle mass is observed.

The investigation of the thermo-optic characteristics of a material is vital in understanding the nonradiative relaxation processes occurring within the sample. Pyrromethene 567 a member of the laser dye family, has gained significant attention due to its excellent photo-physical characteristics, such as excellent laser efficiency, photostability, and quantum yield. The investigation of the photothermal studies in Pyrromethene 567 remains unexplored. Herein, a dual-beam thermal lens technique was performed to analyze the thermal lensing behaviour of Pyrromethene 567 in various solvents. The thermal diffusivity of Pyrromethene 567 in different solvents was calculated. There were no previous reports measuring the thermal diffusivity of Pyrromethene 567 dye. Thermal lens spectroscopy offers several advantages over conventional techniques because of its high sensitivity. The work also discusses the factors that influence the thermal lens signal in Pyrromethene 567. The influence of detector positioning, chopper frequency, and sample positioning, on thermal lens measurements was discussed. Additionally, the thermal lens experiments should be performed at intensities where diffraction patterns due to spatial self-phase modulation are absent to minimise experimental errors.

Using a non-holographic optical setup, we employed a Mueller–Stokes polarimeter to measure both the linear electro-optic and second-order electrogyration effects. The second-order electrogyration effect was observed in a (Bi_{12}SiO_{20}) (BSO) crystal with a (110) cut. This response was found for the electric field applied both parallel and perpendicular to the [001] direction, where the values for the second-order electrogyration are (4.86times 10^{7} , text {pm}^{2}/text {V}^{2}) and (1.87times 10^{7} , text {pm}^{2}/text {V}^{2}), respectively. Additionally, the linear electro-optic coefficient (gamma _{41}) was measured to be (1.17 , text {pm/V}) for (660.5 , text {nm}).

Different laser surface texturing (LST) parameters produce varying effects, prompting the need to rationalize a strategy that optimizes structure for specific functionalities while maintaining manufacturing efficiency. This study applied square groove texturing to 304 stainless steel samples using a combination of scanning paths and Burst-mode to explore strategies that enhance texturing effect. In this paper, the texturing effect is quantified by texturing efficiency and surface quality. The square groove textures were manufactured using four scanning paths under picosecond lasers: 90°, 60°, circular, and horizontal-vertical reciprocating (HVR), along with Burst-mode at various pulses per burst (PPB). Multifactorial experiment systematically analyzed the texturing effect of various combination strategies. Additionally, this study established a geometric simulation model to validate the experimental results’ accuracy. Comparative analysis demonstrated that the simulation model effectively reflects the actual texturing results. The results indicated that this strategy achieves better texturing effect compared to traditional methods. Specifically, with the pulse number fixed at 2, the texturing efficiency of the horizontal-vertical reciprocating (HVR) scanning path is nearly twice that of the 60° scanning path, while also maintaining superior surface quality.

The statistical and squeezing characteristics of the light generated by a two-mode subharmonic generating system in a cavity pumped by two-mode coherent light and coupled to a two-mode thermal reservoir through a single-port mirror have been studied in this study. We construct the c-number Langevin equations linked to the normal ordering using the master equation for the system under discussion, and we establish the correlation characteristics of the noise forces. The mean and variance of the photon number of the cavity light are then determined using the solutions of the resulting differential equations. We have discovered that the cavity light mode’s photon statistics are super-Poissonian because the variance of the photon number is more significant than the mean of the photon number. Additionally, using the same solutions, we were able to extract the antinormally ordered characteristic function, which is used to calculate the Q function. In addition, the photon number distribution for the cavity mode is computed using the Q function. The variance of the plus and minus quadrature of the two-mode cavity light generated by the two-mode subharmonic generating system is also obtained. It is discovered that the cavity mode’s squeezing characteristics are unaffected by the two-mode driving coherent light, however, the thermal light has the effect of decreasing the squeezing of the cavity light and the squeezing takes place in the plus quadrature. Finally, we discovered that when the cavity is coupled to a vacuum reservoir, there is a 50(%) maximum squeezing of the two-mode cavity at a steady state and at the threshold. The nondegenerate subharmonic generator generates a two-mode cavity light that is 50(%) entangled.