Applied Physics B最新文献

A synchronously pumped optical parametric oscillator (SPOPO) operating at 93 MHz is used to generate squeezed states at 1035 nm. The system features a counter-propagating beam at the same wavelength as the quantum state, which simultaneously actively stabilizes the cavity and, after transmission, acts as the local oscillator for homodyne detection. By deriving the local oscillator directly from the SPOPO cavity, the setup establishes an intrinsically excellent spatial mode overlap and high interference visibility, forming a distinctive self-referenced architecture. Two spatial light modulators enable precise spectral shaping of both the pump and the local oscillator in amplitude and phase, allowing investigation of the spectral properties of the generated states. The versatility of the setup further allows exploration of different SPOPO configurations, including regimes with varied finesse and escape efficiency. Representative measurements, including homodyne traces and squeezing levels as functions of pump power and local oscillator bandwidth, demonstrate the performance of the system. Theoretical simulations based on a multimode singular-value-decomposition model reproduce well the measured dependence of squeezing on pump power and LO bandwidth, confirming the accuracy of the description and the robustness of the setup. Measured squeezing levels up to − 3.3 dB are achieved, corresponding to − 5.7 dB at SPOPO output, evidencing the robustness and versatility of this platform for stable pulsed squeezed-light generation and advanced quantum optical applications.

The reflection of shockwaves for the confinement of plasma from semispherical-shaped external cavities of metallic and non-metallic material was investigated to study the effect of confined geometries for laser ablation propulsion. Optimization of variables and constants of the proposed propulsion model measured the best values of propulsion parameters, which may help later in improving the efficiency of the system. Response surface methodology (RSM) is a popular statistical method, for optimization to improve the performance of the system. In the present work, RSM was used for the determination of optimum values of laser ablation propulsion parameters for different variables. Laser ablation propulsion parameters were studied for Aluminum, Silver, and Gold samples at different fluence values and cavity diameter sizes. A pulsed Nd-YAG (1064 nm wavelength) laser was used to ablate the sample. The effect of cavity size, cavity material, and fluence were studied on propulsion parameters i.e. coupling coefficient, specific impulse, and Thrust by employing the RSM model. Responses were calculated for both; individual and interaction terms. Optimized values of Coupling coefficient, Specific impulse, and thrust were obtained using contour plots.

The compact footprint of all solid-state quantum cascade laser frequency combs (QCL-FCs) allows field-compatible applications of dual-comb spectrometers (DCS) such as continuous atmospheric multi-species monitoring, for which long-term frequency stability is critical. We show that by incorporating a stabilized single-mode quantum cascade laser as a frequency reference into one channel of a conventional QCL-DCS system, the combs can be actively stabilized to a molecular transition, which significantly reduces the uncertainties in the DCS frequency axis compared to a free-running system. With the stabilized DCS, the QCL-FCs’ offset frequencies are locked to the reference laser to within 0.3 MHz and the frequency instability for each comb line is estimated to be < 1 MHz for each 100 µs long spectral acquisitions with white noise limited averaging trend for up to 600 s. Additionally, we show that the comb’s optical frequencies can be inferred accurately during the multiheterodyne signal acquisition, as demonstrated through absorption DCS of N₂O at low pressure.

In this manuscript, we present a theoretical investigation of the self-focusing propagation of higher-order circular cosine-hyperbolic-Gaussian beams (CiChGB) in non-relativistic collisionless plasma under the higher-order paraxial approach. The analysis employs the framework of the Wentzel–Kramers–Brillouin approximation (WKB) and supplemented by the higher-order paraxial contribution of the spatial intensity distribution. The study examines the influence of the beam order components of the cosine-hyperbolic function and decentered parameter on the intensity distribution of the CiChGB. The attention is given to the impact of the beam order on the self-focusing propagation of the CiChGB and the higher-order contributions to the local dielectric constant of collisionless plasma. It is observed that, at higher decentered parameter of the beam profile, the higher-order coefficients of dielectric constant of the collisionless plasma are significantly suppressed. This theoretical framework provides insights into the self-focusing propagation of higher-order CiChGB in the plasma environments.

The 1550 nm InGaAsP/InP electro-absorption modulator (EAM) is one of the key components for the data communication applications. To enhance the comprehensive performance of EAM, the continuous iterative optimization is required in both the theoretical mechanisms and the fabrication processes. This paper analyzed the physical mechanisms of EAM by calculating the normalized overlap integral between the electron and the hole energy levels, which yielded the red shift and the absorption intensity of the absorption band under the reverse bias. By analyzing the absorption spectra of the wavelength and the reverse bias, the transmission loss and the extinction ratio at different wavelengths were determined. By optimizing the key parameters such as the barrier composition, the barrier width, the quantum well width, and the number of quantum wells, the extinction ratio of the EAM was improved. The introduction of the P-doped InGaAsP layer into the P-doped waveguide mitigated the electric-field peak at the interface between the P-doped cladding and the P-doped waveguide, thereby further enhancing the modulation efficiency. This study systematically simulated and analyzed the key parameters of the design for the 1550 nm InGaAsP/InP EAM, providing the theoretical reference value for achieving the high-performance EAM.

This paper presents an investigation of the dynamics of a versatile thin-disk multipass laser amplifier (TDMPA) with two seed sources. The study focused on the system’s transient response, analyzing the amplified instantaneous power during and shortly after fast modulation of the individual seed powers. For switching times shorter than the amplifier’s characteristic response time, changes in the total seed power led to retardation and overshooting effects, which are attributed to the gain-saturation dynamics of the active laser medium. An analytical formula to express the dependence of the characteristic response time on the input and output powers and the specific TDMPA architecture was derived and validated. This provides a practical guideline for choosing seed-power switching times that avoid transient overshooting and retardation effects. For pump powers between 599 and 1446 W, and depending on operation conditions, the TDMPA under consideration was measured to exhibit a gain-saturation response time ranging between approximately 30 and 90 µs.

A high-energy acousto-optic Q-switched dual-crystal Tm:YAP laser at 1 kHz repetition rate was investigated. Using two b-cut Tm:YAP crystals in an L-shaped resonator with laser diode dual-end pumped at 793 nm, a pulse energy of 22.31 mJ at 1938.86 nm with 0.19 nm linewidth was achieved, corresponding to a 65 ns pulse width and 343.2 kW peak power, with beam quality factor M² ~ 3.4. In addition, when the pump power was 137.4 W, an average power of 29.96 W was obtained in continuous wave mode. To the best of our knowledge, this work represents the highest pulse energy reported of acousto-optic Q-switched Tm:YAP oscillator lasers at 1.94 μm.

This paper proposes and designs a dynamic radiative cooling smart window based on a metal-dielectric multilayer structure. An improved genetic algorithm is employed to optimize the number of layers, their thickness, and material type to achieve different target visible transmittance levels (from 30 to 60%). The optimal structure identified is a 10-layer stack of VO₂ and BaF₂ on a 1-μm-thick BaF₂ substrate, achieving an average visible transmittance of 50%. This design provides significant spectral control capabilities. Below its phase-transition temperature, the window is in an insulating state with a high near-infrared (NIR, 0.78–2.5 μm) transmittance of 80.8% and a low mid-infrared (MIR, 8–13 μm) emissivity of 6.7%, facilitating passive solar heating. Above the phase-transition temperature, it switches to a metallic state with a low NIR transmittance of 10.6% and a high MIR emissivity of 88.3%, enabling effective radiative cooling. The window exhibits substantial modulation abilities, with |ΔT_NIR| and Δε values of 0.70 and 0.82, respectively. This energy-free, self-adaptive technology, which dynamically regulates thermal radiation in response to ambient temperature, is ideally suited for enhancing energy efficiency in green buildings and smart windows under varying weather conditions.

We propose a technique for wavefront (W) sensing of optical systems using both Bi-Ronchi and Hartmann tests, modified by incorporating the classical tests by including a Spatial Light Modulator (SLM). To this aim, we replace the conventional Hartmann screens with structured apertures with a transmission Liquid Crystal Spatial Light Modulator (LC-SLM) using binary patterns of either circular or square apertures. We build overlapping horizontal and vertical fringe patterns to obtain equidistant square apertures (Bi-Ronchi). In the case of the Hartmann test, we substitute the square apertures with circles serving as binary masks, which we refer to as BRM (Bi-Ronchi Mask) and HM (Hartmann mask). We design an experimental setup in which a collimated laser illuminates the SLM, considering the diffractive effects of the SLM to optimize the identification of centroids, which yields transversal aberrations ((bold{TA}({rho},{theta}))). We assume a vector formulation suitable to interpret TA and thus directly solve (bold{W}({rho }, {theta})) by two-dimensional numerical integration applying directional derivative and Gaussian quadrature. We perform this process for both the Hartmann and Bi-Ronchi tests simultaneously, leveraging the spatial resolution and flexibility of the SLM. We present and discuss our results and compare them with those obtained using dedicated wavefront sensing software using the Ronchi test (under the conditions of our proposal) with the SLM.