Feng Qin

High-precision beam pointing control is essential for achieving reliable data transmission in space laser communication systems, requiring effective suppression of multi-frequency disturbance-induced tracking residuals. To address this issue, a synergistic model predictive control and disturbance observer (DOB-MPC) architecture is developed. The proposed hierarchical control framework is constructed based on gimbal servo dynamics and implemented through the following steps. A frequency-decoupled disturbance observer (DOB) is employed to estimate multi-frequency disturbances using spectral separation principles, while a model predictive controller (MPC) enhances steady-state accuracy by compensating for time-delay effects through trajectory optimization. Crucially, the disturbance estimates are incorporated into the MPC’s prediction horizon via receding-horizon optimization, establishing a cooperative control mechanism. Simulation results demonstrate improvements of greater than 25% in dynamic response and over 80% in residual error reduction compared to conventional methods. Experimental results further validate the efficacy of the proposed architecture for space laser tracking systems.

A wide range oxygen measurement system with the relative measurement error of less than 1.5% across 4 orders of magnitude of oxygen dynamic range has been developed. We proposed a theoretical evaluation method of the measurement capability of oxygen probes, which points that the relative measurement error (δ) is equal to the reciprocal of the product of signal-to-noise ratio (SNR) and relative sensitivity (S _r). A minimum value point in the curve of δ with oxygen concentration is existing due to the opposite trends of SNR and S _r Based on the evaluation results, an oxygen probe group was selected scientifically for wide range oxygen measurement. The efficacy of the developed measurement system, featuring adaptive oxygen probe switching, was verified through testing, confirming its compliance with accuracy requirements for measurements.

The oxygen-varying correlated fluorescence provides an effective strategy to gain the quenching constant K-SV for a non-phosphorescent system. Owing to the absence of detectable phosphorescence emission in general optical spectroscopy, the facticity of this method has never been verified. Here, the correct way to determine K-SV by oxygen-varying correlated fluorescence was systematically studied in detail. We selected gadolinium protoporphyrin IX (Gd-PpIX) to establish a fluorescence and phosphorescence dual emission system. Then, K-SV of Gd-PpIX can be obtained by the change of fluorescence intensity (I-F) with oxygen concentration using the method of correlated fluorescence at intense pump power; meanwhile, the value can also be determined from the relationship of the phosphorescence intensity ratio and oxygen content by the Stern-Volmer equation under relatively low power density. It was found that the K-SV values obtained by the above two methods were 12.2(1) and 11.9(7) kPa(-1), respectively. Our results successfully verified the accuracy of oxygen-varying correlated fluorescence for determining the K-SV by the phosphorescence property and fluorescence saturation of Gd-PpIX.

Because of the absence of phosphorescence, the Stern-Volmerconstant (K (SV)) of the photosensitizeris hard to determine accurately. Although the delayed fluorescenceand correlated fluorescence methods have been proposed to determine K (SV), the weak signal detection and non-uniformexcitation enlarged the measurement error. In this work, a methodwas proposed to accurately determine K (SV) by oxygen-dependent consumption of 1,3-diphenylisobenzofuran. Theconsumption time (& delta;), as a measurable quantity, is introducedand could be obtained by the absorption spectrum with a high signal-to-noiseratio. Analytically, & delta; is linearly related to the inverse ofoxygen content, and the ratio of the intercept to the slope equals K (SV). Experimentally, rose Bengal was selectedto perform this determination; the K (SV) is measured to be 43(1) kPa(-1), and the error isreduced by 1 order of magnitude. In addition, metalloporphyrin wasused to verify this method.

Modern photodynamic therapy has been built on the mechanism of the interaction between the photosensitizer (porphyrin derivatives) and oxygen to produce singlet oxygen, which relies on energy transfer from the triplet excited state (T₁) of porphyrin to the excited state of oxygen. In this process, the energy transfer from the singlet excited state (S₁) of porphyrin to oxygen is believed to be not pronounced as the rapid decay of S₁ and the large energy mismatch. Here, we have evidenced the existence of an energy transfer between S₁ and oxygen, which can contribute to the production of singlet oxygen. For hematoporphyrin monomethyl ether (HMME), the Stern-Volmer constant of S₁ (K_SV') is 0.023 kPa^-1, according to the oxygen concentration-dependent steady fluorescence intensities. In addition, fluorescence dynamic curves of S₁ under various oxygen concentrations have also been measured through ultrafast pump probe experiments to further verify our results.

Environmental heavy atoms can further enhance the room temperature phosphorescence (RTP) emissions of gadolinium-labeled hematoporphyrin monomethyl ether (Gd-HMME) by way of the external heavy atom effect (HAE). However, the macroscopic phosphorescence intensity covered the intrinsic effect of the environmental heavy atoms. In this study, a method of separating the external HAE from the total is performed, and a quantity to describe the intrinsic nature of external HAE is defined. The environmental Gd3+ concentration evolution of the phosphorescent transition rate (kP) is obtained by correlated absorption, emission, and time-resolved spectroscopy. The kP increases linearly with environmental Gd3+ concentration, while the intercept kP0 coincides with that of the internal HAE. The slope κ could be calculated, and it is a quantity free of the Gd3+ concentration and only relies on the type of environmental heavy atoms. In addition, the environmental Lu3+ exhibits similar functionality to Gd3+ in external HAE. Environmental Pd2+ quenches the phosphorescence intensity macroscopically, while it enhances the HAE intrinsically. Our method provides an alternative insight into the intrinsic nature of environmental heavy atoms.

The presence of room temperature phosphorescence emission in metalloporphyrin, via the transition from the excited triplet state (T₁) to the ground state (S₀), relies on the chelated heavy metal ions, which is known as the heavy atom effect (HAE). Despite the HAE being a reliable method to tune the phosphorescence process widely, the realization of the HAE nature is a tough task as the induced phosphorescence process is sensitive to not only the specie of bonded heavy atoms but also chemical environments such as the oxygen quenching and solvent effect. In this study, we have aimed at a quantitative determination of the intrinsic phosphorescent transition rate (k_P) in metalloporphyrin gadolinium-labeled hematoporphyrin monomethyl ether (Gd-HMME). After the theoretical analysis based on the rate equation model to remove the nonintrinsic contribution and the experimental results of phosphorescence, the k_P is calculated to be ∼2.4 × 10^-4 μs^-1. This study enables us to approach the intrinsic energy characteristic of metalloporphyrins; moreover, our work provides an effective pathway for the further optimization of the varied functional metalloporphyrin.

In this work, the transition properties of wide-bandgap compounds are studied by way of the temperature dependence of fluorescence dynamic curves. The YVO₄, CaWO₄, and CaMoO₄ samples are selected in this study owing to their strong absorption in the ultraviolet (UV) region. The fluorescence decay curves of the three samples, in the range of 173–373 K, are measured under excitation by deep UV light-emitting diodes (LEDs). The temperature dependence of transition rate (A) is composed of a constant term, as well as a mono-exponential term which follows the Boltzmann distribution law. The constant term reflects a spontaneous radiative transition rate (W_R), while the mono-exponential term represents the temperature-dependent nonradiative transition rate (W_NR). The nonradiative relaxation is attributed to the upward thermal population rather than the downward multiphonon relaxation (MPR). The thermal populating process is supposed to originate from the bottom of the excited state to the intersection of the ground state and excited state by overcoming the potential barrier of activation energy (E_a), and the E_a values of YVO₄, CaWO₄, and CaMoO₄ samples are calculated.

The achievement of the Stern–Volmer constant (K_SV) of porphyrin, a parameter to describe the ability of energy transfer to oxygen, enables us to understand and engineer the functionalities of porphyrin. In this study, we propose a new method to obtain K_SV by steady fluorescence based on the population correlation between the excited triplet state (T₁) and the singlet excited state (S₁). Nonlinear fluorescence intensity of porphyrin [hematoporphyrin monomethyl ether (HMME)] as a function of pump power is observed, and this nonlinearity is oxygen-concentration-dependent. These observations originated from the population correlation, where more intense pump power introduces a stronger population correlation. Most importantly, we have found that the oxygen content can influence this correlation via the quenching of T₁ based on its sequent change of fluorescence intensity; K_SV ∼ 28 kPa^–1 can be obtained theoretically for HMME. Our investigation not only offers a promising method of achieving K_SV conveniently by steady fluorescence but also enlightens the advances of regulable fluorescence correlation.