8 research outputs found
Giant enhancement of higher-order harmonics of an optical-tweezer phonon laser
Phonon lasers, as mechanical analogues of optical lasers, are unique tools
for not only fundamental studies of phononics but also diverse applications
such as acoustic imaging and force sensing. Very recently, by levitating a
micro-size sphere in an optical tweezer, higher-order mechanical harmonics were
observed in the phonon-lasing regime, as the first step towards nonlinear
levitated optomechanics [Nat. Phys. 19, 414 (2023)]. However, both the lasing
strengths and the quality factors of the observed harmonics are typically very
low, thus severely hindering their applications. Here we show that, by applying
a simple but powerful electronic control to such a levitated micro-sphere,
three orders of magnitude enhancement are achievable in the brightness of the
phonon lasers, including both the fundamental mode and all its higher-order
harmonics. Also, giant improvements of their linewidth and frequency stability
are realized in such an electro-optomechanical system, together with further
improved higher-order phonon coherence. These results, as a significant step
forward for enhancing and controlling micro-object phonon lasers, can be
readily used for a wide range of applications involving nonlinear phonon
lasers, such as acoustic frequency comb, ultra-sound sensing, atmospherical
monitoring, and even bio-medical diagnosis of levitated micro-size objects.Comment: 15 pages, 4 figure
Effects of detection-beam focal offset on displacement detection in optical tweezers
A high-resolution displacement detection can be achieved by analyzing the
scattered light of the trapping beams from the particle in optical tweezers. In
some applications where trapping and displacement detection need to be
separated, a detection beam can be introduced for independent displacement
detection. However, the detection beam focus possibly deviates from the centre
of the particle, which will affect the performance of the displacement
detection. In this paper, we detect the radial displacement of the particle by
utilizing the forward scattered light of the detection beam from the particle.
The effects of the lateral and axial offsets between the detection beam focus
and the particle centre on the displacement detection are analyzed by the
simulation and experiment. The results show that the lateral offsets will
decrease the detection sensitivity and linear range and aggravate the crosstalk
between the x-direction signal and y-direction signal of QPD. The axial offsets
also affect the detection sensitivity, an optimal axial offset can improve the
sensitivity of the displacement detection substantially. In addition, the
influence of system parameters, such as particle radius a, numerical aperture
of the condenser NAc and numerical aperture of the objective NAo on the optimal
axial offset are discussed. A combination of conventional optical tweezers
instrument and a detection beam provides a more flexible working point,
allowing for the active modulation of the sensitivity and linear range of the
displacement detection. This work would be of great interest for improving the
accuracy of the displacement and force detection performed by the optical
tweezers.Comment: 10 pages,11 figure
Effects of Multi-Growth Periods UAV Images on Classifying Karst Wetland Vegetation Communities Using Object-Based Optimization Stacking Algorithm
Combining machine learning algorithms with multi-temporal remote sensing data for fine classification of wetland vegetation has received wide attention from researchers. However, wetland vegetation has different physiological characteristics and phenological information in different growth periods, so it is worth exploring how to use different growth period characteristics to achieve fine classification of vegetation communities. To resolve these issues, we developed an ensemble learning model by stacking Random Forest (RF), CatBoost, and XGBoost algorithms for karst wetland vegetation community mapping and evaluated its classification performance using three growth periods of UAV images. We constructed six classification scenarios to quantitatively evaluate the effects of combining multi-growth periods UAV images on identifying vegetation communities in the Huixian Karst Wetland of International Importance. Finally, we clarified the influence and contribution of different feature bands on vegetation communities’ classification from local and global perspectives based on the SHAP (Shapley Additive explanations) method. The results indicated that (1) the overall accuracies of the four algorithms ranged from 82.03% to 93.37%, and the classification performance was Stacking > CatBoost > RF > XGBoost in order. (2) The Stacking algorithm significantly improved the classification results of vegetation communities, especially Huakolasa, Reed-Imperate, Linden-Camphora, and Cephalanthus tetrandrus-Paliurus ramosissimus. Stacking had better classification performance and generalization ability than the other three machine learning algorithms. (3) Our study confirmed that the combination of spring, summer, and autumn growth periods of UAV images produced the highest classification accuracy (OA, 93.37%). In three growth periods, summer-based UAVs achieved the highest classification accuracy (OA, 85.94%), followed by spring (OA, 85.32%) and autumn (OA, 84.47%) growth period images. (4) The interpretation of black-box stacking model outputs found that vegetation indexes and texture features provided more significant contributions to classifying karst wetland vegetation communities than the original spectral bands, geometry features, and position features. The vegetation indexes (COM and NGBDI) and texture features (Homogeneity and Standard Deviation) were very sensitive when distinguishing Bermudagrass, Bamboo, and Linden-Camphora. These research findings provide a scientific basis for the protection, restoration, and sustainable development of karst wetlands
Enhancing the performance of the counter-propagating dual-beam optical trap with the asymmetric configuration
The trapping stiffness and width are two important parameters to characterize a counter-propagating dual-beam optical trap. We present two types of asymmetric counter-propagating dual-beam optical trap with the different numerical aperture (NA) and trapping power to eliminate the multi-equilibrium positions when two foci of the optical trap are not coincided. Meanwhile, the asymmetric dual-beam trap with the different NA enhances the axial trapping width and stiffness over five and three times, respectively, higher than the standard dual-beam trap with the higher and same average NA. Besides, it increases the transverse trapping stiffness when two foci are not coincided. The asymmetric dual-beam optical trap will benefit the future applications for the study of precision measurement, basic physics and biomaterials
Optical Pulling Using Chiral Metalens as a Photonic Probe
Optical pulling forces, which can pull objects in the source direction, have emerged as an intensively explored field in recent years. Conventionally, optical pulling forces exerted on objects can be achieved by tailoring the properties of an electromagnetic field, the surrounding environment, or the particles themselves. Recently, the idea of applying conventional lenses or prisms as photonic probes has been proposed to realize an optical pulling force. However, their sizes are far beyond the scope of optical manipulation. Here, we design a chiral metalens as the photonic probe to generate a robust optical pulling force. The induced pulling force exerted on the metalens, characterized by a broadband spectrum over 0.6 μm (from 1.517 to 2.117 μm) bandwidth, reached a maximum value of −83.76 pN/W. Moreover, under the illumination of incident light with different circular polarization states, the longitudinal optical force acting on the metalens showed a circular dichroism response. This means that the longitudinal optical force can be flexibly tuned from a pulling force to a pushing force by controlling the polarization of the incident light. This work could pave the way for a new advanced optical manipulation technique, with potential applications ranging from contactless wafer-scale fabrication to cell assembly and even course control for spacecraft
Mangrove species classification using novel adaptive ensemble learning with multi-spatial-resolution multispectral and full-polarization SAR images
ABSTRACTMangroves are one of the important components of Earth's carbon sinks. The current problems of base-model composition strategy of ensemble learning and image features combination are still major challenges in mangrove species classification. This paper constructed two novel adaptive ensemble learning frameworks (AME-EL and AOS-EL) to explored the effect of combing different spatial-resolution optical and SAR images on classification performance, and evaluated the ability in mangrove species classification between dual-polarization and full-polarization SAR images. Finally, we used the SHAP method to explore the effects of different feature interactions on mangrove species classification. The results indicated that: (1) AME-EL and AOS-EL achieve the fine classification of mangrove species with overall accuracies between 77.50% and 94.77%. (2) Combination of Gaofen-7 multispectral and Gaofen-3 SAR improved the classification accuracy for Kandelia candel, with the F1 score increasing from 26.4% to 40.2%. (3) The VV/VH polarization performed better in the classification, with the F1 scores for Aegiceras corniculatum and Kandelia candel were higher than those of HH/HV and AHV polarization by 7%−16.1% and 5.9%−16.1%, respectively. (4) SAR features interacted well with other spectral features, which made a strong contribution to the classification accuracy of mangrove species, and effectively affect the prediction results
Effects of detection-beam focal offset on back-focal-plane displacement detection
High-resolution displacement detection can be achieved by analyzing the scattered light of the trapping beams from the particle in optical tweezers. In some applications where trapping and detecting beams must be separated, a detecting beam can be introduced for independent displacement measurement. However, the detecting beam focus possibly deviates from the center of the particle, which will affect the performance of displacement detection. Here, we detect the displacement of the particle by utilizing the forward scattered light of the detection beam from the particle. The effects of the lateral and axial offsets between the detection beam focus and the particle center on displacement detection are analyzed by the simulation and experiment. These results show that the lateral offsets will decrease the detection sensitivity and linear range. Moreover, it aggravates the crosstalk between the x-direction signal and the y-direction signal of the quadrant photodiode. Besides, the axial offsets also affect the detection sensitivity. More interestingly, an optimal axial offset can improve the sensitivity of displacement detection substantially. In addition, the influence of system parameters, such as particle radius a, numerical aperture of the condenser NAc, and numerical aperture of the objective NAo, on the optimal axial offset is also discussed. This work not only provides ideas for improving the performance of precision measurement by the method of forward scattered light detection but also expands the application of this method in fundamental physics
Giant enhancement of higher-order harmonics of an optical-tweezer phonon laser
Phonon lasers, as mechanical analogues of optical lasers, are unique tools for not only fundamental studies of phononics but also diverse applications such as acoustic imaging and force sensing. Very recently, by levitating a micro-size sphere in an optical tweezer, higher-order mechanical harmonics were observed in the phonon-lasing regime, as the first step towards nonlinear levitated optomechanics [Nat. Phys. 19, 414 (2023)]. However, both the lasing strengths and the quality factors of the observed harmonics are typically very low, thus severely hindering their applications. Here we show that, by applying a simple but powerful electronic control to such a levitated micro-sphere, three orders of magnitude enhancement are achievable in the brightness of the phonon lasers, including both the fundamental mode and all its higher-order harmonics. Also, giant improvements of their linewidth and frequency stability are realized in such an electro-optomechanical system, together with further improved higher-order phonon coherence. These results, as a significant step forward for enhancing and controlling micro-object phonon lasers, can be readily used for a wide range of applications involving nonlinear phonon lasers, such as acoustic frequency comb, ultra-sound sensing, atmospherical monitoring, and even bio-medical diagnosis of levitated micro-size objects