arXiv subjects

Yan Mo

Publications and source records attributed to Yan Mo.

14 recordsLinked to original sources

arXiv2024

Adaptive sampling strategy for tolerance analysis of freeform optical surfaces based on critical ray aiming

The tolerance analysis of freeform surfaces plays a crucial role in the development of advanced imaging systems. However, the intricate relationship between surface error and imaging quality poses significant challenges, necessitating dense sampling of featured rays during the computation process to ensure an accurate tolerance for different fields of view (FOVs). Here, we propose an adaptive sampling strategy called "Critical Ray Aiming" for surface tolerance analysis. By identifying the most sensitive ray to wave aberration at each surface point, our methodology facilitates flexible sampling of the FOVs and entrance pupil (EP), achieving computational efficiency without compromising accuracy in determining tolerable surface error. We demonstrate the effectiveness of our method through tolerance analysis of two different freeform imaging systems.

physics.optics↗

arXiv2024

Surface variation analysis of freeform optical systems over surface frequency bands for prescribed wavefront errors

The surface errors of freeform surfaces reflect the manufacturing complexities and significantly impact the feasibility of processing designed optical systems. With multiple degrees of freedom, freeform surfaces pose challenges in surface tolerance analysis in the field. Nevertheless, current research has neglected the influence of surface slopes on the directions of ray propagation. A sudden alteration in the surface slope will lead to a corresponding abrupt shift in the wavefront, even when the change in surface sag is minimal. Moreover, within the realm of freeform surface manufacturing, variation in surface slope across different frequency bands may give rise to unique surface variation. Within the context of this study, we propose a tolerance analysis method to analyze surface variation in freeform surfaces considering surface frequency band slopes based on real ray data. This approach utilizes real ray data to rapidly evaluate surface variation within a specified frequency band of surface slopes. Crucially, our proposed method yields the capability to obtain system surface variation with significant wavefront aberration, in contrast to previous methodologies. The feasibility and advantages of this framework are assessed by analyzing a single-mirror system with a single field and an off-axis two-mirror system. We expect to integrate the proposed methodology with freeform surface design and manufacturing, thereby expanding the scope of freeform optics.

physics.optics↗

arXiv2023

MUSCLE: Multi-task Self-supervised Continual Learning to Pre-train Deep Models for X-ray Images of Multiple Body Parts

While self-supervised learning (SSL) algorithms have been widely used to pre-train deep models, few efforts [11] have been done to improve representation learning of X-ray image analysis with SSL pre-trained models. In this work, we study a novel self-supervised pre-training pipeline, namely Multi-task Self-super-vised Continual Learning (MUSCLE), for multiple medical imaging tasks, such as classification and segmentation, using X-ray images collected from multiple body parts, including heads, lungs, and bones. Specifically, MUSCLE aggregates X-rays collected from multiple body parts for MoCo-based representation learning, and adopts a well-designed continual learning (CL) procedure to further pre-train the backbone subject various X-ray analysis tasks jointly. Certain strategies for image pre-processing, learning schedules, and regularization have been used to solve data heterogeneity, overfitting, and catastrophic forgetting problems for multi-task/dataset learning in MUSCLE.We evaluate MUSCLE using 9 real-world X-ray datasets with various tasks, including pneumonia classification, skeletal abnormality classification, lung segmentation, and tuberculosis (TB) detection. Comparisons against other pre-trained models [7] confirm the proof-of-concept that self-supervised multi-task/dataset continual pre-training could boost the performance of X-ray image analysis.

cs.CV↗

arXiv2023

Pupil aberrations correction of the afocal telescope for the TianQin project

TianQin is a planned Chinese space-based gravitational wave (GW) observatory with a frequency band of 10-4 to 1Hz. Optical telescopes are essential for the delivery of the measurement beam to support a precise distance measurement between pairs of proof masses. As the design is driven by the interferometric displacement sensitivity requirements, the stability control of optical path length (OPL) is extremely important beyond the traditional requirement of diffraction-limited imaging quality. In a telescope system, the recurring tilt-to-length (TTL) coupling noise arises from the OPL variation due to the wavefront deformation and angular misalignment. The pupil aberrations are preferred option to understand the OPL specifications and further suppress TTL coupling noise. To correct the pupil aberrations, we derive primary pupil aberrations in a series expansion form, and then refine the formulation of merit function by combining the pupil aberration theory and traditional image aberration theory. The automatic correction of pupil aberrations is carried out by using the macro programming in the commercial optical software Zemax, leading to a high performance telescope design. The design results show that on one side the pupil aberrations have been corrected, and on the other side, its optical performance meets the requirements for TianQin project. The RMS wavefront error over the science field of view (FOV) is less than {\lambda}/200 and the maximum TTL coupling noise over the entire 300 urad FOV is 0.0034nm/urad. We believe that our design approach can be a good guide for the space telescope design in any other space-based GW detection project, as well as other similar optical systems.

astro-ph.IM↗

arXiv2022

Recommended high performance telescope system design for the TianQin project

China is planning to construct a new space-borne gravitational-wave (GW) observatory, the TianQin project, in which the spaceborne telescope is an important component in laser interferometry. The telescope is aimed to transmit laser beams between the spacecrafts for the measurement of the displacements between proof-masses in long arms. The telescope should have ultra-small wavefront deviation to minimize noise caused by pointing error, ultra-stable structure to minimize optical path noise caused by temperature jitter, ultra-high stray light suppression ability to eliminate background noise. In this paper, we realize a telescope system design with ultra-stable structure as well as ultra-low wavefront distortion for the space-based GW detection mission. The design requirements demand extreme control of high image quality and extraordinary stray light suppression ability. Based on the primary aberration theory, the initial structure design of the mentioned four-mirror optical system is explored. After optimization, the maximum RMS wavefront error is less than lamda/300 over the full field of view (FOV), which meets the noise budget on the telescope design. The stray light noise caused by the back reflection of the telescope is also analyzed. The noise at the position of optical bench is less than 10-10 of the transmitted power, satisfying the requirements of space gravitational-wave detection. We believe that our design can be a good candidate for TianQin project, and can also be a good guide for the space telescope design in any other similar science project.

physics.optics↗

arXiv2021

Paraxial design of four-component zoom lens system with fixed distance between focal points by matrix optics

In this paper, we propose a systematic approach to design a four-component zoom system with fixed spacing between focal points based on matrix optics. Since the more complex model the higher degree of freedom it has, the task of determining the zoom trajectory is meaningful and challenging. The elements of the system matrix imply the working state of the optical system, and axial displacement equation for the desired zoom system are derived by restricting specific matrix elements. Properly selected trajectory of the particular component described by means of a parametric function can make the model become solvable explicitly. Then the paraxial design problem is transformed into the optimization of these parameters with regard to the merit functions encompassing the primary aberration terms, compactness, smoothness of the trajectories. We adopt Particle Swarm Optimization (PSO) algorithm to globally optimize the parameters to retrieve the optimum zoom trajectory in specific design criteria. The proposed method is demonstrated through two numerical examples under different configurations. The simulation results demonstrate that our proposed method can be a practical and powerful tool for paraxial design of complex multi-group zoom optical systems.

physics.optics↗

arXiv2021

Optical design of the laser launch telescope via physical optics theorem for Laser Guide Star Facility

The Laser Guide Star Facility (LGSF), as the most important part of the adaptive optics system of the large ground-based telescope, is aimed to generate multiple laser guide stars at the sodium layer. Laser Launch Telescope is employed to implement this requirement by projecting the Gauss beam to the sodium layer with a small beam size in LGSF system. As the diffraction and interference effects of laser's long-distance transmission, the conventional optical design based on the geometrical optics mechanism cannot achieve the expected laser propagation. In this paper, we propose a method to design optical system for laser launch telescope based on the physical optics theorem to generate an acceptable light spot at the sodium layer in the atmosphere. Besides, a tolerance analysis method based on physical optics propagation is also demonstrated to be necessitated to optimize the system's instrumentation performance. The numerical results show that the optical design considering physical optics propagation is highly rewarding and even necessitated in many occasions, especially for laser beam propagation systems.

astro-ph.IM↗

arXiv2019

Automated first-order design of double-sided telecentric zoom systems based on PSO algorithms

In this paper, we propose a new approach to automatically retrieve the first-order design of double-sided telecentric zoom systems with high efficiency based on Particle Swarm Optimization (PSO) algorithms. We transform the design problem to realize a zoom lens system with fixed positions of both the front focal point and the rear focal point during zooming. We demonstrate that the proposed algorithm is much more efficient than the Monte Carlo algorithm in designing zoom systems with two fixed foci as well as a given zoom ratio. Furthermore, a compact first-order design of three-component 4X zoom system with two fixed foci is proposed to show the high efficiency and great potential of our proposed algorithm in searching proper first-order configuration for complex optical systems.

physics.optics↗

arXiv2010

Time-dependent density functional theory for quantum transport

Based on our earlier works [Phys. Rev. B 75, 195127 (2007) & J. Chem. Phys. 128, 234703 (2008)], we propose a formally exact and numerically convenient approach to simulate time-dependent quantum transport from first-principles. The proposed approach combines time-dependent density functional theory with quantum dissipation theory, and results in a useful tool for studying transient dynamics of electronic systems. Within the proposed exact theoretical framework, we construct a number of practical schemes for simulating realistic systems such as nanoscopic electronic devices. Computational cost of each scheme is analyzed, with the expected level of accuracy discussed. As a demonstration, a simulation based on the adiabatic wide-band limit approximation scheme is carried out to characterize the transient current response of a carbon nanotube based electronic device under time-dependent external voltages.

physics.chem-ph↗

arXiv2008

Equivalent electric circuit of a carbon nanotube based molecular conductor

We apply our first-principles method to simulate the transient electrical response through carbon nanotube based conductors under time-dependent bias voltages, and report the dynamic conductance for a specific system. We find that the electrical response of the carbon nanotube device can be mapped onto an equivalent classical electric circuit. This is confirmed by studying the electric response of a simple model system and its equivalent circuit.

physics.chem-ph↗

arXiv2007

Time-dependent density-functional theory for open systems

By introducing the self-energy density functionals for the dissipative interactions between the reduced system and its environment, we develop a time-dependent density-functional theory formalism based on an equation of motion for the Kohn-Sham reduced single-electron density matrix of the reduced system. Two approximate schemes are proposed for the self-energy density functionals, the complete second order approximation and the wide-band limit approximation. A numerical method based on the wide-band limit approximation is subsequently developed and implemented to simulate the steady and transient current through various realistic molecular devices. Simulation results are presented and discussed.

quant-ph↗

arXiv2006

Electron transfer theory revisit: Quantum solvation effect

The effect of solvation on the electron transfer (ET) rate processes is investigated on the basis of the exact theory constructed in J. Phys. Chem. B Vol. 110, (2006); quant-ph/0604071. The nature of solvation is studied in a close relation with the mechanism of ET processes. The resulting Kramers' turnover and Marcus' inversion characteristics are analyzed accordingly. The classical picture of solvation is found to be invalid when the solvent longitudinal relaxation time is short compared with the inverse temperature.

physics.chem-ph↗

arXiv2006

Kinetics and thermodynamics of electron transfer in Debye solvents: An analytical and nonperturbative reduced density matrix theory

A nonperturbative electron transfer rate theory is developed based on the reduced density matrix dynamics, which can be evaluated readily for the Debye solvent model without further approximation. Not only does it recover for reaction rates the celebrated Marcus' inversion and Kramers' turnover behaviors, the present theory also predicts for reaction thermodynamics, such as equilibrium Gibbs free-energy and entropy, some interesting solvent-dependent features that are calling for experimental verification. Moreover, a continued fraction Green's function formalism is also constructed, which can be used together with Dyson equation technique, for efficient evaluation of nonperturbative reduced density matrix dynamics.

quant-ph↗

arXiv2004

Exact quantum master equation via the calculus on path integrals

An exact quantum master equation formalism is constructed for the efficient evaluation of quantum non-Markovian dissipation beyond the weak system-bath interaction regime in the presence of time-dependent external field. A novel truncation scheme is further proposed and compared with other approaches to close the resulting hierarchically coupled equations of motion. The interplay between system-bath interaction strength, non-Markovian property, and required level of hierarchy is also demonstrated with the aid of simple spin-boson systems.

quant-ph↗