Retrieving positions of closely packed sub-wavelength nanoparticles from their diffraction patterns

Distinguishing two objects or point sources located closer than the Rayleigh distance is impossible in conventional microscopy. Understandably, the task becomes increasingly harder with a growing number of particles placed in close proximity. It has been recently demonstrated that subwavelength nanoparticles in closely packed clusters can be counted by AI-enabled analysis of the diffraction patterns of coherent light scattered by the cluster. Here we show that deep learning analysis can determine the actual position of the nanoparticle in the cluster of subwavelength particles from a sing-shot diffraction pattern even if they are separated by distances below the Rayleigh resolution limit of a conventional microscope.Comment: 6 pages, 3 figure

An optimization framework of K-means clustering and metaheuristic for traveling salesman problem

In this dissertation, we first studied the optimization framework of K-means clustering genetic algorithm. By comparing with traditional genetic algorithm, we verified that the optimization framework can effectively save computing time when solving large-scale traveling salesman problems and the final path length also meets the requirements. Based on the randomness of the genetic algorithm, we make the improvement of this optimization framework. By adjusting the sequence of operations about the framework, we compute the path length on each iteration during cluster process and select the optimal results through comparison. The improved framework has a better path length than before. In addition, we selected the combination of ant colony algorithm and K-means clustering to form another optimization framework, which also verified the optimization effect on the running time when solving large-scale traveling salesman problems and could decrease calculation error rate. At the same time, we conduct related research on the parameter analysis of ant colony algorithm and summarize properties of each parameter of the ant colony algorithm and their influence on the final optimization result.Master of Science (Computer Control and Automation

Functional Optical Coherence Tomography of Stimulus-Evoked Intrinsic Optical Signals in the Retina

Retinal diseases, such as age-related macular degeneration (AMD), diabetic retinopathy (DR), retinitis pigmentosa (RP), etc., can produce photoreceptor and/or inner neural dysfunctions that lead to severe vision loss or even legal blindness if not diagnosed and treated promptly. It is known that different retinal diseases target different retinal cell types. Therefore, high-resolution assessment of retinal neural function is desirable for early detection of retinal diseases. Stimulus-evoked intrinsic optical signal (IOS) changes, which show tight correlation with retinal physiological dynamics, have been observed in animal and human retinas, promising a high-resolution method for functional imaging of retinal neural function. For testing clinical potential of functional IOS imaging, this dissertation was designed to achieve in-depth understanding of IOS sources and mechanisms, and to demonstrate in vivo IOS mapping of retinal neural dysfunctions in animal models. Three custom-built imaging systems, line-scan time domain optical coherence tomography (TD-OCT), hybrid line-scan confocal microscope and spectral domain OCT (SD-OCT), and in vivo SD-OCT, were employed for both in vitro and in vivo investigation of amphibian (frog) and mammal (mouse) retinas. In vitro OCT of frog retinas revealed rapid IOS response, almost immediately (<3 ms) after the onset of visible light flashes, at photoreceptor outer segment (OS). Quantitative analysis indicated that the fast IOS may originate from G-protein binding and releasing in early phases of phototransduction. In vivo OCT imaging of mouse retinas confirmed fast IOS in photoreceptor OS and slow IOS in inner retinal layers. Comparative IOS and ERG study indicated that the fast IOS in photoreceptor OS may be attributed to the early stage of phototransduction before the hyperpolarization of retinal photoreceptor. Using the hybrid confocal-OCT imaging system, transient OS change was identified as a major contributor to the fast IOS observed in retinal photoreceptors, predominantly in rods. In vivo OCT imaging of retinal degeneration 10 (rd10) mice revealed localized IOS distortions and morphological abnormalities. Comparative ERG recording disclosed consistent abnormalities in the ERG a-wave. The potential for using functional IOS imaging for early detection and progression monitoring of retinal photoreceptor degeneration was demonstrated with the mutant rd10 mouse model

Demonstration of the Systematic Evaluation of an Optical Lattice Clock Using the Drift-Insensitive Self-Comparison Method

The self-comparison method is a powerful tool in the uncertainty evaluation of optical lattice clocks, but any drifts will cause a frequency offset between the two compared clock loops and thus lead to incorrect measurement result. We propose a drift-insensitive self-comparison method to remove this frequency offset by adjusting the clock detection sequence. We also experimentally demonstrate the validity of this method in a one-dimensional 87Sr optical lattice clock. As the clock laser frequency drift exists, the measured frequency difference between two identical clock loops is (240 &plusmn; 34) mHz using the traditional self-comparison method, while it is (&minus;15 &plusmn; 16) mHz using the drift-insensitive self-comparison method, indicating that this frequency offset is cancelled within current measurement precision. We further use the drift-insensitive self-comparison technique to measure the collisional shift and the second-order Zeeman shift of our clock and the results show that the fractional collisional shift and the second-order Zeeman shift are 4.54(28) &times; 10&minus;16 and 5.06(3) &times; 10&minus;17, respectively

Demonstration of the Systematic Evaluation of an Optical Lattice Clock Using the Drift-Insensitive Self-Comparison Method

The self-comparison method is a powerful tool in the uncertainty evaluation of optical lattice clocks, but any drifts will cause a frequency offset between the two compared clock loops and thus lead to incorrect measurement result. We propose a drift-insensitive self-comparison method to remove this frequency offset by adjusting the clock detection sequence. We also experimentally demonstrate the validity of this method in a one-dimensional 87Sr optical lattice clock. As the clock laser frequency drift exists, the measured frequency difference between two identical clock loops is (240 ± 34) mHz using the traditional self-comparison method, while it is (−15 ± 16) mHz using the drift-insensitive self-comparison method, indicating that this frequency offset is cancelled within current measurement precision. We further use the drift-insensitive self-comparison technique to measure the collisional shift and the second-order Zeeman shift of our clock and the results show that the fractional collisional shift and the second-order Zeeman shift are 4.54(28) × 10−16 and 5.06(3) × 10−17, respectively

Recent Advances Concerning the ⁸⁷Sr Optical Lattice Clock at the National Time Service Center

We review recent experimental progress concerning the 87Sr optical lattice clock at the National Time Service Center in China. Hertz-level spectroscopy of the 87Sr clock transition for the optical lattice clock was performed, and closed-loop operation of the optical lattice clock was realized. A fractional frequency instability of 2.8 &#215; 10&#8722;17 was attained for an averaging time of 2000 s. The Allan deviation is found to be 1.6 &#215; 10&#8722;15/&#964;1/2 and is limited mainly by white-frequency-noise. The Land&#233; g-factors of the (5s2)1S0 and (5s5p)3P0 states in 87Sr were measured experimentally; they are important for evaluating the clock&#8217;s Zeeman shifts. We also present recent work on the miniaturization of the strontium optical lattice clock for space applications