High-precision Shack-Hartmann wavefront sensing with a multi-focal diffraction Taiji-lenslet array

Abstract A Hartmann wavefront sensor is a type of wavefront detection instrument that has been widely used in various fields. Traditional Hartmann wavefront sensors usually comprise a monofocal refraction lenslet array to segment the wavefront at the entrance pupil. Each wavelet is focused at the focal plane along the projection of the lenslet, forming the foci array. Unlike the multifocal self-interference Taiji-lenslet array, a type of multifocal diffraction Taiji-lenslet array was proposed in this study to improve the measurement accuracy using the weighted centroid location algorithm of these multifocal spots, where the latter is more easily designed than the former. An optical experiment was implemented using the multifocal diffraction Taiji-lenslet array to verify its effectiveness. As a type of diffractive lens, a large-aperture Taiji-lenslet array can be easily fabricated via lithography, which has great potential for application in the measurement of large-scale laser beams and optical elements.

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Fabrication of large-scale infrared diffractive lens arrays on chalcogenide glass by means of step-and-repeat hot imprinting and non-isothermal glass molding

The International Journal of Advanced Manufacturing Technology ◽

10.1007/s00170-021-07716-w ◽

2021 ◽

Author(s):

Yang Shu ◽

Tiantong Chen ◽

Wenchen Zhou ◽

Zhixiong Zhou ◽

Allen Y. Yi

Keyword(s):

Chalcogenide Glass ◽

Large Scale ◽

Diffractive Lens ◽

Glass Molding

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A Location Algorithm for Autonomous Vehicles in Large-scale Scenarios Using a Multilayer LIDAR

2020 IEEE 9th Joint International Information Technology and Artificial Intelligence Conference (ITAIC) ◽

10.1109/itaic49862.2020.9338753 ◽

2020 ◽

Author(s):

Xiao Zhou ◽

Zhen Jiang ◽

Qi Li

Keyword(s):

Autonomous Vehicles ◽

Large Scale ◽

Location Algorithm

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Simulation of Large Scale KDP Crystal Polishing by Computer Controlled Micro-Nano Deliquescence

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.497.165 ◽

2012 ◽

Vol 497 ◽

pp. 165-169 ◽

Cited By ~ 3

Author(s):

He Ping Zhang ◽

Dong Ming Guo ◽

Xu Wang ◽

Hang Gao

Keyword(s):

Large Scale ◽

Surface Condition ◽

Single Point ◽

Damage Threshold ◽

Diamond Turning ◽

Water Soluble ◽

Optical Elements ◽

Kdp Crystal ◽

Computer Controlled ◽

Laser Induced Damage

Although Single Point Diamond Turning (SPDT) can do pretty well in optical surfacing of large scale KDP crystal, both the surface accuracy and integrity are considerably high; meanwhile as the defects of micro-waveness and stress are inevitable, the laser-induced damage threshold of KDP optical elements after SPDT still cannot be satisfied. Because of the characters of deliquescent and water-soluble, the process of computer controlled Micro-nano deliquescence is attempted to remove the residual micro-waveness on KDP surface after SPDT. Based on the assumption of Preston and the characters of Micro-nano deliquescence, the model of material removal ratio is suggested, the dwell time for ascertained KDP surface is solved, the processing of computer controlled Micro-nano deliquescence is simulated and the processed surface condition on theory is obtained. Besides, the influences of different parameters on the surfacing efficiency and accuracy are analyzed. Finally, three polishing tracks are comparatively analyzed. The simulation results are quite important in guiding the experimental polishing of large scale KDP by computer controlled Micro-nano deliquescence

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Performance Analysis and Validation of Precision Multisatellite RF Measurement Scheme for Microsatellite Formations

Measurement Science and Technology ◽

10.1088/1361-6501/ac37ea ◽

2021 ◽

Author(s):

Chen Lin ◽

Xiaojun Jin ◽

Shiming Mo ◽

Cong Hou ◽

Wei Zhang ◽

...

Keyword(s):

Multiple Access ◽

High Performance ◽

Large Scale ◽

Measurement Accuracy ◽

Media Access Control ◽

Satellite Measurement ◽

Measurement Scheme ◽

Rf Measurement ◽

Code Division Multiple ◽

Time Division

Abstract Almost all existing studies on inter-satellite radio frequency (RF) measurement have focused on two-satellite formations. Although some frequency division multiple access and code division multiple access multisatellite RF measurement schemes have been proposed, their poor scalability does not satisfy the inter-satellite measurement requirements of multisatellite formations, especially large-scale formations. Two-way ranging (TWR), which is based on a time division mechanism, is an effective solution that has been used for inter-satellite links in the global positioning system and Beidou navigation constellations. However, the high measurement accuracy achieved with TWR in these navigation constellations is heavily reliant on high-performance atomic clocks and the assistance of navigation ephemeris, which are not available on microsatellite platforms. This work focuses on a scalable multisatellite measurement scheme that adopts a distributed broadcast-based time division multiple access mechanism as the media access control layer and uses an asymmetric double-side TWR method as the physical layer. The measurement performance of the proposed scheme is evaluated through in-depth theoretical modeling, simulation verification, and experimental validation, along with a comprehensive comparison with the conventional TWR method. The experimental results show that centimeter-level measurement accuracy can be achieved with the proposed scheme when only a common miniaturized frequency source is used. This accuracy level is two orders of magnitude better than that of the TWR method, and thus satisfies the application requirements of general large-scale microsatellite formations.

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On-sky correction of non-common path aberration with the pyramid wavefront sensor

Astronomy and Astrophysics ◽

10.1051/0004-6361/201937033 ◽

2020 ◽

Vol 636 ◽

pp. A88 ◽

Cited By ~ 1

Author(s):

S. Esposito ◽

A. Puglisi ◽

E. Pinna ◽

G. Agapito ◽

F. Quirós-Pacheco ◽

...

Keyword(s):

Adaptive Optics ◽

Critical Issue ◽

Wavefront Sensor ◽

Interaction Matrix ◽

Scientific Instrument ◽

Wavefront Sensors ◽

Successful Operation ◽

Optical Elements ◽

Common Path ◽

External Conditions

The paper deals with with the on-sky performance of the pyramid wavefront sensor-based Adaptive Optics (AO) systems. These wavefront sensors are of great importance, being used in all first light AO systems of the ELTs (E-ELT, GMT, and TMT), currently in design phase. In particular, non-common path aberrations (NCPAs) are a critical issue encountered when using an AO system to produce corrected images in an associated astronomical instrument. The AO wavefront sensor (WFS) and the supported scientific instrument typically use a series of different optical elements, thus experiencing different aberrations. The usual way to correct for such NCPAs is to introduce a static offset in the WFS signals. In this way, when the AO loop is closed the sensor offsets are zeroed and the deformable mirror converges to the shape required to null the NCPA. The method assumes that the WFS operation is linear and completely described by some pre-calibrated interaction matrix. This is not the case for some frequently used wavefront sensors like the Pyramid sensor or a quad-cell Shack-Hartmann sensor. Here we present a method to work in closed-loop with a pyramid wavefront sensor, or more generally a non-linear WFS, introducing a wavefront offset that remains stable when AO correction quality changes due to variations in external conditions like star brightness, seeing, and wind speed. The paper details the methods with analytical and numerical considerations. Then we present results of tests executed at the LBT telescope, in daytime and on sky, using the FLAO system and LUCI2 facility instrument. The on-sky results clearly show the successful operation of the method that completely nulls NCPA, recovering diffraction-limited images with about 70% Strehl ratio in H band in variable seeing conditions. The proposed method is suitable for application to the above-mentioned ELT AO systems.

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Phase-Shift Optimization in AA/PVA Photopolymers by High-Frequency Pulsed Laser

Polymers ◽

10.3390/polym12091887 ◽

2020 ◽

Vol 12 (9) ◽

pp. 1887

Author(s):

Daniel Puerto ◽

Sergi Gallego ◽

Jorge Francés ◽

Andrés Márquez ◽

Inmaculada Pascual ◽

...

Keyword(s):

Phase Shift ◽

High Frequency ◽

Large Scale ◽

Pulsed Laser ◽

Laser Exposure ◽

Continuous Laser ◽

Frequency Limit ◽

Optical Elements ◽

First Time ◽

532 Nm

Photopolymers can be used to fabricate different holographic optical elements, although maximization of the phase-shift in photopolymers has been a challenge for the last few decades. Different material compositions and irradiation conditions have been studied in order to achieve it. One of the main conclusions has been that with continuous laser exposure better results are achieved. However, our results show for the first time that higher phase-shift can be achieved using a pulsed laser. The study has been conducted with crosslinked acrylamide-based photopolymers exposed with a pulsed laser (532 nm). The increment of the phase-shift between the pulsed laser and continuous laser exposure is 17%, achieving a maximum phase-shift of 3π radians and a refractive index shift of 0.0084 at the zero spatial frequency limit, where monomer diffusion does not take place. This allows this photopolymer to be used in large-scale manufacturing.

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