The vortex beam can improve the resolution of the interferometry by converting the continuous phase shift into the rotation angle of the interference image. This research focuses on the high-resolution recognition of rotating interference images in the vortex beam interferometry. The present paper explores deep-learning technology by establishing a residual convolutional neural network to recognize the rotation angles of interference profiles. After well trained, the proposed network model is able to achieve an image rotation recognition resolution of 9.19 milli-radians, and the corresponding displacement measurement resolution is 0.92 nm. Due to the competitive resolution, the proposed method shows great potential in precise measurements.
We incorporate neural networks into the optical design of off-axis three-mirror reflective system, enabling us to achieve design outcomes without relying on iteration or ray tracing methods. Our approach involves combining analytical relations with neural networks during the design process, which yields results covering the entire parameter space with a single user input, and each design is scored simultaneously. Our results demonstrate that neural networks can simulate the complex relationship between performance requirements and structural parameters of an optical system. As such, the structural parameters can be directly obtained from the performance requirements, replacing the iterative optimization process traditionally used. This approach leads to relatively efficient and straightforward optical design. We anticipate that this method can be extended to various optical systems, reducing the experience threshold and difficulty of optical design.
Polarization smoothing is a means to increase the uniformity of the focal spot by using polarization characteristics of light. It can theoretically reduce the contrast of focal spot to 0.707 times, and because of its real-time modulation characteristics, it can significantly suppress backscattering and improve the beam-target coupling performance of high-power laser facilities. However, in the traditional polarization smoothing scheme, the crystal used for polarization smoothing (largeaperture KDP crystal) will produce transverse stimulated Raman scattering in the high-power ultraviolet band, which will cause crystal damage. To prepare for the exploration of new single beamlet polarization smoothing schemes, we conduct a simulation study on the scheme of modulating the full Poincaré beam with a single transmission element. The results show that a single waveplate with a fast axis that rotates with polar angle and a phase retardation that increases with radius can modulate a full Poincaré beam, and we analyze the properties of this full Poincaré beam. Then combined with the engineering parameters, we analyzed the polarization smoothing performance of the full Poincaré beam with square aperture laser input. The performance was quantified by several target focal spot intensity evaluation indexes, and the results show that the use of the full Poincaré beam for polarization smoothing can reduce the contrast of the focal spot effectively, and the reduction range is close to the theoretical maximum value. And there are advantages in suppressing high energy density hot spots and optimizing the spatial frequency of the focal spot.
KEYWORDS: Stray light, Absorption, Glasses, High power lasers, Laser systems engineering, Laser damage threshold, Metals, Solid state lasers, Finite element methods, Interference (communication)
In high power solid-state laser facilities, stray lights may do great damage to optical glass and metal structure and affect the transmission of the main laser and the environment cleanliness inside the facility. On the other hand, the stray may also form noise signal of the main laser pulse and affect the output quality. There are mature solutions for the controlling and absorption of parallel and divergent stray light[2]. However there are no reliable solution for the absorption of the converging stray light near its focal spot. An absorber design are proposed using multiple materials and small angle light cone. And this design can realize effective absorption of the stray light focal spot with the peak fluence up to 40J/cm2.
We presented a novel scheme to improve the stability of the orbital angular momentum (OAM) modes transmission by adding a dip at the edge of the annular high-index region of the air-core fiber. The simulation indicated a larger effective index difference of the vector modes that composed OAM modes in the same order, promising a stable transmission of the OAM modes. The intensity of the modes was concentrated better in this scheme decreasing the crosstalk between adjacent fibers. The propagation properties of the OAM modes in bent fiber were investigated.
Optical poling and frequency doubling effect is one of the effective manners to induce second order nonlinearity and realize frequency doubling in glass materials. The classical model believes that an internal electric field is built in glass when it’s exposed by fundamental and frequency-doubled light at the same time, and second order nonlinearity appears as a result of the electric field and the orientation of poles. The process of frequency doubling in glass is quasi phase matched. In this letter, the physical process of poling and doubling process in optical poling and frequency doubling effect is deeply discussed in detail. The magnitude and direction of internal electric field, second order nonlinear coefficient and its components, strength and direction of frequency doubled output signal, quasi phase matched coupled wave equations are given in analytic expression. Model of optical poling and frequency doubling effect which can be quantitatively analyzed are constructed in theory, which set a foundation for intensive study of optical poling and frequency doubling effect.
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