Chinese Optics Letters

2023, 21(10): 100101

We introduce the Stokes scintillation indices and the corresponding overall Stokes scintillations for quantitatively studying the fluctuations of both the intensity and polarization of an optical vector beam transmitting through the atmospheric turbulence. With the aid of the multiple-phase-screen method, we examine the Stokes fluctuations of a radially polarized beam in Kolmogorov turbulence numerically. The results show that the overall scintillation for the intensity distribution is always larger than the overall scintillation for the polarization-dependent Stokes parameters, which indicates that the polarization state of a vector beam is stabler than its intensity distribution in the turbulence. We interpret the results with the depolarization effect of the vector beam in turbulence. The findings in this work may be useful in free-space optical communications utilizing vector beams.

Stokes scintillations atmospheric turbulence vector beams polarization of light We report the measurement of the electromagnetically induced transparency (EIT) with Rydberg states in ultracold ${}^{40}\mathrm{K}$ Fermi gases, which is obtained through a two-photon process with the ladder scheme. Rydberg–EIT lines are obtained by measuring the atomic losses instead of the transmitted probe beam. Based on the laser frequency stabilization locking to the superstable cavity, we study the Rydberg–EIT line shapes for the $37\mathrm{s}$ and $35\mathrm{d}$ states. We experimentally demonstrate the significant change in the Rydberg–EIT spectrum by changing the principal quantum number of the Rydberg state (*n*$=37/52$ and *l*$=0$ ). Moreover, the transparency peak position shift is observed, which may be induced by the interaction of the Rydberg atoms. This work provides a platform to explore many interesting behaviors involving Rydberg states in ultracold Fermi gases.

atomic and molecular physics hyperfine structure Rydberg states In this Letter, we present a low-cost, high-resolution spectrometer design for ultra-high resolution optical coherence tomography (UHR-OCT), in which multiple standard achromatic lenses are combined to replace the expensive F-theta lens to achieve a comparable performance. For UHR-OCT, the spectrometer plays an important role in high-quality 3D image reconstruction. Typically, an F-theta lens is used in spectrometers as the Fourier lens to focus the dispersed light on the sensor array, and this F-theta lens is one of the most expensive components in spectrometers. The advantage of F-theta lens over the most widely used achromatic lens is that the aberrations (mainly spherical aberration, SA) are corrected, so the foci of the dispersed optical beams (at different wavelengths) with different incident angles could be placed on the sensor array simultaneously. For the achromatic lens, the foci of the center part of the spectrum are farther than those on the side in the longitudinal direction, causing degradations of the spectral resolution. Furthermore, in comparison with the achromatic lens with the same focal length, those with smaller diameters have stronger SA, but small lenses are what we need for making spectrometers compact and stable. In this work, we propose a simple method of using multiple long-focal-length achromatic lenses together to replace the F-theta lens, which is $>8$ -fold cheaper based on the price of optical components from Thorlabs, US. Both simulations and *in vivo* experiments were implemented to demonstrate the performance of the proposed method.

low-cost spectrometer optical coherence tomography spherical aberration suppression ultrahigh-resolution non-invasive imaging In this Letter, we propose a simple structure of an orthogonal type double Michelson interferometer. The orthogonal detection method overcomes the problems of uneven ranging sensitivity and the inability of traditional interferometers to determine the displacement direction. The displacement measurement principle and signal processing method of the orthogonal double interferometer are studied. Unlike the arctangent algorithm, the displacement analysis uses the arc cosine algorithm, avoiding any pole limit in the distance analysis process. The minimum step size of the final experimental displacement system is 5 nm, which exhibits good repeatability, and the average error is less than 0.12 nm.

orthogonal detection nanoscale displacement measurement laser interferometer We propose a method for reconstructing non-diffuse surfaces based on the $\pi $ -phase-shifted two-plus-one phase-shifting method. First, we introduce a 2*f*_{H} + *a* + 2*f*_{M} + 2*f*_{L} method for unwrapped phase extraction. Subsequently, we introduce a new set of $\pi $ -phase-shifted 2*f*_{H} + *a*/2 + 2*f*_{M} + 2*f*_{L} fringe patterns with halved background intensity. The saturated pixels will be replaced with the unsaturated pixels in the $\pi $ -phase-shifted fringe patterns. Finally, we analyze eight fringe replacement cases and give the corresponding phase calculation, and further give the general formulas. Experiments confirm that the sum of the phase error of the proposed method is 81.4% lower than that of the traditional method, and 61.5% lower than that of the adaptive fringe projection method.

non-diffusion π-phase shift two-plus-one phase shift Based on the one-dimensional periodic and Fibonacci-like waveguide arrays, we experimentally investigate localized quantum walks (QWs), both in the linear and nonlinear regimes. Unlike the ballistic transport behavior in conventional random QWs, localization of QWs is obtained in the Fibonacci-like waveguide arrays both theoretically and experimentally. Moreover, we verify the enhancement of the localization through nonlinearity-induced effect. Our work provides a valid way to study localization enhancement in QWs, which might broaden the understanding of nonlinearity-induced behaviors in quasi-periodic systems.

Fibonacci-like waveguide arrays nonlinearity-induced effect localization enhancement We reporte and demonstrate a solid-state laser to achieve controlled generation of order-switchable cylindrical vector beams (CVBs). In the cavity, a group of vortex wave plates (VWPs) with two quarter-wave plates between the VWPs was utilized to achieve mode conversion and order-switch of CVBs. By utilizing two VWPs of first and third orders, the second and fourth order CVBs were obtained, with mode purities of 96.8% and 94.8%, and sloping efficiencies of 4.45% and 3.06%, respectively. Furthermore, by applying three VWPs of first, second, and third orders, the mode-switchable Gaussian beam, second, fourth, and sixth order CVBs were generated.

cylindrical vector beams order-switchable beams vortex wave plates solid-state laser On the basis of the stationary phase principle, we construct a family of shaping nondiffracting structured caustic beams with the desired morphology. First, the analytical formula of a nondiffracting astroid caustic is derived theoretically using the stationary phase method. Then, several types of typical desired caustics with different shapes are numerically simulated using the obtained formulas. Hence, the key optical structure and propagation characteristics of nondiffracting caustic beams are investigated. Finally, a designed phase plate and an axicon are used to generate the target light field. The experimental results confirm the theoretical prediction. Compared with the classical method, the introduced method for generating nondiffracting caustic beams is high in light-energy utilization; hence, it is expected to be applied conveniently to scientific experiments.

nondiffracting structured caustic beams phase plate stationary phase method axicon Curved crystal imaging is an important means of plasma diagnosis. Due to the short wavelengths of high-energy X rays and the fixed lattice constant of the spherical crystal, it is difficult to apply the spherical crystal in high-energy X-ray imaging. In this study, we have developed a high-energy, high-resolution X-ray imager based on a toroidal crystal that can effectively correct astigmatism. We prepared a Ge $\langle 5\text{}1\text{}1\rangle $ toroidal crystal for backlighting Mo Kα1 characteristic lines ($\sim 17.48$ keV) and verified its high-resolution imaging ability in high-energy X-ray region, achieving a spatial resolution of 5–10 µm in a field of view larger than 1.0 mm.

laser plasma diagnostics toroidal crystal monochromatic X-ray imaging In this Letter, we report on the investigations of nonlinear scattering of plasmonic nanoparticles by manipulating ambient environments. We create different local thermal hosts for gold nanospheres that are immersed in oil, encapsulated in silica glass and also coated with silica shells. In terms of regulable effective thermal conductivity, silica coatings are found to contribute significantly to scattering saturation. Benefitting from the enhanced thermal stability and the reduced plasmonic coupling provided by the shell-isolated nanoparticles, we achieve super-resolution imaging with a feature size of 52 nm ($\lambda /10$ ), and we can readily resolve pairs of nanoparticles with a gap-to-gap distance of 5 nm.

noble metal nanoparticles plasmonic scattering effective thermal conductivity super-resolution Hybrid metal-dielectric structures combine the advantages of both metal and dielectric materials, enabling high-confined but low-loss magnetic and electric resonances through deliberate arrangements. However, their potential for enhancing magnetic emission has yet to be fully explored. Here, we study the magnetic and electric Purcell enhancement supported by a hybrid structure composed of a dielectric nanoring and a silver nanorod. This structure enables low Ohmic loss and highly-confined field under the mode hybridization of magnetic resonances on a nanoring and electric resonances on a nanorod in the optical communication band. Thus, the 60-fold magnetic Purcell enhancement and 45-fold electric Purcell enhancement can be achieved. Over 90% of the radiation can be transmitted to the far field. For the sufficiently large Purcell enhancement, the position of emitter has a tolerance of several tens of nanometers, which brings convenience to experimental fabrications. Moreover, an array formed by this hybrid nanostructure can further enhance the magnetic Purcell factors. The system provides a feasible option to selectively excite magnetic and electric emission in integrated photonic circuits. It may also facilitate brighter magnetic emission sources and light-emitting metasurfaces with a more straightforward design.

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