Manipulation of optical orbit-induced localized spin angular momentum using the periodic edge dislocation.

Orbit-induced localized spin angular momentum (OILS) has recently garnered significant attention. This paper introduces periodic edge dislocation (PED) into the tight focusing system. The study delves into the tight focusing characteristics of the radially polarized vortex plane beam with PED, demonstrating that PED serves as a straightforward and effective means of manipulating OILS, especially when both the orbital angular momentum and the polarization of the incident beam are fixed. Our findings indicate that the longitudinal OILS reaches its maximum when the difference between the period of PED and the vortex topological charge is equal to 1. Conversely, when the difference is 0, the transverse OILS reaches its maximum, while the longitudinal OILS reaches its minimum. Similar patterns are also observed in linearly polarized vortex beams. This research proposes a simple and practical way to control OILS, contributing to our understanding of optical orbit-spin coupling.

Multi-focused electric and magnetic field sourcing from an azimuthally polarized vortex circular hyperbolic umbilic beam.

In this paper, one kind of multi-focusing electric and magnetic field which is sourced from an azimuthally polarized vortex circular hyperbolic umbilic beam (APVCHUB) is presented. After passing through a high NA objective, both the electric and magnetic fields of the APVCHUBs will focus multiple times, and a high-purity longitudinal magnetic field (p q =80%) will be generated. Besides, the mutual induction of the vortex phase and azimuthal polarization changes the electric and magnetic fields' vibration state and intensity distribution, making the longitudinal magnetic field carry an m-order concentric vortex. Our findings suggest that the APVCHUB could have potential applications in magnetic particle manipulation, extremely weak magnetic detection, data storage, semiconductor quantum dot excitation, etc.

Autofocusing field constructed by ring-arrayed Pearcey Gaussian chirp beams.

In this work, we propose and demonstrate the ring-arrayed Pearcey Gaussian chirp beams (RAPGCBs) synthesized by multiple two-dimensional Pearcey beams. The general analytical formula for the propagation of RAPGCBs is presented. We find that, depending on synthesized number n, the profiles of the beams present different polygonal shapes, and the autofocusing properties can be controlled by chirp factor ß. Furthermore, we study the properties of the RAPGCBs carrying optical vortices (OVs). It shows that a single OV or two positive OVs form an autofocusing hollow field, and opposite OVs will annihilate, which results in greatly increased autofocusing ability. Our experimental results agree with the simulations. Such beams have potential applications in particle trapping and biology medical fields.

Multi-focus autofocusing circular hyperbolic umbilic beams.

We propose and demonstrate a type of multi-focus autofocusing beams, circular hyperbolic umbilic beams (CHUBs), based on the double-active variable caustics in catastrophe theory. The mathematical form is more general compared to circular Airy, Pearcey and swallowtail beams. The CHUBs can generate multi-focus at its optical axis, while the on-axis intensity fluctuates up to two orders of magnitude that of the maximum intensity in the initial plane. Using the concept of topographic prominence, we quantify the autofocusing ability. We construct the criteria for selecting the effective foci, and then explore the influence of related parameters. Our findings suggest that the CHUBs could be a suitable tool for multi-particle manipulation, optical tweezers, optical lattices and related applications.

Characteristics of an elliptical Airy beam with a circular concentric vortex and its realization.

We theoretically and experimentally study the propagation characteristics of elliptical Airy vortex beams (EAVBs) with a circular concentric vortex. It is found that EAVBs inherit the abruptly autofocusing properties of the circular Airy beams (CABs), but EAVBs will have a better autofocusing performance than circular Airy vortex beams (CAVBs) under certain conditions. It is also found that the initial m-order concentric vortex of EAVBs splits into |m| first-order vortices at the autofocusing plane, and the focusing pattern splits into |m|+1 bright spots with the pattern's tilting direction related to the sign of m [m is the topological charge (TC) of the vortex]. These characteristics of EAVBs may have potential applications in TC detection, optical micromanipulation, communications, and other fields.

Noise-suppressing and lock-free optical interferometer for cold atom experiments.

A novel noise-suppressing and lock-free interferometer is proposed and experimentally demonstrated in the study of the quantum non-destructive (QND) interaction of cold atoms. A QND measurement based on far-off resonant dispersive probing is usually carried out by a Mach-Zehnder type interferometer. It is an experimental challenge in its own right to reduce the classical noise, such as acoustic noise, phase noise and amplitude noise of lasers, and to lock the interferometer at the white-light position that corresponds to a nearly zero path-length difference. Here, we report an interferometer with an inserted acousto-optic modulator (AOM). It is noise immune and lock-free in principle. The experiments show that the new interferometer is able to measure cold atoms for more than 30 minutes and reduce the phase noise by about 30 dB.

Partially coherent radially polarized circular Airy beam.

We propose and demonstrate a new, to the best of our knowledge, kind of partially coherent vector beam called the partially coherent radially polarized circular Airy beam (PCRPCAB). The PCRPCAB inherits the autofocusing ability of the radially polarized circular Airy beam (RPCAB) and can create an optical potential well at the center of the beam, whose depth can be adjusted by changing the coherent width. We find that, as coherent width decreases, the intensity becomes higher in the dark notch caused by the polarization singularity, and the singularity of the degree of polarization (DOP) remains along propagation, with its waist controllable by the coherent width. Our results make the PCRPCAB a good candidate for optical micromanipulation, disordered optical lattices, etc.

Low noise measurement method based on differential optical interferometer for cold atom experiments.

We proposed and realized a low noise measurement method based on differential optical interferometer to measure trapped cold atoms in a magneto-optical trap (MOT). The configuration is based on a Mach-Zehnder type interferometer, which is composed of two beams of different frequencies. A long-term stability in phase monitor has been obtained by use of the vibration immune mechanism through subtraction of the interferograms imaged on the two photodetectors. With this new configuration, the noise caused by environmental perturbation is greatly reduced at low frequency while the signal of phase shift keeps a good long-term stability.

Radiation forces on a Rayleigh particle produced by partially coherent circular Airy beams.

In this work, the radiation force on a Rayleigh dielectric particle induced by the partially coherent circular Airy beam (PCCAB) is investigated. Our numerical results show that the PCCAB can be used to trap and manipulate particles. The radiation force distribution and trapping stability have been analyzed under different coherent lengths. It is found that, with the increase of the spatial coherent length, the radiation force is increased and the particle can be stably trapped at more points. Therefore, the radiation force as well as the depth of potential well can be effectively modulated by controlling the spatial coherent length in optical micromanipulation. The trapping properties of PCCAB have also been studied under other different parameters, including the scale factor and initial radius.

Polarization transitions in the focus of radial-variant vector circular Airy beams.

We propose a new kind of light beam with both autofocusing ability and radial-variant distribution of polarization states, named radial-variant vector circular Airy beam (RVCAB). The polarization transitions in the focus of RVCABs are simulated based on vectorial angular spectrum formalism and theoretically explained by Stokes parameters. Our results reveal the dependence of the pure polarization state near the focus on the distribution of polarization states in the initial plane, which may lead to manipulation of the polarization state near the focus via controlling the distribution of polarization states in the initial plane.

Elliptical Airy beam.

We found a new type of noncircular symmetrical Airy beam called an elliptical Airy beam (EAB). Using a simple single-pixel checkerboard hologram method, we achieved the EAB in an experiment. We observed its unique property of double focusing and the ability of the energy to flow towards the endpoints of the long axis during propagation. These particular properties will have some potential applications.

Multifocus autofocusing Airy beam.

We propose a multifocus autofocusing Airy beam (MAAB) by modifying the frequency spectrum of a symmetric Airy beam (SAB) with a Gaussian band elimination filter. Unlike the original SAB, there are four off-axis foci at the autofocusing plane of the MAAB. The MAAB has a better abruptly autofocusing property than the original SAB. In addition, with the increase of the normalized intensity at the first peak, the focal position (second peak) of the MAAB remains almost the same, whereas the position of the first peak shifts along the propagation direction gradually. These unique characteristics of MAAB have been demonstrated by experiment and indicate potential applications in various fields.

Laser frequency stabilization by combining modulation transfer and frequency modulation spectroscopy.

We present a hybrid laser frequency stabilization method combining modulation transfer spectroscopy (MTS) and frequency modulation spectroscopy (FMS) for the cesium D2 transition. In a typical pump-probe setup, the error signal is a combination of the DC-coupled MTS error signal and the AC-coupled FMS error signal. This combines the long-term stability of the former with the high signal-to-noise ratio of the latter. In addition, we enhance the long-term frequency stability with laser intensity stabilization. By measuring the frequency difference between two independent hybrid spectroscopies, we investigate the short-and long-term stability. We find a long-term stability of 7.8 kHz characterized by a standard deviation of the beating frequency drift over the course of 10 h and a short-term stability of 1.9 kHz characterized by an Allan deviation of that at 2 s of integration time.

Trapping two types of particles by modified circular Airy beams.

The radiation force of modified circular Airy beams (MCAB) exerted on both a high-refractive-index particle and a low-refractive-index particle are analyzed in this paper. Our results show that the two kinds of particles can be simultaneously stably trapped by MCAB at different positions. Compared with the common circular Airy beams (CAB) with the same parameters, trapping forces on the two kinds of particles are greatly increased because of the enhanced abruptly autofocusing property and the appearance of hollow region in MCAB. The trapping forces can be modulated by varying parameters of MCAB, and it is important to choose appropriate parameters to trap particles in practice.

Propagation characteristics of the modified circular Airy beam.

We have proposed a kind of modified circular Airy beam (MCAB) based upon a modification of the Fourier spectrum of circular Airy beams (CAB) in this paper. Unlike most abruptly autofocusing beams, the position of peak intensity of MCAB can be moved to any rings behind. Two apodization parameters are introduced to describe the propagation characteristics of MCAB. It is found that the focal position, focal trajectory and the size of focal spot do not change with the apodization parameters; but the abruptly autofocusing property will be greatly enhanced if appropriately apodization parameters are chosen. Comparing with the common CAB and the previous blocked CAB, the MCAB shows better abruptly autofocusing property. It may have more applications in various fields.

Abruptly autofocusing property of blocked circular Airy beams.

We theoretically and experimentally study the propagation characteristics of the circular Airy beam (CAB) when its first few light rings are blocked. It is shown that the focus position of the blocked CAB will remain the same, and its abruptly autofocusing property will be enhanced. Since the maximum focal intensity almost remains the same when the first ring is blocked, a better result of abruptly autofocusing property can be obtained when only the first ring is eliminated. Compared with the common CAB with a same hollow region, the intensity of the blocked CAB will focus at a different position and the intensity will be increased much larger than the common CAB.

Radiation force of abruptly autofocusing Airy beams on a Rayleigh particle.

The radiation force of circular Airy beams (CAB) on a dielectric Rayleigh particle is investigated in this paper. Our results show that the CAB can be used to trap the particle whose refractive index is larger than the ambient at different positions along the beam axis. Comparing with the Gaussian beam under the same conditions, the longitudinal and the transverse gradient force of CAB on the Rayleigh particle are increased, and the particle can be trapped more stable. Our analyses also demonstrate that the trapping properties of CAB can be modulated by controlling corresponding parameters of CAB.

A digital optical phase-locked loop for diode lasers based on field programmable gate array.

We have designed and implemented a highly digital optical phase-locked loop (OPLL) for diode lasers in atom interferometry. The three parts of controlling circuit in this OPLL, including phase and frequency detector (PFD), loop filter and proportional integral derivative (PID) controller, are implemented in a single field programmable gate array chip. A structure type compatible with the model MAX9382∕MCH12140 is chosen for PFD and pipeline and parallelism technology have been adapted in PID controller. Especially, high speed clock and twisted ring counter have been integrated in the most crucial part, the loop filter. This OPLL has the narrow beat note line width below 1 Hz, residual mean-square phase error of 0.14 rad(2) and transition time of 100 µs under 10 MHz frequency step. A main innovation of this design is the completely digitalization of the whole controlling circuit in OPLL for diode lasers.

Propagation dynamics of abruptly autofocusing Airy beams with optical vortices.

We investigated the propagation dynamics of the Circular Airy Beams (CAB) with optical vortices (OVs) by numerical calculation. Comparing to the common CAB, the maximum intensity of CAB with vortices can be increased greatly at the focal plane and its focal intensity profile is doughnut-shaped when an on-axis vortex is imposed. The case for an off-axis OV and multiple OVs have been investigated as well. We demonstrate that two opposite OVs will annihilate exactly at the focal plane, with the focal intensity is highly increased.

Airy-related beam generated from flat-topped Gaussian beams.

A new kind of Airy-related beam has been obtained from Airy transform for flat-topped Gaussian beams. It is proved in this paper that this beam also possesses an "Airy" profile, quasi-diffraction-free character and transverse accelerating character as the Airy beam generated from the fundamental Gaussian beams. The propagation dynamics of this beam can be modulated by varying N, i.e., the beam order of the flat-topped Gaussian beam.