Higher-order Laser Beams Research Articles

Increased sensitivity of higher-order laser beams to mode mismatches.

This Letter derives explicit factors linking mode-mismatch-induced power losses in Hermite-Gauss optical modes to the losses of the fundamental spatial mode. Higher-order modes are found to be more sensitive to beam parameter mismatches. This is particularly relevant for gravitational-wave detectors, where lasers employing higher-order optical modes have been proposed to mitigate thermal noise, and quantum-enhanced detectors are very susceptible to losses. This work should inform mode matching and squeezing requirements for Advanced+ and third generation detectors.

Higher-order laser beam scintillation in weakly turbulent marine atmospheric medium.

The atmosphere above the sea or ocean, known as the marine atmosphere, affects optical waves propagating through it in a different manner than the atmosphere above land. Like other system design parameters, intensity fluctuations of laser light propagating in marine atmosphere, quantified by the scintillation index, also show different variations. The on-axis scintillations of higher-order laser beams are formulated and evaluated when such excitations are employed in a weakly turbulent marine atmospheric medium. Variations of the scintillation index with respect to the changes in the Gaussian beam size of the higher-order mode, link length, wavelength, and structure constant are reported. Our results can be used in the design of an optical wireless communication link design operating in marine atmospheres.

Dictionary-based image reconstruction for superresolution in integrated circuit imaging.

Resolution improvement through signal processing techniques for integrated circuit imaging is becoming more crucial as the rapid decrease in integrated circuit dimensions continues. Although there is a significant effort to push the limits of optical resolution for backside fault analysis through the use of solid immersion lenses, higher order laser beams, and beam apodization, signal processing techniques are required for additional improvement. In this work, we propose a sparse image reconstruction framework which couples overcomplete dictionary-based representation with a physics-based forward model to improve resolution and localization accuracy in high numerical aperture confocal microscopy systems for backside optical integrated circuit analysis. The effectiveness of the framework is demonstrated on experimental data.

Strong focusing higher-order laser modes: transverse and longitudinal optical fields

The distribution of transverse and longitudinal optical fields in tightly focused higher-order laser beams is investigated. Polarization-dependent fingerprints of transverse and longitudinal optical fields are experimentally captured by means of photoinduced surface deformations in azobenzene polymer thin films.

Scintillations of higher-order laser beams in non-Kolmogorov medium

In an atmospheric medium that shows a non-Kolmogorov turbulence behavior, the variation of the on-axis scintillation index is evaluated when higher-order laser modes are used as the excitation. The Rytov method is employed together with the equivalent structure constant, which makes our results valid in weak turbulence. In the limiting case, our solution correctly reduces to the known scintillation index of the Gaussian beam in Kolmogorov turbulence. For all the higher-order even modes, increase in the power law exponent, α of the non-Kolmogorov spectrum is found to increase the scintillations. When the source size of the higher-order modes is large, higher-order even modes attain almost the same scintillation index values for all α. However, for small source sizes, being valid for any realization of the non-Kolmogorov spectrum, the scintillations decrease as the mode order becomes large. The changes in the propagation distance, structure constant, and the wavelength do not vary these trends.

Strengthening the longitudinal component of the sharply focused electric field by means of higher-order laser beams

We study the sharp focusing of differently polarized low-order and high-order beams, including Bessel and Laguerre-Gaussian (LG) modes, to compare them using several criteria: the size of a light spot, the intensity ratio of the central peak and sidelobes, and the intensity of the longitudinal electric field component. The experiments performed using the near-field microscopy techniques are in general agreement with the results of the numerical simulation. We have validated the growth of the longitudinal component in the focus for high-order modes at moderate NA=0.6-0.8, and essential lower sidelobes of Bessel modes, in comparison with LG modes.

Polarization converter for higher-order laser beams using a single binary diffractive optical element as beam splitter

We propose a new approach to generating a pair of initial beams for a polarization converter that operates by summing up two opposite-sign circularly polarized beams. The conjugated pairs of vortex beams matched with laser modes are generated using binary diffractive optical elements (DOEs). The same binary element simultaneously serves two functions: a beam shaper and a beam splitter. Two proposed optical arrangements are compared in terms of alignment complexity and energy efficiency. The DOEs in question have been designed and fabricated. Natural experiments that demonstrate the generation of vector higher-order cylindrical beams have been conducted.

Polarization‐Dependent SERS at Differently Oriented Single Gold Nanorods

We investigated the influence of the orientation of individual gold nanorods on the polarization-dependent single-particle surface-enhanced Raman spectroscopy (SERS) of adenine. Higher-order laser beams (radial and azimuthal polarizations) have been used in combination with a parabolic mirror-assisted confocal optical microscope. Based on the photoluminescence (PL) patterns of the single gold nanorods and the simulated electric-field distribution in the focus, we distinguished between isolated gold rods and clusters as well as single nanorods with different orientations. We found that for single gold nanorods lying flat on the substrate, the longitudinal particle plasmon resonance (PPR) mode can be excited more efficiently with the in-plane field component in the focus of an azimuthally polarized laser beam, which enables the observation of stronger enhanced adenine Raman spectra from the single gold nanorods compared to the case of a radially polarized beam.

Generating inhomogeneously polarized higher-order laser beams by use of diffractive optical elements

We propose an improved version of the earlier developed optical arrangement for generating inhomogeneously polarized laser light modes with the aid of a diffractive optical element (DOE) with carrier frequency. By eliminating lenses from the optical arrangement, we achieve the miniaturization, reduced light losses, a smaller number of parameters being matched, and a simpler system adjustment procedure. Note that all the capabilities of the previous version, namely, the universality and simple readjustment to different polarization types, are fully retained. The numerical modeling of the polarization mode combiner has made it possible to analyze its performance and capabilities. In the experiments, the quality of the resulting beams is shown to be improved. For generating higher-order cylindrical beams, a lower-order mode at the output of the polarization mode combiner is additionally transformed with a DOE that operates in the zero diffraction order, introducing radial phase changes.

Vectorial structural characteristics of four-petal Gaussian beams in the far field

Based on the vector angular spectrum theory of electromagnetic waves and the method of stationary phase, analytical vector structures of four-petal Gaussian beams (FPGB) in the far field are derived. The energy flux for the TE term, TM term and the whole beam are represented and illustrated with numerical examples. Effects of beam orders and paraxial degrees on energy flux distributions are discussed in detail, and the corresponding analytical explanations are also given. These results may provide a new approach to manipulate other higher-order laser beams in the far field.

Longitudinal anisotropy of the photoinduced molecular migration in azobenzene polymer films

The effects of tightly focused, higher-order laser beams on the photoinduced molecular migration and surface deformations in azobenzene polymer films are investigated. We demonstrate that the surface relief is principally triggered by longitudinal fields, i.e., electric fields polarized along the optical axis of the focused beam. Our findings can be explained by the translational diffusion of isomerized chromophores when the constraining effect of the polymer-air interface is considered.

The elliptical Hermite–Gaussian beam and its propagation through paraxial systems

A new kind of light beam called the elliptical Hermite–Gaussian beam (EHGB) is introduced in this paper by using tensor method. The EHGB can be used to describe the generalized higher-order laser beams, such as hollow laser beams and the twisted Hermite–Gaussian beams conveniently. It includes the conventional Hermite–Gaussian beams as special cases. Using the generalized Collins integral, we derive the propagation formula of the EHGB passing through axially non-symmetrical paraxial optical systems. The EHGB allows us to treat the propagation and transformation of some complicated laser beams analytically. As an application example, we treat the elliptical flattened Gaussian beams by expressing it as superposition of a series of EHGBs by using polynomial expansion.

Phase compensation of laser beam modes: II. Optimization techniques

Phase compensation can lead to a significant improvement in the intensity characteristics of high order laser beam modes. Optimal design procedures for phase compensation structures are described, and the behaviour of the higher order spatial harmonics is considered in detail. The effects of possible phase errors are also derived analytically.

Phase compensation of laser beam modes

A technique is described for improving the propagation characteristics of high order laser beam modes. A thin phase plate inserted in the beam forces all portions of the wave front to oscillate in phase and yields a substantial improvement in the far field intensity distribution. Depending on the mode order, the peak intensity at a distant target may be readily increased by more than a factor of ten.