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Bessel beams generated with non-ideal axicons are affected by aberrations. We introduce a method to retrieve the complex amplitude of a Bessel beam from intensity measurements alone, and then use this information to correct the wavefront and intensity profile using a deformable mirror.
A document discusses overcoming efficient optical coupling to high orbital momentum modes by slightly bending the taper dispersive element. This little shape distortion is not enough to scramble the modes, but it allows the use of regular, free-beam prism coupling, fiber coupling, or planar fiber on-chip coupling with, ultimately, 100 percent efficiency. The Bessel-beam waveguide is bent near the contact with the coupler, or a curved coupler is used. In this case, every Bessel-beam mode can be successfully coupled to a collimated Gaussian beam. Recently developed Bessel-beam waveguides allow long optical delay and very high dispersion. Delay values may vary from nanoseconds to microseconds, and dispersion promises to be at 100 s/nm. Optical setup consisted of a red laser, an anamorphic prism pair, two prism couplers, and a bent, single-mode fiber attached to prisms. The coupling rate increased substantially and corresponded to the value determined by the anamorphic prism pair.
In this paper we address efficient conversion between a Gaussian beam (a truncated plane wave) and a truncated Bessel beam of agiven order, using cylindrical optical waveguides and whispering gallery mode resonators. Utilizing a generator based on waveguides combined with whispering gallery mode resonators, we have realized Bessel beams of the order of 200 with a conversion efficiency exceeding 10 %.
The theory of nondiffracting beam propagation and experimental evidence for nearly-nondiffractive Bessel beam propagation are reviewed. The experimental results are reinterpreted using simple optics formulas, which show that the observed propagation distances are characteristic of the optical systems used to generate the beams and do not depend upon the initial beam profiles. A set of simple experiments are described which support this interpretation. It is concluded that nondiffracting Bessel beam propagation has not yet been experimentally demonstrated.
We present, to the best of our knowledge, a novel method for the generation of multiple Bessel-like (Bessel–Gauss) beams with tilted wavefronts whose optical phases can be controlled independently. In the far field multiple field-free regions develop that are persistent to interference effects and the optical phase. The extent of these field-free regions can be controlled through the tilt angle of the wavefront with a theoretical maximum resolution of 0.1 mrad. Experimentally we employ a spatial light modulator, a lens, and an axicon, each suitable for narrow-band (continuous-wave) and broadband operation. Because of the simplicity in the optical elements, the number of noninterfering Bessel-like beams can be scaled on demand for applications that require multiple sources for coherent imaging or multiple intense beams over a controllable region with the added benefit of a field-free region for detection. Here, for reasons of clarity, we characterized two beams.
A simplified method of generating a beam of light having a relatively high value of angular momentum (see figure) involves the use of a compact apparatus consisting mainly of a laser, a whispering- gallery-mode (WGM) resonator, and optical fibers. The method also can be used to generate a Bessel beam. ( Bessel beam denotes a member of a class of non-diffracting beams, so named because their amplitudes are proportional to Bessel functions of the radii from their central axes. High-order Bessel beams can have high values of angular momentum.) High-angular-momentum light beams are used in some applications in biology and nanotechnology, wherein they are known for their ability to apply torque to make microscopic objects rotate. High-angular-momentum light beams could also be used to increase bandwidths of fiber-optic communication systems. The present simplified method of generating a high-angular-momentum light beam was conceived as an alternative to prior such methods, which are complicated and require optical setups that include, variously, holograms, modulating Fabry-Perot cavities, or special microstructures. The present simplified method exploits a combination of the complex structure of the electromagnetic field inside a WGM resonator, total internal reflection in the WGM resonator, and the electromagnetic modes supported by an optical fiber. The optical fiber used to extract light from the WGM resonator is made of fused quartz. The output end of this fiber is polished flat and perpendicular to the fiber axis. The input end of this fiber is cut on a slant and placed very close to the WGM resonator at an appropriate position and orientation. To excite the resonant whispering- gallery modes, light is introduced into the WGM resonator via another optical fiber that is part of a pigtailed fiber-optic coupler. Light extracted from the WGM resonator is transformed into a high-angular- momentum beam inside the extraction optical fiber and this beam is emitted from the polished flat output end. By adjusting the geometry of this apparatus, it is possible to generate a variety of optical beams characterized by a wide range of parameters. These beams generally have high angular momenta and can be of either Bessel or Bessel-related types.
Theoretical and experimental investigations have demonstrated the feasibility of compact white-light sensor optics consisting of unitary combinations of (1) low-profile whispering-gallery-mode (WGM) resonators and (2) tapered rod optical waveguides. These sensors are highly wavelength-dispersive and are expected to be especially useful in biochemical applications for measuring absorption spectra of liquids. These sensor optics exploit the properties of a special class of non-diffracting light beams that are denoted Bessel beams because their amplitudes are proportional to Bessel functions of the radii from their central axes. High-order Bessel beams can have large values of angular momentum. In a sensor optic of this type, a low-profile WGM resonator that supports modes having large angular momenta is used to generate high-order Bessel beams. As used here, "low-profile" signifies that the WGM resonator is an integral part of the rod optical waveguide but has a radius slightly different from that of the adjacent part(s).
A promising alternative to Gaussian beams for use in strong field science is Bessel–Gauss (BG or Bessel-like) laser beams, as they are easily produced with readily available optics and provide more flexibility of the spot size and working distances. Here we use BG beams produced with a lens-axicon optical system for higher-order harmonic generation (HHG) in a thin gas jet. The finite size of the interaction region allows for scans of the HHG yield along the propagation axis. Further, by measuring the ionization yield in unison with the extreme ultraviolet (XUV), we are able to distinguish regions of maximum ionization from regions of optimum XUV generation. This distinction is of great importance for BG fields, as the generation of BG beams with axicons often leads to oscillations of the on-axis intensity, which can be exploited for extended phase-matching conditions. We observed such oscillations in the ionization and XUV flux along the propagation axis for the first time. As is the case for Gaussian modes, the harmonic yield is not maximum at the point of highest ionization. Finally, despite Bessel beams having a hole in the center in the far field, the XUV beam is well collimated, making BG modes a great alternative when spatial filtering of the fundamental is desired.
The second harmonic (SH) of an axicon generated Bessel-Gauss beam is created through the nonlinear interaction of photons with a crystal, resulting in the energy doubling of the output photons. In this work, we show experimentally that in addition to frequency doubling, the SH of Bessel-Gauss beams under asymmetric aberrations from an elliptic axicon exhibit intriguing beam formation. Particularly, the central region of the SH beam profile is composed of two central spots of various geometries surrounded by nested ellipses; one of which is the configuration of two central gamma dots with similar radius knotted by nested ellipses for a zeroth-order Bessel-Gauss pump. These SH beams consistently maintain their spatial profile throughout propagation, reminiscing the behavior of screw dislocations in wave patterns. Our numerical simulations produce beam dynamics consistent with that of experiments and further implicate the remarkable interweaving of bright spots with dark vortices. This is especially noticeable when the beams dynamically oscillate along the optical axis, resulting in the genesis of spatially polarized beams with a knotted framework. The insights gained from our study establish a novel paradigm for exploring interactions of Bessel-like beams with vortex dynamics. This, in turn, has the potential to spark innovations in optical applications, fostering new methodologies to harness and manipulate complex light structures. Our experimental findings could spur new methods of generating logical states of light and new opportunities for material processing control. Published by the American Physical Society 2025
Optical delay lines of a proposed type would be made from rods of such dielectric materials as calcium fluoride, fused silica, or sapphire. These would offer advantages over prior optical delay lines, as summarized below. Optical delay lines are key components of opto-electronic microwave oscillators, narrow-band opto-electronic microwave filters, evanescent-field optical biochemical detectors, and some Fourier-Transform spectrum analyzers. Heretofore, optical delay lines used in such applications have been of two types: resonators and coiled long optical fibers, both of which have disadvantages: Resonators are compact, but excitation must be provided by narrow-band lasers. Wide-band (including noisy) laser light cannot be coupled efficiently to narrow-band resonators. When light is coupled into a narrowband resonator from a source of reasonably high power, a significant amount of optical energy circulates within the resonator, causing nonlinear loss and significant noise. Typically, a coil-type optical delay line is made of fused-silica fiber, which exhibits fundamental loss. To overcome the limit imposed by the optical loss in fused silica, it would be necessary to use fibers having crystalline cores. Although space is saved by winding fibers into coils, fiber-coil delay lines are still inconveniently bulky. The proposed compact dielectric-rod delay lines would exploit the special class of non-diffracting light beams that are denoted Bessel beams because their amplitudes are proportional to Bessel functions of the radii from their central axes. High-order Bessel beams can have large values of angular momentum. They can be generated with the help of whispering-gallery-mode optical resonators, as described, for example, in "Simplified Generation of High-Angular-Momentum Light Beams" (NPO-42965) NASA Tech Briefs, Vol. 31, No. 3 (March 2007), page 8a. In a delay line according to the proposal, the dielectric rod would be dimensioned to function as a multimode waveguide. Suitably chosen high-angular-momentum modes in such a waveguide exhibit low group velocity (hence, long delay) and no resonance. Such a delay line could perform well at any wavelength or range of wavelengths within the transparency wavelength band of the dielectric material, and the maximum possible group delay achievable through suitable design would be limited only by the optical loss in the rod material.
High thermal gradients and complex melt pool instabilities involved in powder bed fusion–based metal additive manufacturing using focused Gaussian-shaped beams often lead to high porosity, poor morphological quality, and degraded mechanical performance. We show here that Bessel beams offer unprecedented control over the spatiotemporal evolution of the melt pool in stainless steel (SS 316L) in comparison to Gaussian beams. Notably, the nondiffractive nature of Bessel beams enables greater tolerance for focal plane positioning during 3D printing. We also demonstrate that Bessel beams significantly reduce the propensity for keyhole formation across a broad scan parameter space. High-speed imaging of the melt pool evolution and solidification dynamics reveals a unique mechanism where Bessel beams stabilize the melt pool turbulence and increase the time for melt pool solidification, owing to reduced thermal gradients. Consequently, we observe a distinctively improved combination of high density, reduced surface roughness, and robust tensile properties in 3D-printed test structures.
An optical system, device, and method that are capable of generating high-order Bessel beams and determining the orbital angular momentum of at least one of the photons of a Bessel beam are provided. The optical system and device include a tapered waveguide having an outer surface defined by a diameter that varies along a longitudinal axis of the waveguide from a first end to an opposing second end. The optical system and device include a resonator that is arranged in optical communication with the first end of the tapered waveguide such that an evanescent field emitted from (i) the waveguide can be coupled with the resonator, or (ii) the resonator can be coupled with the waveguide.
Recent experimental studies suggest the use of spatially extended laser beam profiles as a strategy to control the melt pool during laser powder bed fusion (LPBF) additive manufacturing. However, linkages connecting laser beam profiles to thermal fields and resultant microstructures have not been established. Herein, we employ a coupled thermal transport-Monte Carlo model to predict the evolution of temperature fields and grain microstructures during LPBF using Gaussian, ring, and Bessel beam profiles. In addition, simulation results reveal that the ring-shaped beam yields lower temperatures compared with the Gaussian beam. Owing to the small melt pool size when using the Bessel beam, the grains are smaller in size and more equiaxed compared to those using the Gaussian and ring beams. Our approach provides future avenues to predict the impact of laser beam shaping on microstructure development during LPBF.
Here, we present results from two new techniques for the generation of meter-scale, low density (~10 17 cm -3 on axis) plasma waveguides, the “two-Bessel” technique, and the “self-waveguiding” technique. Plasma waveguides of this density and length range are needed for demonstration of a ~10 GeV laser wakefield accelerator module, key for future staging for a ~TeV lepton collider. Both techniques require the use of high quality ultrashort pulse Bessel beams to efficiently and uniformly ionize hydrogen gas in meter-scale supersonic gas jets via optical field ionization. We review these two techniques, describe our meter-scale gas jets, and present a new method for correction of optical aberrations in Bessel beams. Finally, we briefly present results from recent experiments employing one of our techniques, demonstrating quasi-monoenergetic acceleration of ~5 GeV electron bunches in 20 cm long, low density plasma waveguides.
Self-healing optical beams are a class of propagation modes that can recover their beam shapes after distortion or partial blockage. This self-healing property makes them attractive for use in applications involving turbid media as they can—in theory—penetrate further into these materials than standard Gaussian beams. In this paper, we characterize the propagation of two different self-healing beams (Bessel and Airy) through a solid scattering material with different scatterer concentrations and find that both beams do recover after scattering for samples below a threshold scatterer concentration. Additionally, we test the applicability of both beam shapes for improved sub-surface spectroscopy in heterogeneous materials using fluorescent particles and find that there is an average fluorescence intensity enhancement of 1.3× using self-healing beams versus a standard Gaussian beam.
We demonstrate a method for generation of beams of light with large angular momenta. The method utilizes whispering gallery mode resonators that transform a plane electromagnetic wave into high order Bessel beams. Interference pattern among the beams as well as shadow pictures induced by the beams are observed and studied.
We demonstrate a method for generation of beams of light with large angular momenta. The method utilizes whispering gallery mode resonators that transform a plane electromagnetic wave into high order Bessel beams. Interference pattern among the beams as well as shadow pictures induced by the beams are observed and studied.
Plant leaf tissues are difficult to image via fluorescent microscopy, largely due to the presence of chlorophyll and other pigments that provide large background fluorescence. An advantage of Lattice Light-Sheet microscopy is its use of Bessel beams that illuminate a thin focal region of interest for microscopy, allowing for the excitation of fluorescent molecules within this region without surrounding chlorophyll-like objects outside of the region of interest. Here, we apply STORM Super-resolution techniques to observe Receptor-Like Kinases in Arabidopsis thaliana leaf cells. By applying this technique with the Lattice Light-Sheet, we can localize immune response proteins in sub-100 nm length scales and reconstruct three-dimensional locations of proteins within individual leaf cells. Using this technique, we observed the effect of the elicitors ATP and flg22, where we observed a significant degree of internalization of cognate receptors P2K1 and FLS2. We were also able to similarly observe differences in colocalization due to stimulation with these elicitors, where we observe proteins on the membrane becoming less colocalized as a result of stimulation, suggesting an immune response mechanism involving receptors internalizing via pathways distinct to the receptor. Further, these data show the Lattice Light-Sheet’s capabilities for imaging tissue with problematic background fluorescence that otherwise makes super-resolution fluorescence microscopy difficult.