Precision alignment using a system of large rectangular fresnel lenses

Vacuum Beam Guide for Large Scale Quantum Networks

The vacuum beam guide (VBG) presents a completely different solution for quantum channels to overcome the limitations of existing fiber and satellite technologies for long-distance quantum communication. With an array of aligned lenses spaced kilometers apart, the VBG offers ultrahigh transparency over a wide range of optical wavelengths. With realistic parameters, the VBG can outperform the best fiber by 3 orders of magnitude in terms of attenuation rate. Consequently, the VBG can enable long-range quantum communication over thousands of kilometers with quantum channel capacity beyond 10^{13}  qubit/sec, orders of magnitude higher than the state-of-the-art quantum satellite communication rate. Remarkably, without relying on quantum repeaters, the VBG can provide a ground-based, low-loss, high-bandwidth quantum channel that enables novel distributed quantum information applications for computing, communication, and sensing.

Generation of ultra-intense vortex laser from a binary phase square spiral zone plate

With the development of ultra-intense laser technology, the manipulation of relativistic laser pulses has become progressively challenging due to the limitations of damage thresholds for traditional optical devices. In recent years, the generation and manipulation of ultra-intense vortex laser pulses by plasma has attracted a great deal of attention. Here, we propose a new scheme to produce a relativistic vortex laser. This is achieved by using a relativistic Gaussian drive laser to irradiate a plasma binary phase square spiral zone plate (BPSSZP). Based on three-dimensional particle-in-cell (3D-PIC) simulations, we find that the drive laser has a phase difference of π after passing through the BPSSZP, ultimately generating the vortex laser with unique square symmetry. Quantitatively, by employing a drive laser pulse with intensity of 1.3 × 1018~W/cm2, a vortex laser with intensity up to 1.8 × 1019~W/cm2, and energy conversion efficiency of 18.61% can be obtained. The vortex lasers generated using the BPSSZP follow the modulo-4 transmutation rule when varying the topological charge of BPSSZP. Furthermore, the plasma-based BPSSZP has exhibited robustness and the ability to withstand multiple ultra-intense laser pulses. As the vortex laser generated via the BPSSZP has high intensity and large energy conversion efficiency, our scheme may hold potential applications in the community of laser-plasma, such as particles acceleration, intense high-order vortex harmonic generation, and vortex X/γ-ray sources.

Propagation and stability characteristics of a 500-m-long laser-based fiducial line for high-precision alignment of long-distance linear accelerators

A laser-based alignment system with a He-Ne laser has been newly developed in order to precisely align accelerator units at the KEKB injector linac. The laser beam was first implemented as a 500-m-long fiducial straight line for alignment measurements. We experimentally investigated the propagation and stability characteristics of the laser beam passing through laser pipes in vacuum. The pointing stability at the last fiducial point was successfully obtained with the transverse displacements of ±40 μm level in one standard deviation by applying a feedback control. This pointing stability corresponds to an angle of ±0.08 μrad. This report contains a detailed description of the experimental investigation for the propagation and stability characteristics of the laser beam in the laser-based alignment system for long-distance linear accelerators.

Experimental investigation on focusing characteristics of a He-Ne laser using circular Fresnel zone plate for high-precision alignment of linear accelerators

We experimentally investigate the focusing characteristics of a He-Ne laser at the focal region for the high-precision alignment of long-distance linear accelerators using a circular Fresnel zone plate. The laser wave passing through the Fresnel zone plate having a focal length of 66.7 m propagates for a 268-m-long distance at atmospheric pressure. A new laser-based alignment system using Fresnel zone plates as the alignment targets is discussed. The transverse displacement of the focused spot of the laser is measured as a function of the displacement of the target by a detector installed at the focal point. Systematic studies on the focusing characteristics and alignment precision have been successfully conducted in this experiment. The experimental results are in good agreement with theoretical calculations, and the alignment precision of the target is determined to be less than ±30 μm. In this study, we perform a detailed experimental investigation on the laser propagation and focusing characteristics using the circular Fresnel zone plate at the focal region along with theoretical calculations.

Square Fresnel zone plate with spiral phase for generating zero axial irradiance

A type of square Fresnel zone plate with spiral phase for generating zero axial irradiance is proposed. Diffraction patterns of the zone plates with different generalized topological charges are given by numerical simulation, which also suggests their potential applications in generating hollow beams.

Diffractive elements of variable optical power and high diffraction efficiency

The generation of diffractive elements of variable optical parameters and high diffraction efficiency is presented. It can be realized by a superposition of two conjugate kinoforms. In particular, the method gives rise to zone plates of variable focusing power as well as to circular and linear gratings of variable deflection angles. The theoretical description is illustrated by an experimental example of the blazed grating with a changeable period; some possible applications are mentioned.

Determination of basic grids for subtractive moire patterns

The simple formula derived in the paper establishes a direct relationship between moire beat patterns and basic grids for minute displacements. The possibilities of finding a basic grid for a desired moire pattern are pointed out. The analysis is illustrated by several examples of Fresnel moire zone plate patterns and concentric equidistant circular moire patterns obtained by changes of scale and rotation. Possible advantages of the practical use of this element are outlined.

Design, production and performance of circular fresnel zone plates

This paper describes the design and the spark-erosion production technique for circular Fresnel zone plates with focal lengths between 3 m and 40 m when illuminated by a HeNe laser emitting light at 633 nm. Their image pattern is theoretically investigated by modifying Lommel's original approach to the problem in order to determine the effects of a decentered beam, varying zone numbers and a range of gaussian illumination parameters. The equations derived are evaluated and their results graphically illustrated. The theoretical predictions are experimentally verified for three typical zone plates. The results are discussed with particular regard to their bearing upon the use of zone plates as the optical reference elements in an alignment system at present in an advanced stage of development at the U.K. National Physical Laboratory.

An asymmetry method for high precision alignment with laser light

A new method of making precision alignment of rectilinear systems of any length without requiring high resolution optics is described. Laser light with antisymmetrical transverse phase is used to produce intensity asymmetries by means of diffraction behind a misaligned target. The apparatus is very simple but flexible enough to attain alignment of extreme accuracy within an operational range from zero to several kilometers. Under favorable conditions, misalignments of less than 0.01 mm are detectable (10(-8) rad at a distance of 1 km). Both visual and automated detection is possible in one as well as in two directions. The advantages of the asymmetry method are discussed with respect to conventional and existing laser techniques; applications and limitations are cited.