Quasi-achromatic Fresnel zone lens with ring focus.

Single shot multispectral multidimensional imaging using chaotic waves.

Abstract: Multispectral imaging technology is a valuable scientific tool for various applications in astronomy, remote sensing, molecular fingerprinting, and fluorescence imaging. In this study, we demonstrate a single camera shot, lensless, interferenceless, motionless, non-scanning, space, spectrum, and time resolved five-dimensional incoherent imaging technique using tailored chaotic waves with quasi-random intensity and phase distributions. Chaotic waves can distinctly encode spatial and spectral information of an object in single self-interference intensity distribution. In this study, a tailored chaotic wave with a nearly pure phase function and lowest correlation noise is generated using a quasi-random array of pinholes. A unique sequence of signal processing techniques is applied to extract all possible spatial and spectral channels with the least entropy. The depth-wavelength reciprocity is exploited to see colour from depth and depth from colour and the physics of beam propagation is exploited to see at one depth by calibrating at another.

Design of multifunctional diffractive optical elements

Abstract: Diffractive optics has traditionally been used to transform a parallel beam of light into a pattern with a desired phase and intensity distribution. One of the advantages of using diffractive optics is the fact that multiple functions can be integrated into one element. Although, in theory, several functions can be combined, the efficiency is reduced with each added function. Also, depending on the nature of each function, feature sizes could get finer. Optical lithography with its 1 μm limit becomes inadequate for fabrication and sophisticated tools such as e-beam lithography and focused ion beam milling are required. Two different techniques, namely, a modulo-2π phase addition technique and an analog technique for design and fabrication of composite elements are studied. A comparison of the beams generated in both cases is presented. In order to be able to compare methods, specific functions of ring generation and focusing have been added in all cases.

All femtosecond optical pump and x-ray probe: holey-axicon for free electron lasers

Abstract: We put forward a co-axial pump (optical)-probe (x-rays) experimental concept and show performance of the optical component. A Bessel beam generator with a central 100 µm diameter hole (on the optical axis) was fabricated using femtosecond (fs) laser structuring inside a silica plate. This flat-axicon optical element produces a needle-like axial intensity distribution which can be used for the optical pump pulse. The fs-x-ray free electron laser (X-FEL) beam of sub-1 µm diameter can be introduced through the central hole along the optical axis onto a target as a probe. Different realisations of optical pump are discussed. Such optical elements facilitate alignment of ultra-short fs-pulses in space and time and can be used in light–matter interaction experiments at extreme energy densities on the surface and in the volume of targets. Full advantage of ultra-short 10 fs-X-FEL probe pulses with fs-pump (optical) opens an unexplored temporal dimension of phase transitions and the fastest laser-induced rates of material heating and quenching. A wider field of applications of fs-laser-enabled structuring of materials and design of specific optical elements for astrophotonics is presented.

Compact generation of superposed higher-order Bessel beams via composite diffractive optical elements

Abstract: Binary composite diffractive optical elements with the functions of a spiral phase plate (SPP), an axicon, and a Fresnel zone lens (FZL) were designed with different topological charges. The element was designed in two steps. In the first step, the function of an SPP was combined with that of an axicon by spiraling the periods of the axicon with respect to the phase of the SPP followed by a modulo- 2π phase addition with the phase of an FZL in the second step. The higher-order Bessel beams generated by the binary phase spiral axicon are superposed at the FZL’s focal plane. Although location of the focal plane is wavelength dependent, the radius of the flower-like beams generated by the element was found to be independent of wavelength. The element was fabricated using electron-beam direct writing. The evaluation results matched well with the simulation results, generating flower-like beams at the focal plane of the FZL.

Conical Fresnel zone lens for optical trapping

Abstract: The phase of a negative axicon is combined with that of a Fresnel zone lens (FZL) to obtain an element labelled as conical FZL, which can generate a focused ring pattern at the focal plane of the FZL. The phase integration is achieved by modifying the location and width of zones of FZL in accordance with the phase variation of the negative axicon. The element was designed for a high power laser with a wavelength of 1064 nm, focal length and diameter of conical FZL of 30 mm and 8 mm respectively and for a ring diameter of 50 μm. The element was fabricated using photolithography. The pattern was transferred from the resist layer to the borosilicate glass plates by dry etching to achieve an etch depth of 1064 nm. The etch depth measured using confocal microscope was 1034 nm at the central part and 930 nm for the outermost part of the device with a maximum error of 12.5% at the outermost part and 3% at the central part. The element was used in an optical trapping experiment. The ring pattern generated by the conical FZL was reimaged into the trapping plane using a tightly focusing microscopic objective. Polystyrene beads with diameters of 3 μm were suspended in deionized distilled water at the trapping plane. The element was found to trap multiple particles in to the same trap.

The Phase Fresnel Lens

Abstract: In order to deform the wave surface passing through an optical system by the amount ϕ(u,v), it is suggested that a phase Fresnel lens be inserted in the pupil of the optical system. Assuming 0⩽ϕ(u,v)

Ring pattern of a lens-axicon doublet illuminated by a Gaussian beam

Abstract: An axicon and a lens are combined to form an optical system producing a ring-shaped pattern. The purpose of this paper is to show that when a lens-axicon combination is illuminated by a Gaussian beam, the transverse distribution of the focal ring is also a Gaussian distribution. The typical width of this distribution was found to be, in the case of the lens-axicon combination, 1.65 times greater than the typical width of the Gaussian beam obtained by focusing the same beam using the lens alone. This focusing system is well suited for the drilling of good quality large diameter holes using a high power laser beam.

Diffraction Patterns and Zone Plates Produced by Thin Linear Axicons

Abstract: We determine the Fraunhofer and Fresnel diffraction patterns produced by a thin linear axicon when it is illuminated by a plane wavefront. An interferometric method of recording zone plates using linear axicons is presented.