Applications Of Diffractive Optical Elements Research Articles

Advancements and Applications of Diffractive Optical Elements in Contemporary Optics: A Comprehensive Overview

Advancements and Applications of Diffractive Optical Elements in Contemporary Optics: A Comprehensive Overview

Design, Fabrication and Analysis of a Hybrid-Order Monolithic Imaging Diffractive Lens on a Germanium Substrate

Diffractive optical elements are gradually replacing some conventional optical elements and becoming a key component of optical systems due to their unique phase modulation function. However, the imaging performance will be reduced due to the fact that this single-sided microstructured lens still produces chromatic aberration. Therefore, the key issue for the application of diffractive optical elements in optical systems is the reduction of chromatic aberration, and diffractive lenses with double-sided microstructures are proposed as a solution. This research describes the design and analysis of a 70-mm-diameter, 296-mm-focal-length double-sided microstructured hybrid-order monolithic imaging diffractive lens operating in the mid-wave infrared region (3.7-4.7 μm). The design minimizes chromatic aberration by up to 30 times compared to a standard harmonic diffractive lens and improves the image performance of a single-lens optical system operating in the infrared range. Experiments indicate that this design is capable of achieving single-lens imaging with high sensitivity for optical systems with a measured NETD ≤ 50 mK. The analysis of the experiments yielded suggestions for future research.

APPLICATION OF DIFFRACTIVE OPTICAL ELEMENTS FOR OPTICAL-ELECTRONIC DIMENSIONAL INSPECTION SYSTEMS

The work is devoted to the application of diffractive optical elements in systems using the structured illumination method to the geometric parameters inspection of industrial articles. The objects of inspection in these systems are: weapon barrels, fuel pellets, fuel elements, spacer grids, ceramic ring insulators. The used diffractive optical elements are computer-synthesized holograms that focus laser radiation into geometric shapes, the configuration of which is optimally combined with the inspected objects shape.

Design of Diffractive Optical Elements by Direct and Indirect Construction of Diffraction Pattern: A Comparative Study

Abstract In this work, we present the design method of diffractive beam splitters via two comparative technical routes, the first referred as the direct scheme and the second referred as the indirect scheme. Comparative study is carried on the design procedures and results. The advantages of the direct design scheme include overcoming the limit on the number of phase pixels and being capable of realizing beam shaping and splitting simultaneously. Numerical simulation shows that the uniformity of spots array pattern in the direct design is close to that of the indirect design. These results are helpful for the design and application of diffractive optical elements (DOEs) in modern optical devices.

Roller nanoimprint lithography for low-cost nanoscale random lattice diffractive optical elements

In this paper, effective fabrication of high-resolution diffractive optical elements on a polymer substrate is demonstrated using roller nanoimprint lithography. A nanoscale diffraction grating mold, which can generate a random laser pattern, is fabricated by scan-and-repeat projection lithography. The mold is imprinted to a thin polymer on the soft substrate via roller nanoimprint lithography, which has high efficiency, high fidelity, and high throughput for mass production. This fabrication process can produce high-resolution nanostructures while reducing the cost substantially. We obtained large-area polymer diffractive optical elements with a flexible substrate, which can generate high-quality diffraction random lattice patterns with sub-250 nm resolution for an 808-nm wavelength laser. The diffractive optical elements have about 83.2% diffraction efficiency and 99.7% uniformity of random pattern intensity. It is believed that this fabrication technique can promote practical applications of diffractive optical elements, such as laser wavefront correction, face and activity recognition, and optical communication.

Implementation of ordinary and extraordinary beams interference by application of diffractive optical elements

We apply diffractive optical elements in problems of transformation of Bessel beams in a birefringent crystal. Using plane waves expansion we show a significant interference between the ordinary and extraordinary beams due to the energy transfer in the orthogonal transverse components in the nonparaxial mode. A comparative analysis of the merits and lack of diffractive and refractive axicons in problems of formation non-paraxial Bessel beams has shown the preferability of diffractive optics application in crystal optics. The transformation of uniformly polarised Bessel beams in the crystal of Iceland spar in the nonparaxial mode by application of a diffractive axicon is investigated numerically and experimentally.

Algorithm for calculation of the power density distribution of the laser beam to create a desired thermal effect on technological objects

Based on the use of methods for solving the inverse problem of heat conduction, we developed an algorithm for calculating the power density distribution of the laser beam to create a desired thermal effect on technological objects. It was shown that the redistribution of power density of moving distributed surface heat sources can adjust the temperature distribution in the treated zone. The results of thermal processes calculation show the ability of the developed algorithm to create a more uniform temperature field across the width of the heat affected zone. Equalization of maximum temperature values is achieved in the center and on the periphery of the heat affected zone with an increase in the width of the regions, where required temperature is reached. The application of diffractive optical elements gives an opportunity to obtain the required properties of treated materials in the heat affected zone. The research performed has enabled parameters of the temperature field in chrome-nickel-molybdenum steel to be adjusted for laser heat treatment. In addition to achieving uniform temperature conditions across the width of the heat affected zone, the proposed approach allows the increase of the width of the isotherms of the temperature fields; this provides an opportunity to process a larger area per unit time at the same laser beam power.

Design of a diffractive optical element for pattern formation in a bilingual virtual keyboard

Pattern formation is one of the many applications of diffractive optical elements (DOEs) for display. Since DOEs have lightweight and slim nature compared to other optical devices, using them as image projection device in virtual keyboards is suggested. In this paper, we present an approach to designing elements that produce distinct intensity patterns, in the far field, for two wavelengths. These two patterns are images of bilingual virtual keyboard. To achieve this with DOEs is not simple, as they are inherently wavelength specific. Our technique is based on phase periodic characteristic of wavefront using iterative algorithm to design the phase profiles.

Diffractive Elements in the Optical System: Successes, Challenges, and Solutions

Correction of aberrations is regarded as one of the most successful applications of diffractive optical elements in the optical system. The ways of overcoming these negative properties of the diffractive elements as spherochromatism and power spectral selectivity are presented. Using the technique given in this paper, a compact plastic–lens refractive–diffractive objective, which can operate in a wide spectral range including the visible and near-infrared radiation, has been designed.

Application of diffractive optical elements for controlling the light beam in ptychography

We designed two pieces of rotary diffractive optical elements (DOE) to control the incident light beam in ptychography. The incident light beam is shaped into the required complex amplitude as employed probes by using double DOEs. The high-quality probes are generated to illuminate on the different positions of the object, which leads to achieving superior ptychographical imaging by rotating DOEs. Consequently, mechanical movement of the specimen is avoided in the imaging process. The numerical experiments demonstrate the double-wheeling DOEs are effective for the ptychographical imaging. Further, the double discs containing several pairs of DOEs are designed for a larger field of view. As a result, the flexibility of ptychography may be improved by employing the rotary double DOEs.

Two-photon polymerization with optimized spatial light modulator

The application of diffractive optical elements can enhance the efficiency of the two-photon polymerization (TPP) process by multiplying the polymerizing beams. Spatial light modulators (SLMs) can dynamically change the light intensity pattern used for polymerization, making single shot polymerization possible. Most reflective, liquid crystal-based instruments, however, suffer from various surface aberrations. In order to enable SLMs to generate suitable polymerizing beams for TPP, these aberrations need to be corrected. Several methods were introduced earlier to compensate SLM aberrations in different applications. For the nonlinear process of TPP, we developed and specifically characterized a correction procedure. We used a simple interferometric method to determine the surface distortion of the SLM, calculated a correcting hologram and confirmed the correction with the polymerization of test structures. The corrected SLM was capable of parallel polymerization of 3D structures with a quality achievable with non-SLM beams.

Encoded complex reconstruction into diffractive optical elements for high power Nd:YAG laser marking system

The applications of diffractive optical elements (DOE) in the domain of laser marking with a pulsed Nd:YAG laser are numerous, but few publications present usable results. In our opinion, the first usage with a Nd:YAG laser of a low cost DOE to mark complex forms such as industrial logos with a sufficient quality is presented in this paper. Besides, the manufacturing costs are very low and the necessary materials are very simple and few in our proposition. The elements have been manufactured by contact photolithography with a commercial resin, that one can find in a supermarket and a silver halide mask. Finally, the effects of the pulse duration on the reconstruction shape are evaluated and displayed with the help of marking test on sensitized paper.

Nonlinear diffraction in gratings based on polymer–dispersed TiO2 nanoparticles

In this letter we report a simple technique to produce volume holographic gratings based on photopolymerizable composites containing TiO2 nanoparticles. Diffraction gratings with high refractive index modulation amplitude (up to 1.25 × 10−2) have been formed due to the periodic distribution of high refractive index nanoparticles in a low refractive index polymer matrix. The diffraction efficiency increases strongly on increasing the nanoparticle concentration. Taking the mixture with 10 wt.% TiO2 nanoparticles, gratings with high diffraction efficiency, low level of scattering and high transparency in the visible-wavelength range have been obtained. This will ultimately lead to different applications of diffractive optical elements based on nanocomposites. The dependence of the gratings’ diffraction efficiency on the intensity of probe laser pulses at 1064 nm has been explored. It is shown that the nonlinear response of the gratings is attributed mainly to the nonlinear properties of the TiO2 nanoparticles embedded in the polymer matrix. The mechanism of the grating formation and the reasons for the nonlinear behavior of the diffraction efficiency are discussed.

Multi-step electron beam technology for the fabrication of high performance diffractive optical elements

Optical performance, i.e. the diffraction efficiency, numerical aperture and wave front quality is of great importance for further successful application of diffractive optical elements in a wide range of research and commercial applications. For the fabrication process, simultaneously large numerical aperture and high diffraction efficiency result in a pattern with sub-wavelength resolution and a multi-level phase profile of nanometer accuracy. To fulfill such high requirements, a multi-step fabrication technique is proposed, in which the electron beam is used both for pattern writing and layout alignment. This method enables the fabrication of a structure with the L = 2 n discrete phase levels in n sequential lithographic steps. In each step, the pattern written in a thin, high contrast resist layer is transferred after development into the substrate by reactive ion etching to form the phase profile. In comparison to the multi-mask binary optics technology, the proposed method offers a higher resolution and reduces the alignment errors to insignificant values. On the other hand, in comparison to the direct write analog technique, our approach allows for a much better control of the phase profile and ensures larger process tolerances. The method has been successfully applied in the fabrication of several types of diffractive elements, including micro-Fresnel lens arrays, phase sampling filters and diffraction gratings on quartz and GaAs wafers. The diffraction efficiencies of these elements were found to be up to 92%. The lens exhibited diffraction-limited focusing characteristics and an insignificant wave front aberration (rms 0.01 λ).

Design of diffractive optical elements for high-power laser applications

Diffractive optical technology is rapidly becoming an indispensable tool for the creation of high-efficiency optical beam-shaping devices within a wide range of industrial and research activities. The high damage thresholds of typical materials used in diffractive optical element fabrication make them highly suited for deployment in high-power laser systems. We present two high-power applications of diffractive optical elements designed using an ultrahigh fidelity, ultrahigh efficiency design technique and demonstrate the advantages, in terms of optical alignment, that can be achieved by combining the diffractive structures with a multilevel diffractive lens.

Excimer laser ablation lithography applied to the fabrication of reflective diffractive optics

We propose a low cost technique for the production of diffractive optical elements (DOE). These elements are devoted to high power lasers beam shaping in the mid-infrared wavelengths. This process called laser ablation lithography (LAL), may seem similar to laser beam writing (LBW) in the way the whole DOE’s design is reproduced pixel by pixel on the substrate placed on a computer controlled XY translation stage. A first difference is that the photoresist is not exposed with UV light but is directly ablated with short excimer laser pulses. Furthermore, with LAL technique the size of the smallest pixel ( 5 μm×5 μm) is more than 10 times greater than those produced by LBW. We discuss in details the experimental set-up for LAL and demonstrate that it gives a resolution up to 10 times greater than photolithography with flexible masks. This makes LAL a promising solution for the production of DOE for use with Nd:YAG lasers. New applications of DOEs are finally introduced with high power lasers sources, such as laser marking or multi-point brazing.

Diffractive light attenuators with variable transmission

A new application of diffractive optical elements (DOEs) for continuous or multistage adjustment of optical radiation intensity is described. The diffractive attenuators are linear or circular gratings (amplitude or phase) with constant period and diffraction efficiency that varies across the grating. The zero order of diffraction is used as the output and transmitted through the grating without angular deviation. The diffractive attenuators, in distinction to conventional analogues, allow one to change the intensity of the light beam according to predetermined function and have no limitations for power of the regulated light beam. These elements can be used in optical systems as a beam splitter with adjusted splitting coefficient. The experimental results on a circular diffractive attenuator fabricated by direct laser writing on a chromium film are presented. The range of transmission variation was 20 times within a 340° angle of attenuator turn. The possibility to use a phase diffractive attenuator as a light radiation modulator for a powerful technological laser is discussed.