Original Grating Research Articles

Concurrent maintenance of both veridical and transformed working memory representations within unique coding schemes

Abstract In the dynamic environment we live in, the already limited information that human working memory can maintain needs to be constantly updated to optimally guide behaviour. Indeed, previous studies showed that leading up to a response, representations maintained in working memory representations are transformed continuously. This goes hand-in-hand with the removal of task-irrelevant items. However, does such removal also include the representations of stimuli as they were originally, prior to transformation? Here, we assessed the neural representation of task-relevant transformed representations, and the no-longer-relevant veridical representations they originated from. We applied multivariate pattern analysis to electroencephalographic data during maintenance of orientation gratings with and without mental rotation. During maintenance, we perturbed the representational network by means of a visual impulse stimulus, and were thus able to successfully decode veridical as well as imaginary, transformed orientation gratings from impulse-driven activity. The impulse response reflected only task-relevant (cued), but not task-irrelevant (uncued) items, suggesting that the latter were quickly discarded from working memory. By contrast, even though the original cued orientation gratings were also no longer task-relevant after mental rotation, these items continued to be represented next to the rotated ones, in different representational formats. This seemingly inefficient use of scarce working memory capacity was associated with reduced probe response times and may thus serve to increase precision and flexibility in guiding behaviour in dynamic environments.

Wakefield stimulated terahertz radiation from a plasma grating

When a short laser pulse propagates in a corrugated plasma, its wakefield interacts with the density and electric field ripples of the plasma. In the present paper, the modulation of the plasma originates from two counter-propagating long laser pulses, i.e. the corrugated plasma can be assumed as a so-called plasma grating. PIC (particle in cell) simulations show electromagnetic wave radiation at a frequency just above the plasma frequency when the wakefield interacts with the grating. An electromagnetic instability is proposed as the reason for the emission process. The electrostatic driver of the electromagnetic instability is the beat of the wake and grating. That beat mode possesses a large wavenumber (originating from the small grating wavelength) and small frequency (of the order of the plasma frequency) when one concentrates on small ratios of the plasma modulation length to the wavelength of the wakefield. The latter situation occurs when the long laser pulses (which generate the grating) as well as the short laser pulse (which drives the wakefield) have similar frequency where is the plasma frequency. The coherent volume emission process lasts for a while. It is finally superseded by terahertz transition radiation at the boundaries of the original grating.

Recording optical vortices in azo polymer films by applying holographic method

In this paper the optical vortices with topological charge <i>q</i> = –1, 1, 2, 4 are recorded in azo polymer films by using holographic technology. The forked holographic gratings formed by the Gaussian beam and optical vortex beam are recorded in the sample films, the original forked holographic grating and the recording rate are analyzed. The vortex beam is reconstructed by illuminating the sample film with a reference beam, and the recording quality is analyzed. Also the erasability and durability of the sample are tested. The experimental results show that the recording rates of vortex beams with different topological charges are relatively uniform, which means that the optical vortices with different topological charges can be recorded at the same speed. The forked holographic grating of the high-order optical vortex splits in the recording process due to the disturbances, such as anisotropic nonlinear light, atmospheric turbulence, and background light field. However, the split vortex beam still maintains a stable ring structure. The reconstructed optical vortex and the original optical vortex are highly consistent in morphology, and the interference fringes of the reconstructed optical vortices are highly consistent with the original vortex holographic gratings, indicating that the topological charge information in the optical vortices can be effectively recorded and read out. The recorded information can be erased by heating the sample to about 97 ℃, and new information can be re-recorded after cooling. There appears no fatigue in the sample after the information has been erased 100 times and good durability is still retained. Optical vortices theoretically have infinite states of topological charges, based on which great success is achieved in optical communication and information encoding. Therefore, storing and reading information of topological charges in optical vortices may have potential applications in optical information storage.

Information hiding scheme based on optical moiré-pixel matrix

An information hiding scheme for visual cryptography based on optical moiré-pixel matrix is introduced in this paper. The hiding information is formed by black and white unit square visual moiré-pixels with half of the period of a visual moiré pattern. The moiré-pixels can be accurately determined by designing the parameters in the original gratings. To verify the designed information hiding scheme, we experimentally conduct the sharing gratings to decrypt the information by using ordinary low-cost digital printing. The concealment of the sharing gratings is good to ensure the confidentiality. Both the simulation and experimental results show that the provoked scheme can afford enough security demand, yielding that the moiré-pixel matrix is a flexible platform for cryptographic security.

Optical analysis of coatings including diffractive pigments using a high-resolution gonioreflectometer

The aim of this article is to demonstrate a new way of measuring and understanding the appearance of pigment flake orientation and texture in special effect pigments for use in industrial coatings. We have used diffractive pigments and analyzed the relative orientation of the particles in the coating layers by evaluating their behavior in two common industry applications: solventborne and powder coatings. We have measured the interference color by taking readings with a high-resolution gonioreflectometer, in order to test the viability of automatic diffractive pigment evaluation. The results were analyzed using both psychophysical (i.e., human) and computational (i.e., mechanical) methods. Our later psychophysical and computational analysis of the visual differences that diffractive pigments present in both solventborne (1) and powder coating (2) systems for in-plane and out-of-plane geometries revealed that solventborne liquid paint systems better preserve the appearance of original diffraction gratings. This is due to enhanced orientation of the anisotropic pigment particles. The powder coating surfaces investigated, on the other hand, preserved higher intensity and thus visibility in randomly oriented solitary flakes, creating a greater sparkle contrast. We confirmed our findings by capturing and visualizing coating appearance by means of a bidirectional texture function. We then compared the diffractive pigment evaluation results with other state-of-the-art measuring device readings. We believe that our work provides valuable information on flake orientation and also compares pigment performance in a range of industrial coating systems, which may enable industrial companies to improve paint spraying processes.

Random antireflective nanostructuring on binary near-wavelength period gratings

Fresnel reflection losses have been reduced by the fabrication of random nanostructures on optical component surfaces, acting as an antireflective treatment. These structures have shown a broadband enhancement over a wide range of angle-of-incidence and polarization insensitivity. The random nanostructures were fabricated on pre-existing, near-wavelength period, fused silica binary gratings, with periods of 1.595 and 1.166 μm, respectively. The diffractive properties and the efficiency were measured and compared prior and postimplementation of the random nanostructures. The postprocessed gratings retained the diffractive properties of the original gratings, such as the propagating diffraction order angles, period, and the fill factor. A selectable multiwavelength He–Ne laser working at 594, 612, and 633 nm was used to test the gratings for both incident polarizations, S (TE) and P (TM). The data were collected at normal and Bragg incidence. The Fresnel reflection was suppressed by a factor of 10 postprocessing, resulting in a reflected intensity of 0.5% to 1.0% for 1.595-μm period grating and around 0.5% to 4% for 1.166-μm period grating. A 10% enhancement was observed for the combined transmission diffraction efficiency at S polarization for the 1.166-μm grating. Beam profiles of the diffracted light show no adverse changes due to the random nanostructuring on both the gratings. The results indicate that random nanostructures can be an antireflective treatment for pre-existing binary gratings, without adverse effects on the grating diffractive properties and beam profiles.

Generation of photonic orbital angular momentum superposition states using vortex beam emitters with superimposed gratings

An integrated approach to produce photonic orbital angular momentum (OAM) superposition states with arbitrary OAM spectrum has been demonstrated. Superposition states between two vector OAM modes have been achieved by integrating a superimposed angular grating in one silicon micro-ring resonator, with each mode having near equal weight. The topological charge difference between the two compositional OAM modes is determined by the difference between the numbers of elements in the two original gratings being superimposed, while the absolute values of the topological charge can be changed synchronously by switching WGM resonant wavelengths. This novel approach provides a scalable and flexible source for the OAM-based quantum information and optical manipulation applications.

Annealing of High Temperature Stable Hydrogen Loaded Fiber Bragg Gratings

We compare the isothermal and isochronal annealing response of ultrafast laser-induced first-order gratings to that of the third-order gratings up to 1000 °C. Both devices are written in $H_{2}$ -loaded SMF-28 fiber with low-energy femtosecond laser pulses. With the first-order gratings, we observed a regeneration process that allows for a final peak index change of roughly 4% of the original grating. A high-temperature stable peak reflectivity of 39% is obtained (−2.14-dB transmission loss). The third-order gratings do not anneal out completely (they do not regenerate) and roughly 26% of the device persists at 1000 °C corresponding to a final peak reflectivity of 24% (−1.17-dB transmission loss). Due to their similar fabrication conditions, these findings suggest a strong link between the regenerated first-order gratings and the stable third-order devices. We estimate that both first- and third-order gratings of $\sim 4.5$ mm in length are good candidates for the development of high-temperature stable fiber sensors.

Tailoring the Plasmonic Modes of a Grating‐Nanocube Assembly to Achieve Broadband Absorption in the Visible Spectrum

Engineered metal‐dielectric‐metal nanostructures with broadband absorbing properties in the visible spectral range are fabricated by combining the plasmonic resonances of different noble metal nanostructures. Silver nanocubes and gold nanogratings couple to each other using a dielectric polymer spacer with controllable thickness, resulting in a large multiplicative enhancement of absorption properties across a broad spectral range. Narrow, long nanogrooves in a gold film are first fabricated using electron beam lithography, after which a polymer spacer layer with a controllable thickness ranging from 4 to 12 nm is assembled by spin‐assisted layer‐by‐layer assembly. Finally, silver nanocubes with different surface coverages ranging from 12% to 22% are deposited using the Langmuir–Blodgett technique. The individual plasmon resonances of these different nanostructures are located at significantly different optical frequencies and are tuned in this study to allow a significant increase of light absorbance of the original gratings to an average value of 84% across the broad wavelength range of 450–850 nm.

Femtosecond laser ablation of microstructures in fiber and application in magnetic field sensing

A novel (to our knowledge) 3D microstructure manufactured by a femtosecond laser in fiber Bragg grating (FBG) fiber cladding is proposed. The special spiral parameters including single thread and double thread with certain pitches of 60 and 80 μm are controlled by the feed and rotation speed of a rotary fixture. Moreover, supermagnetostrictive TbDyFe film with a thickness of nearly 6 μm is deposited on microgrooves of a FBG by magnetron sputtering technology to form the magnetic field sensing probe. Experimental results demonstrate that a FBG with a double-thread microstructure has a sensitivity of 1.1 pm/mT responding to a magnetic field, and in a theoretical situation, it is approximately six times higher than the original optical fiber grating (approximately 0.2 pm/mT). This new microstructure and method show great prospect in the magnetic field sensing domain.

Technical Analysis Method on Diffraction Grating Mechanical Scratching Based on Limited Elements and Cross Experiment

Quality of the groove shap made by original diffraction grating is the main factor to affect the diffraction efficiency .The process of diffraction grating scratch mainly depends on the experience of the operator. However, its shortage is time-consuming, difficult and waste. In order to overcome the issues mentioned above, the new method has been put forward in this paper: simulate the process of diffraction grating scratch by limited element analysis and cross experiment, find out the process factor that affects the quality of the groove by rang analysis and sort. This method provides the reference to the process design of mechanical scratch grating and instruction to the adjustment of the grating trial scratch .It has practical significance on improving the quality of mechanical grating.

Obtaining ruled diffraction gratings with a nonrectangular ruled zone

This paper presents the design of a ruling engine for cutting diffraction gratings equipped with a cutter-control system that makes it possible to vary the length of the lines of the ruled grating along its width. The control system stabilizes the operation of the ruling engine when original diffraction gratings are fabricated with a ruled zone of nonrectangular shape. The characteristics of grating–polarizers fabricated on the indicated machine are presented.

Accuracy of the Sampling Moiré Method and its Application to Deflection Measurements of Large-Scale Structures

Measuring accurate displacement distributions for large-scale structures is an important issue and a very challenging task. Recently, a simple and accurate phase measurement technique called sampling moire method [Exp Mech 50–4:501–508, (2010)] has been developed for small-displacement distribution measurements. In this method, the phase distribution of moire fringes can be analyzed from a single grating image by simultaneously performing down-sampling image processing and intensity-interpolation to generate multiple phase-shifted moire fringe images. In addition, the phase of the original grating can also be obtained from the phase of the moire fringe by adding the phase of the sampling grating. In this study, the measurement accuracy of the sampling moire method was analyzed through computer simulations and a displacement measurement experiment. Four factors of the sampling moire method were investigated, including the sampling pitch, the order of the intensity-interpolation, random noise, and the form of grating. The results show that determining the optimal sampling pitch is an important factor for obtaining better results but it is not critical. In addition, a practical application of the sampling moire method is presented that involves a deflection measurement on a 10-meter-long crane. The experimental results demonstrate that submillimeter deflections of the crane can be successfully detected.

A New Method of Making Grating - Etched by SPM

The original grating is etched by using the nanometer etching function of Scanning Probe Microscopy (SPM). There are five grooves etched on the surface of polymer material. The grating constant is 796.87 nm, so the fringe density is 1254 lp/mm. Diffraction pattern of the original grating is obtained on Michelson interferometer. A new method of making original grating is found. Since the Nominal Tip Radius of Curvature (NTRC) of Etched Silicon Probe (ESP) of used Veeco SPM is 5-10 nm, the etching grating should have fringe density of 50 000 -100 000 lp/mm.

デジタル液晶変調器による格子投影型モアレ三次元計測

A projection type moiré topography by liquid crystal (LC) modulators is proposed for measuring thee-dimensional surface profile. The moiré contour without any original gratings is captured by the CCD camera during the exposure time by moving the pair of LC gratings electrically. The interval of the moiré contour is easily variable by changing the period of original LC grating. The phase shifting technique is applied to this moiré pattern by changing the phase of the both LC gratings. Some experimental results are shown as a practical application.

基准光栅重构傅里叶变换轮廓术

基准光栅重构傅里叶变换轮廓术

Effect of replication on the groove shape of a sinusoidal holographic grating

We study the changes in groove shape and depth that occur when holographic gratings are replicated in plastic. Specifically, we measure the groove profiles and spatial frequencies of electroplated metal shims made from sinusoidal holographic gratings, and also the same properties of the replicas made of polymethylmethacrylate (also metal shims). Nine samples are studied that have spatial frequencies in the range 600 to 2000 mm−1. The shims of the replicated gratings have up to 30% shallower grooves and 13% lower diffraction efficiencies than the shims of the originals. The maximum measured diffraction efficiency for shims of the original gratings having 525- to 620-mm−1 spatial frequencies correspond to a 0.22-µm groove depth, which agrees with the calculated value. We use this information to modify the groove shapes on the holographic gratings to make better plastic replicas.

Measurement of the fraction of reabsorbed light in an Er3+-doped glass

We report on an original continuous holographic grating technique to quantify the excitation transport within the excited states of erbium ions. We measure a very long range effect well beyond the μm distance which is attributed to radiation trapping. We demonstrate that 30% of the emitted light is reabsorbed inside the sample due to total internal reflections (TIR). The effect of reabsorption is totally removed when TIR are reduced by refractive index matching of the surroundings of the sample.

Reversed Café Wall illusion with missing fundamental gratings

The direction of Café Wall illusion was measured for ordinary Café Wall figures comprised of blocks with a square wave profile and for those with a missing fundamental (MF) profile. For the MF version, it was found that the illusion direction alternates according to the patterns’ main component frequency when the shift between adjacent rows was systematically varied. The direction of illusion for the MF version was opposite to that for the original version when the phase shifts of adjacent rows were between 60 and 120 degrees of the original grating. The results indicate that the illusion depends on the physical component rather than the appearance of the pattern. The possibility of the Café Wall illusion being mediated by low-level luminance mechanisms each tuned to a different spatial frequency is discussed based on the results.

Wire Diffraction Gratings

In the summer of 1972, I attended the workshop on recreating classic experiments in physics at Barnard College.1 This was developed by Samuel Devons, and it was a defining experience that set me toward a research career involving early physics teaching apparatus. During the course of the workshop, I became curious about the original diffraction gratings developed by Fraunhofer and built a wire diffraction. A short note about the gratings was published in the American Journal of Physics the next year.2