Transmission Grating Research Articles

Tunneling-induced Talbot effect

We investigate the reforming of a plane wave into a periodic waveform in its propagation through a structural asymmetry four-level quantum dot molecule (QDM) system that is induced by an inter-dot tunneling process and present the resulting tunneling-induced Talbot effect. The tunneling process between two neighborhood dots is provided with the aid of a gate voltage. Using a periodic coupling field the response of the medium to the propagating plane probe beam becomes periodic. The needed periodic coupling field is generated with the interference of two coherent plane waves having a small angle and propagating almost parallel to the probe beam direction. In the presence of the tunneling effect of an electron between two adjacent QDs, for the probe beam propagating through the QDM system, the medium becomes transparent where the coupling fields interfere constructively. As a result, the spatial periodicity of the coupling field modulates the passing plane probe beam. We determine the minimum length of the QDM system to generate a periodic intensity profile with a visibility value equal to 1 for the probe field at the exit plane of the medium. It is also shown that by increasing the propagation length of the probe beam through the QDM medium, the profile of the maximum intensity areas becomes sharper. This feature is quantified by considering a sharpness factor for the intensity profile of the probe beam at the transverse plane. Finally, we investigate free space propagation of the induced periodic field and present the Talbot images of the tunneling-induced periodic patterns at different propagation distances for different values of the QDM medium lengths. The presented dynamically designing method of the periodic coherent intensity patterns might find applications in science and technology. For instance, in optical lithography, the need to use micro/nanofabricated physical transmission diffraction gratings, in which preparation of them is expensive and time-consuming, can be eliminated.

Compact and adjustable compensator for AOD spatial and temporal dispersion using off-the-shelf components.

Random access multiphoton microscopy using two orthogonal acousto-optic deflectors (AODs) allows sampling only particular regions of interest within a plane, greatly speeding up the sampling rate. AODs introduce spatial and temporal dispersions, which distort the point spread function and decrease the peak intensity of the pulse. Both of these effects can be compensated for with a single dispersive element placed a distance before the AODs. An additional acousto-optic modulator, a custom cut prism, and a standard prism used with additional cylindrical optics have been demonstrated. All of these introduce additional cost or complexity and require an extended path length to achieve the needed negative group delay dispersion (GDD). By introducing a telescope between a transmission grating and the AODs, we correct for spatial and temporal dispersions in a compact design using only off-the-shelf components, and we show that the GDD can be tuned by translation of the telescope without adjustment of any other elements.

Measurement of L-shell emission from mid-Z targets under non-LTE conditions using Transmission Grating Spectrometer and DANTE power diagnostics.

In this work, we present the measurement of L-band emission from buried Sc/V targets in experiments performed at the OMEGA laser facility. The goal of these experiments was to study non-local thermodynamic equilibrium plasmas and benchmark atomic physics codes. The L-band emission was measured simultaneously by the time resolved DANTE power diagnostic and the recently fielded time integrated Soreq-Transmission Grating Spectrometer (TGS) diagnostic. The TGS measurement was used to support the spectral reconstruction process needed for the unfolding of the DANTE data. The Soreq-TGS diagnostic allows for broadband spectral measurement in the 120 eV-2000 eV spectral band, covering L- and M-shell emission of mid- and high-Z elements, with spectral resolution λ/Δλ = 8-30 and accuracy better than 25%. The Soreq-TGS diagnostic is compatible with ten-inch-manipulator platforms and can be used for a wide variety of high energy density physics, laboratory astrophysics, and inertial confinement fusion experiments.

Metal-assisted chemical etching of high throughput, high aspect ratio critical-angle transmission gratings with vertical and smooth sidewalls

This paper reports the development of a critical-angle transmission (CAT) grating fabrication process based on metal-assisted chemical etching (MACE), from which grating prototypes with a period of 1 μm were fabricated. The prototype was composed of four 5 mm × 5 mm membrane cells, each of which comprising freestanding grating lines and a large-period cross-support structure. The support structure had a 60 μm period and a 4.5 μm line width. The grating line width was about 200 nm, the duty cycle was about 0.2, and the aspect ratio was up to 50. The effective open grating area reached 92.5%, and the grating sidewall had a roughness less than 0.8 nm and a perpendicularity reaching 89.2°. For the MACE process, the influence of etching solution ratio on the grating sidewall roughness and perpendicularity was explored on a 〈100〉 silicon wafer.

Bend-Insensitive Discrimination of Strain and Temperature Based on Fiber Transmission Grating Inscribed on High Birefringence Photonic Crystal Fiber.

In this paper, we propose a bend-insensitive optical fiber sensor capable of separately measuring strain and temperature by incorporating a fiber transmission grating (FTG) inscribed on high birefringence photonic crystal fiber (HBPCF) with a CO2 laser. The FTG was fabricated by exposing unjacketed HBPCF to CO2 laser pulses using the line-by-line technique. The FTG inscribed on HBPCF, referred to as the HBPC-FTG, has two resonance dips with different wavelengths depending on input polarization. These two resonance dips were utilized as sensor indicator dips denoted by a shorter wavelength dip (SD) and a longer wavelength dip (LD). The strain and temperature responses of the SD and LD were investigated in a strain range of 0 to 3105 μ and a temperature range of 30 to 85 °C, respectively. The measured strain sensitivities of the SD and LD at room temperature (25 °C) were approximately -0.46 and -0.58 pm/μ, respectively. Similarly, the measured temperature sensitivities of the SD and LD without applied strain (0 μ) were ˜5.99 and ˜9.89 pm/°C, respectively. Owing to their linear and independent responses to strain and temperature, strain and temperature changes applied to the HBPC-FTG can be simultaneously estimated from the measured wavelength shifts of the two indicator dips (i.e., SD and LD) using their predetermined strain and temperature sensitivities. Moreover, bend-induced spectral variations of the SD and LD were also examined in a curvature range of 0-4.705 m-1, and it was observed that both dips showed little wavelength shift due to applied bending. Thus, it is concluded from the experimental results that the fabricated HBPC-FTG can be employed as a cost-effective sensor head for bend-insensitive discrimination of strain and temperature.

Design, fabrication, test, and analysis of an out-of-plane plasmonic optical metasurface

Plasmonic metasurfaces with in-plane phase elements have a limit in transmission because they only affect the electric field of incident EM radiation. Recently, a set of out-of-plane plasmonic phase elements was designed using a genetic algorithm to work in the infrared as a Huygens metasurface with significantly improved transmission efficiency. A beam-steering metasurface (i.e., blazed transmissive diffraction grating) was fabricated from this design using membrane projection lithography (MPL) and characterized for its bidirectional transmittance distribution function as a function of scatter angle for normally incident light, and linear incident and transmitted polarizations. Measurements were compared with the designed behavior as predicted by finite element method (FEM) simulations that generated near fields for each phase element and propagated them to the far field as a metasurface using a Stratton–Chu formulation, but measurements showed strong zero-order diffraction not present in the simulation along with the designed +1-diffraction order. We analyze this disagreement between measured and ideal results. Further FEM modeling included the introduction of defects into the phase elements consistent with defects expected from the fabrication process and identified lateral displacement of the plasmonic decoration in the MPL structure as a potential cause for the reduced performance of the fabricated device.

Metasurface T-type high-efficiency transmission grating for 7-channel beam separation

In order to obtain a multi-channel solution of the grating for achieving compact high-efficiency 7-channel beam separation with wideband properties, a metasurface T-type transmission grating is described for field propagation under normal incidence. The inherent coupling mechanism that occurs in the T-type transmission grating is well analyzed and explained by using the modal method. The metasurface T-type grating shows that the efficiency of the seven diffraction orders of TE and TM polarizations is each close to 14 %. Moreover, compared with the reported seven-port grating, efficiencies have been improved for TE and TM polarizations. The new 7-channel T-type grating has a 1 × 7 splitting field propagation with better manufacturing tolerances and excellent incident performance, which will be well applied to develop new types of multi-port diffractive optical beam splitters.

Focus on photonics, spectroscopy, and spectrometry

Focus on photonics, spectroscopy, and spectrometry

High resolution X-ray spectroscopy of Supergiant HMXB 4U1700−37 during the compact object eclipse.

Abstract We present an analysis of the first observation of the iconic High Mass X-ray Binary 4U 1700−37 with the Chandra High Energy Transmission Gratings during an X-ray eclipse. The goal of the observation was to study the structure/physical conditions in the clumpy stellar wind through high resolution spectroscopy. We find that: a) emission line brightness from K shell transitions, corresponding to near neutral species, directly correlates with continuum illumination. However, these lines do not greatly diminish during eclipse. This is readily explained if fluorescence Kα emission comes from the bulk of the wind. b) The highly ionised Fe xxv and Fe xxvi Lyα diminish during eclipse. Thus, they must be produced in the vicinity of the compact object where log ξ > 3. c) to describe the emission line spectrum, the sum of two self consistent photo ionisation models with low ionisation (log ξ ∼ −1) and high ionisation (log ξ ∼ 2.4) is required. From their emission measures, the clump-to-interclump density ratio can be estimated to be nc/ni ∼ 300. To fit the complex He-like Si xiii profile, the plasma requires a broadening with vbulk ∼ 840 km s−1. Reproducing the observed r ≈ f line fluxes requires the addition of a third collisionally ionised plasma. d) Emission lines widths appear unresolved at the hetg gratings resolution with exception of Silicon. There is no clear radial segregation between (quasi)neutral and ionised species, consistent with cold wind clumps interspersed in a hot rarefied interclump medium.

Novel defocus hologram aberration compensation method in digital holography integrated pathology microscope for label free 3-D imaging

In this paper we report successful integration of digital holography in off- axis transmission configuration into a commercially available pathology microscope (PathologyDHM), where Mach-Zehnder interferometric configuration was achieved in pathology microscope using 1 × 2 single mode fiber coupler and custom built optical modules. A smartphone/webcam positioned at the image plane of the finite conjugate microscope captures the interference pattern generated by the system. Using PathologyDHM, we have demonstrated a novel and simple method for compensation of aberration due to microscope objective (MO). The proposed method is called defocus hologram method and it is particularly useful in cases, where samples do not have specimen free or background flat region. Proper validation of the method was done by imaging a transmissive grating (commercial compact disc, CD-R), which doesn't have a flat background region and comparing phase profile of CD-R computed by our proposed method with self-reference conjugated hologram method. For reiterating its biological applications, phase profile of a biological sample, red blood cell smear (RBC smear), was computed with our defocus hologram method and compared with already established reference conjugated hologram method. Phase profiles of CD-R and RBC smear computed with defocus hologram method agree with self-reference and reference conjugated hologram methods respectively, within the phase error limits of the system. Integration of digital holography in to commercial pathology microscope enables 3D imaging, which coupled with artificial intelligence may prove useful in disease diagnostics and monitoring response of cells to treatment.

Programmable High-Resolution Spectral Processor in C-band Enabled by Low-Cost Compact Light Paths

The flexible photonics spectral processor (PSP) is an indispensable element for elastic optical transmission networks that adopt wavelength division multiplexing (WDM) technology. The resolution and system cost are two vital metrics when developing a PSP. In this paper, a high-resolution 1 × 6 programmable PSP is investigated and experimentally demonstrated by using low-cost compact spatial light paths, which is enabled by a 2 K (1080p) liquid crystal on silicon (LCoS) and two cascaded transmission gratings with a 1000 line/mm resolution. For each wavelength channel, the filtering bandwidth and power attenuation can be manipulated independently. The total insertion loss (IL) for six ports is in the range of 5.9~9.4 dB over the full C-band. The achieved 3-dB bandwidths are able to adjust from 6.2 GHz to 5 THz. Furthermore, multiple system experiments utilizing the proposed PSP, such as flexible spectral shaping and optical frequency comb generation, are carried out to validate the feasibility for the WDM systems.

Electrodeposition of Gadolinium Metal from Organic Solvents

Neutron phase contrast imaging (NPCI) is a non-destructive analysis tool currently in use with thermal neutrons. It relies on neutron transmission gratings to detect the phase signal. These gratings are typically fabricated from gadolinium (Gd), as this element has the highest neutron absorption cross section at 250,000 barns. There is a wealth of literature documenting the fabrication process of these gratings, including depositing Gd via sputter coating, evaporation and particle settling techniques at dimensions appropriate to absorb thermal neutrons. However tighter packing density, less contamination and thicker Gd films are necessary for neutrons at higher energy levels ( >0.025 eV). With these requirements in mind, we investigated the electrodeposition of Gd on Si substrate gratings for use with higher energy neutrons.Electrodeposition of Gd alloys is well documented in literature. With a very cathodic reduction potential of -2.28 V (acidic solution), depositing pure Gd metal is a tricky endeavor. In addition to excessive hydrogen evolution during plating, Gd undergoes rapid oxidation when exposed to air. This phenomenon is exacerbated with thin films due to their high surface area and can lead to pyrophoric events and brittle films that sluff off the substrate over time. We investigated aqueous solutions and with the use of many oxygen scavengers, we successfully plated gadolinium oxide (Gd2O3) thin films. However, this technique was not viable due to poor adhesion and rapid oxidation. Hoping for less oxygen contamination, we moved to two polar, aprotic organic solvents with promising potential windows: dimethylformamide (DMF) and dimethylsulfoxide (DMSO). The solubility of gadolinium(III) salts was investigated in the two solvents. At elevated temperatures, gadolinium(III) fluoride and gadolinium(III) chloride were soluble compounds, as well as gadolinium toluenesulfonic acid (GdTsOH). To increase conductivity, potassium chloride (KCl) and tetrabutylammonium tetrafluoroborate (TBATFB) were used as conducting salts. Pulsed plating techniques led to repeatable thin film deposition and EDS confirmed the presence of gadolinium uniformly spread over the surface. However, these films also suffered from poor adhesion, likely due to water contamination in the bath.The limitations outlined above led to electroplating Gd in dimethyl sulfone (DMSO2). DMSO2 is used in industry as a high-temperature solvent; its large dielectric constant reflects its high polarity, indicating strong intermolecular interactions in liquid phase. A melting temperature of 109 °C eliminates the concern of water contamination in the bath. Solubility tests are being repeated in this new polar solvent and linear sweeps and EIS continue to indicate favorable plating conditions. Parameters, such as Gd metal loading and substrate pretreatments are being optimized for thick films with good adhesion. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. SAND2020-5179 A

Long-term X-ray variability of the symbiotic system RT Cru based on Chandra spectroscopy

ABSTRACT RT Cru belongs to the rare class of hard X-ray emitting symbiotics, whose origin is not yet fully understood. In this work, we have conducted a detailed spectroscopic analysis of X-ray emission from RT Cru based on observations taken by the Chandra Observatory using the Low Energy Transmission Grating (LETG) on the High-Resolution Camera Spectrometer (HRC-S) in 2015 and the High Energy Transmission Grating (HETG) on the Advanced CCD Imaging Spectrometer S-array (ACIS-S) in 2005. Our thermal plasma modelling of the time-averaged HRC-S/LETG spectrum suggests a mean temperature of kT ∼ 1.3 keV, whereas kT ∼ 9.6 keV according to the time-averaged ACIS-S/HETG. The soft thermal plasma emission component (∼1.3 keV) found in the HRC-S is heavily obscured by dense materials (>5 × 1023 cm−2). The aperiodic variability seen in its light curves could be due to changes in either absorbing material covering the hard X-ray source or intrinsic emission mechanism in the inner layers of the accretion disc. To understand the variability, we extracted the spectra in the ‘low/hard’ and ‘high/soft’ spectral states, which indicated higher plasma temperatures in the low/hard states of both the ACIS-S and HRC-S. The source also has a fluorescent iron emission line at 6.4 keV, likely emitted from reflection off an accretion disc or dense absorber, which was twice as bright in the HRC-S epoch compared to the ACIS-S. The soft thermal component identified in the HRC-S might be an indication of a jet that deserves further evaluations using high-resolution imaging observations.

White-lighting and WDM-VLC system using transmission gratings and an engineered diffuser.

A white-lighting and wavelength-division-multiplexing (WDM)-visible light communication (VLC) system with over 20 m of free-space distance and 3 m of lighting distance is demonstrated via a red/green/blue (R/G/B) triple-source polarization-multiplexing scheme, transmission gratings, and an engineered diffuser with a double-convex lens. Integrating four-level pulse amplitude modulation (PAM4) with a triple-source polarization-multiplexing scheme, the aggregate transmission rate is noticeably enhanced to 300 Gb/s [50Gb/sPAM4/source×3sources×2polarizations (p- and s-polarizations)]. White-light is produced by multiplexing the R/G/B lights with two transmission gratings and separated by demultiplexing them using the other two transmission gratings. By adopting an engineered diffuser with a double-convex lens, the white-light is diffused over 3 m of free-space distance to provide general white-light illumination (>100lux). This demonstrated white-lighting and WDM-VLC system meets a high aggregate transmission rate with a qualified indoor lighting target. It opens up a new category for lighting and communication.

Fabrication of nanodiamond-dispersed composite holographic gratings and their light and slow-neutron diffraction properties

We demonstrate the use of nanodiamond in constructing holographic nanoparticle-polymer composite transmission gratings with large saturated refractive index modulation amplitudes at both optical and slow-neutron wavelengths, resulting in efficient control of light and slow-neutron beams. Nanodiamond possesses a high refractive index at optical wavelengths and large coherent and small incoherent scattering cross sections with low absorption at slow-neutron wavelengths. We describe the synthesis of nanodiamond, the preparation of photopolymerizable nanodiamond-polymer composite films, the construction of transmission gratings in nanodiamond-polymer composite films and light optical diffraction experiments. Results of slow-neutron diffraction from such gratings are also presented.

Parallel beam generation method for a high-precision roll angle measurement with a long working distance.

A novel measurement system for a high-precision roll angle measurement of long working distance on the basis of two parallel beams in association with two detectors is presented. The measurement system consists of a light source part and a detecting part. The light source part uses transmission grating and a plane mirror to produce a pair of high-precision parallel beams. The nonparallelism of the dual beam caused by the installation error can be compressed to ensure the measurement system achieves high-precision measurement and long working distance. The effectiveness of the measurement system and proposed methods are demonstrated by a series of experiments. The resolution of 0.5'' and measurement accuracy of 1.1'' can be obtained by the set-up measurement system.

Magnetically Tunable Liquid Crystal-Based Optical Diffraction Gratings

We present a theoretical analysis of optical diffractive properties of magnetically tunable optical transmission gratings composed of periodically assembled layers of a polymer and a ferromagnetic liquid crystal (LC). The orientational structure of the LC layers as a function of an applied magnetic field is calculated by minimization of the Landau-de Gennes free energy for ferromagnetic LCs, which is performed numerically and also analytically by using the one-constant approximation and the approximations of the high and the low magnetic fields. Optical diffractive properties of the associated diffraction structure are calculated numerically in the framework of rigorous coupled-wave analysis (RCWA). The presented methodology provides a basis for designing new types of diffractive optical element based on ferromagnetic LCs and simulating their operation governed by the in-plane magnetic field.

X-ray spectra and light curves of cooling novae and a nova like

ABSTRACT We present X-ray observations of novae V2491 Cyg and KT Eri about 9 yr post-outburst of the dwarf nova and post-nova candidate EY Cyg, and of a VY Scl variable. The first three objects were observed with XMM–Newton, KT Eri also with the Chandra ACIS-S camera, V794 Aql with the Chandra ACIS-S camera and High Energy Transmission Gratings. The two recent novae, similar in outburst amplitude and light curve, appear very different at quiescence. Assuming half of the gravitational energy is irradiated in X-rays, V2491 Cyg is accreting at $\dot{m}=1.4\times 10^{-9}{\!-\!}10^{-8}\,{\rm M}_\odot \,{\rm yr}^{-1}$, while for KT Eri, $\dot{m}\lt 2\times 10^{-10}{\rm M}_\odot \,{\rm yr}$. V2491 Cyg shows signatures of a magnetized WD, specifically of an intermediate polar. A periodicity of 39 min, detected in outburst, was still measured and is likely due to WD rotation. EY Cyg is accreting at $\dot{m}\sim 1.8\times 10^{-11}{\rm M}_\odot \,{\rm yr}^{-1}$, one magnitude lower than KT Eri, consistently with its U Gem outburst behaviour and its quiescent UV flux. The X-rays are modulated with the orbital period, despite the system’s low inclination, probably due to the X-ray flux of the secondary. A period of 81 min is also detected, suggesting that it may also be an intermediate polar. V794 Aql had low X-ray luminosity during an optically high state, about the same level as in a recent optically low state. Thus, we find no clear correlation between optical and X-ray luminosity: the accretion rate seems unstable and variable. The very hard X-ray spectrum indicates a massive WD.

Development of x-ray phase tomographic microscope based on Talbot interferometer at BL37XU, SPring-8

An x-ray phase tomographic microscope has been developed by optimizing the optical system for 9-keV synchrotron x rays at BL37XU, SPring-8, Japan. The system consists of a full-field x-ray imaging microscope and a Talbot interferometer. In contrast with our previous system, a Fresnel zone plate for the microscope objective and transmission gratings of the interferometer was designed to improve the refraction sensitivity, with a larger field of view and a higher spatial resolution, utilizing a 28-m space available at BL37XU. An x-ray phase tomographic microscope with a field of view of 375 µm and a spatial resolution of 560 nm was thus constructed, even with a considerably low x-ray dosage. By applying this tomographic microscope to auditory bone specimens of young mice, it was shown that soft tissues in addition to bone tissue could be observed simultaneously without serious radiation damage.

Accurate, Efficient and Rigorous Numerical Analysis of 3D H-PDLC Gratings.

This work presents recent results derived from the rigorous modelling of holographic polymer-dispersed liquid crystal (H-PDLC) gratings. More precisely, the diffractive properties of transmission gratings are the focus of this research. This work extends previous analysis performed by the authors but includes new features and approaches. More precisely, full 3D numerical modelling was carried out in all analyses. Each H-PDLC sample was generated randomly by a set of ellipsoid geometry-based LC droplets. The liquid crystal (LC) director inside each droplet was computed by the minimisation of the Frank elastic free energy as a function of the applied electric field. The analysis carried out considered the effects of Frank elastic constants , and ; the anchoring strength ; and even the saddle-splay constant . The external electric field induced an orientation of the LC director, modifying the optical anisotropy of the optical media. This effect was analysed using the 3D split-field finite-difference time-domain (SF-FDTD) method. In order to reduce the computational costs due to a full 3D tensorial analysis, a highly optimised method for high-performance computing solutions (HPC) was developed. The influences of the anchoring and voltage on the diffraction efficiencies were investigated, showing the potential of this approach.