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Curved Diffractive X-ray Optics for X-ray Astronomy

We report on a concept for curved diffractive X-ray optics (CDXO). CDXO would enable potential new optical designs for X-ray instruments, such as a two element spectrometer, in which the secondary element of an X-ray mirror pair is patterned with an X-ray grating. A two-element spectrometer design eliminates the grating assembly, resulting in decreased instrument mass and reduced power requirements. In addition, a two-element spectrometer may realize cost/schedule savings by eliminating a separate grating alignment effort, and yield increased effective area over three element designs. We present a raytrace concept study of a two-element spectrometer compact enough to fit within a sounding rocket payload. We also review the progress made in electron-beam lithography (EBL) techniques that would enable curved diffractive X-ray optics to be patterned, and outline a procedure by which the accuracy of the EBL patterning process can be measured interferometrically.

Casey T. DeRoo↗
DOE OSTI2019

Bottom emitting vertical-cavity surface-emitting lasers

A bottom-emitting vertical-cavity surface-emitting laser (VCSEL) structure includes a first substrate permitting the passage of light therethrough, an n-doped distributed Bragg reflector (nDBR), a p-doped distributed Bragg reflector (pDBR), one or more active layers, at least one of a high contrast grating mirror and a dielectric-enhanced metal mirror, and a plurality of layers, where the VCSEL structure is configured to be flip chipped to a second substrate. The pDBR and the nDBR define a laser cavity extending vertically therebetween and containing the one or more active layers. The at least one of a high contrast grating mirror and a dielectric-enhanced metal mirror may be disposed over the pDBR. The plurality of layers may be disposed over the at least one of the high contrast grating mirror and the dielectric-enhanced metal mirror to optically and hermetically seal the laser cavity.

42 ENGINEERING↗
DOE OSTI2021

Fiber laser microphones with graphene diaphragms

An acoustic sensor comprises a sensing head comprising an optical fiber having a tip. A graphene diaphragm is disposed on the tip and is configured to vibrate in response to an acoustic signal. A fiber laser is optically coupled to the sensing head. The fiber laser comprises a first set of fiber Bragg gratings and a second set of fiber Bragg gratings. A gap is present between the first set and the second set of fiber Bragg gratings. The fiber laser is configured to generate a sensing optical signal having a first intensity in response to an excitation optical signal, the sensing optical signal impinging on the graphene diaphragm such that a feedback optical signal is reflected from the graphene diaphragm towards the fiber laser and has and has a second intensity modulated by the vibration of the graphene diaphragm that corresponds to the acoustic signal.

Liao, Shaolin↗
DOE OSTI2021

Numerical Analysis of Radiation Effects on Fiber Optic Sensors

Optical fiber sensors (OFS) are a potential candidate for monitoring physical parameters in nuclear environments. However, under an irradiation field the optical response of the OFS is modified via three primary mechanisms: (i) radiation-induced attenuation (RIA), (ii) radiation-induced emission (RIE), and (iii) radiation-induced compaction (RIC). For resonance-based sensors, RIC plays a significant role in modifying their performance characteristics. In this paper, we numerically investigate independently the effects of RIC and RIA on three types of OFS widely considered for radiation environments: fiber Bragg grating (FBG), long-period grating (LPG), and Fabry-Perot (F-P) sensors. In our RIC modeling, experimentally calculated refractive index (RI) changes due to low-dose radiation are extrapolated using a power law to calculate density changes at high doses. The changes in RI and length are subsequently calculated using the Lorentz–Lorenz relation and an established empirical equation, respectively. The effects of both the change in the RI and length contraction on OFS are modeled for both low and high doses using FIMMWAVE, a commercially available vectorial mode solver. An in-depth understanding of how radiation affects OFS may reveal various potential OFS applications in several types of radiation environments, such as nuclear reactors or in space.

42 ENGINEERING↗
DOE OSTI2019

Structured illumination of a sub-wavelength hollow-waveguide array

A hollow-waveguide array with sub-wavelength dimensions was suggested earlier as a space-variant polarization converter. For optimum light transmission through the array, periodic structured illumination is generated by using a dielectric grating with the same period. In this paper various numerical simulations are performed. The transmission depends on numerous parameters. Particularly, it is shown how the grating can be optimized and how longitudinal and lateral displacements influence the results. For the considered configuration it is found that the transmission can be increased by factors up to 1.46 (TE) and 1.35 (TM) compared to a uniform illumination of the hollow waveguide array.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

A hybrid DCF/FBG scheme for dispersion compensation over a 300 km SMF

In this work, the efficient restoration of a dissipated signal over a 300 km long-haul optical fiber is investigated. A hybrid system is proposed including a dispersion compensation fiber (DCF) and a fiber Bragg grating (FBG). Two 150 km standard single mode fibers with a chromatic dispersion of 17 ps/nm km are used in the simulation. Sufficient optical amplification power is supplied using an erbium-doped fiber amplifier to overcome the signal attenuation down the link, yet the signal is totally distorted. The only major reason left interpreting the total data loss would be the chromatic dispersion (CD). A DCF and a-tanh-apodized-linearly-chirped fiber Bragg grating (ACFBG) are implemented individually in a symmetric or a distributed setting in an attempt to compensate for the CD that led mainly to the signal degradation. The proposed hybrid scheme is then tested in a pre, post, symmetric and distributed installations. Several lengths of DCFs and ACFBGs at various parameters are examined. A comparison between the mentioned schemes is performed, seeking the most remarkable, resilient, and cost-effective technique.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

A GaAs-based plasmonic source employing a nanoscale vertical cavity

In this paper, a new structure of a vertical cavity plasmonic source is presented. The structure, which is adopted from a metal–semiconductor–metal plasmonic photodetector, contains a gold substrate, n-type GaAs layer, active GaAs layer and p-type GaAs layer, respectively from bottom to up. A subwavelength aperture and metal gratings on both sides of the aperture are placed on the top of the device and act both as a gold clad and as the contact for applying DC bias. The metal gratings are improved by adding SiO{sub 2} between metal grooves and semiconductor. Applying voltage bias to p-and n-regions leads to photons generation in the active region. The generated photons in the active region excite a resonant surface plasmonic mode in the nanoscale cavity just below the aperture. One can use light outflowing from the nanoscale aperture, with wavelength of 882 nm, as a source to excite an arbitrary plasmonic guiding structure. The output beam has a suitable concentration so that in a 1000 nm distance from the aperture, still 37% of the power is concentrated in a width of 50 nm which is almost a unique specification among plasmonic sources, so far. The function of the device is validated using finite-difference time-domain numerical algorithm.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Role of higher order plasmonic modes in one-dimensional nanogratings

By theoretically investigating the optical behavior of one-dimensional gold nanogratings using Fourier Modal Method, we have shown that both integer and non-integer multiples of surface plasmon polariton wavelengths should be taken into consideration in special optical contrast ratio for highly sensitive sensing. The emergence of higher modes is the key factor for the formation of observed plasmonic band gap. Through considering the significant role of grating period and thickness respectively in horizontal and vertical surface resonances, it was demonstrated that for gold thicknesses below 100 nm, the dominant phenomenon is horizontal surface resonances while for increased thicknesses both horizontal and vertical surface resonances mediate. The transmission minima are insensitive to the grating thickness, which confirms that their origins are not vertical surface resonances. This study can open an avenue towards designing highly sensitive sensors with focus not only on the plasmonic resonance wavelength but also on its integer and non-integer multiples whose origins should be investigated in both horizontal and vertical surface resonances.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Talbot-Lau x-ray deflectometer electron density diagnostic for laser and pulsed power high energy density plasma experiments (invited)

Talbot-Lau X-ray deflectometry (TXD) has been developed as an electron density diagnostic for High Energy Density (HED) plasmas. The technique can deliver x-ray refraction, attenuation, elemental composition, and scatter information from a single Moiré image. An 8 keV Talbot-Lau interferometer was deployed using laser and x-pinch backlighters. Grating survival and electron density mapping were demonstrated for 25–29 J, 8–30 ps laser pulses using copper foil targets. Moiré pattern formation and grating survival were also observed using a copper x-pinch driven at 400 kA, ∼1 kA/ns. These results demonstrate the potential of TXD as an electron density diagnostic for HED plasmas.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Rewritable three-dimensional holographic data storage via optical forces

The development of nanostructures that can be reversibly arranged and assembled into 3D patterns may enable optical tunability. However, current dynamic recording materials such as photorefractive polymers cannot be used to store information permanently while also retaining configurability. Here, we describe the synthesis and optimization of a silver nanoparticle doped poly(2-hydroxyethyl methacrylate-co-methacrylic acid) recording medium for reversibly recording 3D holograms. We theoretically and experimentally demonstrate organizing nanoparticles into 3D assemblies in the recording medium using optical forces produced by the gradients of standing waves. The nanoparticles in the recording medium are organized by multiple nanosecond laser pulses to produce reconfigurable slanted multilayer structures. We demonstrate the capability of producing rewritable optical elements such as multilayer Bragg diffraction gratings, 1D photonic crystals, and 3D multiplexed optical gratings. We also show that 3D virtual holograms can be reversibly recorded. This recording strategy may have applications in reconfigurable optical elements, data storage devices, and dynamic holographic displays.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

A pulse-front-tilt–compensated streaked optical spectrometer with high throughput and picosecond time resolution

A high-throughput, broadband optical spectrometer coupled to the Rochester optical streak system equipped with a Photonis P820 streak tube was designed to record time-resolved spectra with 1-ps time resolution. Spectral resolution of 0.8 nm is achieved over a wavelength coverage range of 480 to 580 nm, using a 300-groove/mm diffraction grating in conjunction with a pair of 225-mm-focal-length doublets operating at an f/2.9 aperture. Overall pulse-front tilt across the beam diameter generated by the diffraction grating is reduced by preferentially delaying discrete segments of the collimated input beam using a 34-element reflective echelon optic. The introduced delay temporally aligns the beam segments and the net pulse-front tilt is limited to the accumulation across an individual sub-element. The resulting spectrometer design balances resolving power and pulse-front tilt while maintaining high throughput.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Measurement of the deuterium Balmer series line emission on EAST

Volume recombination plays an important role towards plasma detachment for magnetically confined fusion devices. High quantum number states of the Balmer series of deuterium are used to study recombination. On EAST (Experimental Advanced Superconducting Tokamak), two visible spectroscopic measurements are applied for the upper/lower divertor with 13 channels, respectively. Both systems are coupled with Princeton Instruments ProEM EMCCD 1024B camera: one is equipped on an Acton SP2750 spectrometer, which has a high spectral resolution ∼0.0049 nm with 2400 gr/mm grating to measure the D{sub α}(H{sub α}) spectral line and with 1200 gr/mm grating to measure deuterium molecular Fulcher band emissions and another is equipped on IsoPlane SCT320 using 600 gr/mm to measure high-n Balmer series emission lines, allowing us to study volume recombination on EAST and to obtain the related line averaged plasma parameters (T{sub e}, n{sub e}) during EAST detached phases. This paper will present the details of the measurements and the characteristics of deuterium Balmer series line emissions during density ramp-up L-mode USN plasma on EAST.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Soft X-ray flat-field VLS spectrographs

We have analysed the capabilities of flat-field spectrometers with concave VLS reflection gratings from the standpoint of spectral imaging in the soft X-ray range. Two types of such instruments are shown to exist: spectrographs with as flat as possible a portion of the focal surface (of Harada spectrograph type) and those with a nearly constant distance from the grating centre to the focal surface, which permits reaching a high spatial resolution with the use of a crossed focusing mirror (without a loss in spectral resolution). Three 0.25, 0.5, and 1.5-m long spectrographs of Harada type were calculated for operation in the ranges 90 – 250, 50 – 200, and 20−110 A-ring , respectively. We show that each of the calculated instruments may be converted to an instrument of the second type for operation in the second and fourth diffraction orders without significant changes in scheme geometry. In this case, the theoretical spatial resolution is equal to ∼10 μm throughout the optimisation range. (x-ray optics)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

Imaging diffraction VLS spectrometer for a wavelength range λ > 120 Å

A broadband stigmatic (imaging) soft X-ray ( λ > 120 Å) spectrometer is experimentally realised. The optical configuration of the spectrometer comprises a plane grazing-incidence reflection grating with a spacing varying across its aperture according to a preassigned law [a so-called varied line-space (VLS) grating] and a broadband spherical normal-incidence mirror with an aperiodic Mo/Si multilayer structure. The average plate scale amounts to ∼5.5 Å mm{sup −1}. The radiation is recorded with a matrix CCD detector (2048 × 1024 pixels of size 13 μm). The line spectra of the multiply charged ions LiIII and FV–FVII excited in laser-produced plasma are recorded with a spatial resolution of ∼26 μm and a spectral resolving power R ≈ 500 is experimentally demonstrated. (paper)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2019

Use of heavily doped germanosilicate fibres with a small core diameter in stretchers of ultrashort laser pulses at a wavelength of 1.03 μm

The use of a heavily doped germanosilicate fibre with a W-profile refractive index and small core diameter in stretchers of ultrashort laser pulses with their subsequent amplification and compression in all-fibre laser systems is considered. The application of fibres of this type makes it possible to stretch, amplify, and then compress a laser pulse with minimum distortions of its initial shape and width. Due to the dispersion properties of these fibres, which allow the pulse duration to be increased significantly at a small fibre length and the third-order positive dispersion of the diffraction-grating-based output compressor to be compensated for, amplified pulses with an energy of 2 μJ and width of 250 fs, free of a picosecond pedestal, are obtained. Several types of fibres intended for the use in stretchers of ultrashort laser pulses are comparatively analysed from the point of view of their dispersion compatibility with a diffraction-grating-based output compressor. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Scanning spectrometer/monochromator for a wavelength range of 50 – 330 Å

A flat-field scanning spectrometer/monochromator of the Hettrick – Underwood type is implemented for a wavelength range λ ≈ 50 – 330 Å. The optical arrangement of the spectrograph comprises a focusing spherical (R = 6000 mm) mirror, mounted at a grazing angle of 8.34 °, and a grazing-incidence plane varied line-space (VLS) grating operating for a constant deflection angle of 16.68 °. The entrance and output slits of the instrument are immobile, and the focal distance varies only slightly over its operating spectral range. The short-wavelength boundary of the operating range is determined by the spectral source brightness and the reflection coefficients of the grating and the mirror rather than by defocusing. Laser-produced plasma spectra excited by a focused laser beam (0.5 J, 8 ns, 1.06 μm) are recorded. A spectral resolving power λ/δλ = 1300 is demonstrated at a wavelength of 182 Å. The configuration of the instrument of this type is suited to soft X-ray reflectometry and metrology with the use of laser-plasma and synchrotron radiation sources, and is perfectly compatible with modern CCD detectors. (x-ray spectrometer)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2019

Flat-field VLS spectrometer for a wavelength range of 50 – 275 Å

A flat-field VLS spectrograph for a wavelength range ∼50 – 275 Å with an average linear dispersion of 0.18 mm Å{sup −1}, which makes use of a grazing-incidence varied line-space (VLS) grating, was calculated and implemented (a spectrograph of Harada class). To fabricate the VLS grating by interference lithography technique, an algorithm was developed for calculating the writing configuration with an auxiliary aberrating mirror (the solution of the inverse problem of interference lithography). The spectrograph was put to a test and line spectra were recorded from the laser-produced plasma of lithium fluoride and teflon targets, which were excited by a focused laser beam (0.5 J, 8 ns, 1.06 μm). A resolving power λ/d l = 800 was demonstrated in a wavelength region of 135 Å. (x-ray spectrometry)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Diffractive optical elements for multiplexing structured laser beams

We consider methods for obtaining a multitude of structured laser beams (multiplexing) from an illuminating beam (both structured and unstructured) with the help of diffractive optical elements (DOEs). An approach of ‘intelligent multiplexing’ is proposed to describe and develop the methods. A DOE is calculated that forms a set of five diffraction orders located in a line. An example of focusing a set of doughnut-shaped azimuthally polarised laser beams using a diffraction beam splitter is presented. Efficient multiplexing of first-order vortex beams in a two-dimensional region is implemented by a two-dimensional diffraction grating. An approach is proposed and realised in which the transmission functions of a two-dimensional diffraction beam splitter and the elements forming structured laser beams with specified parameters are combined into the transmission function of one element. Such DOEs can be used in optical communication systems for encoding and decoding data. The possibility of using binary curved fork-shaped gratings for the formation of doughnut-shaped three-dimensional vortex beams, which are detected outside the focal plane, is demonstrated. This approach provides additional advantages for safe data transmission; it can be used in laser processing of materials and in laser manipulation applications. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗