High Spectral Dispersion Research Articles

Development of a Collective Thomson Scattering diagnostic system on SNU X-pinch device

The Collective Thomson Scattering (CTS) diagnostic system has been developed for the X-pinch device at Seoul National University. The system is designed to measure various parameters of plasma jets, including plasma temperature and plasma flow velocity. For the flow velocity measurement, the second harmonic Nd:YAG laser and the collection optics are oriented in order to ensure the scattering vector is aligned with the flow direction. The collection optics have been optimized to maximize photon efficiency. Due to the requirement of high spectral dispersion and resolution for the diagnosis of CTS spectra, the spectrometer is designed with a dispersion of 0.004 nm/pixel. The spectral dispersion and resolution of the system has been measured. The CTS diagnostic system will contribute to a deeper understanding of X-pinch plasma dynamics and the development of advanced High Energy Density Plasma (HEDP)-based technologies.

Assembly and alignment of the 4-metre multi-object spectroscopic telescope wide field corrector

The 4-metre multi-object spectroscopic telescope (4MOST) is a fiber-fed multi-object spectrograph for the VISTA telescope at the European Southern Observatory (ESO) Paranal Observatory in Chile. The goal of the 4MOST project is to create a general purpose and highly efficient spectroscopic survey facility for astronomers in the 4MOST consortium and the ESO community. The instrument itself will record 2436 simultaneous spectra over a ∼4.2 square deg field of view and consists of an optical wide-field corrector (WFC), a fiber positioner system based on a tilting spine design, and three spectrographs giving both high and low spectral dispersion. The WFC comprises of six lenses grouped into four elements, two of which are cemented doublets that act as an atmospheric dispersion corrector. The first lens element is 0.9 m in diameter while the diameter of the other elements is 0.65 m. For the instrument to meet its science goals, each lens was aligned to be well within ∼100 μm—a major challenge. This was achieved using contact metrology methods supplemented by pencil beam laser probes. In particular, an off-axis laser beam system has been implemented to test the optics’ alignment before and after shipment. This work details the alignment and assembly methods and presents the latest results on the achieved lens positioning and projected performance of the WFC.

High sensitivity static Fourier transform spectrometer.

Static Fourier transform spectrometers (S-FTSs) are well-consolidated instruments providing high throughput and high spectral resolution in a narrow spectral band. They use two reflective gratings as dispersive elements in a Michelson interferometer. Gratings allow high spectral dispersion and consequently high resolution, but, due to the light diffused from their grooves, they are one of the main noise sources in the reconstructed spectrum. In this work, we compare the signal-to-noise ratio performance of a prism-based S-FTS with that of a grating-based S-FTS. As a primary advantage, prisms give intrinsically lower diffused light than gratings. Furthermore, they do not have multiple diffracted orders, reducing thereafter the optical constraints on the instrumental baffling.

Weighted Transmissibility-Based Operational Modal Analysis for Identification of Structures Using Seismic Responses

Transmissibility-based operational modal analysis is an effective approach to identify the modal parameters using the output-only data from the ambient vibrations. This approach, based on the SVD technique, has a good ability to determine the vibrational modes with high certainty. However, the results of the present research indicate that the transmissibility approach has not an appropriate performance in identifying the vibrational modes using the short random records such as seismic records. These records have a high spectral leakage and dispersion due to the non-periodic harmonic components caused by the vibrational characteristics of the system and the strong ambient excitations (e.g., earthquake). In this paper, an efficient approach called weighted transmissibility-based operational modal analysis is proposed to properly identify the natural frequencies and mode shapes using the short seismic records. The proposed approach combines the single-reference weighted transmissibility functions associated with different transferring outputs obtained from single loading condition in a unique matrix formulation. It extracts the vibrational modes using the efficient $${\text{PIS}}\left( \omega \right)$$ function calculated by the singular values of the weighted transmissibility matrices. In this research, several theoretical examples, including 2-DOF, 3-DOF, 5-DOF and 10-DOF systems, have been provided to indicate the capabilities of the proposed approach in identifying the modal parameters of structural systems.

All-optical virtual private network utilizing bit allocation in OFDM-PON system

We propose a new all-optical virtual private network (AOVPN) using bit allocation technique in an orthogonal frequency-division multiplexing-based passive optical network (OFDM-PON) for the first time. The proposed system makes full use of the fundamental advantages of OFDM such as high spectral efficiency, dispersion tolerance, and flexibility in bandwidth allocation. It enables the simultaneous transmission of upstream (U/S) data and VPN data by multiple users. Since the U/S signal and the VPN signal are separated into bits within a high-order symbol, flexible resource management is possible according to real-time requirements. The feasibility of the proposed system is demonstrated in a 20-km single-fiber loopback link as a proof of concept. The experiment is focused on the optical transmission of VPN and U/S data. The results include performance variations of VPN transmission according to the bit allocation in a full-band uplink without multiple access and verification of dynamic bandwidth allocation (DBA) considering the multiple access by multi-users

Adaptive prism using a double quantum dot structure.

This work examined adaptive optical prisms by using a ladder-plus-Y double quantum dot system. A good dispersion angle and high spectral angular dispersion are obtained under the application of two optical fields (pump and probe) or three optical fields where an additional optical field between quantum-dot-wetting layer states is applied. These good results are obtained at a wide window of electromagnetically induced transparency with zero susceptibility.

Spectroscopic transit search: a self-calibrating method for detecting planets around bright stars

Aims. We aim to search for transiting exoplanets around the star β Pictoris using high-resolution spectroscopy and Doppler imaging that removes the need for standard star observations. These data were obtained on the VLT with UVES during the course of an observing campaign throughout 2017 that monitored the Hill sphere transit of the exoplanet β Pictoris b. Methods. We utilized line profile tomography as a method for the discovery of transiting exoplanets. By measuring the exoplanet distortion of the stellar line profile, we removed the need for reference star measurements. We demonstrated the method with white noise simulations, and then looked at the case of β Pictoris, which is a δ Scuti pulsator. We describe a method to remove the stellar pulsations and perform a search for any transiting exoplanets in the resultant data set. We injected fake planet transits with varying orbital periods and planet radii into the spectra and determined the recovery fraction. Results. In the photon noise limited case we can recover planets down to a Neptune radius with an ~80% success rate, using an 8 m telescope with a R ~ 100 000 spectrograph and 20 min of observations per night. The pulsations of β Pictoris limit our sensitivity to Jupiter-sized planets, but a pulsation removal algorithm improves this limit to Saturn-sized planets. We present two planet candidates, but argue that their signals are most likely caused by other phenomena. Conclusions. We have demonstrated a method for searching for transiting exoplanets that (i) does not require ancillary calibration observations, (ii) can work on any star whose rotational broadening can be resolved with a high spectral dispersion spectrograph, and (iii) provides the lowest limits so far on the radii of transiting Jupiter-sized exoplanets around β Pictoris with orbital periods from 15 days to 200 days with >50% coverage.

Metabolic assessment of a migraine model using relaxation-enhanced 1 H spectroscopy at ultrahigh field.

This study evaluates biochemical imbalances in a rat model that reflects dysfunctional pathways in migraine. The high sensitivity and spectral dispersion available to 1 H MRS at 21.1 T expands metabolic profiling in this migraine model to include lactate (Lac), taurine (Tau), aspartate, and Gly-a mixture of glycine, glutamine, and glutamate. Sprague-Dawley male rats were administered in situ an intraperitoneal injection of nitroglycerin (NTG) to induce the migraine analogue or saline as a control. A selective relaxation-enhanced MR spectroscopy sequence was used to target upfield metabolites from a 4-mm3 voxel for 2.5 h after injection. Significant increases were evident for Lac as early as 10 min after NTG injection, peaking over 50% compared with baseline and control (normalized Lac/N-acetyl aspartate with NTG = 1.54 ± 0.65 versus with saline = 0.99 ± 0.08). Tau decreased progressively in controls over 2 h after injection, but remained elevated with NTG, peaking at 105 min after injection (normalized Tau/N-acetyl aspartate with NTG = 1.10 ± 0.18 versus with saline = 0.85 ± 0.14). Total creatine under NTG showed significant decreases with time and compared with saline; Gly demonstrated temporal increases for NTG. These changes indicate an altered metabolic profile in the migraine analogue consistent with early changes in neural activity and/or vasodilation consistent with progressively enhanced neuroprotection and osmoregulation. Magn Reson Med 79:1266-1275, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Performance evaluation of optical OFDM in direct detected systems based on MZM bias and drive voltages

The impact of DC bias and the RF drive voltage of the dual electrode Mach Zehnder Modulator (DE-MZM) on the transmission performance of optical orthogonal frequency division multiplexing (O-OFDM) direct detected systems is analyzed theoretically and verified by simulation. Selection of optimum bias and drive voltage is necessary to minimize the optical signal to noise ratio (OSNR) requirements and the non-linear distortions in the fiber transmission. In this paper, we compare MZM modulation techniques such as double sideband full carrier and single sideband (SSB) [biased at quadrature and minimum power transmission (MPT) point] with a novel modified SSB OFDM technique. To the best of our knowledge for the first time, a mathematical model for above modified SSB technique is developed to evaluate the OSNR requirement, chromatic dispersion of the fiber, spectral efficiency and the receiver sensitivity against other modulation techniques. Our results show that the modified SSB technique provides high spectral efficiency, receiver sensitivity and low chromatic dispersion against other the modulation techniques, while the one biased at MPT minimizes the OSNR requirements.

Software-Reconfigurable System Supporting Point-to-Point Data Communication Between Vehicle Social Networks and Marketers

Social users can be flexibly covered by a vehicle traveling along a certain trajectory in a city. This scenario provides opportunities for marketers to utilize vehicles as recommenders targeting potential customers. As a result, the vehicle social network (VSN) concept emerges. Since a marketer usually operates from a remote central office (CO), an effective communication system is urgently required to support data transmission between VSNs and COs. Orthogonal frequency division multiplexing (OFDM) is a modulation technique characterized by high spectral efficiency and dispersion resistance, and intensity modulation and direct detection (IM/DD) is an effective solution for optical OFDM (OOFDM) data transmission. Performing discrete Fourier transform (DFT) and discrete Hartley transform (DHT) operations can enable the satisfaction of various transmission requirements between a VSN and a CO. In this paper, we support the above claims through theoretical and simulation-based analyses. Moreover, a software-reconfigurable platform is established to achieve flexibility between DFT and DHT functionalities. Thus, diverse transmission requirements can be satisfied by modifying individual modules deployed in a single smart system instead of using multiple rigid network architectures. Simulated and experimental results both demonstrate the feasibility and effectiveness of our solutions.

Fourier‐based approach to overcome anomalies in high‐resolution spectra of vibrational CARS measurements of gases

In this work, we report on an unconventional experimental procedure useful for thermometric measurements on the basis of high‐resolution vibrational coherent anti‐Stokes Raman scattering (CARS) generated using conventional lasers. The high spectral dispersion of 0.02 cm−1/pixel is achieved by means of some specific spectral arrangements (single‐mode pump laser and diffraction grating providing spectra at the sixth order) and is further strengthened by the use of a relay lens system mounted before the charge‐coupled device camera. Surprisingly, at the high spectral dispersion of our measurements, a significant and persistent thermometric inaccuracy is observed. The effect arises from an inevitable spectral modulation of defined frequency hidden in the main CARS signal of the gas under study, and to secure a good thermometric evaluation, we describe a Fourier approach that is experimentally demonstrated for the typical nitrogen CARS spectrum measured at room temperature. Copyright © 2014 John Wiley & Sons, Ltd.

Quantitative and qualitative 1H, 13C, and 15N NMR spectroscopic investigation of the urea–formaldehyde resin synthesis

Urea-formaldehyde resins are bulk products of the chemical industry. Their synthesis involves a complex reaction network. The present work contributes to its elucidation by presenting results from detailed NMR spectroscopic studies with different methods. Besides (1)H NMR and (13)C NMR, (15)N NMR spectroscopy is also applied. (15)N-enriched urea was used for the investigations. A detailed NMR signal assignment and a model of the reaction network of the hydroxymethylation step of the synthesis are presented. Because of its higher spectral dispersion and the fact that all key reactions directly involve the nitrogen centers, (15)N NMR provides a much larger amount of detail than do (1)H and (13)C NMR spectroscopy. Symmetric and asymmetric dimethylol urea can be clearly distinguished and separated from monomethylol urea, trimethylol urea, and methylene-bridged urea. The existence of hemiformals of methylol urea is confirmed. 1,3,5-Oxadiazinan-4-on (uron) and its derivatives were not found in the reaction mixtures investigated here but were prepared via alternative routes. The molar ratios of formaldehyde to urea were 1, 2, and 4, the pH values 7.5 and 8.5, and the reaction temperature 60 °C.

Numerical Simulations of Line-Profile Variation beyond a Single-Surface Approximation for Oscillations in roAp Stars

Abstract Prior to the last decade, most observations of roAp stars have concerned light variations. Recently some new, striking results of spectroscopic observations with high time resolution, high spectral dispersion, and a high signal-to-noise ratio became available. Since the oscillations found in roAp stars are high overtones, the vertical wavelengths of the oscillations are so short that the amplitude and phase of the variation of each spectroscopic line are highly dependent on the level of the line profile. Hence, analyses of the variation of the spectroscopic lines of roAp stars potentially provide us with new information about the vertical structure of the atmosphere of these stars. In order to extract such information, a numerical simulation of the line-profile variation beyond a single-surface approximation is necessary. We carried out a numerical simulation of line-profile variation by taking account of the finite thickness of the line-forming layer. We demonstrated how effective this treatment is, by comparing the simulation with the observed line profiles.

Interaction between femtosecond radiation and sound in a light dispersive delay lines using effect of strong elastic anisotropy

Femtosecond optical amplifiers typically have high nonlinear spectral dispersion breaking relationships of the spectral phases of femtosecond pulse. It is necessary to use some additional dispersive device for controlling of spectral amplitude and phases of amplified laser pulses. We discuss the investigation of light dispersive delay lines based on the light-sound interaction in crystals. The light dispersive delay lines geometry uses the effect of strong elastic, photoelastic and optic anisotropy in the TeO2 single crystal. Different experimental delay lines were designed and tested. The problem of femtosecond laser beam angular chirp compensation was solved also. The experiments were performed at the OPCPA femtosecond laser system.

Enhanced neurochemical profile of the rat brain using in vivo1H NMR spectroscopy at 16.4 T

Single voxel magnetic resonance spectroscopy with ultrashort echo time was implemented at 16.4 T to enhance the neurochemical profile of the rat brain in vivo. A TE of 1.7 msec was achieved by sequence optimization and by using short-duration asymmetric pulses. Macromolecular signal components were parameterized individually and included in the quantitative analysis, replacing the use of a metabolite-nulled spectrum. Because of the high spectral dispersion, several signals close to the water line could be detected, and adjacent peaks could be resolved. All 20 metabolites detected in this study were quantified with Cramér-Rao lower bounds below 20%, implying reliable quantification accuracy. The signal of acetate was detected for the first time in rat brain in vivo with Cramér-Rao lower bounds of 16% and a concentration of 0.52 μmol/g. The absolute concentrations of most metabolites showed close agreement with values previously measured using in vivo (1)H NMR spectroscopy and in vitro biochemical assay.

Dispersing Light with Surface Plasmon Polaritonic Crystals

Spectral dispersion of light on a finite-size surface plasmon polaritonic (SPP) crystal has been studied. The angular wavelength separation of one or more orders of magnitude higher than in other state-of-the-art wavelength-splitting devices available to date has been demonstrated. The two-stage process is responsible for the dispersion value, which involves conversion of the incident light into SPP Bloch modes of a nanostructure followed by the SPP Bloch waves refraction at the SPP crystal boundary. The high spectral dispersion achievable in plasmonic devices may be useful for integrated high-resolution spectroscopy in nanophotonic, optical communication and lab-on-a-chip applications.

First observation of Mars with XMM-Newton

In the first observation of Mars with XMM-Newton, on 20-21 November 2003, this planet is clearly detected as an X-ray source. High resolution X-ray spectroscopy with the Reflection Grating Spectrometer (RGS) confirms that the X-ray radiation from Mars is composed of two different components: one due to fluorescent scattering of solar X-rays in its upper atmosphere and the other one due to solar wind charge exchange in its exosphere. Close to Mars, the RGS spectrum is dominated by two pronounced CO 2 fluorescence lines at 23.5 A and 23.7 A. Fluorescence from N 2 at 31.5 A is also observed. With increasing distance from Mars, these lines fade, while numerous (∼12) emission lines become prominent at the positions expected for de-excitation of highly ionized C, N, O, and Ne atoms, strongly resembling a cometary X-ray spectrum. The He-like O 6+ multiplet is resolved and is dominated by the spin-forbidden magnetic dipole transition 2 3 S 1 → 1 1 S 0 , confirming charge exchange as the origin of the emission, while the resonance line 2 1 P 1 → 1 1 S 0 increases in intensity closer to Mars, where the density of the exosphere is higher. The high spectral dispersion and throughput of XMM-Newton/RGS make it possible to produce X-ray images of the Martian exosphere in individual emission lines, free from fluorescent radiation. They show extended emission out to ∼8 Mars radii, with morphological differences between individual ions and ionization states. This is the first definite detection of charge exchange induced X-ray emission from the exosphere of another planet, providing a direct link to cometary X-ray emission.

Remote infrared observations of parent volatiles in comets: A window on the early solar system

Organic volatiles and water in Oort Cloud comets were investigated at infrared wavelengths. The detected species include H 2O, CO, CH 3OH, CH 4, C 2H 2, C 2H 6, OCS, HCN, NH 3, and H 2CO. Several daughter fragments (CN, OH, NH 2, etc.) are also measured, and OH prompt emission provides a proxy for water. Long-slit spectra are taken at high spectral dispersion and high spatial resolution, eliminating several sources of systematic error. The resulting parent volatile production rates are highly robust, permitting a sensitive search for compositional diversity among comets. Here, seven OC comets are compared. Six (including Halley) exhibit similar compositions (excepting CO and CH 4). Their low formation temperatures (∼30 K) suggest this group probably formed beyond 30 AU from the young sun. However, C/1999 S4 is severely depleted in hypervolatiles and also in methanol, and it likely formed near 5–10 AU. C/2001 A2 is discussed briefly to illustrate future prospects.

Production of ethane and water in comet C/1996 B2 Hyakutake

Ethane (C2H6) and water (H2O) were detected in Comet C/1996 B2 Hyakutake between UT 1996 March 23.4 (Rh = 1.08 AU preperihelion) and 1996 April 12.2 (Rh = 0.64 AU preperihelion). Our long‐slit infrared spectra featured both high spectral dispersion and high spatial resolution about the nucleus, permitting the extraction of rotational temperatures, production rates, and spatial distributions of species along the slit. Production rates were measured for water (on four dates) and ethane (on three dates). Their average relative abundance was C2H6/H2O = (6.2 ± 0.7) × 10−3. The spatial distributions of C2H6 and H2O molecules in the coma were consistent with both species being released directly from the nucleus on all dates, although asymmetries about the nucleus are seen for both gas and dust.

Selffocussing phase transmission grating for an integrated optical microspectrometer

An integrated optical microspectrometer in slab waveguides is presented for broadband spectroscopy in the visible wavelength range. Monomode silicon oxinitride (SiON) waveguides on silicon substrates are structured to produce a novel selffocussing waveguide transmission grating with a waveguide to air index transition endface. Regarding reflection gratings such transmission gratings have four-times larger facettes which is linked to reliable fabrication by standard thin film technology as well as to an exceptional high spectral dispersion. Combined with further functional optic elements, a compact microspectrometer is presented for long-term stable operation. The selffocussing and dispersion properties of the transmission grating are developed theoretically by phase matching and evaluated successively with electromagnetic theory. The spectral and spacial condition of constructive interference is generated in the waveguide plane at a focus length of only 13 mm yielding a miniaturized, integrated optical, chirped ‘grism’ — grating prism — a specially designed planar imaging optic with structured waveguide endfaces results in a compact and monolithical core. The fabrication sequence based on standard thin film technology consists of a single deposition and etching process which allows an economic manufacturing. The realized microspectrometer exhibits high efficiency >60% in the first diffraction order and a spectral range of 350–650 nm with a spectral resolution of 9 nm.