Off-plane Eagle Research Articles

The new PTB beamline for vacuum-ultraviolet radiometry

At the Metrology Light Source, a 630 MeV electron storage ring for the use of synchrotron radiation for metrology applications, a new beamline is dedicated to radiometry in the vacuum-ultraviolet spectral range. The emphasis lies on the traceability of measurements and profound uncertainty analysis. To replace the previously existing normal incidence monochromator beamline which serviced for more than 20 years now at different facilities, a newly designed 2 m off-plane Eagle monochromator beamline concept was developed. Different reflective coatings for mirrors and gratings in combination with order-sorting filters ensure highest spectral purity of the monochromatized radiation in combination with optimized photon flux characteristics. The beamline is planned to go into full operation in late 2022.

Photostimulated phosphor based image plate detection system for HRVUV beamline at Indus-1 synchrotron radiation source

A high resolution vacuum ultraviolet (HRVUV) beamline based on a 6.65m off-plane Eagle spectrometer is in operation at the Indus-1 synchrotron radiation source, RRCAT, Indore, India. To facilitate position sensitive detection and fast spectral recording, a new BaFBr:Eu2+ phosphor based image plate (IP) detection system interchangeable with the existing photomultiplier (PMT) scanning system has been installed on this beamline. VUV photoabsorption studies on Xe, O2, N2O and SO2 are carried out to evaluate the performance of the IP detection system. An FWHM of ~0.5Å is achieved for the Xe atomic line at 1469.6Å. Reproducibility of spectra is found to be within the experimental resolution. Compared to the PMT scanning system, the IP shows several advantages in terms of sensitivity, recording time and S/N ratio, which are highlighted in the paper. This is the first report of incorporation of an IP detection system in a VUV beamline using synchrotron radiation. Commissioning of the new detection system is expected to greatly enhance the utilization of the HRVUV beamline as a number of spectroscopic experiments which require fast recording times combined with a good signal to noise ratio are now feasible.

First commissioning results from high resolution vacuum ultraviolet beamline at Indus-1 synchrotron source

A high resolution vacuum ultraviolet beamline has been developed and installed at the 450 MeV synchrotron source Indus-1 operating at the Raja Ramanna Centre for Advance Technology, Indore, India. This beamline is useful for photoabsorption studies of atoms and molecules in the VUV region of 1050–3000 Å. The beamline consists of three major components: a pre-focusing optical system, a gas phase absorption setup and a 6.65 m vacuum ultraviolet spectrometer in off-plane Eagle mount. The performance of the beamline has been evaluated by recording VUV absorption spectra of xenon, oxygen and sulphur dioxide using synchrotron radiation from Indus-1. The resolution achieved is 0.1 Å with a 1200 ln/mm grating. Spectra obtained agree well with the ones published earlier. Details of the design, development and performance testing of the beamline are discussed.

Development of high-energy resolution inverse photoemission technique

We developed a new inverse photoemission (IPES) machine based on a new idea to improve the energy resolution: off-plane Eagle mounting of the optical system in combination with dispersion matching between incoming electron and outgoing photon. In order to achieve dispersion matching, we have employed a parallel plate electron source and have investigated whether the electron beam is obtained as expected. In this paper, we present the principle and design of the new IPES method and report the current status of the high-energy resolution IPES machine.

HIGH-RESOLUTION AND LOW-TEMPERATURE PHOTOEMISSION SPECTROSCOPY AT THE HISOR HELICAL-UNDULATOR BEAMLINE

We report an experimental system dedicated for high-resolution and low-temperature photoemission spectroscopy installed on the helical-undulator beamline of a compact 700 MeV electron-storage ring (HiSOR) at Hiroshima University. A 3 m off-plane Eagle normal-incidence monochromator at the beamline covers the photon-energy range of hν = 4–40 eV. From the photoemission spectra near the Fermi edge of evaporated Au film, the total energy resolution was estimated to be 4.5 and 7.5 meV at hν = 7.1 and 22.6 eV, respectively. We have also performed photoemission measurements of Yb metal, which demonstrated highly bulk-sensitive spectra for the excitation by low energy photon. The high-resolution photoemission spectra of Y 1 - x Ca x TiO 3 with x = 0.41 in the vicinity of the boundary between the metallic and insulating phases exhibited anomalous temperature dependence in comparison with those of normal metals.

Complete characterization of SU5:: a VUV high resolution beamline with variable polarizations

The SU5 VUV beamline aims towards a dual scientific program: high resolution spectroscopy on dilute targets and linear/circular dichroism on anisotropic systems. A crossed planar/helicoidal electromagnetic undulator has been designed and built, providing both flux and variable polarizations. We have shown a complete versatility of the polarization state of the emitted light with high polarization rates. Besides, the harmonics of the undulator can be suppressed owing to a gas filter, acting as a low-energy pass filter, with rejection factors above 10 5. The beamline is centered around a 6.65 m off-plane Eagle normal incidence monochromator which has shown unprecedented raw resolving powers (117 000 at 21.6 eV, 133 000 at 15.8 eV) with typical flux in a 1/50 000 bandwidth of 10 10–10 9 photons/s between 6 and 30 eV.

Formula omitted] off-plane Eagle monochromator at the helical undulator beamline of HiSOR

The helical/linear undulator based beamline (BL9) with 3 m off-plane Eagle monochromator for the VUV region (4– 40 eV ) has been installed on a compact storage ring, HiSOR. The Rydberg series of Ar 3 s3 p 6n p 1 P 1 up to n=25 has been measured. The resolving power was estimated to be >12 000 at 40 nm with the photon flux ≈9×10 9 photons/s. The ultimate resolving power was obtained from the measurements of the O 2 Schumann–Runge bands. The resolution derived from the deconvolution for the Voigt profile was 0.0061 nm (λ/ Δλ≈30 000 ) in the 180 nm wavelength range.

Very high spectral resolution obtained with SU5: A vacuum ultraviolet undulator-based beamline at Super-ACO

In this article we wish to report on the commissioning of the SU5 undulator-based beamline, whose primary scientific goal deals with high-resolution spectroscopy and photon-induced dynamics in the vacuum ultraviolet range on dilute species. In order to achieve such a scientific program, we have conceived an original optical design, centered around a 6.65 m off-plane Eagle monochromator equipped with two gratings (2400 and 4300 l/mm) illuminated by an astigmatic prefocusing optical system. The different components of the actual beamline, such as the optical elements, their holders/manipulators and the monochromator are described, with a special emphasis on critical aspects such as the mechanical resolution and stability, the vibrations limitations, and the thermal stability. Then, a spectral calibration procedure of the monochromator is described, followed by the presentation of the measured performances of the beamline in terms of ultimate resolution and flux. Owing to a gas phase ion yield experiment on rare gases, we have been able to measure a raw linewidth of 184 μeV at 21.61 eV (18s′ line of Ne) corresponding to a resolving power of 117 000 and a raw (respectively, lifetime-deconvoluted) linewidth of 119 μeV (respectively, 76 μeV) at 15.82 eV (13s′ line of Ar) corresponding to a raw resolving power of 133 000 (respectively, 208 000). The ultimate targeted 105 resolving power is therefore observed on most of the VUV range, which corresponds to an unprecedented performance. The measured photon flux in a 1/50 000 bandwidth is in reasonable agreement with the expected values lying in the 1010–109 photon/s range over the VUV range. These very satisfactory performances, with a slit-limited resolution down to about 15 μm slits aperture, are due to the special care which has been paid at both the conception and construction stages concerning critical issues such as the optical and mechanical design, the vibrations, the driving/encoding system, and the slope errors of the gratings.

Advances in photoionization and photoelectron studies using third generation synchrotron radiation

Abstract In the past few years, we have established a unique high-resolution photoionization–photoelectron facility at the Chemical Dynamics Beamline of the Advanced Light Source. By combining a 6.65-m off-plane Eagle mounted scanning monochromator with the undulator synchrotron radiation source, we have demonstrated photon energy resolving powers up to E /Δ E =72,000–100,000 in the photon energy range of 6–27 eV. We have also developed novel synchrotron-based pulsed field ionization photoelectron (PFI-PE) detection schemes, achieving resolutions of 1–6 cm −1 (FWHM). Using the specially designed photoelectron–photoion apparatus, which features a supersonic molecular beam source and opposing electron and ion time-of-flight spectrometers, we have recently succeeded in performing synchrotron-based PFI-PE photoion coincidence experiments, attaining resolutions limited only by the PFI-PE measurements. Most recently, we have demonstrated a generally applicable synchrotron-based scheme for PFI-photoion measurements. The PFI-PEPICO and PFI-PI methods are expected to have a significant impact in future reaction dynamics studies involving the preparation of rovibronically state-selected reactant ions.

Image Evaluation of the High Resolution VUV Spectrometer at SURF II by Ray Tracing.

A high resolution VUV spectroscopic facility has been in use for several years at SURF II, the Synchrotron Ultraviolet Radiation Facility at the National Institute of Standards and Technology in Gaithersburg, Maryland. At this facility, a combination of three cylindrical mirrors is utilized to focus the light originating in the storage ring onto the horizontal entrance slit of the spectrometer. The spectrometer uses a 6.65 m concave grating having a groove density of 4800 lines/mm in the off-plane Eagle mounting. In preparation for the installation of an array detector in the exit image plane, a ray tracing program has been formulated and spot diagrams have been constructed by plotting the coordinates of the points of intersection of the diffracted rays with the image plane, which is tangent to the Rowland circle. In creating the spot diagrams, we have considered both parallel and tilted configurations of the entrance slit with respect to the grating grooves. It is shown that the line widths of the spectral images can be reduced when the entrance slit is properly tilted. Finally, we have estimated the spectral widths of the images when they are recorded on an array detector placed tangent to the Rowland circle. We conclude that an image spectral width of 0.41 pm to 0.88 pm in first order can be achieved over the wavelength region of 40 nm to 120 nm.

High-flux and high-resolution spectroscopic facility in the VUV region at Super-ACO.

A new spectroscopic facility, consisting of a planar/helical undulator and a 6.65 m off-plane Eagle monochromator, has been designed. It can supply high-flux and high-resolution photons with 'exotic' polarization in the 5-40 eV energy range. The astigmatism can be compromised by horizontally focusing the incident radiation on the grating. The rotation of a post-focusing toroidal mirror compensates for the deviation of the exit beam caused by the grating translation. The whole system will be installed at beamline SU5 of SUPER-ACO (0.8 GeV) at the beginning of 1998. With a 4300 grooves mm(-1) grating, a resolving power of around 10(5) is expected at 20 eV.

Performance of the vacuum ultraviolet high-resolution and high-flux beamline for chemical dynamics studies at the Advanced Light Source

At the Advanced Light Source an undulator beamline, with an energy range from 6 to 30 eV, has been constructed for chemical dynamics experiments. The higher harmonics of the undulator are suppressed by a novel, windowless gas filter. In one branchline high-flux, 2% bandwidth radiation is directed toward an end station for photodissociation and crossed molecular-beam experiments. A photon flux of 1016 photon/s has been measured at this end station. In a second branchline a 6.65 m off-plane Eagle monochromator delivers narrow bandwidth radiation to an end station for photoionoization studies. At this second end station a peak flux of 3×1011 was observed for 25 000 resolving power. This monochromator has achieved a resolving power of 70 000 using a 4800 grooves/mm grating, one of the highest resolving powers obtained by a vacuum ultraviolet monochromator.

VUV high resolution and high flux beamline for chemical dynamics studies at the advanced light source

An undulator beamline, consisting of VUV high resolution and high flux branch lines, devoted to chemical dynamics experiments has been designed at the Advanced Light Source. The radiation source is an undulator having a 10-cm period, and the fundamental in the energy range from 6 to 30 eV is utilized by the experiments. The higher harmonics of the undulator due to the operation at high K values is suppressed by a novel gas filter. In the first branch, high-flux 2% bandwidth radiation is directed toward an end station for photodissociation. A photon flux calculation predicts 10 16 photon/s at this end station. In the second branch, highly monochromatized radiation is sent to an end station for photoelectron spectroscopy and photoionization studies. For this purpose a vertical dispersion 6.65-m off-plane Eagle mounting was chosen for the monochromator in anticipation of achieving a resolving power of ∼ 5 × 10 4 with a 1200 grooves/mm grating and 1 × 10 5 to 2 × 10 5 with a 4800 grooves/mm grating.

Theoretical evaluation of the high-resolution vacuum ultraviolet spectrometer on SURF II

The high-resolution vacuum-ultraviolet spectroscopic facility at SURF II, the Synchrotron Ultraviolet Radiation Facility at the National Institute of Standards and Technology in Gaithersburg, Md., consists of a fore-optics system of three cylindrical mirrors and a 6.65-m concave grating spectrometer using the off-plane Eagle mounting. To prepare for the evaluation of the actual performance of this nationalfacility spectrometer against theoretical expectations, we computed scanning parameters, spectral resolution, and the optimum curvature and tilt of both entrance and exit slits. It is planned eventually to replace the exit slit of this instrument with a two-dimensional array detector to increase data collection efficiency. Therefore a major motivation for this work is that the results on the tilt and curvature of the exit slit can be used to maximize the resolution obtainable with the array detector through data processing.

High-resolution VUV absorption spectroscopy with the 6-VOPE facility (invited)

A high-resolution VUV spectroscopic facility, called 6-VOPE, which consists of a 6.65-m vertical dispersion off-plane Eagle spectrometer and a zero-dispersion-type tandem concave grating predisperser system, was designed and installed at the Photon Factory. This facility attained a resolving power of >2.5×105 at ∼79 nm in the photographic detection mode and >1.5×105 at ∼88 nm in the photoelectric detection mode—the highest resolving power ever demonstrated, in both detection modes, for this spectral region. The nature and the level of the focused stray light in the 6-VOPE facility is discussed. Some examples of absorption spectra are presented to show the capability of the 6-VOPE facility.

Performance of the 6VOPE high resolution VUV spectroscopic facility in the photoelectric detection mode

Absorption measurements of krypton gas have been carried out to evaluate the performance of the high resolution spectroscopic facility 6VOPE using photoelectric detection. The 6VOPE is designed to make use of high spectral orders and consists of a 6.65-m vertical dispersion off-plane Eagle spectrograph/monochromator and a zero-dispersion tandem grating predisperser system. Focal plane scanning is used to achieve high resolving power (>==10(5)) for photoelectric measurements in the 40-200-nm range. A description is given of the mechanism and performance of the 6VOPE in the focal plane scanning mode. The resolving power and focused stray light level at ~88 nm are estimated experimentally to be greater, similar1.5 x 10(5) and less, similar 3%, respectively. Contrary to the usual experience the focused stray light of the 6VOPE is composed entirely of VUV light scattered from the main grating.

High resolution VUV spectroscopic facility at the SURF II electron storage ring

Described in detail is a new high resolution spectroscopic facility which utilizes a 6.65-m off-plane Eagle spectrometer and synchrotron radiation from an electron storage ring light source. This facility has been constructed to provide a national capability for research in the atomic and molecular sciences which combines spectroscopic resolution in excess of 10(5) with a stable and calibrated VUV continuum light source. High resolution is obtained using blazed 4800-groove/mm gratings, which produce linear dispersions of 0.3 A/mm in first order. The fore optics in the beam line portion of the facility enhances the polarization of the VUV radiation from the storage ring to provide light to the experimental areas, which is highly polarized parallel to the plane of the storage ring. The beam line also contains several stages of differential pumping to permit high gas load experiments. There are three principal experimental areas in the facility: in front of the spectrometer's entrance slit, on the carriage which scans along the focal curve of the 6.65-m instrument, and behind the chamber containing the focal curve scanner. Several experiments currently in progress or preparation are discussed briefly.

6.65 m off-plane eagle spectrograph/monochromator at the photon factory

A description is given of the design principle and the performance of a 6.65 m vertical dispersion off-plane Eagle spectrograph/monochromator (6VOPE) constructed at the Photon Factory. 6VOPE has a unique predisperser system of zero dispersion type that effectively separates the overlapping orders by a simple rotation of the fore-gratings and adjustment of the intermediate slit width. The performance of 6VOPE was examined from the viewpoint of resolution by taking absorption spectra of rare gases in the 50–90 nm region with the 6th to 10th orders. The resolving power was estimated from the separation between two closely lying lines of Ar I at ∼ 79 nm to be ≳ 2.5 × 10 5, the highest resolving power ever reported for this wavelength region.

High-resolution VUV spectroscopic facility at the Photon Factory

A high-resolution spectroscopic facility, consisting of a 6.65-m vertical dispersion off-plane Eagle spectrograph/monochromator and a unique predisperser system of zero-dispersion type, has been designed and constructed at the Photon Factory. A description is given of design principle, optical system, mechanical arrangement, vacuum system, control system, and performance in the spectrograph mode. The resolving power was estimated from the separation between two closely lying lines of Ar I at ∼79 nm in the seventh order to be >2.5 × 105 —the highest resolving power ever demonstrated for this spectral region.

Design studies of mirror-grating systems for use with an electron storage ring source at the photon factory

The design method developed during the course of designing several grating instruments for use with a 2.5-GeV electron storage ring at the Photon Factory of the National Laboratory for High Energy Physics is described. The method is shown to be quite effective in designing complete optical trains which are tailored to maximize throughputs and resolution and to minimize aberrations, interference by unwanted wavelenghts and/or specific site-imposed constraints over limited wavelength ranges. The results obtained with this design method are given for the cases of 6.65-m off-plane Eagle type spectrograph/monochromator under construction and a planned 10-m grazing incidence monochromator.