Eagle Mounting Research Articles

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.

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.

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.

Oscillator strengths of ultraviolet V(II) lines (2290–2530 Å) from emission measurements in a stabilized arc

An argon-vanadium plasma has been produced in a wall-stabilized arc. The metal was introduced into the arc as an oxide powder suspended in flowing argon. Before introduction into the arc channel, the suspension was pulsed towards an auxilliary plasma source. The plasma radiation was photographed in the u.v. spectral region with a 10m concave grating vacuum spectrograph using an Eagle mounting. Relative calibration of the emulsions was carried out by using the intensities in the wings of the 2478 and 1931 Å lines of C(I) emitted by an Ar-CO 2 plasma; the primary standard radiation was provided by the continuum emitted from this plasma, which was produced in a stabilized arc. Plasma diagnostics were performed assuming LTE. Absolute gf-values for 33 V(II) lines in the range 2290–2530 Å have been evaluated using a computer program for statistical treatment of the data. Comparisons with theoretical calculations often show discrepancies that are larger than estimated experimental error limit.

オフ・プレン・イーグル型多重スリット分光計

In case of the off-plane Eagle mounting multislit spectrometer, the perfect performance cannot be expected even with a properly designed holographic concave grating (HCG). Any imaging error of a HCG always leads to a decrease in the S/N of the spectrum. Such effects are discussed in detail and the following results are obtained. 1) A HCG which is designed to eliminate the astigmatism at 5890 Å in the first order can be effectively used over the wavelength range from 7000 Å down to the XUV region. 2) Full image width (FIW) depends on the position of point source, and not on the wavelength. 3) Therefore, any exit slot in the exit multislit mask has its own transmission factor (t-factor). 4) Taking the t-factor into account, the S/N of the spectrum obtained with our multislit spectrometer is found to be about 94% of that attainable with the ideal multislit spectrometer.

Vacuum ultraviolet 6-m monochromator

A description is given of the design and construction of the Adelaide 6.65-m VUV monochromator. The instrument has an off-plane Eagle mounting and can be used in the first order over a wavelength range from central image to 460 nm. Digital encoders are used to monitor the angular rotation and linear displacement of the grating to provide servocontrolled wavelength and focusing adjustments which are electronically (rather than mechanically) coupled and operated through a programmable calculator. The monochromator is designed for high resolution studies of photoabsorption in atmospheric gases, and its performance is illustrated by reference to absorption studies in portions of the Schumann-Runge band system of molecular oxygen.

Aberration balancing for grating mountings with large aberrations

We apply the aberration balancing method of Maréchal to diffraction instruments with a symmetric pupil. To this class of instruments belong ruled and holographic diffraction gratings. We apply the theory to specific mountings; we give expressions for the comatic wavelength error of a Rowland mounting V, for the optimum focusing distance of a Wadsworth mounting and, as an example of an off-plane mounting we discuss the optimum image spread of an Eagle mounting.

An Order Sorter of Prism Type in Vacuum-UV Range

An LiF prism order sorter has been constructed for separating the high orders in a 3 m concave grating vacuum spectrograph in Eagle mounting. At 1 400 Å the order for the spectrograph is 4-5 and the free spectral range is 300-400 Å. A reflecting prism together with a concave mirror has been used. To make the prism "self-focussing", the reflecting surface of the prism is ground spherically. The light from the slit falls on the prism and the prism illuminates the concave mirror with light which is practically parallel. The mirror is focussed on the entrance slit of the grating spectrograph.

Optical Transfer Function of Concave Grating Spectrometer Based on Wave Optical Method

Optical transfer functions (OTF) of two types of spectrometer – Eagle mounting and Seya-Namioka mounting – are calculated by the wave-optical method which defines the OTF as the autocorrelation function of the pupil. Results obtained are compared with previous results of the present authors and interpreted as effects of diffraction and aberration on the broadening of point image. The OTFs are calculated also by Fourier transformation of the intensity distribution of point image and compared with those obtained by the first method.

Rotational analysis of the ND [formula omitted] (0,0) band

The spectrum of ND was obtained by flash photolysis of DN 3 using an 11-m concave grating in Eagle mounting. The A 3Π i-X 3Σ − (0,0) band was analyzed. The low rotational temperature permitted identification of the lines of the satellite branches and of the low J lines of the main branches. Wave numbers, term values, and constants were calculated by digital computers. We give some of the derived constants (cm −1): T e + G(0) B λ γ × 10 2 A δ × 10 2 ϵ × 10 3 X 3 Σ − 0.00 ± 2 8.7822 ± 2 0.907 ± 9 3.03 ± 4 A 3Π i 29798.72 ± 3 8.7573 ± 1 −34.56 ± 3 5.61 ± 8 −9.00 ± 7

Monochromator for the Extreme Ultraviolet

The off-plane Eagle mounting has distinct advantages over other types in the construction of grating monochromators for the extreme ultraviolet. A description is given of an adaptation of that principle, employing a Rowland grating movement and a simple drive mechanism to achieve good resolution with little mechanical complication. Differential pumping in three stages allows operation without windows and still attains pressures in the 10−9 Torr range in the measuring chamber.

Design of high-resolution monochromator for the vacuum ultra-violet. An application of off-plane eagle mounting.

Design of high-resolution monochromator for the vacuum ultra-violet. An application of off-plane eagle mounting.

Design of High-Resolution Monochromator for the Vacuum Ultraviolet An Application of Off-Plane Eagle Mounting*†

The possibility of constructing a high-resolution monochromator for the vacuum ultraviolet is discussed; off-plane Eagle mounting is chosen as the most suitable one. Considering all optical restrictions arising from an off-plane setting, the resolving power of the grating in the off-plane Eagle mounting is calculated numerically for the following conditions: 3-m concave grating (5- × 3-in. ruled area) with 30 000 lines/in. or 15 000 lines/in., 0 to 5800 A in the first order, and distance of the entrance slit from the Rowland plane 6 cm. In order to have compactness, a link mechanism introduced by Bair et al. is chosen in the scanning system and a tentative design of a 3-meter vacuum monochromator is shown schematically. As the result, it is recommended to use the off-plane Eagle mounting in constructing a high-resolution monochromator for the vacuum ultraviolet.

Theory of the Concave Grating II Application of the Theory to the Off-Plane Eagle Mounting in a Vacuum Spectrograph*†

A recent treatment of concave grating theory is applied to an off-plane Eagle vacuum spectrograph, especially to that employing a grating of 21-foot radius and 30 000 lines/inch. Three tables and two graphs summarize the numerical calculations on the following factors: (1) change in wavelength from that calculated by the ordinary grating equation; (2) angle of slit rotation with respect to the grating rulings as a function of the angle of incidence; (3) optimum grating size as a function of the angle of incidence and spectral order; (4) resolving power in the 1250 to 2000-A region as affected by emulsion grain size, length of slit illumination, spectral order, and slit width. The calculations are found to be in reasonable agreement with experiment.

Theory of the Concave Grating I*†

The theory of the concave grating has been examined in considerable detail by methods of geometrical optics. The results derived by means of geometrical optics were checked by comparing them with those based on physical optics in special cases. The conditions for image formation and aberrations in the image may be expressed by equations somewhat different from those given by Beutler which are shown to be in error. The astigmatism and other aberrations are treated with respect to finite length of slit illumination, finite grating size and deviations of the optical components from the Rowland plane but still lying on the Rowland cylinder. Within certain limitations, it is shown that the aberrations present in an off-plane Eagle mounting may be corrected by a very small rotation of the slit in a plane perpendicular to the optic axis. The optimum width of the grating, instrumental line half-width, and resolving power of the grating are also discussed. Finally, the Beutler treatment of the concave grating is examined in detail and the important errors are pointed out.

THE NEAR ULTRAVIOLET ABSORPTION SPECTRUM OF 1,2,4-TRIFLUOROBENZENE VAPOR

The vapor spectrum of 1,2,4-trifluorobenzene at 2810–2460 Å was obtained with a 3 meter grating in an Eagle mounting. The band at 37126 cm−1 was taken as the 0–0 band of the A′—A′ transition. The excited state vibrations 698, 746, 1274, and 1369 cm−1, which are totally symmetric, appear in progressions and combinations. Their correlation to vibrational modes is discussed. The 1274 belongs to a C—F bond stretching mode. Possibilities are discussed to explain the structure of the first group upon which the spectrum is built.

A high resolution spectrograph for the vacuum ultraviolet

The construction of a 21-foot Eagle mounting vacuum spectrograph employing a 30,000 line per inch concave grating is described. In this instrument, the slit is horizontal, the plateholder vertical, and both are displaced from the rowland plane. This arrangement, originally designed by Harrison, is quite convenient and simplifies evacuation problems. The bilateral slit can be adjusted without breaking the vacuum, and a movable diaphragm is provided for various purposes. The grating, newly ruled and blazed for the 5000 to 6000A region, is normally employed in that order of the vacuum ultraviolet which falls on the blaze. In the fourth order the reciprocal plate dispersion is 0.3A/mm and an observed resolving power of about 300,000 has been obtained. The plate chamber is cylindrical and possesses an aluminum door through the center of which are mounted various controls for operating the cassette. The method of optical adjustment is described briefly and the techniques peculiar to this field such as light sources, order separation, low temperature work, and wavelength standards are discussed. The high resolving power is demonstrated by a number of photographs of room and low temperature absorption spectra of nitric oxide, and emission spectra of atomic oxygen. The optical theory of the mounting, which permits the slit and plateholder to lie off the Rowland plane, is discussed with respect to the theory given by Beutler. This treatment has been examined in detail and a number of corrections and extensions have been made. It is shown that the off-plane mounting causes no new aberrations not already present in the usual in-plane mounting provided that the off-plane angle is kept below 1°.

DIFFUSE BANDS IN ABSORPTION AROUND THE SODIUM PRINCIPAL DOUBLETS IN THE PRESENCE OF NITROGEN AND HYDROGEN

Following the observation of the diffuse absorption bands near the second member of the principal series of Rb and Cs by Ny and Chen in the presence of foreign gases, we were led to study the absorption spectrum of sodium in the presence of nitrogen and hydrogen with a Hilger E-316 quartz spectrograph and a 10-foot grating spectrograph of Eagle mounting. Corrosion resistant MgO windows were used in the absorption tube so that both the absorbing and the perturbing atoms within the absorbing column had a homogeneous concentration. Diffuse absorption band was observed only by the shorter wave-length side of the third member of the principal series but not by any of the others. The separation between the intensity maximum of the diffuse band and the principal lines is larger in the case of hydrogen than that of nitrogen. They are 3.48 A for nitrogen and 4.17 A for hydrogen. The wavelength of the intensity maximum of these bands are respectively 2849.4 A and 2848.7 A for nitrogen and hydrogen.

Absorption Bands of Li2, Na2, K2 and NaK

Although fairly complete information is available regarding the first two systems of bands of Li2, Na2 and K2, the position with regard to the higher systems cannot yet be considered satisfactory. For this reason the spectra of these alkali-metal molecules, in the regions corresponding to the third, fourth and higher systems of bands, have been investigated in absorption, employing a quartz E1 spectrograph for lithium, and a 21-ft. concave grating (Eagle mounting), having a dispersion of 1.3 A. per mm., for sodium and potassium. A hydrogen discharge tube has been used as source of continuum below λ 3600 and a tungsten lamp above that.