BL-11A Soft X-Ray Grazing Incidence Monochromator Station

Spokesperson :Yoshinori KITAJIMA

Major optical components of BL-11A will be replaced in March, 2014, but concept of the beamline will not change.

1. Outline

BL-11A provides soft X rays in the energy range between 70 eV and 1900 eV with a grazing-incidence monochromator from a bending-magnet source. As there are several stations available at the Photon Factory which cover similar energy ranges with undulator sources, such as BL-13A and BL-16A, the optics of BL-11A has been designed especially under consideration of the availability for wider energy range so that EXAFS spectra for light elements such as C, N, O, F, Na, Mg, and Al can be measured. BL-7A is another soft X-ray station which covers similar energy range.

Layout of BL-11A
Fig. 1: Layout of BL-11A

Synchrotron radiation from the bending magnet B11 (maximum horizontal acceptance of 5 mrad) is reflected by two cylindrical mirrors, M0 and M0', monochromated and focused by a grazing-incidence monochromator consist of spherical mirror, M1 or M2, and varied-line-spacing plane grating, G, between entrance and exit slits, S1 and S2, finaly refocused by a toroidal mirror, Mf, to the sample position. S0 is an aperture to accept center or off-axis beams for linearly or elliptically polarized soft X rays, respectively. Though not shown in the figure, a double-mirror system can be inserted between S2 and Mf to eliminate higher-order reflection.

The monochromator is equipped with mechanisms to exchange two spherical mirrors, M1 and M2, for different included angles, and three gratings with different groove densities, 300 l/mm, 800 l/mm, and 1200 l/mm, according to the appropriate energy ranges, which enables us to use a wide energy range of 70 - 1900 eV without breaking vacuum. Energy scan is achieved by the rotaion of the grating only with a sine-arm mechanism, ensuring high stability and reliability for XAFS measurements. Control system is also simple.

2. Performance

OpticsPre-Focusing Mirrors/Varied-Line-Spacing Plane Grating Monochromator/Refocusing Mirror
Energy Range70 eV - 1900 eV
Resolving PowerE/dE = 500 ~ 4000
Spot Size~ 2 mm (H) x 0.5 mm (V)
Photon Fluxmaximum ~1012 photons/s

At present, three holographically recorded gratings with the groove densities of 300 l/mm, 800 l/mm and 1200 l/mm are installed and another mechanically-ruled grating of 800 l/mm is stored.
Ar 2p Spectrum
Fig. 2: Ar 2p photo-ion yield spectrum recorded with a mechanically ruled 800-l/mm grating and M2.

Figure 2 shows a total photo-ion yield spectrum of Ar gas in the Ar 2p excitation energy region recorded with a mechanically ruled 800 l/mm grating and M2. It is confirmed that the optical elements and those alignments are good enough by the clear observation of the transition to 7d. However, it is noted that the photon flux is much lower, typically two orders of magnitude, than undulator beamlines such as BL-16B.
N-K Spectrum
Fig. 3: N 1s-p* absorption spectra of N2 gas recorded with a mechanically ruled 800-l/mm grating and M2.

Figure 3 shows total photo-ion yield spectra of N2 gas in the N 1s-p* excitation energy region with various slit openings indicated up-left in the figures. Photon fluxes and resolving powers with a mechanically ruled 800-l/mm grating and M2 are also indicated in the up-right of the figures. With a holographically recorded grating of 800 l/mm, the achieved maximum resolving power is slightly lower than the mechanically ruled one, but the available photon flux is higher.

Spectrum from BL-11A
Fig. 4: Available flux distribution with holographically recorded gratings. Note the resolving powers are not constant because the slit opening is fixed in these measurements.

Figure 4 shows flux distribution spectra with holographically recorded gratings. Highly pure soft X rays up to 1900 eV are available with the holographically recorded gratings so that XAFS spectra on Na, Mg, Al K-edges can be measured (see example data).

3. Equippments

4. Remarks

5. References

  1. "Design report for the reconstruction the BL11A & D", KEK Report 95-4 (1995) (in Japanese).
  2. K.Amemiya, Y.Kitajima, T.Ohta and K.Ito, J. Synchrotron Rad., 3, 282 (1996).
  3. K.Amemiya, Y.Kitajima, Y.Yonamoto, T.Ohta, K.Ito, K.Sano, T.Nagano, M.Koeda, H.Sasai and Y.Harada, Proc. SPIE, 3150, 171 (1997).
  4. Y.Kitajima, K.Amemiya, Y.Yonamoto, T.Ohta, T.Kikuchi, T.Kosuge, A.Toyoshima and K.Ito, J. Synchrotron Rad., 5, 729 (1998).
  5. Y.Kitajima, Y.Yonamoto, K.Amemiya, H.Tsukabayashi, T.Ohta and K.Ito, J. Elec. Spectrosc. Relat. Phenom., 101-103, 927 (1999).

6. Publications

List of publications those registered to PF publication database is available.

Last modified: February 23, 2014.