An x-ray monochromator is described, wherin a housing supports a plurality of mirrors forming a plurality of opposed mirror faces in parallel with each other and having thereon multilayer coatings, with each of said pairs of mirror faces being provided with identical coatings which are different from the coatings on the other pairs of mirror faces such that each pair of mirror faces has a peak x-ray reflection at a different wavelength regime. The housing is moveable to bring into a polychromatic x-ray beam that pair of mirror faces having the best x-ray reflection for the desired wavelength, with the mirrors being pivotable to move the mirror faces to that angle of incidence at which the peak reflectivity of the desired wavelength x-rays occurs

Hoover, Richard B.

English

NASA Technical Reports Server

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US005173930A 
United States Patent [19] [ i l l  Patent Number: 5,173,930 
Hoover 1451 Date of Patent: Dec. 22, 1992 
[54] X-RAY MONOCHROMATOR 
[75] Inventor: Richard B. Hoover, Huntsville, Ala. 
[73] Assignee: The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
1211 Appl. No.: 803,268 
1221 Filed: Nov. 22, 1991 
[51] Int. ( 3 . 5  ............................................... G21K 1/06 
[52] U S .  c1. ....................................... 378/85; 378/145 
[58] Field of Search ...................... 378/82, 84, 85, 145 
mi  References Cited 
U S .  PATENT DOCUMENTS 
4.567,605 VI986 Bartels .................................. 378/85 
4,958,363 9/1990 Nelson et al. ......................... 378/85 
Primary Examiner-Craig E. Church 
Attorney, Agent, or Firm-Robert L. Broad, Jr.; John R. 
Manning; Guy M. Miller 
1571 ABSTRACT 
An x-ray monochromator, wherein a housing supports a 
plurality of mirrors forming a plurality of opposed mir- 
ror faces in parallel with each other and having thereon 
multilayer coatings, with each of said pairs of mirror 
faces being provided with identical coatings which are 
different from the coatings on the other pairs of mirror 
faces such that each pair of mirror faces has a peak x-ray 
reflection at a different wavelength regime. The hous- 
ing is moveable to bring into a polychromatic x-ray 
beam that pair of mirror faces having the best x-ray 
reflection for the desired wavelength, with the mirrors 
being pivotable to move the mirror faces to that angle of 
incidence at which the peak reflectivity of the desired 
wavelength x-rays occurs. 
5 Claims, 2 Drawing Sheets 
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FIG. 1 
U.S. Patent Dec. 22, 1992 Sheet 2 of 2 5,173,930 
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Fig. 2 
5,173,930 
1 
X-RAY MONOCHROMATOR 
ORIGIN OF THE INVENTION 
The invention described herein was made by an em- 
ployee of the United States Government and may be 
manufactured and used by or for the Government of the 
United States of America without the payment of any 
royalties thereon or therefor. 
BACKGROUND O F  THE INVENTION 
1. Field of the Invention 
This invention relates to monochromators. 
2. Prior Art 
Monochromators which can produce a monochro- 
matic beam with narrow spectral wavebands are 
known. Such beams are very useful in the testing and 
calibrating of x-ray telescopes and microscopes, in re- 
search in biological and biomedical disciplines, in re- 
search in properties of materials and processing etc. 
Previous monochromators have used metal foil fil- 
ters, gratings, or crystals. Metal foil monochromators 
have the advantage of a high throughput but do not 
have the narrow bandwidth needed for some applica- 
tions. Much higher spectral resolution is possible with 
the use of crystal or grating monochromators but these 
have other disadvantages. 
Natural crystal monochromators are suitable for hard 
x-ray use and even some of the shorter wavelengths in 
the soft x-ray wavelengths but the crystal lattice struc- 
ture in naturally occurring crystals is too small to per- 
mit observations in the longer wavelength soft x- 
r a y / E W  regimes. Grating monochromators are capa- 
ble of covering the soft x-ray/EUV portions of the 
electromagnetic spectrum, which is the concern of the 
present invention, but they have a very low throughput. 
In addition, grating monochromators are difficult to 
fabricate, align and maintain in optical alignment. Also, 
grating monochromators are typically large and expen- 
sive. 
SUMMARY OF THE INVENTION 
An x-ray monochromator wherein a plurality of par- 
allel pairs of facing mirrors are mounted in a housing 
having therein an inlet window and an outlet window 
for each pair of mirrors. Each pair of facing mirrors is 
coated with identical multilayer coatings which reflect 
x-rays at a wavelength which is dependent on the angle 
of incidence of the x-rays on the mirror and the nature 
of the multilayer coating, with different pairs of facing 
mirrors having different multilayer coatings such that 
positioning of the pairs of mirrors in the housing and the 
multilayer coatings on the mirrors. 
FIG. 2 is a plan view of the top of the apparatus 
showing the positioning of guides in which the housing 
5 moves. 
DETAILED DESCRIPTION OF THE 
INVENTION 
Refemng now in detail to the drawing, there is 
10 shown a monochromator which includes a housing 10 
having therein a plurality of mirrors 11, 12, 13 and 14 
having opposed pairs of mirror faces 18,19 and 20, with 
the housing being provided with inlet and outlet win- 
dows 24 and 25, respectively for each of the mirror 
15 pairs. Filters 26 mounted on the windows 24 reject 
visible and ultraviolet light. 
The mirrors 11-14 are mounted in channels 28 which 
are provided with pivot pins 30 which extend through 
apertures (not shown) in the housing to allow the mir- 
20 rors to pivot in the housing. The channels 28 are also 
provided with other pivot pins 33 which extend 
through apertures in a pair of links 35 which serve to 
hold the mirrors in a parallel relationship. The housing 
11, the pivot pins 30 and 33 and the links 35 are pre- 
25 cisely made to accurately hold the opposed mirror faces 
18, 19 and 20 to within less than 1 arc second from 
absolute parallel. 
Also, the opposite surfaces of each of the mirrors 
11-14 are parallel to each other to within less than 1 arc 
30 second. All of the mirror surfaces should be superpol- 
ished to a smoothness of less than about 3 Angstroms 
RMS. When tested with visible light, the mirror sur- 
faces should be flat to better than 1/20th wave. Materi- 
als which can be used for the mirrors and which can be 
Each pair of opposed or facing mirror faces 18, 19 
and 20 is coated with a multilayer coating such that the 
pairs 18, 19 and 20 each have different coatings but the 
coatings on any given pair are identical. These coatings 
40 are made up of alternating layers of high-Z diffractor 
material of a thickness d l  separated by layers of low-Z 
spacer material of thickness d2. Such coatings and the 
methods of making them are known. 
The multilayer coatings constitute synthetic Bragg 
45 crystals, with x-ray reflection taking place by Bragg 
diffraction. The wavelength at which the peak of the 
reflected flux occurs is given by the Bragg relation: 
n(h)=ZDSine, where n is the order of the diffraction 
(usually taken to be unity), D is the multilayer diffractor 
50 and spacer thickness parameter and 8 is the angle at 
which the radiation strikes the mirror surface. 
One skilled in the art will be aware of which high Z 
materials will give the best diffraction ~erformauce at 
35 polished to this degree are known. 
each pair of facing mirrors has a peak reflection of any desired length and which l O w z  spacer mate- 
X-rays at a different wavelength. The mirrors are Pivot- 55 rials should be used with the selected high Z diffractor 
ally mounted in a row in the housing and are intercon- layers. He will also be aware of how to select the de- 
nected SO that al] Of the mirrors pivot at the Same time sired thicknesses d l  and d2 to obtain the desired diffrac- 
and amount SO that the mirror surfaces always remain tor and spacer thickness parameter. 
parallel to each other. The housing is moveable SO that each pair of opposed mirror faces h a  its 
any pair of mirrors can be moved into position to inter- M) own multilayer coating, different from the coatings on 
cept a x-ray beam traveling along a fixed path through the other pairs of faces, it can readily be seen that each 
the inlet window associated with that pair of mirrors to pair of opposed faces will have a peak reflection of 
thereby provide a monochromatic x-ray beam of a de- x-rays at some wavelength which is different from the 
sired wavelength. peak reflection of the other pairs of faces. This allows 
Inasmuch 
65 one to select the pair of mirror faces which provides the 
greatest reflection of x-rays at the wavelength desired. DESCRIPTION OF THE DRAWING 
FIG. 1 is a side view of the apparatus of this invention 
with portions of the structure cut away to show the 
- The housing is mounted for sliding movement be- 
tween a plurality of guides 40, as best shown in FIG. 2. 
,. 5,173,930 
3 
The guides 40 are mounted on a base 41 (FIG. 1) and are 
precisely made and positioned to very accurately posi- 
tion the housing as it is moved from one position to 
another in the guides 40. A driving mechanism of a 
known type 44 mounted on the base 41 is connected to 5 
the housing by a rod 45 for moving the housing 11 
within the guides 40. 
From the above, it will readily be apparent that the 
wavelength of peak reflectivity of x-rays by a multi- 
layer mirror is dependent on the angle at which the 10 
x-ray beam strikes the mirror, so that one can vary the 
wavelength at which maximum reflectivity occurs by 
adjusting the angle of incidence. This is accomplished in 
this apparatus by pivoting the mirrors on the pivot pins 
30. 15 
A traversing mechanism 50 of a known type is 
mounted on the top of the housing and is adapted to 
traverse a rod 51 which is secured to one of the links 35 
to pivot the mirrors to adjust the angle at which a poly- 
chromatic x-ray beam 54 strikes the mirror. It can be 20 
seen that upward movement of the rod 51 increases the 
angle of incidence, while downward movement of the 
rod 51 lowers the angle of incidence. 
In operation, the driving mechanism 44 is actuated to 
move the housing 10 in the guides 40 to bring into the 25 
path of the polychromatic x-ray beam 54 that pair of 
mirror faces, 18,19 or 20 which offer the best reflection 
over the desired wavelength range. The traversing 
mechanism 50 is then actuated to pivot the mirrors to 
change the angle of incidence to select the desired 
wavelength in the output beam 55. The polychromatic 
beam 54 reflects off the surface 20 of the mirror 14 
(when the housing is positioned as shown in FIG. 1) to 
strike the surface 20 of the mirror 13 at the same angle 
of incidence. A monochromatic beam 55 is reflected out 
of the housing 10 through the outlet window 25 associ- 
ated with the mirror pair 13 and 14. 
What is claimed is: 
1. An x-ray monochromator, comprising 
._  
4 
a. a base, 
b. a housing moveably mounted on the base and hav- 
ing in one side thereof an inlet window and in the 
other side thereof an outlet window, 
c. support means mounted in the housing, 
d. a plurality of pairs means, said mirrors defining a 
plurality of pairs of opposed mirror faces parallel to 
each other, each of said pair of opposing faces 
being coated with a multilayer coating, said multi- 
layer coating on each pair of faces being different 
from the multilayer coatings on the other pairs of 
faces so that each pair of mirror faces has peak 
x-ray reflectivity at a different wavelength range, 
e. means on the base for moving the support means to 
bring one face of each pair of mirror faces into the 
path of a polychromatic beam of x-rays at one 
angle of incidence, said mirrors being so positioned 
that the x-ray beam is reflected to the other mirror 
face of said pair at the same angle of incidence and 
is reflected from said other mirror face out of the 
housing through said outlet window, and 
f. means on the housing and connected to the mirrors 
for pivoting the mirrors to change the angle at 
which the polychromatic beam of x-rays strikes the 
pair of mirror faces so that the multilayer coatings 
offer the greatest amount of reflection of the wave- 
length desired. 
2. The amaratus of claim 1 wherein said inlet win- 
dow is co&red by a filter which rejects visible and 
3. The apparatus of claim 2 wherein the housing is 
slidably mounted in a plurality of guides., attached to 
the base. 
4. The apparatus of claim 3 wherein a traversing 
35 mechanism mounted on the housing and connected to 
5. The apparatus of claim 4 wherein the mirrors are 
30 ultraviolet light. 
the mirrors is provided for pivoting said mirrors. 
polished to a smoothness within 3 Angstroms RMS. * * * * *  
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X-ray monochromator

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