Pressed capillary optics

Details Pressed capillary optics Pressed capillary optics

2002-01-22

2004-05-18

Sanghavi, Hemang (Department: 2874)

Optical waveguides

Optical imaging tunnel

C385S125000, C378S145000, C065S393000, C264S001240, C264S001250

Reexamination Certificate

active

06738552

ABSTRACT:

This invention relates to the use of optics to produce a directed beam of radiation by grazing-incidence reflection. More particularly, a monocapillary optic is disclosed which is produced by creating a precisely shaped mold which has the desired figure of the final capillary optic's internal bore. The mold most commonly takes the form of a precisely etched wire. The mold is used as a mandrel for the production of a capillary optic by placing it between two polished and generally flat plates composed of a relatively soft material, and applying pressure. The profile of the mold is imprinted into the surfaces of the flat plates and is thus replicated. The plates are disassembled, the mold removed, and the two plates are reassembled to form the final capillary optic. In some instances, a reflection enhancing film is applied before the final assembly step. More than one mold can be used in the process to create a polycapillary optic. The resultant optics can be used to produce either a collimated beam or a focused spot of photons, neutrons, or charged particles.
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
NOT APPLICABLE
REFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAM LISTING APPENDIX SUBMITTED ON A COMPACT DISK.
NOT APPLICABLE
BACKGROUND OF THE INVENTION
The introduction of x-ray analysis has been one of the most significant developments in twentieth-century science and technology. The use of x-ray diffraction, spectroscopy, imaging, and other techniques has led to a profound increase in our knowledge in all scientific fields. The capabilities of x-ray analysis have expanded consistently with the availability of ever more powerful sources of radiation. The standard x-ray tube has seen a relatively gradual increase in performance over many decades. Notable improvements in x-ray tube technology include the introduction of rotating anode sources and microfocus tubes. Although many experiments are now performed using rotating anode sources that have significantly higher power capabilities than stationary anode tubes, these sources are quite expensive and can consume over ten kilowatts of input power. Recently, with the introduction of improved x-ray focusing optics, the ability to use small, low power microfocus x-ray sources to achieve x-ray beam intensities comparable to that achieved with rotating anode tubes has been demonstrated. It has been demonstrated that a microfocus source running at a few tens of watts input-power, in conjunction with focusing optics, can produce beams with brightness comparable to a multi-kilowatt rotating anode source. Such combined small sources and collection optics will greatly expand the capabilities of x-ray analysis equipment in small laboratories. The optimization of x-ray optics for these applications is of crucial importance for realizing the potential of these laboratory instruments.
The advent of synchrotron radiation sources over the past several decades has produced a revolution in x-ray science. Due to the extreme brightness of these sources, measurements that were not possible in the past have become routine. This brightness allows the use of microfocusing optics to create very small x-ray microbeams with greatly enhanced flux densities. These microbeams have allowed measurements of samples with unprecedented spatial resolution and small size. Improvements to these optics are highly desirable to allow the full potential of synchrotron sources to be achieved.
In addition to sources of X-rays, there has been a significant increase in the capabilities of neutron sources, many of which exist as user facilities in a manner similar to synchrotron radiation sources. Both reactor and spallation sources have been built with ever increasing neutron fluxes. For certain applications such as prompt-gamma activation analysis and neutron depth profiling, it is very desirable to produce a focused beam of thermal or cold neutrons. The use of small beams is also advantageous for neutron diffraction applications. There have been advances in neutron focusing optics over the past few years. Further improvements to these optics will have a large impact on the capabilities of these neutron facilities.
There have been dramatic developments in the field of x-ray optics. Many different types of optical elements have been introduced or improved for the manipulation of short wavelength photons. In the specific area of focusing optics, several different types of lenses and focusing mirrors have been produced. These optics include: zone plates, Bragg-Fresnel zone plates, multi-layer-focusing mirrors, grazing incidence mirrors, compound refractive lenses, and capillary optics. In addition to x-ray photons, these optical elements can be used for the focusing of neutrons and charged particle beams.
In the area of capillary optics, there are two basic types—monocapillary optics and polycapillary optics. The invention we will be discussing here involves improvements to both types of these optics. Although we will concentrate mainly on their use for the manipulation of x-rays, we will also discuss their use for the focusing and collimation of visible and near visible light. In particular, the use of the optics with laser light in fiber-optic communications applications is potentially very important and practical.
Although there exist x-ray optics that use reflection, diffraction, or refraction for their operation, we are concerned specifically with reflective optics in this invention. It is well known that x-rays incident on a surface at sufficiently small angles of incidence will be reflected by total external reflection. The largest angle of incidence for reflection (critical angle) is determined by the refractive index of the material:
n=
1
−&dgr;−i&bgr;
Using Snell's Law, we can derive this angle as:
&thgr;
c
=(2&dgr;)
1/2
(assuming &bgr;=0)
The theoretical value for &dgr; is:
&dgr;=½(
e
2
/mc
2
)(
N
0
&rgr;/A
)
Z&lgr;
2
=2.70×10
10
(
Z/A
)&rgr;&lgr;
2
The angles are quite small since the refractive index for x-rays is very close to unity for all materials. For example, the critical angle for borosilicate glass at &lgr;=1Å is less than 3 milliradians. For achieving the highest critical angles, high-density materials such as gold or platinum are desirable.
In the case of neutrons, grazing incidence reflection can also be used for producing optical devices. The critical angle for reflection of neutrons is:
&thgr;
c
=&lgr;(
Nb
/&pgr;)
1/2
Where b is the coherent scattering length and N is the number of nuclei per cm
3
. The best natural material for achieving the highest critical angle for neutron reflection is nickel. The isotope Ni-58 is especially good, having a critical angle of approximately 2.1 milliradians/Å.
In addition to single-layer reflecting materials, multilayer coatings can be produced which rely on Bragg reflection to achieve high reflectivity. These layers are composed of a high-Z material that exhibits large coherent scattering for the radiation being reflected, with alternating low-Z layers that function as spacers. In the case of x-rays, the most common high-Z materials are tungsten or molybdenum, while the low-Z spacer is usually silicon, carbon, or beryllium. In the case of neutron reflection, these multilayer coatings are often referred to as “supermirrors.” Neutron supermirrors differ from standard x-ray multilayers in that the d-spacing of the layers is not constant, but increases for the layers towards the surface of the mirror. Supermirror structures are generally composed of layers of nickel or a nickel alloy, with spacer layers of titanium.
Reflective x-ray optics can be classified into several different categories. One class of optics uses grazing reflection from extended mirror surfaces. The most common mirror arrangements have an ellipsoidal or toroidal surface figure for two-dimensional focusing of radiation. Another common geometry uses two spherical mirrors oriented sequentially

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