RU2572045C2 - Refracting x-ray lens - Google Patents

Abstract

FIELD: physics, optics.

SUBSTANCE: refracting X-ray lens consists of separate focusing elements in the form of triangular prisms arranged into rows. The geometric dimensions, vertex angle and number of elements in each row, as well as the material from which the focusing elements are made vary depending on the selected photon energy in the range from soft X-rays to gamma-rays. The number of focusing elements in different rows is determined by a set of given energies. Each selected energy can match one to several rows of focusing elements. Focusing elements of each row can be made in the form of both right and oblique prisms of different size, with a different vertex angle and with flat or parabolic lateral sides. A beam can be focused in the form of a line or point.

EFFECT: concentrating radiation in a given energy range at a given distance from the lens.

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Description

The present invention relates to the field of engineering, in particular micromachine engineering, namely the manufacture of elements of microoptics. An X-ray refractive chromatic lens is known from the prior art, which is made of one material and is characterized by a specific profile, at the interface of which with air or vacuum, an X-ray wave is refracted. This lens with a parabolic refractive profile, first patented by the Japanese researcher Tomie (T. Tomie ′ ′ X-ray-lens ′ ′, Japan Patent No. 6-045288, February 18, 1994), was subsequently optimized and implemented in geometry with minimized absorption (L. Shabel′nikov, V. Nazmov, FJ Pantenburg, J. Mohr, V. Saile, V. Yunkin, S. Kouznetsov, V. Pindyurin, I. Snigireva, A. Snigirev ′ ′ X-ray lens with kinoform refractive profile created by x-ray lithography ′ ′, Proc. SPIE 4783, Design and Microfabrication of Novel X-Ray Optics p.176, November 1, 2002; doi: 10.1117 / 12.455688). The disadvantages of this technical solution are the dependence of the focal length and, accordingly, the size of the focus on the photon energy, since x-ray sources, both synchrotrons and x-ray tubes, generate photons in a wide energy range.

Closest to the claimed technical solution is the crushing of a continuous refracting parabolic profile into an integer number of focusing elements of a triangular shape with an increase in the number of focusing elements from the optical axis of the lens to its edge according to the linear law (W. Jark, F. Perennes, M. Matteucci, L. Mancini , F. Montanari, L. Rigon, G. Tromba, A. Somogyi, R. Tucoulou and S. Bohic ′ ′ Focusing X-rays with simple arrays of prism-like structures ′ ′ J. Synchrotron Rad. (2004). 11 248-253 [doi: 10.1107 / S0909049504005825]). Similar to lenses with a continuous parabolic profile, the disadvantages of this technical solution are the previously mentioned dependence of the focusing properties of the lens on the photon energy, and, since the largest number of focusing elements is presented in the outer row of the lens, the large length of the outer row, which determines the total length of the lens, although the contribution of energy to the focus introduced by the outer series can be negligible.

The task to which the invention is directed is to optimize the number and size of focusing elements in each row in order to concentrate photons of a given spectral range of energies at a given distance from the lens. This problem is solved due to the fact that the claimed refractive x-ray lens contains in each row focusing elements of a prismatic shape, the geometric parameters of the cross section of which, as well as the material and quantity vary from row to row, and this change corresponds to the given energies from the spectrum of the incident radiation, and :

- the number of focusing elements in a row can correspond to a given energy, which corresponds to the maximum number of photons in the spectrum of incident radiation;

- the number of focusing elements in different rows can correspond to a set of successively increasing (or decreasing) given energies, and a set of energies calculated from any other considerations, for example, the maximum transmission of radiation by different rows of focusing elements;

- each allocated energy from a given spectrum can respond from one to several rows of focusing elements;

- focusing elements of each row can be made of different sizes;

- focusing elements of each row can be made with different angles at the apex;

- the polychromatic beam can be focused by the lens in either one or two directions, forming a focus either in the form of a line or in the form of a point, respectively;

- the number of focusing elements in the rows corresponding to the required energy can vary taking into account the spatial and energy distribution of radiation both, for example, for synchrotron radiation sources, and taking into account the absorption of each row in the case of focusing radiation with an anisotropic spatial distribution, as is observed for x-ray handsets

- focusing prisms can be made with flat or parabolic sides;

- focusing elements can be made in the form of direct or inclined prisms.

The technical result provided by the given set of features is the concentration of radiation in a given range of energy at a given distance F from the lens. The focal length of the lens F is calculated in the case when the length of the lens is much less than the focal length, using the expression:

where: A is the distance from the optical axis of the lens to the middle of a given series of focusing elements; N is the number of focusing elements in this row; α is the half-angle at the top of the focusing element (figure 1); δ (E) is the decrement of the refractive index of the material of the focusing element for a given photon energy E (refractive index in the x-ray range = 1-iβ + δ, β (E) is the absorption coefficient of the material). Formula (1) is obtained directly from Snell's law for δ (E) << 1, which is observed in the ranges of x-ray and gamma radiation.

Thus, the relationship between the parameters A, N and tgα is specified by expression (1). On the other hand, the effective aperture (a non-radiation-absorbing aperture transmitting a photon flux equal to the photon flux through the lens) for lenses with constant parameters h and α can be determined from the expression (V. Nazmov,, R. Simon, “Mosaic-like micropillar array for hard x-ray focusing-one-dimensional version ”, 23 (2013), pp.095015):

(2), A _eff ≈h + 2δF

(2)

- коэффициент ослабления излучения в геометрии тонкого луча,

=

,

- длина волны излучения. Например, для полимерного материала, используемого при изготовлении рентгеновских линз, δ≈10^-6 и

≈10^-4 мкм^-1 (что соответствует энергии фотонов около 16 кэВ) эффективная апертура достигает нескольких миллиметров при F=1 м (при условии, что еще наблюдается заметное приращение функции lnN с увеличением N, т.е. lnN≈5). Из (2) видно также, что высота треугольников h в сечении фокусирующих элементов должна быть как можно меньше, однако воспроизводимые результаты для h при формировании рентгеновской линзы методом глубокой рентгеновской литографии лежат в области от нескольких микрометров и более.where h is the height of the triangle in the cross section of the focusing element (figure 1),

- attenuation coefficient of radiation in the geometry of a thin beam,

=

,

- wavelength of radiation. For example, for the polymeric material used in the manufacture of x-ray lenses, δ≈10 ^-6 and

≈10 ^-4 μm ^-1 (which corresponds to a photon energy of about 16 keV), the effective aperture reaches several millimeters at F = 1 m (provided that there is still a noticeable increase in the function lnN with increasing N, i.e., lnN≈5). It is also seen from (2) that the height of the triangles h in the cross section of the focusing elements should be as small as possible, however, the reproducible results for h when forming an X-ray lens by deep X-ray lithography lie in the region of several micrometers or more.

The invention is illustrated by drawings, which depict:

- diagram of a section of a prismatic focusing element (figure 1);

- arrangement of prismatic focusing elements in a lens with linear focus (figa) and point focus (fig.2b). Arrows indicate the direction of the wave front of the incident radiation;

- An example of a cross section of a refracting monochrome lens with a linear focus. In this case, the number of focusing elements of the same shape and size varies linearly depending on the distance nh from the optical axis of the lens to the middle of the nth row. For one photon energy E ₁ (figure 3), which determines the decrement of the refractive index δ (E ₁ ), the focal length of the lens:

(3)F =

(3)

where n is the number of the row (the numbering starts from the axis of the lens), m is the number of focusing elements in the first row;

- An example of a cross section of a refracting polychrome lens with a linear focus. The number of focusing elements for a fixed focal length F is given taking into account the distance from the optical axis of the lens A, height h and half-angle at a vertex α of the cross-section of the focusing elements and the photon energy E (Fig. 4).

For a polychrome lens, parameters such as height h _n , vertex angle α _n , number of focusing elements N _n in a row, and quantum energy E _n vary so that the ratio

(4)

(four)

справедливо для монохромной линзы.remained constant, and the constancy of expression

true for monochrome lenses.

The manufacture of a lens with the above focusing elements is based on the technology of creating a mask containing a pattern that includes the required parameters: A, N, tgα and h, and the technology of transferring the mask pattern to the underlying thick layer of material. The first can be both electronic lithography and photolithography, X-ray or ion lithography. The transfer process of the mask pattern can be performed using deep X-ray lithography or deep photolithography, as well as reactive-ion etching (the so-called Bosch process).

The use of the photo-, x-ray-lithographic method of transferring the mask pattern allows the use of various materials in the formation of individual rows of focusing elements. Namely, some rows can be made directly from a polymer photo-, x-ray-sensitive material (resist), metals, such as copper, nickel, gold, rhenium, can be galvanically deposited in other rows after additional masking. In this case, relation (4) can be generalized taking into account the decrement of the refractive index of various materials δ _n and represents the claims expressed mathematically:

(5)

(5)

Description of figures

Figa is a section of one focusing element of a triangular shape, the sides of which can be curved, mainly according to a parabolic law. The angle at the apex, specifying a change in the direction of propagation of the incident wave, α, element height h. The curvature of the sides can also vary. In the general case, the number of focusing elements in a row having different curvatures can be different, up to completely straight sides.

Figure 2. In space, the focusing element is a prism (straight or inclined). Prisms oriented in one direction provide focus in the form of a line (Fig. 2a). Prisms oriented in two mutually perpendicular directions provide focus in the form of a point (fig.2b).

Figure 3. Cross section of a monochrome refractive lens for photon energy E ₁ . For such a lens, the number of focusing elements in each row increases linearly depending on the distance of this row from the optical axis of the lens.

Figure 4. Cross section of a polychrome refractive lens for various photon energies. For such a lens, the number of focusing elements in each row varies depending on the distance of this row from the optical axis of the lens, height h and angle at apex α for certain energies (E ₁ and E ₂ , as shown in the figure, and in this case, E ₁ <E ₂ , since nm ₁ <nm _2. Accordingly, E ₃ <E ₄ , since

The lens works as follows. Initially, the lens is oriented relative to the radiation source so that the direction of radiation propagation coincides with its optical axis. Between the lens and the focus, immediately before the last one, an aperture diaphragm is installed (a slot - in the case of one-dimensional distribution or a hole - in the case of two-dimensional focusing), on the optical axis of the lens. As soon as the optimal position is reached, the photons of the specified energy range will be concentrated in the focus of the lens at the calculated distance from it, which can be detected by an X-ray detector with energy resolution. In the general case, a modified spectrum of primary radiation will be observed at the detector. It is planned to manufacture lenses using LIGA technology on the basis of deep X-ray lithography and use lenses to focus X-ray synchrotron radiation, which has a wide spectrum, onto the sample in order to increase its illumination.

Claims (1)

A refractive x-ray lens consisting of individual focusing elements in the form of triangular prisms, characterized in that the geometric dimensions, the angle at the apex and the number of elements in each row, as well as the material from which the focusing elements are made, vary depending on the selected photon energy in the range from soft x-rays to gamma radiation.

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