JPH0784096A - Zone plate for X-ray illumination - Google Patents

Abstract

PURPOSE:To enable the sharp reduction of uneven illumination by forming a zone plate with equal intervals between X-ray non-transmitting ring zones. CONSTITUTION:This zone plate for X-ray illumination is formed by placing X-ray transmitting ring zones 21 and X-ray non-transmitting ring zones 23 alternately as concentric circles. Moreover, spaces between the non-transmitting ring zones 23 are the same intervals A. In addition, the transmitting ring zones 21 have line widths B1 and the non-transmitting ring zones 23 have line widths B2. Consequently, the equal intervals between non-transmitting ring zones 23 makes X rays from the source parallel luminous flux, which illuminates a sample in such a way as to offset uneven illumination. The is to say, in an X-ray illumination system of the type which creates an image of X rays from the source, uniform illumination is impossible in general because the unevenness of an X-ray luminous source is always projected on a sample. Therefore, this zone illuminates a sample without creating any images of an X-ray source.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray illumination zone plate used for illuminating a sample in an X-ray microscope.

[0002]

2. Description of the Related Art In the fields of medicine and bio-optics, which are rapidly advancing in recent years, ordinary visible light (wavelength λ = about 400 nm to 800 nm) is used.
m), which has a higher resolution than a microscope that uses a living sample (hereinafter referred to as a biological sample), such as cells, bacteria, sperms, chromosomes, mitochondria, flagella, etc. The demand for is increasing day by day.

The reason is that such a biological sample cannot be seen with a conventional high resolution electron microscope. Therefore, in order to enable the observation of such biological samples, an X-ray microscope using soft X-rays having a wavelength λ = 2 to 5 nm instead of visible light has been studied and is being developed specifically.

FIG. 4 shows an example of the structure and optical system of such an X-ray microscope. In the figure, the X-ray generator 1 is shown.
The X-rays emitted from are collected by the illumination optical system 2 and irradiated on the sample capsule 4 containing the biological sample 3.

The X-ray transmitted through the sample capsule 4 is magnified by the magnifying optical system 5, and the image of the sample 3 is formed on the image pickup device 6. In this example, the X-ray generator 1
The optical path length from to the imaging device 6 is, for example, about 2 m.

Further, in the figure, reference numeral 7 indicates a lens barrel vacuum container, reference numeral 8 indicates an exhaust device for evacuating the lens barrel vacuum container 7, and reference numeral 9 indicates a monitor. X mentioned above
In the line microscope, the illumination optical system 2 projects the image of the X-ray source on the surface of the sample 3 as it is, an X-ray illumination zone plate,
An imaging optical system such as a grazing incidence reflection mirror or a multilayer film reflection mirror is used.

FIG. 5 shows an X-ray illuminating zone plate in which transparent ring zones 11 for transmitting X-rays and non-transparent ring zones 12 for not transmitting X-rays are concentrically formed alternately. It is configured.

In this zone plate, the radius r _n of the _nth boundary of the impermeable ring zone 12 is r _n = (nλf) ^1/2 (n = 1, 2, ...,
When the condition of N) is satisfied, it exhibits a lens action. Therefore, by utilizing this action, the image of the X-ray source can be projected onto the surface of the sample 3 to illuminate the sample 3.

[0009]

However, in the conventional X-ray microscope, since the image of the X-ray source is directly projected onto the surface of the sample 3, the intensity distribution of the X-ray source (light source unevenness) remains as it is. There is a problem in that it is very inconvenient when observing because it is projected on the screen and uneven illumination occurs.

The present invention has been made in order to solve such a conventional problem, and an object thereof is to provide an X-ray illuminating zone plate capable of significantly reducing the uneven illumination.

[0011]

A zone plate for X-ray illumination according to the present invention is for X-ray illumination in which a transparent ring zone that transmits X-rays and a non-transparent ring zone that does not transmit X-rays are concentrically alternately formed. In the zone plate, the gaps between the impermeable ring zones are the same.

[0012]

In the X-ray illuminating zone plate of the present invention, the intervals of the non-transmissive zones are set to be the same, so that the X-rays from the X-ray source are made into parallel light beams, and the sample is made to cancel the uneven illumination. Illuminated.

That is, in general, in an image-forming X-ray illumination system for forming an image of X-rays emitted from an X-ray source, X-rays must always be displayed on the sample.
Light source unevenness of the radiation source is projected, and uniform illumination cannot be achieved. Therefore, in the present invention, when illuminating a sample with X-rays emitted from an X-ray source, the X-rays are magnified by NA (Numerical Aperture) of an optical system.
ture; numerical aperture) to form parallel rays, and a parallel illumination optical system that illuminates the sample is used to solve the problem.

That is, the X-ray illuminating zone plate of the present invention illuminates the sample without forming the image of the X-ray source at all by breaking the image forming condition of the illumination optical system which has been a conventional image forming type. Is.

On the other hand, in general, in the illumination optical system of the X-ray microscope, the NA of the illumination optical system and the NA of the objective magnifying optical system need to be substantially equal to each other in order to use X-rays efficiently. It is necessary that the illumination area of the sample is necessary and sufficiently large, and it is desirable that there is no illumination unevenness.

The X-ray illuminating zone plate satisfying the above-mentioned conditions becomes parallel illumination in conformity with 1/2 of the NA of the magnifying optical system (in the case of an aperture of the annular zone, the NA of the center of the annular zone). It can be obtained by determining the condition.

That is, in FIG. 1, if the angle of the aperture to be fitted is θ, then θ = arcsin (NA / 2) or θ = arcsin (NA at the center of the annular zone), so sinθ = NA / 2. .

If the n-th boundary of the X-ray illumination zone plate 13 is r _n , the X-rays of the radial wavefront W ₁ emitted from the X-ray source K are the X-ray illumination zone plate 13.
After passing through, the parallel rays forming the wavefront W ₂ and forming the angle θ from the optical axis may be formed.

Therefore, the light ray emitted from the X-ray source K and reaching the center C of the X-ray illumination zone plate 13 and the light ray emitted from the X-ray source K at the _nth boundary r _{n of the} X-ray illumination zone plate 13. The optical path difference between the diffracted ray and the ray reaching C'in the figure is nλ / 2. When n is an even number, they strengthen each other.
When n is an odd number, they may be weakened to form the wavefront W ₂ .

That is, a ray passing through the center of the optical axis, r
passes through the _n, considering the optical path difference between the light rays reaching the wavefront W _2, a _{z = s + r n sinθ-} nλ / 2 s = z-r n sinθ + nλ / 2.

Focusing on s ² = z ² + r _n ² , and solving for r _n , s ² = z ² + r _n ² = z ² + r _n ² sin ² θ + (nλ / 2) ² −nλr _n sin θ + n
^{_{λz-2zr n sinθ r n 2}} (1-sin 2 θ) + r n (nλ + 2z) sinθ -nλz- (nλ / 2) 2 = 0 Thus, if put as _{^{ar n 2 + 2br n + c}} = 0, a = 1- sin ² θ b = {(nλ + 2z) sin θ} / 2 c = −nλz− (nλ / 2) ² .

In the X-ray region where λ is sufficiently small, n
When λ << z, it can be approximated as follows. ^{a = 1-sin 2 θ b} = zsinθ c = -nλz Therefore, r _{n is, r n = {- b +} (b 2 -ac) 1/2} / a = [- zsinθ + {z 2 sin 2 θ + (1 −sin ² θ) nλz}
^{1/2] / (1-sin 2} θ) ^{where, z 2 sin 2 θ» (1} -sin 2 θ) nλz, {z 2 sin 2 θ + (1-sin 2 θ) nλz} 1/2 ≒ zsinθ + (1-sin ² θ) From nλz / 2zθ, r _n = nλ / 2sinθ, and by using the X-ray illumination zone plate 13 in which the annular zones are approximately evenly spaced, it is possible to obtain a parallel light flux whose NA is approximately matched. The sample 3 can be illuminated.

The size of the X-ray source is converted into the NA distribution of the illumination light, and the NA of the X-ray taken in is converted into the size of the illumination area.

[0024]

The present invention will be described in detail below with reference to the drawings. FIG. 2 shows an embodiment of the X-ray illumination zone plate of the present invention.
A transparent ring zone 21 that transmits X-rays and an opaque ring zone 23 that does not transmit X-rays are concentrically formed alternately.

The intervals between the impermeable ring zones 23 are the same. Further, the line width of the transparent ring zone 21 is B ₁ , and the line width of the non-transparent ring zone 23 is B ₂ .

FIG. 3 shows an X-ray microscope optical system using the above-mentioned X-ray illumination zone plate 25. In this optical system, the laser light from the laser device 27 is condensed by the condenser lens 29. Then, the plasma X-ray source 31 is irradiated and X-rays are generated.

The generated X-rays pass through the X-ray illumination zone plate 25, illuminate the biological sample 33, pass through the zone plate 35 of the magnifying optical system, and reach the X-ray camera 37 which is an image pickup device. .

The sample 3 is directly fed from the X-ray source 31.
Since the 0th-order light emitted to 3 deteriorates the image, in this example, a shield plate 39 for cutting the 0th-order light is arranged in front of the X-ray illumination zone plate 25.

Generally, the NA of the zone plate 35 of the magnifying optical system is determined by the size r _{n of the} zone plate 35.
And the focal length f. In this example, the zone plate 35 of the magnifying optical system has a diameter of 0.1 mm and a focal length of 5
mm, NA 0.01 is used.

Therefore, when the wavelength of X-ray is 3 nm which is suitable for observing living things, the boundary r _n of the opaque ring zone 23 of the X-ray illumination zone plate 25 is r _n = 0.3 × n [ μm], and in this example, the interval A between the impermeable ring zones 23 is 0.3
The one of μm is used.

In the X-ray illumination zone plate 25 described above, however, the intervals between the opaque orbicular zones 23 are set to the same interval A, so that the X-rays from the X-ray source 31 are made into parallel light fluxes and uneven illumination occurs. Since the sample 33 is illuminated so as to cancel each other, it is possible to significantly reduce uneven illumination as compared with the conventional case.

In the embodiment described above, the transparent ring zone 2
The example in which the line width of No. 1 and the line width of the opaque ring zone 23 are different has been described. However, by making the line width of the transparent ring zone and the line width of the opaque ring zone the same, uneven illumination is further improved. It can be surely reduced.

[0033]

As described above, in the X-ray illuminating zone plate of the present invention, the intervals of the non-transmissive ring zones are the same, so that the X-rays from the X-ray source are made into a parallel light beam and the illumination is performed. Since the sample is illuminated so as to cancel out the unevenness, there is an advantage that the unevenness in illumination can be significantly reduced as compared with the conventional case.

[Brief description of drawings]

FIG. 1 is an explanatory diagram for explaining an operation of an X-ray illumination zone plate of the present invention.

FIG. 2 is a front view showing an embodiment of the X-ray illumination zone plate of the present invention.

FIG. 3 is an explanatory view showing an X-ray microscope optical system in which the X-ray illumination zone plate of FIG. 2 is arranged.

FIG. 4 is an explanatory diagram showing a conventional X-ray microscope.

5 is a front view showing the X-ray illumination zone plate of FIG. 4. FIG.

[Explanation of symbols]

 21 Transparent ring zone 23 Non-transparent ring zone 25 Zone plate for X-ray illumination

Claims (1)

[Claims] 1. An X-ray illuminating zone plate in which transparent X-ray transmitting zones and non-transmissive non-transmissive zones are formed concentrically and alternately. A zone plate for X-ray illumination characterized by the following.