JPH0432392B2 - - Google Patents

Description

[Detailed Description of the Invention] [Summary] The distribution of transmittance when an electron beam or a charged particle beam passes through a sample of an observation target is expressed by the amount of phase shift of interference fringes between a reference wave and an illumination wave. A two-beam image hologram image is created, and a moiré mask is superimposed on the two-beam image hologram image, and the amount of phase shift of the interference fringes is converted into phase contour lines by the moire method for observation. At this time, the phase of the reference wave is continuously changed with respect to the illumination wave, and at the same time, the moiré mask is moved in synchronization with the phase change while changing the offset amount at each synchronization. By integrating the image information during this time, it is possible to reproduce in real time clear phase contour lines with high contrast and no artifacts, and without using a low-pass filter.

[Industrial application field]

The present invention relates to a device that performs real-time reproduction of information regarding the complex amplitude transmittance (absolute amplitude and phase) of an observation target from a two-beam image hologram image generated using an electron beam or a charged particle beam as irradiation light. be.

[Problems to be solved by conventional technology and invention]

In a two-beam image hologram using a laser beam or a highly coherent electron beam, information regarding the complex amplitude transmittance of an object is observed as intensity changes and disturbances of interference fringes. In particular, when the object is nearly transparent and the amount of phase shift is large, the phase information of the object appears as a local position shift of equally spaced fine interference fringes.

FIG. 8 shows a conventional example of such an electron optical system for electron beam hologram photography.

In FIG. 8, the incident wave of the parallel electron beam 1 is divided into a reference wave that passes through the sample 2 and a reference wave that does not pass through the sample 2, each of which is focused by the objective lens 3 and focused on the first imaging plane 6. imaged.

Here, an electron beam vibrism 4 provided between the objective lens 3 and the first imaging surface 6 bends the illumination wave and the reference wave toward the optical axis and superimposes them on the first imaging surface 6. , forming interference fringes.

The interference fringes formed on this first imaging plane 6 include
As shown in FIG. 9, a phase shift occurs due to the reduction in the propagation speed of the illumination wave passing through the sample, and this is projected onto the second imaging plane 8 of the photographic film by the magnifying lens 7, forming a hologram. It is burned as. In order to visualize the phase shift of such interference fringes as contour lines, a method is generally used in which a hologram printed on photographic film is irradiated with laser light and a reconstructed image is obtained through an appropriate optical system.

However, such a two-stage reproduction method lacks real-time performance. One way to relatively easily perform real-time playback of such objects is to
This is a method in which a hologram image is captured and sampled using a TV imaging device, and the reconstructed image is displayed after digital calculation processing. However, this method requires a large amount of image data to be sampled and multiple calculations involving Fourier transform, so it requires a large amount of memory and is extremely difficult to perform real-time processing on the order of seconds.

Another reproduction method that can directly visualize the amount of phase shift of interference fringes in the form of contour lines is a method that uses moiré fringes. This method utilizes the fact that a mask pattern having the same pitch as the interference fringes of the hologram is directly superimposed on the hologram image, and the resulting moiré image exactly corresponds to the phase contour lines.

Although such a moiré method is originally capable of ultra-high-speed direct reproduction, it has the following problems, especially for electron beam holograms.

(1) The contrast of the interference fringes on the phosphor screen for hologram observation is actually quite small, so the contrast of the reproduced phase contour lines is reduced.

(2) An optical low-pass filter is usually used to remove the moiré mask grating image that creates breaks in the resulting phase contours, making them appear as continuous lines. This results in the loss of high spatial frequency information from the sample.

(3) In the case of electron beam holograms, it is not possible to change the intensity ratio of the illumination wave and the reference wave because there is no appropriate light attenuation means, and as a result, unnecessary mutual interference between strong scattered waves from the observation sample occurs. Artifacts caused by this cannot be removed.

The present invention aims to solve the above-mentioned problems in a two-beam image hologram reproduction device using an electron beam or a charged particle beam.

[Means to solve the problem]

The present invention continuously changes the phase of the reference wave, and moves the moiré generation mask pattern in synchronization with the phase change of the reference wave while sequentially changing the offset amount, and generates one cycle or multiple cycles of the moiré generation mask pattern. By integrating the image, the contrast of the phase contour lines is improved, and the grating image of the moiré mask and artifacts in the phase contour lines are removed.

The basic configuration of a real-time reproduction device for a two-beam image hologram using an electron beam or a charged particle beam according to the present invention, which has been embodied in this manner, is shown in FIG. 1 by way of example. Although FIG. 1 shows an example using an electron beam for convenience, the principle is the same when a charged particle beam is used.

In FIG. 1, reference numeral 1 denotes a parallel electron beam as a source of destruction, and two areas are defined in advance, one for illumination and one for reference. In the following description, the electron beam will be treated as a wave, and the electron beams in each area for illumination and reference will be referred to as an illumination wave and a reference wave.

2 is a sample placed within the illumination area and transmitted by the illumination wave.

3 is an objective lens that focuses the input parallel illumination wave and reference wave.

Reference numeral 4 denotes an electron beam biprism, which bends the illumination wave and the reference wave toward each other so that their respective regions overlap.

Reference numeral 5 denotes a phase variable means, which acts on the electron beam biprism 4 to continuously vary the phase of the reference wave relative to the illumination wave.

6 is a first imaging surface, and interference fringes are formed on the surface according to the phase difference between the illumination wave and the reference wave. At this time, a phase change that occurs when the illumination wave passes through the sample 2 appears as a distortion (shift) of the interference fringes.

A magnifying lens 7 enlarges and projects the image on the first imaging surface 6.

8 is a second imaging surface, and is provided with a fluorescent screen to form a hologram image.

9 is a moire mask having a periodic grating.

Reference numeral 10 denotes a moire mask moving means, which is controlled to move the moire mask 9 in a direction perpendicular to its periodic grating.

Reference numeral 11 denotes an imaging means that images a hologram image of the second imaging plane 8 through the periodic grating of the moiré mask 9 and converts it into a video signal.

Reference numeral 12 denotes a controller which controls the phase variable means 5 and the moire mask moving means 10 to synchronize with the phase change of the reference wave with various offset amounts and to move the moire mask to follow.

13 is an image integrator which, under the control of the controller 12, inputs the input image for n periods (n is an integer of 1 or more) of the phase change of the reference wave and the movement of the moiré mask that synchronizes with this with various offset amounts. Integrate with positive load weighting.

14 is a CRT display device, and an image integrator 13
The phase contour information output from is displayed on the screen.

[Effect]

The basic configuration of the present invention shown in FIG. 1 changes the phase of the reference wave, moves the moiré mask in synchrony with this, and integrates the image during that time to create contour lines. Since the moire mask pattern included in the image can be erased, the problem of missing high-frequency image information due to the use of a low-pass filter, which was a drawback of the conventional direct-cut moire mask method, is solved.

In addition, since the offset amount between the phase change of the same reference wave and the movement of the moiré mask is changed, image components that do not change with respect to the phase change of the reference wave are eliminated by performing image integration with positive load weighting. Therefore, it is possible to improve the contrast of phase contour lines and remove artifacts due to mutual interference of strong scattered waves from the observation sample.

FIG. 2 shows how the interference fringes move when the phase of the reference wave is changed with respect to the illumination wave. In the figure, Δφ represents the phase difference between the reference wave and the illumination wave, and for one fringe, Δφ=0, π/2,
The movement positions of the stripes in the cases of π and 3π/2 are shown.

With an image hologram, the outer shape of the target sample (image created by the incident wave) can be observed at the same time as the interference fringes.
This outer shape does not change at all in response to a change in the phase difference Δφ of the reference wave. At the same time, artifacts caused by interference between strong scattered waves emitted from the sample also do not change with respect to changes in the phase difference Δφ of the reference waves.

The principle of phase contour reconstruction using the moire method is that when a moire mask with the same fringe spacing as the interference fringe spacing is superimposed on the obtained hologram, the portion with fringe shifts intersects the lattice lines of the moire mask, resulting in a moire image. It depends on the appearance of contour lines.

〔Example〕

The details of the present invention will be explained below with reference to examples.

FIG. 3 is a block diagram of one embodiment of the present invention. This is a concrete embodiment of the basic configuration shown in FIG.

In FIG. 3, 20 is a parallel electron beam, 21 is a sample, 22 is an objective lens, 23 is an electron beam biprism, 24 and 24' are electrode plates, 25 is an electrode wire,
26 is a moving mechanism for the electrode wire 25, 27 is a variable voltage source for image shift correction, 28 is a first image forming surface, 29 is a magnifying lens, 30 is a striped fluorescent screen constituting a second image forming surface, and 31 is a striped fluorescent screen. A moving mechanism for the striped fluorescent screen 30, 32 an imaging camera, 33 a controller, 34 and 35 a D/A converter DAC,
36 is an image integrator, 37 is a CRT display device, 38
is a data processing device.

In the embodiment shown in FIG. 3, the phase change of the reference wave is performed by an electron beam biprism 23. The electron beam biprism 23 creates an electric field between two electrode plates 24, 24' and a thin metal electrode wire (usually 1 μm or less) 25, and moves the electrode wire 25 by a moving mechanism 26 using a piezoelectric element or the like. Drive back and forth in the direction of the arrow. This is equivalent to moving the optical biprism laterally, and changes the relative phase between the reference wave and the illumination wave.

Note that this causes a slight movement of the image on the first imaging plane 28, so the electrode plates 24, 24' are used as deflection plates and an appropriate voltage is applied from the variable voltage source 27 to compensate for the movement of the image. do. As a result, as shown in FIG. 2, only the interference fringes can be moved without moving the image.

Further, in the embodiment shown in FIG. 3, a striped phosphor screen 30 functions as a moire mask without providing a special moire mask.

When observing the movement of interference fringes on this striped phosphor screen 30, it appears that the phase contour fringes caused by moiré move continuously.

If the striped phosphor screen 30 is moved in a direction that follows the movement of the interference fringes due to the phase change of the reference wave, the phase contour lines caused by moiré will no longer move. However, the stripes on the fluorescent screen move.

Therefore, if the phase change of the reference wave is selected from 0 to 2π (or an integer multiple thereof) and is continuously changed, the striped fluorescent screen 30 is also moved in synchrony and the image is continuously integrated during that time.
moves by one period (or an integral multiple thereof), so as a result of integration, it uniformly changes to the background component, and the phase contour line remains. In other words, it can be seen that the low-pass filter conventionally used to remove the stripe pattern becomes unnecessary.

Although the above-mentioned method of synchronized movement of the reference phase and Moiré mask eliminates the need for a low-pass filter, the reproduced image contains not only the phase contour lines but also the sample image formed by only the incident light, In addition, artifacts caused by mutual interference between strong scattered waves remain, and these can cause serious problems, especially in the case of electron beam holograms. For the purpose of removing these, a double movement method is used.

First, convert the phase change of the reference wave from 0 to 2π, and convert the amount of movement of the corresponding moiré mask to the phase, and convert it to 0 to 2π.
An image is an image taken by changing continuously.

Next, the phase of the reference wave is set to 0 to 2π, and an image is obtained by continuously changing the movement amount of the moire mask from π to 3π. The difference between the images is that they respond to changes in the phase of the reference wave, and only the phase contour lines are reversed.

The sample image due to the incident wave and the mutual interference image of the scattered waves are unrelated to the phase of the reference wave and do not change from image to image. Therefore, by subtracting the image from the image, only the image component of the phase contour line can be extracted.

In the apparatus of the embodiment shown in FIG. 3, the moving mechanism 26 for the electron beam biprism 23, the variable voltage source 27 for image shift correction, and the moving mechanism 31 for the striped fluorescent screen 30 serving as a moiré mask are all controlled by a controller 33. Managed by DAC34,35
Configure them through. Since the amount of movement of the birhythm and the fluorescent screen is minute, it is quite possible to complete one period (or integral multiple) of movement in one frame (1/30 second) of the TV system. Therefore, if the image is integrated frame by frame by the image integrator 36, and the previous image is weighted positively and the previous image is weighted negatively under the control of the controller 33, It is possible to display phase contour lines in real time on a CRT in two frame times (~1/15 seconds). In this way, by using the double shift method and the positively loaded weighted integral of the image, unnecessary image information can be removed from the electron beam image hologram and phase contour lines can be reproduced at extremely high speed.

By incorporating the principle of fringe scanning interferometry, known as a high-sensitivity phase difference detection method, into the above method, quantitative information on the complex amplitude transmittance of the sample can be obtained, and the phase difference contour lines obtained by amplifying the phase difference can be reproduced. be able to. For this purpose, image; reference wave phase change 0~2π Moire mask movement 0~2π Image; reference wave phase change 0~2π Moire mask movement 0~3π Image; reference wave phase change 0~2π Moire mask movement π/2~ 2π+π/2 image; reference wave phase change 0 to 2π Moiré mask movement π+π/2 to 3π+π/2 Four images are obtained and transferred to a data processing device (generally a digital computer) 38 to perform the following image calculations. First, we obtain I〓 _r (x, y) = (image - image) I〓 _I (x, y) = (image - image). Each of these processes is performed by the image integrator 3.
It is also possible to perform this in advance using the positive load weighted integral of 6. The spatial distribution of the phase delay of the complex amplitude transmittance of the object is φ(x, y), and the absolute amplitude transmittance is A(x,
y), then A(x, y)=k√ ² _r (,)+ ² (,)
(k: proportionality constant) φ (x, y) = tan ^-1 (I〓 _r (x, y) / I〓 _I (x, y
)). The phase contour line shown earlier is I〓 _r (x, y) or 1/K・A(x,y)・cos
(φ (x, y)). In addition to quantitatively finding the complex amplitude transmittance through such pixel-by-pixel calculations, we also calculate n・tan ^-1 (I〓 _r (x, y)/I〓 _I (x, y)), and calculate cos (nφ (x, y)), it is also possible to obtain an n-times phase amplified image.

The above calculation is normally realized in an off-line format, but since it is a pixel-by-pixel calculation, it can be sped up using dedicated hardware and a table lookup method. With a large amount of high-speed RAM, it is also possible to display online at video rates.

Next, another embodiment of the reference wave phase variable means applicable to the present invention is shown in FIG. In this implementation, the electron beam biprism 40 is fixed, and the deflection plates 39 and 41 provided before and after it are biased in opposite directions, so that the electron biprism moves relatively, so that the same effect as that of the electron biprism can be obtained. I'm trying to make it happen.

Next, other embodiments (part 1), (part 2), and (part 3) of moire masks applicable to the present invention are shown in FIGS. 5 to 7.

In the embodiment (part 1) of FIG. 5, an opaque mask pattern 44 is printed in advance on a glass plate 42 on which a fluorescent substance 43 is applied, and is equivalent to the striped fluorescent screen in the embodiment of FIG. It has the following functions.

In the embodiment (part 2) of FIG. 6, a reduction moiré mask 48 is provided outside the mirror body away from the fluorescent screen 45, and the light from the fluorescent screen 45 is taken out through a window 46, and is directed onto the reduction moiré mask 48 using an imaging lens 47. An image is formed, and the light passing through the reduction moiré mask 48 is projected onto the image pickup tube 40 via the relay lens 49. By moving the reduction moiré mask 48, it functions similarly to each of the embodiments described above.

The embodiment (part 3) of FIG. 7 uses an electronic mask pattern instead of using an optical moiré mask, and the electronic mask pattern generator 51 is synchronized with the raster scanning of the image pickup tube 50. The multiplier 52 generates a mask pattern signal, which is multiplied by the video signal in a multiplier 52.

〔Effect of the invention〕

As described above, according to the present invention, information regarding the complex amplitude transmittance of an object, especially the phase information, can be obtained directly in real time from the image of a two-beam image hologram generated using an electron beam or a charged particle beam as illumination light. Contour lines can be easily obtained. As a result,
Conventionally, the results of electron beam holograms were known only after developing the film and reproducing it with an optical system, but now it is possible to see the results on the spot, which has the effect of significantly streamlining the development, research, and evaluation of thin film materials.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the basic configuration of the present invention, Fig. 2 is an explanatory diagram of the phase change of the reference wave and movement of the fringe, Fig. 3 is a block diagram of one embodiment of the present invention, and Fig. 4 is the phase of the reference wave. An explanatory diagram of another embodiment of the variable means, FIG. 5 is a block diagram of another embodiment of the moire mask (part 1), FIG. 6 is a block diagram of another embodiment of the moire mask (part 2), and FIG. Fig. 7 is a block diagram of another example (part 3) of the moire mask, Fig. 8 is a block diagram of a conventional example of an electron optical system for electron beam hologram photography, and Fig. 9 is an explanation of the phase shift of interference fringes due to the sample. It is a diagram. In Fig. 1, 1: parallel electron beam, 2: sample, 3: objective lens, 4: electron beam biprism, 5: phase variable means, 6: first imaging plane, 7: magnifying lens, 8:
Second imaging plane, 9: moire mask, 10: moire mask moving means, 11: imaging means, 12: controller, 13: image integrator, 14: CRT display device.

Claims (1)

[Claims] 1. An illumination wave consisting of a part of a parallel electron beam or charged particle beam, a reference wave consisting of another part, and an objective lens that focuses the illumination wave and reference wave that have passed through the sample. a first imaging plane for forming an image of the focused illumination wave and the reference wave; and an objective lens and the first imaging plane for superimposing the illumination wave and the reference wave on the first imaging plane to generate interference fringes. It consists of a biprism installed between the two, a magnifying lens that magnifies and projects the interference fringe image formed on the first imaging plane, and a fluorescent screen, and projects the magnified interference fringe image to create a hologram image. a second imaging surface that displays a hologram image as a moire image; An imaging means for converting into a signal, an image storage means for accumulating the image signal, an image integration means for integrating the image signal over a designated period, and a phase variable means for changing the phase of the reference wave with respect to the illumination wave by acting on the biprism. means, a moire mask moving means for moving the moire mask in a direction perpendicular to the periodic grating thereof, a phase changing means and a moire mask moving means; and control means for integrating the image signal by instructing the image integration means to change the amount of offset between the images and the image signal, and to instruct the image integration means to specify one period or a plurality of periods of phase change and the polarity of the image signal. A real-time reproduction device for a two-beam image hologram using an electron beam or a charged particle beam.