JPH02298983A - Real-time reproducing device for double luminous flux image hologram using electron beam or charged particle ray - Google Patents

Abstract

PURPOSE:To reproduce clear phase contours in real time by moving a mask pattern for moire generation synchronously with the phase variation of a reference wave and integrating an image for one or plural cycles. CONSTITUTION:An electric field is produced between electrode plates 24 and 24' and a thin metallic electrode wire 25 and an electron-beam biprism 23 which reciprocates the wire 25 by a moving mechanism 26 varies the phases of a reference wave and an illumination wave relatively. A voltage is applied from a variable voltage source 27 to compensate the movement of an image and only interference fringes are moved without any movement of the image. When a striped fluorescent surface 30 is moved to follow up the movement of the interference fringes due to the phase variation of the reference wave, phase contours of moire do not move. For the purpose, the phase of the reference wave is varied continuously, the surface 30 is also moved synchronously, and integration is performed continuously during the period, so that the phase contours are left sine the surface 30 moves by one cycle. Consequently, the clean phase contours are reproduced in real time.

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 phase shift M 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 a highly pure phase image using the moire method for viewing. 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 while changing the offset amount for each cycle in synchronization with the phase change. 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.

[Prior art and problems to be solved by the 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 obtained from intensity changes and disturbances of interference fringes. It is observed as

Especially when the object is nearly transparent and the amount of phase shift is not 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 biprism 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. ,
Form interference fringes.

The interference fringes formed on this first imaging plane 6 include:

As shown in FIG. 9, a phase shift occurs due to a decrease 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 a contour pure, 9
A commonly used method is to irradiate a hologram printed on photographic film with laser light and obtain a reconstructed image through an appropriate optical system.

However, such a two-stage reproduction method lacks real-time performance. One way to perform real-time playback of such objects is relatively easy.

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 a large number of calculations involving Fourier transform, so it requires a large amount of memory and is quite difficult to perform real-time processing on the order of one second.

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

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

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

(2) An optical low-pass filter is usually used to remove the moiré mask lattice image that creates a break in the obtained phase contour line and make the single phase contour line appear as a continuous line. This results in the loss of high spatial frequency information from the sample.

(3) In the case of electron beam holograms, there is no appropriate light attenuation means, so the intensity ratio of the illumination wave and the reference wave cannot be changed, resulting in (1) unnecessary mutual interference of strong scattered waves from the observation sample; The 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 for Solving the Problems] The present invention continuously changes the phase of a reference wave, and moves a moiré generation mask pattern in synchronization with the phase change of the reference wave while sequentially changing the offset amount. 1
By integrating images for a period or multiple periods,
This method improves the contrast of phase contour lines, and also removes moiré mask grating images and artifacts in phase contour lines.

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 is shown in FIG. 1 by way of example. Although this example uses a charged particle beam, the principle is the same when using a charged particle beam.

In FIG.

Reference numeral 1 denotes a parallel electron beam as a wave source, and two areas are defined in advance for illumination and reference. In addition.

In the following explanation, the electron beam will be treated as a wave, and the electron beams in the 5 illumination and reference regions 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.

Reference numeral 3 denotes an objective lens that focuses the parallel illumination wave and reference wave that are applied by one person.

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, the phase change that occurs when the illumination wave passes through the sample 2 causes distortion of the interference fringes (
shift).

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

8 is a second image forming surface, and a fluorescent screen is provided thereon.

A hologram image is formed.

9 is a moiré mask having two periodic gratings.

IO is 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, which images the hologram image on 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 two-phase variable means 5 and the moiré mask moving means 10 to synchronize with the phase change of the reference wave with various offset amounts to move the moire mask to follow.

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

Reference numeral 14 denotes a CRT display device which displays phase contour information output from the one-image integrator 13 on a screen.

[Effect]

In the principle configuration of the present invention shown in FIG.

By changing the phase of the reference wave and moving the moiré mask in sync with this, the moiré mask pattern included in the first contour line can be erased by integrating the image during that time, which eliminates the conventional direct moiré pattern. This solves the problem of missing high-frequency image information due to the use of a low-pass filter, which was a drawback of the mask method.

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 the two-phase contour lines and to remove artifacts caused by 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 the movement position of the fringe in the cases of Δφ−〇, π/2゜π, and 3π/2 is shown for one particular fringe. There is.

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 external shape does not change at all in response to a change in the phase difference Δφ of the reference wave. Similarly, artifacts caused by mutual interference between strong scattered waves emitted from the sample also occur. It does not change with respect to a change in the phase difference Δφ of the reference wave.

The principle of phase contour line 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 contour lines will intersect with the lattice lines of the partial camoire mask with fringe shifts, and the contour lines will be formed as a moire image. By appearing.

〔Example〕

The details of the present invention will be explained below based on 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 Figure 3 *, 20 is a parallel electron beam, 21 is a sample, 22
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, and 28 is a first image forming The surface 129 is a magnifying lens, 30 is a striped phosphor screen constituting a second imaging surface, and 31 is a striped phosphor screen 3.
0 is a moving mechanism, 32 is a close-up camera, and 33 is a controller.

34 and 35 are D/A converters DAC, 36 is an image integrator, 37 is a CRT display device, and 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 biprism 23, which consists of two electrode plates 24, 24' and a thin metal electrode wire (usually 1 μm or less) 25. An electric field is created between the two electrodes, and the electrode wire 25 is reciprocated in the direction of the arrow by a moving mechanism 26 using a piezoelectric element or the like. 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 image forming plane 28, so the electric 8i temporary 24, 24' is used as a deflection plate,
A suitable voltage is applied from variable voltage source 27 to compensate for image movement. 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 are moving continuously.

If the striped phosphor screen 3o 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, the striped faint light surface 30 is Because it moves for one cycle (or an integral multiple thereof).

As a result of the integration, the background component uniformly changes, and the two-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 simultaneous movement method of the reference wave phase and the moiré mask eliminates the need for a low-pass filter, the reconstructed image contains not only one phase contour line but also the sample image formed only by the incident wave, and 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, the phase change of the reference wave is converted from θ to 2π, the amount of movement of the corresponding moiré mask is converted to the phase, and an image photographed while continuously changing from 0 to 2π is defined as image (2).

Next, the phase of the reference wave is set to 0 to 2π, and an image obtained by continuously changing the movement amount of the moiré mask from π to 3π is defined as image (2). The difference between image ■ and image ■ is 1 in the part that responds to the phase change of the reference wave.
Only the phase contours are inverted.

The sample image due to the incident wave, the scattering, and the wave phase pressure interference image are:
It is unrelated to the phase of the reference wave and does not change between images (2) and (2). Therefore, by subtracting image (2) from image (2), only the image components of the nine phase contour lines can be extracted.

In the apparatus of the embodiment shown in FIG. 3, the electron beam biprism 23 moving mechanism 26. Variable voltage source 27 for image shift correction. In addition, the movement mechanism 31 of the striped phosphor screen 30 that becomes the moiré mask is managed by the controller 33 and set through the DACs 34 and 35.Since the amount of movement of the biprism and the phosphor screen is minute, it is difficult to control the movement of the TV system. It is quite possible to complete one period (or integral multiple) of movement within one frame (1/30 second).

Therefore, by integrating the image frame by frame by the two-image integrator 36, and applying a positive weight to the previous image ■ and a negative weight to the previous image ■ under the control of the controller 33, two frames can be obtained. C in one hour time (~l/15 seconds)
It becomes possible to display phase contour lines on RT in real time. 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 highly sensitive phase difference detection method, into the above method.

It is possible to obtain quantitative information on the complex amplitude transmittance of the sample and to reproduce the phase difference contour lines amplified by two phase differences. For this purpose, image ■; reference wave phase change 0 to 2π.

Moiré mask movement O~2π Image ■: Reference wave phase change O~2π.

Moiré mask movement 0~3π Image ■: Reference wave phase change O~2π.

Image ■: Reference wave phase change 0 to 2π.

4 images are obtained and transferred to a data processing device (generally a digital computer) 38 to perform the following image operations.
First '1. (x, y) = (Image ■ - Image ■) L (x, y) = (Image ■ - Image ■) We obtain. Each of these processes can also be executed in advance by positive load weighted integration of the image integrator 36. The phase-lag spatial distribution of the complex amplitude transmittance of the object is defined as φ(x,
y),! ! ! Let the amplitude transmittance be A(x, y).

(k: constant of proportionality) It is determined by The phase contour lines shown earlier are.

7r(x, y) i.e. −・A (x, y)・cos
(φ(x, y)). Through such pixel-by-pixel calculations, the complex amplitude transmittance can be quantitatively determined.

・By calculating cos(nφ(x, y)), n
It is also possible to obtain a double phase amplified image.

Although the above calculations are usually realized in an offline format.

Because it is a pixel-by-pixel calculation, it is performed using dedicated hardware.

Speed-up can be achieved using a table lookup method. Also, if a large amount of high-speed RAM is used, online display at video rates is also possible.

Next, another embodiment of the reference wave phase varying means applicable to the present invention is shown in FIG.
．． 41 are biased in opposite directions so that an effect equivalent to the relative movement of electronic biprisms occurs.

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.
As shown in the figure.

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. Let it form an image.

The light passing through the reduction moiré mask 48 is projected onto the image tube 50 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 bridge image tube 50. A mask pattern signal is generated by the multiplier 52, which is multiplied by the video signal in a multiplier 52.

〔Effect of the invention〕

As explained above, according to the present invention, information regarding the complex amplitude transmittance of the object, especially the phase Equivalent purity can be easily obtained. As a result.

Conventionally, the results of electron beam holograms were known only after the film was developed and reproduced using 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 configuration diagram of another embodiment of the moire mask (part 1), and FIG. 6 is another embodiment of the moire mask (part 2)
Fig. 7 shows another embodiment of the moire mask (part 3).
), FIG. 8 is a configuration diagram of a conventional example of an electron optical system for electron beam hologram imaging, and FIG. 9 is an explanatory diagram of phase shift of interference fringes caused by a sample. 1 in Figure 1: Parallel electron beam 2: Sample 3: Objective lens 4: Electron beam biprism 5: Phase variable means 6; First imaging surface 7: Magnifying lens 8: Second imaging surface 9: Moiré mask 1 (l Moiré mask moving means 11tll Image means 12: Controller 13; Image integrator 14: CRT display device

Claims (1)

[Claims] An illumination wave consisting of a part of a parallel electron beam or a charged particle beam, a reference wave consisting of another part, and an objective lens that focuses the illumination wave and the reference wave that have passed through a sample. , a first imaging plane for imaging 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 in the middle, 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 as a hologram image. a second image forming surface to be displayed; a moire mask having a periodic grating and generating a moire image by superimposing the periodic grating on a hologram image on the second image forming surface; and capturing the generated moire image and transmitting an image signal. image storage means for accumulating image signals; image integration means for integrating image signals over a designated period; and phase variable means for acting on a biprism to change the phase of a reference wave with respect to an illumination wave. , a moire mask moving means for moving the moire mask in a direction perpendicular to the periodic grating thereof, a phase variable means and a moire mask moving means, and in this case, the phase change of the reference wave with respect to the illumination wave and the movement of the moire mask are controlled. control means for integrating the image signal by instructing the image integration means to change the amount of offset between the images and the period for one or more 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 charged particle beam.