DE2136761A1 - Diffraction grating - Google Patents

Description

SIEMEiTS AXTIEMGESEILSCHATi "Munich 2 _S 22, JUU1971 Berlin and Munich Witteisbacherplatz 2

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Diffraction grating

The invention "relates to a diffraction grating for diffraction τοπ Beams of light using two electrodes, between which a liquid crystal layer is arranged.

There are known some nematic liquid crystal layers show the so-called domains, if the liquid crystal layer between (transparent \ electrode is arranged, and if a voltage of the order of about 10 V is applied to these electrodes. These domains appear under the microscope as a regular strip-shaped Huster and represent an optical diffraction grating. Such domains are described, for example, in the journal "Journal of Chemical Physics" Vol. 39 (1963), pages 384 to 388.

It is known that just above the voltage threshold for domain formation in the liquid crystal layer form turbulent, disordered flows, so the domains are destroyed / grounded, whereby on the layer incident light is scattered in all directions. It is also known that turbulence and light scattering also increase with increasing tension.

In the journal "Physical Review Letters" Vol 24 (1970), No. 5, pages 209 to 212 and in the journal "Proceedings of the IEEE" Vol. 58 (July 1970), pages 1163 to 1164 describe controllable diffraction gratings, using certain cholesteric liquids

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Crystalline layers are produced in particular with mixtures of such. The lattice constant changes non-linearly with the applied field, and the lattice constant increases with increasing field strength. This effect is not very suitable for technical applications because it has the following further disadvantages in addition to the mentioned near linearity: A relatively high control voltage of about 500 Y is required. The cholesteric liquid crystal layers are not chemically stable and separate. Hysteresis phenomena occur, due to which different angles of deflection occur when the control voltage is increased than when the voltage is decreased. The Cemperaturbereich within which the diffraction is controllable is only about 1O ⁰ C, and is more stable liquid crystal layers above the room temperature, and further, the diffraction efficiency (the ratio of the undiffracted light to the diffracted) only about 1 ^.

The invention is based on the object of using liquid crystal layers to provide an electrically controllable To create diffraction grating in which the disadvantages of known controllable diffraction grating are avoided.

According to the invention, a nematic liquid crystal layer is provided in a diffraction grating of the type mentioned at the beginning for the electrically controllable diffraction of the light rays, the thickness of which is a maximum of 10 / U - preferably at least 1 / U and a maximum of 6 Ai - whose specific resistance is at least 10 ° and a maximum of 10 ^ 3 Ohm / cm - preferably at least 10 ¹ ^ and at most 10 ¹ ^ ohms / cm. In addition, a control voltage is connected to the electrodes, by means of which the diffraction angle can be controlled.

The diffraction grating according to the invention is characterized by high diffraction efficiency, since practically no diffuse

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Light scattering occurs. Another advantage of this diffraction grating can be seen in the fact that only relatively small control voltages are required for control Compare to the control voltages that are using cholesteric substances are needed. Another advantage of the invention is that as a liquid crystal layer nematic substances and mixtures of such substances are available that chemically and as a mixture are much more stable than known cholesteric substances, which were previously controllable as constituents Diffraction gratings were used. The diffraction grating according to the invention is thus long and reliable Operating time.

Another advantage of the diffraction grating according to the invention can be seen in the fact that it shows no hysteresis phenomena, i.e. that a certain control voltage has a certain Diffraction angle is assigned, regardless of whether this control voltage is increased by increasing a smaller control voltage or by lowering a higher control voltage.

Finally, the invention is also characterized by this from the fact that it can be used within a relatively wide temperature range. This temperature range is only limited by the temperature range in which the Substance is nematic because the influence of temperature on the domain width is negligible.

A mixture which is designated by the abbreviation N4 and has proven itself as a nematic liquid crystal layer consists of two substances. The first substance is:

N-p-Methoxybenzyl-IT ^ p-butylphenyl-diimide-II oxide The second substance is:

if-p-Methoxyhenzyl-Ii '-p-butylphenyl-diimide-N · oxide.

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Except for this mixture N4 of the first and second Substance has a third substance as a liquid crystal layer; proven, which is designated with the abbreviation MBBA and whose JTame is more detailed as follows:

p-methoxy-benzylidene-butyl-aniline.

A DC voltage of around 5 to 100 volts can be applied to the electrodes as a control voltage. An alternating voltage can also be applied as a control voltage with a maximum frequency of 10 kHz and a maximum amplitude of at least 5 V and a maximum of 100 V. amounts to. Finally, equal voltage pulses can also be applied to the electrodes as a control voltage, whose amplitude is at least 5 volts and a maximum of 100 volts and whose pulse repetition frequency is up to a maximum of 10 kHz. "'

The invention and exemplary embodiments are described below the same described with reference to Figures 1 to 11, wherein The same components and terms shown in several figures are identified by the same reference numerals. Show it

a liquid crystal cell in a basic representation,

a liquid crystal cell in transmission mode,

a liquid crystal cell in reflection mode, an arrangement for changing the color and intensity in transmission operation, an arrangement for changing the color and Intensity of the light in reflection mode, an arrangement for displaying characters • using segment-like electrodes,

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figure 1 figure 2 figure
figure 3
A. figure 5 figure 6th

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FIG. 7 shows an arrangement for displaying characters using matrix-like electrodes,

FIG. 8 shows an image converter in a basic representation,

FIG. 9 shows an arrangement for the analog display in a basic representation,

FIG. 10 shows an arrangement for deflecting the light in two coordinate directions and

FIG. 11 shows an arrangement for the spectral decomposition of light in a basic representation.

Figure 1 shows a liquid crystal cell consisting of the nematic liquid crystal layer 1, the electrodes 2 and 3 and the carrier plates 4 and 5. The electrodes 2 and 3 are either both translucent or there is only one translucent and the other reflective. A control voltage is applied to the two electrodes 2 and 3 is, then the longitudinal axes of the liquid crystal molecules are aligned in the manner of so-called domains, which ever have a width d. The thin lines represent the Longitudinal axis of the liquid crystal molecules. The thick ones Arrows indicate the direction of the superimposed material dripping. Because of the birefringence of the liquid crystals an optical diffraction grating is formed by such domains.

If the liquid crystal layer 1 consists of certain nematic liquid crystals, and if the layer thickness A has a certain amount, then the domain width d decreases linearly with increasing, at the two electrodes 2 and 3 applied control voltage (field strength), without diffuse, dynamic light scattering occurring. The liquid crystal cell shown in principle in Figure 1 is thus an electrically controllable diffraction grating, whose lattice constant can be changed linearly with the field strength. Only the component of the light is bent,

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the perpendicular to the domain longitudinal aclise (perpendicular to the image plane) swings.

The substance of the liquid crystal layer 1 should be as pure as possible and correspondingly high resistance so as not to allow the formation of turbulence. The tendency towards the formation of turbulence is greater, the less pure and the lower the resistance of the nematic substance. Substances with a specific T / resistance of at least 10 ¹⁰ HfCm and a maximum of 10 ¹² & cm have proven particularly useful.

The thickness A of the layer 1 should not exceed 10 / a. otherwise the build-up of turbulence is to be expected. Layer thicknesses of at least 1 ai and at most 6 / a have proven particularly useful.

/ ^l

The substance of the liquid crystal layer 1 should have a large refractive index anisotropy An = 0.2, i.e. in a liquid crystal layer in which all longitudinal axes of the molecules have the same direction, the refractive index in this classification differs from the refractive index perpendicular to this direction by more than 0.2. This refractive index anisotropy Δη should be at least 0.1 and at most Be 0.5. The greater this refractive index anisotropy, the greater the diffraction efficiency.

A substance that is sold under the trade name ΪΓ4 by E. Merck, Darmstadt and is formed from $ 60 (percent by weight) of substance B and from $ 40 (percent by weight) of substance C has proven successful as the liquid crystal layer 1 :
Substance B: CH ₅ OQ -N (O) = IS-Q ~ ^c 4 ^H q

Np-methoxybenzyl-li ^f -p-butylphenyl-diimide-II-oxide VPA 9/240/1068 '. ~ 7 -

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Substance C: CH, 0-Ol? = H (0) -6-C _A H _q

Np-Methoxybensyl-U ¹ -p-butylphenyl-diimide-iT ¹ -oxide The hexagonal structures are supposed to represent the benzene ring. -.

As the liquid crystal layer 1, there is another substance usable under the name:

p-Hethoxy-benayliden-butyl-aniline is known, the turter of the name MBBA is marketed and the can be characterized by the following structural formula:

As the liquid crystal layer 1, a nematic Use substance from LCI (Liquid Crystal Industries).

The temperature range within which controllable diffraction is possible is restricted only by the temperature range within which the liquid crystal layer is nematic, since the influence of temperature on the domain width d is negligibly small. Using the mixture 2Ϊ4 a controllable diffraction within the temperature range of 16 ⁰ C to 76 ⁰ C can be obtained. Using the substance MBBA the corresponding temperature range is 2Q ⁰ C to 41 ⁰ C, and using the agent developed by LCI the corresponding temperature range is from 18 ⁰ C to 8O ⁰ C.

If both electrodes 2 and 3 are translucent (transmission operation), then the effect of the diffraction grating causes the undiffracted light to move in the direction of the arrows 6 in diffracted in the direction of the arrows 7, the diffraction angle being dependent on the control voltage applied to the electrodes 2 and 3.

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If electrode 3 is translucent, but electrode 2 is reflective (reflection mode), then- ' by the action of the diffraction grating the undiffracted light in the direction of the arrows 6 as diffracted light in The direction of the arrows 8 is reflected, the diffraction angle again being different from that applied to the electrodes 2 and 3 Control voltage is dependent.

The voltage applied to the electrodes 2 and 3 S expensive can be a DC voltage in the range between 5 volts and 100 ToIt can be varied. When creating a DC voltage of 10 volts and the use of green light results in a diffraction angle of 2 ° and when applied a direct voltage of 100 volts results in a diffraction angle of 20 °. As a tax voltage but an alternating voltage with a frequency of up to 10 kHz can also be applied to electrodes 2 and 3. the obtained diffraction angles are of the amplitude uca of Frequency of this alternating voltage dependent. For example, at a frequency of 500 Hz and at an alternating voltage amplitude (maximum amplitude) of 20 V a maximum diffraction angle of 3 ° and with an alternating voltage of 200 V (maximum amplitude) results a maximum diffraction angle of 30 °. DC voltage pulses to the electrodes 2 can also be used as the control voltage and 3 are created. The angles of diffraction depend on the pulse repetition frequency and on the amplitudes of this direct voltage s impulses dependent. For example, results in a pulse repetition rate of 100 Rs and an A_mplitude of 10 V a diffraction angle of 2 ° and with an amplitude of 100 V a diffraction angle of 20 °.

All of these details relate to the control voltage to a layer thickness A of 6 / U. If the layer thickness A is lowered to 3 / U, then lower yourself

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Also, the stated control voltages by around $ 50.

FIG. 2 shows in principle an arrangement for controllably changing the color. This arrangement consists of the liquid crystal cell 10a, as shown in more detail in FIG. It is assumed that the two electrodes 2 and 3 of the liquid crystal cell 10a are transparent and thus the liquid crystal cell 10a is operated in transmission mode. The other light from the light source 12 is irradiated as parallel light onto the liquid crystal cell 10a using the collimator 11, which spectrally decomposes the parallel light. The directional filter 13 is located on the front side of the liquid crystal cell 10a and only allows light to pass through which is perpendicular to the directional filter. Depending on the control voltage applied to the electrodes 2, 3 (Figure 1), the domain width d changes and the domain ^{lattice becomes finer or coarser and the r} file of the diffracted light that is perpendicular to the directional filter 13 has a certain wavelength corresponding to one of the spectral colors. Since red light is more strongly diffracted than blue light, red light can pass through the directional filter 13, for example with a small control voltage (larger domain width d), and blue light can pass through the directional filter 13 with a larger control voltage.

By means of the diffuser 14, all light that the Directional filter 13 happens, again made divergent, so that it is in a large angular range for an observer 15 is visible. As a directional filter 13, for example, a fiberglass pane made of individual There is glass fibers with light-absorbing cylinder walls.

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The arrangement according to FIG. 3 also serves to controllably change colors that are emitted from a display surface, but the liquid crystal cell 10b is operated in reflection mode. The electrode facing the undiffracted light is therefore transparent, whereas the rear electrode is reflective. A radiated from the light source 12,
white light is returned to by means of the collimator 11
Converted parallel light and diffracted and reflected using the liquid crystal cell 10b. As with the arrangement shown in FIG. 2, the observer 15 sees colored light, the wavelength of which is dependent on the applied control voltage.

If, in the arrangements according to FIGS. 2 and 3, the light source 12 is the light of a certain wavelength (monochrome Light), then intermediate brightness levels can be achieved by applying appropriate control voltages be sucked into. Y / if pulsed control voltages are applied, then the apparent color or intensity shift equal to the instantaneous shift averaged over the period of the pulse train.

Through the combined use of two liquid crystal cells, the color and the brightness can be adjusted
of the light controllably · The arrangements according to Figures 4 and 5 are used for this.

According to FIG. 4- both liquid crystal cells 10a and 10aa are operated in transmission mode. The liquid crystal cell 10aa and the alignment filter 13a form a
electrically controllable intensity filter. Depending on the control voltage applied to the electrodes 2 and 3 (FIG. 1), the permeability of this becomes

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Intensity fliters controlled. If that in particular is off the liquid crystal cell 10aa and the directional filter 13a blocks the intensity filter formed, then becomes in the direction no light is emitted to the observer 15.

The liquid crystal cell 10a and the directional filter 13b form a color filter, the color of which is electrically controllable is. In particular, using this color filter, red, green and blue can be displayed one after the other Generate light in an electrically controllable manner. In combination with the liquid crystal cell 10aa and the directional filter 13a can display the individual colors in variable intensity be emitted to the observer 15. With a suitably rapid succession of the three colors, through Overlay a color and intensity modulated image.

With the arrangement according to FIG. 5, such a color- and intensity-modulated image can be produced using the Liquid crystal cell 10aa and the directional filter 13a created in reflection mode "

As is well known, xinter use of liquid crystal layers, which are arranged between two electrodes, characters are displayed. For example, this can be done in the so-called segment display according to FIG. 6 is done. Figure 6a shows fourteen different sigments 16, to which control voltages can be applied via the supply lines 17 are. The second electrode 18 (counter electrode) is shown in FIG. 6b with the corresponding leads 19 shown. When the control voltage is applied to some of the leads 17 and segments 16 on the one hand and to the leads 19 and the electrode 18 is applied on the other hand, characters are displayed on the screen, as shown, for example, in FIG. 6c.

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The principle illustrated with reference to FIGS. 1 to 5 can be applied to the segment representation according to FIG. For this purpose, one of the two electrodes 2 or 3 (FIG. 1) can be designed like the segments 16 according to FIG. 6a and the other electrode like the electrode 18 according to FIG. 6b. Using the arrangements according to FIGS Control voltages applied to the supply lines 17 and 19 are shown in colored characters. For example, the segments 16 and the electrode 18 according to FIG. 6 can be used instead of the electrodes of the liquid crystal cell 10a according to FIG The electrode of the liquid crystal cell 10b according to FIG. 3 and the W segments 16 according to FIG. 6a can be used instead of the transparent electrode of the liquid crystal cell 10b according to FIG. 3.

Through the combined use of the arrangements according to FIGS. 4, 5 and 6, color- and intensity-modulated Images of characters are effected.

Using liquid crystal layers can be ~ • It is known that individual characters can also be represented by combining several points. The two electrodes are between which the liquid crystal layer is located, formed point-like, as Figure 7 shows. In Figure 7a a series of such point electrodes 21 is shown, which are controlled via the supply lines 22. The corresponding second point-like electrodes are shown in FIG. 7a which are controlled via the switching point 24. By combined activation of individual electrodes 21 and 23 can be represented, for example, the character "F" shown in FIG. 7c.

The principle described with reference to Figures 1 to 5 can

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apply to the matrix representation explained with reference to FIG. For this purpose, for example, the electrode 2 can after 1 in the manner of the electrodes 21 (FIG. 7a) and the electrode 3 according to FIG. 1 like the electrodes 23 (FIG. 7b). Depending on the number of lines 22 and control voltage applied to node 24 and using the arrangements according to FIG. 2 or FIG. 5, the characters shown in FIG. 7c are reproduced in color, whereby the color depends on the applied control voltage. Using the arrangements according to FIG 4, 5 and 7 can be displayed with color and intensity modulated characters.

The front and back electrodes can also be formed as two mutually perpendicular transparent conductor rail systems _r as shown in figure 7d and 7e, each Kreuaungspunkt of the traces representing a pixel. The combination of based on the figure. 7 is particularly advantageous because in this case the problem of crosstalk due to the directional filtering using the directional filters 13, 13a, 13b is eliminated. In the case of matrix display devices with a large number of electrodes 23, it is advantageous to radiate polarized light onto the liquid crystal cells 10a and 10b according to FIGS. 2 to 5.

Color matrix screens with a larger image volume (up to 1 million pixels) are due to the relatively long Response times and the relatively short decay times, intermediate storage is necessary. The one in the patent application of class 74d with the file number P 20 37 676.5 (internal file number VPA 70/2107) described display device (which uses a ferroelectric ceramic layer as a buffer) is a liquid crystal cell 10 (Figure 1) can be used if the liquid crystal layer

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2 according to FIGS. 7 and 11 of this patent application P 20 37 676.5 by a nematic liquid crystal layer 1 according to Figure 1 of the present invention will. Such a display device modified according to the present invention can be used in the arrangement according to the figures instead of the liquid crystal cell 10a or 10b 2 and 4 baw. 3 and 5 of the present invention can be employed.

FIG. 8 shows schematically an image converter, consisting from two glass plates 26 and 27 on which the electrodes 28 and 29 are applied, further consisting of the liquid crystal layer 30, the layer 31 of a photoconductor and also of the intermediate electrode 33 · These Intermediate electrode 33 is formed from individual, mutually electrically isolated, reflective cells, whose Area determines the desired pixel size. The resistance of layer 31 of the photoconductor is dimensioned such that that in the dark it is significantly higher (for example by a factor of 10) than that of the liquid crystal layer, and when illuminated is significantly lower (also by a factor of 10) than that of the liquid crystal layer 30. A constant equilibrium is applied to both electrodes 28 and 29. Since the resistance of the photoconductor 31 at the exposed areas is substantially lowered, the voltage applied to the liquid crystal layer 30 changes. This corresponds to each cell of the intermediate electrode 33 has a liquid crystal element and one photoconductor element each. The voltages applied to the individual liquid crystal elements are dependent on the exposure of the associated photoconductor element.

If the principle described with reference to FIGS. 1 to 4 is applied to the image converter shown in principle in FIG

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is applied and the image converter in place of the liquid crystal cell 10b according to Figure 3 thus used in reflection, then imaged onto the photoconductor 31 (pro31zierte) ₉ low contrast intensity distribution of a visible or non-visible light radiation (for example, ultraviolet radiation or infrared radiation) into a visible high-contrast color distribution transferred. Doubling the intensity of an image point results, for example, in a Άο t / blue shift. The light reflected and diffracted on the reflective layer 33 is reflected against the directional filter 13 and a color image is emitted from the diffusing screen 14.

The liquid crystal cell 10c for analog display, shown in principle in FIG. 9, consists of the two carrier plates 4 and 5) the electrodes 3 and 40, the nematic /! Liquid crystal layer 1, the Sp aimungs source 43 and the leads to the electrodes 3 and 40. The electrode 3 has a relatively small longitudinal resistance, so that there is approximately the same potential at all points of this electrode. In contrast to this, the electrode 40 has a considerable series resistance such that a linear voltage drop occurs along the electrodes 3 and 40 and different voltages are applied to the liquid crystal layer 1. The liquid crystal cells 10 (FIG. 1) and 10c (FIG. 9) thus differ in the electrodes 2 and 40, respectively. The electrode 2 (FIG. 1) has a very low series resistance, so that there is an equal voltage drop in the control voltage along the liquid crystal layer 1. In contrast to this, the electrode 40 according to FIG. 9 causes various voltage drops along the electrodes 3 and 40 which change linearly in the present exemplary embodiment.

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If this liquid crystal cell 10c shown in FIG. 9 is used instead of the liquid crystal cell 10a according to FIG is set, and if also the light of a certain wavelength, for example red light in the direction of the arrow 41 (FIG. 9) is radiated, then the observer 15 sees a red stripe according to FIG. 2, deo: parallel ziir border line 4-2 of Figure 9 runs, and the can be moved along the carrier plate 5 as a function of the voltage of the voltage source 43. Included relates to this combined arrangement resulting from the combination of the arrangements according to FIGS. 2 and 9 the transmission operation.

In the case of the arrangement according to FIG. 9, it was previously assumed that the two electrodes 3 and 40 are translucent. But it is also possible for the electrode 3 to be translucent and make the electrode 40 reflective. Such a liquid crystal cell 10c can operate in reflection mode can be used instead of the liquid crystal cell 10b according to FIG. When again the light of a certain Color is irradiated (in the direction of arrow 44), then the observer 15 sees a colored stripe which depending on the voltage of the voltage source 43 is displaceable in the longitudinal direction of the carrier plate 5 «

By combining the arrangements according to FIGS. 4 and 9, white light being emitted by the collimator 11 and the liquid crystal cell 10aa is replaced by the liquid crystal cell 10c shown in FIG Arrangement suitable for displaying a colored strip. The color of this colored stripe is through the control voltage adjustable, which is applied to the electrodes of the Liquid crystal cell 10a is applied. This colored stripe can be changed by changing the voltage of the voltage source 43 ' be moved in the longitudinal direction of the carrier plate 5.

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This arrangement works in transmitted light - (Trans-r mission operation). Similarly, by combining the arrangements according to Figure 5 and 9 create an arrangement that works in reflection mode. In this Pail is the liquid crystal cell 10aa of Figure 5 through replaces the liquid crystal cell 10c according to FIG. The observer 15 sees a colored stripe, its color is adjustable by means of the control voltage at the electrodes of the liquid crystal cell 10b and its movement in The direction of the carrier plate 5 depends on the voltage of the voltage source 43.

The liquid crystal line 10 shown in principle in FIG. 1 is also used to deflect the light in one or two Coordinate directions can be used. An arrangement suitable for this is shown schematically in FIG. This arrangement consists of the laser 45 »of the liquid crystal cell 1Ox or 1Oy for deflecting the light in the direction χ or y, the stop diaphragm 46x or 46y and the plate 47. The in the X-direction polarized laser light is from the liquid crystal cell 1Ox with its aligned in the z-direction Domains in the xy plane deflected by the controllable angle ex * from the plate 47 by 90 ° in its direction of polarization rotated, then in the liquid crystal cell 10y Diit its domains aligned in the x-direction deflected in the yz plane by the controllable angle β. The non-deflected beams 48 and 49 of the zeroth diffraction order and the around -ct or. - {3 deflected beams 51 or «52 are using the stop diaphragms 46x and 46y hidden. Likewise, higher diffraction orders, which are generally much weaker in intensity, faded out. It is also possible to work in an area in which these higher diffraction orders are negligible. With control voltages that are applied to the switching points 53 and 54 and which are approx. 40 V

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gen, deflection angles of 4-5 ° and more can be achieved. Finally, using the arrangement shown in FIG. 10, the one emanating from laser 45 becomes Light beam deflected in the direction of light beam 55.

The liquid crystal cell 10a shown in FIG. 11 can also be used as a relatively coarse light emitter (monochromator). The white light emanating from the light source 12 is converted into a parallel light bundle using the collimator 11, and this is spectrally dispersed by the liquid crystal cell 10a, similarly to using a prism or an optical diffraction grating. By changing the desired spectral color to the electrodes of the liquid crystal cell 10a f applied control voltage can, using the diaphragm 56 to hide,

8 claims
11 figures

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Claims (7)

Claims 1.! Diffraction grating'for the diffraction of light rays by turning two electrodes between which a liquid crystal layer is arranged, characterized in that a nematic liquid crystal layer (1) is seen for the electrically controllable diffraction of the light rays, the thickness (A) of which is maximum 10 yu - preferably at least 1yu and a maximum of 6 / a - whose specific resistance is at least 1 cm and a maximum of 10 '5 "preferably at least 10 ^ X _1n ^ a maximum of 1012 ohm / cm - and that a control voltage is connected to the electrodes, by means of which the diffraction angle can be controlled. 2. diffraction α grating according to claim 1, characterized in that the plus-crystal layer (1) has a refractive index anisotropy which is greater than 0.1 - preferably greater than 0.2 - is. 3. Diffraction grating according to claim 1, characterized in that the liquid crystal layer (1) is a mixture (1T4-) »consisting of the substance n ~ p methoxybenzyl-li'-p butyphenyl ~ diimide-l-oxide and the substance ΪΤ- p-methoxybenzyl-H'-p-butyl-phenyl-diimide Ii ¹ is used oxide. 4. Diffraction grating according to claim 1, characterized in that that as liquid crystal slides (1) the substance p-methoxy-benzylidene-butyl-aniline (MBBA) is used. 5. diffraction grating according to claim 1, characterized ge ~ mark t that the control voltage is a DC voltage is applied to the electrodes (2,3), which is 5 to 200 Y. VPA _9/240/10 68 _{209 8B /} 0632 _- ²⁰ - BATH 6. diffraction grating according to claim 1, dad.urch characterized in that a control voltage
AC voltage is applied, the frequency of which is maximum
10 MiK and its maximum amplitude at least 5 V and a maximum of 200 V. 7. Diffraction grating according to claim 1, characterized in that that as S expensive voltage equalization pulses are applied to the electrodes (2,3), the amplitude of which is at least 5 "V and a maximum of 200 V. δ «diffraction grating according to claim 1, characterized in that that one of the two electrodes (40) has such a large longitudinal resistance that the two electrodes (3, 40) different in one direction - vorzugöWR.i se linear, changing - Sparurumgsaballe appear. VPA 9/24 0/1 OGfJ