DE2057183C3 - Device for acousto-optical light deflection - Google Patents

Description

solves that this medium consists of monocrystalline tellurium dioxide (TeO ₂ ).

The use of single crystals of tellurium dioxide as the light-deflecting medium has markedly increased the stability, the reliability and consequently the efficiency of the light deflection and further markedly reduced the capacity of the input voltage source and the production costs of a device with this medium.

In the following the invention is based on the Drawing explained in more detail in exemplary embodiments.

F i g. Fig. 1 is an explanatory perspective view of a one-dimensional acousto-optic apparatus Light deflection using only one unit of a single crystal of tellurium dioxide;

F i g. Fig. 2 is an explanatory perspective view of an apparatus for two-dimensional Acousto-optical deflection of light, whereby only one unit of a single crystal made of tellurium dioxide is used will;

F i g. 3 is an explanatory perspective view of an apparatus for two-dimensional acousto-optic light deflection using two units of a single crystal of tellurium dioxide, as

It will now be understood with reference to FIG. 1 the general arrangement and the principle of an acousto-optical Described light deflection according to the present invention. When ultrasonic waves passing through a are generated with a microwave source 2 in the range from VHF to UHF connected transmitter 1, are sent through a solid medium in a suitable direction, slight changes occur in the refractive index of this medium, which result in a lattice effect of this refractive index. When light rays 4 from a light source 5 onto the solid medium 3 at a certain angle with respect to this grating, some or all of these light rays that pass through this medium 3 pass through, deflected at a certain angle to their direction of incidence. This deflection angle the Light rays is essentially inversely proportional to the length of the acoustic waves that pass through this medium 3 run. Accordingly, a change in the frequency of the input signal 6 from the Microwave source 2 is fed to the transmitter, and consequently the acoustic frequency, the spatial Change the position of the deflected light beam 7 as desired. The passage of the deflected light rays 7 by an optical device 8, such as. B. a lens has a focus to the optical spot 10 in one Figure level 9 results. The aforementioned type of light diverter is conventional Usually, an acoustic absorber 11 on the back of the signal input surface of the deflecting medium 3 to be attached so that running acoustic waves enter this medium 3 in place of standing waves.

The present invention is characterized in that the deflecting medium 3 consists of a single crystal of rutile type tellurium dioxide (hereinafter referred to as TeO, abbreviated to). This single crystal is generally produced by the pulling method, whereby a good quality single crystal having a volume larger than a minimum size of 10-10-10 mm required for a deflecting medium can generally be produced. The single crystal of tellurium dioxide is of excellent optical quality and allows essentially all light with a wavelength of 0.35 to 5 μm to pass through. The crystal belongs to the tetragonal system, where ρ, ρ and ν in equations (1) and (2) have different values depending on the orientation of the crystal. Accordingly, different combinations of the direction of propagation of the ultrasonic waves and the direction of polarization of the light rays enable the figures of merit M and M 'to assume different values; some of these combinations are given in Table 1 below. For comparison, Table 2 only gives a combination of the direction of propagation of the ultrasonic waves and the direction of polarization of the light beams with reference to the single crystals of the known deflection media: LiNbO ₃ , a-HJO ₃ , PbMoO ₄ , Te or GaAs. In both tables, the longidutinal and shear (or transversal) waves are shown as the modes of the acoustic waves by the letters L and S, respectively. The values of M and M 'given there were obtained with optical waves having a wavelength of 6328 Å.

Table 1
Experimental results with a TeO ₂ element

Reproductive Acoustic wave speed weakening Vibration direction Displacement (· 10 ⁵ cm / sec) (db / cm) Type [001] direction 4.26 2.5 (at 500 MHz) L. [001] _ 4.26 2.5 (at 50OMHz) L. [101] - 3.64 - L. [100] - 2.98 1.5 (at 200 MHz) L. [110] - 0.617 6 (at 100 MHz) S. [101] [HO] 2.08 6 (at 100 MHz) S. [1,38,1,0] (010) S. [1,1,38,0]
[V®, 1.0] 0.93 5 (at 100 MHz) or [T, 1.38, 0] in (001)

Table 1 (continued)

Optical wave Polarization Figure of merit M. M ' Usable optical Vibration Reproductive direction (-10 - '"SeCVg) (• lO-'cm'sec / g) Wavelength range Type direction l [001] 34.5 142 (μπι) L. in (001) [001] 25.6 113 0.35 to 5 L. in (001) [010] 33.4 101 0.35 to 5 L. [101] [011] 20.4 42.6 0.35 to 5 L. [OH] arbitrarily 793 68.6 0.35 to 5 S. [001] [100] 77.7 76.4 0.35 to 5 S. [010] arbitrarily 210 41 0.35 to 5 S. [001] 0.35 to 5

Table 2
Experimental results with other elements

Reproductive Acoustic wave Displacement speed weakening Single crystal and
SchwincuncstVD direction direction (10 ^s cm / sec) (db / cm) UVl ITTIt l ^ h * 4 llp * "» J J ^ 11120] 6.57 0.15 (1GHz) LiNbO ₃ L [001] - 2.44 2.5 (500 MHz) Ot-HJO ₃ L (001) - 3.75 2.7 (500 MHz) PbMoO ₄ L [1120] - 2.20 - Te L [110] - 5.15 1.8 (200MHz) GaAs L

Optical wave Polarization Figure of merit M. M ' Usable optical hinkristau and
Schwinounßstvn Reproductive direction (• lO-'Kscc '/ g) (· 10 "'cm * scc / g) Toilet length range UVl IVTII IQb ** * (? Vl direction [1120] 7.0 66.5 (μΓη) LiNbO ₃ L [0001] UOO] 86 103 0.5 to 4.5 A-HJO ₃ L [010] JL [OOl] 37 124 0.4 to 1.3 PbMoO ₄ L in (001) [112M] 4400 10200 0.4 to 5.5 Te L [0001] 1110] 104 925 3.5 to more than 10 GaAs L UlO] 1 to more ulslS in (110)

Table 1 shows that the L-type acoustic wave propagating along the [001] direction of the TeO _a crystal used as a light blocking medium shows rather large values of M and Af 'and subject to very small transmission losses so that high frequency ultrasonic waves can be used. Therefore, the above-mentioned L-type acoustic waves are of very great importance for large-capacity deflection media and further have an advantage of moving at an accelerated speed due to their high acoustic speed. In contrast, the S-type acoustic wave which propagates along the [110] direction and causes a shift in the pIO] direction has a very low acoustic velocity and has an extremely large M value. As shown in Table 1, since ν has a value of 0.617 · 10 'cm / see and M has a value of 793 ^{· 10'"sec a} / g, the above-mentioned S-type acoustic wave enables a highly effective deflection medium to be produced , although this wave does not propagate very quickly. In addition, the L-type acoustic waves traveling along the [101] and [100] directions and the S-type acoustic wave show the lungs

If the [101] direction is running, the deflection efficiency is also quite good.

If the direction of propagation of the ultrasonic waves deviates from the [110] direction, the value of M decreases sharply. If z. B. in the case of an S-type acoustic wave propagating along the T10] direction and in the [T10] direction oscillates, the direction of propagation of this wave should deviate by 5 ° in the (001) plane, then the value of M will drastically change from 793, as in the table

βο shown to decrease to about 400. Even if the white of M is reduced to such an extent, a value of 400 is still considered to be conspicuously large, so that mun can guess that the aforementioned S-type acoustic wave is a very effective light al

steering effects. In this case, caution should be exercised since the S-type ultrasonic wave is not an entirely rhyming vibration type or mode, which results in ha dal) the direction of propagation of the energy and d

7 ~ 8

Direction perpendicular to the ultrasonic wavefront does not correspond to the photoelastic constant of other crystals, so that a large amount of over-specified, which are necessary with this abnormal Bragg reflection, which are connected with the construction:
must be respected. However, since this is not an essential;

technical problem in connection with the 5 * -Al »P ₃ (sapphire) P ₄₄ - = 0.085

Light deflection mil brings, the above-mentioned JP's _{44th-_} 0,022

S-type acoustic wave good for using Li I au, \ P ₄₁ = - 0.024

suitable with a light deflecting medium. , ρ __ .. q, “c

It was further found that the acoustic wave \ quartz \ p ⁴⁴ _ o'rui

of the S-type running along one of the directions [1,38,1,0], io ⁴¹

[1, 1,38, 0), [T, 1,38, 0] and [TM, 1, 0] of the above- It is therefore possible to run a light deflector from what is known as single-crystal TeO ₂ , a tem- per-crystalline TeO ₂ the large temperature coefficient of the acoustic speed of the photoelastic constant P ₄₄ is used. In addition it has 0. When changes in acoustic velocity are required, acoustic transverse waves occur in a light deflecting medium that travel along the [001] direction and in the (001) direction, the light rays will generally oscillate in directions or plane of this crystal which are deflected along those other than the predetermined one. (OOl) -plane run and the shift in the This occasionally interferes with the operation of a light- [O01] -direction, abnormal with a suitable deflector seriously. Therefore if a deflector let decaying rays of light interact. It is suggested that from a medium with a large 20 it is easy to foresee that a light deflector with this temperature coefficient of acoustic velocity construction has a much higher interaction between it, it is necessary that such a deflector deflects the acoustic waves and the light rays at a fixed temperature in a thermal show is used as the same kind of a conventional stat. The above-mentioned acoustic wave Lichtablenkcrs (see RW Dixon, IEEE Journal of the S-type, produced by the TcO ₂ - 35 Quantum Electronics according to the invention; Vol. QE-3, p. 85, 1967).
Medium running eliminates the need for the F i g. Figure 2 shows a system arranged so that

To subject the TeO ₂ medium to such a treatment, it enables a two-dimensional light deflection to be drawn. The value of M, which is given by this acoustic and that on the one-dimensional Lichtablcnkvor-Wcllc of the S-type, is 210, as in the direction of FIG. 1 is based. In the system shown in Table 1, a far smaller value than the 30F i g. 2 acoustical transversal or M-Wcrt of 793 is planted with another acoustic thrust through a monocrystalline medium along a wave of the S-type running along the [RO] direction, two equivalent [110] -directions that intersect is obtained. The said value of 210 is still much more at right angles intersecting, and optically greater than the values provided by other vibrational rays which are essentially along the [001] -direction types of acoustic waves. 35 run, interact with these thrust

When the direction of propagation of the acoustic waves is brought so that they ab-waves in two dimensions be bent by the [1,38, I, 01 -direction in the (001) -Ebcnc. The reference numerals of FIG. 2 cntabwcicht, shows the temperature coefficient of the acutely speaking those of FIG. 1, and its description is The larger speed of these waves has been omitted.

Changes. However, if the above figure 4 »F i g. 3 is another two-dimensional deviation from this [1,38, 1, O] direction in a system that is a modification of that of FIG. 2 narrow range of z. B. less than L 2.5 ° fills shows. The system of FIG. 3 falls over two lights, the change in temperature remains to ablcnkmcdicn. Rays of light falling in a certain less than | 50 ppm limited. If this deflection is within 1.5 ° of deflection due to the first deflection, the values are 45 °, but a second deflection is used to deflect changes in the profile in less of a direction perpendicular to this. than ι 100 ppm. Therefore, if the deviations are as small as described above, the polarization direction of the small as described above, the light incident in the first and second medium will be; deflecting be suitable medium, its behavior radiation suitable to spin, this is achieved in that j to satisfy \ ways depending on the requirements of this research medium 30 between the first and second medium comprises a dcrungcn full. suitable optical device for rotating the

The above medium, which is used as a light deflector polarization plane, such as. B. an A / 2 plate 12, ge

' is used, takes advantage of the phenomenon of the so-called is brought. The reference numerals of FIG. 3 ent ·; normal Bragg reflection. A distracting speak to those of the fig. 2, and its description is medium that the so-called abnormal Bragg reflection 35 is omitted.

■ exploits, on the other hand, generally has no noticeable As in FIGS. 1, 2 and 3 takes a

; high degree of deflection. Such a light deflector is generally acoustic absorber 11 ^! directing medium, on the other hand, has the advantage that one and Ua to cause the acoustic waves

ί large number of deflected points of light received to progress through the medium. The conditions, 1 will. Accordingly, the use of the phenomenon βο that of a suitable material from which the the abnormal Brugg-Rcflexlon is promising for absorbers, are required that the

viewed the future. From the symmetry absorber it has a mechanical impedance qv that ^c . transactions of TeO 1st to recognize ₄ -Kristalls that this 1st approximately equal to that of the deflecting medium, and '^"J crystal has a noticeably large value of the photo- that occurring in the acoustic absorber' · elastic Konstuntc P has ₄₄ closely with of these 85 losses are great.

^r is related to abnormal Bragg reflection, It was the acoustic waves of the S-type that run along the

'· Found that the ΤοΟ, -Krlstall has a Ρ ,, - Wcri of [110] · and [1,38, 1, O] -direction of the above

^{c has} about 0.17. For comparison, the values below are monocrystalline TeO ₁ , have acoustic waves

ίο

speeds of 0.617 · ⁵ cm / sec or 0.930 · ΙΟ ⁵ cm / sec. These are exceptionally low values for a solid light deflecting medium. With a light deflecting medium using such S-type acoustic waves, metals such as. B. Al, Pb and a Pb-Sn-Bi alloy (a soft, low melting point solder) shown in Table 3 show excessively large ρ ν values, and in contrast, organic compounds such as epoxy resin and electron wax show very much small qv values. Accordingly, both groups of materials are unsuitable for use as absorbers. Briefly summarized are chalcogen glasses such. B. arsenic selenide glass and arsenic sulfide glass, matched in impedance relatively well with the above-mentioned S-type acoustic waves passing through a TeOj medium and also cause a noticeably large acoustic loss, so that such chalcogen glasses are good for use as absorbers are suitable.

The extent to which the acoustic energy of the shear waves traveling along the [110] direction is transmitted from the light deflecting medium to the absorber is _{96% for As 2} Se ₃ -GIaS and 96% for

ίο As ₃ S ₃ -GIaS 95%. Therefore, the chalcogen glasses fully serve the purpose as an absorber. In the case of shear waves traveling along the [1,38, 1,0] direction, a good impedance match is achieved, ie all acoustic waves are essentially transmitted into the absorber.

Table 3 Properties of absorber substances for acoustic shear waves

substance

Acoustic thrust wheels speed Mechanical density Reproductive ν (· 10 ⁵ cm / sec) Impedance judgment 0.617 () v (10 ^s g / cm ^: scc) 5.99 [110] 0.930 3.70 [1,38,1,0] 1.20 5.57 4.6 - 1.80 5.52 3.2 - 3.08 5.76 2.7 - 0.70 8.3 11.4 - 1.06 8.0 9.95 0.8 10.5 1.05 - 1.0 0.8 0.9 - 0.9

TeO ₂

As ₂ Se ₃ -GIaS ..
As ₂ S ₃ -GIaS ...

Al

Pb

Pb-Sn-Bi ....
Epoxy resin.
Elcktron wax

As stated above, the complete use of cine-crystalline titanium oxide as a light-deflecting medium enables the production of a light-deflector which, over a wide range from the visible to the infrared, exhibits much better properties than the devices known from the prior art. These excellent properties are derived from the excellent optical quality of the single crystal TcO, the cinfochcn production of TcO _a in the form of a single crystal, the absence of optical defects bc ^{1 of} this crystal and its constant quality.

The principle given above, monocrystalline TcOj to use as a light deflecting medium and optical rays with ultrasonic waves passing through this Allowing the medium to run, to alternate, is not only applicable to a light deflector, but even an optical modulator or an optical correlator with the same is excellent Effect as with the LiclUablenkcr.

For this purpose 2 sheets of drawings

Claims (2)

The following is: Claim: ^ the refractive index of the optical medium; Acousto-optic light deflection device P its photoelastic constant; with a device for transmitting S ρ its density, and ultrasonic waves through a medium in a suitable v dje above-mentioned acoustic phase velocity direction, a device for absorbing the density. Ultrasonic waves emerging from the medium and with a device for transmitting M is a measure of the intensity of the deflected light rays through this medium, thereby 10 light rays in relation to the ultrasonic waves, characterized in that this medium has a certain frequency, ie the Active single-crystalline tellurium dioxide consists. grail of distraction. M 'is a measure of this deflection efficiency, with a deviation tolerance from the Bragg condition given by the following equation Incidence transmission of ultrasonic waves through a measuring angle, which is fixed by the light rays and the ultradium in a suitable direction, a device for sound waves, absorption of the ultrasonic waves emerging from the medium and with a device for sjn Q = _A_ Sending rays of light through this medium. 2 Λ So far, a mechanical deflector has been widely used, which consists of a prism or a Q ψ. k j def is determined mechanically by the incident light mirror> n oscillation or rotation * 5 acoustic wave front; is offset, whereby incident optical rays, ", _. 1 »· 1.", ,, be spatially distracted. This type of deflector is the wavelength of acoustic waves, but has the disadvantage that, since it contains mechanically movable parts, long use is a factor in the wavelength of light rays. If a light deflecting medium for practical light spot is not manufactured with a markedly accelerated application, it is necessary to be able to travel at speed. Material of this medium taking into account the As a substitute for this, in recent years M / M 'ratios in accordance with the various deflectors have been proposed to select a standard of 35 required for this element. Electro-optic or solid deflection media based on ultrasound waves generally provide an acousto-optic effect. In particular, the good stability of the deflection in long-term use, the latter method includes an optical medium, and are subject to low acoustic losses, which is permeable to the light used, so that they are more suitable for practice than liquid whose surface is an electromechanical transmitter 4 ° or gaseous. Known materials that are vapor-deposited as solid or transducers, or two media of light deflecting media, include simple construction, mostly with a super-Liithiummetaniobat (LiNbO3), α-iodic acid (a-HJ03), are connected, whereby the Rays of light egg molybdate (PbMoO4) and thallium iodine bromide can be deflected in two dimensions. According to- (TlJBr) used in the visible range, the latter process offers economical 45 LiNbO3 but gives small values of M and M '; Advantages and is suitable to keep the device compact a.-HJO3 is unsuitable for use as a result. However, this type of deflector still exhibits its high water solubility; PbMoO4 tends to pose a crystalline problem in the selection of the material which is graphically used for cleavage and for optical analysis as an optical medium. Phrases unsuitable; TlJBr is unsuitable for the practical use of an optical medium for acousto-optical light because of its low deflection, which causes the interaction phenomenon of permeability for visible light. Taking advantage of other known solid light rays and ultrasonic waves, deflection media that only meet two extremely important requirements in the infrared range should be used: metallic tellurium (Te) and gallium arsenide (GaAs). These substances each have 1. The acousto-optical quality ₅₅ described later, but the drawbacks that a low Te Transparent numbers M and M 'show large values, and having lceit to infrared rays, while in GaAs 2. the acoustic attenuation coefficient is small. difficult is a large single crystal with good to maintain optical properties. To further increase the speed of movement the object of the invention is to provide a solid medium To indicate a spot of a deflected light beam which is suitable for acousto-optic light deflection, it is desirable that a large acoustic over a wide range of wavelengths from the visible phase velocity perpendicular to the acoustic wave to the infrared is suitable, furthermore the large wave front is obtained. Values of M and M ' and other excellent phy- The above-mentioned acousto-optic figures of merit M should have physical properties, and the outside and M ' are defined by the following equations: 65 which should show different effects if one Light rays and ultrasonic waves in each M = «V / e» ⁾ allows 3 (1) different directions to pass through. M ' = rPp ^ QV . (2) According to the invention, this object is achieved by