JPH0668035U - Acousto-optic deflector - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide an acousto-optic deflector which greatly expands the polarization angle or separation angle of diffracted light and is capable of high-speed angle modulation and has excellent responsiveness. [Constitution] Acousto-optic medium 11 satisfying the Bragg diffraction condition
Is an acousto-optic deflector that diffracts laser incident light by using. One or more prisms 15, 21, 22 are arranged on the diffracted light side 11A of the acousto-optic medium 11. The acousto-optic medium 11 is made of glass or a single crystal such as lead molybdate single crystal that satisfies the Bragg diffraction condition. The prisms 15, 21, and 22 having a light-transmitting property with respect to the laser light used are used, and the prism angle is set to 30 degrees or more. Prism 1
5, 21, 22 can increase the deflection angle or separation angle of the diffracted light.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an acousto-optic deflector applied to high-speed spectroscopy such as a laser microscope, a spectrum analyzer, and an acousto-optic filter in place of an angle modulation such as a polygon mirror or a galvano mirror. The present invention relates to an acoustooptic deflector capable of setting a large deflection angle, which is an angle formed by a 0th-order folded light and a 1st-order or more diffracted light.

[0002]

[Prior art]

Conventional acousto-optic deflectors have mainly utilized anisotropic Bragg diffraction using tellurium dioxide (TeO ₂ ) single crystals to obtain large angle modulation. This crystal has a peculiar property that when a transverse ultrasonic wave is generated from a plane inclined by a certain angle from a certain crystal axis, its traveling direction is greatly inclined from the axis.

FIG. 4 shows a typical anisotropic Bragg diffractive acousto-optic deflector. In the figure, 1 is an acousto-optic medium. The acousto-optic medium 1 is composed of the tellurium dioxide single crystal. 2 is an oscillator having a frequency of f _{1 to} f ₂ . Reference numeral 3 is a transducer which is in contact with the acousto-optic medium 1 and transmits ultrasonic waves into the acousto-optic medium 1 by a frequency signal from the oscillator 2. In the tellurium dioxide single crystal, when the wavefront normal direction of the ultrasonic wave is inclined by 5 degrees from the [110] axis, the traveling direction of the ultrasonic wave, that is, the energy propagation direction is inclined by about 45 degrees (the direction of arrow 4 in the figure). [110] transverse acoustic wave axis progression [110] axis displacement, because a small elastic constant _{(C 11 -C 12) / 2} , the sound velocity is very slow and 616m / sec. When the laser incident light 5 is incident on the acousto-optic medium 1 and the frequency of the oscillator 2 is driven in the range from f ₁ to f ₂ , in addition to the 0th-order diffracted light 6, the 1st-order diffracted lights 7 and f ₂ diffracted by f ₁ are emitted. The first-order diffracted light 8 diffracted by is obtained. The angle formed by the first-order diffracted light 8 by f ₁ and f ₂ is the separation angle. In addition, 9 is a sound absorbing material attached to the acousto-optic medium 1.

By the way, when the frequency of the oscillator 2 is f, the laser light wavelength is λ, and the sound velocity in the acousto-optic medium 1 is v, the angular displacement δθ between the 0th-order diffracted light and the 1st-order diffracted light is δθ = λf / (2 v) is approximated. In order to increase the angular displacement δθ, the slower the sound velocity v in the acousto-optic medium 1, the better. In this respect, the transverse wave elastic wave of the [110] axis traveling [110] axis displacement of the tellurium dioxide single crystal is excellent.

[0005]

[Problems to be solved by the device]

 However, the conventional acousto-optic deflector has the following problems.

(1) The conventional acousto-optic deflector is configured using the acoustic optical medium 1 that satisfies the anisotropic Bragg diffraction condition as described above, but this acousto-optic deflector provides high diffraction efficiency. To achieve this, the laser incident light must be in a specific polarization state (circular polarization). Further, the diffracted light due to this has a polarization state different from that of the incident light. That is, clockwise (or counterclockwise) circularly polarized light is required as laser incident light, and conversely, the circularly polarized light is counterclockwise (or clockwise) circularly polarized light. For this reason, the laser light source used must be circularly polarized light, but the polarization state of the laser light source is generally linearly polarized light. A plate (λ / 4 plate) must be used. As a result, the cost of parts increases.

(2) Further, since the diffracted light is circularly polarized light opposite to the incident light, the usage conditions are limited.

(3) Generally, the response of the acousto-optic deflector is better as the time (access time τ) required for the ultrasonic wave to cross the beam of the laser light is faster. There is a relationship of τ = D / v between the access time τ, the beam diameter D of the laser light, and the sound velocity v in the acoustooptic medium 1. The slower the sound velocity v, the longer the access time τ. This defeats the purpose of angularly modulating the laser light at high speed. On the other hand, the sound velocity in the conventional acousto-optic medium 1 is extremely slow at 616 m / sec, which is good for increasing the angular displacement δθ, but it is against the purpose of high-speed angle modulation.

(4) The acousto-optic medium 1 of anisotropic Bragg diffraction has a very low accuracy in the azimuth angle of the crystal, so that the yield rate is low. Therefore, the cost of the acousto-optic deflector increases in combination with the wave plate.

The present invention has been made in view of the above problems, and a first object of the present invention is to reduce the cost by eliminating the need for an expensive wave plate and using a material with a high yield rate for the acousto-optic medium. Especially. The second purpose is to use linearly polarized light as the incident light and to make the diffracted light linearly polarized light to eliminate the limitation of the use conditions. A third object is to provide an acousto-optic deflector which is capable of high-speed angle modulation and has excellent responsiveness. A fourth object is to provide an acousto-optic deflector that can obtain a large value of angle modulation by using Bragg diffraction without using anisotropic Bragg diffraction.

[0011]

[Means for Solving the Problems]

 In order to solve the above-mentioned problems, the acousto-optic deflector according to the present invention comprises: (1) a laser incident light is diffracted using an acousto-optic medium satisfying the Bragg diffraction condition, and the frequency is adjusted to rotate the diffracted light. In an acousto-optic deflector that changes the bending angle, one or more prisms that change the traveling direction of the diffracted light are disposed on the emission side of the acousto-optic medium that is the first-order or second-order or more diffracted light. The configuration is characterized in that the deflection angle with respect to the folded light or the separation angle of the diffracted light due to the difference in the frequency is greatly widened.

(2) In the acousto-optic deflector of the constitution 1, the acousto-optic medium is constituted by glass or a single crystal satisfying the Bragg diffraction condition.

(3) In the acousto-optic deflector of configuration 1 or 2, the prism has a property of transmitting the used laser light, and the prism angle is configured to be 30 degrees or more. And

[0014]

[Action]

 According to the above configuration 1, the deflection angle or the separation angle of the diffracted light can be increased by the prism arranged on the diffracted light emitting side of the acousto-optic medium. According to the configuration 2, since the acousto-optic medium is made of glass or single crystal that satisfies the Bragg diffraction condition, it is possible to efficiently obtain linearly polarized light with less restrictions on use conditions. According to the configuration 3, by using a prism that is transparent to the laser light used and has a prism angle of 30 degrees or more, efficient angular polarization of the diffracted light becomes possible. .

[0015]

【Example】

 Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[First Embodiment] FIG. 1 is a sectional view showing an acousto-optic deflector according to a first embodiment of the present invention.

Reference numeral 11 in the drawing is an acousto-optic medium. The acousto-optic medium 11 is made of lead molybdate (PbMoO ₄ ) single crystal. This lead molybdate single crystal has a high figure of merit as an acoustic optical medium. That is, since lead molybdate single crystal has a relatively low ultrasonic absorption coefficient, it can operate up to a driving frequency of about 500 MHz and has a high sound speed of 3630 m / sec. The birefringence, which is the difference between the ordinary and extraordinary ray indices, is small, and the amount of change in diffraction efficiency due to the difference in the polarization state of the laser incident light is extremely small.

Reference numeral 12 is an oscillator. The oscillator 12 is set so that its frequency can be changed from 60 MHz (f ₁ ) to 100 MHz (f ₂ ). Reference numeral 13 denotes a transducer which is in contact with the acousto-optic medium 11 and which is electrically connected to the oscillator 12 and propagates ultrasonic waves into the acousto-optic medium 11 by the frequency signal from the oscillator 12. Reference numeral 14 is a sound absorbing material that is in contact with the acousto-optic medium 11.

A prism for polarizing the traveling angle of the diffracted light from the acousto-optic medium 11 on the side of the emission surface 11 A (the right side surface in FIG. 1), which is the surface from which the laser light incident on the acousto-optic medium 11 is emitted. 15 are provided. The refractive index n of the prism 15 is set as appropriate according to the angle to be deflected. The distance between the acousto-optic medium 11 and the prism 15 is set appropriately. Since the prism 15 only uses its angle, the distance does not matter in operation, but it is better to provide the prism 15 as close to the acousto-optic medium 11 as possible for the miniaturization of the acousto-optic deflector. . Here, in the main cross section ABC of the prism 15, the apex angle (∠B AC) formed by the light incident side surface AB and the light emitting side surface AC is referred to as a prism angle. Conditions such as the prism angle, the material of the prism 15 (refractive index of the prism 15 with respect to the laser light used, etc.) and the incident angle of the laser light on the prism 15 are determined by the law of refraction and the law of refraction in order to obtain large angle modulation. The relation of geometrical optics must be satisfied. That is, the prism angle is φ, the incident angle at the incident side surface AB (the angle formed by the traveling direction of the light incident on the surface AB and the normal direction of the surface AB) is i ₁ , and the refraction angle (the light refracted at the surface AB is R _{1 is} the angle formed by the traveling direction and the normal to the surface AB, the incident angle at the exit side surface AC is r ₂ , the refraction angle is i _2, and the direction of the incident light to the incident side surface AB is the exit direction. When the deflection angle, which is the angle formed by the direction of the light emitted from the side surface AC, is ψ, the following relational expression is obtained according to the law of refraction and the relation of geometrical optics.

[Incident side surface AB] sini ₁ = nsinr ₁ [incident side surface BC] sini ₂ = nsinr ₂ [prism angle] φ = r ₁ + r ₂ [deflection angle] ψ = i ₁ + i ₂ −φ When the refractive index is n = 1.52 and the prism angle φ is 45 degrees, there is a certain relationship shown in FIG. 2 between the change of the incident angle i ₁ on the incident side surface AB and the change of the deflection angle ψ. From the relationship curve between the incident angle i ₁ and the shake angle ψ shown in FIG. 2, it can be seen that the larger the shake angle ψ, the greater the slope of the relationship curve. When this inclination is large, the deflection angle ψ changes greatly with a slight change in the incident angle i ₁ . That is, the difference Δψ {= ψ ₁ between the deflection angles ψ between the incident angle i ₁₁ and the refraction angle i ₂₁ when the frequency f ₁ = 60 MHz and the incident angle i ₁₂ and the refraction angle i ₂₂ when the frequency f ₂ = 100 MHz. −ψ ₂ = (i ₁₁ + i ₂₁ −φ) − (i ₁₂ + i ₂₂ −φ)} becomes large.

When laser light (wavelength 633 nm) from a He—Ne laser is used as the laser incident light, the separation angle of the first-order diffracted light by the acousto-optic medium 11 is 6.9 mrad (about 0.4 degrees). When the incident frequency i ₁₁ of the first-order diffracted light when the driving frequency f ₁ of the oscillator 12 is 60 MHz is 6 degrees, the deflection angle ψ ₁ = 47.7033 degrees. On the other hand, when the drive frequency f ₂ = 100 MHz, the incident angle i ₁₂ of the first-order diffracted light is 6.4 (6 + 0.4) degrees, and the deflection angle ψ ₂ = 44.6 592 degrees. Therefore, the difference between the deflection angles ψ is Δψ = 3.0441 degrees.

As a result, when the drive frequency of the oscillator 12 is frequency-modulated from f ₁ (= 60 MHz) to f ₂ (= 100 MHz), the separation angle of the first-order diffracted light emitted from the acousto-optic medium 11 is 0.4 degrees. However, by passing through the prism 15, the deflection angle becomes 3 degrees, which is about 10 times the separation angle.

The laser light used here is linearly polarized light. Further, FIG. 1 shows only the diffraction and refraction states at the driving frequency f ₁ (= 60 MHz).

As a result, unlike the conventional acousto-optic deflector using the acousto-optic medium 1 that satisfies the anisotropic Bragg diffraction condition, it is possible to use the polarization plane of the laser light as it is without the need for an expensive wave plate. Therefore, the cost of parts can be reduced. Further, the lead molybdate single crystal, which is the material of the acousto-optic medium 11, has a relatively large diameter and is pulled up quickly during crystal growth, so that the manufacturing cost can be reduced. Further, the prism can be made of inexpensive optical glass such as BK-7. By these, a low cost acousto-optic deflector can be provided.

Further, since the laser light incident on the acousto-optic medium 11 is linearly polarized light, the limitation on the use conditions is greatly eased as compared with the conventional anisotropic Bragg diffractive acousto-optic deflector.

Since the prism 15 is provided and its angle amplifying effect is utilized, an angle modulation of about 10 times can be obtained as compared with an acousto-optic deflector not using the prism 15.

Further, since the acoustic velocity of the acousto-optic medium 11 is 6 times as fast as that of tellurium dioxide which is a conventional acousto-optic medium, an acousto-optic deflector excellent in high-speed response can be realized.

[Second Embodiment] FIG. 3 is a sectional view showing an acousto-optic deflector according to a second embodiment of the present invention.

In the acousto-optic deflector of the present embodiment, a first prism 21 similar to the prism 15 is provided on the exit surface 11 A side of the acousto-optic medium 11, and the exit surface AC of the first prism 21 has a first prism 21. A second prism 22 made of the same material as the prism 21 is provided. The prisms 21 and 22 are arranged such that the refraction directions of the laser light by them are the same, that is, the laser light passing through the apex angle side of the first prism 21 also passes through the apex angle side of the second prism 22. ing. With this arrangement, the angular displacement is added as a whole.

The prism angle of the first prism 21 is φ ₁ , the incident angle on the incident side surface AB is i ₁ , the refraction angle is r ₁ , the incident angle on the exit side surface AC is r ₂ , the refraction angle is i ₂ , and the deflection angle is Let ψ ₁ be the following relational expression due to the bending law and the relation of geometrical optics.

[Incident side surface AB] sini ₁ = nsinr ₁ [incident side surface BC] sini ₂ = nsinr ₂ [prism angle] φ ₁ = r ₁ + r ₂ [deflection angle] ψ ₁ = i ₁ + i ₂ −φ ₁ The prism angle of the second prism 22 is φ ₂ , the incident angle at the incident side surface AB is i ₃ , the refraction angle is r ₃ , the incident angle at the exit side surface AC is r ₄ , the refraction angle is i ₄ , and the deflection angle is ψ _2. Then, the following relational expression is obtained.

[Incoming Side AB] sini ₃ = nsinr ₃ [Incoming Side BC] sini ₄ = nsinr ₄ [Prism Angle] φ ₂ = r ₃ + r ₄ [Swing Angle] ψ ₂ = i ₃ + i ₄ −φ ₂ 1st Letting δ be the angle between the exit side surface AC of the prism 21 and the entrance side surface DE of the second prism 22, δ = i ₂ + i ₃ . Further, the combined deflection angle by the first and second prisms 21 and 22 is ψ ₁₂ = ψ ₁ + ψ ₂ = i ₁ + i ₄ + δ- (φ ₁ + φ ₂ ) from the above equation.

Similar to the first embodiment, when the refractive index of each prism 21 and 22 is n = _1.52 and the prism angle φ is 45 degrees, the first-order diffracted light when the driving frequency f ₁ = 60 MHz is the first When the incident angle i ₁ incident on the incident side surface AB of the prism 21 is 6 degrees and the incident angle i ₂ incident on the incident side surface DE of the second prism 22 is also 6 degrees, the case of the driving frequency f ₂ = 100 MHz The combined shake angle, which is the difference between, is 6 (3 + 3) degrees.

As a result, a sufficiently large deflection angle can be obtained as compared with the case of using the conventional medium satisfying the anisotropic Bragg diffraction condition.

Although lead molybdate single crystal was used as the acousto-optic medium, the present embodiment is not limited to this, and other materials can be used as long as they satisfy the Bragg diffraction condition and have a high figure of merit as an acousto-optic medium. For example, other crystals satisfying the Bragg diffraction condition (for example, GaAs, GaPb, TeO ₂ ) or glass (for example, glass manufactured by Hoya Co., Ltd., AOT-5, AOT-401) or water may be used.

Although the prism apex angle φ is set to 45 degrees in the above-mentioned angular embodiments, if the angle is 30 degrees or more, it is possible to obtain the same operation and effect as described above.

Although the prism 15 is formed in a triangular shape, it is not limited to this shape and may be another shape such as a polygon.

In each of the above embodiments, the case where one prism 15 is provided and the case where two prisms 21 and 22 are provided have been described as examples, but three prisms are provided depending on the size of the angle at which the angle modulation is desired to be performed. The above may be provided.

[0039]

[Effect of device]

 As described in detail above, the present invention has the following effects.

(1) Since one prism is arranged on the diffracted light side of the acousto-optic medium, a large value of angle modulation can be obtained by using Bragg diffraction instead of anisotropic Bragg diffraction. (2) Since one or more prisms are further arranged on the outgoing light side of the prism, a larger value of angle modulation can be obtained.

(3) Since the acousto-optic medium is made of glass or a single crystal that satisfies the Bragg diffraction condition, linearly polarized light can be efficiently obtained with less restrictions on use conditions.

(4) Since the prism has a light-transmitting property with respect to the laser light used and the prism angle is configured to be 30 degrees or more, efficient angular polarization of the diffracted light becomes possible.

(5) By using Bragg diffraction, an expensive wave plate is not required, and a material with a high yield rate is used for the acousto-optic medium, so that the cost can be reduced.

(6) Since a material with a high sound velocity can be used as the acousto-optic medium, high-speed angle modulation is possible, and an acousto-optic deflector with excellent responsiveness can be provided.

[Submission date] March 24, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0035

[Correction method] Change

[Correction content]

Although lead molybdate single crystal was used as the acousto-optic medium, the present embodiment is not limited to this, and other materials can be used as long as they satisfy the Bragg diffraction condition and have a high figure of merit as an acousto-optic medium. , for example, Bragg diffraction condition is satisfied other crystalline (e.g. GaA s, gaPb, TeO ₂₎ and glass (e.g. Jolla Co. glass, AOT-5, a OT- 40) may be or water.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an acousto-optic deflector according to a first embodiment of the present invention.

FIG. 2 is a graph showing a relationship between a deflection angle and an incident angle on a prism.

FIG. 3 is a schematic configuration diagram showing an acousto-optic deflector according to a second embodiment of the present invention.

FIG. 4 is a schematic configuration diagram showing a conventional acousto-optic deflector.

[Explanation of symbols]

11 ... Acousto-optic medium, 12 ... Oscillator, 13 ... Transducer, 15 ... Prism, 21 ... First prism, 22 ...
Second prism.

Claims (3)

[Scope of utility model registration request] 1. An acousto-optic deflector that diffracts laser incident light using an acousto-optic medium satisfying the Bragg diffraction condition and adjusts the frequency to change the diffraction angle of the diffracted light. One or two or more prisms that change the traveling direction of the diffracted light are arranged on the exit side of the diffracted light of the second order or higher, and the deflection angle for the 0th order diffracted light or the separation angle of the diffracted light due to the difference in the frequency is increased Acousto-optic deflector characterized by widening. 2. The acousto-optic deflector according to claim 1, wherein the acousto-optic medium is made of glass or a single crystal satisfying a Bragg diffraction condition. 3. The acousto-optic deflector according to claim 1, wherein the prism has a light-transmitting property with respect to the laser light used, and the prism angle is set to 30 degrees or more. And an acousto-optic deflector.