JPH01216316A - Acousto-optical q switch element - Google Patents

Abstract

PURPOSE:To execute Q switching with a high diffraction efficiency by placing two pieces of acousto-optical elements so that the propagation directions of an ultrasonic wave are orthogonal to each other, and also, an incident laser light passes through the optical surfaces of two acousto-optical elements and emitted. CONSTITUTION:Two pieces of acousto-optical elements 6 provided with a transducer 2 for generating an ultrasonic wave of a longitudinal wave on one face of an acousto- optical medium 1 are placed so that the propagation directions of an ultrasonic wave which is propagated in the acousto-optical medium 1 are orthogonal to each other, and also, an incident laser light 3 passes through the optical surface of two acusto- optical elements 6 and emitted. That is, in case of the ultrasonic wave of a longitudinal wave, the diffraction efficiency is deteriorated in other polarized light direction than a specific polarized light direction of the incident light, therefore, two acousto-optical elements 6 are used and placed so that the propagation directions of the ultrasonic wave are orthogonal to each other, and also, the incident light passes through the respective optical surfaces, and divided into one piece each as a vector and covered in any polarized light direction. In such a way, a large output laser light of every polarized light surface can be brought to Q switching with a high diffraction efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an acousto-optic Q-switch element with high diffraction efficiency used in a high-output laser.

[Prior Art] Conventionally, in order to Q-switch a high-output laser using an acousto-optic Q-switch element, various technical improvements have been made as described below in an attempt to obtain high diffraction efficiency.

i) The width of the piezoelectric body of the transducer is locally widened or narrowed to locally concentrate the ultrasonic power.

ii) Increase the driving power.

1ii) A transducer that generates a longitudinal wave with a large figure of merit is provided.

-However, since there are restrictions on the overall shape of the Q-switch element and the aperture of the laser, there is also a limit on the size of the piezoelectric body of the transducer. In general, if the width of the piezoelectric material is widened, the diffraction efficiency decreases, and if the width is made narrow, the damage to the human power of the piezoelectric material increases, and there is a restriction that the width cannot be made smaller than the aperture of the laser. Therefore, the above method i cannot be expected to have a great effect.

In addition, the larger the drive power, the more difficult it is to manufacture the drive circuit, and the greater the amount of heat generated by the acousto-optic medium and transducer, the more likely failures such as cracks in the piezoelectric body occur, and the larger the cooling device becomes. , method ii above also has limitations. The above method iii has a drawback that the diffraction efficiency of longitudinal ultrasound waves is low in directions other than a specific polarization direction (direction perpendicular to the propagation direction of the ultrasound waves). Therefore, it has conventionally been difficult to obtain an acousto-optic Q-switch element that is small and has high diffraction efficiency.

[Problems to be Solved by the Invention] An object of the present invention is to overcome the above-mentioned drawbacks of the prior art.

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems, and includes two transducers each of which is provided with a transducer that generates longitudinal ultrasonic waves on one surface of an acousto-optic medium. Acousto-optic elements are arranged such that the propagation directions of the ultrasonic waves propagating in the acousto-optic medium are orthogonal to each other and the incident laser beam passes through the optical surfaces of the two acousto-optic elements and is emitted. An optical Q-switch element is provided.

As the acousto-optic medium of the present invention, quartz glass whose optical surface through which the laser light passes is coated with an antireflection film is preferable, and lead molybdate, tellurium oxide, and the like may also be used. Lithium niobate is used for the piezoelectric body of the transducer, and the polarization direction of the piezoelectric body is set parallel to the propagation direction of the ultrasonic wave so that longitudinal ultrasonic waves with a high figure of merit are generated. It is preferable to use aluminum, which is lightweight and has high heat dissipation properties, for the package, but other materials such as copper and brass can also be used.

[Function] In the present invention, since longitudinal ultrasonic waves have a large figure of merit for a certain plane of polarization, they work to increase diffraction efficiency, allowing the use of a small acousto-optic Q-switch element as a Q-switch for a high-output laser. is possible. The diffraction efficiency η is expressed as in equation (1), where M is the figure of merit and k is the coupling coefficient.

ηocsin"A5k"・(11M-k" of longitudinal wave ultrasound is approximately twice as large as that of conventional transverse wave ultrasound, and is determined by the factor A determined by the piezoelectric body shape, driving power, and laser wavelength.
If they are the same, the longitudinal ultrasonic wave has a larger η. However, in the case of longitudinal ultrasound, the diffraction efficiency decreases in polarization directions other than the specific polarization direction of the incident light. The diffraction efficiency can be increased by arranging the optical surface so that the incident light passes through it, and dividing the polarization direction vectorwise into one side and covering the other.

[Example] An example of the present invention is shown in FIG. The shape of the acousto-optic medium l made of lithium niobate is approximately a rectangular parallelepiped, which is the same as that used in conventional transverse wave ultrasound, and the ultrasound reflecting surface is cut obliquely into a tapered shape. The optical surface through which the laser beam 3 passes is made of ZrO□, Sin□, MgF.
A single-layer or multi-layer antireflection film such as a is provided. The transducer has two piezoelectric bodies measuring 1 x 21 mm, and the size of the electrodes on the piezoelectric bodies is I.
Q, 2X 20.2mm. The two acousto-optic elements 6 have ultrasonic propagation directions perpendicular to each other and a laser beam 3.
are arranged on a straight line so that the light passes through each optical surface and is emitted. The material of the package is aluminum, its overall shape is a rectangular body of 86×90×107 mm+, and the height of the optical axis of the laser beam 3 is 24 mm from the bottom surface. Each acousto-optic element 6 is held within the whole package by a frame lO via an aluminum package 11 (different from the whole package), as shown in FIG. Four rotation adjustment screws 7 are installed around the ball bearing 9 provided at the position where
Rotatably mounted. Two metal rods 8 are provided on the left and right sides of the ball bearing 9 to smooth the rotation of the acousto-optic element in the front and back direction, as shown in FIG. 2(b). In addition, as shown in FIG. 2(a), the rod 8 can be used to finely adjust the horizontal rotation of the acousto-optic element.
A clearance between the package 11 and the package 11 is provided. As shown in FIGS. 2(a) and 2(b), four rotation adjustment screws 7 allow rotation in any direction.

In addition, as shown in FIG. 2(c), four m1 rear movable groove screws 12 are attached to the frame lO so as to be able to move linearly in the front-rear direction.
The four corners of the upper surface of the package 11 are provided so that the four corners of the upper surface of the package 11 can be pressed and fixed. A cooling path through which cooling water passes is provided around the acousto-optic element 6, and a cooling water inlet/outlet 4 into which a 171 inch diameter joint is inserted is provided on the front of the package.
is provided. moreover.

A thermostat is connected to each acousto-optic element, and when the temperature exceeds a certain level, the power supply is stopped and the Q-switch operation is stopped. Drive frequency and drive power are 60
MIIz, 100W is optimal.

Figure 3 shows the diffraction efficiency (%) versus driving power (W) for an acousto-optic Q-switch element consisting of an acousto-optic Q-switch element of the present invention and one acousto-optic element using conventional transverse ultrasound. It is a graph showing values. Laser output c
w 5 W, aperture φ4 mm, multi-mode YAG laser with random polarization plane, wavelength 1.064 μm, 50 Ml1z, 100 W driving frequency, power, diffraction efficiency is approximately twice as much as the conventional 40%. No. 8
It is 5% and has an excellent effect.

[Effects of the Invention] The acousto-optic Q-switching element of the present invention is capable of Q-switching high-output laser light of any polarization plane with high diffraction efficiency, and has the advantage of enabling high-output laser pulses. It has a great effect. Therefore, it has the effect of expanding the range of materials to be processed by the laser, and at the same time making it possible to perform fusing and fine processing in a shorter time.

[Brief explanation of the drawing]

1 to 3 show examples of the acousto-optic Q-switch element according to the present invention, and FIG. 1 is a partially cutaway perspective view showing the basic configuration of the acousto-optic Q-switch element, and
Figures (a) and (b) are a front view and a side view showing the rotating structure of the acousto-optic element, and Figure 2 (c) is a plan view showing the back and forth movable structure of the acoustooptic element. The figure is a graph comparing the driving power and diffraction efficiency values of the present invention and a conventional acousto-optic Q-switch element. 1... Acousto-optic medium 2... Transducer 3... Laser light 6... Acousto-optic element force
1st time stone 2nd time o---4th time e month's 1L column g-t1 character ΩL switch red motoμ 3rd time

Claims (1)

[Claims] Two acousto-optic elements each having a transducer that generates longitudinal ultrasonic waves on one surface of an acousto-optic medium are arranged so that the propagation directions of the ultrasonic waves propagating in the acousto-optic medium are perpendicular to each other and two incident laser beams are connected to each other. An acousto-optic Q-switch element, characterized in that the acousto-optic Q-switch element is arranged to emit light through an optical surface of the acousto-optic element.