JPS5842637B2 - laser beam angler - Google Patents

Description

[Detailed description of the invention] □Akira Honka is concerned with improvements to laser output stabilization devices.

Conventional □ laser output stabilizing devices are applied to laser oscillation devices that have a characteristic that the laser output is proportional to the discharge current, for example, in which argon or krypton is sealed.

That is, as shown in FIG. 1, such a laser output stabilizing device inputs a laser beam oscillated from a laser oscillation unit 1 into a beam splitter 2, and
The laser beam obtained by being transmitted through is used for the main purpose, and the laser beam obtained by being reflected by the -□it-mus splitter 2 is received by a photodetector 3.

That is, the laser beam incident on the beam splitter 2 is reflected on the outside of one side and the inside of the other side of the beam splitter 2, and is taken out as two systems of reflected laser beams and received by the photodetector 3. .

The laser beam received by the photodetector 3 is converted into an electric signal and compared with a reference voltage of a subsequent comparator circuit 4 to extract a power control signal.

This signal is then supplied to an excitation power supply unit 5 which includes a discharge current control circuit, and the signal obtained by this excitation power supply unit 5 controls the discharge current of the laser oscillation unit 1 to stabilize the laser output.

The laser oscillation unit 1 filled with argon or krypton has a discharge current-laser output characteristic as shown in Fig. 2, and the laser output increases or decreases in accordance with the increase or decrease in the discharge current. .

Therefore, we believe that if a part of the laser output is detected and the discharge current of the laser oscillation unit 1 is controlled, a constant laser output can be obtained, and a highly stable output can be obtained over a long period of time. It is being

However, the beam splitter 2 usually has 1. CI! L
A parallel flat plate made of glass or quartz having a thickness of ~2c/n is used, and the laser beam incident on the beam splitter 2 at a predetermined angle of incidence is reflected by the beam splitter 2 as shown in FIG. It is reflected on both sides, that is, one side outside 2a and the other side inside 2b, and even the laser beam itself! Considering that this has a divergence angle of about 1 milliradian, the 2 obtained by reflection from the beam splitter 2
There is a considerable risk of interference with systematic laser beams.

For example, in order to minimize the positional deviation between the optical axis of the laser oscillation unit 1 and the laser beam transmitted through the beam splitter 2 in relation to other optical systems, the beam splitter 2
When the thickness of the plate is made thinner, the two systems of laser beams reflected by the beam splitter 2 are already laser beams before they reach the photodetector 3, that is, as shown in FIG. or, as shown in FIG. 8, may interfere before reaching the photodetector 3.

The total amount of light from these two systems of laser beams that interfere with each other is no longer necessarily directly proportional to the laser output, and therefore, the power control signal taken out from the comparator circuit 4 is an erroneous signal fed back, and in reality it is not stable. It is not possible to obtain laser power.

In view of the above, the present invention sets the thickness of the beam splitter to a value that prevents the two systems of laser beams obtained by being reflected by the beam splitter from interfering with each other. The present invention provides a laser output stabilizing device capable of keeping the output of a laser oscillation part highly stable for a long period of time by using the laser beam obtained by the laser beam.

The device of the present invention is characterized by a beam splitter, and its fine light detector 3, comparator/rake circuit 4, etc. are the same as before, so please refer to Fig. 1 for detailed explanation. Omitted.

First, referring to FIG. 4, the thickness d of the beam splitter 40 is
Explain how to find.

That is, the laser beam diameter is D1, the plate thickness is d, and the incident angle is θ.
1. The refraction angle is θ2, and the refractive index of the beam splitter 40 is n.
l, the refractive index of air is n.

(=1), then from Snell's law, n I Sin
Since θ2 ” noSinθ, it becomes.

On the other hand, in order for the reflected laser beams a and b not to overlap, since BE>BA, the following relationship holds true.

Therefore, from equations (1) and (2), it becomes.

This equation (3) is calculated using only the beam diameter.
This is the formula for the plate thickness d, but if the distance to the light-receiving surface of the photodetector 3 is considered and the divergence angle is taken into account, the beam diameter at the light-receiving surface can be replaced with the beam diameter in equation (3). Bye.

Now, assuming that the beam divergence angle is θ radian and the distance between the beam splitter 40 and the light receiving surface of the photodetector 3 is l, the beam diameter D' at the light receiving surface is given by:

Substituting this equation (4) into equation (3), the plate thickness d of the -mus splitter 40 must be set to be Bi*.

Here, we will use a specific example to calculate the plate thickness d of the beam splitter 40.

Now, the wavelength of 0.5μ is applied to the quartz glass beam splitter 40.
When a laser beam of m is incident at an incident angle of 45°, the beam diameter is 1 mφ, the divergence angle is 11 mrad, and the distance from the beam splitter 40 to the light receiving surface of the photodetector 3 is 20 c.
IrL, n: 1.465, n□: 1, the plate thickness d of the beam splitter 40 is as follows.

That is, the plate thickness of the beam splitter 40 As d, It must be at least 1.6 peaks or 1.6 mm.

Note that the plate thickness d of the beam splitter 40 is a value that changes depending on various conditions, as determined from equation (5).

Beam splitter 40 with plate thickness d obtained in this way
A stable laser output can only be obtained by arranging the beam splitter 2 at the position shown in FIG. 1.

That is, the laser beam from the oscillator 1 is split by the beam splinter 40 into a transmitted laser beam and two systems of reflected laser beams, and each of the reflected laser beams is received by the photodetector 3 without interference.

The output of this detector 3 is sent to the excitation power supply unit 5 as a power supply control signal via the comparator circuit 2.

Since this power supply control signal is obtained in proportion to the laser beam output, stable laser output can be obtained over a long period of time.

As detailed above, according to the present invention, in the apparatus for controlling the laser output of a laser oscillation unit using two systems of laser beams obtained by reflection by a beam splitter, the thickness of the beam splitter is By setting and using values such that the two systems of laser beams do not interfere with each other, the light intensity of the two systems of laser beams can be made directly proportional to the laser output. Therefore, the laser oscillator can always provide stable laser output. It can be taken out.

This allows the laser output obtained using this device to be used for highly accurate applications, and the reliability of the laser oscillation device can be further improved.

[Brief explanation of the drawings] Figure 1 shows the constituent countries of a commonly used laser output stabilizing device, Figure 2 shows the relationship between discharge current and laser output, and Figures 3 a and b show the reflection of the laser beam. A diagram showing the state, FIG. 4 is an explanatory diagram for determining the plate thickness of the beam splitter in the present invention. 1... Laser oscillation section, 2, 40... Beam splitter, 2a... Outer side of one side, 2b
...Inner side of the other side, 3...Photodetector,
4... Comparator circuit, 5... Excitation power supply section.

Claims (1)

[Claims] 1. A laser beam oscillated by a laser oscillation unit and reflected by a beam splitter is detected by a photodetector, and the output signal of the photodetector is used to detect the laser beam of the laser oscillation unit. In a device that controls the center beam, the two systems of laser beams obtained by reflecting the vinyl splitter on the outside of one side and the inside of the other side of the beam splitter are prevented from interfering with each other. 1. A laser output stabilizing device, characterized in that the laser output is set to a certain temperature, and a two-system laser beam obtained by the vinyl splitter is made to enter the photodetector. □゛