JPH0239479A - Laser oscillator - Google Patents

Abstract

PURPOSE:To automatically return the title oscillator to optimum conditions even with an optical axis displaced by allowing control means to control drive means based on an output from laser light detector means so as to maximize the output and thereby changing an angle of an external mirror. CONSTITUTION:In normal operation, laser oscillation is started between a reflection mirror and an external mirror 5, and part of a laser light L passes through the external mirror 5 and is incident upon a photodiode 12 after passing through a through-hole 7a in an adjusting plate 7, a through-hole 8a in a support 8. The amount of the laser light L is converted to an electric output through the photodiode 12, and fed to control means 13 for monitoring at all times. When an angle (displacement angle) between the laser light L and a perpendicular line normal to the reflecting surface of the existence mirror 5 is 0 deg., forward and backward paths of the laser light are coincident to assure maximum intensity laser oscillation and further assure a maximum output of the photodiode 12. The output of the photodiode 12 is reduced even in any case of the displacement angle where it takes an angle other other than 0 deg.. Hereby, angular control for the external mirror 5 is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a laser oscillator, and more specifically, to an external mirror type laser oscillator that automatically controls the angle of an external mirror to always maintain the best laser oscillation.

(Prior art) Among various laser oscillators, external mirror type laser oscillators are
The external reflection mirror (external mirror) is replaceable, and the optical axis can be easily adjusted using this external mirror. Instead, it has the feature of directly using the high-density laser light inside the resonator, and for this reason, for example, when used in a scattered light type particle meter, it is possible to detect particles as small as 0.1 μm. It is suitable.

FIG. 6 shows an example of such a conventional external mirror type laser oscillator. In the figure, 1 is a discharge tube which is a light source, and a discharge part which is an excitation medium is enclosed, and a reflecting mirror 2 which forms part of a resonator is disposed at one end, and at the other end. A Brewster window 4 is provided. Inside the discharge tube 1 is a laser medium such as He-Ne or C.
A gas 3 such as o, etc. is enclosed. On the optical axis extension of the discharge tube 1, an external mirror 5, which forms another part of the resonator, is disposed opposite the Brewster window 4. The external mirror 5 is integrally fixed to an adjustment plate 7, and this adjustment plate 7 is fixed to a support plate 8 via a leaf spring 9.

The support plate 8 is fixed to a base (not shown),
Further, a plurality of adjustment screws 6 are screwed into this support plate 8, and the tips of each adjustment screw 6 are in contact with the adjustment plate 7. Therefore, by turning the adjustment screws 6 appropriately to change the position of each tip in the axial direction, the angle of the adjustment plate 7 and therefore the angle of the external mirror 5 can be adjusted as desired.

By the way, the angle of this external mirror 5 is very important in an external mirror type laser oscillator. That is, laser oscillation occurs between the reflecting mirror 2 disposed at one end of the discharge tube 1 on the opposite side of the Brewster window 4 and the external mirror 5, but at this time, as shown in FIG. The light beam emitted from the Brewster window 4 passes through the optical path A, reaches the external mirror 5, is reflected, and then passes through the same path as the outgoing path, that is, the optical path A, and must be incident on the Brewster window 4. For example, if the angle of the external mirror 5 deviates by θ as shown by the broken line and the reflected light from the external mirror 5 passes through the optical path B, the above relationship will not be satisfied and the laser oscillation will weaken or stop. . On the other hand, even if the discharge tube 1 moves and the optical axis shifts, the laser oscillation weakens or stops in exactly the same way.

By the way, as described above, when either the external mirror or the discharge tube is displaced, readjustment is performed by changing the angle of the external mirror, which is easier to adjust.

[Problem that the invention seeks to solve]

By the way, in the conventional external mirror type laser oscillator,
Adjustment of the external mirror 5 to make the optical axis optimal for laser oscillation was performed manually by turning the aforementioned adjustment screw 6. Therefore, it is necessary to adjust the angle of the external mirror 5 of the laser oscillator one by one by turning the adjustment screw 6 to obtain the best laser oscillation every time the environment, state, etc. of the laser oscillator changes, which is complicated.

In other words, for example, if the environmental temperature changes, each part of the laser oscillator will expand or contract in response to this temperature change, and the angle of the optical axis of the external mirror will eventually deviate from the optimal angle, weakening the laser oscillation, resulting in a decrease in output and eventually stopping the laser oscillation. This will lead to a situation. For example, if the angle of the external mirror is adjusted so that the output of the laser oscillator is maximized at room temperature (2.0 to 25°C), the practical operating temperature range is 5 to 25°C unless readjusted. It is limited to 35°C.

In addition, for example, when an external force such as an impact is applied to the laser oscillator after adjustment, relative positional and angular changes may occur in each part of the laser oscillator. In this case, the optical axis also shifts and the laser This will cause a decrease in output and eventually stop laser oscillation.

Furthermore, the optical axis may shift even in the absence of any mechanical misalignment. That is, the gas between the discharge tube within the resonator and the external mirror is usually air. In this case, it is assumed that the laser oscillates through the optical path A as shown in FIG. However, for example, when using a particle meter using a laser oscillator to measure particles in a gas other than air, when this gas is introduced into a resonator, the resonator must be placed in an atmosphere of this gas. becomes. In this case, due to the relationship between the refractive index of the material used for the Brewster window 4 provided in the laser discharge tube 1 and the refractive index of the gas, the laser beam moves in a different direction than when it was in the air. For example, the light passes through optical path B, causing the optical axis to shift, resulting in a decrease in the laser output as described above, and even a stoppage of laser oscillation.

As described above, the optical axis of a laser oscillator can shift quite easily, and the optical axis must be adjusted frequently during use. If the laser oscillator is built into equipment and the optical axis cannot be adjusted or is difficult to adjust, the operating temperature range will be limited as mentioned above, or the laser oscillator will be susceptible to mechanical shock, or if it is difficult to adjust the optical axis. If the angle of the external mirror is set based on the premise of use, there are problems such as the oscillation becoming weaker or not oscillating at all in gases other than air.

[Purpose of the invention]

An object of the present invention is to provide a new external mirror type laser oscillator that automatically adjusts the optical axis even when mechanical positional deviation or environmental changes occur and always maintains optimal laser oscillation.

Means for Solving Problem C] In order to achieve the above object, the present invention provides an external mirror type resonator comprising a light source section comprising an excitation medium and a laser medium, and a resonator having at least one external mirror. The laser oscillator includes: a laser beam detection means for converting the intensity of the laser beam generated by the external mirror type laser oscillator into a signal; a driving means for changing the angle of the external mirror; and a control means for controlling the driving means. Based on the output of the laser beam detection means, the control means controls the drive means to maximize the output, and changes the angle of the external mirror.

(Example) An example according to the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of a detection section of a light scattering particle meter using a laser oscillator to which the present invention is applied.

In FIG. 1, numeral 1 is a discharge tube which is a light source, and a discharge tube which is an excitation medium and a gas 3 such as He-Ne, Go, etc. which is a laser medium are sealed inside.

Further, a reflecting mirror 2 (not shown) forming part of a resonator is disposed at one end of the discharge tube 1, and a Brewster window 4 is disposed at the other end. Note that this discharge tube 1 is fixed to a base (not shown).

The Brewster window 4 is located on the optical axis extension of the discharge tube 1.
An external mirror portion 30 is disposed opposite to. This external mirror part 30 has the following parts: a support 8 fixed to a base to which the discharge tube 1 is fixed and having a through hole 8a formed therein, and a support 8 fixed to the support 8. A plurality of piezoelectric actuators 1 serving as driving means, an adjusting plate 7 having a through hole 7a and abutting against the driving shaft 11a of the driving means 11, and a leaf spring connecting the adjusting plate 7 and the support body 8. 9
, a spring 10 for drawing the adjusting plate 7 to the support 8, and an external mirror 5 fixed to the adjusting plate 7 and forming another part of the resonator through which a part of the laser beam can pass.
and a photodiode 12, which is a laser beam detection means, arranged on the axis of a through hole 8a formed in the support 8, on the back side of the external mirror 5, and behind the support 8.

Note that, for example, when the adjustment plate 7 and the support body 8 are made of a transparent material, the through holes 7a and 8a are unnecessary.

Reference numeral 13 denotes a control section, to which the photodiode 12 is connected, and the control output of this control section 13 is connected to the plurality of drive means 11. Note that this control section 13 is supplied with electricity from the outside.

As shown in detail in FIG. 2, numeral 31 is an inlet nozzle from which a sample containing fine particles to be measured is blown out, and a gas sample 32 blown out from this inlet nozzle 31 intersects with the laser beam and is sucked through an outlet nozzle 33, and then Emitted from the particle meter. At this time, when the fine particles pass through the irradiation area 3.4 intersecting the laser beam, the fine particles emit scattered light, so this scattered light is focused by the lens system 35 and guided to the photoelectric conversion element 36, and the photoelectric conversion is performed. The output of the element is subjected to electrical processing, and finally measurement results such as the particle size distribution and number of fine particles are obtained.

Next, to describe the operation of the laser resonator of the above embodiment, under normal conditions, laser oscillation occurs between the reflecting mirror (not shown) and the external mirror 5, and a part of the laser beam is transmitted externally. The light passes through the mirror 5, passes through the through hole 7a of the adjustment plate 7, and further passes through the through hole 8a of the support body 8, and hits the photodiode 12.

The amount of this laser light is converted into electrical output by the photodiode 12 and sent to the control means 13, where it is constantly monitored. By the way, when the angle of the external mirror 5 is changed along any one direction, the magnitude of the output of the photodiode 12 will be distributed as shown in FIG. That is, when the angle θ (deviation angle) between the laser beam and the perpendicular to the reflective surface of the external mirror 5 is Oo, the forward and backward paths of the laser beam coincide, and laser oscillation with maximum intensity is obtained. The output of the photodiode 12 also becomes maximum. No matter which direction the deviation angle θ deviates from Oo, the output of the photodiode 12 will decrease. This fact is utilized to control the angle of the external mirror.

That is, assuming that the angle of the external mirror 5 deviates from the laser beam by θ1, the control means 13 first stores the current magnitude (I,) of the output of the photodiode 12. Then, the drive means 11 described above is driven to drive the drive shaft 11a.
Then, the angle of the adjustment plate 7 and therefore the external mirror 5 is slightly changed by a certain value in a certain direction, and the photodiode 12 at this time is
Obtain the magnitude of the output (r2) and compare it with the value before changing.

If this result decreases, i.e. I, >1. When this happens, it is determined that the control is in the wrong direction, and the driving means 11 is controlled to change the angle in the opposite direction, and the above-described operation is repeated. On the other hand, if the controlled result increases, that is, ■1≦
At the time of I2, it is determined that the output of the photodiode 12 has not yet reached the maximum value, and the above-described process is repeated. That is, the angle of the external mirror 5 is further changed in the same direction, and the angle is compared and determined with the value immediately before the change. Continuing this kind of action,
As a result of changing the angle, the output size of the photodiode 12 (
When I2) is smaller than the output magnitude (I,) before changing the angle, that is, I>12, it is determined that the maximum value has been exceeded, and the driving means is set so that the direction of changing the angle is reversed. 11. Since this operation is continued continuously, the angle of the external mirror 5 is kept very close to the angle at which the output of the photodiode is maximum. Incidentally, since a plurality of drive means 11 are provided and support the adjustment plate 7 at multiple points, the adjustment plate 7, and therefore the external mirror 5, can be adjusted in angle in any direction, and control in only one direction is insufficient. In some cases, the process of performing the same control as described above in another direction different from the above-mentioned direction (for example, the orthogonal direction) is included, and by performing control in both directions alternately, the best external mirror for laser oscillation can be obtained. The angle of 5 is automatically maintained.

An embodiment using a microcomputer for the above-mentioned control will be shown below.

FIG. 4 shows an embodiment of the configuration of the control means 13.

41 is a microcomputer section, which includes a CPU and a RAM.
, program ROM, and registers.

42 is an A/D conversion means, into which the voltage output from the photodiode 12 mentioned above is input and converted into a digital value. This A/D conversion means 42 is connected to the microcomputer section 41 through a pass line.

Reference numeral 43 denotes a D/A conversion means, which is connected to the microcomputer section 41 by a pass line, and whose conversion output is connected to the drive means 11 described above.

In this embodiment, two D/A converting means are provided to adjust the angle of the axis of the external mirror 5 in any direction, and each drives two corresponding driving means 11.

In the control means 13 configured in this way, the microcomputer section 41 takes in the output of the A/D conversion means 42, that is, the output of the photodiode 12, evaluates it, and converts it to the external mirror 5 via the D/A conversion means 13. The angle of the laser oscillation is adjusted to maximize the intensity of laser oscillation.

An example of the above-mentioned control process will be described below with reference to the flowchart shown in FIG. Note that P1 to P1□ in the figure indicate each step of the flowchart.

First, the direction in which the angle of the external mirror 5 is adjusted (movement direction)
is set in the X direction (P2). Next, the direction in which the external mirror 5 is to be moved (movement direction) is set to be positive among the two directions in the set movement direction (
P3). Next, the moving direction is changed (P4). Then, the value of the counter N is set to 0 (P,).

Then, it is determined whether or not it is N22 (pa). Here, if it is N22, repeat the steps from (P4). If N<4, set N=N+1. That is, the counter value N is increased by one (P7). Next, the laser beam conversion means 1 at the current position of the external mirror 5
The output voltage of No. 2 (light amount value, 11) is converted into a numerical value by the A/D conversion means 42 and then stored (P8). Next, the two D/A conversion means 43 are controlled to apply desired voltages to each of the two driving means 11 (P,). For this reason, the driving means 1
1 increases the angle of the external mirror 5 by a certain value in the currently set moving direction, in accordance with this voltage. Next, the output voltage (light amount value, I2) of the laser beam conversion means 12 at the position of the external mirror after the angle change is measured using an A/D converter.
It is converted into a numerical value by the conversion means 42 and then stored (Pl,). Then, 11 obtained in (P8) and I2 obtained in (P,.) are compared to determine whether I2≧I.
,,). If ■2≧11, repeat the steps from (P8). If IZ<It, the direction of movement is reversed, that is, if it is positive, it is set to negative, and if it is negative, it is set to positive (Plz). After this (PI□), the steps from (P8) are repeated as in the case of ■2≧11. In this way, the angle of the external mirror 5 is continued to be controlled alternately five times in two directions so that the oscillation intensity of the laser beam is maximized.

Although a piezoelectric actuator is used as the driving means in this embodiment, the same effect can of course be obtained by using other driving means, such as a motor or a voice coil.

Further, in this embodiment, two driving means are used to control the external mirror in two axial directions, but depending on the application, it may be sufficient to control it in one axial direction, and in this case, only one driving means is sufficient.

Furthermore, although one photodiode is used as a laser beam detection means in this embodiment, a plurality of photodiodes may be arranged to transmit the direction of deviation of the optical axis or a signal corresponding to the direction to the control unit. In this way, the configuration of the control section can be made simpler.

Further, the laser light detection element may be located between the external mirror and the support plate 8, and furthermore, a part of the laser light may be extracted and detected without being placed on the axis. In short, it is sufficient to detect the amount of laser light generated by laser oscillation and convert it into a corresponding electrical signal, and the location does not matter.

Furthermore, in this embodiment, one of the two reflecting mirrors of the resonator is fixed inside the discharge tube, but it goes without saying that both of the two reflecting mirrors may be used as external mirrors to form an external mirror type laser resonator. It is.

In this embodiment, the light source section is a discharge tube, but the present invention is not limited to this, and may be any light source such as a solid-state laser.In short, any laser oscillator that configures a resonator using an external mirror can be used. , can be applied regardless of type.

〔Effect of the invention〕

As explained above, according to the present invention, in an external mirror type laser oscillator including a light source section including an excitation medium and a laser medium, and a resonator having at least one external mirror, the external mirror type laser oscillator generates light. comprising a laser beam detection means for converting the intensity of the laser beam into a signal, a driving means for changing the angle of the external mirror, and a control means for controlling the driving means, based on the output of the laser beam detection means, Since the control means controls the drive means and changes the angle of the external mirror so as to maximize this output, optimal laser oscillation can be performed in a wider temperature range than in the conventional method. In addition, even if the optical axis of the laser resonator is shifted due to mechanical shock, it can automatically return to the optimal state. Furthermore, the laser resonator can be placed in various gases with different refractive indexes. Even when operating, the best laser oscillation can always be obtained automatically.

As described above, it is possible to realize a laser resonator that is easier to use than the conventional one, and its effects are extremely large.

[Brief explanation of the drawing]

FIG. 1 is a side view of the main part of the particulate detection part of a light scattering particulate meter which is an embodiment of the present invention, and FIG. 2 is a schematic diagram of the main part of the same light scattering particulate meter including the condensing optical system. FIG. 3 similarly shows a characteristic diagram for explaining its operation. FIG. 4 is a block diagram showing one embodiment of the control section, and FIG. 5 is a flowchart showing the control process. FIG. 6 is a side view of a conventional laser oscillator, and FIGS. 7 and 8 are side views of the main parts thereof. 1... Discharge tube (light source section) 5... External mirror 11.
... Drive means 12 ... Laser light detection means 13 ...
control means

Claims (1)

[Claims] In an external mirror laser oscillator comprising a light source section including an excitation medium and a laser medium, and a resonator having at least one external mirror, the intensity of laser light generated by the external mirror laser oscillator is a laser beam detection means for converting the output into a signal, a driving means for changing the angle of the external mirror, and a control means for controlling the driving means, and the output is adjusted to a maximum based on the output of the laser beam detection means. An external mirror type laser oscillator, wherein the control means controls the drive means to change the angle of the external mirror.