JPS5995510A - Optical parts protecting device for power laser - Google Patents

Abstract

PURPOSE:To reduce the thermal gradient of optical parts and to attain protection against breakage, etc. by providing a heater to the circumference of optical parts for a power laser, and amplifying the difference between the output of a sensor which detects the temperature of the optical parts and a reference temperature signal and controlling the heating of the heater. CONSTITUTION:A heater 2 is provided to the circumference of a window material 1 made of the optical parts for the power laser such as a lens. The heater 2 is made of, for example, a sheathed heater and a sensor 3 detects the temperature of the window material 1. The difference between the detection signal of the sensor 3 and reference temperature signal is amplified by a differential amplifier 7 and the heating value of the heater 2 is controlled on the basis of the output signal of the amplifier 7. Thus, the thermal gradient of the window material 1 is reduced as much as possible to prevent the breakage of optical parts of the window material 1 during laser irradiation and to eliminate variation in convergence effect.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protection device for optical parts for a power laser, such as a window material and a lens of a laser generator.

Currently, it is used for power laser lenses, window materials, etc.

Zinc selenium (Zn5e) or KCl, KBr
Alkali halide materials such as are used. Although these materials have relatively low light absorption rates, they still have an order of 10 to 10 for zinc selenium and 10-4 to 10-5 for KCj' and KBr. Therefore, when applied to a high-output power laser such as a carbon dioxide laser, it absorbs laser light of several tens to hundreds of watts and generates heat at a high temperature. In order to prevent the effects of such heat generation on surrounding components, current efforts are being made to cool local parts of window materials and lenses.

However, when cooling a local part of a window material or lens, because the heat conduction rate of the window material or lens is lower than that of metal, only the local part is cooled, and the central part remains high temperature, resulting in a thermal gradient. becomes more intense than before cooling (curve in Figure 4)
(See curve (b)) As a result, distortion due to heat occurs as shown in curve (b), often resulting in breakage. In addition, even before damage occurs, a thermal lens effect occurs due to uneven distribution of refractive index due to uneven heat distribution, which changes the light focusing effect of the lens and causes unnecessary damage to the window material. It also has the disadvantage of producing a light condensing effect. This is due to the fact that thermal strain differs between the center and local parts of the window material or lens.

In view of this, the present invention does not cool the local part of the optical component for a power laser, but instead heats it, and in addition to simply heating it, it also controls the amount of heating so that the thermal gradient is as small as possible. This is an attempt to eliminate the above-mentioned drawbacks and ensure complete protection of optical components.

That is, the protection device for a power laser optical component according to the present invention includes a heater provided around a power laser optical component such as a lens, a sensor that detects the temperature of the optical component, and a reference temperature signal generator. and a differential amplifier that amplifies the voltage difference between the signal detected by the sensor and the reference temperature signal, and the heater is configured to be heated by the output signal of the differential amplifier. .

An embodiment of the present invention will be described below based on the drawings. 1st
The figure is a schematic configuration diagram showing an embodiment of the present invention, in which 1 is a window material provided as an optical component for a power laser, for example, at the output part of a CO□ laser generator, and 2 is a window material provided locally in the window material 1. An example of the heater is a sheathed heater, and 3 is a sensor for detecting the temperature of the window material l. As the sensor, a thermistor, thermopile, platinum resistance wire, etc. can be used. The sensor is preferably provided in a local part of the window material 1 so that temperature changes caused by the heater 2 can be detected with good responsiveness. The window material 1 must be provided in the generator frame in a highly airtight manner in order to maintain the degree of vacuum inside the laser generator. Therefore, the heater 2 and the sensor 3 are inserted between the window material 1 and the metal holder 4 as shown in FIG. It is better to stop it. In this case, it is necessary to use a material with good thermal conductivity as the filler 5 so that the heat from the heater 2 can be quickly transferred to the window material 1. As such a filler, for example, silicon resin containing beryllium oxide may be used.

6 is a reference temperature signal generator, and 7 is a differential amplifier that amplifies the difference between the detection signal of the sensor 3 and the reference temperature signal.

The output signal of the amplifier 7 is applied to the heater 2 to control the amount of heat generated by the heater 2. Note that the reference temperature signal eS generated by the reference temperature signal generator 6 is
is set to a value corresponding to the temperature at which it generates heat when irradiated with a laser.

In this configuration, if the power of the laser beam irradiated to the window material 1 is W, and the absorption coefficient of the window material 1 is k, then the window material 1 absorbs the power of W = W, k...tl). .

Here, if ρ is a coefficient determined by the specific heat, heat radiation coefficient, etc. of the window material 1, the temperature t at which the window material 1 is heated by the above-mentioned heat wave W is 2W・ρ1 (2) .

Further, if α is a temperature-electrical quantity conversion coefficient, the electrical 'Be' corresponding to the temperature t is e - α@t (3). By substituting equation (2) and equation (tl) into equation (3), e can be expressed as e −a * p·k *J − (4)1.

On the other hand, the heater 2 is heated by the output current of the differential amplifier 7, thereby increasing the voltage applied to the window material 1 by W.
. , the coefficient determined by the specific heat, mass, heat radiation coefficient, etc. of window materials, heaters, etc. is ρ. Then, the temperature t at which the window material 1 is heated by the heat generated by the heater 2. is tO2WO・tO・・・・(5
) becomes. The amount of electricity e corresponding to this temperature is e −
α・tO...(6) From equations (5) and (6), it can be expressed as e −α·tO·WO (7).

Electricity generated by equation (4) above (7)
The electricity me□ generated by the formula becomes the sum and acts to heat the window material 1, and the sensor 3 detects this sum of electricity, so the electricity quantity e detected by the sensor 3 is: e = It can be expressed as el+ eO-[8). In this way, the differential amplifier 7 amplifies the voltage difference between the detected quantity of electricity e and the reference temperature signal es, and its output causes the heater 2 to generate heat and heat the window material 1. window material by
The following relationship exists between the voltage Wo given to , and the above e and es.

(-e+88) G = Wo.+9) Here, G is the amplification factor of the differential amplifier 7. In equation (9) above, (8), (7
), by substituting and rearranging equations (4), the following equation is obtained.

Here, since the amplification factor G is sufficiently large, it can be written as (G sin 1).

Also, generally ρ, −ρ. Therefore, the above equation can be written as follows.

The first term on the right side of the above equation is a constant, and the second term is the wattage W of the laser light absorbed by the window material 1 from the +I+ equation.
Therefore, if the constant is K, the above (1) can be written as follows.

As is clear from the above equation 03), the sum of the wattage at which the window material 1 absorbs the laser beam and the wattage given by the heater 2 is always constant. In this case, let the value of K be W
If K is set to a value equal to or larger than the expected maximum wattage (K≧W), equation (I3) can be satisfied even at the maximum wattage for absorbing laser light. What is wattage and temperature? (2)
) Since there is a proportional relationship as shown in the equation, the fact that the total wattage (Wo+W) applied to the window material 1 is constant (K) means that the temperature of the window material is constant. However, the part where the temperature is constant is the peripheral part of the window material where the sensor 3 is installed, but this part is the part with the lowest temperature if the heater 2 is not installed, so the temperature of this part is (13) Being kept constant so as to satisfy the equation means that the temperature gradient of the window material is small and smooth as shown in FIG. 3(a). Therefore, since there is not much temperature difference between the center and local parts of the window material 1, the thermal strain caused by the temperature difference per minute length is reduced as shown in Figure (b), protecting the window material from damage. It is possible. Furthermore, when a lens is used instead of a window material, it is possible to prevent the light gathering effect of the lens from changing.

In FIG. 3, the curve (C) is the temperature distribution of the window material when no laser beam is incident, that is, the temperature distribution of the window material caused only by the heat generation of the heater 2, and the curve (d) is the thermal strain in that case.

Note that the voltage W0 given to the window material by the heat generated by the heater 2 is equal to the output current of the differential amplifier 7. .

Letting the resistance of the heater be Ro, it is given by Wo-IRo, so if we substitute equation (14) into equation (14) and rearrange it, we get: In this equation, ■2 and W are linear By the way, W changes when optical parts such as window materials and lenses deteriorate, so if we monitor the current ■ in the above configuration, we can calculate the deterioration of window materials, etc. from equation (15) or equation 05. It can be said that the degree can be known.

Since the protection device for power laser optical components according to the present invention is configured as described above, it is possible to alleviate the thermal gradient of optical components such as window materials and lenses as much as possible, and therefore prevent optical components such as window materials from being damaged during laser irradiation. It has the advantage that it can be used with confidence without causing any change in the light gathering effect. In addition, as described in the embodiment, there is the convenience of being able to know the degree of deterioration of the optical components used by monitoring the output current of the differential amplifier.

2 is a diagram showing the peripheral part of the optical component in detail, FIG. 3 is a diagram showing the temperature distribution and strain in the diametrical direction of the optical component, and FIG. 4 is a diagram showing the optical component in detail.
The figure is a diagram showing the temperature distribution and strain in the diametrical direction of the optical component in the conventional means.

1. Optical component, 2. Heater, 3. Sensor, 6. Reference temperature signal generator, 7. Differential amplifier.

Figure 2 Figure 3 Lazy Oo○J Besen) Bow 9 White 0- Window material 0 diameter direction -

Claims (1)

[Claims] A heater provided locally in a power laser optical component such as a lens, a sensor that detects the temperature of the optical component,
It is equipped with a reference temperature signal generator and a differential amplifier that amplifies the voltage difference between the signal detected by the sensor and the reference temperature signal, and is configured to heat the heater by the output signal of the differential amplifier. An optical component protection device for power lasers, which is characterized by: