JPS632090B2 - - Google Patents

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, zinc selenium (ZnSe) or alkali halide materials such as KCl and KBr are used for lenses, window materials, etc. for power lasers. Although these materials have relatively low light absorption, they still have a light absorption of 10 ^-2 to 10 ^-3 for zinc selenium and 10 ^-4 for KCl and KBr.
It is on the order of ~10 ^-5 . Therefore, when applied to a high-output power laser such as a carbon dioxide laser, it absorbs several tens to hundreds of watts of laser light and generates heat at a high temperature. In order to prevent such heat generation from affecting surrounding components, current efforts are being made to cool the surrounding parts of window materials and lenses.

However, when cooling the peripheral parts of window materials, lenses, etc., only the peripheral parts are cooled, and the central part remains hot because the heat conduction rate of the window materials and lenses is lower than that of metals. , the thermal gradient becomes more severe than before cooling (see curve a in FIG. 4), resulting in distortion due to heat 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 lenses and causes unnecessary damage to window materials. 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 the periphery of the window material or lens.

In order to solve this problem, the present invention does not cool the peripheral part of the optical parts for power lasers, but instead heats them, and in addition to simply heating them, the amount of heating is controlled so that the thermal gradient is as small as possible. This is an attempt to eliminate the above-mentioned drawbacks and to 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. It is said that

An embodiment of the present invention will be described below based on the drawings. FIG. 1 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 ₂ laser generator, and 2 is a peripheral portion of the window material 1. An example of the heater provided is a sheathed heater, and 3 is a sensor that detects the temperature of the window material 1. As the sensor, a thermistor, thermopile, platinum resistance wire, etc. can be used. Heater 2 is the location to install the sensor.
The peripheral portion of the window material 1 is desirable in order to be able to detect temperature changes caused by the temperature change 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 sensor 3 are inserted between the window material 1 and the metal holder 4 as shown in FIG.
It is preferable to fill the space between the window material 1 and the holder 4 in a highly airtight manner. 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, a silicone microwave containing lyllium rather than an acid may be used.

6 is a reference temperature signal generator; 7 is the sensor 3;
This is a differential amplifier that amplifies the difference between the detection signal 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. The reference temperature signal _es generated by the reference temperature signal generator 6 is set to a value corresponding to the temperature at which the window material 1 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 _i and the absorption coefficient of the window material 1 is k, then the window material 1 absorbs the power as follows: W=W _i・k...(1) do.

Here, if ρ _i 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 voltage W is t=W・ρ _i ...(2) Become. Further, when α is a temperature-electrical quantity conversion coefficient, the electrical quantity e _i corresponding to the temperature t is as follows: e _i =α·t (3). Substituting equations (2) and (1) into equation (3), e _i
can be expressed as e _i =α.ρ _i・k・W _i ……(4).

On the other hand, the heater 2 is heated by the output current of the differential amplifier 7, and thereby the voltage W _p given to the window material 1, the specific heat of the window material, the heater, etc., the mass,
If the coefficient determined by the heat radiation coefficient etc. is ρ _p , then heater 2
The temperature t _p at which the window material 1 is heated by the heat generated by is t _p =W _p ·ρ _p (5). The amount of electricity e _p corresponding to this temperature is e _p = α・t _p (6). From equations (5) and (6), it can be expressed as e _p =α.ρ _p・W _p (7).

The quantity of electricity e _i expressed by equation (4) above and the quantity of electricity e _p expressed by equation (7) are summed and act to heat the window material 1, and the sensor 3 detects this sum of electricity quantity. Therefore, the amount of electricity detected by sensor 3 e
can be expressed as e=e _i +e _p (8). In this way, the differential amplifier 7 amplifies the voltage difference between the detected quantity of electricity e and the reference temperature signal e _s , and its output causes the heater 2 to generate heat and heat the window material 1 . Wattage given to window material 1 by heat generation of 2
The following relationship exists between W _p and the above e and e _s .

(-e+ _es )G= _Wp ...(9) Here, G is the amplification factor of the differential amplifier 7. the above
Substituting equations (8), (7), and (4) into equation (9) and rearranging, we get the following equation.

W _p = G/1 + α・ρ _p・G (−α・ρ _i・k・W _i +e _s ) ...(10) Here, since the amplification factor G is sufficiently large (G≫1), W _p = 1/ α・ρ _p (−α・ρ _i・k・W _i +e _s ) ∴W _p =−ρ _i /ρ _p・k・W _i +1/α・ρ _p・e _s ……(11
) can be written.

Also, since it is generally considered that ρ _i ≒ ρ _p , the above equation can be written as follows.

W _p = 1/α・ρ _p・e _s −kW _i ...(12) The first term on the right side of the above equation is a constant, and the second term is (1)
From the formula, it is the wattage W of the laser light absorbed by the window material 1, so if the constant is expressed as K,
The above (12) can be written as follows.

W _p +W=K...(13) However, 1/α・ρ _p・e _s =K.

As is clear from the above equation (13), 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, set the value of K to a value equal to or greater than the maximum expected value of W (K≧
When set to W), formula (13) can be satisfied even when the wattage for absorbing laser light is at its maximum. Since wattage and temperature are in a proportional relationship as shown in equation (2), the fact that the total wattage applied to window material 1 (W _p + W) is constant (K) means that the temperature of the window material is constant. It means that. 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) The fact that the temperature gradient of the window material is kept constant to satisfy the equation means that the temperature gradient of the window material is the third
This means that it is small and smooth as shown in Figure a. Therefore, since there is not much temperature difference between the center and the periphery 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. Also, if a lens is used instead of window material,
This also prevents problems caused by changes in the light-gathering effect of the lens.

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 generated only by heat generation from the heater 2, and the curve d is the thermal strain in that case.

Note that the voltage W _p given to the window material by the heat generated by the heater 2 is the output current of the differential amplifier 7 as I _p ,
Letting the resistance of the heater be R _p , it is given by W _p = I ² R _p , so Then, by substituting equation (12) into equation (14) and rearranging it, we get Alternatively, I ² =1/α・ρ _p・R _p・e _s −1/R _p・W (15′). In this equation, I ² and W _i are linear functions and are proportional. By the way, W changes when optical components such as window materials and lenses deteriorate, so if the current I is monitored in the above configuration, the degree of deterioration of window materials, etc. can be determined from equation (15) or (15'). I can say that it can be done.

Since the protection device for power laser optical components according to the present invention is configured as described above, it is possible to reduce 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. or
The effect is that it can be used with confidence without causing any change in the light gathering effect. In addition, as described in the embodiments, 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.

[Brief explanation of the drawing]

The figures show one embodiment of the present invention, in which Fig. 1 is a schematic overall configuration diagram, Fig. 2 is a detailed view of the peripheral part of the optical component, and Fig. 3 is a diagram showing the temperature distribution and strain in the diametrical direction of the optical component. 4 are diagrams 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.

Claims (1)

[Claims] 1. A heater provided around a power laser optical component such as a lens, a sensor that detects the temperature of the optical component, a reference temperature signal generator, and a signal detected by the sensor and a reference temperature signal. 1. An optical component protection device for a power laser, comprising: a differential amplifier that amplifies a voltage difference; and an output signal of the differential amplifier heats the heater.