JP2003294526A - Laser power detection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure a power accurately over long hours just after reception of a laser beam in a laser power detection device for measuring the power of the laser beam mainly in an infrared region or of several W or more. <P>SOLUTION: This device is equipped with an operation means 5 for calculating the laser power based on the difference between the output of a first temperature detection means 2 and the output of a second temperature detection means 3 for detecting the temperatures of two points on a light receiving plate 1 in a noncontact way, to thereby compensate the influence of fluctuation of an ambient temperature. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to a laser power detecting device for measuring the power of laser light in the infrared region or several W or more.

[0002]

2. Description of the Related Art In recent years, as a laser power detecting device of this type, there has been one disclosed in, for example, Japanese Patent Application Laid-Open No. 5-3353. In FIG. 4, after the partial transmission mirror 42 facing the output mirror 41, an output detection sensor 43 composed of four elements 43A to 43D which are symmetrical with respect to the axis is provided in parallel, and an addition amplification circuit 44 is used to provide elements. 43A ~
The sum of the output voltages Va to Vd of 43D is amplified and displayed by the power meter 48, and the difference between the output voltages Va and Vb of the elements 43A and 43B arranged in the Y-axis direction on one side of the differential amplifier circuit 45 is On the other hand, the position meter 9 displays the position of the laser light by amplifying the difference between the output voltages Vc and Vd of the elements 43C and 43D arranged in the X-axis direction.

In Japanese Patent Laid-Open No. 5-180694, the power fluctuation frequency of laser light is measured over a wide band by combining the outputs of a power sensor having a slow response speed and a power sensor having a fast response speed. It keeps the accuracy uniform.

Generally, in the case of detecting a laser beam having a large power in a laser power detector, the laser beam is made incident on an integrating sphere having a wide inner wall area and then taken out, or a laser beam having a large heat capacity is absorbed by the laser beam to generate heat. It is configured to be converted to. Further, laser power detection elements include a thermocouple sensor such as a thermocouple and a thermopile that temporarily converts laser light into heat, and a pyroelectric sensor that utilizes the pyroelectric effect due to a change in crystal temperature.

However, in such a conventional laser power detecting device, a measurement error occurs when the laser power detecting element is heated by the laser beam or when the ambient temperature changes. A thermal sensor that detects laser light having high power density after converting it into heat once has a slow response speed, and it takes time for the output to stabilize after the laser light begins to be incident.

On the other hand, the pyroelectric sensor cannot detect the power unless it is chopped, and the chopper is heated during the measurement, so that the output value gradually appears small. Since the chopper needs a driving means such as a motor fan, there are problems that the heat and wind generated from this driving means may cause a measurement error and may easily cause a mechanical failure. Shape sensors are often used.

Also, a method has been devised in which a thermocouple is attached to the back side of a light receiving plate having a small heat capacity, and the laser power is estimated based on a temperature rise curve after the laser light starts to be incident, but over a long period of time. It was not possible to detect continuously, and there was a problem in measurement accuracy. That is, it has been difficult to accurately measure the laser power for a long time immediately after the emission of the laser light.

[0008]

SUMMARY OF THE INVENTION In view of the above problems of the prior art, an object of the present invention is to achieve accurate power measurement for a long time immediately after receiving a laser beam. In particular, with regard to the device built-in laser power detection device in which the laser incident position is determined in advance,
One of the purposes is to extract a signal having excellent S / N performance. It is another object of the present invention to extend the life of the device and stabilize the output characteristics without directly injecting the laser into the laser power detection device. Another object is to suppress a measurement error caused by heat generation of the laser power detection element without increasing the size of the entire apparatus.

[0009]

In order to solve the above-mentioned problems, a laser power detecting apparatus of the present invention comprises a light receiving plate for receiving a laser beam, and a plurality of non-contact detecting temperatures at a plurality of points on the light receiving plate. The temperature detecting means and the calculating means for calculating the laser power based on the difference between the outputs of the plurality of temperature detecting means.

The second technical means is a light receiving plate for receiving a laser beam, first temperature detecting means and second temperature detecting means for detecting the temperatures of two points on the light receiving plate in a non-contact manner.
It is provided with a calculating means for calculating the laser power based on the difference between the output of the first temperature detecting means and the output of the second temperature detecting means.

In the third technical means, one temperature detecting means detects the temperature near the laser light incident point of the light receiving plate, and the other temperature detecting means is located at a position apart from the laser light incident point of the light receiving plate by a predetermined distance. It detects the temperature of.

In a fourth technical means, a plurality of temperature detecting means detect the temperature of the side surface of the light receiving plate opposite to the laser light incident surface.

In a fifth technical means, a plurality of temperature detecting means are provided on a metal mounting base apart from the light receiving plate to detect infrared rays emitted from the side opposite to the laser light incident surface of the light receiving plate. It is a thing.

In the sixth technical means, the plurality of temperature detecting means are thermopiles.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The above-mentioned object of the present invention can be achieved by adopting the constitution described in each claim as an embodiment. Therefore, the action of the constitution is described together with the constitution of each claim below. At the same time, a detailed description will be added to specific terms that require an explanation among the configurations described in the claims, and the embodiments of the present invention will be described.

According to the first aspect of the present invention, there is provided arithmetic means for calculating laser power based on output differences of a plurality of temperature detecting means for non-contact detection of temperatures at a plurality of points on the light receiving plate for receiving the laser light. Be prepared.

The invention according to claim 2 is based on the output difference between the first temperature detecting means and the second temperature detecting means for detecting the temperature at two points of the light receiving plate for receiving the laser beam in a non-contact manner. It is provided with a calculation means for calculating the laser power.

According to each of the above-described embodiments, even if the ambient temperature surrounding the plurality of temperature detecting means, which is the laser power detecting element, becomes high due to the temperature rise of the light receiving plate, the mutual influence is exerted by the output difference of the plurality of temperature detecting means. Can be offset. Further, since it only detects the temperatures at a plurality of points on the back side of the light-receiving plate of the laser light, it is not necessary to separately provide a sensor for temperature compensation in a place where the temperature does not fluctuate, and it is not necessary to increase the size of the entire apparatus. .

According to the third aspect of the present invention, particularly when the laser light incident position is determined in advance, one temperature detecting means detects the temperature near the laser light incident point of the light receiving plate and the other temperature detecting means. By arranging the means so as to detect the temperature of the light receiving plate at a position distant from the laser light incident point by a predetermined distance, the heat flow corresponding to the laser power is efficiently applied to the light receiving plate as a temperature difference between a plurality of points to achieve S / N. A signal with excellent performance can be extracted. Further, by appropriately selecting the heat capacity of the light receiving plate and the distance between the plurality of temperature detecting means, the response delays of the plurality of temperature detecting means are canceled out, and the rise and fall characteristics for the start and stop of receiving the laser light are significantly increased. The laser power can always be measured with high accuracy.

Further, according to the invention of claim 4, the plurality of temperature detecting means detect the temperature of the side surface of the light receiving plate opposite to the laser light incident surface, so that the plurality of temperature detecting means which are laser power detecting elements. Since no laser light is directly incident on the device, the life of the device can be extended and the output characteristics can be stabilized.

According to the fifth aspect of the present invention, since the plurality of temperature detecting means are provided on the metal mounting base apart from the light receiving plate, it is possible to suppress the deviation of the ambient temperature in the plurality of temperature detecting means. The measurement accuracy is further improved. It is preferable that the metal mounting base is made of a material having excellent thermal conductivity such as copper or aluminum and has a volume (heat capacity) of a predetermined value or more. Further, the plurality of temperature detecting means respectively detect the infrared rays emitted from the side surface of the light receiving plate opposite to the laser light incident surface, and are insulated from the light receiving plate itself. As a result, it is possible to suppress a measurement error caused by heating the entire temperature detecting means, which is a laser power detecting element, and it is possible to accurately detect the laser power.

(Embodiment 1) FIG. 1 is a configuration diagram of a laser power detection apparatus according to an embodiment of the present invention. 1
Is a disc-shaped light receiving plate made of aluminum for receiving the laser light, the surface of which is black-painted, the incident laser light is converted into heat without being reflected, and the laser light is exactly at the center point of the light receiving plate 1. Are arranged so as to be incident vertically.

The light receiving plate 1 is designed so as to reach thermal equilibrium promptly (within a few seconds) even when the maximum expected laser power is incident. That is, the holding means 1a for holding the light receiving plate 1 on the outer periphery of the light receiving plate 1 has a structure in which heat is constantly exchanged with the ambient temperature and naturally cooled. In such a light receiving plate 1, when laser light is vertically incident, a heat flow corresponding to the laser power is generated from the center toward the periphery, and a concentric temperature gradient distribution is formed.

Reference numeral 2 is a first temperature detecting means, 3 is a second temperature detecting means, and these are thermopile elements. Then, the first temperature detecting means 1 detects the infrared rays indicated by the dotted line emitted from the side surface of the light receiving plate 1 opposite to the laser beam incident surface in a non-contact manner. The second temperature detecting means 3 is the light receiving plate 1.
Infrared rays indicated by a dotted line emitted from a point distant by a predetermined distance from the center of the side surface opposite to the laser light incident surface are detected without contact.

Further, the first temperature detecting means 2 and the second temperature detecting means 3 are attached to a mounting base 4 made of aluminum having excellent thermal conductivity, and the first temperature detecting means 2 and the second temperature detecting means 2 are attached.
Of the respective outputs of the temperature detecting means 3, the cold junction side is electrically connected, and further electrically and thermally connected to the mounting base 4. Reference numeral 5 denotes a microcomputer for calculating laser power based on a voltage difference which is a difference between a thermoelectromotive force which is an output of the first temperature detecting means 2 and a thermoelectromotive force which is an output of the second temperature detecting means 3 and its periphery. It is a calculation means composed of a circuit.

The calculation means 5 has a first sensitivity correction means 5a, a second sensitivity correction means 5b, a differential amplification means 5c and a linearization means 5d, respectively. First sensitivity correction means 5
a, the second sensitivity correction means 5b is provided for each of the temperature detection means 2, 3
The output voltage sensitivities K1 and K2 peculiar to the above are corrected. The differential amplifying means 5c is the difference between the outputs of the first temperature detecting means 2 and the second temperature detecting means 3 corrected via the first sensitivity correcting means 5a and the second sensitivity correcting means 5b. Amplify the voltage difference.

The linearizing means 5d linearly converts the difference signal, which is a nonlinear curve with respect to the laser power, into a proportional output. Reference numeral 6 is a display unit for displaying a signal corresponding to the laser power output from the calculation unit 5. The light receiving plate 1 has a heat insulating layer 8 for air formed between the light receiving plate 1 and the mounting base 4, and is closed by the light receiving plate 1 to prevent dust from accumulating on the temperature detecting means 2 and 3. Is an annular connecting body that connects the outer periphery of the mounting base 4.

The thermopile elements constituting the first temperature detecting means 2 and the second temperature detecting means 3 are provided with a silicon window which transmits infrared rays, as in the thermopile element used in a normal radiation thermometer. , 100 pairs or more of dissimilar metals are joined so as to generate a thermoelectromotive force by the Seebeck effect. The hot junction side is in thermal contact with the heat absorbing material (gold black) provided in the central portion, and the temperature instantly rises according to the incident infrared rays.
The cold junction side is disposed in the periphery and is in thermal contact with a TO-5-shaped can housing. The inside of the can housing is sealed with an inert gas to prevent deterioration of output characteristics due to aging.

In the above embodiment, when the laser light is incident on the light receiving plate 1 as shown in FIG. 1, the viewpoint temperature (that is, the temperature at the hot junction of the first temperature detecting means 2) is Ta (K). , The ambient temperature of the first temperature detecting means 2 (that is, the temperature of the cold junction side of the first temperature detecting means 2) is Tb.
Assuming (K), the thermoelectromotive force V1 output from the first temperature detecting means 2 is given by the following equation (Equation 1) according to the Stefan-Boltzmann law.

[0030]

[Equation 1] Of course, the viewpoint temperature Ta on the light receiving plate 1 detected by the first temperature detecting means 2 is directly behind the laser light incident point and becomes the highest temperature on the side opposite to the laser light incident surface, but since it is non-contact, it is the first temperature. A signal can be efficiently detected by directly irradiating the temperature detecting means 2 with laser light without degrading the thermopile element. In general, laser light has a very high power density, and if the first temperature detecting means 2 receives the laser light directly without passing through the light receiving plate 1, only a specific position is abnormally overheated and a failure or characteristic deterioration occurs. In some cases, the contact is made so as to prevent this. In addition, the infrared transmission window provided in the thermopile element has a transmittance shift depending on the wavelength, and when the laser light that is a monochromatic light is directly incident, the light receiving plate 1 receives the problem that the output sensitivity varies from element to element. , It is solved by converting into heat.

Since the first temperature detecting means 2 and the second temperature detecting means 3 are attached to the mounting base 4 made of aluminum having excellent thermal conductivity, it is considered that the ambient temperature Tb of both is always common. To be Since the mounting base 4 does not directly contact the light receiving plate 1 and the air as the heat insulating layer 8 is interposed, the viewpoint temperature Ta of the light receiving plate 1 in the first temperature detecting means 2 is changed by the incidence of the laser light. Even if it rises sharply,
Ambient temperature T of the temperature detecting means 2 and the second temperature detecting means 3 of
b does not rise suddenly.

In the second temperature detecting means 3, the light receiving plate 1
The upper viewpoint temperature (that is, the temperature of the hot junction side of the second temperature detecting means 3) is Tc (K), and the ambient temperature of the second temperature detecting means 3 (that is, the cold junction side of the second temperature detecting means 3). If the temperature) is Tb (K), the thermoelectromotive force V2 output by the second temperature detecting means 3 is expressed by the following equation (Equation 2) similarly to the first temperature detecting means 2.

[0033]

[Equation 2] The thermoelectromotive force V1 of the first temperature detection means 2 is input to the first sensitivity correction means 5a, and the thermoelectromotive force V2 of the second temperature detection means 3 is input to the second sensitivity correction means 5b. The inherent output voltage sensitivities K1 and K2 of the temperature detecting means are corrected. Thus, the thermoelectromotive force V1 of the first temperature detecting means 2 and the thermoelectromotive force V2 of the second temperature detecting means 3 described above can be converted into the following equations (Equation 3) and (Equation 4), respectively.

[0034]

[Equation 3]

[0035]

[Equation 4] Then, the converted thermoelectromotive force V1 ′ of the first temperature detecting means 2 and the converted thermoelectromotive force V2 ′ of the second temperature detecting means 3 are taken into the differential amplifying means 5c, and the thermoelectromotive force V1 ′ and the thermoelectromotive force V1 ′. The voltage difference of the electromotive force V2 ′, that is, K × (Ta ⁴ −Tc ⁴ ) corresponds to the power of the incident laser light. As a result, the first temperature detecting means 2 and the second temperature detecting means 3 can detect the laser power accurately without depending on the ambient temperature Tb. Further, the thermoelectromotive force V1 ′ and the thermoelectromotive force V
The difference signal which is the voltage difference of 2'is converted by the linearizing means 5d so as to be a proportional output, and the signal corresponding to the laser power is displayed on the display means 6.

FIGS. 2A and 2B are equivalent circuits of the heat transfer system of the light receiving plate 1. As is well known, if the heat resistance in the heat transfer system is a resistance and the heat capacity is a capacitor, temperature can be replaced by voltage and heat flow can be replaced by current on the electric circuit. Generally, a heat transfer model is described in a distributed constant system as shown in FIG. 2A, but the description will be simplified as shown in FIG. 2B. Now, when a pulsed laser beam is incident on the center of the light receiving plate 1, the temperature of the point instantly rises from the ambient temperature. Along with this, the viewpoint temperature Ta at the point on the opposite side of the laser light incident surface rises with a response delay corresponding to the heat capacity. Furthermore, the viewpoint temperature Tc (the temperature on the hot junction side of the second temperature detecting means 3) that is away from that point by a predetermined distance continues to increase until it reaches the equilibrium temperature with a response delay depending on the distance and the heat capacity. When the incidence of the laser light is stopped, the ambient temperature settles back to the original ambient temperature with the same response delay.
FIG. 3 shows temperature change curves of the temperatures Ta, Tc and the difference between Ta and Tc on the light receiving plate 1. As is clear from FIG. 3, the difference between the temperatures Ta and Tc is the temperature Ta or the temperature T.
The response of rising and falling is faster than that of c. That is,
If the heat capacity and the detection position of the light receiving plate 1 are appropriately selected, even if the temperature Ta, Tc immediately after the laser light incidence is rising or the temperature Ta, Tc immediately after the laser light incidence is stopped is in a transient state, It is possible to obtain a laser power detection device having excellent response characteristics regardless of the absolute value of the laser power.
Furthermore, since the two temperature detecting means 2 and 3 are structured to be covered by the light receiving plate 1, there is also an effect that deterioration with age is unlikely to occur, for example, dust adheres to the thermopile element and the sensitivity characteristic shifts.

As described above, in the present embodiment, the ambient temperature Tb of both temperature detecting means is the same by mounting the first temperature detecting means and the second temperature detecting means on the mount having excellent thermal conductivity. In addition, since the difference between the outputs of the first temperature detecting means and the second temperature detecting means is calculated by the calculating means, even if the ambient temperature Tb of both temperature detecting means fluctuates, the influence thereof will be exerted. It is possible to cancel out, and the laser power can be measured with high accuracy for a long time immediately after receiving the laser.

In the present embodiment, the first temperature detecting means detects the highest temperature point on the light receiving plate at a non-contact position apart from the light receiving plate, so that a larger thermoelectromotive force is generated. A signal having excellent S / N performance can be taken out, and the temperature detecting means has an arrangement structure that is hard to be heated, so that a measurement error can be suppressed.

Further, in this embodiment, the first difference is used.
By canceling the output response delays of the temperature detecting means and the second temperature detecting means, it is possible to perform highly accurate power measurement excellent in rising and falling characteristics.

Further, in the present embodiment, since the laser light is not directly incident on the temperature detecting means which is the laser power detecting element, it is possible to prolong the life of the element and stabilize the output characteristics, and at the back side of the light receiving plate. Since the temperature of only two points is detected, it is not necessary to separately provide a sensor for temperature compensation in a place where the temperature does not fluctuate, and it is possible to prevent the size of the entire apparatus from increasing.

The simplest method of constructing the first sensitivity correction means 5a and the second sensitivity correction means 5b in the above-described embodiment is the output voltage sensitivity K of the first temperature detection means 2.
Of the output voltage sensitivities K2 of the first and second temperature detecting means 3, only the one having the higher sensitivity is resistance-divided by that ratio and input to the differential amplifying means 5c. It is possible to have an input amplifier circuit and perform sensitivity correction, difference, and linearization by digital signal processing.

In the above embodiment, the linearizing means 5d is used.
Although a differential signal that is a non-linear curve with respect to the laser power is provided as a proportional output, when the laser power is relatively small, the signal output is regarded as it is proportional to the laser power and linearization conversion is not necessary. good.

Although the thermopile element is used as the temperature detecting means in the above embodiment, for example, a heat sensitive film for converting infrared rays into heat is provided, and a thin film thermistor for detecting temperature is attached to the heat sensitive film. The temperature may be measured from the change in resistance value. You can use a thermocouple or platinum temperature measuring element.

Further, in the present embodiment, the fluctuation factors of the ambient temperature and the ambient temperature Tb of each of the temperature detecting means 2 and 3 are neglected, but the same operational effect can be expected even if the factors are taken into consideration. Further, the infrared rays radiated from the side opposite to the laser light incident surface of the light receiving plate 1 is detected in a non-contact manner, but the temperature of the laser light incident surface may be detected obliquely from the side.
Further, a reflector may be configured to detect from another angle. The holding means 1a of the light receiving plate 1 and the mounting base 4 on which the two temperature detecting means 2 and 3 are mounted may not be integrated, but may be a completely separated structure.

Further, in the present embodiment, the first and second temperature detecting means 2 and 3 are used. However, not only these two but also a large number of them may be combined to determine the heat flow and the temperature gradient generated on the light receiving plate 1. You may measure so that it may become higher resolution. Further, each of the temperature detecting means 2 and 3 uses a one-dimensional line sensor or a two-dimensional area sensor having a large number of elements arranged on a line as one unit, instead of a single detection element, to reduce measurement error. You may. Further, instead of providing two temperature detecting means, the laser power may be detected by the difference in temperature information obtained from different pixels of one line sensor or area sensor.

Further, in the present embodiment, only the differential signal is taken out in order to confirm whether or not one of the temperature detecting means is broken or short-circuited. However, this is not the case. The signals may be input independently. The shape of the light receiving plate 1 is not limited to a circular plate and may be a rod shape, and a large number of V-shaped concentric circular grooves may be provided on the laser light incident surface to suppress reflection. Also,
Although the detected laser power is displayed on the display means 6, some device control may be performed based on the detected laser power measurement value without the display means 6.

[0047]

As described above, the present invention has the following effects.

(1) Even if the ambient temperature of the temperature detecting means fluctuates, its influence can be canceled out.

(2) A signal having excellent S / N performance can be taken out.

(3) The temperature detecting means is hard to be warmed and the measurement error can be suppressed.

(4) The response characteristics are excellent, and high accuracy can be maintained for both short time measurement and long time measurement.

(5) The life of the detection element can be extended and the output characteristics can be stabilized.

(6) It is possible not to upsize the entire device.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a laser power detection device according to a first embodiment of the present invention.

FIG. 2 (a) is a heat transfer model diagram showing an equivalent circuit of a heat transfer system of a light receiving plate in the same laser power detection device as a distributed constant system. (B) An equivalent circuit of a heat transfer system of a light receiving plate in the same laser power detection device. A simplified diagram of the heat transfer model showing

FIG. 3 is a diagram showing temperature change curves of temperatures Ta and Tc of the light receiving plate and a difference between Ta and Tc.

FIG. 4 is a configuration diagram of a conventional laser power detection device.

[Explanation of symbols]

1 Light receiving plate 2 First temperature detecting means 3 Second temperature detecting means 4 mounting base 5 computing means

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Fumio Sugada             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Yasuo Shibata             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F term (reference) 2G065 AA04 AB09 BA11 BA14 CA30                       DA05                 2G066 AC20 BA08 CA11

Claims (6)

[Claims] 1. A light receiving plate for receiving a laser beam, a plurality of temperature detecting means for detecting temperatures of a plurality of points on the light receiving plate in a non-contact manner, and a laser power based on a difference between outputs of the plurality of temperature detecting means. A laser power detection device comprising: a calculation unit for calculating 2. A light receiving plate for receiving a laser beam, a first temperature detecting means and a second temperature detecting means for detecting the temperatures of two points on the light receiving plate in a non-contact manner, and the first temperature detecting means. A laser power detection device comprising: a calculation means for calculating a laser power based on a difference between the output of the means and the output of the second temperature detection means. 3. One of the temperature detecting means detects a temperature near a laser light incident point of the light receiving plate, and the other temperature detecting means detects a temperature of a position apart from the laser light incident point of the light receiving plate by a predetermined distance. The laser power detection device according to claim 1 or 2. 4. The laser power detecting device according to claim 1, wherein the plurality of temperature detecting means detect temperatures of a side surface of the light receiving plate opposite to the laser light incident surface. 5. The plurality of temperature detecting means are provided on a metal mounting base apart from the light receiving plate, and detect infrared rays emitted from a side surface of the light receiving plate opposite to the laser light incident surface. The laser power detection device according to any one of claims 1 to 4. 6. The laser power detecting device according to claim 1, wherein the plurality of temperature detecting means are thermopiles.