A solid-state laser apparatus which can improve its durability is provide.In the solid-state laser apparatus 1, a main pipe 11 for circulating a coolant through a solid-state laser medium 3 is provided with a heat exchanger 14, whereby the laser medium 3 is prevented from raising its temperature. When the coolant becomes acidic or alkaline, a controller 24 controls a flow regulating valve 23, so as to increase the flow rate of the coolant flowing into a bypass pipe 21 provided with a deionizing filter 22, whereby the acidity or alkalinity of the coolant can be weakened. This can prevent the coolant from deteriorating a predetermined part of the laser apparatus 3, and thus can improve the durability of the solid-state laser apparatus 1. Also, since the bypass pipe 21 connected in parallel to a part of the main pipe 11 is provided with the deionizing filter 22, the flow rate of the coolant circulating through the main pipe 11 can be restrained from decreasing, and the cooling efficiency of the laser medium 3 can be prevented from lowering.

TECHNICAL FIELD

The present invention relates to a laser apparatus which cools a solid-state laser medium with a coolant.

BACKGROUND ART

A conventional example of this kind of techniques is a zigzag-slab solid-state laser apparatus disclosed in Non-patent Document 1. This solid-state laser apparatus circulates a coolant through a laser medium, so as to prevent the laser medium from raising its temperature. This is done in order to prevent the pumping light generated by a semiconductor laser from raising the temperature of the laser medium and causing a thermal lens effect and the like.Non-patent Document 1: “Amplification Analysis of High-Output LD-Pumped Zigzag-Slab Nd Glass Laser”, Digest of Technical Papers, the 23rd Annual Meeting of the Laser Society of Japan, p. 51

DISCLOSURE OF THE INVENTION

Problem to be Solved by the Invention

However, even when neutral deionized water is used as a coolant in a solid-state laser apparatus such as the one mentioned above, the coolant may contain carbon dioxide gas in its circulating process or impurity ions generated from piping and the like, thereby becoming acidic or alkaline. When the coolant becomes acidic or alkaline, a predetermined part of the solid-state laser apparatus may deteriorate, thereby damaging the durability of the solid-state laser apparatus. When the coolant is brought into direct contact with the laser medium in particular, the quality of emitted laser light may deteriorate in a short period since surfaces of the laser medium are likely to corrode.

In view of such circumstances, it is an object of the present invention to provide a solid-state laser apparatus which can improve its durability.

Means for Solving Problem

For achieving the above-mentioned object, the solid-state laser apparatus in accordance with the present invention is a solid-state laser apparatus adapted to cool a solid-state laser medium with a coolant; the apparatus comprising a main pipe for circulating the coolant through the solid-state laser medium; cooling means, provided in the main pipe, for cooling the coolant; a bypass pipe connected in parallel to at least a part of the main pipe; neutralizing means, provided in the bypass pipe, for weakening an acidity or alkalinity of the coolant; flow regulating means, provided upstream of the neutralizing means in the bypass pipe, for regulating a flow rate of the coolant flowing into the bypass pipe; and control means for controlling the flow regulating means such as to increase the flow rate of the coolant flowing into the bypass pipe when the coolant is acidic or alkaline.

Since the main pipe for circulating the coolant through the solid-state laser medium is provided with cooling means for cooling the coolant, this solid-state laser apparatus can prevent the solid-state laser medium from raising its temperature. When the coolant becomes acidic or alkaline, the control means controls the flow regulating means, so as to increase the flow rate of the coolant flowing into the bypass pipe provided with the neutralizing means, whereby the acidity or alkalinity of the coolant can be weakened. This can prevent an acidic or alkaline coolant from deteriorating a predetermined part of the solid-state laser apparatus, and thus can improve the durability of the solid-state laser apparatus. Also, since the bypass pipe connected in parallel to at least a part of the main pipe is provided with the neutralizing means, the flow rate of the coolant circulating through the main pipe can be restrained from decreasing, whereby the cooling efficiency of the solid-state laser medium can be prevented from lowering.

Preferably, the control means increases the flow rate of the coolant flowing into the bypass pipe as the acidity or alkalinity of the coolant is stronger. This can rapidly weaken the acidity or alkalinity of the coolant.

Preferably, the coolant comes into direct contact with the solid-state laser medium. This can improve the cooling efficiency of the solid-state laser apparatus. In this case, there is a fear of the solid-state laser medium being likely to be corroded by the acidic or alkaline coolant. However, the solid-state laser apparatus in accordance with the present invention can weaken the acidity or alkalinity of the coolant as mentioned above, and thus can prevent the coolant from corroding the laser medium surface. Therefore, the durability of the laser medium itself can be improved, while the quality of emitted laser light can be maintained favorably for a long period.

Preferably, the main pipe is provided with a pump for circulating the coolant, whereas the bypass pipe is connected in parallel to at least a part of the main pipe between the solid-state laser medium and an intake of the pump. This allows the coolant discharged from the pump to reach the solid-state laser medium without decreasing its flow rate, and thus can more reliably prevent the cooling efficiency of the solid-state laser medium from lowering.

Preferably, the main pipe is provided with a tank for storing the coolant, whereas the control means detects the acidity or alkalinity of the coolant stored in the tank. When the acidity or alkalinity of the coolant once stored in the tank is detected, a highly accurate result of detection can be obtained.

Preferably, the bypass pipe is connected in parallel to at least a part of the main pipe between the solid-state laser medium and an inlet of the tank. In this case, the coolant having lowered its acidity or alkalinity through the bypass pipe (i.e., through the neutralizing means) and the coolant having traveled the main pipe mingle with each other in the tank, whereby the acidity or alkalinity of the coolant reaching the solid-state laser medium can be detected with a higher accuracy.

EFFECT OF THE INVENTION

The present invention can improve the durability of the solid-state laser apparatus.

EXPLANATIONS OF NUMERALS

BEST MODES FOR CARRYING OUT THE INVENTION

In the following, preferred embodiments of the solid-state laser apparatus in accordance with the present invention will be explained in detail with reference to the drawings.

As shown inFIG. 1, the solid-state laser apparatus1is one in which a solid-state laser medium3of a slab type (having a rectangular plate form here) accommodated in a laser head2is cooled with a coolant. In the laser medium3in the laser head2, end faces opposing each other in its longitudinal direction are an entrance face3aand an exit face3bfor light L to be amplified, whereas wider end faces orthogonal to the entrance face3aand exit face3bare reflecting surfaces3c,3dfor the light L to be amplified. Here, the laser medium3is one in which phosphate-based glass for laser as a matrix is doped with neodymium as a laser active species, though not restricted thereto. For example, silica-based glass for laser or crystal materials such as YAG, YLF, YVO4, S-FAP, sapphire, alexandrite, forsterite, and garnet may be used as the matrix. As the laser active species, rare-earth elements such as Yb, Er, Ho, and Tm or transition elements such as Cr and Ti may be used.

A semiconductor laser4for irradiating the laser medium3with pumping light is arranged at a position opposing each reflecting surface3c, whereas a window member6which transmits the pumping light therethrough is placed between the reflecting surface3cand semiconductor laser4opposing each other. Each window member6is watertightly secured to a holding part7which is a part of a housing (not depicted) of the laser head2, whereas a flow path8through which the coolant flows as indicated by solid arrows inFIG. 2is formed between the watertightly secured window member6and holding part7and the reflecting surface3cof the laser medium3.

In thus configured laser head2, the light L to be amplified incident on the laser medium3from the entrance face3ais repeatedly reflected by the reflecting surfaces3c,3copposing each other, so as to propagate through the laser medium3in a zigzag fashion while being amplified, and exits from the exit face3b.Though the pumping light generated by the semiconductor laser4heats the laser medium3, the coolant comes into direct contact with the reflecting surfaces3cof the laser medium3, and thus can efficiently deprive the laser medium3of heat. This can prevent the laser medium3from raising its temperature and causing a thermal lens effect and the like.

As shown inFIG. 1, the solid-state laser apparatus1further comprises a main pipe11laid out in a ring form so as to circulate the coolant through the laser medium3by way of the above-mentioned flow path8within the laser head2. Namely, the flow path8constitutes a part of the main pipe11. A tank12for storing the coolant is provided in the middle of the main pipe11, whereas a pump13for discharging the coolant from within the tank12toward the laser medium2is connected to the main pipe11between the outlet12aof the tank12and the laser medium3. The pump13causes the coolant within the tank12to circulate through the laser medium3by way of the main pipe11as indicated by solid arrows inFIG. 1.

A heat exchanger (cooling means)14for cooling the coolant is connected to the main pipe11between the laser medium3and the inlet12bof the tank12. The heat exchanger14cools the coolant such that a temperature within a predetermined temperature range is attained according to a result of measurement of a temperature sensor15which monitors the temperature of the coolant within the tank12. Therefore, the coolant having raised its temperature by depriving the laser medium3of heat in the laser head2is cooled by the heat exchanger14to a temperature within the predetermined temperature range, and then is returned into the tank12. In addition, the main pipe11is provided with a pressure gauge17for monitoring the pressure of the coolant flowing into the laser head2, and a flow meter18for monitoring the flow rate of the coolant flowing out of the laser head2. According to results of their measurement, when the pressure is outside of a predetermined pressure range or the flow rate is outside of a predetermined flow rate range, an alarm is rung as a warning or an interlock works.

Further, a bypass pipe21is connected in parallel to a part of the main pipe11between the laser medium3and the inlet12bof the tank12. More specifically, the upstream end21aof the bypass pipe21is connected to the main pipe11between the flow meter18and the heat exchanger14, whereas the downstream end21bof the bypass pipe21is connected to the tank12. A deionizing filter (neutralizing means)22made of an ion exchange resin which turns an acidic or alkaline coolant into a substantially neutral state is connected to the bypass pipe21. A flow regulating valve (flow regulating means)23for regulating the flow rate of the coolant flowing into the bypass pipe21as indicated by broken arrows inFIG. 1is connected to the upstream side of the deionizing filter22on the bypass pipe21.

The flow regulating valve23is controlled by a controller (control means)24such as to increase the flow rate of the coolant flowing into the bypass pipe21when the coolant is acidic or alkaline. More specifically, the controller24includes a pH sensor25for monitoring the hydrogen ion exponent (pH value) of the coolant within the tank12, and a feedback circuit26for regulating the opening of the flow regulating valve23. The feedback circuit26causes the flow regulating valve23to open when the pH value of the coolant within the tank12is outside of a predetermined pH range (e.g., a range centered at pH 7) (i.e., when the acidity or alkalinity of the coolant within the tank12exceeds a predetermined strength), and makes the opening of the flow regulating valve23greater as the acidity or alkalinity of the coolant is stronger.

Thus, the pH sensor25of the controller24detects the acidity or alkalinity of the coolant once stored in the tank12. Also, in the tank12, the coolant having become substantially neutral through the bypass pipe21(i.e., through the deionizing filter22) and the coolant having traveled the main pipe11mingle with each other. Therefore, the pH sensor25can detect with a very high accuracy the pH value of the coolant reaching the laser medium3.

Here, the pH sensor25is one utilizing an ion-sensitive field-effect transistor (ISFET) employing a thin film of SiO2/Si3N4as a sensitive part, generates an interfacial potential corresponding to the hydrogen ion amount in the coolant by bringing the coolant into contact with an Si3N4film on its gate, and takes out this potential as an output voltage. Namely, the pH sensor25can measure the pH dependence of the coolant. However, the pH sensor25is not restricted to the above, whereas those measuring the pH value by detecting an ion amount with a glass electrode having KCl or Ag/AgCl deposited thereon and those calculating the pH value by measuring the electric conductivity of the coolant may also be used, for example.

While the pump13causes the coolant in the tank12to circulate through the laser medium3by way of the main pipe11in thus configured solid-state laser apparatus1, the coolant is cooled by the heat exchanger14so as to attain a temperature within a predetermined temperature range, and thus can prevent the laser medium3from raising its temperature. Here, the pH value of the coolant in the tank12may fall out of a predetermined pH range because of various reasons, e.g., because the coolant contains gases such as carbon dioxide, oxygen, and nitrogen stored in the upper part within the tank12and because the coolant contains impurity ions generated by the laser head2, the main pipe11, and the like. In this case, the controller24opens the flow regulating valve23, so that the coolant flows into the bypass pipe21having the deionizing filter22connected thereto, whereby the coolant becomes substantially neutral and returns into the tank12, which weakens the acidity or alkalinity of the coolant. Consequently, the acidic or alkaline coolant can be prevented from deteriorating a predetermined part of the solid-state laser apparatus1, whereby the durability of the solid-state laser apparatus1can be improved.

Here, the opening of the flow regulating valve24is made greater as the acidity or alkalinity of the coolant is stronger, whereby the flow rate of the coolant flowing into the bypass pipe21increases as the acidity or alkalinity of the coolant is stronger. Therefore, the acidity or alkalinity of the coolant can be weakened rapidly. The flow regulating valve21may be opened to a predetermined extent from when the solid-state laser apparatus1begins operating, so as to allow a predetermined amount of the coolant to pass through the deionizing filter22, and the flow rate of the coolant flowing into the bypass pipe21may be increased when the acidity or alkalinity of the coolant becomes stronger.

While the coolant comes into direct contact with the solid-state laser medium3as mentioned above, the solid-state laser apparatus1can weaken the acidity or alkalinity of the coolant, and thus can prevent the coolant from corroding the surfaces (i.e., reflecting surfaces3c) of the laser medium3. As a consequence, the quality of emitted laser light can be maintained favorably for a long period by preventing the light L to be amplified from being scattered by the reflecting surfaces3cand so forth, while the durability of the laser medium3itself can be improved.

Since the bypass pipe21connected in parallel to a part of the main pipe11is provided with the deionizing filter22, the flow rate of the coolant circulating through the main pipe11can be restrained from decreasing, whereby the cooling efficiency of the solid-state laser medium3can be prevented from lowering. Also, since the bypass pipe21is connected in parallel to a part of the main pipe11between the laser medium3and the inlet12bof the tank12, i.e., between the laser medium3and the intake13aof the pump13, the coolant discharged from the pump13reaches the laser medium3without lowering its flow rate. Therefore, the cooling efficiency of the laser medium3can more reliably be prevented from decreasing.

The present invention is not limited to the embodiment mentioned above. For example, though the deionizing filter22acting as the neutralizing means is one which turns the acidic or alkaline coolant into a substantially neutral state, those which weaken the acidity or alkalinity of the coolant (make the pH value approach 7) can also be employed.

INDUSTRIAL APPLICABILITY

As explained in the foregoing, the present invention can improve the durability of the solid-state laser apparatus.