JP2006331748A - Discharge induction method and discharge induction device using hybrid laser - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To further improve a discharge induction property when guiding a discharge from an electrode to a conductor by utilizing a laser beam. <P>SOLUTION: When guiding a discharge from thunder cloud (an electrode) 2 to a lightning rod (a conductor) 3 by utilizing a laser beam L, an ultra-short pulse laser beam L is irradiated toward tip part of the lightning rod 3. A leader extending from the lightning rod 3 toward the thunder cloud 2 is induced by using a high density plasma generated by condensing the ultra-short pulse laser beam L with short focus, and the other ultra-short pulse laser beam L is irradiated toward the thunder cloud 2. The leader is guided in long distance by using filaments generated by condensing the ultra-short pulse laser beam L with long focus. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a discharge induction method and apparatus using a hybrid laser. More specifically, the present invention relates to an improvement in a discharge induction technique suitable for implementing a so-called laser lightning or laser gap switch that guides lightning to a lightning rod by a plasma channel generated in the air by laser light.

Conventionally, a laser discharge induction method and a discharge induction device have been proposed (see, for example, Patent Document 1). Furthermore, as a technique for guiding lightning to a safe place, a technique of guiding to a specific lightning rod using a laser has been proposed. This method uses a laser to generate a plasma channel and, when a thundercloud approaches, creates an upward leader (precursor discharge) from the tip of the lightning rod, and safely guides the lightning to the target lightning rod (patent) Reference 2). CO ₂ lasers, excimer lasers, glass lasers, etc. have been proposed as lasers used to implement such lightning strikes, and basic experiments have been carried out, but long plasmas that do not allow continuous plasma channels There are problems such as channel failure.

  On the other hand, there is an ultrashort pulse laser as a laser capable of generating a continuous and long plasma channel. An ultrashort pulse laser is a pulse laser with a pulse width of picoseconds or less. By reducing the pulse width, high-power laser light can be generated instantaneously even if the energy per pulse is small. it can. For example, in the case of a laser with a pulse width of 50 femtoseconds, if the energy per pulse is 50 mJ, the instantaneous output is 1 terawatt. The following two methods have been proposed for using such an ultrashort pulse laser for laser induced lightning. One is a method using a focused plasma generated by focusing a laser beam with a short focus. In this method, the result of conducting discharge induction by condensing laser light at the center between electrodes has been reported. Another method is a method using a filament generated by condensing or irradiating in parallel with a long focal point. A filament is a light that propagates for a long distance while being condensed, and there is a report that a filament is generated over several hundreds of meters to several kilometers by using an ultrashort pulse laser. Furthermore, there has been reported an example in which a filament is generated between the electrodes, and discharge induction with a length of 3.8 m between the electrodes is performed using a plasma channel generated in the filament.

JP-A-7-142190 JP-A-8-064385

  However, although the plasma channel generated when condensing ultrashort pulse laser light with a short focus is thick and dense, it is difficult to guide the discharge over a long distance because the length is as short as several meters. There is a point. On the other hand, filaments generated by condensing or irradiating ultrashort pulse laser light with a long focal point can be generated over several hundred meters, but the thickness is as short as 1 mm or less, and the plasma density is also compared. Therefore, it is difficult to trigger discharge (generate a leader). In particular, naturally induced lightning usually behaves like a direct current, and thunderclouds are negatively charged. Therefore, the lightning rod that should induce lightning is DC positive polarity. Usually, it is difficult to generate a leader from a DC positive electrode, and it is considered difficult to generate an upward leader using a filament from such a DC positive lightning rod.

  Therefore, an object of the present invention is to provide a discharge induction method and apparatus capable of further improving the performance of discharge induction when a discharge from an electrode is induced to a conductor using laser light.

  In order to achieve this object, the present inventor has repeatedly conducted various studies and has obtained certain findings as a result. In other words, a combination of a condensing plasma generated by condensing an ultrashort pulse laser with a short focal point and a filament generated by converging with a long focal point or irradiating in parallel, the performance of laser induced lightning, laser gap switch, etc. Is to improve. To put it another way, we have come up with a new technology that, when hybridized with a filament and a leader, forms a “hybrid laser” to induce discharge, thereby improving the characteristics of discharge induction. .

  The present invention is based on such knowledge. First, the invention described in claim 1 is a discharge induction method using a laser for inducing a discharge from an electrode to a conductor using a laser beam. A leader that extends from the conductor to the electrode is induced using high-density plasma generated by irradiating the ultrashort pulse laser light toward the tip of the conductor and condensing the ultrashort pulse laser light at a short focal point. In addition, the other ultrashort pulse laser beam is irradiated toward the electrode, and the reader is guided over a long distance using a filament generated by condensing the other ultrashort pulse laser beam with a long focal point. is there.

  The discharge induction method using this hybrid laser is a laser combining a condensing plasma generated by condensing ultrashort pulse laser light with a short focus and a filament generated by condensing with a long focus or irradiating in parallel. Improve the performance of lightning and laser gap switches. That is, a method in which a focused plasma and a filament are simultaneously irradiated onto the tip of a conductor (for example, a lightning rod), a leader is generated by the focused plasma that triggers discharge, and the generated leader is guided for a long distance by the filament. . If this method is used, it is possible to guide the leader generated from the tip of the conductor to several tens of meters or more, so that the laser lightning performance is significantly improved.

  Here, the filament can be generated either when the ultrashort pulse laser beam is condensed with a long focal point or when the ultrashort pulse laser beam is irradiated in parallel. In other words, since the filament in the present invention can be generated even when the focal length is ∞ (infinity), the long focus in the present invention includes the focal length ∞ (infinity) in a broad sense. It can be said that it is a concept.

  Further, in performing the discharge induction as described above, as described in claim 2, by using a multifocal reflection mirror that partially varies the focal length as a reflection mirror that condenses the ultrashort pulse laser beam, It is preferable to condense a part of the short pulse laser beam with a short focal point and the remaining part with a long focal point. Alternatively, as described in claim 3, a mirror having a short focal length and a mirror having a long focal length are separately used as reflecting mirrors for collecting the ultrashort pulse laser light, and a part of the ultrashort pulse laser light is reflected on one side. It is also preferable to collect light with a short focal point using a mirror and to collect the remaining light with a long focal point using the other reflecting mirror. In any case, the ultrashort pulse laser beam is irradiated in two types of modes, that is, an ultrashort pulse laser beam focused at a short focus and an ultrashort pulse laser beam focused at a long focus. In such a case, a condensed plasma is generated by the ultrashort pulse laser beam condensed at a short focal point, and a filament is generated by the ultrashort pulse laser beam condensed (reflected) at a long focal point.

  Further, the reflection mirror in the case of carrying out the discharge induction as described in claim 2 or 3 has a local convex part or concave part as in claim 4, and a filament is generated using this reflective mirror. And it is preferable to control. The ultrashort pulse laser beam applied to the reflecting mirror having a local convex or concave part gives local spatial modulation to the beam wavefront according to the local convex or concave part of the mirror surface during reflection. This becomes a starting point (seed) and forms a filament in the course of beam propagation. Since this filament is stably generated due to the presence of local convex portions or concave portions on the surface of the reflecting mirror, by forming the local convex portions or concave portions at arbitrary positions, any arbitrary beam cross section can be formed. Formed uniquely continuously at the position.

  Alternatively, as in claim 5, the reflecting mirror is provided with a global concave portion around the local convex portion or concave portion, which is global compared to the local convex portion or concave portion, It is also preferred to generate and control the filament using this reflective mirror. The energy of the ultrashort pulse laser beam reflected by the global concave portion or the peripheral intensity spot can be collected around the intensity spot formed at an arbitrary position of the beam cross section reflected by the local convex part or concave part. .

  Furthermore, it is also preferable to use a surface shape variable reflection mirror that can change the surface shape as the reflection mirror. It is also possible to change the local distribution of convex portions or concave portions by changing the surface shape.

  The invention according to claim 7 is also based on the above-mentioned knowledge, and in a discharge induction device using a laser for inducing discharge from an electrode to a conductor using laser light, an ultrashort pulse is used as laser light. A laser beam is used to irradiate the tip of the conductor with this ultrashort pulse laser beam, and the ultrashort pulse laser beam is focused at a short focal point and directed from the conductor to the electrode using high-density plasma. In addition to inducing an upwardly extending reader, the other ultrashort pulse laser beam is irradiated toward the electrode, and the other ultrashort pulse laser beam is focused at a long focal length to produce a long reader. A laser oscillator for guiding the distance is provided.

  This discharge induction device using a hybrid laser is a laser that combines a condensing plasma generated by condensing an ultrashort pulse laser beam with a short focal point and a filament generated by condensing or irradiating with a long focal point in parallel. Improve the performance of lightning and laser gap switches. In other words, the focused plasma and filament are simultaneously irradiated onto the tip of a conductor (for example, a lightning rod), an upward leader is generated by the focused plasma that triggers discharge, and the generated leader is guided over a long distance by the filament. is there. According to this, since it is possible to guide the upward leader generated from the conductor tip by several tens of meters or more, the performance of laser induced lightning is remarkably improved.

  The discharge induction device using the above hybrid laser is a mirror that changes the path of the laser beam by reflecting the laser beam as in claim 8, and is a multifocal reflection mirror that partially differs in focal length. A part of the ultra-short pulse laser light emitted from the laser oscillator is reflected and collected by the mirror part with a short focal length of the reflection mirror, and the rest of the ultra-short pulse laser light is adjusted to the focal length of the reflection mirror. It is preferable to reflect on a long mirror part. Alternatively, as described in claim 9, a short-focus reflection mirror that reflects the laser beam and changes the path of the laser beam and a long-focus reflection mirror are provided, and the ultrashort pulse laser beam emitted from the laser oscillator is shortened. It is also preferable to reflect and condense with a focal reflecting mirror and to reflect other ultrashort pulse laser light with a long focal reflecting mirror. In any case, the ultrashort pulse laser beam is irradiated in two types of modes, that is, an ultrashort pulse laser beam focused at a short focus and an ultrashort pulse laser beam focused at a long focus. In such a case, a condensed plasma is generated by the ultrashort pulse laser beam condensed at a short focal point, and a filament is generated by the ultrashort pulse laser beam condensed (reflected) at a long focal point.

  In either of the cases of claim 8 and claim 9, the ultrashort pulse laser light is collected in two modes: an ultrashort pulse laser beam focused at a short focus and an ultrashort pulse laser beam focused at a long focus separately. Laser light is irradiated. In such a case, a condensed plasma is generated by the ultrashort pulse laser beam condensed at a short focal point, and a filament is generated by the ultrashort pulse laser beam condensed (reflected) at a long focal point.

  Further, the reflection mirror in the case of performing discharge induction as described in claim 8 or 9 has a local convex part or concave part as in claim 10, and a filament is generated by using this reflective mirror. However, it is preferable that it can be controlled. The ultrashort pulse laser beam applied to the reflecting mirror having a local convex or concave part gives local spatial modulation to the beam wavefront according to the local convex or concave part of the mirror surface during reflection. This becomes a starting point (seed) and forms a filament in the course of beam propagation. Since this filament is stably generated due to the presence of local convex portions or concave portions on the surface of the reflecting mirror, by forming the local convex portions or concave portions at arbitrary positions, any arbitrary beam cross section can be formed. Formed uniquely continuously at the position.

  Alternatively, according to the eleventh aspect, the reflecting mirror includes a global concave portion that is more global than the local convex portion or concave portion around the local convex portion or concave portion. It is also preferred that the filaments can be produced and controlled by using. The energy of the ultrashort pulse laser beam reflected by the global concave portion or the peripheral intensity spot can be collected around the intensity spot formed at an arbitrary position of the beam cross section reflected by the local convex part or concave part. .

  Furthermore, as in claim 12, the reflecting mirror is preferably a surface shape variable reflecting mirror capable of changing its surface shape. It is also possible to change the local distribution of convex portions or concave portions by changing the surface shape.

  According to the discharge induction method using the hybrid laser according to the first aspect, it is possible to significantly improve the discharge induction performance by simultaneously forming both the filament and the focused plasma by the “hybrid laser”. Therefore, according to the discharge induction method using this hybrid laser, the above-mentioned second problem, that is, when the ultrashort pulse laser beam is condensed with a short focal point and when it is condensed with a long focal point (or parallel irradiation) Can easily solve the problem of each. That is, the ultrashort pulse laser beam focused at a short focal point generates a condensed plasma, and at the same time, the ultra short pulse laser beam focused at a long focal point (or parallel irradiation) generates a filament. It is possible to guide a leader generated from the tip of several tens of meters or more, and according to the present invention, it is possible to form a state in which discharge is easily induced and to greatly improve the performance of laser induced lightning and the like.

  According to the discharge induction method using the hybrid laser according to claim 2, there are two types of ultrashort pulse laser light that is focused with a short focus and ultrashort pulse laser light that is focused with a long focus (or parallel irradiation). In this mode, the ultrashort pulse laser light is irradiated. Therefore, the condensed plasma is generated by the ultrashort pulse laser beam focused at the short focus, and the ultrashort pulse laser beam focused at the long focus (or parallel irradiation) is used. A filament can be generated, and a situation where discharge is easily induced can be formed.

  According to the discharge induction method using the hybrid laser of claim 3, the short focus mirror and the long focus mirror are separately used, and the ultrashort pulse laser beam focused at the short focus and separately focused at the long focus ( (Or, parallel irradiation) Since the ultrashort pulse laser beam is irradiated in two types of modes: ultrashort pulse laser beam, a focused plasma is generated by the ultrashort pulse laser beam focused at a short focal point and collected at a long focal point. A filament is generated by the ultrashort pulse laser beam that is irradiated with light (or parallel irradiation), and a situation in which discharge is easily induced can be formed.

  According to the discharge induction method using the hybrid laser of claim 4, since the filament is generated and controlled using the reflection mirror having the local convex portion or concave portion, such a local convex portion or concave portion is formed. By forming at arbitrary positions, filaments can be uniquely and continuously formed at arbitrary positions in the beam cross section. In addition, if the position of the local convex part or concave part formed on the surface of the reflecting mirror can be formed at an arbitrary position on the reflecting surface, the number of filaments can be changed by changing the position of the intensity spot that is the starting point of filament generation It becomes possible to control the length and the generation position.

  According to the discharge induction method using the hybrid laser according to claim 5, an ultrashort pulse reflected by a global concave portion around an intensity spot formed at an arbitrary position of a beam cross section reflected by a local convex portion or concave portion. It is possible to increase the electric field strength of the intensity spots at arbitrary positions by gathering the energy of the laser light or surrounding intensity spots.

  According to the discharge induction method using the hybrid laser according to claim 6, the distribution of the local convex portions or concave portions is changed by changing the surface shape of the reflecting mirror, and thereby the intensity unevenness that becomes the starting point of filament generation. It becomes possible to further control the production state of the filament by changing the position of the.

  According to the discharge induction device using the hybrid laser of claim 7, it is possible to remarkably improve the discharge induction performance by simultaneously generating both the filament and the leader by the “hybrid laser”. Therefore, according to the discharge induction device using this hybrid laser, the second problem described above, that is, when the ultrashort pulse laser beam is condensed with a short focus and when it is condensed with a long focus (or parallel irradiation) Can easily solve the problem of each. That is, the ultrashort pulse laser beam focused at a short focal point generates a condensed plasma, and at the same time, the ultra short pulse laser beam focused at a long focal point (or parallel irradiation) generates a filament. It is possible to guide an upward leader generated from the tip of several tens of meters or more, and according to the present invention, it is possible to form a state in which discharge is easily induced and to greatly improve the performance of laser induced lightning and the like.

  According to the discharge induction device using the hybrid laser according to claim 8, there are two types of ultrashort pulse laser light focused at a short focal point and ultra short pulse laser light focused at a long focal point (or parallel irradiation). In this mode, the ultrashort pulse laser light is irradiated. Therefore, the condensed plasma is generated by the ultrashort pulse laser beam focused at the short focus, and the ultrashort pulse laser beam focused at the long focus (or parallel irradiation) is used. A filament can be generated, and a situation where discharge is easily induced can be formed.

  Furthermore, according to the discharge induction device using the hybrid laser according to claim 9, the short focus mirror and the long focus mirror are separately used, and the ultrashort pulse laser beam that focuses at the short focus and the long focus separately. Since the ultrashort pulse laser beam is irradiated in two types of modes (ultrashort pulse laser beam) (or parallel irradiation), a condensed plasma is generated by the ultrashort pulse laser beam focused at a short focal point, and at a long focal point. Filaments are generated by the ultrashort pulse laser beam that is focused (or parallel irradiated), and a situation in which discharge is easily induced can be formed.

  According to the discharge induction device using the hybrid laser according to claim 10, by forming the local convex portion or concave portion of the reflection mirror at an arbitrary position, the filament is uniquely continuously arranged at an arbitrary position of the beam cross section. Can be formed. In addition, if the position of the local convex part or concave part formed on the surface of the reflecting mirror can be formed at an arbitrary position on the reflecting surface, the number of filaments can be changed by changing the position of the intensity spot that is the starting point of filament generation. It becomes possible to control the length and the generation position.

  According to the discharge induction device using the hybrid laser according to claim 11, an ultrashort pulse reflected by a global concave portion around an intensity spot formed at an arbitrary position of a beam cross section reflected by a local convex portion or concave portion. It is possible to increase the electric field strength of the intensity spots at arbitrary positions by gathering the energy of the laser light or surrounding intensity spots.

  According to the discharge induction device using the hybrid laser according to claim 12, the distribution of the local convex portions or concave portions is changed by changing the surface shape of the reflecting mirror, and thereby the intensity unevenness that becomes the starting point of filament generation. It becomes possible to further control the production state of the filament by changing the position of the.

  Hereinafter, the configuration of the present invention will be described in detail based on the best mode shown in the drawings.

  FIG. 1 shows an embodiment of the present invention. A discharge induction apparatus 1 using a hybrid laser according to the present invention is an apparatus for inducing a discharge from an electrode 2 to a conductor 3 using a laser beam L. The so-called hybrid type discharge induction device 1 in the present embodiment is a device including a laser oscillator 4 and a reflection mirror 5, and a hybrid of a filament and a reader forms a “hybrid laser” to induce discharge. This improves the discharge induction characteristics. In the embodiment described below, a case where the discharge induction device 1 is applied to laser induced lightning will be described (see FIG. 1 and the like). In this case, a thundercloud corresponds to the electrode 2 (hereinafter referred to as a thundercloud 2 with reference numeral 2), and a lightning rod corresponds to the conductor 3 (hereinafter referred to as a thundercloud 3 with reference numeral 3). Called). The lightning rod 3 is a device for preventing lightning damage, and includes, for example, a steel tower (lightning tower) with a metal rod at the tip.

  Here, first, laser lightning performed in this embodiment will be briefly described. Using lightning rod 3 or the like to artificially guide lightning to a safe place is called “trigger lightning”. Among these, to induce lightning using laser light L is called “laser lightning”. . That is, as shown in FIG. 1, laser induced lightning is a technique for avoiding lightning damage by irradiating the lightning cloud 2 with laser light L and guiding lightning to the lightning rod 3. This laser-induced lightning is performed by generating a high-density / long plasma channel between the ground and the thundercloud 2 using laser light L. The plasma generated in this case has high electrical conductivity. Therefore, this guides the lightning discharge path to a safe place. In other words, the energy of the laser beam L is increased to generate plasma with good conductivity in the air, thereby forming a path through which lightning easily passes.

  The hybrid type discharge induction device 1 in the present embodiment is a device including a laser oscillator 4 and a reflection mirror 5. Among these, the laser oscillator 4 uses the ultrashort pulse laser beam L as the laser beam L, and irradiates the ultrashort pulse laser beam L toward the tip of the lightning rod 3. In this case, an upward leader extending from the lightning rod 3 toward the thundercloud 2 is induced using high-density plasma generated by condensing the ultrashort pulse laser beam L with a short focal point, and other ultrashort pulse laser beams. L is directed toward the thundercloud 2 and the other ultra-short pulse laser beam L is condensed at a long focal point to guide the upward reader over a long distance (see FIG. 1).

  Further, the reflection mirror 5 in the discharge induction device 1 is a mirror that reflects the ultrashort pulse laser light L and changes the path of the laser light L, and is a multifocal type mirror (multiplexing partly different in focal length). Focusing mirror). That is, the reflection mirror 5 reflects and condenses a part of the ultrashort pulse laser beam L emitted from the laser oscillator 4 by a mirror portion having a short focal length, and the remaining focal length of the ultrashort pulse laser beam L. Reflected by a long mirror part. The ultrashort pulse laser beam L reflected by the mirror portion having a short focal length is directed toward the tip of the lightning rod 3 to generate high-density plasma and induce an upward leader extending toward the thundercloud 2. On the other hand, the ultrashort pulse laser beam L reflected by the mirror portion having a long focal length is condensed at a long focal point (or parallel irradiation) to generate many filaments in the atmosphere (in this specification, in this atmosphere Filaments produced in large numbers at the same time are called "multifilaments").

  Hereinafter, an embodiment in the case of performing lightning strike using the above-described discharge induction device 1 will be described. First, the laser beam L generated from the laser oscillator 4 is irradiated onto the reflection mirror (multifocal mirror) 5. As described above, the reflecting mirror 5 of the present embodiment has two focal lengths, and one example has a focal length of 10 m and the other has a focal length of 30 m. The laser light L condensed at a focal distance of 10 m is condensed on the tip of the lightning rod 3 to generate high-density focused plasma at the tip of the lightning rod 3 (see FIG. 1). At the same time, a filament is generated by the laser light L reflected from the portion having a focal length of 30 m. At this time, it is desirable to adjust the focal length of the reflecting mirror 5 so that the filament is generated before the tip of the lightning rod 3. In such a case, it is possible to generate an upward leader by high-density focused plasma generated by condensing with a focal length of 10 m, and to guide the reader with a filament generated by condensing with a focal length of 30 m. If you guide the upward leader for several tens of meters, it will naturally reach the thundercloud 2, so that you can reliably guide the subsequent lightning stroke to the lightning rod 3 (see Fig. 1).

  Here, the case where a multifocal mirror is used as an example of the reflection mirror (condensing mirror) 5 has been described. However, the present invention is not limited thereto, and the reflection mirror 5 having a short focal length and the reflection mirror 5 having a long focal length are separately provided. It is good also as combining a mirror. In this case, although the system is slightly complicated, there is an advantage that the cost can be reduced because a special mirror such as a multifocal mirror is not used. In addition, it is conceivable that the generation state of the filaments is different due to the influence of weather conditions, etc. However, if separate reflection mirrors 5 having different focal distances are used, only the reflection mirror 5 having a long focal distance, for example, according to changes in weather conditions or the like There is also an advantage that it is possible to cope with it simply by replacing the.

  Here, as a method for generating and controlling the filament, the use of the reflecting mirror 5 having local convex portions or concave portions is preferable in that the filament can be generated at an arbitrary position designed in advance. . Further, as a method for generating and controlling the filament, if the reflecting mirror 5 in which a global concave portion is added to the local convex portion or concave portion as compared with the local convex portion or concave portion is used, any position can be obtained. It is also preferable in that the intensity of the laser beam can be concentrated. In such a case, the energy of the ultrashort pulse laser beam reflected by the global concave portion or the peripheral intensity irregularity is reflected around the intensity spot formed at an arbitrary position of the beam cross section reflected by the local convex part or concave part. By gathering, the electric field strength of the intensity spot at an arbitrary position can be further increased, and filament generation during beam propagation can be made more reliable. Further, as a method for generating and controlling the filament, the surface shape variable reflecting mirror 5 in which a local convex portion or a concave portion is added with a global concave portion as compared with the local convex portion or concave portion is used. In this case, the generation position of the filament on the beam cross section can be controlled in real time by controlling the formation position of the global recess. As a result, even when the filament generation conditions change due to changes in weather conditions or the like, the filaments can be generated at optimal positions.

  The reflection mirror 5 in the present embodiment has a local convex portion or concave portion as described above, and is a mirror that reflects the laser light L and changes the path of the laser light L. The reflection mirror 5 is used to generate and control multifilaments. Below, the suitable form in the case of producing | generating a filament in air | atmosphere using such a laser oscillator 4 and the reflective mirror 5 is demonstrated (refer FIGS. 2-14). Here, an ultrashort pulse laser beam (hereinafter also referred to as “ultrashort pulse laser beam”) L is applied to the reflection mirror 5 having a local convex portion or concave portion 9 and reflected by the local convex portion or concave portion 9. The origin of filament generation is created by creating intensity spots at any part of the beam cross section.

  That is, by interposing the reflecting mirror 5 having local convex portions or concave portions 9 on the optical path of the ultrashort pulse laser beam L, when the ultrashort pulse laser beam L is reflected, local reflection on the mirror surface is performed. A local spatial modulation corresponding to the convex portion or the concave portion 9 is given to the wavefront of the beam, which becomes a starting point (seed) and forms a filament in the course of beam propagation. Since this filament is stably generated due to the presence of the local convex portion or concave portion 9 on the surface of the reflecting mirror 5, by forming the local convex portion or concave portion 9 at an arbitrary position, the beam cross section Are continuously formed uniquely at arbitrary positions. It should be noted that at least one local convex portion or concave portion 9 is provided at any position in the region irradiated with the beam on the surface / reflecting surface of the reflecting mirror 5, but two or more portions are provided as necessary. Is also possible.

  Further, the reflecting mirror 5 having the local convex portion or concave portion 9 has a global concave portion (in FIG. 4) larger than the local convex portion or concave portion 9 in addition to the local convex portion or concave portion 9. It is preferable that the display is provided with a reference numeral 10. That is, the ultrashort pulse laser beam L is emitted by the reflecting mirror 5 having the global concave portion 10 as compared with the local convex portion or concave portion 9 simultaneously with or before and after the step of creating intensity spots by the local convex portion or concave portion. If the energy of the ultrashort pulse laser beam L or the surrounding intensity spots are gathered toward the center of the global recess 10 by reflection, the electric field intensity of the intensity spots that become the starting point of filament generation is made stronger. Thus, filament generation during beam propagation can be made more reliable. More specifically, the global concave portion 10 is located around the local convex portion or concave portion 9 or at a position corresponding to the local convex portion or concave portion 9 in the beam cross section as compared with the local convex portion or concave portion 9. By reflecting the ultrashort pulse laser beam L with the reflecting mirror 5 having the above, the energy of the reflected beam or the surrounding intensity spots are gathered around the intensity spots around the center, and the electric field of the intensity spots that becomes the starting point of filament generation It is possible to increase the intensity to ensure filament generation during beam propagation and to generate a filament of any density at any part of the cross section of the reflected beam.

  Further, by controlling the formation position of the global recess 10, the generation position of the filament on the beam cross section can be controlled. That is, the local convex or concave portion 9 formed in advance on the reflecting surface of the reflecting mirror 5 causes local spatial modulation as a starting point (seed) to form a filament on the wave front of the beam in the course of beam propagation. The number of local convex portions or concave portions 9 in the region irradiated with the laser beam is provided to form a reflected beam, and the energy of the ultrashort pulse laser beam L or the intensity of the surroundings is generated for some of the intensity spots. If the global concave portion 10 is formed on the reflecting surface so that the spots are gathered, the electric field strength of the intensity spots at the center of the global concave portion 10 is further increased, and further, the peripheral intensity spots gather or merge. This ensures that a denser or stronger filament is produced at a location located at the center of the global recess 10 in the beam cross section. Therefore, by controlling the formation position of the global recess 10, it is possible to control to generate an arbitrary density or number of filaments at an arbitrary position on the beam cross section. According to this, it becomes possible to actively generate multifilaments composed of a large number of filaments in the atmosphere.

  The step of generating the filament generation start point and the step of collecting the energy of the ultrashort pulse laser beam L or the surrounding intensity spots around the intensity spots are not only performed at the same time, but either one is performed first. Also good. However, when the step of collecting the energy of the simultaneous or ultrashort pulse laser beam L or the surrounding intensity spots around the intensity spots is performed later, it is one of the filament generation starting points. Alternatively, it is easy to further increase the electric field strength of a plurality of intensity spots and promote the generation of filaments.

  Here, as a method for forming a filament that simultaneously performs the step of generating an intensity spot that is the starting point of filament generation and the step of collecting the energy of the ultrashort pulse laser beam L around the intensity spot, for example, a reflecting surface It can be arbitrarily deformed so as to have a local convex portion or concave portion 9 and to form a global concave portion 10 around the local convex portion or concave portion 9 as compared with the local convex portion or concave portion 9. The variable reflection mirror 5 is used. In this case, the generation position of the intensity spots formed by the local protrusions or recesses 9 and the energy of the ultrashort pulse laser beam L generated by the global recesses 10 or the gathering positions of the surrounding intensity spots are associated in advance. Thus, the electric field strength of the intensity spot at an arbitrary position on the beam cross section is more reliably increased.

  In addition, as a filament forming method for continuously performing the step of generating the filament generation starting point and the step of collecting the energy of the ultrashort pulse laser beam L around the intensity spots, for example, a local convex portion or concave portion 9 is used. The reflecting mirror 5 having the above and the reflecting mirror 5 which forms a global concave portion 10 at a position corresponding to the local convex portion or concave portion 9 in the beam cross section as compared with the local convex portion or concave portion 9 are separated. The light may be reflected by the reflection mirror 5 in order. In this case, the energy of the ultrashort pulse laser beam L generated by the global concave portion 10 independently of the intensity unevenness uniquely formed at an arbitrary position in the beam cross section after reflection by the local convex portion or concave portion 9. Alternatively, a set of surrounding intensity spots is controlled.

  In the case of using the deformable reflecting mirror 5 in which the reflecting surface can be arbitrarily deformed by providing a plurality of independently controllable actuators, at least the number of mounted global recesses 10 is formed on the reflecting surface. Therefore, it is preferable to provide a local convex portion or concave portion 9 for each position corresponding to the center of each global concave portion 10 or in the vicinity thereof.

  2 and FIG. 2 show an example of a filament forming apparatus capable of forming a filament by applying a local spatial modulation corresponding to the local convex portion or concave portion 9 on the mirror surface to the ultrashort pulse laser beam L as described above. 3 shows. This filament forming apparatus uses a variable reflection mirror 5 having a plurality of independently controllable actuators, and a reflection mirror 5 whose reflection surface can be arbitrarily deformed (hereinafter also referred to as a variable mirror), The actuator 6 is connected to the back side of the deformable mirror 5 and applies a displacement to the deformable mirror 5, and the deformable mirror 5 can be globally deformed by driving the actuator 6.

  Here, as the deformable mirror 5, a thin flat mirror whose reflection surface can be arbitrarily deformed by driving a plurality of independently controllable actuators 6 is employed. In the case of the present embodiment, the actuator has rigidity enough to easily form a desired global recess 10 by driving the actuator 6. For example, a square mirror having a vertical and horizontal dimension of about 100 × 100 (mm) is thick. It is preferable to use a thin plane mirror having a thickness of about 3 mm.

  The back surface of the reflection mirror 5 is connected to the actuator 6 and supported by the frame 11 via the actuator 6. In the present embodiment, the 13 actuators 6 are arranged on the entire back surface of the deformable mirror 5 vertically and horizontally and diagonally at almost equal intervals, but the number is not particularly limited.

  The actuator 6 includes a rod 13 fixed to the back surface of the reflecting mirror 5, and the rod 13 is detachably connected to a movable portion of the actuator 6 (rod holder 14 in the present embodiment). For example, the actuator 6 is provided with a hole for fitting the rod 13 on at least the end side of the rod holder 14 fixed to the tip of the drive element 16 and fixing the rear end side of the rod 13. The rod 13 is detachably fixed by tightening the rod 13 with a screw 15. In the present embodiment, the rod 13 is fixed by frictional force by pressing the outer peripheral surface of the rod 13 with the tip of the screw 15 screwed into the screw hole of the rod holder 14. You may connect so that attachment or detachment is possible. When it is necessary to replace the deformable mirror 5, such as when the reflection characteristics of the deformable mirror 5 deteriorate due to the structure in which the rod 13 can be easily attached and detached, the screw 5 is loosened and the rod holder 14 is removed from the rod holder 14. By removing 13, only the deformable deformable mirror 5 (including the rod 13 bonded to the back surface) can be replaced. That is, the rod holder 14, the actuator 6 and the support frame 11 can be reused as they are, which is economical.

  In the case of this embodiment, the actuator 6 and the deformable mirror 5 are connected by using an epoxy resin adhesive 17 and bonding the tip of the rod 13 to the back surface of the deformable mirror 5. In this case, in the thin deformable mirror 5 having a thickness of 3 mm, the influence of the stress change when the adhesive 17 is cured is likely to appear on the mirror surface, and the surface side of the deformable mirror 5 at the portion where the actuator 6 is adhered ( The reflective surface side) may be slightly raised. For example, in one example in which the rod 13 was bonded with the epoxy resin adhesive 17, a convex portion (bump) 9 having a diameter of 0.4 μm was formed (see FIG. 3). Here, if the convex part (or concave part) 9 formed by hardening or solidification of the adhesive 17 is local, a local space given to the wavefront of the beam generated when the ultrashort pulse laser beam L is reflected. The modulation is sufficient to be the starting point for forming the filament. In addition, if the protrusion or depression having a height of about 0.4 μm generated by using the adhesive 17 is manufactured by forming the mirror surface of the deformable mirror 5 by vapor deposition, a perforated mask is previously provided in front of the vapor deposition surface. It is also possible to form the local convex portion (or concave portion) 9 by setting and locally controlling the film thickness of the mirror vapor deposition during the vapor deposition step.

  Here, even if the thickness of the deformable mirror 5 is flexible enough to form the global recess 10, the local protrusion or The recess 9 may not be formed. For example, the surface shape of the deformable mirror 5 having a thickness of 3 mm is shown in FIG. In this case, point-like local protrusions (convex portions) or depressions (concave portions) are generated. On the other hand, FIG. 7 shows the surface shape of the deformable mirror 5 having a thickness of 6 mm. In this case, unlike the deformable mirror 5 of FIG. 8, no dot-like local bulge (convex portion) or depression (concave portion) is generated. This is presumably because the deformable mirror 5 is too thick, and no local bulge or depression occurs due to shrinkage or stress when the adhesive 17 is cured or solidified. For this reason, when the local convex portion (or concave portion) 9 is formed on the mirror surface by bonding the rod 13, it is preferable to use a mirror having a thickness of about 2 to 3 mm. Of course, if the local convex portion (or concave portion) 9 is not formed by directly attaching the back surface of the deformable mirror 5 and the actuator 6 with the adhesive 17, the local convex portion (or, for example, by controlling the deposited film) If the concave portion 9 is formed, the thickness can be implemented as long as the thickness is flexible enough to form the global concave portion 10 by driving the actuator 6.

  Further, as the drive element 16, a drive source capable of minute displacement of the deformable mirror 5, such as a piezoelectric element (PZT: Pb-Zr-Ti) or an electrostrictive element (PMN: Pb-Mg-Nb) is used. It has been. In the case of a driving element such as an electrostrictive element, use is preferable because the direction and amount of displacement of the driving element 16 can be easily controlled by switching the magnitude and direction of the applied voltage, but the present invention is not limited to this. The drive element 16 is fixed to a wall 11b arranged perpendicular to the base of the frame 11, and the rod holder 14 serving as a movable part can be moved forward and backward in the front-rear direction (left and right in the figure) through the wall 11a having a through hole. It is supported (see FIG. 2). The deformable mirror 5 appropriately controls the driving of a plurality of actuators 6 arranged in parallel to each other, that is, by combining the actuator 6 that pushes the rod 13 forward with the actuator 6 that pulls back or the actuator 6 that does not drive the rod 13. The deformable mirror 5 is deformed to form a global recess 10 in a desired region.

  It will be described below that the filament is generated when the ultrashort pulse laser beam L is incident on the filament forming apparatus configured as described above and the reflected light is propagated in the atmosphere. In order to simplify the description, the diameter of the ultrashort pulse laser beam L is set to 50√2 mm with respect to a mirror having a side of 100 mm, so that five of the 13 actuators 6 near the center (reference E) , J, K, L, M) (see FIG. 3 etc.).

  First, a method for forming a filament using only the reflecting mirror 5 having the local convex portion (or concave portion) 9 on the reflecting surface will be described. By interposing the reflection mirror 5 in which the dot-like local bulge (convex portion) or dent (concave portion) as shown in FIG. 8 is generated on the optical path of the ultrashort pulse laser beam L, the wavefront is changed. Even in the case of the arranged ultrashort pulse laser beam L (see FIG. 5A), the local spatial modulation according to the local convex portion (or concave portion) 9 on the mirror surface is included in the reflected beam. (See FIG. 4 (B)), and the local spatial modulation given to the wavefront of the beam in the course of beam propagation becomes more prominent (see FIG. 4 (C) and FIG. 4 (D)). ), Which becomes the starting point (seed) and forms the filament in the course of beam propagation. Since this filament is stably generated by the presence of the local convex portion (or concave portion) 9 on the surface of the reflecting mirror 5, the local convex portion (or concave portion) 9 is formed at an arbitrary position. Thus, it is continuously formed uniquely at an arbitrary position of the beam cross section. 11 shows the cross-sectional intensity distribution of the reflected beam (indicated by reference numeral 19 in FIG. 11 and the like) at a short distance, and FIG. 12 shows the cross-sectional intensity distribution of the reflected beam 19 at a long distance. Thus, it can be seen that a single filament (indicated by reference numeral 20 in FIG. 11 and the like) is preferentially generated by the local convex portion (or concave portion) 9 formed in the central portion of the mirror. When the ultrashort pulse laser beam L is reflected and propagated in the atmosphere, the origin of the filament (indicated by reference numeral 8 in FIG. 8) is generated in the cross section of the reflected beam 19 due to intensity spots, and further propagation proceeds. It was found that the filament 20 grew.

  Next, a method of forming a filament using the reflecting mirror 5 having the local convex portion (or concave portion) 9 and the larger global concave portion 10 will be described. As shown in FIG. 10, five actuators 6, E, J, K, L, and M are driven, and the deformable mirror 5 is pulled from the back surface side, so that the surface side of the deformable mirror 5 is depressed globally. Do not deform. Even in this state, as shown in FIG. 4, a special surface shape in which the mirror surface shape is formed in the global concave portion 10 and the local convex portion (or concave portion) 9 exists is realized by the actuator 6. (See FIG. 11). As a result, the intensity centered on the energy of the reflected beam or the surrounding intensity spots around the local convex part (or concave part) 9 or at a position corresponding to the local convex part (or concave part) 9 of the beam cross section. By gathering around the spots, the electric field intensity of the intensity spots that are the starting points of filament generation is made stronger, and filament generation during beam propagation is made more reliable. FIG. 13 shows the state of the beam cross section when the central portion of the deformable mirror 5 is pulled. When the global concave portion 10 is formed in the mirror central portion by pulling the actuator (E) in the central portion of the mirror corresponding to the central portion of the beam, peripheral intensity spots are gathered in the central portion of the beam to form a high-density filament 20 ( (See FIG. 13).

  Furthermore, the position where the filament 20 is generated can be controlled by controlling the formation position of the global recess 10 on the beam cross section. For example, when a global concave portion 10 is formed in the mirror central portion by pulling the actuator (E) in the central portion of the mirror corresponding to the central portion of the beam, peripheral intensity spots gather at the central portion of the beam to form a high-density filament 20. (See FIG. 13). On the other hand, the actuator (M) corresponding to the mirror peripheral portion (beam peripheral portion) in the region irradiated with the beam of the reflecting mirror 5 (indicated by reference numeral 18 in FIG. 7 and the like) is pulled to globally surround the mirror peripheral portion. When the concave portion 10 was formed, the intensity unevenness was also shifted to the beam peripheral portion, and the filament formation was more remarkable in the peripheral portion, and a high-density filament 20 was formed (see FIG. 14). From this, the formation position of the global recess 10 formed on the surface of the reflection mirror 5 without changing the position of the local projection (or recess) 9 that becomes the starting point of filament generation on the surface of the reflection mirror 5 It was revealed that the position where the filament is formed remarkably and the position where the high-density filament is formed can be controlled by controlling.

  Therefore, this filament can be applied to control of the discharge path, for example. Propagation using a filament is accompanied by a non-linear effect of the refractive index and thus has a multi-wavelength and continuous spectrum, and can be applied to simultaneous measurement for a wide variety of measurement types in atmospheric environment measurement and the like. In addition, when the ultrashort pulse laser beam L is propagated in a high-density gas, the generation of plasma is more remarkable than when it is propagated in the atmosphere. Since an ultrahigh intensity laser electric field is localized in the filament, electrons can be accelerated by the interaction between the generated plasma and the laser electric field. In addition, when the generated plasma is used as an optical amplification medium, dielectric emission is possible, and amplification efficiency is improved by using a long and continuous filament. Furthermore, even when an ultrashort pulse high intensity laser is propagated in a solid medium such as glass, the generation of filaments is remarkable. Since the composition of the medium changes during propagation, it can be finely processed and modified by locally changing the refractive index and transmittance. If a long continuous filament is used, a waveguide, etc. It is thought that the processing of this will be easier.

  Therefore, in addition to the laser-induced lightning technology described above, atmospheric environment measurement using multiple simultaneous measurements, optical amplification that stimulates and emits filaments as an optical amplification medium, particle acceleration that accelerates electrons, and laser that changes the composition of the medium It can be applied to processing.

  According to the discharge induction device 1 of the present embodiment, using the laser oscillator 4 and the reflection mirror 5 as described above, the condensed plasma generated by condensing the ultrashort pulse laser light L with a short focal point, and the long focal point. Combining filaments produced by condensing or irradiating in parallel can improve the performance of laser induced lightning, laser gap switches, and the like. More specifically, a focused plasma and a filament are formed at the same time, the focused plasma generates an upward leader that triggers discharge, and the generated upward leader can be guided over a long distance by the filament. . According to this lightning strike method, the upward leader generated from the tip of the lightning rod 3 can be guided by several tens of meters or more, so that the performance or characteristics of the laser lightning strike is further improved.

  Here, a supplementary description of “long distance guidance” (or “long distance guide”) that appears several times in this specification is as follows (see FIGS. 16 to 19). That is, in the case where the upward leader starts from the plasma channel and progresses to thundercloud 2, the leader here is a precursor phenomenon of discharge, and the discharge that occurs later (in the case of laser induced lightning, the successor in FIG. 19). It works to create a road (discharge path). By the way, in laser-induced lightning, the leader progresses upward, so it is called “upward leader”. It is important that this leader reaches the other electrode (Thundercloud 2 in the case of laser-induced lightning). According to a rough calculation, if the leader is guided about 30 to 40m, the leader will progress in the future. It is thought to reach thundercloud 2. That is, first, it is important to generate a leader from the lightning rod (conductor) 3, and for this purpose, focused plasma is used. The inventor believes that the filament can be used to advance (guide) the leader once generated by several tens of meters. Based on the above idea, guiding a necessary amount (for example, about 30 to 40 m) of a leader is “long-distance guidance” in this specification.

  Further, the definition of “ultrashort pulse laser light” in this specification is not clear at this point, but laser light having a short pulse to the extent that a sufficiently long filament is generated in the atmosphere is roughly applicable. As such an ultrashort pulse laser beam, an ultrashort pulse high intensity laser beam is particularly desirable. The ultrashort pulse high-intensity laser beam is a laser having a peak (instantaneous) output of terawatt or more with a pulse width of picosecond or less. In this case, a titanium sapphire laser or a glass laser may be used as a laser medium, and the pulse energy may be amplified using a technique called chirp pulse amplification.

  The above-described embodiment is an example of a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the scope of the present invention. For example, in the present embodiment, the case where a novel discharge induction technique is applied to laser induced lightning has been described as an example, but the same discharge induction technique can be applied to, for example, a long gap discharge switch, a laser trigger type gap switch, and the like. Incidentally, in the present embodiment applied to laser induced lightning, a specific example of the electrode 2 that generates discharge is a thundercloud, and a specific example of the conductor 3 is a lightning rod. It goes without saying that specific examples of the body 3 can be various.

  Further, in the above-described embodiment, the preferred form in the case of generating a filament in the atmosphere has been described with reference to FIGS. Here, a local convex portion (or concave portion) 9 and a global concave portion 10 are formed by using a deformable mirror 5 made up of a single thin reflector as shown in FIG. 6A to generate a starting point of filament generation. In the above, an example in which the process of collecting and the process of aggregating the energy of the ultrashort pulse laser beam L or peripheral intensity spots around the central intensity spot is given as an example. ) Combine at least two mirrors of the first mirror 5 ′ having 9 and the second mirror 5 ″ having the global recess 10 on the optical path, and the above two steps are moved back and forth by the separate reflecting mirrors 5. (Refer to FIG. 6B.) This also generates a filament of an arbitrary density at an arbitrary part of the cross section of the reflected beam, or controls the position where the global recess 10 is formed. thing It is also possible to arbitrarily control the more generation position of the filament.

  In the case of an apparatus for forming a filament by combining the first mirror 5 ′ having the local convex portion (or concave portion) 9 and the second mirror 5 ″ forming the global concave portion 10 as described above, The local convex portion (or concave portion) 9 of the first mirror 5 ′ and the global concave portion 10 of the second mirror 5 ″ may be fixedly fixed so as not to be displaced or deformed, but may be movable. For example, as shown in FIG. 15, the first reflection mirror 5 ′ having the local convex portion 9 on the optical path of the ultrashort pulse laser beam L and the global position at a position corresponding to the local convex portion 9 in the beam cross section. A second reflecting mirror 5 ″ composed of a deformable mirror forming a concave portion 10 is arranged, and the ultrashort pulse laser beam L is reflected between the first and second mirrors 5 ′ and 5 ″. In the meantime, the intensity of the ultrashort pulse laser beam L or the surroundings is created around any one or more of the intensity spots formed around the spot by creating an intensity spot at any part of the beam cross section. It is also possible to collect intensity spots. Here, since the first reflecting mirror 5 ′ and the second reflecting mirror 5 ″ can be controlled independently, the first reflecting mirror 5 ′ can be controlled in the XY direction by reflecting the reflecting surface. It is possible to change the position of the local convex portion 9 formed on the beam cross section on the beam cross section.The second reflecting mirror 5 ″ made of the deformable mirror has a plurality of independently controllable elements on the back side of the deformable mirror. Therefore, the actuator 6 is driven to make the reflecting surface a global concave portion 10 having an arbitrary curvature, or by controlling the central position and shape of the curvature of the global concave portion 10 so that the filament in the beam cross section can be controlled. The formation position, strength, density, etc. can be freely controlled. In addition, as the first reflecting mirror 5 ′, another mirror in which the local convex portion 9 is formed at a different position is prepared in some cases, and the local convex portion (or concave portion) 9 is replaced by replacing this mirror. The position of can be changed.

  In the above-described embodiment, the structure in which the rod 13 is directly bonded to the back surface of the deformable mirror 5 with the adhesive 17 is shown. However, the driving element itself of the actuator 6 or the tip of the member fixed to the driving element is attached. The deformable mirror 5 can also be directly supported by the actuator 6 by directly bonding to the back surface of the mirror.

  In the above, what has been described so far is the case of performing a so-called hybrid type lightning strike using filaments generated in the atmosphere and high-density plasma. With respect to this lightning strike technology, the present inventor conducted a lightning strike experiment to confirm the characteristics. The hybrid lightning experiment will be described below as an example (see FIGS. 20 to 23).

  FIG. 20 shows an example of the results of experiments conducted by the inventor in connection with the present invention. At this time, a DC voltage of 400 kV was applied between the electrodes with an interval of 1 m, and a laser beam with a pulse width of about 70 femtoseconds and a pulse energy of about 200 mJ was collected using a concave mirror with a focal length of 10 m. At this time, the focal position of the laser beam is almost the tip of the high-voltage electrode seen on the left side in the figure, and when the laser beam profile at the high-voltage electrode position is observed, it is condensed to a diameter of about 3 mm, and the filament is observed. There wasn't. On the other hand, a plurality of filaments were observed in the beam near the tip of the ground electrode on the right side in the figure. In addition, since the photography of the discharge shown in FIG. 20 is taken with an exposure time of several seconds or more, and the DC voltage is applied during that time, the discharge after the dielectric breakdown moves and the discharge is seen as seen in the photograph. Has been observed to wave up and down. Therefore, the actual breakdown is considered to be a linear portion observed on the upper side or the lower side of the discharge. When this linear part is observed, it turns out that it is not a straight line but a step shape. From this, it is considered that the first discharge progresses so as to hop between a plurality of filaments. The polarity of the discharge in this case is positive, and as described above, the DC positive polarity discharge induction, which is difficult to induce discharge, has been successfully achieved. In this experiment, when the position of the laser beam condensing mirror (reflection mirror) was moved to shift the focal position of the laser beam, the discharge induction characteristics were extremely deteriorated. In addition, when a condensing mirror with a focal length of 20 m was used, no discharge was induced no matter where the focal position of the laser beam with respect to the electrode was set. In general, when the focal length of the condenser mirror is increased, the beam diameter at the focal point is increased. Therefore, when using a condensing mirror with a focal length of 20 m, the beam diameter at the condensing point is larger than when using a condensing mirror with a focal length of 10 m, thereby reducing the plasma density and triggering discharge. Probably not. From the above results, in order to perform DC positive polarity discharge induction, it is important to focus laser light near the electrode using a short focus mirror with a focal length of 10 m or less in this experimental condition. I came to a conclusion.

  From the above results, in this experiment, the discharge was triggered from the DC positive electrode by the focused plasma generated using a mirror with a focal length of 10 m, and the generated reader was along the filament generated before focusing. Propagated and reached the negative electrode, and it was thought that it finally reached dielectric breakdown.

  However, when the light is collected by a mirror with a focal length of 10 m, the distance generated by the filament is short. An experiment in which the plasma length contributing to the discharge induction when the ultrashort pulse laser is focused will be described with reference to FIGS.

  The inventors of the present invention measured changes in the DC discharge induction characteristics along the propagation path of the filament, and investigated the relationship with the focal length of focus and the propagation distance. The experimental system is shown in FIG. An ultrashort pulse laser beam having a pulse width of 70 femtoseconds and a pulse energy of about 240 mJ was collected by a concave mirror (indicated by reference numeral 5 in FIG. 21) having a focal length of 10 m and 20 mm to generate a filament. A laser beam was propagated between a sphere electrode having a diameter of 5 cm and a gap length of 4 cm to apply a DC electric field, and a change in dielectric breakdown voltage along the laser beam was measured.

FIG. 22 shows changes in the breakdown voltage drop due to laser irradiation with respect to the laser beam propagation distance from the concave mirror. The decrease in breakdown voltage was determined from the ratio of the breakdown voltage (V _L ) during laser irradiation to the breakdown voltage (V ₀ ) when no laser was irradiated. Before condensing, the laser beam was slightly divergent, and when the light was collected using a concave mirror with a focal length of 20 m, a decrease in dielectric breakdown voltage due to laser irradiation was observed from the point where it propagated 13.5 m from the concave mirror. Thereafter, the breakdown voltage drop was about 20% over about 6 m between the propagation distances from the concave mirror of 15.5 m to 21.5 m. After the laser beam propagated 21.5m, the decrease in breakdown voltage due to laser irradiation became small, and it was about 10% at the 25.5m point. The above results show that a plasma channel having a discharge inducing effect is generated over 10 m or more.

  FIG. 23 shows the change of the laser beam profile with respect to the laser light propagation distance from the concave mirror. The point that appears bright in the beam profile is the filament. No filament was observed at the point of propagation distance 11.5m where there was no decrease in breakdown voltage due to laser irradiation, and multifilament was observed at a point after 15.5m where the breakdown voltage decreased. In addition, when the light was collected using a concave mirror having a focal length of 10 m, the maximum breakdown voltage drop was about 20%, as in the case of using a concave mirror having a focal length of 20 m. However, as can be seen from FIG. 22, when a concave mirror with a focal length of 10 m is used, the plasma length contributing to discharge induction is less than half that when a concave mirror with a focal length of 20 m is used.

  Based on the above experimental results, in order to improve the discharge induction characteristics, ultra-short pulse laser light is condensed using a short-focus condenser mirror to generate a high-density focused plasma. It came to be considered effective to guide the discharge using a long filament generated by triggering the discharge and condensing at a long focal point or irradiating in parallel. However, in the discharge induction with a gap length of about 10 m, as shown in the above experimental results, simply setting the above experimental arrangement using only one mirror with a focal length of about 10 m enables effective and effective discharge induction. Is possible.

It is a figure explaining one Embodiment at the time of applying the discharge induction method and apparatus using a hybrid laser concerning the present invention to laser induced lightning. It is a schematic explanatory drawing which shows the form of the filament control apparatus of an ultrashort pulse laser beam. It is a front view (reflecting surface side) of the deformable mirror of this embodiment. It is a principle figure which shows the relationship between the local convex part in the reflective surface of a mirror, and a global recessed part. It is explanatory drawing which shows the change of the wave front before and behind reflection of an ultrashort pulse laser beam, (A) is an incident beam wavefront, (B)-(D) is a beam wavefront reflected by the reflective surface which has a local convex part. The time-dependent change of is shown. It is a principle figure which shows the example which implements the filament formation method, (A) is an example which implement | achieves a local convex part and a global recessed part with one mirror, (B) is a local combining two reflection mirrors. Examples of realizing a convex part and a global concave part are shown respectively. It is explanatory drawing which shows the surface shape of the deformable mirror of thickness 6mm. It is explanatory drawing which shows the surface shape of a deformable mirror of thickness 3mm. It is explanatory drawing which shows the surface shape at the time of pushing and deforming a deformable mirror to the mirror surface side with an actuator. It is explanatory drawing which shows the surface shape at the time of pulling the deformable mirror of embodiment to the mirror back surface side with an actuator, and carrying out a hollow deformation | transformation. It is explanatory drawing which shows the beam cross-sectional intensity | strength of short distance. It is explanatory drawing which shows the beam cross-sectional intensity | strength of a long distance. It is explanatory drawing which shows the beam cross-sectional intensity | strength at the time of deform | transforming a hollow shape by pulling the center part of a mirror with an actuator. It is explanatory drawing which shows the beam cross-sectional intensity | strength at the time of deform | transforming a hollow shape by pulling the mirror peripheral part with the actuator of the deformable mirror of embodiment. It is a principle figure of the example which implement | achieves a local convex part and a global recessed part by combining two reflective mirrors. It is one of the diagrams showing the concept for laser induced lightning. It shows how thunderclouds are generated and approached, and corona discharge occurs at the tip of a lightning rod. This is one of the diagrams showing the concept of laser-induced lightning. Laser light emitted from a laser oscillator passes through an optical system consisting of a reflection mirror, and as a result, plasma is generated from the tip of the lightning rod to the sky. It shows how you are. It is one of the diagrams showing the concept of laser-induced lightning. It shows how an upward leader is generated from the plasma channel and progresses to the thundercloud. It is one of the diagrams showing the concept of laser-induced lightning. It shows how electric charges in a thundercloud flow through the lightning rod to the ground. It is an image which shows the mode of the simulation experiment of the induced lightning using a hybrid laser. It is a figure which shows the filament propagation characteristic experimental system in an Example. In the examples, the ratio of the breakdown voltage (V _L ) at the time of laser irradiation to the breakdown voltage (V ₀ ) at the time of not irradiating the laser with respect to the propagation distance of the laser beam from the concave mirror and the change in the sound intensity from the filament It is a graph. It is an image showing the change of the laser beam profile during laser light propagation, and the propagation distance from the concave mirror is (a) 11.5m, (b) 15.5m, (c) 19.5m, (d) 23.5m, respectively. is there.

Explanation of symbols

1 Discharge induction device 2 Thundercloud (electrode)
3 Lightning rod (conductor)
4 Laser oscillator 5 Reflecting mirror 9 Local convex portion or concave portion 10 Global concave portion

Claims (12)

  In a discharge induction method using a laser for inducing a discharge from an electrode to a conductor using a laser beam, an ultrashort pulse laser beam is irradiated toward the tip of the conductor, and the ultrashort pulse laser Inducing a leader extending from the conductor toward the electrode using high-density plasma generated by condensing light at a short focal point, and irradiating the electrode with another ultrashort pulse laser beam, A discharge induction method using a hybrid laser, wherein the reader is guided for a long distance using a filament generated by condensing the other ultrashort pulse laser beam with a long focal point.   By using a multifocal reflection mirror that partially varies the focal length as a reflection mirror that condenses the ultrashort pulse laser beam, a portion of the ultrashort pulse laser beam is condensed at a short focal length and the rest is long. 2. The discharge induction method using a hybrid laser according to claim 1, wherein the light is condensed at a focal point.   A mirror with a short focal length and a mirror with a long focal length are separately used as a reflection mirror for condensing the ultrashort pulse laser beam, and a part of the ultrashort pulse laser beam is short-focused with the one reflection mirror. The discharge induction method using a hybrid laser according to claim 1, wherein the remaining light is condensed and the remaining light is condensed at a long focal point by the other reflection mirror.   The discharge using the hybrid laser according to claim 2 or 3, wherein the reflection mirror has a local convex portion or a concave portion, and the filament is generated and controlled using the reflection mirror. Guidance method.   The reflection mirror is provided with a global concave portion around the local convex portion or concave portion, which is global compared to the local convex portion or concave portion. 5. The discharge induction method using a hybrid laser according to claim 4, wherein the filament is generated and controlled.   The discharge induction method using a hybrid laser according to claim 4 or 5, wherein a surface shape variable reflection mirror capable of changing a surface shape is used as the reflection mirror.   In a discharge induction device using a laser for inducing a discharge from an electrode to a conductor using a laser beam, an ultrashort pulse laser beam is used as the laser beam, and the ultrashort pulse laser beam is applied to the conductor. A high-density plasma generated by irradiating toward the tip and condensing the ultrashort pulse laser beam with a short focal point is used to induce a leader extending from the conductor to the electrode, and other ultrashort A laser oscillator that guides the reader over a long distance using a filament that is generated by irradiating the electrode with a pulse laser beam and condensing the other ultrashort pulse laser beam with a long focal point, Discharge induction device using hybrid laser.   A mirror that reflects the laser light and changes the path of the laser light, and includes a multifocal reflection mirror that partially differs in focal length, and a part of the ultrashort pulse laser light emitted from the laser oscillator 8. The reflecting mirror is configured to reflect and collect light at a mirror portion having a short focal length, and to reflect the remainder of the ultrashort pulse laser light at a mirror portion having a long focal length among the reflecting mirrors. A discharge induction device using the hybrid laser described in 1.   A short focus reflecting mirror that reflects the laser light and changes the path of the laser light, and a long focus reflecting mirror are provided, and the ultrashort pulse laser light emitted from the laser oscillator is reflected by the short focus reflecting mirror. 8. The discharge induction device using a hybrid laser according to claim 7, wherein the laser is condensed and another ultrashort pulse laser beam is reflected by the long focal reflection mirror.   10. The reflecting mirror according to claim 8, wherein the reflecting mirror has a local convex portion or a concave portion, and the filament can be generated and controlled by using the reflecting mirror. Discharge induction device using the described hybrid laser.   The reflecting mirror has a global concave portion around the local convex portion or concave portion, which is global compared to the local convex portion or concave portion, and the filament can be obtained by using the reflective mirror. The discharge induction device using a hybrid laser according to claim 10, wherein the discharge induction device can be generated and controlled. 12. The discharge induction device using a hybrid laser according to claim 10, wherein the reflection mirror is a surface shape variable reflection mirror that can change a surface shape thereof.