PatentDe  


Dokumentenidentifikation EP0936708 07.12.2006
EP-Veröffentlichungsnummer 0000936708
Titel System zur Kontrolle des Unterschiedes der optischen Pfadlänge in Festkörperlasern
Anmelder Northrop Grumman Corp., Los Angeles, Calif., US
Erfinder Randall J. St., Pierre, Santa Monica, CA 90405, US
Vertreter derzeit kein Vertreter bestellt
DE-Aktenzeichen 69933722
Vertragsstaaten DE, FR, GB
Sprache des Dokument EN
EP-Anmeldetag 05.02.1999
EP-Aktenzeichen 991023169
EP-Offenlegungsdatum 18.08.1999
EP date of grant 25.10.2006
Veröffentlichungstag im Patentblatt 07.12.2006
IPC-Hauptklasse H01S 3/131(2006.01)A, F, I, 20051017, B, H, EP
IPC-Nebenklasse H01S 3/042(2006.01)A, L, I, 20051017, B, H, EP   

Beschreibung[en]
BACKGROUND

The present invention is directed to the field of solid state lasers and, more particularly, to a system for controlling the optical path difference in the lasing medium.

Solid state lasers typically comprise a lasing medium having a slab geometry. The lasing medium includes side faces and edge faces. During operation of the laser, the side faces are pumped by a radiation source to generate a laser beam. The pumping process creates a substantial amount of excess heat within the lasing medium. Surface cooling of the side faces and edge faces is conventionally utilized to remove some of this excess heat from the lasing medium, so as to control its temperature. Ideally, the temperature distribution throughout the lasing medium is uniform to eliminate temperature gradients which produce associated thermal strains and index variations. Thermal strains produce thermal dimensional distortions in the lasing medium.

Temperature gradients through the thickness of the lasing medium are averaged out by passing the laser beam along the length of the lasing medium in a zig-zag pattern. Temperature gradients across the width of the lasing medium are controlled by using edge control bars disposed at the edge faces.

Surface cooling does not achieve temperature uniformity within the lasing medium, however, and thermal distortion of the lasing medium causes associated detrimental effects on the laser beam. Consequently, the laser beam quality and average power capabilities of known solid state lasers are limited. The thermal strains and associated thermal distortions cause a thermal optical path difference (OPD) in the lasing medium. The OPD causes different portions of the laser beam to travel at different speeds through the lasing medium relative to other portions. As a result, the laser beam has a non-flat wavefront.

It is important to control the OPD in the lasing medium to maintain a high level of optical quality needed to achieve high performance of the solid state laser system. An increase in the OPD results in reduced performance of the laser by limiting the laser beam average power and diminishing the laser beam quality. The OPD can reach such a high level that the laser is unsuitable for use in certain applications such as phase conjugation or unstable resonator which require precise OPD control.

It is an object of the present invention to provide a method and apparatus for closely controlling the OPD in a lasing medium in a solid state laser system that overcomes the above-described deficiencies of known techniques.

JP 05-226732 A discloses a method of controlling the temperature distribution in a lasing slab of a solid state laser. The slab is provided at its opposed edge faces with tubular heaters. A pair of thermo couples measure the temperatures near the center of one of the side faces of the slab and near one of the edge faces. The heaters are controlled so that the measured temperatures are always equal for any laser configuration.

SUMMARY OF THE INVENTION

To achieve the above object, the present invention provides a method of controlling the thermal optical path difference of a lasing medium in a solid state laser according to claim 1. The present invention also provides a system for controlling the thermal optical path difference in a lasing medium in a solid state laser according to claim 4 and a solid state laser according to claim 8.

In one embodiment, the present invention provides a method and apparatus for controlling the thermal optical path difference (OPD) of a lasing medium in a solid state laser that satisfies this need. The lasing medium includes a pair of side faces that are optically pumped by a light source and a pair of edge faces. The method comprises controlling heat transfer through the outer surface of the lasing medium to control the OPD. Particularly, the method comprises determining a temperature difference, &Dgr;Tmin, between the side faces and the edge faces that corresponds with approximately a minimum, OPDmin, in the value of the OPD in the lasing medium.

The value of &Dgr;Tmin is determined for a given solid state laser configuration. For the configuration, &Dgr;Tmin is substantially independent of the duty (pulse repetition) cycle of the pump source and OPDmin corresponds with about a constant value of &Dgr;Tmin over a range of duty cycles. &Dgr;Tmin can be determined at one duty cycle level and this temperature difference can be maintained at other duty cycle levels of the pump source as well. &Dgr;Tmin can be predetermined, or alternately it can be determined during the laser system operation. Once &Dgr;Tmin is determined for a laser configuration, this temperature difference can be maintained during pumping of the lasing medium to maintain the OPD at about OPDmin.

The temperature difference, &Dgr;T, between the edge faces and the side faces of the lasing medium is controlled by controlling heat transfer at the edge faces. This is achieved by monitoring the temperatures of at least one of the edge faces and at least one of the side faces of the lasing medium during laser operation, and adjusting the temperature of the edge faces as needed to maintain about &Dgr;Tmin. &Dgr;T can be actively controlled using feedback circuitry such that the method can be automated. Consequently, OPDmin can be automatically maintained during the operation of the solid state laser, thus enabling the production of a consistent, high-quality laser beam.

The system for controlling the OPD of the lasing medium during operation of the solid state laser comprises at least one sensor for monitoring the temperature of the edge faces of the lasing medium; at least one sensor for monitoring the temperature of the side faces of the lasing medium; means connected to the temperature sensors for determining the temperature difference, &Dgr;T, between the edge faces and the side faces; and means for controlling the edge face temperature such that &Dgr;T equals about &Dgr;Tmin and OPD equals about OPDmin.

The temperature of the edge faces of the lasing medium can be controlled using edge control bars. The edge control bars can heat and/or cool the edge faces depending on the edge control bar configuration.

The OPD can be measured using conventional interferometry techniques.

DRAWINGS

These and other features, aspects and advantages of the present invention will become better understood from the following description, appended claims and accompanying drawings, where:

  • Fig. 1 is a schematic illustrational view of a zig-zig solid lasing medium in a solid state laser being optically pumped at its side faces, and showing temperature sensors located to measure the temperatures at the edge faces and the side faces during pumping;
  • Fig. 2 is a schematic block diagram showing the loop between the temperature sensors, the temperature control means and the edge control bars.
  • Fig. 3 is a plot of experimental data for the optical path difference (OPD) versus the difference in temperature (&Dgr;T) between the edge faces and the side faces of the lasing medium over a range of duty cycles of the pump source, showing a minimum in the OPD.

DESCRIPTION

The present invention is a method and apparatus for controlling the thermal optical path difference (OPD) in a lasing medium in a solid state laser. Fig. 1 illustrates a typical parallelepiped-shaped slab lasing medium 10 including side faces 12, edge faces 16 and end faces 14. The lasing medium 10 has a length L, a width W, and a thickness T. During operation of the laser, the side faces 12 are optically pumped by a light source such as laser diode arrays or flash lamps as depicted by arrows P, to generate a laser beam B. The laser beam B is passed longitudinally along the lasing medium 10 in a zig-zag pattern by internal reflections from the side faces 12. The lasing medium 10 is typically disposed in a resonator cavity, with mirrors 18 positioned adjacent to the end faces 14 or used as an amplifier to amplify the laser beam B produced by a resonator cavity.

The pumping of the side faces 12 generates a substantial amount of heat which increases the temperature of the lasing medium 10. Due to the generally poor thermal conductivity of the lasing medium 10 as well as non-uniform heating effects, the temperature profile within the lasing medium 10 is non-uniform. As a result of the non-uniform temperature profile, the lasing medium 10 is thermally strained and distorted. An important effect of the thermal distortion of the lasing medium 10 is the distortion of the laser beam B wavefront passing through the lasing medium 10 caused by some portions of the wavefront traveling at a greater speed through the laser medium 10 relative to other portions of the wavefront due to the distortions and dimensional changes in the lasing medium 10. This non-uniformity of the wavefront speed produces a non-flat wavefront. The lasing medium 10 is referred to as having an optical path difference (CPD). The OPD increases with an increase in the thermal distortion of the lasing medium 10. Increasing the OPD limits the average power output of the laser achievable for a given laser beam quality.

The OPD is dependent on the composition and thermal conductivity of the material of the lasing medium 10. As the thermal conductivity of the lasing medium 10 decreases, the ability to control temperature gradients in the lasing medium 10 by surface cooling techniques is diminished, making it generally more difficult to control the OPD.

Propagating the laser beam B in a zig-zig pattern between the side faces 12 through the lasing medium 10 (i.e., in the thickness T direction) reduces the OPD, by averaging the laser beam B over the temperature aberrations in the thickness direction.

Thermal distortion of the lasing medium 10 is typically further controlled by surface cooling the lasing medium 10 during pumping. The temperature profile across the side faces 12 (i.e., across the width W of the lasing medium 10) is ideally uniform so that the temperature distribution is one-dimensional. The temperature profile across the edge faces 16 (i.e., across the thickness T of the lasing medium) is ideally symmetrical.

The side faces 12 are typically cooled by flowing a coolant such as water over them. The side faces 12 are typically at a surface temperature of within about 10°F of the temperature of the coolant.

The edge face 16 temperature is typically controlled by edge control bars 20 which control heat transfer to and from the edge faces 16. The edge control bars 20 reduce the temperature gradient in the width W direction of the lasing medium 10 by heating and/or cooling the edge faces 16. The edge control bars 20 can comprise a fluid circuit for flowing liquids or gases at a selected temperature and flow rate through the edge control bars 20 to heat and/or cool the edge faces 16. The edge control bars 20 can optionally be electrically heated to heat the edge faces 16. The edge control bars 20 can be independently controlled.

According to the present invention, the temperature difference, &Dgr;T, between the temperature, Te, of the edge faces 16, and the temperature, Ts, of the side faces 12, of the lasing medium 10 (i.e., &Dgr;T = Te - Ts) can be controlled during pumping of the lasing medium 10 to control the OPD. Particularly, there is a value of &Dgr;T, &Dgr;Tmin, that corresponds with about a minimum in the OPD, OPDmin. Once &Dgr;Tmin is experimentally determined for a given laser configuration, the temperature difference can then be maintained at about &Dgr;Tmin to maintain the OPD at about OPDmin during pumping of the lasing medium 10.

The edge control bars 20 are heated or cooled depending on whether they absorb or reflect heat generated by the pump source. If the edge control bars 20 are optically absorptive, they are cooled during pumping to maintain the temperature difference, &Dgr;Tmin. If the edge control bars 20 are optically reflective, they are heated during pumping to maintain the temperature difference, &Dgr;Tmin.

The temperature difference, &Dgr;T, between the edge faces 16 and the side faces 12 can be determined by monitoring the temperatures of at least one of the edge faces 16 and at least one of the side faces 12 using respective temperature sensors 22, 24. Preferably, sensors 22 are placed on both control bars 20 and sensors 24 are placed at both side faces 12 as shown in Fig. 1. The sensors 22, 24 can detect problems with the cooling of the side faces 12 and with the performance of the edge control bars 20. The sensors 22, 24 can be, for example, an electrical resistor such as a thermistor or the like, having a resistance that varies with temperature. As depicted in Fig. 1, the sensors 22 for monitoring the temperature of the edge faces 16 can be disposed on the outer surface of the edge control bars 20. The sensors 22 are typically disposed inside the edge control bars 20. Preferably, the sensors 22 are located as near to the edge faces 16 as possible so that the temperatures measured by the sensors 22 are about the actual temperature of the edge faces 16.

The operation of the edge control bars 20 are controlled by a temperature control means. Referring to Fig. 2, the sensors 22, 24 are connected via respective electrical conductors 26, 28 to a means 30 for determining &Dgr;T. The &Dgr;T determining means 30 can be, for example, a voltmeter or the like. The &Dgr;T determining means 30 is connected via an electrical conductor 32 to a control means 34 for controlling the temperature at the edge faces 16. The control means 34 is connected to the edge control bars 20 via electrical conductors 36. The control means 34 can be a device such as a proportional output controller that provides an output to the edge control bars 20 that is proportional to &Dgr;T. The control means 34 can include a digitally controlled on/off switch (not shown).

Typically, the lasing medium 10 is pumped in about the same manner at both of the side faces 12 and both side faces 12 are cooled such that the temperatures of the side faces 12 are approximately equal. Accordingly, it is typically sufficient to measure the temperature at only one of the side faces 12 and to assume the other side face 12 is at this same temperature. In lasers in which only one side face 12 is pumped due to the laser configuration, the approximate temperature of the non-pumped side face 12 can be extrapolated from the measured temperature of the pumped face. The side face 12 temperature can then be determined based on some selected relationship between the measured temperature and the extrapolated temperature, such as the average temperature.

Similarly, the temperatures of the edge faces 16 of the lasing medium 10 are typically approximately equal, and so it is typically sufficient to measure the temperature at only one of the edge faces 16. The average temperature or some other selected relationship between the two edge faces 14 can be determined in lasers which do not control the temperature of both of the edge faces 16.

The OPD can be determined using a conventional interferometer such as a Mach-Zehnder interferometer or the like.

The values of &Dgr;Tmin and OPDmin can be either predetermined or determined as the laser system is actually being operated to perform some function. Preferably, these two values are predetermined. As described below, once the value of &Dgr;Tmin is determined for a given laser configuration, this value can be used to optimize the OPD under different pumping conditions of the lasing medium 10.

The value of &Dgr;Tmin depends on various factors including the distance between the location of the edge face sensors 22 and the edge faces 16, the composition of the bonding material used to bond the edge control bars 20 to the edge faces 16, and the composition of the lasing medium 10. As the laser configuration is changed, the value of &Dgr;Tmin can change also.

Tests were conducted to determine the value of &Dgr;Tmin for a Nd:YAG slab lasing medium having a configuration as shown in Fig. 1. The side faces of the lasing medium were pumped by diode laser arrays at duty (pulse repetition) cycles of 20 Hz, 30 Hz and 40 Hz, and also under static conditions with the diode lasers turned off. The side faces of the lasing medium were water cooled. The temperatures of both of the edge faces was controlled using edge control bars. Temperature sensors were located at approximately the center of each of the side faces close to the edge and on each of the edge control bars. The OPD was measured using a Mach-Zehnder interferometer including a He-Ne laser.

Referring to Fig. 3, the value of &Dgr;Tmin was about 0°C for each of the four test conditions for the laser configuration. The value of OPDmin was about 1.5 wavelengths (wave peak - wave valley) of the He-Ne laser at this temperature. Accordingly, the test results establish that, for a given laser configuration, the value of &Dgr;Tmin need not be redetermined for different duty cycles of the pump source, and &Dgr;Tmin is also applicable to maintain the OPD at about OPDmin at other pumping conditions.

The approximately constant value of &Dgr;Tmin over a range of duty cycles for a given laser configuration enables the temperature difference between the edge faces and the side faces of the lasing medium to be actively controlled such that the present method can be automated using a temperature control system with automatic feedback circuitry such as shown in Fig. 2. Consequently, OPDmin can be closely maintained during the operation of solid state lasers, thus enabling the production of a consistent, high-quality laser beam that is advantageous for a range of applications, and especially those that require precise control of the OPD.

Although the present invention has been described in considerable detail with reference to certain preferred embodiments thereof, other embodiments are possible. Therefore, the scope of the appended claims should not be limited to the description of the preferred embodiments contained herein.


Anspruch[de]
Ein Verfahren zum Steuern des thermisch-optischen Wegunterschieds eines Lasermediums (10) in einem Festkörperlaser, wobei das Lasermedium (10) ein Paar von Seitenflächen (12) zur Strahlungsaufnahme während des Pumpens und ein Paar von Kantenflächen (16) zwischen und angrenzend zu den Seitenflächen (12) einschließt; gekennzeichnet durch die Schritte: - Ermitteln eines Zieltemperaturunterschieds &Dgr;Tmin zwischen den Seitenflächen (12) und den Kantenflächen (16), der ungefähr einem Minimum OPDmin in dem thermisch-optischen Wegunterschied des Lasermediums (10) entspricht; und - Steuern des Temperaturunterschieds &Dgr;T zwischen den Seitenflächen (12) und den Kantenflächen (16) auf ungefähr den Zieltemperaturunterschied &Dgr;Tmin während des Pumpens des Lasermediums (10). Das Verfahren gemäß Anspruch 1, wobei der Schritt des Steuerns Beobachten der Temperaturen Te, Ts von wenigstens einer der Kantenflächen (16) und wenigstens einer der Seitenflächen (12) des Lasermediums (10) während des Pumpens und aktives Anpassen der Temperatur an jeder der Kantenflächen (16) umfasst, um einen Temperaturunterschied von ungefähr dem Zieltemperaturunterschied &Dgr;Tmin beizubehalten. Das Verfahren gemäß Anspruch 2, wobei der Schritt des Steuerns Beobachten der Temperaturen jeder der Kantenflächen (16) und jeder der Seitenflächen (12) des Lasermediums (10) während des Pumpens umfasst. Ein System zum Steuern des thermisch-optischen Wegunterschieds in einem Lasermedium (10) in einem Festkörperlaser, wobei das Lasermedium (10) ein entgegengesetzt angeordnetes Paar von Seitenflächen (12) zur Strahlungsaufnahme während des Pumpens und ein entgegengesetzt angeordnetes Paar von Kantenflächen (16) zwischen und angrenzend an die Seitenflächen (12) einschließt, wobei das System umfasst: - wenigstens einen Kantenflächensensor (22), von denen jeder zum Überwachen der Temperatur (Te) einer der Kantenflächen (16) des Lasermediums (10) vorgesehen ist; - wenigstens einen Seitenflächensensor (24), von denen jeder zum Überwachen der Temperatur (Ts) einer der Seitenflächen (12) des Lasermediums (10) vorgesehen ist; und - Temperatursteuermittel (30, 34), die mit dem Kantenflächensensor (22) und dem Seitenflächensensor (24) zum Steuern des Temperaturunterschieds (&Dgr;T) zwischen den Kantenflächen (16) und den Seitenflächen (12) während des Pumpens des Lasermediums (10) verbunden sind; dadurch gekennzeichnet, dass die Temperatursteuermittel (30, 34) dazu vorgesehen sind, den Temperaturunterschied &Dgr;T auf ungefähr einen Zieltemperaturunterschied &Dgr;Tmin zu steuern, der so festgelegt ist, dass er ungefähr einem Minimum OPDmin in dem thermisch-optischen Wegunterschied des Lasermediums (10) entspricht. Das System gemäß Anspruch 4, umfassend ein Paar von Kantenflächensensoren (22) und ein Paar von Seitenflächensensoren (24). Das System gemäß Anspruch 4 oder 5, wobei die Temperatursteuermittel (30, 34) umfassen: - ein temperaturunterschied-bestimmendes Mittel (30), das zur Bestimmung des Temperaturunterschieds &Dgr;T mit dem Kantenflächensensor (22) und dem Seitenflächensensor (24) verbunden ist; und - ein Kantenflächentemperatur-Steuermittel (34), das mit dem temperaturunterschiedbestimmenden Mittel (30) verbunden ist, um die Kantenflächentemperatur Te während des Pumpens aktiv zu steuern. Das System gemäß Anspruch 6, umfassend ein Paar von Kantensteuerstäben (20), wobei jeder an einer der Kantenflächen (16) des Lasermediums (10) angebracht ist; wobei das Kantenflächentemperatur-Steuermittel (34) mit den Kantensteuerstäben (20) verbunden ist, um die Kantensteuerstäbe während des Pumpens aktiv zu steuern. Ein Festkörperlaser, umfassend: - ein Lasermedium (10), das ein entgegengesetzt angeordnetes Paar von Seitenflächen (12) und ein entgegengesetzt angeordnetes Paar von Kantenflächen (16) einschließt; - eine Pumpquelle (P) zum optischen Pumpen der Seitenflächen (12) des Lasermediums (10); dadurch gekennzeichnet, dass er auch ein System gemäß einem der Ansprüche 4 bis 7 umfasst. Der Festkörperlaser gemäß Anspruch 8, wobei das Lasermedium (10) aus Nd:YAG besteht.
Anspruch[en]
A method of controlling the thermal optical path difference of a lasing medium (10) in a solid state laser, the lasing medium (10) including a pair of side faces (12) for receiving radiation during pumping and a pair of edge faces (16) between and adjacent to said side faces (12);

characterized by the steps of: - determining a target temperature difference &Dgr;Tmin between the side faces (12) and the edge faces (16) that corresponds to about a minimum OPDmin in the thermal optical path difference of the lasing medium (10); and - controlling the temperature difference &Dgr;T between the side faces (12) and the edge faces (16) at about the target temperature difference &Dgr;Tmin during pumping of the lasing medium (10).
The method of claim 1, wherein the step of controlling comprises monitoring the temperatures Te, Ts of at least one of the edge faces (16) and at least one of the side faces (12) of the lasing medium (10) during pumping and actively adjusting the temperature at each of the edge faces (16) to maintain a temperature difference of about the target temperature difference &Dgr;Tmin. The method of claim 2, wherein the step of controlling comprises monitoring the temperatures of each of the edge faces (16) and each of the side faces (12) of the lasing medium (10) during pumping. A system for controlling the thermal optical path difference in a lasing medium (10) in a solid state laser, the lasing medium (10) including an opposed pair of side faces (12) for receiving radiation during pumping and an opposed pair of edge faces (16) between and adjacent to said side faces (12), the system comprising: - at least one edge face sensor (22), each for monitoring the temperature (Te) of one of the edge faces (16) of the lasing medium (10); - at least one side face sensor (24), each for monitoring the temperature (Ts) of one of the side faces (12) of the lasing medium (10); and - temperature control means (30, 34) connected to the edge face sensor (22) and to the side face sensor (24) for controlling the temperature difference (&Dgr;T) between the edge faces (16) and the side faces (12) during pumping of the lasing medium (10); characterized in that the temperature control means (30, 34) are configured to control the temperature difference &Dgr;T at about a target temperature difference &Dgr;Tmin so determined as to correspond to about a minimum OPDmin in the thermal optical path difference of the lasing medium (10). The system of claim 4, comprising a pair of edge face sensors (22) and a pair of side face sensors (24). The system of claim 4 or 5, wherein the temperature control means (30, 34) comprises: - temperature difference determining means (30) connected to the edge face sensor (22) and the side face sensor (24) for determining the temperature difference &Dgr;T; and - edge face temperature control means (34) connected to the temperature difference determining means (30) to actively control the edge face temperature Te during pumping. The system of claim 6, comprising a pair of edge control bars (20), each disposed at one of the edge faces (16) of the lasing medium (10); wherein the edge face temperature control means (34) is connected to the edge control bars (20) to actively control the edge control bars during pumping. A solid state laser comprising: - a lasing medium (10) including an opposed pair of side faces (12) and an opposed pair of edge faces (16); - a pump source (P) for optically pumping the side faces (12) of the lasing medium (10); characterized in that it also comprises a system according to one of claims 4 to 7. The solid state laser of claim 8, wherein the lasing medium (10) is comprised of Nd:YAG.
Anspruch[fr]
Procédé de commande de la différence de trajet thermo-optique d'un milieu actif (10) dans un laser à solide, le milieu actif (10) comprenant une paire de faces latérales (12) pour recevoir un rayonnement pendant un pompage et une paire de faces de bord (16) entre lesdites faces latérales (12), et de façon adjacente à celles-ci, caractérisé par les étapes consistant à : - déterminer une différence de température cible &Dgr;Tmin entre les faces latérales (12) et les faces de bord (16) qui correspond à environ un minimum OPDmin de la différence de trajet thermo-optique du milieu actif (10) ; et - commander la différence de température &Dgr;T entre les faces latérales (12) et les faces de bord (16) à environ la différence de température cible &Dgr;Tmin pendant le pompage du milieu actif (10). Procédé selon la revendication 1, dans lequel l'étape de commande comprend la surveillance des températures Te, Ts d'au moins l'une des faces de bord (16) et d'au moins l'une des faces latérales (12) du milieu actif (10) pendant le pompage et l'ajustement actif de la température à chacune des faces de bord (16) pour maintenir une différence de température d'environ la différence de température cible &Dgr;Tmin. Procédé selon la revendication 2, dans lequel l'étape de commande comprend la surveillance des températures de chacune des faces de bord (16) et de chacune des faces latérales (12) du milieu actif (10) pendant le pompage. Système de commande de la différence de trajet thermo-optique dans un milieu actif (10) dans un laser à solide, le milieu actif (10) comprenant une paire opposée de faces latérales (12) pour recevoir un rayonnement pendant un pompage et une paire opposée de faces de bord (16) entre lesdites faces latérales (12), et de façon adjacente à celles-ci, le système comprenant : - au moins un capteur de face de bord (22), chacun pour surveiller la température (Te) de l'une des faces de bord (16) du milieu actif (10) ; - au moins un capteur de face latérale (24), chacun pour surveiller la température (Ts) de l'une des faces latérales (12) du milieu actif (10) ; et - des moyens de commande de température (30, 34) connectés au capteur de face de bord (22) et au capteur de face latérale (24) pour commander la différence de température (&Dgr;T) entre les faces de bord (16) et les faces latérales (12) pendant le pompage du milieu actif (10) ; caractérisé en ce que les moyens de commande de température (30, 34) sont configurés pour commander la différence de température &Dgr;T à environ une différence de température cible &Dgr;Tmin déterminée afin de correspondre à environ un minimum OPDmin de la différence de trajet thermo-optique du milieu actif (10). Système selon la revendication 4, comprenant une paire de capteurs de face de bord (22) et une paire de capteurs de face latérale (24). Système selon la revendication 4 ou 5, dans lequel les moyens de commande de température (30, 34) comprennent : - des moyens de détermination de différence de température (30) connectés au capteur de face de bord (22) et au capteur de face latérale (24) pour déterminer la différence de température &Dgr;T ; et - des moyens de commande de température de face de bord (34) connectés aux moyens de détermination de différence de température (30) pour commander activement la température de face de bord Te pendant le pompage. Système selon la revendication 6, comprenant une paire de barres de commande de bord (20), chacune disposée à l'une des faces de bord (16) du milieu actif (10) ; dans lequel les moyens de commande de température de face de bord (34) sont connectés aux barres de commande de bord (20) pour commander activement les barres de commande de bord pendant le pompage. Laser à solide, comprenant : - un milieu actif (10) comprenant une paire opposée de faces latérales (12) et une paire opposée de faces de bord (16) ; - une source de pompage (P) pour un pompage optique des faces latérales (12) du milieu actif (10 ; caractérisé en ce qu'il comprend en outre un système selon l'une quelconque des revendications 4 à 7. Laser à solide selon la revendication 8, dans lequel le milieu actif (10) se compose de Nd:YAG.






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