High-power gas-discharge lasers with emission-line helium-blast narrowing module

FIELD: laser engineering; emission-line narrowing devices built around diffraction grating.

SUBSTANCE: emission-line narrowing device has diffraction grating, master working side of diffraction grating, chamber for accommodating at least mentioned diffraction grating, helium source for blasting mentioned chamber, beam expanding device that functions to expand mentioned laser beams, turning gear for guiding mentioned expanded beam to working side of diffraction grating to select desired wavelength range from mentioned expanded beam. Method for regulating laser frequency dispersion involves guiding of gaseous helium flow to working side of diffraction grating; in the process pressure of blast gas is reduced to cut down optical effects of hot gas layer.

EFFECT: minimized thermal distortions in narrow-line lasers generating high-power and high-repetition-rate beams.

15 cl, 12 dwg

 

The scope of the invention

The present invention relates to lasers and, in particular, to a powerful gas discharge lasers module narrow line emission using a diffraction grating.

Description of the prior art to which the invention relates.

Narrow band gas discharge lasers

Ultraviolet gas discharge lasers used as light source for microlithography integrated circuits, have a narrowed line radiation. In the prior art preferably narrowing of the line of radiation is carried out using a module narrowing of the line radiation from the diffraction grating along with the output communication device in such a way as to form a selective laser resonator. In such resonator amplifying the environment is created by electric discharge pumped laser gas, such as krypton, fluorine and neon (KrF laser); argon, fluorine and neon (ArF excimer laser); or fluorine and helium and/or neon (for F2laser).

How narrow the line of radiation, known from the prior art

The scheme is similar to the system known from the prior art, represented in figure 1, taken from the Japanese patent No. 2696285. The system includes an output device communication (WAC) (or front mirror 4, the laser discharge chamber 3, the window 11 of the discharge chamber, and the module 7 narrowing whether the AI radiation using a diffraction grating. Module 7 narrow radiation line is usually provided in photolithographic laser system in the form of an easily replaceable module and is sometimes called "complex narrow radiation line" or for short "XL(LNP)". This module includes two extending beam prism 27 and 29, as well as diffraction grating 16 that is installed under the scheme Litrow. The diffraction grating used in such systems are extremely sensitive optical elements and quickly destroyed under the action of ultraviolet radiation in the presence of oxygen in normal air. Based on these considerations, the optical elements of the modules narrowing of the line radiation include lasers typically, during operation, continuously blown through with nitrogen.

For many years developers narrowband lasers believed that the distortion of the laser beam can be caused by a leaking gas near the working side of the diffraction grating. Therefore, developers of lasers in the old days was made special efforts to keep nitrogen purged from flowing directly on the working side of the diffraction grating. Some examples of these efforts are described in the aforementioned Japanese patent No. 2696285. In the example shown is taken from a patent figure 1, the flow of purge gas is directed from gas cylinder 44 with the nitrogen to the reverse side of fractionnal grid 16 through the port 46.

The formula of the diffraction grating

Another example of excimer laser systems known from the prior art that uses a diffraction grating for selection of the spectral lines shown in figure 2. The laser resonator is formed by the output coupling element 4 and the diffraction grating 16, which operates as a reflector and spectral selective element. The output coupling element 4 reflects part of the light back into the laser, and the other part 6, which is the output radiation of laser passes. Prisms 8, 10 and 12 form a beam expander, which expands the beam before it fall on the diffraction grating. The mirror 14 is used to direct the beam so, i.e. its distribution towards the diffraction grating, driving, thus, the angle of incidence. The Central wavelength of the laser is usually reconstructed by the rotation of the mirror 14. Generating a gain is generated in the discharge chamber 3.

Diffraction grating provides a selection wavelength by reflection of light with different wavelengths at different angles. Consequently, only those light rays which are reflected back into the laser, will be enhanced laser gain medium, while the remaining light rays with different wavelengths will be lost.

Diffraction grating in this example, laser, known from the prior technology is key, works on the so-called Littrow scheme when it accurately reflects light back. For this scheme the incidence angle (diffraction) and wavelength are related by the formula:

where α is the incidence angle (diffraction) diffraction grating, m is the order of diffraction, n is the refractive index of the gas, and d is the period of the diffraction grating.

Since the imaging lens microlithography is very sensitive to chromatic aberrations of the light source, it is necessary that the laser generated radiation with a very narrow line width of the spectrum. For example, in the prior art excimer lasers currently generated width of a spectral line on the order of 0.5 PM, measured at half maximum intensity, and 95% of the energy of light radiation is concentrated in a region of about 1.5 PM. The new generation of imaging tools microlithography will need more stringent spectral requirements. In addition, it is very important that the Central wavelength of the laser radiation were also maintained with a high degree of accuracy. In practice, it is necessary that the Central wavelength of the laser radiation was maintained with stability better than 0.05 to 0.1 PM. The prior art excimer lasers microlithography not have a built-in spectrometer, which could control the length vilniusarea radiation with the required accuracy. The problem, however, is that for operation of the spectrometer, the laser must generate pulses. Therefore, when the laser is continuously exhibits of the plate, the spectrometer can control the wavelength with the required accuracy. The problem occurs when the exposure stops, for example, to change the plates. Change plates may take a minute or two, and during this time the laser does not need to emit pulses. When the laser emits, it produces large amounts of heat. When the laser does not radiate, it is cooled. Such cooling can change the laser wavelength due to thermal drift. One possible reason for the drift is the change in the refractive index n of the gas with temperature according to the above equation. Such a change in n will cause a change in the wavelength of the Littrow diffraction grating and, therefore, change the center operating wavelength of the laser. Therefore, the first few pulses after the laser will resume generation, often at wavelengths different from those required. If these pulses are used to expose the plate, the chromatic aberration will cause deterioration of image quality. This, in turn, will cause a reduction in yield. One of the solutions to the problem are the two which is the fact that in order to expose the plates do not use these first few pulses. This procedure can be performed by closing a mechanical shutter of the laser during the first pulse. Unfortunately, as the closing and opening of the mechanical shutter takes time, it will lead to decreased performance. In the production of semiconductor lithography lasers work together with a number of very expensive devices. Therefore, even a 1% reduction in performance of the laser will lead to a substantial increase in price indices.

The increased pulse repetition rate

Ultraviolet lasers with narrowed line emission, which are currently used in the manufacture of integrated circuits, usually give about 10 MJ per pulse at a repetition frequency of about 2000 Hz and have a fill factor of about 20 percent. The increased production of integrated circuits can be achieved at higher repetition frequencies and high fill factors. Applicants and their research staff has designed and tested a discharge lithography laser, operating at a frequency of 4000 Hz. Currently, applicants are experimenting with even higher repetition frequencies, and also try to minimize the drift of the Central wavelength of the laser. Zaya is Italy faced difficulties maintaining a narrow continuous spectral bands at such high repetition frequencies and fill factors.

There is a need for a reliable device with a narrowed line, and also in the technique of gas-discharge lasers operating at high repetition frequencies with high fill factors.

The invention

The present invention provides a helium purge device for narrowing the line of radiation on the basis of the diffraction grating to minimize thermal distortions in laser narrowed line, which generate high-energy laser beams with high repetition frequencies. Applicants have shown significant improvement in performance using a helium purge in comparison with nitrogen purging, known from the prior art.

In preferred embodiments of the invention, the flow of helium gas is directed to the working side of the diffraction grating. In other embodiments of the invention, the pressure of the purge gas is reduced to reduce the optical effects of the hot gas layer.

Brief description of drawings

The invention is further explained in the description of specific variants of its embodiment with reference to the accompanying drawings, in which:

Figure 1 presents the first laser system with a narrowed line of the prior art,

Figure 2 shows a second laser system with a constricted line out level is ehniki

Figure 3 presents an adverse effect on the spectral band of the hot gas layer located on the working side of the diffraction grating, narrowing the line

On figa and 4B shows the preferred embodiment of the present invention,

On figa presents the curves of the line width of the radiation at various frequencies repeat with the blowing of the prior art,

On FIGU depicted curves line width of the radiation at different repetition frequencies according to the present invention,

On Figa, 6B and 6C presents alternative options for implementation of the present invention,

7, 8 and 8A-D depict complexes XL equipped for rapid regulatory feedback

Fig.9 illustrates the heating of the gas layer on the surface of the diffraction grating,

Figure 10 depicts a method of reducing the pressure of the purge gas,

Figure 11 depicts the preferred embodiment of the present invention,

On Fig presents a graph comparing nitrogen purging with helium purge.

A detailed description of the preferred variants of the invention

Performance laser with high average power

Excimer KrF laser with a narrowed line, known from the prior art, operating at relatively low average power, usually men who e 5 W, will form a laser beam centered at a wavelength of approximately 248 nm with a bandwidth of less than 0.6 PM. The laser can operate with a high repetition frequency up to 2000 Hz and even higher as long as the average power remains below 5 watts. Conventional photolithographic KrF excimer laser has a pulse energy of 10 MJ. Hence, to keep the average power is low, it should work with a relatively low fill factor. For example, it can operate with a frequency of 2 KHz in packs of 200 pulses with a pause between batches approximately 0,45 sec. This mode will produce average power:

Problems associated with the regulation of the width of the stripes start to appear, when the average power increases. This occurs, for example, when the reduced delay between the burst. For example, a laser operating with the same packs of 200 pulses, but with a delay between packets is equal to 0.1 sec, will have an average power:

If the maximum power of the laser operates in continuous mode at 2000 Hz and pulse energy of 10 MJ is equivalent to an average power of 20 watts.

When the laser system known from the prior art, works with high average power, the line width of the radiation gradually increases is carried out over a period of time approximately 5-20 minutes with the initial values of the bandwidth, average of less than 0.6 PM, and remains significantly higher than the 0.6 PM. This increase line width of the radiation should be avoided in microlithographic production cycles, because it is due to chromatic changes of the projection lens will cause the image will become blurred. Another important application is when the laser is used for testing, with high fill factors, thermal photolithographic properties of other components, such as themselves projection lens. In this application, it is assumed that the laser maintains its line width of the radiation and other parameters within the given technical conditions during the test duration.

The sharp increase in the line width of the radiation can be adjusted using a special device regulation band width.

Figure 2 broadly depicts the module narrowing of the radiation line, known from the prior art made by the Corporation Cymer, as part of a photolithographic KrF laser system with a narrowed line, comprising such a device. The module includes three extending beam prisms 8, 10 and 12, the rotary mirror 14 and the diffraction grating 16. Note that nitrogen purged from the cylinder 44 enters the module on the opposite side of the rotating mirror 46 to prevent flow of the blown gas neposredstvennoy working side of the diffraction grating. In this system, the wavelength of the laser beam 6 is regulated with a feedback scheme in which the wavelength of the beam is measured by the monitor 22, and a computer controller 24 uses the information about the wavelength thereby to adjust the angular position of the rotatable mirror 14, and thereby to adjust the wavelength to the desired value. The device 20 to control the line width of the radiation used for the mechanical bending of the diffraction grating 16 so as to make it, for example, slightly concave. Such a device is described in U.S. patent No. 5095492 transferred to the assignee Cymer. The use of this device allows to reduce the bandwidth, but still goes beyond the given specifications, when the laser operates at a high fill factors.

Figure 3 depicts one such example, when the line width of the radiation is beyond the scope of specified technical conditions for the operation of the laser of the prior art with an average power of 20 watts (continuous, 10 MJ, 2000 Hz). Regulation line width of the radiation can be optimized for one specific mode of action, but photolithographic lasers must be able to operate in several different modes. For example, a typical operating mode could be:

(1) pack of 600 pulses with energies in the mpulse 10 MJ with a frequency of 2000 Hz for 0.3 sec,

(2) idle speed of 0.3 sec,

(3) repeats the mode (1) and (2) for 85 packs, and

(4) idle 9 seconds.

The heated layer purge gas

Applicants have determined that poor working performance with higher repetition frequencies, as shown in figure 3, are the result of the development of the heated layer of nitrogen, which is formed during a period of approximately 5 minutes on the working side of the diffraction grating 48.

This hot gas is heated by the surface of the diffraction grating, which in turn is heated by absorption of the incident beam of laser radiation. Typically, the surface of the diffraction grating can absorb almost 15-20% of the energy of the incident radiation. The surface temperature of the diffraction grating may rise by 10-15°C. This increase in temperature is inhomogeneous, it is higher in the middle of a diffraction grating and lower edges, as shown in Fig.9. Therefore, the air on the middle part, with the front side of the diffraction grating hotter than the air at the edges of the diffraction grating. Therefore, when the laser beam 80 falls on the surface 86 of the diffraction grating, it passes through this boundary layer 82. Due to the fact that the air has a certain pressure, the hotter the air, the lower its density. So, the air near the center of the diffraction is esedi is less dense than the air near the edges. Because of this, the laser beam 80 will have different phase shifts, when he goes to the middle part of the diffraction grating and the edges. Thus, the outgoing beam parallel wavefront 88 will have a curved wave front 90 corresponding to a divergent beam. This happens even when the diffraction grating 16 is completely flat.

To address this heated layer of nitrogen applicants have developed a preferred modification module narrow radiation line.

The flow on the pressure side of the diffraction grating

The first preferred embodiment of the present invention depicted in figa and 4B. In this case, the purged nitrogen flowing at the rate of 2 liters per minute up through holes with a diameter of approximately 1 mm, spaced at 1/4 inch in the tube length of 10 inches with an inner diameter of 3/8 inch, functioning as a valve purge gas. Barrier plate 60 and the barrier cover 62 direct the greater part of the flow of the blown nitrogen in the direction of the arrows shown on figb. This arrangement gave excellent results as shown in the graph, figure 5. In this case, the increase in average output power of 0.1 W to 20 W leads to variations in the range of 0.4-0.5 PM. It is interesting to note that when the average power of 10 W is the line width of the irradiation the Oia is actually slightly less than 0.1 watts.

It is important that the flow of purge gas on the working side of the diffraction grating was carefully adjusted to avoid distortions associated with the stream. Applicants have experienced different flow rate and determined that excessive flow can do more harm than good. For example, a flow rate of 20 liters per minute gave very poor results. Preferred flow rates are in the range of about 0.5 liters per minute to 10 liters per minute.

It is also important to note that this blown gas does not significantly reduce the temperature of the diffraction grating. Diffraction grating remains hot. What insufflated gas makes, is that he is more continuously moves the air from the front side of the diffraction grating, so that the air does not get warm diffraction grating. Very small flow rate and, consequently, the velocity of the gas prevents the effect of distortion of the air, caused by the thread on the laser performance.

Other layout purge

There are many potential configurations that can provide the gas flow on the working side of the diffraction grating, preventing the formation of a thermal layer that causes the problem shown in figure 3. For example, instead of the small holes you could use a narrow slit width arr is siteline 0.5 mm, passing the length of the pipe. Also a smoother flow could be provided with a slit-type nozzle, as shown in cross section on figa, or slot nozzles could be provided both on the top and bottom diffraction gratings, as shown in figb. The flow on the working side of the diffraction grating may be provided with a very small fan in a semi-closed system, as shown in figv. In this case, regular nitrogen purge may be provided as in the prior art, as shown in figure 2. In a variant implementation of the invention depicted in FIGU, the space between the diffraction grating and the barrier is not sealed, and purged gas is able to circulate in the cavity and from it, as shown by the number of items 64 and 66. Tube 68 leading to the fan 70 and are connected near the center of the slotted pipes 72 and 74, which are located just above and below the hot area of the diffraction grating 16.

Reduced gas pressure

The second solution heated gas layers is to reduce the gas pressure in the complex narrow radiation line.

Convection gas spatially modulates the density of the gas, causing an inhomogeneous distribution of the refractive index, which in turn causes the aberration of the phase front. The value of any aberration, calling the authorized variation of the density of the gas, due to the convection of gas near the heated surface of the diffraction grating, is approximately linearly dependent on the rated values of the susceptibility or the refractive index and, thus, the density of the gas.

Convection cooling of the surface of a diffraction grating and other optical components is not significantly reduced as long as the average free path length of gas molecules is not less than the distances between "hot" and "cold" surfaces in XL. If we assume that these distances are approximately equal to 10 cm, then as a rough empirical approximation could be said that the gas pressure does not necessarily decrease below the pressure at which the mean free path length is approximately 10 cm of This pressure lies in the range from approximately 1 to 10 mbar, so that the gas density in XL is approximately from 0.1 to 1.0 percent density at atmospheric conditions.

Figure 10 depicts a sketch showing the system to maintain a controlled pressure in XL at the level of approximately 1 to 10 millibars. Nitrogen enters the sealed XL 7 through the nozzle 90. To create a vacuum in XL used vacuum pump, and the desired vacuum is maintained by a controller 94, using the feedback signal from the sensor 96 of the pressure distribution to the additional needle valve 98. Because XL is a sealed system, and the pressure is approximately in equilibrium, the sensor 96 may be a thermocouple.

Purging with helium

Another solution associated with the reduction effect of the hot layer is blowing XL helium. Helium has a smaller differential refractive index, so that the hot layer will cause less distortion. In addition, helium has much better properties of heat transfer than nitrogen. With some advantages, you can also use argon. However, helium is much more expensive than nitrogen.

The equation for the Littrow wavelength (see equation in section description of the prior art) potentially has two members, which may change with temperature, d (the period of the diffraction grating) and n (the refractive index of the gas). In prior art microlithographic excimer lasers typically have a diffraction grating type asellota. Substrate such diffraction gratings are usually made from a material with very low thermal expansion, such as glass brand ULE with zero thermal expansion, produced by Corning company. The coefficient of thermal expansion (CTE, CTE) such material is very small, typically of order 10-81/°therefore, changes of the period d is very small. On the other hand, the refractive index n of the gas depends on the temperature, which is described by the following equation:

where T is the temperature in °C, k - coefficient of proportionality. For nitrogen and for light at a wavelength of 248 nm: k=3·10-4. Therefore, for nitrogen we have Δn=1·10-6for ΔT=1°C. According to the equation (1) such a difference Δn will lead to Δλ=0,25 PM (1° (C) for light with a wavelength of 193 nm. This is a very strong temperature dependence, which means that if we want the drift was less than 0.05 PM, the temperature of the gas in XL must be maintained with an accuracy better than 0.2 degrees Celsius. Technically, this is a very difficult task.

The laser according to the preferred implementation variant of the invention shown figure 11. This laser expanding the beam prisms 8, 10 and 12, a mirror 14, and the diffraction grating 16 is placed in a tightly sealed case 34. The building has one entrance and one exit for gas. This case is filled with helium. In the path of the beam 20 in the housing is hermetically window 30. Near a window 30 is placed aperture 36. The input port is a long thin tube to prevent back diffusion of air molecules.

For helium, the coefficient k is approximately k=3,8·10-5or approximately 8 times less than that for nitrogen. Therefore, for helium we have Δn=1,25·10-7, the La Δ T=1°C. According to the equation (1) such a difference Δn will lead to Δλ=0,03 PM (1° (C) for light with a wavelength of 248 nm and approximately 0,025 PM (1° (C) for light with a wavelength of 193 nm. Now we can keep the temperature inside XL within 2 degrees, which is much better managed the problem. Indeed, thermal mass of the complex CSL, which in a preferred variant embodiment weighs approximately 5-10 pounds is sufficient to keep the temperature within this range for several minutes. Because helium has very different properties from nitrogen and air, building XL must be very well sealed and must have one input port for gas and one or more output ports for helium purged. The output port must have a long flexible tube attached thereto for preventing the return flow of outside air in XL.

Fig depicts a comparison of drifts Central line, measured for nitrogen and helium purge complexes XL.

Professionals should be clear that in addition to the above specific variants of implementation of the present invention, there are many other variants of implementation, able to cope with the distortions caused by a layer of hot gas. Another method of dealing with layer Naga is this gas is to ensure active management of the width of the radiation line to correct the adverse effects of the layer of heated gas. Methods for significant regulation in real time several parameters wavelength is described in patent application U.S. No. 09/390579, filed September 3, 1999, and in the patent description U.S. No. 09/703317, filed October 31, 2000, which is incorporated herein by reference. These methods include rapid regulation with position feedback extends the beam prisms, the curvature of the diffraction grating and the position of the rotary mirror. It also provides the position control of the laser discharge chamber. 7 depicts a combined block diagram - schematic drawing of the entire laser system, and figa and 8B depict drawings XL with added features - regulation with feedback. In a variant implementation, in accordance with Fig curvature of the diffraction grating is governed by the stepper motor (SM) 30 regulation of curvature of the diffraction grating to offset the distortion caused by a layer of hot gas on the pressure side of the diffraction grating. In a variant implementation, in accordance with figa-8G curvature of the diffraction grating 82 is regulated by a family of piezoelectric devices 86, acting through seven envarovich rods 84, located opposite the rear of the block 88 and the pressure of the spring 90. This embodiment provides a very quick setting of curvature of the working side of the diffraction grating.

The scope is the future of the invention should be determined by the attached claims, as well as its equivalents.

1. The device of the narrow line emission using a diffraction grating to narrow line laser that generates laser beams of high energy containing (A) a diffraction grating that defines the working side of the diffraction grating, (B) a chamber for receiving at least mentioned diffraction grating, (C) a source of helium to provide helium purge to purge the said chamber, (D), the expansion unit beam for expanding the beam of the above-mentioned laser designed to produce an expanded beam, (E) a rotary device for directions mentioned advanced beam on the working side of the diffraction grating, to select of these advanced beam of the desired range of wavelengths, in which the mentioned advanced beam provides heating of the working side of the diffraction grating, producing a temperature increase on the working side of the diffraction grating, which, in turn, heats the helium purged gas in the layer of heated purge gas adjacent to the working side of the diffraction grating, and further comprises a pipeline purge gas for directions blown helium gas on the pressure side of the diffraction grating to divert mentioned layer blown g is for, to reduce optical distortion caused by the said layer is heated purge gas.

2. The device according to claim 1 in which the said pipeline purge gas contains a device to control the flow of gas blowing through the diffraction grating to control the flow of gas on the pressure side of the diffraction grating.

3. The device according to claim 2, in which the said device to control the flow of purge gas includes structure that defines a flow path on said working side of the diffraction grating and then from the working side of the diffraction grating.

4. The device according to claim 1 in which the said pipeline purge gas contains at least one long narrow slit.

5. The device according to claim 4 in which the said slit is a long rectangular nozzle.

6. The device according to claim 1 in which the said flow of the blown helium gas on the pipeline has a speed of less than 20 l/min

7. The device according to claim 1 in which the said flow of purged gaseous helium has a speed of approximately 2 l/min

8. The device according to claim 1, which further contains a vacuum pump for creating a vacuum in said chamber.

9. The device according to claim 10, in which the said vacuum has a pressure of approximately from 1 to 10 mbar.

10. The device of claim 8, the which the said vacuum is chosen to the gas molecules inside the said chamber had an average free path length from 5 to 30 cm

11. The device according to claim 1, which further contains a control unit, including feedback curvature of the diffraction grating designed to ensure active management of curvature of the working side of the diffraction grating.

12. The device according to claim 1, which further contains a fan and at least one conduit configured to discharge the flow of helium gas on the working side of the diffraction grating.

13. Method of adjusting frequency distortion narrow band gas discharge laser having a module of narrow line emission on the basis of the diffraction grating, which specifies the working side of the diffraction grating, the method that contains the time that the expanded beam provides heating of the working side of the diffraction grating, producing a temperature increase on the working side of the diffraction grating, which, in turn, heats the helium purged gas in the layer of heated purge gas adjacent to the working side of the diffraction grating, and contains the stage discharge gas flow from the pipeline purge gas for directions blown helium gas on the working side of fractionnal gratings for drainage mentioned layer purge gas, to reduce optical distortion caused by the said layer is heated purge gas.

14. The method according to item 13, in which the said gas stream has a speed of less than 20 l/min

15. The method according to 14, in which the said gas stream has a velocity between 1 and 8 l/min



 

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15 cl, 14 dwg

FIELD: physics.

SUBSTANCE: invention relates to an optical pumping structure for a laser which includes: an active medium in the form of a cylindrical rod (1) with a circular cross-section, wherein ends of the rod are inserted into two rings (11) made of a thermally conductive material; at least three stacks (21, 22) of small pumping diode rods arranged in the form of a star around the rod; and a support (5) temperature-regulated by a Peltier-effect module (8). The rings (11) are in contact with the support (5), and a stack of diodes, called the bottom stack (21), is situated between the rod (1) and the support (5), and has for each other stack (22), a thermal conduction block (7) forming a support for said stack (22), these blocks (7) being mounted on the cooled support (5) and not being in contact with one another or with the rings (11).

EFFECT: high cooling efficiency with smaller dimensions of the device.

6 cl, 3 dwg

FIELD: physics.

SUBSTANCE: diode pumped optical amplifier head has, in a housing, an active element in form of a rod, arrays of diode lasers placed on holders along the active element, and a cooling system having a glass tube encircling the active element to form a radial channel δ. Damping elements are placed at both ends of the glass tube. Cooling channels with inlet and outlet pipes, which form a double-loop cooling system, are placed in the housing, holders and arrays of diode lasers.

EFFECT: high laser radiation output energy and achieving stability of output energy parameters at pulse repetition frequency of up to 100 Hz.

2 cl, 7 dwg

FIELD: physics.

SUBSTANCE: invention relates to laser technology and specifically to liquid coolants of solid-state lasers (e.g., neodymium or holmium lasers) which are simultaneously an optical filter for ultraviolet (UV) radiation of the laser pumping lamp. The coolant can be used anywhere, where solid-state lasers, having a liquid cooling system with filtration of UV radiation of the pumping lamp, are designed or used. The liquid coolant contains 2-oxy-4-(C7-C9-alkyl)oxybenzophenone, butyl alcohol and octane, with the following content of components, wt %: 2-oxy-4-(C7-C9-alkyl)oxybenzophenone 0.3-0.6, butyl alcohol 35-45, octane - the balance.

EFFECT: longer service life of the laser.

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