Laser-excited light source and laser ignition method for plasma

Abstract

In a laser-pumped plasma light source (100) equipped with a gas-filled chamber (1), the means for plasma ignition is a solid-state laser system (7) that generates two pulsed laser beams (8,9) focused within the chamber (1), the first beam (8) being generated in free-running mode and the second beam (9) being generated in Q-switched mode. The solid-state laser system (7) includes a single active element (10), a radiation source (11) for pumping the active element (10), and optical resonators (12,13) ​​that provide multiple passages for the laser beam through the active element (10). One of the optical resonators (13) is equipped with a Q-switch (14) positioned on the path of the second beam (9), such that the Q-switch overlaps with only a portion (15b) of the cross-section of the laser beam.

Description

[Technical Field]

[0001] <Cross-reference of related applications> The present invention relates to a broadband light source having continuous optical discharge (COD), and to a method for initiating ignition of a plasma maintained by continuous laser radiation. [Background technology]

[0002] One of the challenges associated with generating high-luminosity COD-based light sources is the reliable starting and ignition of the COD.

[0003] For example, as known from U.S. Patent No. 9,368,337 issued on June 14, 2016, in a laser-pumped plasma light source, two pin electrodes located on the axis of a transparent chamber are used to initiate plasma ignition (or plasma ignition), during which a short arc discharge is generated. The CW laser beam is focused to the center of the chamber within the gap between the two electrodes. The light source is characterized by high brightness and ease of use. The latter is mainly due to the fact that commercially available products are quartz chambers or valves having two electrodes containing a gas, particularly high-pressure Xe (10 atm or more, i.e., 1 MPa or more).

[0004] However, relatively low-temperature electrodes located near the high-temperature plasma region create turbulence in the convective gas flow within the chamber, consequently impairing the spatial and energetic stability of the laser-excited plasma light source. Furthermore, the presence of electrodes near the radiating plasma region is characterized by a "dead" spatial angle that restricts the exit of the plasma radiation. In addition, sputtering of the electrode material can lead to a decrease in the transparency of the valve walls, which in turn can lead to degradation of the light source over time.

[0005] This drawback is largely overcome in a high-brightness broadband light source known from U.S. Patent No. 9,357,627, issued on May 31, 2016. In this embodiment, after COD ignition, the laser beam focal region and, correspondingly, the radiating plasma region are moved from the gap between the ignition electrodes toward the chamber wall. By selecting the relative positions of the laser beam, chamber axis, and radiating plasma region, high spatial and power stability is provided for the broadband laser-pumped plasma light source.

[0006] However, the need to move the radiating plasma region complicates the design and operation of the light source. Furthermore, it becomes more difficult to achieve sharp focusing of the laser beam, potentially limiting the brightness of the light source. Disadvantages of electrode-containing chambers also include the complex techniques required to seal the metal / glass joint and the complex chamber geometry, which causes stress concentrations that reduce the chamber's strength when operating under high gas pressures.

[0007] The aforementioned drawbacks do not exist in the electrodeless laser-pumped plasma light source known from the patent application publication JPS61-193358 A, published on August 27, 1986, in which case the laser is used for both initiating plasma ignition and maintaining COD.

[0008] However, the threshold power of the laser radiation required for plasma ignition is typically around 10 to several hundred kilowatts or more, while the laser radiation intensity sufficient for COD maintenance is usually only a few tens of watts. Therefore, using the same laser with high power for both plasma ignition and COD maintenance is redundant, expensive, and therefore impractical, either because the lifespan of the light source is shortened (when all laser power is used for COD maintenance) or because only a portion of the total laser power is used to maintain COD.

[0009] Patent US10,057,973, issued on August 21, 2018, proposes overcoming this challenge by using a single CW laser with an output of less than 250 watts and a wavelength of less than 1.1 pm. It was suggested that sharp focusing of a CW laser beam with a focal area cross size of less than 1 to 15 microns (i.e., 1 to 15 micrometers) and a focal area length of 6 microns or less (i.e., 6 μm or less) would provide COD ignition and persistence.

[0010] However, this solution is not versatile because it places very high demands on laser focusing and does not guarantee high functional reliability of the proposed light source. In addition, the approximately 250 watts of laser power supplied to the light source may be too high for various applications.

[0011] These drawbacks are overcome in a known light source from patent FR2554302, issued on May 3, 1985, where a focused pulsed laser beam intended for initial plasma ignition or optical breakdown (or optical dielectric breakdown) is used as the means for plasma ignition, and a CW laser is used for COD maintenance. The above approach eliminates the lifetime problem of the laser-pumped plasma light source.

[0012] However, achieving both plasma ignition and high brightness in laser-pumped plasma light sources requires sharp focusing of the laser beam. Therefore, extremely precise adjustment of the pulsed laser focusing region and the CW laser focusing region is necessary. This leads to complexity and insufficient reliability in laser ignition, making stable COD ignition in high-brightness light sources a problem.

[0013] These drawbacks are partially overcome in light sources known from U.S. Patent No. 10,244,613 issued on May 25, 2017. In one embodiment of this invention, the beams of one or more ignition lasers and one or more CW lasers for COD maintenance are introduced into optical fibers used to deliver the radiation of the lasers to a focusing or aligning optical system. In the apparatus, if the wavelengths of the lasers are similar, superposition of the focusing regions of the pulsed laser and the CW laser is achieved.

[0014] However, if the pulsed laser wavelength and the CW laser wavelength are different, their focused regions will diverge due to chromatic aberration. Furthermore, transmitting high-power laser pulses used for reliable COD ignition (hundreds of kW) over optical fiber can lead to optical fiber failure, which determines the drawback of this solution.

[0015] The closest technical solution, sometimes referred to as a prototype in this specification, is a light source known from Russian Patent No. 2732999 (also U.S. Patent No. 10,770,282 B2), issued on September 28, 2020, where the plasma ignition means is a solid-state laser system that generates two laser beams focused within a chamber. The laser beam generated in Q-switched mode is designed to optically destroy a gas. Simultaneously, the laser beam generated in free-running mode, which cannot optically destroy on its own, is designed to generate plasma after optical destruction, and the volume and density of the plasma are sufficient for its steady-state maintenance by the continuous laser. In other words, the joint effect of the two laser beams generated in giant-pulse mode and free-running mode results in the formation of a plasma, whose combustion is picked up by the continuous laser. Thus, reliable electrodeless ignition of a laser-pumped plasma light source is provided. This generates the brightest broadband light source with high spatial and energy stability and allows for the collection of plasma radiation at large spatial angles.

[0016] However, the presence of two active elements complicates solid-state laser systems and light sources, reducing their reliability and convenience of operation. When using a common resonator in a pulsed laser system, there are fairly stringent requirements regarding the parallelism of the ends of the two active elements, which are made in the form of rods. Furthermore, the difference in thermal effects in different rods becomes a problem when obtaining two parallel beams. Additionally, the use of two spatially separated pulsed laser beams, along with a continuous laser beam, complicates their introduction into the chamber, requiring the use of dichroic mirrors. The latter, in turn, necessitates the use of polarized laser radiation passing through the dichroic mirrors to reduce reflection losses, imposing limitations on the selection of ignition and continuous laser radiation wavelengths, making it difficult to use pulsed and CW lasers with similar radiation wavelengths. [Disclosure of the Invention] [Problems that the invention aims to solve]

[0017] The technical problem that this invention aims to solve relates to the creation of a method and apparatus for reliable laser ignition of continuous photodischarge, and, based thereon, to the development of a high-brightness, highly stable laser-pumped plasma light source.

[0018] The technical results of this invention are to significantly simplify the design of light sources, improve their reliability and ease of use, and based on this, to create electrode-free, high-brightness, broadband light sources with high spatial and output stability. [Means for solving the problem]

[0019] The object of the present invention can be achieved by a laser-excited plasma light source comprising a gas-filled chamber that is at least partially optically transparent, a region of radiant plasma maintained within the chamber by a focused beam of a continuous-wave (CW) laser, and means for plasma ignition.

[0020] The above-mentioned light source is a solid laser system that generates two pulsed laser beams whose means for plasma ignition are focused in the chamber. One of the two pulsed laser beams is generated in the free-running mode, and the other pulsed laser beam is generated in the Q-switching mode.

[0021] The above-mentioned solid laser system includes a single active element (i.e., only one active element), a radiation source for pumping the active element, and an optical resonator that provides a plurality of passages (i.e., repeated passages) of the intracavity laser beam passing through the active element. The optical resonator includes a Q-switch installed on the path of the intracavity laser beam, and the Q-switch is provided so as to overlap only a part of the cross-section of the intracavity laser beam.

[0022] In one embodiment of the present invention, the Q-switch is a saturable absorber made of chromium-doped yttrium aluminum garnet crystal Cr 4+ :YAG.

[0023] In one embodiment of the present invention, the Q-switch overlaps a small part of the cross-section of the intracavity laser beam and is 30% or less of its area.

[0024] In one embodiment of the present invention, the pulsed laser beam and the beam of the CW laser are focused into the chamber by a focusing optical element, and the beam of the CW laser directed to the focusing optical element does not cross the pulsed laser beam directed to the focusing optical element.

[0025] In one embodiment of the present invention, a deflection mirror is attached on the path of the beam of the CW laser outside the path of the pulsed laser beam.

[0026] In one embodiment of the present invention, a deflection mirror is mounted on the path of a pulsed laser beam outside the path of a CW laser beam.

[0027] In one embodiment of the present invention, the output power of the CW laser is 30 watts or less, which is sufficient to ignite and maintain the radiant plasma.

[0028] In one embodiment of the present invention, the axis of the focused beam of the CW laser is directed vertically upward, or at an angle of 10 degrees or less from the vertical, approaching the vertical.

[0029] In one embodiment of the present invention, the density of gas particles (or gas particles) in the chamber is 90.10 19 cm -3 This is less than , which corresponds to a gas pressure (or gas pressure) of 33 atmospheres (i.e., 3.3 MPa) at room temperature, and the temperature of the inner surface of the chamber is 600K or higher.

[0030] In one embodiment of the present invention, the temperature of the inner surface of the chamber is 900K or less, and the density of gas particles is 45.10 19 cm -3 This is the result, and this corresponds to a gas pressure of 16.5 atmospheres at room temperature.

[0031] In one embodiment of the present invention, the radiant plasma is 50 MW / (mm 2 It is characterized by high spectral brightness exceeding (nm·sr) and low relative brightness instability σ of less than 1%.

[0032] In one embodiment of the present invention, the gas belongs to the group of inert gases. This group includes the elements xenon, krypton, argon, and neon, but the gas may be a mixture of these.

[0033] In another embodiment, the present invention relates to a method for plasma ignition in a laser-pumped plasma light source, comprising directing a focused beam of a continuous-wave (CW) laser into a gas-filled chamber in which at least a portion is optically transparent, and maintaining a steady state of a radiating plasma and igniting the plasma using the focused beam of the CW laser.

[0034] This method is characterized in that a plasma is ignited by a solid-state laser system having a single active element, generating two parallel pulsed laser beams focused within a chamber, one of the two pulsed laser beams being generated in free-running mode, and the other pulsed laser beam being generated in Q-switched mode by a Q-switch installed in an optical cavity that overlaps with only a portion of the cross-section of the intracavity laser beam. In other words, the first beam is generated in free-running mode, and the second beam is generated in Q-switched mode.

[0035] In one embodiment of the present invention, a pulsed laser beam and a CW laser beam are focused by a focusing optical element into a region for maintaining a radiant plasma, and the CW laser beam directed towards the focusing optical element does not intersect with the pulsed laser beam directed towards the focusing optical element.

[0036] When the light source is implemented in the proposed configuration, the use of a laser system with only one active element for plasma ignition reduces the number of elements in the laser system, simplifies the design as much as possible, and increases the reliability of the means for laser plasma ignition and the radiation source. Compared to the prototype, problems associated with combining the focal points of two pulsed laser beams due to the different prisms (prismatics) of the two active elements, and problems associated with the possible separation of the two active elements due to thermal effects are eliminated.

[0037] In addition, by generating the beams with a single active element, maximum spatial focusing of the two pulsed laser beams is achieved, eliminating the need to inject the pulsed and continuous laser beams into the chamber using a dichroic mirror, and eliminating the need to use polarized laser radiation passing through a dichroic mirror.

[0038] Furthermore, Cr 4+ The use of a passive Q-switch in the form of a YAG crystal, particularly in the form of a plate-shaped saturated absorber, provides automated operation of a two-beam laser system.

[0039] This also simplifies the design of radiation sources, increases their reliability, and makes them easier to operate.

[0040] Reliable ignition of continuous optical discharge is achieved by the following factors: Optical destruction is brought about by a laser beam generated in Q-switched modulation mode. However, there are problems with igniting COD with only one laser beam. One reason for this is the difficulty in combining the focal region of a continuous laser with the optical destruction region, which is usually very small and does not exceed about 50 μm. Even when the focal regions of a pulsed laser beam and a continuous laser beam are combined, achieving COD ignition with only one laser beam remains difficult. This is due to the fact that the optical destruction produced by laser radiation is explosive. Explosive processes, particularly shock waves, can lead to the extinction of optical discharges that are usually maintained by low-power continuous lasers not exceeding 300 watts. According to the present invention, this problem is solved by the fact that a laser beam generated in free-running mode, which cannot perform optical destruction on its own, brings about plasma ignition after optical destruction by a laser beam generated in Q-switched mode. The parameters of the laser beam generated in free-running mode are selected so that the photodischarge itself sustained by it does not exhibit explosive phenomena, and at the same time, is resistant to disturbances caused by previous optical breakdown. In addition, the laser beam generated in free-running mode provides sufficient plasma volume and density for reliable steady-state maintenance by a relatively low-power continuous laser up to 30 watts after the ignition laser pulse is turned off (or after the end of the ignition laser pulse is cut off).

[0041] Therefore, reliable electrodeless ignition of continuous photodischarge is achieved. The elimination of electrodes reduces disturbances in the convective gas flow near the emission plasma region, simplifies the chamber, reduces turbulence in the convective gas flow, and allows for optimization of its design to minimize optical aberrations, especially when plasma radiation is emitted through the transparent portion of the chamber, and to increase the spatial angle of plasma radiation collection.

[0042] According to the present invention, 50 MW / (mm 2The continuous generation of plasma radiation with a high spectral brightness of over (nm·sr) and a relative brightness σ instability of less than 0.1% is achieved by keeping the density of gas particles in the chamber as low as possible, ensuring a gas pressure of approximately 50 atmospheres or higher, and keeping the temperature of the inner surface of the chamber as high as possible during operation.

[0043] All of this makes it possible to create the brightest, broadband light source with a large spatial angle of plasma radiation collection, characterized by maximum spatial and energy stability.

[0044] The specific purposes, features, and advantages of the present invention, as well as the invention itself, will be better understood from the subsequent description of the options for carrying out the invention, illustrated by the accompanying drawings. [Brief explanation of the drawing]

[0045] The technical essence and operating principle of the proposed device are explained with reference to the drawings:

[0046] [Figure 1] Figure 1 is a schematic diagram of a light source having a pulsed solid-state laser system for plasma ignition, and shows a cross-sectional view of the region of its optical resonator in the plasma laser ignition device.

[0047] [Figure 2] Figure 2 shows a characteristic oscillogram of the radiation intensity of a solid-state laser system used for plasma ignition.

[0048] In the drawings, matching elements of the device have the same reference number.

[0049] These drawings neither cover nor limit the entire range of options for implementing this technical solution, but are merely illustrative examples of specific cases of its implementation. [Modes for carrying out the invention]

[0050] This description is provided to illustrate how the present invention may be carried out, but is not intended to limit the scope of the invention.

[0051] According to an embodiment of the present invention (Figure 1), the laser excitation light source 100 includes a chamber 1 filled with high-pressure gas. At least a portion of the chamber 1 is optically transparent. Figure 1 shows a modified chamber made of an optically transparent material, such as fused silica. Inside the chamber 1 is a region of radiant plasma 2 maintained within the chamber by a focused beam 3 of a continuous laser 4 (e.g., a CW laser).

[0052] At least one plasma radiation beam 5, directed towards the optical radiation collection system 6 and intended for further use, exits the chamber 1. The optical radiation collection system 6, which may include axisymmetric elliptical mirrors (Figure 1), forms a plasma radiation beam that is transported, for example, via a system of optical fibers or mirrors to an optical system that uses broadband plasma radiation.

[0053] The light source also includes a plasma ignition device that uses a solid-state laser system 7, which is made capable of generating two laser beams 8, 9 focused within a chamber 1. One of the two laser beams 8 (first beam) is generated in free-running mode, and the other laser beam 9 (second beam) is generated in Q-switched mode. In this case, the solid-state laser system includes only one active element 10 (i.e., a single active element), a radiation source 11, for example, a small pulsed xenon lamp for pumping the active element, and an optical resonator having mirrors 12, 13 and a Q-switch 14. The optical resonator provides multiple passes (i.e., repeated passes) of the laser radiation flux 15 through the active element 10. Since the resonator with mirrors 12, 13 can be thought of as being implemented as a cavity between the mirrors, the flux 15 can be called an "intracavity laser beam". In this case, the Q-switch 14 is positioned on the path of the intracavity laser radiation flux 15 such that it covers only a portion of the aperture of the laser radiation flux 15.

[0054] A portion of the intracavity laser radiant flux 15a does not have a Q-switch 14 in its path, which results in the generation of the laser beam 8 in free-running mode.

[0055] Another portion 15b of the intracavity laser radiant flux has a Q-switch 14 in its path and generates a laser beam 9 in Q-switched mode.

[0056] As can be seen from the cross-section AA of the solid-state laser system 7 in Figure 1, in the embodiment of the present invention, the apertures of the laser radiation fluxes 15a and 15b, and the corresponding apertures of the laser radiation beams 8 and 9 emanating from the resonator, have the form of circular segments with different cross-sections.

[0057] Laser beam 9 (generated in Q-switch mode), and laser beam 8 (generated in free-running mode) are focused into chamber 1, i.e., into the chamber region designed to maintain the emission plasma.

[0058] Laser beam 9 (generated in Q-switch mode) is designed for the initial plasma ignition or optical breakdown in chamber 1. Laser beam 8 (generated in free-running mode) is designed to ignite the plasma after the optical breakdown performed by laser beam 8 (generated in Q-switch mode). In this case, Q-switch 14 preferably covers only a small portion 15b of the aperture of laser radiation beam 15, preferably 30% or less of its area (at mirror 13), in order to ensure an optimal energy ratio of laser beams 8 and 9 from the viewpoint of plasma ignition.

[0059] Laser beam 8 (generated in free-running mode) is designed to ignite the plasma after the optical breakdown performed by laser beam 9 (generated in Q-switch modulation mode). In this embodiment, the generation of pulsed laser radiation in solid laser system 7 is performed at wavelength λ1 = 1.064 μm.

[0060] Q-switch 14 may be passive, made of an anisotropic material, for example, a saturable absorber in the form of a chromium-doped yttrium aluminum garnet crystal:Cr 4+ :YAG. Q-switch 14 is not limited to this option only and can be made in the form of a plate. In other embodiments of the present invention, Q-switch 14 may be active.

[0061] In a preferred embodiment of the present invention, the focusing of all laser beams into the chamber region intended to maintain the emission plasma 2 (i.e., the radiation plasma) is performed by a single focusing optical element 16, for example, in the form of a condenser lens 16, but is not limited to this option only.

[0062] In the embodiment of the apparatus shown in Figure 1, a continuous laser beam 17 is directed into the chamber using a rotating mirror 18 positioned outside the path of the pulsed laser beams 8 and 9. The pulsed laser beams 8 and 9 can also be directed directly into the chamber using another rotating mirror positioned outside the beam path. In these embodiments of the present invention, the continuous laser beam 17 directed to the focusing optical element 16 does not intersect with the beams 8 and 9 of the solid-state laser system, which are also directed to the focusing optical element 16.

[0063] In this embodiment of the present invention, known limitations associated with the use of dichroic mirrors are relaxed.

[0064] The plasma ignition method in a laser-pumped plasma light source is carried out as follows: The focused beam 3 of a continuous laser 4 is directed into a chamber 1 containing a high-pressure gas, for example, using a total internal reflection rotating mirror 18 (Figure 1). Various gas mixtures, including metal vapors, such as xenon containing mercury or other inert gases and mixtures thereof, as well as halogen-containing gases, are used as highly efficient plasma-forming media.

[0065] Plasma initiation and ignition are provided by a solid-state laser system 7 having one active element 10. After switching on a radiation source 11 designed for pulse pumping of the active element 10, two parallel laser beams 8, 9 are generated and focused within a chamber, entering a region designed to maintain the emitted plasma 2. In this case, one pulsed laser beam 8 is generated in free-running mode, and the other pulsed laser beam 9 is generated in Q-switched mode by using a Q-switch 14 installed in a resonator with mirrors 12, 13, which provides multiple passes of the laser radiant flux 15 through the active element 10. The Q-switch 14 is positioned on the path of the intracavity laser radiant flux 15 so as to cover only a portion of the aperture of the laser radiant flux 15b. In this case, the pulsed laser beam 9 generated in Q-switched mode is used to provide optical destruction, and then the pulsed laser beam 8 generated in free-running mode is used to ignite a plasma whose volume and density are sufficient for steady-state plasma maintenance by the focused beam 3 of the continuous laser 4.

[0066] In steady mode, high-intensity broadband radiation is emitted through the optically transparent portion of chamber 1 and exits the region of the continuous photodischarge-emitting plasma 2 by at least one beam 5 of useful plasma radiation intended for further use.

[0067] In the embodiment of the present invention, the gas pressure Xe in the chamber is 30 atmospheres (i.e., 30 MPa) at room temperature, and the wavelength of the continuous laser is λ CW The thickness is 0.808 μm, and its output varies from 30 watts to 100 watts.

[0068] Figure 2 shows the characteristic time dependence of the power of the laser radiation generated by the solid-state laser system. In this embodiment, the energy of the laser beam generated in peak free-running mode is approximately 150 mJ, the duration is approximately 100 microseconds, and the wavelength of the radiation is λ1 = 1 ,The size is 0.64 μm. The generation in the passive Q-switched mode occurs with a time delay and is characterized by a laser pulse energy of 3 mJ with a duration of 20 ns. The optically disrupted plasma has a characteristic size of 50–100 μm.

[0069] The optical destruction mode does not provide reliable ignition of a continuous photodischarge. Therefore, after optical destruction, the plasma is ignited by a laser beam generated in free-running mode, and its volume (1 mm) 3 up to) and density (10 18 cm -3 A power level (above) is sufficient for maintaining a steady-state plasma with a focused beam of a continuous laser. Preferably, as shown in Figure 2, the laser beam emission pulse generated in free-running mode terminates 50 microseconds after the termination of the laser beam emission pulse generated in Q-switched mode. A time of approximately 50 microseconds ensures attenuation of disturbances from optical disruption, as well as the development of plasma size and density to values ​​sufficient for maintaining a steady-state plasma with a focused beam of a relatively low-power continuous laser.

[0070] Other embodiments of the present invention aim to further improve laser-pumped plasma light sources.

[0071] In embodiments of the present invention, the radiant power of the solid-state laser system 7 when generating giant pulses is such that the use of optical fibers to transport the radiation, which may be damaged, is not feasible. Therefore, only a continuous laser has optical fiber radiant output (not shown).

[0072] Simultaneously, the output of the continuous laser emission 4 is preferably carried out within an optical fiber (not shown). At the exit (or output) of the optical fiber, the expanding laser beam is directed to a collimator (not shown), and then the expanded parallel beam of the continuous laser is directed to a focusing optical element 16, for example, in the form of an aspherical focusing lens. The focusing optical element 16 provides sharp focusing of the beam 3 of the continuous laser 4, which is necessary to ensure high brightness of the light source.

[0073] Due to the absence of laser ignition of the plasma and the ignition electrode, in a preferred embodiment of the present invention, the output of the useful plasma radiation beam 5 from the chamber is shown in all directions along Figure 1. This means that in the azimuthal plane passing through the region of the emitted plasma 2 perpendicular to the axis of the continuous laser beam 3, the useful plasma radiation is emitted along all directions from 0 to 360 degrees. In a preferred embodiment of the present invention, the flat aperture angle (in the plane of Figure 1) of the useful plasma radiation beam 5 is at least 90°. This means that the emission of the useful plasma radiation beam 5 from the chamber 1 to the radiation collection system 6 is performed at a spatial angle of at least 9 sr or more than 70% of the total solid angle.

[0074] In this embodiment, the axis of the focused beam 3 of the continuous laser is directed vertically upward, i.e., against gravity, or in a near-vertical direction, within ±10° of its axis. Preferably, the chamber 1 is axially symmetric, and the axis of the focused beam 3 of the continuous laser is aligned with the axis of symmetry of the cavity. When implemented in the proposed form, maximum stability of the radiant power of the laser excitation source is achieved.

[0075] According to the present invention, in the mode for maintaining the radiant plasma, the temperature of the inner surface of the chamber is in the range of 600-900K or higher, provided that higher temperatures do not significantly adversely affect the intensity and transparency of the chamber. The positive effects achieved by the present invention stem from the fact that, for a given amount of gas in a given volume of the chamber, the gas pressure increases with the chamber temperature. Since the temperature of the emitted plasma is practically fixed (about 15,000K, and attempting to raise this temperature is difficult as it only involves an increase in plasma volume), and the pressure in the plasma is equal to the pressure in the chamber, the density of the emitted plasma increases with the increase in the pressure in the chamber (which means with the increase in the temperature of the chamber walls). The increase in the density of the emitted plasma leads to an increase in the volumetric brightness of the emitted plasma, resulting in an increase in the brightness of the light source over a wide optical range in which the emitted plasma is substantially transparent.

[0076] An increase in brightness can also be achieved by increasing the gas pressure at a given chamber temperature. However, in this case, the gas density and the refraction associated with this density increase, which, due to turbulence, leads to significant instability (variation) in the brightness of the light source, both in the region and around the emission plasma.

[0077] To sufficiently reduce brightness instability to σ ≤ 0.1%, the density of gas particles in the chamber was experimentally set to an upper limit of 90.10. 19 cm -3 This was determined to be 33.5 atmospheres (i.e., 3.3 MPa) at room temperature. At the same time, 50 MW / (mm 2 To obtain a light source spectral brightness close to the highest achievable value at a specified temperature, exceeding (nm·sr), the gas pressure, and therefore the density of the emitted plasma, must be high enough to ensure an optimal gas pressure of approximately 50 bar or higher in steady-state operation. For this purpose, the density of gas particles in the chamber corresponds to a gas pressure of at least 17 atmospheres (i.e., 1.7 MPa) at room temperature, according to an experimentally determined lower limit of 46·10. 19 cm -3 It is selected beyond the limits.

[0078] Therefore, in order to ensure high spectral brightness and low relative brightness instability, the density of gas particles should be as low as possible, and the temperature of the inner surface of the chamber during operation should be as high as possible while ensuring a gas pressure of approximately 50 bar or more within the chamber.

[0079] According to the present invention, the use of inert xenon as the gas is preferred, which ensures the safe operation and long lifespan of the light source. In addition, compared to plasmas emitting other inert gases, Xe plasma is characterized by the highest optical output over a wide spectral range, including the UV, visible, and near-IR regions.

[0080] As the continuous laser 4, it is preferable to use a high-efficiency near-infrared diode laser. The choice of preferred wavelength from two high-efficiency diode lasers, 976 nm and 808 nm, is due to the following factors: Strong Xe absorption lines are located around the 976 nm laser wavelength, and lower states become more widespread (populated) as the temperature increases. Around 808 nm, such lines are further away from the absorption lines, and therefore, at a given laser power, sufficient absorption to sustain the photodischarge is achieved at higher plasma densities and temperatures than at 976 nm (or, therefore, at a given laser power with sufficient absorption to sustain the photodischarge, it is achieved at higher plasma densities and temperatures than at 976 nm).

[0081] Therefore, in a preferred embodiment of the present invention, the gas filling the chamber is xenon, and the continuous laser has a wavelength of 808 nm.

[0082] In other modifications, a high-efficiency solid-state laser or fiber laser may be used as a continuous laser. In this case, the wavelengths of radiation from the continuous laser and the solid-state laser system may be close together or coincide.

[0083] In addition to ensuring high stability of output parameters, the present invention realizes the possibility of achieving maximum brightness of a broadband laser-excited light source, particularly by optimizing the shape and size of the electrodeless chamber. Accordingly, in a preferred embodiment of the present invention, the outer and inner surfaces of the chamber or its transparent portion have a concentric spherical shape, and the region of the emitted plasma 2 is located at the center of these concentric spheres (Figure 1). In this version of the present invention, aberrations that distort the path of rays in the beam 5 of useful plasma radiation are eliminated, and its brightness is increased.

[0084] To ensure the output of plasma radiation across a broad spectral range from ultraviolet to near-infrared, the optically transparent portion of the chamber is preferably made from a substance (or material) belonging to the group of crystalline magnesium fluoride (MgF2), crystalline calcium fluoride (CaF2), crystalline sapphire or leucosapphire (Al2O3), or molten or crystalline quartz.

[0085] In general, the proposed invention makes it possible to ensure the high reliability of plasma ignition maintained by laser radiation, and based on this, it is possible to generate an electrodeless, high-brightness, broadband light source with the highest possible spatial and energy stability, as well as the ability to collect plasma radiation at spatial angles exceeding 9 sr.

[0086] When the light source is implemented in the proposed configuration, the design is simplified as much as possible, and the reliability of the means for laser ignition of the plasma and the entire radiation source is increased. Compared to the prototype, the problems of aligning the focus of two pulsed laser beams and separating the two active elements of the operating laser system are eliminated. The limitations associated with the use of dichroic mirrors, which are typically used to inject several laser beams into the chamber, are removed. In general, when the light source is implemented in the proposed configuration, reliable ignition of this COD is achieved. In addition to optimizing the conditions for maintaining the COD, this makes it possible to create an electrodeless, high-brightness, broadband laser-excited light source characterized by the highest possible spatial and energy stability.

[0087] The high-brightness, highly stable laser-excited light source fabricated according to the present invention can be used in various projection systems for spectrochemical analysis, for spectral trace analysis of biological objects in biology and medicine, in microcapillary liquid chromatography, for inspection of optical lithography processes, for spectrophotometric methods, and for other sustained purposes. The following is the invention as originally described in the application. <Claim 1> A laser-excited plasma light source (100) comprising a gas-filled chamber (1) which is at least partially optically transparent, a region of radiant plasma (2) maintained within the chamber by a focused beam (3) of a continuous-wave laser (4) referred to as a CW laser (4), and means for plasma ignition, wherein the laser-excited light source (100) is The means for plasma ignition is a solid-state laser system (7) that generates two pulsed laser beams (8,9) focused within the chamber (1), one of the two pulsed laser beams (8) being generated in free-running mode and the other pulsed laser beam (9) being generated in Q-switched mode. The laser-pumped plasma light source is characterized in that the solid-state laser system (7) includes a single active element (10), a radiation source (11) for pumping the active element (10), and optical resonators (12, 13) that provide multiple passages of an intracavity laser beam (15) through the active element (10), wherein the optical resonators (12, 13) are equipped with a Q-switch (14) positioned on the path of the intracavity laser beam, and the Q-switch overlaps with only a portion (15b) of the cross-section of the intracavity laser beam. <Claim 2> The light source (100) according to claim 1, wherein the Q switch (14) is a saturable absorber made of a chromium-doped yttrium aluminum garnet crystal Cr4+:YAG. <Claim 3> The light source (100) according to claim 1 or 2, wherein the Q-switch (14) overlaps with a small portion (15b) of the cross-section of the intracavity laser beam (15) and its area is 30% or less. <Claim 4> A light source (100) according to any one of claims 1 to 3, wherein the pulsed laser beam (8,9) and the CW laser (4) beam (17) are focused into the chamber by a focusing optical element (16), and the CW laser (4) beam (17) directed toward the focusing optical element (16) does not intersect with the pulsed laser beam (8,9) directed toward the focusing optical element (16). <Claim 5> A light source (100) according to any one of claims 1 to 4, wherein a deflection mirror (18) is mounted on the path of the beam (17) of the CW laser (4) outside the path of the pulsed laser beam (8,9). <Claim 6> A light source (100) according to any one of claims 1 to 4, wherein a deflection mirror (18) is mounted on the path of the pulsed laser beam (8,9) outside the path of the beam of the CW laser (4). <Claim 7> The light source (100) according to any one of claims 1 to 6, wherein the output power of the CW laser (4) is 30 watts or less, which is sufficient to ignite and maintain the radiant plasma. <Claim 8> The light source (100) according to any one of claims 1 to 7, wherein the axis of the focused beam (3) of the CW laser is directed vertically upward or at an angle of 10 degrees or less that approaches the vertical. <Claim 9> A light source (100) according to any one of claims 1 to 8, wherein the density of gas particles in the chamber (1) is less than 90·1019 cm⁻³, which corresponds to a gas pressure of 33 atmospheres at room temperature, and the temperature of the inner surface of the chamber is 600K or higher. <Claim 10> A light source (100) according to any one of claims 1 to 8, wherein the temperature of the inner surface of the chamber is 900K or less, and the density of the gas particles is 45·1019 cm⁻³ or more, which corresponds to a gas pressure of 16.5 atmospheres at room temperature. <Claim 11> The radiant plasma is a light source (100) according to any one of claims 1 to 10, characterized by a high spectral brightness exceeding 50 MW / (mm²·nm·sr) and a low relative instability σ of less than 1% brightness. <Claim 12> A light source (100) according to any one of claims 1 to 11, wherein the gas belongs to the group of inert gases including xenon, krypton, argon, and neon, or the gas includes a mixture thereof. <Claim 13> A plasma ignition method in a laser-excited plasma light source (100) comprising directing a focused beam (3) of a continuous-wave (CW) laser (4) into a gas-filled chamber (1) that is at least partially optically transparent, and maintaining a steady state and igniting a radiant plasma (2) by the focused beam (3) of the CW laser, wherein the method is A plasma ignition method characterized in that the plasma is ignited by a solid-state laser system (7) having a single active element (10), the single active element generates two parallel pulsed laser beams (8,9) focused within the chamber, one of the two pulsed laser beams (8) is generated in free-running mode, and the other pulsed laser beam (9) is generated in Q-switched mode by a Q-switch (14) installed in an optical cavity, where only a portion (15b) of the cross-section of the intracavity laser beam (15) overlaps. <Claim 14> The method according to claim 13, wherein the pulsed laser beam (8,9) and the beam (3) of the CW laser (4) are focused by a focusing optical element (16) into a region for maintaining the radiant plasma (2), and the beam (17) of the CW laser directed toward the focusing optical element does not intersect with the pulsed laser beam (8,9) directed toward the focusing optical element (16).

Claims

1. A laser-excited plasma light source (100) comprising a gas-filled chamber (1) which is at least partially optically transparent, a region of radiant plasma (2) maintained within the gas-filled chamber by a focused beam (3) of a continuous-wave laser (4) called a CW laser (4), and means for plasma ignition, wherein the laser-excited plasma light source (100) is The means for plasma ignition is a solid-state laser system (7) that generates two pulsed laser beams (8, 9) focused within the gas-filled chamber (1), wherein one of the two pulsed laser beams (8) is generated in free-running mode and the other pulsed laser beam (9) is generated in Q-switched mode. A laser-pumped plasma light source (100) is characterized in that the solid-state laser system (7) includes a single active element (10), a radiation source (11) for pumping the active element (10), and optical resonators (12, 13) that provide multiple passages of an intracavity laser beam (15) through the active element (10), wherein the optical resonators (12, 13) are equipped with a Q-switch (14) positioned on the path of the intracavity laser beam (15), and the Q-switch overlaps with only a portion (15b) of the cross-section of the intracavity laser beam (15).

2. The Q-switch (14) is a chromium-doped yttrium aluminum garnet crystal Cr ４＋ A laser-excited plasma light source (100) according to claim 1, wherein the absorber is saturable, consisting of YAG.

3. The laser-excited plasma light source (100) according to claim 1 or 2, wherein the Q-switch (14) overlaps with a small portion (15b) of the cross-section of the intracavity laser beam (15) and its area is 30% or less.

4. The laser-excited plasma light source (100) according to claim 1 or 2, wherein the pulsed laser beams (8, 9) and the beam (17) of the CW laser (4) are focused into the gas-filled chamber by a focusing optical element (16), and the beam (17) of the CW laser (4) directed toward the focusing optical element (16) does not intersect with the pulsed laser beams (8, 9) directed toward the focusing optical element (16).

5. A laser-excited plasma light source (100) according to claim 1 or 2, wherein a deflection mirror (18) is attached to the path of the beam (17) of the CW laser (4) outside the path of the pulsed laser beams (8, 9).

6. A deflection mirror (18) is mounted on the path of the pulsed laser beams (8, 9) outside the path of the beam of the CW laser (4) according to claim 1 or 2, the laser-excited plasma light source (100).

7. The laser-excited plasma light source (100) according to claim 1 or 2, wherein the output power of the CW laser (4) sufficient to ignite and maintain the radiant plasma is 30 watts or less.

8. The laser-excited plasma light source (100) according to claim 1 or 2, wherein the axis of the focused beam (3) of the CW laser is directed vertically upward or at an angle of 10 degrees or less that approaches the vertical direction.

9. The density of gas particles filling the chamber is 90.10 １９ cm －３ The laser-excited plasma light source (100) according to claim 1 or 2, wherein the gas pressure at room temperature is less than 33 atmospheres, and the temperature of the inner surface of the gas-filled chamber is 600K or higher.

10. The temperature of the inner surface of the gas-filled chamber is 900K or less, and the density of the gas particles filling the chamber is 45.10 １９ cm －３ The above describes the laser-excited plasma light source (100) according to claim 1 or 2, wherein the gas pressure at room temperature corresponds to 16.5 atmospheres.

11. The aforementioned radiant plasma is 50 MW / (mm²). ２ A laser-excited plasma light source (100) according to claim 1 or 2, characterized by a high spectral brightness exceeding nm·sr and a low relative instability σ of less than 1% brightness.

12. The laser-excited plasma light source (100) according to claim 1 or 2, wherein the gas filling the chamber belongs to the group of inert gases including xenon, krypton, argon, and neon, or the gas filling the chamber includes a mixture thereof.

13. A plasma ignition method in a laser-excited plasma light source (100) comprising directing a focused beam (3) of a continuous-wave (CW) laser (4) into a gas-filled chamber (1) in which at least a portion is optically transparent, and maintaining a steady state and igniting a radiant plasma (2) by the focused beam (3) of the CW laser, wherein the method is A plasma ignition method characterized in that the plasma is ignited by a solid-state laser system (7) having a single active element (10), the solid-state laser system generates an intracavity laser beam (15) in an optical cavity, and generates two parallel pulsed laser beams (8, 9) focused in the gas-filled chamber, one of the two pulsed laser beams (8) is generated in free-running mode, and the other pulsed laser beam (9) is generated in Q-switched mode by a Q-switch (14) installed in the optical cavity, where only a portion (15b) of the cross-section of the intracavity laser beam (15) overlaps.

14. The method according to claim 13, wherein the pulsed laser beams (8, 9) and the beam (3) of the CW laser (4) are focused by a focusing optical element (16) into a region for maintaining the radiating plasma (2), and the beam (17) of the CW laser directed toward the focusing optical element (16) does not intersect with the pulsed laser beams (8, 9) directed toward the focusing optical element (16).

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