Liquid flat-jet for debris management in laser-driven x-ray sources

Abstract

A liquid jet for debris management in laser-driven X-ray sources. The liquid jet, having a flat portion with a front surface and back surface, can serve as a target for laser pulse interaction to generate X-rays. The front surface can receive laser pulses, and debris from the interaction can be expelled through the back surface. The liquid jet can be a continuously flowing target, composed of liquid metal or a slurry with metallic or non-metallic phases. A laser-driven plasma X-ray system incorporates a laser source, the liquid jet target, and optical elements to focus laser pulses, all housed within a vacuum chamber. The method involves providing the liquid jet target, focusing laser pulses, and delivering them to generate X-rays and expel debris through the back surface of the liquid jet.

Description

LIQUID FLAT-JET FOR DEBRIS MANAGEMENT IN LASER-DRIVEN X-RAYSOURCESCROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims benefit from U.S. Provisional Patent Application Serial No. 63 / 623,176, filed January 19, 2024, and U.S. Provisional Patent Application Serial No.63 / 623,164, filed January 19, 2024, and U.S. Provisional Patent Application Serial No.63 / 623,180, filed January 19, 2024, and U.S. Provisional Patent Application Serial No.63 / 626,493, filed January 29, 2024, and U.S. Provisional Patent Application Serial No.63 / 550,575, filed February 6, 2024, which are all hereby incorporated by reference in their entirety herein.FIELD OF THE INVENTION

[0002] The present invention relates generally to laser-driven plasma X-ray sources (LPXS) and more particularly, to a liquid flat-jet for debris management in LPXS.BACKGROUND

[0003] LPXSs are used in various scientific and industrial applications, including medical imaging, material analysis, and semiconductor manufacturing. LPXSs rely on the interaction between high-intensity laser pulses and a target material to produce X-rays. At the target material, a plasma is formed which accelerates electrons to high kinetic energies resulting in the generation of X-rays. Laser interaction with the target material creates debris, which may consist of target material pieces, vapor, and ions. Oftentimes, the debris is ejected primarily in the direction normal to the target surface, i.e. substantially into the direction of the laser optics focusing the light onto the target. The debris is deposited on the optics and quickly blocks and obscures incoming laser light. Any X-ray window or optics located on the same side as the laser optics also gets coated and becomes X-ray opaque. Various solutions for cleaning the optics exist but with limited effectiveness, because in LPXSs having high average laser power the level of debris deposited onto laser and X-ray optics quickly overwhelms all cleaning processes.

[0004] The efficiency and quality of the X-ray generation process can be influenced by the characteristics of the target material and the management of debris deposited during generation of X-rays. Traditional methods often face challenges in maintaining a stable target andeffectively managing debris, which can affect the performance and longevity of the X-ray source. In the pursuit of improving X-ray generation, researchers have explored various target materials and configurations. Liquid targets have been used due to their ability to provide a continuously renewing target surface, which can enhance the consistency of the X-ray production process. However, the management of debris remains an issue, as it can interfere with the optical components and reduce the overall effectiveness of the system. There is a need for innovative approaches that can address these challenges, ensuring high-quality X-ray output while minimizing maintenance and operational disruptions.SUMMARY OF THE INVENTION

[0005] The following presents a simplified summary of the innovation to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.

[0006] In one aspect the present invention provides an apparatus for debris management in a laser-driven plasma X-ray sources. The apparatus can include a nozzle configured to provide a flat liquid jet. The liquid jet exiting the nozzle can have a flat portion with a front surface and a back surface. The liquid jet can be configured as a target for interacting with at least one laser pulse to generate X-rays. The front surface can receive one or more laser pulses and any debris generated by the interaction can be expelled through the back surface of the liquid jet.

[0007] One or more of the following features may be included. The liquid jet can be made of a liquid metal, and the flat portion of the liquid jet can have a thickness between the front surface and the back surface of less than 100 micrometers (pm). In some examples, the liquid jet can be made of a liquid metal, and the flat portion of the liquid jet can have a thickness between the front surface and the back surface of less than 20 micrometers (pm). The nozzle can be a monolithic nozzle and may be made of ceramic, metal, diamond, or sapphire. The flat portion of the liquid jet can have a thickness of less than 100 micrometers, and in some examples, it can be 20 micrometers. The liquid jet can be a continuously flowing target. The liquid jet can be composed of a liquid metal including gallium, gallium alloy, indium, indium alloy, tin, tin alloy, bismuth, bismuth alloy, or a combination thereof. In some examples, the liquid jet may be a slurry having a liquid and a solid phase. The liquid jet can be a metal alloy slurry. The liquid jetcan be a slurry having a metallic liquid phase or a non-metallic liquid phase. Tn some examples, the liquid jet can be non-metallic.

[0008] In another aspect, the present invention provides an LPXS system that can include a laser source configured to emit at least one laser pulse. The LPXS system can have a liquid jet configured as a target for interacting with one or more laser pulses to generate X-rays. The liquid jet can have a flat portion with a front surface and a back surface. The front surface can receive one or more laser pulses, and debris generated by the interaction can be expelled through the back surface. At least one optical element may be located between the laser source and the liquid jet for focusing laser pulses onto one or more locations on the front surface to generate X- rays.

[0009] One or more of the following features may be included. The liquid jet can be made of a liquid metal, and the flat portion of the liquid jet can have a thickness between the front surface and the back surface of less than 100 micrometers (pm). In some examples, the liquid jet can be made of a liquid metal, and the flat portion of the liquid jet can have a thickness between the front surface and the back surface of less than 20 micrometers (pm). A vacuum chamber can be included for housing the liquid jet, optical elements, and debris shields. The flat portion of the liquid jet can have a thickness of less than 100 micrometers, and in some examples, it can be 20 micrometers. The liquid jet can be a continuously flowing target. The liquid jet in the system may be composed of a liquid metal, which can include any one of gallium, gallium alloy, indium, indium alloy, tin, tin alloy, bismuth, bismuth alloy, or a combination thereof. In some examples, the liquid jet may be a slurry containing a liquid and a solid phase, or it can be a metal alloy slurry. The liquid jet can be a slurry having a metallic liquid phase or a non-metallic liquid phase. In some cases, the liquid jet can be non-metallic.

[0010] In another aspect, the present invention provides a method for debris management in a LPXS that may involve providing a liquid jet target for interacting with at least one laser pulse to generate X-rays. The liquid jet target can have a flat portion with a front surface and a back surface. The front surface can receive one or more laser pulses, and debris generated by the interaction can be expelled through the back surface. The method may include utilizing at least one optical element, located between a laser source and the liquid jet target, to focus at least one laser pulse onto the front surface of the flat portion of the liquid jet target. The method may also involve delivering at least one laser pulse to one or more locations on the front surface of theliquid jet target to generate X-rays and expel debris through the back surface. In some examples of the method, delivering the laser pulse onto the liquid jet target may include positioning the liquid jet target in a vacuum chamber.

[0011] The present invention provides many improvements and advantages over existing LPXS systems and debris management systems for LPXS. For example, the present invention prevents or greatly reduces debris emissions and deposits on optical elements in LPXS systems. Debris generated by laser pulse interaction with the liquid jet surface is expelled through the back surface of the liquid jet and away from the LPXS optical elements and components. The invention can be used in a wide range of applications, including but not limited to, semiconductor metrology, medical imaging, security scanning, non-destructive imaging, x-ray diffraction, and scientific research.

[0012] These and other features and advantages will be apparent from a reading of the following detailed description and a review of the associated drawings. It is to be understood that both the foregoing general description and the following detailed description are explanatory only and are not restrictive of aspects as claimed.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The invention will be more fully understood by reference to the detailed description, in conjunction with the following figures.

[0014] FIG. 1 A illustrates an example nozzle and liquid jet for debris management in an LPXS in accordance with an aspect of the present invention.

[0015] FIG. IB illustrates a side view of the example nozzle and liquid jet shown in FIG. 1A.

[0016] FIG. 2A illustrates a cut-away view of an example nozzle for use in accordance with an aspect of the present invention.

[0017] FIG. 2B illustrates internal structural view of an example nozzle configured in accordance with an aspect of the present invention.

[0018] FIG. 3 illustrates an exemplary embodiment of an LPXS configured in accordance with an aspect of the present invention.

[0019] FIG. 4 illustrates another embodiment of an LPXS configured in accordance with an aspect of the invention.

[0020] FIG. 5 is a flow diagram illustrating the process of debris management and X-ray generation in an LPXS in accordance with an aspect of the present invention.DETAILED DESCRIPTION

[0021] The subject innovation is now described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth to provide a thorough understanding of the present invention. It may be evident, however, that the present invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form to facilitate describing the present invention.

[0022] As used in this application, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or.” That is, unless specified otherwise, or clear from context, “X employs A or B” is intended to mean any of the natural inclusive permutations. That is, if X employs A, X employs B, or X employs both A and B, then “X employs A or B” is satisfied under any of the foregoing instances. Moreover, articles “a” and “an” as used in the subject specification and annexed drawings should generally be construed to mean “one or more” unless specified otherwise or clear from context to be directed to a singular form.

[0023] Generally, the present invention provides an apparatus, system, and method for debris management in LPXSs during X-ray generation. Unlike conventional LPXSs in which high- intensity laser interaction with a target material generates debris (e.g., target material pieces, vapor, ions) that can be deposited on laser optics and other LPXS components rendering them X- ray opaque, the present invention can mitigate this problem by using a flat liquid jet as the target material. The liquid jet can be configured as a continuously flowing target. In an embodiment, the liquid jet can be composed of a liquid metal and can have a thickness less than 100 micrometers. In other embodiments, the thickness of the liquid jet can be less than 20 micrometers. During laser interaction with the liquid jet to generate X-rays, any debris produced is expelled through the back surface of the liquid jet and away from the laser optics and other LPXS components. The thin, flat profile of the liquid jet permits debris to propagate through the back surface of the liquid jet.

[0024] Referring to FIG. 1A, in one aspect, the present invention provides an apparatus 100 for debris management in a LPXS. Referring also to FIG. IB that shows a side view 150 of apparatus 100, in an embodiment, apparatus 100 can include a nozzle 102 designed to create a flat liquid jet 103 that can be utilized as a target for interaction with at least one laser pulse 106 to generate X-rays. The liquid jet 103 can have a flat portion 104 with a front surface 105 and aback surface 152. The front surface 105 can be configured to receive one or more laser pulses 106 and any debris generated by this interaction can be expelled through the back surface 152 of the liquid jet 103.

[0025] Referring also to FIG. 2A showing a cut-away view 200 of nozzle 102 and FIG. 2B showing an internal structural view 250 of nozzle 102, in an embodiment, the nozzle 102 can be a monolithic nozzle body 202 and, in various embodiments, may be composed of materials such as ceramic, metal, diamond, or sapphire. A flow channel 204 can be machined in the nozzle body 202 that is not symmetric around the center axis of a liquid flow. The internal walls 206 in one dimension may converge at a much steeper angle toward an outflow opening 208 than in the orthogonal direction. This creates converging fluid flows that after leaving the nozzle 102 result in a liquid jet 103 that spreads out in one dimension with increasing distance to the nozzle opening 208. The flat portion 104 of liquid jet 103 can be fully developed after a few millimeters of free flow. The nozzle 102 is simply one non-limiting example of a component that can be utilized to create the liquid jet 103. Instead of a nozzle 102, simple slit-nozzles, slit nozzles with internal flow channel structures, and other mechanisms and devices can be utilized to create the liquid jet 103.

[0026] In an embodiment, the flat portion 104 of the liquid jet 103 can have a thickness of less than 100 micrometers (pm), and in a preferred embodiment, less than 20 micrometers (pm). The liquid jet 103 can be a continuously flowing target material that provides a continuously renewing target surface for laser interaction and X-ray generation. Also, a continuously flowing target can be mechanically simple and does not typically require precise mechanical-optical timing. The liquid jet 103 can be composed of a liquid metal, which may include gallium, gallium alloy, indium, indium alloy, tin, tin alloy, bismuth, bismuth alloy, or combinations thereof. Alternatively, the liquid jet 103 can be a slurry with both liquid and solid phases, which may be a metal alloy slurry, or have either a metallic or non-metallic liquid phase. In an embodiment, the liquid jet 103 can also be entirely non-metallic.

[0027] In another embodiment, the liquid jet 103 can have a shape other than the non -limiting example shape shown in FIG. 1 A. Depending on how the liquid jet 103 is created, the shape of the liquid jet 103 may vary and may, for example, include a continuous sheet of liquid metal with uniform width dimensions. Such varying shapes are within the scope of the inventionprovided that the thickness between a front surface and a back surface of the liquid jet is less than 100 micrometers (pm).

[0028] Referring to FIG. 3, an exemplary embodiment of an LPXS system 300 configured with debris management functionality in accordance with an aspect of the present invention is illustrated. In one aspect, the system 300 can include, among other things, a laser source 302, configured to emit at least one laser pulse, a liquid jet 103 configured as a target for interacting with one or more laser pulses 320 to generate X-rays, and at least one focusing optical element 310 positioned between the laser source 302 and the liquid jet 103. The liquid jet 103 and other components can be housed in a vacuum chamber 306. The vacuum chamber 306 can be further configured with an affixed laser window 308, optical elements 310, X-ray windows 312 and 314, debris shields 316 and 318, a receptacle 326 or other mechanism for capturing expelled debris 324, and an external liquid metal circulation pump 328 with associated piping 330.

[0029] The laser source 302 can be selected to have a repetition rate range from 1Hz to 1MHz and a pulse duration range from 10 femtoseconds to 100 picoseconds. In an embodiment, the high-intensity laser source 302 can be an Ytterbium laser having a repetition rate of 5kHz, a pulse duration of 850 femtoseconds, and a wavelength of 1030nm. In various embodiments, laser source 302 can be an Ytterbium laser (e.g., Yb:YAG), Thulium laser (e.g., Tm:YLF), or pulsed CO2 laser. Other types of laser sources (e.g., fiber laser, slab laser) can also be used, provided they have similar performance specifications including repetition rates, and pulse durations. In various embodiments, multiple lasers of different types can be used simultaneously as the laser source 302.

[0030] In an embodiment, the laser source 302 can emit linearly polarized Gaussian laser pulses 304 that can be propagated through the laser window 308 on the vacuum chamber 306. The laser pulses 304 can then be propagated through at least one optical element 310 that focuses the laser pulses 304 and delivers the focused laser pulses 320 onto one or more locations 106 on the front surface 105 of the liquid jet 103 to generate X-rays. The optical element 310 can be positioned between the laser source 302 and the liquid jet 103.

[0031] In an aspect, the liquid jet 103 can be configured as a continuously flowing target material. This can be accomplished by utilizing external circulation pump 328 and associated piping 330 to continuously circulate the liquid jet 103 between nozzle 102 and return reservoir 322. As a continuously flowing target material, liquid jet 103 can provide a continuouslyrenewing target surface for laser interaction and X-ray generation. An advantage of a continuously flowing target is that the circulation mechanism can be mechanically simple and does not typically require precise mechanical -optical timing. Referring also to FIG. 4, in an embodiment, the LPXS system 400 can enclose a circulation pump 402 and associated piping 404 within the vacuum chamber 306.

[0032] In an aspect, the liquid jet 103 can be composed of a liquid metal, which may include gallium, gallium alloy, indium, indium alloy, tin, tin alloy, bismuth, bismuth alloy, or combinations thereof. Alternatively, the liquid jet 103 can be a slurry with both liquid and solid phases, which may be a metal alloy slurry, or have either a metallic or non-metallic liquid phase. In an embodiment, the liquid jet can also be entirely non-metallic.

[0033] As discussed above in connection with other embodiments, the liquid jet 103 can have a flat portion 104 with a front surface 105 and a back surface 152. The front surface 105 can receive laser pulses 320 and generate X-rays. The flat portion 104 can have a thickness between the front surface 105 and the back surface 152 of less than 100 pm, and in preferred embodiments, less than 20 pm. This minimal thickness permits any debris 324 generated by the laser interaction to be expelled through the back surface 152 and away from the optical elements 310, laser window 308, X-ray windows 312 and 314, and debris shields 316 and 318.

[0034] In operation, when the focused laser pulses 320 are delivered onto the liquid jet 103 a plasma is produced on the liquid jet 103 at the focus, and electrons in the plasma are accelerated to generate X-rays as fluorescence (line) emission or Bremsstrahlung (continuum) emission. The generated X-rays can be emitted from the vacuum chamber through X-ray windows 312 and 314. In addition to generating X-rays, the laser interaction with the liquid jet 103 also generates debris 324. Unlike conventional LPXS systems where the debris is oftentimes ejected towards the incoming laser light and deposited on the optical elements causing X-ray opaqueness, the present invention avoids this problem by expelling debris 324 through the back surface 152 of the liquid jet 103 and away from the optical elements. In an embodiment, a receptacle 326 or other mechanism can be placed in the vacuum chamber 306 to capture the debris 324.

[0035] Referring to FIG. 5, in an aspect, the present invention features a method (500) for debris management in an LPXS. The method can involve providing (502) a liquid jet target for interacting with at least one laser pulse to generate X-rays. The liquid jet target can have a flat portion with a front surface and a back surface. The front surface can be configured to receive atleast one laser pulse, and debris generated by the interaction can be expelled through the back surface. The method can include utilizing (504) at least one optical element located between a laser source and the liquid jet target to focus the laser pulse onto the front surface of the flat portion of the liquid jet target. The method can include (506) delivering at least one laser pulse to one or more locations on the front surface of the liquid jet target to generate X-rays and expel debris through the back surface. In some examples of the method, delivering the laser pulse onto the liquid jet target may include positioning the liquid jet target in a vacuum chamber.

[0036] While example embodiments have been particularly shown and described, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the embodiments encompassed by the appended claims. For example, other useful implementations could be achieved if steps of the disclosed techniques were performed in a different order and / or if components in the disclosed systems were combined in a different manner and / or replaced or supplemented by other components. Accordingly, other implementations are within the scope of the disclosure.

Claims

CLAIMSWhat is claimed is:

1. An apparatus for debris management in a laser-driven plasma X-ray source comprising: a nozzle configured to provide a flat liquid jet; and a liquid jet exiting the nozzle and having a flat portion with a front surface and a back surface, the liquid jet configured as a target for interacting with at least one laser pulse to generate X-rays, wherein the front surface is configured to receive the at least one laser pulse and debris generated by the interaction is expelled through the back surface of the liquid jet.

2. The apparatus of claim 1, wherein the liquid jet is made of a liquid metal and the flat portion of the liquid jet has a thickness between the front surface and the back surface of less than 100 micrometers (pm).

3. The apparatus of claim 1, wherein the liquid jet is made of a liquid metal and the flat portion of the liquid jet has a thickness between the front surface and the back surface of less than 20 micrometers (pm).

4. The apparatus of claim 1, wherein the nozzle is a monolithic nozzle.

5. The apparatus of claim 1, wherein the nozzle is made of a ceramic, a metal, a diamond, or a sapphire.

6. The apparatus of claim 1, wherein the flat portion of the liquid jet has a thickness less than 100 pm.

7. The apparatus of claim 1, wherein with flat portion of the liquid jet has a thickness less than 20 pm.

8. The apparatus of claim 1, wherein the liquid jet is a continuously flowing target.

9. The apparatus of claim 1, wherein the liquid jet is a liquid metal including any one of gallium, gallium alloy, indium, indium alloy, tin, tin alloy, bismuth, bismuth alloy, or combination thereof.

10. The apparatus of claim 1, wherein the liquid jet is a slurry having a liquid and a solid phase.

11. The apparatus of claim 1, wherein the liquid jet is a metal alloy slurry.

12. The apparatus of claim 1, wherein the liquid jet is a slurry having a metallic liquid phase.

13. The apparatus of claim 1, wherein the liquid jet is a slurry having a non-metallic liquid phase.

14. The apparatus of claim 1, wherein the liquid jet is non-metallic.

15. A laser-driven plasma X-ray system comprising: a laser source configured to emit at least one laser pulse; a liquid jet configured as a target for interacting with the at least one laser pulse to generate X-rays, the liquid jet having a flat portion with a front surface and a back surface, wherein the front surface is configured to receive the at least one laser pulse and debris generated by the interaction is expelled through the back surface of the liquid jet; and at least one optical element located between the laser source and the liquid jet, the at least one optical element focusing the at least one laser pulse onto one or more locations on the front surface to generate X-rays.

16. The laser-driven plasma X-ray system of claim 15, wherein the liquid jet is made of a liquid metal and the flat portion of the liquid jet has a thickness between the front surface and the back surface of less than 100 micrometers (pm).

17. The laser-driven plasma X-ray system of claim 15, wherein the liquid jet is made of a liquid metal and the flat portion of the liquid jet has a thickness between the front surface and the back surface of less than 20 micrometers (pm).

18. The laser-driven plasma X-ray system of claim 13, further comprising a vacuum chamber for housing the liquid jet and the at least one optical element.

19. The laser-driven plasma X-ray system of claim 13, wherein the flat portion of the liquid jet has a thickness less than 100 pm.

20. The laser-driven plasma X-ray system of claim 13, wherein with flat portion of the liquid jet has a thickness less than 20 pm.21 . The laser-driven plasma X-ray system of claim 13, wherein the liquid jet is a continuously flowing target.

22. The laser-driven plasma X-ray system of claim 13, wherein the liquid jet is a liquid metal including any one of gallium, gallium alloy, indium, indium alloy, tin, tin alloy, bismuth, bismuth alloy, or combination thereof.

23. The laser-driven plasma X-ray system of claim 13, wherein the liquid jet is a slurry containing a liquid and a solid phase.

24. The laser-driven plasma X-ray system of claim 13, wherein the liquid jet is a metal alloy slurry.

25. The laser-driven plasma X-ray system of claim 13, wherein the liquid jet is a slurry having a metallic liquid phase.

26. The laser-driven plasma X-ray system of claim 13, wherein the liquid jet is a slurry having a non-metallic liquid phase.

27. The laser-driven plasma X-ray system of claim 13, wherein the liquid jet is non-metallic.

28. A method of debris management in a LPXS comprising: providing a liquid jet target for interacting with at least one laser pulse to generate X- rays, the liquid jet target having a flat portion with a front surface and a back surface, wherein the front surface is configured to receive the at least one laser pulse and debris generated by the interaction is expelled through the back surface of the liquid jet target; utilizing at least one optical element located between a laser source and the liquid jet target to focus at least one laser pulse onto the front surface of the flat portion of the liquid jet target; and delivering the at least one laser pulse to one or more locations on the front surface of the liquid jet target to generate X-rays and expel debris through the back surface.

29. The method of claim 24, wherein delivering the at least one laser pulse onto the liquid jet target includes positioning the liquid jet target in a vacuum chamber.

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