1. Field of the Invention
The present invention relates to laser-sustained plasma illuminator systems. More particularly, the invention relates to systems and methods for compensating for optical aberrations to optimize plasma performance and UV light collection.
2. Description of Related Art
Plasmas sustained by lasers have shapes defined by the laser light intensity distribution near the laser focus. The laser light intensity distribution may be a function of optical aberrations (e.g., how well the light is focused in the plasma cell). Many optical aberrations present in typical laser-sustained plasma illuminator systems are aberrations introduced by an enclosure (e.g., a bulb) used to contain the gas and the plasma. Such bulb-introduced aberrations may be significant optical aberrations, especially for plasmas sustained by lasers operating in the near IR range (wavelengths of about 1000 nm). These significant optical aberrations may result in large size plasmas, the inability to control the bulb envelope, and/or irreproducible plasma shapes.
Aberrations may become particularly large when a high NA (numerical aperture) is used for pumping the plasma. Large pump laser NAs are used as light sources in many current laser-sustained sustained plasma illuminator systems. U.S. Pat. No. 7,705,331 to Kirk et al., which is incorporated by reference as if fully set forth herein, describes an example of a high NA system.
In addition to the aberrations introduced by the enclosure itself, the refractive index of the gas inside the enclosure is another source of aberrations in the system. Gas related aberrations may be especially significant in high-pressure enclosures.
U.S. Pub. Pat. Appl. Nos. 2007/0228288 and 2007/0228300 to Smith, each of which is incorporated by reference as if fully set forth herein, disclose one method of compensating for aberrations introduced by the refractive index of the walls of the enclosure by modifying the shape of the reflector (e.g., a reflective ellipse). Modifying the shape of the reflector, however, can only account for aberrations from reproducible enclosure shapes. Modifying reflector shapes for each individual enclosure shape and/or different fill pressures is difficult to impractical to implement for most laser-sustained plasma illuminator systems.
In certain embodiments, a laser-sustained plasma illuminator system includes at least one laser light source to provide light. At least one reflector focuses the light from the laser light source at a focal point of the reflector. An enclosure substantially filled with a gas is positioned at or near the focal point of the reflector. The light from the laser light source at least partially sustains a plasma contained in the enclosure. The enclosure has at least one wall with a thickness that is varied. The enclosure wall thickness may be varied to compensate for optical aberrations in the system.
In certain embodiments, a method for compensating for optical aberrations in a laser-sustained plasma illuminator system includes providing light from at least one laser light source and focusing the light from the at least one laser light source to an enclosure substantially filled with a gas. A plasma may be generated in the enclosure. The enclosure may have at least one wall with a thickness that is varied to compensate for optical aberrations in the system.
In certain embodiments, a method for compensating for optical aberrations in a laser-sustained plasma illuminator system includes providing an enclosure for containing a plasma to the laser-sustained plasma illuminator system. The enclosure may have at least one wall with a thickness that is varied to compensate for optical aberrations in the system.
Features and advantages of the methods and apparatus of the present invention will be more fully appreciated by reference to the following detailed description of presently preferred but nonetheless illustrative embodiments in accordance with the present invention when taken in conjunction with the accompanying drawings in which:
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. The drawings may not be to scale. It should be understood that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but to the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.
In certain embodiments, the wall thickness of an enclosure (e.g., a bulb) is adjusted to compensate for shape aberrations in the enclosure and/or aberrations induced by the gas refractive index (e.g., fill pressure aberrations).
In certain embodiments, enclosure 400C is a bulb. The bulb may be, for example, a lamp made of glass (fused silica) using a bulb-specific manufacturing process. In some embodiments, enclosure 400C is any other type of enclosure, vessel, or container that encloses/contains gas and has walls made of a transparent material. Enclosure 400C may be an enclosure made of glass, quartz, sapphire, CaF2, MgF2, or similar materials with proper sealing to enclose/contain a gas. For example, enclosure 400C may be a tube or cell made of glass with sealing to enclose a gas.
In certain embodiments, the thickness variation in walls 408 (e.g., the shape of the walls as defined by changes in the wall thickness along a section of the wall) is defined based on the shape of the envelope of enclosure 400C and/or the gas fill pressure of the enclosure. Varying the thickness of the walls of enclosures (e.g., walls 408 of enclosure 400C) to compensate for aberrations in the enclosures (e.g., enclosure wall thickness compensation) allows a single uncompensated reflector to be used for all types of enclosures with varying shapes and/or fill pressures. Thus, a laser-sustained plasma illuminator system using enclosures with enclosure wall thickness compensation may have improved performance and/or improved cost efficiency compared to typical current laser-sustained plasma illuminator systems (e.g., systems using modified reflector shapes for aberration compensation).
In some embodiments, enclosure wall thickness compensation is used to compensate for aberrations in the collected light path (e.g., the path of light before the light enters the enclosure or the path of light from the light source (laser) through focusing optics (such as mirrors and/or reflectors). In some embodiments, enclosure wall thickness compensation is used to introduce a controlled amount of aberration into a laser-sustained plasma illuminator system. For example, wall thickness may be varied to provide a controlled amount of aberration to optimize plasma performance in the laser-sustained plasma illuminator system.
In some embodiments, enclosure wall thickness compensation is used in combination with other compensation methods. Combining enclosure wall thickness compensation with other compensation methods may provide higher levels of control of aberrations in a laser-sustained plasma illuminator system. For example, in one embodiment, enclosure wall thickness may be varied in combination with the shape of the enclosure. In some embodiments, enclosure wall thickness compensation is combined with compensation using modified reflector shapes to provide greater control of the shape of the plasma.
It is to be understood the invention is not limited to particular systems described which may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting. As used in this specification, the singular forms “a”, “an” and “the” include plural referents unless the content clearly indicates otherwise. Thus, for example, reference to “a wall” includes a combination of two or more walls and reference to “a gas” includes mixtures of gases.
Further modifications and alternative embodiments of various aspects of the invention will be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the invention. It is to be understood that the forms of the invention shown and described herein are to be taken as the presently preferred embodiments. Elements and materials may be substituted for those illustrated and described herein, parts and processes may be reversed, and certain features of the invention may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description of the invention. Changes may be made in the elements described herein without departing from the spirit and scope of the invention as described in the following claims.
This patent claims priority to U.S. Provisional Patent Application No. 61/767,917 filed Feb. 22, 2013, which is incorporated by reference in its entirety.
Number | Date | Country | |
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61767917 | Feb 2013 | US |