Device for reshaping a laser beam

A device for reshaping a laser beam may include a first optical element to receive the laser beam. The device may also include a second optical element to invert and reshape the laser beam to substantially correspond to a aperture of a beam director.

BACKGROUND OF THE INVENTION

The present invention relates to optics and laser beam shaping and more particularly to a device for reshaping a laser beam to correspond to an aperture of a beam director or other optical device.

Most solid state and some chemical lasers produce laser beams that are substantially square or rectangular, and do not have a central region which is un-illuminated (e.g., central obscuration.) Such laser beams may be directed onto targets at a great distance using a beam director or similar optical device. Beam directors typically include a moveable spherical telescope with an output aperture that is circular with a circular central obscuration through which the laser beam may not be projected. Accordingly, the most desirable shape for a laser beam to be projected from such a beam director is a “donut” (annulus) shape with the same ratio of inner and outer diameters that corresponds to the usable output aperture of the beam director. With this beam configuration, the entire laser beam can be placed onto, and substantially entirely fill, the usable output aperture of the beam director. If the laser beam, after suitable geometric scaling with telescopes both internal and external to the beam director, projects outside of the beam director aperture or within the central obscuration, the beam should be trimmed or “clipped” on the outside and “cored” inside the periphery of the beam. Typically this is performed using mirrors that reflect the unwanted portion of the laser beam out of the propagation path of the laser beam, for example into a beam dump. The beam power to be projected by the beam director is thereby reduced. Similarly, if the laser beam does not completely fill the aperture of the beam director the beam will not be focused as effectively, reducing the intensity or brightness of the focused laser beam at the target. In either event the intensity of the laser beam at the target is diminished.

BRIEF SUMMARY OF THE INVENTION

In accordance with an embodiment of the present invention, a device for reshaping a laser beam may include a first optical element to receive the laser beam. The device may also include a second optical element to invert and reshape the laser beam to substantially correspond to an aperture of a beam director.

In accordance with another embodiment of the present invention, a device for reshaping a laser beam may include a first reflector element to reflect the laser beam in a circular pattern from the first reflector and a second reflector element to reflect the circular pattern laser beam from the first reflector element. The device may also include a third reflector element to reflect the circular pattern laser beam from the second reflector element and a fourth reflector element to reflect and reshape the circular pattern laser beam with a central portion corresponding substantially to a central obscuration of an aperture of a beam director.

In accordance with another embodiment of the present invention, a system for reshaping a laser beam may include a laser source to generate the laser beam. The system may also include a beam director to project a reshaped laser beam on a target. The system may further include an optical device to invert and reshape the laser beam to substantially correspond to an aperture of the beam director.

In accordance with another embodiment of the present invention, a system for reshaping a laser beam may include a laser source to generate the laser beam. The laser beam may be a substantially square or rectangular laser beam with an illuminated central portion. The system may also include a first axicon configured to reshape the laser beam into a substantially circular laser beam and a second axicon configured to substantially remove any illumination in a predetermined central portion of the circular laser beam and to compact the laser beam to substantially correspond to a form geometrically similar to the useful aperture of a beam director. The system may further include a beam director to project the reshaped laser beam on a target.

In accordance with another embodiment of the present invention, a method for reshaping a laser beam may include inverting a substantially square or rectangular laser beam with an illuminated central portion into a substantially circular laser beam. The method may also include substantially removing any illumination in a predetermined central portion of the circular laser beam.

In accordance with another embodiment of the present invention, a method of making a device for reshaping a laser beam may include forming a first axicon configured to reshape a laser beam with an illuminated central portion into a substantially circular laser beam. The method may also include forming a second axicon configured to substantially remove any illumination in a predetermined central portion of the circular laser beam and to compact the laser beam to substantially correspond to a form geometrically similar to the useful aperture of a beam director or other optical device.

Other aspects and features of the present invention, as defined solely by the claims, will become apparent to those ordinarily skilled in the art upon review of the following non-limited detailed description of the invention in conjunction with the accompanying figures.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description of embodiments refers to the accompanying drawings, which illustrate specific embodiments of the invention. Other embodiments having different structures and operations do not depart from the scope of the present invention.

FIG. 1is an illustration of a footprint of a non-circular or substantially square laser beam100superimposed on an aperture102of a beam director for projecting a laser beam on a target. Examples of a laser source that may generate a non-circular or substantially square laser beam, such as beam100may include a solid state laser source, a chemical laser or the like. As illustrate inFIG. 1, because the non-circular laser beam100does not correspond to the aperture102of the beam director, laser power is lost and portions of the aperture102of the beam director that could be used for projecting laser energy are not used. The corner portions104of the square laser beam100extend beyond a perimeter106of the aperture102and the power in these portions of the beam100are lost. Additionally, segments108of the aperture102are not illuminated or filed by the square laser beam100and therefore do not transmit or project any of the beam100. Accordingly, these segments108are not used to project any laser energy on a target and the aperture102is being inefficiently utilized. Furthermore, the aperture102of the beam director includes a substantially circular central obscuration110. Any laser illumination or energy corresponding to the obscuration110would also be lost. Depending on the application, the dimensional relationship between the non-circular laser beam100and the aperture102may be adjusted such that there is a greater or lesser amount of laser power beyond the aperture102, and correspondingly lesser or greater portions of the aperture102remain unilluminated by the laser beam100.

The present invention makes maximum utilization of a non-circular laser beam and the aperture configuration of a beam director by providing a device for reshaping a non-circular laser beam, such as a substantially square or rectangular laser beam, or a multiplicity of laser beams configured in a non-circular arrangement. The device of the present invention reshapes the non-circular laser beam to substantially correspond to the aperture102of the beam director to direct substantially maximum power and intensity of the original laser beam or beams on a target.

FIG. 2is a block diagram of a system200for projecting a laser beam202on a target204in accordance with an embodiment of the present invention. The system200may include a laser source206for generating laser beam202aor the like. The laser beam202amay be a high energy laser beam. The power of such a high energy laser beam may be in excess of about 1 kilowatt (kW), more desirably in the range of about 100 kW to above 1 Megawatt (MW). The laser power may be continuous wave (CW) or may be in a pulsed format, with pulse frequencies ranging from about 10 Hertz (Hz) up to beyond 1 Megahertz (MHz) depending on the nature of the laser. For pulsed lasers, the percentage of time on may typically be as high as about 20 percent and can be as low as a fraction of 1 percent. Examples of laser sources206for generating high energy laser beams may include solid state lasers, chemical lasers or similar laser sources. Such high energy laser sources typically generate laser beams with non-circular footprints or laser cross-sections, e.g., a substantially square or rectangular footprint. Other laser sources or high energy laser sources that may be used may generate multiple beams (a phased array) that may each be substantially square or rectangular and which may be arranged in a non-circular pattern for propagation.

An optical device208, which may include beam alignment optics, beam shaping optics and other optical elements may receive the laser beam or beams202afrom the laser source206to produce a compact, substantially square beam202b. If the laser beam202ais a substantially rectangular beam, the optical device208or devices may include a cylindrical telescope with magnification to convert the rectangular beam202ainto a substantially square or nearly square footprint. If the laser beam202ais a multiplicity of beams, the optical device208may also include optical elements to combine the beams into a compact shape with minimal un-illuminated areas. For example, eight beams can be arranged in a rectangle, while seven beams may be configured into rows of 2:3:2 beams in a symmetric way such as to approximate a hexagon. As appropriate, the compacted grouping of beams may also be passed through a cylindrical telescope so as to produce a relatively symmetric shape (e.g., one having approximately equal height and width.) This array of beams may then be processed as described herein for a single substantially square beam.

The optical devices208may also include beam steering mirrors or the like to direct the resulting beam202binto a beam reshaping device210. The beam reshaping device210may include beam reshaping optics to convert the beam to a footprint or cross-section that substantially corresponds to an aperture of a beam director214. An example of a device for reshaping a laser beam that may be used for the reshaping device210will be described in more detail with reference toFIGS. 3 and 4. The beam reshaping device210may include at least one axicon to invert and reshape the laser beam to substantially correspond to the aperture geometry of the beam director214, similar to the beam director aperture102illustrated inFIG. 1.

The system200may also include other optical devices212to receive the reshaped beam202cfrom the beam reshaping device210. The other optical device or devices212may include beam steering elements to direct the beam202din the aperture of the beam director214. The other optical device or devices212may also include a coring element or optics to remove any laser power illumination in an obscuration (similar to obscuration110inFIG. 1) of the beam director214. The footprint or cross-section of the beam202cresulting from the beam reshaping device210may include a central portion corresponding to the beam director obscuration that is has a runcible or scalloped shape caused by inverting the substantially square laser beam. These illuminated scallops can be removed with minimal loss of power or brightness of the resulting laser beam202d. The optical devices212may include an aperture, filter or other optics to core or remove the scalloped central portion of the beam202cso that the resulting beam202dcorresponds substantially to the aperture of the beam director214to substantially uniformly fill the aperture with minimal loss of power and intensity of the original beam202a.

The beam director214may include optical elements that include a movable spherical telescope with an output aperture that is circular with the circular central obscuration as previously described. The beam director214may also include optical elements to direct the laser beam onto the optical elements that comprise the movable spherical telescope. The laser beam202emay be projected by the beam director214on the target204.

FIG. 3is a perspective view of an optical device300to convert a non-circular laser beam to a shape that is substantially geometrically similar to an aperture of a beam director, similar to aperture102ofFIG. 1, in accordance with an embodiment of the present invention. The optical device300may be used for the beam reshaping device210in the system200ofFIG. 2. Referring also toFIG. 4,FIG. 4is a cross-sectional view of the optical device300ofFIG. 3taken across lines4-4. The optical device300may include a first optical element302to receive and redirect a laser beam304as best shown inFIG. 4. The first optical element302may be a reflector or a mirror. The optical device300may also include a second optical element306that may be defined by a first axicon308and a second axicon310or other optical elements that accomplish substantially the same results. The second optical element306may invert and reshape the laser beam304so that it is substantially geometrically similar to an aperture of a beam director, similar to beam director aperture102illustrated inFIG. 1. The second optical element306may be adapted to invert and reshape the laser beam304while maintaining substantially a maximum power and intensity of the original laser beam. In other words, the second optical element306may be adapted to invert and reshape the laser beam to provide substantially a minimal loss of power caused by the inverted and reshaped laser beam extending beyond the aperture of the beam director and to provide an optimum intensity at a target on which the inverted and reshaped laser beam312may be projected.

As described herein, the device300or second optical element306may include an axicon or a first axicon308and a second axicon310configured to invert the laser beam304and then resize the beam to provide a resultant beam312with a ratio of an outer beam diameter D1to that of an un-illuminated central portion diameter D2(FIG. 4) of the resultant beam312being about equal to or slightly greater than the aperture of the beam director. The first axicon308may be configured to invert a substantially square or rectangular laser beam with an illuminated central portion into a substantially circular laser beam with a central obscuration geometrically much greater than that of the usable aperture of the beam director. The second axicon310may be configured so that the beam from the first axicon308is not inverted and such that the resulting circular laser beam312has no illumination in a predetermined central portion314of the beam such that the central obscuration is geometrically equal to or slightly smaller than that of the usable aperture of the beam director.

The first axicon308may include a first axicon annular reflector316or mirror and a first axicon substantially cone-shaped reflector318or mirror disposed within the annular reflector316to reflect the laser beam304to the first axicon annular reflector316as illustrated inFIG. 4. As is apparent fromFIGS. 3 and 4, the first axicon substantially cone-shaped reflector318will reflect the incident laser beam304in a circular pattern from the cone-shaped reflector318. The annular reflector316and the cone-shaped reflector318are arranged such that the laser beam304when projected onto first the cone-shaped reflector318and then onto the annular reflector316produces an outgoing beam that propagates in a substantially parallel direction to the laser beam304. This requires that the orientation of a reflective surface330of the annular reflector316to be oriented at a complementary angle to a reflective surface331of the cone-shaped reflector318. This may be conveniently achieved by arranging the reflective surface330of the annular reflector316to be oriented at 45° to the propagation direction of the laser beam304and the reflective surface331of the cone-shaped reflector318to be oriented perpendicular to the reflective surface330of the annular reflector316.

The second axicon310may include a second axicon annular reflector320or mirror to reflect the laser beam304from the first axicon annular reflector316to a second axicon substantially cone-shaped reflector322or mirror disposed within the second axicon annular reflector320. The second axicon substantially cone-shaped reflector322may include a central cylindrical opening324. The central cylindrical opening may extend between a base326and a top portion328or apex of the second axicon cone-shaped reflector322as shown inFIG. 4. The central cylindrical opening324may have a predetermined radius R that may correspond substantially to a radius R′ (FIG. 1) of a central obscuration of the beam director, such as obscuration110inFIG. 1. The central cylindrical opening324creates an un-illuminated portion329in the inverted and reshaped laser beam312that corresponds substantially to the shape of the obscuration of the beam director. In accordance with the description of the first axicon308, a reflective surface323of the substantially cone-shaped reflector322is oriented at 45° to the propagation direction of the laser beam304, and a reflective surface332of the second axicon annular reflector320is oriented perpendicular to reflective surface323of the substantially cone-shaped reflector322. In that way the incoming laser beam from optical element302and the outgoing laser beam312are parallel but propagate in opposite directions.

The first and second axicon annular reflectors316and320may each have a right triangular cross-section, as illustrated inFIG. 4, and reflective surfaces330and332or mirrors, respectively, defined by a hypotenuse of the right triangular cross-section. As is apparent fromFIG. 4, the laser beam304is inverted by the annular reflectors316and320so that an interior portion334of the laser beam304becomes a exterior portion336of the inverted and reshaped laser beam312, if the broken lines338are traced through the device300inFIG. 4. Similarly, an exterior portion340of the laser beam304is inverted and defines the interior or central portion314of the inverted and reshaped beam312if the broken lines342are traced through the device300inFIG. 4. Thus, the inverted and reshaped beam312will have a substantially circular donut shaped footprint or cross-section geometrically similar to the aperture102of the beam director illustrated inFIG. 1.

The first and second axicons308and310may be retained in proper alignment relative to each other by a fixture, housing or other support structure344. Where necessary support structure may be placed internal to the optical device300so as to assure adequate dimensional control internal and external to the first and second axions308and310, respectively. This internal support structure may intercept some portion of the laser beam traversing between the first and second axicons308and310. The support structure may include provisions to reflect or adsorb the intercepted portions of the laser beams.