Systems and methods for modifying wavefronts by amplifying stroke

A system and method modifying wavefront shape is provided. Generally, the system contains a wavefront shape modifying device for modifying the shape of the wavefront. The system also contains a series of optical devices for returning the modified wavefront to the wavefront modifying device with an orientation that enables further modification of the modified wavefront by the wavefront modifying device. The method contains the steps of: reflecting a wavefront from a surface of a wavefront shape modifying device, resulting in the wavefront having a modified shape; and reflecting the wavefront having a modified shape from the surface of the wavefront shape modifying device a second time resulting in a final wavefront having a shape that has been modified twice.

FIELD OF THE INVENTION

The present invention is generally related to optics, and more particularly is related to systems and methods for modifying wavefront shape.

BACKGROUND OF THE INVENTION

Adaptive optics is utilized to modify optical wavefronts. As an example, adaptive optics may be used to correct for existing aberrations recognized by optical systems. Specifically, adaptive optics may be used to correct aberrant wavefronts by modifying shape of the wavefront. Such correction appeals to many fields, including, but not limited to, astronomy, ophthalmology, and microscopy. As an example, in the field of astronomy adaptive optics may compensate for aberrations due to atmospheric turbulence and/or telescopic errors (i.e., lens errors). As a further example, in the field of ophthalmology, adaptive optics provide a means of measuring and compensating for aberrations in human vision. In addition, adaptive optics may be utilized to modify optical wavefronts without consideration of aberrations. It should be noted herein that a wavefront can be defined as a plurality of locations in space having a constant phase.

It should be noted that the term “optical phase” refers to the difference between the place or time where the sinusoidal amplitude of the electromagnetic field that is a light wave is at peak, and the place or time at which it is reduced, simply because it is a sine wave. E=A sin(2πft+phase). Since light extends in three dimensions, we call a surface of constant phase a wavefront. It is the shape of this surface that the deformable mirror will change, and we describe that as a change in the local phase, but the term should be understood to mean a change in the local shape of this surface of constant phase.

Adaptive optics attempt to correct for existing aberrations via use of wavefront sensors, controllers, and/or wavefront corrective devices.FIG. 1is a schematic diagram illustrating an example of a basic adaptive-optical wavefront modification system10that contains a wavefront sensor20, a controller30, a wavefront corrective device40, such as a deformable mirror40, and a beam splitter50. As is known by those having ordinary skill in the art, the wavefront sensor20assesses, or measures, aberrations in an aberrant wavefront received by the adaptive-optical wavefront modification system10. An example of a wavefront sensor20is a Shack-Hartmann sensor, such as a WaveScope wavefront measurement system manufactured by Adaptive Optics Associates of Massachusetts, USA.

Typically, a wavefront sensor20uses software to assess changes in wavefront shape caused by the deformable mirror40, after energizing by the controller30, as explained below. As an example, information regarding wavefront shape changing may be used by the wavefront sensor20to create a conjugate shape on the deformable mirror40to correct wavefront aberrations. The wavefront sensor20may use a least-squares estimation of the wavefront to determine the changes in the deformable mirror40caused by energizing.

The beam splitter50is used by the basic adaptive-optical wavefront modification system10to separate a part of the corrected wavefront. Since one having ordinary skill in the art would understand how such separation is performed, a detailed description of separation performed by the beam splitter50is not provided herein.

After assessing aberrations, the wavefront sensor20transmits information to the controller30regarding requirements to create the conjugate shape on the deformable mirror40, as signified by the dotted line located between the wavefront sensor20and the controller30. In accordance with requirements to provide the conjugate shape, the controller30transmits control signals, such as, but not limited to, a voltage, to the deformable mirror40. The received voltage causes actuators (not shown) located within the deformable mirror40to move in a surface normal direction in accordance with stroke of each actuator and the control signals, thereby providing a small local step within the deformable mirror40, or deforming the deformable mirror40. For simplicity, in the remainder of this document the deformation of the deformable mirror or wavefront correcting device will be described as a step, though in practice this deformation may not be step-like: it might be smooth, ramped, or arbitrarily shaped. The step of the deformable mirror40modifies the wavefront so as to impress on the wavefront a change of shape in the areas of the wavefront that have been reflected by the step of the deformable mirror40.

The step, through the change of phase in the wavefront, corrects aberrations in the received aberrant wavefront by canceling aberrations with the conjugate shape provided. Specifically, the conjugate shape provided to the aberrant wavefront is intended to cancel the aberrations. Since one having ordinary skill in the art would understand how the actuators are caused to move, a detailed description of actuator movement is not provided herein. It should be noted that in the present disclosure, the term actuator is utilized to identify elements of a deformable mirror that have a stroke.

More commonly known deformable mirrors have actuators that are either piezoelectric or electrostatic devices. Unfortunately, known deformable mirrors are characterized as being difficult to achieve more than a few microns of actuator stroke without greatly increasing expense and/or complexity of the deformable mirror. In addition, it is a general rule that the larger the actuator stroke of a deformable mirror, the more that aberrations in an aberrant wavefront may be removed. Therefore, aberrant wavefront correction by current adaptive-optical wavefront modification systems is restricted. In addition, the amount of altering of the shape of a wavefront is restricted.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide systems and methods for modifying shape of a wavefront by increasing effective stroke of a deformable mirror. Briefly described, in architecture, one embodiment of the system, among others, can be implemented as follows. The system contains a wavefront shape modifying device for modifying the shape of the wavefront and a series of optical devices for returning the modified wavefront to the wavefront shape modifying device with an orientation that enables further modification of the modified wavefront by the wavefront shape modifying device.

The present invention can also be viewed as providing methods for providing arbitrary wavefront shapes by amplifying the effect of a deformable mirror on phase of a wavefront. In this regard, one embodiment of such a method, among others, can be broadly summarized by the following steps: reflecting a wavefront from a surface of a wavefront shape modifying device, resulting in the wavefront having a modified shape; and reflecting the wavefront having a modified shape from the surface of the wavefront shape modifying device a second time resulting in a final wavefront having a shape that has been modified twice.

DETAILED DESCRIPTION

The present optical stroke amplification system multiplies the physical stroke of actuators located within a deformable mirror to assist in modifying shape of a wavefront, thereby increasing the effective stroke of the deformable mirror. Therefore, the effective stroke of the deformable mirror is increased without physically increasing a step of the deformable mirror, or increasing the physical stroke of the deformable mirror actuators. It should be noted that the present systems and methods of modifying shape of a wavefront may be utilized in the fields of astronomy, ophthalmology, microscopy, or any other field that uses optics and/or a wavefront corrector or wavefront phase modifying device.

The present description is provided with reference to use of an optical stroke amplification system within an adaptive optical wavefront modification system that is used to correct aberrant wavefronts, however, it should be noted that the optical stroke amplification system may instead be used to alter shape of a wavefront without consideration of wavefront aberrations. Therefore, while the following describes measuring wavefront aberrations, it is not a requirement for the optical stroke amplification system to be used in a system that first measures wavefront aberrations. In fact, the optical stroke amplification system may be used without measuring wavefront aberrations or any other properties of a wavefront. As an example, the optical stroke amplification system may be used to distort a wavefront to provide a focus adjustment for a camera, or simply to distort the wavefront in the fields of ophthalmology (e.g., for testing physiological response of an eye) and microscopy (e.g., for providing a prescribed distortion for a microscope in order to extend depth focus of the microscope). As a result, while the following discusses use of a wavefront sensor, one having ordinary skill in the art will appreciate that use of the optical stroke amplification system does not require use of a wavefront sensor.

FIG. 2is a schematic diagram illustrating an adaptive optical wavefront modification system100that may contain the present optical stroke amplification system120. It should be noted that the adaptive optical wavefront modification system100ofFIG. 2is provided merely for exemplary purposes and that the optical stroke amplification system120may instead be located within different adaptive optical wavefront modification systems.

As is shown byFIG. 2, the adaptive optical wavefront modification system100contains a wavefront sensor110, the optical stroke amplification system120, a controller150, and a beam splitter160.

The wavefront sensor110assesses, or measures, aberrations in an aberrant wavefront received by the adaptive optical wavefront modification system100. An example of a wavefront sensor110is a Shack-Hartmann sensor, such as a WaveScope wavefront measurement system manufactured by Adaptive Optics Associates of Massachusetts, USA.

The wavefront sensor110uses software to assess changes in wavefront shape caused by a deformable mirror located within the optical stroke amplification system120(shown byFIG. 3), after energizing by the controller150, as explained below. As an example, information regarding wavefront shape changing may be used by the wavefront sensor110to create a conjugate shape on the deformable mirror to modify shape of the wavefront, thereby correcting for wavefront aberrations. The wavefront sensor110may use a least-squares estimation of the wavefront or, other fitting techniques to determine the changes in the deformable mirror caused by energizing.

After assessing aberrations, the wavefront sensor110transmits information to the controller150regarding requirements to create the conjugate shape on the deformable mirror, as signified by the dotted line located between the wavefront sensor110and the controller150. In accordance with requirements to provide the conjugate shape, the controller150transmits control signals, such as, but not limited to, a voltage, to the deformable mirror. The received voltage causes actuators (not shown) located within the deformable mirror to move in a surface normal direction in accordance with stroke of each actuator and the control signals, thereby providing steps within the deformable mirror, or deforming the deformable mirror. The steps of the deformable mirror are used to modify the local optical phase of the wavefront, thereby correcting aberrations in the received aberrant wavefront by canceling aberrations with the conjugate shape provided. Specifically, the conjugate shape provided to the aberrant wavefront is intended to cancel the aberrations. Since one having ordinary skill in the art would understand how the actuators are caused to move, a detailed description of actuator movement is not provided herein.

The optical stroke amplification system120then multiplies the physical stroke of actuators located within the deformable mirror to assist in correcting aberrant wavefronts, thereby increasing the effective stroke of the deformable mirror. This increase in the effective stroke of the deformable mirror is performed without excessive additional cost to the adaptive optical wavefront modification system100and without having to increase the physical stroke of actuators located within the deformable mirror.FIG. 3, which is described below, further illustrates the optical stroke amplification system120ofFIG. 2and components located therein. In addition, a detailed description of how the effective stroke of the deformable mirror is performed is provided below.

FIG. 3is a schematic diagram further illustrating the optical stroke amplification system120ofFIG. 2, in accordance with a first exemplary embodiment of the invention. As is shown byFIG. 3, the optical stroke amplification system120contains a deformable mirror112, a pair of optical lenses122containing a first lens124and a second lens126, and a mirror132. The deformable mirror112contains a series of actuators (not shown) each having a specific stroke. Collaboratively, the stroke of each actuator within a deformable mirror112is denoted herein as the stroke of the deformable mirror112. When multiple actuators move in a direction normal to the plane of the deformable mirror112, the actuators create a step, which, as is described below, is utilized to modify shape of received wavefronts. Since the maximum step of the deformable mirror112is restricted by the maximum physical stroke of actuators located within the deformable mirror112, the optical stroke amplification system120utilizes optical devices, examples of which are described below, to increase the effective stroke of the deformable mirror112(i.e., increase the corrective results of the deformable mirror112step without physically increasing stroke of the deformable mirror actuators).

The first lens124is located one focal length of that lens from the deformable mirror112. In addition, the second lens126is located the sum of the focal lengths of the two lenses from the first lens124. Therefore, a focal point of the first lens124and a focal point of the second lens126are coincident and are located between the lenses124,126. The pair of lenses124,126work together to invert an image of the deformable mirror112now encoded in the wavefront, and focus that image on mirror132. Specifically, if a wavefront enters from the right of the first lens124, traverses the first lens124, exits from the left of the first lens124, enters from the right of the second lens126, traverses the second lens126, and exits from the left of the second lens126, the image of mirror112, formed at mirror132, will be inverted. In addition, if a wavefront enters from the left of the second lens126, traverses the second lens126, exits from the right of the second lens126, enters from the left of the first lens124, traverses the first lens124, and exits from the right of the first lens124, then the image at mirror132will fall on mirror112and be again inverted. Thus, the wavefront encoding the image of mirror112traverses the optical elements and returns to mirror112, exactly matching that mirror in the transverse directions X and Y, but with the longitudinal direct Z reversed.

FIG. 4is a schematic diagram demonstrating wavefront shape throughout traversal of the optical stroke amplification system120(FIG. 3). As is shown byFIG. 4, an originating collimated wavefront1traveling in a positive Z-axis direction is reflected in a negative Z-axis direction and provided with a step extending forward in the negative Z-axis direction by the deformable mirror112, thereby resulting in wavefront2. The first lens124and the second lens126collaboratively invert wavefront2, thereby resulting in wavefront3, which is still traveling in the negative Z-axis direction with the step extending forward in the negative Z-axis direction.

The mirror132reflects wavefront3, resulting in wavefront4, which travels in the positive Z-axis direction with the step extending forward in the positive Z-axis direction. The second lens126and the first lens124collaboratively invert wavefront4, thereby resulting in wavefront5, which is still traveling in the positive Z-axis direction with the step extending forward in the positive Z-axis direction. The deformable mirror112then reflects wavefront5in a negative Z-axis direction and provides an additional step extending forward in the negative Z-axis direction, thereby resulting in wavefront6. It should be noted that wavefront6has a step double the size of the step originally provided by the deformable mirror112to wavefront1. Therefore, the effective stroke of the deformable mirror112is increased without physically increasing a step of the deformable mirror112, or increasing the physical stroke of the deformable mirror actuators that are used to correct for aberrant wavefronts.

Returning toFIG. 3, the mirror132is located in an optical path of the lenses124,126so that the mirror132may reflect a wavefront received from the second lens126back to the second lens126. In addition, the mirror132is located one focal length from the second lens126so that if the mirror132were replaced by a screen, an inverted image of the deformable mirror112would be displayed on the screen. Reflection and wavefront traversal is described in detail below with reference toFIG. 5. Preferably, the mirror132is situated so that it is perpendicular to a central axis of the first lens124and the second lens126. It should be noted that the mirror132may be replaced by a different reflective device; or reflector, that is capable of accurately reflecting a received wavefront to the second lens126without deforming the received wavefront. Although the present description provides a lens pair122, one having ordinary skill in the art will appreciate that other optical elements may be supplemented, such as, but not limited to, mirrors. In addition, more or fewer lenses may be utilized, examples of which are provided below.

FIG. 5is a flowchart300illustrating a method of correcting an aberrant wavefront by modifying shape of the wavefront, as performed via use of the optical stroke amplification system120ofFIG. 3, in accordance with the first exemplary embodiment of the invention. It should be noted that any process descriptions or blocks in flowcharts should be understood as representing modules, segments, portions of code, or steps that include one or more instructions for implementing specific logical functions in the process, and alternate implementations are included within the scope of the present invention in which functions may be executed out of order from that shown or discussed, including substantially concurrently or in reverse order, depending on the functionality involved, as would be understood by those reasonably skilled in the art of the present invention.

As is shown by block302, a wavefront associated with a beam of light traveling in a positive Z-axis direction is received. Specifically, the wavefront is received by the deformable mirror112(FIG. 3). Preferably, the received wavefront has been collimated so as to provide a flat wavefront. It should be noted, however, that the present system and method does not require collimation of the incoming wavefront.

As mentioned above, the wavefront is characterized as having aberrations, which are to be corrected by the optical stroke amplification system120(FIG. 3). Since the deformable mirror112(FIG. 3) has at least one step (described herein-below as one step for ease of description), the size of which has been defined by control signals received from the real-time controller150, the wavefront is reflected and shape of the wavefront is modified by the deformable mirror112to correct for aberrations, thereby creating a modified wavefront (block304).

As an example, to maximize correction capability of the deformable mirror112(FIG. 3), specific actuators within the deformable mirror112(FIG. 3) are instructed by the controller150(FIG. 2), via, for example, a transmitted voltage, to move in a direction normal to the plane of the deformable mirror112(FIG. 3), thereby defining the step. Movement of the actuators is limited by the physical stroke of each actuator, however, the optical stroke amplification system120(FIG. 3) increases the effective stroke of the actuators, as is further explained below.

The modified wavefront reflects off of the deformable mirror112(FIG. 3) at an angle and in a negative Z-axis direction. In addition, after reflection by the deformable mirror112(FIG. 3), the modified wavefront has a step therein, where the step extends forward in the negative Z-axis direction. It should be noted that upon reflection from a mirror with a step, a wavefront reflecting from the step is shifted in phase by an amount equal to twice the step height in the Z direction (or whichever direction the step extends). That is, for example, a one micrometer step excursion in the mirror produces a two micrometer step excursion in the reflected wavefront phase. The optical stroke amplification system120(FIG. 3) may double (or otherwise amplify) the effect of the actuator, so that a one micron stroke, resulting in a two micron wavefront modification, has the effect of a two micron stroke, resulting in a four micron wavefront modification.

Unfortunately, as has been mentioned above, the step provided by the first deformable mirror distortion is typically not more than a few microns. Since the step thus provided is minimal, minimal aberrations are corrected with the first deformable mirror distortion.

As is shown by block306, the modified wavefront encodes an image of the deformable mirror112(FIG. 3) that is a real image at mirror132. A side effect of that image formation is that the image at mirror132is inverted in the X-axis and Y-axis direction. Specifically, the first lens124(FIG. 3) and the second lens126(FIG. 3) together invert the modified wavefront in the X-axis and Y-axis direction, resulting in the modified wavefront step moving to an opposite side of an optic axis of the lenses124,126(FIG. 3). In other words, the lenses124,126(FIG. 3) flip the lateral orientation of the modified wavefront. It should be noted, however, that after inversion the step of the modified wavefront still extends in the minus Z-axis direction.

The modified wavefront then reflects off of the mirror132(FIG. 3) (block308) in the direction of the deformable mirror112(FIG. 3). Upon reflection off of the mirror132(FIG. 3) the modified wavefront has the same X-axis and Y-axis orientation, however, the wavefront traverses in the positive Z-axis direction, with the step extending in the positive Z-axis direction.

As is shown by block312, the reflected modified wavefront is again inverted in the X-axis and Y-axis direction by the lenses124,126, and maintained in the positive Z-axis direction. It should be noted that after being inverted the second time by the lenses124,126(FIG. 3) the modified wavefront matches the modified wavefront immediately after distortion of the original wavefront by the deformable mirror112(FIG. 3), except that the modified wavefront is reversed in the Z-axis direction. To achieve this orientation (no change in X and Y, but reversal in Z) is the function of the optical elements of the stroke amplifier.

As is shown by block314, the modified wavefront is reflected and shape of the wavefront is modified a second time by the deformable mirror112(FIG. 3) to correct for aberrations. Since the step portion of the modified wavefront protrudes from the rest of the modified wavefront, and the deformable mirror112(FIG. 3) still has the step therein, the step portion of the modified wavefront is reflected first, thereby providing a final wavefront having a step that has twice the extent of phase modification that it had after one pass of the deformable mirror112(FIG. 3). A physical step of one micrometer on the deformable mirror would therefore impose a four micrometer step on the optical wavefront phase. Specifically, when the modified wavefront is received by the deformable mirror112(FIG. 3) a second time, the modified wavefront is aligned such that the step of the modified wavefront is reflected by the step of the deformable mirror112(FIG. 3). Therefore, the optical stroke amplification system120(FIG. 2) doubles the effect of the deformable mirror112(FIG. 3) actuator stroke.

Preferably, the mirror132is angled so that the final wavefront, is directed in a desired direction that does not interfere with incoming aberrant wavefronts. As an example, a separation angle of 0.5 degrees may be suitable to separate the incoming aberrant wavefront from the final wavefront. In addition, the pair of lenses124,126(FIG. 3) are used to ensure that the final wavefront has a desired size and a desired orientation. Alternatively, a beam splitter may be used to separate the final wavefront from an incoming aberrant wavefront.

It should be noted that the optical stroke amplification system120(FIG. 2) may be modified to provide more than double the effect of the deformable mirror actuator stroke. In fact, by reintroducing the modified wavefront back to the optical stroke amplification system120(FIG. 3) the optical stroke amplification system120(FIG. 3) may provide an effect that is three or four times or more than that of the deformable mirror actuator stroke. Examples of such modifications are described below as further embodiments of the invention, however, it should be noted that other modifications are possible and that these modifications are not intended to be limited to the embodiments described herein.

FIG. 6is a schematic diagram of an optical stroke amplification system300, in accordance with a second exemplary embodiment of the invention. As is shown byFIG. 6, the optical stroke amplification system300contains a deformable mirror302, a relay mirror312and a doubler mirror322, where the doubler mirror322is a concave mirror. Most simply, the deformable mirror302is at a focal point of mirror312, and the focal point of mirror322coincides with a focal point of mirror312, although this is not required. What is required is that mirrors302and322be optically conjugate. That is, a real image of mirror302falls on mirror322(and then, of course, a real image of mirror322falls on mirror302). Other arrangements of the optical elements that do not satisfy the requirement of optical conjugation are possible, but more complex.

Preferably, an incoming wavefront has been collimated so as to provide a flat wavefront. As with other embodiments of the invention, however, there is no requirement that the incoming aberrant wavefront be collimated. Since the deformable mirror302has at least one step (described herein-below as one step for ease of description), the size of which has been defined by control signals received from the real-time controller150(FIG. 2), the wavefront is reflected and the shape of the wavefront is modified by the deformable mirror302, thereby creating a modified wavefront.

The modified wavefront reflects off of the deformable mirror302at an angle and in a negative Z-axis direction. In addition, after reflection by the deformable mirror302, the modified wavefront has a step therein, where the step extends forward in the negative Z-axis direction.

The modified wavefront is reflected off of the relay mirror312to have the same X-axis and Y-axis orientation, however, the wavefront traverses in the positive Z-axis direction, with the step extending in the positive Z-axis direction. The modified wavefront is then reflected off of the doubler mirror322to have the same X-axis and Y-axis orientation, however, the wavefront traverses in the negative Z-axis direction, with the step extending in the negative Z-axis direction.

The modified wavefront is then reflected off of the relay mirror312a second time to have the same X-axis and Y-axis orientation, however, the wavefront then traverses in the positive Z-axis direction, with the step extending in the positive Z-axis direction.

The modified wavefront is then reflected and the shape of the modified wavefront is modified by the deformable mirror302. Since the step portion of the modified wavefront protrudes from the rest of the modified wavefront, and the deformable mirror302still has the step therein, the step portion of the modified wavefront is reflected first, thereby providing a final wavefront having a step that is twice the height of the step after one pass of the deformable mirror302. Specifically, when the modified wavefront is received by the deformable mirror302a second time, the modified wavefront is aligned such that the step of the modified wavefront is reflected by the step of the deformable mirror302. Therefore, the optical stroke amplification system300of the second exemplary embodiment of the invention doubles the effect of the deformable mirror302actuator stroke.

Preferably, the relay mirror312and the doubler mirror322are angled so that the final wavefront is directed in a desired direction that does not interfere with incoming aberrant wavefronts. Alternatively, a beam splitter may be used to separate the final wavefront from an incoming aberrant wavefront.

FIG. 7is a schematic diagram of an optical stroke amplification system400, in accordance with a third exemplary embodiment of the invention. As is shown byFIG. 3, the optical stroke amplification system400contains a deformable mirror402, a lens404, and a curved mirror406. Preferably, the deformable mirror402and focal points of the optical stroke amplification system400are located at focal lengths of the lens404, although this is not required.

Preferably, an incoming aberrant wavefront has been collimated so as to provide a flat wavefront. As with other embodiments of the invention, however, there is no requirement that the incoming aberrant wavefront be collimated. Since the deformable mirror402has at least one step, the wavefront is reflected and the shape of the wavefront is modified by the deformable mirror402, thereby creating a modified wavefront.

The modified wavefront reflects off of the deformable mirror402at an angle and in a negative Z-axis direction. In addition, after reflection by the deformable mirror302, the modified wavefront has a step therein, where the step extends forward in the negative Z-axis direction.

The modified wavefront is focused by the lens404to the curved mirror406, which is still in the negative Z-axis direction. The curved mirror406reflects the modified wavefront back toward the lens404. Reflection of the modified wavefront by the curved mirror406causes the modified wavefront to travel in the positive Z-axis direction, with the step extending in the positive Z-axis direction. The lens404then focuses the modified wavefront back to the deformable mirror402where the modified wavefront is reflected a second time and the shape of the modified wavefront is modified a second time resulting is a final modified wavefront.

After the second reflection and modification by the deformable mirror402the final modified wavefront travels in the negative Z-axis direction, with the step extending in the negative Z-axis direction. In addition, the step of the final modified wavefront is twice the height of the step after one pass of the deformable mirror402. Therefore, the optical stroke amplification system400of the third exemplary embodiment of the invention doubles the effect of the deformable mirror402actuator stroke.

Preferably, the lens404focuses the modified wavefront at an angle to the deformable mirror402so that the final modified wavefront is directed in a desired direction that does not interfere with incoming aberrant wavefronts. Alternatively, a beam splitter may be used to separate the final modified wavefront from an incoming aberrant wavefront.