US20140340691A1

US20140340691A1 - Enhancements to integrated optical assembly

Info

Publication number: US20140340691A1
Application number: US14/365,079
Authority: US
Inventors: Daniel Gene Smith
Original assignee: Nikon Corp
Current assignee: Nikon Corp
Priority date: 2011-12-23
Filing date: 2012-12-23
Publication date: 2014-11-20
Also published as: JP6040992B2; WO2013093633A3; US20210025697A1; JP2015505050A; US20180031367A1; US10837763B2; US11578969B2; WO2013093633A2

Abstract

An integrated optical assembly is provided, with enhancements that are particularly useful when the integrated optical assembly forms part of a laser radar system. The integrated optical assembly produces a reference beam that is related to the optical characteristics of a scanning reflector, or to changes in position or orientation of the scanning reflector relative to a source. Thus, if the scanning reflector orientation were to shift from its intended orientation (due e.g. to thermal expansion) or if characteristics of the scanning reflector (e.g. the index of refraction of the scanning reflector) were to change on account of temperature changes, the reference beam can be used to provide data that can be used to account for such changes. In addition, if the scanning reflector were to be positioned in an orientation other than the orientation desired, the reference beam can be used in identifying and correcting that positioning.

Description

RELATED APPLICATION/CLAIM OF PRIORITY

This application is related to and claims priority from provisional application Ser. No. 61/580,118, filed Dec. 23, 2011, and entitled Enhancements to Integrated Optical assembly, which provisional application is incorporated by reference herein.

INTRODUCTION AND SUMMARY OF THE PRESENT INVENTION

The present invention provides an optical assembly for focusing a beam from a light source along a line of sight, and to a method of producing useful data in such an optical assembly. The optical assembly and method of the present invention is particularly useful in an integrated optical assembly (IOA) of the type described in a laser radar system of the type shown in U.S. application Ser. No. 13/281,393, which is incorporated by reference herein. A copy of U.S. application Ser. No. 13/281,393 is exhibit A hereto.
In an IOA of the type shown in Exhibit A, a measurement beam from a light source (e.g. that is produced through an optical fiber tip, such that the optical fiber tip can be considered the light source) is directed along a line of sight, by a lens, a scanning reflector (e.g. an adjustable corner cube) and a fixed reflector that are oriented relative to each other such that a beam from the light source is reflected by the scanning reflector to the fixed reflector, and reflected light from the fixed reflector is reflected again by the scanning reflector and directed along the line of sight through the lens. The measurement beam is directed at a target, and light returned from the target (e.g. measurement beam light that is reflected or scattered from the target) is directed to the optical fiber tip that functions as the light source, and is detected and processed to produce data about the target. The scanning reflector is moveable relative to the source, the lens and the fixed reflector, to adjust the focus of the beam along the line of sight. Thus, the scanning reflector may also be referred to as an “adjustable reflector”, and since the scanning reflector that is preferred in the present invention is a corner cube that also functions as a retroreflector (because of the manner in which it reflects and transmits light, as it redirects the light), the scanning reflector may also be referred to as a “scanning retroreflector”
According to the present invention, the integrated optical assembly produces a reference beam that is related to the optical characteristics of the scanning reflector, or to changes in position or orientation of the scanning reflector relative to the source. That reference beam is useful in several ways in an IOA of the type shown in Exhibit A. For example, if the scanning reflector orientation were to shift from its intended orientation (due e.g. to thermal expansion) or if characteristics of the scanning reflector (e.g. the index of refraction of the scanning reflector) were to change on account of temperature changes, the reference beam can be used to provide data that can be used to account for such changes. In addition, if the scanning reflector were to be positioned in an orientation other than the orientation desired, the reference beam can be used in identifying and correcting that positioning. Essentially, the reference beam can be used to subtract out errors that could be caused by such factors.
The present invention provides several implementations by which an IOA can produce the reference beam. For example, the optical assembly can include a lens between the source and the scanning reflector that is configured to produce a continuous collimated reference beam that traverses the scanning reflector at least twice and is then refocused on the source. The lens is oriented off center, in relation to the source, to collimate the beam at a slight angle to the source, and the optical assembly is further configured so that after two passes through the scanning reflector, the reference signal is refocused on a reflector next to the source, traverses the scanning reflector twice more and is then refocused on the source.
According to another implementation of the present invention, the measurement and reference beams are directed through a pair of fibers, so that the measurement and reference beams that are produced through the pair of fibers effectively comprise the “source” (and both those measurement and reference beams can originate from the same light source that is split into the measurement and reference beams). The measurement beam produced through one fiber is reflected by a fold mirror, traverses the scanning retroreflector (corner cube), is reflected by the fixed reflector, traverses the scanning retroreflector again, and is directed along the line of sight through the lens. The reference beam produced through the other fiber is reflected by a fold mirror, traverses the scanning retroreflector, is reflected by a prism or some other suitable optical element that shifts the reference beam, traverses the scanning retroreflector again, is reflected by a small fixed retroreflector that reflects that reference beam on axis back to the scanning retroreflector which it traverses again and is then reflected by the prism or other suitable optical element that was used in a previous step to shift the beam so that the beam traverses the scanning retroreflector once more before arriving back at the reference beam fiber. Thus, the reference beam is a collimated reference signal that traverses the scanning retroreflector at least twice (four times in this case) and is then refocused on the source (in the i.e. the reference beam fiber).
Further features of the present invention will be further apparent from the following detailed description and the accompanying drawings

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an IOA of the type shown in Exhibit A;

FIG. 2 a is a schematic illustration of one version of an enhancement to the IOA of Exhibit A, according to the present invention;

FIG. 2 b is an enlargement of a portion of FIG. 2 a;

FIG. 3 is a schematic illustration of beam paths (and some modifications thereof) that can be used in the version of FIGS. 2 a, 2 b;

FIG. 4 is a schematic illustration of the steps of a method according to the present invention;

FIG. 5 is a schematic illustration of a laser radar system, in which an IOA with an optical assembly according to the present invention, is provided

FIG. 6 is a front view of a preferred type of laser radar system

FIGS. 7-9 schematically show an alternative configuration for an optical assembly implementing the present invention.

FIG. 10 is a block diagram of a structure manufacturing system 700; and

FIG. 11 is a flowchart showing a processing flow of the structure manufacturing system 700.

DETAILED DESCRIPTION

As described above, the present invention provides enhancements to an integrated optical assembly (IOA) and method that are particularly useful with an IOA for a laser radar system of the type described in Exhibit A. The present invention is described herein in connection with an IOA of the type shown in exhibit A, and from that description the manner in which the present invention can be employed in connection with various devices comparable to the IOA of Exhibit A will be apparent to those in the art.
The enhancements to the IOA, according to the present invention, are particularly useful in a laser radar system and method as described in Exhibit A. As explained in Exhibit A, laser radar is a versatile metrology system that offers non-contact and true single-operator inspection of an object (often referred to as a target). Laser radar metrology provides object inspection that is particularly useful in acquiring high quality object inspection data in numerous industries, such as aerospace, alternative energy, antennae, satellites, oversized castings and other large-scale applications. The laser radar can be used, e.g. for manufacturing a structure, comprising: producing a structure based on design information; obtaining shape information of structure by using of the apparatus; obtaining shape information of a structure by arranging a produced structure; comparing a obtained shape information with a design information.
In the laser radar system and method of Exhibit A and FIGS. 5 and 6, the integrated optical assembly (IOA) is provided as part of a laser radar system 200. The IOA is designed to be compact, and to utilize a relatively simple assembly of elements for directing and focusing a pointing beam and a measurement beam at an outlet of the optical radar system. The “source” of the pointing and measurement beams comprises an optical fiber, in the sense that light produced by a light source is directed through the optical fiber. The pointing beam is produced in a visible (e.g. red such as around 610 nm to 750 nm) wavelength range, and the measurement beam is produced in a different, predetermined wavelength range (e.g. infra red such as around 0.7 μm to 10 μm, or IR).
In the laser radar system of FIG. 5, the pointing beam is used to identify a point on a target 220 at which the measurement beam is directed. The measurement beam is reflected from the target and a portion of that reflected or scattered measurement beam is received back at the laser radar system, where it is directed back through the fiber, transmitted to a detector, and processed by a control unit to provide the type of useful information that is characteristic of a laser radar system.
As shown in FIG. 6, the laser radar system 200 includes a housing (e.g. a rotatable cylinder 113) in which the optical assembly is located and secured, so that the optical assembly moves as a unit with the cylinder 113 relative to the base 110 of the laser radar system. The laser radar system includes an outlet 120 in the housing 113, and through which radiation (e.g. in the two wavelengths of the pointing and measurement beams) is directed from the laser radar system. The base 110 contains the processing features of the laser radar system, that are disclosed in U.S. Pat. Nos. 4,733,609, 4,824,251, 4,830,486, 4,969,736, 5,114,226, 7,139,446, 7,925,134, and Japanese Patent #2,664,399. The size of the system should be small enough to allow camera 140 to be located on the moving part of the laser radar system.
Yet another concept laser radar system has a rotating scanning (pointing) mirror, that rotates relative to other parts of the laser radar system, and is used to achieve a desired beam direction. Other concepts for Laser radar systems are disclosed in U.S. Pat. Nos. 4,733,609, 4,824,251, 4,830,486, 4,969,736, 5,114,226, 7,139,446, 7,925,134, and Japanese Patent #2,664,399 which are incorporated by reference herein. The laser beam from the laser radar system (referred to herein as the “measurement beam”) is controlled by the laser radar system optics, and is directed from the laser radar system and at the target.
FIG. 1 is a schematic illustration of the IOA of FIG. 12 of Exhibit A. In that IOA, a beam from a light source (i.e. a fiber tip 100 supported by a ferule 102 in a glass window 101) is directed along a line of sight, by a lens 104, a scanning reflector 106 (e.g. a corner cube) and a fixed reflector (a mirror 108 supported on the glass window 101) that are oriented relative to each other such that a beam from the light source 100 is reflected by the scanning reflector 106 to the fixed reflector 108, and reflected light from the fixed reflector is reflected again by the scanning reflector and directed along the line of sight 138 through the lens 104. The scanning reflector 106 is moveable relative to the source 100, the lens 104 and the fixed reflector 108, to adjust the focus of the beam along the line of sight 138.
According to enhancements provided by the present invention, the integrated optical assembly is configured to produce a reference beam that is related to the optical characteristics of the scanning reflector 106, or to changes in position or orientation of the scanning reflector relative to the source (i.e. the fiber tip 100). That reference beam is useful in several ways in an IOA of the type shown in Exhibit A and in FIG. 1. For example, if the scanning reflector 106 orientation were to shift from its intended orientation (due e.g. to thermal expansion), or if characteristics of the scanning reflector (e.g. the index of refraction of the scanning reflector), were to change on account of temperature changes, the reference beam (which is detected by the detector and processed by the control unit shown in FIG. 5) can be used to provide data that can be used to account for such changes. In addition, if the scanning reflector 106 were to be positioned in an orientation other than the orientation desired, the reference beam can be used in identifying and correcting that positioning. Essentially, the reference beam can be used to subtract out errors that could be caused by the foregoing factors.
FIGS. 2 a, 2 b show one version of an IOA configured to produce such a reference signal, according to the present invention. The optical assembly includes a lens 110 between the source 100 and the scanning reflector 106 that is configured to produce a continuous collimated reference signal that traverses the scanning reflector 106 at least twice and is then refocused on the source 100. The lens 110 is oriented off center, in relation to the source 100, to collimate the beam at a slight angle to the source, and the optical assembly is further configured so that after two passes through the scanning reflector, the reference signal is refocused on a reflector 112 (e.g. a window, ferrule, etc) next to the source 100, traverses the scanning reflector 106 twice more and is then refocused on the source 100.
The underlying principle of this version is to use the off-center lens 110 to collimate the beam at a slight angle to the fiber axis (and return mirror normal), so that after one pass, it is refocused on the reflector 112 next to the fiber tip 100. After that reflection, the beam traverses the corner cube system a second time and is then focused on the fiber tip 100 as the reference beam. This focusing happens automatically and is simply a property of the imaging system; no particularly difficult alignment is needed.
With the version of the present invention shown in FIGS. 2 a and 2 b, a stable and sensitive reference beam is provided throughout the focus range by the double pass collimated reference path, which traverses the scanning retroreflector four times. In FIGS. 2 a and 2 b, the offset of lens 110 is exaggerated somewhat for a visualization purposes. It is possible to also include annular reflective regions 110 a, 110 b on the lens 110 (FIG. 3) to increase the efficiency of the ghost, while not limiting the power used by the measurement beam. Further more, the lens 110 could be mounted directly in a recess cut into the window 101 (or mirror 108), which could include the needed offset Another modification, shown in FIG. 2 a, is to use a reflective ferule 112, or to place a reflector very close to the fiber tip 100 since this will allow the lens to be smaller.
As schematically illustrated in FIGS. 2 a, 2 b and 3, the double pass configuration achieves the right amount of sensitivity needed to compensate the range measurement. The collimated reference beam allows the system to maintain high power at all ranges. The lens 110 or any other optical element that generates the collimated beam, must also allow a non-collimated measurement beam to pass through at the same time. This could be accomplished with a Fresnel zone plate or some other holographic lens, but another approach is to use a zero power lens, that also has a collimated ghost reflection (see e.g. FIG. 3). Such lens designs have zero power for the twice refracted path, but the twice reflected path, referred to as the ghost path, is collimated by virtue of a finite focal length.
It is possible to also include the annular reflective regions 110 a, 110 b on the lens 110 (FIG. 3) to increase the efficiency of the ghost, while not limiting the power used by the measurement beam. This results in an annular reference beam. Furthermore, the lens could mounted directly in a recess cut into the window (or mirror), which could include the needed offset This would make a reflective ferule 112, and other methods for placing a reflector very close to the fiber tip 100, attractive since this will allow the lens 110 to be smaller.
A consequence of having a window near the fiber tip 100 that is substantially parallel (doesn't have to be perfect) to the return mirror, is that this path can be used to generate a reference signal at one focus position.
As schematically shown in FIG. 4, in a method according to the present invention the optical assembly includes the lens, the scanning reflector and the fixed reflector oriented relative to each other such that a beam from the light source is reflected by the scanning reflector to the fixed reflector, and reflected light from the fixed reflector is reflected again by the scanning reflector and directed along the line of sight through the lens, and wherein the scanning reflector is moveable relative to the source, the lens and the fixed reflector, to adjust the focus of the beam along the line of sight. The optical assembly directs a measurement beam at a target, and returned light is transmitted to the detector and processed by the control unit, while the reference beam is produced that is related to the orientation of the scanning reflector relative to the source. That reference beam is useful in several ways in an IOA of the type shown in Exhibit A and in FIG. 1. For example, if the scanning reflector orientation were to shift from its intended orientation (due e.g. to thermal expansion) or if characteristics of the scanning reflector (e.g. the index of refraction of the scanning reflector) were to change on account of temperature changes, the reference beam can be used to provide data that can be used to account for such changes. In addition, if the scanning reflector were to be positioned in an orientation other than the orientation desired, the reference beam can be used in identifying and correcting that positioning. Essentially, the reference beam can be used to subtract out errors that could be caused by such factors.
Thus, the reference beam can be used to produce data to account for changes in the reflection or refraction characteristics of the scanning reflector due to (i) changes in the intended orientation of the scanning reflector, (ii) changes in the angular orientation of the scanning reflector, changes in the temperature of the scanning reflector.
The method can be practiced, e.g. by producing between the scanning reflector and the source a continuous collimated reference signal that traverses the scanning reflector at least once (and preferably 4 times, as shown in FIGS. 2 a, 2 b) and is then refocused on the source. As shown in FIGS. 2 a, 2 b, the beam is collimated at a slight angle to the source, and the optical assembly is configured so that after two traversals of the scanning retroreflector, the reference beam is refocused on a reflector next to the source, and after reflection, the beam traverses the scanning reflector a third and fourth time and is then refocused on the source (see e.g. FIGS. 2 a, 2 b).
The method of the invention can also be implemented in the manner schematically shown in FIGS. 7-9. FIG. 7 schematically shows the primary components of that implementation; FIG. 8 shows the path of the measurement beam of that implementation, and FIG. 9 shows the path of the reference beam in that implementation. In implementation of FIGS. 7-9, the measurement and reference beams are directed through a pair of fibers having tips 200 a, 200 b, respectively. Thus, the measurement and reference beams that are directed through the pair of fibers effectively comprise the “source” (and both those measurement and reference beams can originate from the same light source that is split into the measurement and reference beams). As seen from FIGS. 7 and 8, the measurement beam from fiber tip 200 a, is reflected by a fold mirror 204, traverses the scanning retroreflector 202 (which is preferably a moveable corner cube), is reflected by a fixed reflector 206, traverses the scanning retroreflector 202 again, and is directed along the line of sight through one or more lens and reflecting elements 208. Thus, the path of the measurement beam is the same as shown and described in connection with FIG. 1. As seen from FIGS. 7 and 9, the reference beam from fiber 200 b, is directed through a lens 209, reflected by a fold mirror 210, traverses the scanning retroreflector 202, is reflected by a prism 212 or some other suitable optical element that shifts the reference beam, traverses the scanning retroreflector 202 again, is reflected by a small fixed retroreflector 214 that reflects that reference beam on axis back to the scanning retroreflector 202 which it traverses again and is then reflected back to the reference beam fiber tip 200 b. Thus, the reference beam is a collimated reference signal that traverses the scanning retroreflector 202 at least twice and is then refocused on the source (in the embodiment, on the reference beam fiber tip 200 b).
Thus, the present invention provides enhancements to an IOA of the type that is particularly useful in a laser radar system. The enhancement of the present invention provides an IOA (and also to a method) that produces a reference beam that is related to the optical characteristics of the scanning reflector, or to changes in position or orientation of the scanning reflector relative to the source. With the foregoing disclosure in mind, the manner in which such enhancements may be implemented in various types of IOA assemblies will be apparent to those in the art.
The reference path of IOA assemblies described here must traverse the scanning reflector at least once, and in all cases it is possible for the reference beam and measurement beam to be measurement beams of separate interferometers having internal references of their own. The a reference interferometer will have a path length that increases with the position of the scanning reflector, where the increase is in proportion to twice the number of traversals that it makes (2nx) where x is the change in position of the scanning reflector and n is the number of traversals, with the minimum number of traversals being one. The measurement interferometer path also increases with scanning reflector position but by a factor of 8x. So the measurement path can be compensated for scanning reflector shifts by subtracting the change in measurement path times a factor of 4/n.
The preferred embodiment is to allow the reference beam to interfere with the measurement beam so that the reference beam and measurement beam form an interferometer with the position of the scanning reflector contributing minimally to the path difference between the reference beam and measurement beams. This occurs only when the reference beam makes four traversals of the scanning reflector as described, for example, in FIGS. 2 a and 2 b.
In the disclosed embodiments, the measurement path and reference path uses the same corner cube (106, 202). However the corner cube of the measurement path may be different than the corner cube of the reference path. Therefore the movement of the corner cube of measurement path may have synchronized movement with the corner cube of the reference path.
Next, explanations will be made with respect to a structure manufacturing system provided with the measuring apparatus (laser radar system 200) described hereinabove.
FIG. 9 is a block diagram of a structure manufacturing system 700. The structure manufacturing system is for producing at least a structure from at least one material such as a ship, airplane and so on, and inspecting the structure by the profile measuring apparatus 200. The structure manufacturing system 700 of the embodiment includes the profile measuring apparatus 200 as described hereinabove in the embodiment, a designing apparatus 610, a shaping apparatus 620, a controller 630 (inspection apparatus), and a repairing apparatus 640. The controller 630 includes a coordinate storage section 631 and an inspection section 632.
The designing apparatus 610 creates design information with respect to the shape of a structure and sends the created design information to the shaping apparatus 620. Further, the designing apparatus 610 causes the coordinate storage section 631 of the controller 630 to store the created design information. The design information includes information indicating the coordinates of each position of the structure.
The shaping apparatus 620 produces the structure based on the design information inputted from the designing apparatus 610. The shaping process by the shaping apparatus 620 includes such as casting, forging, cutting, and the like. The profile measuring apparatus 200 measures the coordinates of the produced structure (measuring object) and sends the information indicating the measured coordinates (shape information) to the controller 630.
The coordinate storage section 631 of the controller 630 stores the design information. The inspection section 632 of the controller 630 reads out the design information from the coordinate storage section 631. The inspection section 632 compares the information indicating the coordinates (shape information) received from the profile measuring apparatus 200 with the design information read out from the coordinate storage section 631. Based on the comparison result, the inspection section 632 determines whether or not the structure is shaped in accordance with the design information. In other words, the inspection section 632 determines whether or not the produced structure is nondefective. When the structure is not shaped in accordance with the design information, then the inspection section 632 determines whether or not the structure is repairable. If repairable, then the inspection section 632 calculates the defective portions and repairing amount based on the comparison result, and sends the information indicating the defective portions and the information indicating the repairing amount to the repairing apparatus 640.
The repairing apparatus 640 performs processing of the defective portions of the structure based on the information indicating the defective portions and the information indicating the repairing amount received from the controller 630.
FIG. 11 is a flowchart showing a processing flow of the structure manufacturing system 700. With respect to the structure manufacturing system 700, first, the designing apparatus 610 creates design information with respect to the shape of a structure (step S101). Next, the shaping apparatus 620 produces the structure based on the design information (step S102). Then, the profile measuring apparatus 100 measures the produced structure to obtain the shape information thereof (step S103). Then, the inspection section 632 of the controller 630 inspects whether or not the structure is produced truly in accordance with the design information by comparing the shape information obtained from the profile measuring apparatus 200 with the design information (step S104).
Then, the inspection portion 632 of the controller 630 determines whether or not the produced structure is nondefective (step S105). When the inspection section 632 has determined the produced structure to be nondefective (“YES” at step S105), then the structure manufacturing system 700 ends the process. On the other hand, when the inspection section 632 has determined the produced structure to be defective (“NO” at step S105), then it determines whether or not the produced structure is repairable (step S106).
When the inspection portion 632 has determined the produced structure to be repairable (“YES” at step S106), then the repair apparatus 640 carries out a reprocessing process on the structure (step S107), and the structure manufacturing system 700 returns the process to step S103. When the inspection portion 632 has determined the produced structure to be unrepairable (“NO” at step S106), then the structure manufacturing system 700 ends the process. With that, the structure manufacturing system 700 finishes the whole process shown by the flowchart of FIG. 11.
With respect to the structure manufacturing system 700 of the embodiment, because the profile measuring apparatus 200 in the embodiment can correctly measure the coordinates of the structure, it is possible to determine whether or not the produced structure is nondefective. Further, when the structure is defective, the structure manufacturing system 700 can carry out a reprocessing process on the structure to repair the same.
Further, the repairing process carried out by the repairing apparatus 640 in the embodiment may be replaced such as to let the shaping apparatus 620 carry out the shaping process over again. In such a case, when the inspection section 632 of the controller 630 has determined the structure to be repairable, then the shaping apparatus 620 carries out the shaping process (forging, cutting, and the like) over again. In particular for example, the shaping apparatus 620 carries out a cutting process on the portions of the structure which should have undergone cutting but have not. By virtue of this, it becomes possible for the structure manufacturing system 700 to produce the structure correctly.
In the above embodiment, the structure manufacturing system 700 includes the profile measuring apparatus 200, the designing apparatus 610, the shaping apparatus 620, the controller 630 (inspection apparatus), and the repairing apparatus 640. However, present teaching is not limited to this configuration. For example, a structure manufacturing system in accordance with the present teaching may include at least the shaping apparatus and the profile measuring apparatus.
Thus, the present invention provides new and useful concepts for an apparatus, optical assembly, method for inspection or measurement of an object and method for manufacturing a structure. With the foregoing description in mind, the manner in which those concepts (e.g. the optical assembly of the present embodiments) can be implemented in various types of laser radar systems, as well as other types of optical systems and methods, will be apparent to those in the art.

Claims

1. An optical assembly for focusing a beam from a light source along a line of sight, where a lens, a scanning reflector and a fixed reflector are oriented relative to each other such that a beam from the light source is reflected by the scanning reflector to the fixed reflector, and reflected light from the fixed reflector is reflected again by the scanning reflector and directed along the line of sight through the lens, wherein the scanning reflector is moveable relative to the source, the lens and the fixed reflector, to adjust the focus of the beam along the line of sight, and wherein the optical assembly is configured to produce a reference signal that is related to the location of the scanning reflector relative to the source.

2. The optical assembly of claim 1, wherein the optical assembly includes a lens between the source and the scanning reflector that is configured to produce a continuous collimated reference signal that traverses the scanning reflector at least twice and is then refocused on the source.

3. The optical assembly of claim 2, wherein the lens is oriented off center, in relation to the source, to collimate the beam at a slight angle to the source, and the optical assembly is further configured so that after two passes through the scanning reflector, the reference signal is refocused on a reflector next to the source, traverses the scanning reflector at least twice more and is then refocused on the source.

4. The optical assembly of claim 1, wherein the measurement and reference beams are directed through a pair of fibers, wherein the measurement beam produced through one fiber

a. is reflected by a fold mirror,

b. traverses the scanning reflector,

c. is reflected by the fixed reflector,

d. traverses the scanning reflector again, and is directed along the line of sight through the lens, and

wherein the reference beam produced through the other fiber

a. traverses the scanning reflector,

b. is reflected by an optical element that shifts the reference beam,

c. traverses the scanning reflector again, and

d. is transmitted back to the reference beam fiber.

5. A method for producing useful data in an optical assembly for focusing a beam from a light source along a line of sight, where the optical assembly includes a lens, a scanning reflector and a fixed reflector are oriented relative to each other such that a beam from the light source is reflected by the scanning reflector to the fixed reflector, and reflected light from the fixed reflector is reflected again by the scanning reflector and directed along the line of sight through the lens, and wherein the scanning reflector is moveable relative to the source, the lens and the fixed reflector, to adjust the focus of the beam along the line of sight, the method comprising producing produce a reference signal that is related to the orientation of the scanning reflector relative to the source.

6. The method of claim 5, wherein the reference signal is produced between the scanning reflector and the source by a continuous collimated reference beam that traverses the scanning reflector at least twice and is then refocused on the source.

7. The method of claim 6, wherein the collimated reference beam is collimated at a slight angle to the source, and configuring the optical assembly is further configured so that after two passes through the scanning reflector, the reference signal is refocused on a reflector next to the source, traverses the scanning reflector twice more and is then refocused on the source.

8. The method of claim 5, wherein as the optical assembly is focusing the beam along the line of sight the reference signal provides data to account for changes in the refraction or reflection characteristics of the optical assembly.

9. The method of claim 5, wherein the reference signal is used in producing data to account for changes in the reflection or refraction characteristics of the scanning reflector due to changes in the intended orientation of the scanning reflector.

10. The method of claim 5 wherein the reference signal is used in producing data to account data to account for changes in the reflection or refraction characteristics of the scanning reflector due to changes in the angular orientation of the scanning reflector.

11. The method of claim 5, wherein the reference signal is used in producing data to account for changes in the reflection or refraction characteristics of the scanning reflector due to changes in the temperature of the scanning reflector.

12. A method for manufacturing a structure, comprising:

producing the structure based on design information;

obtaining shape information of structure by using of the method of claim 4;

comparing the obtained shape information with the design information.

13. The method for manufacturing the structure according to claim 11 further comprising reprocessing the structure based on the comparison result.

14. The method for manufacturing the structure according to claim 12, wherein reprocessing the structure includes producing the structure over again.