Methods and systems for aligning optical instrument

Abstract

To provide a more compact, stable, reliable, and easily controlled optical device for aligning a beam in an optical instrument.SOLUTION: One optical steering mechanism includes a first lens defining a first focal length having a first magnitude and a first polarity, and a second lens defining a second focal length having a second magnitude and a second polarity. The first and second magnitudes are substantially equal and the first and second polarities are opposite. The second lens is positioned to directly receive an optical beam passing through the first lens. The optical beam steering mechanism also includes at least one rotary motor coupled to one of the first and second lenses and configured to swing the lens coupled thereto in an arcuate path. An optical beam path of the optical beam passed through the second lens is adjustable by operating the rotary motor.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a method and system for aligning optical devices, and more particularly to aligning one or more beam paths of a microscope such as a Raman microscope.

Summary of the Invention

[0002] In one aspect, the present disclosure provides an optical beam steering mechanism comprising a first lens defining a first focal length having a first amplitude and a first polarity, and a second lens defining a second focal length having a second amplitude and a second polarity. The first amplitude and the second amplitude are substantially equal, the first polarity and the second polarity are opposite, and the second lens is positioned to directly receive the optical beam passing through the first lens. The optical beam steering mechanism also includes at least one rotary motor coupled to one of the first lens and the second lens and configured to oscillate the coupled lens within an arcuate path. The optical beam path of the optical beam passing through the second lens is adjustable by operating the rotary motor.

[0003] In another aspect, the present disclosure provides an optical instrument comprising an electromagnetic radiation source for generating an optical beam, a sample stage for holding a sample, a detector for receiving light from the sample, and at least one optical beam steering mechanism. The optical beam steering mechanism comprises a first lens defining a first focal length having a first amplitude and a first polarity, and a second lens defining a second focal length having a second amplitude and a second polarity. The first amplitude and the second amplitude are substantially equal, the first polarity and the second polarity are opposite, and the second lens is positioned to directly receive the optical beam passing through the first lens. The optical beam steering mechanism also comprises at least one rotary motor coupled to one of the first lens and the second lens and configured to swing the coupled lens within an arcuate path. The optical beam path of the optical beam passing through the second lens is adjustable by operating the rotary motor. The optical beam steering mechanism is configured to direct the optical beam either towards the sample stage or towards the detector for light from the sample.

[0004] In yet another aspect, the present disclosure provides a method for aligning a beam in an optical device. The method includes turning on the power of an optical device that includes a first lens and a second lens driven by a first motor and a second motor, respectively, and further includes a first motor position encoder and a second motor position encoder, wherein the first lens and the second lens define focal lengths of substantially equal amplitudes and opposite polarities, and the second lens is positioned to directly receive the beam passing through the first lens. The method also includes operating the first motor and the second motor to move one or both of the first lens and the second lens to respective calibration positions, wherein the calibration positions correspond to a desired optical beam path alignment for the beam to pass through the first lens and the second lens, and maintaining power to the first motor and the second motor as long as the optical device is powered on. The method further includes using feedback from the first motor position encoder and the second motor position encoder to maintain the calibration positions as long as the power of the optical device is on.

[0005] Other aspects of the present disclosure will become apparent by considering the detailed description and the accompanying drawings.

Brief Description of the Drawings

[0006]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Best Mode for Carrying Out the Invention

[0007] An automatic alignment mechanism is useful for maintaining the functions of optical instruments such as a spectroscopic microscope, an infrared photothermal device, and other optical instruments against mechanical drifts and replacements of optical components. For example, an automatic optical alignment mechanism is useful for maintaining the functions of a spectroscopic microscope against mechanical drifts and replacements of optical components.

[0008] In one embodiment, a pair of lenses can be sequentially attached along the optical axis. Angular deviation may be introduced by translating one lens relative to the other. This configuration is described in U.S. Patent No. 6,661,509, which is hereby incorporated by reference in its entirety into this application. The applicant recognizes that a large and expensive linear motor may be required to translate the lens. Since the space within the optical instrument is limited, it may be difficult to attach an encoder to the linear motor. Further, in order to reduce noise and heat that may affect other optical components and introduce inaccuracies in measurements during operation of the optical instrument such as during measurement, it is necessary to turn off the power of the linear motor. Therefore, there is a need for a smaller, more stable, reliable, and easily controllable optical device for aligning the beam in an optical instrument.

[0009] To address the above problems, a beam steering mechanism, an optical device including the beam steering mechanism, and a method for aligning an optical beam are disclosed herein. These provide improved design flexibility and robustness, along with reduced size, cost, and complexity. The optical beam steering mechanism includes a first lens defining a first focal length having a first amplitude and a first polarity, and a second lens defining a second focal length having a second amplitude and a second polarity, wherein the first amplitude and the second amplitude are substantially equal and the first polarity and the second polarity are opposite. That is, the magnifications of the first lens and the second lens are substantially the same, but one has a positive polarity (convex) and the other has a negative polarity (concave). The first lens and the second lens are configured to receive an optical beam path therethrough. The second lens directly receives the light that has passed through the first lens. In other words, no optical components are positioned between the first lens and the second lens. In some embodiments, the optical beam steering mechanism may include only the first lens and the second lens and may not include other lenses. In one embodiment, the first lens is positioned substantially parallel to the second lens. In one embodiment, the first lens and the second lens are spaced apart from each other by a relatively small distance. The distance may be 5% or less of the focal length, or 1% or less of the focal length, etc.

[0010] At least one of the first lens and the second lens may be pivoted within an arcuate path by operating a rotary motor coupled to the first lens or the second lens. The arcuate path is substantially parallel to the first lens or the second lens. By pivoting one of the lenses, the optical path of the optical beam passing through the two lenses is adjusted.

[0011] The lenses may be spaced apart from each other by a distance much shorter than their focal lengths. The net refractive power of a pair of lenses is approximately zero (0). When the lenses are centered with respect to each other, they produce no net optical effect. When one or both lenses are displaced with respect to the light beam by operating a rotation motor, the net refractive power is substantially unchanged, but the lenses deflect the beam

[0012]

Number

[0013] The rotary motor is less expensive and has a smaller occupied volume than the linear motor. The applicant has found that oscillating each of the lenses in an arc is surprisingly effective for achieving beam control at a level equivalent to that of a beam steering mechanism that independently moves the lens in the x and y directions using two-axis control. Such a linear beam steering mechanism requires a stepping linear actuator and additional mechanical components to constrain the movement of the lens so that the assembly is robust and repeatable. The bearings of the rotary motor provide sufficient restraint by themselves without the need to add additional components to constrain the movement of the lens to a reproducible path. The rotary system is also more resistant to vibration and maintains better position accuracy, for example, than a linear motor regulator. In this way, the alignment of the microscope may be achieved by applying a small angular deviation (e.g., on the order of a few milliradians or less) to one or more light beams via the beam steering mechanism. This configuration provides improved design flexibility and robustness, along with a reduction in size, cost, and complexity, compared to translating the lens using a linear motor.

[0014] In some embodiments, at least one of the first lens and the second lens may be coupled to the rotary motor via a shaft extending from the rotary motor and an arm coupled between the shaft and the lens. The arm defines the radius of the arcuate path. The rotary motor may be a rotary stepping motor driven with a low current (e.g., with microstep drive). A rotary position encoder may be coupled to the shaft to measure the rotational position of the shaft. As an example, the encoder may provide 16,384 counts per revolution, i.e., 61 microradians per count. The lens position may be finely adjusted by operating the rotary motor based on the feedback of the encoder.

[0015] In one embodiment, each of the two lenses is coupled to a rotary motor. The first rotary motor may have a first motor shaft extending therefrom, and the second rotary motor may have a second motor shaft extending therefrom. A first rotary position encoder may be used to sense the rotational position of the first motor shaft, and a second rotary position encoder may be used to sense the rotational position of the second motor shaft. A radius may be defined between each motor shaft rotation axis and each lens center. The first arm may be operably coupled to the first motor shaft and configured to hold the first lens, and the second arm may be operably coupled to the second motor shaft and configured to hold the second lens. Thus, the first arm may define a first radius between a portion of the arm that couples to the motor shaft (which coincides with the motor shaft axis) and a portion of the arm that holds the lens (which defines the lens center), and the second arm may similarly define a second radius. The radii are transverse to each other when the lenses are placed centered, for example, when arranged with any angle less than 180 degrees between them. The lenses are centered when the optical axes of the lenses overlap. In one embodiment, the radii may be perpendicular to each other when the lenses are centered about the optical axis. In other embodiments, the radii may be arranged relative to each other at angles such as 85 - 95 degrees, 80 - 100 degrees, 70 - 110 degrees, 60 - 120 degrees, etc. In one embodiment, a radius of 25 mm is sufficient to separate the motor body from the optical axis and results in a deviation of each lens of approximately 1.5 microns per count. For lenses with focal lengths of +1000 and -1000 mm, the resulting angular deviation is 1.5 microradians per count. The electronic controller may be configured to receive feedback from the first rotary position encoder and the second rotary position encoder. The electronic controller may further be configured to maintain the positions (e.g., calibration positions) of the first lens and the second lens based on the feedback.

[0016] The beam steering mechanism may be included in an optical device such as a spectrograph, a microscope, an infrared photothermal device, a combination of the aforementioned devices, or any other device having an electromagnetic radiation source that defines an optical beam path. In some embodiments, one or more beam steering mechanisms are included in a Raman microscope. For example, the beam steering mechanism may be positioned downstream of the illumination source to adjust the beam path of the illumination light. The beam steering mechanism may be positioned upstream of the spectrograph to adjust the path of the beam collected by the spectrograph.

[0017] In one embodiment, the optical instrument includes a beam steering mechanism that is powered on while acquiring sample data. That is, during data collection, the power of one or more rotary motors is turned on. The optical beam path passes through a first lens and a second lens of the beam steering mechanism. The first lens and the second lens define focal lengths of substantially equal amplitude and opposite polarities. The first motor and the second motor may move one or both of the first lens and the second lens to a calibration position before data acquisition. The calibration position corresponds to the desired optical beam path alignment. As long as the power of the optical instrument is on, the power to the first motor and the second motor is maintained. Using feedback from the first motor position encoder and the second motor position encoder, the lens may be maintained at the calibration position as long as the optical instrument is powered on. This provides positional reliability through measurement against gravity, for example, which acts to swing the lens away from the calibration position. The first motor and the second motor may be rotary motors, but the method may be used with other types of motors to provide positional reliability. The calibration position of the lens may be determined through a calibration process performed by the manufacturer or the user, for example, by an actuator configured to trigger a calibration sequence programmed into the controller. Once determined, the calibration position is stored in the controller. When the power of the instrument is turned off, the calibration position of the lens may not be maintained, for example, due to the influence of gravity pulling on the lens. Therefore, when the instrument is turned on, the controller is programmed to return the lens to their latest calibration position. The encoder may facilitate the return of the lens to the calibration position by finding a zero reference position and then moving to the calibration position relative to the zero reference position, and thus provide position reproducibility. The user may periodically update the calibration position after any change in environmental parameters (e.g., temperature) or before measuring a sample in the same work session. The encoder may provide continuous feedback to keep the lens at the calibration position against gravity, vibration, etc., as long as the instrument is on.

[0018] Before any implementation of the present disclosure is described in detail, it is to be understood that the present disclosure is not limited in its application to the details of the structures and the arrangements of the components described in the following description or illustrated in the following drawings. The present disclosure is capable of other implementations and of being carried out or executed in various ways.

[0019] In the present disclosure, "deviation" refers to the angular deviation of a beam, and "displacement" refers to the lateral displacement of a beam or an optical element away from the optical axis. "Optical" may refer to a part or all of the electromagnetic spectrum. More specifically, in some implementations, "optical" may refer to the visible, ultraviolet, and infrared parts of the electromagnetic spectrum, and even more specifically, in still other implementations, "optical" may refer to the visible part of the electromagnetic spectrum.

[0020] The optical apparatus is generally indicated at 10 in FIG. 1. The optical apparatus 10 may be a spectroscopic microscope system suitable for Raman spectroscopy, but the optical apparatus 10 may include other types of optical systems having a beam path, such as a confocal fluorescence microscope, other optothermal devices, other spectroscopic devices, other types of microscopes, other combinations thereof, and the like. The optical apparatus 10 includes an optical microscope shown in a simplified form within the dashed lines labeled 11 in FIG. 1. The optical microscope 11 includes an objective lens 12 and an eyepiece 14. The eyepiece 14 may be used for direct viewing by an observer, or may form part of a lens within a video camera 15, or may be in addition to the lens within the video camera 15. Light from a sample placed on the stage 40 is thus returned through the objective lens 12 on the beam path 17 in a conventional manner to the eyepiece 14, forming an image that the operator can view directly or using the video camera 15 and a video display terminal.

[0021] In the optical instrument 10 of FIG. 1, illumination light suitable for Raman spectroscopy may be provided from a light source 20, typically a laser, on the illumination beam path 21, through a beam steering mechanism 22, to a deflection mirror and notch filter 24 that redirects the illumination beam path 21 towards the Raman interface module deflection mirror 26. The deflection mirror 26 may be formed as a plane mirror or as a dichroic mirror mounted on an electric slide for selective insertion into and removal from the beam path 17. When the deflection mirror 26 is moved to a position within the beam path 17, the deflection mirror 26 deflects the illumination beam path 21 to be collinear with the microscope optical beam path 17. The objective lens 12 focuses the irradiation beam at the focal point 28. In other implementations, the optical instrument 10 may include any electromagnetic radiation source.

[0022] The optical instrument 10 also includes a Raman return beam path 30, which is formed as a parallel beam that is collected by the objective lens 12 and deflected by the deflection mirror 26 to the position of the notch filter 24 on a path collinear with the illumination beam path 21, and includes scattered light. The notch filter 24 is formed to transmit the wavelength of Raman radiation in the return beam path 30 and reflect the wavelengths of the illumination beam path 21 and Rayleigh radiation. The notch filter 24 may be a holographic filter and is used for Rayleigh rejection in the manner described in Spectrochemica Acta, Vol. 46A, No. 2, 1990, pp. 153 - 159, by F.J. Burgin. After passing through the notch filter 24, the Raman radiation in the return beam path 30 passes through a beam steering mechanism 34 and through an input lens 35 that focuses the return beam path 30 towards the input aperture 36 of a spectrograph 37. The spectrograph 37 may be formed to spatially distribute the wavelength of the light in the return beam path 30, and then it is incident on a detector 38, which detects the intensity of light of various wavelengths and provides an output signal indicating the Raman spectrum of the sample.

[0023] When the optical instrument 10 is performing alignment, a reference sample such as the alignment device 39 may be placed on the stage 40. As will be further described below, the alignment device 39 includes a spatially restricted stage entrance opening 41 that is positioned by the operator to coincide with the central axis of the beam path 17. The controller 44 (e.g., an electronic controller) provides control signals to the alignment device 39 and receives signals from the alignment device 39 on lines 162, 168. Further, the controller 44 is connected to the light source 20 by a control line 46, to the beam steering mechanism 22 by a line 47, to the detector 38 by a line 48, and to the beam steering mechanism 34 by a line 49. As will be further described below, once the operator positions the alignment device 39 such that the stage entrance opening 41 is aligned with the focus of the optical instrument 10, the controller 44 can perform an automatic alignment adjustment using the beam steering mechanisms 22, 34 under software control.

[0024] The effect of misalignment of the beam within the optical instrument 10 is shown in FIG. 2, which shows the illumination beam path 21 that is focused to a focus 28 in the focal plane 51 of the microscope 11 passing through the objective lens 12. The angular deviation in the parallel portion of the illumination beam path 21 (see 21') is converted to a spatial translation r in the focal plane (see 28') according to r = fθ (where r = spatial translation away from the center of the optical axis, f = focal length of the lens, and θ = angular deviation of the beam). For example, the focal length of a 100x objective lens 12 is 1.6 mm, a 50x objective lens 12 is 3.2 mm, and a 20x objective lens 12 is 8 mm. As an example, a typical focal length for a spectrograph input is 40 mm.

[0025] The beam steering mechanisms 22, 34 are provided to accurately align the illumination beam path 21 with the focus 28 and the return beam path 30 with the entrance aperture 36 of the spectroscope. The beam steering mechanisms 22, 34 may be disposed at any of the beam paths disclosed herein or at any location within any other beam path of an optical beam within any device. An adjustment signal is supplied to the beam steering mechanisms 22, 34 by a controller 44, and the controller 44 receives, respectively, an input from a detector 38 (described below) and an input from an alignment device 39 located on or within the sample stage 40 of the microscope 11. The alignment device 39 includes a stage entrance aperture 41, and the stage entrance aperture 41 is positioned to coincide with the central axis of the microscope optical beam path 17 by the operator viewing the alignment device 39 with the eyepiece optical element 14 and / or the video camera 15. The alignment device 39 includes therein a stage light source 160 (e.g., a high-brightness light emitting diode (LED)) operated by a line 162 communicating with the controller 44, and a stage light sensor 165 (e.g., a silicon photodiode) positioned to receive light transmitted through the LED / stage light source 160. The stage light sensor 165 emits a stage light sensor output signal to the controller 44 along a line 168 in response to receiving light. In one embodiment, the controller 44 turns on the stage light source 160 and then performs alignment by controlling the beam steering mechanism 34 until the return beam path 30 from the stage light source 160 is aligned to the maximum brightness position on the detector 38, thereby indicating that when such a return beam path 30 is generated via the illumination light beam path 21 from the light source 20, such a return beam path 30 is also well aligned with the entrance aperture 36 of the spectroscope and the detector 38. Similarly, the beam steering mechanism 22 can be controlled by the controller 44 until the stage light sensor 165 measures the maximum output from the light source 20, indicating that the illumination beam path 21 is properly aligned.In other words, the input beam or reference beam for spectroscopic measurement is optimized via the beam steering mechanism 22 by a signal from the stage optical sensor 165 within the alignment device 39 (the stage optical sensor 165 is stimulated by the light source 20), and the return beam path 30 for spectroscopic measurement is optimized via the beam steering mechanism 34 by a signal from the detector 38 within the spectroscope 37 (the detector 38 is stimulated by the stage light source 160). It should be noted that the controller 44 communicates with the light source 20 via line 46, the beam steering mechanism 22 via line 47, the detector 38 via line 48, and the beam steering mechanism 34 via line 49, and communicates with the stage optical sensor 165 via line 168 and with the stage light source 160 via line 162. Once alignment is achieved, the alignment device 39 may be removed from the sample stage 40 (if not incorporated therein) so that the microscope 11 can be used to analyze the sample. The current positions of the beam steering mechanisms 22 and 34 may be set as calibration positions and stored in the non-transitory memory of the controller. It should be understood that "line" may be embodied as a wired connection or a wireless connection.

[0026] In another embodiment, the alignment of the microscope beam path 17 may be performed by causing the observer light sensor 15 to receive a microscope alignment optical signal from the optical elements 12, 26, and 14 and generate a corresponding output signal from the observer light sensor 15. Next, the output signal from the observer light sensor 15 is supplied to the controller 44 (e.g., via line 170), and the controller 44 may reposition the stage light source 160 (or, more generally, the alignment device 39) in response to the output signal from the observer light sensor 15. As an example, when the observer light sensor 15 is provided in the form of a video camera, the controller 44 may utilize the pixel values captured by the camera 15 and supply an instruction to move the alignment device 39 such that the maximum / brightest pixel value comes to the center within the pixel array (i.e., such that the stage light source 160 is aligned with the central optical axis of the observer light sensor / video camera 15). The movement of the alignment device 39 may be achieved by using a suitable actuator 176 configured to be controlled by the controller 44 (e.g., via line 173).

[0027] The return light source 172 can be positioned in alignment with the entrance aperture 36 of the spectroscope and the optical elements 35, 24, 26, and is operable to emit an alignment optical signal through the entrance aperture 36 of the spectroscope. Next, the optical elements 35, 24, 26, and 12 may send the alignment optical signal to the alignment device 39. The stage optical sensor 165 then emits an output signal in response to the spectrometer alignment optical signal received through the stage entrance aperture 41. The output signal from the stage optical sensor 165 can then be supplied to the controller 44 (by line 168), and the controller 44 repositions the stage optical sensor 165 (and / or adjusts the beam steering mechanism 34) to maximize the output signal from the stage optical sensor 165, thereby indicating that the return beam 30 has achieved a suitable alignment. This configuration may appear to overlap with the alignment achieved by the use of the stage light source 160 and the detector 38, but it should be noted that the alignment by the use of the return light source 172 and the stage optical sensor 165 can be advantageous in that the return light source 172 emits an "ideal" alignment signal: the signal is emitted from the entrance aperture 36 of the spectroscope, which has a fixed position (different from the movable position of the stage entrance aperture 41), and the alignment optical signal is projected onto the alignment device 39 from the entrance aperture 36 of the spectroscope. Next, the spot (dot-shaped shadow) from the alignment optical signal can be roughly aligned with the stage entrance aperture 41 (and the stage optical sensor 165) by user visualization, and fine alignment can be performed between the entrance aperture 36 of the spectroscope and the stage optical sensor 165 by causing the controller 44 to reposition the alignment device 39 to achieve signal maximization.

[0028] Within the spectroscopic camera 37, the return light source 172 is preferably movable between an emission position where the return light source 172 emits a spectroscopic camera alignment optical signal to the optical element through the entrance aperture 36 of the spectroscopic camera, and a non-rotating position (indicated by the dashed line of 172i) where the return light source 172 does not emit a spectroscopic camera alignment optical signal through the entrance aperture 36 of the spectroscopic camera. This enables the spectroscopic camera 37 to be used for normal purposes (i.e., to receive light into the entrance aperture 36 of the spectroscopic camera for delivery to the detector 38), or to emit a spectrometer alignment optical signal from the entrance aperture 36 of the spectroscopic camera for delivery to the stage optical sensor 165. Instead of moving the return light source 172, a movable reflector 174 may be provided that receives the spectrometer alignment optical signal and redirects it through the entrance aperture 36 of the spectroscopic camera towards the optical element, but the reflector 174 is movable between a non-rotating position (the position of the reflector 174 shown in FIG. 1) and an emission position (the position occupied by the return light source 172 in FIG. 1).

[0029] Further details regarding the alignment method using the elements shown in FIG. 1 are disclosed in U.S. Patent Nos. 6,661,509 and 7,460,229, the entire contents of both of which are incorporated herein by reference.

[0030] The configuration of each of the beam steering mechanisms 22 and 34 for adjusting the beams 21 and 30 is schematically shown in FIG. 3. The beam steering mechanisms 22, 34 have substantially the same configuration as each other, differing only in their arrangement within the optical apparatus 10, and thus any description of one of the beam steering mechanisms 22, 34 is equally applicable to the other and need not be repeated. Each beam steering mechanism 22, 34 includes a pair of lenses 70 and 71 sequentially mounted (within the beam path 21 or 30). One or both of the lenses 70 and 71 (e.g., the lens 71 shown in FIG. 2) are mounted so as to move within a plane perpendicular to the optical axis 73 (e.g., the central axis) of the incident beam 21 or 30. No other optical components are positioned between the lenses 70 and 71.

[0031] Figure 3 schematically shows a pair of lenses 70, 71 used to deflect an optical beam. The optical beam passes through a pair of lenses 70, 71 whose focal lengths f1, f2 are of substantially equal magnitude but opposite polarities and are separated from each other by a distance d that is much less than the focal length (e.g., "much less" may mean that the distance d is 5% or less of the focal length, or may mean that the distance d is 1% or less of the focal length, whereby the overall refractive power 1 / f is not substantial for the use of the alignment device). Any suitable focal length magnitude may be used. "Substantially equal magnitude" means that the magnitudes are very close to each other such that, as given by the "compound lens formula" described herein, the net optical refractive power is zero or nearly zero. As an example, the focal length of the first lens 70 may be +1000 mm and the focal length of the second lens 71 may be -1000 mm. The distance d may be 50 mm or less in this example. For example, the distance d may be 10 mm. The net optical refractive power of the pair of lenses 70, 71 is approximately

[0032]

Number

[0033]

Number

[0034] The "compound lens type" gives the total refractive power 1 / f of the lens pair. When two thin lenses are separated by a distance d in air, the focal length of the combined system is given by the following formula.

[0035]

Equation

[0036] Since d is much shorter than f1 and f2, the contribution of the third term is almost zero. Since the lenses have opposite focal lengths, the first two terms sum to zero or almost zero. Therefore, the lens pair has substantially no net refractive power.

[0037] As best shown in FIG. 5, each of the lenses 70, 71 has respective diameters D1, D2 of about 25 mm in the illustrated embodiment. In some embodiments, the diameters D1, D2 may be 10 mm to 100 mm, more specifically 15 mm to 50 mm, and even more specifically 20 mm to 30 mm. However, the diameters D1, D2 may have any desired value depending on the application.

[0038] As shown in FIGS. 4 to 5, in the illustrated embodiment, the first lens 70 may be mounted on a first arm 80 that is directly driven by a first motor 82 (e.g., a rotary motor) to control the position of the lens 70 in the X-Y plane. The second lens 71 may be mounted on a second arm 81 that is directly driven by a second motor 85 (e.g., a rotary motor) to control the position of the lens 71 in the X-Y plane. "Directly driven" may also include the use of a shaft encoder or other type of encoder disposed between the motors 82, 85 and the arms 80, 81 (described in more detail below). Each of the motors 82, 85 swings its respective lens 70, 71 in an arc (α and β, respectively). The respective radii R1, R2 of each arc are such that swinging each of the respective lenses 70, 71 provides an approximation of linear motion in the respective X and Y directions, and the effect of the arc is relatively small, i.e., in an arc path having a relatively large radius R, as described in more detail mathematically below, is large enough. At least, R must be greater than the physical radius of the motor so that the motor does not block the beam. In a preferred configuration, R is approximately 10 times the diameter of the laser beam, thereby minimizing the coupling between the two axes of motion and maintaining sufficient clearance for the beam passing through both lenses. The radii R1, R2 are transverse to each other when the lenses 70, 71 are centered about the optical axis 73, e.g., when they are disposed at any angle less than 180 degrees between them. In the illustrated embodiment, the radii R1, R2 are perpendicular to each other when the lenses 70, 71 are centered on the optical axis 73. In other embodiments, the radii R1, R2 may be disposed at angles such as 85 to 95°, 80 to 100°, 70 to 110°, 60 to 120°, 45 to 135°, etc.

[0039] FIG. 5 shows the movement of the lenses 70, 71. The motors 82, 85 swing by angles α and β, and the respective pivot axes 90, 91 of the motors 82, 85 are at distances R1, R2 from the optical axis 73, respectively. The centers of the lenses 70, 71 are the amounts

[0040] [Number] It is only offset.

[0041] Approximate value

[0042] [Number] And

[0043] [Number] Given a certain value, when the angle is small, the mechanism provides approximately orthogonal coordinate axes x and y:

[0044] [Number]

[0045] As shown in FIG. 4, the first motor 85 and the second motor 82 are attached to the base 87. The arms 80, 81 are respectively coupled to the shafts 83, 86 of the motors 82, 85. There is sufficient clearance between the motors 82, 85 so that the arms 80, 81 do not collide with the shafts 83, 86 and the beam is not blocked by either of the motors 82, 85. The base 87 includes an opening 88 through which the beam can pass so that the base 87 does not block the beam.

[0046] Lens 70 may be directly attached to an arm 80 that can be directly attached to motor 82, and lens 71 may be directly attached to an arm 81 that can be directly attached to motor 85. Both motors 82, 85 may be powered by controller 44 to drive lenses 70, 71 to desired positions. Motors 82, 85 preferably operate independently of each other so that new measurements can be made in each step, for example, with a raster pattern. In the illustrated implementation (see FIG. 4), position encoders 92, 93 (e.g., position sensors) may be coupled to respective motors 82, 85. Position encoders 92, 93 provide feedback signals corresponding to the rotational positions of respective motor shafts 83, 86 to controller 44. The feedback signals may travel along lines 47, 49 (FIG. 1). Feedback from encoders 92, 93 may be used by controller 44 to control motors 82, 85 to maintain the desired positions of lenses 70, 71. Encoders 92, 93 may be configured to provide absolute or incremental feedback signals with any desired resolution. The encoders may have any suitable configuration (e.g., shafted, hollow shaft, ring mount, etc.). The encoders may sense position optically, magnetically, or using any other suitable principle. In one embodiment, motors 82, 85 are rotary stepping motors (e.g., with microstep drive) driven at low current using encoders 92, 93 (e.g., rotary position encoders) coupled to provide closed-loop feedback. As one example, encoders 92, 93 may provide 16,384 counts per revolution, i.e., 61 microradians per count. However, encoder resolutions of 10 to 250 microradians per count are readily available and may be used if they meet the requirements of the application. In one embodiment, radii R1, R2 of 25 mm are sufficient to separate the bodies of motors 82, 85 from optical axis 73, resulting in a deviation of lenses 70, 71 of approximately 1.5 microns per count.For lenses 70, 71 with focal lengths of +1000 and -1000 mm, the resulting angular deviation is 1.5 microradians per count. This example also applies when the lens is replaced, for example, in the cases of -1000 mm and +1000 mm. Ray tracing modeling shows that this focal length is sufficient to avoid adding an unacceptable level of aberration to the beam when lenses 70, 71 are eccentric. In one example, the Raman microscope preferably has an objective lens 12 with a focal length of 1.8 mm and a numerical aperture of 0.9 (a commercially available "100x" objective lens), and may achieve a spatial resolution of approximately 0.3 microns at visible wavelengths. This spatial resolution corresponds to a deviation of approximately 170 microradians.

[0047] With a resolution of 1.5 microradians, the beam steering mechanisms 22, 34 can accurately "find" the center of a spot that is 170 microradians wide in terms of angle. At the same time, lenses 70, 71 with a clear aperture of 25 mm enable the control of a 5 mm diameter beam with a total angular range of 20 milliradians, which has been found to be sufficient to cover the mechanical tolerances between these when multiple optical assemblies are exchanged within the system. Therefore, the system has both sufficient resolution and range to 1) correct for misalignments that occur during the storage and use of the device, for example, due to thermal drift, mechanical creep, etc., and 2) correct for variations in the alignment of other components within the system, for example, when a component is replaced with another component.

[0048] By displacing one or both of lenses 70, 71 from the optical axis 73 of the input optical beam 75, an angular deviation is imparted to the beam passing through it. Such a mechanism allows for significant mechanical advantages and enables the use of a motor drive with a relatively coarse mechanical resolution. Therefore, the deviation angle α can be controlled using an arcuate lens movement.

[0049] The controller 44 may include a programmable processor 94 (e.g., a microprocessor, a microcontroller, or another suitable programmable device) and a memory 95 such as a non-transitory memory. The memory 95 may include, for example, a program storage area 96 and a data storage area 97. The program storage area 96 and the data storage area 97 may be a combination of different types of memories such as read-only memory ("Read-Only Memory, ROM"), random access memory ("Random Access Memory, RAM") (e.g., dynamic RAM ["Dynamic RAM, DRAM"], synchronous DRAM ["Synchronous DRAM, SDRAM"], etc.), electrically erasable programmable read-only memory ("Electrically Erasable Programmable Read-Only Memory, EEPROM"), flash memory, hard disk, SD card, or other suitable magnetic memory devices, optical memory devices, physical memory devices, electronic memory devices, or other data structures. The controller 44 may also or alternatively include integrated circuits and / or analog devices, such as transistors, comparators, operational amplifiers, etc., to perform the functions described herein.

[0050] As an example, the controller 44 may be configured to adjust the positions of the lenses 70, 71. The controller 44 may automatically perform adjustment or calibration in response to an input signal and stop the adjustment when the desired position is found. The input signal may communicate with the controller 44 to initiate the control of one or both of the motors 82, 85 and perform calibration adjustment based on feedback. The input signal may be transmitted to align the beam as part of the manufacturing process and / or may be transmitted by an on-site operator. The input signal may be automatically transmitted via the actuator 98 (FIG. 1) or by an algorithm programmed into the controller 44 (e.g., programmed to initiate calibration periodically). In one example, the actuator 98 is provided to initiate the calibration of one or both of the beam steering mechanisms 22, 34 via the control line 99. In other examples, separate actuators may be provided for each of the beam steering mechanisms 22, 34. The actuator 98 may be any type of actuator capable of receiving human input, such as a button, touch screen, voice command receiver, etc., and the actuator 98 may be physically disposed on the optical device 10 or may be disposed remotely from the optical device 10. For example, the remote actuator 98 may include an app or program on a smartphone, tablet, computer, or other device that wirelessly communicates with the optical device 10.

[0051] During operation, the beam steering mechanisms 22, 34 are used to align one or more optical beams of the optical instrument. FIG. 6 shows a flowchart of a method 600 for operating the optical instrument 10 and aligning the optical instrument before sample measurement. The method 600 may include any one or more of steps 601-606 in any combination, among other additional and intermediate steps that are apparent from the present disclosure. In step 601, the optical instrument 10 is turned on and begins to receive power. One or more rotary motors receive power and are actuated. At least steps 602-605 may involve the use of the controller 44, for example, to automatically execute the steps. In step 602, each motor shaft 83, 86 is moved to the zero position upon power-up of the optical instrument 10. The zero position can be found using the encoders 92, 93, each having a zero position reference that returns its respective motor shaft 83, 86 to the zero position. In a preferred embodiment, the motor is moved to a calibration position (such as the "index" position of the encoder itself), and then to a "zero" position a known number of steps away from the index position. The index position is a characteristic of the encoder itself. The zero position is acceptably close to the position where the angular deviation of the optical beam is 0. The index position and the zero position may vary slightly due to assembly variations, for example, if the lens is not correctly mounted on the shaft in the exact correct position. However, the index position is repeatable, and thus, it is reliable to first find the index position and then move a known number of steps to the zero position. Other means for determining the zero position are possible, for example, using an optical limit switch, overdriving the arms 80, 81 against a stop, etc.

[0052] In 602, the method includes, optionally, providing an actuator 98 configured to trigger the calibration or alignment of one or both of the first lens 70 and the second lens 71. For alignment, an alignment instrument (such as the alignment instrument 39 in FIG. 1) may be attached to the optical instrument. The actuator 98 may be actuated at any time by the manufacturer or the user as long as the optical device 10 is on. Calibration uses the controller 44 to, for example, determine the desired optical beam path alignment as described in more detail above, and, for example, when drift or swapping of optical components causes a change in the beam path, store the corresponding calibration position in the controller 44. This new calibration position can become the most recent calibration position such that when the optical device 10 is shut down, this new calibration position is restored when the optical device 10 is powered on (see step 601).

[0053] In operation 603, one or both of the lenses 70, 71 are moved to a calibrated position by moving their respective motor shafts 83, 86 to a calibrated shaft position relative to a zero position reference. Moving may include rocking one or both of the lenses 70, 71 in an arc. In one embodiment, the calibrated positions of the motors 82, 85 are stored in the controller 44, and the controller 44 is configured to return the motors 82, 85 to their calibrated positions upon power-up. In another embodiment, the calibrated position is obtained at 602. The calibrated position may be a desired or optimal position recorded during calibration / alignment advantageous for a particular application, e.g., the position where the beam is at a desired location at a particular instant (i.e., when calibration is performed). Calibration and alignment may be used synonymously herein. The calibrated position may be initially determined in a manufacturing setting (before the appliance is sent to the customer) and / or by an operator performing the calibration during use of the appliance, e.g., after a component has been replaced, after drift has occurred, etc. Calibration may be initiated by using the actuator 98. Thus, multiple calibrated positions are possible and may be stored in the controller 44. The most recent calibrated position stored in the controller 44 may be used to position the lenses 70, 71.

[0054] In operation 604, a sample is loaded into the optical instrument, and measurements or images are collected from the sample. Sample data is acquired while power to motors 82, 85 is maintained as long as the optical instrument 10 is on. Maintaining continuous power to motors 82, 85 enables positional reliability for maintaining the calibration positions of lenses 70, 71. Gravity can tend to pull on arms 80, 81 and move respective motor shafts 83, 86 from their calibration positions. Thus, maintaining power to motors 82, 85 counteracts the effects of gravity and maintains positional reliability. Feedback from rotary encoders 92, 93 is used to maintain the positions of lenses 70, 71 at their calibration positions. Encoder feedback may be used continuously as long as the optical instrument 10 is powered on. Using rotary encoders 92, 93 reduces the current required to maintain the calibration positions as long as the optical instrument 10 is on, and thus reduces heat.

[0055] In operation 606, the method determines whether another sample needs to be measured. If the answer is "YES", in 604, another sample is loaded and measured. Otherwise, in 607, the power to the optical instrument can be turned off.

[0056] Subsequent or intermediate further method steps in method 600 may be apparent from the above disclosure. For example, additional method steps may include using any of the components of the optical instrument 10 described herein and using any of the functions of the controller 44 described herein.

[0057] Accordingly, the present disclosure provides, among other things, beam steering mechanisms 22, 34 and an optical instrument 10 having beam steering mechanisms 22, 34. The present disclosure also provides a method of aligning a beam in an optical instrument 10. The various features and advantages of the present disclosure are set forth in the following sections and claims.

[0058] Item 1. An optical beam steering mechanism, the optical beam steering mechanism comprising: a first lens defining a first focal length having a first amplitude and a first polarity; and a second lens defining a second focal length having a second amplitude and a second polarity, the first amplitude and the second amplitude being substantially equal, the first polarity and the second polarity being opposite, the second lens being positioned to directly receive an optical beam passing through the first lens, at least one rotary motor being coupled to one of the first lens and the second lens and configured to swing the coupled lens within an arcuate path, the optical beam path of the optical beam passing through the second lens being adjustable by operating the rotary motor.

[0059] Item 2. The optical beam steering mechanism according to Item 1, wherein the first lens and the second lens are positioned substantially parallel to each other, and the arcuate path is in a plane substantially parallel to the first lens and the second lens.

[0060] Item 3. The optical beam steering mechanism according to either Item 1 or 2, wherein at least one rotary motor coupled to one of the first lens and the second lens includes a first rotary motor coupled to the first lens and a second rotary motor coupled to the second lens.

[0061] Item 4. The optical beam steering mechanism according to Item 3, wherein the first lens is swung around a first axis of rotation by the first rotary motor, the second lens is swung around a second different axis of rotation by the second rotary motor, and the first axis of rotation is parallel to the second axis of rotation.

[0062] Item 5. The optical beam steering mechanism according to Item 3, further comprising: a first motor shaft extending from the first rotary motor; a second motor shaft extending from the second rotary motor; a first rotary position encoder configured to sense a rotational position of the first motor shaft; and a second rotary position encoder configured to sense a rotational position of the second motor shaft.

[0063] Item 6. An electronic controller configured to receive feedback from a first rotational position encoder and a second rotational position encoder, the electronic controller further configured to adjust the positions of the first lens and the second lens based on the feedback, the optical beam steering mechanism according to item 5, further comprising the electronic controller.

[0064] Item 7. A first arm operably coupled to a first motor and configured to hold a first lens, the first arm defining a first radius from a first rotational axis of the first rotational motor to a center of the first lens, a first arm, a second arm operably coupled to a second motor and configured to hold a second lens, the second arm defining a second radius from a second rotational axis of the second rotational motor to a center of the second lens, the optical beam steering mechanism according to item 3, further comprising the second arm.

[0065] Item 8. The optical beam steering mechanism according to item 7, wherein the first radius and the second radius are substantially perpendicular to each other when the first lens and the second lens are centered.

[0066] Item 9. The optical beam steering mechanism according to item 7, wherein the first radius and the second radius are between 45 and 135 degrees from each other when the first lens and the second lens are centered.

[0067] Item 10. The first lens and the second lens are separated from each other by a distance that is a distance of 5% or less of the first amplitude, the optical beam steering mechanism according to any one of items 1 to 9.

[0068] Item 11. An optical instrument, comprising: an electromagnetic radiation source that generates an optical beam; a sample stage for holding a sample; a detector for receiving light from the sample; and at least one optical beam steering mechanism according to Item 1, wherein the optical beam steering mechanism is configured to direct the optical beam towards the sample stage or direct the light from the sample towards the detector.

[0069] Item 12. The optical instrument according to Item 11, wherein the detector is a spectrograph and the electromagnetic radiation source is configured to emit illumination light suitable for Raman spectroscopy.

[0070] Item 13. The optical beam steering mechanism includes a first rotary motor coupled to a first lens, a second rotary motor coupled to a second lens, a first rotary position encoder coupled to the first rotary motor, and a second rotary position encoder coupled to the second rotary motor. The optical instrument further includes an electronic controller configured to receive feedback from the first rotary position encoder and the second rotary position encoder, and the electronic controller is further configured to maintain the positions of the first lens and the second lens with respect to the optical beam based on the feedback as long as the power supply of the optical instrument is on. The optical instrument according to any one of Items 11 to 12.

[0071] Item 14. The optical instrument according to Item 13, wherein the electronic controller is further configured to operate the first rotary motor and the second rotary motor to align the optical beam with respect to the sample or the light from the sample with respect to the spectrograph, and store the positions of the first rotary position encoder and the second rotary position encoder corresponding to the calibration positions of the first lens and the second lens.

[0072] Item 15. The optical instrument according to Item 14, wherein the electronic controller is further configured to continuously supply power to the rotary motors to maintain the first lens and the second lens at the calibration positions while sample data is being acquired by the optical instrument.

[0073] Item 16. The optical device according to any one of Items 11 to 15, wherein at least one optical beam steering mechanism configured to direct an optical beam toward a sample stage or direct light from a sample toward a detector includes a first optical beam steering mechanism configured to direct an optical beam toward the sample stage and a second optical beam steering mechanism configured to direct light from the sample toward the detector.

[0074] Item 17. A method for aligning a beam in an optical device, the method comprising turning on the power of an optical device including a first lens and a second lens respectively driven by a first motor and a second motor, and further including a first motor position encoder and a second motor position encoder, wherein the first lens and the second lens define focal lengths of substantially equal amplitude and opposite polarities, and the second lens is positioned to directly receive the beam passing through the first lens, and operating the first motor and the second motor to move one or both of the first lens and the second lens to their respective calibration positions, the calibration positions corresponding to a desired optical beam path alignment for the beam to pass through the first lens and the second lens, maintaining power to the first motor and the second motor as long as the power of the optical device is on, and using feedback from the first motor position encoder and the second motor position encoder to maintain the calibration positions as long as the power of the optical device is on.

[0075] Item 18. The method according to Item 17, wherein the first motor and the second motor are rotary motors, and moving one or both of the first lens and the second lens to the calibration position includes operating one or both of the first rotary motor and the second rotary motor to swing one or both of the first lens and the second lens along their respective arcuate paths.

[0076] Item 19. The method according to any one of Items 17 to 18, wherein turning on the power of the optical device includes turning on the power of the spectroscopic microscope.

[0077] Item 20. The method according to any one of Items 17 to 19, further comprising determining a calibration position by performing image processing on a reference sample while adjusting one or both of the motors, and storing the calibration position.

Claims

1. A light beam steering mechanism, comprising: a first lens defining a first focal length having a first amplitude and a first polarity; a second lens defining a second focal length having a second amplitude and a second polarity, the first amplitude and the second amplitude being substantially equal and the first polarity and the second polarity being opposite, the second lens positioned to directly receive the light beam passing through the first lens; and at least one rotary motor coupled to one of the first lens and the second lens and configured to oscillate the coupled lens in an arcuate path, wherein a light beam path of the light beam passing through the second lens is adjustable by operating the rotary motor.

2. 2. The light beam steering mechanism of claim 1, wherein the first lens and the second lens are positioned substantially parallel to one another and the arcuate path lies in a plane substantially parallel to the first lens and the second lens.

3. 2. The light beam steering mechanism of claim 1, wherein at least one rotary motor coupled to one of the first lens and the second lens comprises a first rotary motor coupled to the first lens and a second rotary motor coupled to the second lens.

4. 4. The light beam steering mechanism of claim 3, wherein the first lens is oscillated about a first rotation axis by the first rotary motor, and the second lens is oscillated about a different second rotation axis by the second rotary motor, the first rotation axis being parallel to the second rotation axis.

5. a first motor shaft extending from the first rotary motor; a second motor shaft extending from the second rotary motor; a first rotational position encoder configured to sense a rotational position of the first motor shaft; 4. The light beam steering mechanism of claim 3, further comprising: a second rotational position encoder configured to sense a rotational position of the second motor shaft.

6. 6. The light beam steering mechanism of claim 5, further comprising an electronic controller configured to receive feedback from the first and second rotational position encoders, the electronic controller further configured to adjust positions of the first and second lenses based on the feedback.

7. a first arm operably coupled to the first rotary motor and configured to hold the first lens, the first arm defining a first radius from a first rotational axis of the first rotary motor to a center of the first lens; 4. The light beam steering mechanism of claim 3, further comprising: a second arm operably coupled to the second rotary motor and configured to hold the second lens, the second arm defining a second radius from a second axis of rotation of the second rotary motor to a center of the second lens.

8. 8. The light beam steering mechanism of claim 7, wherein the first radius and the second radius are substantially perpendicular to each other when the first lens and the second lens are centered.

9. 8. The light beam steering mechanism of claim 7, wherein the first radius and the second radius are between 45 and 135 degrees from each other when the first lens and the second lens are at center.

10. 2. The light beam steering mechanism of claim 1, wherein the first lens and the second lens are spaced apart from each other by the distance that is less than or equal to 5% of the first amplitude.

11. 1. An optical instrument comprising: an electromagnetic radiation source generating a light beam; a sample stage for holding a sample; a detector for receiving light from the sample; 13. An optical instrument comprising at least one light beam steering mechanism according to claim 1 , wherein the light beam steering mechanism is configured to either direct the light beam to the sample stage or direct the light from the sample to the detector.

12. 12. The optical instrument of claim 11, wherein the detector is a spectrograph and the electromagnetic radiation source is configured to emit illumination light suitable for Raman spectroscopy.

13. the optical beam steering mechanism includes a first rotary motor coupled to the first lens, a second rotary motor coupled to the second lens, a first rotary position encoder coupled to the first rotary motor, and a second rotary position encoder coupled to the second rotary motor; and the optical instrument includes:

12. The optical instrument of claim 11, further comprising an electronic controller configured to receive feedback from the first and second rotational position encoders, the electronic controller further configured to maintain a position of the first and second lenses relative to the light beam based on the feedback as long as the optical instrument is powered on.

14. 14. The optical instrument of claim 13, wherein the electronic controller is further configured to continuously supply power to the rotation motor to maintain the first lens and the second lens in a calibrated position while sample data is acquired by the optical instrument.

15. 14. A method for aligning a beam in an optical instrument according to claim 13, said method comprising: powering on the optical instrument; activating the first rotation motor and the second rotation motor to move one or both of the first lens and the second lens to a calibration position, respectively, the calibration position corresponding to a desired optical beam path alignment where the beam passes through the first lens and the second lens; maintaining power to the first rotation motor and the second rotation motor as long as the optical instrument is powered on; and maintaining the calibrated position as long as the optical instrument is powered on using feedback from the first rotational position encoder and the second rotational position encoder.

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