Method and system for aligning optical instruments

Abstract

A beam steering mechanism and a method of using the same. A beam 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 magnitude and the second magnitude are substantially equal and the first polarity and the second polarity are opposite, and wherein the second lens is positioned to directly receive a light beam passing through the first lens. The 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 lens coupled to the rotary motor in an arcuate path. A beam path of the beam passing through the second lens can be adjusted by operating the rotary motor.

Description

Technical Field

[0001] The present disclosure relates to methods and systems for aligning optical instruments 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 a beam steering mechanism that includes: a first lens that defines a first focal length having a first magnitude and a first polarity; and a second lens that defines a second focal length having a second magnitude and a second polarity. The first magnitude and the second magnitude are substantially equal and the first polarity and the second polarity are opposite, and wherein the second lens is positioned to directly receive a beam of light passing through the first lens. The beam steering mechanism further includes at least one rotary motor coupled to one of the first lens and the second lens and configured to swing the lens coupled to the rotary motor in an arcuate path. The beam path of the beam passing through the second lens can be adjusted by operating the rotary motor.

[0003] In another aspect, the present disclosure provides an optical instrument that includes: an electromagnetic radiation source that generates a beam of light; a sample stage for holding a sample; a detector for receiving light from the sample; and at least one beam steering mechanism. The beam steering mechanism includes: a first lens that defines a first focal length having a first magnitude and a first polarity; and a second lens that defines a second focal length having a second magnitude and a second polarity. The first magnitude and the second magnitude are substantially equal and the first polarity and the second polarity are opposite, and wherein the second lens is positioned to directly receive a beam of light passing through the first lens. The beam steering mechanism further includes at least one rotary motor coupled to one of the first lens and the second lens and configured to swing the lens coupled to the rotary motor in an arcuate path. The beam path of the beam passing through the second lens can be adjusted by operating the rotary motor. The beam steering mechanism is configured to direct the beam of light to the sample stage or direct the light from the sample to the detector.

[0004] In another aspect, the present disclosure provides a method for aligning a light beam in an optical instrument. The method includes: powering on the optical instrument, the optical instrument including a first lens and a second lens respectively driven by a first motor and a second motor, and the optical instrument further including a first motor position encoder and a second motor position encoder, wherein the first lens and the second lens define focal lengths having substantially equal magnitudes and opposite polarities, and wherein the second lens is positioned to directly receive the light beam passing through the first lens. The method further includes: actuating the first motor and the second motor to move one or both of the first lens and the second lens to a calibrated position, wherein the calibrated position corresponds to a desired light beam path alignment at which the light beam passes through the first lens and the second lens; and maintaining power to the first motor and the second motor as long as the optical instrument is powered on. The method further includes: using feedback from the first motor position encoder and the second motor position encoder to maintain the calibrated position as long as the optical instrument is powered on.

[0005] Other aspects of the present disclosure will become apparent in view of the detailed description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 is a schematic diagram of an optical instrument having a light beam path in accordance with the present disclosure.

[0007] Figure 2 is a schematic diagram illustrating the effect of misalignment of the light beam path in an optical instrument.

[0008] Figure 3 is a schematic diagram of a pair of lenses that can be used to adjust the light beam path in an optical instrument.

[0009] Figure 4 is in Figure 1 is a perspective view of a beam steering mechanism used in an optical instrument of

[0010] Figure 5 is Figure 4 is an orthographic view of the beam steering mechanism of

[0011] Figure 6 is a flowchart of a method in accordance with the present disclosure. DETAILED DESCRIPTION

[0012] An automatic alignment mechanism can be used to maintain the operation of an optical instrument (such as a spectral microscope, an infrared photothermal device, and other optical instruments) to prevent mechanical drift and interchange of optical components. For example, an automatic optical alignment mechanism can be used to maintain the operation of a spectral microscope to prevent mechanical drift and interchange of optical components.

[0013] In one example, a pair of lenses can be mounted sequentially along an optical axis. An angular deviation can be introduced by translating one lens relative to the other lens. Such an arrangement has been discussed in U.S. Patent No. 6,661,509, the full text of which is incorporated herein by reference and used for all purposes. The applicant recognizes that translating the lens requires a linear motor, which can be large and expensive. In cases where space is limited in an optical instrument, it may be difficult to attach an encoder to the linear motor. Additionally, during the operation of the optical instrument (such as during measurement), the linear motor needs to be powered off to reduce noise and heat, which may affect other optical components and introduce inaccuracies to the measurement results. Therefore, there is a need for a more compact, stable, reliable, and easy-to-control optical device to align a light beam in an optical instrument.

[0014] To address the above problems, a beam steering mechanism, an optical instrument including the beam steering mechanism, and a method for aligning a light beam are disclosed herein. These provide improved design flexibility and robustness while reducing size, cost, and complexity. The beam steering mechanism includes: a first lens that defines a first focal length having a first magnitude and a first polarity; and a second lens that defines a second focal length having a second magnitude and a second polarity, where the first magnitude and the second magnitude are substantially equal, and the first polarity and the second polarity are opposite. That is, the first lens and the second lens have substantially the same magnification, but one has a positive polarity (convex) while the other has a negative polarity (concave). The first lens and the second lens are configured to receive a light beam path passing through them. The second lens directly receives the light passing through the first lens. In other words, no optical component is positioned between the first lens and the second lens. In some examples, the beam steering mechanism may include only the first lens and the second lens without including other lenses. In one example, the first lens is positioned substantially parallel to the second lens. In one example, the first lens and the second lens are spaced a relatively small distance from each other. This distance can be 5% or less of the focal length, or 1% or less of the focal length, etc.

[0015] By operating a rotary motor coupled to the first lens or the second lens, at least one of the first lens and the second lens can swing in an arcuate path. The arcuate path is substantially parallel to the first lens or the second lens. By swinging one of the lenses, the optical path of the light beam passing through the two lenses is adjusted.

[0016] The lenses can be spaced a much smaller distance from each other than their focal lengths. The net optical power of the pair of lenses is approximately zero. When the lenses are centered with respect to each other, they do not produce a net optical effect. When one or both lenses are displaced relative to the light beam by operating the rotary motor, the net optical power remains substantially unchanged, but the lenses deflect the light beam by an angle in radians. where y is the displacement and f is the focal length of the lens. Since f can be large (e.g., 1000 mm), a large lens displacement can produce a very small angular deviation of the light beam. The focal length acts as a "lever" to reduce the effect of the lens displacement to a small beam deviation angle. In this way, a relatively coarse lens displacement can be used to precisely adjust the angular deviation of the light beam. The focal length can be greater than 100 mm.

[0017] Rotary motors are less expensive and take up less volume than linear motors. The applicant has found that it is unexpectedly effective to swing each of the lenses in an arc in achieving a beam control level comparable to that of a beam steering mechanism that uses dual-axis linear control to independently move a lens in the x and y directions. Such linear beam steering mechanisms require stepper linear actuators 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 itself provide sufficient constraint without the need to add additional components to constrain the movement of the lens to a reproducible path. The rotary system is also more vibration tolerant, e.g., better maintaining position accuracy than a linear motor regulator. In this way, alignment of the microscope can be achieved by applying a small angular deviation (e.g., about a few milliradians or less) to one or more beams via the beam steering mechanism. This configuration provides improved design flexibility and robustness while reducing size, cost, and complexity compared to translating the lens using a linear motor.

[0018] In some examples, at least one of the first lens and the second lens can 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 can be a rotary stepper motor driven with low current (e.g., having microstep drive). A rotary position encoder can be coupled to the shaft to measure the rotational position of the shaft. As an example, the encoder can provide 16,384 counts per revolution, or 61 microradians per count. The lens position can be precisely adjusted by operating the rotary motor based on encoder feedback.

[0019] In one example, each of 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 axis of rotation and the corresponding lens center. A first arm is operatively coupled to the first motor shaft and configured to hold the first lens, and a second arm is operatively coupled to the second motor shaft and configured to hold the second lens. Thus, the first arm may define a first radius between the portion of the arm coupled to the motor shaft (coinciding with the motor shaft axis) and the portion of the arm holding the lens (which defines the lens center), and the second arm may define a second radius in the same manner. When the lenses are centered, e.g., set to have any angle less than 180 degrees, these radii intersect transversely with each other. The lenses are centered when their optical axes overlap. In one example, when the lenses are centered on the optical axis, these radii may be perpendicular to each other. In other examples, these radii may be set at an angle of 85 degrees to 95 degrees, 80 degrees to 100 degrees, 70 degrees to 110 degrees, 60 degrees to 120 degrees, etc. relative to each other. In one example, a radius of 25 mm is sufficient to separate the body of the motor from the optical axis and results in a deviation of approximately 1.5 microns per count for the corresponding lens. Using lenses with focal lengths of +1000 mm and –1000 mm, the resulting angular deviation is 1.5 micro-radians per count. An electronic controller may be configured to receive feedback from the first rotary position encoder and the second rotary position encoder. The electronic controller may also be configured to maintain the positions (e.g., calibrated positions) of the first lens and the second lens based on the feedback.

[0020] The beam steering mechanism may be included in an optical instrument (such as a spectrometer, a microscope, an infrared photothermal device, a combination of the foregoing instruments) or any other instrument having an electromagnetic radiation source that defines a beam path. In some examples, 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 spectrometer to adjust the path of the beam collected by the spectrometer.

[0021] In one example, the optical instrument includes a beam steering mechanism that is powered on while acquiring sample data. That is, one or more rotary motors are powered on during data collection. The 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 having substantially equal magnitudes and opposite polarities. The first motor and the second motor can move one or both of the first lens and the second lens to a calibrated position before data acquisition. The calibrated position corresponds to a desired beam path alignment. Power is maintained to the first motor and the second motor as long as the optical instrument is powered on. Feedback from a first motor position encoder and a second motor position encoder can be used to hold the lenses in the calibrated position as long as the optical instrument is powered on. This provides position reliability throughout the measurement process, e.g., resisting gravity acting to swing the lenses away from the calibrated position. The first motor and the second motor can be rotary motors, but the method can be used with other types of motors to provide position reliability. The calibrated position of the lenses can be determined by a calibration process performed by the manufacturer or the user (e.g., by an actuator configured to trigger a calibration sequence programmed into the controller). Once determined, the calibrated position is stored in the controller. When the instrument is powered off, the calibrated position of the lenses may not be maintained, e.g., due to the pulling effect of gravity on the lenses. Thus, when the instrument is powered on, the controller is programmed to return the lenses to their most recently calibrated position. The encoder can facilitate returning the lenses to the calibrated position by finding a zero reference position and then moving to the calibrated position relative to the zero reference position, thus providing position repeatability accuracy. The user can periodically update the calibrated position after any change in environmental parameters (e.g., temperature) or before measuring a sample during the same work session. The encoder can provide continuous feedback to continue holding the lenses in the calibrated position against gravity, vibration, etc. as long as the instrument is on.

[0022] Before explaining any specific embodiments of the present disclosure in detail, it is to be understood that the present disclosure is not limited in its application to the details of the construction and arrangement of components set forth in the following description or illustrated in the following drawings. The present disclosure is capable of other embodiments and of being practiced or carried out in various ways.

[0023] In the present disclosure, "deviation" will refer to the angular deviation of the beam, and "displacement" will refer to the lateral displacement of the beam or the optical device away from the optical axis. "Optical" can refer to some or all of the electromagnetic spectrum. In some specific embodiments, "optical" can more specifically refer to the visible, ultraviolet, and infrared regions of the electromagnetic spectrum, and in still other specific embodiments, can even more specifically refer to the visible portion of the electromagnetic spectrum.

[0024] The optical instrument is in Figure 1The whole is shown generally at 10. The optical instrument 10 can be a spectral microscope system suitable for Raman spectroscopy, but the optical instrument 10 can include other types of optical systems having a beam path, such as, for example, confocal fluorescence microscopes, other photothermal devices, other spectroscopic devices, other types of microscopes, other combinations thereof, etc. The optical instrument 10 includes an optical microscope shown in simplified form within the dashed lines labeled 11 in Figure 1 The optical microscope 11 includes an objective lens 12 and one or more eyepieces 14, which can be used for direct viewing by an observer or which can form part of or supplement the lenses within a camera 15. Thus, light from a sample mounted on the stage 40 passes through the objective lens 12 in a conventional manner back to the eyepiece 14 on the beam path 17 to form an image that can be directly viewed by the operator or viewed using the camera 15 and a video display terminal.

[0025] In Figure 1 the optical instrument 10, illumination light suitable for Raman spectroscopy can be provided from a light source 20 (usually a laser) on an illumination beam path 21 through a beam steering mechanism 22 to a deflection mirror and a notch filter 24, which redirects the illumination beam path 21 towards a Raman interface module deflection mirror 26. The deflection mirror 26 can be made as a plane mirror or a dichroic mirror mounted on a motorized slide for selectively inserting and removing from the beam path 17. When the deflection mirror 26 is moved into position in the beam path 17, the deflection mirror deflects the illumination beam path 21 to become collinear with the microscope beam path 17. The objective lens 12 focuses the illumination beam onto a focal point 28. In other specific embodiments, the optical instrument 10 can include any source of electromagnetic radiation.

[0026] The optical instrument 10 further includes a Raman return beam path 30 which includes scattered light collected by the objective lens 12 and formed into a collimated beam, and the collimated beam is deflected by the deflection mirror 26 onto a path collinear with the illumination beam path 21 until it reaches the position of the notch filter 24. The notch filter 24 is made to transmit the wavelength of the Raman radiation in the return beam path 30 and reflect the wavelengths of the illumination beam path 21 and the Rayleigh radiation. The notch filter 24 can be a holographic filter and is used for Rayleigh suppression in the manner described in F.J. Bergin, Spectrochemica Acta, Vol. 46A, No. 2, 1990, pp. 153-159. After passing through the notch filter 24, the Raman radiation in the return beam path 30 passes through the beam steering mechanism 34 and through the input lens 35 which focuses the return beam path 30 towards the input aperture 36 of the spectrometer 37. The spectrometer 37 can be made to spatially distribute the wavelengths of the light subsequently incident on the detector 38, and the detector detects the intensities of light of various wavelengths to provide an output signal indicative of the Raman spectrum of the sample.

[0027] When the optical instrument 10 is being aligned, a reference sample (such as an alignment instrument 39) can be mounted on the stage 40. As further explained below, the alignment instrument 39 includes a spatially restricted stage entrance aperture 41 which 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 instrument 39 on lines 162, 168 and receives signals from the alignment instrument. In addition, the controller 44 is connected to the light source 20 via the control line 46, to the beam steering mechanism 22 via the line 47, to the detector 38 via the line 48, and to the beam steering mechanism 34 via the line 49. As further discussed below, once the operator has positioned the alignment instrument 39, the controller 44 can perform automatic alignment adjustments using the beam steering mechanisms 22, 34 under software control so that the stage entrance aperture 41 is aligned with the focal point of the optical instrument 10.

[0028] The effects of misalignment of the beam within the optical instrument 10 are in Figure 2is illustrated, which shows the illumination beam path 21 passing through the objective lens 12 and focusing on the focal point 28 located in the focal plane 51 of the microscope 11. According to r = fθ (where r = the spatial translation away from the center of the optical axis, f = the focal length of the lens, and θ = the angular deviation of the beam), the angular deviation (see 21') in the collimated portion of the illumination beam path 21 is transformed into a spatial translation r (see 28') at the focal plane. For example, the focal length of a 100× objective lens 12 is 1.6 mm, that of a 50× is 3.2 mm, and that of a 20× is 8 mm. As an example, the typical focal length of the spectrometer input is 40 mm.

[0029] 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 spectrometer entrance aperture 36. The beam steering mechanisms 22, 34 can be disposed anywhere in any of the beam paths disclosed herein or in any other beam path of a beam in any device. Adjustment signals are fed to the beam steering mechanisms 22, 34 by a controller 44 that receives inputs respectively from a detector 38 (discussed below) and from an alignment instrument 39 located on or within the sample stage 40 of the microscope 11. The alignment instrument 39 includes a stage entrance aperture 41 that is positioned by an operator by observing the alignment instrument 39 using the eyepiece optics 14 and / or the camera 15 to coincide with the central axis of the microscope beam path 17. The alignment instrument 39 includes within it a stage light source 160 (e.g., a high-intensity light-emitting diode (LED)) and a stage light sensor 165 (e.g., a silicon photodiode positioned to receive light transmitted through the LED / stage light source 160) actuated by a line 162 in communication with the controller 44, where the stage light sensor 165 transmits a stage light sensor output signal along a line 168 to the controller 44 in response to the receipt of light. In one example, the controller 44 performs alignment by turning on the stage light source 160 and then controlling the beam steering mechanism 34 until the return beam path 30 from the stage light source 160 is recorded at maximum intensity on the detector 38, indicating that if a return beam path 30 is generated via the illumination beam path 21 from the light source 20, such a return beam path 30 will also be well aligned with the spectrometer entrance aperture 36 and the detector 38. Similarly, the beam steering mechanism 22 can be controlled by the controller 44 until the stage light sensor 165 measures a maximum output from the light source 20, indicating that the illumination beam path 21 is correctly aligned. In other words, the input or reference beam for spectrometry is optimized via the beam steering mechanism 22 by a signal from the stage light sensor 165 in the alignment instrument 39 (where the stage light sensor 165 is excited by the light source 20), and the return beam path 30 for spectrometry is optimized via the beam steering mechanism 34 by a signal from the detector 38 in the spectrometer 37 (where the detector 38 is excited by the stage light source 160). Note that the controller 44 communicates with the light source 20 via a line 46, with the beam steering mechanism 22 via a line 47, with the detector 38 via a line 48, and with the beam steering mechanism 34 via a line 49, and communicates with the stage light sensor 165 via a line 168 and with the stage light source 160 via a line 162. Once alignment is achieved, the alignment instrument 39 can be removed from the sample stage 40 (if it is not built in) so that the microscope 11 can be used to analyze the sample.The current positions of the beam steering mechanisms 22 and 34 can be set to calibrated positions and stored in the non-transitory memory of the controller. It should be understood that a "line" can be embodied as a wired connection or a wireless connection.

[0030] In another example, which can be performed separately or in combination with the above alignment method, alignment of the microscope beam path 17 is performed by having the viewer light sensor 15 receive the microscope alignment light signals from the optical elements 12, 26, and 14 and generating a corresponding output signal from the viewer light sensor 15. Subsequently, the output signal from the viewer light sensor 15 (e.g., via line 170) is supplied to the controller 44, which can reposition the stage light source 160 (or more generally, the alignment instrument 39) in response to the output signal from the viewer light sensor 15. As an example, if the viewer light sensor 15 is provided in the form of a camera, the controller 44 can utilize the pixel values captured by the camera 15 and can supply instructions to move the alignment instrument 39 such that the maximum / brightest pixel value is centered within the pixel array (i.e., such that the stage light source 160 is aligned with the central axis of view of the viewer light sensor / camera 15). Movement of the alignment instrument 39 can be achieved by using a suitable actuator 176 configured to be controlled by the controller 44 (e.g., via line 173).

[0031] The spectrometer 37 also includes a return light source 172 that can be positioned in line with the spectrometer entrance aperture 36 and the optical elements 35, 24, and 26, and the return light source can be actuated to emit a spectrometer alignment optical signal through the spectrometer entrance aperture 36. Subsequently, the optical elements 35, 24, 26, and 12 can deliver the alignment optical signal to the alignment instrument 39. The stage light sensor 165 then emits an output signal in response to any spectrometer alignment optical signal received through the stage entrance aperture 41. Subsequently, the output signal from the stage light sensor 165 can be supplied to the controller 44 (e.g., via line 168), and the controller can reposition the stage light sensor 165 (and / or adjust the beam steering mechanism 34) to maximize the output signal from the stage light sensor 165, thereby indicating that the return beam 30 has achieved proper alignment. It is noted that while this arrangement may appear to duplicate the alignment achieved by using the stage light source 160 and the detector 38, alignment by using the return light source 172 and the stage light sensor 165 can be advantageous because the return light source 172 emits an "ideal" alignment signal: the signal is emitted from the spectrometer entrance aperture 36, which has a fixed position (different from the movable position of the stage entrance aperture 41), and the alignment optical signal is projected from the spectrometer entrance aperture 36 onto the alignment instrument 39. Subsequently, the spot from the alignment optical signal can be visually aligned with the stage entrance aperture 41 (and the stage light sensor 165) by the user approximately, and precise alignment can occur between the spectrometer entrance aperture 36 and the stage light sensor 165 by repositioning the alignment instrument 39 by the controller 44 to obtain signal maximization.

[0032] Within the spectrometer 37, the return light source 172 is preferably capable of moving between an emission position and an inactive position (shown in dashed lines at 172i), in the emission position, the return light source 172 emits a spectrometer alignment optical signal through the spectrometer entrance aperture 36 and emits it to the optical elements, in the inactive position, the return light source 172 does not emit a spectrometer alignment optical signal through the spectrometer entrance aperture 36. This allows the spectrometer 37 to be used for normal purposes (i.e., receiving light into the spectrometer entrance aperture 36 for delivery to the detector 38), or emitting a spectrometer alignment optical signal from the spectrometer entrance aperture 36 for delivery to the stage light sensor 165. As an alternative to moving the return light source 172, a movable reflector 174 can be provided that receives the spectrometer alignment optical signal and redirects it through the spectrometer entrance aperture 36 and to the optical elements, where the reflector 174 is capable of moving between an inactive position (at the position of the reflector 174 shown) and an emission position (at the position occupied by the return light source 172 in Figure 1 the position of the reflector 174 shown) and an emission position (at the position occupied by the return light source 172 in Figure 1 ).

[0033] Regarding the use of Figure 1Further details of the alignment methods of the illustrated components are disclosed in US Pat. No. 6,661,509 and US Pat. No. 7,460,229, both of which are incorporated herein by reference in their entirety.

[0034] Figure 3 The arrangement of each of the beam steering mechanisms 22 and 34 for adjusting the beams 21 and 30 is schematically shown. The beam steering mechanisms 22, 34 have substantially the same configuration as one another and differ only in their placement within the optical instrument 10, so 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 mounted in sequence (in the beam path 21 or 30). One or both of the lenses 70 and 71 (e.g., as Figure 2 The lens 71 shown is mounted for movement in a plane perpendicular to an optical axis 73 (eg, a central axis) of the incident light beam 21 or 30. No other optical components are positioned between the lenses 70 and 71.

[0035] Figure 3 The pair of lenses 70, 71 is schematically shown for deflecting the light beam. The light beam passes through the pair of lenses 70, 71, the focal lengths f1, f2 of the pair of lenses (respectively) having substantially equal magnitude but opposite polarity and being spaced apart from each other by a distance d much smaller than the focal length (e.g., "much smaller" may mean that the distance d is 5 times the focal length). , % or less, or may mean that the distance d is 1% or less of the focal length, etc., so that the total optical power 1 / f is unimportant for use with the alignment device). Any suitable focal length magnitudes may be used. "Substantially equal magnitudes" means so close in magnitude to one another as to have zero net optical power or close to zero net optical power, as given by the "compound lens formula" explained herein. As an example, the focal length of the first lens 70 may be +1000 and the focal length of the second lens 71 may be -1000 mm. In this example, the distance d may be 50 mm or less. For example, the distance d may be 10 mm. The net optical power of the pair of lenses 70, 71 is approximately P≈1 / f+1 / (-f), which is zero or approximately zero. When the lenses are centered with respect to each other, they produce substantially no net optical effect. When a lens is displaced relative to the beam 21, 30, the net optical power is substantially unchanged, but the lens deviates the beam 21, 30 by an angle α in radians (α≈y / f, where y is the displacement and f is the focal length of the lens 70, 71). Because f can be large (e.g., 1000 mm), large displacements can produce very small amounts of deviation. The focal length acts as a "lever" to reduce the effect of the displacement to small angles.

[0036] The "compound lens formula" gives the total optical power 1 / f of a 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:

[0037]

[0038] Since d is much smaller than f1 and f2, the contribution of the third term is almost zero. Since the lenses have opposite focal lengths, the sum of the first two terms is zero or close to zero. Therefore, the lens pair has essentially no net optical power.

[0039] As Figure 5 best illustrated, in the illustrated specific implementation, each lens 70, 71 has corresponding diameters D1, D2 of approximately 25 mm. In some specific implementations, the diameters D1, D2 can be 10 mm to 100 mm, or more specifically 15 mm to 50 mm, or even more specifically 20 mm to 30 mm. However, depending on the application, the diameters D1, D2 can have any desired value.

[0040] In the illustrated specific implementation, as Figures 4 to 5 shown, the first lens 70 can 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 can 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. "Direct drive" can also include using shaft encoders or other types of encoders (to be described in more detail below) disposed between the motors 82, 85 and the arms 80, 81. Each motor 82, 85 swings the corresponding lens 70, 71 in an arc (α and β respectively). The corresponding radii R1, R2 of each arc are large enough such that swinging each corresponding lens 70, 71 provides an approximately linear motion in the corresponding X and Y directions (i.e., in an arc path with a relatively large radius R), where the influence of the arc is relatively small, as explained in more detail mathematically below. At a minimum, R must be greater than the physical radius of the motor such that the motor does not block the light beam. In a preferred arrangement, R is approximately 10 times the diameter of the laser beam, which minimizes the coupling between the two axes of motion and maintains a sufficient gap for the light beam passing through the two lenses. When the lenses 70, 71 are centered on the optical axis 73, e.g., set at any angle less than 180 degrees, the radii R1, R2 intersect transversely with each other. In the illustrated specific implementation, when the lenses 70, 71 are centered on the optical axis 73, the radii R1, R2 are perpendicular to each other. In other examples, the radii R1, R2 can be set at angles such as 85 degrees to 95 degrees, 80 degrees to 100 degrees, 70 degrees to 110 degrees, 60 degrees to 120 degrees, 45 degrees to 135 degrees, etc.

[0041] Figure 5 Illustrates the movement of lenses 70, 71. Motors 82, 85 swing angles α and β, and the pivot axes 90, 91 of each of motors 82, 85 are respectively at distances R1, R2 from the optical axis 73. The centers of lenses 70, 71 are offset by the following amounts:

[0042] y≈R(sinβ + cosα - 1)

[0043] x≈R(sinα + cosβ - 1).

[0044] Given the approximations sin x≈x and cos x≈1, when the angles are small, this mechanism provides approximately orthogonal coordinate axes x and y:

[0045] y≈Rβ

[0046] x≈Rα.

[0047] As Figure 4 illustrated, the first motor 85 and the second motor 82 are mounted to the base 87. Arms 80, 81 are respectively attached to the shafts 83, 86 of motors 82, 85. There is sufficient clearance between motors 82, 85 such that arms 80, 81 do not collide with shafts 83, 86, and the light beam is not blocked by either motor 82, 85. The base 87 includes a hole 88 through which the light beam can pass, such that the base 87 does not block the light beam.

[0048] Lens 70 can be directly mounted to arm 80, which can be directly mounted to motor 82; and lens 71 can be directly mounted to arm 81, which can be directly mounted to motor 85. Both motors 82, 85 can be powered by a controller 44 to drive lenses 70, 71 to a desired position. Motors 82, 85 preferably operate independently of each other such that new measurements can be made at each step (e.g., in a raster pattern). In the illustrated embodiment (see Figure 4 ), position encoders 92, 93 (e.g., position sensors) can be respectively coupled to each motor 82, 85. Position encoders 92, 93 provide feedback signals to the controller 44 corresponding to the rotational positions of the respective motor shafts 83, 86. The feedback signals can travel along lines 47, 49 ( Figure 1) Feedback from encoders 92, 93 can be used by controller 44 to control motors 82, 85 to maintain the desired positions of lenses 70, 71. Encoders 92, 93 can be configured to provide absolute feedback signals or incremental feedback signals with any desired resolution. The encoders can have any suitable configuration, e.g., shaft-mounted, hollow-shaft, ring-mounted, etc. The encoders can sense position optically, magnetically, or using any other suitable principle. In one example, motors 82, 85 are rotary stepper motors driven with low current (e.g., with microstep drive), where encoders 92, 93 (e.g., rotary position encoders) are coupled to the rotary stepper motors to provide closed-loop feedback. As an example, encoders 92, 93 can provide 16,384 counts per revolution, or 61 micro-radians per count. However, encoder resolutions from 10 micro-radians to 250 micro-radians per count are readily available and can be employed if they meet the requirements of the application. In one example, radii R1, R2 of 25 mm are sufficient to separate the bodies of motors 82, 85 from the optical axis 73 and result in a deviation of approximately 1.5 microns per count for lenses 70, 71. With lenses 70, 71 having focal lengths of +1000 mm and –1000 mm, the resulting angular deviation is 1.5 micro-radians per count. This example also holds if the lenses (e.g., –1000 mm and +1000 mm) are swapped. Ray tracing modeling has shown that this focal length is sufficient to avoid adding unacceptable levels of aberration to the light beam when lenses 70, 71 are eccentric. In one example, the Raman microscope can preferably have an objective lens 12 (commercial “100x” objective lens) with a focal length of 1.8 mm and a numerical aperture of 0.9, and achieve a spatial resolution of approximately 0.3 microns at visible light wavelengths. This spatial resolution corresponds to a deviation of approximately 170 micro-radians.

[0049] With a resolution of 1.5 micro-radians, the beam steering mechanisms 22, 34 can accurately “find” the center of a spot that is 170 micro-radians wide in angle. At the same time, lenses 70, 71 with a 25 mm clear aperture will allow control of a 5 mm diameter beam over a total angular range of 20 milliradians, which has been found to be sufficient to cover the mechanical tolerances between these optical components when multiple optical components are interchanged within the system. Thus, the system has sufficient resolution and range to: 1) correct misalignments that occur during storage and use of the instrument (e.g., due to thermal drift, mechanical creep, etc.), and 2) correct changes in alignment of other components in the system (e.g., when one component is replaced by another).

[0050] By shifting one or both of the lenses 70, 71 from the optical axis 73 of the input beam 75, an angular deviation is provided to the beam passing through the lens. Such mechanisms allow significant mechanical advantages, thus allowing the use of motor drives with relatively coarse mechanical resolution. Therefore, the deviation angle α can be controlled using the movement of the arcuate lens.

[0051] The controller 44 can 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 can 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 can include a combination of different types of memories (such as read-only memory (“ROM”), random access memory (“RAM”) (e.g., dynamic RAM [“DRAM”], synchronous DRAM [“SDRAM”], etc.), electrically erasable programmable read-only memory (“EEPROM”), flash memory, hard disk, SD card, or other suitable magnetic, optical, physical, electronic memory devices or other data structures). The control system 44 can also or alternatively include integrated circuits and / or analog devices (e.g., transistors, comparators, operational amplifiers, etc.) to perform the functions described herein.

[0052] As an example, the controller 44 can be configured to adjust the positions of the lenses 70, 71. The controller 44 can automatically perform the adjustment or calibration in response to an input signal and stop the adjustment when the desired position is found. The input signal can communicate with the controller 44 to initiate the control of one or both of the motors 82, 85 and perform the calibration adjustment based on the feedback. The input signal can be sent as part of the manufacturing process to align the beam and / or can be sent by an operator on-site. The input signal can be sent through an actuator 98 ( Figure 1 ) or automatically sent by an algorithm programmed into the controller 44 (e.g., programmed to periodically initiate calibration). In one example, an actuator 98 is provided to initiate the calibration of one or both of the beam steering mechanisms 22, 34 via a control line 99. In other examples, a separate actuator can be provided for each of the beam steering mechanisms 22, 34. The actuator 98 can be any type of actuator capable of receiving manual input, such as a button, a touch screen, a voice command receiver, etc. The actuator 98 can be physically disposed on the optical instrument 10 or located away from the optical instrument 10. For example, the remote actuator 98 can include an application or program on a smart phone, a tablet computer, a computer, or other device that wirelessly communicates with the optical instrument 10.

[0053] In operation, the beam steering mechanisms 22, 34 are used to align one or more beams of the optical instrument. Figure 6A flowchart illustrating a method 600 of operating an optical instrument 10 and aligning the optical instrument prior to sample measurement is shown. Method 600 may include any combination of any one or more of steps 601-606, as well as other additional and intermediate steps that will be apparent from the present disclosure. At step 601, the optical instrument 10 is powered on and begins receiving power. One or more rotary motors receive power and are actuated. At least steps 602-605 may involve the use of a controller 44, for example, to automatically perform these steps. At step 602, when the optical instrument 10 is powered on, each respective motor shaft 83, 86 is moved to a zero position. The zero position may be found using encoders 92, 93, each of which has a zero position reference that returns each respective motor shaft 83, 86 to the zero position. In a preferred embodiment, the motor is moved to a calibrated position (such as an "index" position on the encoder itself), and then to a "zero" position, which may be a stored distance away from the index position. The index position is a characteristic of the encoder itself. The zero position is acceptably close to a position where the angular deviation of the light beam is zero. The index position and the zero position may vary slightly due to assembly variations (such as when a lens is not attached to the shaft at exactly the correct location, for example). However, the index position is repeatable, and thus, it is reliable to first find the index position and then travel a known number of steps to reach the zero position. Other ways of determining the zero position are also possible, such as using optical limit switches, over-driving arms 80, 81 against stops, etc.

[0054] At 602, the method optionally includes providing an actuator 98 configured to trigger calibration or alignment of one or both of a first lens 70 and a second lens 71. For alignment, an alignment instrument (such as the alignment instrument 39 in Figure 1 may be loaded into the optical instrument. The actuator 98 may be actuated by the manufacturer or the user at any time as long as the optical instrument 10 is on. Calibration includes: using the controller 44 to determine the desired beam path alignment, as discussed in more detail above; and storing the corresponding calibrated position in the controller 44, for example, when drift or exchange of optical components causes a change in the beam path. The new calibrated position may become the most recently calibrated position, such that if the optical instrument 10 is turned off, the new calibrated position is returned when the optical instrument 10 is powered on (see step 601).

[0055] At step 603, one or both of the lenses 70, 71 are moved to a calibrated position by moving the respective motor shafts 83, 86 to a calibrated shaft position relative to a zero position reference. The movement can include swinging one or both of the lenses 70, 71 in an arc. In one example, 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 example, the calibrated positions are obtained at 602. The calibrated position can be a desired or optimal position recorded during calibration / alignment that is advantageous for a particular application, e.g., the position at which the light beam is in a desired orientation at a particular moment (i.e., when calibration occurs). Calibration and alignment can be used as synonyms herein. The calibrated position can be initially determined in a manufacturing setting (before the instrument is shipped to the customer), and / or can be determined by an operator performing the calibration during use of the instrument (e.g., after components have been exchanged, drift has occurred, etc.). Calibration can be initiated by using the actuator 98. Thus, multiple calibrated positions are possible and can be stored in the controller 44. The most recently calibrated position stored in the controller 44 can be used to position the lenses 70, 71.

[0056] At step 604, a sample is loaded into the optical instrument, and measurements or images are collected from the sample. Sample data is acquired while maintaining power to the motors 82, 85 as long as the optical instrument 10 is on. Maintaining continuous power to the motors 82, 85 allows for position reliability in maintaining the calibrated positions of the lenses 70, 71. Gravity can tend to pull on the arms 80, 81 and move the respective motor shafts 83, 86 out of their calibrated positions. Thus, maintaining power to the motors 82, 85 counteracts the effect of gravity to maintain position reliability. Feedback from the rotary encoders 92, 93 is used to hold the positions of the lenses 70, 71 at the calibrated positions. Encoder feedback can be used continuously as long as the optical instrument 10 is powered on. Using the rotary encoders 92, 93 while the optical instrument 10 is on reduces the current required to maintain the calibrated positions, which in turn reduces heat.

[0057] At step 606, the method checks whether another sample needs to be measured. If the answer is "yes", another sample is loaded and measured at 604. Otherwise, the optical instrument can be powered off at 607.

[0058] Additional method steps subsequent to or intermediate in method 600 may be apparent from the foregoing disclosure. For example, additional method steps can 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.

[0059] Accordingly, the present disclosure also provides beam steering mechanisms 22, 34 and an optical instrument 10 having the beam steering mechanisms 22, 34. The present disclosure also provides a method for aligning a beam in the optical instrument 10. The various features and advantages of the present disclosure are set forth in the appended articles and claims.

[0060] Article 1. A beam steering mechanism, the beam steering mechanism comprising: a first lens defining a first focal length having a first magnitude and a first polarity; a second lens defining a second focal length having a second magnitude and a second polarity, wherein the first magnitude and the second magnitude are substantially equal and the first polarity and the second polarity are opposite, and wherein the second lens is positioned to directly receive a 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 swing the lens coupled to the rotary motor in an arcuate path, wherein the beam path of the beam passing through the second lens can be adjusted by operating the rotary motor.

[0061] Article 2. The beam steering mechanism according to Article 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.

[0062] Article 3. The beam steering mechanism according to any one of Articles 1 to 2, wherein the 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.

[0063] Article 4. The beam steering mechanism according to Article 3, wherein the first lens is swung about a first axis of rotation by the first rotary motor, the second lens is swung about a different second axis of rotation by the second rotary motor, and the first axis of rotation is parallel to the second axis of rotation.

[0064] Article 5. The beam steering mechanism according to Article 3, the beam steering mechanism 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 the rotational position of the first motor shaft; and a second rotary position encoder configured to sense the rotational position of the second motor shaft.

[0065] Clause 6. The beam steering mechanism according to Clause 5, wherein the beam steering mechanism further comprises: an electronic controller configured to receive feedback from the first rotational position encoder and the second rotational position encoder, wherein the electronic controller is further configured to adjust the position of the first lens and the position of the second lens based on the feedback.

[0066] Clause 7. The beam steering mechanism according to Clause 3, wherein the beam steering mechanism further comprises: a first arm operatively coupled to the first motor and configured to hold the first lens, the first arm defining a first radius from the first rotational axis of the first rotational motor to the center of the first lens; and a second arm operatively coupled to the second motor and configured to hold the second lens, the second arm defining a second radius from the second rotational axis of the second rotational motor to the center of the second lens.

[0067] Clause 8. The beam steering mechanism according to Clause 7, wherein when the first lens and the second lens are centered, the first radius and the second radius are substantially perpendicular to each other.

[0068] Clause 9. The beam steering mechanism according to Clause 7, wherein when the first lens and the second lens are centered, the first radius and the second radius are at an angle of 45 degrees to 135 degrees with respect to each other.

[0069] Clause 10. The beam steering mechanism according to any one of Clauses 1 to 9, wherein the first lens and the second lens are spaced apart from each other by a distance, wherein the distance is 5% or less of the first magnitude.

[0070] Clause 11. An optical instrument, comprising: an electromagnetic radiation source that generates a beam; a sample stage for holding a sample; a detector for receiving light from the sample; and at least one beam steering mechanism according to Clause 1, wherein the beam steering mechanism is configured to direct the beam to the sample stage or direct the light from the sample to the detector.

[0071] Clause 12. The optical instrument according to Clause 11, wherein the detector is a spectrometer, and the electromagnetic radiation source is configured to emit illumination light suitable for Raman spectroscopy.

[0072] Clause 13. The optical instrument according to any one of Clauses 11 to 12, wherein the 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, a second rotary position encoder coupled to the second rotary motor, and the optical instrument further includes: an electronic controller configured to receive feedback from the first rotary position encoder and the second rotary position encoder, wherein the electronic controller is further configured to maintain the positions of the first lens and the second lens relative to the beam based on the feedback as long as the optical instrument is powered on.

[0073] Clause 14. The optical instrument according to Clause 13, wherein the electronic controller is further configured to: operate the first rotary motor and the second rotary motor to align the beam relative to the sample or to align the light from the sample relative to the spectrometer; and store the positions of the first rotary position encoder and the second rotary position encoder, the positions corresponding to the calibrated positions of the first lens and the second lens.

[0074] Clause 15. The optical instrument according to Clause 14, wherein the electronic controller is further configured to continuously supply power to the rotary motors to hold the first lens and the second lens at the calibrated positions while the optical instrument acquires sample data.

[0075] Clause 16. The optical instrument according to any one of Clauses 11 to 15, wherein the at least one beam steering mechanism configured to direct the beam to the sample stage or to direct the light from the sample to the detector includes: a first beam steering mechanism configured to direct the beam to the sample stage; and a second beam steering mechanism configured to direct the light from the sample to the detector.

[0076] Clause 17. A method for aligning a light beam in an optical instrument, the method comprising: powering on the optical instrument, the optical instrument including a first lens and a second lens respectively driven by a first motor and a second motor, and the optical instrument further including a first motor position encoder and a second motor position encoder, wherein the first lens and the second lens define focal lengths having substantially equal magnitudes and opposite polarities, and wherein the second lens is positioned to directly receive the light beam passing through the first lens; actuating the first motor and the second motor to move one or both of the first lens and the second lens to a calibrated position, wherein the calibrated position corresponds to a desired light beam path alignment at which the light beam passes through the first lens and the second lens; maintaining power to the first motor and the second motor as long as the optical instrument is powered on; and using feedback from the first motor position encoder and the second motor position encoder to maintain the calibrated position as long as the optical instrument is powered on.

[0077] Clause 18. The method according to clause 17, wherein the first motor and the second motor are rotary motors, and wherein moving one or both of the first lens and the second lens to the calibrated position includes: actuating 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.

[0078] Clause 19. The method according to any one of clauses 17 to 18, wherein powering on the optical instrument includes: powering on a spectral microscope.

[0079] Clause 20. The method according to any one of clauses 17 to 19, the method further comprising: determining the calibrated position by imaging a reference sample while adjusting one or both of the motors and storing the calibrated position.

Claims

1. A light beam steering mechanism, comprising: a first lens defining a first focal length having a first magnitude and a first polarity; a second lens defining a second focal length having a second magnitude and a second polarity, wherein the first magnitude and the second magnitude are substantially equal and the first polarity and the second polarity are opposite, and wherein the second lens is positioned to directly receive the light beam that passed through the first lens; and At least one rotary motor is coupled to one of the first lens and the second lens and is configured to swing the lens coupled to the rotary motor in an arc path, wherein the beam path of the light beam passing through the second lens can be adjusted by operating the rotary motor.

2. The beam steering mechanism of claim 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.

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

4. The beam steering mechanism according to claim 3, wherein the first lens is swung around a first rotation axis by the first rotation motor, and the second lens is swung around a different second rotation axis by the second rotation motor, and the first rotation axis is parallel to the second rotation axis.

5. The light beam steering mechanism according to claim 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 is configured to sense a rotational position of the second motor shaft.

6. The light beam steering mechanism according to claim 5, further comprising: An electronic controller is configured to receive feedback from the first rotary position encoder and the second rotary position encoder, wherein the electronic controller is further configured to adjust the position of the first lens and the second lens based on the feedback.

7. The light beam steering mechanism according to claim 3, further comprising: a first arm operatively coupled to the first motor and configured to hold the 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; and A second arm is operatively coupled to the second motor and configured to hold the 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.

8. The 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. The beam steering mechanism of claim 7, wherein when the first lens and the second lens are centered, the first radius and the second radius are 45 degrees to 135 degrees from each other.

10. The beam steering mechanism of claim 1, wherein the first lens and the second lens are spaced a distance from each other, wherein the distance is 5% or less of the first magnitude.

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

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

13. The optical instrument of claim 11, wherein the beam steering mechanism comprises 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, a second rotary position encoder coupled to the second rotary motor, and the optical instrument further comprises: An electronic controller configured to receive feedback from the first rotary position encoder and the second rotary position encoder, wherein the electronic controller is further configured to maintain the position of the first lens and the second lens relative to the light beam based on the feedback as long as the optical instrument is powered on.

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

15. A method for aligning a light beam in an optical instrument according to claim 13, the method comprising: applying power to the optical instrument; actuating the first motor and the second motor to move one or both of the first lens and the second lens, respectively, to a calibrated position, wherein the calibrated position corresponds to a desired beam path alignment at which the light beam passes through the first lens and the second lens; maintaining power to the first motor and the second motor as long as the optical instrument is powered; as well as Feedback from the first motor position encoder and the second motor position encoder is used to maintain the calibrated position as long as the optical instrument is powered on.

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