An optical device

Abstract

A spectroscopy apparatus comprising an optical input (205), a plurality of laser sources (201a to 20 If) and an optical device (100). The optical device (100) comprises a shaft (102) mounted for rotation about a longitudinal axis (A-A), a motor (103) for driving rotation of the shaft (102) and a plurality of mirrors (104a to 104f) mounted to the shaft (102). Each mirror (104a, 104b, 104c, 104d, 104e, 104f) is mounted at a different axial position along the shaft (102) and a different circumferential position about the shaft (102). The optical device (100) is configured such that, for different rotary positions of the shaft (102), a different one of the mirrors (104a to 104f) reflects a corresponding laser beam from a different one of the laser sources (201a to 20 If) to the optical input (205).

Description

[0001] AN OPTICAL DEVICE

[0002] Field of Invention

[0003] This invention concerns an optical device and, in particular, an optical device for directing a beam selected from any one of a plurality of beams to an optical input of an optical apparatus, for example of a spectroscopy apparatus such as a Raman spectroscopy apparatus. The plurality of beams may be a plurality of laser beams.

[0004] Background

[0005] The Raman Effect is a phenomenon in which a sample scatters incident light of a given frequency into a frequency spectrum, which has characteristic peaks caused by interaction of the excitation light, typically a laser beam, with the molecules making up the sample. Different molecular species have different characteristic Raman peaks, and so the effect can be used to analyse the molecular species present. Raman spectroscopy apparatus are configured to detect the Raman scattered light for analysis.

[0006] It is known to provide multiple laser sources in Raman spectroscopy apparatus to enable excitation of the sample with different wavelengths of light. In such apparatus an optical device is provided for directing a laser beam selected from any one of a plurality of laser beams to an optical input from where the laser beam is directed on to the sample. The optical device would typically be a linear slide on which a mirror is mounted, the linear slide configured to move the mirror in and out of the laser beam path in order to selectively direct the laser beam to the optical input.

[0007] Summary of Invention

[0008] According to a first aspect of the invention there is provided an optical devicecomprising a shaft mounted for rotation about a longitudinal axis, a motor for driving rotation of the shaft and a plurality of mirrors mounted to the shaft, each mirror mounted at a different axial position along the shaft and a different circumferential position about the shaft.

[0009] In this way, the optical device can be used for selectively directing a laser or light beam from any one of a plurality of sources, each source directing a corresponding laser or light beam to a different one of the axial positions, using the mirror located at that axial position by rotating the shaft such that the mirror is inserted into the optical path of the laser beam or other light beam. Hence each mirror may be configured for reflecting a corresponding laser or light beam from a different optical path. Each mirror has a different circumferential position about the shaft such that the corresponding laser or light beam can be reflected by the mirror from the different optical path along the shaft without another one of the mirrors obstructing a path of the corresponding laser or light beam. Alternatively, the optical device can be used to direct an incoming beam to a selected detector from any one of a plurality of detectors. In general, a rotary element can be made with fewer parts and with lower cost bearings than a linear slide. Accordingly, the optical device may provide a cheaper alternative to the linear slide(s).

[0010] Each mirror of the plurality of mirrors may be arranged to reflect the corresponding laser or light beam from or along a common optical path, for example an optical path parallel to the longitudinal axis of the shaft. The different optical paths may be a plurality of parallel optical paths. The parallel optical paths may be transverse, and preferably perpendicular, to the longitudinal axis. A surface of each mirror may be arranged at the same angle, such as 45°. to the longitudinal axis. Each mirror may comprise a planar mirror.

[0011] Each mirror may be mounted to the shaft by a corresponding mirror mount. The mirror mount may be configured to enable adjustment to a position of the mirror relative to the longitudinal axis.The optical device may comprise two shaft supports for supporting the shaft such that the shaft can rotate about the longitudinal axis. The shaft supports may be mounted on a mounting plate. The shaft and the mounting plate may be made of the same material, for example aluminium or steel. In this way, differential thermal expansion between the mounting plate and shaft is mitigated or even eliminated. In one embodiment, the mounting plate may be used as a heat sink and, as such, is preferably made of material with a high thermal conductivity, such as aluminium.

[0012] The optical device may comprise an encoder for directly or indirectly measuring a rotary position of the shaft. The encoder may measure a rotary position of a motor shaft. In one embodiment, the motor is connected to the shaft by a gear mechanism, such as worm drive. A position of the shaft may be determined from a known ratio of motor shaft turns to rotations of the shaft, for example from a gear ratio. Locating the encoder on the motor shaft is a cheaper solution than directly measuring angular rotation of the shaft and / or enables a more compact solution.

[0013] The motor may be arranged to maintain the shaft in a particular rotary position based on measurements from the encoder.

[0014] In combination, a controller and the optical device of the first aspect of the invention, the controller configured to control operation of the motor to servo the shaft to a desired position. The desired position may be a position in which a selected laser or light beam is reflected along the common path. The controller may be configured to control operation of the motor such that the shaft can be maintained in a continuum of positions (rather than a set of indexed positions). This allows the positioning of the shaft to be adjusted for changes in the optical device, for example due to thermal changes, with time. This may also allow an alignment of the optical device with the laser or light beam sources to be carried out remotely.

[0015] According to a second aspect of the invention there is provided a spectroscopyapparatus comprising an optical input, a plurality of laser sources and an optical device according to the first aspect of the invention configured such that, for different rotary positions of the shaft, a different one of the mirrors reflects a corresponding laser beam from a different one of the laser sources to the optical input.

[0016] In this way, the optical device performs the task of selecting which laser beam is delivered to the optical input.

[0017] In one aspect there is provided a spectroscopy apparatus comprising an optical device comprising an optic for directing a laser or light beam to an optical input and a motor for positioning the optic to adjust a position of the laser or light beam relative to the optical input; a controller configured to control operation of the motor; and a detector for detecting a position of the laser or light beam reflected to the optical input, the controller configured to output positional data based on signals from the detector and receive commands on a position of the optic of the optical device, the controller configured to control the motor based on the commands.

[0018] The optical device may be in accordance with the first aspect of the invention, wherein the optic is one of the mirrors of the optical device.

[0019] The spectroscopy apparatus may comprise a network connection for connecting the controller to a network, such as the Internet. The controller may be configured to output the positional data to the network and receive commands from the network.

[0020] In this way, adjustment, such as alignment, of the laser or light beam can be carried out remotely.

[0021] Description of the DrawingsFIGURE 1 is a perspective view of an optical device according to an embodiment of the invention;

[0022] FIGURE 2 is an enlarged perspective view of two of the mirrors and corresponding mirror mounts;

[0023] FIGURE 3 is an exploded view of the motor and drive mechanism; and

[0024] FIGURE 4 is a schematic of a spectroscopy apparatus according to an embodiment of the invention.

[0025] Description of Embodiments

[0026] An optical device 100 comprises a shaft 102 mounted on two shaft supports 105a, 105b for rotation about a longitudinal axis A-A. The two shaft supports 105a, 105b are secured to a mounting plate 106. The shaft 102 and the mounting plate 106 are made of the same material, in this embodiment aluminium.

[0027] A plurality of planar mirrors 104a-104f are mounted to the shaft 102 at 45° to the longitudinal axis A-A. Each mirror 104a-104f is mounted at a different axial position along the shaft 102 and a different circumferential position about the shaft 102. A mirror mount 115a-l 15f mounting the mirror 104a-104f to the shaft 102 is configured to enable adjustment in a position of the mirror 104a-104f relative to the longitudinal axis A-A using an appropriate adjustment mechanism. In this embodiment, the mirror mount 115a-115f allows for adjustment of a pitch of the mirror 104a-104f via interface 116, and movement of the mirror mount 115a-l 15f along the shaft 102 by releasing fasteners 113a, 113b. Adjustment of apitch ofthe mirror 104a-104f adjusts an angle of a reflected beam relative to the longitudinal axis A-A. Moving the mirror mount 115a-l 15f up / down on the shaft brings the reflected beam further from or closer to the shaft 102. Rotation of the mirror mount 115a-l 15f about the shaft 102 allows the mount to be positioned so as not to obstructother reflected beams and / or reflect the beam onto other ones of the mirror mounts. In this embodiment, the interface 116 and fasteners 113a, 113b are screws. A flexure 114 on the mirror mount 115a-115f enables the mirror mount 115a-115fto be clipped on and off the shaft 102 and provide resistance / a retaining force to hold the mirror mount 115a-l 15f in place when adjusting the mirror 104a-104f position.

[0028] A motor 103 drives rotation of the shaft 102. Referring to Figure 3, the motor 103 drives rotation of the shaft 102 via a gear mechanism, in this embodiment a worm 107 connected to a drive shaft of the motor and worm wheel 108 connected to shaft 102. The gear mechanism provides a gear reduction such that motor 103 completes multiple rotations for a single rotation of shaft 102.

[0029] An encoder 109 is provided for measuring a position of the drive shaft of the motor 103. In this embodiment, the encoder 109 is a rotary encoder working with a magnet on a rear of the motor shaft. A rotary position of the shaft 102 is determined from the position measurements of the encoder 109 and the known gear ratio of the worm 107 and worm wheel 108. A controller 112 is configured to receive position measurements from the encoder 109 and control movement of the motor 103 to rotate the shaft 102 to locate a selected mirror 104a-104f in the path of a corresponding laser beam 111 to reflect the laser beam along a common optical path 110. Figure 1 illustrates mirror 104d located to reflect a corresponding laser beam 111 along the common path 110. However, it will be understood that another one of the plurality of mirrors 104a-104f could be rotated to a position in which that other mirror reflects a different laser beam (not shown) along the common optical path 110. The common path 110 is parallel with the longitudinal axis A-A of the optical device 100.

[0030] The controller 112 is preset with the rotary positions that correspond to a position of each mirror 104a-104f in the path of the corresponding laser beam. These preset positions may be determined from an initial calibration of the device, for example, once it has been mounted in an apparatus comprising the lasers. However, changesmay occur in the alignment due to transport and / or thermal changes in the environment. Accordingly, a subsequent calibration may be carried out, for example after the apparatus has been moved and / or periodically. The motor 103 can maintain the shaft 102 in a continuum of positions such that modifications can be made to the preset positions to take account of any changes that may have occurred.

[0031] Referring to Figure 4, a spectroscopy apparatus 200, such as a Raman spectroscopy apparatus, is shown comprising a plurality of lasers 20 la-20 If, the optical device 100, a spectrometer 202 and a system controller 203. The lasers 20 la-20 If are configured to generate laser beams along different, parallel optical paths (as indicated by the dotted lines). The optical device 100 is located such that each mirror 104a-104f is positionable by rotation of the shaft 102 to reflect a corresponding one of the laser beams along the common optical path 110. The common optical path 110 is aligned with an optical input 205 of the spectrometer 202.

[0032] In a first method of using the spectroscopy apparatus 200, at any one time, only one of the lasers 20 la-20 If generates a laser beam corresponding to the mirror 104a-104f positioned to reflect the beam along the common optical path 110 (in Figure 4, laser 20 Id is generating a laser beam as indicated by the thicker dotted line, whereas lasers 20 la-201c, 20 le and 20 If are not generating laser beams).

[0033] In a second method of using the spectroscopy apparatus 200, two or more of the lasers 20 la-20 If generate a laser beam at the same time. The optical device 100 is operated to direct, in turn, each of the two or more laser beams to the optical input 205 of the spectrometer 202 by positioning the corresponding mirror 104a-104f as required through rotation of shaft 102. The one or more laser beams that are not directed along the common optical path 110 at a particular time hit the sides of mirror mounts 115d, 115e and are scattered within the laser bay. With a suitably small laser input 205 and optionally other baffles within the spectrometer, thescatered laser light may be prevented from reaching the sample or otherwise entering the spectrograph. Alternatively, motorised blocking components may be provided in the laser bay for blocking the or each laser beam that is not currently in use. Generating two or more laser beams at the same time, allows the laser beam being used for spectroscopy to be switched in a time frame shorter than that required for the laser to stabilise after the laser has been activated to begin generating a laser beam (because it was allowed to stabilise before the switch).

[0034] The controller 112 of the optical device 100 is connected to a system controller 203 of the spectroscopy apparatus such that signals can be sent between the system controller 203 and the controller 112 of the optical device 100. The system controller 203 sends commands to the controller of the optical device 100 requesting a desired mirror 104a-104f is aligned with the corresponding laser beam path or a defined rotary position of the shaft 102. The system controller 203 has an external connection to a network 204, such as the Internet, to enable remote control of the spectroscopy apparatus.

[0035] The spectroscopy apparatus 200 further comprises a user interface 206 to enable as user to input into the system controller 203 the laser 201a-201f the user desires to use for spectroscopy. In response to the receiving identification of the laser 20 la-20 If to be used, the system controller 203 sends a command to the controller 112 to move the shaft 102 to align the corresponding mirror with the laser beam path of the identified laser 20 la-20 If. On receiving the command, the controller 112 activates the motor 103 to move the shaft as required. A signal is then generated by the controller 112, informing the system controller 203 that the action has been completed. The system controller 203 may then be involved in activating the desired laser 201a-201f in order to carry out spectroscopy on a sample. Typically, the different lasers 201a-201f will generate laser beams of different wavelengths and the optical device 100 of the spectroscopy apparatus 200 direct a selected laser beam along the common optical path 110 into the spectrometer 202.The spectrometer 202 comprises a detector 207 for detecting a position of the laser beam. The measurements of this detector 207 are used to determine whether the laser beam is correctly aligned within the spectrometer 202. The measurements are sent to system controller 203 and the system controller 203 may be used to adjust the position of the shaft 102 to correct for any detected misalignments. Such an alignment of laser beam may be carried out by sending the measurements and receiving commands to correct misalignments over the network 204. This may avoid the need for a skilled engineer to be present on-site.

[0036] It will be understood that modifications and alterations may be made to the abovedescribed embodiments without departing from the invention as defined herein. For example, the optical device may be used in optical apparatus other than spectroscopy apparatus. Furthermore, the optical device may be used in “reverse” to direct electromagnetic radiation travelling along the common path 110 to a selected detector from any one of a plurality of detectors located in place of the lasers. The planar mirrors may be replaced with other mirror types that may act to focus or defocus the beam. Rather than an encoder, a detent mechanism may be used to defined indexed positions corresponding to the mirrors being located in the desired positions. The laser paths to the optical device 100 may not be parallel and may not be in the same plane. Preferably, the laser beam paths are perpendicular to the longitudinal axis even if not all the paths are in the same plane. In such an embodiment, the mirrors are mounted on the shaft 102 taking account of the different directions of the laser beam paths of the laser beams.

Claims

CLAIMS1. A spectroscopy apparatus comprising an optical input, a plurality of laser sources and an optical device, the optical device comprising a shaft mounted for rotation about a longitudinal axis, a motor for driving rotation of the shaft and a plurality of mirrors mounted to the shaft, each mirror mounted at a different axial position along the shaft and a different circumferential position about the shaft, the optical device configured such that, for different rotary positions of the shaft, a different one of the mirrors reflects a corresponding laser beam from a different one of the laser sources to the optical input.

2. A spectroscopy apparatus according to claim 1, wherein each mirror is configured for reflecting a corresponding laser or light beam from a different optical path.

3. A spectroscopy apparatus according to claim 2, wherein each mirror has a different circumferential position about the shaft such that the corresponding laser or light beam can be reflected by the mirror from the different optical path along the shaft without another one of the mirrors obstructing a path of the corresponding laser or light beam.

4. A spectroscopy apparatus according to claim 2 or claim 3, wherein each mirror of the plurality of mirrors is arranged to reflect the corresponding laser or light beam along a common optical path.

5. A spectroscopy apparatus according to claim 4, wherein the common optical path is an optical path parallel to the longitudinal axis of the shaft.

6. A spectroscopy apparatus according to claim 4 or claim 5, wherein the different optical paths are a plurality of parallel optical paths.

7. A spectroscopy apparatus according to claim 6. wherein the parallel optical paths are transverse to the longitudinal axis.

8. A spectroscopy apparatus according to claim 7, wherein the parallel optical paths are perpendicular to the longitudinal axis.

9. A spectroscopy apparatus according to any one of the preceding claims, wherein a surface of each mirror is arranged at the same angle to the longitudinal axis.

10. A spectroscopy apparatus according to claim 9, wherein a surface of each mirror is arranged at 45° to the longitudinal axis.

11. A spectroscopy apparatus according to any one of the preceding claims, each mirror comprises a planar mirror.

12. A spectroscopy apparatus according to any one of the preceding claims, wherein each mirror is mounted to the shaft by a corresponding mirror mount, the mirror mount configured to enable adjustment in a position of the mirror relative to the longitudinal axis.

13. A spectroscopy apparatus according to any one of the preceding claims, comprising two shaft supports for supporting the shaft such that the shaft can rotate about the longitudinal axis, the shaft supports mounted on a mounting plate, wherein the shaft and the mounting plate are made of the same material.

14. A spectroscopy apparatus according to claim 13, wherein the same material is aluminium.

15. A spectroscopy apparatus according to any one of the preceding claims, comprising an encoder for directly or indirectly measuring a rotary position of the shaft.

16. A spectroscopy apparatus according to claim 15, wherein the encoder measures a rotary position of a motor shaft.

17. A spectroscopy apparatus according to claim 15 to claim 16, wherein the motor is arranged to maintain the shaft in a particular rotary position based on measurements from the encoder.

18. A spectroscopy apparatus according to any one of claims 1 to 17, comprising a controller configured to control operation of the motor to servo the shaft to a desired position.

19. A spectroscopy apparatus according to claim 18, wherein the controller is configured to control operation of the motor such that the shaft can be maintained in a continuum of positions.

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