Laser

Abstract

A laser device comprising a laser cavity (or amplifier cavity which may comprise a bow-tie ring cavity) having a plurality of reflectors 204 a-d. An optical oven 100, which may comprise a mount otherw

Description

Field

[0001] The present disclosure relates to a laser, including an optical oven. In particular the disclosure is concerned with an optical oven which allows for radial temperature control (typically cooling) of an optic mounted in the oven. Background

[0002] Spectral selection is important to maintain the frequency and intensity output of a laser. Selection can be provided intracavity using various optical filters, however such filters introduce a spectrally varying loss in the cavity. Moreover, it is desirable that any optical element introduced in a laser cavity is aligned precisely to sub-milliradian optical accuracy. Additionally, in order to keep the filter stable, the temperature of the element must be kept constant. In certain optical systems, it is desirable to maintain sub-millikelvin variations in temperature across an optic.

[0003] A particular class of optical mounts known as optical ovens are used to efficiently control the temperature of optical elements so as to ensure stable transmission of a (laser) beam through the optic. Here a cooling effect is applied to the mount (termed a cold plate in the art) which in turn cools the optic mounted therein.

[0004] In one example, the cooling effect is applied by a suitable cooler unit arranged at a convenient side of the mount (e.g., top, bottom, left side, right side). In this way a substantially linear temperature gradient is applied to the optic orthogonal to the direction of the beam line. In other words, the temperature of the optic is linearly graded in the cross section of the laser beam as it passes through the optic: e.g., where the cooler is arranged at the bottom of a mount, the bottom of the lens will be cooler than the top of the lens. The result is that transmission of the beam through the optic may be different across the cross section of the beam, causing energy losses in the system.

[0005] To address the issue of linear cooling in an optical oven, more recent designs take a radial cooling approach. Here cooling pipes, or similar, are arranged around side edges of the mount. Assuming the optic is positioned substantially centrally in the mount, then the temperature profile changes substantially radially with respect to the centre of the optic (again in the plane orthogonal to the direction of beam propagation). Even though there is still potentially a temperature gradient, such a gradient is cylindrically symmetrical across the cross section of the beam as it passes through the optic, resulting in far less loss compared to linear cooling techniques. However, the specialist cooling equipment and arrangement required for such radial cooling increase the complexity, size, and cost of the oven, meaning that such an oven is not appropriate for use in a wide range of applications.

[0006] Hence it is now desired to provide an improved optical oven for a laser to previously available designs. Summary

[0007] The present invention is defined according to the independent claims. Additional features will be appreciated from the dependent claims and the description herein. Any embodiments which are described but which do not fall within the scope of the claims are to be interpreted merely as examples useful fora better understanding of the invention.

[0008] The example embodiments have been provided with a view to addressing at least some of the difficulties that are encountered with current optical ovens, whether those difficulties have been specifically mentioned above or will otherwise be appreciated from the discussion herein. The example embodiments are particularly concerned with providing radially cooled, tiltable optical filters that are used intracavity.

[0009] In one aspect of the invention there is provided a laser device (or laser the terms can be used interchangeably), the laser device comprising: a laser cavity formed by a plurality of reflectors which are reflective for a laser beam and an optical oven (sometimes simply termed an optical mount). The optical oven is within the laser cavity and comprises a mount (cold plate), configured to receive and hold an optic and thermally couple to the optic, and a thermoelectric cooling unit, such as a peltier cooler, thermally coupled to the mount. The mount comprises a first aperture and the thermoelectric cooling unit comprises a second aperture, the first aperture and second aperture being optically aligned to propagate the laser beam through the optical oven via the optic. Advantageously the arrangement of the cooler substantially surrounding the optical axis of the oven (i.e., the beam line) allows for radial cooling which achieves sub-millikelvin variations in temperature across the optic. The arrangement is also more compact manner than previously available designs so that the optical oven is suitable for use intracavity in a laser device. For example, the optical oven may be used with an etalon to provide intracavity frequency selection in the laser device, and / or may be used for reference frequency locking of the laser device.

[0010] In one example, the thermoelectric cooling unit may be configured to generate a radial temperature gradient across the optic in a plane orthogonal to the propagation of the laser beam through the optical oven. That is, to the extent the lens can be imagined as substantially two dimensional, the lens cooling effect is applied in the plane of the lens. For example, when the direction of propagation is substantially in an x-axis, the temperature gradient is applied in a y-z plane.

[0011] In one example, the first aperture and second aperture may be coaxially aligned with a central axis of the optic, in particular where the mount comprises a recess into which the optic may be inserted, the first aperture being provided at the base of the recess coaxially aligned with the optic and recess. Suitably, the thermoelectric cooling unit may be configured to apply the radial cooling substantially symmetrically about the optical axis of the optic. In one example, the optic may be suitably arranged to abut an inner surface of the base of the recess, and the thermoelectric cooling unit is configured to abut an outer surface of the base of the recess, in order to achieve the desired thermal coupling to apply radial cooling.

[0012] In an example the mount / cold plate comprises copper as this is a good thermal conductor which thereby improves cooling of the optic. Other suitably heat conducting metals may also be used.

[0013] In an example the optic oven also comprises a heatsink, (hotplate) thermally coupled to the thermoelectric cooling unit (on an opposite side to the mount / cold plate), the heatsink comprises a third aperture in optical alignment with the first and second apertures, once again thereby allowing on axis beam propagation while allowing for compactness of the cooler unit and overall oven.

[0014] In an example the heatsink is rotatably coupled to a frame. When the oven is in use in an optical system, the oven may be secured in place in the optical system via the frame. In one example, the rotatable coupling allows for control of a pitch of the optic (and more generally the optic - cold plate - cooler - hot plate arrangement) with respect to the beam line. That is rotational movement a vertical, x-z, plane, wherein x axis corresponds to the direction of beam propagation and z axis is orthogonal to the direction of beam propagation. The frame may also comprise means to adjust at least one of a translation and yaw of the optic; that is, an angle of the in a horizontal, x-y, plane with respect to the direction of beam propagation corresponding to the x-axis. The rotational control aspects particularly may be suitably configured with sub-milliradian accuracy.

[0015] In an example, the optical oven comprises a clamp configured to secure the received optic in the recess. The clamp may be in the form of a plate arranged to substantially cover a part of the mount and optic, and configured with a fourth aperture optically aligned with the first, second, and third apertures. Other forms ofclamp (that may not require an aperture but still allow beam propagation) may also be utilised.

[0016] In one arrangement, the plurality of reflectors may form a ring resonator, more specifically a bow-tie ring resonator with four reflectors.

[0017] There may be a feedback mechanism to control the thermoelectric cooling unit, wherein the feedback mechanism comprises at least one thermistor which is supported in the mount and which measures a temperature of the mount. The at least one thermistor may be mounted in a bore within the mount.

[0018] In another aspect of the disclosure there is also provided an optical oven for use in a laser. The optical oven has the features described above. As stated above, the oven described herein is particularly suited for compact optical systems where sub-millikelvin variations in optic temperature are desired and sub-milliradian angular control desired. Brief Description of the Drawings

[0019] For a better understanding of the present disclosure reference will now be made by way of example only to the accompanying drawings, in which:

[0020] Fig. 1 shows a schematic of an example optical oven in perspective view;

[0021] Fig. 2 shows the example of Fig. 1 sectioned through the centre of the x-z axis;

[0022] Fig. 3 shows the section of Fig. 2 in plan view;

[0023] Fig. 4 shows an exploded view of the example optical oven;

[0024] Fig. 5 shows another exploded view of the example optical oven;

[0025] Fig. 6 is a drawing showing the components of the laser and the beam path within the optical cavity;

[0026] Fig. 7a plots gain against wavelength for various cavity modes;

[0027] Fig. 7b plots gain against wavelength for an etalon signal;

[0028] Fig. 7c replots Fig.7b following a change in temperature; and

[0029] Fig. 8 plots a reference signal and an etalon signal to show the change in signal for different voltages. Detailed Description

[0030] With reference to Figures 1 to 5, there is shown an example optical oven 100, otherwise termed an optical mount, for controlling the temperature of an optic 102 mounted therein.

[0031] The optical oven 100 comprises a mount 104 (otherwise termed a cold-plate in the art) configured to receive the optic 102 and hold the optic 102 in position in the oven. The mount 104 is configured to contact the optic 102 to provide a thermal path between mount 104 and optic 102. That is, the mount 104 is configured to thermally couple to the optic 102. Desirably, the mount 104 makes contact with the optic 102 at as large an interface as possible. That is, it is desirable to maximise surface contact between the mount 104 and optic 102. In this way the thermal coupling between the mount 104 and optic 102 is improved. Suitably, to better facilitate thermal coupling between the mount 104 and optic 102, the mount 104 may be formed from a heat conducting metal. In a preferred example, the mount 104 comprises copper. The mount may also comprise one or more bores 105 into which a thermistor may be placed in order to gather temperature measurements from the mount 104.

[0032] Suitably, in the present example, the mount comprises a recess 106 to receive the optic 102 with the dimensions of the recess 106 chosen such that the optic 102 tightly fits within the recess 106. In the present example the recess 106 is cylindrical with cylindrical axis aligned with the direction of beam propagation (x axis in the Figures). Here, the optic 102 abuts the inner surface of the base 115 of the recess 106, an outer circumferential surface 108 of the optic 102 (which is also cylindrically shaped) is in contact with a congruently shaped circumferential inner surface 110 of the recess 106, and a front surface 112 of the optic 102 lies slightly inset with respect to a front surface 114 of the mount 104 when the optic 102 is fully slotted into the recess 106. By way of example, the optic 102 may be about 6 mm diameter by 2 mm wide, corresponding to a similarly sized recess in the mount 104.

[0033] The base 115 of the recess 106 comprises an aperture 116 through which a laser beam 10 propagates when the oven 100 is in use in an optical system (e.g., intracavity in a laser device). Preferably the aperture 116 is centred on the optical axis (i.e., the centre) of the recess 106, corresponding to the optical axis (again, centre) of the optic 102. Put another way, the recess 106 and the aperture 116 are coaxially aligned. The aperture is preferably circular for simplicity and interoperability with different systems, although different shapes may be chosen to match a specific beam profile if desired. By way of example, for a 6 mm diameter optic 102, the aperture 116 in the mount may be about 2 mm diameter.

[0034] The optic 102 may be secured in place in the mount 104 by a clamp 118. Here a rear surface 120 of the clamp 118 is a substantially flat so that the surface 120 may abut the front surface of the 114 of the mount. The clamp 118 may also comprise a groove 122 for and O-ring 124, the O-ring being provided to press against the optic 102 (the clamp 118 otherwise not touching the optic due to the inset within the recess 106). Suitably one or more connectors 126, such as screws or nuts and bolts, may be provided between the mount 104 and clamp 118 to attach the clamp 118 to the mount 104. Moreover, the clamp 118 comprises an aperture 128 optically aligned (e.g., coaxial) with the aperture 116 in the mount 104 to allow propagation of the laser beam 10 to / from the optic 102 through the clamp 118. The diameter of the aperture 128 may be about 3 mm.

[0035] Other techniques for clamping the optic 102 in place in the mount 104 may also be utilised, such as suitably configured (miniature) G-clamps, or slidable / rotatable locks, and the like, which may or may not necessitate providing the clamp with an aperture.

[0036] The oven 100 also comprises a thermoelectric cooling unit 130, preferably a peltier cooler. Such coolers 130 provide temperature control by the application of (direct) electric current, and suitably the cooling plate 130 comprises electrical connectors 132 to provide such current. The cooling unit 130 is disposed in abutment with a rear surface 134 of the mount 104, such that the cooling plate is thermally (conductively) coupled to the mount 104 across as large a surface area as possible. Arranging the cooling unit 130 on the rear (outer) surface 134 of the mount allows the temperature control to be applied in the plane orthogonal to the direction of beam propagation (x axis); that is, cooling is applied evenly to the optic in the y-z plane, ensuring an even radial temperature gradient across the optic. If there is any significant temperature gradient, it is in the x direction (i.e., along the beamline), which does not lead to significant losses.

[0037] As mentioned above, a thermistor is mounted in a bore 105 in the mount 104. The thermistor forms part of a feedback mechanism to control the temperature of the mount 104. The thermistor measures the temperature and an electronic feedback cycle then calculates the voltage feedback into the thermoelectric cooler 130. The higher the voltage of the direct electric current, the higher the pumping within the thermoelectric cooler 130 and thus the feedback cycle can adjust the amount of the voltage being applied to give the desired amount of pumping (i.e. cooling / heating). In addition to controlling the amount, the feedback cycle can control the voltage polarity. When the voltage polarity is swapped then the direction of pumping changes. For example positive voltage may provide cooling and a negative voltage may apply heating or vice versa. The compactness and the small thermal mass of the mount 104 mean a quick thermal response which then enables sub-milikelvin cooling. For example in a laser cavity the intracavity power circulating is about 30 W, if we assume 0.1% loss in absorption that means that the mount 104 is absorbing about 30 mW of thermal power, which can fluctuate with ambient temperature changes of thermal convection. The electronic feedback mechanism is thereby enhances allows greater temperature stability through the appropriate heating / cooling.

[0038] The cooling unit 130 comprises an aperture 136 optically aligned (i.e., coaxial) with the aperture 116 of the mount 104 (and when present the aperture 128 of the clamp 118). Suitably a beam may propagate through the cooling unit 130 to / from the optic 102. Beneficially, the aperture 136 allows for beam propagation without overly impacting the radial cooling of the optic 102. In the present example, the aperture 136 may have a diameter of about 3.4 mm. In this way radial cooling of the optic may be provided while allowing for a compact oven that allows for on axis propagation of a beam through the oven. Indeed, an oven 100 configured as discussed herein has been determined by the Applicant to have less than a one millikelvin temperature variation across the optic 102.

[0039] The oven 100 may also comprise a heatsink 138 (otherwise termed a hotplate in the art) disposed in abutment with the cooler unit 130. Specifically, a front surface 140 of the heatsink 138, which may be substantially flat, may be disposed in contact with a rear surface 142 of the thermoelectric cooler unit 130. In this way the heatsink 138 may be thermally coupled to the cooler unit 130.

[0040] Suitably the heatsink 138 also comprises an aperture, 144, which is optically aligned (i.e., coaxial) with the aperture 116 of the mount 104 and the aperture 136 of the cooler 130 (and when present the aperture 128 of the clamp 118). Again the aperture 144 allows for propagation of the beam 10 through the oven 100. That is, all of the first to fourth apertures of the oven described above (116, 136, 144, 128) may be considered optically aligned to allow for beam propagation. By way of example the aperture 144 may be about the same diameter as the diameter of the aperture 136 in the cooler unit 130.

[0041] The heatsink 138 may be suitably attached the mount 104 by one or more connectors 146 such as screws, nuts and bolts, and the like. Preferably, such connectors are also provided with insulation, such as insulating washers, to thermally isolate the mount 104 (coldplate) from the heatsink 138 (hotplate) to ensure that the only thermal conduction path between the two components is via the cooler unit 130. Suitably, the cooling unit 130 need not be physically attached to either the mount 104 or heatsink 138, but may be held in place by compression from being sandwiched between the hot and cold plates of the oven.

[0042] The heatsink 138 is attached to a frame 146 by which the aforementioned structures are held in position. In a preferred example the heatsink 138 is rotatably coupled to the frame 146 by suitably rotating attachments means 148, here comprising oppositely arranged dowel pins. Here the means are arranged to provide a rotational axis on the y plane - that is, in the plane orthogonal to the direction of beam propagation - so that a pitch (i.e., x-z planar movement) of the optic 102 may be suitably adjusted. Beneficially sub-milliradian tuning of the optical alignment may be readily provided.

[0043] The frame 146 may also comprise means for allowing horizontal adjustment (i.e., in the x-y plane) of the oven 100 once it is installed in an optical system. The horizontal may be one or both of translational (i.e., in the y direction) or rotational (i.e., in an arc in the x-y plane). In the present example, the frame 146 comprises oppositely aligned cut-outs 150, oriented toward the x axis (beam line) of the oven, by which x-y adjustments of the oven 100 may be made within an optical system by inserting a screw into the one or both of the cut-outs 150 and pushing against the frame 146. Suitably the same screws may be used to tighten the frame in position once the horizontal angle has been set.

[0044] Figure 6 shows an example of the optical oven 100 in use in an optical system such as a laser. In this example, the optical oven 100 is in a laser cavity (which may also be termed an amplifier cavity) and which comprises a bow-tie ring resonator. The ring resonator is formed by four reflectors 204a, 204b, 204c, 204d which are highly reflective for radiation (or light, the terms are used interchangeably) at the laser fundamental frequency co. Due to a nearly 100% reflectivity of the cavity mirrors about the laser fundamental frequency, the cavity resonates and enhances the circulating laser power at frequency ©. Each reflector 204a, 204b, 204c, 204d comprises a mirror held in a mount. An active (laser gain) medium 206 is held in a mount within the cavity. The active medium 206 can be any suitable solid state laser material, for instance, a Neodymium doped laser crystal or a Praseodymium doped crystal. Laser light is output from the laser device through output 250.

[0045] A ring resonator has a travelling wave which requires unidirectional operation. Accordingly, an optical diode 220 may be located within the cavity (i.e. intracavity). The optical diode 220 prevents the laser from lasing in one direction but allows it to laser in the other. In this example, the laser is an intracavity Second Harmonic Generation (SHG) laser. Thus, the laser further comprises a SHG nonlinear crystal 240 which generates second harmonic light, i.e. light at frequency 2co. There is also a first optical element 242 and a second optical element 244 which direct light towards the output. It will be appreciated that a bow-tie resonator can be used without the SHG crystal. Similarly, it will be appreciated that this is just one suitable arrangement of resonator

[0046] As illustrated by the dotted line, there may be leakage of radiation 204 at the fundamental wavelength. This leaked radiation 204 may be reflected to an optional feedback mechanism using a reflector 210, particularly when using an optical oven 100 with a high finesse broadband coated etalon in which the fundamental frequency has been locked using fringe locking as described in more detail below. The leaked radiation 204 is then split using a beam splitter 236 to generate two separate signals, each of which are received separately at a photodiode 234. A first signal is an intensity reference signal and a second signal is spectrally selected by a second etalon 232. These signals may be used to measure the light leakage. One of the reflectors, in this example the first reflector 204a may be attached to a piezoelectric element 214 which can be used to change the optical length within the laser cavity based on the measured light leakage. As an alternative to using a piezoelectric element, a birefringement optical element (such as an electro optic modulator) may be used.

[0047] Figure 6 shows the beam path within the ring resonator. Here a light beam is incident on a first reflector 204a which reflects the incident light at a fundamental frequency co through an optical diode 220 towards a second reflector 204b. The second reflector 204b reflects the light at the fundamental frequency co so that it passes through a Second Harmonic Generation (SHG) crystal 240 to generate a second harmonic wavelength. Two wavelengths are now circulating intracavity: the fundamental wavelength 201 which is shown in red and the second harmonic wavelength 202 which is shown in blue. The fundamental wavelength 201 is incident on the third reflector 204c and is reflected towards the fourth reflector 204d. As the wave travels between the third and fourth reflectors, the wave passes through the optical oven 200 comprising the etalon which ensures only the fundamental frequency is propagated and any potentially parasitic frequencies are not. The fourth reflector 204d then reflects the wave back towards the first reflector 204a. The first, second, third and fourth reflectors thus form a bow-tie resonator in which the beam path for the light at the fundamental frequency resembles a bowtie.

[0048] When used in a laser device as described above, the etalon may be configured to provide intracavity frequency selection in the laser device. In other words, the etalon may be used to filter the radiation within the cavity to the desired single frequency, i.e. the desired fundamental frequency, and the filtering effect of the etalon may be controlled by use of a coating applied to one or both surfaces of the etalon. For example, Figure 7a plots gain against wavelength and shows the cavity modes which are selected by the gain medium. Figure 7a also plots the gain and the threshold for lasing. Figure 7b shows that by using an etalon, the plurality of modes shown in Figure 7a can be narrowed to a single mode which in this illustrative example has a wavelength of approximately 813nm. By using a higher reflectivity coating on the etalon, the steepness of each peak in the etalon curve can be increased. In other words, the width for each peak may be reduced. In this way, the likelihood of selecting only a single mode by the etalon is increased.

[0049] Figure 7c shows the effect of a temperature shift which moves the etalon curve. In this example, the etalon curve is not steep enough to select a single mode and there are two possible two cavity modes. The temperature tunability of the etalon may be expressed as: . . d-R)2 Transmissionelaion = where R is the etalon reflectivity and the phase 0 is defined as: 0 = 4nvt0 + a(T - To) where a is an expansion factor (e.g. 7x106 for fused silica), T - To is the temperature change and v is the applied voltage from a piezoelectric element.

[0050] Thus, it is important to control the temperature of the mount and hence the etalon accurately as described above. The use of the reflective coating may further improve the accuracy of the frequency selection. It is also noted that an etalon without any coating may be used. In such cases, there is still Fresnel reflection, which is about 3.44% for Fused Silica materials in air.

[0051] In another example, a high finesse (e.g., >100) broadband coated etalon may be utilised within the optical oven to lock the laser frequency in a process known as fringe locking. In fringe locking, the laser is locked to the middle point of a Gaussian etalon transmission curve, e.g. as shown in Figure 7b. An error signal may then be generated using a reference signal which is a spectrally independent signal and which may be normalised summation of the output intensity of the laser. Figure 8 plots both a reference signal and an etalon signal over a range of piezoelectric voltages. The error signal is the difference between the etalon signal (i.e. the signal passing through the etalon) and the reference signal. Thus the error signal is zero at the crossing point. As shown in Figure 8, the crossing point is aligned to the middle of the etalon’s peak which is the steepest point on the graph and which thus gives the highest possible sensitivity for the locking circuitry.

[0052] This feedback mechanism may be considered to be converting frequency information into intensity information which can be measured by a photodetector, for example the photodiodes shown in Figure 6. Additionally, by shifting the crossing point to the middle of the peak, a sign dependent error signal is achieved, meaning that a positive shift in the cavity’s frequency results in a signal increase, while the opposite results in a signal decrease. The sign dependence then enables the use of a feedback loop, using for example a PID algorithm. For example, if the photodetector signal goes down then the laser cavity optical length is increased or if the signal goes up, the laser cavity optical length is decreased. The piezoelectric element can be used to change the optical length of the cavity because the piezoelectric element expands linearly with an applied voltage and thus changes the cavity length. This may be quantified as: AL Av = The piezoelectric element has a quick response and can thus rapidly compensate for the change in the cavity output frequency and keep it continuously locked to the reference etalon’s midpoint.

[0053] As an alternative to using a piezoelectric element, an electro optical modulator may be used. In such a system, the input RF frequency is changed to change the electro optical modulator in a similar manner to changing the voltage changes the piezoelectric element. An etalon used in this fashion in the oven described herein has been determined to provide a frequency reference with sub-MHz locking stability. Indeed, the overall linewidth and locking stability over days is <20 MHZ.

[0054] In summary, exemplary embodiments of an optical oven and a laser using the optical oven have been described. The described exemplary embodiments provide for an improved optical oven which establishes radial cooling profile on an optic in a compact fashion. In addition the described optical oven comprises means for fine tuning of the optic angle, etc, in an optical system. Additionally, the described exemplary embodiments are convenient to manufacture and straightforward to use.

[0055] The described optical oven may be manufactured industrially. An industrial application of the example embodiments will be clear from the discussion herein.

[0056] Various combinations of optional features have been described herein, and it will be appreciated that described features may be combined in any suitable combination. In particular, the features of any one example embodiment may be combined with features of any other embodiment, as appropriate, except where such combinations are mutually exclusive. Throughout this specification, the term “comprising” or “comprises” means including the component(s) specified but not to the exclusion of the presence of others.

[0057] Although reference has been made herein to front and rear, and so on, this is not intended to convey a preferred orientation of the device with respect to a direction of beam propagation, unless specifically stated. To the extent that the present discussion focusses on cooling of an optical element, it will be appreciated that the techniques apply broadly to temperature control, such that “cooling” discussed herein could instead be “heating” in certain scenarios.

[0058] As used herein, unless otherwise expressly specified, all numbers such as those expressing values, ranges, amounts or percentages may be read as if prefaced by the word "about", even if the term does not expressly appear. The term “about”, or substantially, when used herein means + / - 5% of the stated value. Also, any numerical range recited herein is intended to include all sub-ranges subsumed therein, and the terms “from” and “to” a pair of values are intended to indicate such values are included in the range. Singular encompasses plural and vice versa. Additionally, although the present invention has been described in terms of “comprising”, the processes, materials, and coating compositions detailed herein may also be described as “consisting essentially of’ or “consisting of’.

[0059] Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[0060] All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0061] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. Although a few preferred embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims.

Claims

1. A laser device comprising:a laser cavity formed by a plurality of reflectors which are reflective for a laser beam; andan optical oven within the laser cavity, the optical oven comprising:a mount configured to receive and hold an optic, and configured to thermally couple to the optic, anda thermoelectric cooling unit configured to thermally couple to the mount to apply radial cooling to the optic via the mount;wherein the mount comprises a first aperture and the thermoelectric cooling unit comprises a second aperture, the first aperture and second aperture being optically aligned for propagating the laser beam through the optical oven via the optic.

2. The laser device of claim 1, wherein the thermoelectric cooling unit is configured to apply the radial cooling comprising generating a radial temperature gradient across the optic in a plane orthogonal to the propagation of the laser beam through the optical oven.

3. The laser device of claim 1 or 2, wherein the first aperture and second aperture are configured coaxially with an optical axis of the optic.

4. The laser device of claim 3, wherein the thermoelectric cooling unit is configured to apply the radial cooling substantially symmetrically about the optical axis of the optic.

5. The laser device of any preceding claim, wherein the mount comprises a recess for receiving and holding the optic, and the first aperture is arranged at a base of the recess.

6. The laser device of claim 5, wherein the optic is arranged to abut an inner surface of the base of the recess, and the thermoelectric cooling unit is configured to abut an outer surface of the base of the recess.

7. The laser device of any preceding claim, wherein the optical mount comprises copper.

8. The laser device of any preceding claim, further comprising a heatsink configured to thermally couple to the thermoelectric cooling unit, and wherein the heatsink comprises a third aperture in optical alignment with the first and second apertures.

9. The laser device of claim 8, further comprising a frame and means for rotatably coupling the heatsink to the frame.

10. The laser device of claim 9, wherein the means for rotatably coupling the heatsink, to the frame provide rotational freedom in a vertical, x-z, plane, wherein x axis corresponds to the direction of beam propagation and z axis is orthogonal to the direction of beam propagation.

11. The laser device of claim 9 or 10, wherein the frame comprises means to adjust at least one of a translation or angle of the in a horizontal, x-y, plane with respect to the direction of beam propagation corresponding to the x-axis.

12. The laser device of any preceding claim, further comprising a clamp configured to secure the received optic in the recess.

13. The laser device of claim 12, wherein the clamp comprises a fourth aperture optically aligned with the first, second, and when present, third, apertures.

14. The laser device of any preceding claim, further comprising a feedback mechanism to control the thermoelectric cooling unit, wherein the feedback mechanism comprises at least one thermistor which is supported in the mount and which measures a temperature of the mount.

15. The laser device of any preceding claim, wherein the optic is an etalon.

16. The laser device of claim 15, wherein the etalon is for intracavity frequency selection in a laser device.

17. The laser device of claim 15, wherein the etalon is for reference frequency locking of a laser device.

18. An optical oven, comprising:a mount configured to receive and hold an optic, and configured to thermally couple to the optic, anda thermoelectric cooling unit configured to thermally couple to the mount to apply radial cooling to the received optic via the mount;wherein the mount comprises a first aperture and the thermoelectric cooling unit comprises a second aperture, the first aperture and second aperture being optically aligned for propagating a laser beam through the optical oven via the received optic.

19. The oven of claim 18, wherein the thermoelectric cooling unit is configured to apply the radial cooling comprising generating a radial temperature gradient across the optic in a plane orthogonal to the propagation of the laser beam through the optical oven.

20. The oven of claim 18 or 19, wherein the first aperture and second aperture are configured coaxially with an optical axis of the received optic.

21. The oven of claim 20, wherein the thermoelectric cooling unit is configured to apply the radial cooling substantially symmetrically about the optical axis of the received optic.

22. The oven of any of claims 18 to 21, wherein the mount comprises a recess for receiving and holding the optic, and the first aperture is arranged at a base of the recess.

23. The oven of claim 22, wherein the received optic is arranged to abut an inner surface of the base of the recess, and the thermoelectric cooling unit is configured to abut an outer surface of the base of the recess.

24. The oven of any one of claims 18 to 23, wherein the optical mount comprises copper.

25. The oven of any one of claims 18 to 24, further comprising a heatsink configured to thermally couple to the thermoelectric cooling unit, and wherein the heatsink comprises a third aperture in optical alignment with the first and second apertures.

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