System and method for emitting a laser beam into space

Abstract

The laser source (220) generates a first laser beam with a wavelength less than an eye-safe subset of the near-infrared spectrum. The laser source (220) is independent of the mount (230) by virtue of an offset comprising a hollow-core optical fibre (223). A hollow-core fibre-based wavelength matching device (221) converts the first laser beam into a second laser beam the wavelength of which is within the eye-safe subset of the near-infrared spectrum. The second laser beam is transmitted to the beam expander (210) via the hollow-core optical fibre (223) in order to be emitted into space.

Description

[0001] SYSTEM AND METHOD FOR EMITTING A LASER BEAM INTO SPACE

[0002] TECHNICAL FIELD

[0003] The present invention relates to a system for emitting a laser beam into space, in particular but not exclusively in the context of observation by telescope of a body in space including a telescope and a laser source.

[0004] STATE OF PRIOR ART

[0005] Laser beams are transmitted into space. These laser beams are used, for example, in telemetry systems, such as satellite laser ranging (SLR) systems. In such telemetry applications, telescopes coupled with laser sources are used. The telescope and the laser source are attached to a mount that has joints allowing alignment between the telescope and the laser emission.

[0006] A suitable arrangement is schematically illustrated in Fig. 1A. A telescope 100 is attached to a mount 130. A laser source 120 and a beam expander 110 are also attached to the mount 130. The beam expander 110 is arranged to enlarge the size of a laser beam emitted by the laser source 120, in order to reduce the divergence of the laser beam emitted by the laser source 120. A beam expander with a magnification ratio of G typically allows the initial divergence to be approximately divided by G.

[0007] The wavelength of the laser beam emitted by the laser source 120 is typically in the range of 1.4 pm to 2 pm, which corresponds to an eye-safe subset of the near-infrared (NIR) spectrum. Indeed, the cornea of ​​the human eye strongly attenuates wavelengths beyond 1.4 pm. Using such laser beams, with wavelengths in the eye-safe subset of the near-infrared spectrum, therefore limits the risks of retinal damage. A problem posed by such laser sources is their size and weight. To ensure fine adjustment of alignment between the telescope and the laser emission, the mount 130 is then a complex mechanical structure capable of supporting the weight and size of such laser sources.

[0008] It is also possible to achieve laser beam emissions into space without coupling the laser source with a telescope on the mount. This arrangement is schematically illustrated in Fig. 1B. The mount 131 used, however, remains highly complex, due to the size and weight of the laser source, despite the absence of the telescope on this mount 131.

[0009] Furthermore, high-energy laser sources (i.e., suitable for emission into space, typically with an energy greater than 10 mJ) and high pulse frequency, which emit laser beams with wavelengths in the range of 1.4 to 2 pm are themselves highly complex equipment. Less complex laser sources exist, but these laser sources, on the one hand, have an even larger size and weight, and on the other hand, emit laser beams at wavelengths that are below the eye-safe subset of the near-infrared spectrum, which presents higher risks of retinal damage to the human eye.

[0010] It is therefore desirable to overcome these disadvantages of the state of the art. In particular, it is desirable to provide a solution that makes it possible to reduce the complexity of systems using laser emissions into space, particularly of the frame used, while ensuring eye safety.

[0011] STATEMENT OF THE INVENTION

[0012] To this end, a system is proposed herein for performing laser emission into space, the system including a laser source, a beam expander from which the laser emission into space originates, and a mount to which the beam expander is attached, the mount being arranged to allow direction adjustment of the laser emission from the beam expander. The laser source is arranged to generate a first laser beam of wavelength less than an eye-safe subset of the near-infrared spectrum. The system further includes a hollow-core fiber-based wavelength matching device, a shift device using a hollow-body optical fiber to connect the shift device to the beam expander such that the laser source is independent of the mount.And the wavelength matching device is arranged to convert the first laser beam into a second laser beam, injected at the input of the offset device, the wavelength of which is included in the eye-safe subset of the near-infrared spectrum. Thus, the system uses a low-complexity laser source without the frame supporting the weight and bulk of the laser source, while limiting the risks of eye damage. The complexity of the system is thus reduced overall.

[0013] In a particular embodiment, the laser source is based on neodymium-doped yttrium-aluminum garnet amplifying media. Thus, a low-complexity, high-energy laser source can be easily found off-the-shelf.

[0014] According to a particular embodiment, the laser source, the wavelength matching device and the offset device are placed in a controlled environment room, and the beam expander and the mount are placed outside the controlled environment room. Thus, laser emission to space is easily achieved, with high laser beam stability.

[0015] According to a particular embodiment, the order of magnitude of the wavelength of the first laser beam is 1 pm and the order of magnitude of the wavelength of the second laser beam is greater than 1.4 pm.

[0016] According to a particular embodiment, the system further comprises a telescope, the telescope also being fixed on the mount, the mount being arranged to allow alignment between the telescope (200) and the laser emission towards space.

[0017] Also provided herein is a method of emitting a laser beam into space by the system disclosed above in any of its embodiments, the method including: generating the first laser beam; changing the wavelength of the first laser beam to obtain the second laser beam; conveying the second laser beam by optical fiber; emitting the second laser beam into space by performing beam enlargement.

[0018] In a particular embodiment, when the system comprises a telescope as mentioned above, the method further comprises capturing, via the telescope, light information induced by the second emitted laser beam. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The characteristics of the invention mentioned above, as well as others, will appear more clearly on reading the following description of at least one exemplary embodiment, said description being made in relation to the attached drawings, among which: [Fig. 1 A] schematically illustrates an arrangement carrying out laser emission towards space, according to a first embodiment of the state of the art;

[0020] [Fig. IB] schematically illustrates an arrangement carrying out laser emission towards space, according to a second embodiment of the state of the art;

[0021] [Fig. 2A] schematically illustrates a system arrangement performing laser emission towards space using a remote laser source, according to a first particular embodiment;

[0022] [Fig. 2B] schematically illustrates a system arrangement performing laser emission into space using a remote laser source, according to a second particular embodiment; and

[0023] [Fig. 3] schematically illustrates a flowchart of a process implemented by the system of Fig. 2A or Fig. 2B.

[0024] DETAILED PRESENTATION OF IMPLEMENTATION METHODS

[0025] In relation to Fig. 2A, a system is schematically presented including a mount 230 on which a beam enlarger 210 is fixed. The mount 230 is arranged to allow the direction of a laser emission from the beam enlarger 210 to be adjusted. To do this, the mount 230 comprises various articulations offering the degrees of freedom necessary for adjusting the direction of this laser emission.

[0026] The system therefore also includes a laser source 220. Unlike the systems of Figs. 1 A and 1B, the laser source 220 of the system of Fig. 2A is independent of the mount 230. The laser source 220 is thus not fixed to the mount 230 supporting the beam expander 210. The complexity of the mount 230 is thus reduced.

[0027] The laser source 220 is thus offset from the mount 230 by means of a offset device 222 which uses a hollow-core optical fiber 223 filled with a gas and which comprises a device for injecting a laser beam into the optical fiber 223. The use of a hollow-core optical fiber makes it possible to support high-energy laser beams, which is not possible with a solid-body optical fiber. The optical fiber 223 is connected to the input of the beam expander 210 so that, by enlarging the size of the beam, the divergence of the laser beam supplied at the output of the optical fiber 223 is reduced.

[0028] The offset device 222 is arranged to emit into the optical fiber 223 a laser beam which is injected at the input of said offset device 222.

[0029] The laser source 220 is arranged to generate a high-energy laser beam of wavelength below the eye-safe subset of the near-infrared spectrum. In a particular embodiment, the laser source 220 is configured to generate a laser beam whose wavelength order of magnitude is equal to 1 pm. For example, the laser source generates a laser beam of 1.054 pm or 1.064 pm.

[0030] The laser source 220 is then heavier and bulkier than if the laser source were configured to generate a laser beam of wavelength included in the eye-safe subset of the near-infrared spectrum. But since the laser source 220 is independent of the mount 230, it is not useful to arrange the mount 230 to support the weight and bulk induced by the laser source 220. This also makes it possible to place the laser source 220 in a stabilized environment, for example horizontal, which allows the laser source 220 not to be subjected to vibrations or mechanical stresses.

[0031] For example, the 220 laser source is a high-energy laser source based on neodymium-doped yttrium-aluminum garnet (Nd YAG) amplifier media.

[0032] Between the laser source 220 and the offset device 222, the observation system includes a wavelength matching device 221 based on a hollow core fiber. The hollow body fiber is filled with a gas. In a particular embodiment, the hollow core fiber is stretched, typically over several meters, in order to induce a wavelength conversion by Raman effect of the light injected into it.

[0033] The gas filling the hollow body fibers used by the system is matched to the wavelengths of the laser beams used.

[0034] The wavelength matching device 221 is thus arranged to convert the laser beam supplied by the laser source 220 into a laser beam, injected at the input of the offset device 222, the wavelength of which is included in the eye-safe subset of the near-infrared spectrum. For example, the order of magnitude of the wavelength of the laser beam at the output of the wavelength matching device 221 is greater than 1.4 pm. Because the laser beam at the output of the laser source 200 is high energy, the laser beam at the output of the wavelength matching device 221 is also high energy.

[0035] Thus, thanks to this arrangement, the mount 230 does not have to support the laser source 220 and therefore does not need to be able to support its weight and bulk. A reduction in complexity is then achieved by using a laser source producing a high-energy laser beam with a wavelength below the eye-safe subset of the near-infrared spectrum, by alleviating the mechanical stresses on the mount 230, and without risk of retinal damage to the human eye. In addition, such a system can easily support high pulse frequencies.

[0036] In a particular embodiment, the laser source 220, the wavelength adaptation device 221 and the offset device 222 are placed in a room with a controlled environment, in particular in terms of temperature and humidity, and the beam expander 210 and the mount 230 are placed outside the room with a controlled environment. The laser beam generated by the laser source 220 and the wavelength conversion carried out by the wavelength adaptation device 221 are thus more stable.

[0037] In connection with Fig. 2B, a system is shown schematically including a telescope 200 attached to a mount 231. The system of Fig. 2B is adapted to carry out telemetry operations.

[0038] The beam enlarger 210 is also fixed to the mount 231. The mount 231 is arranged to allow alignment to be achieved between the telescope 200 and a laser emission from the beam enlarger 210. To do this, the mount 231 comprises various joints providing the degrees of freedom necessary to achieve this alignment between the telescope and the laser emission.

[0039] In a particular embodiment, the alignment of the telescope 200 and the laser emission from the beam enlarger 210 is controlled by a computer system. The computer system includes electronic circuitry configured to implement software functions. The telescope 200 is for example provided with a dichroic mirror which divides an incident light flux into a first sub-flux in the visible spectrum and a second sub-flux in the near-infrared spectrum. A first camera is arranged to capture images of the first sub-flux in order to allow a first software functionality to carry out tracking of a body in space (satellite, debris, etc.).A second camera is arranged to capture images of the second sub-stream in order to allow a second software functionality to perform contour detection making it possible to detect backscattered laser pulses, to ensure the alignment of the telescope and the laser emission from the beam enlarger 210. A single photon avalanche diode SP AD (Single Photon Avalanche Detector) and a digital time converter TDC (Time Digital Converter) make it possible to perform ranging operations from the backscattered laser pulses of the second sub-stream.

[0040] Thus, the mount 231 is more complex than the mount 230 shown in connection with Fig. 2A. However, the mount 231 is less complex than the mount 131 of Fig. 1B, thanks to the offset of the laser source 220 using the hollow-body optical fiber 223 and the offset device 222. It should be noted here that, when a telescope is used, reducing the complexity of the mount supporting the telescope is an even more important issue.

[0041] Fig. 3 schematically illustrates a flowchart of a method implemented by the system of Fig. 2A or Fig. 2B.

[0042] In a step 301, the system generates a first laser beam of wavelength less than the eye-safe subset of the near-infrared spectrum (eg, of the order of 1 pm). The first laser beam is of high energy (typically greater than 10 mJ). In Figs. 2A and 2B, the first laser beam is generated by the laser source 220.

[0043] In a step 302, the system modifies the wavelength of the first laser beam in order to obtain a second laser beam whose wavelength is included in the eye-safe subset of the near-infrared spectrum (eg, of the order of 1.5 pm). A hollow-core fiber filled with a gas is used for this purpose. In Figs. 2A and 2B, the second laser beam is generated by the wavelength matching device 221.

[0044] In a step 303, the system conveys the second laser beam by hollow body optical fiber. This makes it possible to withstand the high energy of the laser beam. In Figs. 2A and 2B, the second laser beam is conveyed by the offset device 222 and the optical fiber 223 to the beam expander 210. In a step 304, the system emits the second laser beam into space by performing beam enlargement. In Figs. 2A and 2B, the beam enlargement and the emission into space are performed by the beam expander 210. The second laser beam has characteristics, in particular energy characteristics, allowing it to reach space.

[0045] In the particular embodiment of Fig. 2B where the telescope is coupled to the laser source, in a step 305, the system captures, via the telescope 200, light information induced by the second emitted laser beam. Tracking of a body in space by the system, and telemetry operations, can then be carried out, as already described above.

Claims

CLAIMS 1. A system for performing laser emission into space, the system including a laser source (220), a beam expander (210) from which the laser emission into space originates, and a mount (230, 231) on which the beam expander (210) is fixed, the mount (230, 231) being arranged to allow adjustment of the direction of the laser emission, characterized in that the laser source (200) is arranged to generate a first laser beam of wavelength less than an eye-safe subset of the near-infrared spectrum, the system further includes a wavelength matching device (221) based on a hollow core fiber, an offset device (222) using a hollow-body optical fiber (223) to connect the offset device (222) to the beam expander (210) so that the laser source (220) is independent of the mount (230, 231),and the wavelength adaptation device (221) being arranged to convert the first laser beam into a second laser beam, injected at the input of the offset device (222), the wavelength of which is included in the eye-safe subset of the near-infrared spectrum., 2. The system of claim 1, wherein the laser source (220) is based on neodymium-doped yttrium-aluminum garnet amplifying media.

3. The system of claim 1 or 2, wherein the laser source (220), the wavelength matching device (221) and the offset device (222) are placed in an environmentally controlled room, and the beam expander (210) and the mount (230, 231) are placed outside the environmentally controlled room.

4. The system according to any one of claims 1 to 3, wherein the order of magnitude of the wavelength of the first laser beam is 1 pm and the order of magnitude of the wavelength of the second laser beam is greater than 1.4 pm.

5. The system according to any one of claims 1 to 4, further comprising a telescope (200), the telescope (200) also being fixed on the mount (231), the mount (230, 231) being arranged to allow alignment between the telescope (200) and the laser emission towards space.

6. A method of emitting a laser beam into space by the system according to any one of claims 1 to 4, the method including: - generate (301) the first laser beam; - modifying (302) the wavelength of the first laser beam in order to obtain the second laser beam; - conveying (303) the second laser beam by optical fiber; and - emit (304) the second laser beam into space by performing beam enlargement.

7. The method of claim 6, wherein the system is according to claim 5, and wherein the method further comprises: - capture (305), via the telescope, light information induced by the second emitted laser beam.

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