FR2732472A1 - SURFACE DEVICE COMPRISING AN OPTICAL DETECTOR AND A LASER TELEMETER, AND APPLICATIONS FOR HARMONIZATION AND TARGET VIEWING - Google Patents

Abstract

The invention relates to a sighting device comprising at least one optical detector (D) operating in a spectal band (F1) and a laser range finder (T) whose transmitter emits a beam whose frequency (s) (F2) are outside of the spectral band (F1). According to the invention, the device also comprises a removable frequency converter (H) which can be interposed on the path of the laser beam from the transmitter to transform this beam into a laser beam comprising a frequency or a frequency band (F'1) located in the spectral band (F1) of the detector. The invention applies in particular to sighting devices for helicopters.

Description

The invention relates to a sighting device which comprises at least one

  optical detector operating in a spectral band and a laser range finder whose emitter emits a beam whose frequency or frequencies are outside said spectral band, which can be used in particular for military purposes. The problem arises in a sighting device comprising a detector and a range finder to harmonize the line of sight of the detector and the axis of the beam of the rangefinder to be sure that the distance information provided by the range finder corresponds to the distance from the

target targeted by the detector.

  To achieve this harmonization, it is known to use mechanical means but these means are generally heavy and would not be suitable, for example, when the sighting device is

  boarded an aircraft, in particular aboard a helicopter.

  It is also known to achieve the harmonization using optical return but these optics must be very precise and

  are therefore very expensive.

  Moreover, in both cases, the harmonization thus obtained is sensitive to vibrations and variations in

temperature.

  An object of the invention is to provide a sighting device which makes it possible to easily achieve harmonization by being franked.

disadvantages above.

  It is achieved according to the invention by providing the device with a removable frequency converter interposable on the beam path of the transmitter to transform the beam into a laser beam having a frequency or a frequency band located

  in the spectral band of the detector.

  To harmonize the line of sight of the detector and the axis of the rangefinder beam, the detector observes the multispectral image formed by the beam of the range finder on a control target, which observation is made possible by the fact that this image includes minus a frequency located in the spectral band of the detector and the result of this observation and, if applicable, the information provided by the range finder on the distance of this target, to correct

  the lack of possible harmonization.

  The correction methods can be manual or automatic. In the manual case, the operator operates the means until the multispectral image is on the axis of the detector. In the automatic case, an image processing system extracts the image formed in the detector and performs

automatically corrections.

  Correction based on the distance from the target is only necessary if the output optics of the detector and the range finder are not coaxial. The insertion of the distance correction is obvious if the process is automatic. In manual, it requires placing on one of the reticle bars a graduated scale allowing the operator to shift the reticle of the value corresponding to the

  distance it can read through the rangefinder.

  In preferred embodiments, the device of the invention may also have one or more of the following characteristics: it comprises another detector whose spectral band is different from that of said detector; it comprises a detector sensitive to one or more frequencies of the visible range and a detector sensitive to one or more frequencies of the infrared range; the frequency converter is constituted by one or more nonlinear crystals; the frequency converter is placed at a point of the laser beam where the energy of the beam has been concentrated;

  - it includes one or more cameras as detector (s).

  To aim an objective with the device of the invention, a control target is first aimed at with the optical detector, the frequency converter being interposed on the path of the laser beam of the transmitter so that the beam of the range finder forms on the target a multispectral image detectable by the detector, it determines the correction to be made to harmonize the line of sight of the detector and the axis of the beam emitted by the range finder and, after harmonization, it retracts the frequency converter to aim the objective and

  measure its distance with the rangefinder.

  The control target can be the goal itself or a

  target usually closer.

  For example, while the device is normally used to target targets located several kilometers away, a target target of a distance of about five hundred meters will preferably be used as a control target, to take into account the attenuation of the target. energy of the laser beam due to the interposition of the frequency converter. The invention is not limited to a particular device for allowing the retraction of crystals. For example, the crystals are

  mounted in a rotating barrel or drawer device.

  When one or more nonlinear crystals are used to carry out the frequency conversion, the crystals are chosen according to the

desired conversion.

  For example, to obtain one or more frequencies of the visible range, the crystals selected from the group consisting of potassium diphosphate and lithium niobiate (Li Nb 03) are interposed on the path of the beam emitted by the emitter of the rangefinder. potassium triphosphate, barium borate and borate

lithium.

  If one wants to obtain frequencies of the infrared range, one uses for example crystals chosen from the group consisting of silver and gallium sulphide (Ag Ga S2), silver and gallium selenide (Ag Ga Se2), Zinc and germanium phosphide (Zn Ge

P2)

  The use of crystals for the frequency conversion of a laser beam has been known per se since the 1960s, and therefore it is not necessary to describe it in more detail. For example, reference may be made to the following recent publications: Inorganic Crystals for Nonlinear Optical Frequency Conversion (BORDUI P.F. and FEJER M.M in Annu Rev. Mater Sci 23, 1993).

PB-321-379);

  - "Nonlinear materials and new sources" (Robert FREY and Christos FLYTZANIS in Science and Defense 94, DUNOD 1994, pp.

39-51)

EXAMPLES

  a) A CO2 laser emitting with a frequency allowing a direct infra-red detection is used and a frequency conversion is carried out to obtain a frequency of the visible range. b) An eye-safe laser (YAG + Raman shift) emitting at 1.54 micron wavelength is used and a frequency conversion is performed so that the emitted beam also has a wavelength of 0.6 band. - 1 micrometer (detectable with a camera sensitive to visible radiation) and a wavelength of the band 3 to 5 microns or the band 8 to 12 micrometers (detectable

  with a camera sensitive to infrared radiation).

  The figures of the attached drawing are explanatory diagrams of the harmonization method: FIG. 1 is a diagram illustrating a lack of harmonization in the case of a device comprising a detector and a rangefinder whose output optics are combined, and - FIG. 2 is a diagram illustrating a lack of harmonization in the case of a device comprising a detector and a rangefinder of which

  the output optics are separated.

  In the device of FIG. 1, an optical return, for example a system with semi-transparent mirrors M sends the beam of the rangefinder T in the output optics of a detector D, for example

a camera.

  In the case the difference E measured is indeed the parallelism gap between the axes AD and AT and no telemetric measurement is

  necessary to correct this gap and make the axes parallel.

  In the device of FIG. 2, the two beams come out by

  separate output optics S v, S2 ..

  In the case, we measure an angular difference E1 which must be corrected by the value e / d, when d is large before e, for

  determine the true angular difference E2.

  The line of sight of the detector can be corrected in several ways: By acting on the optical means of collimation. For example by angularly shifting a mirror or a prism in the optical path of the camera or the rangefinder; - If it is a camera, we can shift the detector in the focal plane or if there is a scanning device, shift the latter; It is also possible to move the materialization means of the optical axis as a reticle by moving it until it coincides with the image produced by the range finder. This can be done either with an optically projected reticle or with a reticle.

embedded in a Video Image.

  According to the invention, one or more non-linear crystals H. chosen as a function of the frequency of the laser emitter of the rangefinder and the detection band of the camera, are interposed during the harmonization procedure and are then retracted. The crystals are, for example, mounted on a rotating support P or on a sliding support. The invention is not limited to the choice of a

particular editing.

  In the case of a device of the type of FIG. 2 where the rangefinder is used to determine the distance of the target during the harmonization procedure, it is useful to separate the emission and reception functions of the range finder so that the return signal does not pass through the frequency converter

Claims (8)

  1. A sighting device, usable in particular for military purposes, which comprises at least one optical detector (D) operating in a spectral band (F1) and a laser rangefinder (T) whose emitter emits a beam whose frequency or frequencies ( F2) are outside said spectral band, characterized in that it also comprises a removable frequency converter (H) interposable in the path of the laser beam of the transmitter to transform this beam into a laser beam having a frequency or a frequency band   (FI) located in the spectral band (F1) of the detector.   2. Device according to claim 1 wherein the device comprises another detector whose spectral band (F2) is   different from that (F1I) of said detector (1).   3. Device according to claim 2 and which comprises a detector sensitive to one or more frequencies of the visible range and a   detector responsive to one or more frequencies of the infrared range.   4. Device according to one of claims 1 to 3, wherein the   frequency converter (H) is constituted by one or more crystals nonlinear.   5. Device according to one of claims 1 to 4 wherein the   frequency converter, (H) is placed at a beam point   laser where the energy of the beam has been concentrated.   6. Device according to one of claims 1 to 5, characterized in   it includes one or more cameras (D) as detector (s).   7. Application of a device according to one of claims 1 to 6,   the harmonization of the line of sight of the optical detector and the axis   the beam emitted by the range finder.   8. Application of a device according to one of claims 1 to 6,   for the purpose of an objective in which a target target (C) is aimed at, with the optical detector (D), the frequency converter (H) being interposed on the path of the laser beam of the transmitter, the correction is determined to perform to harmonize the line of sight of the detector and the axis of the beam emitted by the range finder and, after harmonization, retract the frequency converter (H) to   aim at the objective and measure its distance with the rangefinder.