Laser active optronic system with improved detectivity

#The present Application is based on International Application No. PCT/EP2004/053370, filed on Dec. 9, 2004, which in turn corresponds to FR 03/14602 filed on Dec. 12, 2003, and priority is hereby claimed under 35 USC §119 based on these applications. Each of these applications are hereby incorporated by reference in their entirety into the present application.

#The invention relates to a laser active optronic system with improved detectivity, and applies in particular to an active imaging system or to a laser telemetry system, and in general to any active optronic system comprising a laser emission channel and a laser receive channel, and more particularly in systems referred to as “eye-safe”.

#Laser active optronic systems have numerous applications, including in particular telemetry, based on the flight time measurement of a laser pulse emitted by the system and backreflected by the target, or active imaging systems in which a target to be imaged is illuminated by a non-natural source of the laser source type. For eye-safe reasons, it is necessary to avoid the use of emission sources whose wavelengths are in the visible. Eye-safe wavelength emission sources are preferred, that is to say those having wavelengths at which the regions of the eye anterior to the retina (the cornea, the aqueous humor and the lens) are absorbent so that the retina is protected from the impact of a laser beam in the eye. These wavelengths belong to the near infrared (typically above 1 μm) and the sources conventionally used are for example erbium-doped lasers (1.5 μm emission wavelength) or neodinium-doped lasers (1.06 μm emission source) which are associated with nonlinear optical devices such as optical parametric oscillators, in order to emit at wavelengths above 1 μm. The use of such sources requires, for the optronic systems, components (optic, receiver, etc.) that are sensitive to these wavelengths.

#Still other objects and advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein the preferred embodiments of the invention are shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious aspects, all without departing from the invention.

#Accordingly, the drawings and description thereof are to be regarded as illustrative in nature, and not as restrictive.

#FIGS. 1A and 1B, diagrams of one example of an optronic system according to the invention in two embodiments;

#In the figures, identical elements are indicated by the same reference numbers.

#FIG. 1A shows, in the form of a simplified diagram, one example of a laser active optronic system, according to the invention. This is for example a telemetry system or an active imaging system. It comprises a channel 1 for the emission of a laser beam for illuminating a target and a channel 2 for receiving the wave backscattered by the target. In this example, the two channels are separate, but the system could just as well be monostatic, that is to say one having an input window common to the two channels. The channel 1 comprises, in a known manner, a source 10 for emitting a laser beam 11 intended for illuminating a target (not shown), a beam-shaping objective 12, and an output window 13. The laser emission source is advantageously a pulse source, but a continuous or quasi-continuous emission source is also conceivable in certain applications, especially in active imaging. The receive channel 2 for the beam 20, corresponding to the light flux backscattered by the target, further includes the input window 21 and an objective 22, which is intended to focus the light beam 20 onto detection means 23 connected to an electronic signal processing device (not shown).

#According to the invention, an optical switching device 24 that receives the backscattered wave 20 is positioned in the receive channel 2. This device comprises an optical gain medium 241 and pumping means 242 for pumping the gain medium, such that the gain medium is absorbent and the wavelength of the emission laser 10 becomes substantially transparent when it is pumped, in such a way as to allow the switching device to be actuated in the off mode or on mode respectively. The switching device further includes a control unit 243 for controlling the pumping means, allowing the switching device to be actuated in the on mode in at least one temporal window of predetermined duration, triggered at a predetermined instant after the start of emission of the illuminating laser beam.