Optical refrigerator and sensor including such a refrigerator

Abstract

An optical refrigerator for cooling an infrared detector or sensor, that includes a laser radiation source, a cooling crystal for receiving laser radiation from the source and to be cooled, an element to be cooled, and a thermal link in heat exchange between the crystal and the element to be cooled, in order to transfer frigories from the crystal to the element to be cooled. The thermal link comprises two plates having respective first ends in heat exchange with two distinct surfaces of the crystal, respectively, the two plates having second ends in heat exchange with the element to be cooled.

Claims

1. An optical refrigerator for cooling an infrared detector or sensor, the refrigerator comprising a source of laser radiation, a cooling crystal configured to receive the laser radiation from the source and to be cooled, an element to be cooled and a thermal link in heat exchange between the crystal and the element to be cooled in order to transfer frigories from the crystal to the element to be cooled, wherein the thermal link comprises two plates having respective first ends in heat exchange with two distinct surfaces of the crystal, respectively, and respective second ends in heat exchange with the element to be cooled.

2. The refrigerator of claim 1, wherein one of the second ends is in heat exchange with one surface of the element to be cooled that is distinct from another surface of the element to be cooled that is in heat exchange with the other of the second ends.

3. The refrigerator of claim 2, wherein the second ends of the two plates sandwich the element to be cooled.

4. The refrigerator of claim 1, wherein the first ends of the two plates sandwich the crystal.

5. The refrigerator of claim 1, wherein: the plates each have a “J” or doglegged shape that extends in a plane non-rectilinearly; and the ends of the plate in heat exchange with the crystal and the element to be cooled, respectively, are located at two ends located on either side of a dogleg or corner, respectively.

6. The refrigerator of claim 1, wherein the plates are made of a transparent material.

7. The refrigerator of claim 6, wherein the plates are made of glass or sapphire.

8. The refrigerator of claim 1, further comprising at least two mirrors placed around the crystal in order to concentrate the light in the crystal.

9. The refrigerator of claim 1, further comprising baffles for absorbing the light radiation generated by the crystal, the baffles being placed around the crystal.

10. The refrigerator of claim 9, further comprising baffles for absorbing the light radiation generated by the crystal also around the faces of the crystal that are linked to the plates.

11. The refrigerator of claim 1, wherein the element to be cooled is a cold finger or a focal plane intended to transfer frigories to a load.

12. A detector comprising a measuring unit and refrigerator of the measuring unit, wherein the refrigerator is the refrigerator of claim 1.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Other particular features and advantages will become apparent from reading the following description, given with reference to the figures, in which:

(2) FIG. 1 shows a schematic and partial side view illustrating an example of the structure and operation of an optical refrigerator;

(3) FIG. 2 shows a schematic and partial side view of a detail of an example of the optical refrigerator structure according to the invention;

(4) FIG. 3 shows a schematic and partial face-on view of a detail of the optical refrigerator of FIG. 2;

(5) FIG. 4 shows a schematic and partial perspective view of one portion of another example of the optical refrigerator structure according to the invention, integrated into a sensor with a view to the cooling thereof;

(6) FIGS. 5 and 6 show schematic and partial perspective views of the refrigerator of FIG. 4 in two partially disassembled configurations.

DETAILED DESCRIPTION OF THE INVENTION

(7) FIG. 1 illustrates the structure and the operating principle of an optical refrigerator.

(8) Such a refrigerator 1 comprises a source 2 of laser radiation configured to emit radiation toward a cooling crystal 3 (cf. FIG. 5 also). The crystal 3 is framed between at least two reflective mirrors 7 in order to concentrate the light in the crystal 3. The assembly (and in particular the type of crystal 3 or equivalent) is configured to generate cooling of the crystal 3 via an “anti-Stokes” effect.

(9) The crystal 3 is placed in heat exchange (contact) with an element 4, 5 to be cooled via a thermal link 6.

(10) As illustrated in FIGS. 2 to 6, the thermal link comprises two plates 6 having respective first ends in heat exchange (preferably direct contact) with two distinct surfaces of the crystal 3, respectively, the two plates 6 having second ends in heat exchange (preferably direct contact) with the element 4 to be cooled.

(11) As illustrated, preferably the second ends of the two plates 6 are in heat exchange with two distinct surfaces or flanks of the element 4 to be cooled, respectively. For example, the second ends of the two plates 6 sandwich (clasp laterally) the element 4 to be cooled, i.e. the plates 6 are placed on either side of two opposite flanks of the element 4 to be cooled (cf. FIGS. 2 to 6).

(12) In the same way, the first ends of the two plates 6 preferably sandwich the crystal 3, i.e. the plates 6 are placed on either side of two opposite flanks of the crystal 3.

(13) The plates 6 preferably each have a “J” or doglegged shape, i.e. each plate 6 extends in a plane non-rectilinearly, the ends of the plate 6 in heat exchange with the crystal 3 and the element 4 to be cooled, respectively, being located at two ends located on either side of the dogleg or corner, respectively.

(14) The plates 6 for example have a thickness comprised between 0.5 and 5 mm, a width comprised between 1 and 10 mm and a length comprised between 2 and 40 mm. At each end the plates 6 make contact with the crystal 3 and the element to be cooled in an area for example of size comprised between 1 mm.sup.2 and 75 mm.sup.2 and 1 mm.sup.2 and 100 mm.sup.2, respectively.

(15) The areas of contact for the heat exchange are thus significantly increased with respect to known solutions without increasing the bulk of the device.

(16) The two plates 6 are for example made of sapphire or any other suitable transparent material: glass, etc. By transparent what is in particular meant is: transparent at suitable wavelengths (for example in order to let pass the radiation emitted by the crystal, which is symbolized by lines or arrows in the figures).

(17) This geometry makes it possible to limit the amount of anti-Stokes radiation emitted from the crystal toward the element 4 to be cooled.

(18) In addition, this architecture of the thin plates 6 allows the mirrors 7 and optical baffles 8 to be easily placed around the crystal 3. The optical baffles 8 (sometimes called “optical screens”) are provided to insulate the crystal and in particular to absorb radiation around the crystal 3. These baffles 8 may in particular be made of metal, copper, aluminum, etc.

(19) As may be seen in FIGS. 3, 4 and 5 in particular, optical baffles 8 may be placed on either side of the first ends of the plates 6 in contact with the crystal 3. In particular, and as illustrated in the figures, the architecture of the thermal link 6 allows optical baffles 8 to be placed all the way around the crystal 3. Thus, in the case of a crystal 3 of parallelepipedal shape, a baffle 8 may be placed facing the six faces of the crystal 3.

(20) This allows the crystal 3 to be optically isolated more completely than in the prior art and in particular under the bottom face of the crystal (i.e. the face turned toward the element 4 to be cooled). This improves the efficiency of the system.

(21) As illustrated in FIG. 5, the laser source 2 may be configured to direct a beam through an orifice in a baffle 8.

(22) FIGS. 4 to 6 illustrate an example of a structure of an integrated assembly comprising a cooler 1 and a detector (in particular an infrared detector).

(23) The volume of the refrigerator portion may be decreased for example to a cubic volume of less than ten cm side length.

(24) With respect to existing solutions, apart from the decrease in size, the detection platen may be simplified.

(25) In the example of FIG. 4, the thermal link is in exchange with a part 4 that may be a focal plane in heat exchange with a component 5 of the sensor to be cooled such as an optical sensor of a space-based apparatus (satellite, etc.).

(26) This architecture also has a faster thermal response. Specifically, it appears to be possible to achieve a time to cool down to the target temperature (without load) of about 10 minutes approximately.

(27) The invention may also be applied to in situ cooling of microelectronic components (for example power transistors or microcircuits) at temperatures close to ambient, and to the cooling of crystals used in the high-power (continuous-wave or pulsed) lasers.

(28) While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

(29) The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.

(30) “Comprising” in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing i.e. anything else may be additionally included and remain within the scope of “comprising.” “Comprising” is defined herein as necessarily encompassing the more limited transitional terms “consisting essentially of” and “consisting of”; “comprising” may therefore be replaced by “consisting essentially of” or “consisting of” and remain within the expressly defined scope of “comprising”.

(31) “Providing” in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.

(32) Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

(33) Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.

(34) Ali references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited.