IL47716A

IL47716A - Liquid cooled mirror

Info

Publication number: IL47716A
Application number: IL47716A
Authority: IL
Original assignee: Hughes Aircraft Co
Priority date: 1974-09-20
Filing date: 1975-07-15
Publication date: 1977-12-30
Also published as: IT1046920B; IL47716A0; GB1451597A; FR2285620B1; FR2285620A1

Description

Liquid cooled mirror HUGHES AIRCRAFT COMPAlfY C. 45416 PD-73024 LIQUID COOLED MIRROR FREDRICK J. MCCLUNG, JR.

ABSTRACT OF THE DISCLOSURE Mirror face plate has water passage formed in the back. The water passage has support posts throughout. Below the face plate, a splitter plate has a water passage in the back, again with support posts distributed therethrough. A backup plate structure provides connections to both the water passages. The face plate, splitter plate and backup plate structure are secured together to provide support and cooling for the face plate.

BACKGROUND This invention is directed to a liquid cooled mirror •structure, and particularly a mirror suitable for use in high power laser structures. ^|ft Patent 3,748,594 shows a laser structure particularly suited for high power applications. It provides for flow of 47716/2 the lasing gas, for gas cooling. The mirrors which define the ends of the optical cavity in that patent absorb energy!^ because they are not completely reflective. When lasing action is at a fairly high pulse rate, the energy absorbed in the mirrors causes temperature rise thereof and resultant deflection and distortion. The mirrors can go out of focus by means of such thermal distortion, to reduce laser efficiency.

In order to aid i the understanding of this invention it can be stated in essentially summary form that its directed to a liquid cooled mirror, particularly useful in a laser. The liquid cooled mirror has a face plate with a water passage formed in the rear thereof, and support posts distributed throughout the water passage for support thereof. The face plate is supported on a splitter plate which also has a water passage therethrough with posts supporting the plate. A backup plate structure supports the assembly to maintain the mirror face substantially free of mechanical and terminal distortions.

It is thus an object of this invention to provide a liquxd^mirror comprising. a face plate, said face plate having a reflective front surface, a portion of said reflective front surface being a beam footprint area for beam illumination and reflection, said face plate also having a rear surface, a single liquid coolant channel formed in the back of said face plate and extending laterally beyond said beam area with said channel being formed to leave integral support posts on the back of said face plate behind said beam area; 47716/2 a splitter plate having a front surface and a rear surface, said rear surface of said face plate and said posts¾ of said face plate being engaged against said front surface of said splitter plate, a single liquid coolant channel formed in back of said splitter plate extending laterally beyond said beam area with integral support posts left on the back of said splitter plate behind said beam area so that said liquid coolant channel in the back of said splitter plate is around said splitter plate support posts, said splitter plate being imperforate behind said beam area, first and second openings through said splitter plate away from said beam area to connect said single coolant channel in the back of said face plate with said single liquid coolant channel in the back of said splitter plate; and support means for supporting said splitter plate and 3aid face plate, said support means having a front surface against which the rear surface and said posts of said splitter plate engage so that said splitter plate and said face plate are supported by said support means, said support means being imperforate behind said beam area, inlet and outlet liquid coolant passages in said support means, said coolant passages being connected with said first and second openings in said splitter plate so that liquid coolant turbulently circulates as a single sheet flow throug each of said coolant passages in the same direction to minimize thermal gradients parallel to said mirror face without flow normal to the mirror face within the beam area to eliminate heat flow into said support means behind said beam area by coolant low to minimize thermal distortion of said mirror face.

Other objects and advantages of this invention will become apparent from a study of the following portion of the specification, and the claims and the attached drawings.

Fig. 1 is a front view of the liquid cooled mirror of this invention.

Fig. 2 is an enlarged section taken generally along line 2-2 of Fig. 1.

Fig. 3 is a view of the water passages , as taken along the line 3-3 of Fig. 2.

Fig. 4 is a further enlarged section showing the cooling liquid connection between the various structures within the liquid cooled mirror.

The liquid cooled mirror of this invention is generally indicated at 10. As is best seen in Fig. 2, mirror 10 is built up out of four members. Starting from the back , these members are secondary backup plate 12 , primary backup plate 14 , splitter plate 16 and face plate 18.

Face plate 18 has a front surface 20 which is of suitable optical characteristic to serve as mirror in a laser.

High levels of flatness and reflectivity are required for the service. Molybdenum is a suitable metal.

V7ater channel 22 is formed in the back surface of face plate 18. It is formed by machining or etching, with^ integral support poete 24 left behind. The size of the poet and the size of the passage is such that about 50% of the otherwise full flow area is taken up with the support posts.

The support posts are preferably circular and are equally spaced, and are of the nature of the support posts shown in FIG. 3.

Splitter plate 16 has a front surface 26 against which the back surface of face plate 18 and its support posts 24 rest. Similarly to the front plate, splitter plate 16 has a water passage 28 therethrough. Similarly to the face plate, splitter plate 16 has support posts 30 therein to support the structure. The view in FIG. 3 shows the circular character of posts 30, but the view of FIG. 3 could just as well be a partial view of the back of face plate 18, showing its liquid passage 22 and support posts 24. Preferably, the support posts and the two plates are offset from each other to minimize direct through metal to metal thermal paths. Slot 32 is cut through and part way across the splitter plate at one end thereof while slot 34 is cut through and part way across the splitter plate toward -the other end thereof. These slots 32 and 34 are flow slots to permit the passage of liquid coolant into the coolant channels in the face plate and splitter plate. -4- Primary backup plate 14 is positioned behind the splitter plate. The posts on the splitter plate and the edges of the splitter plate around the coolant channels engage against the front of primary backup plate 14.

Primary backup 14 has slots 36 and 38 across the front thereof respectively behind slots 32 and 34. Similarly, the backup plate 14 has slots 40 and 42 across the back thereof. These slots extend only partway through the backup plate. A plurality of cylindrical holes 44 inter-connects slots 36 and 40 while the plurality of cylindrical holes 46 interconnects slots 38 and 42, see also PIG. 1.

Secondary backup plate 12 has an inlet 48 and an outlet 50. These are respectively 'connected to passages 52 and 54 which are respectively at least partially in alignment with slots 40 and 42. By this interconnection, the inlet and outlet are connected to the coolant channels 22 and 28 so that as liquid coolant is passed into inlet 48 it flows up through passage 52, slot 42, and then through the plurality of holes 46 into slots 38 and 34 so that the liquid is distributed to the end of both of the liquid coolant channels. The liquid flows down through both of the coolant channels and out through slots 32, 36, holes 44 and slot 40 and thence through passage 54 and outlet 50.

As is seen in the drawings, the mirror is circular in construction, but only a rectangular area thereof is cooled. The entire face of each mirror is polished to provide optimum optical fabrication controls. However, the beam footprint, seen at 56 in FIG. 1, is rectangular and the cooled area is -5- 1 greater than the illuminated area 56. The flow of coolant 2 is transverse across the minimum length of the rectangular 3 beam footprint. This provides maximum cooling with minimum 4 pressure drop. 5 All of the parts are preferably made out of a metal 6 of high thermal conductivity, reasonable physical strength and 7 low thermal coefficient of expansion. Molybdenum is a suitable 8 metal for this purpose. Each of the four plates can be 9 machined by suitable machining methods, including electron 10 beam machining and chemical etch methods. When the support 11 posts are produced by etching, the pattern can be formed by 12 a photoresist. The plates can be assembled into a monolithic 13 structure by furnace brazing. In the liquid flow channels, 14 the support posts are typically of about 0.015 inches in height, 15 with a 0.040 inches diameter and a separation of 0.080 inches. 16 The preferred coolant is water and the two layers in 17 the cooling system can be supplied in parallel as shown or 18 in series, depending upon application requirements. The short 19 stiff columns in closer spacing thereof provides proper support 20 to the mirror face. With a water pressure of about 500psi, this 21 design can transfer heat at a rate of greater than 22 3 x 104 BTu hr"1 ft"2 OF"1. 23 This invention having been described as a preferred 24 embodiment, it is clear it is susceptible to numerous modifi- 25 cations and embodiments within the ability of those skilled in 26 the art and without the exercise of the inventive faculty. 27 Accordingly, the scope of this invention is defined by the 28 scope of the following claims.

AAD/cp

[225] -6- 47716/2

Claims

1. A liquid cooled mirror comprising: ¾ a face plate, said face plate having a reflective front surface, a portion of said reflective front surface being a beam footprint area for beam illumination and reflection, said face plate also having a rear surface, a single liquid coolant channel formed in the back of said face plate and extending laterally beyond said beam area with said channel being formed to leave integral support posts on the back of said face plate behind said beam area; a splitter plate having a front surface and a rear surface, said rear surface of said face plate and said posts of said face plate being engaged against said front surface of said splitter plate, a single liquid coolant channel formed in back of said splitter plate extending laterally beyond said beam area with integral support posts left on the back of said splitter plate behind said beam area so that said liquid coolant channel in the back of said splitter plate is around said splitter plate support posts, said splitter plate being imperforate behind said beam area, first and second openings through said splitter plate away from said beam are to connect said single coolant channel in the back of said face plate with said single liquid coolant channel in the back of said splitter plate; and support means for supporting said splitter plate and said face plate, said support means having a front surface against which the rear surface and said posts of said splitter plate engage so that said splitter plate and said face plate are supported by said support means, said support means being imperforate behind said beam area, inlet and outlet liquid coolant passages in said support first and second openings in said splitter plate so that liquid coolant turbulently circulates as a single ^ sheet flow through each of said coolant passages in the same direction to minimize thermal gradients parallel to said mirror face without flow normal to the mirror face within the beam area to eliminate heat flow into said support means behind said beam area by coolant flow to minimize thermal distortion of said mirror face.

2. The liquid cooled mirror of Claim 1 wherein said support means comprises primary and secondary backup plates, said secondary backup plate being toward said splitter plate and being engaged by said splitter plate and supporting said splitter plate, and said secondary backup plate being engaged by said primary backup plate and supporting said primary backup plate.

3. The liquid cooled mirror of claim 2 wherein inlet and outlet liquid coolant connections are formed in said secondary backup plate in communication with said coolant passages and positioned outside of said beam area. /~\

4. The liquid cooled mirror of claim 1 wherein at least two op¾nings are formed through saidsplitter plate for connecting liquid coolant flow through said coolant channel in said face plate, said openings being positioned laterally outside said beam.

5. The liquid cooled mirror of claim 1 wherein said liquid coolant channels are formed into the back of said face plate and said splitter plate and said support posts are integrally formed as, part of said splitter and said face plate.

6. The liquid cooled mirror of claim 5 wherein at least two openings are formed through said splitter plate for connecting liquid coolant flow through said coolant channel in said face plate, said openings being positioned laterally outside said beam area.

7. The liquid cooled mirror of claim 6 wherein said opening through said splitter plate is a slot.

8. The liquid cooled mirror of claim 7 wherein a slot is formed in said support means in substantial alignment with said slot in said splitter plate, said slot in said support means forming a part of said coolant passages.

9. The liquid cooled mirror of claim 8 wherein said liquid coolant channels in said face plate and said splitter plate are each connected to both said inlet and said outlet passages so that flow through liquid coolant channels is in parallel. For fhe AppFfeanfe DR. REINHOLO COHN AND PARTNERS' - 8 -