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One of the methods of geometrical summation of radiation from a plurality of
lasers (including laser diodes) is known as "knife-edging". Idf somaeone is
interested in the details, please read here.
After getting bored of gluing the mirrors after each replacement of laser
diodes (including cleaning purposes), I've needed to think is there a way to
make a tunable device, which is not needed to be reassembled each time.
Common lasers use "mirror alignment mounts" for fine tuning of position of
their mirrors. One way to make them in DIY condition was described here.
However those ones are too bulky to use them for the geometrical addition of
rays of diode lasers. There also exist some commercial miniature alignment
plates, but they are way too expensive.
So it was needed to invent how to manufacture micro-sized alignment plates in
the home-kitchen-garage conditions. The result of this is the topic of the
present guide. The size is of most importance here, so one needs to put the
parts at minimal distance one from another. It means that the precision is of
most importance too. If You allow a millimeter bias in the position of a hole,
You will trash the whole part. Dont be lazy - do the sketching (marking) well.
Use master-templates at any possibility. Use a computer to prepare the
templates. Even a common (paper using) printer is a good aid here. Use punching
to avoid shifting of the drill-bit when drilling.
We will need the next expendables:
- Aluminium angle-stock having the wall thickness of 2 mm. The sizes of the
sidewalls You can choose as You like, but if they were close to the sizes of
the future alignment plate, the less material would come to waste.
- M2 x 6 screws, not less than 3 pcs. En excess would not harm, because a
spoilage is possible.
- a steel plate 1-2 mm thick. One can use any magnetic steel, and better it to
be plane.
- A cylindrical neodimium magnet. 4 mm in diameter and 10 mm long.
- An epoxy resin of a good quality.
Cut a blank of the "body" of the future alignment plate from the aluminium
angle stock. If You are going to use the templates from this guide the size of
the "facial" side of the blank should me 9x16 mm. The "leg" - the part used to
attach the mirror mount to the basement - may be any of Your choice.
-
Print (using a common printer and common paper) the template for the facial
side of the mirror mount blank. You can download the template from here or
You can design Your own. The file for printing also contains vertical and
horizontal scaling marks. Get some ruler out there and use it to ensure that
both horizontal and vertical scaling marks are really equal to one centimeter
after printing. If not - dig the settings of Your printer until it is able
to print at 1:1 scale.
-
Glue the paper template onto the facial side of the mirror mount blank and
cut off the excess of paper.
-
Punch the centers of the holes (where the cross lines are on the template).
And drill the holes then. The central hole must have its diameter equal to the
diameter of the neodymium magnet You use. (In our case - 4 mm.) For the side
holes use 1.5 mm drill bit.
-
In small holes make thread M2.
-
Then sharpen the end of the threaded part of the screw. One can do it by
hands or either to use a drill and dremel. However to chuck it properly one
needs to screw a batch of nuts there beforehand.
Also screw head needs to be reduced in diameter to 3 mm.
-
Screw the screws in the mount so that the tips of the screws stick out half millimeter.
-
Put the mount on a steel plate. Use the epoxy resin to glue cylindrical
magnet into the central hole in the mirror mount body. One could position
it flush, but it may be better if it protrudes a bit from the facial side
of the mirror mount body (a half of millimeter would be enough).
-
Get a plate of steel and from there cut a rectangle that fits the face size
of the alignment plate
(9 x 10 mm).
-
Paint one of the sides of the steel plate with a black marker.
-
When the epoxy has cured. Place a steel plate on the mount body, with the
painted side turned to the bolts. Move the plate on the mount, first
vertically and then horizontally. Remove the steel plate and you will get
precise marking with the location of the points of the adjustment screws.
Use a drill bit or a chamfer bit to make these conical pits. It will be
the places for the alignment screws to abut. Therefore the conical pits should
be placed exactly under the holes in the body of the mirror mount. If they miss
the alignment plate will jam when it works, ant the position of mirror will be
unstable. The better You've done the previous stage, the better will the pits
be positioned.
All the parts are ready. One needs only
to assemble the mirror mount. As You can see the magnet does perfectly carry
the duties of a disk spring (an maybe even better).
-
The mirror should be glued over the steel plate. It is handy that one can
always remove this plate without disassembling all the other parts of mirror
mount.
When the mirror mount works not only the steel plate is being tracted to the
magnet, but the screws themselves do also work as magnetic conductors,
providing the additional tracting forces it the points of support. It makes
the alignment to be even more stable.
This kind of mirror mount was used by me with a great success in kinife-edged
systems of geometrical summation of power of laser diodes.
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