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Description  |
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The invention relates to a beam guiding optical system for laser radiation,
especially for the radiation of a medical laser, for the continuous
adjustment of the focal length, having at least one concave reflector and
adjusting means acting on parts of the beam guiding optical system.
A beam guiding optical system for surgical purposes is disclosed in U.S.
Pat. No. 4,396,285. The laser system therein described, which has a
working laser and an aiming laser, has a pivoting, concavely curved mirror
whereby the position of the focal point of the laser beam in the working
plane can be varied. This arrangement does not provide the possibility of
varying the focal length and with it the position of the focal point.
Also known are lens systems for laser systems, which usually have a
helium-neon aiming laser and a CO.sub.2 working laser; in these lasers the
focal length can be variably adjusted by displacing the lenses. Such
optical systems, which contain lenses, have dispersion, so that, as a
result of the different wavelengths of the aiming laser and working laser,
the focal points of the aiming laser and working laser do not coincide in
their position in space. If beams strike the center of the lenses, the
focal points diverge longitudinally. If they strike them off-center, they
also diverge laterally; thus the aiming beam fails its purpose.
It is an object of the present invention, therefore, to provide a new and
improved beam guiding optical system for laser radiation which avoids one
or more of the disadvantages of such prior systems.
It is another object of the present invention to provide a new and improved
beam guiding optical system, especially for the radiation of a medical
laser, in which the focal length is continuously variable, and any
aberration, e.g., due to the dispersion of optical lens imaging systems,
is largely avoided.
These objects are achieved by the fact that the adjusting means comprises a
linearly movable carriage which carries at least two carriage mirrors
disposed with respect to one another, at least one of these carriage
mirrors being concavely or convexly curved; that the beam axis of the
input beam falling on the one mirror is parallel to the beam axis of the
beam issuing from the adjusting means, the axis of displacement of the
carriage being parallel to the beam axis of the input and output beam;
that at least one deflecting mirror is disposed in the beam path outside
of the adjusting means, which has a carriage mirror of a curvature
complementary to the curvature of the aforesaid at least one curved
carriage mirror, the mirrors of complementary curvature, which are surface
elements composed of solids of revolution of conic sections, being aligned
with one another such that the corresponding focal points of the
particular mirror lie in the plane which is spanned by the incident and
reflected beam of the particular mirror.
It is important that the laser beams be reflected both by a concave and by
a convex mirror before they fall upon the working field. The mirrors
disposed for adjustment of the distance between them permit shifting the
focal point in the direction of the beam. Aberrations due to dispersion
are largely prevented by the two mirrors of complementary curvature
disposed in the beam path, since no optical refraction occurs, as would be
the case with optical lenses. The use of mirrors of complementary
curvature, which are surfaces of solids of revolution of conic, sections,
i.e., ellipsoids or paraboloids which have anisotropic radii of curvature
in at least one of the two directions perpendicular to one another,
prevent aberrations. The geometrical shape of the ellipsoids and
paraboloids can be computed by means of the known mathematical formulas
for the determination of conic sections, the necessary focal lengths being
able to be given by the geometric optical or Gaussian optical course of
the beam.
If slight aberrations are to be tolerated, then toroidal mirrors can be
used instead of the solids of revolution of conic sections. For example,
the radii of curvature of such toroidal mirrors are to be selected as R/k
and, in the direction perpendicular thereto, as R.times.k, wherein
k=.sqroot.2 (for an angle of incidence of 45.degree.). By arranging the
mirrors within the carriage such that the beam axes of the beam entering
and leaving the adjusting means are parallel to one another and the
carriage is to be shifted parallel to the beam axes, i.e., in the
direction of the beam axes, it is possible in a simple manner to adjust
the focal length of the optical system and with it the position of the
focal point.
The concavely or convexly curved mirror is used preferably as the carriage
mirror on the exit side, with regard to the beam direction. A planar
mirror can be used as the entry side carriage mirror within the adjusting
means or carriage.
Depending on the desired location of the focal point and on the required
beam diameter, the carriage mirror on the entry side can be in the form of
a convex or concave mirror, in which case the at least one deflecting
mirror provided in the beam path outside of the adjusting means, which
reflects the beam toward the working plane, has a curvature corresponding
to the carriage mirror on the entry side.
Preferably the deflecting mirror is disposed for pivoting about at least
one axis perpendicular to the beam axis, so that, in addition to the focal
point adjustment, the system permits the focal point to swing in a
particular working plane. This permits the focal point of the laser
radiation to be adjustable in two additional directions in space, i.e., a
total of three.
The adjusting means and the deflecting mirror can be made in a single unit,
which is then preferably disposed on a beam guiding arm having a plurality
of articulations, so that the focal point can be moved about by such a
beam guiding optical system in a variety of working planes variously
oriented in space.
In a constructively simple embodiment, the carriage is displaced linearly
by means of a gear drive, preferably such that the carriage is guided in a
groove and bears a rack which is displaced together with the carriage by a
pinion meshing therewith. Other displacement mechanisms are possible,
especially in the form of a cylinder and piston.
In accordance with the invention, a beam guiding optical system for laser
radiation, especially for the radiation of a medical laser, for the
stepless variation of the focal length comprises adjusting means acting on
parts of the beam guiding optical system. The adjusting means comprises a
linearly movable carriage which bears at least two carriage mirrors
disposed with respect to one another. At least one of these carriage
mirrors is concavely or convexly curved. An entry beam falls on a mirror
having a beam axis which is parallel to a beam axis of a beam emerging
from the adjusting means. The carriage has an axis of displacement which
is aligned parallel to the beam axis of the entry and emerging beams. At
least one deflecting mirror is disposed in a beam path outside of the
adjusting means, which has a carriage mirror of a curvature complementary
to the curvature of the aforesaid at least one curved carriage mirror. The
mirrors of complementary curvature, which are surface elements of solids
of rotation of conic sections, are aligned with one another such that the
corresponding focal points of the at least one deflecting mirror in the
beam path outside the adjusting means lie in the plane which is spanned by
the incident and reflected beam of the aforesaid at least one deflecting
mirror.
For a better understanding of the invention, together with other and
further objects thereof, reference is made to the following description,
taken in connection with the accompanying drawings, and its scope will be
pointed out in the appended claims.
Referring now to the drawings:
FIG. 1 shows diagrammatically a laser system with a beam guiding optical
system according to the invention;
FIG. 2 is a detailed diagrammatic representation of the beam guiding
optical system of FIG. 1;
FIG. 3 shows diagrammatically a system in which, in contrast to the
embodiment of FIG. 2, the displaceable carriage and one deflecting mirror
are mechanically uncoupled from the beam guiding arm;
FIG. 4 is a diagrammatic representation of a system in which the adjusting
means is displaceable vertically;
FIG. 5 is a diagrammatic representation of a system in which, in contrast
to the embodiment in FIG. 4, a rotatable deflecting mirror is used and the
carriage is vertically displaceable; and
FIG. 6 shows diagrammatically a system similar to FIG. 5, but with a
horizontally displaceable carriage.
Referring now more particularly to FIG. 1, the laser system shown in FIG. 1
has a neon laser as its pilot or aiming laser 1, and as its working laser
2 a carbon dioxide laser; their beams are brought together before they
fall upon a deflecting mirror 4. From this deflecting mirror 4 the beams
strike a concave mirror 5 and a convex mirror 6 in the direction of the
working plane as indicated by the arrow 7.
As FIG. 2 shows, the concave mirror 5, as it is indicated in FIG. 1, is
disposed at the end of a beam guiding arm 8. This beam guiding arm 8,
which is an articulated mirror arm, has three planar mirrors 9, each in a
link 10, which deflect the beam each by 45.degree.. The individual links
10 are joined together by two joints 11; an additional joint 11 is
disposed between the first joint 11, as seen in the direction of the beam,
and an arm 12. By means of the three joints 11, and in some cases by an
additional joint (not shown) at the end of the last line 10a, the concave
mirror 5 and the deflecting mirror 6 can be turned in any desired
direction in space, and from this it follows that the deflecting mirror 6
is also carried by the beam guiding arm.
The parallel laser beams are focused on a common focal point 14 by the two
mirrors 5 and 6, the deflecting mirror 6 being a convex mirror in the
embodiment according to FIG. 2. To vary the position of the focal point 14
perpendicular to the working plate 15, the distance between the convex
deflecting mirror 6 and the concave mirror 5 is varied. For this purpose
the beam guiding arm 8 preferably is made displaceable horizontally in the
direction of the arrow 16, in guides which are not shown in detail. To be
able to adjust continuously the distance between the two mirrors,
preferably a pinion 19 engages a rack 18 which is fastened to the upper
end of the carriage 17. This drive can also, for example, be in the form
of a worm gear drive.
In the embodiment according to FIG. 2, the distance between the convex
deflecting mirror 6 and the concave deflecting mirror 5 is varied for the
adjustment of the focal point 14 (the range of adjustment of the focal
point is indicated by the arrows 20) by varying the beam guiding arm 8
with the concave mirror 5 disposed therein, relative to the deflecting
mirror 6. In the embodiment according to FIG. 3, however, both the
deflecting mirror 6 and the beam guiding arm 8' are fixed in their
distance one from the other, but the carriage 17 is displaced between the
deflecting mirror 6 and the beam guiding arm 8' by means of the
rack-and-pinion drive 18 and 19. Within the carriage 17, in contrast to
the embodiment in FIG. 2, an additional planar mirror 21 is disposed,
which reflects the beam from the last planar mirror 9 toward the concave
mirror 5. Since both the mirror 9 and the mirror 21 are planar mirrors,
the beam will run parallel between these two mirrors, so that the
variation of the distance will have no effect on the beam. The
displacement of the focal point 14 is produced only by varying the
distance between mirrors 5 and 6. In another embodiment, which is not
represented, the curvatures of the mirrors 5 and 6 can be reversed. The
beam 25 is therefore expanded, which results in a focal point 14 at a
smaller distance from the mirror 6 which can be refracted according to
Gaussian optical formulas.
In an additional embodiment alternative to FIG. 3, the carriage in the
embodiment shown in FIG. 4 is displaceable vertically, and likewise has at
the entry end an additional planar mirror 21 plus a concave mirror 5.
Outside of the carriage 17, an additional deflecting mirror 22 of convex
curvature is provided in addition to the deflecting mirror 6' which has a
concave curvature, for the purpose of throwing the beam emerging from
carriage 17 through mirror 5 onto the mirror 6' which in this example is
concave. In the illustrated embodiment, the convex curvature of the mirror
22 is divided between the two mirrors 5 and 6'. If the curvatures of
mirrors 5 and 22 are suitable, the mirror 6' can also be replaced by a
planar mirror. The mirror 9, which throws the beam onto the additional
planar mirror 21 in the carriage 17, can be the exit mirror of the beam
guiding arm 8'.
To be able to move the mirror and the focal point 14 in the working plane,
the mirror 6', which in FIG. 5, for example, is a planar mirror, is
mounted for rotation about two axes 23 which are perpendicular to one
another, and of which only one is shown. In the rest of the arrangement of
the mirrors, the embodiment in FIG. 5 is the same as that of FIG. 4.
In the embodiment according to FIG. 6, as in the embodiment in FIG. 5, a
planar mirror is used as a rotating mirror on the exit side of the beam
system. If a curved mirror is rotated in this case, the laser beam will
strike the mirror, not at 45.degree., but at a variable angle. In the case
of angles of incidence other than 45.degree., the result is an aberration
(astigmatism) which intolerably deforms the caustic of the beam in the
focusing range. This does not happen with flat mirrors of this kind.
In contrast to the embodiment in FIG. 5, the deflecting mirror 22, marked
22' in FIG. 6, is a planar mirror. Furthermore, the carriage 17 preferably
is shifted horizontally, thereby changing the distance between the mirrors
5 and 21. The focal length of the mirror 21 (paraboloid of rotation)
according to FIG. 6 preferably amounts to -100 mm, and that of the mirror
5 (ellipsoid of rotation, image scale 1:3) preferably is about 90 mm. The
range of displacement 16 of the carriage 17 preferably amounts to 20 mm,
the distance between the mirrors 5 and 21, indicated by the arrows 27,
preferably is a minimum of 15 mm and a maximum of 35 mm; the focal length,
referenced 26 in FIG. 6, preferably is accordingly a minimum of 250 mm and
a maximum of 400 mm.
As can be seen in the Figs. the axes of displacement of the carriage 17,
which are indicated by the arrows 16, are parallel to the beam axes of the
entry beam 24 striking the entry mirror of the carriage, and of the exit
beam 25. Basically, the displacement of the carriage 17 varies the
distance between a convex and a concave mirror, so that the focal plane
changes with the change in the distance. The two mirrors of complementary
curvature, which are surface elements of solids of rotation of cone
segments, i.e., ellipsoid-of-rotation or paraboloid-of-rotation surface
elements, are so aligned with one another that the corresponding focal
points of the deflecting mirror in the path outside the adjusting means
are in a plane which is spanned by the incident and the reflected beams of
that deflecting mirror.
While there have been described what are at present considered to be the
preferred embodiments of this invention, it will be obvious to those
skilled in the art that various changes and modifications may be made
therein without departing from the invention, and it is, therefore, aimed
to cover all such changes and modifications as fall within the true spirit
and scope of the invention.
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