The invention relates to a method for reproducible positioning
a target object into the effective volume of a first laser radiation,
in particular a pulsed laser radiation, which after a deflection optics,
which is highly reflective for
the first laser radiation and transmissive for at least a second laser radiation,
can be focused by means of a focusing optics in the effective volume. The
Invention further relates to a system having the same features,
in particular for carrying out the
The invention is based on the fact that it is known in the art with laser pulses, in particular high-intensity laser pulses with powers of terawatts (10 12 watts) or more, to illuminate target objects, the so-called targets, and thus to produce physically desired processes, which are largely dependent on depend on the achieved light intensity in the focus.
Thus, it is known that, for example, from light intensities of 10 18 watts per square centimeter, the running processes are highly nonlinear, resulting in a variety of novel physical effects. Examples are the acceleration of electrons to several 100 million electron volts and the acceleration of protons to several 10 million electron volts on an acceleration distance of only a few microns. Likewise, in some cases very strongly directed particle beams with these properties can be generated in an extremely short time, for example less than 10 picoseconds (10 -12 seconds), e.g. B. for medical applications, such as in the radiation therapy of cancer or the production of short-lived radiopharmaceuticals, are of interest.
It is also possible to use ultrashort coherent X-ray pulses with the aid of lasers
generate, in addition to an application in medicine, for example
also in microchip production, d. H. for lithographic processes,
of extremely large
the above-described or other desired effects is an accurate one
Focusing the laser beam or the laser pulse on the target object
or the target. This is usually
the beam with mirror optics of the shortest possible focal length instead of
Lenses made to the intensity in the focal spot on the material
of the target object, which is used to produce particles or X-rays
should be used to maximize, as well as an extension
the pulse duration by dispersive effects when passing through the
to avoid optical material.
is due to the very strong focus of the highest intensity area only in
reached a very small effective volume, allowing for a maximum
Efficiency of the distance between the focusing optics and the surface of the
Target object highest
must be adjusted to a few microns accurate.
is all the more problematic, since used focusing optics in these
high-intensity pulses can be formed by focusing mirror, in particular
parabolic focusing mirrors that have very high masses of several
whereas the targets are typically only a few microns in size
form, which consist for example of metal or plastic films.
is it there that a misadjustment of the distance between these
Objects squared in a loss of light intensity.
To prevent this problem, it is known in the art,
that permanent lights of the amplifier medium of a used
Lasers, the so-called reinforced
spontaneous emission or English Amplified Spontaneous Emission,
ASE, on the surface
focus on a target object and with the help of powerful telescopes
to observe. There then takes place an adjustment of the distance between
the focusing optics, ie in particular a parabolic concave mirror
and the target object until the experimenter has gained the impression
to have approached an optimal position. This procedure will
single laser pulse,
for generating the aforementioned particles or X-rays
should be used.
It is that the above procedure is extremely tedious and inaccurate
is because it is personal
Impression of the experimenter turns off and beyond that non-destructive
since already on sensitive targets the focused spontaneous
Emission of the non-Q-switched
Lasermediums can reach such a high intensity that a
sensitive target object, especially plastics o. Ä., Even
already affected by this radiation or even
High yield production applications are therefore known
The object of the invention is to provide a method of the aforementioned generic type and a system with which a reproducible positioning of a target object can be achieved, in particular to achieve high yields or repetition rates and in particular a shot to shot reproducibility. It is white terhin object of the invention to provide a method and an apparatus with which the focusing of the laser beam on a target object quickly, accurately, quantifiable and beyond even in further delimitation from the prior art nondestructive or without influencing the target object is feasible.
Task is according to the invention
that to the desired
Position of a target object to be positioned in the effective volume of the first,
in particular pulsed laser radiation, the image of a mask element
through the deflection optics, in particular with a second laser radiation,
is projected and the degree of defocusing the image of the
Mask element determined on the target object to be positioned,
is minimized in particular.
The core idea of the invention is to be seen in that to that
Position within the effective volume of a focused laser beam, the
to be performed
Experiment is considered optimal, projecting the image of a mask element
is positioned so that at one in the focus environment of the laser beam
Target object of this target object serves as a projection surface for the image and thus
based on the sharpness
or the degree of defocusing of the image of the mask element
on the target object can be determined whether the target object at the optimal
Position is positioned in the effective volume or whether there is still a shift in the
Target object or a change
the distance between the focusing optics and the target object requires this
to set the optimum position.
can be a target object first
(roughly) positioned within the effective volume and then in his
Position can be optimized, due to the determination of the degree
the defocusing and the usual
very short focal lengths of the focusing optics are carried out to a highly accurate extent
can. It may be provided, the image of the mask object
to observe by an appropriate observation optics, so
determine the degree of defocusing, both manually as
Also particularly preferred can be made automated.
is a particular advantage of the method according to the invention,
that the projection of the image of the mask element on the target object, which
the adjustment serves as a projection surface,
is made through the deflection optics, the incident an
Laser beam or laser pulse directed to the aforementioned focusing optics.
Thus, by the method according to the invention or with a
the adjustment of the beam path for focusing the first, in particular
pulsed laser radiation completely untouched,
Thus, no further influence by the implementation of the
makes noticeable in the experiment setup.
to let the projection through the deflection optics take place
it is as mentioned above
provided that this deflection optics for those used in the experiment
first, in particular pulsed laser radiation is highly reflective,
the for the
Illustration of the mask element is used, especially for a second
Laser radiation with a different laser wavelength.
Deflection optics are used for example dichroic mirrors,
having the corresponding dielectric coatings. Farther
are in today's high power lasers, which are usually radiation
in the infrared wavelength range
emit, the mirror used highly reflective for this
however, usually transitive for the visible wavelength range,
so that here the proposed method or system no adjustment or change
already existing optics required.
The above-mentioned method or system can thus be provided
be that to avoid any interference with the beam path of the
to be focused first laser radiation, the focusing optics for the first
Laser radiation forms part of the imaging optics for the mask element. This
For example, can be made such that the imaging optics for the mask element
is done by two focusing optics, with one of the optics
Illustration in the beam path in front of the deflection optics of the first, in particular
pulsed laser radiation is arranged and the second focusing
Optics formed by the focusing optics of the first laser radiation
is, so in this sense, the imaging optics for the mask element mapping
to the deflection optics in the beam path of the first, in particular pulsed
Laser radiation is arranged around.
In a further embodiment of the invention, it may be provided that the image of the mask element generated on the target object to be positioned, ie the temporary projection surface, is again imaged, namely here opposite the original imaging direction through the deflection optics into a second image plane, so that it is according to the invention may be provided, in this embodiment, not to determine the degree of defocusing directly on the target object, but in the second image plane and in particular to minimize. Thus, in particular by the further mapping, an enlargement of the image of the mask element located on the target object can be made so as to achieve yet another simplified adjustment. This also makes it easier to automate the method since it is possible to position a detector, in particular a camera, in the second image plane and thus to enable an apparatus-supported examination of the degree of defocusing.
again with this second figure, however, this figure
here in the backward direction
through the deflection optics for
the first laser radiation takes place, remains for this imaging measure the
Beam path of the first laser radiation completely untouched. Here too
is preferably the focusing optics for the first laser radiation
as part of the imaging optics for
used this second figure, especially as one of two
According to the invention it can
be provided to assess the degree of defocusing,
the contrast of the image either on the serving as a projection surface
Target object or preferably in the second image plane and thus based
of the detector signal, in particular on the basis of a camera image.
will only become the target when the contrast is maximized
its optimal position in the effective volume, in particular focus of the first
Laser beam have reached. It may be provided for this purpose
that from the detector signal, in particular thus from the camera image
a contrast function is formed and evaluated, in particular
based on the gradient of the contrast function. So can a shift
of the target object and thus focusing or defocusing
depending on the direction of displacement a clear maximum in the amount
of the gradient, for example
may be to position the target object where exactly the maximum
There is thus the possibility
to build an electronic control system, which the aforementioned
Evaluates detector signals and in particular formed gradients and
thus an automatic positioning device for modification
of the distance between the focusing object and the target object.
For example, an iteration process can also automatically take place
the optimal position of the target object can be found in the effective volume,
the modulation transfer function of the entire imaging system.
For the realization
the first image of the mask element on the target object and
thus also for
the optionally used second figure in a second
Image level may be provided, the mask element with a second
To illuminate laser radiation while the transmitted light of the mask element
to divert by means of a beam splitter and so the mask through the
Deflection optics of the first laser radiation through to the desired position
Imagine the effective volume, as mentioned above, the
Imaging optics from two focusing optics and here in particular
the focusing optics of the first laser radiation as one of these
to train both optics.
the use of a beam splitter for deflecting the light passing through the mask
can thereby be effected that in the optionally provided according to the invention
second figure in the second image plane this more illustration
in transmission can be done by this beam splitter. So will
ensures that the image in the second image plane is not on the
Mask itself back,
but the second image plane of the object plane of the mask element
in this connection
it is felt to be particularly advantageous if the mask element
by means of collimated laser radiation, possibly after a previous one
Widening through a telescope is illuminated, as is the possibility
There is an afocal mapping of the mask element on the target object
achieve, d. h., it is avoided that to illuminate the
Masking element used laser beam also focused on the target
is, so that thereby known from the prior art
Problems influencing or destroying the target object
focused adjustment radiation is completely avoided.
Accordingly, it may be in a preferred embodiment for the implementation of
Procedure and realization of the system be provided that the
two focusing optics of the imaging optics with the mask element
and imaging the mask element in the effective volume into a 4F optic configuration
forms, especially in the mask element and the image of
Mask element in the effective volume are in mutually conjugate planes.
Similarly, it can thus be provided that the two
focusing optics of the imaging optics together with the imaging of the
Mask element in the effective volume and the image of the mask image
in the second image plane, thus with the detector in the
second image plane can be arranged, a 4F optical configuration
forms, in particular in the image of the mask object in the effective volume
and the detector are in planes conjugate to each other.
As mentioned above, just by the realization of the 4F optical configuration for gege if appropriate both images, but at least for the first image of the mask element on the target object, an afocal image in the effective volume are achieved by the telecentric imaging system thus formed, wherein the second laser beam both at the location of the mask and at the location of the image of the mask element on the target object is expanded, so is not focused and thus any destruction or interference risks are eliminated.
For the inventive method
or system, it is further advantageous that a positioning
the mask image in the effective volume to a desired position, ie in particular
the optimal position of the focus of the first laser radiation
a shift of the mask can be achieved, causing the
Object level of the mask in the imaging system changes and thus the image plane
is shifted in the effective volume.
another image in said second image plane, in the
a detector can be arranged, it can then be provided in addition
be that same with the displacement of the mask as well
the detector distance changed
what can be, as the imaging system for both pictures is identical
can be done with the same displacement. This can be, for example
by an automatic coupling of two displacement units both
the mask element as well as the detector done.
For a basic adjustment
a possible detector, such as a camera in
the second image plane, it can be provided in addition, behind
the aforementioned beam splitter within the two imaging systems
and the beam path in front of the deflection optics for the first laser beam a
Arrange autocorrelation optics, with the mask image directly
is reproducible in the second image plane, so that by such a
Correlation optics first
the optimal distance of the detector to the beam splitter and thus the
optimal position in the second image plane can be adjusted.
Again, this can be fully automatic according to the invention
The aforementioned method or the system used in the same way can therefore be used particularly advantageously according to the invention for positioning a target object, such as metal or plastic foils in the focus of a laser pulse, for example a pico (10 -12 ) or femto (10 ). 15 ) seconds high-energy laser pulse, which can achieve more than 10 18 watts per square centimeter in the focus area.
the method and the system regarding the
Beam path, the for
the deflection and focusing of the laser pulse is provided, not completely
invasive, there are no changed experimental conditions
and a system for implementation
of the method can thus be complete
externally coupled to this without influencing the experiment
arise in particular automatically and in particular objective
for assessing an optimal adjustment position of the target object
in the effective volume. It can also be considered that the
Focus on a high-intensity laser pulse, possibly outside
the geometric focal length
used the focusing concave mirror, z. B. due to
notable non-linear properties,
because the mask image at each desired
Position can also be set differently from the geometric focus
especially after finding the optimal position once
of a target object (target) within the effective volume, the mask image in
exactly this optimal position can be placed and as an adjustment aid
for future positioning
of target objects, in particular as part of an automated procedure,
The invention is explained in the following figure.
The single FIGURE shows a first beam path in this embodiment of the method according to the invention I , which with reference to the representation coming from above via a deflection mirror 1 is deflected by about 90 degrees to the right. At the mirror 1 it may be a dichroic mirror that is highly reflective for the wavelength of laser used in the experiment and transmissive for an alignment laser beam. Instead of a Justagelasers can also be used in general, any other. Also not incoherent light source.
In the beam path 1 , followed by the deflecting a focusing element 2 , which is shown here symbolically and is usually formed in practice as a parabolic concave mirror. These concave mirrors can be specially designed, in particular in ultrashort pulses in the femtosecond range, in order to avoid temporal pulse extension due to dispersion effects of the dielectric coatings.
It is clear here that by the focusing element 2 in particular a parabolic concave mirror in the beam path 1 a focus 3 is generated around the center of which an effective volume is formed, in which to perform an experiment, a target object 4 is to be positioned accurately.
In order to mark this position P, it is provided according to the invention, the image of a mask element 5 by an imaging optics, by a focusing optics 6 , For example, a first lens or a first concave mirror, and the focusing optics 2 is formed.
So it is provided here, the mask element 5 by a telescopically arranged by two particular focusing elements 7 and 8th , in particular lenses, to illuminate with a laser beam of a second wavelength, for which the deflection mirror 1 is transmissive. Through the focusing elements 7 and 8th The laser beam is both expanded and collimated, so that between mask element 5 , focusing element 6 , focusing element 2 and the image of the mask element 3 a 4F configuration and thus a telecentric afocal image results, which means that an image of the mask 5 arises at the position P, while the collimation, ie, the parallel beam path of the laser beam of the second wavelength is maintained and thereby no destructive increase in intensity of the laser beam of the second wavelength is carried out on the target.
Here it is provided that of the mask element 5 outgoing light through a second beam path II Imaged by a beam splitter 9 is deflected and after passing through the deflection 1 with the beam path I of the first laser beam coincides.
This results from the beam splitter 9 both an excellent adjustment of the beam path II as well as the possibility of a backward image of the projected mask image of a target object inserted into the effective volume 4 in a second image plane B make in which a detector, such as a camera can be positioned.
In this second image, the light of the mask image backscattered by the target object passes through the beam splitter 9 so that the image does not fall back on itself and thus the second image can be used for evaluation by means of a detector. Here, for the second image, as well as for the first image, as the imaging system, the focusing optics 6 and 2 used, with the focusing optics 2 with the focusing optics in the beam path 1 of the experimental laser beam.
It is clear here that by the construction of the adjustment system no interference with the beam path of the adjusted laser beam I is made.
Thus, an inventive adjustment system can also be used later on an existing experimental arrangement without having to make an intervention in the arrangement. Furthermore, it may be provided here, an autocorrelation optics 10 provided, which is not shown here and which is a part of the mask element 5 outgoing light, which through the beam splitter 9 has gone through, thrown back into itself, so that by the reflection at the beam splitter 9 an immediate mapping of the mask element into the image plane B can take place.
can by this autocorrelation optics first for the implementation of the
made an optimal adjustment of the detector in the image plane B.
become. Sources of error due to misalignment of the detector within the
Image plane B, focusing on an unsatisfactory positioning
of the target object,
Thus, be avoided because it is first ensured that
the adjustment aid system is optimally adjusted in itself.
It should be noted that those mentioned in connection with an execution
technical features not only used in the specific execution
but also in the other versions. All disclosed technical
Features of this invention description are essential to the invention
be classified and combined with each other or in isolation