Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
  • G02B27/64—Imaging systems using optical elements for stabilisation of the lateral and angular position of the image
  • G02B27/646—Imaging systems using optical elements for stabilisation of the lateral and angular position of the image compensating for small deviations, e.g. due to vibration or shake

Definitions

• the invention relates to a method for stabilizing a laser beam, which performs a pendulum motion about a pivot point, at a site of investigation.
• Such a movement of a laser beam has the disadvantage that it makes itself noticeable in experimental setups in which a laser beam is used and, for example, superimposes the actual measurement result which it is to be detected.
• the object of the invention is to provide a method with which without a metrological control to achieve a significant increase in the beam stability at a site, in particular at least at a first site, possibly also at other subsequent sites.
• the object is achieved by a method for stabilizing a laser beam at a test site, which performs a pendulum motion about a pivot point, wherein the pivot point of the pendulum motion by means of an arrangement with at least one focusing element, which is arranged at a certain distance from the pivot point to the examination site is projected.
• the essence of the invention lies in the finding that a beam instability in a laser is by no means indeterminate, but it has been found that often occurs a movement of a laser beam emitted by a laser, around a pivot point around.
• the emitted laser beam makes a pendulum motion about such a pivot point.
• a pivot point of the pendulum motion can be both within a laser resonator and outside a laser resonator. In particular, it has been found that such a fulcrum does not have to coincide with the aperture of the laser resonator.
• the invention further makes use of the proposed method that at the pivot point of the pendulum movement itself, the laser beam does not have any beam instability, at least none which is attributable to the pendulum motion, with the result that after a projection of this Fulcrum of the pendulum motion at a study site, which may be located eg at a distance to the laser resonator, also no pendulum motion of the laser beam is detectable at this location, but the laser beam behaves in terms of its instability at the projected location of the fulcrum as the original fulcrum, if necessary , depending on the arrangement of the focusing elements used only with the exception of the direction of the pendulum motion, due to the reflection generated by the focusing elements if necessary.
• the place of investigation is understood to be the location at which a projected fulcrum lies. It may then be placed in a study site in practical use e.g. to act a place where an experiment is performed, e.g. an examination or the measurement result of a possibly performed on another examination.
• the pivot point of the pendulum movement is projected by means of a combination of two focusing elements, which are arranged at a certain distance from each other and to the pivot point, to an examination location.
• focusing lenses are used as focusing elements, which are arranged confocally.
• focusing mirrors may be advantageous in the field of laser technology due to higher reflection levels, since reflection layers of the mirrors can be optimally adapted to the wavelength of a respective laser.
• the converging lenses or generally to be used two focusing elements can be further achieved that when using different focal lengths of these focusing elements in addition to the actual projection of the pendulum motion at a site and a change in the beam diameter, in particular a beam expansion can be achieved, provided that the first focusing element has a lower focal length than the second, in the beam direction subsequent focusing element.
• expansion factors or reduction factors are achieved which correspond to the ratio of the focal lengths used of the respective focusing elements.
• the focusing elements in particular the converging lenses, are arranged confocally, which means that the respective focuses of these focusing elements coincide, e.g. the focus of the first convergent lens lies in the focus of the second condenser lens.
• the divergence of the laser is reduced.
• the method which is so preferred can be used if a parallel laser beam bundle is also to be present at the examination location, such as at the fulcrum, if necessary only with deviation in diameter and divergence at the examination site, if a confocal telescope with two different focal lengths is used.
• the method can also be used with an arrangement of only one focusing element, e.g. a single condensing lens. In this case, however, due to the focussing characteristics at the examination site where the projected fulcrum is not a parallel beam, there is a converging or diverging beam corresponding to the focussing.
• this can be achieved, for example, that at a first site by means of a laser beam, a manipulation of a sample to be examined takes place, whereas at the second site the actual measurements take place.
• it can be achieved here by the double or multiple use of the method that neither the manipulation of the sample at the first examination location nor the detection of the measured values at the second examination location is superimposed by artifacts resulting from a movement of the laser beam.
• Essential for the implementation of the method according to the invention is the knowledge of the position of the fulcrum, which may be as mentioned above both inside and outside the resonator of a laser. If this fulcrum is not known from the outset, for example by a manufacturer's statement, it may be provided according to the invention that the position of the fulcrum of the laser beam is determined by observing the pendulum motion in at least two different observation planes.
• This type of procedure is based on the fact that due to the pendulum movement about a pivot point of the laser beam ultimately moves within a cone whose tip is located in the center of rotation and the center axis along the idealized propagation direction of the laser beam.
• a cone may have circular, elliptical or other base surfaces.
• the laser beam in each plane of observation perpendicular to the idealized propagation describes movements within such a surface.
• the amplitude of the pendulum motion will increase with increasing distance from the pivot, so that from this the position of the pivot point of the laser beam can be determined.
• the pivot point is determined from the amplitudes of the pendulum movement in the at least two planes of motion and the distance of the planes of motion, for example by the application of the rule of three.
• a detector in particular a quadrant sensor, a CCD, CMOS, or linear sensor is used in the movement planes for observing and evaluating the oscillatory movements, the generated signal of which is evaluated in order to determine the amplitude of the oscillating movements.
• the combination of the two focusing elements can then be adjusted in the desired and necessary predetermined distance to effect the projection of the pivot point to the examination site.
• the arrangement of the focusing elements obey the above-mentioned conditions.
• the method according to the invention may e.g. be used to project the fulcrum of a laser beam to the examination and / or detection of an optical tweezers.
• an optical tweezers means a device for manipulation, i. in particular, for holding and moving minute objects that are usually transparent at the laser wavelength used.
• a laser beam is focused into an object plane in which an object lying in the focus of the laser beam can be held, since any positional deviation of the object located in the optical tweezer causes that object to be returned to focus by impulse transmission upon refraction of the laser beam is withdrawn.
• a projection of the pivot point of the laser beam is such that the projected Fulcrum, ie coincides with the focus of the optical tweezers as designated according to the invention, so that just at this location oscillations of the laser has no negative effect on the measurement, which is performed with the optical tweezers. It can also be provided that the projection of the fulcrum takes place in the plane of the focusing lens of the optical tweezers.
• the fulcrum of the laser beam movement again with the aforementioned arrangement to the location of the measured value recording of the optical tweezers, so for example.
• the obtained measurement results also at the location of the detector does not depend on the movement of the laser beam.
• Another application in which the method provides significant advantages may be e.g. can be seen in that the pivot point of the laser beam on the cantilever of a force microscope, if necessary, is projected with an additional focusing element.
• this ensures that only the movements of the cantilever of a force microscope dominate the recorded measurement results and these measurements have no proportions that are due to the movement of the laser beam at the point of impact of the cantilever.
• the inventive method will lead to a significantly increased accuracy of the measurement results.
• the method according to the invention described above is not limited to the applications exemplified here, but can be used wherever it depends on a particular beam stability of a laser beam at the site of a study or measurement or at the sample location. It can also be provided that in the case of a projection of the fulcrum to an examination site at which measurement results are acquired, a system to be examined with only laser-deflecting but not focussing properties can be arranged somewhere between the original fulcrum and the examination site.
• Figure 1 An embodiment with a confocal telescope
• Figure 2 An embodiment with only one focusing lens.
• a first pivot point D1 which should be identified as the pivot point around which the laser beam generated performs a pendulum motion around and can, for example, lie inside or outside a laser cavity.
• the figure also shows in dashed lines the optical beam path which a laser beam takes at different deflections, in each case around this first pivot point D1.
• the laser beam passes through a confocal telescope comprising two confocally arranged converging lenses L1 and L2 with the focal lengths F1 and F2, wherein it can be seen that regardless of the deflection of the laser beam relative to the stationary pivot point D1 of the beam path of the laser beam at a distance D from the first pivot point in turn coincides with a second pivot point D2, so that it can be said that the first pivot point D1 is projected into the second pivot point D2.
• D A + F 1 + 2 F 2 + (F 2 2 / F 1 ) -A * (F 2 2 / F 1 2 ) with the further condition that A ⁇ F 1 + (F 1 2 / F 2 ), where as can be seen in the figure here, D corresponds to the distance between the first and second fulcrum (projection width),
• the first fulcrum and location and that further A is the distance between the first condenser lens and the first fulcrum
• Fi and F 2 are the respective focal lengths of the first and second condenser lenses.
• the illustration of the confocal telescope in the upper part of the figure clearly shows that this confocal telescope can also be used in addition to the projection of the fulcrum with the conditions mentioned here to increase the diameter of the laser beam, the widening of the laser beam Laser beam is given by the ratio of the focal lengths of the two converging lenses L1 and L2.
• a divergent radiation beam results in this case, whereby at the location D2 the beam diameter corresponds to the diameter at the fulcrum D1 multiplied by F 1 / (A-F 1 ).

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Length Measuring Devices By Optical Means (AREA)

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Citations (5)

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• 2006
  • 2006-12-20 DE DE200610060937 patent/DE102006060937A1/de not_active Withdrawn
• 2007
  • 2007-12-20 WO PCT/EP2007/011265 patent/WO2008074505A1/de active Application Filing

Patent Citations (5)

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