EP2810345A1 - Laser co2 à commande de puissance rapide - Google Patents

Laser co2 à commande de puissance rapide

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Publication number
EP2810345A1
EP2810345A1 EP13712472.3A EP13712472A EP2810345A1 EP 2810345 A1 EP2810345 A1 EP 2810345A1 EP 13712472 A EP13712472 A EP 13712472A EP 2810345 A1 EP2810345 A1 EP 2810345A1
Authority
EP
European Patent Office
Prior art keywords
laser
resonator
power
radiation
workpiece
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP13712472.3A
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German (de)
English (en)
Inventor
Gisbert Staupendahl
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Feha Lasertec GmbH
Original Assignee
IAI Industrial Systems BV
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Filing date
Publication date
Application filed by IAI Industrial Systems BV filed Critical IAI Industrial Systems BV
Publication of EP2810345A1 publication Critical patent/EP2810345A1/fr
Withdrawn legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/08—Construction or shape of optical resonators or components thereof
    • H01S3/08054—Passive cavity elements acting on the polarization, e.g. a polarizer for branching or walk-off compensation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/03—Observing, e.g. monitoring, the workpiece
    • B23K26/032—Observing, e.g. monitoring, the workpiece using optical means
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
    • B23K26/062—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam
    • B23K26/0622—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam by shaping pulses
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
    • B23K26/062—Shaping the laser beam, e.g. by masks or multi-focusing by direct control of the laser beam
    • B23K26/0626—Energy control of the laser beam
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
    • B23K26/064—Shaping the laser beam, e.g. by masks or multi-focusing by means of optical elements, e.g. lenses, mirrors or prisms
    • B23K26/066—Shaping the laser beam, e.g. by masks or multi-focusing by means of optical elements, e.g. lenses, mirrors or prisms by using masks
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
    • B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
    • B23K26/067—Dividing the beam into multiple beams, e.g. multifocusing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/70—Auxiliary operations or equipment
    • B23K26/702—Auxiliary equipment
    • B23K26/704—Beam dispersers, e.g. beam wells
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/08—Construction or shape of optical resonators or components thereof
    • H01S3/08004—Construction or shape of optical resonators or components thereof incorporating a dispersive element, e.g. a prism for wavelength selection
    • H01S3/08009—Construction or shape of optical resonators or components thereof incorporating a dispersive element, e.g. a prism for wavelength selection using a diffraction grating
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/10061—Polarization control
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
    • H01S3/22—Gases
    • H01S3/223—Gases the active gas being polyatomic, i.e. containing two or more atoms
    • H01S3/2232—Carbon dioxide (CO2) or monoxide [CO]
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/005—Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping
    • H01S3/0064—Anti-reflection devices, e.g. optical isolaters
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/11—Mode locking; Q-switching; Other giant-pulse techniques, e.g. cavity dumping
    • H01S3/1123—Q-switching
    • H01S3/115—Q-switching using intracavity electro-optic devices
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/11—Mode locking; Q-switching; Other giant-pulse techniques, e.g. cavity dumping
    • H01S3/1123—Q-switching
    • H01S3/117—Q-switching using intracavity acousto-optic devices
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/11—Mode locking; Q-switching; Other giant-pulse techniques, e.g. cavity dumping
    • H01S3/1123—Q-switching
    • H01S3/121—Q-switching using intracavity mechanical devices

Definitions

  • Modern solid-state laser systems (diode-pumped Nd: YAG lasers, disk lasers, fiber lasers, Ti: sapphire lasers, etc.) are characterized by wide-ranging variable pulsability (from 100 fs over ps and ns to the ts range), but are in view on the costs and above all the long-term experience in the industrial employment still far behind the C0 2 -Laser back.
  • Jump means several aspects: a) The applications that were previously realized with the C0 2 laser could be carried out even more efficiently. b) Numerous applications previously reserved for other laser types (eg precision drilling and cutting of copper and aluminum and other metals whose processing is linked to special pulse parameters - called titanium) or completely new applications could be achieved with such a C0 2 laser realize. c) The flexibility of the system would be extremely high, as it could handle a wide variety of tasks which, in the current state of the art, would be linked to different types of lasers. Here is the overall efficiency in the production, for example one
  • the C0 2 laser is available for a wide variety of Q-switching types with power up to one
  • Infrared by 1 ⁇ a variety of excellent suitable optical materials, e.g. Crystals or glasses, which are u.a. due to low absorption, high
  • a general problem is the limited radiation load capacity, whereby not primarily the destruction of the component by too high
  • the interference - decoupling element in the range of higher average power to the power sensitivity of the crucial component, the interference - decoupling element.
  • Pulse peak power relative to the cw power of the laser with a very high pulse repetition rate The problem of radiation exposure is not solved here either. Because of the significantly better optical properties of Ge compared to CdTe, the Q-switching of C0 2 lasers by means of acousto-optic modulators based on Ge is of interest. In DE 112008001338 T5 such a laser is described. Special arrangements in the
  • the aim of the arrangement according to the invention is to C0 2 laser conventional design, especially lasers used in material processing such as slow or fast lijnsgeströmte systems, but also those with stationary gas filling to modify so that completely novel ways of fast
  • Radiation pulses result, which are characterized by a very wide range of parameters, in particular on the one hand the timing down to the ns range and on the other hand, a power range, with peak pulse powers up to the order of 100 kW and in the average power up to the kW range.
  • a beam through the polarization beam splitter is not kinked only if its two major surfaces are exactly orthogonal to the beam.
  • angled polarization beam splitter is a twofold bend of the beam, wherein the beam path on the two sides (exit or entrance) is parallel to each other.
  • Pressure range to a maximum of about 0.1 bar, so that cw operation is possible by appropriate pumping power, and with respect to conventional C0 2 laser resonators, which by a highly reflective end mirror on the one and a decoupling element at the other end of the active medium are modified
  • a resonator characterized in that between the one end of the active medium and a first resonator end mirror of high reflectivity, which is preferably greater than 99%, a ⁇ / 4 phase shifter and between the other end of the active medium and a second Resonatorendador high reflectivity , which is also preferably greater than 99%, a polarization beam splitter is arranged and the
  • Polarization beam splitter one from the direction of the active medium impinging on him beam with any
  • Polarization divides into a linearly polarized outcoupling beam of power P A and a
  • the ⁇ / 4 phase shifter or the polarization beam splitter are rotatably mounted around the resonator axis, so that by setting a freely selectable angle ⁇ between a characteristic axis of the ⁇ / 4 phase shifter, which is perpendicular to the resonator axis , and a characteristic axis of the polarization beam splitter which is also perpendicular to the resonator axis, any desired power ratio P A / PR
  • Resonatorendspiegel ie in the feedback branch of
  • Resonator elements for beam shaping, in particular
  • the active medium can only in the area between the first Resonatorendapt and the
  • the electrodes are typically electrical electrodes.
  • the polarization beam splitter may be a ZnSe-based thin film polarizer arranged at Brewster angle a B to the resonator axis 11.
  • In the feedback branch of the resonator can be a
  • In the feedback branch of the resonator can be a
  • a telescope preferably of Galilei type, be arranged for adjusting the beam diameter D to the free opening d of the acousto-optic modulator, wherein the ratio D / d is preferably between 1.2 and 5, and that two absorbers intercept the beam components, which are bent out of the resonator beam path when a switching voltage is applied to the acousto-optic modulator.
  • acousto-optic modulator diffracted beam can be reflected from the second Resonatorendspiegel and as
  • Interference laser radiation modulator so be arranged at a small angle ⁇ its optical axis to the direction of the Wegzukoppelnden beam that reflected by him radiation components from the
  • the feedback branch of the resonator can optionally
  • Prisms preferably Doppelbrewster prisms of ZnSe or NaCl, or interference filters are used as wavelength-selective elements.
  • the resonator can be a Kepler-type telescope with intermediate focus and a
  • the second resonator end mirror may be a preferably fast tilt mirror and, between the latter and the polarization beam splitter, optionally a telescope, preferably of the Galilean type, for adapting the
  • Beam diameter D be arranged at the free opening d of the fast tilting mirror, wherein the ratio D / d is preferably between 1.2 and 10.
  • Power modulation elements can be either Galilei or Kepler telescopes in lens design or Galilei regarding. Kepler telescopes in mirror design or
  • Combinations of a collective lens or a Be collecting mirror with a second Resonatorendspiegel be suitable curvature.
  • the laser can be forced to work on a fixed, but freely selectable line of the rotational oscillation spectrum of the C0 2 laser in the range 9 ⁇ ⁇ ⁇ 11 ⁇ , the properties of the other optical elements of the laser , in particular the ⁇ / 4 phase shifter and the polarization beam splitter, adapted to this selected line.
  • All listed optical elements can be accommodated in a common vacuum-tight enclosure and the beam to be coupled out through a window of transparent material, preferably of ZnSe leaves the laser.
  • a material processing system can in the beam path between the laser output and the
  • the transmitted beam runs as a power-regulated beam in the direction of the workpiece and the reflected beam optionally one
  • Absorber / detector for destruction or for on-line measurement is supplied.
  • an acousto-optic modulator can be integrated with the proviso that the deflected beam as a power-regulated beam in the direction of workpiece (33) runs, while the non-deflected beam either an absorber / detector for destruction or on- line measurement is supplied, optionally between the
  • Modulator Elements for beam shaping e.g. a telescope and / or a special aperture, optionally arranged.
  • the basic idea of the solution according to the invention consists in modifying the usually used basic structure of the laser resonator with a 100% level at the one and the decoupling element at the other end of the system so that the resonator is subdivided into a high-power branch, which i.a. is formed by the active medium and a special decoupling element, and in a low-power feedback branch, u.a the
  • Feedback branch is a polarization beam splitter.
  • a thin film polarizer (TFP) based on ZnSe can be used for this purpose.
  • the latter is characterized in that the TFP is brought into the beam path at the Brewster angle a B and, as a result of the special coating, an incident beam of power P 0 is split so that its portion of the power P p polarized parallel to the plane of incidence of the TFP is fully transmitted and its polarized perpendicular to the plane of incidence
  • the TFP will be around in the place of the usual
  • Auskoppelspiegels positioned and also serves in the laser according to the invention as a decoupling element, ie either the TFP reflected or the transmitted beam is coupled out and leaves the resonator.
  • the other sub-beam is used for the resonator feedback, which is achieved, for example, by an adjustable 100% mirror, which sends the beam back into itself can be.
  • the beam path between this mirror and the TFP forms the said low-power feedback branch, in which any elements for the power control of the laser can be arranged.
  • a second central idea of the invention is devoted to the problem of how the power ratio P p / P s can be set as flexibly as possible, so that the laser modified in each case according to the invention corresponds to the gain of its active medium in accordance with its basic properties, in particular its performance the respective desired goal of the novel to be achieved
  • Parameter in particular special pulse parameters, is adjustable to the optimum. This is achieved by the targeted influencing of the polarization properties of the radiation generated in the laser by "at the other end" of the resonator, in front of the existing end mirror with about 100% reflectivity, a device with a phase shift of ⁇ / 4 per passage is arranged. For high-performance C0 2 laser one will be doing in the
  • each of these two beams can be considered a laser beam
  • the laser is to be operated without additional elements for power modulation, i. the beam transmitted at the TFP falls directly on the second 100% end mirror S2, where it is exactly in itself
  • Forming the known axial mode structure leads.
  • the two waves are also linear in the laser according to the invention, but polarized perpendicular to each other, so that no interference and thus no axial mode structure occurs.
  • the laser according to the invention has a very simple and flexible at the same time
  • the ⁇ / 4 phase shifter is rotatable about its beam axis, which in this case is the axis of the beam incident thereon from the direction of the active medium.
  • the phase shifter is rotated against its "ideal" position, no linear, but a more or less elliptically polarized one runs
  • the main application of the C0 2 laser according to the invention are applications requiring a fast
  • Interference laser radiation modulators the simple chopper disk and fast oscillating
  • EOM electro-optical modulators
  • Pulse repetition frequency off While in the visible and near infrared spectral range, many very suitable crystals for electro-optical
  • Wavelength range of C0 2 laser practically limited exclusively to commercially available CdTe modulators.
  • CdTe modulators By their compared to ZnSe substantially less favorable optical properties, in particular their relatively high absorption, these modulators
  • the laser according to the invention offers here by its special
  • Beam diameter e.g. with help of a
  • the switching or modulation function then runs as follows.
  • Resonator beam path out and intercepted by an absorber i. the feedback goes to zero. Radiation generation stops at the moment that it generates
  • AOM acousto-optic modulators
  • Modulators based on the acousto-optic effect are usually made of crystals for C0 2 lasers. These are, as well as CdTe, in their allowable load capacity, which is given by the requirement that the beam path in the resonator must remain largely unaffected even with changing loads, for example, when varying the laser power, significantly limited. 100 W / cm 2 should not be exceeded.
  • the principle of the laser according to the invention provides the way out. Since AOM is limited in its free opening analogous to the EOM, the basic structure is described in a) similar, ie a telescope is used and to the position of the EOM comes the AOM. The free laser function is typically given again for the stress-free AOM. The shutdown of the laser, so the reduction of the feedback below the threshold, can be achieved by
  • Modulation frequencies in the MHz range can be realized.
  • Advantages of the AOM use are u.a. the higher robustness and optical homogeneity of Ge compared to CdTe, the lower
  • Modulators of this type are based on the principle of the Fabry-Perot interferometer (FPI) and are typically equipped with two ZnSe plates as optically active elements. Because of the very favorable features of ZnSe and its great Range of application in C0 2 laser technology offers ILM the advantage that on the one hand they can be easily adapted to the intracavity beam diameter, so that in general no additional telescopes are required, and on the other hand the radiation load capacity is significantly higher than for CdTe and Ge. As a result, with such modulators and multi-kW laser of
  • ILMs operate as variable beam splitters, i.
  • the incident laser power becomes practical
  • Pulse repetition frequencies up to the order of 10 Hz. Since ILM modulators can be loaded with up to several 100 W, average laser output powers of several kW can be achieved.
  • Invention can also be simple mechanical
  • Tilting mirror be used advantageously.
  • a Kepler telescope with a sharp intermediate focus can be placed in the feedback branch, and at this point, this focus can be switched by means of a rapidly rotating perforated or slotted disk in short times in the ⁇ range, depending on the number and arrangement of the free openings on the disk and Their rotational speed can be a very efficient implementation of the available average power of the laser in pulse with high power increase at
  • Pulse repetition frequencies up to several 10 kHz and typical pulse durations in the ⁇ range can be achieved. Again, the low affects
  • Radiation intensity in the feedback branch favorable: When generating powerful pulses, the switching edges of the rotating Disc exposed to high intensities, which in conventional lasers can lead to Abtragsreaen and thus a relatively rapid destruction of the sharp switching edges, while this is avoided in the laser according to the invention.
  • the laser according to the invention due to its special resonator structure a very specific mode of operation -
  • Start radiation beam starts at the end of the active medium, which is at the TFP, and moves towards the interior of the active medium, ie in the direction of the ⁇ / 4 phase shifter.
  • the bundle is amplified, its unpolarized state, which is typical of the spontaneously emitted start radiation beam, remains practically preserved.
  • This also changes the path section phase shifter - 100% end mirror - phase shifter nothing, because here all radiation components are rotated equally by 90 °, so the bundle remains unpolarized.
  • After further amplification during the second pass through the active medium it now strikes the TFP and is essentially split into two equally strong sub-beams, which are polarized linearly but perpendicular to one another. One of them is decoupled, the other fed back. The latter now runs again in the direction of ⁇ / 4 phase shifter through the active medium, but is significantly modified in its properties compared to the start radiation beam: First, it is linearly polarized and has secondly through induced emission already a much higher
  • Resonator it is further amplified and - which is crucial for the self-oscillation - at
  • Pulse repetition frequency f imp of fimp c / 4L, where c is the speed of light. For typical resonator lengths of several meters arise
  • Pulse repetition frequencies in the order of 10 MHz.
  • the prerequisite is that the population inversion in the active medium by the quadruple passage of the
  • the C0 2 laser according to the invention offers a further attractive advantage in practical use in one
  • metals are processed, which reflect or scatter a significant portion of the incident radiation. Since this radiation is usually directed by the focusing element very well in parallel back towards the laser and through the
  • Decoupling element can penetrate into the resonator, the intracavity radiation generation is significantly disturbed, resulting in a deterioration of the
  • Laser radiation passes in the direction of the workpiece, but absorbs returning portions.
  • the effect of the ATFR mirror is inherent in the laser in the form of the polarization beam splitter.
  • the beam leaves the laser linearly polarized. Passing twice on a ⁇ / 4-phase retarder mirror on the way to and from the workpiece, its polarization plane is rotated by 90 °, so it is automatically on impact with the polarization beam splitter from the
  • Resonator beam path is deflected and can be intercepted by an absorber.
  • temperature-sensitive component itself absorbed, but deflected out of the beam path in the desired manner and fed to a suitable absorber.
  • Laser power vary. Usually this is done via an intervention in the laser process itself, i.a. via a variation of the pump energy supply. However, this will affect the beam quality, i. the K-number changes with the retrieved performance, resulting in a reduced processing quality.
  • external modulators which, while maintaining the beam quality, are a variation of the
  • the laser according to the invention has for a certain selected parameter set, e.g. Pulse duration,
  • acousto-optic and interference laser radiation modulators which can each be placed in the vicinity of the laser output and further beam shaping measures, if necessary, z, B.
  • the above-discussed radiation decoupling Läse - workpiece do not disturb.
  • the AOM it is convenient to use the diffracted beam as a processing beam, since it can be regulated in its power from 0 to the maximum value.
  • the undeflected portion can either be destroyed by an absorber or, for example, be supplied to a detector for on-line control of the laser power.
  • beam-shaping elements are provided for optimally adapting the radiation field coming from the laser to the modulator.
  • the ILM can be integrated into the beam path without such additional elements, since the free diameter of the interferometer plates can easily be adapted to the laser radiation.
  • the FPN plates made of ZnSe can be loaded with several hundred watts of radiant power, without a deterioration of the beam quality in the transmitted beam, which will typically be used as a processing beam occurs.
  • the unused reflected portion can either be destroyed by an absorber or used for on-line control.
  • FIG. 1 Schematic representation of the C0 2 laser according to the
  • FIG. 2 Basic arrangement of a ⁇ / phase retarder mirror (PRS) as ⁇ / phase shifter
  • PRS phase retarder mirror
  • FIG. 3 The Functioning of a ZnSe-based Thin-Film Polarizer (TFP)
  • Figure 8 arrangement variant for fast
  • FIG. 9 Arrangement variant for pulse generation by means of
  • Chopper disk Figure 10 Arrangement variant for pulse generation by means of
  • FIG. 11 Radiation decoupling laser - workpiece
  • FIG. 12 For external power control of the
  • FIG. 13 Vacuum-tight enclosure at the coupling-out end of the
  • FIG. 1 shows in a highly schematic manner the basic structure of the C0 2 laser according to the invention. It does not play at first Role, which concrete geometrical conditions, in particular with regard to the active medium 1,
  • the resonator is terminated at both ends by a highly reflective mirror 3 and 4 respectively.
  • the resonator is transformed into a high power branch, which i.a. contains the active medium 1, and the feedback branch 14, which is characterized by relatively low power divided. This desired division is made by the
  • End mirror 4 again the polarization beam splitter 5, is amplified in the active medium 1 and passes through the ⁇ / 4 phase shifter 2. Depending on which angle ⁇ now
  • Polarization beam splitter 5 and a characteristic axis 12 of the ⁇ / 4 phase shifter 2 has been set, this can change the polarization state of the incident linearly vertically polarized wave. In the first special case it remains unchanged, in the second special case it will be circular, in the general case elliptical.
  • low power can now different elements for beam shaping 15, in particular elements for fast Power modulation and / or wavelength selection and, for example, suitable spatial filter to ensure the high beam quality of the laser to be integrated.
  • elements for beam shaping 15 in particular elements for fast Power modulation and / or wavelength selection and, for example, suitable spatial filter to ensure the high beam quality of the laser to be integrated.
  • FIG. 2 A favorable practical solution for the ⁇ / phase shifter 2 is illustrated in FIG. 2, namely the use of a ⁇ / 4-phase retarder mirror (PRS) 16. These mirrors are also suitable for high powers in the kW range.
  • PRS 4-phase retarder mirror
  • adjustable end mirror 3 the right image the possibility of rotation of this unit about the resonator axis 11.
  • the relative arrangement of the components must be chosen so that the angle ß both between the resonator axis 11 and the
  • Polarization reflects, so runs virtually unchanged back into the active medium. However, as shown in the picture on the right, rotate the unit by an angle ⁇
  • a decisive feature of the laser according to the invention is that, by means of the described unit, linearly polarized radiation emerging from the active medium (for example perpendicularly polarized as in FIG.
  • a thin film polarizer (TFP) 17 based on ZnSe is suitable for C0 2 lasers. Its operation is illustrated in FIG. 3.
  • a specially coated ZnSe plate is brought into the beam path at the Brewster angle a B and divides an incident beam of arbitrary polarization into a transmitted beam which is incident in the beam path
  • the TFP 17 now allows the division according to the invention of a beam 6 coming from the direction of the active medium into a powerful beam 7 to be coupled out (power P A ) and a relatively low-power backfeed
  • Beam forming which can be integrated into the feedback branch 14, is extremely low. As already described, this ratio can easily be over the
  • Angle ⁇ can be set and optimized.
  • the beam splitting at the TFP 17 can in principle be done in two ways. Either one disengages the reflected beam and uses the transmitted to the feedback or vice versa. Both variants have advantages and disadvantages, which result mainly from two properties of the TFP 17: First, the absorption for the p-component is much higher than for the s-component of the radiation and, secondly, as shown in FIG. 3, the reflectivity strongly dependent on the wavelength for the p-component.
  • the reflected beam and the transmitted one are now coupled back, one has the two advantages of firstly reflecting the strong power component as the s-component at the front side of the TFP 17 and only minimal absorption losses, and secondly the ⁇ -dependence of the transmitted one and for the Feedback competent p-component even for the laser has a function-stabilizing effect.
  • a certain disadvantage is the double passage of the back-coupling beam as a p-component, ie at a relatively high level
  • Avoidance of the oscillation unwanted laser lines makes an additional wavelength selection in the feedback path 14 is required.
  • the latter variant is shown in FIG. 4 with a grating mirror 25 as a wavelength-selective element.
  • FIG. 5 a illustrates the most important case with the TFP 17 as a beam splitter and elements 15 for power modulation in the feedback branch 14 as well as the typical polarization ratios.
  • the returning beam 43 with linearly perpendicular polarization 9 is at the ⁇ / -phase slider 2 at the first pass in radiation with weakly elliptical polarization 46 and after reflection at the end mirror 3 at the second pass in radiation with highly elliptical polarization 47th
  • FIGS. 5b) and c) illustrate the special case of self-oscillation.
  • Phase shifter 2 which is set exactly (via the angle ⁇ ), that the bundle after the first round has exactly circular polarization 49 and therefore after
  • Radiation bundle 7 depends complex on the laser parameters and can be determined only by solving the balance equations or of course experimentally.
  • FIGS. 6 to 10 show characteristic examples.
  • an EOM 18 is first inserted into the feedback branch 14 of the resonator.
  • Switching crystals e.g. from CdTe, which require high switching voltages and in their optical
  • the laser according to the invention offers significant advantages, solve the mentioned problems.
  • FIG. 7 shows a similar arrangement, but with AOM 19. Since the switching speed depends, inter alia, on the free diameter d (small d-high switching speed), these modulators are generally only available with d ⁇ 10 mm, so that in most cases the integration of a telescope Galilei type 22 is required. Since germanium, which is used as an acousto-optic crystal in C0 2 lasers, also reacts relatively sensitively to high intensities, the low power is again in the
  • FIG. 7 shows two variants of the AOM insert.
  • the feedback ie the state in which the laser operates, takes place via the directly from the AOM 19 without
  • Control signal in the direction of end mirror 4 transmitted beam When applying a control signal, so the
  • the laser can be brought below its threshold and thus completely switched off - cleaner
  • the beam 29 diffracted by the modulator upon application of a control signal is used for the feedback.
  • control signal 0 also the feedback becomes 0, thus the laser is switched off.
  • lasers with a very high gain can be used, even for very small ones
  • Wavelength selectivity inherent in the diffraction process So may, if necessary, to others
  • Wavelength-selective elements are omitted in the resonator beam path.
  • Wavelength-selective elements are omitted in the resonator beam path.
  • FIG. 8 illustrates the use of ILM 20 for rapid power control of the C0 2 laser according to the invention.
  • Overcosting beam 8 is not "chopped" at its original diameter, but in the intermediate focus of a Kepler-type telescope 23rd
  • Feedback branch 14 is in this system is that despite the sharp focus in the telescope even when generating very powerful pulses at the switching edge no sparking and thus no material removal takes place, which would greatly reduce the life of the chopper wheel 21.
  • FIG. 10 illustrates, in order to show how the lens-based telescopes can be replaced by mirror versions, a Galilean telescope consisting of a concave mirror 50 and a curving mirror 51 is used here. That through this telescope in his
  • Diameter reduced beam 8 hits the tilting mirror 52, which replaces the end mirror 4.
  • Pulse repetition frequencies are in the order of 10 4 Hz. Since this pulse repetition frequency depends on the mass of the tilting mirror 52 and thus its diameter, the reduction of the bundle diameter makes sense. Again, the low power in the feedback path 14 is extremely advantageous because very small mirror diameter in the order mm and thus very high pulse repetition frequencies without risk
  • Polarization beam splitter in Figure 11 so the TFP 17, can automatically fulfill. After passing through the external ⁇ / 4-phase shifter 34 twice that is from the
  • FIG. 12 illustrates two possibilities that can be used in conjunction with the C0 2 laser according to the invention.
  • FIG. 12a shows the use of an ILM 54 for external power modulation.
  • the beam 35 coming from the laser is split by the ILM 54 into the power-regulated transmitted beam 59, which is fed to the workpiece 33, and into the reflected beam 58, with the remaining power.
  • the latter is in the component 55, the optional one
  • Absorber or a radiation detector can be either destroyed or used for on-line monitoring.
  • ILM in its relatively high radiation load capacity, but the modulation speed is limited to typical times in the range 10 to 100 ⁇ .
  • the achievable maximum-minimum modulation range of the power depends on the interferometer plates used. Allow typical ILM models Attenuation of the laser beam 35 by factors between 10 and 100.
  • the i.a. optical elements for beam shaping 56 e.g. a telescope for adjusting the beam diameter and a special aperture for securing the beam quality
  • the diffracted beam is supplied to the workpiece 33 as a power-regulated beam 59.
  • the residual beam 58 is selectively destroyed or measured again in an absorber / detector 55.
  • Another advantage of this arrangement is the fact that the beam 59 can be attenuated as much as desired, in the minimum to 0 W.
  • the controllable power is limited.
  • FIG. 13 shows in a highly schematized form a factor which is important for the practical realization of the C0 2 laser according to the invention.
  • the entire system should be housed in a vacuum-tight enclosure 31.
  • FIG. 12 shows this for the laser end with the
  • the outgoing beam 7 leaves the laser through the window 32 of transparent material, preferably of ZnSe.
  • the elements at the other end of the resonator, ie the ⁇ / 4-phase retarder mirror 16 and the end mirror 3 are to be included in the enclosure.
  • the entire vacuum-tight enclosure 31 can be connected to the volume of the active medium 1.
  • EOM Electro-Optical Modulator

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  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Electromagnetism (AREA)
  • Mechanical Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Lasers (AREA)
  • Laser Beam Processing (AREA)

Abstract

L'invention concerne un laser à CO2 qui permet une modulation de puissance rapide, en particulier un déclenchement à haut rendement. Le concept de base consiste ici à subdiviser le résonateur en une branche à haute puissance, contenant entre autres le milieu actif (1), ainsi qu'en une branche de rétroaction à faible puissance (14) dans laquelle sont disposés les éléments de formation du faisceau sensibles à la puissance, en particulier les modulateurs. Ceci est rendu possible par une disposition appropriée d'un diviseur de faisceau de polarisation (5) et d'un déphaseur λ/4 (2). Grâce à la possibilité de régler librement un angle φ entre ces deux composants, différents modes de fonctionnement peuvent être réalisés de manière extraordinairement flexible, en particulier l'optimisation du degré de rétroaction lors de la génération des impulsions.
EP13712472.3A 2012-02-03 2013-01-31 Laser co2 à commande de puissance rapide Withdrawn EP2810345A1 (fr)

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DE102012002470A DE102012002470A1 (de) 2012-02-03 2012-02-03 CO2-Laser mit schneller Leistungssteuerung
PCT/DE2013/000069 WO2013113306A1 (fr) 2012-02-03 2013-01-31 Laser co2 à commande de puissance rapide

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CN (1) CN104380544B (fr)
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Families Citing this family (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102014013567B3 (de) 2014-09-18 2015-10-08 Iai Industrial Systems B.V. Gütegeschaltetes CO2-Laser-Materialbearbeitungssystem mit akustooptischen Modulatoren
DE102015211999A1 (de) * 2015-06-29 2016-12-29 Trumpf Werkzeugmaschinen Gmbh + Co. Kg Laserbearbeitungskopf und Laserbearbeitungsmaschine damit
US10374384B2 (en) 2015-07-20 2019-08-06 Afl Telecommunications Llc Laser feedback control systems
US11123822B2 (en) * 2016-03-31 2021-09-21 AGC Inc. Manufacturing method for glass substrate, method for forming hole in glass substrate, and apparatus for forming hole in glass substrate
DE102017104392A1 (de) * 2017-03-02 2018-09-06 Active Fiber Systems Gmbh Schnelle Modulation von Laserstrahlung hoher Leistung
CN106918920B (zh) * 2017-04-20 2023-02-07 长春理工大学 利用偏振co2激光干涉加工镜片防雾结构的装置与方法
WO2018217206A1 (fr) * 2017-05-25 2018-11-29 Bae Systems Information And Electronic Integration Systems Inc. Commutateur q mécanique
DE112019002638T5 (de) * 2018-05-24 2021-03-11 Panasonic Intellectual Property Management Co., Ltd. Austauschbare laser-resonator module mit winkelverstellung
CN108581189B (zh) * 2018-06-01 2020-04-17 业成科技（成都）有限公司 激光切割方法
CN110434470B (zh) * 2019-07-04 2020-06-12 中国科学院西安光学精密机械研究所 一种大幅面透明曲面零件减反功能微纳结构加工方法及系统
US11374375B2 (en) * 2019-08-14 2022-06-28 Kla Corporation Laser closed power loop with an acousto-optic modulator for power modulation
CN111129915B (zh) * 2019-12-23 2021-04-13 北京航天控制仪器研究所 一种用于光纤激光器的防反射系统及方法
JP2022128033A (ja) * 2021-02-22 2022-09-01 住友重機械工業株式会社 レーザ加工装置及びレーザ加工方法
CN115121938B (zh) * 2022-08-10 2023-09-26 南京辉锐光电科技有限公司 激光头监测模组、多波段激光光路系统及激光加工设备
US11813697B1 (en) * 2023-04-07 2023-11-14 Intraaction Corp Laser methods of fabrication of clothing

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102010002433A1 (de) * 2009-02-27 2010-10-07 Gigaphoton Inc., Oyama-shi Lasergerät und Extrem-Ultraviolett-Lichtquellen-Gerät

Family Cites Families (19)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4176327A (en) * 1978-01-25 1979-11-27 United Technologies Corporation Method for cavity dumping a Q-switched laser
US4484333A (en) * 1982-02-12 1984-11-20 United Technologies Corporation Coupled waveguide freespace laser
US4498179A (en) * 1982-07-30 1985-02-05 The Unites States Of America As Represented By The Secretary Of The Army Modulated infrared laser with two coupled cavities
DD256439A3 (de) * 1986-01-09 1988-05-11 Halle Feinmech Werke Veb Verfahren zur steuerung der inneren und unterdrueckung der aeusseren strahlungsrueckkopplung eines co tief 2-hochleistungslasers
US5150370A (en) * 1989-06-14 1992-09-22 Matsushita Electric Industrial Co., Ltd. Narrow-band laser apparatus
JPH0797680B2 (ja) * 1989-06-14 1995-10-18 松下電器産業株式会社 狭帯域化レーザ装置
DE4438283C2 (de) * 1994-10-26 1997-04-10 Lambda Physik Gmbh Laser zur Erzeugung schmalbandiger Strahlung
DE19603637C1 (de) * 1996-02-01 1997-07-31 Lambda Physik Gmbh Laser zur Erzeugung schmalbandiger Strahlung
JP2000138410A (ja) * 1998-11-04 2000-05-16 Matsushita Electric Ind Co Ltd 狭帯域放電励起レーザ装置
US6697408B2 (en) 2001-04-04 2004-02-24 Coherent, Inc. Q-switched cavity dumped CO2 laser for material processing
ATE453232T1 (de) 2001-04-04 2010-01-15 Coherent Deos Gütegeschalteter co2 laser für materialbearbeitung
JP3846573B2 (ja) * 2002-06-14 2006-11-15 三菱電機株式会社 レーザ加工装置及び該加工装置の制御方法
US20050211680A1 (en) * 2003-05-23 2005-09-29 Mingwei Li Systems and methods for laser texturing of surfaces of a substrate
JP5100990B2 (ja) * 2004-10-07 2012-12-19 ギガフォトン株式会社 極端紫外光源装置用ドライバーレーザ及びｌｐｐ型極端紫外光源装置
JP5086677B2 (ja) * 2006-08-29 2012-11-28 ギガフォトン株式会社 極端紫外光源装置用ドライバーレーザ
US7411989B2 (en) * 2006-12-13 2008-08-12 Coherent, Inc. Mechanically Q-switched CO2 laser
US7903699B2 (en) 2007-05-24 2011-03-08 Coherent, Inc. Acousto-optically Q-switched CO2 laser
US8149886B2 (en) * 2009-04-28 2012-04-03 High Q Technologies Gmbh Laser amplifier system and laser amplifier method
JP6021454B2 (ja) * 2011-10-05 2016-11-09 ギガフォトン株式会社 極端紫外光生成装置および極端紫外光生成方法

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102010002433A1 (de) * 2009-02-27 2010-10-07 Gigaphoton Inc., Oyama-shi Lasergerät und Extrem-Ultraviolett-Lichtquellen-Gerät

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DE102012002470A1 (de) 2013-08-08
JP6473926B2 (ja) 2019-02-27
WO2013113306A1 (fr) 2013-08-08
CN104380544A (zh) 2015-02-25
US20150014286A1 (en) 2015-01-15
WO2013113306A8 (fr) 2014-01-09
CN104380544B (zh) 2017-12-19
KR20140122239A (ko) 2014-10-17

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