EP4272288A1 - Appareil laser à conversion de fréquence - Google Patents

Appareil laser à conversion de fréquence

Info

Publication number
EP4272288A1
EP4272288A1 EP22715545.4A EP22715545A EP4272288A1 EP 4272288 A1 EP4272288 A1 EP 4272288A1 EP 22715545 A EP22715545 A EP 22715545A EP 4272288 A1 EP4272288 A1 EP 4272288A1
Authority
EP
European Patent Office
Prior art keywords
frequency
polarization
laser device
light
laser
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.)
Pending
Application number
EP22715545.4A
Other languages
German (de)
English (en)
Inventor
Wolfgang SCHÜSSLBAUER
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.)
Photon Energy GmbH
Original Assignee
Photon Energy GmbH
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Photon Energy GmbH filed Critical Photon Energy GmbH
Publication of EP4272288A1 publication Critical patent/EP4272288A1/fr
Pending 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
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/35—Non-linear optics
    • G02F1/3501—Constructional details or arrangements of non-linear optical devices, e.g. shape of non-linear crystals
    • G02F1/3507—Arrangements comprising two or more nonlinear optical devices
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/35—Non-linear optics
    • G02F1/355—Non-linear optics characterised by the materials used
    • G02F1/3551—Crystals
    • 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
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/106—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity
    • H01S3/108—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity using non-linear optical devices, e.g. exhibiting Brillouin or Raman scattering
    • H01S3/109—Frequency multiplication, e.g. harmonic generation
    • 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
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
    • H01S3/0941—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light of a laser diode
    • H01S3/09415—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light of a laser diode the pumping beam being parallel to the lasing mode of the pumped medium, e.g. end-pumping
    • 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
    • H01S3/1106—Mode locking
    • H01S3/1109—Active mode locking
    • 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
    • H01S3/14—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
    • H01S3/16—Solid materials
    • H01S3/1601—Solid materials characterised by an active (lasing) ion
    • H01S3/1603—Solid materials characterised by an active (lasing) ion rare earth
    • H01S3/1611—Solid materials characterised by an active (lasing) ion rare earth neodymium
    • 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
    • H01S3/16—Solid materials
    • H01S3/163—Solid materials characterised by a crystal matrix
    • H01S3/1671—Solid materials characterised by a crystal matrix vanadate, niobate, tantalate
    • H01S3/1673—YVO4 [YVO]

Definitions

  • the invention relates to a frequency-converting laser device, i.e. an optical device for generating and optionally for guiding, shaping, converting and/or amplifying a laser beam.
  • Solid-state lasers are often used for industrial applications such as engraving or inscribing using laser radiation, i.e. laser devices whose active optical medium is formed by a crystalline or glass-like (i.e. amorphous) solid.
  • the light generated by such solids is usually in the infrared range, especially at wavelengths above 800 nm.
  • no suitable (particularly commercially replaceable) solid materials have been available to date for the generation of shorter-wave light, as is required for many applications .
  • a conventional method to generate laser light in the green, blue, violet or ultraviolet spectral range using a solid-state laser is what is known as frequency conversion.
  • part of the light initially generated in a fundamental frequency (also: base frequency) is converted into light of a different frequency by an (optically) non-linear medium.
  • the frequency of the converted light is often a multiple of the fundamental frequency, in particular two or three times the fundamental frequency.
  • the frequency converted light is coherent with the fundamental frequency light from which it originates and is emitted in the same direction.
  • the non-linear medium is often arranged in the resonator cavity of the laser device, so that the frequency-converted light is produced in the resonator.
  • this method of frequency conversion is therefore also referred to as "Intra Cavity Nonlinear Frequency Conversion".
  • the light of the fundamental frequency passes through the non-linear medium on its way between the resonator mirrors in both directions, with frequency conversion taking place in each case.
  • the frequency-converted light is emitted by the nonlinear medium not only in the forward direction (ie towards the output coupling mirror of the resonator), but also in the reverse direction (ie towards the opposite end mirror of the resonator).
  • the portion of the frequency-converted light emitted in the forward direction can be used easily by coupling out of the resonator
  • the portion of the frequency-converted light emitted in the reverse direction usually represents an unwanted interference signal, since this light is caused by negative interference with the frequency-converted light emitted in the forward direction
  • Light affects the efficiency and stability of laser activity.
  • the portion of the frequency-converted light emitted in the reverse direction leads to increased stress (and thus increased wear) on the components of the resonator, in particular the active medium.
  • frequency-converting laser devices are sometimes equipped with a kinked resonator.
  • a deflection mirror is arranged between the two resonator mirrors, which deflects the light of the fundamental frequency and thus divides the resonator into two arms.
  • the active medium is arranged in one arm of the kinked resonator, while the non-linear medium is arranged in the second arm.
  • the deflection mirror is permeable for the frequency of the converted light. What is achieved here is that the converted light only circulates in the second arm of the resonator.
  • Such kinked resonators require high production costs due to the significantly higher complexity of the structure, which limits the commercial usability of corresponding laser devices.
  • active stabilization measures are often necessary in order to match the length of the two resonator arms or resonator cavities to one another.
  • kinked resonators take up a comparatively large amount of space, which also limits the usability of corresponding laser devices.
  • the invention is based on the object of specifying an effective, but at the same time simple to implement, frequency-converting laser device.
  • the laser device comprises, in a conventional manner, an optical resonator which has two resonator mirrors, namely an output mirror and an end mirror.
  • the outcoupling mirror represents the front side of the resonator. Accordingly, the propagation direction of the light thrown onto the outcoupling mirror is referred to as the "forward direction”.
  • Light hitting the end mirror propagates in the “reverse direction”.
  • the resonator also includes an optically active medium (laser medium) that generates light at a first frequency during operation of the laser device.
  • the first frequency is also referred to as the "fundamental frequency”.
  • the light of the first frequency is correspondingly referred to as "fundamental wave”.
  • the laser device includes an (optically) non-linear medium which, during operation of the laser device, converts light of the first frequency, in other words a part of the fundamental wave, into light of a different frequency.
  • the other frequency is preferably, but not necessarily, an integer multiple of the fundamental frequency, in particular twice, three times or four times.
  • the frequency-converted light of the other frequency is generally referred to below as “converted wave” to distinguish it from the fundamental wave. If the other frequency is an integer multiple of the fundamental frequency, the frequency-converted light is also referred to as a "harmonic wave” or "harmonic” for short.
  • the frequency-converted light is also referred to as the "second harmonic", in the case of a frequency trebling as the "third harmonic", etc.
  • the output mirror is designed in such a way that it is transparent to the converted wave (entirely or at least partially).
  • both resonator mirrors are preferably impermeable to the fundamental wave.
  • the optically non-linear medium is placed inside the resonator. Both the optically active medium and the optically non-linear medium are therefore arranged in a beam path between the resonator mirrors.
  • the laser device now includes, in addition to the parts described above, a (first) polarization-influencing laser optics, which polarizes the light of the first frequency (i.e. the fundamental wave) reflected by the output mirror in the direction of the end mirror in such a way that a frequency conversion of this polarized light takes place during Passage through the non-linear re medium is suppressed.
  • This first polarization-influencing laser optics (hereinafter referred to as “(first) polarizer” without loss of generality) is in particular between the non-linear medium and the decoupling mirror in the beam path of the resonator.
  • the first polarizer causes the fundamental wave propagating backwards through the nonlinear medium to cause no frequency conversion, or at least a weaker frequency conversion than in the absence of the first polarizer.
  • the frequency conversion caused by the fundamental wave passing through the non-linear medium in the reverse direction is minimized in particular by suitable polarization of the fundamental wave.
  • polarization or “polarize” is generally understood to mean a change in the polarization properties.
  • the light polarized by the first polarizer therefore has different polarization properties than before.
  • a polarization direction of the fundamental wave is rotated, linear polarization is converted into circular polarization, or circular polarization is converted into linear polarization by the first polarizer.
  • Type I frequency conversion
  • Type II frequency conversion
  • Optically nonlinear media that, by their nature and/or configuration, cause a "Type I” or “Type II” frequency conversion are also referred to hereinafter as “Type I” or “Type II media” for short (in the case of nonlinear optical crystals as “Type I” or “Type II crystals”).
  • the invention is based on the finding that, in particular, type I frequency conversion in optically nonlinear media regularly has a pronounced dependence on the polarization of the incident light. Light of a specific polarization direction is converted with maximum effectiveness. converted while light of a polarization direction perpendicular thereto with minimal effectiveness or even not converted at all. This effect is exploited according to the invention in order to increase the efficiency of the resonator.
  • the laser device comprises, in addition to the first polarizer described above, a second polarization-influencing laser optics, which is referred to below (again without loss of generality) as the “second polarizer” for short.
  • This second polarizer has an opposite effect compared to the first polarizer in that it polarizes the light of the first frequency propagating in the direction of the output mirror (i.e. the fundamental wave propagating in the forward direction) in such a way that a frequency conversion of this polarized light occurs when it passes through the nonlinear medium promoted, in particular maximized.
  • the second polarizer which is arranged in particular between the laser medium and the non-linear medium in the beam path of the resonator, thus causes the fundamental wave propagating in the forward direction through the non-linear medium to produce a greater frequency conversion than in the absence of the first polarizer.
  • the first polarizer and - if present - also the second polarizer are preferably a wave plate (also: retardation plate), in particular a 1/4 plate, or a polarization rotator, eg a Faraday rotator, a quartz crystal rotator or a liquid crystal rotator.
  • the two polarizers can be of the same type or of different types within the scope of the invention.
  • a 1/4 plate is used as the first polarizer. Chen and used as a second polarizer polarization rotator.
  • the polarization rotator is designed in particular in such a way that it rotates the direction of polarization of the incident fundamental wave by 45°.
  • both the first polarizer and the second polarizer are each formed by a polarization rotator.
  • These polarization rotators are also designed in particular in such a way that they each rotate the polarization direction of the incident fundamental wave by 45°.
  • the concentration of the frequency conversion achieved by the at least one polarizer on the fundamental wave traveling in the forward direction enables a simple design of the resonator without having to accept poor resonator efficiency.
  • a kinked design of the resonator is neither necessary nor preferred.
  • the resonator has a linear beam path; i.e. the resonator mirrors, the laser medium, the optically non-linear medium and the or each polarizer are lined up along a straight optical axis. Due to this simple structure, a high level of stability of the laser beam generated during operation of the laser device is achieved with comparatively little effort. Active stabilizers are not necessary and therefore not provided in a preferred embodiment of the invention.
  • the laser device in a preferred embodiment includes, in addition to the first polarizer and - if present - the second polarizer, a third polarization-influencing laser optics (also referred to as "third polarizer"), which are connected downstream of the output mirror and thus outside of the resonator is arranged.
  • a third polarization-influencing laser optics also referred to as "third polarizer”
  • This third polarizer is designed to compensate for the influence of the first polarizer on the converted wave (and thus on the laser beam coupled out of the resonator). In other words the effect of the first polarizer on the converted wave is reversed by the third polarizer.
  • the first polarizer and the third polarizer are formed by 1/4 plates which are identical in construction but are rotated relative to one another by 90° around the optical axis.
  • the term "l/4" refers to the wavelength of the fundamental wave for both polarizers.
  • the laser device within the scope of the invention can be operated as a continuously emitting laser (CW laser) or as a pulsed laser.
  • CW laser continuously emitting laser
  • pulsed laser pulsed laser
  • the laser device is preferably a q-switched laser.
  • the laser device also includes a q-switch arranged in the beam path of the resonator, in particular between the laser medium and the non-linear medium or - if present - the second polarizer, through which the quality of the Resonators can be changed.
  • the Q-switch is preferably an active Q-switch based, for example, on an electro-optical functional principle (e.g. Pockels cell, Kerr cell or electro-optical modulator) or an acousto-optical functional principle (e.g. Bragg cell).
  • the laser device can also contain a passive Q-switch, in particular in the form of a semiconductor absorber mirror (SESAM) or a non-linear crystal (e.g. a Cr:YAG crystal).
  • the laser device is a mode-locked laser.
  • the laser device is preferably a solid-state laser.
  • the active optical medium preferably contains a solid body, in particular a neodymium-doped yttrium orthovanadate crystal (Nd:YVO 4 crystal).
  • the non-linear medium preferably includes a medium adapted for Type I frequency conversion (ie frequency conversion in Type I phase-match configuration) in terms of its type and/or configuration, eg orientation to the direction of propagation of the incident wave.
  • the medium is preferably a solid, namely an optically nonlinear (type I) crystal, in particular a crystal of lithium triborate (LBO).
  • the non-linear medium has at least two optically non-linear crystals, in particular LBO crystals, connected downstream of one another, in particular for the generation of higher harmonics of the first fundamental wave.
  • a first of the two crystals is a crystal in a Type I phase-match configuration.
  • This first crystal serves to generate a first converted wave of medium frequency (e.g. twice the frequency of the fundamental frequency) from the fundamental wave.
  • the second crystal which is used in particular to generate a second converted wave of higher frequency (e.g. a wave with three times the fundamental frequency) with the interaction of the fundamental wave and the first converted wave, can in principle also be replaced by a crystal in a type I Be formed phase match configuration.
  • a crystal in a Type II phase-match configuration is used for the second crystal.
  • Fig. 1 in a schematically simplified representation of the basic principle of a laser device according to the invention
  • FIG. 2 in representation according to FIG. 1, a first specific embodiment of the laser device and
  • FIG. 3 shows a second specific embodiment of the laser device in a representation according to FIG. 1.
  • Fig. 1 shows a roughly schematic view of a laser device 2 with an optical resonator 4.
  • the resonator 4 is formed by two resonator mirrors 6, 8, namely a decoupling mirror 6 and an end mirror 8. It also includes a (laser) medium 10, which is energetically excited (“pumped”) during operation of the laser device 2 by means of a pump device 12, only indicated in FIG. 1, by supplying light or electrical energy.
  • a (laser) medium 10 which is energetically excited (“pumped”) during operation of the laser device 2 by means of a pump device 12, only indicated in FIG. 1, by supplying light or electrical energy.
  • the laser medium 10 excited by the pumping device 12 emits light of a fundamental frequency f i which travels between the resonator mirrors 6, 8 in a forward direction 14 (aligned from the end mirror 8 to the output mirror 6) and in a forward direction 14 (from the output mirror 6 to the end mirror 8 aligned) reverse direction 16 circulates.
  • a fundamental frequency f i which travels between the resonator mirrors 6, 8 in a forward direction 14 (aligned from the end mirror 8 to the output mirror 6) and in a forward direction 14 (from the output mirror 6 to the end mirror 8 aligned) reverse direction 16 circulates.
  • the fundamental wave F the output mirror 6 and the end mirror 8 are impermeable (within the quality of the resonator mirror 6.8 realized in terms of production technology).
  • an optically nonlinear medium 18 is arranged in the resonator 4, which converts part of the fundamental wave F into light of a second frequency f2 during operation of the laser device 2.
  • the frequency-converted light of the second frequency f2 is therefore referred to as harmonic wave H below.
  • the outcoupling mirror 6 is designed in such a way that it is transparent to the harmonic wave H (completely or at least as far as possible within the framework of the achievable quality of the outcoupling mirror 6).
  • the non-linear medium 18 is arranged within the resonator 4, ie between the resonator mirrors 6.8.
  • a first polarizer 20 is connected between the non-linear medium 18 and the output mirror 6 .
  • This first polarizer 20 influenced in the Operation of the laser device 2 changes the polarization of the fundamental wave F reflected by the output mirror 6 and thus propagating in the reverse direction 16 in such a way that the fundamental wave F polarized in this way passes through the non-linear medium 18 in the reverse direction 16 without triggering a frequency conversion.
  • the polarization of the fundamental wave F by means of the first polarizer 20 thus suppresses emission of frequency-converted light in the reverse direction 16 .
  • a second polarizer 22 is connected between the laser medium 10 and the non-linear medium 18 .
  • this second polarizer 22 influences the polarization of the fundamental wave F emitted by the laser medium 10 in the forward direction 14 in such a way that the fundamental wave F polarized in this way triggers maximum frequency conversion when it passes through the nonlinear medium 18.
  • the polarization of the fundamental wave F by means of the second polarizer 22 thus maximizes the emission of frequency-converted light in the forward direction 14 .
  • the interaction of the two polarizers 20 and 22 ensures that the harmonic wave H is emitted by the non-linear medium 18 with maximum intensity exclusively in the forward direction 14 .
  • the harmonic wave H is coupled out of the resonator 4 when it strikes the coupling-out mirror 6, as a result of which a laser beam L with the second frequency f2 is generated.
  • the end mirror 8, the laser medium 10, the second polarizer 22, the non-linear re medium 18, the first polarizer 20 and the output mirror 6 are arranged downstream of one another along a straight optical axis 23 and thus along a linear beam path.
  • FIG. 2 shows a first specification of the laser device 2, which is shown only generally in FIG.
  • the laser device 2 shown in FIG. 2 is a solid-state laser that uses a neodymium-doped laser medium 10 yttrium orthovanadate crystal (Nd:YV04 crystal 24).
  • Nd:YV04 crystal 24 a neodymium-doped laser medium 10 yttrium orthovanadate crystal
  • the fundamental wave F emitted by the laser medium 10 in the forward direction 14 is linearly polarized with a polarization direction to which the angle 0° is assigned here and below.
  • the pump device 12 is formed by a diode laser 26, which optically excites the Nd:YV04 crystal 24 with a pump laser beam P.
  • the second polarizer 22 downstream of the Nd:YV04 crystal 24 in the forward direction 14 is designed as a Faraday rotator 28, which rotates the direction of polarization of the fundamental wave F by an angle of 45°.
  • the optically non-linear medium 18 is formed here by a crystal, namely a lithium triborate crystal (LBO crystal 30) in a type I phase-match configuration, which causes a frequency doubling of the fundamental frequency fi.
  • the harmonic wave H generated by the LBO crystal 30 is the second harmonic H2 of the fundamental wave F, which has a wavelength l2 of 532 nm and is therefore in the spectral range of green visible light.
  • the LBO crystal 30 is also aligned in the beam path of the resonator 4a in such a way that it converts the light of the fundamental frequency fi into the light of the second frequency f2 with maximum efficiency if the light of the fundamental frequency fi is linearly polarized with a polarization direction of 45°.
  • the Faraday rotator 28 and the LBO crystal 30 are thus matched to one another in such a way that the efficiency of the frequency doubling for the passage of the fundamental wave F through the LBO crystal 30 in the forward direction 14 is maximized.
  • the second polarizer 22 downstream of the LBO crystal 30 in the forward direction 14 is formed in the example from FIG.
  • the 1/4 plate 32 is arranged in the beam path of the resonator 4 in such a way that it (re)polarizes the fundamental wave F incident in the forward direction 14 as a linearly polarized wave with a polarization direction of 45° into a circularly polarized light wave.
  • the fundamental wave F is reflected at the downstream output mirror 6 and is thus thrown back onto the 1/4 plate 32 in the reverse direction 16 .
  • the fundamental wave F incident in the reverse direction 16 as a circularly polarized light wave is now polarized by the 1/4 plate 32 into a linearly polarized light wave with a polarization direction of 135° (um).
  • the fundamental wave F polarized in this way now passes through the LBO crystal 30 in the reverse direction 16 . Due to the anisotropy of the LBO crystal 30 and the polarization of the fundamental wave F, the frequency doubling efficiency for the fundamental wave F propagating in the reverse direction 16 is minimized.
  • the direction of polarization of the fundamental wave F is again rotated by 45°.
  • the fundamental wave F thus leaves the Faraday rotator 28 in the reverse direction 16 as a linearly polarized wave with a polarization direction of 180°, which corresponds to the original polarization direction of 0°.
  • the fundamental wave F is thrown back onto the laser medium 10 (ie the Nd:YVO 4 crystal 24) and the cycle described above begins again.
  • the second harmonic H2 is emitted by the LBO crystal 30 (at least approximately) exclusively in the forward direction 14.
  • the second harmonic H2 is initially present as a linearly polarized light wave with a direction of polarization direction of 135°. Since the 1/4 plate 32 is tuned to the fundamental wave F (and the associated wavelength li), it has no defined polarization-influencing effect on the second Flarmonic H2. The second Flarmonic H2 is therefore present after passing through the 1/4 plate 32 with indeterminate polarization properties.
  • the second Flarmonic FH2 is coupled out of the resonator 4 via the coupling-out mirror 6 in order to form the laser beam L.
  • a third polarizer 34 in the form of a further 1/4 plate 36 is connected downstream of the output mirror 6 outside of the resonator 4 .
  • This additional 1/4 plate 36 is constructed in the same way as the 1/4 plate 32 and is therefore also tuned to the wavelength 11 of the fundamental wave F. However, it is rotated by 90° about the optical axis 23 in relation to the 1/4 plate 32 .
  • the additional 1/4 plate 36 thereby compensates for the effect of the 1/4 plate 32 on the second Flarmonic FH2.
  • the laser device 2 from FIG. 2 is designed as a Q-switched, pulsed-operated laser.
  • the laser device 2 has a Q-switch 38 as a further component, which, in the representation according to FIG. is interposed.
  • the Q-switch 38 is designed as an example of an acousto-optical modulator 40 (Bragg cell).
  • the quality of the resonator 4 is reduced at intervals by the Q-switch 38 between two laser pulses, so that the laser activity of the resonator 4 is prevented and thus a particularly strong excitation of the laser medium 10 (i.e. the Nd:YV04 crystal 24) is enforced.
  • the quality of the resonator 4 is temporarily increased by the quality switch, so that the laser activity begins.
  • the course of the fundamental wave F and the harmonic wave H is indicated schematically in FIG. 2 below the resonator 4 for the purpose of clarification.
  • the embodiment of the laser device 2 shown in FIG. 3 differs from the embodiments described with reference to FIG. 2 in that the optically non-linear medium 18 has a second crystal made of lithium triborate (LBO crystal 42) in addition to the frequency-doubling LBO crystal 30. has, which is connected between the LBO crystal 30 and the first polarizer 20 (here again in the form of the 1/4 plate 32) in the beam path of the resonator 4.
  • LBO crystal 42 lithium triborate
  • This frequency tripled light is emitted from the LBO crystal 42 as the third harmonic H3. It has a wavelength l3 of 354 nm and is in the ultraviolet region of the electromagnetic spectrum.
  • both the second harmonic H2 and the third harmonic H3 are coupled out of the resonator 4 via the coupling mirror 6 .
  • the second LBO crystal 42 is preferably a type II phase match crystal.
  • the second LBO crystal 40 is also aligned in the beam path of the resonator 4 in such a way that the frequency conversion (in this case frequency tripling) is maximized for the fundamental wave F propagating in the forward direction 14 .
  • the fundamental wave F propagating in the reverse direction 16 does not trigger frequency tripling due to the lack of a second Flarmonic H2 in the LBO crystal 40 .
  • the third Flarmonic H3 (at least approximately) is emitted exclusively in the forward direction 14.
  • a frequency doubling in the LBO crystal 30 due to the fundamental wave F propagating in the reverse direction 16 is in turn suppressed by the polarization of the fundamental wave F by means of the 1/4 plate 32 .
  • the third polarizer 34 (also formed here by the 1/4 plate 36) downstream of the output mirror 6 restores the original linear polarization destroyed by the 1/4 plate for both the second harmonic H2 and the third harmonic H3 .
  • the laser device 2 according to FIG. 1 is permeable to the light of the third frequency f3, so that the third harmonic H3 coupled out of the resonator 4 passes through the mirror 42 to form the laser beam L.
  • the second harmonic H2 coupled out of the resonator 4 is deflected by the mirror 42 . In this case, for example, it is thrown onto a light sensor 46 used to detect the laser activity.
  • the object of the invention is particularly clear from the exemplary embodiments described above, but is in no way limited thereto. Much more further embodiments of the invention can be derived from the claims and the above description.
  • the The third polarizer 34 described with reference to FIGS. 2 and 3 and the Q-switch 38 can also be used in other embodiments of the laser device 2 according to the invention.
  • the first polarizer 20 and/or the second polarizer 22 can also be designed in a different way than shown in FIGS. 2 and 3.
  • a Faraday rotator can be used for the first polarizer 20 instead of the 1/4 plate 32 , which rotates the direction of polarization of the fundamental wave by 45°.
  • suitable materials other than those described by way of example may be used for the laser medium 10 and the optically nonlinear medium 18 .

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Nonlinear Science (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • General Physics & Mathematics (AREA)
  • Lasers (AREA)
  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)

Abstract

L'invention concerne un appareil laser à conversion de fréquence (2) efficace tout en présentant une structure simple, qui comprend un résonateur optique (4) qui présente deux miroirs de résonateur (6,8), à savoir un miroir d'injection (6) et un miroir final (8). L'appareil laser (2) comprend également un milieu optiquement actif (10) pour générer de la lumière ayant une première fréquence (f1) et un milieu optiquement non linéaire (18) pour convertir la lumière de la première fréquence (f1) en lumière d'une autre fréquence (f2,f3). Le milieu optiquement actif (10) et le milieu optiquement non linéaire (18) sont disposés dans un trajet de rayonnement entre les miroirs de résonateur (6,8). L'appareil laser (2) comprend en outre un premier système optique laser influant sur la polarisation (20) qui polarise la lumière de la première fréquence (f1) réfléchie par le miroir d'injection (6) dans la direction du miroir final (8), de façon qu'une conversion de fréquence de la lumière ainsi polarisée de la première fréquence (f1) soit supprimée, en particulier réduite au minimum, lors du passage à travers le milieu non linéaire (18).
EP22715545.4A 2021-03-11 2022-03-02 Appareil laser à conversion de fréquence Pending EP4272288A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE102021202391.6A DE102021202391A1 (de) 2021-03-11 2021-03-11 Frequenzumwandelndes Lasergerät
PCT/EP2022/055236 WO2022189223A1 (fr) 2021-03-11 2022-03-02 Appareil laser à conversion de fréquence

Publications (1)

Publication Number Publication Date
EP4272288A1 true EP4272288A1 (fr) 2023-11-08

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EP22715545.4A Pending EP4272288A1 (fr) 2021-03-11 2022-03-02 Appareil laser à conversion de fréquence

Country Status (6)

Country Link
US (1) US20230420906A1 (fr)
EP (1) EP4272288A1 (fr)
JP (1) JP2024510583A (fr)
CN (1) CN116964880A (fr)
DE (1) DE102021202391A1 (fr)
WO (1) WO2022189223A1 (fr)

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4933947A (en) 1988-02-18 1990-06-12 Amoco Corporation Frequency conversion of optical radiation
DE3917902A1 (de) 1989-06-01 1990-12-13 Adlas Gmbh & Co Kg Frequenzverdoppelter laser
US7471707B2 (en) * 2004-08-27 2008-12-30 Photop Technologies, Inc. Low noise, intra-cavity frequency-doubling micro chip laser with wide temperature range
US8213470B2 (en) 2010-11-24 2012-07-03 Photop Technologies, Inc. Intra-cavity frequency doubled microchip laser operating in TEM00 transverse mode

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Publication number Publication date
US20230420906A1 (en) 2023-12-28
CN116964880A (zh) 2023-10-27
DE102021202391A1 (de) 2022-09-15
JP2024510583A (ja) 2024-03-08
WO2022189223A1 (fr) 2022-09-15

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