• 专利附录
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    • 专利摘要:
    A matte chip laser comprises a monolithic resonator (1) which has a birefringent laser crystal (2), wherein a laser beam (9) coupled out of the resonator (1) has a laser wavelength. along a laser beam axis (12) emerges from the resonator (1) and the length (L) of the resonator (1) related to the direction of the laser beam axis (12) is less than 150 μm. The laser crystal (2) has a thickness (D) related to the direction of the laser beam axis (12) such that when the laser beam (16) incidence of a laser beam (16) occurs in the direction of the laser beam axis (12), the laser crystal (2) intervenes the ordinary and the extraordinary beam (17, 19) into which the light beam (16) is divided in the laser crystal (2), a single pass through the laser crystal (2) a phase shift in the range of rr / 2 +/- lT / 4 occurs.
    公开号:AT515789A4
    申请号:T543/2014
    申请日:2014-07-07
    公开日:2015-12-15
    发明作者:Daniel Dr Kopf
    申请人:Daniel Dr Kopf；
    IPC主号:
    专利说明:

    The invention relates to a microchip laser with a monolithic resonator having a birefringent laser crystal, wherein a laser beam coupled out of the resonator and having a laser wavelength emerges from the resonator along a laser beam axis and the length of the resonator related to the direction of the laser beam axis is less than 150 pm is.
    Microchip lasers are solid-state lasers with a monolithic resonator and are characterized by a particularly small structure. End mirrors of the resonator are formed by coating the active laser medium and / or an end-element-having or forming optical element, for example a SESAM, is materially connected to the active laser medium. Such connection techniques are known as "bonding". known.
    Due to the short resonator lengths, short pulses can be easily formed with microchip lasers. Thus, Q-switching pulses can be achieved with pulse lengths of less than a nanosecond or even less than 100 picoseconds, in extreme cases less than 20 picoseconds. Such pulses are of interest, for example, for micromachining.
    Existing mode-locked lasers with which such short pulses can be generated are much larger. Typical resonator lengths are more than 1 m and such resonators can be accommodated by multiple convolution in a cube with an edge length of more than 10 cm. In contrast, a resonator of a microchip laser can be accommodated in a cube with an edge length of less than 1 mm.
    Also, a gain switching (= "gain-switching") may be performed for a microchip laser, whereby pulses with pulse durations in the nanosecond range or below may be generated. In principle, a microchip laser can also be operated continuously (in cw mode).
    Microchip lasers have a potentially low cost production because surface laser buildup can be made in a batch process (wafer process) so that well over 100 laser resonators can be obtained from an area of 10mm x 10mm.
    Due to the monolithic structure, a special stability of a microchip laser is made possible.
    Microchip lasers of the type mentioned above with particularly short pulse durations are described in WO 2011/147799 A1 and in Mehner E. et al. "Sub-20-ps pulses from a passively Q-switched microchip laser at 1 MHz repetition rate", OPTICS LETTERS, Vol. 39, NO. 10 / May 15,2014,2940-2943. Other publications are mentioned in these publications in which microchip lasers are disclosed in which with a Q-switching pulses with pulse lengths below 100 ps are achieved.
    For short cavity lengths and low gain bandwidths of the active laser material, microchip lasers typically emit at a single frequency, i. the laser beam coupled out of the resonator has a defined laser wavelength. The short cavity length results in a large "freespectral range," that is, a large spacing of adjacent wavelengths resonant in the resonator. For microchip lasers, the active laser medium used is often a laser crack formed by a vanadate, in particular Nd ^ t YVO. Nd3 *: YV04 has as laser material advantageous properties, such as a comparatively high small signal gain and good absorption of the pump radiation. Nd3 +: YV04 is a birefringent crystal, and past experience has shown that a Nd3 *: YV04 microchip laser as a laser crystal can laser at a polarization corresponding to the ordinary beam or corresponding to the extraordinary beam.
    Birefringent crystals are optically anisotropic in optically uniaxial birefringent crystals except for light in the direction of the crystal optical axis. For optically uniaxial birefringent crystals, on incidence parallel to the single crystal-optical axis, the refractive index is independent of the polarization direction of the light. For light incidence angular to the crystallooptic axis, the light beam is split into two linearly polarized sub-beams whose directions of polarization are perpendicular to each other and which are referred to as the ordinary beam and the extraordinary beam. The refractive indices are different for the ordinary ray and the extraordinary ray, and in a light incident direction perpendicular to the crystal-optical axis, the difference of the refractive indices assumes its maximum value. In such an incidence of light perpendicular to the crystal-optical axis and on an entrance surface of the birefringent crystal at right angles to the light incident direction, there is no spatial separation of the orthogonal and extraordinary rays polarized at right angles to each other.
    A birefringent crystal may also have more than one crystal-optical axis.
    The object of the invention is to provide an advantageous microchip laser of the type mentioned, which has a high stability of the polarization direction of the laser beam coupled out of the resonator. According to the invention, this is achieved by a microchip laser having the features of claim 1.
    In the microchip laser according to the invention, the laser crystal has a thickness in the direction of the laser beam axis such that, when the laser beam has an incidence of a laser beam wavelength incident on the laser crystal between the ordinary and extraordinary beams into which the light beam is split in the laser crystal. during a single pass through the laser crystal, a phase shift occurs in the range of π / 2 +/- π / 4, preferably π / 2 +/- π / 8. Thus, the birefringent laser crystal behaves like a lambda / 4 plate with respect to the ordinary and extraordinary beams, and deviation is possible in the aforementioned range.
    The inventive arrangement provides polarization selection of the coupled-out laser beam with a high tolerance to external influences, such as temperature, but also to manufacturing variations, e.g. with respect to the formed length of the resonator achieved.
    The length of the resonator in the direction of the laser beam axis is 150 μm or less, preferably 100 μm or less, particularly preferably 50 μm or less. Such a short resonator results in a large "freespectral range", that is a large distance between the wavelengths resonant in the resonator, which is important for a stable suppression of the unwanted polarization direction. Moreover, with such a short resonator, short pulse lengths can be easily achieved, advantageously by means of a passive Q-switching, in which a SESAM can be used in particular as an end mirror.
    A laser according to the invention can in principle be operated as a continuous wave laser. However, training as a pulsed laser is advantageous for many applications. The desired pulse duration depends on the application. There are applications in which pulse lengths in the ns range or also in the range of 100 ps -1 ns are advantageous. Such pulse durations may be achieved, for example, by a gain circuit of the optical pumping arrangement ("gain switching").
    In advantageous embodiments, the pulse duration of the pulses may be less than 100 ps, preferably less than 50 ps, with pulse durations of less than 20 ps being conceivable and possible. The pulse energy may be more than 10 nJ or even more than 30 nJ. In particular, such short pulse durations can be achieved by the already mentioned passive Q-switching.
    When pulse durations are referred to in the present specification, they are related to the half-width of the intensity (FWHM).
    In an advantageous embodiment of the invention, the laser crystal is Nds *: YVO 4. Instead of YVO 4, other vanadates are also contemplated for forming the laser crystal, e.g. Nd3 *: GdVO "or Nd3 ',: GdYV04. Instead of vanadates, other birefringent crystals with appropriate doping, e.g. Nd having laser active properties, e.g. LSB, used as a laser crystal.
    The resonator-forming layer system is formed so that a resonance for the desired polarization is at the maximum of the gain of the laser crystal or has only a slight deviation, preferably less than 0.5 nm. The wavelength of the decoupled laser beam for which the laser mode in the laser crystal at the maximum the gain of the laser crystal is referred to in this document as "gain wavelength " designated. For Nd3 *: YV04, this is about 1064 nm. The bandwidth within which there is sufficient gain to produce a laser mode is about 1 nm around this value.
    Advantageously, the laser beam axis along which the laser beam exits the resonator coincides with the axis of the laser beam within the resonator and the laser beam axis is perpendicular to a crystal optical axis of the laser crystal, preferably having only one crystal optical axis (= optically uniaxial) and related thereto is optically isotropic to an incident parallel to the single crystal-optical axis. The difference in the refractive indices for beams with perpendicular polarizations, corresponding to the ordinary and extraordinary beams, is maximum in such a configuration that the axis of the laser beam is perpendicular to the crystal-optical axis. Here, a light beam entering the laser crystal parallel to the laser beam axis is not spatially separated into a major and extraordinary beam, i. the ordinary and extraordinary beams coincide but have polarization directions perpendicular to each other.
    In particular, the resonator on both sides limiting end mirror, at leastwhen no pump radiation incident into the laser crystal, flat and perpendicular to the right perpendicular to the laser beam axis. Here, too, the end faces of the laser crystal through which the laser beam cooperates with the end mirrors, at least when no pumping radiation incident on the laser crystal, are flat and perpendicular to the right perpendicular to the laser beam axis.
    The laser wavelength of the decoupled laser beam advantageously has a very narrow frequency distribution, preferably with a half-width of intensity (FWHM) of less than 1 nm, more preferably less than 0.3 nm. The effects of the frequency distribution with respect to the intensity suppression of the undesired polarization direction can thereby be neglected. Strictly speaking, when the laser wavelength is mentioned in this document, it refers to the maximum of the frequency distribution of the coupled-out laser beam.
    Further advantages and details of the invention are explained below with reference to the accompanying drawings. In this show:
    Fig. 1 is a schematic representation of a microchip laser according to a first embodiment of the invention;
    FIG. 2 shows a view of the resonator in the direction of the laser beam axis; FIG.
    Fig. 3 is a schematic illustration of the E fields for a case where the resonator resonates at a laser wavelength corresponding to the amplification wavelength of the laser crystal for laser radiation linearly polarized perpendicular to each other, as a comparative example;
    Fig. 4 is a schematic representation of the E fields of the ordinary and extraneous beams for a laser beam incident laser beam beam on the laser crystal in the direction of the laser beam axis;
    Figures 5a and 5b are schematic representations of the ordinary and extraordinary beams in the case of a light beam incident on the laser crystal in the direction of the laser beam axis;
    Fig. 6 is a table for explaining a simulation calculation for a resonant-simulating layer system;
    Figures 7 and 8 are graphs for resonant lines of the resonator for polarizations corresponding to the ordinary and extraordinary beams, at a thickness of the laser crystal according to the invention;
    9 and 10 are diagrams corresponding to FIGS. 7 and 8 for a non-inventive thickness of the laser crystal, as a comparative example;
    Fig. 11 is a schematic representation of a microchip laser according to the invention according to another possible embodiment.
    A possible embodiment for a microchip laser according to the invention is shown schematically in FIGS. 1 and 2. The microchip laser has a resonator 1 formed in the form of a monolithic block. The laser active medium of the resonator 1 is the laser crystal 2. The laser crystal 2 has opposing end faces 3,4. Through these opposite end surfaces, a laser beam forming in the laser crystal 2 during operation of the laser (= laser mode) interacts with end mirrors 5, 6 of the resonator 1. The first end mirror 5 is formed from an optical coating of the end face 3 of the laser crystal 2. The second end mirror 6 is formed in the embodiment in the form of a Bragg mirror and part of a SESAM, which also has a Abberrschicht 7, which forms a saturable absorber. Between the absorber layer 7 of the SESAM and the laser crystal 2 there is still a reflection layer 8 for the pump radiation which is at least partially transparent, e.g. B. 30%.
    The reflection layer 8 is applied to the resonator 1 as an optical coating. The SESAM comprising the absorber layer 7 and the second end mirror 6 is formed on a support substrate 21 in the form of GaAs (eg, 0.4 mm thick). The unit comprising the SESAM and the support substrate 21 is bonded by bonding with the reflection layer 8-coated resonator 1 connected.
    The second end mirror 6 is formed partially reflecting, to decouple the laser beam 9.
    The carrier substrate 21 itself does not form part of the resonator 1. On the side of the carrier substrate 21 facing away from the laser crystal 2, an antireflection layer for the laser beam is favorably applied.
    An embodiment with a carrier substrate 21 could also be omitted in other embodiments.
    The first end mirror 5 is used in the exemplary embodiment for coupling the pump radiation and is designed to be as transmissive as possible for the pump radiation 10, while it is highly reflective for light with the optical frequency of the laser radiation.
    For the emission of the pump radiation, a laser diode or a laser diode array is used, wherein the pump radiation is supplied to the resonator in the schematically illustrated embodiment by an optical waveguide 11, of which an end is shown schematically in FIG. An arrangement of the laser diode or of the laser diode array directly in front of the resonator 1 is conceivable and possible. Additional lenses for focusing the pump radiation may be provided, but are not shown in the schematic Fig. 1.
    Advantageously, the diameter of the pump radiation in the laser crystal is less than 100 pm, preferably less than 50 pm, particularly preferably less than 30 pm, based on the half-width of the intensity (ie FWHM). The diameter of the pumping beam can in this case also be adapted to the thickness D of the laser crystal 2, whereby a pumping volume of substantially the same diameter and the same length can be achieved.
    The monolithic resonator 1 may have further and / or different optical elements. "Monolithic " in this case means that the elements forming the resonator are interlocked, in particular by means of a conventional bonding. Bonding is known, for example, in the form of diffusion bonding, wringing or adhesive bonding (by means of an adhesive layer).
    The resonator 1 is a standing wave resonator. At least as long as no pump radiation is incident into the laser crystal 2, in the shown microchip laser the end faces 3, 4 of the laser crystal 2 are flat and lie parallel to one another. Likewise, the end mirrors 5 and 6 are flat and lie parallel to each other. During operation of the laser, when the pump radiation 10 enters the laser crystal 2, a thermal lens is formed, including a certain curvature of the end faces 3, 4 and thus the end mirror 5, 6. The formation of laser modes of microchip lasers taking into account the thermal lens is known.
    Microchip lasers are kept in operation mostly by means of heating and / or cooling elements in a predetermined operating temperature range, for example by means of a Peltier element. At least one such heating and / or cooling element in order to keep the microchip laser in operation within a predetermined temperature range is preferably provided in the laser according to the invention, but not shown in FIG. 1 for the sake of simplicity.
    The laser beam 9 coupled out of the resonator 1 has a laser beam axis 12. In the resonator 1, the axis of the laser beam (= the laser mode) likewise corresponds to the laser beam axis 12.
    The laser crystal 2 in the exemplary embodiment is Nd3 +: YV04. Such a laser crystal is birefringent. YV04 has orthogonal a-axes 35, 36 and a perpendicular c-axis 37 to the a-axes 35, 36, cf. Fig. 1 and 2. YV04 is birefringent and optically uniaxial, having the c-axis 37 as the only crystal-optical axis. Therefore, with respect to the c-axis 37, YV04 is optically isotropic. It therefore has the same refractive index for directions of polarization of the light parallel to the two a-axes 36, 36. For an incidence of an unpolarized light beam at an angle to the crystal-optical axis, in the exemplary embodiment thus to the c-axis 37, the light beam is split into sub-beams which are polarized at right angles to one another, corresponding to the normal and extraordinary beam. In an incidence of an unpolarized light beam perpendicular to the crystal optical axis, in the exemplary embodiment, ie in the plane of the a-axes 35, 36, for example parallel to one of the a-axes 35, 36, wherein the entrance surface is perpendicular to the direction of incidence of the light beam, there is no spatial Separation of the ordinary and extraordinary ray, so they coincide, but they have parallel to the crystal optical axis (for the extraordinary beam) and perpendicular thereto (for the ordinary beam) lying polarization directions, in the embodiment so parallel to the c-axis 37 and parallel to the (other) a -Achse35.
    The axis of the laser beam 9 in the laser crystal 2 of the resonator 1 is perpendicular to the crystal optical axis, in the embodiment parallel to the a-axis 36, wherein the axis of the laser beam 9 in the laser crystal 2 in another direction perpendicular to the crystal optical axis, in the embodiment so in the a -Axis 35,36 plane spanned, for example, parallel to the other a-Achse35 could lie. The laser beam 9 can therefore basically assume a polarization parallel to the crystal-optical axis, in the exemplary embodiment of the c-axis 37, or at right angles thereto, in the exemplary embodiment parallel to the a-axis 35. For which of these polarizations a laser beam (laser mode) occurs and is decoupled from the resonator 1 will be explained below.
    For a laser mode to form in the resonator, the mode constraint must be satisfied: L = 1/2 * m * laser wavelength / n where L is the resonator length, m is an integer value and the mode number and n are the refractive index. Since the laser crystal is birefringent, the refractive indices n0 are different for the polarizations corresponding to the ordinary and extraordinary ray. For the laser wavelength, the gain wavelength (as defined further forward) is used. A value sufficiently close to this (within the gain bandwidth of, for example, +/- 1 nm) would still result in a laser mode. The intensity maximum is reached at the maximum of the gain. For YV04, the refractive index n4 for a polarization parallel to the c-axis 2.16 and the refractive index nc for a polarization parallel to the a-axis is 1.96 (relative to the amplification wavelength of 1064 nm). The refractive index difference in this case is about 0.2, thus about 10%.
    FIG. 3 shows by way of example a length L of the resonator in which resonance occurs both for standing waves with a polarization parallel to the c-axis 37 and parallel to the a-axis 35. The gain wavelength, z. 1064 nm for Nd3 +: YV04 is correspondingly compressed in the resonator according to the refractive index for the respective polarization. As a solid line 30 is shown in Fig. 3, the E
    Field for the polarization parallel to the c-axis 37, ie the polarization corresponding to the extraordinary ray, and as a dotted line 31 the E-field for the polarization parallel to the a-axis 35, ie for the polarization according to the particular beam, respectively along the laser beam axis 12, shown. Due to the higher refractive index, the wavelength for the polarization of the extraordinary beam is compressed from that of the ordinary beam.
    In the situation according to FIG. 3, the formation of a mode is basically possible for both polarizations. This leads to instabilities. Which mode will actually develop depends on small changes in the parameters, for example the temperature.
    In Fig. 3, as well as in the above-mentioned mode condition, it has been assumed for the sake of simplicity and illustration that the material of the laser crystal is present over the entire length of the resonator. In fact, an educated portion of the length L of the resonator may be formed by layers of other materials, such as the absorber layer 7 or reflective layer 8. The refractive index present in these regions is to be considered for the mode condition in a more specific manner. If these additional layers are not birefringent, the wavelengths for both polarization directions in these regions are the same.
    The situation for a laser designed in accordance with the invention is shown in FIG. 4 forth. The solid line 32 corresponds to the E-field for the laser beam, which is polarized in the direction of the extraordinary beam, in the exemplary embodiment, in the direction of the c-axis 37, along the laser beam axis 12. The resonator is resonant for this laser beam (the mode has nodes on the two ends of the resonator). In other words, for this laser beam having the laser wavelength corresponding to the amplification wavelength after being coupled out, for Nd3 *: YVO, that is, about 1064 nm, the mode condition is satisfied. By contrast, for the polarization corresponding to the ordinary ray, that is, in the embodiment parallel to the a-axis 35, the mode condition is not met. The E-field for an imaginary mode with the polarization corresponding to the ordinary ray would have a node at one end of the resonator but a vibular abdomen at the other end. The dashed line 32 in Fig. 4 illustrates this situation. Such a mode is thus suppressed and the output laser beam has a polarization corresponding to the extraordinary beam.
    In Fig. 4, the extension of the laser crystal 2 is drawn, which has this in the direction of the laser beam axis 12, ie its thickness D. In the laser crystal 2 is the wavelength for the polarization corresponding to the ordinary beam lambda11 o and the wavelength corresponding to the extraordinary beam lambda 11 e , specifically for the case of Nd3 +: YVO <:
    Lambda 11 o - lambda / nc - 1064 nm / 1.96 = 542.85 nm
    Lambda 11 e = lambda / n, = 1064 nm / 2.16 = 492.59 nm (" compressed ")
    Lambda here is the laser wavelength of the decoupled laser beam 9, which corresponds to the amplification wavelength.
    If no birefringent material is present in the region of the resonator which is located outside the laser crystal, lambda 11 o = lambda 11 e is in this region. The phase relationship between the E fields of the polarities polarized perpendicular to each other thus remains here. Even if the refractive indices in the region outside the laser crystal should be different for the two polarizations, the effect can be neglected if the phase shift caused outside the laser crystal region is sufficiently small, in particular <π / 8, preferably <π / 16 ,
    In Fig. 4 is shown as a difference between L and D for the sake of simplicity just half the wavelength. But this is only symbolically represented. In the
    In practice, the length difference between L and D will generally differ.
    By assuming that the laser crystal having the thickness D assumes that an unpolarized light beam having the laser wavelength is incident on the laser crystal 2 in the direction of the laser beam axis 12, the light beam in the laser crystal is divided into a regular and an extraordinary beam since the laser crystal 2 is birefringent , If the incidence is perpendicular to the crystal-optical axis, for Nd3 +: YV04 perpendicular to the c-axis, and to an incident surface perpendicular to the incident lightfall, then the extraordinary and ordinary rays are not spatially separated in this case, but are polarized at right angles to each other, and Although the extraordinary ray is in the direction of the crystal-optical axis, for Nd3 *: YV04 in the direction of the c-axis, and the ordinary ray is perpendicular to it, ie for Nd3 *: YV04 in the plane defined by the a-axes, for example parallel to one of the a-axes. Axes, polarized.
    In FIG. 5 a, the light beam 16 incident on the laser crystal is plotted along with the particular beam 17 whose polarization is indicated by the arrow 18 at right angles to the crystal-optical axis. In Fig. 5b, the incident light beam 16 is shown together with the extraordinary beam 19, the polarization of which is indicated parallel to the crystal-optical axis by the cross 20. The extraordinary ray E-field corresponds to the solid line 32 over the area of the laser crystal 2 (ie, the extent corresponding to D) in FIG. 4, and the ordinary ray E-field corresponds to the dashed line 33 over the extent corresponding to D in FIG ,
    The thickness D of the laser crystal in the direction of the laser beam axis is straight in Fig. 4 such that the phase position of the E-field of the extraordinary beam 19 is opposite to the phase position of the ordinary beam 17 at the end of the laser crystal (ie at the end of the pass through the laser crystal) of the laser crystal (ie the beginning of the pass through the laser crystal) by a quarter
    Wavelength, i. delayed by π / 2. The laser crystal 2 thus acts as a lambda / 4 plate with respect to the ordinary ray for the extraordinary ray. Thus, for this thickness D of the laser crystal, when the laser mode of the polarization direction corresponding to the extraordinary ray in the resonator is resonant, the laser mode with the polarization direction orthogonal thereto, that is, the ordinary ray, is &quot; best &quot; suppressed, i. is as far as possible removed from the fulfillment of the mode condition in the resonator.
    As already mentioned, it is assumed here that there are no further phase shifts between the modes outside the laser crystal, or if they are sufficiently low (preferably less than π / 8, particularly preferably less than π / 16), so that these not into weight traps.
    Even with a deviation from the stated design of the laser crystal 2 as lambda / 4-plate still a sufficient suppression of the unwanted polarization is achieved, as long as the deviation is not too large. The amount of allowable deviation also depends on the length of the resonator and the "free spectral range" associated therewith. from. For a relatively short resonator, due to the larger "free spectral range", greater deviation is allowed than with a longer resonator. Thus, for a resonator length of 50μηη or less, a phase shift between the minor and extraordinary beams may be allowed for a single pass through the laser crystal that is in the range of +/- ji / 4, but preferably deviates less from π / 2. For a length of the resonator 1 which is at least 50 μηη but less than 100 μηη, the phase shift is desirably at least in the range of π / 2 +/- π / 6. If the length of the resonator 1 is at least 100 μηη but less than 150 μιτι, the phase shift is favorably at least in the range π / 2 +/- π / 8.
    In the following, results of numerical calculations of resonance lines of a resonator at two different thicknesses of the laser crystal 2 and corresponding different lengths of the resonator 1 (the resonator 1 is otherwise formed the same) are shown by way of illustration. The calculations were made for a resonator according to a modified embodiment of a microchip laser, which is shown schematically in FIG. 11:
    The resonator 1 comprises a birefringent laser crystal 2, for example Nd **: W04. On the first end face 3, an optical coating is applied as the first end mirror 5. This is permeable to the pump radiation and partially reflecting the laser beam. The other end face 4 is coated with a reflection layer 8 which reflects the pump radiation to which the laser beam is transmissive. The laser crystal 2 coated with the reflective layer 8 is bonded with a SESAM comprising a saturable absorber layer 7 and the second end mirror 6. The reflective layer could be applied to the SESAM prior to bonding. The SESAM is here applied to a heat sink 26, for example made of copper.
    The coupling-out of the laser beam 9 takes place in this exemplary embodiment through the first end mirror 5. The laser crystal 2 with the optical coating forming the first end mirror 5 is bonded to an undoped YVO 4 crystal 22 which lies outside the resonator. By the material connection of the laser crystal 2 with the YVO 4 crystal 22, the mechanical processing of the laser crystal 2 for forming the laser crystal 2 with a small thickness D is substantially simplified. On the YV04 crystal 22 is still a window 27 (antireflection coated for the pump radiation and the laser beam) applied.
    The radiation source for the pump radiation is a laser diode or a laser diode array. The transmission can be effected by means of a light guide 11, of which an end is shown schematically in FIG. Such a light guide may also be omitted. In Fig. 11 are also lenses 23,24 for focusing the
    Pump radiation indicated For the separation of the laser beam from the pumping radiation is used in this embodiment, a dichroic beam splitter 25. For a layer system according to the resonator 1 of Fig. 11 numerical calculations were performed. For the sake of simplicity, however, the reflection layer 8 and the absorber layer 7 have been omitted. The length L of the resonator 1 thus corresponds to the thickness D of the laser crystal 2. The table of Fig. 6 describes the system for which the calculations were actually performed. In the table, the first column designates the number assigned to each layer. The column d denotes the thickness of the respective layer in nm. The column indicates the "optical thickness", which is the thickness t times the refractive index. The column QWOT denotes the optical thickness with respect to the number of quarter wavelengths. Finally, the last column M designates the material of the respective layer.
    Layers 1 to 10 represent a Bragg mirror formed by five quarter wavelength pairs (based on wavelength 1064 nm). The reflectivity of these ten layers at 1064 nm is about 98%, that is close to a high reflector. Increasing the number of layers of the Bragg mirror could further increase the reflectivity.
    Layer 11 represents the laser crystal, in the present case Nd3 +: YVO. Initially, a thickness of 33.25 μιτι was considered. For the laser crystal 2, in the table of Fig. 6, the refractive index ne was set for the polarization in the direction of the extraordinary ray (symbolized by Nd3 +: YV04 11c, that is, for the case of Nd3 +: YV04.2.16) For the calculation of the reflectivity for a beam having a polarization corresponding to the ordinary ray, the refractive index of the laser crystal nol is thus taken to be 1.96 in the case of Nd3 +: YV04.
    The layers 12 to 20 represent the first end mirror 5, which in the embodiment is almost completely transmissive at the 808 nm wavelength of the pump radiation and has 95% reflectivity at the laser wavelength of 1064 nm in the embodiment. In the embodiment of Fig. 11, the layer 20 would be disposed on YV04 as a supporting substrate.
    The layer materials used herein are TiO 2 and SiO 2, although other materials common in coating technology are possible, e.g. Ta205.
    The result of calculating the reflectance in% as a function of the wavelength for the polarization parallel to the ordinary ray and parallel to the extraordinary ray is shown in Figs. 7 and 8. From Fig. 7 it is apparent that there is a drop in the reflectivity of the system at a wavelength of about 1064 nm, so the gain wavelength of the material of the laser crystal. This corresponds to a resonance in the resonator for a laser beam coupled out with this wavelength. The adjacent resonances occur at wavelengths of about 1056 nm and 1072 nm. The "free spectral range" is thus about 8 nm.
    Fig. 8 shows the resonances for the polarization in the direction of the extraordinary ray. The closest resonances to the 1064 nm amplification wavelength are at about 1060 nm and 1068 nm, and thus have the maximum possible spacing of 1064 nm.
    For the thickness D of the laser crystal 2 corresponding to the length L of the resonator 1 in the observed layer system, of 33.25 μm, the polarization in the direction of the extraordinary ray is L / f Lambda / nJ = 67.5, i.e.,. the wavelength fits 67.5 times in the laser crystal (corresponding to the mode number of m = 135). For polarization in the direction of the ordinary ray, L ^ lambda / nJ = 61.25, that is, the mode number m would be 122.5, which is not an integer mode number, since there is no valid polarization mode in the ordinary beam direction at the amplifier spar length, as desired. For a thickness D of the laser crystal of 33.25 pm, therefore, a passage through the laser crystal 2 results in a phase shift between the ordinary ray and the extraordinary ray of π / 2.
    Figs. 9 and 10 are diagrams corresponding to Figs. 7 and 8 for a comparative example in which the laser crystal has a thickness of 49.998 μm. Again, the polarization in the direction of the extraordinary ray is resonated at 1064 nm as desired In the direction of desordentliche ray is the next resonance in this case at about 1065nm. The distance is thus too small at this thickness D of the laser crystal, as a stable operation of the laser with the desired polarization sets in parallel to the extraordinary beam.
    Thus, in order to determine an appropriate thickness of the laser crystal for stable operation of the laser in one of the polarization directions, on the one hand, the condition must be satisfied that the resonator for the desired polarization direction corresponding to the extraordinary or ordinary ray has resonance at the laser wavelength corresponding to the amplification wavelength. In addition, it is necessary to satisfy the condition that the phase shift for the polarization directions corresponding to the extraordinary and ordinary ray is in the above-described range. In the concrete example described, the polarization corresponding to the extraordinary beam was selected and the polarization suppressed at a right angle thereto. For Nd3 *: YV04, this is advantageous because there is a higher gain for the polarization direction corresponding to the extraordinary beam than for the polarization direction at right angles thereto. In an analogous manner, however, a polarization direction corresponding to the ordinary ray can be selected and the polarization direction corresponding to the extraordinary ray can be suppressed.
    Various modifications of the illustrated embodiments are conceivable and possible, without departing from the scope of the invention, for example with regard to the layer structure of the resonator and with regard to the birefringent material of the laser crystal. In advantageous embodiments of the invention, the birefringent material of the laser crystal has only one crystal optical axis, but could also have more than one crystal optical axis, where the axis of the laser beam in the laser crystal and the laser beam axis of the outcoupled laser beam could be perpendicular to one of the crystal optical axes.
    Legend to the reference numbers: 1 resonator 19 extraordinary beam 2 laser crystal 20 cross 3 end face 21 carrier substrate 4 end face 25 22 YV04 crystal 5 first end mirror 23 lens 6 second end mirror 24 lens 7 absorber layer 25 beam splitter 8 reflection layer 26 heat sink 9 laser beam 30 27 window 10 pump radiation 30 Line 11 optical fiber 31 line 12 laser beam axis 32 line 16 light beam 35 a-axis 17 ordinary beam 35 36 a-axis 18 arrow 37 c-axis
    权利要求:
    Claims (10)
    [1]
    1. Microchip laser with a monolithic resonator (1) having a birefringent laser crystal (2), wherein one of the resonator (1) coupled out laser beam (9) having a laser wavelength along a laser beam axis (12) from the resonator ( 1) and the length (L) of the resonator (1) related to the direction of the laser beam axis (12) is less than 150 pm, characterized in that the laser crystal (2) has a thickness (D) related to the direction of the laser beam axis (12) in that, in the direction of the laser beam axis (12), an incidence of a laser beam (16) on the laser crystal (2) exists between the ordinary and extraordinary beams (17, 19) into which the light beam (16) in the laser crystal (16) 2), during a single pass through the laser crystal (2), a phase shift occurs that is in the range of π / 2 +/- π / 4.
    [2]
    2. Microchip laser according to claim 1, characterized in that the phase shift is in the range of ä / 2 +/- π / 8.
    [3]
    A microchip laser according to claim 1 or 2, characterized in that the length (L) of the resonator (1) relative to the direction of the laser beam axis (12) is &lt; = 100 pm, preferably &lt; = 50 pm.
    [4]
    4. Microchip laser according to one of claims 1 to 3, characterized in that the microchip laser is passively Q-switched, wherein the pulse length is preferably less than 100 ps, more preferably less than 50 ps, even more preferably less than 20 ps.
    [5]
    5. microchip laser according to one of claims 1 to 4, characterized in that the resonator (1) on both sides limiting end mirror (5, 6) at least without a incident on the resonator pump radiation (10) are flat and parallel to each other and perpendicular to the laser beam axis (12 ) lie.
    [6]
    Microchip laser according to one of claims 1 to 5, characterized in that the laser beam axis (12) is perpendicular to a crystal optical axis of the laser crystal (2), the laser crystal preferably having only one crystal optical axis with respect to which the laser crystal (2) is optically isotropic is.
    [7]
    7. Microchip laser according to one of claims 1 to 6, characterized in that the laser crystal (2) is a vanadate, preferably Nd **: YVO.
    [8]
    Microchip laser according to one of Claims 1 to 7, characterized in that the length (L) of the resonator relative to the direction of the laser beam axis (12) is less than 30%, preferably less than 15%, greater than that of the direction of the laser beam axis (12) is the thickness (D) of the laser crystal (2).
    [9]
    Microchip laser according to one of Claims 1 to 8, characterized in that it comprises a light beam polarized in the direction of the discrete beam (17) and having a laser wavelength polarized in the direction of the extraordinary beam (19) at a wavelength single pass through layers additionally present in the resonator (1) in addition to the laser crystal (2) results in a phase shift of less than π / 8, preferably less than π / 16.
    [10]
    A method of forming a microchip laser with a monolithic resonator (1) comprising a birefringent laser crystal (2), wherein a laser beam (9) having a laser wavelength coupled out of the resonator (1) projects along a laser beam axis (12) the resonator (1) and the length (L) of the resonator (1) related to the direction of the laser beam axis (12) is smaller than 150 μηη, satisfying the condition that the resonator (1) is in a desired polarization direction corresponding to an extraordinary or ordinary ray in the laser crystal has a resonance at the laser wavelength, in which there is a maximum of the gain of the laser crystal, characterized in that for an incident in the direction of the laser beam axis (12) incidence of the laser wavelength having a light beam on the laser crystal! (2) a phase shift between the ordinary and extraordinary beams (17, 19) into which the light beam is split in the laser crystal is calculated for a single pass through the laser crystal (2) and the thickness (D) related to the laser beam axis (12) of the laser crystal (2) is chosen so that the phase shift is in the range of nil +/- π / 4, preferably π / 2 +/- π / 8.
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    同族专利:
    公开号 | 公开日
    US10148057B2|2018-12-04|
    AT515789B1|2015-12-15|
    EP3167516A1|2017-05-17|
    WO2016004446A1|2016-01-14|
    EP3167516B1|2020-02-19|
    US20170133815A1|2017-05-11|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    EP1978611A1|2007-04-03|2008-10-08|Topcon Corporation|Q- switched microlaser apparatus and method for use|
    EP2577818A1|2010-05-28|2013-04-10|Daniel Kopf|Ultrashort pulse microchip laser, semiconductor laser, laser system, and pump method for thin laser media|
    US6373604B1|1999-10-01|2002-04-16|New Focus, Inc.|Optical MUX/DEMUX|
    US7457330B2|2006-06-15|2008-11-25|Pavilion Integration Corporation|Low speckle noise monolithic microchip RGB lasers|
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    US7742509B2|2008-09-25|2010-06-22|Photop Technologies|Single-longitudinal mode laser with orthogonal-polarization traveling-wave mode|
    DE102012005492A1|2012-03-17|2013-09-19|Batop Gmbh|Passively quality-switched microchip laser used as pulsed light source in e.g. material treatment, has optical pumping device that is provided for pumping optical gain medium, for producing repetition frequency of optical laser pulse|US10622780B2|2018-06-22|2020-04-14|Candela Corporation|Handpiece with a microchip laser|
    AT521943A1|2018-12-14|2020-06-15|Dr Daniel Kopf|Q-switched solid-state laser|
    AT521942A1|2018-12-14|2020-06-15|Dr Daniel Kopf|Q-switched solid-state laser|
    AT522108A1|2019-01-31|2020-08-15|Montfort Laser Gmbh|Passively Q-switched solid-state laser|
    法律状态:
    优先权:
    申请号 | 申请日 | 专利标题
    ATA543/2014A|AT515789B1|2014-07-07|2014-07-07|Microchip Laser|ATA543/2014A| AT515789B1|2014-07-07|2014-07-07|Microchip Laser|
    EP15737952.0A| EP3167516B1|2014-07-07|2015-06-23|Microchip laser|
    US15/318,764| US10148057B2|2014-07-07|2015-06-23|Microchip laser|
    PCT/AT2015/000090| WO2016004446A1|2014-07-07|2015-06-23|Microchip laser|
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