阅读说明：本技术 具有交替的折射率变化的光学元件及其应用 (Optical element with alternating refractive index variation and use thereof ) 是由 M·朱佩 D·里斯陶 于 2018-11-26 设计创作，主要内容包括：在光学元件(1)中,在沿光轴(7)彼此相继的至少三个区域(9,10,11,13,14)中通过交替的折射率变化(6)构造反射器(12),并且在每两个彼此相继的反射器(12)之间构造谐振器(15)用于沿所述光轴(7)入射的具有设计波长的光。所述谐振器(15)中的至少一个包括克尔活性材料。所述谐振器(15)中的至少两个的总折射率n(i)＝n<Sub>0</Sub>(i)+I<Sub>Res</Sub>(i)·n<Sub>2</Sub>(i)中的非线性分量I<Sub>Res</Sub>(i)·n<Sub>2</Sub>(i)的量值相差两个非线性分量I<Sub>Res</Sub>(i)·n<Sub>2</Sub>(i)中的较小者的量值的至少50％,其中,I<Sub>Res</Sub>(i)是沿所述光轴(7)辐射的具有所述设计波长(λ)的光的强度I<Sub>Res</Sub>(i),所述强度由于相应的谐振器(15)在所述反射器(12)之间的布置而得出,n<Sub>2</Sub>(i)是相应的谐振器(15)的非线性折射率。(In the optical element (1), reflectors (12) are formed by alternating refractive index variations (6) in at least three regions (9, 10, 11, 13, 14) that follow one another along an optical axis (7), and a resonator (15) is formed between each two following reflectors (12) for light of a design wavelength that is incident along the optical axis (7). In the resonator (15)At least one of which includes a kerr active material. A total refractive index n (i) ═ n of at least two of the resonators (15) 0 (i)+I Res (i)·n 2 (i) Non-linear component I in Res (i)·n 2 (i) By two non-linear components I Res (i)·n 2 (i) Of the lesser of which is at least 50%, wherein I Res (i) Is the intensity I of light having the design wavelength (lambda) radiated along the optical axis (7) Res (i) The intensity being derived as a result of the arrangement of the respective resonator (15) between the reflectors (12), n 2 (i) Is the non-linear refractive index of the corresponding resonator (15).)

1. An optical element (1) having an optical axis (7), a design wavelength (λ) and alternating refractive index variations (6) along the optical axis (7),

wherein, in at least three regions (9, 10, 11, 13, 14) which follow one another along the optical axis (7), a reflector (12) for light (8) incident along the optical axis (7) having the design wavelength (λ) is formed by the alternating refractive index variations (6),

wherein an optical resonator (15) for the light (8) having the design wavelength (λ) incident along the optical axis (7) is formed between each two of the successive reflectors (12) by the alternating refractive index variations (6),

wherein at least one of the resonators (15) comprises a Kerr active material,

it is characterized in that the preparation method is characterized in that,

a total refractive index n (i) ═ n of at least two of the resonators (15)₀(i)+I_Res(i)·n₂(i) Non-linear component I in_Res(i)·n₂(i) By the magnitude of said two non-linear components I_Res(i)·n₂(i) At least 50% of the magnitude of the smaller of,

wherein, I_Res(i) Is the following intensity of light (8) having the design wavelength (λ) incident along the optical axis (7): the intensity is derived in the respective resonator (15) as a result of the arrangement of the respective resonator (15) between the reflectors (12),

wherein n is₂(i) Is the non-linear refractive index of the respective resonator (15).

2. Optical element (1) according to claim 1, characterized in that the reflector (12) is constructed at least predominantly of a non-kerr-active material having a total refractive index n (k) n, which is related to the intensity I of the light (8)₀(k)+I·n₂(k) Wherein the non-linear refractive index n₂(k) Is not of the at least one resonator (15) with the Kerr active materialLinear refractive index n₂(i) At most half, or at most one quarter, or at most one eighth of the amount of (c).

3. Optical element (1) according to claim 2, characterized in that the non-linear refractive index n of the non-kerr active material of the reflector (12)₂(k) Is less than or equal to 4.0 × 10^-16cm²/W, or less than or equal to 3.0 × 10^{- 16}cm²/W, or less than or equal to 2.0 × 10^-16cm²/W。

4. Optical element (1) according to one of the preceding claims, characterized in that at least one further resonator of the resonators (15) is constructed at least predominantly from a non-kerr-active material, such that it has n (p) ═ n₀(p)+I·n₂(p) total refractive index, wherein the non-linear refractive index n₂(p) is the non-linear refractive index n of the at least one resonator (15) with the Kerr active material₂(i) At most half, or at most one quarter, or at most one eighth of the amount of (c).

5. Optical element (1) according to claim 4, characterized in that the nonlinear refractive index n of at least one other of the resonators (15)₂(p) is less than or equal to 4.0 × 10^-16cm²/W, or less than or equal to 3.0 × 10^-16cm²/W, or less than or equal to 2.0 × 10^-16cm²/W。

6. Optical element (1) according to any one of the preceding claims, characterized in that the kerr active material of at least one of the resonators (15) is TiO₂And optionally at least one of the following features:

the Kerr active material of at least one other of the resonators (15) consists of Ta₂O₅Or other goldBelongs to the composition of oxides, and the preparation method comprises the following steps of,

at least one of the reflectors (12) has SiO₂As a non-kerr active material with low refraction,

at least one of the reflectors (12) has Ta₂O₅Or other metal oxides as highly refractive non-kerr active materials.

7. Optical element (1) according to any one of the preceding claims, characterized in that the nonlinear refractive index n of the kerr active material of at least one of the resonators (15) is n₂Is greater than or equal to 1 × 10^-14cm²/W, or greater than or equal to 1 × 10^-12cm²/W, or greater than or equal to 1 × 10^-10cm²/W, or greater than or equal to 1 × 10^-8cm²/W, or greater than or equal to 1 × 10^-6cm²/W, the Kerr active material having a total refractive index n related to the intensity I of the light (8)_Kerr＝n₀+I·n₂。

8. Optical element (1) according to any one of the preceding claims, characterized in that the kerr-active material of at least one of the resonators (15) is a polymer.

9. Optical element (1) according to any one of the preceding claims, characterized in that the kerr-active material of at least one of the resonators (15) is doped with nanoparticles having at least one metal or semiconductor.

10. Optical element (1) according to claim 9, characterized in that the nanoparticles have a particle size in the range of 1 to 100 nm.

11. Optical element (1) according to claim 9 or 10, characterized in that the nanoparticles are at least predominantly constructed from gold, silver, platinum, palladium or copper.

12. Optical element (1) according to any one of the preceding claims, characterized in that an increase of the intensity I of the light (8) incident along the optical axis (7) having the design wavelength (λ) either reduces or increases the transmittance of the optical element (1) in a pass band (19, 20, 22, 28) around the design wavelength (λ).

13. An optical element (1) having an optical axis (7), a design wavelength (λ) and alternating refractive index variations (6) along the optical axis (7), in particular according to any one of the preceding claims,

wherein, in at least two regions (9, 10, 11, 13, 14) which follow one another along the optical axis (7), a reflector (12) for light (8) incident along the optical axis (7) having the design wavelength (λ) is formed by the alternating refractive index variations (6),

wherein an optical resonator (15) for the light (8) having the design wavelength (λ) incident along the optical axis (7) is formed between each two of the reflectors (12) that follow one another by the alternating refractive index variations (6),

wherein at least one of the resonators (15) comprises a Kerr-active material such that the at least one resonator has a refractive index n (I) n which is related to the intensity I of the light (8)₀(i)+I·n₂(i)，

It is characterized in that the preparation method is characterized in that,

a non-linear refractive index n of the Kerr-active material of at least one of the resonators (15)₂Is greater than or equal to 1 × 10^-14cm²/W, or greater than or equal to 1 × 10^-12cm²/W, or greater than or equal to 1 × 10^-10cm²/W, or greater than or equal to 1 × 10^-8cm²/W, or greater than or equal to 1 × 10^-6cm²W, the Kerr active material having an intensity I related to the light (8)Refractive index n of_Kerr＝n₀+I·n₂，

Wherein the Kerr active material of at least one of the resonators (15) is a polymer and/or doped with nanoparticles having at least one metal or semiconductor.

14. Use of an optical element (1) according to any one of claims 1 to 13 as an optical switch in a laser resonator (32).

15. Use of an optical element (1) according to any one of claims 1 to 13 as a mode coupler and/or a Q-switch and/or a power protection switch in a laser resonator (32).

Technical Field

The invention relates to an optical element having an optical axis and a design wavelengthAlternating refractive index variations along the optical axis, and other features of the preamble of independent claim 1. Furthermore, the invention relates to the use of such an optical element in a laser resonator.

Background

An optical device is known from EP 0541304B 1, which comprises a first reflective element and a second reflective element spaced apart from the first reflective element for constructing a Fabry-perot Etalon (Fabry-perot-Etalon) having a plurality of optical resonance frequencies between the first reflective element and the second reflective element. The semiconductor material of the optical device, which is arranged between the first reflective element and the second reflective element, has a non-linear optical absorption at a predetermined optical frequency. The optical frequency is located between two adjacent optical resonant frequencies such that the optical frequency is substantially at an optical frequency corresponding to an anti-resonance condition of the fabry-perot etalon. The semiconductor material acts as a saturable absorbing element that becomes transparent only from the point where the intensity of the light reaches the saturation limit. The optical element is also referred to as a saturable fabry-perot absorber. The optical element belongs to the class of SESAMs (semiconductor saturable absorbers) and can be used for mode coupling or for Q-switching in laser resonators. In the practical application of SESAMs, common problems arise in terms of damage resistance at high light intensities, optical losses and Degradation of the absorber (Degradation). Furthermore, there are no practical absorbers available in the wavelength range below 780 nm.

An optical element having a stack of optical layers made of a third-order nonlinear material is known from EP 3217489 a 1. The optical element is arranged to modulate the light in accordance with the intensity of the light. In particular, the reflectivity or transmittance of the optical element should depend on the intensity of the light. This correlation is based on the Kerr effect (Kerr-Effekt), according to which n is equal to n₀+I·n₂The total refractive index n of the third-order nonlinear material depends on the intensity of light I and the nonlinear refractive index n₂. In addition to the kerr effect, the absorption of light and therefore the thermal load on the optical element is a function of the intensity I and the nonlinear refractive index n of the light₂Product of (I) n₂And (4) rising. Thus, according to EP 3217489A 1, the non-linear magnitude n₂Should remain less than 10^-12cm²From EP 3217489A 1, doped polymer films have approximately 1.7 × 10^-6cm²Non-linear refractive index n of/W₂. The stack of kerr active optical layers of the optical element may have at least one full wave cavity that is resonant at the center wavelength of light. The resulting resonator achieves field amplification within the stack so that with appropriate intensity of the incident light, a non-linear effect is also achieved on the refractive index. By means of a plurality of such cavities, the optical kerr effect should be further enhanced.

Schnelle Schalter durch in M.Jup é et alan Ausgellegte Mehrs-chichtsysme (2016) (see https:// www.photonikforschung.de/service/nachrichten/detailansicht/schnelle-Schalter-durch-praezise-Ausgellegte-mehrschichtsystem. html) proposes a Kerr-Band-Schalter switch for realizing saturable semiconductor mirrors of alternative modal coupling designs(so-called SESAMs ("semiconductor saturable absorption mirrors")) which are based on the use of the kerr effect in thin-film systems. A kerr strip switch is composed of a layer system of a medium, in which one or more kerr active layers are embedded. When high light intensities are produced, the refractive index of the kerr active layer changes slightly, thereby affecting the transmission properties of the part. Thus, the kerr band switch enables a lossless switching of the resonance quality of the laser resonator.

Disclosure of Invention

The object of the invention is to provide an optical element which is particularly suitable for use as an optical switch in a laser resonator and has a high damage threshold

Making it also suitable for switching of light with very high intensity and also for switching of light with long wavelengths below 780 nm.

According to the invention, this object is achieved by an optical element having the features of independent claim 1. The dependent claims 2 to 13 relate to advantageous configurations of the optical element according to the invention. Claims 14 and 15 relate to advantageous uses of the optical element according to the invention in laser resonators.

The invention relates to an optical element having an optical axis, a design wavelength and alternating refractive index variations along the optical axis, wherein reflectors for light of the design wavelength incident along the optical axis are formed by the alternating refractive index variations in at least three mutually successive regions along the optical axis, and an optical resonator for light of the design wavelength incident along the optical axis is formed between each two of the mutually successive reflectors, wherein at least one of the resonators comprises a Kerr-active material. According to the invention, the optical element is characterized in that the total refractive index n (i) ═ n of at least two of the resonators₀(i)+I_Res(i)·n₂(i) Non-linear component I in_Res(i)·n₂(i) By two non-linear components I_Res(i)·n₂(i) Of smaller of theAt least 50% of the value, wherein_Res(i) Is the intensity of light incident along the optical axis at the design wavelength, which is derived in the respective resonator as a result of the arrangement of the respective resonator between the reflectors, n₂(i) Is the nonlinear refractive index of the corresponding resonator.

In general, the term "light" is used here and elsewhere in the specification and claims to mean electromagnetic radiation selected from the wavelength range of infrared up to ultraviolet. The electromagnetic radiation may in particular relate to laser radiation. Here and elsewhere in this specification and claims, the term "intensity" of light refers to the spatial power density of electromagnetic radiation. Intensity I derived in the reflector_Res(i) Depending on the overall input intensity of light incident along the optical axis. It can therefore be understood that the total refractive index n (i) ═ n is observed for the same input intensity₀(i)+I_Res(i)·n₂(i) Of the non-linear component I_Res(i)·n₂(i) The relationship (2) of (c).

The term "optical axis" as used herein and elsewhere in this specification and in the claims does not necessarily mean that the optical axis has a fixed spatial relationship with respect to the structure of the optical element, i.e. for example extends orthogonally to the layers of the layer structure with respect to the optical element. More precisely, the optical axis is defined by the effect of the optical element on light incident along the optical axis. In this way, light can also impinge on the layers of the layer structure of the optical element at angles significantly different from 90 °. This can be used, for example, for the targeted use of optical elements in order to influence only light of a certain polarization direction.

The design wavelengths of the optical elements are the following wavelengths: at this wavelength, the optical element responds particularly strongly to high intensities by its change in optical properties between reflection and transmission. At least three reflectors are constructed by alternating refractive index changes for the design wavelength, between which two resonators are arranged. The expression "alternating refractive index variation" here means that the refractive index of the optical element decreases and increases alternately along the optical axis. These decreases and increases in the refractive index can occur in a sudden manner between two respective layers following one another along the optical axis or extend continuously as in the case of the so-called Rugate structure (Rugate-Strukturen). Furthermore, the maximum and minimum values of the refractive index achieved by the alternating refractive index variation may be constant or may be varied along the optical axis by the optical element. The amount of alternating refractive index change required to construct the reflector depends on the magnitude of the refractive index change. In the case of sufficiently large refractive index differences, two refractive index changes (which in the layer structure correspond to three layers one behind the other) are sufficient for the construction of the reflector. More refractive index change is required with smaller refractive index difference. The period of the alternating refractive index changes along the optical axis is typically half the design wavelength, with the optical spacing between individual refractive index changes being one quarter of the design wavelength. The resonators each have an optical extension in the direction of the optical axis of one or more times the half design wavelength. The optical dimensions of the reflector and the resonator do not have to be precise and do not correspond to the above data in all cases. The basic correspondence is sufficient.

The kerr-active material can be strongly localized (stark lokalisieren) in the optical element according to the invention. In particular, it can be achieved that the kerr-active material is arranged only in the at least one resonator. Here, the kerr active material does not have to be present in the entire resonator, but may be limited to a partial region of the resonator. In other words, at least one resonator and any other resonator of the optical element according to the present invention may have a multilayer structure. In the optical element according to the invention, the strong positioning by the kerr active material ensures: even when the absorption of light by the kerr active material increases with the kerr effect, the absolute absorption remains low and therefore the thermal load of the optical element as a whole remains low. At the same time, the optical element according to the present invention has a high efficacy, i.e., the sensitivity of the optical element in terms of the change in optical properties between reflection and transmission as the intensity of light having the design wavelength increases. This can be attributed to: the reflectors of the optical elements are tuned to one another in such a way that they exhibit a distinctly different kerr effect, i.e. are detuned (vertemmen) or harmonised to different extents with the intensity of the light incident along the optical axis. By these of the resonators being mutually detuned or mutually coordinated, the effect of the kerr effect on the optical performance of the optical element (with respect to the variation of the optical performance of the optical element between reflection and transmission at the design wavelength) is enhanced. Furthermore, a kerr active material is used at the location where the highest intensity of the incident light is found (i.e. in one of the resonators).

Specifically, as the intensity of light having the design wavelength increases, the resonators can all be ideally tuned to the design wavelength from an initial state at a low intensity of light having the design wavelength incident along the optical axis (in which initial state at least one of the resonators is detuned at the design wavelength relative to an ideal resonator) so that the optical element becomes transparent to light having the design wavelength. In contrast, in the case of a low intensity of light having the design wavelength, resonators ideally tuned with a high intensity of light having the design wavelength are detuned from each other.

As long as optical materials are available for the construction of reflectors and resonators located between the reflectors by means of alternating refractive index changes, the optical element according to the invention can be designed for a design wavelength in the extension from ultraviolet to infrared, since in the case of all optical materials at least a certain kerr activity occurs.

For a total refractive index n (i) n of at least two of the standard resonators₀(i)+I_Res(i)·n₂(i) Non-linear component I in_Res(i)·n₂(i) By two non-linear components I_Res(i)·n₂(i) At least 50% of the smaller "includes the following possibilities: non-linear refractive index n of two resonators₂(i) With different symbols. The following possibilities are also included: in particular due to the different resulting intensities I in the respective resonators_Res(i) Two non-linear components I_Res(i)·n₂(i) Different. The derived intensity I_Res(i) The strength increase in the resonators is taken into account, which is caused according to the construction of the "resonators and reflectors limiting these resonators". Here, the case where light having a designed wavelength incident along the optical axis has a fixed intensityIn the case of individual resonators, the intensity I should always be taken into account_Res(i) In that respect Here, the consideration may be made in the case where light having a design wavelength incident along the optical axis has low intensity and/or high intensity.

In the optical element according to the invention, the reflector may be constructed entirely or at least predominantly of a non-kerr-active material having n (k) n₀(k)+I·n₂(k) Wherein the non-linear refractive index n₂(k) Of the magnitude of (A) is the nonlinear refractive index n of at least one resonator with a Kerr active material₂(i) At most half the magnitude of. The non-kerr active material or kerr inactive material is defined in terms of a difference in magnitude of the respective non-linear refractive index n (k) or n (i) compared to the kerr active material of the at least one resonator. This difference in size can also be more pronounced and results in the refractive index n of the material of the reflector₂(k) Of at least one resonator having a Kerr active material₂(i) At most one quarter or even at most one eighth of the magnitude of (c).

In terms of absolute value, the non-linear refractive index n of the total refractive index n (k) of the reflector material₂(k) May be less than or equal to 4.0 × 10^-16cm²W, or even less than or equal to 3.0 × 10^-16cm²W, or even less than or equal to 2.0 × 10^-16cm²and/W. The typically higher non-linear refractive index of the generally more refractive optical materials, which are suitable for high light intensities and correspondingly for optical elements in laser resonators, also falls within this range. By using the total refractive index n (i) ═ n in the different resonators in the optical element according to the invention₀(i)+I_Res(i)·n₂(i) Different non-linear components I in_Res(i)·n₂(i) To account for the different kerr effects to cause the desired change between reflection and transmission of light having the design wavelength, a material having only a relatively low kerr activity according to absolute criteria suffices as the kerr active material in the at least one resonator. However, this by no means excludes the use ofMaterials with high kerr activity (i.e., with a high non-linear refractive index).

Like the reflectors, at least one further of the resonators may also be constructed at least predominantly of a non-kerr-active material, such that it has n (p) ═ n₀(p)+I·n₂(p) refractive index, wherein the non-linear refractive index n₂The magnitude of (p) is the nonlinear refractive index n of at least one resonator with a Kerr active material₂(i) At most half, or even at most one quarter, or even at most one eighth of the amount of (c). Also in terms of absolute value, the non-linear refractive index n of the total refractive index n (p) of at least one other of the resonators₂The magnitude of (p) may be as great as in the case of the non-kerr active material of the reflector, i.e., less than or equal to 4.0 × 10^-16cm²/W, or less than or equal to 3.0 × 10^-16cm²/W, or less than or equal to 2.0 × 10^-16cm²/W。

In general, in the optical element according to the invention, not only at least two resonators but also three, four or five resonators are arranged between the reflectors. In principle, the number of resonators can also be larger. The overall construction of the optical element is thus more complex, wherein this complexity is worthwhile only in few cases because of the improvement in the optical properties of the optical element achieved therewith.

In particular, the kerr active material of at least one resonator that can be used in the case of an optical element according to the invention, titanium dioxide (TiO) should be cited₂). The non-kerr active material of at least one other of the resonators may consist essentially of Ta₂O₅Or other metal oxide compositions. Silicon dioxide (SiO)₂) Low refractive non-kerr active material suitable as reflector, and Ta₂O₅Or other metal oxides may be used as the highly refractive non-kerr active material of the reflector. These materials can be exposed to the high intensity of the laser without losses in the resonator in which a titanium sapphire crystal (titansaphirkrill) is arranged as the laser active material.

As already mentioned, in the optical element according to the invention, it is also possible to use a kerr-active material in at least one resonator, which kerr-active material has only a low kerr-activity in terms of absolute value. However, high kerr activity, i.e. the non-linear refractive index n of kerr active materials₂Has a total refractive index n depending on the intensity of the light (8)_Kerr＝n₀+I·n₂-may be advantageous. The magnitude | n₂I may be, for example, greater than or equal to 1 × 10^-14cm²/W, or may be greater than or equal to 1 × 10^-12cm²/W, or may even be greater than or equal to 1 × 10^-10cm²/W, or may even be greater than or equal to 1 × 10^-8cm²/W, or may even be greater than or equal to 1 × 10^-6cm²and/W. Thus, the magnitude | n₂In particular, | can be compared with the quantities considered to be significant in EP 3217489 a1 (10 is provided for this purpose)^-12cm²The limit of/W) is much larger. Due to the small amount of kerr active material, which is usually limited to a single resonator, the absorbed light energy and the resulting heating of the optical element in the new element according to the invention remains small, even if it substantially increases with the kerr effect that occurs.

Total refractive index n of Kerr active material_kerrOf the above-mentioned high and very high non-linear refractive index n₂For example by means of polymers and/or by doping nanoparticles. As such, the kerr active material of at least one of the resonators may be a polymer and/or doped with nanoparticles having at least one metal or semiconductor. It should be noted here that in the present application the term "semiconductor" refers to the chemical composition of the material, so that the semiconductor may be, for example, GaAs.

Nanoparticles, which are doped in the kerr-active material and have an increasing effect on their kerr activity, can in particular have a particle size in the range from 1 to 100nm and/or be constructed at least predominantly from gold, silver, platinum, palladium or copper (i.e. noble metals). Here, it cannot be determined by what mechanism the nanoparticles increase the kerr activity of kerr active materials. The increasing effect of the nanoparticles on the kerr activity can be demonstrated anyway.

The use of kerr-active materials, which are essentially polymers and/or doped with nanoparticles in order to have a high kerr activity, in the resonator between the reflectors realized by alternating refractive index variations can be seen as an independent invention, independent of whether a plurality of kerr-active reflectors of different strengths are provided.

To apply the optical element according to the invention it has been implemented: an increase in the intensity I of light incident along the optical axis at the design wavelength can be exploited to either reduce or increase the transmission of the optical element in the passband (Durchlassband) around the design wavelength. As such, the optical element may be particularly useful as an optical switch that switches between transmission and reflection according to the intensity of light incident along the optical axis having a wavelength in the pass band.

If the switching from transmission to reflection is performed as the intensity of the incident light increases, mode coupling or Q-switching in the laser resonator can thereby be achieved. By switching from reflection to transmission, the intensity of the light in the laser resonator may be limited upwards, for example, or a single high-energy pulse may be coupled out of the laser resonator.

Advantageous embodiments of the invention result from the claims, the description and the drawings. The advantages of the features and the combination of features mentioned in the description are merely exemplary and can act alternatively or cumulatively without the advantages of embodiments according to the invention having to be realized compulsorily. Without thereby altering the subject matter of the appended claims, the following applies in respect of the disclosure of the original application and the patent: other features, in particular the geometry shown, as well as the relative dimensions of the various components with respect to one another, as well as the relative arrangement and operative connection of the various components, can be derived from the drawings. Combinations of features of different embodiments of the invention or combinations of features of different claims can also be realized and activated differently than the selected references of the claims. This also relates to the features shown in the individual figures or mentioned in the description. These features may also be combined with the features of different claims. Features realized in the claims may also be omitted for other embodiments of the invention.

The features mentioned in the claims and in the description are to be understood as being understood in quantity: where the adverb "at least" is not expressly used, it is necessary that exactly this number be present, or a number greater than the number mentioned. For example, if reference is made to an "element," it is understood that there is exactly one element, two elements, or more than one element. The features realized in the claims may be supplemented by further features or be unique features with respect to the respective optical element or its application.

The inclusion of reference signs in the claims does not limit the scope of the protected objects by the claims. Reference signs have been included for the sole purpose of making the claims easier to understand.

Drawings

The invention will be further elucidated and described with reference to a preferred embodiment shown in the drawings.

Figure 1 shows highly schematically an embodiment of an optical element according to the invention;

fig. 2 shows the variation of the spectral characteristics of a first embodiment of an optical element according to the invention;

fig. 3 shows the results of an intensity-dependent transmission measurement of a first practical embodiment of an optical element according to the invention, as based on fig. 2;

fig. 4 shows the change in the spectral characteristics of a first variant of the first practical embodiment of the optical element, as is based on fig. 2;

fig. 5 shows the variation of the spectral characteristics of a second variant of the first practical embodiment of the optical element according to the invention, as is based on fig. 2;

fig. 6 shows the change in the field strength distribution of a second variant of the first practical embodiment of the optical element according to the invention, accompanied by a change in the spectral characteristic according to fig. 5;

fig. 7 shows the variation of the spectral characteristics of a second practical embodiment of the optical element according to the invention;

fig. 8 illustrates highly schematically a first application of an optical element according to the invention in a laser resonator;

fig. 9 also schematically illustrates another application of another optical element according to the invention in a laser resonator, as in fig. 8.

Detailed Description

The optical element 1 according to the invention, which is illustrated schematically in fig. 1, has successive layers 2 to 5, wherein a refractive index change 6, which jumps here due to the different refractive indices of the layers 2 to 5, is formed between each of the two immediately successive layers 2 and 3, 3 and 2, 2 and 4, 4 and 2, 2 and 5, and 5 and 2. The refractive index variations 6 follow one another along the optical axis 7 and are arranged at defined intervals for light 8 of the wavelength λ incident along the optical axis 7, so that a plurality of regions 9 to 11, 13 and 14 of the device 1 following one another along the optical axis 7 fulfill different functions. In the three regions 9, 10 and 11, the spacing between the refractive index variations is equal to λ/4, that is to say the optical thicknesses of the layers 2 and 3 are each a quarter of the design wavelength λ. The regions 9, 10 and 11 thus form a reflector 12 for the light 8. Between two of the reflectors 12, a resonator 15 for the light 8 having the design wavelength λ is formed in the two regions 13 and 14. The respective optical layer thicknesses of the layers 4 and 5 located in these regions 13 and 14 are in this case λ/2 or integer multiples of λ/2. In principle, all resonators 15 of the optical element 1 can be constructed by layers 4 and 5 having the same optical layer thickness. However, the resonators 15 are not identical. More precisely, the kerr activity of the material of the resonators and/or the resulting intensity I of the light 8 in the regions 13 and 14 of the resonators_ResDifferently, so that a significantly different kerr effect is produced in the regions 13 and 14. Specifically, the total refractive index n (i) ═ n of at least two of the resonators 15 of the optical element 1₀(i)+I_Res(i)·n₂(i) Non-linear component I in_Res(i)·n₂(i) By two non-linear components I_Res(i)·n₂(i) The smaller of themAt least 50% of the total weight of the composition. Here, I_Res(i) Is the already mentioned resulting intensity of the light 8 in the regions 13, 14 of the respective reflector 15, and n₂(i) Is the nonlinear refractive index of the corresponding resonator.

The resonators 15 are differently detuned due to the different kerr effects in the regions 13 and 14 as the intensity I of the light 8 increases, or they are tuned to each other if they are detuned from each other in the case of a lower intensity I of the light 8. In this way, for light 8 having the design wavelength λ, the optical characteristics of the optical element 1 vary with increasing intensity between transmission, which occurs when all resonators 15 are tuned to the design wavelength λ at the respective intensity I, and reflection, in which case at least one of the resonators, but not all resonators 15, is detuned to the same extent with respect to the design wavelength λ.

Fig. 2 shows the change in the spectral characteristics of a first practical embodiment of an optical element 1 according to the invention, which has a total of 97 layers 2 to 5, which form six reflectors 12 and five resonators 15 arranged between them. The effect of the kerr effect occurring only in the middle resonator 15 is shown here. Curve 16 shows the initial situation in the case of no change in the refractive index in the region of the middle resonator. Curve 17 shows the effect of a change of 0.35% in the refractive index n (i) in the region of the middle resonator, while curve 18 shows the effect of a change of 1% in the refractive index n (i) in the region of the middle resonator. As the refractive index changes in the region of the middle resonator, more precisely in a relatively wide pass band 19 around the design wavelength λ, the transmission drops from an initial over 95% to below 30%. At a design wavelength λ of 1064nm, the transmission drops from 99.9% to 76.2% with a change of 0.35% in the refractive index n (i) in the region of the middle resonator, and to 27.8% with a change of 1% in the refractive index n (i) in the region of the middle resonator.

Fig. 3 shows the results of an intensity-dependent transmission measurement of a first practical embodiment of the optical element 1 according to the invention, as is based on fig. 2, i.e. the kerr effect which increases selectively with the intensity of the light 8 in the middle resonator 15. However, the optical element 1, which here performs transmission measurements, is designed for a design wavelength λ of 1030 nm. It can be seen that as the energy density increases, the fraction transmitted by the optical element 1 becomes smaller as are the laser pulses with a design wavelength λ of 1030nm and a pulse duration of 350 fs.

Fig. 4 shows the corresponding change in the spectral properties of an optical element with 97 layers (including five resonators) which occurs when the refractive index changes by 0.35% or 1% in the direction of incidence of the light 8 in the second resonator according to fig. 1. The secondary maximum of transmission at higher wavelengths, as can be seen in fig. 2, does not occur. Here, at a design wavelength λ of 1064nm, the transmittance decreases from 99.9% to 81.4% as the refractive index n (i) in the region of the second resonator changes by 0.35%, and the transmittance decreases to 34.7% as the refractive index n (i) in the region of the second resonator changes by 1%.

Fig. 5 is again based on an optical element 1 with 97 layers (including five resonators) and shows the effect when the refractive index in the second and fourth resonators is changed. Here, the transmittance for the long-wave part of the pass band 19 around the design wavelength λ drops almost to zero. Specifically, at a design wavelength λ of 1064nm, the transmittance decreases from 99.9% to 52.4% as the refractive index n (i) in the region of the second and fourth resonators changes by 0.35%, and decreases to 11.7% as the refractive index n (i) in the region of the second and fourth resonators changes by 1%. In contrast, a transmission of more than 95% occurs in another narrow bandwidth pass band 20 at higher wavelengths (where the optical element 1 is first fully reflected) when the refractive indices in the resonators 2 and 4 change by 1%. In the use of the optical element 1 according to fig. 1, the dips (Einbruch) in the transmission in a part of the pass band 19 and in the other pass bands 20 can be used in a targeted manner.

Fig. 6 shows the change in the field strength distribution of an optical element 1 having 97 layers (including five resonators), which occurs with a change in the spectral characteristics according to fig. 5. Curve 29 corresponds here to the field intensity distribution at the optical element 1 without kerr effect, while curves 30 and 31 correspond to the field intensity distribution at a change of 0.35% or 1% in the refractive index n (i) in the region of the second and fourth resonators. The field intensity distribution has a local maximum in the region of the resonator 15, respectively. With increasing kerr effect, i.e. an increasing change in the refractive index n (i) in the region of the second and fourth resonators, the field strength is concentrated on the left-hand region of the layer structure, which corresponds to a reduced transmission and a corresponding increased reflection of the light 8 incident from the left.

Fig. 7 shows the change in the spectral properties of a further optical element 1 according to the invention with a total of 59 layers 2 to 5, which form three resonators 15 between four reflectors 4. Curve 21 shows the initial case in which all resonators 15 are tuned to the design wavelength λ. Creating a pass band 22 around the design wavelength lambda. If the refractive index of all reflectors 15 changes (i.e. increases) by 1%, a course of the transmission T with wavelength is produced, which is shown by curve 23. This curve means that the pass band 22 is purely shifted to the same width pass band 24 at larger wavelengths. On the other hand, if the refractive index is selectively changed by 1% in the first or second resonator, an almost identical course of the transmission with wavelength according to the curves 25 and 26 is obtained. These curves mean that the reflectivity in the original pass band 22 drops significantly without shifting. Conversely, if the refractive index is selectively varied by 1% in the intermediate resonator, a curve 27 results, which means that the transmission in the pass band 22 and in the additional narrow-bandwidth pass band 28 is also reduced more strongly.

Fig. 8 shows highly schematically a laser resonator 32 constructed between a mirror 33 and the optical element 1. A laser-active material 34 pumped by means of a pump light source 35 is arranged in the laser resonator 32. In the case of a low intensity of the light 8 in the resonator, the optical element 1 acts here as an end mirror (Endspiegel), which becomes transparent when the intensity of the light 8 exceeds a predetermined intensity at the design wavelength of the optical element 1.

Fig. 9 illustrates a further use of the optical element 1 in a laser resonator 32, which is constructed here between a mirror 33 and a semi-transparent mirror 36. The optical element 1 acts here as a mode coupler or Q-switch and becomes transparent only when the light 8 exceeds a certain minimum intensity at the design wavelength in the light-limited, optically active material 34-containing part of the resonator 32.

List of reference numerals

1 optical element

2 layers of

3 layers of

4 layers of

5 layers of

6 refractive index change

7 optical axis

8 light

9 region

10 area

11 region

12 reflector

Region 13

14 region

15 resonator

16 curve

Curve 17

18 curve

19 pass band

20 other pass bands

Curve 21

22 pass band

Curve 23

24 shifted pass bands

Curve 25

26 curve

Curve 27 of

28 narrow bandwidth pass band

Curve 29

Curve 30

Curve 31

32 laser resonator

33 end mirror

34 laser material

35 pumping light source

36 semi-transparent mirror

Lambda design wavelength