Apparatus for transmitting and / or receiving terahertz radiation and uses thereof - Patents.com

Abstract

1. An apparatus for transmitting and / or receiving terahertz radiation, comprising at least one terahertz element configured to generate and / or detect a terahertz signal, and at least one electromagnetic field shaping element specifically assigned to the at least one terahertz element, wherein the at least one terahertz element is arranged in a region of a first surface of the electromagnetic field shaping element.

Description

[Technical field]

[0001] The present disclosure relates to devices for transmitting and / or receiving terahertz (THz) radiation. The present disclosure further relates to uses of such devices. Summary of the Invention

[0002] A preferred embodiment relates to an apparatus for transmitting and / or receiving terahertz (THz) radiation, comprising at least one terahertz element configured to generate and / or detect a terahertz (THz) signal and at least one electromagnetic field shaping element specifically assigned to the at least one terahertz element, where the at least one terahertz element is arranged in a region of a first surface of the electromagnetic field shaping element.

[0003] In a further preferred embodiment, it is provided that the at least one terahertz element is arranged with respect to the first surface of the electromagnetic field shaping element, in particular at least locally, such that there is an evanescent coupling between the at least one terahertz element and the electromagnetic field shaping element. In this way, for example, terahertz radiation generated by the at least one terahertz element can be efficiently coupled into the electromagnetic field shaping element and / or terahertz radiation to be received can be efficiently coupled from the electromagnetic field shaping element into the terahertz element. This This increases the efficiency of coupling of terahertz radiation between the components.

[0004] In a further preferred embodiment, it is provided that the at least one terahertz element is arranged with respect to a first surface of the electromagnetic field shaping element such that, in particular at least locally, frustrated total internal reflection can and / or may occur between the at least one terahertz element and the electromagnetic field shaping element.

[0005] In a further preferred embodiment it is provided that the electromagnetic field shaping element comprises and / or is formed as at least one lens.

[0006] In a further preferred embodiment it is provided that at least one lens is formed as a hemispherical lens, or as a hyper-hemispherical lens, or as an aspherical lens.

[0007] In a further preferred embodiment, it is provided that the electromagnetic field shaping element has low dispersion, preferably with a refractive index change of less than 5%, and / or low absorption, preferably less than 2%, for terahertz radiation, especially in the range of 1 THz to 10 THz.

[0008] In a further preferred embodiment it is provided that the electromagnetic field shaping element at least partially comprises or is formed from at least one of the following materials: a) silicon, b) a polymeric material, in particular PE and / or HDPE and / or PP and / or PTFE and / or polymethylpentene, PMP, c) a polymeric material, in particular PE and / or HDPE and / or PP and / or PTFE and / or PMP, with at least one additive material, in particular a refractive index increasing additive material, such as titanium dioxide, TiO2 and / or aluminium dioxide, Al2O3.

[0009] In a further preferred embodiment, the electromagnetic field shaping element has, in at least one surface region, in particular on a first surface region and / or on a second surface opposite the first surface, a surface modification having a reflection-reducing effect, preferably an anti-reflection coating, wherein it is provided that the reflection-reducing effect, in particular the anti-reflection coating, is optimized for a frequency range between 1 THz and 10 THz, in particular between 1 THz and 10 THz, more in particular between 4.5 THz and 6.5 THz.

[0010] In a further preferred embodiment it is provided that at least locally a bonding layer, in particular an adhesive layer, is arranged between the at least one terahertz element and the first surface of the electromagnetic field shaping element.

[0011] In a further preferred embodiment it is provided that the layer thickness of the bonding layer is less than 50 micrometers (μm), in particular 10 μm or less, in particular 7 μm or less, more particularly 4.0 μm or less, more particularly 1.0 μm or less.

[0012] In a further preferred embodiment, it is provided that the layer thickness of the bonding layer is smaller than a quarter of the wavelength of the terahertz signal in the bonding layer, in particular smaller than a quarter of the wavelength of the maximum frequency of the terahertz signal in the bonding layer.

[0013] In a further preferred embodiment it is provided that the bonding layer partially comprises or is formed from at least one of the following materials: a) polymeric materials, in particular PE and / or HDPE and / or PP and / or PTFE and / or PMP, b) polymeric materials, in particular PE and / or HDPE and / or PP and / or PTFE and / or PMP, comprising at least one additive material, in particular a refractive index increasing additive material, such as titanium dioxide, TiO2 and / or aluminium oxide, Al2O3, c) adhesive materials, in particular adhesive materials with at least one additive material, in particular a refractive index increasing additive material, such as titanium dioxide, TiO2 and / or aluminium dioxide, Al2O3.

[0014] In a further preferred embodiment it is provided that the bonding layer has a refractive index n greater than or equal to 1.6, in particular greater than 2.0, in particular greater than 3.0.

[0015] In a further preferred embodiment, the at least one terahertz element is connected, in particular at least locally, to the electromagnetic field shaping element in a force-matching and / or form-matching and / or material-matching manner, in particular a clamp connection and / or a solder connection is provided.

[0016] In a further preferred embodiment, at least locally, a gap, in particular an air gap, more in particular a technical zero gap, is provided between the at least one terahertz element and the first surface of the electromagnetic field shaping element.

[0017] In a further preferred embodiment it is provided that the at least one terahertz element is areally mounted, in particular at least locally, on a first surface of an electromagnetic field shaping element having a first surface.

[0018] In a further preferred embodiment, it is provided that the at least one terahertz element comprises a first substrate and an electrode array, in particular the electrode array is arranged on a first surface of the first substrate. According to a further preferred embodiment, the electrode array can be used for example to provide an electrical DC voltage that can be used to generate terahertz pulses or to derive a current that is generated when receiving a terahertz signal, for example for signal amplification and / or signal evaluation.

[0019] In a further preferred embodiment it is provided that the first surface of the first substrate faces the first surface of the electromagnetic field shaping element, in particular whereby the first surface of the first substrate contacts the first surface of the electromagnetic field shaping element, in particular at least locally, by an area.

[0020] In a further preferred embodiment, at least one terahertz element and / or the first substrate comprises a photoconductive material, in particular the photoconductive material comprises at least one of the following materials: a) indium phosphide, InP, b) gallium arsenide, GaAs, c) indium gallium arsenide, InGaAs, in which in particular the photoconductive material is doped in particular with iron.

[0021] In a further preferred embodiment, the at least one terahertz element comprises one or more further substrates, and a first substrate is arranged, in particular at least locally, on one further substrate or on multiple further substrates, in particular the first substrate has a second surface opposite to the first surface and is arranged, in particular at least locally, on the at least one further substrate, in particular on a first surface of the at least one further substrate.

[0022] In a further preferred embodiment, it is provided that the first substrate and / or the at least one further substrate is at least partially transparent to optical radiation in the wavelength range between 1450 nanometers (nm) and 1650 nm and / or in the wavelength range between 850 nm and 1650 nm.

[0023] In a further preferred embodiment, the first substrate and / or the at least one further substrate have a relatively high transmittance for optical radiation, in particular in the aforementioned wavelength range.More preferably, the relatively high transmittance can be achieved by the choice of material (e.g. silicon, Si, silicon dioxide, SiO2) and / or a reflection reducing coating on at least one surface of the (at least one further) substrate, in particular on the surface or side of the (at least one further) substrate on which the optical radiation can be irradiated.

[0024] In a further preferred embodiment it is provided that a) a second surface opposite to the first surface or the second surface of the first substrate and / or b) a second surface opposite to the first surface of at least one further substrate can be exposed to a first optical radiation, in particular laser radiation, in particular laser radiation in the wavelength range from 1450 nm to 1650 nm.

[0025] In a further preferred embodiment, an irradiation device is provided for at least temporarily exposing at least one region of the terahertz element to the first optical radiation or to the first optical radiation, the irradiation device comprising at least one optical fiber or formed as an optical fiber.

[0026] In a further preferred embodiment it is provided that the irradiation device, in particular the optical fiber, is positioned and / or aligned with respect to the first substrate and / or the at least one further substrate such that an output surface for coupling the first optical radiation therethrough is exposed to the first optical radiation a) a second surface opposite to the first surface or the second surface of the first substrate and / or b) a second surface opposite to the first surface of the at least one further substrate, in particular aa) the second surface of the first substrate and / or bb) the second surface of the at least one further substrate.

[0027] In a further preferred embodiment it is provided that the optical fiber is a monomode optical fiber, in particular a polarization-maintaining optical fiber.

[0028] In a further preferred embodiment it is provided that the device comprises a plurality of terahertz elements, where a) at least two, preferably all, of the plurality of terahertz elements are arranged in a region of a first surface of the electromagnetic field shaping element and / or b) at least one electromagnetic field shaping element is assigned to at least two of the plurality of terahertz elements.

[0029] In a further preferred embodiment it is provided that at least two, preferably all, of the plurality of terahertz elements are arranged side by side, where in particular the respective electrode arrangements of at least two, preferably all, terahertz elements lie in the same first imaginary plane, in particular the first imaginary plane being parallel to a first surface of the electromagnetic field shaping element.

[0030] In a further preferred embodiment it is provided that at least two, preferably all, of the plurality of terahertz elements are arranged one behind each other, in particular where the respective electrode arrangements of at least two terahertz elements, preferably all terahertz elements, lie in respective imaginary planes that are different from each other, in particular where at least two of the imaginary planes are parallel to the first surface of the electromagnetic field shaping element.

[0031] In a further preferred embodiment, at least two of the plurality of terahertz elements are arranged to at least partially overlap spatially.

[0032] In a further preferred embodiment it is provided that a common electrode structure is assigned to a number of terahertz elements.

[0033] In a further preferred embodiment, it is provided that the device is configured to output terahertz radiation in the form of a diverging beam. The diverging beam can in particular be realized with one or more mirrors, in particular with a parabolic mirror, in particular with an off-axis parabolic mirror. In a further preferred embodiment, it is provided that the device is configured to output terahertz radiation in the form of a parallel beam.

[0034] In a further preferred embodiment, the apparatus comprises at least one manipulation device for manipulating the beam path of the terahertz radiation, in particular the at least one manipulation device comprises a reflecting device for the terahertz radiation, in particular at least one mirror.

[0035] In a further preferred embodiment, the reflecting device comprises at least a first mirror and a second mirror, and the device is configured to a) selectively position the first mirror or the second mirror in the beam path of the terahertz radiation, and / or b) at least temporarily position the first mirror and at least temporarily position the second mirror in the beam path of the terahertz radiation.

[0036] In a further preferred embodiment, the first mirror has a first focal length and the second mirror has a second focal length different from the first focal length.

[0037] In further preferred embodiments, the second mirror can be driven and / or changed and / or replaced without tools and / or by a motor, where for example it can further be replaced by, for example, a third mirror, and the beam directions of the terahertz radiation after the second and third mirrors are preferably collinear. In further preferred embodiments, this can be realized, for example, by a number of stops, in particular for example axial and lateral positioning of the respective mirrors.

[0038] In a further preferred embodiment it is provided that the apparatus comprises at least one of: a) a click module; b) a magnetic holder; c) a turret, in particular for at least temporarily holding and / or positioning at least the first and / or second mirror.

[0039] In a further preferred embodiment, the device is configured to apply, at least temporarily, to at least one terahertz element a first pulsed laser radiation having a first pulse frequency and a second pulsed laser radiation having a second pulse frequency, in particular the second pulse frequency being different from the first pulse frequency.

[0040] In a further preferred embodiment, the device is adapted to provide a protective gas flow comprising a protective gas in at least one region of the beam path of the terahertz radiation, in particular of the terahertz signal, where in particular the protective gas comprises or is formed from at least one of the following elements: (a) dry air, (b) dry gas, (c) dry gas mixture, (d) at least one gas that has no absorption lines in the frequency range of the terahertz radiation. In particular, the protective gas has a dew point temperature of -20°C (degrees Celsius) or less, preferably -30°C or less, more preferably -40°C or less, and in particular the protective gas preferably causes an attenuation of the terahertz radiation along the beam path of less than or equal to 0.1 dB for each frequency of the terahertz radiation.

[0041] In a further preferred embodiment, it is provided that the apparatus further comprises: a) at least one supply device for at least temporarily providing a flow of protective gas, and / or b) at least one pressure operating member for operating the pressure of the protective gas.

[0042] In a further preferred embodiment, the apparatus further comprises at least one nozzle, wherein in particular it is provided that the nozzle is adapted and / or configured for the protective gas flow or at least a part of the protective gas flow to flow into at least one region of the beam path of the terahertz radiation, in particular that the at least one nozzle is a free jet nozzle.

[0043] In a further preferred embodiment, it is provided that the apparatus comprises at least one optical sensor device, e.g. an optical distance sensor, e.g. an optical triangulation sensor, and / or at least one three-dimensional imaging device, e.g. a laser scanner, capable of detecting or determining at least one of the following factors: a) the distance of the measurement object relative to the apparatus, b) the inclination of the apparatus relative to the measurement object, c) the shape, in particular the surface shape, of the measurement object.

[0044] Further preferred embodiments relate to a measuring device, in particular for determining at least one physical parameter of an object, comprising at least one device according to the embodiment.

[0045] In a further preferred embodiment it is provided that the measuring device is adapted to determine the layer thickness of at least one layer to be measured, in particular by using a model-based method, in which a model of the at least one layer is used.

[0046] Further preferred embodiments relate to the use of the device according to the embodiments and / or the measuring device according to the embodiments for at least one of the following: a) transmitting and / or receiving terahertz radiation, in particular terahertz pulses, b) determining, in particular a layer thickness of one or more layers on a component, in particular based on a model, c) at least temporarily positioning a first mirror in the beam path of the terahertz radiation, d) providing at least temporarily and / or at least locally evanescent coupling between the at least one terahertz element and the at least one electromagnetic field shaping element, e) at least temporarily applying a protective gas, in particular a protective gas flow in the at least one spatial region, whereby at least temporarily applying in the at least one spatial region a protective gas, in particular a protective gas flow synchronous with the transmission and / or reception of the terahertz radiation, f) applying radiation, terahertz radiation, in particular terahertz pulses, in or in the spatial region to which the protective gas or protective gas is applied.

[0047] Further characteristics, possible applications and advantages of the invention can be derived from the following description of embodiments of the invention illustrated in the drawing figures, in which: In this context, all the features described or shown constitute the subject matter of the invention, individually or in any combination, regardless of any references in the claims or between the claims and independently of their formulation or representation in the specification or drawings. [Brief description of the drawings]

[0048] [Figure 1] 1 shows a schematic side view of an apparatus according to a preferred embodiment; [Diagram 2] 2 shows a schematic side view of an apparatus according to a further preferred embodiment; [Diagram 3] 2 shows a schematic side view of an apparatus according to a further preferred embodiment; [Figure 4] 2 shows a schematic side view of an apparatus according to a further preferred embodiment; [Diagram 5] 2 shows a schematic side view of a terahertz element according to a further preferred embodiment; [Figure 6] 2 shows a schematic side view of a terahertz element according to a further preferred embodiment; [Figure 7] 2 shows a schematic side view of an apparatus according to a further preferred embodiment; [Figure 8] 2 shows a schematic side view of an apparatus according to a further preferred embodiment; [Figure 9] 2 shows a schematic side view of an apparatus according to a further preferred embodiment; [Figure 10] 3 shows a schematic top view of a terahertz element according to a further preferred embodiment; [Figure 11] 2 shows a schematic side view of a terahertz element according to a further preferred embodiment; [Figure 12A] 2 shows a schematic side view, partly in section, of an apparatus according to a further preferred embodiment; [Figure 12B] 2 shows a schematic side view, partly in section, of an apparatus according to a further preferred embodiment; [Figure 13] 2 shows a schematic side view of an apparatus according to a further preferred embodiment; [Figure 14] 2 shows a schematic side view of an apparatus according to a further preferred embodiment; [Figure 15] 10 illustrates diagrammatically an exemplary use of the device according to a further preferred embodiment; [Figure 16] 3 shows a schematic side view of a measurement object according to a further preferred embodiment; [Figure 17] 1 shows a schematic representation of a measuring device according to a further preferred embodiment; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0049] The preferred embodiment relates to a device 100 for transmitting and receiving terahertz radiation TS1, TS2. Fig. 1 shows an exemplary side view of such a device 100 according to a preferred embodiment. The device 100 comprises at least one terahertz element 110, which is configured in particular to generate a transmitted terahertz signal TS1 and / or to detect a received terahertz signal TS2. At least one electromagnetic field shaping element 120 is assigned in particular to the at least one terahertz element 110, which is arranged in the region of a first surface 121 of the electromagnetic field shaping element 120.

[0050] In a further preferred embodiment, it is provided that the at least one terahertz element 110 is arranged with respect to the first surface 121 of the electromagnetic field shaping element 120 such that, in particular at least locally, there is an evanescent coupling between the at least one terahertz element 110 and the electromagnetic field shaping element 120. In this way, for example, terahertz radiation TS1 generated by the at least one terahertz element 110 can be efficiently coupled into the electromagnetic field shaping element 120 to be received and / or terahertz radiation TS2 can be efficiently coupled from the electromagnetic field shaping element 120 into the terahertz element 110. This enhances the efficiency of the coupling of the terahertz radiation TS1, TS2 between the components 110, 120. In particular, according to preferred embodiments, undesired attenuation and / or pulse broadening of the terahertz radiation can thus also be advantageously reduced.

[0051] In a further preferred embodiment, it is provided that the at least one terahertz element 110 is arranged with respect to the first surface 121 of the electromagnetic field shaping element 120 such that frustrated total internal reflection can and / or occurs between the at least one terahertz element 110 and the electromagnetic field shaping element 120, in particular at least locally.

[0052] In a further preferred embodiment, it is provided that the electromagnetic field shaping element 120 comprises and / or is formed as at least one lens 120 .

[0053] In a further preferred embodiment, the at least one lens 120 is provided as a hemispherical or hyper-hemispherical lens 120a (see device 100a in FIG. 2) or as an aspherical lens.

[0054] In further preferred embodiments, the electromagnetic field shaping element 120 (FIG. 1) may also include at least one terahertz radiation reflector (not shown), such as a reflector or mirror. In further preferred embodiments, the electromagnetic field shaping element 120 may also be formed as a metamaterial-based element and / or a gradient index lens.

[0055] In a further preferred embodiment, it is provided that the electromagnetic field shaping element 120, 120a at least partially comprises or is formed from at least one of the following materials: a) silicon, b) a polymeric material, in particular PE and / or HDPE and / or PP and / or PTFE, c) a polymeric material, in particular PE and / or HDPE and / or PP and / or PTFE and / or PMP and / or PMP, comprising at least one additive material, in particular a refractive index increasing additive material, such as titanium dioxide, TiO2 and / or aluminum dioxide, Al2O3.

[0056] In a further preferred embodiment, the electromagnetic field shaping element 120, 120a is provided with a surface modification 124 in the region of at least one surface 121, 122, in particular in the region of the second surface 122 opposite the first surface 121 and / or on the second surface 122 opposite the first surface 121, having a reflection-reducing effect (for at least one wavelength of terahertz radiation TS1, TS2), preferably an anti-reflection coating 124, whose reflection-reducing effect, in particular the anti-reflection coating 124, is optimized in particular for a frequency range between 3 THz and 10 THz, in particular between 4.5 THz and 6.5 THz.

[0057] In a further preferred embodiment (FIG. 1), it is provided that, at least locally, a bonding layer 130, in particular an adhesive layer 130, is arranged between at least one terahertz element 110 and the first surface 121 of the electromagnetic field shaping element 20.

[0058] In a further preferred embodiment, it is provided that the layer thickness d1 (FIG. 1) of the bonding layer 130 is less than 50 micrometers (μm), in particular 10 μm or less, in particular 7 μm or less, in particular 4.0 μm or less, in particular 1.0 μm or less.

[0059] In a further preferred embodiment, it is provided that the layer thickness d1 of the bonding layer 130 is smaller than a quarter of the wavelength of the terahertz signals TS1, TS2 in the bonding layer 130, in particular, smaller than a quarter of the wavelength of the maximum frequency of the terahertz signals TS1, TS2 in the bonding layer 130.

[0060] In a further preferred embodiment, it is provided that the bonding layer 130 is at least partially formed from at least one of the following materials: a) a polymeric material, in particular PE and / or HDPE and / or PP and / or PTFE and / or PMP, b) a polymeric material, in particular PE and / or HDPE and / or PP and / or PTFE and / or and / or PMP, with at least one additive material, in particular a refractive index increasing additive material, such as titanium dioxide, TiO2 and / or aluminium dioxide, Al2O3, c) an adhesive material, in particular an adhesive material comprising at least one additive material, in particular a refractive index increasing additive material, such as titanium dioxide, TiO2 and / or aluminium dioxide, Al2O3.

[0061] In a further preferred embodiment, it is provided that the bonding layer 130 has a refractive index n greater than or equal to 1.6, in particular greater than 2.0, in particular greater than 3.0.

[0062] In a further preferred embodiment, referring to the device 100b according to FIG. 3, it is provided that the at least one terahertz element 110 is at least locally connected to the electromagnetic field shaping element 120, 120a in a force-fitting and / or form-fitting and / or material-fitting manner, in which case a specific clamp connection and / or solder connection 136, e.g. a glass solder, is provided.

[0063] In a further preferred embodiment, referring to FIG. 3, it is provided in particular that, at least locally, a gap 135, in particular an air gap, or even a technical zero gap, is provided between at least one terahertz element 110 of the electromagnetic field shaping element 121 and the first surface 121.

[0064] In a further preferred embodiment, referring to device 100c of FIG. 4, it is provided that at least one terahertz element 110 is mounted on a first surface 121 of an electromagnetic field shaping element 120 having a first surface 111, in particular at least locally, preferably over the entire area.

[0065] In a further preferred embodiment, referring to FIG. 5 , it is provided that at least one terahertz element 110a comprises a first substrate 114 and an electrode arrangement 115, in particular, the electrode arrangement 115 is arranged on a first surface 114a of the first substrate 114.

[0066] In a further preferred embodiment, it is provided that the first surface 114a of the first substrate 114 faces the first surface 121 of the electromagnetic field shaping element 120. Here, in particular, the first surface 114a of the first substrate 114 contacts the first surface 121 of the electromagnetic field shaping element 120, in particular at least locally, preferably over the entire area. Further preferably, the electrode arrangement 115 is located between the first substrate 114 and the first surface 121 of the electromagnetic field shaping element 120, 120a, in particular such that the surface 115a of the electrode arrangement 115 contacts the first surface 121 of the electromagnetic field shaping element 120, 120a, at least locally.

[0067] In a further preferred embodiment, at least one terahertz element 110, 110a and / or the first substrate 114 (FIG. 5) comprises a photoconductive material, in particular the photoconductive material comprises at least one of the following materials: a) indium phosphide, InP, b) gallium arsenide, GaAs, c) indium gallium arsenide, InGaAs, where in particular the photoconductive material is doped in particular with iron.

[0068] In a further preferred embodiment, referring to FIG. 6 , the at least one terahertz element 110b comprises at least one further substrate 116, wherein the first substrate 114 is arranged, in particular at least locally, on the at least one further substrate 116, in particular where the first substrate 114 has a second surface 114b opposite its first surface 114a and is arranged, in particular at least locally, on the at least one further substrate 116, in particular on the first surface 116a of the at least one further substrate 116.

[0069] In a further preferred embodiment, it is provided that the first substrate 114 and / or the at least one further substrate 116 are at least partially transparent (in particular with a transmission of more than about 95 percent) to optical radiation in the wavelength range between 1450 nm and 1650 nm and / or in the wavelength range between 850 nm and 1650 nm, which allows the optical radiation S1 to be efficiently introduced through the first and / or at least one further substrate 114, 116 into the area of ​​the electrode array 115 where, for example, generation and / or detection of terahertz radiation can take place according to a further preferred embodiment.

[0070] In a further preferred embodiment it is provided that a) the second surface 114b opposite to the first surface 114a or the second surface 114b of the first substrate 114 and / or b) the second surface 116b opposite to the first surface 116a of the at least one further substrate 116 can be exposed to a first optical radiation S1, in particular to laser radiation S1, particularly preferably to pulsed laser radiation S1, in the wavelength range from 1450 nm to 1650 nm.

[0071] In a further preferred embodiment, an irradiation device 140 is provided for at least temporarily exposing at least one region of the terahertz elements 110, 110a, 110b to the first optical radiation S1 or the first optical radiation S1, and the irradiation device 140 comprises at least one optical fiber 140 or is formed as an optical fiber 140.

[0072] In a further preferred embodiment, the irradiation device 140 may also include a laser source (not shown) for generating the first optical radiation S1, and according to a further preferred embodiment, the laser source may be arranged in the area of ​​the terahertz element 110b, for example to the left of the terahertz element 110b in FIG. 6. In this regard, according to a further preferred embodiment, it may also be possible in some cases to omit, for example, the provision of the optical fiber 140. That is, the first optical radiation S1 may be directly irradiated from the laser source to the terahertz element 110b. In a further preferred embodiment, the laser source may also be provided and / or arranged remotely from the terahertz element 110b, and the first optical radiation S1 may be guided from the laser source to the terahertz element 110b, for example by the optical fiber 140, and irradiated to the terahertz element 110b via the exit aperture 141.

[0073] In a further preferred embodiment, it is provided that the irradiation device 140, in particular the optical fiber 140, has an output surface 141 for coupling the first optical radiation S1 arranged and / or aligned with respect to the first substrate 114 and / or the at least one further substrate 116 such that a) the second surface 114b facing the first surface 114a or the second surface 114b of the first substrate 114 and / or b) the second surface 116b facing the first surface 116a of the at least one further substrate 116, in particular aa) the second surface 114b of the first substrate 114 and / or bb) the second surface 116b of the at least one further substrate 116 can be exposed to the first optical radiation S1.

[0074] In a further preferred embodiment, it is provided that the optical fiber 140 is a monomode optical fiber, in particular a polarization-maintaining optical fiber 140 .

[0075] In a further preferred embodiment, with reference to Fig. 7, it is provided that the device 100d comprises a plurality of terahertz elements 110_1, 110_2, where a) at least two, preferably all, of the plurality of terahertz elements 110_1, 110_2 are arranged in the region of a first surface 121 of the electromagnetic field shaping element 120, and / or b) at least one electromagnetic field shaping element 120 is assigned to at least two of the plurality of terahertz elements 110_1, 110_2. Thus, in a further preferred embodiment, an electromagnetic field shaping element 120 that is "common" to the plurality of terahertz elements 110_1, 110_2 may be used to shape the terahertz radiation TS1_1, TS1_2 associated with each terahertz element 110_1, 110_2.

[0076] Although Fig. 7 shows two terahertz elements 110_1, 110_2 as an example, according to further preferred embodiments it is also possible to provide more than two terahertz elements, in particular to assign them to the electromagnetic field shaping element 120. As can be derived from Fig. 7, in the present case both terahertz elements 110_1, 110_2 are arranged on the first surface 121 of the electromagnetic field shaping element 120 by means of an adhesive layer 130. In further preferred embodiments, at least some or all of the multiple terahertz elements 110_1, 110_2 can be arranged on the adhesive layer 130 by means of solder joints 136 (Fig. 3) and / or clamp joints in the region of the first surface 121 of the electromagnetic field shaping element 120. A combination of adhesive layers 130 and / or solder connections 136 (Fig. 3) and / or clamp connections is also conceivable according to further preferred embodiments.

[0077] In a further preferred embodiment, referring to the device 100e of Fig. 8, it is provided that at least two, preferably all, of the plurality of terahertz elements 110_1, 110_2 are arranged side by side, where in particular the respective electrode arrangements 115_1, 115_2 of at least two, preferably all, of the terahertz elements 110_1, 110_2 lie in the same first imaginary plane E1, in particular the first imaginary plane E1 being parallel to the first surface 121 of the electromagnetic field shaping element 120. In a further preferred embodiment, the first imaginary plane E1 may for example coincide with the first surface 121 of the electromagnetic field shaping element 120.

[0078] In a further preferred embodiment, it is provided that both terahertz elements 110_1, 110_2 rest with their respective first surfaces 111_1, 111_2, in particular at least locally, on the first surface 121 of the electromagnetic field shaping element 120.

[0079] In a further preferred embodiment, referring to the device 100f of Fig. 9, it is provided that at least two, preferably all, of the plurality of terahertz elements 110_1, 110_2 are arranged behind the other (in particular with respect to the (main) propagation direction of the terahertz radiation, i.e. for example along a virtual horizontal line as shown in Fig. 9), where in particular at least two respective electrode arrangements 115_1, 115_2, preferably all terahertz elements 110_1, 110_2 lie in respective virtual planes E1, E2 different from each other, in particular at least two of the virtual planes E1, E2 being parallel to the first surface 121 of the electromagnetic field shaping element 120a. In this example, the second terahertz element 110_2 is arranged on the surface 110_1a of the first terahertz element 110_1.

[0080] In a further preferred embodiment, at least two of the plurality of terahertz elements are arranged to at least partially overlap spatially (not shown).

[0081] In a further preferred embodiment, referring to Fig. 10, a common electrode structure 115_12 is assigned to a number of terahertz elements 110_1, 110_2. According to a further preferred embodiment, the arrangement of the structures 110_1, 110_2, 115_12 shown in Fig. 10 on the electromagnetic field shaping element 120, 120a may for example be similar to the structures according to Figs. 1 or 3 or 7 or 8.

[0082] In a further preferred embodiment, it is provided that the device 100 (FIG. 1) is configured to output the terahertz radiation TS1 in the form of a collimated beam (i.e. a parallel beam), thereby reducing or eliminating the distance dependency of the measurement based on the terahertz radiation TS1 on the measurement object.

[0083] In a further preferred embodiment, it is provided that the device 100 (FIG. 1) is configured to output the terahertz radiation TS1 in the form of a diverging beam, where, according to a further preferred embodiment, (further) beam shaping is performed with one or more further optical elements, for example to obtain a collimated beam, whereby a distance dependence of the measurement based on the terahertz radiation TS1 with respect to the measurement object is reduced or eliminated.

[0084] In a further preferred embodiment, with reference to the device 100g in Fig. 11, the device 100g comprises at least one optical sensor device 170, e.g. an optical distance sensor, in particular a triangulation sensor and / or for example at least one three-dimensional imaging device (such as a laser scanner), which is able to detect or determine at least one of the following factors: a) the distance of the measurement object relative to the device 100g, b) the inclination of the device 100g relative to the measurement object, c) the shape, in particular the surface shape, of the measurement object.

[0085] By using an optical distance sensor, in particular a triangulation sensor, for example the distance of the device 100g or in particular the distance of one of the components 110 from the measurement object to which the terahertz signal TS1 (FIG. 1) is applied can be advantageously determined based on optical measurement principles, thus further increasing the accuracy of the terahertz radiation-based measurement by the device 100g.

[0086] In a further preferred embodiment, referring to the device 100h of Fig. 12A, the device 100h is adapted to provide a protective gas flow SGS comprising a protective gas SG in at least one region of the beam path BP of the terahertz radiations TS1, TS2, in particular the protective gas SG comprises or is formed from at least one of the following elements: (a) dry air, (B) dry gas, (c) dry gas mixture, (d) at least one gas that has no absorption lines in the frequency range of the terahertz radiations TS1, TS2. In particular the protective gas SG is below -20°C, preferably below -30°C, more preferably below -40°C, in particular the protective gas SG produces an attenuation of the terahertz radiations TS1, TS2 along the beam path BP of preferably less than 0.1 dB for each frequency of the terahertz radiations TS1, TS2.

[0087] In a further preferred embodiment, it is provided that the apparatus 100h further comprises: a) at least one supply device 150 for at least temporarily providing a protective gas flow SGS, and / or b) at least one pressure operating member (not shown) for operating the pressure of the protective gas SG.

[0088] In a further preferred embodiment, the device 100h further comprises at least one nozzle 152, where in particular the nozzle 152 is adapted and / or adjusted to direct the protective gas flow SGS or at least a part of the protective gas flow SGS into at least one region of the beam path BP of the terahertz radiation TS1, TS2, in particular the at least one nozzle 152 is a free-jet nozzle. As a result, the beam path BP of the terahertz radiation TS1, TS2, in particular preferably substantially the entire beam path BP of the terahertz radiation TS1, TS2, between the terahertz element 110 and the measurement object OBJ can be exposed to the protective gas SG in a defined manner, whereby particularly precise measurements can be made by the terahertz radiation TS1, TS2. For example, according to a further preferred embodiment, this also allows the generation of a substantially laminar protective gas flow SGS along the beam path BP. In particular, according to a further preferred embodiment, the direction of the protective gas flow SGS can also be, for example, at least approximately parallel to the propagation direction of the terahertz radiation TS1, TS2.

[0089] FIG. 12B shows an example of the device 100i according to a further preferred embodiment, in which a housing 154 is provided. In particular, the at least one terahertz element 110 may be arranged inside the housing 154, as well as at least parts of the supply device 150. The protective gas SG allows a particularly precise measurement with the terahertz radiation TS1, TS2, since the medium SG in the area of ​​the beam path BP thereby has a defined, in particular particularly low, absorption of the terahertz radiation TS1, TS2 compared to regular ambient air. Further preferably, the device 100i can be configured to generate a laminar protective gas flow SGS in the area of ​​the beam path BP, which allows the precision of the measurement based on the terahertz radiation TS1, TS2 to be further increased.

[0090] In a further preferred embodiment, referring to the device 100j, it is provided that the device 100j comprises at least one steering device 160 for steering the beam path BP of the terahertz radiations TS1, TS2. In particular, the at least one steering device 160 comprises a reflecting device 162 for the terahertz radiations TS1, TS2, in particular at least one mirror 162a1, 162a2. As a result, the terahertz radiations TS1, TS2 can be efficiently guided from the terahertz element 110a' (which may for example have the configuration 110a according to FIG. 5) to the object OBJ' to be measured and / or vice versa.

[0091] In a further preferred embodiment, the reflecting device 160 comprises at least a first mirror 162a1 and a second mirror 162a2 (and in this embodiment also an optional third mirror 162c), and the apparatus 100j is configured to a) selectively position the first mirror 162a1 or the second mirror 162a2 in the beam path BP of the terahertz radiations TS1, TS2, and / or b) at least temporarily position the first mirror 162a1 and at least temporarily position the second mirror 162a2 in the beam path BP of the terahertz radiations TS1, TS2, as diagrammatically indicated by block arrow A1.

[0092] In a further preferred embodiment, it is provided that the first mirror 162a1 has a first focal length and the second mirror 162a2 has a second focal length different from the first focal length, so that the imaging properties of the beam path BP for the terahertz radiation TS1, TS2 can be effectively changed, preferably dynamically (during operation of the apparatus 100j), by so to speak "switching" A1 between the mirrors 162a1, 162a2.

[0093] In a further preferred embodiment, it is provided that the second mirror 162a2 can be driven and / or changed and / or replaced without tools and / or by a motor, whereby it can furthermore be replaced, for example, by a third mirror, whereby preferably the beam directions of the terahertz radiation TS1, TS2 downstream of the second and third mirrors are preferably collinear. In a further preferred embodiment, this can be realized, for example, by several stops (not shown), in particular for example the axial and lateral positioning of the respective mirrors.

[0094] In a further preferred embodiment, it is provided that the device 100j comprises at least one of the following elements: a) a click module 164a, b) a magnetic holder 164b, c) a turret 164c, in particular for at least temporarily holding and / or positioning at least the first mirror 162a1 and / or the second mirror 162a2.

[0095] In a further preferred embodiment, referring to the device 100k of Fig. 14, the device 100k is adapted to temporarily apply a first pulsed laser radiation S2a having a first pulse frequency and a second pulsed laser radiation S2b having a second pulse frequency to at least one terahertz element 110, in particular the second pulse frequency being at least temporarily different from the first pulse frequency. Preferably, the pulsed laser radiations S2a, S2b can be provided by at least one optical fiber (by way of example, two fibers 140a, 140b are shown here) and are for example emitted onto the terahertz element 110. Optionally, a respective laser source (not shown) can be provided for generating the pulsed laser radiations S2a, S2b, which can be arranged according to a further preferred embodiment locally or remotely relative to the terahertz element 110. In this respect, according to a further preferred embodiment, what has been described above with reference to Fig. 6 also applies in a corresponding manner to the arrangement 100k according to Fig. 14.

[0096] A further preferred embodiment, with reference to Fig. 15, concerns the use 200 of this embodiment for at least one of the following elements: a) transmitting 202 and / or receiving 204 (Fig. 1) terahertz radiation TS1, TS2, in particular terahertz pulses, b) determining based on a particular model, in particular determining 206 a layer thickness of one or more layers on a component, c) at least temporary positioning 207a (Fig. 13) of the first mirror 162a1 and / or at least temporary positioning 207b of the second mirror 162a2 in the beam path BP of the terahertz radiation TS1, TS2, d) at least temporary and / or at least local positioning of the at least one terahertz element 110 and the electromagnetic field shaping element 120 and the electromagnetic field shaping element 120. 15), f) transmission 210 of terahertz radiation TS1, in particular a terahertz pulse, into or into the spatial region to which the protective gas SG (Figures 12A, 12B) or protective gas flow SGS, respectively, is applied.

[0097] FIG. 16 shows a schematic side view of a measurement object OBJ″ comprising a substrate 10 and a layer arrangement arranged on a first surface 10a of the substrate 10 and comprising, for example, three layers 11, 12, 13. The three layers 11, 12, 13 have thicknesses t1, t2, t3 and can represent, for example, paint layers of the body part 10. In a further preferred embodiment, at least one device according to the embodiment may be used to apply terahertz radiation TS1 (FIG. 1) to the measurement object OBJ″ according to FIG. 16. The terahertz radiation TS1 is reflected, in particular at the respective boundary layers between the elements 10, 11, 12, 13 or at the surface of the top layer 13 of FIG. 16 and, according to a further preferred embodiment, is received by the at least one device (and / or at least one device of the same or similar type) as reflected terahertz radiation TS2 and the respective layer thicknesses t1, t2, t3 can be determined, for example, by a model-based method based on time domain reflectometry.

[0098] FIG. 17 shows a schematic representation of a measuring device 1000 according to a further preferred embodiment. The measuring device 1000 has a measuring head 1002 in which at least one device 100i according to the embodiment is arranged for applying terahertz radiation TS on a measuring object OBJ"' (for example a body part) and receiving terahertz radiation TS R reflected from or at the measuring object OBJ"', which may contain information in particular about the layer structure of the measuring object OBJ"', in particular about paint layer thicknesses. Optionally, the measuring device 1000 comprises a positioning system 1004, which may for example be a robot, in particular an industrial robot. According to a further preferred embodiment, the measuring device 1000 can be efficiently used in production facilities and / or production lines for performing measurements based on terahertz radiation in an accurate and efficient manner.

Claims

1. An apparatus (100; 110a; 100b; 100c; 100d; 100e; 100f; 100g; 100h; 100i; 100j; 100k) for transmitting and / or receiving terahertz radiation (TS1, TS2), comprising: at least one terahertz element (110; 110a; 110b; 110a'; 110_1, 110_2) configured to generate and / or detect terahertz radiation (TS1, TS2); at least one electromagnetic field shaping element (120; 120a) assigned to at least one said terahertz element (110; 110a; 110b; 110a'; 110_1, 110_2); Including, said at least one terahertz element (110; 110a; 110b; 110a'; 110_1, 110_2) is arranged in the region of a first surface (121) of said electromagnetic field shaping element (120; 120a), at least one said terahertz element (110; 110a; 110b; 110a'; 110_1, 110_2) is arranged with respect to said first surface (121) of said electromagnetic field shaping element (120; 120a) such that at least locally evanescent coupling occurs between said at least one said terahertz element (110; 110a; 110b; 110a'; 110_1, 110_2) and said electromagnetic field shaping element (120; 120a), At least one of the terahertz elements (110; 110a; 110b; 110a'; 110_1, 110_2) comprises a first substrate (114) and an electrode arrangement (115), the electrode arrangement (115) is disposed on a first surface (114a) of the first substrate (114); said electromagnetic field shaping element (120; 120a) having in an area of ​​a second surface (122) opposite said first surface (121) a surface modification having a reflection reducing effect, said device (100; 110a; 100b; 100c; 100d; 100e; 100f; 100g; 100h; 100i; 100j; 100k) configured for temporarily applying a first pulsed laser radiation (S2a) having a first pulse frequency and a second pulsed laser radiation (S2b) having a second pulse frequency to at least one of said terahertz elements (110; 110a; 110b; 110a'; 110_1, 110_2), the second pulse frequency being at least temporarily different from the first pulse frequency; Device.

2. The apparatus (100; 100a; 100b; 100c; 100d; 100e; 100f; 100g; 100h; 100i; 100j; 100k) of claim 1, wherein the second surface (122) opposite the first surface (121) of the electromagnetic field shaping element (120; 120a) has a surface modification having a reflection reducing effect as an anti-reflective coating (124).

3. The device (100; 100a; 100b; 100c; 100d; 100e; 100f; 100g; 100h; 100i; 100j; 100k) of claim 1, wherein the reflection reduction effect is optimized for a frequency range between 3 THz and 10 THz.

4. A bonding layer (130) is arranged at least locally between at least one of the terahertz elements (110; 110a; 110b; 110a'; 110_1, 110_2) and the first surface (121) of the electromagnetic field shaping element (120; 120a), The device (100; 100a; 100b; 100c; 100d; 100e; 100f; 100g; 100h; 100i; 100j; 100k) according to claim 1, wherein the layer thickness (d1) of the bonding layer (130) is less than 50 μm.

5. An apparatus (100; 100a; 100b; 100c; 100d; 100e; 100f; 100g; 100h; 100i; 100j; 100k) as described in claim 4, wherein the layer thickness (d1) of the bonding layer (130) is less than one-quarter of the wavelength of the terahertz radiation (TS1, TS2) in the bonding layer (130).

6. An apparatus (100; 100a; 100b; 100c; 100d; 100e; 100f; 100g; 100h; 100i; 100j; 100k) as described in claim 4, wherein the layer thickness (d1) of the bonding layer (130) is less than one-quarter of the wavelength of the maximum frequency of the terahertz radiation (TS1, TS2) in the bonding layer (130).

7. The apparatus (100; 100a; 100b; 100c; 100d; 100e; 100f; 100g; 100h; 100i; 100j; 100k) of claim 4, wherein the bonding layer (130) at least partially comprises or is formed from at least one of the following materials: a) PE and / or HDPE and / or PP and / or PTFE and / or PMP, b) PE and / or HDPE and / or PP and / or PTFE and / or PMP comprising at least one additive material, c) an adhesive material comprising at least one additive material.

8. The apparatus (100; 100a; 100b; 100c; 100d; 100e; 100f; 100g; 100h; 100i; 100j; 100k) of claim 4, wherein the bonding layer (130) has a refractive index n of 1.6 or greater.

9. The apparatus (100; 100a; 110b; 110a'; 110_1, 110_2) of claim 1, wherein at least one of the terahertz elements (110; 110a; 110b; 110a'; 110_1, 110_2) or the first substrate (114) comprises a photoconductive material, the photoconductive material comprising at least one of the following materials: (a) indium phosphide (InP); (b) gallium arsenide (GaAs); (c) indium gallium arsenide (InGaAs). At least one of the terahertz elements (110; 110a; 110b; 110a'; 110_1, 110_2) comprises at least one further substrate (116), said first substrate (114) is at least locally arranged on at least one further substrate (116); 2. The apparatus (100; 100a; 100b; 100c; 100d; 100e; 100f; 100g; 100h; 100i; 100j; 100k) according to claim 1, wherein the first substrate (114) comprises, at least locally on at least one of the further substrates (116), a second surface (114b) opposite to the first surface (114a) of the first substrate (114), on at least one of the further substrates (116), on a first surface (116a) of the at least one of the further substrates (116).

11. An apparatus (100; 100a; 100b; 100c; 100d; 100e; 100f; 100g; 100h; 100i; 100j; 100k) as described in claim 1, wherein the first substrate (114) and / or at least one further substrate (116) is at least partially transparent to optical radiation (S1) in the wavelength range between 1450 nm and 1650 nm or in the wavelength range between 850 nm and 1650 nm, with a transmittance of more than 90 percent.

12. The apparatus (100; 100a; 100b; 100c; 100d; 100e; 100f; 100g; 100h; 100i; 100j; 100k) described in claim 10, wherein at least one of the further substrates (116) comprises a material different from the material of the first substrate (114).

13. The apparatus (100; 100a; 100b; 100c; 100d; 100e; 100f; 100g; 100h; 100i; 100j; 100k) of claim 10, wherein a) a second surface (114b) or the second surface (114b) opposite the first surface (114a) of the first substrate (114), or b) a second surface (116b) opposite the first surface (116a) of at least one further substrate (116) is exposed to a first optical radiation (S1).

14. The apparatus (100; 100a; 100b; 100c; 100d; 100e; 100f; 100g; 100h; 100i; 100j; 100k) described in claim 13, wherein the first optical radiation (S1) is laser radiation (S1) in a wavelength range between 1450 nm and 1650 nm.

15. The method of claim 1, wherein an irradiation device (140) is provided for at least temporarily exposing at least one area of ​​said terahertz element (110; 110a; 110b; 110a'; 110_1, 110_2) to said first optical radiation (S1), the illumination device (140) includes or is formed as at least one optical fiber (140); said optical fiber (140) having an output surface (141) for coupling said first optical radiation (S1) opposite to a) a second surface (114b) or a second surface (114b) opposite to said first surface (114a) of said first substrate (114), or b) a second surface (116b) opposite to said first surface (116a) of at least one further substrate (116); 14. The apparatus (100; 100a; 100b; 100c; 100d; 100e; 100f; 100g; 100h; 100i; 100j; 100k) according to claim 13, wherein aa) the second surface (114b) of the first substrate (114), or bb) the second surface (116b) of at least one further substrate (116), or both, are positioned or aligned with respect to the first substrate (114) and / or at least one further substrate (116) so as to be exposed to the first light radiation (S1).

16. 16. The apparatus (100; 100a; 100b; 100c; 100d; 100e; 100f; 100g; 100h; 100i; 100j; 100k) of claim 15, wherein the optical fiber (140) is a polarization-maintaining optical fiber.

17. The apparatus (100; 100a; 100b; 100c; 100d; 100e; 100f; 100g; 100h; 100i; 100j; 100k) comprising a plurality of terahertz elements (110_1, 110_2, ...), a) at least two of the plurality of terahertz elements (110_1, 110_2, ...) are arranged in the region of the first surface (121) of the electromagnetic field shaping element (120; 120a), and / or b) at least one said electromagnetic field shaping element (120; 120a) is assigned to at least two of said plurality of terahertz elements (110_1, 110_2), A) at least two of the plurality of terahertz elements (110_1, 110_2, ...) are arranged side by side, and respective electrode arrangements (115_1, 115_2) of at least two of the terahertz elements (110_1, 110_2, ...) lie at least in a same first imaginary plane (E1), the first imaginary plane (E1) being parallel to a first surface (121) of the electromagnetic field shaping element (120; 120a), or B) The apparatus (100; 100a; 100b; 100c; 100d; 100e; 100f; 100g; 100h; 100i; 100j; 100k) of claim 1, wherein at least two of the plurality of terahertz elements (110_1, 110_2, ...) are arranged in front of and behind the beam direction of the terahertz radiation (TS1, TS2), and the electrode arrangements (115_1, 115_2) of the at least two terahertz elements (110_1, 110_2, ...) are located in respective imaginary planes (E1, E2) that are different from each other, and at least two of the imaginary planes (E1, E2) are parallel to the first surface (121) of the electromagnetic field shaping element (120; 120a).

18. At least two of the plurality of terahertz elements (110_1, 110_2) at least partially overlap in space, or 18. The device (100; 100a; 100b; 100c; 100d; 100e; 100f; 100g; 100h; 100i; 100j; 100k) according to claim 17, wherein a common electrode structure (115_12) is assigned to a number of said terahertz elements (110_1, 110_2).

19. The apparatus (100; 110a; 100b; 100c; 100d; 100e; 100f; 100g; 100h; 100i; 100j; 100k) of claim 1, wherein the apparatus (100; 110a; 100b; 100c; 100d; 100e; 100f; 100g; 100h; 100i; 100j; 100k) is configured to output or receive, or to output and receive, the terahertz radiation (TS1, TS2) in the formation of a collimated beam.

20. The apparatus (100; 110a; 100b; 100c; 100d; 100e; 100f; 100g; 100h; 100i; 100j; 100k) of claim 1, comprising a first laser source (140a) for generating and / or providing the first pulsed laser radiation (S2a) and a second laser source (140b) for generating and / or providing the second pulsed laser radiation (S2b).

21. The apparatus (100; 110a; 100b; 100c; 100d; 100e; 100f; 100g; 100h; 100i; 100j; 100k) of claim 1 is configured to provide a protective gas flow (SGS) comprising a protective gas (SG) to at least one beam path (BP) of the terahertz radiation (TS1, TS2), the protective gas (SG) comprising or formed from at least one of: (a) dry air; (b) dry gas; (c) dry gas mixture; (d) at least one gas that has no absorption lines in the frequency range of the terahertz radiation (TS1, TS2).

22. The apparatus (100; 100a; 100b; 100c; 100d; 100e; 100f; 100g; 100h; 100i; 100j; 100k) described in claim 21, wherein the protective gas (SG) has a dew point temperature of -20°C or less, and the protective gas (SG) causes an attenuation of the terahertz radiation (TS1, TS2) along the beam path (BP) of 0.1 dB or less for each frequency of the terahertz radiation (TS1, TS2).

23. The apparatus (100; 110a; 100b; 100c; 100d; 100e; 100f; 100g; 100h; 100i; 100j; 100k) of claim 21 further comprising: a) at least one supply device (150) for at least temporarily providing the protective gas flow (SGS); or b) at least one pressure operating member for operating the pressure of the protective gas (SG).

24. The apparatus (100; 110a; 100b; 100c; 100d; 100e; 100f; 100g; 100h; 100i; 100j; 100k) of claim 21 further comprises at least one nozzle (152), the nozzle (152) adapted or arranged to direct the protective gas flow (SGS) or at least a portion of the protective gas flow (SGS) into at least one region of the beam path (BP) of the terahertz radiation (TS1, TS2), and at least one of the nozzles (152) is a free jet nozzle.

25. The apparatus (100; 110a; 100b; 100c; 100d; 100e; 100f; 100g; 100h; 100i; 100j; 100k) according to claim 1, comprising at least one optical sensor device (170) capable of measuring or determining at least one of a) the distance of a measurement object (OBJ'; OBJ") relative to the apparatus (100), b) the inclination of the apparatus (100) relative to the measurement object (OBJ'; OBJ"), c) the shape of the measurement object (OBJ; OBJ'; OBJ").

26. A measuring device (1000) for determining at least one physical parameter of a measurement object (OBJ; OBJ'; OBJ", OBJ"'), comprising at least one said device (100; 110a; 100b; 100c; 100d; 100e; 100f; 100g; 100h; 100i; 100j; 100k) as defined in claim 1, wherein the measuring device (1000) is configured to determine layer thicknesses (t1, t2, t3) of the at least one layer (11, 12, 13) of the measurement object (OBJ; OBJ'; OBJ", OBJ"') by using a model-based method using a model of the at least one layer (10, 11, 12).

27. Use of the device (100; 100a; 100b; 100c; 100d; 100e; 100f; 100g; 100h; 100i; 100j; 100k) according to claim 1 and / or the measuring device (1000) according to claim 26, a) transmitting (202) or receiving (204), or transmitting (202) and receiving (204), terahertz radiation (TS1, TS2; TS; TSR); b) determining (206) layer thicknesses (t1, t2, t3) of one or more layers on the part (10); c) at least temporarily positioning (207a) a first mirror (162a1) and at least temporarily positioning (207b) a second mirror (162a2) in a beam path (BP) of said terahertz radiation (TS1, TS2; TS; TSR); d) providing (208) at least temporarily or at least locally, or at least temporarily and locally, an evanescent coupling between at least one of said terahertz elements (110; 110a; 110b; 110a'; 110_1, 110_2) and said electromagnetic field shaping element (120; 120a); e) providing (209a) a protective gas (SG) at least temporarily to at least one spatial region, said providing (209a) at least temporarily to at least one spatial region of said protective gas (SG) being synchronized with the transmission (202) and / or reception (204) of terahertz radiation (TS1, TS2; TS; TSR); To provide, f) applying (209b) terahertz radiation (TS1, TS2; TS; TSR) to said spatial region or to said spatial region to which said protective gas (SG) is applied; Use for at least one of the following:

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