Reflection and/or Diffraction-Based Method and Setup to Generate High-Energy Terahertz Pulses

Abstract

A technique to generate terahertz radiation is disclosed, where a pump beam (12) is coupled into an optical element (50) made of a medium with non-linear optical properties having plane-parallel front and rear boundary surfaces (51, 52), wherein the pump beam (12) is split into a set of partial pump beams (121) by reflection and/or diffraction on a periodic relief structure (53) of said optical element (50). The partial pump beams travels along a direction at an angle γ that satisfies the velocity matching condition of v.sub.p,cs, cos(γ)=v.sub.THz,f within the given medium, where v.sub.p;cs is the group velocity of the pump beam, v.sub.THz;f is the phase velocity of the terahertz radiation and the speed a planar envelope (212) travels toward the front boundary surface (51) of the optical element (50), and γ is the angle formed by the pulse front envelope and the phase front of the pump beam.

Claims

1. A method to generate terahertz radiation (60) comprising: providing a plane-parallel optical element (50) formed of medium with nonlinear optical properties having a plane entry surface (51) and a rear boundary surface (52) parallel to the entry surface (51), coupling a pump beam (12) into the optical element (50) through the entry surface (51), perpendicularly to the entry surface (51), directing said pump beam (12) along a first propagation direction to one of: a periodic relief structure (53) formed in the rear boundary surface (52) of the optical element (50); or a periodic relief structure (153) formed in a surface (151) of an additional element (150), said surface (151) facing the rear boundary surface (52), extending parallel to the rear boundary surface (52) and being optically coupled to the rear boundary surface (52) of the optical element (50), subjecting the pump beam (12) to at least one of reflection or diffraction, splitting thereby the pump beam (12) into partial beams (121), said partial beams (121) having a common planar envelope (212), and generating terahertz radiation (60) by the partial beams (121), as pump beams, in the nonlinear optical medium through nonlinear optical interaction, and decoupling the terahertz radiation (60) from the optical element (50) through the entry surface (51), wherein said one of the periodic relief structure (53; 153) comprises: at least first zones perpendicular to the first propagation direction and parallel to each other, individual ones of said first zones having a symmetrical V-shape in a plane section along the first propagation direction, a magnitude of angles formed by legs of said V-shape and the rear boundary surface (52) being half an angle (γ) of pulse-front-tilting required to satisfy the velocity matching condition of
v.sub.p,cs cos(γ)=v.sub.THz,f   (1) within the optical medium, wherein v.sub.p;cs is a group velocity of the pump beam (12), v.sub.THz;f being is a phase velocity of the terahertz radiation (60) and γ is the angle of pulse-front-tilting, and wherein, after said reflection and/or diffraction, the partial beams (121) propagate at an angle γ to the first propagation direction, and the planar envelope (212) travels at a speed V.sub.THz;f towards the entry surface (51) of the optical element (50).

2. The method according to claim 1, further comprising directing the pump beam (12) along the first propagation direction to the periodic relief structure (53; 153) and subjecting the pump beam (12) to reflection, wherein said periodic relief structure (53; 153) further comprises second zones perpendicular to the first propagation direction, parallel to each other, and arranged alternately with said first zones, wherein each of said second zones form an angle with the rear boundary surface (52) which results in pulse-front-tilting the pump beam (12) to an angle which is insufficient to satisfy the velocity matching condition of relation (1).

3. The method according claim 2, wherein the second zones are substantially parallel to the rear boundary surface (52).

4. The method according to claim 2, wherein a width (u) of said second zones is at most 5% of a width (2w) of said first zones.

5. The method according to claim 1, further comprising separating the terahertz radiation (60) from the pump beam (12) for further use after being detached from the optical medium.

6. The method according to claim 1, further comprising of separating the terahertz radiation (60) from the pump beam (12) by arranging a dichroic mirror in the path of the terahertz radiation (60).

7. The method according to claim 1, further comprising separating the terahertz radiation (60) from the pump beam (12) by slightly rotating the optical element (50) about an axis perpendicular to the first propagation direction.

8. The method according to claim 1, wherein the non-linear optical medium is lithium niobate (LN), lithium tantalate (LT), or a semiconductor selected from the group consisting of GaP, ZnTe, and GaAs.

9. (canceled)

10. The method according to claim 1, wherein the pump beam (12) is a laser pulse in the visible, near-infrared or medium-infrared range, with a pulse length ranging from at least 5 femtoseconds to at most a few picoseconds.

11. An optical element to generate terahertz radiation (60) with a pump beam (12), the optical element comprising: a medium with non-linear optical properties bounded in longitudinal direction by front and rear boundary surfaces (51, 52) parallel to each other, and including a periodic relief structure (53) formed in the rear boundary surface (52), said relief structure (53) comprising at least first zones perpendicular to the longitudinal direction and parallel to each other, each of said first zones having a symmetrical V-shape in a plane section along the longitudinal direction, a magnitude of angles formed by legs of said V-shape and the rear boundary surface (52) being half an angle (γ) of pulse-front-tilting required to satisfy the velocity matching condition of
v.sub.p,cs cos(γ)=v.sub.THz,f   (1) within the optical medium, wherein (1) v.sub.p;cs is a group velocity of the pump beam (12), V.sub.THz;f being is a phase velocity of the terahertz radiation (60) and γ is the angle of pulse-front-tilting.

12. An optical element to generate terahertz radiation (60) with a pump beam (12) comprising: the optical element, the optical element being formed of a medium with non-linear optical properties bounded in longitudinal direction by front and rear boundary surfaces (51, 52) parallel to each other, wherein the rear boundary surface (52) of the optical element (50) is optically coupled to a surface (151) of an additional element (150), said surface (151) facing the rear boundary surface (52) and extending parallel to the rear boundary surface (52), wherein a periodic relief structure (153) is formed in said surface (151), said relief structure (153) comprising at least first zones perpendicular to the longitudinal direction and parallel to each other, individual ones of said first zones having a symmetrical V-shape in a plane section along the longitudinal direction, a magnitude of angles formed by legs of said V-shape and the rear boundary surface (52) being half an angle (γ) of pulse-front-tilting required to satisfy the velocity matching condition of
v.sub.p,cs cos(γ)=v.sub.THz,f   (1) within the optical medium, (1) wherein v.sub.p;cs is a group velocity of the pump beam (12), v.sub.THz;f is a phase velocity of the terahertz radiation (60) and γ is the angle of pulse-front-tilting.

13. The optical element according to claim 12, wherein the additional element (150) is made of a metal.

14. The optical element according to claim 12, wherein a metal coating is applied to the periodic relief structure (153) formed in the surface (151) of the additional element (150) facing the rear boundary surface (52), said gold layer having a layer thickness up to a few microns.

15. The optical element according to claim 12, wherein a refractive index matching medium (155) is arranged between the rear boundary surface (52) and the surface (151) of the additional element (150) facing the rear boundary surface (52) to provide the optical coupling.

16. The optical element of claim 15, wherein the refractive index matching medium (155) is a semiconductor nanocrystal emulsion.

17. The optical element according to claim 11, wherein the periodic relief structure (53; 153) is a blazed relief structure.

18. The optical element according to claim 11, wherein the periodic relief structure (53; 153) further comprises second zones perpendicular to the longitudinal direction, parallel to each other, and arranged alternately with said first zones, individual ones of said second zones forming an angle with the rear boundary surface (52) which results in pulse-front-tilting the pump beam (12) to an angle which is insufficient to satisfy the velocity matching condition of relation (1).

19. The optical element of claim 18, wherein the second zones are substantially parallel to the rear boundary surface (52).

20. The optical element according to claim 18, wherein a width (u) of the second zones is at most 5% of a width (2w) of the first zones.

21. The optical element according to claim 11, wherein the medium with nonlinear optical properties is made of a substance having a nonlinear optical coefficient of at least 160 pm/V, whose refraction indices in the terahertz and the visible domains significantly differ from each other.

22. The optical element according to claim 11, wherein the medium with nonlinear optical properties is lithium niobate (LiNbO3), lithium tantalate (LiTaO3), or a semiconductor selected from the group consisting of GaP, ZnTe., and GaAs.

23. (canceled)

24. A terahertz radiation source (100; 100′), comprising a pump source (10) to emit and couple a pump beam (12) into a light path; an optical element (50) according to claim 11 arranged in the light path in such a way that the front and rear boundary surfaces (51, 52) are substantially perpendicular to said light path to generate the terahertz radiation (60); a mechanism to separate the terahertz radiation (60) exiting the optical element (50) and the pump beam (12) coupled into the light path.

25. The radiation source (100, 100′) according to claim 24, wherein the mechanism comprises a dichroic mirror (70) arranged in the path of the generated terahertz radiation (60).

26. The radiation source (100, 100′) according to claim 24, wherein the mechanism comprises a tilting mechanism which slightly tilts the front boundary surface (51) of the optical element (50) in the light path relative to the pump beam (12) striking substantially perpendicular onto said front boundary surface (51).

27. The radiation source (100, 100′) according to claim 24, wherein the pump source (10) is a pump source configured to emit laser pulses in the visible, near-infrared or medium-infrared range, with a pulse length ranging from at least 5 femtoseconds to at most a few picoseconds.

28. The method according to claim 1 further comprising using the generated terahertz radiation (60) to monochromatize and synchronously accelerate electrically charged particles.

29. The optical element according to claim 12, wherein the additional element (150) is made of at least one of stainless steel and aluminum.

30. The optical element according to claim 12, wherein a gold layer is applied to the periodic relief structure (153) formed in the surface (151) of the additional element (150) facing the rear boundary surface (52), said gold layer having a layer thickness up to a few microns.

31. The optical element according to claim 12, wherein the periodic relief structure (153) is a blazed relief structure.

32. The optical element according to claim 12, wherein the periodic relief structure (153) further comprises second zones perpendicular to the longitudinal direction, parallel to each other, and arranged alternately with said first zones, individual ones of said second zones forming an angle with the rear boundary surface (52) which results in pulse-front-tilting the pump beam (12) to an angle which is insufficient to satisfy the velocity matching condition of relation (1).

33. The optical element of claim 32, wherein the second zones are substantially parallel to the rear boundary surface (52).

34. The optical element according to claim 32, wherein a width (u) of the second zones is at most 5% of a width (2w) of the first zones.

35. The optical element according to claim 12, wherein the medium with nonlinear optical properties is made of a substance having a nonlinear optical coefficient of at least 160 pm/V, whose refraction indices in the terahertz and the visible domains significantly differ from each other.

36. The optical element according to claim 12, wherein the medium with nonlinear optical properties is lithium niobate (LiNbO3), lithium tantalate (LiTaO3), or a semiconductor selected from the group consisting of GaP, ZnTe, and GaAs.

Description

[0036] FIG. 1 shows a preferred embodiment of a so-called rear-side reflection/diffraction type terahertz beam generating setup and a radiation source 100 for generating terahertz radiation in accordance with the invention. The beam source 100 comprises a pump source 10 providing a pump beam 12 and an optical element 50 made of a medium with non-linear optical properties in which the terahertz radiation is actually generated. The light-transmitting optical element 50 is bounded by a front boundary surface forming an entry plane 51 and a parallel reflection/diffraction rear boundary surface 52 having a periodic structure 53; consequently, the optical element 50 is preferably formed as a plane-parallel element. As the pump beam 12 passes through the optical element 50, as a result of the nonlinear optical interaction of the material of the pump beam 12 and the optical element 50, preferably by means of second harmonic generation or optical rectification, second harmonic radiation with a frequency higher than the frequency of the pump beam 12, and terahertz radiation with a frequency about two orders of magnitude lower than the frequency of the pump beam 12 arise. However, in the absence of phase matching (or, in terms of optical rectification, velocity matching according to relation (1)), the radiation generated by both the second harmonic generation and the optical rectification is of negligible intensity, and the pump beam 12 reaches the rear boundary surface 52 of the optical element 50 substantially unchanged. Here, said pump beam 12 suffers reflection and/or diffraction depending on the wavelength of the pump beam 12 and the size of the period of the periodic relief structure 53. In order to achieve a high degree of reflection, optionally, the rear boundary surface 52 is coated with a layer 54 (e.g., a metal or multilayer dielectric layer) that provides a high reflection in terms of the pump beam. As the rear boundary surface 52 comprises a periodic relief structure 53 with a spatial period of 2w, a plurality of pumping partial beams 121 of size w along a direction inclined in the plane of FIG. 1 is generated from the pump beam 12 via reflection and/or diffraction. In this case, the periodic relief structure 53 is formed in the rear boundary surface 52 in such a way that one period thereof consists of two flat parts. One of said flat parts is rotated clockwise, while the other is rotated counter-clockwise by an angle of γ/2 from the average plane of the rear boundary surface 52. Here, γ corresponds to the angle in the velocity matching condition of relation (1). The reflected and/or diffracted partial beams 121 are of width w, in which pulse fronts 211 (so-called pulse front segments) of width w and length Ti×v.sub.p,cs, corresponding to the pulse length Ti of the pump beam, travel at a velocity v.sub.p,cs along a direction at angle γ relative to the propagation direction of the pump beam before its reflection and/or diffraction (i.e., the first propagation direction). Thus, the pulse fronts 211 individually do not satisfy the velocity matching condition of relation (1). At the same time, the planar envelope 212 of the segmented pulse front formed by the set of 211 pulse front segments travels towards the entry plane 51 (perpendicularly to the entry plane 51) at a velocity v.sub.p,cs×cos γ, i.e., it satisfies the velocity matching condition of relation (1). Thus, through nonlinear optical interaction (preferably optical rectification or difference frequency generation), the segmented pulse front effectively generates such 60 terahertz radiation which travels in a direction identical to the propagation direction of the segmented pulse front (i.e., perpendicular to the input plane 51), and the wavelength of which is at least twice the size w×sinγ in the propagation direction of the individual pulse front 211 segments in the optical element 50.

[0037] The terahertz radiation 60 generated in the optical element 50 exits the optical element 50 through the inlet surface 51 and thus becomes usable for further applications.

[0038] The material of the optical element 50 has got a high nonlinear optical coefficient and is transparent at the wavelength of the pump beam. Examples of such materials are LN and LT, as well as several semiconductors, such as ZnTe, GaP, GaAs, GaSe.

[0039] The pump source 10 is preferably a laser source capable of emitting laser pulses, i.e., the pump beam 12, with a pulse length of at least 5 fs but at most a few hundred fs in the visible, near or medium infrared range, e.g. a diode-pumped Yb laser emitting at a central wavelength of 1030 nm, a titanium-sapphire laser emitting at a central wavelength of 800 nm, or a Ho laser emitting at a central wavelength of 2050 nm. Other lasers and optical parametric amplifiers can also be used as the pump source 10.

[0040] The periodic relief structure 53 is formed by a machining process (e.g., micromilling) known to a person skilled in the art in accordance with the enlarged part A or B of FIG. 1. If the optical element 50 has got such refractive index values at the wavelength of the pump beam 12 or the terahertz radiation 60 generated that the velocity matching condition of relation (1) is satisfied at angles less than 60° (such a material is most semiconductor), then, as is illustrated in the enlarged part A of FIG. 1, a single period consists of a first zone formed by two flat parts which, alternately clockwise or counterclockwise, form an angle γ/2 with the average (or center) plane of the rear boundary surface 52. If γ is greater than 60°, a portion of the cross section of the partial beams 121 would collide into the rear boundary surface 52 of the optical element 50 after reflection. To avoid this, width of the reflected partial beams 121 is limited in such a way that, as is shown in the enlarged part B of FIG. 1, a second zone of width u is formed in each case between the two oblique zones of width w, which is parallel to the entry plane 51. For LN, for example, when γ=62°, u/2w is only 6%.

[0041] The pump beam 12 arrives at the elements of width w of the relief structure 53 formed in the rear boundary surface 52 of the optical element 50 with an angle of incidence γ/2. This angle is greater than the limit of the total reflection for both LN and LT and most semiconductors (e.g., GaP, ZnTe). Thus, the reflection efficiency is high even without making use of reflection efficiency enhancing layers 54. Otherwise, it will be necessary to use a reflection efficiency enhancing layer 54.

[0042] The refractive indices of LN and LT for the pump beam 12 are, in general, greater than 2, and the refractive indices of most semiconductors approach or even exceed the value of 3. Therefore, in order to reduce reflection losses, it is preferable (but not necessary) to apply an antireflection coating well-known to a person skilled in the art on the entry plane 51 of the optical element 50.

[0043] The optical element 50 is made of a material which has an exceptionally high non-linear optical coefficient, i.e. the magnitude of which preferably is, in practice, at least 1 pm/V, typically higher than several tens pm/V. The optical element 50 is preferably made of LN or LT, as well as semiconductor materials, e.g. of GaP or ZnTe, preferably with a crystal axis orientation that is the most advantageous in terms of the generation efficiency of nonlinear optical processes, e.g. terahertz radiation generation through optical rectification.

[0044] Since the optical element 50 used in the terahertz beam source 100 has plane-parallel front and rear boundary surfaces, and both the pump beam 12 and the terahertz radiation 60 generated propagate perpendicular to these surfaces (in opposite directions), there is a need to separate the pump beam 12 and the terahertz beam 60. This can be done by well-known techniques. FIGS. 2A and 2B, as well as FIG. 3 show, by way of example, some suitable techniques and separation mechanisms.

[0045] FIG. 2A shows a technical solution wherein the beams are separated by a dichroic mirror 70 inserted between the pump source 10 and the optical element 50. In the case illustrated in FIG. 2A, the dichroic mirror 70 exhibits high transmission at the wavelength of the pump beam 12 and high reflection at the wave-length of the terahertz radiation 60. For example, a sheet of quartz coated with an indium tin oxide (ITO) layer behaves in this way. FIG. 2B shows an arrangement wherein the dichroic mirror 70 exhibits high reflection at the wavelength of the pump beam 10 and high transmission at the wavelength of the terahertz radiation 60. For example, a sheet of quartz with a suitable dielectric layer structure applied thereon behaves in this way. The dichroic mirrors 70 used in these arrangements separate and transmit the terahertz radiation 60 generated and the pump beam 12 in different directions on the basis of a difference in their wavelengths, as is known to a skilled person in the art.

[0046] FIG. 3 shows a simple further technical solution to separate the pump beam 12 and the terahertz radiation 60 from one another. Here, the optical element 50 is slightly (typically in a few degrees, preferably in 1° to 10°, more preferably in 5° to 10°) tilted from its perpendicular position relative to the first propagation direction of the pump beam 12 in a plane perpendicular to the plane of FIG. 1 or FIG. 2, which is preferably effected by a suitable tilting device (e.g. a device rotating the optical element 50 at a small angle about an axis perpendicular to the first propagation direction of the pump beam 12). In this way, and by arranging the pump source 10 and the optical element 50 at a suitable distance from each other, spatial separation of the pump beam 12 and the terahertz radiation 60 is realized.

[0047] In order to operate the terahertz source 100 according to the present invention with high efficiency, the half-period w of the periodic structure 53 of the optical element 50 is chosen to be less than a half, preferably a third, more preferably a quarter of the wavelength of the terahertz radiation 60 within the optical element 50. This choice ensures that the phases of terahertz radiation generated at different parts of the pulse front 211 segments do not differ significantly from each other, and thus, constructive interference takes place amongst them. The length L of terahertz-generation is preferably in the order of cm, more preferably 5 to 15 mm, most preferably 5 to 10 mm, and depends on the material quality of the optical medium itself.

[0048] FIG. 4 illustrates a possible further embodiment of a rear-side reflection type optical element 50 with nonlinear optical properties used in the terahertz source according to the present invention. For the optical element 50 forming part of the terahertz source 100′ shown in FIG. 4, the periodic relief structure is provided as a relief structure 153 formed in a surface 151 of a separate (additional) element 150, wherein said surface 151 faces to and extends in parallel to the rear boundary surface 52 of the optical element 50 and is in optical coupling with the rear boundary surface 52 of said optical element 50 with nonlinear optical properties. The design of the relief structure 153 formed in the element 150 (i.e., the parameters u, w) is identical to that of the relief structure 53 formed in the rear boundary surface 52 of the optical element 50 and described in detail above. The optical coupling between the rear boundary surface 52 of the optical element 50 and the element 150 or rather the relief structure 153 formed on/in said element 150, which serves to ensure smooth propagation of the pump beam and/or the partial pump beams, is provided by a refractive index matching medium 155 arranged between said elements. Said medium 155 is preferably a semiconductor nanocrystal emulsion, wherein the semiconductor nanocrystals are preferably e.g. GaN and/or ZnO nanocrystals, while the solvent is preferably e.g. butanol; semi-conductor nanocrystal emulsions useful for the present invention and their preparation are known to the skilled person in the art and will not be described in detail here. The element 150 is generally made of metal, preferably stainless steel or aluminum. The relief structure 153 is provided by e.g. a gold metal coating which is evaporated on a desired surface structure formed previously in the surface 151 of the element 150 by a suitable mechanical machining procedure (preferably micromilling). The layer thickness of the coating is preferably a few microns. To improve the quality of the optical coupling, protruding portions of the relief structure 153 of the optical element 150 are preferably in contact with the rear boundary surface 52 of the optical element 50 or located in a close vicinity thereof at a distance of up to a few microns.

[0049] FIG. 5 shows how the efficiency of terahertz radiation generation, according to theoretical calculations, depends on the crystal length at pumping pulse lengths of 100 fs and 1.0 ps for terahertz sources constructed in accordance with the present invention and with the previously proposed plane-parallel hybrid echelon assembly (see L. Pálfalvi et al., Optics Express, vol. 25, issue 24, pp. 29560-29573 (2017)). In the case of pumping at 100 fs (see solid squares, circles) w=80 μm, which is justified by the fact that for the previously proposed plane-parallel terahertz radiation source, the maximum terahertz-generation efficiency is associated with this value of w. In the case of pumping at 1.0 ps (see empty squares, circles) w=100 μm. As can be seen, in terms of the efficiency at 100 fs and at 1.0 ps, the previous arrangement (see squares) is approx 3.6 times and approx. 2.5 times, respectively, more favorable than the setup according to the present invention (see circles). It should be noted, however, that when using wide beams, the ratio of generating efficiencies for the two constructions decreases to less than two for shorter pumping lengths, since in the previous arrangement, the theoretically obtained efficiency is only achievable in the middle of the beam and significantly decreases at the beam edges, as is obvious in light of FIG. 6A.

[0050] The lower generation efficiency belonging to the setup according to the present invention is fully compensated by the fact that its design/construction is significantly simpler than that of the previous terahertz-generation schemes, and the setup itself contains significantly fewer elements, so that a more compact design is possible. Furthermore, the setup according to the invention does contain no imaging element, thus when used, there are, of course, no imaging errors and, hence, no associated pump pulse elongation appears.

[0051] FIGS. 6A and 6B show the time course of the electric field strength in the terahertz radiation generated by a beam source 100 implemented with a rear-side reflection assembly of the present invention and in the terahertz radiation generated by the formerly proposed plane-parallel structure (for further details, see L. Pálfalvi et al., Optics Express, vol. 25, issue 24, pp. 29560-29573 (2017)) for pump beams 12 comprised of 100 fs and 1.0 ps pulses, respectively, at the intensities of 200 GW/cm.sup.2 and 40 GW/cm.sup.2 and with a central wavelength of 800 nm, obtained through model calculations. According to the example, the values of w are 80 μm and 100 μm, respectively, the optical element 50 is made of LN and is cooled to a temperature of T=100 K during terahertz generation. For pump pulses of 100 fs, the former arrangement generates terahertz pulses of smaller amplitude and lower frequency at the edges of the beam (see FIG. 6A and its insert (b), dashed line) than in the center of the beam (see FIG. 6A and its insert (b), dotted line). In contrast, in a radiation source 100 according to the present invention, an electric field with the same time course is generated everywhere in the cross section of the pump beam 12 (see FIG. 6A, solid line). This is highly advantageous for many applications of terahertz pulses, especially when strong focusing of the terahertz beam is required. Here, the term “strong focusing” refers to a focusing with a numerical aperture in value close to 1, in harmony with literature.

[0052] A detailed description of the model underlying the derivation of each of the curves shown in FIGS. 5 and 6 goes beyond the scope of the present application; it is part of a scientific publication by the inventors to be published in the near future. However, it is apparent from FIG. 6B that a radiation source 100 comprising the setup according to the invention is suitable for generating single-cycle terahertz pulses which are free of post-oscillation. Such pulses can be advantageously used, for example, to accelerate electrically charged particles.

[0053] It is also important to note that the radiation source 100 comprising the setup according to the present invention—when using with a suitable pump laser—is also capable of producing any number of multi-cycle terahertz pulses at high efficiency.

[0054] Summary: A novel terahertz generation setup suitable for generating high-energy terahertz radiation with a periodic structure formed in the rear-side surface of a nonlinear optical medium bounded by planar front-side (entry) and rear-side surfaces has been elaborated. The greatest advantage of the obtained setup is that the nonlinear optical crystal can be used in the setup as a unit with parallel surfaces. As a result, terahertz beams with excellent beam quality and physical properties can be generated at high generation efficiency. Since the setup does not include imaging optics or a separately adjustable optical grating, the size of the pump beam and thus the energy of the terahertz pulses generated in the setup can be arbitrary in practice. The terahertz radiation source and method according to the invention based on the inventive setup is particularly advantageous in the production of high-energy terahertz radiation which requires the usage of wide pump beams.