JP6510776B2 - Terahertz wave generator - Google Patents

Description

  The present invention relates to a terahertz wave generator.

  The terahertz wave is a type of electromagnetic wave having a frequency of approximately 0.5 THz to 3.0 THz. Terahertz waves are expected to be applied to a wide range of fields such as drug inspection, semiconductor defect detection, and electromagnetic wave communication. Methods of generating terahertz waves include a method of utilizing difference frequency generation, a method of utilizing a feature in which the oscillation spectrum of a femtosecond laser exists in a wide range, or a method of micromachining a semiconductor wafer to form an antenna element . For example, Non-Patent Document 1 describes a wavelength tunable terahertz light source. This wavelength tunable terahertz light source generates terahertz light by exciting a nonlinear optical crystal using excitation light and injection light.

  A difference frequency generation type terahertz wave generator using two types of lasers having different oscillation wavelengths has been studied. In this terahertz wave generator, for example, a laser diode (LD) pumped passive Q-switched solid laser is used as a light source of pump light, and a Fabry-Perot type wavelength tunable semiconductor laser is used as a light source of seed light. In such a terahertz wave generator, even if the longitudinal mode of the pump light is a single mode, a terahertz wave is generated under a predetermined condition if the transverse mode is a multi mode, but the characteristics of the terahertz wave are accurately There are times when it can not be evaluated. Specifically, since the peak value of the terahertz wave fluctuates with time in the wavelength band, it is difficult to accurately evaluate the average output and peak value of the terahertz wave. Therefore, in a passive Q-switched solid state laser used as pump light, a single mode is required in the longitudinal mode and the transverse mode of the emitted light.

Kawase, K. et al., “High-power, compact wavelength-tunable terahertz optical parametric light source,” Proceedings of the 59th Joint Conference of the Association of Applied Physics Proceedings, The Institute of Applied Physics, 2012, 4th, p. 253.

  In the wavelength tunable terahertz light source of Non-Patent Document 1, seed light having a circular beam profile is incident on the nonlinear optical crystal. An external resonant semiconductor laser device is used as a light source for generating seed light. Light having an elliptical beam profile is emitted from this external resonant semiconductor laser device. Therefore, the wavelength tunable terahertz light source has an optical processing system disposed between the seed light source and the nonlinear crystal. The optical processing system shapes the elliptical beam profile emitted from the semiconductor laser into a circular beam profile.

  In the technical field using such a terahertz wave generator, miniaturization of the terahertz wave generator is desired. However, a terahertz wave generator having an optical processing system for shaping a beam profile is difficult to miniaturize.

  Then, an object of this invention is to provide the terahertz wave generator which can be miniaturized.

  A terahertz wave generator according to one aspect of the present invention includes a seed light output unit that outputs seed light along a first optical axis, and a pump light output unit that outputs pump light along a second optical axis. A seed light and a pump light are input, and the seed light is input to the difference frequency generation unit, which generates a terahertz wave having a frequency corresponding to a difference frequency between the seed light and the pump light. The seed light output portion has a seed light incident surface for emitting the seed light, and the seed light output portion emits the seed light and the photonic crystal type surface emitting laser for generating the seed light. And a light contact surface that contacts the seed light incident surface.

  This terahertz wave generator includes a photonic crystal surface emitting laser as a light source of seed light. According to the photonic crystal surface emitting laser, it is possible to obtain circular seed light having a light density of Gaussian distribution in the circular emitter area. Such seed light does not have to shape the beam profile. For this reason, since the terahertz wave generator does not require an optical processing system for shaping a beam profile, it is possible to reduce the number of parts. Therefore, the terahertz wave generator can be miniaturized. Furthermore, since it is not necessary to dispose an optical processing system between the seed light output unit and the difference frequency generation unit, the light contact surface of the seed light output unit should be in contact with the seed light incidence surface of the difference frequency generation unit. Can. That is, there is no need to provide a space between the seed light output unit and the difference frequency generation unit. Therefore, since it becomes possible to make small the component space | interval which comprises a terahertz wave generator, the further miniaturization is attained.

  The difference frequency generation unit has a non-linear optical crystal, and the non-linear optical crystal includes a seed light incident surface, a pump light incident surface, and a light mixing unit in which the seed light and the pump light intersect at a predetermined crossing angle. It may be included. According to this configuration, the positional relationship between the seed light output unit and the pump light output unit is defined by the nonlinear optical crystal alone. Therefore, since the additional component for defining the positional relationship between the seed light output unit and the pump light output unit is not necessary, the configuration of the terahertz wave generator can be simplified.

  The seed light output unit outputs the seed light so that the first optical axis is orthogonal to the light contact surface, and the angle between the seed light incident surface and the pump light incident surface is set based on the intersection angle It may be done. According to this configuration, the positional relationship between the seed light output unit and the pump light output unit is defined by the seed light incident surface and the pump light incident surface. As a result, since the seed light output unit in which the first optical axis is orthogonal to the light contact surface can be used, the configuration of the seed light output unit is simplified and the size is further reduced. Therefore, the terahertz wave generator can be easily miniaturized.

  The seed light incident surface and the pump light incident surface may be included in the same plane, and the angle between the first optical axis and the light contact surface may be set based on the intersection angle. According to this configuration, since the seed light incident surface and the pump light incident surface are included in the same plane, the non-linear optical crystal constituting the difference frequency generation unit is processed to form the seed light incident surface and the pump light It is not necessary to form the incident surface in a predetermined angular relationship. Therefore, the components of the terahertz wave generator can be easily prepared.

  The difference frequency generation unit includes a nonlinear optical crystal and a light transmissive optical component disposed on the first optical axis, and the nonlinear optical crystal includes a pump light incident surface, seed light and pump light. The light transmissive optical component may include a seed light incident surface, which includes a light mixing section intersecting at a predetermined crossing angle. According to this configuration, the seed light output unit in which the first optical axis is orthogonal to the light contact surface is used. Further, it is not necessary to form the seed light incident surface and the pump light incident surface in the relationship of a predetermined angle. Therefore, the components of the terahertz wave generator can be easily prepared.

  The seed light output unit outputs the seed light so that the first optical axis is orthogonal to the light contact surface, and the angle between the seed light incident surface and the pump light incident surface is set based on the intersection angle It may be done. According to this configuration, the positional relationship between the seed light emitting unit and the pump light emitting unit can be defined with a simple configuration.

  The crossing angle may be a phase matching angle at which the seed light and the pump light satisfy the phase matching condition. According to this angle, the terahertz wave can be generated efficiently.

  A terahertz wave generator according to another aspect of the present invention includes a seed light output unit that outputs seed light along a first optical axis, and a pump light output unit that outputs pump light along a second optical axis. And a difference frequency generation unit that receives the seed light and the pump light and generates a terahertz wave having a frequency corresponding to the difference frequency between the seed light and the pump light, and the difference frequency generation unit receives the seed light The seed light output surface has an external resonant type surface emitting laser that generates seed light and the seed light is emitted. And a light contact surface that contacts the seed light incident surface.

  The seed light output unit of this terahertz wave generator has an external resonant type surface emitting laser. According to the laser light emitted from the external cavity surface emitting laser, the optical processing system for shaping the beam profile is unnecessary, so it is possible to reduce the number of parts. Therefore, the terahertz wave generator can be miniaturized. Furthermore, since it is not necessary to dispose an optical processing system between the seed light output unit and the difference frequency generation unit, it is possible to reduce the interval between components constituting the terahertz wave generation device. Therefore, further miniaturization is possible.

  According to the present invention, a terahertz wave generator that can be miniaturized is provided.

It is a figure which shows the structure of the terahertz wave generator concerning 1st Embodiment. It is a figure which shows the structure of the seed light output part shown by FIG. It is a figure which shows the structure of the terahertz wave generator concerning 2nd Embodiment. It is a figure which shows the structure of the terahertz wave generator concerning 3rd Embodiment. It is a figure which shows the structure of the seed light output part shown by FIG. FIG. 7 is a diagram showing a configuration of a terahertz wave generator according to a first modification. FIG. 7 is a diagram showing a configuration of a terahertz wave generator according to a second modification. (A) is a figure which shows the structure of the seed light output part shown by FIG. 6, (b) is a figure which shows the structure of the seed light output part shown by FIG.

First Embodiment
Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

As shown in FIG. 1, the terahertz wave generator 1 includes a seed light output unit 2, a pump light output unit 3, and a difference frequency generation unit 4. The terahertz wave generator 1 generates a terahertz wave using the principle of difference frequency generation. Specifically, the terahertz wave generator 1 optically mixes the seed light SL and the pump light PL inside the difference frequency generator 4. Then, a terahertz wave T having a frequency (ω _T = | ω _S −ω _P |) corresponding to the difference frequency between the frequency ω _S of the seed light SL and the frequency ω _P of the pump light PL is generated.

  As shown in FIG. 2, the seed light output unit 2 outputs the seed light SL along the first optical axis L1. The seed light output unit 2 has a photonic crystal surface emitting laser 6, a cap 7, and a stem 8. The term "surface emitting laser" as used in the present embodiment refers to a laser having a structure in which light is emitted perpendicularly to the semiconductor substrate.

  Photonic Crystal Surface Emitting Laser (hereinafter, also referred to as “PCSEL”) 6 is a vertical resonance surface emitting laser provided with a photonic crystal. In a surface emitting laser, a photonic crystal is a layer formed of nanostructures in which materials having different refractive indices are periodically arranged, and a plurality of holes are periodically formed in a compound semiconductor layer such as GaAs, for example. A structure in which a plurality of holes are used as they are, or another compound semiconductor having a different refractive index from the compound semiconductor material based on the plurality of holes is embedded, and is disposed between the active layer and the cladding layer ing. The light confined in the active layer oscillates at the resonance in the photonic crystal, and a part of the light is diffracted in the vertical direction by the second-order Bragg diffraction to cause laser oscillation. Therefore, the photonic crystal determines the wavelength of the resonating laser light and generates the laser light by the resonance of the light. According to the photonic crystal, a stable oscillation state of laser light can be obtained. Further, in PCSEL6, since the emitter shape of the element structure involved in the laser oscillation is a perfect circle, it is possible to obtain output light having a circular beam profile. Also, the light density distribution of the output light is uniform in the form of concentric circles.

  The PCSEL 6 is attached to the chip carrier 9. The chip carrier 9 is attached to the heat sink 11. The heat sink 11 is attached to the stem 8. The heat sink 11 has a carrier mounting surface 11 a to which the chip carrier 9 is attached and a stem mounting surface 11 b fixed to the stem 8. The carrier mounting surface 11a is parallel to the stem mounting surface 11b.

  The cap 7 accommodates the PCSEL 6 and the like in its inside. The inside of the cap 7 is filled with nitrogen gas and sealed from the outside. The lower end edge 7 a of the cap 7 is fixed to the stem 8. The upper end surface (light contact surface) 7 b of the cap 7 is parallel to the stem 8. The upper end face 7b has a light exit window 7c. The light emission window 7c is configured such that the hole formed on the upper end surface 7b is closed by the transparent optical member 7d to which the AR coating is applied. Further, the upper end surface 7b is in contact with the difference frequency generation unit 4 and is adhesively fixed by an optical adhesive (see FIG. 1). The stem 8 is provided with a plurality of lead pins 12. A current is supplied to the PCSEL 6 through the lead pin 12.

  Here, the stem mounting surface 11 b of the heat sink 11 is fixed to the mounting surface 8 a of the stem 8. The carrier mounting surface 11a is parallel to the stem mounting surface 11b. The chip carrier 9 carrying the PCSEL 6 is attached to the carrier attachment surface 11 a. The PCSEL 6 emits the seed light SL in the direction orthogonal to the carrier attachment surface 11 a. That is, the first optical axis L1 is orthogonal to the mounting surface 8a. The upper end surface 7 b of the cap 7 is parallel to the mounting surface 8 a of the stem 8. Therefore, the first optical axis L1 is orthogonal to the upper end surface 7b.

  The seed light output unit 2 is mechanically and electrically connected to the substrate 13. The substrate 13 has a control element for driving the PCSEL 6 and the like. The substrate 13 also has a heater 13 a for controlling the temperature of the PCSEL 6.

  As shown in FIG. 1, the pump light output unit 3 outputs the pump light PL along the second optical axis L2. The pump light output unit 3 is, for example, a passive Q-switched laser (Nd: YAG laser). The pump light output unit 3 emits pump light in which both the longitudinal mode and the transverse mode are single mode. The pump light PL has a pulse width of 100 psec to 1000 psec (for example, 450 psec), and energy per pulse is, for example, 500 μJ / pulse. Also, the beam quality M2 of the pump light PL is, for example, 1.5 or less.

The difference frequency generator 4 has a non-linear optical crystal 5. Examples of the nonlinear optical crystal 5 include MgO-doped LiNbO ₃ crystal (MgO: LN crystal), LiTaO ₃ crystal (sLT crystal), ZnTe, GaP, GaSe, and the like, which have a constant ratio composition resistant to optical damage. The difference frequency generation unit 4 has a substantially rectangular parallelepiped shape in which a part of the end face 5a is cut off. The nonlinear optical crystal 5 has a seed light incident surface 5b, a pump light incident surface 5c, a light mixing portion 17, and a light emitting surface 5d.

  The seed light incident surface 5b is a slope formed by cutting off a part of the end surface 5a. An optical polishing process is performed on the seed light incident surface 5b. The seed light output unit 2 is bonded to the seed light incident surface 5b. Specifically, the upper end surface 7b of the cap 7 is adhered. Here, the first optical axis L1 is orthogonal to the upper end surface 7b. Then, the first optical axis L1 is also orthogonal to the seed light incident surface 5b in contact with the upper end surface 7b.

  The pump light incident surface 5c is a portion left uncut at the end surface 5a. Therefore, the corner A2 between the pump light incident surface 5c and the seed light incident surface 5b forms a predetermined angle φ. The predetermined angle φ will be described in detail later. The pump light PL is perpendicularly incident on the pump light incident surface 5c. That is, the second optical axis L2 is orthogonal to the pump light incident surface 5c.

The first optical axis L1 is orthogonal to the seed light incident surface 5b. The second optical axis L2 is orthogonal to the pump light incident surface 5c. The corner A2 between the pump light incident surface 5c and the seed light incident surface 5b is an angle φ. Therefore, since the first optical axis L1 and the equal phase surface of the second optical axis L2 intersect on their extension line, the first light axis L1 and the second optical axis L2 are mutually An action area is formed, and a terahertz wave is generated. This interaction area is the light mixing unit 17. In the light mixing unit 17, the first optical axis L1 and the second optical axis L2 intersect at a predetermined intersection angle. The crossing angle is a phase matching angle θ _PM that satisfies a phase matching condition between the seed light SL and the pump light PL. The phase matching angle θ _PM is determined based on the law of conservation of momentum. In order to make the first optical axis L1 cross the second optical axis L2 with the phase matching angle θ _PM , the seed light incident surface 5b is only at the angle φ with respect to the end surface 5a including the pump light incident surface 5c. You need to tilt. The relationship between the phase matching angle θ _PM and the angle φ is φ = (180−θ _PM ) [deg].

  The light emission surface 5d is a surface from which the pump light and the seed light transmitted without being phase-matched are emitted in the phase-matched region, and is formed on the end surface opposite to the pump light incidence surface 5c. That is, the light emitting surface 5d is on the second optical axis L2 and is orthogonal to the second optical axis L2.

  The terahertz wave generator 1 further includes a control unit 19. The control unit 19 controls the operation of the seed light output unit 2 and the pump light output unit 3. For example, the control unit 19 controls the intensity and the wavelength of the seed light SL and the pump light PL. The terahertz wave generator 1 controls the wavelength of the terahertz wave T by controlling the wavelength of the seed light SL. The wavelength of the output light of the PCSEL 6 that generates the seed light SL changes with the element temperature. Therefore, the control unit 19 controls the wavelength of the seed light SL by controlling the temperature of the PCSEL 6. For example, according to the control unit 19 and the heater 13a, it is possible to control the temperature of the PCSEL 6 in increments of 0.1 ° C.

  In the edge emitting semiconductor laser, one of the X direction and the Y direction of the beam profile has a shape longer than the other. Therefore, the beam profile of the laser beam is shaped using an optical system having a plurality of lenses. However, it is difficult to completely round the beam profile in the shaping process by the optical system. Further, the light density distribution of the laser light is also concentrically nonuniform distribution. In order to improve this nonuniform light density distribution, the laser light is passed through an optical fiber and light mixed.

  On the other hand, the terahertz wave generator 1 includes the PCSEL 6 as a light source of the seed light SL. According to PCSEL6, it is possible to obtain circular seed light SL having a uniform light density. Such seed light SL does not have to be shaped in beam profile. Therefore, since the terahertz wave generator 1 does not require an optical processing system for shaping a beam profile, the number of parts can be reduced. Therefore, the terahertz wave generator 1 can be miniaturized.

Further, the phase matching angle θ _{PM at which} the pump light PL and the seed light SL intersect is very small. Therefore, the distance from the seed light output unit 2 and the pump light output unit 3 to the light mixing unit 17 becomes long. Then, it may occur that the seed light output unit 2 blocks the light path of the pump light PL and the pump light output unit 3 blocks the light path of the seed light SL.

  On the other hand, since it is not necessary to dispose an optical processing system between the seed light output unit 2 and the difference frequency generation unit 4, the upper end surface 7 b of the seed light output unit 2 is on the seed light incident surface 5 b of the difference frequency generation unit 4. It can be made to abut. That is, since there is no need to provide a space between the seed light output unit 2 and the difference frequency generation unit 4, the distance from the seed light output unit 2 and the pump light output unit 3 to the light mixing unit 17 can be shortened. it can. Therefore, the optical paths of the seed light SL and the pump light PL are not blocked. Furthermore, since it is possible to reduce the distance between the components constituting the terahertz wave generator 1, further downsizing can be achieved.

  Further, in the terahertz wave generator 1, the positional relationship between the seed light output unit 2 and the pump light output unit 3 is defined by a single nonlinear optical crystal. Specifically, the positional relationship between the seed light output unit 2 and the pump light output unit 3 is defined by the seed light incident surface 5 b and the pump light incident surface 5 c. As a result, the additional components for defining the positional relationship between the seed light output unit 2 and the pump light output unit 3 become unnecessary, and the configuration of the seed light output unit 2 becomes simple. Therefore, the terahertz wave generator 1 can be further miniaturized.

<Example>
Hereinafter, an example of the drive conditions of the terahertz wave generator 1 will be described. The frequency band of the terahertz wave T output from the terahertz wave generator 1 is 0.5 THz to 3.0 THz. The wavelength of the pump light PL is a constant value (1064.2 nm). Then, in order to achieve a variable wavelength range (0.5 THz to 3.0 THz) of the terahertz wave T, the wavelength of the seed light SL is changed in the range of 1075.65 nm to 1066.10 nm. For example, when the wavelength of the seed light SL is 1068.37 nm, the frequency of the terahertz wave T is 1.10 THz. When the wavelength of the seed light SL is 1068.41 nm, the frequency of the terahertz wave T is 1.11 THz. Therefore, if the frequency of the terahertz wave T is controlled in 0.01 THz steps, it is necessary to control the wavelength of the seed light SL in approximately 0.04 nm or less.

  Here, in the semiconductor laser using the external resonant grating element according to the comparative example, it is difficult to control the wavelength of the emitted light with high precision to two decimal places. On the other hand, as described above, the temperature control accuracy of the PCSEL 6 by the control unit 19 is 0.1 ° C. When this accuracy is converted into a wavelength, the wavelength control accuracy of the PCSEL 6 by the control unit 19 is 0.007 nm / K. Therefore, according to the above-described driving conditions, it is possible to control the frequency of the terahertz wave T in steps of, for example, 0.01 THz.

  The wavelength-temperature characteristic of PCSEL 6 that generates seed light SL is, for example, 0.07 nm / K. Therefore, when the temperature control range is set to 40 ° C., the wavelength band (1075.65 nm to 1066.10 nm) required for the seed light SL can be realized by providing three PCSELs having different central wavelengths. When the temperature control range is set to 120 ° C., a wavelength band required by one PCSEL can be realized.

Second Embodiment
Next, as shown in FIG. 3, the terahertz wave generator 1A according to the second embodiment will be described. The terahertz wave generator 1A is different from the terahertz wave generator 1 according to the first embodiment in that the difference frequency generator 4A includes the light transmissive optical component 21. Further, the terahertz wave generator 1A is different from the terahertz wave generator 1 according to the first embodiment in that the nonlinear optical crystal 22 of the difference frequency generator 4A is not cut out and processed. The other configuration is the same as that of the terahertz wave generator 1 according to the first embodiment. Hereinafter, the difference frequency generation unit 4A will be described in detail.

  The difference frequency generation unit 4A includes a non-linear optical crystal 22 and a light transmissive optical component 21. The nonlinear optical crystal 22 is made of the same material as the nonlinear optical crystal 5 of the first embodiment. The non-linear optical crystal 22 is not processed so that a part of the end face 22a is cut off. The light transmissive optical component 21 is bonded to a portion corresponding to the cut-off portion in the first embodiment. That is, the light transmissive optical component 21 is fixed to the end face 22a including the pump light incident face 22c.

The light transmissive optical component 21 fixes the seed light output unit 2 to the nonlinear optical crystal 22. Specifically, the attitude of the seed light output unit 2 such that the first optical axis L1 of the seed light output unit 2 intersects the second optical axis L2 at the phase matching angle θ _PM that satisfies the phase matching condition. Hold. That is, in the difference frequency generator 4A according to the second embodiment, the light transmissive optical component 21 has the seed light incident surface 21a, and the nonlinear optical crystal 22 has the pump light incident surface 22c.

The light transmissive optical component 21 is made of a material that is transparent to the seed light SL. The light transmissive optical component 21 has a triangular prism shape whose cross section is a right triangle. The seed light output unit 2 is in contact with and bonded to the seed light incident surface 21 a which is a slope of the light transmissive optical component 21. Further, the bottom surface 21 b opposite to the seed light incident surface 21 a is in contact with and bonded to the end surface 22 a of the nonlinear optical crystal 22. The corner A3 between the seed light incident surface 21a and the bottom surface 21b is set based on the phase matching angle θ _PM that satisfies the phase matching condition. The triangle formed by the bottom surface 21b, the seed light incident surface 21a, and the first optical axis L1 is similar to the triangle formed by the first optical axis L1, the second optical axis L2, and the end face 22a. is there. Therefore, the corner A3 between the bottom surface 21b of the light transmissive optical component 21 and the seed light incident surface 21a corresponds to the corner A1 between the first optical axis L1 and the second optical axis L2. Therefore, when the corner A1 between the first optical axis L1 and the second optical axis L2 is the phase matching angle θ _PM , a material having the same refractive index as the light transmissive optical component 21 and the nonlinear optical crystal 22 In this case, the corner A3 is also the phase matching angle θ _PM . If the light transmissive optical component 21 and the non-linear optical crystal 22 are materials having different refractive indexes, the corner portion A3 has an angle according to Snell's law.

  The terahertz wave generator 1A can be miniaturized as in the terahertz wave generator 1 according to the first embodiment. Further, in the terahertz wave generator 1A, the seed light output unit 2 in which the first optical axis L1 is orthogonal to the upper end surface 7b is used. Further, the components of the terahertz wave generator 1A can be easily prepared only by forming the seed light incident surface 21a and the pump light incident surface 22c in a predetermined angle relationship.

Third Embodiment
Next, as shown in FIG. 4, the terahertz wave generator 1B according to the third embodiment will be described. The terahertz wave generator 1B is different from the terahertz wave generator 1 according to the first embodiment in the emission direction of the seed light SL in the seed light output unit 2A. The terahertz wave generator 1B is different from the terahertz wave generator 1 according to the first embodiment in that the nonlinear optical crystal 22 of the difference frequency generator 4B is not cut out and processed. The other configuration is the same as that of the terahertz wave generator 1 according to the first embodiment. The seed light output unit 2A and the difference frequency generation unit 4B will be described in detail below.

In the seed light output unit 2A, the emission direction of the seed light SL (that is, the first optical axis L1) is not orthogonal to the upper end surface 7b of the cap 7. That is, the first optical axis L1 is inclined with respect to the upper end surface 7b. The corner A4 between the normal line L3 of the upper end surface 7b and the first optical axis L1 is a complex angle of the corner A1 between the first optical axis L1 and the second optical axis L2. Therefore, when the corner A1 between the first optical axis L1 and the second optical axis L2 is the phase matching angle θ _PM , the corner A4 is also set to the phase matching angle θ _PM .

  As shown in FIG. 5, the seed light output unit 2 </ b> A has a slope base 23. The inclined base 23 is disposed between the stem 8 and the heat sink 11. The inclined base 23 has a stem mounting surface 23a fixed to the mounting surface 8a and a heat sink mounting surface 23b opposite to the stem mounting surface 23a. The heat sink mounting surface 23b is not parallel to the stem mounting surface 23a.

The corner A5 (see FIG. 5B) between the stem mounting surface 23a and the heat sink mounting surface 23b is set based on the phase matching angle θ _PM . The angle A5 formed by the stem mounting surface 23a and the heat sink mounting surface 23b is an angle defined by Snell's law with respect to the angle A1 formed by the first optical axis L1 and the second optical axis L2 or the end face 22a. ing. That is, when the corner A1 between the first optical axis L1 and the second optical axis L2 is the phase matching angle θ _PM , the corner A5 is an angle defined by Snell's law, and the phase matching angle θ is It will not be _PM .

As shown in FIG. 4, the non-linear optical crystal 22 is not processed so that a part of the end face 22 a is cut off. The seed light incident surface 22 b is set in a portion corresponding to the cut-off portion in the first embodiment. That is, in the present embodiment, the end face 22a includes the seed light incident surface 22b and the pump light incident surface 22c. Then, as described above, the first optical axis L1 of the seed light output unit 2A is inclined with respect to the upper end surface 7b. Therefore, if the upper end face 7b of the seed light output part 2A is brought into contact with the end face 22a of the non-linear optical crystal 22 and fixed, the first optical axis L1 and the second light in the light mixing part 17 of the non-linear optical crystal 22 are fixed. The axis L2 intersects with the phase matching angle θ _PM that satisfies the phase matching condition.

  The terahertz wave generator 1B can be miniaturized as in the terahertz wave generator 1 according to the first embodiment. Further, in the terahertz wave generator 1B, since the seed light incident surface 22b and the pump light incident surface 22c are included in the same plane, the nonlinear optical crystal 22 constituting the difference frequency generation unit 4 is processed, It is not necessary to form the seed light incident surface 22b and the pump light incident surface 22c in a predetermined angle relationship. Therefore, the components of the terahertz wave generator 1B can be easily prepared.

  The present invention is not limited to the embodiments described above, and various modifications can be made without departing from the scope of the present invention.

<Modification 1>
As shown in FIG. 6, the seed light output unit 2B of the terahertz wave generator 1C is an external cavity surface emitting laser (also referred to as a vertical cavity surface emitting laser, referred to as Vertical External Cavity Surface Emitting Laser: VECSEL). May be included. As shown in FIG. 8A, the external cavity surface emitting laser does not form a Bragg reflector equivalent to an output mirror of a commonly called surface emitting laser (VCSEL: Vertical Cavity Surface Emitting Laser). An external mirror is provided as a separate part. Although the surface emitting laser device (hereinafter referred to as a semiconductor chip) 26 having no Bragg reflector can not oscillate by itself, the semiconductor chip 26 and the emitting mirror 27 separate from the semiconductor chip 26 are predetermined on the heat sink. By arranging the heat sink on the heat sink at intervals, and substituting a Bragg reflector for the external mirror, the resonator length becomes very long compared to a general surface emitting laser, and the beam can be emitted with a fairly narrow spread angle. . Further, the seed light output unit 2B has a heat sink 11 for supporting the semiconductor chip 26, a stem 8 for supporting the heat sink 11, and a cap 28 for housing the semiconductor chip 26 and the emission mirror 27. The semiconductor chip 26 is fixed to the mounting surface 8 a of the stem 8 via the heat sink 11. A light emission window 28 b from which laser light is emitted is formed on the upper end surface 28 a of the cap 28. The light exit window 28 b is closed by a transparent optical member 28 c having an AR coating. The emission mirror 27 is disposed on the upper end surface 7 b side inside the cap 28. Further, between the semiconductor chip 26 and the emission mirror 27, a Brewster material 29 for polarizing the laser light is disposed.

  In the seed light output unit 2B having the external cavity surface emitting laser, the light generated in the light emitting unit resonates between the emission mirror 27 and the reflection mirror, and the laser light is emitted from the light emission window 28b to the outside. According to such a seed light output unit 2B, it is possible to suitably obtain seed light having a circular beam profile.

<Modification 2>
As shown in FIG. 7, the seed light output unit 2C of the terahertz wave generator 1D may have an external cavity surface emitting laser different from that of the first modification. In the seed light output unit 2C, an emission mirror 34 on the emission side is formed on the seed light incident surface 5b of the nonlinear optical crystal 5. As shown in FIG. 8B, the external cavity surface emitting laser includes a heat sink 30, a semiconductor chip 31 and a spacer 32 disposed on the heat sink 30, and a lead 33. The light generated in the semiconductor chip 31 resonates between a reflection mirror (not shown) included in the semiconductor chip 31 and an emission mirror 34 formed on the seed light incident surface 5 b, and is input into the nonlinear optical crystal 5. . According to such a seed light output unit 2C, it is possible to suitably obtain seed light having a circular beam profile.

1, 1A, 1B, 1C, 1D: terahertz wave generator, 2, 2A, 2B, 2C: seed light output unit, 3: pump light output unit, 4, 4A, 4B: difference frequency generation unit, 5, 22 Non-linear optical crystal, 5b, 22b: Seed light incident surface, 5c, 22c: Pump light incident surface, 6: Photonic crystal surface emitting laser, 7b: Upper end surface (light contact surface), L1: First optical axis, L2 ... second optical axis, PL ... pump light, SL ... seed light, T ... terahertz wave, θ _PM ... phase matching angle.

Claims (5)

A seed light output unit that outputs seed light along the first optical axis;
A pump light output unit that outputs pump light along a second optical axis;
A difference frequency generation unit which receives the seed light and the pump light and generates a terahertz wave having a frequency corresponding to a difference frequency between the seed light and the pump light;
The difference frequency generation unit has a seed light incident surface on which the seed light is incident, and a pump light incident surface on which the pump light is incident;
The seed light output unit is a photonic crystal surface emitting laser that generates the seed light.
And a light contact surface which emits the seed light and abuts on the seed light incident surface;
The difference frequency generation unit has a non-linear optical crystal,
The non-linear optical crystal includes the seed light incident surface, the pump light incident surface, and a light mixing unit in which the seed light and the pump light intersect at a predetermined intersection angle.
The seed light output unit outputs the seed light so that the first optical axis is orthogonal to the light contact surface,
The angle which the said seed light entrance plane and the said pump light entrance plane make is set based on the said crossing angle, THz wave generator. A seed light output unit that outputs seed light along the first optical axis;
A pump light output unit that outputs pump light along a second optical axis;
A difference frequency generation unit which receives the seed light and the pump light and generates a terahertz wave having a frequency corresponding to a difference frequency between the seed light and the pump light;
The difference frequency generation unit has a seed light incident surface on which the seed light is incident, and a pump light incident surface on which the pump light is incident;
The seed light output unit is a photonic crystal surface emitting laser that generates the seed light.
And a light contact surface which emits the seed light and abuts on the seed light incident surface;
The difference frequency generation unit includes a non-linear optical crystal and a light transmissive optical component disposed on the first optical axis,
The non-linear optical crystal includes the pump light incident surface, and a light mixing unit in which the seed light and the pump light intersect at a predetermined crossing angle,
The light transmissive optical component includes the seed light incident surface, and
The seed light output unit outputs the seed light so that the first optical axis is orthogonal to the light contact surface,
The angle which the said seed light entrance plane and the said pump light entrance plane make is set based on the said crossing angle, THz wave generator.   The terahertz wave generation device according to claim 1, wherein the crossing angle is a phase matching angle at which the seed light and the pump light satisfy a phase matching condition. A seed light output unit that outputs seed light along the first optical axis;
A pump light output unit that outputs pump light along a second optical axis;
A difference frequency generation unit which receives the seed light and the pump light and generates a terahertz wave having a frequency corresponding to a difference frequency between the seed light and the pump light;
The difference frequency generation unit has a seed light incident surface on which the seed light is incident, and a pump light incident surface on which the pump light is incident;
The seed light output unit includes an external cavity surface emitting laser that generates the seed light, and a light contact surface that emits the seed light and that abuts on the seed light incident surface.
The difference frequency generation unit has a non-linear optical crystal,
The non-linear optical crystal includes the seed light incident surface, the pump light incident surface, and a light mixing unit in which the seed light and the pump light intersect at a predetermined intersection angle.
The seed light output unit outputs the seed light so that the first optical axis is orthogonal to the light contact surface,
The angle which the said seed light entrance plane and the said pump light entrance plane make is set based on the said crossing angle, THz wave generator. A seed light output unit that outputs seed light along the first optical axis;
A pump light output unit that outputs pump light along a second optical axis;
A difference frequency generation unit which receives the seed light and the pump light and generates a terahertz wave having a frequency corresponding to a difference frequency between the seed light and the pump light;
The difference frequency generation unit has a seed light incident surface on which the seed light is incident, and a pump light incident surface on which the pump light is incident;
The seed light output unit includes an external cavity surface emitting laser that generates the seed light, and a light contact surface that emits the seed light and that abuts on the seed light incident surface.
The difference frequency generation unit includes a non-linear optical crystal and a light transmissive optical component disposed on the first optical axis,
The non-linear optical crystal includes the pump light incident surface, and a light mixing unit in which the seed light and the pump light intersect at a predetermined crossing angle,
The light transmissive optical component includes the seed light incident surface, and
The seed light output unit outputs the seed light so that the first optical axis is orthogonal to the light contact surface,
The angle which the said seed light entrance plane and the said pump light entrance plane make is set based on the said crossing angle, THz wave generator.

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