Multi-frequency terahertz radiation source based on waveguide
Technical Field
The invention belongs to the technical field of terahertz wave application, and particularly relates to a waveguide-based multi-frequency terahertz radiation source.
Background
Terahertz waves (THz for short) mean that the frequency is 0.1-10THz (1 THz is 10)12Hz), the band of which lies between the millimetre wave and the infrared in the electromagnetic spectrum, is the transition region from photonics and electronics, macroscopic theory to microscopic theory. The terahertz wave is located at a special position, so that the terahertz wave has great scientific research value and wide application prospect in the basic research fields of physics, chemistry, astronomy, molecular spectrum, life science, medical science and the like, and the application research fields of medical imaging, environmental monitoring, material detection, food detection, radio astronomy, mobile communication, satellite communication, military radar and the like. Terahertz waves are mainly applied in the following fields:
(1) field of imaging
The transient electromagnetic field generated by the terahertz electromagnetic pulse can be directly measured by utilizing the terahertz time-domain spectroscopy technology, and the dielectric constant of a sample can be directly measured.
(2) The field of biochemistry
Because the rotation absorption spectrum of a plurality of biomacromolecules is in the terahertz frequency band, the molecular motion condition information in the reaction can be obtained by utilizing the research on the terahertz absorption spectrum of biochemical reaction. Provides a powerful means for further researching the biochemical reaction.
(3) Field of astronomy
In the universe, a large number of substances emit terahertz electromagnetic waves. Carbon (C), water (H)2O), carbon monoxide (CO), nitrogen (N)2) Oxygen (O)2) And a large number of molecules can be detected in the terahertz frequency band.
(4) Field of communications
Terahertz waves are good broadband information carriers and can carry audio or video signals for transmission. The terahertz wave is used for communication, and the wireless transmission speed of 10GB/s can be obtained, which is hundreds to thousands of times faster than the current ultra-wideband technology.
(5) The field of homeland security
In the field of homeland security, due to the non-ionization property and strong penetrability of the terahertz waves, the terahertz waves can provide long-distance and large-range early warning for hidden dangerous goods such as explosives, contraband, weapons, drugs and the like in airports, stations and the like.
The lack of terahertz sources capable of generating high-power, high-quality and high-efficiency terahertz waves and operating at room temperature with low cost is a major problem at present. At present, the terahertz wave generation method mainly comprises an electronics method and a photonics method. The electronic method is a process that the wavelength of electromagnetic radiation is generally extended from millimeter waves to a terahertz waveband, namely, the process is equivalent to a frequency increasing process, but when the frequency is greater than 1THz, the process is hindered greatly, so that the efficiency is low, and meanwhile, a terahertz wave radiation source generated by the electronic method is large in size, so that the application of the terahertz wave radiation source in many fields is limited. The main direction of the photonics method is to convert visible light or infrared light to a terahertz wave band. The method has the advantages that the generated terahertz radiation source has high coherence and directivity, but the terahertz wave generated at the present stage is low in power and efficiency.
Disclosure of Invention
The invention aims to provide a waveguide-based multi-frequency terahertz radiation source which is used for solving the problems of low power, low efficiency and the like of the existing terahertz waves.
The object of the invention is achieved in the following way:
a multi-frequency terahertz radiation source based on a waveguide comprises a first pump source, a second pump source, a first GaP waveguide GaP with different thickness distribution1A second GaP waveguide GaP2… … n-th GaP waveguide GaPnFirst parabolic mirror M1A second parabolic mirror M2… … nth parabolic mirror MnA beam combining mirror 9 and a phase delay system.
The first pump light emitted from the first pump source enters the beam combining mirror, and the second pump light emitted from the second pump source enters the beam combining mirror through the phase delay system. The first pump light and the second pump light are mixed into a mixed light beam in the beam combiner.
The mixed light passes through a telescope system and enters a first GaP waveguide GaP1In the middle, or mixed light is directly incident into the first GaP waveguide, and cascade light C is generated by cascade optical difference frequency effect1And a frequency doubling terahertz wave T1(ii) a Frequency doubling terahertz wave T1Via a first parabolic mirror M1Reflected output, cascade light C1Through a first parabolic mirror M1GaP into a second GaP waveguide2In the middle, cascade light C is generated through the cascade optical difference frequency effect2And a frequency-doubled terahertz wave T2(ii) a Frequency-doubling terahertz wave T2Via a second parabolic mirror M2Reflected output, cascade light C2By means of a second parabolic mirror M2Then the light enters the next GaP waveguide;
by analogy, cascade light Cn-1GaP incident on the n-th GaP waveguidenIn the method, cascade light C is generated through a cascade optical difference frequency effectnAnd n frequency multiplication terahertz wave Tn(ii) a n frequency multiplication terahertz wave TnThrough the nth parabolic mirror MnReflected output, cascade light CnThe GaP waveguide is incident to the next piece of GaP waveguide through the nth parabolic mirror;
the plane of light beam propagation is a plane determined by an X axis and a Z axis, the Y axis is perpendicular to the plane of light beam propagation, the initial propagation direction of first pump light emitted from the first pump source 1 is the positive direction of the X axis, the initial propagation direction of second pump light emitted from the second pump source is the negative direction of the Z axis, and the propagation directions of all terahertz waves are the negative directions of the Y axis.
The first pump light and the second pump light have different frequencies.
The first pumping source adopts a pulse laser, and the second pumping source adopts a pulse laser.
The phase delay system consists of a first reflector, a second reflector, a third reflector and a fourth reflector, and second pumping light emitted from the second pumping source enters the beam combining mirror after passing through the phase delay system consisting of the first reflector, the second reflector, the third reflector and the fourth reflector.
The first reflector, the second reflector, the third reflector and the fourth reflector are plane mirrors, and the positions and the angles of the plane mirrors are adjustable; the first reflector, the second reflector, the third reflector and the fourth reflector are used for totally reflecting the second pump light.
The first GaP waveguide GaP1A second GaP waveguide GaP2… … n-th GaP waveguide GaPnThe terahertz wave waveguide is a terahertz wave waveguide, and the equivalent refractive index of the terahertz wave in the waveguide is changed along with the change of the thickness of the waveguide. Frequency doubling terahertz wave T1Frequency-doubled terahertz wave T2… … n frequency doubling terahertz wave TnOf the first GaP waveguide GaP1A second GaP waveguide GaP2… … n-th GaP waveguide GaPnThe thickness distribution of (a) is also different. The distribution of the waveguide thickness satisfies that the phase mismatch from the 1 st order Stokes cascade difference frequency to the high order Stokes cascade difference frequency is 0 step by step along the waveguide length.
The first parabolic mirror M1A second parabolic mirror M2… … nth parabolic mirror MnThe center is provided with a small hole which only allows cascade light of each step to pass through.
And the first pump light and the second pump light which pass through the beam combiner are propagated in a collinear way.
Said light transmitted through the first parabolic mirror M1A second parabolic mirror M2… … Nth parabolic mirror MnEach of the cascade lights of (1) is a mixed light formed by mixing a plurality of cascade lights and is propagated in a collinear manner. Cascade light C1、C2……CnThe frequency difference of the cascade light of the adjacent orders is equal to one frequency multiplication terahertz wave T1Of (c) is detected.
The frequency doubling terahertz wave T1The frequency of the second pump light is equal to the frequency difference of the first pump light and the second pump light, and the frequency of the second pump light is doubled terahertz wave T2Frequency is a frequency doubling terahertz wave T1Frequency doubling, analogizing, n frequency doubling terahertz wave TnFrequency is a frequency doubling terahertz wave T1N times the frequency.
Compared with the prior art, the multi-frequency terahertz radiation source based on the waveguide has the following advantages compared with the existing terahertz radiation source based on the optical difference frequency effect:
(1) by setting the frequency difference between the two pumping lights, the terahertz waves of integral multiples of the frequency doubling terahertz waves can be obtained simultaneously.
(2) Through setting the thickness distribution of the GaP waveguide, the equivalent refractive index of the terahertz wave can be changed, the phase mismatch of Stokes cascade difference frequency is reduced, and the conversion efficiency of the terahertz wave is greatly improved.
Drawings
Fig. 1 is a schematic structural diagram of an embodiment of the present invention.
Fig. 2 is a corresponding relationship between the thickness of the first GaP waveguide and the frequency of the cascade light when the frequency of the first frequency doubling terahertz wave is equal to 0.5 THz.
Fig. 3 is a corresponding relationship between the thickness of the second GaP waveguide and the frequency of the cascade light at the frequency of the double-frequency terahertz wave equal to 1.0 THz.
Fig. 4 is a correspondence relationship between the thickness of the third block GaP waveguide and the frequency of the cascade light at the frequency of the frequency tripling terahertz wave equal to 1.5 THz.
Fig. 5 is a correspondence between the thickness of the fourth GaP waveguide and the frequency of the cascade light at a frequency of the quadruple terahertz wave equal to 2.0 THz.
Detailed Description
While the invention will be described in detail and with reference to the drawings and specific examples, it is to be understood that the invention is not limited to the precise construction and details shown and described herein, but is capable of numerous rearrangements and modifications as will now become apparent to those skilled in the art. In the present invention, unless otherwise specifically defined and limited, technical terms used herein shall have the ordinary meaning as understood by those skilled in the art to which the present invention pertains.
As shown in figure 1, the multi-frequency terahertz radiation source based on the waveguide comprises a first pump source 1, a second pump source 3, a first GaP waveguide GaP with different thickness distribution1A second GaP waveguide GaP2… … n-th GaP waveguide GaPnFirst parabolic mirror M1A second parabolic mirror M2… … nth parabolic mirror MnA beam combining mirror 9 and a phase delay system.
The first pump light 2 emitted from the first pump source 1 enters the beam combining mirror 9. The second pump light 4 emitted from the second pump source 3 enters the beam combining mirror 9 through the phase delay system. The first pump light 2 and the second pump light 4 are mixed in the beam combiner 9 to form a mixed light beam 10. The mixed light 10 is incident on the first GaP waveguide GaP via a telescope system 111In the medium or mixed light 10 is directly incident on the GaP of the first GaP waveguide1In the method, cascade light C is generated through cascade optical difference frequency1And a frequency doubling terahertz wave T1. Frequency doubling terahertz wave T1Via a first parabolic mirror M1Reflected output, cascade light C1Through a first parabolic mirror M1GaP into a second GaP waveguide2In the method, cascade light C is generated through cascade optical difference frequency2And a frequency-doubled terahertz wave T2. Frequency-doubling terahertz wave T2Via a second parabolic mirror M2Reflected output, cascade light C2By means of a second parabolic mirror M2And then incident on the next GaP waveguide. By analogy, cascade light Cn-1GaP incident on the n-th GaP waveguidenIn the method, cascade light C is generated through cascade optical difference frequencynAnd n frequency multiplication terahertz wave Tn. n frequency multiplication terahertz wave TnThrough the nth parabolic mirror MnReflected output, cascade light CnAnd the GaP waveguide is incident to the next piece of GaP waveguide through the nth parabolic mirror.
The plane of light beam propagation is a plane determined by an X axis and a Z axis, the Y axis is vertical to the plane of light beam propagation, the initial propagation direction of first pump light 2 emitted from a first pump source 1 is the X axis positive direction, the initial propagation direction of second pump light 4 emitted from a second pump source 3 is the Z axis negative direction, the propagation directions of all terahertz waves are the Y axis negative direction, and the propagation direction of all cascade light entering the next GaP waveguide is the X axis positive direction.
The purpose of one pump light passing through the phase delay system is to synchronize the phases of the two pump lights.
Frequency of the first pump light 2 and the second pump light 4The rates are different. The frequency difference of the cascade light of adjacent orders in the cascade light C1, C2 … … Cn is equal to the frequency difference of the first pump light and the second pump light, and is also equal to one frequency doubling terahertz wave T1Of (c) is detected.
The frequency doubling terahertz wave T1The frequency of the second pump light is equal to the frequency difference of the first pump light and the second pump light, and the frequency of the second pump light is doubled terahertz wave T2Frequency is a frequency doubling terahertz wave T1Frequency doubling, analogizing, n frequency doubling terahertz wave TnFrequency is a frequency doubling terahertz wave T1N times the frequency.
The phase delay system is composed of a first reflector 5, a second reflector 6, a third reflector 7 and a fourth reflector 8, and the second pump light 4 emitted from the second pump source 3 enters the beam combiner 9 through the phase delay system composed of the first reflector 5, the second reflector 6, the third reflector 7 and the fourth reflector 8. The pump light does not change the propagation direction of the light through the phase delay system, and the pump light can also pass through more than one phase delay system.
In this embodiment, the first pump source 1 is a pulse laser, the frequency of the first pump light 2 is 193.55 THz, the second pump source 3 is a pulse laser, and the frequency of the second pump light 4 is 193.05 THz. The repetition frequency of the two pump sources is 10Hz, and the single pulse energy is 20 mJ.
In this embodiment, the objective of using the telescope system is to reduce the beam to 0.02 mm. The purpose of the beam-reduction is to let the pump light pass completely through the following arrangement, and when the beam-reduction is not needed, the telescope system can be dispensed with.
In this embodiment, the first reflector 5, the second reflector 6, the third reflector 7, and the fourth reflector 8 are plane mirrors, and the positions and angles thereof are adjustable; the first mirror 5, the second mirror 6, the third mirror 7, and the fourth mirror 8 totally reflect the second pump light 4.
The thickness direction of each GaP waveguide is along the Y-axis direction, and the GaP of the first GaP waveguide1A second GaP waveguide GaP2… … n-th GaP waveguide GaPnAll are terahertz wave waveguides, and the thickness of the waveguide changes, the terahertz waves in the waveguide are equalThe effective refractive index also changes. Frequency doubling terahertz wave T1Frequency-doubled terahertz wave T2… … n frequency doubling terahertz wave TnOf the first GaP waveguide GaP1A second GaP waveguide GaP2… … n-th GaP waveguide GaPnThe thickness distribution of (a) is also different. The distribution of the waveguide thickness satisfies that the phase mismatch from the 1 st order Stokes cascade difference frequency to the high order Stokes cascade difference frequency is 0 step by step along the waveguide length. The length of the GaP waveguide is forward along the X-axis.
In this embodiment, as shown in fig. 2, when n =1, a frequency doubling terahertz wave T is generated1Is equal to 0.5 THz, a first GaP waveguide GaP1The thickness is reduced from 218 μm to 162 μm; as shown in fig. 3, when n =2, the frequency-doubled terahertz wave T2Is equal to 1.0 THz, a second GaP waveguide GaP2The thickness is reduced from 108 μm to 80 μm; as shown in fig. 4, when n =3, the frequency tripled terahertz wave T3Is equal to 1.5 THz, and a third block GaP waveguide GaP3The thickness is reduced from 71.2 μm to 53.5 μm; as shown in fig. 5, when n =4, the quadruple frequency terahertz wave T4Is equal to 2.0 THz, a fourth GaP waveguide GaP4The thickness was reduced from 52.5 μm to 39.7. mu.m. The above-described distribution of the waveguide thickness satisfies that the phase mismatch from the 1-step Stokes cascade difference frequency to the high-order Stokes cascade difference frequency is 0 step by step along the waveguide length.
In this embodiment, the first parabolic mirror M1A second parabolic mirror M2… … nth parabolic mirror MnThe center is provided with a small hole which only allows cascade light of each step to pass through.
In this embodiment, the first pump light 2 and the second pump light 4 that pass through the beam combiner 9 propagate in a collinear manner.
In this embodiment, the light is transmitted through the first parabolic mirror M1A second parabolic mirror M2… … Nth parabolic mirror MnEach of the cascade lights of (1) is a mixed light formed by mixing a plurality of cascade lights and is propagated in a collinear manner. Cascade light C1、C2……CnThe frequency difference of the cascade light of the adjacent orders is equal to one frequency multiplication terahertz wave T1I.e. 0.5 THz.
In this embodiment, the frequency-doubled terahertz wave T1Is equal to 0.5 THz, a frequency-doubled terahertz wave T2The frequency is 1.0 THz, and so on, and the frequency of the n frequency doubling terahertz wave TnFrequency is a frequency doubling terahertz wave T1N times the frequency.
The above-mentioned embodiments are merely examples and illustrations of the technical solutions of the present invention, which are convenient for those skilled in the art to understand the technical solutions of the present application, but not all embodiments, and the scope of the present invention is not limited thereto. The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features. Where combinations of features are mutually inconsistent or impractical, such combinations should not be considered as being absent and not within the scope of the claimed invention. The basic idea of the present invention is to design various modified models, formulas and parameters without any creative effort for those skilled in the art and any skilled in the art without departing from the spirit of the present invention and the general concept of the present invention. Variations, modifications, substitutions, equivalents, and variations of the embodiments may be made without departing from the principles and spirit of the invention, which should also be considered as the scope of the invention.