CN111697414A - System and method for generating terahertz waves by exciting air plasma through three-color field laser - Google Patents
System and method for generating terahertz waves by exciting air plasma through three-color field laser Download PDFInfo
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Abstract
The utility model provides a system for three colour field laser arouses air plasma to produce terahertz wave, it includes laser instrument, spectroscope, optical parametric amplifier, first BBO crystal, first dichroic mirror, first electronic translation device, first speculum, half wave plate, second mirror, decay piece, second BBO crystal, 400nm filter, third speculum, fourth speculum, electronic translation device of second, fifth speculum, second dichroic mirror, first focusing lens, second focusing lens and first off-axis parabolic reflecting mirror. The method utilizes the fitting of the multicolor laser field with determined wavelength, amplitude and phase to obtain the electromagnetic waveform which is as close to an ideal sawtooth waveform as possible, and has higher terahertz energy conversion efficiency compared with the traditional mode of exciting air plasma to generate terahertz waves by using a bicolor field, thereby being capable of obtaining a terahertz source with higher power. The terahertz wave generated by the invention has stronger energy and wider spectrum, is beneficial to spectral measurement, and has stronger scientific research and practical application values.
Description
Technical Field
The invention relates to the technical field of terahertz waves and lasers, in particular to a system and a method for generating terahertz waves by exciting air plasma with three-color field laser.
Background
The technology of focusing an ultra-short laser pulse in air to directly generate terahertz waves has attracted extensive attention in recent years and has obtained a lot of excellent experimental research results and theoretical research results.
In previous researches, a monochromatic field with the wavelength of 800nm and the long wavelength (1200nm-1600nm) excites air plasma to generate terahertz waves; the BBO crystal is used for generating the second harmonic wave with the wavelength of 800nm and the long wavelength and is mixed with the second harmonic wave to focus and generate the terahertz wave, and the extraordinary proportion of the mixed bicolor field with different wavelengths (such as the wavelength ratio of 2: 3 and 1: 4) is focused and excited by air plasma to generate the terahertz wave, and the like, so that the research progress is good, and the development is continuously carried out towards the high terahertz generation efficiency.
The generation of terahertz by three-color fields and even multi-color fields is a necessary way to obtain terahertz sources with higher power and wider frequency spectrum. In terahertz generation by laser focusing air, what is crucial to the generated terahertz energy is the obvious asymmetry of the pump waveform relative to the field extremum, which determines the electron drift velocity. The superposed field with the sawtooth-shaped time domain waveform can promote the tunnel induced photocurrent to trigger to generate the highest terahertz wave signal, and the electric field waveform optimizing the free electron trajectory can be obtained by using the multi-frequency laser pulse, so that electrons can obtain the maximum drift velocity. This can make the conversion efficiency of terahertz improve to 2%, compare with the two-color pulse of standard, can improve terahertz conversion efficiency in principle and reach 2 orders of magnitude. However, at present, no method for improving the conversion efficiency of the terahertz wave and obtaining a terahertz source with higher power by using the principle is particularly practicable.
Disclosure of Invention
In the mode of generating terahertz by exciting air plasma by laser, the determining factor of terahertz generation efficiency is the obvious asymmetry of a pump light waveform relative to a field extreme value, which determines the drift velocity of electrons, namely if an electric field is an asymmetric field, the total motion effect of ionized free electrons in the electric field is the movement towards one direction, terahertz can be generated, and the higher the net current of the direction is, the higher the terahertz intensity can be obtained. The document [ p.gonzalez de alazamartinez, i.babushkin, l.berge, s.skupin, e.cabrera-Granado, c.kohler, u.morgrener, a.husakou, and j.herrmann, phys.rev.lett.114,183901(2015) ] discloses the following formula:
wherein, UTHz: terahertz energy, omegaCO: cutoff terahertz frequency, ω: the frequency of the terahertz waves is set to be terahertz,
at t ═ tnNet current, p, at a time related to ionizationn: photon ionization rate, vf(tn): free electron drift rate, n: at time n.
As can be seen from the formula, the larger the drift velocity of electrons is, the higher the energy for generating terahertz is under the same pump light power condition. Among all available laser field waveforms, the field with the sawtooth-shaped time domain waveform has the greatest asymmetry, and the closer the sawtooth waveform is to the ideal, the higher the terahertz conversion efficiency is. A sawtooth-shaped time domain waveform pump light source is obtained by utilizing multi-color field laser fitting, the more laser fields with different frequencies, the closer the obtained fitted waveform is to an ideal sawtooth wave, and the larger the generated terahertz power is.
The Fourier series expansion formula of the periodic sawtooth wave is
Wherein, A: amplitude of sawtooth wave, T1: period of sawtooth wave, omega1，2，3...: … fundamental frequency, second harmonic, third harmonic
Therefore, in order to obtain the ideal sawtooth waveform as much as possible, the frequency of each light wave is required to be a multiple relation, the invention selects long wavelength (such as 1200-1600nm) laser, and superposes the frequency of the laser by two, three, four, etc., and the sawtooth waveform is formed by fitting by controlling the amplitude and phase of the laser. The amplitude ratio of the fundamental frequency wave, the frequency doubling wave, the frequency tripling wave and the frequency quadrupling wave … … is
Controlling the initial phase of each light wave to be
The polarization directions of the light waves are the same.
The invention provides a system and a method for generating terahertz waves by exciting air plasmas through three-color field laser, which are used for obtaining a terahertz source with higher power.
In order to achieve the above object, the present invention provides a system for generating terahertz waves by exciting air plasma with three-color field laser, which includes a laser, a beam splitter, an optical parametric amplifier, a first BBO crystal, a first dichroic mirror, a first electric translation device, a first reflector, a half-wave plate, a second reflector, an attenuator, a second BBO crystal, a 400nm filter, a third reflector, a fourth reflector, a second electric translation device, a fifth reflector, a second dichroic mirror, a first focusing lens, a second focusing lens, and a first off-axis parabolic reflector, wherein:
the laser is used for emitting laser with the wavelength of 800nm, the laser with the wavelength of 800nm obtains a first light beam and a second light beam after passing through the spectroscope,
the first light beam outputs signal light with the wavelength of 1200nm after passing through an optical parametric amplifier, part of the signal light with the wavelength of 1200nm is unchanged in wavelength after passing through a first BBO crystal, the other part of the signal light with the wavelength of 1200nm is converted into second harmonic signal light with the wavelength of 600nm, then the first dichroic mirror splits the signal light with the wavelength of 1200nm and the second harmonic signal light with the wavelength of 600nm, the second harmonic signal light with the wavelength of 600nm is reflected to a half wave plate through a first electric translation device after controlling the optical path thereof, and then is reflected to a second dichroic mirror, focused through a second reflecting mirror, focused through a second dichroic mirror and reflected and emitted through a second dichroic mirror in turn, the signal light with the wavelength of 1200nm is focused through the first focusing lens and then transmitted and emitted through the second dichroic mirror, the second harmonic signal light with the wavelength of 600nm and the signal light with the wavelength of 1200nm emitted through the second collinear dichroic mirror are off-axis confocal and incident to a small hole on the back surface of the first parabolic,
the second light beam is attenuated by the attenuation sheet and then enters the second BBO crystal, one part of emergent light is second harmonic signal light with the wavelength of 400nm, the other part of emergent light is laser with the wavelength of 800nm, then the laser with the wavelength of 800nm is filtered by the 400nm filter, the second harmonic signal light with the wavelength of 400nm which is emitted from the 400nm filter enters the second electric translation device through the third reflector and the fourth reflector, the second harmonic signal light with the wavelength of 400nm which is emitted from the second electric translation device enters the first off-axis parabolic reflector after being reflected by the fifth reflector,
the polarization directions of the second harmonic signal light with the wavelength of 600nm emitted by the half-wave plate, the signal light with the wavelength of 1200nm emitted by the second dichroic mirror and the second harmonic signal light with the wavelength of 400nm emitted by the second electric translation device are consistent, the phases of the signal light with the wavelength of 1200nm and the second harmonic signal with the wavelength of 400nm are consistent, and the initial phase is the same
The initial phase of the second harmonic signal light with a wavelength of 600nm is
The second harmonic signal light with the wavelength of 600nm, the signal light with the wavelength of 1200nm and the second harmonic signal light with the wavelength of 400nm emitted by the first off-axis parabolic reflector are confocal excitation air.
In an embodiment of the present invention, the laser is a femtosecond laser amplifier.
In an embodiment of the invention, the system for generating terahertz waves by exciting air plasma with three-color field laser further comprises a terahertz intensity detection device, which comprises a second off-axis parabolic mirror, a THz filter, a chopper, a silicon wafer, a fixed mirror, a movable mirror, a third off-axis parabolic mirror and a terahertz intensity detector, wherein a terahertz light beam emitted from the first off-axis parabolic mirror is incident on the second off-axis parabolic mirror, is reflected by the second off-axis parabolic mirror, sequentially passes through the THz filter, the chopper and the silicon wafer, is incident on the movable mirror and is reflected back to the silicon wafer again by the movable mirror, the silicon wafer projects the part of the terahertz light beam to the third off-axis parabolic mirror and is received by the terahertz intensity detector,
the other part of the terahertz beams are transmitted through a silicon wafer, then reflected through a fixed mirror, then transmitted through the silicon wafer to a third off-axis parabolic reflector, reflected by the third off-axis parabolic reflector and focused on a terahertz wave intensity detector, the optical path difference between the two terahertz beams is changed by changing the position of a movable mirror, and the terahertz wave intensity detector performs autocorrelation processing on a plurality of groups of received two terahertz beams with different optical path differences, so that an autocorrelation graph of the terahertz radiation source is obtained.
In an embodiment of the invention, the terahertz wave intensity detector is a golay detector.
In an embodiment of the invention, the frequency of the chopper is 12-20 Hz.
In an embodiment of the present invention, a power ratio of the second harmonic signal light with a wavelength of 600nm emitted by the half-wave plate, the signal light with a wavelength of 1200nm emitted by the second dichroic mirror, and the second harmonic signal light with a wavelength of 400nm emitted by the second electric translation device is 9: 36: 4.
in an embodiment of the present invention, the frequency, amplitude, and phase combination of the second harmonic signal light with a wavelength of 600nm emitted from the half-wave plate, the signal light with a wavelength of 1200nm emitted from the second dichroic mirror, and the second harmonic signal light with a wavelength of 400nm emitted from the second electric translation device conform to the taylor expansion formula of the sawtooth waveform.
The invention also provides a method for generating terahertz waves by exciting air plasmas through three-color field laser, which is applied to the system for generating terahertz waves by exciting air plasmas through three-color field laser.
The method utilizes the fitting of the multicolor laser field with determined wavelength, amplitude and phase to obtain the electromagnetic waveform which is as close to an ideal sawtooth waveform as possible, and has higher terahertz energy conversion efficiency compared with the traditional mode of exciting air plasma to generate terahertz waves by using a bicolor field, thereby being capable of obtaining a terahertz source with higher power. The terahertz wave generated by the invention has stronger energy and wider spectrum, is beneficial to spectral measurement, and has stronger scientific research and practical application values.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a schematic structural diagram of a system for generating terahertz waves by exciting air plasmas with three-color field laser provided by the invention;
FIG. 2 is a graph of the excitation electric field, free electron density, net current versus time for a two-color field (1200nm in combination with its second harmonic 600 nm);
FIG. 3 is a graph of the excitation electric field, free electron density, net current over time for a three color field (1200nm in combination with its second and third harmonics, 600nm and 400 nm);
FIG. 4 is a simulated terahertz time-domain signal diagram;
fig. 5 is a graph of a simulated terahertz frequency domain signal.
Description of reference numerals: 1-a laser; 2-a spectroscope; 3-an optical parametric amplifier; 4-first BBO crystal; 5-a first dichroic mirror; 6-a first motorized translation device; 7-a first mirror; 8-one-half wave plate; 9-a second mirror; 10-an attenuation sheet; 11-a second BBO crystal; a 12-400nm filter; 13-a third mirror; 14-a fourth mirror; 15-a second motorized translation device; 16-a fifth mirror; 17-a second dichroic mirror; 18-a first focusing lens; 19-a second focusing lens; 20-a first off-axis parabolic mirror; 21-a second off-axis parabolic mirror; 22-THz filter; 23-a chopper; 24-a silicon wafer; 25-fixing a mirror; 26-moving mirror; 27-a third off-axis parabolic mirror; 28-terahertz wave intensity detector; a-terahertz intensity detection device.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive effort based on the embodiments of the present invention, are within the scope of the present invention.
Fig. 1 is a schematic structural diagram of a system for generating terahertz waves by exciting air plasma with three-color-field laser, as shown in fig. 1, the system for generating terahertz waves by exciting air plasma with three-color-field laser includes a laser 1, a spectroscope 2, an optical parametric amplifier 3, a first BBO crystal 4, a first dichroic mirror 5, a first electric translation device 6, a first reflecting mirror 7, a half-wave plate 8, a second reflecting mirror 9, an attenuator 10, a second BBO crystal 11, a 400nm filter 12, a third reflecting mirror 13, a fourth reflecting mirror 14, a second electric translation device 15, a fifth reflecting mirror 16, a second dichroic mirror 17, a first focusing lens 18, a second focusing lens 19, and a first off-axis parabolic reflecting mirror 20, where:
the laser 1 is used for emitting laser with the wavelength of 800nm, the laser with the wavelength of 800nm obtains a first light beam and a second light beam after passing through the spectroscope 2,
the first light beam outputs signal light with the wavelength of 1200nm after passing through the optical parametric amplifier 3, the signal light with the wavelength of 1200nm passes through the first BBO crystal 4, a part of the signal light with the wavelength of 1200nm is unchanged, the other part of the signal light with the wavelength of 1200nm is converted into second harmonic signal light with the wavelength of 600nm, then the first dichroic mirror 5 splits the signal light with the wavelength of 1200nm and the second harmonic signal light with the wavelength of 600nm, the second harmonic signal light with the wavelength of 600nm is controlled by a first electric translation device 6, then is reflected to the half-wave plate 8 by the first reflecting mirror 7, then is reflected by the second reflecting mirror 9, is focused by the second focusing lens 19, and is reflected by the second dichroic mirror 17, the signal light with the wavelength of 1200nm is focused by the first focusing lens 18, then is transmitted and emitted by the second dichroic mirror 17, and the second harmonic signal light with the wavelength of 600nm emitted by the second dichroic mirror 17, The signal light with the wavelength of 1200nm is collinearly and confocally incident to the small hole on the back surface of the first off-axis parabolic reflector 20,
the second light beam is attenuated by the attenuator 10 and then enters the second BBO crystal 11, a part of emergent light is the second harmonic signal light with the wavelength of 400nm, the other part of the emergent light is the laser with the wavelength of 800nm, then the laser with the wavelength of 800nm is filtered by the 400nm filter 12, the second harmonic signal light with the wavelength of 400nm which is emitted from the 400nm filter 12 enters the second electric translation device 15 through the third reflector 13 and the fourth reflector 14, the second harmonic signal light with the wavelength of 400nm which is emitted from the second electric translation device 15 enters the first off-axis parabolic reflector 20 after being reflected by the fifth reflector 16,
second harmonic signal light having a wavelength of 600nm emitted from the half-wave plate 8 and signal having a wavelength of 1200nm emitted from the second dichroic mirror 17The polarization directions of the light and the second harmonic signal light having a wavelength of 400nm emitted from the second electric translation device 15 are the same, the phases of the signal light having a wavelength of 1200nm and the second harmonic signal having a wavelength of 400nm are the same, and the initial phase is the same
The initial phase of the second harmonic signal light with a wavelength of 600nm is
The second harmonic signal light with a wavelength of 600nm, the signal light with a wavelength of 1200nm and the second harmonic signal light with a wavelength of 400nm emitted from the first off-axis parabolic reflector 20 are confocal-excited in air.
The laser 1 in fig. 1 may be, for example, a femtosecond laser amplifier, such as the femtosecond laser amplifier Spitfire manufactured by Spectra-Physics, usa.
As shown in fig. 1, the system for generating terahertz waves by exciting air plasma with three-color field laser in this embodiment further includes a terahertz intensity detection device a, which includes a second off-axis parabolic mirror 21, a THz filter 22, a chopper 23, a silicon wafer 24, a fixed mirror 25, a movable mirror 26, a third off-axis parabolic mirror 27 and a terahertz intensity detector 28, wherein a terahertz beam emitted from the first off-axis parabolic mirror 20 is incident on the second off-axis parabolic mirror 21, reflected by the second off-axis parabolic mirror 21, and then sequentially passes through the THz filter 22, the chopper 23 and the silicon wafer 24, a portion of the terahertz beam is incident on the movable mirror 26 and is reflected back to the silicon wafer 24 again by the movable mirror 26, the silicon wafer 24 projects the portion of the terahertz beam to the third off-axis parabolic mirror 27 and is received by the terahertz intensity detector 28,
the other part of the terahertz beams are transmitted through a silicon wafer 24, then reflected through a fixed mirror 25, then transmitted through the silicon wafer 24 to a third off-axis parabolic reflector 27, reflected by the third off-axis parabolic reflector 27 and focused on a terahertz wave intensity detector 28, the optical path difference between the two terahertz beams is changed by changing the position of a movable mirror 26, and the terahertz wave intensity detector 28 performs autocorrelation processing on a plurality of groups of received two terahertz beams with different optical path differences, so as to obtain an autocorrelation diagram of the terahertz radiation source.
In fig. 1, the polarization direction of the laser light with wavelength of 1200nm emitted from the optical parametric amplifier 3 is perpendicular to the polarization direction of the laser light with wavelength of 800nm emitted from the laser 1, and when the first BBO crystal 4 is fixed in the phase matching direction (i.e., the position where the second harmonic conversion efficiency is the maximum), the second harmonic polarization direction is perpendicular to the fundamental frequency polarization direction, so that the polarization directions of the laser light with wavelength of 1200nm and the laser light with wavelength of 400nm are the same, and the polarization direction of the laser light with wavelength of 600nm is perpendicular to the polarization directions thereof. The specific process of rotating the polarization direction is to place the optical axis direction of the half-wave plate 8 at 45 ° to the polarization direction of the 600nm laser, so that the polarization state of the 600nm laser is rotated by 90 ° to become codirectional with the 1200nm and 400nm lasers.
In fig. 1, the main components of the first electric translation device 6 and the second electric translation device 15 are two mutually perpendicular mirrors, wherein a mirror surface of one mirror is at 45 degrees to the incident light beam, the other mirror is perpendicular to the above-mentioned mirror, so that the outgoing light beam is parallel to the incident light beam, the moving directions of the first electric translation device 6 and the second electric translation device 15 are the directions of arrows shown in fig. 1, and move along the directions of the arrows to change the optical path, and the moving direction of the moving mirror 26 is also shown in the figure.
The terahertz intensity detection device a in fig. 1 applies the principle of the michelson interference system, wherein the terahertz wave intensity detector 28 may be, for example, a golay detector, and the chopper 23 may have a frequency of, for example, 12-20Hz, and is used for modulating the terahertz wave pulses to improve the detection accuracy.
In the present embodiment, the signal light having a wavelength of 1200nm emitted from the second dichroic mirror and the second harmonic signal light having a wavelength of 400nm emitted from the second electric translation device are phase-synchronized at a confocal point, and the initial phase is controlled to be
Second harmonic emitted by half wave plate and having wavelength of 600nmThe initial phase of the signal light at the confocal point position is
The ratio of the 1200nm, 600nm and 400nm light beam power is 36: 9: and 4, exciting air plasma with co-polarization to generate terahertz waves. In addition, the frequency, amplitude and phase combination of the second harmonic signal light with the wavelength of 600nm emitted by the half wave plate, the signal light with the wavelength of 1200nm emitted by the second dichroic mirror and the second harmonic signal light with the wavelength of 400nm emitted by the second electric translation device conforms to the Taylor expansion formula of a sawtooth waveform, so that the multi-color field superposition wave is close to an ideal sawtooth wave as much as possible, and the generation efficiency of the terahertz wave is improved to the maximum extent.
In fig. 1, the first focusing lens 18 and the second focusing lens 19 may be quartz lenses having relatively high transmittances for 600nm laser light and 1200nm laser light. The first reflecting mirror 7 and the second reflecting mirror 9 may be metal mirrors highly reflective to 600nm laser light, and the fourth reflecting mirror 14 and the fifth reflecting mirror 16 may be metal mirrors highly reflective to 400nm wavelength light. When the optical distances of the 400nm laser and the 1200nm laser are consistent between the confocal points of the three beams of light from the spectroscope 2 to the first off-axis parabolic reflector 20, and the initial phase difference between the 600nm laser and the lasers (the 400nm laser and the 1200nm laser) is pi, the strong terahertz waves with the highest efficiency can be radiated outwards.
The invention also provides a method for generating terahertz waves by exciting air plasmas through three-color field laser, which is applied to a system for generating terahertz waves by exciting air plasmas through three-color field laser as shown in figure 1.
Experiments were carried out using the system shown in fig. 1, fig. 2 is a graph of the change of the excitation electric field, the free electron density, and the net current with time of a two-color field (1200nm combined with 600nm, the second harmonic), fig. 3 is a graph of the change of the excitation electric field, the free electron density, and the net current with time of a three-color field (1200nm combined with 600nm, the second harmonic, and 400 nm), fig. 4 is a graph of a simulated terahertz time-domain signal, and fig. 5 is a graph of a simulated terahertz frequency-domain signal. Wherein the total power of the laser light of fig. 2 is the same as that of fig. 3.
In fig. 2 and 3, the black solid line is the light field fitting curve of the two-color field and the three-color field, the black dotted line is the free electron density, and the gray solid line is the net current curve at the plasma. The parameter representing the terahertz generation intensity is the position of a deviation zero point after a net current oscillation curve is stabilized, the larger the value is, the larger the net current is at the moment, the stronger the generated terahertz can be obtained by a terahertz proportional formula, and as can be seen from the figure, the stable net current of the graph 3 is larger than that of the graph 2, so that the three-color field can have higher terahertz generation efficiency than that of a two-color field.
The method utilizes the fitting of the multicolor laser field with determined wavelength, amplitude and phase to obtain the electromagnetic waveform which is as close to an ideal sawtooth waveform as possible, and has higher terahertz energy conversion efficiency compared with the traditional mode of exciting air plasma to generate terahertz waves by using a bicolor field, thereby being capable of obtaining a terahertz source with higher power. The terahertz wave generated by the invention has stronger energy and wider spectrum, is beneficial to spectral measurement, and has stronger scientific research and practical application values.
Those of ordinary skill in the art will understand that: the figures are merely schematic representations of one embodiment, and the blocks or flow diagrams in the figures are not necessarily required to practice the present invention.
Those of ordinary skill in the art will understand that: modules in the devices in the embodiments may be distributed in the devices in the embodiments according to the description of the embodiments, or may be located in one or more devices different from the embodiments with corresponding changes. The modules of the above embodiments may be combined into one module, or further split into multiple sub-modules.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (8)
1. The utility model provides a system for three colour field laser arouses air plasma to produce terahertz wave, a serial communication port, including laser instrument, spectroscope, optical parametric amplifier, first BBO crystal, first dichroic mirror, first electronic translation device, first speculum, half wave plate, the second mirror, the decay piece, second BBO crystal, 400nm filter, third speculum, fourth speculum, the electronic translation device of second, fifth speculum, second dichroic mirror, first focusing lens, second focusing lens and first off-axis parabolic mirror, wherein:
the laser is used for emitting laser with the wavelength of 800nm, the laser with the wavelength of 800nm obtains a first light beam and a second light beam after passing through the spectroscope,
the first light beam outputs signal light with the wavelength of 1200nm after passing through an optical parametric amplifier, part of the signal light with the wavelength of 1200nm is unchanged in wavelength after passing through a first BBO crystal, the other part of the signal light with the wavelength of 1200nm is converted into second harmonic signal light with the wavelength of 600nm, then the first dichroic mirror splits the signal light with the wavelength of 1200nm and the second harmonic signal light with the wavelength of 600nm, the second harmonic signal light with the wavelength of 600nm is reflected to a half wave plate through a first electric translation device after controlling the optical path thereof, and then is reflected to a second dichroic mirror, focused through a second reflecting mirror, focused through a second dichroic mirror and reflected and emitted through a second dichroic mirror in turn, the signal light with the wavelength of 1200nm is focused through the first focusing lens and then transmitted and emitted through the second dichroic mirror, the second harmonic signal light with the wavelength of 600nm and the signal light with the wavelength of 1200nm emitted through the second collinear dichroic mirror are off-axis confocal and incident to a small hole on the back surface of the first parabolic,
the second light beam is attenuated by the attenuation sheet and then enters the second BBO crystal, one part of emergent light is second harmonic signal light with the wavelength of 400nm, the other part of emergent light is laser with the wavelength of 800nm, then the laser with the wavelength of 800nm is filtered by the 400nm filter, the second harmonic signal light with the wavelength of 400nm which is emitted from the 400nm filter enters the second electric translation device through the third reflector and the fourth reflector, the second harmonic signal light with the wavelength of 400nm which is emitted from the second electric translation device enters the first off-axis parabolic reflector after being reflected by the fifth reflector,
the polarization directions of the second harmonic signal light with the wavelength of 600nm emitted by the half-wave plate, the signal light with the wavelength of 1200nm emitted by the second dichroic mirror and the second harmonic signal light with the wavelength of 400nm emitted by the second electric translation device are consistent, the phases of the signal light with the wavelength of 1200nm and the second harmonic signal with the wavelength of 400nm are consistent, and the initial phase is the same
The initial phase of the second harmonic signal light with a wavelength of 600nm is
The second harmonic signal light with the wavelength of 600nm, the signal light with the wavelength of 1200nm and the second harmonic signal light with the wavelength of 400nm emitted by the first off-axis parabolic reflector are confocal excitation air.
2. The system for generating terahertz waves by exciting air plasmas through three-color field laser according to claim 1, wherein the laser is a femtosecond laser amplifier.
3. The system for generating terahertz waves by exciting air plasma with tri-color field laser according to claim 1, further comprising a terahertz intensity detecting device comprising a second off-axis parabolic mirror, a THz filter, a chopper, a silicon wafer, a fixed mirror, a movable mirror, a third off-axis parabolic mirror and a terahertz intensity detector, wherein the terahertz light beam emitted from the first off-axis parabolic mirror is incident on the second off-axis parabolic mirror, is reflected by the second off-axis parabolic mirror, then sequentially passes through the THz filter, the chopper and the silicon wafer, a part of the terahertz light beam is incident on the movable mirror and is reflected back to the silicon wafer again by the movable mirror, the silicon wafer projects the part of the terahertz light beam to the third off-axis parabolic mirror and is received by the terahertz intensity detector,
the other part of the terahertz beams are transmitted through a silicon wafer, then reflected through a fixed mirror, then transmitted through the silicon wafer to a third off-axis parabolic reflector, reflected by the third off-axis parabolic reflector and focused on a terahertz wave intensity detector, the optical path difference between the two terahertz beams is changed by changing the position of a movable mirror, and the terahertz wave intensity detector performs autocorrelation processing on a plurality of groups of received two terahertz beams with different optical path differences, so that an autocorrelation graph of the terahertz radiation source is obtained.
4. The system for generating terahertz waves by exciting air plasmas according to claim 3, wherein the terahertz wave intensity detector is a Gayle detector.
5. The system for generating terahertz waves by exciting air plasmas through three-color field laser according to any one of claims 1-4, wherein the frequency of the chopper is 12-20 Hz.
6. The system for generating terahertz waves by exciting air plasmas through three-color field laser according to claim 1, wherein the power ratio of second harmonic signal light with the wavelength of 600nm emitted by the half-wave plate, signal light with the wavelength of 1200nm emitted by the second dichroic mirror and second harmonic signal light with the wavelength of 400nm emitted by the second electric translation device is 9: 36: 4.
7. the system for generating terahertz waves by exciting air plasmas through three-color field laser according to claim 6, wherein the frequency, amplitude and phase combination of second harmonic signal light with the wavelength of 600nm emitted by the half-wave plate, signal light with the wavelength of 1200nm emitted by the second dichroic mirror and second harmonic signal light with the wavelength of 400nm emitted by the second electric translation device conforms to the taylor expansion formula of sawtooth waveform.
8. A method for generating terahertz waves by exciting air plasmas through three-color field laser, which is applied to the system as claimed in any one of claims 1 to 7.
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| CN114389125A (en) * | 2021-12-14 | 2022-04-22 | 首都师范大学 | System and method for generating terahertz waves by using circular Airy three-color field laser |
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| CN114389125A (en) * | 2021-12-14 | 2022-04-22 | 首都师范大学 | System and method for generating terahertz waves by using circular Airy three-color field laser |
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