CN101794957B - Shaping method of difference frequency terahertz pulse and shaping system thereof - Google Patents
Shaping method of difference frequency terahertz pulse and shaping system thereof Download PDFInfo
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- CN101794957B CN101794957B CN2010101099092A CN201010109909A CN101794957B CN 101794957 B CN101794957 B CN 101794957B CN 2010101099092 A CN2010101099092 A CN 2010101099092A CN 201010109909 A CN201010109909 A CN 201010109909A CN 101794957 B CN101794957 B CN 101794957B
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Abstract
The invention discloses a shaping method of a difference frequency terahertz pulse and a shaping system thereof. In the shaping method, a laser pulse shaping device is used for realizing the programmable shaping of a laser pulse; two arrays of laser pulses passing through the converting and shaping device are regulated to be mutually vertical in polarization directions and then are overlaid in a non-linear crystal and subjected to difference frequency to generate a terahertz wave; and through controlling the wave forms and the phases of the two arrays of the laser pulses with mutually vertical polarization directions, the wave form and the electric field polarization direction of the generated terahertz pulse can be controlled and the wave form and the polarization direction of generated terahertz radiation can be detected. The invention not only can control the wave form and the pulse interval of the terahertz pulse, but also can control the electric field polarization direction of the terahertz pulse. Compared with a scheme for shaping the terahertz pulse by using a photoconductive antenna or through an optical rectification process, the invention has obvious advantages.
Description
Technical field
The invention belongs to the Terahertz Technology field, be based on the optical difference frequency process Terahertz waveform is controlled, through the terahertz pulse sequence of pulse-shaping technique generation needs.
Background technology
At present, the method that produces the terahertz pulse of any controlled waveform mainly contains three kinds: one, directly produce the terahertz pulse of random waveform, but up to the present, also have no a kind of device can produce waveform terahertz pulse arbitrarily as required.Two, come the photoconduction antenna of array of designs form according to the waveform of required terahertz pulse; Requirement according to Waveform Control applies the spatial distribution of different bias voltages with control photoconduction antenna photoelectric current to each photoconduction antenna; Control the waveform of the terahertz emission that is produced like this through stack, but can cause bigger power loss usually with this way.The terahertz pulse shaping of three, optical rectification effect is just at first carried out shaping to the light pulse that excites terahertz emission, excites terahertz emission with the light pulse after the shaping.
Above-mentioned terahertz pulse shaping defective based on photoconductive antenna and optical rectification effect is: though can realize the waveform and the pulsewidth of terahertz pulse are modulated; But can't control the electric field polarization direction of terahertz pulse, can't satisfy chemical kinetic process and Terahertz communication requirement the waveform of Terahertz.
Along with the development of shaping for laser pulse technology, almost can produce the ultrashort light pulse sequence of arbitrary shape in recent years.So-called shaping for laser pulse technology is that the ultrashort laser pulse that femto-second laser produces is realized the output laser pulse waveform and the control able to programme in pulse spacing through laser pulse shaping device.Therefore, the shaping of carrying out terahertz pulse in this way has bigger flexibility.Produce in the method for broadband terahertz pulse with optical means what grow up at present; No matter be that photoconduction antenna or optical rectification produce terahertz emission; The intensity of terahertz emission all is proportional to the second dervative of photoelectric current to the time; Therefore, can realize control fully through the waveform of shaping for laser pulse technology control excitation pulse, but can't realize the modulation of Terahertz electric field polarization direction the terahertz pulse waveform.
Summary of the invention
The present invention can't realize the technical problem of Terahertz electric field polarization direction modulation for solving existing terahertz pulse shaping methods, and a kind of terahertz pulse shaping methods based on difference frequency is provided.
The present invention provides a kind of orthopedic systems of implementing said method simultaneously.
For realizing above-mentioned purpose, difference frequency terahertz shaping pulse method of the present invention is:
The first step: utilize existing laser pulse shaping device to realize the shaping able to programme of ultrashort laser pulse; In the shaping process, adopt control spatial light modulator able to programme that the spatial distribution of ultrashort laser pulse is carried out Modulation and Amplitude Modulation and phase modulated, and synthetic new time domain laser pulse sequence;
Second step: it is vertical each other that two row are adjusted into the polarization direction through the laser pulse of above-mentioned changing and shaping device, in nonlinear crystal, superposes then, produces THz wave through difference frequency.
The 3rd step: through controlling the waveform and the phase place of the mutually perpendicular laser pulse in two row polarization directions, control the waveform and the electric field polarization direction of the terahertz pulse that produces, and the waveform and the polarization direction of generation terahertz emission are detected.
The further shaping step of the present invention is:
The first step: after the ultrashort laser pulse that femto-second laser is produced is converged through an optical grating diffraction and lens; On the back focal plane of lens, light field is carried out amplitude and phase modulated, realize the control able to programme of laser pulse shape with control spatial light modulator able to programme; Again through synthetic new time domain laser pulse sequence after another lens and the grating reciprocal transformation.
Second step: two row are vertical each other through λ/2 wave plates are adjusted into the polarization direction through the same laser pulse sequence of first step shaping; Playing the synthetic row of inclined to one side beam splitter through one again converges on the nonlinear crystal; In nonlinear crystal, superpose then, produce THz wave through difference frequency.
The 3rd step: the waveform that utilizes the modulator adjustment incident laser pulse in the laser pulse shaping device; Utilize the polarization direction of λ/2 wave plates adjustment incident laser pulse; Through controlling the waveform and the phase place of the mutually perpendicular laser pulse in two row polarization directions; Control the waveform and the electric field polarization direction of the terahertz pulse that produces, and the waveform and the polarization direction of generation terahertz emission are detected.
For realizing said method; The present invention provides a kind of difference frequency terahertz shaping pulse system; This system is made up of following components and parts: femto-second laser, an inclined to one side beam splitter, laser pulse space-time transformation apparatus for shaping, λ/2 wave plates, total reflective mirror, semi-transparent semi-reflecting lens, nonlinear crystal, THz sniffer and lock-in amplifier, and the optic path relation of above-mentioned components and parts is:
The emitting laser pulse is divided into two row laser of polarization through an inclined to one side beam splitter from femto-second laser, and row are as pump light, and row are as surveying light.Pump light plays inclined to one side beam splitter through one again and is divided into two row, and this two row laser carries out shaping through laser pulse space-time transformation apparatus for shaping separately respectively, and the two row laser pulses that will pass through after the shaping are vertical each other through λ/2 wave plates are adjusted into the polarization direction respectively; The vertical laser in two row shaping polarization directions plays the synthetic row of inclined to one side beam splitter through one again, converges in the nonlinear crystal, produces terahertz pulse through beat effect; Exploring laser light is realized time delay through an automatically controlled displacement platform (also being accurate electric appearance platform), incides the waveform of surveying terahertz pulse in the THz detection system.
Described laser pulse space-time transformation apparatus for shaping structure is: it comprises two identical gratings, two identical lens and five components and parts of a control spatial light modulator able to programme; These five components and parts exhaust positions are: first grating, first lens, control spatial light modulator able to programme, second lens and second grating, the spacing between each element all equals the focal distance f of lens.
Through the modulation principle of Terahertz waveform purposes of the present invention and advantage are described below: two list in and penetrate laser and pass through laser pulse space-time transformation apparatus for shaping respectively; The waveform and the pulse spacing of the pulse of control emitting laser in the changing and shaping device; Through control laser pulse shape control terahertz pulse waveform, the polarised direction of terahertz pulse electric field just can be adjusted in the polarization direction of controlling two row laser pulses.The present invention utilizes the optical difference frequency process to produce terahertz emission, and to the technical scheme that terahertz pulse waveform and pulse spacing are adjusted, not only can control the waveform and the pulse spacing of terahertz pulse, can also control terahertz pulse electric field polarization direction.This with photoconductive antenna or through optical rectification process the scheme ratio that terahertz pulse carries out shaping is had remarkable advantages.
Description of drawings
Fig. 1 is a laser pulse space-time transformation apparatus for shaping embodiment sketch map;
Fig. 2 is a terahertz pulse orthopedic systems embodiment sketch map of the present invention;
Fig. 3 is the difference frequency sketch map in < 110>ZeTe crystal.
Among the figure: PBS-plays inclined to one side beam splitter, BS-semi-transparent semi-reflecting lens, ZnTe-crystal.
Embodiment
Below in conjunction with accompanying drawing and concrete shaping step the present invention is elaborated:
Difference frequency terahertz shaping pulse system configuration of the present invention is as shown in Figure 2, as can be seen from the figure.The inclined to one side beam splitter PBS of emitting laser pulse process the first I is divided into two row laser of polarization from femto-second laser, and row are as pump light, and row are as surveying light.Pump light plays inclined to one side beam splitter PBS II through second again and is divided into two row; The first row pump light 1 directly gets into laser pulse space-time transformation apparatus for shaping 1; Secondary series pump light 2 gets into laser pulse space-time transformation apparatus for shaping 2 through the total reflective mirror reflection; Two row pump lights produce the laser pulse of arbitrary shape respectively through control spatial light modulator able to programme in laser pulse space-time transformation apparatus for shaping 1 and 2; It is vertical each other that two row laser pulses after the shaping are adjusted into the polarization direction through λ/2 respectively, plays the synthetic row of inclined to one side beam splitter PBS III through the 3rd again, is divided into two row through semi-transparent semi-reflecting lens BS; One row get into the waveform that lock-in amplifier is observed incident laser, and another row converge among the nonlinear crystal ZnTe and export terahertz pulse.Realize time delay from the exploring laser light that the inclined to one side beam splitter PBS of the first I tells through an automatically controlled displacement platform, incide the waveform of surveying terahertz pulse in the Terahertz detection system.
The structure of above-mentioned laser pulse shaping device is as shown in Figure 1, and it comprises that the grating I, the mirror that set gradually pass through I, control spatial light modulator able to programme, lens II and five elements of grating II, and the spacing between each element all equals the focal distance f of lens.
During enforcement, chromatic dispersion takes place at grating I in incident laser pulse, gets-1 order diffraction, and dispersion equation is following:
D is a grating constant in the formula, and λ is a lambda1-wavelength, θ
i, θ
dBe respectively the incidence angle and the angle of diffraction.The different frequency composition of optical grating diffraction converges through lens, on the focal plane of lens I, uses liquid crystal light modulator that the distribution of light field is modulated.Behind the light process lens II and grating II after the modulation, different frequency components is reassembled into new time domain pulse train, and the waveform of pulse is relevant with the transmittance function of modulator.Use liquid crystal modulator able to programme to modulate and to realize the control able to programme in output laser pulse waveform and pulse spacing.
Shaping principle of the present invention can be analyzed through following formula.
When electric field E propagates in electrooptic crystal, second order electric light tensor x, the expression formula of second nonlinear polarization intensity P does
The new second nonlinear polarization vibration that produces promptly is the source that produces terahertz emission.We suppose second order electric light tensor x and frequency-independent in the formula.Can find out nonlinear polarization intensity P by (2) formula
iDirection depend on electric field E
jWith respect to electric field E
kDirection (like Fig. 3), through changing electric field E
jWith respect to electric field E
kDirection, promptly can change nonlinear polarization intensity P
iDirection.If only use a branch of smooth incident, two mutually perpendicular electric field component phase places are identical, when changing electric field E
jDirection the time, electric field E
KDirection change E in (2) formula thereupon
j(t) E
* k(t) become E
2(t), be optical rectification process, the terahertz emission that is produced is only relevant with the incident light intensity.If control nonlinear polarization intensity P
iDirection, we must use two-beam incident, through control two-beam waveform and phase place, promptly control E
j(t) and E
k(t) control polarization intensity P
iDirection, thereby the waveform of the control terahertz pulse that produces is also controlled the direction of terahertz emission electric field.
Claims (2)
1. difference frequency terahertz shaping pulse method is characterized in that step is following:
The first step: after the ultrashort laser pulse that femto-second laser is produced is converged through an optical grating diffraction and lens; On the back focal plane of lens, light field is carried out amplitude and phase modulated, realize the control able to programme of laser pulse shape with control spatial light modulator able to programme; Again through synthetic new time domain laser pulse sequence after another lens and the grating reciprocal transformation;
Second step: two row are vertical each other through λ/2 wave plates are adjusted into the polarization direction through the same laser pulse sequence of first step shaping; Playing the synthetic row of inclined to one side beam splitter through one again converges on the nonlinear crystal; In nonlinear crystal, superpose then, produce THz wave through difference frequency;
The 3rd step: the waveform that utilizes the modulator adjustment incident laser pulse in the laser pulse shaping device; Utilize the polarization direction of λ/2 wave plates adjustment incident laser pulse; Through controlling the waveform and the phase place of the mutually perpendicular laser pulse in two row polarization directions; Control the waveform and the electric field polarization direction of the terahertz pulse that produces, and the waveform and the polarization direction of generation terahertz emission are detected.
2. difference frequency terahertz shaping pulse system; It is characterized in that; It is made up of following components and parts: femto-second laser, an inclined to one side beam splitter, laser pulse space-time transformation apparatus for shaping, λ/2 wave plates, total reflective mirror, semi-transparent semi-reflecting lens, nonlinear crystal, THz sniffer and lock-in amplifier; The optic path relation of above-mentioned components and parts is: the emitting laser pulse is divided into two row laser of polarization through an inclined to one side beam splitter from femto-second laser; One row are as pump light, and row are as surveying light; Pump light plays inclined to one side beam splitter through one again and is divided into two row, and this two row laser carries out shaping through laser pulse space-time transformation apparatus for shaping separately respectively, and the two row laser pulses that will pass through after the shaping are vertical each other through λ/2 wave plates are adjusted into the polarization direction respectively; The vertical laser in two row shaping polarization directions plays the synthetic row of inclined to one side beam splitter through one again, converges in the nonlinear crystal, produces terahertz pulse through beat effect; Survey light and realize time delay, incide the waveform of surveying terahertz pulse in the THz detection system through an automatically controlled displacement platform;
Described laser pulse space-time transformation apparatus for shaping structure is: it comprises two identical gratings, two identical lens and five components and parts of a control spatial light modulator able to programme; These five components and parts exhaust positions are: first grating, first lens, control spatial light modulator able to programme, second lens and second grating, the spacing between each components and parts all equals the focal distance f of lens.
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| CN103639601B (en) * | 2013-12-19 | 2015-05-20 | 北京理工大学 | Three-dimensional periodic structure processing method based on electronic dynamic control |
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| CN104076532A (en) * | 2014-05-22 | 2014-10-01 | 西南科技大学 | Terahertz light guide antenna space power synthesizer |
| CN104852269A (en) * | 2015-05-26 | 2015-08-19 | 山西大学 | Device and method for accurately modulating pulse laser phase |
| CN105181155B (en) * | 2015-10-19 | 2018-03-27 | 南开大学 | Terahertz pulse single detection system and detection method based on single-mode fiber |
| CN105628642A (en) * | 2016-01-08 | 2016-06-01 | 上海理工大学 | Method for improving frequency spectrum signal-to-noise ratio of tera-hertz optical detection system |
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| CN108803194B (en) * | 2018-07-02 | 2024-03-22 | 天津大学 | Terahertz wave internal modulation device |
| CN110456514B (en) * | 2019-08-22 | 2021-09-10 | 北京环境特性研究所 | Terahertz wave beam shaping method and device |
| CN112260048B (en) * | 2020-09-23 | 2022-09-16 | 武汉光谷航天三江激光产业技术研究院有限公司 | Device and method for periodically changing laser wavelength |
| CN112271441B (en) * | 2020-10-30 | 2023-04-07 | 北京维信诺光电技术有限公司 | Semiconductor device, manufacturing method thereof and antenna system |
| CN112582859A (en) * | 2020-12-14 | 2021-03-30 | 济南量子技术研究院 | Tunable terahertz wave generation device and method |
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