CN109445226A - Terahertz frequency comb generation device and method based on polar molecule coherence rotation - Google Patents
Terahertz frequency comb generation device and method based on polar molecule coherence rotation Download PDFInfo
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- CN109445226A CN109445226A CN201811400583.1A CN201811400583A CN109445226A CN 109445226 A CN109445226 A CN 109445226A CN 201811400583 A CN201811400583 A CN 201811400583A CN 109445226 A CN109445226 A CN 109445226A
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- G—PHYSICS
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- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/35—Non-linear optics
- G02F1/353—Frequency conversion, i.e. wherein a light beam is generated with frequency components different from those of the incident light beams
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
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- G02F2203/56—Frequency comb synthesizer
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Abstract
The present invention provides a kind of Terahertz frequency comb generation device and method based on polar molecule coherence rotation, device includes: femto-second laser, the first film beam splitting eyeglass, seed THz wave generation device, the first delay line and polar molecule chamber；Nozzle is provided in polar molecule chamber, nozzle is for spraying polar molecule；Femtosecond laser signal enters polar molecule chamber after the first delay line carries out delay disposal, the polar molecule of injection nozzle injection, the induced dipole square of excitation polar molecule interacts with laser field, so that coherence rotation transition occurs for molecule, generates the rotational wave packet of polar molecule；Femtosecond laser signal generates seed THz wave after the processing of seed THz wave generation device, and the seed THz wave of generation enters polar molecule chamber, irradiates the rotational wave packet of polar molecule, obtains Terahertz frequency comb.The present invention obtains Terahertz frequency comb using the coherence rotation of polar molecule, opens a kind of new thought for obtaining Terahertz frequency comb.
Description
Technical field
The present invention relates to optical frequency com technical fields, and in particular to a kind of Terahertz based on polar molecule coherence rotation
Frequency comb generation device and method.
Background technique
THz wave refers to that frequency is in 0.1~10THz, wavelength is in electromagnetic radiation within the scope of 0.03~3mm.Terahertz
Hereby frequency is opened up in terms of non-destructive testing, spectrum analysis, target imaging and empty day between infrared laser and microwave
Wide application prospect is shown.Terahertz field is quickly grown in recent years, but the current development in the field is primarily limited to
In the exploitation and development of light source and detector, especially the generation of the frequency comb of Terahertz frequency imaging, characterization, quickly
There is great research potential and application value in terms of detection and high-acruracy survey etc..
Optical frequency com is the novel stabilized light source of one kind after laser, has equidistant light spoke on frequency spectrum
It penetrates, has been widely used in superhigh precision detection, chemical component quick detection, optical communication and sensing and long haul communication etc.
Aspect.Frequency comb can carry out accurate measurement to laser, atom and other physical by as the ruler in frequency.Optical frequency
The producing method of comb determines to obtain detected minimum time precision.It is often necessary to the spectrum of the different colours to pole wide spectrum
Line carries out mode locking, obtains synchronously driven frequency, and the frequency range that these are synchronized is wider, composed frequency comb temporal resolution
It is higher, and the light source for preparing this relevant wideband is difficult.
Currently, the production method of frequency comb mainly includes micro-ring resonant cavity, high-order nonlinear optical fiber, F-P resonator, photoelectricity
The modes such as oscillator, and the exploitation of the frequency comb in Terahertz frequency range is still challenging.Currently, the Terahertz based on modulator
Optical frequency comb generation method and Terahertz frequency comb method based on quantum cascade laser proposed in succession, but the former
Frequency far surpass the usual range of definition of 0.1~10THz, closer to infrared band (100 Terahertzs or more), and the latter
Dependent on the quantum cascade laser close to absolute zero or low temperature environment, while the terahertz emission efficiency of its high order rank
It is lower.
Summary of the invention
For the problems of the prior art, the present invention provides a kind of Terahertz optical frequencies based on polar molecule coherence rotation
Comb generation device and method.
Specifically, the present invention provides following technical schemes:
In a first aspect, the present invention provides a kind of Terahertz frequency comb generation device based on polar molecule coherence rotation,
It include: femto-second laser, the first film beam splitting eyeglass, seed THz wave generation device, the first delay line and polar molecule chamber
Room；
The femtosecond laser that the femto-second laser generates obtains the first via after the first film beam splitting eyeglass beam splitting and flies
Second laser signal and the second road femtosecond laser signal；
Nozzle is provided in the polar molecule chamber, the nozzle is for spraying polar molecule；
The first via femtosecond laser signal enters the polar molecule after first delay line carries out delay disposal
Chamber injects the polar molecule of the nozzle injection, the induced dipole square of polar molecule is excited to interact with laser field,
So that coherence rotation transition occurs for molecule, the rotational wave packet of polar molecule is generated；
The second road femtosecond laser signal generates seed Terahertz after seed THz wave generation device processing
The seed THz wave of wave, generation enters the polar molecule chamber, irradiates the rotational wave packet of the polar molecule, obtains terahertz
Hereby frequency comb.
Further, the seed THz wave generation device includes: optical path regulation device and the first optical path focus device；
The optical path regulates and controls device, and for carrying out optical path regulation to the second road femtosecond laser signal, it is flat to generate polarization
Capable, that the time is overlapped, the adjustable two-color laser field of relative phase；
The first optical path focus device generates plasma acquisition terahertz for being focused to the two-color laser field
Hereby wide range radiates, and the Terahertz wide range radiation is the seed THz wave.
Further, the optical path regulates and controls device, comprising: Optical doubling frequency crystal, the dispersion compensation crystal, light set gradually
Wedge adjusts crystal to polarization；
By obtaining frequency multiplication emergent light after the Optical doubling frequency crystal, described times occurs frequently the second road femtosecond laser signal
The polarization direction of light is penetrated perpendicular to the second road femtosecond laser signal, and the central wavelength of the frequency multiplication emergent light is described
The half of two road femtosecond laser signal center wavelength；
The dispersion compensation crystal is used to provide negative color to the second road femtosecond laser signal and the frequency multiplication emergent light
Dissipate compensation；
The wedge pair constructs identical wedge by two panels and forms, for the second road femtosecond laser signal and institute
It states frequency multiplication emergent light and positive dispersion is provided, change the positive dispersion that transmission distance changes two-color laser field, to the opposite of two-color laser field
Phase is controlled；
The polarization adjusts crystal, is realized by dual wavelength wave plate, adjusts crystal by the polarization and makes second tunnel
Femtosecond laser signal and the frequency multiplication emergent light shake along same polarization direction.
Further, the polar molecule chamber, comprising: first window, the second window, third window, the second optical path are poly-
Burnt device and third optical path focus device；The first window is located at the left side of the polar molecule chamber, described in penetrating
First via femtosecond laser signal, and after the second optical path focus device focusing, the polar molecule of the nozzle injection is injected,
The induced dipole square of excitation polar molecule interacts with laser field, so that coherence rotation transition occurs for molecule, generates pole
The rotational wave packet of property molecule；Second window is located at the upper left side of the polar molecule chamber, for penetrating the seed too
Hertz wave, and after the second optical path focus device focusing, the rotational wave packet of the polar molecule is irradiated, the terahertz is obtained
Hereby frequency comb；The third window is located at the lower right of the polar molecule chamber, by the Terahertz frequency comb through described
It is exported after the processing of three optical path focus devices；Wherein, the first window is quartz window, second window and the third window
Mouth is High Resistivity Si window, polyethylene window or polystyrene window.
Further, the polar molecule chamber is vacuum chamber.
Further, the polar molecule is polar diatomic or polyatom linear molecule, molecule rotational transition
Energy is in Terahertz magnitude.
Further, the nozzle is sprayed using continuous nozzle or the pulsed supersonic speed synchronous with the femto-second laser
Mouth.
Further, the Terahertz frequency comb generation device based on polar molecule coherence rotation, further includes: terahertz
Hereby frequency comb signal detecting device, the Terahertz frequency comb of femtosecond laser and generation for being generated using the femto-second laser
The PGC demodulation relationship itself having is detected by Terahertz frequency comb of the electro optic sampling principle to generation, obtains terahertz
The hereby time domain waveform of frequency comb.
Further, the Terahertz frequency comb signal detecting device, comprising: the second film beam splitting eyeglass, the second delay
Line, the 4th optical path focus device, nonlinear crystal, 1/4 λ wave plate, polarization beam splitting crystal, the first photodetector, the second photoelectricity
Detector and lock-in amplifier；
The femtosecond laser that the femto-second laser generates obtains third road after the second film beam splitting eyeglass beam splitting and flies
Second laser signal；The third road femtosecond laser signal is focused after the delay of second delay line by the 4th optical path
Device is overlapped after being focused with the Terahertz frequency comb in time, and Terahertz frequency comb excites in the nonlinear crystal
Instantaneous bubble Ke Ersi effect, so that femtosecond laser becomes oval thickness from circular deflection after by 1/4 λ wave plate；Then pass through
The first photodetection is respectively adopted in the two components by two components that ellipse inclined THz wave is obtained after the polarization beam splitting crystal
Device and the second photodetector are detected and obtain the time domain waveform signal of Terahertz frequency comb by the lock-in amplifier.
Second aspect, the present invention also provides a kind of Terahertz frequency comb generation side based on polar molecule coherence rotation
Method, comprising:
S1, the polar molecule being emitted from nozzle is injected using femtosecond laser, femtosecond laser excites the induced dipole square of molecule
It interacts with laser field, so that coherence rotation transition occurs for molecule, generates the rotational wave packet of polar molecule；
S2, the rotational wave packet that the polar molecule is irradiated using the seed THz wave handled by femtosecond laser, by
There is coherence in the rotating state that polar molecule is stimulated, it is right with rotational transition institute to give off at the reproduction moment of rotational wave packet
The energy level difference answered, these THz waves given off have the characteristics that on frequency spectrum it is equally spaced, in the time domain every preset time
Interval can obtain primary radiation, the characteristic with PGC demodulation and high repetition frequency, therefore obtain Terahertz frequency comb.
As shown from the above technical solution, the Terahertz frequency comb provided by the invention based on polar molecule coherence rotation generates
Device, comprising: femto-second laser, the first film beam splitting eyeglass, seed THz wave generation device, the first delay line and polarity point
Sub-chamber；The femtosecond laser that the femto-second laser generates obtains first via femtosecond after the first film beam splitting eyeglass beam splitting
Laser signal and the second road femtosecond laser signal；Nozzle is provided in the polar molecule chamber, the nozzle is for spraying pole
Property molecule；The first via femtosecond laser signal enters the polar molecule chamber after first delay line carries out delay disposal
Room injects the polar molecule of the nozzle injection, excites the induced dipole square of polar molecule to interact with laser field, make
It obtains molecule and coherence rotation transition occurs, generate the rotational wave packet of polar molecule；The second road femtosecond laser signal is through described kind
Seed THz wave is generated after sub- THz wave generation device processing, the seed THz wave of generation enters the polar molecule chamber
Room irradiates the rotational wave packet of the polar molecule, obtains Terahertz frequency comb.The present invention using the coherence rotation of polar molecule come
Terahertz frequency comb is obtained, a kind of new thought for obtaining Terahertz frequency comb is opened.The present invention utilizes ultrafast femtosecond laser
It irradiates the polar molecule that be emitted from nozzle, after the coherence rotation wave packet for exciting molecule, then the injection of seed Terahertz light wave is concerned with
In rotational wave packet, terahertz emission relevant to molecule rotational transition energy can be generated at the rotation reproduction moment of polar molecule,
The radiation correspond to polar molecule rotational energy level energy difference, have the characteristics that it is equidistant, can be used as PGC demodulation it is relevant too
Hertz frequency comb source.The present invention is driven by femtosecond laser, the Terahertz frequency comb for being radiated, therefore being obtained by relevant rotational wave packet
Coherence with PGC demodulation.Simultaneously because the rotation recurring temporal of molecule is only picosecond magnitude, therefore the terahertz obtained
Hereby frequency comb has the output characteristics of high repetition frequency.
Detailed description of the invention
In order to more clearly explain the embodiment of the invention or the technical proposal in the existing technology, to embodiment or will show below
There is attached drawing needed in technical description to be briefly described, it should be apparent that, the accompanying drawings in the following description is the present invention
Some embodiments for those of ordinary skill in the art without creative efforts, can also basis
These attached drawings obtain other attached drawings.
Fig. 1 is the Terahertz frequency comb generation device based on polar molecule coherence rotation that one embodiment of the invention provides
A kind of structural schematic diagram；
Fig. 2 is the structural schematic diagram for the optical path regulation device that one embodiment of the invention provides；
Fig. 3 is the structural schematic diagram for the polar molecule chamber that one embodiment of the invention provides；
Fig. 4 is the Terahertz frequency comb generation device based on polar molecule coherence rotation that one embodiment of the invention provides
Another structural schematic diagram；
Fig. 5 is the Terahertz frequency comb frequency-region signal point measured using carbon monoxide experiment that one embodiment of the invention provides
Cloth schematic diagram；
Fig. 6 be another embodiment of the present invention provides the Terahertz optical frequency comb generation method based on polar molecule coherence rotation
Flow chart.
Specific embodiment
In order to make the object, technical scheme and advantages of the embodiment of the invention clearer, below in conjunction with the embodiment of the present invention
In attached drawing, the technical scheme in the embodiment of the invention is clearly and completely described, it is clear that described embodiment is
A part of the embodiment of the present invention, instead of all the embodiments.Based on the embodiments of the present invention, those of ordinary skill in the art
Every other embodiment obtained without creative efforts, shall fall within the protection scope of the present invention.
The Terahertz frequency comb based on polar molecule coherence rotation that Fig. 1 shows one embodiment of the invention offer generates dress
The structural schematic diagram set.As shown in Figure 1, the Terahertz frequency comb provided in an embodiment of the present invention based on polar molecule coherence rotation
Generation device, comprising: femto-second laser (the Ti:Sapphire laser in Fig. 1), the first film beam splitting eyeglass, seed terahertz
Hereby wave generation device, the first delay line (delay line 1 in Fig. 1) and polar molecule chamber；
The femtosecond laser that the femto-second laser generates obtains the first via after the first film beam splitting eyeglass beam splitting and flies
Second laser signal and the second road femtosecond laser signal；
The second road femtosecond laser signal generates seed THz wave after entering the seed THz wave generation device；
The first via femtosecond laser signal enters the polar molecule after first delay line carries out delay disposal
Chamber is provided with nozzle in the polar molecule chamber, and the nozzle is for spraying polar molecule, into the polar molecule chamber
The first via femtosecond laser signal of room injects the polar molecule of the nozzle injection, excites the induced dipole square of polar molecule and swashs
Light field interacts, so that coherence rotation transition occurs for molecule, generates the rotational wave packet of polar molecule；
Wherein, the delay time of first delay line needs to be greater than or equal to first via pumping polar molecule and is concerned with
The time of rotation namely the first via femtosecond laser need to carry out time delay to carry out phase to first via pumping polar molecule
After dry rotation, then irradiate polar molecule.At this time since the rotating state of molecule is driven by femtosecond laser, rotational wave Bao Huijin
Relevant (comprising the time) when row contains to develop, the period developed is the rotation period of molecule；
It should be noted that first via femtosecond laser is generated by delay line 1 shown in FIG. 1 with the second road femtosecond laser
Seed THz wave be spatially overlapped.
The second road femtosecond laser signal generates seed Terahertz after seed THz wave generation device processing
The seed THz wave of wave, generation enters the polar molecule chamber, irradiates the rotational wave packet of the polar molecule, obtains terahertz
Hereby frequency comb.
In the present embodiment, the femto-second laser is preferably by Ti:Sapphire laser stimulated radiation centre frequency substantially at 800 nanometers
Neighbouring femtosecond laser (subsequent 800 nanometer laser of abbreviation herein), the laser peak power of focusing need to reach 1013W/cm, realize
Excitation to molecule rotational wave packet.
In the present embodiment, it should be noted that by the evolution of polar molecule rotational wave packet, especially for polarity
Linear small molecule, energy needed for rotational transition are in terahertz wave band, and polar micromolecules are very weak since vibration turns to couple,
Rotation spectrum can show the discrete spectral line structure of comb teeth-shaped equidistantly distributed, be a kind of natural Terahertz frequency comb source.
In addition, the energy difference of molecule rotational transition is corresponding with rotation angular-momentum quantum number, the more high corresponding Terahertz frequency comb of angular-momentum quantum number
Cut-off energy it is wider, and these molecule rotating state, due to being by Laser Driven transition, the radiation of itself is the same phase that is concerned with
, meet the needs of radiation of frequency comb different frequency itself is for PGC demodulation.
In the present embodiment, the polar molecule being emitted from nozzle, femtosecond laser are injected using the first via femtosecond laser
The induced dipole square of excitation molecule interacts with laser field, so that coherence rotation transition occurs for molecule, rotating state is again
Layout；Then, the rotational wave packet of the seed THz wave irradiation polar molecule generated using the second road femtosecond laser；Finally, by
There is good coherence in the rotating state that polar molecule is stimulated, can give off and rotate jump at the reproduction moment of rotational wave packet
Move corresponding energy level difference, these THz waves given off have the characteristics that on frequency domain it is equally spaced, in the time domain every one
Fixing time, interval acquisition is primary to be radiated, therefore the characteristic with PGC demodulation and high repetition frequency.
It should be noted that the frequency interval for the Terahertz frequency range optical frequency com that the present embodiment obtains can pass through change
The type of molecule is regulated and controled, and the frequency interval of polar molecule is 2B0, and the molecular frequency interval for carbon monoxide is about
0.116THz, the frequency interval for carbonyl sulfur are about 0.012THz, and the intrinsic dipole moment of opposed polarity molecule itself is different, more
The spacing of the molecule frequency comb of weight is narrower.Namely obtain the time interval once radiated and molecule at regular intervals in the time domain
Rotary inertia it is related, for example, the radiation recurring temporal interval of carbon monoxide molecule is about 8.6 picoseconds, the weight of carbonyl sulfur molecule
Existing time interval is about 82.1 picoseconds.
By content above it is found that the present embodiment utilizes the polar molecule of ultrafast Gold Films Irradiated by Femtosecond Laser nozzle outgoing, excitation point
After the coherence rotation wave packet of son, then by seed Terahertz light wave injection coherence rotation Bo Baonei, reappeared in the rotation of polar molecule
Moment can generate terahertz emission relevant to molecule rotational transition energy, which corresponds to the rotational energy level energy of polar molecule
It is poor to measure, and has the characteristics that equidistant, can be used as the relevant Terahertz frequency comb source of PGC demodulation.As it can be seen that the device is swashed by femtosecond
The Terahertz frequency comb that optical drive is radiated by relevant rotational wave packet, therefore obtained has the coherence of PGC demodulation.Simultaneously
Since the rotation recurring temporal of molecule is only picosecond magnitude, the Terahertz frequency comb obtained has the output of high repetition frequency
Characteristic.
Content based on the above embodiment, in a kind of optional embodiment, referring to Fig. 1, the seed THz wave is produced
Generating apparatus further comprises: optical path regulates and controls device and the first optical path focus device；
The optical path regulates and controls device, and for carrying out optical path regulation to the second road femtosecond laser signal, it is flat to generate polarization
Capable, that the time is overlapped, the adjustable two-color laser field of relative phase；
The first optical path focus device generates plasma acquisition terahertz for being focused to the two-color laser field
Hereby wide range radiates, and the Terahertz wide range radiation is the seed THz wave.
In the present embodiment, optical path regulation device is for generating two-color laser field, and then utilizes optical path focus device pair
Two-color laser field, which is focused, generates plasma acquisition Terahertz wide range radiation, to obtain seed THz wave.Below one
A specific embodiment (as shown in Figure 2) gives the specific implementation side of the regulation device of the optical path for generating two-color laser field
Formula, wherein containing the arrangement mode of different crystal and these crystal.It should be noted that in other implementations of the invention
In mode, the seed THz wave generation device can also include the optical path that can generate three color laser fields or Multi Colour Lasers field
Regulate and control device, generation plasma is then focused to three color laser fields or Multi Colour Lasers field by optical path focus device again and is obtained
The radiation of Terahertz wide range is obtained, to obtain seed THz wave.Specific implementation of the present invention to seed THz wave generation device
Mode without limitation, as long as can generate frequency coverage polar molecule rotational transition energy wide range radiation seed THz wave i.e.
It can.It should be noted that the optical path regulation device of three color laser fields or Multi Colour Lasers field can be generated relative to light shown in Fig. 2
Road regulates and controls for device, needs some crystal of more increases or needs while changing some arrangement modes again to be just able to achieve.
Fig. 2 shows the structural schematic diagrams for the optical path regulation device that one embodiment of the invention provides.As shown in Fig. 2, described
Optical path regulates and controls device, further comprises: Optical doubling frequency crystal, dispersion compensation crystal, the wedge set gradually is adjusted to polarization
Crystal；
By obtaining frequency multiplication emergent light after the Optical doubling frequency crystal, described times occurs frequently the second road femtosecond laser signal
The polarization direction of light is penetrated perpendicular to the second road femtosecond laser signal, and the central wavelength of the frequency multiplication emergent light is described
The half of two road femtosecond laser signal center wavelength；
The dispersion compensation crystal is used to provide negative color to the second road femtosecond laser signal and the frequency multiplication emergent light
Dissipate compensation；
The wedge pair constructs identical wedge by two panels and forms, for the second road femtosecond laser signal and institute
It states frequency multiplication emergent light and positive dispersion is provided, change the positive dispersion that transmission distance changes two-color laser field, to the opposite of two-color laser field
Phase is controlled；
The polarization adjusts crystal, is realized by dual wavelength wave plate, adjusts crystal by the polarization and makes second tunnel
Femtosecond laser signal and the frequency multiplication emergent light shake along same polarization direction.
In the present embodiment, the second road femtosecond laser regulates and controls device by optical path as shown in Figure 2, and it is parallel to obtain polarization
, the time be overlapped, the adjustable two-color laser field of relative phase (such as 800 nanometers with 400 nanometers of femtosecond light).800 nanometers first
Femtosecond laser obtains polarization perpendicular to 800 nanometers of incidences by Optical doubling frequency crystal (generally use β-BBO and carry out optical frequency-doubling)
400 nanometers of frequency multiplication emergent lights of pumping.Subsequent optical path since 800 nanometers different in brilliant intracorporal refractive index from 400 nanometers of light,
The time difference can be introduced both when having passed through normal dispersion medium, to separately cannot effectively generate seed terahertz in time
Hereby wave radiation.Therefore, it is necessary to carry out anomalous dispersion compensation to two-way light by dispersion compensation crystal, (adoptable crystal is α-
BBO or calcite provide negative dispersion), the polarization adjusts crystal and realizes that the laser for 400 nanometers is by dual wavelength wave plate
Full-wave plate, the laser for 800 nanometers are half-wave plates, and 400 nanometers and 800 nanometers of light edges can be made by adjusting crystal by polarization
Same polarization direction concussion.Seed THz wave is generated by lens focus air again.It is noted that here not only can be with
Using bloomed lens focal beam spot, can equally using low-angle coated reflection formula metal plano-concave reflecting mirror, (focal length is usually 10
To 30 centimetres, depending on femto-second laser energy) or throwing face mirror is focused off axis.In addition, the lens mirror, reflecting mirror or
The metal film of throwing face mirror can be aluminium, silver or gold, and metallic film surface can plate the Anti-reflective coating of corresponding wavelength.As it can be seen that described second
Road Terahertz radiation source regulates and controls device by femtosecond laser, by optical path, generates parallel two-color fields laser, produces after conllinear focusing
Raw plasma obtains the radiation of Terahertz wide range.
Fig. 3 shows the structural schematic diagram of the polar molecule chamber of one embodiment of the invention offer.As shown in figure 3, described
Polar molecule chamber, comprising: first window, the second window, third window, the second optical path focus device and third optical path focalizer
Part；The first window is located at the left side of the polar molecule chamber, for penetrating the first via femtosecond laser signal, and passes through
After the second optical path focus device focuses, the polar molecule of the nozzle injection is injected, the induced dipole of polar molecule is excited
Square interacts with laser field, so that coherence rotation transition occurs for molecule, generates the rotational wave packet of polar molecule；Described
Two windows are located at the upper left side of the polar molecule chamber, for penetrating the seed THz wave, and through second optical path
After focus device focuses, the rotational wave packet of the polar molecule is irradiated, the Terahertz frequency comb is obtained；Third window position
It is in the lower right of the polar molecule chamber, the Terahertz frequency comb is defeated after third optical path focus device processing
Out；Wherein, the third optical path focus device is converted into directional light for the terahertz light that is emitted again after focusing, thus from the
Three windows project.It should be noted that the focus of the second optical path focus device and the third optical path focus device needs
It is overlapped, is projected in order to be converted into directional light to the light after focusing.Wherein, the first window can be quartz window, described
Second window and the third window can be High Resistivity Si window.
It should be noted that the THz wave that the second road femtosecond laser generates swashs as seed pulse irradiation first via femtosecond
The polar molecule rotational wave packet that light generates obtains THz wave frequency comb using the rotational transition between molecule rotating state and radiates.
As shown in figure 3, Terahertz seed light is incident from upper left second window of chamber, the Terahertz frequency comb of acquisition is along chamber bottom right
The third window outgoing of side.In addition, the first window for being responsible for incidence and the third window for being responsible for outgoing are not limited to
High Resistivity Si window, can also for polyethylene perhaps polystyrene window and polyethylene or polystyrene window transmission effect
Rate can be some higher.
Content based on the above embodiment, in a kind of optional embodiment, the polar molecule chamber is vacuum chamber.
In the present embodiment, the polar molecule chamber is vacuum chamber, since the whole optical path of THz wave is placed in very
In Altitude, to reduce polar molecule to the re-absorption of the Terahertz frequency comb of generation.
It should be noted that the nozzle for spraying polar molecule is in vacuum environment, the diameter of polar molecule injection
About 100-300 microns, ultrasonic air-flow is given off from nozzle to vacuum environment.Wherein, polar molecule is injected in nozzle
Gas backpressure range be 0.5 to 6 standard atmospheric pressure.
Content based on the above embodiment, in a kind of optional embodiment, the polar molecule is polar diatomic
Or polyatom linear molecule, molecule rotational transition energy is in Terahertz magnitude.
In the present embodiment, since molecule is diatomic or polyatomic molecule so vibration turns coupling effect very weak, institute
There is apparent equal frequency intervals characteristic with the rotational energy level of molecule, can be used as Terahertz frequency comb source.For example, the molecule
It can be carbon monoxide, the diatomic of carbonyl sulfur isopolarity or polyatom linear molecule.
Content based on the above embodiment, in a kind of optional embodiment, the nozzle using continuous nozzle or with
The synchronous pulsed superonic flow nozzzle of the femto-second laser.
In the present embodiment, continuous nozzle or the pulsed supersonic speed synchronous with femto-second laser spray can be used in nozzle
Mouth.Wherein, using pulsed superonic flow nozzzle can be better than continuous nozzle because pulsed nozzle to chamber spray gas when,
Level of vacuum is higher in chamber, and the translational velocity that injection gas molecule is emitted supersonic expansion out of connection steel cylinder nozzle is got over
Fastly.At this point, between translation molecule highdensity shock meeting so that molecule rotation vibration energy toward shifting on translational energy, thus reality
The cooling of existing molecule.Cooling molecule is easier to receive the excitation of femtosecond laser, so that the good rotational wave packet of coherence is obtained,
And develop.
Fig. 4 shows the Terahertz frequency comb generation device provided in an embodiment of the present invention based on polar molecule coherence rotation
Another structural schematic diagram.As shown in figure 4, the Terahertz frequency comb generation device based on polar molecule coherence rotation,
Further include: Terahertz frequency comb signal detecting device, femtosecond laser and generation for being generated using the femto-second laser
The PGC demodulation relationship that Terahertz frequency comb itself has is visited by Terahertz frequency comb of the electro optic sampling principle to generation
It surveys, obtains the time domain waveform of Terahertz frequency comb.
Content based on the above embodiment, in a kind of optional embodiment, referring to fig. 4, the Terahertz frequency comb letter
Number detection device, comprising: the second film beam splitting eyeglass, the second delay line (delay line 2 in Fig. 4), the 4th optical path focus device,
Nonlinear crystal (the ZnTe crystal in Fig. 4), 1/4 λ wave plate, polarization beam splitting crystal, the first photodetector (photoelectricity in Fig. 4
Detector 1), the second photodetector (photodetector 2 in Fig. 4) and lock-in amplifier (being not shown in Fig. 4)；
Referring to fig. 4, the femtosecond laser that the femto-second laser generates obtains after the second film beam splitting eyeglass beam splitting
Third road femtosecond laser signal；The third road femtosecond laser signal is after the delay of the delay line 2, by the 4th optical path
Focus device is focused to be overlapped with the Terahertz frequency comb being emitted from polar molecule chamber in time afterwards, Terahertz frequency comb
Bubble Ke Ersi effect instantaneous in zinc telluridse crystal is excited, so that femtosecond laser is become after by 1/4 λ wave plate from circular deflection
Oval thickness；Then by obtaining two components of ellipse inclined THz wave after the polarization beam splitting crystal, the two components are distinguished
The time domain wave of Terahertz frequency comb is detected and obtained by lock-in amplifier using photodetector 1 and photodetector 2
Shape signal.
In the present embodiment, it should be noted that third road femtosecond laser signal by delay line 2 shown in Fig. 4, with from
The Terahertz frequency comb of polar molecule chamber outgoing carries out the coincidence of the time and space in zinc telluridse crystal.Third road femtosecond laser
The main purpose of signal is measured to the time domain waveform of Terahertz frequency comb, while the available Terahertz of Fourier transformation
The frequency domain information of frequency comb.Fig. 5 provides the Terahertz frequency comb spectrogram obtained using carbon monoxide polar molecule, corresponding
Polar molecule rotational transition marks in figure.It should be pointed out that third road femtosecond laser signal is used for Terahertz optical frequency
Comb signal is characterized and is detected, and first via femtosecond laser signal and the second road femtosecond laser signal are for obtaining terahertz light
Frequency comb radiation.The present embodiment is the Terahertz frequency comb generated using the Lu Guangyu using third road femtosecond laser signal purpose
The PGC demodulation relationship itself having, is detected by electro optic sampling principle.If the polar molecule of use is changed to other points
Son may cause different Terahertz frequency comb frequency discriminations, but this frequency discrimination is related with the type of molecule, does not limit to
In carbon monoxide molecule above-mentioned.As shown in Figure 4, electro optic sampling method is used to Terahertz frequency comb characteristic manner,
For the crystal used for zinc telluridse crystal, gallium phosphide is also can be used within 3 Terahertzs in characteristic response frequency in actual experiment
It is detected Deng other nonlinear crystals, or using ABCD (air-biased coherent detection) method, it can be with
Obtain broader frequency domain spectra.
As shown from the above technical solution, the Terahertz frequency comb provided in this embodiment based on polar molecule coherence rotation produces
Generating apparatus obtains Terahertz frequency comb using the coherence rotation of polar molecule, opens and a kind of obtains Terahertz frequency comb
New thought.The polar molecule that the present invention utilizes ultrafast Gold Films Irradiated by Femtosecond Laser to be emitted from nozzle, excites the coherence rotation wave of molecule
Bao Hou, then seed Terahertz light wave is injected into coherence rotation Bo Baonei, it can generate and divide at the rotation reproduction moment of polar molecule
The relevant terahertz emission of sub- rotational transition energy, the radiation correspond to the rotational energy level energy difference of polar molecule, have it is equal between
Away from the characteristics of, can be used as the relevant Terahertz frequency comb source of PGC demodulation.The present invention is driven by femtosecond laser, by relevant rotation
The radiation of wave packet, therefore the Terahertz frequency comb obtained has the coherence of PGC demodulation.Simultaneously because the rotation of molecule reappears
Time is only picosecond magnitude, therefore the Terahertz frequency comb obtained has the output characteristics of high repetition frequency.
Another embodiment of the present invention provides a kind of Terahertz optical frequency comb generation method based on polar molecule coherence rotation,
Referring to Fig. 6, this method comprises the following steps:
Step 101: the polar molecule being emitted from nozzle is injected using femtosecond laser, femtosecond laser excites the induction of molecule even
Polar moment interacts with laser field, so that coherence rotation transition occurs for molecule, generates the rotational wave packet of polar molecule.
Step 102: the rotational wave of the polar molecule is irradiated using the seed THz wave handled by femtosecond laser
Packet can give off and rotate jump at the reproduction moment of rotational wave packet since the rotating state that polar molecule is stimulated has coherence
Move corresponding energy level difference, these THz waves given off have the characteristics that on frequency spectrum it is equally spaced, in the time domain every pre-
If time interval can obtain primary radiation, the characteristic with PGC demodulation and high repetition frequency, therefore obtain Terahertz optical frequency
Comb.
It should be noted that the Terahertz frequency comb generation side provided in this embodiment based on polar molecule coherence rotation
Method, using the polar molecule of ultrafast Gold Films Irradiated by Femtosecond Laser nozzle outgoing, after the coherence rotation wave packet for exciting molecule, then too by seed
Hertz light wave injects coherence rotation Bo Baonei, can generate and molecule rotational transition energy phase at the rotation reproduction moment of polar molecule
The terahertz emission of pass, the radiation correspond to the rotational energy level energy difference of polar molecule, have the characteristics that equidistant, can be used as phase
The relevant Terahertz frequency comb source of position locking.This method is driven by femtosecond laser, is radiated by relevant rotational wave packet, therefore is obtained
Terahertz frequency comb have PGC demodulation coherence.Simultaneously because the rotation recurring temporal of molecule is only picosecond magnitude,
Therefore the Terahertz frequency comb obtained has the output characteristics of high repetition frequency.
It should be noted that since the Terahertz frequency comb provided in this embodiment based on polar molecule coherence rotation generates
Method can use the Terahertz frequency comb generation device described in above-described embodiment based on polar molecule coherence rotation to realize,
Concrete operating principle is similar with technical effect, and and will not be described here in detail, and particular content can be found in the introduction of above-described embodiment.
In the description of the present invention, it should be noted that the orientation or positional relationship of the instructions such as term " on ", "lower" is base
In orientation or positional relationship shown in the drawings, it is merely for convenience of description of the present invention and simplification of the description, rather than indication or suggestion
Signified device or element must have a particular orientation, be constructed and operated in a specific orientation, therefore should not be understood as to this
The limitation of invention.Unless otherwise clearly defined and limited.It should also be noted that, herein, first and second etc.
Etc relational terms be only used to distinguish one entity or operation from another entity or operation, and be not necessarily intended to
Ask or imply that there are any actual relationship or orders between these entities or operation.Moreover, term " includes ",
"comprising" or any other variant thereof is intended to cover non-exclusive inclusion so that include a series of elements process,
Method, article or equipment not only include those elements, but also including other elements that are not explicitly listed, or are also wrapped
It includes as elements inherent to such a process, method, article, or device.In the absence of more restrictions, by sentence " including
One ... " limit element, it is not excluded that there is also another in the process, method, article or apparatus that includes the element
Outer identical element.
The above examples are only used to illustrate the technical scheme of the present invention, rather than its limitations；Although with reference to the foregoing embodiments
Invention is explained in detail, those skilled in the art should understand that: it still can be to aforementioned each implementation
Technical solution documented by example is modified or equivalent replacement of some of the technical features；And these are modified or replace
It changes, the spirit and scope for technical solution of various embodiments of the present invention that it does not separate the essence of the corresponding technical solution.
Claims (10)
1. a kind of Terahertz frequency comb generation device based on polar molecule coherence rotation characterized by comprising femtosecond laser
Device, the first film beam splitting eyeglass, seed THz wave generation device, the first delay line and polar molecule chamber；
The femtosecond laser that the femto-second laser generates obtains first via femtosecond after the first film beam splitting eyeglass beam splitting and swashs
Optical signal and the second road femtosecond laser signal；
Nozzle is provided in the polar molecule chamber, the nozzle is for spraying polar molecule；
The first via femtosecond laser signal enters the polar molecule chamber after first delay line carries out delay disposal,
The polar molecule for injecting the nozzle injection, excites the induced dipole square of polar molecule to interact with laser field, so that
Coherence rotation transition occurs for molecule, generates the rotational wave packet of polar molecule；
The second road femtosecond laser signal generates seed THz wave after seed THz wave generation device processing, produces
Raw seed THz wave enters the polar molecule chamber, irradiates the rotational wave packet of the polar molecule, obtains terahertz light
Frequency is combed.
2. the Terahertz frequency comb generation device according to claim 1 based on polar molecule coherence rotation, feature exist
In the seed THz wave generation device includes: optical path regulation device and the first optical path focus device；
The optical path regulates and controls device, for carrying out optical path regulation to the second road femtosecond laser signal, generate polarization it is parallel,
Time is overlapped, the adjustable two-color laser field of relative phase；
The first optical path focus device, it is wide for being focused generation plasma acquisition Terahertz to the two-color laser field
Spectrum radiation, the Terahertz wide range radiation is the seed THz wave.
3. the Terahertz frequency comb generation device according to claim 2 based on polar molecule coherence rotation, feature exist
In the optical path regulates and controls device, comprising: Optical doubling frequency crystal, dispersion compensation crystal, the wedge set gradually is adjusted to polarization
Crystal；
The second road femtosecond laser signal is by obtaining frequency multiplication emergent light, the frequency multiplication emergent light after the Optical doubling frequency crystal
Polarization direction perpendicular to the second road femtosecond laser signal, and the central wavelength of the frequency multiplication emergent light is second tunnel
The half of femtosecond laser signal center wavelength；
The dispersion compensation crystal is used to provide negative dispersion to the second road femtosecond laser signal and the frequency multiplication emergent light and mend
It repays；
The wedge pair constructs identical wedge by two panels and forms, for the second road femtosecond laser signal and described times
Frequency emergent light provides positive dispersion, changes the positive dispersion that transmission distance changes two-color laser field, to the relative phase of two-color laser field
It is controlled；
The polarization adjusts crystal, is realized by dual wavelength wave plate, adjusts crystal by the polarization and makes second road femtosecond
Laser signal and the frequency multiplication emergent light shake along same polarization direction.
4. the Terahertz frequency comb generation device according to claim 1 based on polar molecule coherence rotation, feature exist
In the polar molecule chamber, comprising: first window, the second window, third window, the second optical path focus device and third light
Road focus device；The first window is located at the left side of the polar molecule chamber, for penetrating the first via femtosecond laser
Signal, and after the second optical path focus device focusing, the polar molecule of the nozzle injection is injected, polar molecule is excited
Induced dipole square interacts with laser field, so that coherence rotation transition occurs for molecule, generates the rotational wave of polar molecule
Packet；Second window is located at the upper left side of the polar molecule chamber, for penetrating the seed THz wave, and described in warp
After second optical path focus device focuses, the rotational wave packet of the polar molecule is irradiated, the Terahertz frequency comb is obtained；Described
Three windows are located at the lower right of the polar molecule chamber, by the Terahertz frequency comb through the third optical path focus device at
It is exported after reason；Wherein, the first window is quartz window, second window and the third window be High Resistivity Si window,
Polyethylene window or polystyrene window.
5. the Terahertz frequency comb generation device according to claim 1 based on polar molecule coherence rotation, feature exist
In the polar molecule chamber is vacuum chamber.
6. the Terahertz frequency comb generation device according to claim 1 based on polar molecule coherence rotation, feature exist
In the polar molecule is polar diatomic or polyatom linear molecule, and molecule rotational transition energy is in Terahertz amount
Grade.
7. the Terahertz frequency comb generation device according to claim 1 based on polar molecule coherence rotation, feature exist
In the nozzle uses continuous nozzle or the pulsed superonic flow nozzzle synchronous with the femto-second laser.
8. described in any item Terahertz frequency comb generation devices based on polar molecule coherence rotation according to claim 1~7,
It is characterized by further comprising: Terahertz frequency comb signal detecting device, the femtosecond for being generated using the femto-second laser is swashed
The PGC demodulation relationship that light and the Terahertz frequency comb of generation itself have, by electro optic sampling principle to the terahertz light of generation
Frequency comb is detected, and the time domain waveform of Terahertz frequency comb is obtained.
9. the Terahertz frequency comb generation device according to claim 8 based on polar molecule coherence rotation, feature exist
In the Terahertz frequency comb signal detecting device, comprising: the second film beam splitting eyeglass, the second delay line, the 4th optical path focus
Device, nonlinear crystal, 1/4 λ wave plate, polarization beam splitting crystal, the first photodetector, the second photodetector and locking phase amplification
Device；
The femtosecond laser that the femto-second laser generates obtains third road femtosecond after the second film beam splitting eyeglass beam splitting and swashs
Optical signal；The third road femtosecond laser signal is after the delay of second delay line, by the 4th optical path focus device
It is overlapped in time after being focused with the Terahertz frequency comb, Terahertz frequency comb excites instantaneous in the nonlinear crystal
Bubble Ke Ersi effect so that femtosecond laser is by becoming oval thickness from circular deflection after 1/4 λ wave plate；Then by described
Two components that ellipse inclined THz wave is obtained after polarization beam splitting crystal, to the two components be respectively adopted the first photodetector and
Second photodetector is detected and obtains the time domain waveform signal of Terahertz frequency comb by the lock-in amplifier.
10. a kind of Terahertz optical frequency comb generation method based on polar molecule coherence rotation characterized by comprising
S1, the polar molecule being emitted from nozzle is injected using femtosecond laser, femtosecond laser excites the induced dipole square of molecule and swashs
Light field interacts, so that coherence rotation transition occurs for molecule, generates the rotational wave packet of polar molecule；
S2, the rotational wave packet that the polar molecule is irradiated using the seed THz wave handled by femtosecond laser, due to pole
Property the rotating state that is stimulated of molecule there is coherence, the reproduction moment of rotational wave packet can give off with corresponding to rotational transition
Energy level difference, these THz waves given off have the characteristics that on frequency spectrum it is equally spaced, in the time domain every prefixed time interval
Primary radiation can be obtained, the characteristic with PGC demodulation and high repetition frequency, therefore obtain Terahertz frequency comb.
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