A kind of two-dimentional terahertz imaging system and formation method thereof
Technical field
The present invention relates to the optical imagery detection range, specifically is a kind of two-dimentional terahertz imaging system and formation method thereof.
Background technology
THz wave typically refer to frequency range at 0.1 THz to 10 THz (1 THz=10
12Hz) electromagnetic wave in interval is between microwave and infrared light.THz wave has a lot of characteristics, and the photon energy that comprises THz wave is merely the per mille of visible light far below visible light and X ray, 1,000,000 of X ray/and, minimum to human harm; The THz wave wavelength is grown (1 THz~300 μ m), and is less demanding to the sample surfaces roughness when being used for measuring, and receives the material diffuse transmission influence little; THz wave has very strong penetrability to a lot of opaque medium materials like plastics, pottery, leather, semiconductor crystal wafer etc. in addition.These characteristics make the terahertz imaging technology in fields such as quality control and safety detection wide application prospect arranged.
The conventional optical imaging method normally utilizes the light beam that sends from single source to be expanded the whole imaging object of bundle back irradiation; Light beam through imaging object projects (for example sensitive film, CCD camera etc.) on the detection array through an imaging len; Because pass through the information that the light beam of target has carried object, on detection array, just can obtain the image of object like this.But this conventional optical imaging method is applied to the Terahertz field and is subject to many limitations.At first be to make the Terahertz detection array, particularly have the Terahertz detection array of enough pixels very difficult, price is very expensive; Secondly the sensitivity of Terahertz detection array is also very low, like this terahertz signal energy is sub-divided into whole detector array and lists the signal to noise ratio (S/N ratio) (Signal to Noise Ratio) that can greatly reduce system, has a strong impact on image quality.Because these reasons, the mode that the terahertz imaging method that adopts at present all is based on point by point scanning obtains two dimensional image, obtains the time that a width of cloth Terahertz image needs labor like this, has greatly limited the terahertz imaging The Application of Technology.
Summary of the invention
The technical matters that the present invention will solve provides a kind of two-dimentional terahertz imaging system and formation method thereof, and it is consuming time long and lack efficient 2-d Terahertz detection array so that the problem that can't carry out two-dimentional efficiently Terahertz direct imaging to solve existing Terahertz point by point scanning formation method.
Technical scheme of the present invention is:
A kind of two-dimentional terahertz imaging system includes the femto-second laser, diffraction light-dividing device, laser focusing lens, terahertz light lead antenna array, terahertz imaging lens, Terahertz condenser lens and the terahertz detector that are provided with in order.
Described diffraction light-dividing device is selected spectro-grating for use.
Described terahertz detector is selected Terahertz power detector or Terahertz field detector for use.
The formation method of a kind of two-dimentional terahertz imaging system may further comprise the steps:
(1), earlier imaging object is positioned between terahertz imaging lens and the Terahertz condenser lens;
(2), the laser beam that sends of femto-second laser is divided into aplanatic, as to be equidistant array distribution sets of beams through the diffraction light-dividing device, sets of beams shines on the terahertz light lead antenna array terahertz wave beam group that produces isocandela, is array distribution through laser focusing lens;
(3), the terahertz wave beam group shines on the imaging object through behind the terahertz imaging lens, the terahertz wave beam group through imaging object is converged on the terahertz wave detector by the Terahertz condenser lens then, obtains two-dimentional Terahertz image.
The design concept of the present invention's two dimension terahertz imaging system is:
According to the light path principle of reversibility, if in imaging system, replace detection array with array of source, replace single source with single detector, the point of each on the array of source is equivalent to a pixel like this, each point on the corresponding imaging object; Carrier wave through imaging object converges on the single detector through condenser lens; As long as the signal that each point source sends on the array of source is distinguishable; Just can obtain the information of the signal that each point source sends like this with single detector simultaneously, thereby obtain the two-dimensional image information of object.
The laser beam group correspondence on terahertz light lead antenna array that is produced by the diffraction light-dividing device excites generation terahertz wave beam group.Utilize the terahertz wave beam group to carry out two-dimensional imaging as light source, needing each bundle THz wave is distinguishable on the single terahertz detector at terminal.This can realize through the AC bias voltage that each antenna on the terahertz light lead antenna array is applied different frequency.When laser excitation terahertz light lead antenna produces THz wave, on antenna, apply frequency and do
fAC bias voltage, be equivalent to THz wave is modulated, modulating frequency does
fAccordingly, all apply AC bias voltage for each the photoconduction antenna on the photoconduction aerial array, and frequency has nothing in common with each other, each Terahertz wave source is all modulated like this.In end of probe, utilize lock phase detection technique, just can differentiate the signal (pixel) that each terahertz light lead antenna is sent come out, thereby obtain two-dimentional Terahertz image.
Advantage of the present invention is:
The two-dimentional terahertz imaging device of employing diffraction light-dividing device of the present invention beam split can directly obtain two-dimentional Terahertz image, and the more traditional point by point scanning formation method of image taking speed improves greatly.Each terahertz light lead antenna needs the exciting power of about 10 mW, and the femtosecond laser of a 1W output can be divided into the sets of beams of 10X10 through the diffraction light-dividing device, the photoconduction aerial array of deexcitation 10X10, and image taking speed can improve 100 times in theory like this.And this imaging device need not adopt the Terahertz detection array, and this has also reduced the complexity of system, has practiced thrift cost.
Description of drawings
Fig. 1 is the utilization structure synoptic diagram of the present invention's two dimension terahertz imaging system.
Embodiment
See Fig. 1, a kind of two-dimentional terahertz imaging system includes the femto-second laser 1, diffraction light-dividing device 2, laser focusing lens 3, terahertz light lead antenna array 4, terahertz imaging lens 5, Terahertz condenser lens 7 and the terahertz detector 8 that are provided with in order; Diffraction light-dividing device 2 is selected spectro-grating for use; Terahertz detector 8 is selected Terahertz power detector or Terahertz field detector for use.
See Fig. 1, the formation method of a kind of two-dimentional terahertz imaging system may further comprise the steps:
(1), earlier imaging object 6 is positioned between terahertz imaging lens 5 and the Terahertz condenser lens 7;
(2), the laser beam that sends of femto-second laser 1 is divided into aplanatic, as to be equidistant array distribution sets of beams through diffraction light-dividing device 2, sets of beams shines on the terahertz light lead antenna array 4 the terahertz wave beam group that produces isocandela, is array distribution through laser focusing lens 3;
(3), the terahertz wave beam group shines on the imaging object 6 after through terahertz imaging lens 5, the terahertz wave beam group through imaging object 6 is converged on the terahertz wave detector 8 by Terahertz condenser lens 7 then, obtains two-dimentional Terahertz image.
Each antenna on the terahertz light lead antenna array 4 applies AC bias voltage; And the frequency of the alternating voltage on each antenna is all inequality; When the laser that sends when femto-second laser 1 causes terahertz light lead antenna array 4 and produces THz waves, on antenna, apply frequency and do
fAC bias voltage, be equivalent to THz wave is modulated, modulating frequency does
fBecause the antenna that laser causes on the terahertz light lead antenna array 4 has all applied alternating voltage, every like this bundle THz wave is all modulated, and modulating frequency is all inequality.In end of probe; The output signal of terahertz detector 8 inserts lock-in amplifier; At this moment; With the reference signal of the AC signal identical with the modulating frequency of a certain antenna as lock-in amplifier, the signal that has only this antenna to send like this can be measured by lock-in amplifier, and the signal of other antenna is all filtered.Change the frequency of reference signal successively, just can obtain the signal that corresponding antenna is sent.According to the numbering and the corresponding signal that records of antenna, structure is painted two dimensional image again.Also can utilize a plurality of lock-in amplifier parallel measurements,, improve image taking speed to save the time that reference signal is measured that changes successively.
Present embodiment is to utilize the terahertz wave beam that sees through imaging object to come object is carried out to picture; Also can be used to obtain the image information of imaging object in addition through the THz wave of imaging object surface reflection or scattering, the inventive method also can directly be used under both of these case.