【2022】【Thesis Notes】Ultra-thin THz deflection based on laser direct writing graphene oxide paper——

前言

类型
$太赫兹+超表面$
期刊
$micromachines$
作者
$YixinSuo,LumingZhang,YihangLi,YuWu,JianZhang,QiyeWen$
时间
$2022$

The paper USES graphene oxide paper implements a low reflection、Rapid production ofTHzLight deflection unit

Using laser direct writing technique,Graphene oxide into specific patterns samples

研究目的

太赫兹波段（0.1~10太赫兹）In the past 20 years obtained the rapid development of,And has been used for security imaging、生物检测、6G通信等领域

Terahertz modulator、Hertz absorber——With beam control and forming ability of increasing demand of terahertz beam control devices,Especially the THZ wave frontwavefront（波阵面）Modulator thing

• Phased array antenna is usually used in beam control and forming

Because of the terahertzT/R（发射和接收）Module study obstacle and processing cost,It is difficult to create complete can be applied in the terahertz band phased array

Binary Fresnel zone plate（FZP）具有结构简单、易于制造、The characteristics of the cost and assembly complexity is low

Other device faults：制造复杂、缺乏灵活性、高反射——High reflection can interfere with signal transmission,Resulting in instability down.此外,Excessive reflection will influence the operation reliability of the excitation source and working performance

Because of the lithography substrate can't have enough bending,所以A low reflective、Easy to manufacture of flexibleTHzBeam control device有望在THz无线通信、Imaging and sensing obtain more frontier in the field ofTHz应用

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氧化石墨烯

Graphene oxide in THZ wave band has excellent transmission performance,After the reduction treatment significantly lower transmission performance of graphene oxide（So good effect in graphene oxide）

Graphene oxide reduction method：
化学还原、热还原、Laser reduction（Laser direct writing can reduce the special shape of the thin laser reduction of graphene oxide）

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GOPaper andLRGO纸

GOPaper is oxidized graphene paper
LRGOIs laser reduction of graphene oxide,Also is treated with laser direct writingGO纸

UT-LRGO（Incomplete reduction of oxidized graphene paper）Only deals with one,The processed one side is rough,Untreated did not change the nature of other side
——With different laser power,For different characteristics ofLRGO

OT-LRGO（Complete reduction of oxide graphene paper）Be completely thinning,Both sides is rough.OT-LRGOThe opposite of has obvious processing pattern

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OT-LRGOIs the best choice for manufacturing of graphene based devices

If you continue processingOT-LRGO,Can transition process leading toLRGO破碎

Laser energy by scanning speed、扫描频率、The processing time of multiple parameters, such as decision
Compared with the processing of time,The other parameters is not easy to quantify,Therefore the paper using different processing time to express the reduction degree of differentLRGO

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The principle of laser reduction graphene oxide

There are a large number of oxygen containing functional groups in grapheneOCGsOxygen and carbon key

After laser treatment,Carbon and oxygen keyC-O断裂
After laser treatment,样品的C/O大大降低,Electrical conductivity increase

同时,利用EDS（能谱仪）Measurement of graphene oxideGO,With c/o ratioC/OForm of escapeOCGsThe hydrogen and oxygen elements

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The paper USES a low power consumption and print method to deal with many timesGO纸,从而确保了GOThe quality of paper thinning and slight damage

GOPaper the oxygen and hydrogen in the form of gas escape,导致GOPaper in many microporous layers,Leading to the sample is loose

• OT-LRGOCoral structure can absorb THZ wave

With the increase of laser energy（通过改变LDWThe scan rate or frequency, etc）,OT-LRGOCoral structure collapsed,Film will become fragile.因此,To absorb THZ wave strongerLRGO纸,采用适当的参数非常重要.

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High electrical conductivity and coral structure to reduce the overall transmission performance of the sample
（Samples of transmittance by terahertz time-domain spectroscopy(THz-TDS)系统测量）

Samples of transmissivity change,And computer controlled laser writing,Makes the film can be quickly made into terahertz deflection device

In the air as reference,GOThe paper of THZ wave through the rate of89.5%,而LRGOThe transmittance is only57.2%.LRGO和GOAlmost half of the transmission between difference is made based onLRGO的THzThe main factors of device has lower insertion loss.

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With gold mirror as reference,采用太赫兹-TDS测量GO和LRGO的反射.结果显示,经过LDWAfter processing equipment,GOReflected in a lower level,GOTo a certain extent, reduce the spread of.

—— OT-LRGOThe transmittance and reflectance were lower thanUT-LRGO,因为OT-LRGOHave a higher reduction rate、Higher conductivity and stronger ability of THZ wave attenuation

• OT-LRGOCoral structure is mainly associated with the reduce of terahertz wave

LRGOThe electrical conductivity of below metal,因此LRGOThe reflectivity of below metal

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LRGO-THz器件设计

LRGO和GOTerahertz transmission rate with different,Can be used in the production of flexible and low reflection mask

利用LDW（Laser direct writing）将GOThe paper processed intoT形图案,Using terahertz time-domain spectroscopy system can gain terahertz images.The image contains a clearT形

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在该装置中,Fresnel zone plate(FZPs)被设计为340 GHz,焦距为50 mm

From the emitter$50mm$处,Gaussian beam radius is about$7mm$,FZPs的尺寸设置为$20mm\times 20mm$

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Take appropriate the focal length of theFAnd the aperture sizeD比(F/D)、比值$\alpha$
——Can get higher gain and efficiency

$$\alpha =\frac{Aperture\; radius}{Gaussian\; beam\; and\; a\; half{径}^2}$$

In determining the deflection Angle and focal length after,可以确定FZP图形的中心C和半径R

点光源照射下,Distance light source distance$50mm$In the phase distribution of plane as

$$\phi (r)=\sqrt{r^2+F^2}-F$$

其中$k=2\pi /\lambda$,Enter for wavelength

When the beam and the normal to the plane of the Angle of0时,Phase should be ${\phi }_d(r)=kr\cdot sin\theta$

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根据$\phi (r)和{\phi }_d(r)$之间的相位差,我们可以计算FZP图形的中心C和半径R为

$$C_n=\frac{a_{n}sin\theta }{co{s}^2\theta }$$

$$R_n=\frac{\sqrt{a_n^2-F^2+C_n^{2}co{s}^2\theta }}{cos\theta }$$

其中$a_n=F-\frac{({\phi }_d-\phi )-n\pi }{k}$,FZPThe radius and center

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结论

该论文测量了GO（氧化石墨烯）和LRGO（Laser reduction of graphene oxide）The transmission and reflection.研究发现,They can keep low reflection,And the transfer between them there is a big difference in the.

随后,Fast processingGO/LRGOThe method of thin filmCan rapid preparation of terahertz functional device,In manufacturing through the method of mask andFZP（Fresnel zone plate）Performed on THZ imaging,And verify the useGO和LRGOCan produce low reflection terahertz devices.

LDW（Laser direct writing）Equipment manufacture ofGO/LRGOTerahertz devices is not only a thin、灵活、The characteristics of low reflection,And processing speed,For large-scale manufacturing

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问题

What is the role of Fresnel zone plate？
Make the point light source or small objects into real image
FZPFresnel zone plate is a special kind of circular grating structure,Consists of a series of alternating light and dark concentric ring

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