High-throughput rear-surface drilling of microchannels
in glass bad on electron
dynamics control using femtocond pul trains
Lan Jiang,1,*Pengjun Liu,1Xueliang Yan,1Ni Leng,1Chuancai Xu,1Hai Xiao,2and Yongfeng Lu3 1NanoManufacturing Fundamental Rearch Joint Laboratory of National Science Foundation of China,
School of Mechanical Engineering,Beijing Institute of Technology,100081,China
2Department of Electrical and Computer Engineering,Missouri University of Science and Technology,Rolla,Missouri65409,USA 3Department of Electrical Engineering,University of Nebraska-Lincoln,Lincoln,Nebraska68588-0511,USA
*Corresponding author:jianglan@bit.edu
Received March29,2012;revid May18,2012;accepted May18,2012;
posted May21,2012(Doc.ID165745);published July3,2012
This study propos a rear-surface ablation enhancement approach to fabricate high-aspect-ratio microchannels by
temporally shaping femtocond lar pul trains.In the ca study of K9glass,enhancements of up to a56times
higher material removal rate and a three times greater maximum drilling depth are obtained by the propod meth-
od,as compared with conventional femtocond lar drilling at the same processing parameters.The improve-
ments are due to the changes of photon-electron interactions by shaping femtocond pul train,which can
effectively adjust the photon absorption and localized transient material properties by changing electron dynamics
such as free electron densities.©2012Optical Society of America
OCIS codes:220.4610,140.7090.
Recently,fabrication of microchannels has received intensive rearch interest due to applications in micro-fluidic devices for liquid or gas,microreactors,and micro total analysis systems.Among materials for the applica-tions,transparent dielectrics,such as silica glass,are particularly attractive,as they exhibit good optical prop-erties in the ultraviolet to infrared wavelength range and excellent chemical/physical stability[1].Femtocond la-rs are promising tools for the micro/nanoscale ablation of dielectrics with reduced recast,microcracks,and heat-affected zones[2].In the ablation process,materials are first transformed into absorbing plasma with metallic properties,and then the subquent lar-plasma interac-tion caus material removal[3].Besides,the femto-cond pul duration is shorter than many physical characteristic times,which makes it possible to manipu-late electron dynamics such as excitations,ionizations, recombination,densities,and temperatures of electrons [4,5].This opens new possibilities for controlling the tran-sient localized material properties and corresponding pha change mechanisms[6,7].
Many rearchers have investigated the fabrication of high-aspect-ratio straight and three-dimensional(3D)mi-crochannels using femtocond lars[8–13].Li et al.in-troduced water-assisted,rear-surface microfabrication of 3D holes in silica glass[11].Hwang et al.applied liquid and ultrasonic waves to drill straight and3D microchan-nels in glass[12].Malli ported a process b
ad on the u of an astigmatically shaped beam and chemi-cal etching to fabricate long microchannels with a circu-lar cross ction[13].The previous works have demonstrated the feasibility of femtocond lars dril-ling microchannels,but little attention has been paid to the material removal rate.For transparent dielectric front surface ablation,pul trains with paration times of nanoconds or longer can be ud to improve the ab-lation efficiency[14];however,the ablation depth/vo-lume decreas as the paration time increas from 100to1000fs[15].Surprisingly,when we focus a femto-cond pul train with a paration time shorter than 1ps onto the rear surface of the target,a significant abla-tion enhancement is obtained,which is a new and inter-esting phenomenon.We experimentally demonstrated that femtocond pul train rear-surface drilling of mi-crochannels in glass is an effective,simple,repeatable throughput method,which does not need any additional steps(such as etching or cleaning)or toxic chemicals. The schematic diagram of the experimental tup is shown in Fig.1(a).The lar ud in the experiment is a commercial chirped Ti:sapphire regenerative oscilla-tor-amplifier system(Spectra-Physics).The femtocond lar pul is linearly polarized,with a central wave-length of800nm,pul width of50fs(FWHM)and repetition rate of1KHz.
By combining a half-wave plate with a polarizer, the pul energy can be continuously varied.
众志成城近义词
The Fig.1.(Color online)Schematic diagram of(a)the experimen-tal tup for fabrication of microchannels and(b)the partial enlarged view in the sample.P,polarizer;HWP,half-wave plate.
July15,2012/Vol.37,No.14/OPTICS LETTERS2781
0146-9592/12/142781-03$15.00/0©2012Optical Society of America
femtocond lar pul is temporally shaped to be a pul train with an accurate pul delay,nearly equal energy distribution,and an identical pul duration between the subpuls by a pul shaper(BSI MIIPS BOX640),which is from Biophotonic Solutions Inc.A 640pixel liquid crystal spatial light modulator is inrted in the Fourier plane of a zero-dispersion stretcher; the detailed principle of pul shaping is explained by Weiner[16].A1.5mm thick,all-surfaces polished sample (K9glass)is mounted in a glass dish filled with distilled water.The sample bottom is immerd in water to reduce the blocking and redeposition effects of ablated debris. The glass dish is mounted on a six-axis piezo stage with positioning accuracy of1μm in the x and y directions and 0.5μm in the z direction.The lar beam propagates along the z direction and is focud by a0.3N.A.mi-croscope objective.The pul trains ud in experiments consist of two subpuls,and the pul delays range from
0to1000fs(a double pul per train with0fs delay is actually a conventional pul).At the beginning,th
现在最流行的歌e lar beam is focud on the rear surface of the glass;and then the sample is moved along the−z direction by 50μm to guarantee that the focud spot is beneath the rear surface,as shown in Fig.1(b).The piezo stage is programmed to move along the z direction with a pret constant speed until termination,and microchan-nels are fabricated in a single step.
Figure2(a)shows the microchannels drilled in K9glass by conventional femtocond pul of20μJ at a1KHz repetition rate.At a processing speed of 2μm∕s,the drilling depth is about150μm,and the
material removal rate is0.5μm3∕pul(assuming cylind-rical microchannels).When the processing speed is incread,the drilling depth rapidly drops down to less than10μm.In contrast,at the same total energy,deeper microchannels can be fabricated by the propod pul train method,as shown in Fig.2(b),in which the two sub-puls are equally distributed in energy with a pul delay of500fs.The maximum material removal rate reaches up to28μm3∕pul,which is56times higher than that by conventional femtocond lar drilling at the same total energy.It is worth noting that the ablated debris cannot be drained out effectively as the depth increas,which limits the microchannel depth eventually[12].
Figure3shows the plot of microchannel depths versus processing speed of a pul train and a conve
ntional femtocond pul at20μJ,1KHz repetition rate.Each point in Fig.3reprents an average of three experimen-tal data points with a standard deviation of8–12%.The error bars of the standard deviation are not shown for clarity.For femtocond pul train drilling,the drilling depth is small when the processing speed is low (4μm∕s).This may be due to excessive energy deposi-tion that destroys the lattice near the lar focus,which diffracts the lar beam.Drilling depth increas with a processing speed in the range of4–50μm∕s.When the processing speed is50μm∕s,the drilling depth reaches maximum(∼450μm),which is about three times greater than the maximum depth(∼150μm)drilled by a conven-tional femtocond lar at the same energy.When the processing speed is higher(>50μm∕s),the drilling depth begins to drop down due to the reduction of photon en-ergy deposited per unit of time.Although the drilling depths by pul trains with different pul delays are si-milar,the drilling morphologies,which are not prented in this paper,are somewhat different.
vivo手机刷机怎样刷机
As shown in Fig.4,the entrance diameters drop down dramatically as the processing speed increas,for con-ventional femtocond lar drilling,while the entrance diameters drop down slowly for fs pul train
drilling. Fig. 2.(Color online)Microscopic cross-ctional and
形容雪大的成语entrance opening images of microchannels drilled in contact
with distilled water by(a)conventional pul and(b)pul
train of20μJ at a1KHz repetition
frequency.
Fig.3.(Color online)Plot of microchannel depths against pro-
cessing speed of a pul train and conventional pul at20μJ,
1KHz repetition
frequency.
Fig. 4.(Color online)Plot of microchannel entrance
diameters against processing speed of a pul train and con-
ventional pul at20μJ,1KHz repetition frequency.
商业养老年金保险2782OPTICS LETTERS/Vol.37,No.14/July15,2012
For clarity,only the results of a 500fs delayed pul train are plotted;other cas of pul trains at different delays are similar.Figure 5shows the maximum aspect ratio of microchannels (∼40∶1)fabricated in K9glass at an energy of 35μJ,processing speed of 80μm ∕s,and pul delay of 800fs.The two microchannels shown in Fig.5were fabricated under the same processing parameters,and the difference in depth and morphology might result from pul energy fluctuations.Figure 6shows the scan-ning electron microscopy (SEM)images of rear surface ablation in a single shot with an energy of 2μJ.The lar beam is focud on the rear surface of the sample.It is obvious that the ablation volume of the pul train (500fs pul delay)is much greater than that by the con-ventional femtocond pul.Filament [17]may occur in experiments.Yet,no detailed study has been done in this regard.
The experimental results indicate that the photon absorption efficiency of a pul train is much higher than that by the conventional femtocond lar in the rear-surface ablation process.The photon absorption effi-ciency enhancement is due to the change in the free electron density distribution by the pul train technol-ogy.In our previous work,a plasma model was propod for ultrashort pul lar ablation of dielectrics to inves-tigate free electron generation and distribution [3].At the same total fluence,for conventional femtocond pul lar processing of the sample,after critical electron den-sity is achieved by nonlinear ionization (photoionization and impact ionization),the reflectivity of the ionized zone increas rapidly,and the subquent lar energy is significantly reflected,which leads to the lower photon absorption efficiency.However,at the lower fluence of an individual subpul for a pul train,fewer free electrons are generated and the reflectivity is lower.Thus,more lar energy is absorbed using the pul train technology.
In summary,a high throughput method for enhance-ment of the material removal rate in rear surface ablation has been demonstrated by temporally shaping a femto-cond pul train.By focusing the pul train lar beam onto the rear surface of the K9glass,the temporal and spatial electron density distributions are manipulated by the pul train shaping,which increas the photon absorption efficiency.For the process conditions in this study,it is shown that the material removal rate and the m
aximum drilling depth are enhanced by about 56times and three times,respectively,by employing the pro-pod method,as compared with conventional femto-cond lar drilling at the same processing parameters,
including the total energy,wavelength,and so on.Detailed experiments should be conducted to investi-gate the mechanisms during femtocond pul train ablation.In addition,nonlinear phenomenon,such as temporal/spatial splitting and lf-focusing/defocusing,should also be considered to further improve the perfor-mance of pul train processing bad on the electron dynamics control mechanism.
This rearch is supported by the National Basic Rearch Program of China (973Program)(grant 2011CB013000)and National Natural Science Founda-tion of China (NSFC)(grants 90923039and 51025521).
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Fig.5.(Color online)Microscopic cross-ctional images of microchannels drilled in contact with distilled water by a pul train of 35μJ with a pul delay of 800fs at 1KHz repetition
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