Estimation of deformed laser heat sources and thermal analysis on laser assisted turning of square member

Laser assisted machining （LAM） has difficulties in estimating temperature after applying a LAM process due to its very small heat input area, large energy and movement. In particular, in the case of laser assisted turning （LAT） process, it is more difficult to estimate the temperature after preheating because it has a shape of ellipse when a laser heat source is rotated. A prediction method and thermal analysis method for heat source shapes were proposed as a square shaped member was preheated. The temperature distribution was calculated according to the rotation of the member. Compared with the results of the former study, the maximum temperature of the calculation results, 1 407.1 ℃, is 8.5 ℃ higher than that of the square member, which is 1 398.6 ℃. In a LAT process for a square member, the maximum temperature is 1 850.8 ℃. It is recognized that a laser power control process is required because square members show a maximum temperature that exceeds a melting temperature at around a vertex of the member according to the rotation.

Laser controlled quantum motion of two Paul trapped ions

We investigate the quantum motion of two ions stored in a Paul trap and interacting with a time-periodic laser field. In the pseudopotential approximation and large detuning condition, we find that the relative motion is independent of the laser field, but the exact centre-of-mass motion is closely related to the laser field. By adjusting the laser intensity and frequency, we can well control the quantum motion of the centre-of-mass. We illustrate some physical properties described by the centre-of-mass states, such as the squeezed coherent property, the widths and heights of the wavepackets of probability density, the classical-quantum correspondence, the resonance ladders of expectation energy and the transition probabilities between time-dependent quantum levels.

Laser pulse design for coherent laser control of potassium atoms

In this paper, the dynamics of coherent laser control of potassium atoms is studied by using the time-dependent multilevel approach （TDMA）. The calculation results of population transfer are presented with different laser fields. The results show that the population can be transferred to target state completely by a specially designed laser field.

Controlling Three-Dimensional Electron-Electron Correlation via Elliptically Polarized Intense Laser Field

The three-dimensional electron-electron correlation in an elliptically polarized laser field is investigated based on a semiclassical model. Asymmetry parameter α of the correlated electron momentum distribution is used to quantitatively describe the electron-electron correlation. The dependence of α on elliptieity e is totally different in three directions. For the z direction （maJor polarization direction）, α first increases and reaches a maximum at ε = 0.275, then it decreases quickly. For the y direction in which the laser field is always absent, the ellipticity has a minor effect, and the asymmetry parameter fluctuates around α = -0.15. However, for the x direction （minor polarization direction）, α increases monotonously with ellipticity though starts from the same value as in the y direction when ε = 0. The behavior of α in the x direction actually indicates a transformation from the Coulomb interaction dominated correlation to the laser field dominated correlation. Therefore, our work provides an efficient way to control the three-dimensional electron electron correlation via an elliptically polarized intense laser field.

Design and development of a synchronized operation control system for Thomson scattering diagnostic on J-TEXT

A Thomson scattering diagnostic system is under construction at the Joint Texas Experimental Tokamak（J-TEXT）. A 1064 nm Nd：YAG laser with 50 Hz repetition rate is used as the laser source. We have used a software for careful and precise control of the laser through serial communication. A time sequence operating system has been developed to synchronize the laser control and data acquisition system with the central control system（CSS）. The system operates commands from the CSS of J-TEXT and generates triggers for the laser and data acquisition system in the proper sequence. It also measures an asynchronous time value that is needed for accurate time stamping. All functions are served by a field-programmable gate array development platform that is suitable for high-speed data and signal processing applications.Several embedded peripherals, including Ethernet and USB 2.0, provide communication with the CSS and the server.

Design and test of laser-controlled paddy field levelling-beater

The technology for implementing a precise soil beating after precise soil levelling was proposed to improve the flatness of the paddy field and shorten the cycle time between the soil beating and levelling;in addition,a laser-controlled paddy field levelling-beater was designed according to the working principle.And the grade and tilt of the levelling scraper and beating mechanism are automatically controlled according to the levelling-beater vertical height and the tractor roll angle,respectively.The designed levelling-beater is capable of precise levelling and beating paddy fields at the same time with an adjustable beating depth.A paddy field test of the levelling-beater was conducted to compare the performance under both manual and automatic control modes,with the roll angles of the tractor and the levelling-beater measured using two attitude and heading reference systems(AHRSs),and the change in grade of the levelling-beater was measured using a global navigation satellite system(GNSS).The test results demonstrate that the operational quality of the levelling-beater is more stable when operating in automatic control mode than when operating in manual control mode.More specifically,the elevation of the levelling-beater varied±4 cm around the mean elevation and roll angle varied within the range of±0.5°when operating in automatic control mode.However,when operating in manual control mode,the elevation and roll angle were greater than±11 cm and±2.5°,respectively.The test results also demonstrate that the laser-controlled paddy field levelling-beater significantly improves the paddy field flatness,and enables it to operate at a stable depth to realise an even levelling and beating layer.More specifically,the maximum variation of elevation was reduced from 26.4 cm before the levelling and beating operation to 11.5 cm after the operation.In addition,the standard deviation of the elevation was reduced from 4.13 cm to 2.18 cm after the operation.The total number of flatness sampling points with the absolute difference of the desired elevation less than or equal to 3cm was more than 86%.The effective beating depth was 14.2 cm,compared with the set beating depth of 15cm,and the standard deviation of the beating depth was 2.46 cm.

Principle demonstration of fine pointing control system for inter-satellite laser communication

Due to high data rates and reliability,inter-satellite laser communication has developed rapidly in these days.However,the stability of the laser beam pointing is still a key technique which needs to be solved;otherwise,the beam pointing jitter noise would reduce the communication quality or,even worse,would make the inter-satellite laser communication impossible.For this purpose,a bench-top of the fine beam pointing control system has been built and tested for inter-satellite laser communication.The pointing offset of more than 100rad is produced by the steering mirror.With beam pointing control system turned on,the offset could be rapidly suppressed to lower than 100 nrad in less than 0.5 s.Moreover,the pointing stability can be kept at 40 nrad for yaw motion and 62 nrad for pitch motion,when the received beam jitter is set at 20rad.

Electromagnetic Control of the Weld Pool Dynamics in Partial Penetration Laser Beam Welding of Aluminium Alloys

The main characteristic feature of deep penetration laser beam welding is a large temperature difference between the plasma cavity(keyhole)in the weld pool centre and the melting/solidification front.Large temperature gradients in the weld pool result in very intensive thermocapillary(Marangoni)convection.The weld pool surface width becomes very large and unstable.However,an externally applied oscillating magnetic field can stabilize the surface of the melt.In the present work this technology was used to stabilize the weld pool surface in partial penetration 4.4 kW Nd:YAG laser beam welding of AW-5754 aluminium alloy in PA position.An AC magnet was mounted on the laser welding head.The oscillating magnetic field was oriented perpendicular to the welding direction.It was found that the AC magnetic field can drastically reduce the surface roughness of welds.X-ray image analysis shows a drastic reduction of welds porosity.This effect can be explained as a result of electromagnetic rectification of the melt.

Novel technique of controlled laser air-force detection for rheological properties of polymers

A novel controlled laser air-force detection(CLAFD)technique was developed to detect the rheological properties of polymers with the characteristics of non-destruction and cross-contamination free.Dynamic testing and static testing were carried out in the technique.Back propagation neural network algorithm was used to establish the air-force control model.The replicability of CLAFD system was analyzed,the viscoelastic properties of polyurethane were investigated using alternating load testing.A comparative analysis of performances was made between the CLAFD and the texture analysis(TA)on the testing of creep-recovery and stress relaxation.The results demonstrated that the CLAFD system had good replicability.The lagging phase angle was between 0°-90°in the testing of alternating load.This illustrated that the CLAFD technique could be used to detect viscoelasticity.The parameters of response speed and the precision of the CLAFD entirely surpassed the TA on the creep-recovery testing.The CLAFD technique will provide a new real-time,non-destruction and cross-contamination-free detection method for material science,especially for those materials such as artificial biological tissue and function food products.

Two-Photon Direct Laser Writing Beyond the Diffraction Limit Using the Nanopositioning and Nanomeasuring Machine

Since the first realization of two-photon direct laser writing(DLW)in Maruo et al.(Opt Lett 22:132-134,1997),the manufacturing using direct laser writing techniques spread out in many laboratories all over the world.Photosensitive materials with different material properties open a new field for micro-and nanofabrication.The achievable structuring resolution using this technique is reported to be sub-100 nm(Paz et al.in J.Laser Appl.24:042004,2012),while a smallest linewidth of 25 nm could be shown in Tan et al.(Appl Phys Lett 90:071106,2007).In our approach,the combination of DLW with the nanopositioning and nanomeasuring machine NMM-1 offers an improvement of the technique from the engineering side regarding the ultra-precise positioning(Weidenfeller et al.in Adv Fabr Technol Micro/Nano Opt Photon Ⅺ 10544:105440E,2018).One big benefit besides the high positioning resolution of 0.1 nm is offered by the positioning range of 25 mm×25 mm×5 mm(Jager et al.in Technisches Messen 67:319-323,2000;Manske et al.in Meas Sci Technol 18:520-527,2007).Thus,a trans-scale fabrication without any stitching or combination of different positioning systems is necessary.The immense synergy between the highly precise positioning and the DLW is demonstrated by the realization of resist lines and trenches whose center-to-center distance undergoes the modified diffraction limit for two-photon processes.The precise positioning accuracy enables a defined distance between illuminated lines.Hence,with a comparable huge width of the trenches of 1.655|im due to a low effective numerical aperture of 0.16,a resist line of 30 nm between two written trenches could be achieved.Although the interrelationships for achieving such narrow trenches have not yet been clarified,much smaller resist lines and trench widths are possible with this approach in the near future.

A beam flexure-based nanopositioning stage supporting laser direct-write nanofabrication

A nanopositioning system of both millimetric stroke and nanometric tracking accuracy is a key component for nanofabrication in many applications. In this paper, a novel bi-axial beam-flexure nano servo stage is proposed to support a direct writing system for femtosecond laser nanofabrication. The important features of the stage lie in: a mirror symmetric instead of rotational symmetric configuration is adopted to restrict cross axis coupling, and a novel Z-shaped guidance module is proposed to achieve relative large linear stiffness range, in addition a redundant constraints module is introduced to increase off-axis stiffness of the stage. Mechanical analysis and system identification are provided, with which a feedback control algorithm demonstrates the tracking capability for laser fabrication purposes. Based on the fabricated XY nano-stage, real time control and measurements are deployed, demonstrating the millimetric operating workspace and 77.8 nm(RMS) error of tracking a circular trajectory.