[Experimental Investigation on the Electron Temperature of Laser-Induced Mg Plasmas].

A series of plasma characteristic spectral lines of Mg alloy were obtained under nanosecond laser shock produced by a pulsed Nd : YAG laser (1 064 nm, maximum energy 500 mJ), which was taken under standard atmospheric pressure and at room temperature. Results indicated that the evolutionary rates of spectral lines were different, and the laser energy was enough to ionization Mg alloy under this experimental condition by the spectral lines of MgⅠ, MgⅡ. The electron temperature of Mg plasma were calculated by the measured relative Emission-line intensity(MgⅠ383.2 nm, MgⅠ470.3 nm, MgⅠ518.4 nm). The experimental results showed that the secondary excitation Mg atoms could be got under this experimental condition. The electron temperature of Mg plasma decreased with the laser energy reduced while the laser energy was in the range of 200～500 mJ. When the laser energy was in the range of 350～500 mJ, the electron temperature changed rapidly. When the laser energy was in the range of 200～350 mJ, the electron temperature changed slowly and tended towards stability. It is found that when the laser energy was 300 mJ, the plasma temperature raised suddenly, which could not accord with the trend because of plasma shielding. When the laser energy was 300 mJ, the relative intensity of spectral lines was reduced which was lower than that of 350 and 250 mJ. And it is against the variation trend of the relative intensity of spectral lines increases with the increase of laser energy, which prove plasma shielding phenomenon had occurred and plasma with high power laser separate the coupling between laser and material. The plasma temperature was increased significantly, which is not consistent with the trend .When the plasma shielding phenomenon happened, laser energy was absorbed by the plasma, resulting in the rise of plasma temperature.

Prediction of SMILE surgical cutting formula based on back propagation neural network.

AIM: To predict cutting formula of small incision lenticule extraction (SMILE) surgery and assist clinicians in identifying candidates by deep learning of back propagation (BP) neural network. METHODS: A prediction program was developed by a BP neural network. There were 13 188 pieces of data selected as training validation. Another 840 eye samples from 425 patients were recruited for reverse verification of training results. Precision of prediction by BP neural network and lenticule thickness error between machine learning and the actual lenticule thickness in the patient data were measured. RESULTS: After training 2313 epochs, the predictive SMILE cutting formula BP neural network models performed best. The values of mean squared error and gradient are 0.248 and 4.23, respectively. The scatterplot with linear regression analysis showed that the regression coefficient in all samples is 0.99994. The final error accuracy of the BP neural network is -0.003791±0.4221102 µm. CONCLUSION: With the help of the BP neural network, the program can calculate the lenticule thickness and residual stromal thickness of SMILE surgery accurately. Combined with corneal parameters and refraction of patients, the program can intelligently and conveniently integrate medical information to identify candidates for SMILE surgery.

[Micromachining of Au film by femtosecond pulse laser].

Femtosecond laser micromachining of film is an emerging technology for fabrication of MEMS devices. A Ti: sapphire laser (130 fs, 1000 Hz)was used to irradiate the thin film with variations in process parameters such as pulse energy. The film thickness is about 4 microm which was measured by AFM. When we used single pulse to excite the film, the ablation diameter increased along with the energy ascending; when the energy of single pulse was invariable, the diameter had little change when altering the number of pulses. The single pulse threshold fluence of Au film was Fth = 0.7 J x cm(-2) at this ultrashort pulse-length in air. By changing the energy of excitation pulse it was found that when the energy was lower than the threshold, the line on the film was heaved; when the energy was higher than the threshold, the line was concave, which was detected by AFM. It was also found that the width of line decreased along with the increase in process speed when the pulse energy remained unchanged; the width of line increased along with the pulse energy ascending when the process speed was fixed.

[Micro- and nano-structures on metal induced by femtosecond laser radiation].

In the present study the authors performed surface treatment of stainless steel 65Mn (the thickness is 60 microm) by femtosecond laser (pulse duration 148 fs, wavelength 775 nm). The single-pulse threshold could be obtained directly to be about 0. 2 J x cm(-2). The authors found that the femtosecond laser produced a large number of micro-structures such as nano-pores and nano-protrusions. Then the authors discussed the influence of pulse power and the number of shots on the formed surface structures. The authors found that with the change in the power and the number of pulses, the period of multiple parallel grooved surface patterns remained unchanged, which is about on the sub-micron level. Finally the authors processed the array of holes and the lines with different speed and number of pulses.

[Application of laser induced breakdown spectroscopy (LIBS) to microdetection of Au film machining].

Film micro-machining is a core in micro- and nano- technology, micro-electro-mechanical systems and photoelectron field. However, it is difficult to control the quality of machining in processing film. In the present paper the authors propose a method to solve this problem by using laser induced breakdown spectroscopy (LIBS). The authors investigated the relation between excitation condition and the quantity of plasma in the process of micro-machining by pulse laser. At low frequency (<20 Hz), when the excitation energy was confirmed, the quantity of plasma was steady and independent of the number of pulses. When the authors used single pulse to excite the film, the quantity of plasma increased with the energy ascension. Based on the quantity of plasma and the species of elements, the authors realized the real-time control of micro-machining become true.

[The theory and the influential factors of laser induced breakdown spectroscopy].

The laser-induced breakdown spectroscopy (LIBS) technique, due to its lack of pretreatment of the material and the speed of analysis, has shown a great potential for a wide range of industrial applications. The current situation of application and study of LIBS are reviewed. Meanwhile, the laser used to explode the Cr and Co film had a pulse duration of 10 ns, the highest single pulse energy was 50 mJ at a repetition rate of 20 Hz, and a wavelength of 1064 nm. When the excitation energy was less than 10 mJ, there was little difference in spectral signal excited by different energy for Cr film. Otherwise, the signal showed obvious change when excitation energy was higher than 10 mJ. The principle, characters, history and recent trend of LIBS were introduced systematically. The factors influencing LIBS performances, including the characteristic of laser, delay time, experiment setting, the kind and the pressure of surrounding. Gas, single or dual pulse, and the analysis method were analyzed.

Phacoemulsification combined with transpupillary removal of silicone oil and intracapsular intraocular lens implantation.

AIM: To estimate the effectiveness of phacoemulsification and foldable intraocular lens (IOL) implantation combined with transpupillary silicone oil removal. METHODS: There were 168 eyes of 168 candidate patients with cataract and silicone oil-filled eyes recruited in our study. All of the patients received the intraocular silicone oil removal surgery by transpupillary drainage and cataract extraction by phacoemulsification. Then the IOL implantation were also performed through corneal incision. RESULTS: The surgery was successfully completed in all eyes. Best corrected visual acuity (BCVA) and postoperative complications were recorded in three months after surgery. There were 143 eyes with BCVA improved, otherwise 25 eyes remained stable at the last follow-up visit. The mean BCVA statistically improved from 20/400±0.02 to 20/100±0.15 (P<0.001) and mean postoperative IOP was 13.85±2.18 mm Hg (P=0.415). No intra-operative complications were reported. CONCLUSION: Phacoemulsification combined with transpupillary removal of silicone oil is a safe and simple effective method. In general, it enables quick recovery of visual acuity with less complication rate.