Effect of sample temperature on femtosecond laser ablation of copper

We conduct an experimental study supported by theoretical analysis of single laser ablating copper to investigate the interactions between laser and material at different sample temperatures,and predict the changes of ablation morphology and lattice temperature.For investigating the effect of sample temperature on femtosecond laser processing,we conduct experiments on and simulate the thermal behavior of femtosecond laser irradiating copper by using a two-temperature model.The simulation results show that both electron peak temperature and the relaxation time needed to reach equilibrium increase as initial sample temperature rises.When the sample temperature rises from 300 K to 600 K,the maximum lattice temperature of the copper surface increases by about 6500 K under femtosecond laser irradiation,and the ablation depth increases by 20%.The simulated ablation depths follow the same general trend as the experimental values.This work provides some theoretical basis and technical support for developing femtosecond laser processing in the field of metal materials.

How long does the recovery of corneal sensitivity in different corneal regions take after LASEK?

AIM:To determine the corneal sensitivity recovery period after laser-assisted sub-epithelial keratectomy(LASEK)refractive surgery and investigate the effects of ablation depth on it.METHODS:In this study examinations were performed on 90 right eyes of 90 people(34 males and 56 females)with an age range of 20-35 and an average of 22.26±3.8 years old.A sensation of 5 corneal regions,including the center and 4 mid-peripheral regions,i.e.,nasal,inferior,temporal,and superior,each at a distance of 2 mm from the center of the cornea were measured with a Cochet-Bonnet esthesiometer device in 3-time points including before LASEK,1 and 3mo after the surgery,respectively.LASEK was performed on individuals with stabilized myopia of -1.00 to -7.00 diopters and astigmatism of less than 2.00 diopters.Furthermore,the individuals were divided into three groups regarding ablation depth.RESULTS:The highest level of corneal sensitivity before surgery was related to the center of the cornea(59.1±7.76),and the highest level of corneal sensitivity loss was also related to this region.The sensation of all measured corneal regions significantly reduced 1mo postoperatively and returned to their preoperative levels 3mo after surgery(mean of 5 corneal regions in levels of preoperation:58.2±6.48,1mo postoperation:57.3±5.84,3mo postoperation:58.2±5.49;P<0.05).A significant relationship was found between ablation depth and corneal sensitivity changes in the center and temporal regions(P<0.05).CONCLUSION:Corneal sensitivity in myopia and low astigmatism decreases after LASEK and reaches the preoperative level within 3mo.The depth of ablation during surgery affected the recovery of corneal sensitivity.