Yunpeng Ren

Optical properties and thermal response of copper films induced by ultrashort-pulsed lasers

A critical point model with three Lorentzian terms for interband transition was proposed to describe temperature-dependent reflectivity (R) and absorption coefficient (α) for copper irradiated by ultrashort-pulsed lasers of wavelength 200–1000 nm. After validated with experimental data at room temperature, it was incorporated into a two-temperature model to study ultrafast laser-material interactions. The dynamic changes of optical properties R and α, distributions of laser heat density, electron and lattice temperature, and phase changes of a copper film were investigated. Comparing with the experimental data of average absorption showed that the proposed two-temperature model together with the critical point model can simulate satisfying results for temperature-dependent R and α. The drastic changes in R and α could alter laser energy deposition in a heated target, leading to different thermal responses than those predicted with constant R and α at room temperature.

Ultrashort laser pulse energy deposition in metal films with phase changes

Four optical models of reflectivity and absorption coefficient are investigated in this letter. After compared with existing experimental data, the extended Drude model is incorporated into a two-temperature model to simulate laser energy deposition and thermal response, including solid–liquid and liquid–vapor phase change, in a gold film irradiated by a femtosecond laser pulse. Dynamic reflectivity and absorption coefficient should be employed in modeling ultrafast laser heating except for very low laser fluencies.

Inverse Estimation of the Front Surface Temperature of a 3-D Finite Slab Based on the Back Surface Temperature Measured at Coarse Grids

The accuracy of the solution of the inverse heat conduction problem (IHCP) can be improved by using fine grids, but measured temperature data on fine grids are usually not available due to limits imposed by the size and spacing of the temperature sensors. A new method is proposed to recover the front surface temperature of a finite slab using fine grids based on the back surface temperature measured with coarse grids. Effects of heat conduction in the sensor substrate and contact thermal rsesistance are also taken into account. The proposed method is applied to solve a three-dimensional IHCP with stainless steel and aluminum target slabs. The results show that the front surface temperature can be recovered with satisfactory accuracy. Both the distortion of the temperature distribution and the discrepancy from the exact solutions are reduced by using the new method.

Amplitude stabilization and active control of a terahertz quantum cascade laser with a graphene loaded split-ring-resonator array

We demonstrate the amplitude stabilization of a 2.85 THz quantum cascade laser with a graphene loaded split-ring-resonator array acting as an external amplitude modulator. The transmittance of the modulator can be actively changed by modifying the graphene conductivity via electrostatic back-gating. The modulator operates at room temperature and is capable of actively modulating the quantum cascade laser power level and thus stabilizing the power output via a proportional-integral-derivative feedback control loop. The stability was enhanced by more than 10 times through actively tuning the modulation. Furthermore, this approach can be used to externally control the laser power with a high level of stability.We demonstrate the amplitude stabilization of a 2.85 THz quantum cascade laser with a graphene loaded split-ring-resonator array acting as an external amplitude modulator. The transmittance of the modulator can be actively changed by modifying the graphene conductivity via electrostatic back-gating. The modulator operates at room temperature and is capable of actively modulating the quantum cascade laser power level and thus stabilizing the power output via a proportional-integral-derivative feedback control loop. The stability was enhanced by more than 10 times through actively tuning the modulation. Furthermore, this approach can be used to externally control the laser power with a high level of stability.

The Development Situation of Selective Laser Melting Metal Powder Based on 3D Printing

This paper make a review of some researches on selective laser melting, including its history, materials, working principle, industry use and working processes. Meanwhile, it points out that the development potential of the Selective Laser Melting and its prospects.

Transient Optical and Thermal Response of Metal Films Induced by Ultrashort-Pulsed Lasers

In this paper, a critical point model with three Lorentzian terms for interband transition was proposed for dielectric permittivity of metal films. After validated, it was incorporated into a two-temperature model (TTM) to study transient optical and thermal response for a copper film irradiated by an ultrashort laser pulse. The dynamic changes of reflectivity (R) and absorptivity coefficient (α) during laser irradiation, electron and lattice temperature, and phase change were investigated. It was shown that for an ultrashort laser pulse with relatively high laser fluence, both R and α could drastically decrease, leading to significantly different thermal response than that described by using constant R and α at room temperature (RT).Copyright