Influence of target temperature on femtosecond laser-ablated brass plasma spectroscopy

Spectral intensity,electron temperature and density of laser-induced plasma(LIP) are important parameters for affecting sensitivity of laser-induced breakdown spectroscopy(LIBS).Increasing target temperature is an easy and feasible method to improve the sensitivity.In this paper,a brass target in a temperature range from 25℃ to 200℃ was ablated to generate the LIP using femtosecond pulse.Time-resolved spectral emission of the femtosecond LIBS was measured under different target temperatures.The results showed that,compared with the experimental condition of 25℃,the spectral intensity of the femtosecond LIP was enhanced with more temperature target.In addition,the electron temperature and density were calculated by Boltzmann equation and Stark broadening,indicating that the changes in the electron temperature and density of femtosecond LIP with the increase of the target temperature were different from each other.By increasing the target temperature,the electron temperature increased while the electron density decreased.Therefore,in femtosecond LIBS,a hightemperature and low-density plasma with high emission can be generated by increasing the target temperature.The increase in the target temperature can improve the resolution and sensitivity of femtosecond LIBS.

Effect of distances between lens and sample surface on laser-induced breakdown spectroscopy with spatial confinement

Spatial confinement can significantly enhance the spectral intensity of laser-induced plasma in air. It is attributed to the compression of plasma plume by the reflected shockwave. In addition,optical emission spectroscopy of laser-induced plasma can also be affected by the distance between lens and sample surface. In order to obtain the optimized spectral intensity, the distance must be considered. In this work, spatially confined laser-induced silicon plasma by using a Nd：YAG nanosecond laser at different distances between lens and sample surface was investigated.The laser energies were 12 mJ, 16 mJ, 20 mJ, and 24 mJ. All experiments were carried out in an atmospheric environment. The results indicated that the intensity of Si（I） 390.55 nm line firstly rose and then dropped with the increase of lens-to-sample distance. Moreover, the spectral peak intensity with spatial confinement was higher than that without spatial confinement. The enhancement ratio was approximately 2 when laser energy was 24 mJ.

Influence of target temperature on AlO emission of femtosecond laser-induced Al plasmas

The influence of the target temperature on the molecular emission of femtosecond laser-induced breakdown spectroscopy(LIBS) was investigated experimentally. An Al target was ablated to produce laser-induced plasma. The Al target was uniformly heated to a maximum of 250℃. The measured molecular emission was AlO(△ν=0) from the femtosecond LIBS of the Al target.The measurements indicated that the molecular emission of AlO increased as the temperature of the Al target increased. In addition, a two-temperature model was used to simulate the evolution of the electron and lattice temperature of the Al target with different initial temperatures. The simulated results showed that the electron and lattice temperatures of Al irradiated by the femtosecond laser increased as the initial temperature of the Al target increased;also, the simulated ablated depth increased. Therefore, an increase in the initial Al target temperature resulted in an enhancement in the spectral signal of AlO from the femtosecond LIBS of Al,which was directly related to the increase in the size of the ablated crater. The study suggested that increasing the temperature of the target improves the intensity of molecular emission in femtosecond LIBS.