Ultra-broadband supercontinuum generation in fluoride glass by filamentation

The mid-IR supercontinuum (SC) light source is in demand for many chemical, biological, medical, and astronomical applications. It is of great significance to develop a mid-IR SC light source whose spectrum is wide and flat. We obtained ultra-broadband mid-IR SC by using a piece of fluoride glass through filamentation. Though the SC generation by filamentation needs a powerful laser chain to be the pump source, it has some advantages in comparison with that based on fiber. First, the optical path length in the glass can be very short due to the adopted high pump power. The negative influence of accumulated loss can be reduced greatly, so the transparent range of glass is much larger than fiber. Secondly, it is convenient in light-coupling, and the coupling efficiency can be high. In comparison with it, the coupling of the small core (usually the core is small to ensure a high nonlinearity) mid-IR glass fiber is troublesome. Thirdly, the glass piece is cost-effective, and can be fabricated easily. We obtained a SC spectrum covering 0.2-8.0 mu m by using a 32mm-thick fluoride glass sample. The 3 dB bandwidth covers 1.15-4.76 mu m. The 20 dB bandwidth spans from 0.39 to 7.4 mu m. The glass thickness, optical path, and pump conditions are optimized to enable the SC to be as wide as possible. This work shows that the SC generation through filamentation in bulk glass can be an effective way to obtain an ultra-broadband mid-IR light source, which will find various applications in mid-IR regions.