# New Candidate Multicomponent Chalcogenide Glasses for Supercontinuum Generation
## 2 Optical and Physical Properties and Composition: Glasses
As noted for bulk materials above, variations in the deposition methods of thin films with identical composition can lead to concomitant variations in optical properties; thus, proper design of the processing method is also an important consideration for SC material fabrication [68]. Co-evaporation methods have been shown to be useful for the deposition of complex (>3) constituent glasses. However, deposition methodologies must be optimized and be compatible with both the processing method (avoiding preferential evaporation that leads to stoichiometric variation) and the underlying substrates (minimization of thermal expansion mismatch), as well as for their co-existence with other on-chip materials and their optical function. Similar challenges exist for material selection of SC candidates for use in fiber form. A glass' viscosity (\(\eta\))-temperature (\(T\)) behavior dictates an optimal draw temperature range as well as the materials' upper use temperature if the candidate SC material is to be used in fiber form. The \begin{table}
\begin{tabular}{c c c c c} \hline \multirow{2}{*}{**Form**} & **Composition** & **Measurement** & **Laser Damage** & \multirow{2}{*}{**Ref**} \\  & **(mol\%)** & \(\lambda\) (\(\mu\)m) & **(MW/cm\({}^{2}\))** & \\ \hline \multirow{6}{*}{Bulk} & Ge\({}_{25}\)Sb\({}_{12}\)Se\({}_{60}\) & 1.5 & \textgreater{}1000 & 68 \\  & Ge\({}_{x}\)As\({}_{y}\)Se\({}_{1-x-y}\) & 1.064 & 1000–4000 & 69 \\  & Ge\({}_{25}\)Sb\({}_{70}\) & 1.06 & 7200 & 27 \\  & Ge\({}_{15}\)GaSe\({}_{35}\)Sb\({}_{70}\) & 1.06 & 6300 & 27 \\  & Ge\({}_{18}\)GaSe\({}_{35}\)Sb\({}_{75}\)Se\({}_{2}\) & 1.06 & 6000 & 27 \\  & Ge\({}_{18}\)GaSe\({}_{35}\)Sb\({}_{75}\)Se\({}_{55}\) & 1.06 & 5400 & 27 \\  & As\({}_{24}\)S\({}_{38}\)Se\({}_{38}\) & 1.06 & 3500 & 27 \\  & As\({}_{2}\)S\({}_{3}\) & 1.06 & 8400 * & 27 \\  & GeAs\({}_{2}\)Se\({}_{2}\) & 1.064 & 5500–6000 & 19 \\ \hline \multirow{6}{*}{Fiber} & As\({}_{2}\)S\({}_{3}\) & 3.5 & 200 & 70 \\  & As\({}_{2}\)S\({}_{3}\) & 5.4 & 1000 & 71 \\ \cline{1-1}  & As\({}_{2}\)S\({}_{3}\) & 1.5 & 1000 & 72 \\ \cline{1-1}  & As\({}_{2}\)S\({}_{3}\) & 1.064 & 1800 & 73 \\ \cline{1-1}  & As-Se-Te & 1.064 & 130 & 73 \\ \cline{1-1}  & As-Se-Te & 2.94 & 30.6 & 73 \\ \hline \end{tabular}
\end{table} 
Table 2: A summary of laser damage values for a variety of ChG glasses in bulk and fiber forms. * indicates specifically surface damage resistance value and pulse duration of measurement. steepness of such a \(\eta\)-\(T\) curve for a given glass can vary dramatically across composition space, such as the As-Se system [see Figure 1a] that impacts (along with the glass' crystallization stability) the ease by which long lengths of low loss fiber can be processed [82; 83]. Observe, for a small variation in As content (10-40 mol%), how the fiber draw temperature (typically shown to be in the 10\({}^{4}\)-10\({}^{6}\) Pa-S range [83]) can vary by more than 100 K; additionally, note the subtle change in the d \(\eta\)/d\(T\) slope, which defines the temperature control needed over the possible drawing range (\(\Delta\)T) that enables high quality fiber formation. Similarly, the composition and average bond strength of the glass' constituents defines the absolute position in temperature space for the \(\eta\)-\(T\) curve. As an example of the breadth of glass property variation, Figure 1b illustrates the variation of \(\eta\)-\(T\) curve for five commercially available SCHOTT glasses (IRG22-26) [84]. Shown are how each \(\eta\)-\(T\) curve (as measured via the probe penetration technique) varies with the network constituent (element) and their respective glass transition temperature, \(T_{\text{g}}\), as both are defined by the glass' average bond strength. Hence, the definition of a glass with attractive optical properties may or may not have suitable manufacturability into fiber or film form.