Tungsten needles typically have a refractive index of around 2.1, which is relatively high compared to most other materials commonly used in microscale optics applications. This high refractive index makes tungsten needles useful for applications such as near-field scanning optical microscopy (NSOM), where the high refractive index enables better resolution of features at the nanoscale level. However, the refractive index of tungsten needles is still lower than some other materials that are commonly used in microscale optics, such as diamond or sapphire, which have refractive indices of around 2.4 and 1.8-1.9, respectively. Therefore, the choice of material for a particular microscale optics application will depend on a variety of factors, including the desired optical properties, mechanical properties, and cost.
