Index matching based on gas to liquid phase change

An optical element comprising:

• a first substrate and a second substrate that are optically transparent, wherein a cavity is formed between the first substrate and the second substrate;
• a material that is optically transparent, wherein a liquid state of the material has a refractive index that matches a refractive index of at least one of:
• the first substrate, the second substrate;
• a liquid reservoir that is to be employed to hold the liquid state of the material;
• a gas reservoir that is to be employed to hold a gaseous state of the material;
• means for converting the gaseous state of the material into the liquid state of the material, said means for converting being connected to the gas reservoir and to the liquid reservoir;
• at least one fluid channel connecting the cavity to the liquid reservoir and to the gas reservoir;
• and
• means for controlling a supply of the liquid state of the material to the cavity through the at least one fluid channel and for controlling a replacement of the liquid state of the material with the gaseous state of the material in the cavity,
• wherein a given optical power is produced by the optical element when the cavity is filled with the gaseous state of the material.