optics - What longest time ever was achieved at holding light in a closed volume?

For what longest possible time it was possible to hold light in a closed volume with mirrored walls?

I would be most interested for results with empty volume but results with solid-state volume may be also interesting.

Answer

The set-up you are describing is essentially an optical cavity, and you are asking what is the longest lifetime which has been achieved in such a cavity.

In this paper (also described here), S. Kuhr et. al. describe a supraconducting cavity with a 130 ms lifetime. It is essentially 2 curved mirrors face to face. It works in microwaves (51 GHz), which has a long wavelength (6 mm), and this makes the manufacturing of mirror smooth at this scale much easier. This cavity is one of the key-element of this lab CQED (Cavity Quantum Electrodynamics) experiments.

I do not know if it is the best one, but I'm pretty sure it's more or less the state of the art in this domain.