#Fused Quartz with Gold or Silver Nanoparticles Etched by Femtosecond Laser

Some articles on this technique [here](http://live.iop-pp01.agh.sleek.net/2016/05/19/optical-memory-enters-5d-realm/), [here](http://spie.org/news/6365-eternal-5d-data-storage-via-ultrafast-laser-writing-in-glass) and [here](https://spie.org/about-spie/press-room/press-releases/background-on-billion-year-5d-storage-breakthrough-published-by-spie?SSO=1), and a wikipedia article with more references [here](https://en.wikipedia.org/wiki/5D_optical_data_storage). According to that first article, 

>The current data-writing system is not much different from that found in CD or DVD drives. Ultrashort laser pulses with a wavelength of 1030 nm are focused inside a spinning glass disc and the position, power and polarization of each pulse are simultaneously modulated depending on the encoded information – leaving a trace of pits with different optical characteristics. Reading the data is more complicated because it requires a microscope-based birefringence measurement system, but we are now working on how to solve this problem.

The [original paper](https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.112.033901) says that they estimate how long the data will last by looking observed decay rate of the nanovoids (the 'pits' made by the laser as mentioned above) at "several annealing temperatures in the range from 1173 to 1373 K", and then using the [Arrhenius equation](https://en.wikipedia.org/wiki/Arrhenius_equation) to extrapolate the decay rate at other temperatures. In fig. 4 they present the following chart showing the "thermally activated decay time" $\tau$ (which they mention is equal to $1 / k$, where $k$ is the decay rate in the Arrhenius equation) as a function of the temperature $T$:

[![enter image description here][1]][1]

So, though one would have to preserve the fused quartz records in a place where they will be extremely well-protected from shattering (as fused quartz is a type of glass), the time that would pass before the information would degrade due to ordinary thermal decay is extremely long--longer than the current age of the universe (13.8 billion years) at a temperature of 462 K (189 C) or less, and $3 * 10^{20}$ years at a room temperature of 303 K (30 C).


  [1]: https://i.sstatic.net/fafC6.jpg