Phonon Laser - Part 2

3 years ago, I highlighted a report on 2 papers advancing the concept of phonon/acoustic laser. This week, it looks like significant progress has been made.

Now, the paper of Mahboob et al. reports a significant step towards this goal. The authors create a purely mechanical system of three energy levels that is reminiscent of a three-level laser scheme (see Fig. 1, top panel). In a three-level laser, atoms are excited by an optical pump (usually another laser or a flashlamp) from the ground level (1) to a higher energy level (3), and then quickly relax through spontaneous emission and accumulate in the upper laser level (2). If the population of level 2 exceeds that of level 1 (a condition known as population inversion), photons resonant with the 1→2 laser transition get amplified through stimulated emission: the medium acts as an optical amplifier and, when placed within a cavity, lasing occurs if the gain exceeds the losses.

The link given above gives you access to the actual paper, so don't miss it.

Zz.