Figure 25.3 — Laser cooling of a nanoparticle Figure 25.3 — Laser cooling of a nanoparticle. (a) Image of light scattered by a laser-cooled silica nanoparticle confined in optical tweezers in ultrahigh vacuum. (b) This light is measured interferometrically with three detectors, labeled PDx , PDy and PDz . Each detector signal is frequency-doubled and phase-shifted. The sum of these signals is used to modulate the intensity of the trapping beam. A feedback cooling scheme, where the same beam is used for trapping and cooling, is then used to reach temperatures as low as 50 mK for the particle centre-of-mass motion.Reprinted figure from Gieseler et al., Phys. Rev. Lett. 109, 103603. Copyright (2012) by the American Physical Society.