We report the development of a phonon laser based on the center-of-mass oscillation of an optically levitated silica nanosphere in a free-space optical dipole trap. A parametric feedback scheme based on the detection of the oscillator’s center-of-mass is used to provide a cooling signal that intrinsically depends on the oscillator’s mean phonon occupation. When an amplification signal is added to the feedback at the mechanical resonance, these two signals produce center-of-mass dynamics that are analogous to those of a single-mode optical laser. Observed phenomena include a threshold in oscillation amplification, a transition from Brownian motion below threshold to coherent oscillation above threshold, reduction in the linewidth of the oscillation spectrum, and gain saturation. We also analyze the statistical phonon number distributions above and below threshold. The observed dynamics are described by a model that includes both stimulated and spontaneous emission of center-of-mass phonons. Importantly, the operation of this phonon laser relies on externally controllable, feedback-based parameters and therefore allows tuning of the threshold via these parameters. We also explore the use of the levitated nanoparticle phonon laser as a detector of weak external forces via injection locking.
Nitrogen-vacancy (NV) centers in diamond provide a platform for room temperature spin manipulation, making them a strong candidate for inclusion in optical levitation experiments seeking to couple mechanical and spin degrees of freedom. Here, we report progress on the coherent manipulation of single NV center spins contained within optically levitated nanodiamond in a free-space optical dipole trap. The NV center spin is coherently manipulated at both atmospheric pressure and low vacuum, and while the trapping beam causes a reduction in the fluorescence emitted by the center, no reduction in the spin coherence is observed. Further, after an initial exposure to low vacuum, the nanodiamond remains at near room temperatures at all pressures and trapping powers considered in these experiments.
When left and right circularly polarized beams of light from a pump laser interfere in a nematic liquid crystal doped with
azo dye, a polarization twisted nematic (PTN) grating is formed in the sample. The same is not true when linearly
polarized light interferes, regardless of the polarization. For circularly polarized light, the easy axis is rotated toward the
polarization direction of interfering beams. The irradiance is uniform so there is less contribution to refractive index
variations. In the latter case the diffraction grating arises from variation in refractive index. Gratings written with
Disperse Orange 3 (DO3) as the dopant disappear after removal of the pump beams, whereas grating written with Methyl
Red (MR) as the dopant tend to be semi-permanent.