The Temperature of an Optically Trapped, Rotating Microparticle

Abstract

The measurement of temperature at the mesoscopic scale is challenging but important in a wide variety of research fields, including the investigation of single molecule and cell mechanics and interactions as well as fundamental studies in heat transfer and Brownian 1

Initiating revolutions for optical manipulation: the origins and applications of rotational dynamics of trapped particles

“…constant damping rate), ω max rot linearly increases with the applied laser power (see blue dashed line in Figure 8(a)). Departure from this linear behaviour of ω max rot vs P laser in optically heated rotors has been observed (blue dots and solid line in Figure 8(a)) and used to determine the laser-induced thermal loading [16,147,151,152]. This thermal-to-kinetic energy transfer process has been reported to be able to determine the temperature change with sub-degree accuracy, which is more than one order of magnitude more accurate than measurements done in the same experimental conditions with luminescence-based thermometric techniques that use the thermally induced spectral changes of the particle emission to infer temperature [151].…”

“…This motivated the search for novel optically anisotropic materials such as liquid-crystal emulsions [47,148,149] (Figure 5(c)), polymers [70,80] or birefringent synthetic crystals. Micro and nanoparticles made of fluoride crystals, such as LiYF 4 (YLF) [83,150] and NaYF 4 [17,18,61,151,152] (Figure 5(d)), have also been aligned and spun in optical traps. The main feature of these particles is that the synthesis procedure allows them to be doped with rare-earth ions that provide them with special characteristics such as the ability to control [83,150] and measure [152] temperature.…”

“…Micro and nanoparticles made of fluoride crystals, such as LiYF 4 (YLF) [83,150] and NaYF 4 [17,18,61,151,152] (Figure 5(d)), have also been aligned and spun in optical traps. The main feature of these particles is that the synthesis procedure allows them to be doped with rare-earth ions that provide them with special characteristics such as the ability to control [83,150] and measure [152] temperature. Other types of dielectric particles, such as those made of rutile TiO 2 [153] or Hg 2 Cl 2 (Calomel) [101], present higher refractive indices which enhance the applied optical forces and torque.…”

“…The maximum rotation rate will also be determined by γ rot , which depends on the orientation of the particle in respect to the rotation axis (through I); on the mass, volume and shape of the particle 9 ; and also on the properties of the environment, i.e. viscosity/pressure [82,145] and temperature [152]. In analogy to the translational motion (see Equations 2 and 3), the rotational damping rate for a spherical particle (I ¼ 2=5Ma 2 ) spinning at low pressure (l > > a) is given by…”

“…When the optically trapped spinning particle is not in thermal equilibrium with the environment, the temperature of the internal (green triangles) and the rotational (cyan circles) degrees of freedom differs from that measured for the centre-of-mass (navy squares). Reprinted with permission from [152]. Copyright 2016 American Chemical Society.…”