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Towards Stirling engine from a single up-converting particle confined in an optical trap at pump-wavelength exhibiting Hot Brownian Motion
Date Issued
01-01-2022
Author(s)
Suresh, Sarangi
Lokesh, Muruga
Nalupurackal, Gokul
Vaippully, Rahul
Roy, Srestha
Indian Institute of Technology, Madras
Abstract
Up-converting particles (UCP) absorb wavelengths in IR region and emit light in visible region by multiphoton absorption process. When optically trapped with 975 nm laser, these particles show active Hot Brownian Motion (HBM) due to the temperature difference created across the particle by the trapping laser. This is akin to an active particle optically confined in a tweezers with properly oriented motion. However, the activity vanishes when trapped with 1064 nm laser. We carefully maneuver the activity dependence of UCPs on laser wavelength to build a Stirling engine. A Stirling cycle consists of an isothermal expansion followed by isochoric cooling, isothermal compression and isochoric heating. Here, activity of the UCP in an optical trap is analogous to effective temperature which is controlled by the 975 nm laser. Whereas, the confinement of the trapped particle is similar to volume which can be altered by changing the trap stiffness of the 1064 nm laser trap. In this work, We first trap a UCP simultaneously with 1064 nm laser and 975 nm laser. Gradually decreasing 1064 nm laser power keeping 975 nm laser power constant decreases the trap stiffness resulting in less confinement of the UCP while keeping the activity constant. This process is considered as isothermal expansion. There can also be another process where 975 nm is increased and 1064 nm laser power is reduced leaving the total intensity constant. That would amount to isochoric process. We explore all these processes towards the Stirling cycle.
Volume
12198