Near field imaging of a nanofiber

Introduction Nanofibers have interesting properties, among which: fair coupling efficiency to emitters on their surface[1], light chirality[2], built-in integration to fibered systems. For these reasons they make an exciting... [ view full abstract ]

Introduction

Nanofibers have interesting properties, among which: fair coupling efficiency to emitters on their surface[1], light chirality[2], built-in integration to fibered systems. For these reasons they make an exciting playground for emitter-emitter interactions[3][4] and quantum optics in general. Using near field techniques, we probe the vicinity of a suspended nanofiber in the visible domain, and manipulate emitters on nanofibers.

Methods

An Atomic Force Microscope (AFM) tip is endowed with a radiative emitter (100 nm fluorescent bead). Its intensity and lifetime give information about the local density of states (LDOS) of the electromagnetic field near the nanofiber. The tip is scanning perpendicularly (x-direction) above the nanofiber and its height (z-direction) can be controlled, since the slightest contact with the fiber is detected by the AFM.

The nanofiber is suspended on an inverted microscope, thus, excitation of the emitter can be done in free space perpendicularly to the fiber or directly through it. Detection can also be done in either way. The bead can be dropped and retrieved on the nanofiber.

Results

As preliminary result, we can observe how the field is warped by a nanofiber (diameter is 600 nm) (fig. a)). 3D electromagnetic FDTD simulations show similar patterns (fig. b)). By comparing these two figures, the snap-in distance, height below which the AFM tip snaps into contact with the nanofiber due to attractive forces, is estimated around 400 nm.

Discussion

As we've already measured, the emitter in contact with the nanofiber exhibits a shorter lifetime (as well as a higher emission rate), due to a higher LDOS on the surface. If we can explore the 200 nm above the fiber we will map the LDOS of the evanescent field. To do so, stretching the fiber to its limits should reduce the snap-in distance.
Once this milestone reached, we will proceed with single photons emitters (colloidal quantum dots), taking advantage of our ability to deterministically place several of them on the nanofiber.

[1]Schell et al., ACS Photonics, 2017, 4, 761–767
[2]Joos et al., QIM 2017, QT2B.3
[3]Bouchet et al., Phys. Rev. Lett. 116, 037401
[4]Bouchet et al., Phys. Rev. A 95, 033828