Our main setup for optically and electrically characterizing nano-antennas has at its core a Nikon TE2000 microscope and, hence, it is named “Nikon setup”. It is purposely built for electro-optical measurements and in the following I will describe it to show how a typical optical lab/setup looks like.
As for optical measurements every photon counts, an optical lab has to be dark to reduce background noise. However, it is no pleasure to put masking tape on every LED of every devices, switch the monitors off for each measurement and always sit in the absolute dark. Therefore, it is common to build specific housings around critical beam paths or even a light-tight enclosure around the whole setup.
Furthermore, to avoid the need for constant realignments of the optical paths due to distortions of the table and thermal expansions, setups are usually built on a rigid “optical table” inside an air-conditioned lab. Dust on mirrors and sensible optics is also far from beneficial. Therefore, flow boxes, which always provides a stream of filtered air, combined with a flow management is more than nice to have to prevent that.
Fortunate, a couple of years back we got two new and empty laboratories inside the RCCM building. They have state-of-the-art infrastructure and in one we built up the Nikon setup.
We organized optical tables and supporting legs which isolate the setups from vibration on the ground. Then I constructed a housing consisting of a flow box, light/laser-tight curtains as well as remote lighting and we realized it with our mechanical workshop.
The center piece of the setup — the inverted optical microscope — had to be mechanical stable and extensible such that it could easily be outfit with a manual and piezo-electrical stage. Instead of a home-built solution we opted for a commercial one as a lot of accessory is typically available for them.
However, one issue is that modern inverted optical microscopes are usually nicely automated, e.g., you press a button, and a motor will change the objective for you. Unfortunately, in the case that our electro-optical nano-antennas are contacted via the micromanipulator needles, they are very sensitive to electromagnetic radiation: when for example the motor starts rotating, significant stray fields are emitted that can coupled to the needles which are relatively close by. These induced fields will the propagate along the electrodes towards the antennas and can let them explode. Therefore, we opted for a used mechanical microscope — the Nikon TE2000 — and upgraded it heavily.
A senior Nikon engineer helped removing some inner parts (the second tube lens), it got new mounts to screw it tightly to the table, we built custom beam splitters and entrance optics, installed a mechanical/piezo-electric stage (Mad City Labs Nano-View 200), added two workshop-made magnetic platforms for the micromanipulators and, finally, a camera to have an overview look from above.
With the already covered lasers and detectors it is then straight forward to characterize the samples optically. For example, one can illuminate an individual antenna with a white-light beam, block the directly reflected light and obtain a scattering spectrum of it. Another way would be to use one of the lasers to achieve similar things utilizing one- or two-photon photoluminescence.
For electro-optical characterizations, one simply needs to bring an antenna into focus, contact the associate electrode with the micromanipulator, use the source meter to apply a voltage and collect the emitted light with the EMCCD. The right software helps a lot for doing this.