Platform
Excitation can be provided by three different laser sources:
- pulsed Ti:Sa laser
- continuous laser diode
- supercontinuum light source that can be filtered down to < 2 nm width with a LLTF
The polarisation and power of the excitation beam can be controlled with the use of two polarisers with orthogonal axis and a half-waveplate in between.
Thus when the half-waveplate is rotated, the transmitted excitation power is varied.
If instead, both the half-waveplate and analysing polariser are rotated, with a rotation of the polariser that is twice that of the half-waveplate, the polarisation of the excitation beam can be rotated while keeping a constant excitation power.
The excitation path is then isolated from the rest of the setup with the use of a motorised shutter that only opens up when an acquisition is made.
To scan the surface of the sample inside the cryostat, we have two possibilities:
- using piezo positioners
- using a steering mirror
We do both.
With the steering mirror, the excitation beam can be moved in a area as large as 200x200 um² without moving the sample. This is achieved by using the steering mirror in a 4f configuration, where the rotation of the mirror is directly mapped onto a lateral shift on the sample without the need to realign the objective entrance pupil.
With the piezos, we can access larger areas on the order of a few mm².
The emission is separated from the excitation with a long-pass filter, and several things can be performed before its detection either with avalanche photodiodes (APDs) or a charge-coupled device (CCD) camera.
The polarisation of the emission can be probed with a set of motorised half-waveplate and a polariser aligned with the detection channel polarisation axis.
The emission can also be directed to a 50/50 beamsplitter for intensity-interferometry experiments. In this case, the two arms can be detected with two avalanche photodiodes each placed after a monochromator. Otherwise, the emission can also be analysed spectrally in one of the arms with a CCD detector.